FIELD OF THE INVENTION

The present invention relates in general to renewable energy systems and more specifically to wind solar hybrid system and method.

BACKGROUND OF THE INVENTION

In recent years, due to increasing cost of energy from conventional sources such as fossil fuels and emission of greenhouse gases, alternative sources of energy such as wind and solar energy have gained significant prominence for their clean nature and wide availability. However, wind and solar energy suffer from the drawback of having variable and intermittent power output when compared to conventional fuels. A lot of research and progress has been made in harnessing renewable forms of energy as these sources are eco-friendly and sustainable as opposed to fossil fuels which are limited in quantity. Wind and solar energy when combined together are complimentary in nature. Solar power peaks during the day and wind power is prevalent during the late evenings and early mornings. Combining both these forms of energy will thus provide a more stable power output throughout the day and also reduce the grid intermittency. Also, it will result in better utilization of the grid infrastructure due to the different peaking intervals of wind and solar as a large portion of the power evacuation infrastructure used for establishing the wind farm or solar park remains redundant during the absence of either forms of energy.

At present, wind with solar systems that have been developed are mostly co-located in nature where two largely independent power generation systems are present next to each other in order to share the larger transmission network such as the substation and transmission lines. However, these systems have a drawback in terms of the efficiency and wastage of infrastructure used at two independent sites resulting in lower hybridization of the system. In view of the same, there is a need to integrate the two systems together in a more efficient manner. In order to solve the above problems, the invention presented below provides an improved wind solar hybrid power generation system and method.

OBJECTS OF THE INVENTION It is an object of the present invention to provide a wind-solar hybrid power generation system and method which shares common components and resources between the wind turbine and solar park. It is also an object of the present invention to provide a wind-solar hybrid power generation system and method which more efficiently utilizes the power evacuation and grid infrastructure facilities of the combined system.

Yet another object of the present invention is to provide a wind- solar hybrid power generation system and method which better utilizes the land and power evacuation infrastructure of a wind turbine by adding solar power.

Yet another object of the present invention is to provide a wind-solar hybrid power generation system and method that provides better utilization of grid due to different peaking intervals (or complimentary nature) of wind and solar.

Yet another object of the present invention is to provide a wind- solar hybrid power generation system and method which provides a less volatile and more stable power output. Yet another object of the present invention is to provide a wind- solar hybrid power generation system and method that reduces the intermittency of the generated power which greatly improves grid stability.

Yet another object of the present invention is to provide a wind- solar hybrid power generation system and method which more efficiently combines the power output from a wind turbine and solar park.

Yet another object of the present invention is to provide a wind- solar hybrid power generation system and method that can be integrated with an energy storage system.

Yet still another object of the present invention is to provide a wind-solar hybrid power generation system and method that reduces cost of evacuation. Yet still another object of the present invention is to provide a wind-solar hybrid power generation system and method that provides a higher plant load factor.

Yet still another object of the present invention is to provide a wind-solar hybrid power generation system and method that eliminates the need for separate power converter/inverter for the wind turbine and solar park.

Yet still another object of the present invention is to provide a wind-solar hybrid power generation system and method that increases the efficiency of inverter/power-converter as the hybrid converter consistently operates closer to its rated power when compared to operating as standalone system.

Yet still another object of the present invention is to provide a wind-solar hybrid power generation system and method that is easy and cost effective to maintain.

SUMMARY OF THE INVENTION

The present invention relates to a wind-solar hybrid power generation system and a method for integrating energy output from solar generators like PV cells, wind turbine and storage system by utilizing the infrastructure of a wind turbine or hybrid inverter (209) and implementing solar and energy storage units as add-on units to provide a stable and efficient output.

According to an aspect of the present invention there is provided a wind solar hybrid integration method that utilizes the power converter of the wind turbine as a common inverter for both wind and solar system. The combined output of the system is capped such that it does not exceed the rated power output of the wind turbine or the hybrid inverter. Hence, the remaining electrical infrastructure of the wind turbine which includes the transformers, yard electricals, transmission lines, substation etc. is shared/common for both wind and solar systems. This leads to the evacuation capacity of the combined system remaining the same as that of the wind turbine or the hybrid inverter. However, the utilization factor of the grid is significantly improved due to constant loading throughout the day since wind and solar are complementary in nature. This method of wind solar hybrid integration at power converter/inverter level has been termed by ReGen as "true hybrid".

