DYNAMIC ENERGY DEMAND MANAGEMENT SYSTEM FIELD OF THE INVENTION

The invention is intended to utilize the surplus of renewable electrical energy generated for self-consumption in internal electric grids (microgrids) of buildings or vehicles. The utilization of the surplus is achieved by shifting various energy-intensive tasks and processes to times of low power demand within microgrids, or by storing the surplus in different forms of energy in cases where said excess energy fails to be stored as electrical energy or fails to be transmitted to the distribution network either partially or completely.

BACKGROUND OF THE INVENTION

In the existing applications, the surplus of the renewable electricity produced for self- consumption in microgrids is utilized generally according to the methods below: a) The On-Grid System: Inverters are power electronic components which condition the current generated by electricity generators (e.g. photovoltaic panels, wind turbines, etc.) from renewable resources in accordance with grid standards (i.e. frequency and voltage). While carrying out said process, an inverter varies the electrical variables (voltage or frequency) applied to the generator to obtain the highest electrical power output from the intermittent renewable resource. This process is briefly defined as driving the generator.

The inverter adjusts a direct current (DC) generator's (e.g. photovoltaic panels, fuel cells, etc.) operating point on its current-voltage curve to the voltage (Um _PP ) at which the generator will obtain the highest power from the renewable resource (Maximum Power Point Tracker). The inverter inverts the DC obtained from the generator at said voltage to an alternating current (AC) at a frequency and voltage suitable to grid standards.

If a turbine, mechanically connected to a generator, converts the energy of an intermittent renewable resource to mechanical energy via rotational movement first (e.g. wind turbines, internal combustion engines, Stirling engines, water turbines, etc.), a gearbox transmits the angular speed and torque of the turbine to the generator rotating at a frequency suitable to grid standards. Due to the mechanical connection between the generator and the turbine, the turbine's frequency depends on the network frequency in accordance with the transmission ratio of the gearbox and the slip ratio of the asynchronous generator. This turbine frequency, however, may be unequal to the frequency by which the highest power will be obtained from the instantaneous potential of the renewable resource.

The direct drive turbine technology, designed thanks to recent developments in power electronics, replaces the mechanical connection between the turbine and the grid over a gearbox by an electrical connection by means of an inverter. The inverter applies a voltage to the generator based on the optimal frequency (ΪΜΡΡ) of the turbine. At this frequency, the turbine can transmit the highest mechanical power output of the renewable resource to the generator rotating on the same shaft with the turbine. Therefore the frequency of the AC generated by the generator is quite different from the grid frequency. To cope with grid standards, the generator current is rectified by means of a rectifier within the inverter. The inverter inverts the DC from the rectifier to AC suitable to grid standard and transmits this current to the distribution or transmission grid. In case the rectifier is placed in the inverter, said system is simply referred to as turbine driver.

If the electricity is generated by a hybrid system having different generators generating DC along with AC generators, the current obtained from the DC generators can be transmitted to a DC bus between the AC generator's rectifier and inverter. In this case, the DC generator is driven by a DC converter optimizing the generator's DC voltage to maximize its power output. Subsequently, the converter converts this DC to the DC bus voltage level. In this case, the turbine is driven by a variable-frequency rectifier instead of an inverter. The inverter, in turn, inverts the DC on the DC bus to AC suitable to grid standards.

The power generation methods above used to exploit intermittent renewable resources are increasingly being implemented in power plants which primarily provide the power demand of a facility or building instead of directly transmitting the plant's power output to the grid. This emerging distributed energy generation application aims to increase power supply safety of such facilities and the distribution network to which the facility is connected. Since both power generation and consumption are performed within such facilities, the internal electric grid of such facilities is defined as a microgrid. The distribution or transmission grid providers encourage the microgrid manager to invest in renewable energy by making a commitment to buy energy supplied by the microgrid from a predetermined tariff price for a certain period of time. However, due to the intermittency of renewable resources, grid operators may limit the total installed renewable power capacity within a low voltage grid. If a connection request from a new power plant construction within a microgrid exceeds the low voltage grid's transformer capacity reserved for renewable energy, the grid operator will limit the production capacity of such a new plant to a certain maximum power.

Following the activation of installed capacities within limits of the distribution network, the potential production within the grid may still exceed the consumption if renewable resource supply in the distribution and transmission networks is abundant due to daily or seasonal natural conditions. In this case, the transmission or distribution network operator has to turn off some of the renewable energy generators so that network frequency or voltage will remain within requested limits of grid standards, and thus limiting potential production from renewable resources. However, during periods of scarce renewable energy resources, plants powered by fossil resources must be put into use to meet the grid demand. Increasing renewable energy supply has decreased the annual operating hours of fossil-fuel plants negatively impacting the amortization of the investment costs of these plants. Further, frequent activation/deactivation of these plants depending on renewable resource supply causes operation-related problems. These problems, in turn, may require a more frequent maintenance and repair of the used equipment, or may shorten the technical and economic life thereof.

