Technical Field

The invention relates to a new type of inverter structure that delivers energy output at a high voltage level.

Prior Art

The existing inverter structures in the known state of the art can output at low voltage level and the connections of the inverters with the network are carried out through amplifier transformers. Existing inverters cannot be used directly at high voltage level. Thus, additional electrical connection systems are needed and a certain installed power level cannot be exceeded with existing inverters.

Brief Description and Purposes of the Invention

The subject invention relates to a new inverter in order to eliminate the above- mentioned disadvantages and to bring new technical advantages to the relevant field.

The invention has been developed especially for solar energy installations. Since the dimensions of the solar energy field installations are growing day by day, they meet the requirement for a new inverter type.

The structure of the invention can be used in photovoltaic-based renewable energy plants that generate electricity using solar energy. The realized inverter adapts the electrical energy at the direct current level obtained through the photovoltaic panels to the grid parameters. It can be directly connected to high voltage levels (medium voltage in the old standard) of 22kV or 36kV unlike conventional inverter systems. Conventional inverter systems can be connected to the electricity network to the high voltage level by means of an amplifier transformer. All conventional inverter systems are connected at low voltage level in this way. Electrical energy is supplied to the network at high voltage level at the alternative current point in the proposed new model. A simpler installation without the amplifier transformer can be contemplated in this way. The inverter directly generates high voltage thanks to its voltage doubler electronic circuit structures. The voltage doubler structure used in the inverter is a unique design that has not been used before. In addition, there is galvanic insulation at 3 kV level and optical insulation between each voltage doubler circuit to increase the safety level. A more practical installation, less workmanship, and less network connection inefficiencies can be achieved in this way. The operating voltage for each layer is 3 kV and the insulation level for each layer is 5 kV regarding the provision of the aforementioned processes. Photovoltaic panels are connected to each other in series in the field where they are installed, creating sequences with higher direct current voltages. This direct current voltage must be brought to the alternative current level required by the electricity network first. Afterwards, the voltage is increased with the help of amplifier transformers to ensure compatibility with the voltage level of the connection point. A system that can be connected to the network has to make the voltage level, frequency, phase angle, and phase sequence parameters the same as the network. In this way, equalizing currents or failure situations do not occur and a healthy operation is ensured. In addition, the proposed new inverter, which uses high voltage level, can be manufactured at powers (>3 MWe) that are too large to be obtained at low voltage level. This structure can also be adapted to wind, biogas, fuel cells, energy storage, smart grids, military electronics, aviation, and electric vehicle charging systems.

One of the main purposes of the invention is to use standard electronic components as well as to keep the conversion rate at a low level by keeping the DC and AC voltages close to each other.

The advantages obtained by the invention are as follows;

• It is possible to design a more efficient structure. The efficient structure is provided as follows; It is known that the efficiency level can increase with the decreasing current in high-voltage systems. In addition, the reduction in the number of connection points, the absence of a distribution board on the low voltage alternating current side, and the decrease in connection losses are also positive effects on the efficiency. In addition, the values of the passive elements in the LCL filter in the inverter internal structure can be reduced by optimizing the switching frequency, thus contributing to the efficiency increase.

• Achieving a more compact design,

• Reducing indirect costs by using less labor,

• Aiming to obtain a more reliable inverter structure (The fact that the structure is of great power is important in terms of providing more stable operating parameters. The operation of a single device with great power provides simplicity in terms of the control system. In addition, the selection of the passive elements used was made to confirm this feature. The probability of failure is reduced by reducing the system, component, and connection points used.),

• Ensuring that for great powers, inverter structures that cannot be obtained at low voltage level can be obtained with high voltage inverters,

• Use of direct current voltage doublers in realizing SST structure,

• Using multiple switching frequencies in the inverter (New generation inverters use a higher level of switching frequency to achieve the network frequency. More than one voltage doubler structure is used and a new impulse is given to transmit energy from one layer to the other within the scope of the proposed new technology. It is clear that in this way that there is a need for a second switching frequency at a higher frequency and that this secondary switching frequency will be at least as large as the ratio at which the voltage is doubled.),