According to an aspect of the present invention there is provided a wind-solar hybrid system comprising: a wind generator connected to a rectifier wherein the rectifier is connected to a power conditioning unit which is further connected to a common capacitor bank; a solar generator connected to a DC junction wherein the DC junction is connected to a power conditioning unit which is further connected to the common capacitor bank (DC link); and the common capacitor bank is electrically connected to an inverter which is further connected to a transformer and the output from the transformer is fed into a High- Voltage line.

According to another aspect of the present invention power output from the hybrid system is capped at the wind turbine's rated power capacity. According to another aspect of the present invention the power output from the hybrid system is capped at the hybrid inverter's rated power capacity.

According to another aspect of the present invention the wind and solar sections include controllers to control power generation, error monitoring and data acquisition of the respective system.

According to another aspect of the present invention the hybrid inverter is designed such that the electrical energy pumped from the solar generators and wind generators are intelligently controlled to be capped within the available evacuation limits.

According to another aspect of the present invention energy generated from the wind and solar generators are pooled together at the system level or the inverter level.

According to another aspect of the present invention the inverter, the power transformer and evacuation lines are capped at the rated power capacity of the wind turbine.

According to another aspect of the present invention there is provided a storage system controlled via a controller and connected to the outputs of the wind and solar sections. According to still another aspect of the present invention a wind-solar hybrid system comprising: a wind generator connected to a hybrid converter wind and inverter section; a solar generator connected to a hybrid converter solar section; and a transformer connected to output of the hybrid inverter section and the output thereof from the transformer is fed into a High- Voltage line.

According to still another aspect of the present invention the hybrid converter wind section includes a common integrated inverter for wind and solar section. According to still another aspect of the present invention the output from the hybrid converter solar section is fed to the hybrid converter wind and inverter section.

According to still another aspect of the present invention a storage system operating bi- directionally taking/supplying power to the capacitor bank (DC-link) is provided which is connected to the hybrid inverter.

According to yet another aspect of the present invention there is provided a method for wind- solar hybrid system comprising the steps of dnitialization the system wherein a hybrid unit starts operation after a manual command or auto-start command; in the next step of standstill a controller checks for the system OK status signal and solar voltage, after which the unit is set into starting mode; in the next step of starting the solar unit is connected to an inverter and the hybrid unit monitors the DC voltage from solar panels, when the voltage reaches optimum value (V _t h _re sh), the hybrid unit moves to a power production mode; and in the power production mode, the Maximum Power Point Tracking (MPPT) is enabled and the hybrid unit starts generating power.

According to yet another aspect of the present invention the method further includes the steps of initialization the system wherein a hybrid unit starts operation after a manual command or auto-start command; in the next step of standstill a controller checks for the system OK status signal and speed of the wind generator, if the conditions are satisfied the unit is set into starting mode; in the next step of starting the wind unit is connected to an inverter and the hybrid unit monitors the speed of the wind generator, when the speed reaches optimum value (n _t h _re sh), the hybrid unit moves to a power production mode; and in the step of power production mode wherein the Maximum Power Point Tracking (MPPT) is enabled and the hybrid unit starts generating power.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 illustrates a co-located conventional wind-solar hybrid system.

Fig. 2 illustrates a block diagram of a wind-solar hybrid system according to an embodiment of the present invention.

Fig. 3 illustrates a field layout of the wind-solar hybrid system according to an embodiment of the present invention.

Fig. 4 illustrates a field layout of a storage enabled wind-solar hybrid system according to an embodiment of the present invention.

Fig. 5 illustrates a detailed block diagram of the storage enabled wind-solar hybrid system explained in Fig. 4 according to an embodiment of the present invention.

Fig. 6 illustrates a method for controlling the wind-solar hybrid system according to an embodiment of the present invention.

Fig. 7 illustrates the control units and their associated parameters present according to an embodiment of the present invention

Fig. 8 illustrates the concept of capping of output power of the hybrid system to the rated capacity of the wind turbine according to an embodiment of the present invention

DETAILED DESCRIPTION OF THE INVENTION

The detailed description set forth below in connection with the appended drawings is intended as a description of various embodiments of the present invention and is not intended to represent the only embodiments in which the present invention may be practiced. Each embodiment described in this disclosure is provided merely as an example or illustration of the present invention, and should not necessarily be construed as preferred or advantageous over other embodiments. The detailed description includes specific details for the purpose of providing a thorough understanding of the present invention. However, it will be apparent to those skilled in the art that the present invention may be practiced without these specific details.

Figure 1 illustrates a conventional co-located hybrid system. The conventional system includes photo voltaic cells (PV) or any other solar generator (101), a wind generator (103), independent power converting units (105, 113), a high voltage line (107) and two transformers (109, 111). This system includes two independent electricity generation systems i.e. solar and wind to combine their independent outputs on a high voltage line. However, the system described in Fig. 1 is not a wind-solar hybrid as it does not fully integrate the solar and wind systems for generating energy.

