A wind turbine generator outputting low frequency electric power

Abstract

The application discloses a wind turbine generator system outputting low-frequency electric energy, wherein a wind turbine, a generator, a current conversion module and a transformer are connected in series and then connected with a low-frequency power grid; the current conversion module is used for converting the electric energy output by the generator into low-frequency electric energy; and the transformer is used for boosting the voltage of the low-frequency electric energy and then delivering the low-frequency electric energy to the low-frequency power grid. Through the modification of the existing power-frequency wind turbine generator system and the energy-taking system, the application overcomes the problem that the existing power-frequency wind turbine generator system is not matched with the low-frequency alternating current system, and is favorable for further promoting the development of the low-frequency alternating current transmission technology and the safe and stable operation of the system.

Description

Technical Field

[0001] This invention relates to the field of wind power technology, and more specifically to a wind turbine that outputs low-frequency electrical energy. Background Technology

[0002] To combat global warming, vigorously developing renewable energy and achieving a clean energy transformation has become a major trend in the energy sector. Existing flexible low-frequency transmission technology offers advantages such as long transmission distances, large transmission capacity, and high reliability, which can greatly promote the aggregation and transmission of wind power from offshore or remote areas rich in wind resources. However, existing wind turbines and their control systems are designed and manufactured according to power frequency standards, making direct connection to low-frequency transmission systems impossible. Therefore, to promote wind power transmission and the application of low-frequency technology, developing wind turbines capable of outputting low-frequency electrical energy has become an urgent need. Summary of the Invention

[0003] Therefore, the technical problem to be solved by the present invention is to overcome the complex problems faced when the power frequency wind turbine is a low frequency wind turbine, and to meet the requirement of low cost, thereby providing a wind turbine that outputs low frequency electrical energy.

[0004] To achieve the above objectives, the present invention provides the following technical solution:

[0005] This invention provides a wind turbine generator that outputs low-frequency electrical energy, comprising: a wind turbine, a generator, a converter module, and a transformer. The wind turbine, generator, converter module, and transformer are connected in series and then connected to a low-frequency power grid. The converter module is used to convert the electrical energy output by the generator into low-frequency electrical energy. The transformer is used to boost the voltage of the low-frequency electrical energy and then transmit it to the low-frequency power grid.

[0006] In one embodiment, the wind turbine that outputs low-frequency electrical energy further includes: a machine-side circuit breaker and a grid-side circuit breaker; the generator is connected to the first end of the converter module through the machine-side circuit breaker; the second end of the converter module is connected to the transformer through the grid-side circuit breaker; the machine-side circuit breaker is used to connect and disconnect the electrical energy on the line between the generator and the converter module; the grid-side circuit breaker is used to connect and disconnect the converter module and the transformer.

[0007] In one embodiment, the wind turbine that outputs low-frequency electrical energy further includes: a low-frequency filter for filtering out electrical noise; the second end of the converter module is connected to the grid-side circuit breaker through the low-frequency filter.

[0008] In one embodiment, the converter module includes: a generator-side converter module, a DC capacitor, and a grid-side converter module; the AC side of the generator-side converter module is connected to the generator via a generator-side circuit breaker, and the DC side of the generator-side converter module is connected in parallel with the DC capacitor and then connected to the DC side of the grid-side converter module; the AC side of the grid-side converter module is connected to the grid-side circuit breaker via a low-frequency filter.

[0009] In one embodiment, the generator-side converter module includes a first converter and a second converter; the AC side of the first converter and the AC side of the second converter are both connected to the generator through a generator-side circuit breaker, and the DC side of the first converter and the DC side of the second converter are connected in series and then connected in parallel with a DC capacitor.

[0010] In one embodiment, the wind turbine that outputs low-frequency electrical energy further includes: an energy harvesting system; the energy harvesting system harvests energy from the low-voltage side of the transformer and outputs AC power of a preset frequency so that the energy harvesting system provides AC power of the preset frequency to the AC load; and / or, the energy harvesting system harvests energy from a DC capacitor and outputs DC power so that the energy harvesting system supplies power to the DC load.

[0011] In one embodiment, the energy harvesting system includes any one or a combination of several of the following: an AC / AC converter, a frequency multiplier transformer, a DC / DC converter, and a DC / AC converter; the AC / AC converter and the frequency multiplier transformer both harvest energy from the low-voltage side of the transformer and output AC power of a preset frequency; the DC / DC converter and the DC / AC converter both harvest energy from a DC capacitor and output DC power.

[0012] In one embodiment, the wind turbine that outputs low-frequency electrical energy further includes: a composite energy harvesting system; the composite energy harvesting system harvests energy from a DC capacitor and the low-voltage side of a transformer; the composite energy harvesting system is used to filter the low-frequency electrical energy output by the converter module; provides dynamic reactive power compensation when there is an AC short-circuit fault on the output side of the grid-side converter module; and outputs AC electrical energy after harvesting energy from the DC capacitor, so that the composite energy harvesting system supplies power to the AC load.

[0013] In one embodiment, the composite energy harvesting system includes: a coupling reactor, a first electronic switch, a second electronic switch, a rectifier, and an inverter; the primary side of the coupling reactor is connected in series with the AC line of the low-voltage side of the transformer to harvest energy from the low-voltage side of the transformer; the DC side of the inverter harvests energy from a DC capacitor, and the AC side of the inverter is connected to an AC load; the AC side of the rectifier is connected to the secondary side of the coupling reactor through the first electronic switch, and the AC side of the rectifier is also connected to the AC line through the second electronic switch; the DC side of the rectifier is connected in parallel with an energy storage battery and then connected in series with the DC side of the inverter.