Such drawbacks regarding the fossil-resource plants causes the grid operators to supply electrical energy with higher costs, when those plants are operated only during periods of scarce renewable energy supply. If the distribution companies are committed to supply electricity to their clients uninterruptedly and wish to remain unaffected by daily or seasonal fluctuations in market prices due to intermittent resources, they can alternatively store electricity within their grids or increase available capacity (e.g. diesel gensets), which are also costly solutions. Either way, their customers will buy electricity at a higher price. If the prices can not be increased along with increased costs, that is, if power plants and grid distributors cannot agree on a market price for electricity then power cuts will occur. The On-Grid System with Limited Production: In order to balance the power demand and supply within the grid and to ensure the grid standards, certain measures are taken at all connection points with renewable intermittent generators. The inverters of renewable electricity generators in the microgrid are controlled with a signal sent from a smart meter in order to control the power transmitted from the microgrid to the distribution network. The inverter shifts the generator's operating point (voltage or frequency)to a less efficient one according to the signal value and limits the generator's power output to a desired value, including zero. In microgrids connected to smart distribution networks, said process is performed remotely by the distribution network and the grid's supply-demand equilibrium is ensured without switching off the generators in microgrids. All these measures limit energy production to a level below its potential and wastes the renewable resource increasing the turnaround period of the investment. c) On-Grid System with energy storage for Self-Consumption: The surplus electrical energy not consumed within the microgrid may be stored using devices such as batteries or super capacitors. When the storage device is fully charged, the surplus power is transmitted, partially or completely, to the distribution network as in options a, or b. When the microgrid's power consumption exceeds its generation, said excess amount is discharged from the battery into the microgrid, thereby reducing the total energy drawn from the distribution network. Moreover, the microgrid's power supply is secured even if it is connected to a distribution network with frequent power cuts. A further advantage of this option over the options a and b is that it is also applicable to microgrids with no connection to a distribution network.

However, high kWh cost of power storage might constrain an investor to choose a low- cost storage method decreasing cycle(charging/discharging) efficiency and life or to choose a low-capacity storage system. Such compromises result in failing to fully exploit the available renewable energy, or choosing a lower power production capacity than an economically feasible one. d) Demand management: Today, innovative implementations of smart grids are capable of switching on/off a device within a connected microgrid for certain periods of time depending on the grid load. Devices frequently operated or consuming high power such as refrigerators, swimming pool circulation pumps, and electric water heaters are controlled according to the grid's supply and demand balance. Consequently, the distribution network is less affected by fluctuations of intermittent power supply and demand, resulting in fewer electricity price fluctuations. Therefore grid operators are eager to give discounts in electricity price to their customers allowing this application in their homes. The devices subject to switching on/off (hereinafter referred to as digital load) are equipped with sensors for the customer's convenience. A communication network connected to the distribution network transfers the data from sensors to a centralized computer. The centralized computer ensures that the digital load is switched on/off so that the sensor data will remain above or below a given limiting value. Thus, the power demand is approximated to the power supply to secure grid standards and avoid regional blackouts.

Negative effects of intermittent renewable energy resources on the distribution and transmission networks can be possibly minimized by integrating option d with options a, b, and c. Such integrated demand management applications may also be implemented to converge the demand of a microgrid to its renewable power supply. However, the supply- demand discrepancy can not be converged down to a satisfactory finitely small value by switching on/off a device because the number of digital loads in a microgrid is too few and the ratio of the device load to the total microgrid load is not low enough compared to a distribution network.

BRIEF DESCRIPTION OF THE INVENTION The present invention has been developed for overcoming the aforementioned disadvantages and providing additional advantages in the related technical field.

The main objective of the invention is to shift various energy-intensive processes to times when renewable electricity surplus exists in the microgrid without compromising on quality or comfort. For example, these processes include but are not limited to heating, cooling, ventilation, water purification and circulation, compressed air production, and chemical production. In line with this, the microgrid's surplus renewable energy is stored in the microgrid upon being converted into different forms of energy in case the distribution network does not need it, in case the transmission of the whole or a part of the surplus to the distribution network is not desired or possible because of various reasons, or in case the microgrid does not have the sufficient electric power storage capacity. Moreover, some energy-intensive works and processes, timing of which are not relevant to their quality, are shifted to periods with an excess of renewable resource. In addition to these implementations, the surplus power of an industrial microgrid is exploited to produce the inputs of the related industrial field, for example ice, compressed air, vacuum, hydrogen production; and stored for further use in manufacturing processes during times of scarce renewable resources. During periods of sufficient renewable energy, the proposed invention minimizes the difference between the power consumption and generation of a microgrid by transmitting a finite small control power from the distribution network to the microgrid. Besides switching on/off some of the devices in the microgrid, the power consumption of some other devices within the microgrid is decreased or increased to such an extent, that the microgrid's power consumption conforms to its instantaneous production potential. Such devices will be referred to as an analog load, wherein the current transmitted to the microgrid is adjusted by changing the power consumed by said analog load. The current fed to the analog load is adjusted by controlling the output voltage of a variable-voltage power source (VPS) or the output frequency of a variable-frequency driver (VFD).Both VPS and VFD feed an analog load with electric power. The electrical input variables applied to the analog load must remain within certain limits to ensure a harmless operation of the load.

The control cycle employed in the proposed dynamic energy demand management system is as follows:

Electric motors which rotate analog loads such as pumps, compressors and fans are driven with a variable-frequency driver (VFD), if the motor's frequency is to be varied to control the power fed to the load. Within the scope of the invention, this frequency is adjusted according to the microgrid's excess renewable power. A microgrid analyzer, placed at the boundary between the microgrid and the distribution network, measures continuously the power fed to the microgrid. The analyzer sends a signal to the controllers (VFD and VPS) of the analog loads depending on the magnitude of the power fed to the microgrid.