Figure 2 illustrates a block diagram of wind-solar hybrid system according to an embodiment of the present invention. A typical gearless wind turbine consists of three stages (AC-DC- AC) frequency converter which includes a wind generator (203) which generates alternating current (AC). The wind generator (203) is connected to a rectifier that rectifies the alternating current generated by the wind generator (203) into a direct current (DC). The rectifier is connected to a step-up chopper (or similar power conditioning unit) to be stepped-up to a constant DC voltage. This stepped-up DC voltage is then available across a common huge capacitor bank (or similar devices) i.e. DC-link capacitors (213). The system also includes photovoltaic (PV) (or similar solar power generating units) cells mounted on panels to generate solar energy. The varying DC power generated by the solar generators is passed through a DC junction and then through a step-up chopper or stepped down (or any other type of similar power conditioning). The varying DC is power conditioned to a constant DC voltage and made available across the common DC-link capacitors. The common DC-link capacitor (213) is electrically connected to an inverter (209) which inverts the electrical power available across the common DC-link (213) into AC. This output AC voltage is then stepped-up through a transformer (211) and fed into a High- Voltage line. According to an embodiment of the present invention, the power output from the hybrid system is capped at wind turbine's rated power capacity. Both the wind and solar sections have separate controllers (215 and 217) which control the power generation, error monitoring and data acquisition of the respective system. The overall control system of the hybrid inverter (209) is designed such that the electrical energy pumped from the solar generators and wind generators are intelligently controlled to be capped within the evacuation limits. Further, during integration of large solar installations with wind turbine, multi-MPPT (maximum power point tracker) option may be enabled in the hybrid unit (205 from figure 2) to generate maximum power from a park of the solar generators.

According to an embodiment of the present invention, energy generated from both wind and solar generators are pooled together at the system level or the inverter level. Further, most of the solar panels are erected on the land available around the wind turbine. This enables the hybrid system to utilize the entire common infrastructure between wind and solar generation systems efficiently. Figure 3 illustrates a possible field layout of the wind-solar hybrid system according to an embodiment of the present invention wherein the wind (207) and solar (205) convertor systems have a single inverter system integrated in the hybrid converter wind section.

According to an embodiment of the present invention the wind system (207) may or may not be in operation for solar to share its resources, and the vice-versa also applies good; i.e. the wind system (207) can operate with or without the solar (205) section. However, the common inverter (209) needs to be operational for either of the systems to operate. The inverter (209) is driven by a driver circuit (219) which integrates the energy of wind and solar to AC. The data from the driver circuitry (219) is logged through the wind controller (217) (alternatively the solar controller (215) can also be used). The power electronics driver (219) inside the inverter (209) operates independent of the wind and solar controllers (215 and 217). The wind controller and solar controller exchange data via the industrial communication protocol or similar communication systems (represented by dotted lines). In addition to this, the safety controllers in both the systems are connected electrically to form a safety chain. When this chain is broken, all the sub-systems will go into respective safe modes.

The wind controller (217) in the hybrid solution operates as per its standard behaviour in the standalone solution except limiting its output power when solar is in operation and the pooled output exceeds the rated power of the hybrid inverter. The solar controller (215) receives the operation data of wind controller (217) via industrial communication protocol and safety status through safety chain. The vice-versa is also possible based on the requirement of the application where the hybrid system is used; i.e. energy from the solar generator can also be curtailed to maintain the maximum output power combined is never more than the rated power of the hybrid inverter.

The solar section (205) follows the sequence to generate power as illustrated in figure 6. The said figure illustrates the flow chart for method of operating the wind-solar hybrid according to an embodiment of the present invention. Since, the invention is implemented on a wind turbine by using solar system as an add on unit, it is advantageous to use a connection and control strategy in which the wind energy converter is treated as a master unit and solar energy converter unit is treated as a slave unit, the vice-versa is also possible. Both the wind and solar systems use independent controllers and hardware components. Data is exchanged between the master and slave through industrial communication protocol or equivalent. The sequence for generating power is explained as a flow chart in figure 6 and its details are given below:

1. Initialization Mode: The Hybrid unit starts operation after a manual command or autostart command

2. Standstill Mode: The controller checks for the system OK status signal and solar voltage, after which the unit is set into the starting mode.

3. Starting Mode: The hybrid unit monitors the DC voltage from the solar panels, when the voltage reaches optimum value (Vthresh), the hybrid unit moves to the Power Production Mode.