• The voltage stress is distributed to the layers (Each layer contains two MOSFETs connected in HERIC type with 3 kV strength and two passive elements of C (capacitor)with 3 kV strength. Another voltage level below 3 kV can also be used, for example, when we consider the level of 2 kV, there will be 14 serial connected layers for 3 kV, while there will be 21 serial connected layers when 2 kV is used. Basically, it is sufficient to use 12 layers to provide 36 kV level. This way, each layer will work at 3 kV. The safety level has been further increased and a system that can operate safely even at 42 kV level at a level of approximately 15% higher than 36 kV has been designed with a practical approach. This is not theoretically necessary, but it is necessary because there will be instantaneous voltage pulses in the network in practical use. MOSFET used can allow up to 4.5 kV level, 3 kV level has been selected for a certain safety band. This structure repeats itself 14 times and the effect of the high voltage is divided equally into each layer since the layers are connected in series with each other. The element C can also ensure that this voltage sharing is equal. Stress caused by high voltage at this point is also distributed by being lowered on electronic components.),

• Ensuring electrical insulation between the layers (The said electrical insulation is related to the gate ends of the MOSFETs. The layers are basically connected to each other through capacitor and MOSFET elements. There is a separate drive circuit structure in each layer for the MOSFET drive signal section. Unwanted short circuit formations are prevented in this way. The signal circuit in each layer is connected to the next layer following the same by optical coupling. This prevents impact voltages from entering the driver circuit in case of a possible fault.),

• Using an independent MOSFET driver per layer,

• Transmission of data between layers by optical coupling (optical coupling basically carries out galvanic insulation. However, the voltages that can be isolated from each other will not be above a certain value at this point. Therefore, each layer is connected to the next layer through optical isolation and transmits the signal in this way.),

• Provision of electrical insulation at 3000 Volt level.

Detailed Description of the Invention

The innovation subject to the invention is described with examples in the way to create no limiting effect and only for a better understanding of the subject in this detailed description.

The invention relates to a new type of inverter that eliminates the need for an amplifier transformer. It can also be called a solar inverter.

That being said, there is no need to use the connection systems between the inverter and the transformer. The proposed structure includes electronic circuits with SST (Solid State Transformer) feature. Voltage doubler structures were used to obtain high voltage in the proposed inverter device. The structure used is basically the combined form of the Cockcroft Walton structure and the HERIC type structure. It is the circuit structure which is tried out for the first time and used in inverters for the first time. It is not a multi-layer inverter structure. Two different switching frequencies should be used for this mode of operation and the driver circuit software should be specially prepared for this purpose.

The structure used for this purpose is a Cockcroft Walton voltage doubler circuit adapted to the alternating current system. Each layer of the voltage doubler system is positioned to correspond to a direct current level of 3000 Volt. In this way, the voltage stress on each electronic element was limited to a certain value and an SST high voltage structure was obtained with accessible electronic components. Basically, the voltage doubler structure consists of 14 repetitive voltage doubler circuits. The CockCraft Walton DC voltage doubler circuit used has been changed and made suitable for AC. The new structure has been constructed with four semiconductor components suitable for HERIC (high efficiency and reliable inverter concept) type structure in return for each semiconductor diode for this purpose.

The inverter structure in the invention includes the following series steps. The device sheath is manufactured in standard ISO container sizes.

Serial stages consist of Input Terminals, DC Separators, DC Fuses, DC Surge Arresters, MPPT Units, 300 Volt DC Bus, Standard H Bridge Structures, SST High Frequency Transformers, Cockcroft Walton Voltage Doubler Circuits in Converted Structure (made suitable for AC), 36 kV LCL Filter, 36 kV Surge Arresters, 36 kV Current- Voltage Transformers, 36 kV Fuses, 36 kV Separator, Control System, Independent MOSFET Driver Circuits in Each Stage, Environmental Measurement Unit, Network Measurement Unit, Auxiliary Power Supply, Communication Unit, Outer Sheath and Cooling Systems. These circuits were combined in series and the inverter structure was obtained.