If the analog load is a device, which can be fed with variable voltage instead of variable frequency, the device controller will be a VPS. In this case the VPS adjusts the current passing over the device by adjusting the device's input voltage, output voltage of VPS, so that the signal coming from the microgrid analyzer will be maintained at the desired value. If the device has a resistor to be converted to an analog load for heating or lighting purposes, it will be more convenient to facilitate the automatic control with a variable-voltage power source. If the analog load is an electrolyzer producing a gas like hydrogen, the VPS will control the current fed to the electrolyzer, hence its gas output, by adjusting the electrolyzer's electrode potential according to the signal coming from the microgrid analyzer.

The effect of the supply/demand differences occurring within the microgrid on the analog loads:

If the signal sent by the microgrid analyzer becomes stronger depending on the power transmitted to the microgrid, the motor is slowed down by decreasing the driver frequency to reduce the power fed to the micogrid. If the renewable energy generated in the microgrid approaches its consumption (for example, if the control power transmitted to the microgrid reduces to 1W instead of the set value 10W), the signal amplitude will reduce. Consequently, the VFD will increase the motor frequency and adjust the power transmitted to the microgrid so that the signal amplitude will not fall below the set value. Thus, the microgrid can prevent the transmission of its surplus production to the distribution network. The same method can be applied to analog loads controlled by a variable-voltage power source which adjusts the current fed to the load by changing the load's input voltage according to the signal's set value, said load being dependent on said voltage.

The Application of Dynamic Energy Demand Management System to Off-Grid Systems:

If the relevant microgrid is an off-grid microgrid which is not connected to any distribution network (e.g. the microgrid of a sailing boat), a battery storing the electrical energy is required for a stable operation of the microgrid. In this case, the power to be charged/discharged to/from the battery is adjusted by controlling the adjustable loads according to the excess/deficient power in the microgrid. The power fed to adjustable loads can be varied according to the charge of the battery, as well as predicted meteorological data such as solar irradiation or wind velocity so that the battery will neither be fully charged nor discharged.

The charging/discharging current, calculated using such an algorithm based on these data, is fed from the generator to the battery, or from the battery to the microgrid, by dynamically adjusting the power fed to analog or digital loads as described above. The battery of a microgrid with adjustable loads will power the microgrid for longer periods and harvest more renewable resource for an economic operation than a battery with the same capacity, but powering a microgrid without adjustable loads.

Analog loads to which the dynamic energy demand management can be applied:

There are various fields and adjustable loads related thereto where the analyzer-driver control cycle described above are applicable to a microgrid. For instance, devices like pump motors of a pool or water well, compressor motors of air conditioners, refrigerators, or heat pumps, and water heaters, electrolyzers may be controlled by an appropriate drive or power source depending on the microgrid load. Devices like heat pumps should transfer heat to/from a heat/cold energy storage in a building instead of heating/cooling the building directly. The storage tank or medium will provide the buildings with instantaneous heat demand, so the requested comfort conditions in the building will remain unaffected by the intermittent renewable energy surplus. The increase of a building's cooling load with solar irradiation intensity and ambient temperature, enables a convenient implementation of a dynamic energy management system within a building's microgrid. In heating applications, wind energy might be a suitable resource to provide its surplus power to heat up a building's heat storage via a heat pump if ambient temperatures fall with increasing wind velocity. Storing the surplus renewable energy as heat or cold requires less investment per kWh energy compared to storing it as electrical energy in batteries. The circulation pump of an outdoor swimming pool is also a very convenient analog load to be powered with a microgrid's solar electric power surplus because the algae formation in pool water increases substantially with solar irradiation intensity and water temperature. Agricultural irrigation increases also with increasing solar irradiation intensity and ambient temperature. Therefore, a pump, supplying water to a water storage tank for agricultural irrigation from an underground water source can act as an analog load for a microgrid's dynamic energy management system.

An industrial plant that uses compressed air for its production process, can utilize surplus renewable power to compress more air than instantaneously required. The compressor acts as an analog load and the excess compressed air stored in a pressure vessel can be utilized when the microgrid's load exceeds its renewable power generation.

If a chemical plant requires hydrogen in its production process or the microgrid owner has a vehicle driven by a fuel cell, an electrolyzer is a convenient analog load powered by a variable-voltage DC power source. Provided that the electrode potential of the electrolyzer is kept between certain limits, the DC source changes said voltage depending on the instantaneous renewable energy surplus. The current fed to the electrolyzer adjusts gas generation so that the microgrid's surplus electric energy is converted to chemical energy. The excess gas is stored in a pressure vessel and can be utilized when renewable energy potential can't meet the demand of the process.

Increasing the Capacity and Quality of Energy Storage Systems for Heating-Cooling Purposes Using Phase Change Materials for Dynamic Energy Demand Management System Application

The temperature of a storage medium (for example, water) used for heat or cold storage, changes with the amount of energy stored in the medium. If the medium's temperature is constrained to a minimum and maximum level for the energy consuming task, the medium's storage capacity is considerably reduced. Performing heating or cooling tasks while the temperature level of storage is kept constant or at a narrow low-high temperature range is only possible, if a storage material releases its latent heat at this temperature. Phase change materials (PCM) performing solid-liquid phase change are applied as storage medium, in order to minimize the change of medium's volume during phase change. Phase change must occur at a temperature that is higher than the heating temperature, but lower than the cooling temperature. Thanks to the thermal inertia of such a storage solution, the storage temperature will not be affected by the instantaneous cooling and heating loads for a long period of time; as a result, the heating and cooling loads of the building will not have an impact on comfort conditions. During this period, the driver controlling the compressor motor of the heat pump adjusts the motor load in accordance with the signal coming from the microgrid analyzer, thereby allowing the storage to be heated or cooled independent of the heating and cooling load of the building. Thus, it is possible to store heat or cold at constant temperature for periods when renewable energy supply is scarce due to natural conditions such as solar irradiation intensity, wind velocity. If due to seasonal conditions, renewable energy surplus cannot meet the average heating or cooling load, the deficient energy will be supplied from fossil resources or the distribution network.