4. Power Production: Maximum Power Point Tracking (MPPT) is enabled and the hybrid unit starts generating power.

5. Idle/Starting: The slave controller sets the hybrid unit to idle mode if the sunlight is too low (during the night or when clouded) for power production, where the unit will be energized but pulsing of the insulated-gate bipolar transistors (IGBTs) will be stopped. During this mode the hybrid unit continuously monitors the solar voltage and system OK signal, when the voltage goes above the set threshold; the unit goes back to the power production mode.

6. Service mode: The Wind-solar DC breaker and DC breakers from the solar generator side are automatically disconnected and the solar unit is completely de-energized for service personals to act safely.

7. Error: When the error logic within the slave detects any abnormal event (temperature rise above threshold, voltage rise above threshold or negative status feedback from a fan etc.) the slave programmable logic controller (PLC)/controller sets the solar unit into stop mode (The Wind-solar DC breaker and DC breakers inside the SSCBs are automatically disconnected and the solar unit is completely de-energized). The error event is logged with time stamps for analysis. 8. Power sharing control between wind and solar

Power Control Modes: There are totally 2 types of power sharing controls in hybrid. The detailed steps are explained below and in Figure 7. a. Wind preference Mode:

The preferred source of power is wind. If the plant output is less than its rated capacity or set limit the deficit power is supplied by the solar slave unit. If wind output is sufficient to meet the plant load, solar unit goes into idle mode. b. Solar preference Mode:

The preferred source of power is solar. The solar output is limited by its rated capacity and minimum power at which the wind generator can operate at the prevailing wind speed. The wind output is limited by the output of solar generator through a power set point. Control Blocks: Figure 7 highlights the important control blocks used in the hybrid unit, the details of which are given below.

Solar power predictor:

This block calculates the solar power available and predicts future value based on rising or falling trend. The output of this block "calc_solar_power_output" is given as input to the block "set-point controller". This block is disabled if the wind power output has priority over solar power output. This block is implemented inside the wind controller.

Set-point controller:

This block calculates individual set-points for solar slave and wind master respectively. This block is implemented inside wind controller.

PID regulators for power control: The individual set-points are used internally by wind master and solar slave respectively to control power output. There are two PID blocks each on solar and wind controllers respectively. According to another embodiment of the present invention a bi-directional storage system (401) may be integrated in the system as indicated in figure 4 and figure 5. Advantageously, the storage system (401) is not restricted to any particular kind of storage device including but not limited to lead acid battery, a lithium-ion battery, a flow battery or the like. The storage system (401) consists of DC power based charger and discharger connected with storage device or similar systems. The charging and discharging of the storage system is controlled by a separate controller marked as (501) in figure 5. Integration of storage system (401) allows generation and storage of power even in cases where grid is not available. This ensures that energy is generated and stored when grid is not available and evacuated when the load requirement is high.

Thus, the output power of the present invention would be less volatile and more stable compared to wind or solar standalone. Further, better utilization of grid is possible due to different peaking intervals of wind and solar. Also, as the evacuation lines are fixed at the rating of the wind park, the Capacity Utilization Factor (CUF) of the hybrid park is higher than either Wind or Solar could individually offer.

Further, solar panels can be installed to a running wind turbine without any modification to the evacuation system and the transmission lines. This is possible only because the power output is peaked at the capacity of the wind turbine or the hybrid inverter. Also, transmission losses are decreased (since hybrid is operated at higher AC voltage than the stand alone solar) and better utilization of transmission equipment is possible owing to shared electrical infrastructure. Further, inverter's efficiency is improved since it runs closer to full capacity, thus improving the CUF of the system. Wind and solar energy could have different tariffs based on different policies drafted by the governing agencies. Hence the following method is proposed to bifurcate how much energy is being generated by the wind and solar sources respectively. Separate metering for solar and wind in the hybrid system can be easily done using Direct Current Multi-Function Transducer (DC-MFT) or DC meters. The utility and regulatory bodies are not at any disadvantage as actual billing will only be done post-losses on the High Voltage (HV) side as already being done. DC-MFT will be used only to bifurcate the share of generation from solar and wind individually from the total energy fed in to the grid. The following formula is proposed: (From figure 2: H - AC meter reading, W - Wind DC-MFT, S - Solar DC-MFT)

S

Solar Gen = H—— - w ^{+ s} Wind Gen = H— w+s

Since other modifications and changes to fit particular requirements and environments will be apparent to those skilled in the art, the invention is not considered limited as described by the present preferred embodiments which have been chosen for purposes of disclosure, and covers all changes and modifications which do not constitute departure from the spirit and scope of this invention.