Since the number of voltage doublers is an element related to the desired high voltage level, it can be changed in accordance with the purpose and need. Likewise, the DC bus voltage is related to the strength values of the switching components to be used. If the design is revised for a different MOSFET, it would not be limited to 3000 Volt DC level and could be changed. Some definitions of the components are as follows,

• Input Terminals are the connection points of the DC energy coming from Photovoltaic Panels, in normal applications, there is a voltage level below 2000 Vdc. The voltage that solar panels and solar cables can withstand is at this level.

• DC Separators allow for independently disconnecting each one of the solar inputs connected to the inverter from the system. Some of the panels in the photovoltaic system can be separated for maintenance purposes or at the time of failure.

• DC Fuses are input fuses for protection purposes, internal type thermoplastic fuses are used for this purpose.

• DC Surge Arresters are protection equipment aimed at suppressing electric shocks and lightning strikes that may occur at the entrance.

• Maximum Power Point Monitoring (MPPT) Units are electronic structures that optimize operating voltages and currents for more efficient operation of the Photovoltaic system. It is the first electronic input part in the system.

• The 3000 Volt DC Bus is the structure that increases the DC voltage in the system from the MPPT level to a constant DC level and at this point, collects the DC voltages from all units at a single point. The inverter comprises relatively large pairs of DC busbars along the ISO container in which it is located.

• Standard H Bridge Structures are standard structures formed by four switching elements. More than one is used in the system. The switching signal (drive signal) used is different from the other inverters (original).

• SST High Frequency Transformers, ferrite core transformer with 1/1 rotation rate that can function at high frequency is used since galvanic insulation is desired to be provided in the inverter device (the System). Basically, this section is used because it increases the safety level of the device (since it reduces the possibility of a short circuit between input and output). This element is an optional element and the inverter device can operate without this element. • Cockcroft Walton Voltage Doubler Circuits in Converted Structure, which provide direct high voltage generation, comprising capacitor elements that ensure that two HERIC type connected independent MOFSETs and two voltage shares are equal, in return for semiconductor diodes in each layer. This structure is a new inverter topology and is a unique part of the system. The driver signal should also be changed and rearranged since the related structure is used.

• 36 kV (6 different levels between 28.5 kV and 36 kV are used in Turkey. The design refers to the highest value. The same structure can also be used at lower voltage levels.) LCL Filter is the largest part (in terms of volume and weight) in the filter system used. It ensures that the disruptive effects of high frequency do not affect the network. It is the most important element affecting system design and optimization.

• 36 kV (6 different levels between 28.5 kV and 36 kV are used in Turkey. The design refers to the highest value. The same structure can also be used at lower voltage levels.) Surge Arresters were tried to prevent shock effects such as voltage pulses and lightning by using surge arresters on the network side (AC).

• 36 kV (6 different levels between 28.5 kV and 36 kV are used in Turkey. The design refers to the highest value. The same structure can also be used at lower voltage levels.) Current- Voltage Transformers; current transformers and voltage transformers are used to monitor AC power and electrical parameters transmitted to the network side.

• 36 kV (6 different levels between 28.5 kV and 36 kV are used in Turkey. The design refers to the highest value. The same structure can also be used at lower voltage levels.) Fuses; serial connected fuses used on the network side (AC) ensure that the failure and fault effects do not affect the system.

• 36 kV (6 different levels between 28.5 kV and 36 kV are used in Turkey. The design refers to the highest value. The same structure can also be used at lower voltage levels.) Separator; a three-blade separator assembly has been added to the system to disconnect the system from the AC network if necessary. The separator system is a simple switch system that can be used at high voltage. There are three different mechanical switching leads since there are 3 phases (RST) in question. • The Control System provides the operation of the structure with the software embedded in electronic components (microprocessor) of the system. All necessary parameters are transmitted to the relevant user interfaces (web- mobile) and interventions are made when desired.

• In each stage (Each stage indicates the structure of each voltage doubler circuit used. Voltage up to 3 kV level can be tolerated in each layer and the system can provide up to 42 kV level strength in total. Each voltage doubler circuit includes its own drive structure and is separated from each other by optical insulation.) Independent MOSFET Driver Circuits; the data transmitted from the control system is provided through an optical isolation (must be high speed). The data that the control system supplies to the first layer through optical isolation is supplied to the next card (layer) through another optical isolation element. Thus, each layer is galvanically isolated with each other (with the next one following the same) and with the control system. This is an unusual method of data transmission; however, it is necessary since high voltage is in question.