The Advantages of the Dynamic Energy Demand Management System for Smart Distribution networks: The microgrid analyzer can be managed by a smart distribution network, called a smart grid, via a communication network. In this case, the smart grid will determine the control power of the microgrid analyzer. A near-zero positive value of the control power minimizes the power transmitted to the microgrid from the distribution network. On the other hand, the smart grid can adjust this control power to an arbitrary negative value instantaneously, equal to the surplus of the microgrid's renewable power supplied to the smart grid. Hence, not only positive (consumers) or negative (producers) loads of the distribution network become more foreseeable and adjustable, but also the manager of the microgrid benefits from his investment because such capacities can be regarded as a back-up facility by the smart grid. The central computer of the smart grid requires various data about the microgrids' power production and consumption. These data can be provided by sensors embedded in the microgrid. The sensors inform the smart grid about the renewable power generated by microgrids, the consumption of digital, analog, and other non-adjustable loads, the temperature of the heat and cold storages, ambient temperature and the desired and actual room temperature of microgrids, instantaneously. The instantaneous total available distributed capacity is calculated based on the sensor data from all microgrids with adjustable loads in the smart grid. The centralized computer decides which microgrid will meet how much of this capacity based on the sensor data from the energy storages of the microgrids. Thus, fossil resources for heating-cooling purposes are substituted by the idle capacity of renewable energy resources. Moreover, the wide spread use of such adjustable loads as installed capacities in microgrids will enable smart grids to operate their own fossil resource based back-up plants to a lesser extent and more efficiently.

The embodiment of the present invention and advantages thereof with the additional components must be considered together with the drawings explained below in order to be fully understood.

BRIEF DESCRIPTION OF THE FIGURES

Fig. 1 is the single line diagram of the battery assisted on grid system with dynamic energy demand management.

Fig. 2 is the basic single line diagram of the on-grid system with dynamic energy demand management.

Fig. 3 is the single line diagram of the off-grid system with dynamic energy demand management.

Fig. 4 is the single line diagram of the on-grid system of the prior art.

Fig. 5 is the single line diagram of the production-restricted on-grid system of the prior art. Fig. 6 is the single line diagram of the on-grid system with storage of the prior art.

REFERENCE NUMERALS

1 Direct Current Generator

1 ' Alternating Current Generator

2 Inverter

2a Direct Current Converter

2a' Variable-Frequency Rectifier

2b Variable-Frequency Driver

2b' Variable-Frequency Inverter

2c Variable-Voltage Alternating Current Source

2c' Variable- Voltage Direct Current Source 3 Generator Meter

4 Bidirectional Meter

5 Circuit Breaker

6 Distribution network

7 Digital Load

8 Smart Meter

8a Smart Meter Control Signal

9 Battery

9' Electrolyzer (Analog Load Connected to the Variable-Voltage Direct Current Source) 10 Microgrid Analyzer

10a Analog Load-Analyzer Signal

10b Analyzer- Battery Voltage Signal

10d Digital Load-Analyzer Signal

1 1 Analog Load (Motor Connected to the Variable-Frequency Driver on Alternating Current Line)

1 1 ' Analog Load (Motor Connected to the Variable-Frequency Inverter on Direct Current Line)

12 Analog Load (Load Connected to the Variable- Voltage Alternating Current Source) 12' Analog Load (Load Connected to the Variable- Voltage Direct Current Source) DETAILED DESCRIPTION OF THE INVENTION

In this detailed description, the novelty according to the invention is described by way of illustrations only for a better understanding of the subject matter, without any limitations. The microgrid refers to the internal electric grids of the buildings and vehicles while the distribution network (6) refers to the grid from which the instantaneous power demand of the microgrid is supplied or to which the instantaneous power surplus is transferred.

Within the scope of the invention, the microgrid's consumption is adjusted to its generation by feeding the microgrid with a finitely small control power from the distribution network (6) during periods of renewable energy surplus. This adjustment is enabled by switching on/off some of the devices in the microgrid, and by decreasing or increasing the power fed to some other devices to the desired level without switching them off. The devices controlled by switching on/off are referred to as digital load (7) while the devices the power consumption of which is adjusted, are referred to as analog load (9', 1 1 ,1 1 ', 12,12'). The analog loads (9',1 1 ,1 1 ',12,12') and digital loads (7) will be jointly referred to as adjustable loads. Fig. 1 is the single line diagram of the on-grid system, i.e. in connection with the distribution network, provided with the dynamic energy demand management according to the invention. Accordingly, the system comprises:

• At least one direct current generator (1 ) converting the energy obtained from renewable energy resources to direct current electrical energy and/or at least one alternating current generator (1 ') converting the same to alternating current electrical energy,

• In order to achieve the highest value of the energy conversion efficiency of the generator (1 ,1 '):

o A direct current converter (2a) which adjusts the optimal voltage level (UMPP) applied to the direct current generator (1 ) and converts the voltage of the generated power to the voltage level of the direct current bus, and/or

o a variable-frequency rectifier (2a') which rectifies the variable-frequency alternating current that it obtains by driving the alternating current generator (1 ') at optimal frequency (ΪΜΡΡ), to the voltage level of the direct current bus,

• An inverter (2) which converts the direct current on the direct current bus to alternating current suitable to grid standards or an inverter (2) which also adjusts the optimal voltage and/or frequency applied to the generator (1 ,1 ') if directly plugged with the inverter.