• Environmental Measurement Unit, each inverter follows data such as environmental radiation, wind, time, location, and can test its own operation values with theoretical calculations.

• Network Measurement Unit, operating parameters of the electricity network can be measured and recorded.

• The Auxiliary Power Supply is constructed with an auxiliary voltage reducing system and energy storage to feed the control, recording and monitoring systems.

• Communication Unit, they are an auxiliary structure that provides data transmission to user interfaces (web-mobile).

• The Outer Sheath, the device is planned to be placed in the standard ISO container so that the ease of transport, placement and sizing is achieved. The outer sheath is a shipping container modified in accordance with the requirements.

• Cooling Systems, there are metal cooling plates that are independent from each other and electrically insulated from each other, connected to the switching elements in the inverter device. In addition, there is a general-purpose cooling system as an auxiliary structure in the system. (There is an air conditioning (air-to-air heat pump) system that can cool the inside of the container. The air conditioner operates when necessary (in the case of heating) and cools the electronic systems in the device because the device is hermetically closed to the outside (IP65 or IP66 protection class). In general terms, it is stated that it is a commonly used structure.)

The invention is an inverter device that provides energy output at high voltage level based on the above detailed explanations, characterized in that it comprises the following elements and the elements other than the sheath element are connected to each other in series;

• At least one Input Terminal, which is the connection points of DC (direct current) energy coming from photovoltaic panels,

• At least one DC Separator, which allows for independently disconnecting each one of the solar inputs connected to the inverter from the inverter device,

• At least one DC input fuse used for protection against any malfunction,

• At least one DC Surge Arrester, which is the protection equipment that provides suppression of electric shocks and lightning strikes that may occur at the inlet of the inverter device (refers to the direct current electrical energy coming from photovoltaic panels (input product) and the alternative current high voltage electrical energy supplied to the network at the outlet (output product)),

• At least one maximum power point monitoring (MPPT) unit which allows for (optimizes) keeping voltage and current values at the required level for more efficient operation of the photovoltaic system (MPPT device (maximum power point tracker) is a standard structure in each solar inverter). The photovoltaic panel is used to keep the current and voltage values at the required level. The optimization condition is that the power value, which is the mathematical multiplication of the current and voltage values, is at the maximum value. The operation structure is specific to the sector),

• The structure that increases the DC voltage from the maximum power point monitoring (MPPT) level to a constant DC level and at this point, collects the DC voltages from all maximum power point monitoring units at a single point is at least one 3000 Volt DC Bus (The lower limit for the voltage value is theoretically absent, there is an upper limit due to the electrical strength of the material. The lower the voltage is selected, the higher the number of layers that double the voltage.),

• At least two Standard H Bridge Structures formed by four switching elements,

• At least one Cockcroft Walton Voltage Doubler Circuit in a converted structure that provides direct high voltage generation, comprising capacitor components that ensure that two HERIC type connected independent MOSFETs and two voltage shares are equal, in return for each semiconductor diode in each layer,

• At least one 36 kV LCL Filter (6 different levels between 28.5 kV and 36 kV are used in Turkey. The design refers to the highest value. The same structure can also be used at lower voltage levels.), which ensures that the disruptive effects of high frequency do not affect the network,

• At least one 36 kV AC Surge Arrester (6 different levels between 28.5 kV and 36 kV are used in Turkey. The design refers to the highest value. The same structure can also be used at lower voltage levels.), which ensures that shock effects such as voltage pulses and lightning are prevented on the AC network side,

• At least one 36 kV Current- Voltage Transformer (6 different levels between 28.5 kV and 36 kV are used in Turkey. The design refers to the highest value. The same structure can also be used at lower voltage levels.), which enables the monitoring of AC (alternating current) power and electrical parameters (These network parameters are Voltage Value, Current Value, Power Factor, Frequency Value, Harmonic Value) transmitted to the network side,