· A variable-frequency driver (2b) connected to the alternating current line and which changes the frequency (f _var ) applied to the motor driving the analog load (1 1 ) in connection therewith for adjusting the power fed to it from the microgrid,

• A variable-frequency inverter (2b') which inverts the DC fed from the DC bus to the frequency (f _var ) applied to the analog load (1 1 ') in connection therewith by means of pulse width modulation,

• An AC variable-voltage power source (2c) which controls the voltage (U _va r) of the analog loads (12) in connection therewith for adjusting the power fed to the analog loads (12) from the microgrid,

• A DC variable-voltage power source (2c') which controls the voltage (U _va r) of the analog loads (9',12') in connection therewith for adjusting the power fed to the analog loads (9',12') from the microgrid,

• A generator meter (3) measuring the energy transferred to the microgrid by the inverter (2),

• A bidirectional meter (4) measuring the net energy transfer between the microgrid and the distribution network (6) at predetermined periods, A circuit breaker (5) used for separating the microgrid from the distribution network

(6),

A smart meter (8) which allows reducing the generator's power output potential from its maximum to the requested level by manipulating the optimal voltage and/or frequency level applied to the generators (1 ,1 '),

A smart meter signal (8a) for manipulating the voltage and/or frequency applied to the generator (1 ,1 ') by the inverter (2) or direct current converter (2a) and/or variable- frequency rectifier (2a'), to a value different from the optimal,

A battery (9) allowing the storage of the renewable electricity excess,

An electrolyzer (9') converting the renewable electricity excess to chemical energy of the chemicals used in the inputs of the plant,

A microgrid analyzer (10) which measures the power transmitted to the microgrid and sends a signal with an amplitude which depends on the measured value, to controllers of all adjustable loads like the variable-frequency driver (2b), variable- frequency inverter (2b') and variable-voltage power sources (2c,2c') of the analog loads (9',1 1 ,1 1 ',12,12'), to the digital loads (7), and/or to the distribution network (6), An analog load-analyzer signal (10a) which is sent by the microgrid analyzer (10) to the variable-frequency driver (2b), variable-frequency inverter (2b') and variable- voltage power sources (2c,2c') of the analog loads (9',1 1 ,1 1 ',12,12') and the amplitude of which depends on the power transmitted to the microgrid from the distribution network (6),

An analyzer-battery signal (10b) informing the microgrid analyzer (10) about the battery (9) voltage level, and

A digital load-analyzer signal (1 Od) sent by the microgrid analyzer (10) to the digital loads (7) for switching on/off the latter when the power fed to the microgrid from the distribution network (6) is under/above the predetermined level.

Within the scope of the invention, in case analog loads (9',1 1 ,1 1 ',12,12') take priority over digital loads (7), each digital load (7) is activated when the consumption capacities of the analog loads (9',1 1 ,1 1 ',12,12') are used up. After turning on each priority digital load (7), power consumption of analog loads decrease to the extent of the digital load (7), thereby decreasing supply-demand difference back to the desired level. If any digital load (7) takes priority over the analog load(s) (9',1 1 ,1 1 ',12,12'), the digital load (7) is turned on when the total consumption of the non-priority analog load(s) (9',1 1 ,1 1 ',12,12') exceeds the nominal consumption capacity of this digital load (7). Consequently, the released capacity by turning off the non-priority analog loads (9',1 1 ,1 1 ',12,12') is transferred to the priority digital load (7). The priority of loads may be changed manually or based on sensor data (the temperature of the heat or cold storage, storage pressure, ambient temperature, room temperature, date, hour, tariff, etc.) obtained from several sensors. In case an air-conditioner compressor becomes an analog load (1 1 ), the air-conditioner compressor's electric motor is driven by a variable-frequency driver (2b). The motor frequency depends on the surplus of renewable energy to be consumed provided that the room temperature remains within determined limits. In case a circulation pump becomes an analog load (1 1 ), its motor frequency is adjusted by a variable-frequency driver (2b).

If a heat pump compressor becomes an analog load (1 1 ,1 1 '), it may be driven by a variable- frequency driver (2b) connected to the AC line or by a variable-frequency inverter (2b') connected to the DC bus. The frequency (f _var ) of the variable-frequency driver (2b) or the variable-frequency inverter (2b') is also controlled by the analog load-analyzer signal (10a) sent from the microgrid analyzer (10). The signal's amplitude depends on the magnitude of the surplus of renewable power within the microgrid. If the generated heat or cold by the heat pump exceeds the instantaneous demand, the surplus is stored in a heat or cold storage. The phase change material present in the heat or cold storage increases the capacity as well as the quality of the storage.

The analog load (12,12') may also be a resistor for heating or lighting purposes. The resistor embedded in the heat storage is driven by an automated variable-voltage power source (2c, 2c') in order to utilize the surplus of renewable electricity. If the variable-voltage power source (2c') is connected to the DC bus, the power source is a DC/DC converter. It adjusts the voltage applied to the resistor so that the power transmitted between the microgrid and the distribution network is controlled (Fig. 3). The current passing over the load is regulated by changing the voltage ( U _va r) applied to the load (12') located at the output of the converter.