• At least one 36 kV Fuse (6 different levels between 28.5 kV and 36 kV are used in Turkey. The design refers to the highest value. The same structure can also be used at lower voltage levels.), which is used by the AC network and ensures that the failure and error effects do not affect the system,

• At least one 36 kV Separator (6 different levels between 28.5 kV and 36 kV are used in Turkey. The design refers to the highest value. The same structure can also be used at lower voltage levels.) with three blades used at high voltage, which enables separation of the inverter device from the AC network when necessary (can be used in case of network maintenance, network failure, device failure), • At least one Control System that provides the operation of the inverter device(structure) with the software embedded in electronic components (microprocessor) in the inverter device, ensuring that all necessary parameters are transmitted to the relevant user interfaces (web-mobile) and intervened when desired,

• At least one independent MOSFET Drive Circuit, which provides the data transmitted from the control system (Related data are the switching signals required for the operation of the MOSFETs. These are the on and off commands given to the MOSFETs) through optical isolation (must be high speed), located at each stage (Each stage indicates the structure of each voltage doubler circuit used. Voltage up to 3 kV level can be tolerated in each layer and the system can provide up to 42 kV level strength in total. Each voltage doubler circuit comprises its own drive structure and is separated from each other by optical insulation.),

• At least one Environmental Measurement Unit, which enables each inverter to follow data such as environmental radiation, wind, time, location, and to test its own operation values with theoretical calculations,

• At least one Network Measurement Unit, which enables the measurement and recording of the operating parameters of the electricity network (in the form of Electricity Network Parameters, Voltage Value, Current Value, Frequency Value, Power Factor, Harmonic Value),

• At least one Auxiliary Power Supply to feed the control, recording, and monitoring systems (These are the systems that are carried out i to see all the quantitative values described in the previous section by the user and to record them electronically. It is necessary to have a user interface.) provided with an auxiliary voltage reducing system and energy storage,

• At least one Communication Unit that provides data transmission to user interfaces (web-mobile),

• At least one Outer Sheath used as the transportation container in which the inverter device is located (The inverter device is very large and six times larger than the equivalent solar inverters made to date. This device, which is quite large in size, is 12 meters long (40") (it may vary, being not limited to this value) in a standard ISO container. For ease of transport, the device is made in the shipping container.),

• At least one Cooling System comprising an auxiliary cooler that provides cooling against overheating with metal cooling plates that are independent of each other and electrically insulated from each other, connected to the switching elements in the inverter device, also providing cooling inside the container.

It comprises at least one SST High Frequency Transformer, which functions at high frequency in providing galvanic insulation, reduces the possibility of short circuit between the input and output of the inverter device and increases the security level of the device, and is connected in series to other elements except the sheath, which is one of the elements in the inverter device.

The electrical parameters monitored in the said current-voltage transformers are the voltage value, current value, power factor, frequency value, and harmonic value.

The data transmitted in the said control system are the switching signals required for the operation of the MOSFETs.

The parameters of the electricity network, which are measured and recorded by the said network measurement unit, are Electricity Network Parameters, Voltage Value, Current Value, Frequency Value, Power Factor, Harmonic Value.

Regarding the 36 kV value mentioned above, 6 different levels used are 28.5 kV 30 kV 31.5 kV 33 kV, and 36 kV. It is the standard practice in this sector. When the obtained structure achieves 36 kV level, it can also perform lower voltage levels. This is performed depending on the mains voltage in that area during the use of the device.

AC surge arresters can be of both internal or external types at 36 kV level while DC surge arresters are of internal type at 2 kV or 3 kV level.

The said voltage doubler circuits are 14 repetitive circuits. A 14-layer structure with certain safety gaps is presented as the optimum solution since the switching element discussed allows up to 4.5 kV level. The number of layers may decrease when electrical strength levels reach higher values with the developments in electronic technology.

The said voltage doubler circuits are connected by optical coupling to each circuit to ensure signal transmission.

The said DC bus voltage is 3000 V.

The voltages of the said LCL filter, AC surge arrester, current-voltage transformers, fuse, separator elements are between 28.5 and 36 Kv.