If said load is a resistor, the power converted into heat is the power fed to the analog load (12') from the microgrid. If, on the other hand, said load is an electrolyzer (9') (Fig. 1 ), the output voltage of the DC power source defines the potential difference between the electrodes of the electrolyzer (9'). Depending on this difference, a current determines the gas flow rate obtained from the electrolyzer (9'). Unlike a resistor, a linear correlation between the electrolyzer's (9') current and potential is present only within certain voltage limits. The signal (10a) from the microgrid analyzer (10) defines the output voltage (U _va r) of the converter acting on the resistor or electrolyzer (9'). In case the power source is a variable-voltage power source (2c) connected to the alternating current bus, then the power source may be a transformer. The primary coil of the transformer is fed by the alternating current line while the load is in the same circuit as the secondary coil (Fig. 2). The coil contains a ferromagnetic core inside to constitute an inductor. The voltage induced on this inductor depends on its inductance. While the primary coil's inductance is held constant, the secondary coil's inductance (L _va r) must be variable to reduce the voltage applied to the load. An adequate capacitor is connected to the primary circuit to maintain the phase angle between the current and voltage of the primary circuit at the requested level.

For an automated control of the secondary coil's inductance, a motor moves the core within the secondary coil. The alteration of the inductance L _var of the secondary coil, in turn, allows the adjustment of the voltage induced on the coil. The change in the induced voltage also changes the current passing over the load and adjusts the power fed to the load through the primary coil of the transformer. In order to adjust the power fed to the microgrid, the motor (servo) of the power source is controlled by the signal (10a) from the microgrid analyzer (10).

Instead of a transformer, an automatically controlled switch can actuate the variable-voltage power source, if a moving part like a motor won't be used. Such a switch comprises a current controlled transistor consisting of positive and negative doped semiconductors with a certain sequence. The transistor behaves like a conductor or insulator depending on the current transmitted to its base semiconductor. The transistor constitutes a switch closing or opening a circuit at the requested frequency by holding the base current above a threshold value or equal to zero. While the switch remains closed, the transistor transmits a current to the load. Opening the switch prevents the transmission of the current to the load.

Powering with an intermittent source may harm the load. A filter consisting of inductors and capacitors can be switched between the transistor and the load to prevent a harmful operation. This filter stores energy reducing the voltage applied to the load while the transistor transmits current. The filter powers the load with the stored energy when the transistor cuts the current. This measure obtains a steady power feed with a mean voltage applied to the load, although the power source is intermittent due to switching frequency. The transistor's switching frequency is much higher than the grid's one. The higher the switching frequency, the smoother is the applied voltage to the load because a high switching frequency decreases filter discharging. The ratio of the period during which the circuit remains closed (transistor conducts), to its total period (on+off) determines the effective level of the variable voltage (U _var ). Although the load is powered steadily, the transistor's switching withdraws an intermittent current from the grid. Harmonic fluctuations of the grid's current and voltage must be prevented due to the switching frequency of the transistor. The circuit's current input must be provided with suitable filters in accordance with the switching frequency to prevent harmonics affecting the microgrid and distribution network (6), adversely. Whether the analog load (12) is controlled by a switching circuitry or a transformer depends on which method is suitable for the load. If the analog load is applied to lighting, a motion or photo cell sensor's digital signal might replace the microgrid analyzer's (10) analog signal (10a) instantaneously, to convert the load from an analog to a digital load so that its resistor or diode is fed by nominal (maximum) voltage or turned off. In line with the explanation above, the operating mode of the system according to the invention is as follows:

If the generator is a direct current generator (1 ) converting energy to DC (fuel cells, photovoltaic modules, etc.), the DC convertor (2a) adjusts the generator's (1 ) voltage to its maximum power point voltage (Um _PP ) so that the generator (1 ) will obtain maximum power from the resource. The direct current convertor (2a) converts the generator's (1 ) DC output at this voltage to the DC bus' voltage level.

If the generator is an alternating current generator (1 '), converting energy to AC by rotational movement due to its design (wind turbines, internal combustion engines, Stirling motors, water turbines, etc.), a variable-frequency rectifier (2a') will rectify the generator's (1 ') AC output to DC at the voltage level of the DC bus. The rectifier adjusts also the frequency and voltage applied to the generator (1 '), said frequency and voltage being dependent on one another according to certain rules, to the maximum power point frequency and voltage (f _mp p and U _mp p) by which maximum power will be generated.

Adjusting the frequency and/or voltage applied to the generator (1 ,1 ') to obtain maximum power generation is simply defined as driving the generator (1 ,1 ') while the converters (2a) and rectifiers (2a') performing said process are also called as generator drivers.

The inverter (2) inverts DC obtained from the drivers (2a,2a') of the generators (1 ,1 ') to AC suitable to grid conditions. In case an additional DC bus does not exist between the generator (1 ,1 ') and inverter (2), or if it is a DC busbar contained within the inverter (2), the generator (1 ,1 ') can be directly driven by the inverter (2). If the inverter (2) drives a DC generator (1 ), the inverter will directly invert the generator's (1 ) DC to the grid's standards. If the inverter (2) drives an AC generator (1 '), the inverter (2) will first rectify AC to DC to invert the rectified DC on the busbar according to the grid's standards.

In case the microgrid is provided with a battery (9) for power storage or with an electrolyzer (9') which converts surplus of electrical energy to chemical energy, those DC devices can be efficiently connected to the DC bus. In this case, the DC bus voltage level can be adjusted to the optimal battery (9) charging/discharging voltage or to the optimal electrode potential of the electrolyzer (9') by means of the generator's (1 ,1 ') driver (2a,2a'). If multiple DC devices are connected to a microgrid's DC bus, one of them can be driven by the generator driver (2a,2a') adjusting the DC bus voltage to the input voltage of this device. All other DC devices are driven with their own DC/DC converter (2a) because their input voltages won't coincide with the DC bus voltage. If a DC bus is not present in the microgrid, then the battery (9) and/or the electrolyzer (9') may be controlled by an additional inverter (2) connected to the AC line.

The generator meter (3) records the energy transferred to the microgrid by the inverter (2). In order to maintain the difference between the generation and self-consumption, the digital loads (7) of the microgrid are switched on/off in accordance with certain rules, while adjusting the consumption of the analog load (9',1 1 ,1 1 ',12,12'). The analog loads (1 1 ,1 1 ') connected to rotational actuators like electric motors are driven by the variable-frequency driver (2b) connected to the AC line or the variable-frequency inverter (2b') connected to the DC bus. The other analog loads (9',12,12'), on the other hand, are driven by the variable-voltage power source (2c) connected to the alternating current line or the variable-voltage power source (2c') connected to the direct current line.

The bidirectional meter (4) provides offsetting by measuring the energy changed between the microgrid and distribution network (6) at certain time intervals. The circuit breaker (5) between the generator meter (3) and the microgrid is used for separating the microgrid from the distribution network (6). The smart meter (8) monitors the energy transmitted to or from the distribution network (6), said energy being the difference between the energy generated and consumed by the microgrid, and based on said difference, it sends a control signal (8a) to the drivers (2,2a,2a') of the generators (1 ,1 '). If the power transferred to the distribution network (6) exceeds the maximum power desired to be transferred, then the smart meter (8) adjusts frequency (fm _PP ) and/or the voltage ( Um _PP ) to be applied to the generators (1 ,1 ') by their drivers (2,2a,2a') to a value different from the optimal one by sending a signal (8a) to them, thereby limiting the power transferred to the distribution network (6) to the desired level.

The microgrid analyzer (10), as in the case of the smart meter (8), instantaneously measures the power exchanged between the distribution network (6) and the microgrid. However, unlike the smart meter (8), the microgrid analyzer (10), sends signals to the drivers (2b,2b',2c,2c') of the adjustable loads (7,9', 1 1 , 1 1 ',12, 12') in the microgrid according to the magnitude of the power measured thereby and adjusts the power consumption to the desired level. The microgrid analyzer (10) sends an analog signal (10a) to the variable-frequency drivers (2b), variable-frequency inverter (2b'), and variable-voltage power sources (2c,2c'), all of which are embedded in the microgrid. The microgrid analyzer (10) also sends a digital load-analyzer signal (1 Od) to the digital loads (7) in the microgrid for switching on/off the same. The generator driver (2a,2a') adjusts the voltage level of the DC bus with respect to the charging voltage of the battery (9). It sends an analog signal (10b) about said voltage to the microgrid analyzer (10), which is dependent on the battery (9) charge. The amplitude of the (10a,10d) signals sent to the adjustable loads (7, 9', 1 1 , 1 1 ',12, 12') is also dependent on this signal (10b) because the planned battery charging/discharging current is obtained by adjusting the amplitude of the signal (10a, 10d) sent to adjustable loads. The battery charging or discharging current may be planned on a daily, seasonal basis, or based on a tariff, in accordance with the renewable energy potential varying with the meteorological conditions, and with the microgrid demand.

Here, the microgrid manager aims to adjust the amount of power to or from the distribution network (6) to the desired level making use of these signals (10a,10b,10d). During periods of excess renewable power generation in the microgrid, the consumption by the analog (9',1 1 ,1 1 ',12,12') and digital loads (7) and hence their benefit is increased, instead of reducing the production potential of the generator (1 ,1 ') by the smart meter (8). The variable-frequency drivers (2b) first rectify the grid's AC to a constant voltage DC by means of a rectifier, and subsequently convert the DC to an AC at the desired frequency applied to the analog loads (1 1 ) via pulse width modulation (PWM). The variable-frequency drivers (2b) and the variable-frequency inverters (2b') adjust the frequency (1 1 ,1 1 ') of the analog loads connected thereto while the variable-voltage power sources (2c,2c') adjust the voltage of the analog loads (9',12,12') connected thereto, to a value so that the amplitude of the signal (10a) from the analyzer (10) will be maintained at the desired value. Hence, the power transmitted from the distribution network (6) fluctuates around the value adjusted on the microgrid analyzer (10). The amplitude of this fluctuation is dependent on the power input of a switched load, or on the power output changes of the generator (1 ,1 ') or on the power input changes of the analog loads (9',1 1 ,1 1 ',12,12'). One of the analog loads (9',1 1 ,1 1 ',12,12') or digital loads (7) may be given priority based on the sensor data and certain rules.

Connecting the consumer drivers (2b', 2c') to the DC bus allows to power those directly from the generator drivers (2a,2a') without inverting their power input in the inverter (2), whereby the conversion efficiency during consumption of the renewable energy in the microgrid is increased. Said process is carried out only by the variable-frequency inverter (2b') which drives the analog load(s) (1 1 ') connected thereto and generates AC for the motors, and by the variable-voltage power source (2c') which changes DC voltage for the loads such as resistors (12') and electrolyzers (9'). The inverter (2), however, inverts the remaining DC power from the battery (9), variable-frequency inverter (2b'), and the variable-voltage DC source (2c') to AC at grid standard.

If the entire capacity of the analog loads (9',1 1 ,1 1 ',12,12') is consumed, the battery (9) is full and the power transmitted to the distribution network (6) is surpassing the desired level, then the non-priority digital loads (7) can be activated. The maximum power allowed to pass to the distribution network (6) through the microgrid analyzer (10) must be set to a value less than the maximum power allowed to pass to the distribution network (6) through the smart meter (8).This adjustment enables the coordination of the microgrid analyzer (10) and the smart meter (8) for maximum renewable resource harvesting. The smart meter (8) will limit the power generation of the generators (1 ,1 ') only if the total capacity of all adjustable loads (7,9', 1 1 , 1 1 ',12, 12') is activated. Thus, the instantaneous value of the power transmitted to the distribution network (6) will fluctuate between two limiting values. It will be more than the control power adjusted by the microgrid analyzer (10), but less than the control power adjusted by the smart meter (8). The difference between these limiting values can also be further varied based on sensor data about the charge level of energy storages.

In case the distribution network (6) is a smart grid, the power to be transmitted through the smart meter (8) and/or microgrid analyzer (10) to the distribution network (6) is determined by the centralized computer controlling the grid (6) via a communication network. The sensors mounted in the microgrid provide the smart grid with the required data to obtain the maximum benefit for both the smart grid (6) and the microgrid. The data are sent to the centralized computer by means of said communication network. The centralized computer of the distribution network (6) may change the maximum power to be transmitted through the microgrid analyzer (10) to the distribution network (6) instantaneously, by evaluating said sensors' data and its own load.

If a microgrid manager owns multiple microgrids and power generation facilities within a distribution network, the distribution or transmission grid operator may allow offsetting power generated and consumed in these facilities and claim only the distribution and transmission fees of the transmitted power between these multiple microgrids. If the purchase price of power is higher than the selling price for the microgrid, its manager would like to minimize the instantaneous power exchanged between the distribution network and the microgrids. If some of the generators (1 ,1 ') and their associated drivers (2, 2a, 2a') and meters (3) are placed outside of such economically integrated microgrids, the microgrids' analyzers and generator meters should send their sensor data via a private communication network to the microgrid's central computer, called a virtual microgrid, providing the data flow and decision making system below:

· a communication channel informing the virtual microgrid about the sensor signals based on the powers measured by the generator meters (3) outside the microgrid(s),

• the sensor signals based on the power transmitted through the analyzer(s) (10) of the microgrid(s) to/from the distribution network,

• the signals based on the sensor data having an impact on the adjustable loads (7,9', 1 1 , 1 1 ',12, 12') and energy storages of the microgrid(s),

• the control signals (8a) sent to the generator drivers (2, 2a,2a'), the load signals (10a, 10d) of the microgrid analyzer(s) (10), and the signals carrying the sensor data and

• a centralized computer which constitutes and operates the virtual microgrid, said computer calculating the difference between the total generation of the generator meters (3) inside and outside the microgrid(s) and the total consumption of the virtual microgrid; evaluating the current sensor data, and thus based on this difference, calculating the analog (10a) and digital load (1 Od) signals sent to the drivers (2b,2b',2c,2c') of the adjustable loads (7,9',1 1 ,1 1 ',12,12') of the virtual microgrid; and transmitting these load signals via a communication channel to each microgrid analyzer to which these load drivers are connected.

If the microgrid is not connected to a distribution network (6) (off-grid system), as shown in Fig. 3, then the task of the distribution network (6) is performed by the battery (9). In this case, the microgrid analyzer (10) is located between the battery (9) and the DC bus and the consumption of the adjustable loads (7,9', 1 1 ,1 1 ',12,12') is controlled based on the excess or deficient power charged/discharged to/from the battery (9) in lieu of the distribution network (6). As the microgrid analyzer (10) operates in direct connection with the battery (9), the potential (Ub) between the poles of the battery (9) showing its charge state is equal to that measured in the analyzer and this data is not required to be transmitted to the analyzer via an additional communication signal (10b). The consumption of the analog loads (9',11,11',12,12') is adjusted by the analog load-analyzer signal (10a) sent to the variable- frequency driver (2b), the variable-frequency inverter (2b'), the variable-voltage power sources (2c,2c'). The consumption of digital loads (7) is adjusted by digital load-analyzer signal (1 Od) sent to the digital loads (7). Said signals are dependent on the battery voltage (Ub) in order not to exceed the maximum charging/discharging current of the battery according to the battery's charge status. Thus, the desired charging/discharging current is adjusted to prevent the generators (1,1') and the loads from overcharging and over discharging the battery (9), respectively. Further, the surplus renewable power can be exploited optimally by the adjustable loads (7,9', 11 ,11 ',12,12'), in case the battery (9) is fully charged.

In an actual case, there may be more analog loads (9',11,11',12,12') and digital loads (7) than the number of analog loads (9',11,11',12,12') and digital loads (7) shown in Fig.1,. The microgrid manager makes the decisions regarding the temperature of outdoor, indoor environments, heat storages; which loads will be activated under what conditions depending on the season; and which load will be turned into an adjustable load (7,9', 11,11 ',12,12') and in what order, wherein the microgrid automation is programmed accordingly.