[0014] In one embodiment, when the AC line is normal, the first electronic switch is open and the second electronic switch is closed. The rectifier uses the id-iq method to filter out harmonics and maintain the DC voltage of the composite energy harvesting system. The inverter uses AC voltage control to generate the AC voltage amplitude and frequency required by the AC load. When an AC voltage drop occurs, the first electronic switch is closed and the second electronic switch is open. The composite energy harvesting system draws energy from the DC capacitor and maintains the DC voltage. The rectifier is connected to provide reactive power to the AC system.

[0015] The technical solution of this invention has the following advantages:

[0016] The wind turbine generator provided by this invention, which outputs low-frequency electrical energy, comprises a wind turbine, a generator, a converter module, and a transformer connected in series and then connected to a low-frequency power grid. The converter module converts the electrical energy output by the generator into low-frequency electrical energy, and the transformer boosts the voltage of the low-frequency electrical energy before transmitting it to the low-frequency power grid. This invention overcomes the mismatch problem between existing power-frequency wind turbine generators and low-frequency AC systems by modifying existing power-frequency wind turbine generators and energy harvesting systems, which is beneficial for further promoting the development of low-frequency AC power transmission technology and the safe and stable operation of the system. Attached Figure Description

[0017] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0018] Figure 1 A composition diagram of a specific example of a wind turbine provided in an embodiment of the present invention;

[0019] Figure 2 A composition diagram of another specific example of a wind turbine provided in an embodiment of the present invention;

[0020] Figure 3 A composition diagram of another specific example of a wind turbine provided in an embodiment of the present invention;

[0021] Figure 4 A topology diagram of a specific example of a wind turbine provided in an embodiment of the present invention;

[0022] Figure 5 A topology diagram of a specific example of a machine-side converter module provided in an embodiment of the present invention;

[0023] Figure 6 A block diagram of a control method for a machine-side converter module provided in an embodiment of the present invention;

[0024] Figure 7 A topology diagram of a specific example of a wind turbine provided in an embodiment of the present invention;

[0025] Figure 8 A topology diagram of a specific example of a composite energy harvesting system provided in an embodiment of the present invention;

[0026] Figure 9 A block diagram of a control method for a rectifier in a composite energy harvesting system provided in an embodiment of the present invention. Detailed Implementation

[0027] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0029] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can also refer to the internal connection of two components; and they can refer to a wireless connection or a wired connection. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0030] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0031] Example

[0032] This invention provides a wind turbine generator that outputs low-frequency electrical energy, such as... Figure 1 As shown, it includes: wind turbine 1, generator 2, converter module 3, and transformer 4. The wind turbine 1, generator 2, converter module 3, and transformer 4 are connected in series and then connected to the low-frequency power grid.

[0033] Specifically, the wind turbine 1 is mechanically connected to the generator 2 and is controlled by the control system; the generator 2 is electrically connected to the converter module 3 and the transformer 4.

[0034] Specifically, the transformer 4 is optimized according to the operating frequency, including the main insulation, longitudinal insulation, short-circuit force, and temperature rise distribution, to reduce the size and weight of the transformer 4. It can realize the transformation function of low-frequency power and transmit low-frequency power.

[0035] Furthermore, the converter module 3 is used to convert the electrical energy output by the generator 2 into low-frequency electrical energy; the transformer 4 is used to boost the voltage of the low-frequency electrical energy and then transmit it to the low-frequency power grid.

[0036] Specifically, the converter module 3 in this embodiment of the invention is actually an AC-AC frequency converter, which is used to convert the input high-frequency electrical energy into low-frequency electrical energy. Its topology can be a mature frequency converter topology in the prior art, and is not limited here.

[0037] In one specific embodiment, such as Figure 2 As shown, the wind turbine generator that outputs low-frequency electrical energy also includes: a machine-side circuit breaker 5 and a grid-side circuit breaker 6; the generator 2 is connected to the first end of the converter module 3 through the machine-side circuit breaker 5; the second end of the converter module 3 is connected to the transformer 4 through the grid-side circuit breaker 6; the machine-side circuit breaker 5 is used to conduct and disconnect the electrical energy on the line between the generator and the converter module; the grid-side circuit breaker 6 is used to conduct and disconnect the converter module and the transformer.

[0038] Specifically, both the machine-side circuit breaker 5 and the grid-side circuit breaker 6 are low-frequency circuit breakers. To address the issue of extended fault breaking time under low-frequency AC voltage, these low-frequency circuit breakers employ phase selection operation, or optimized expansion chamber, or compressed air chamber, or exhaust channel structural design to meet low-frequency breaking requirements and increase contact life.

[0039] Specifically, low-frequency circuit breakers should be able to interrupt low-frequency large currents, which can generally be achieved by optimizing power frequency circuit breakers, replacing them with DC circuit breakers, or replacing them with machine-side low-frequency circuit breakers.

[0040] Specifically, considering cost and the speed of interrupting low-frequency current, this embodiment of the invention selects a low-frequency circuit breaker that optimizes the structure of a power frequency circuit breaker to achieve the switching of low-frequency current. When an AC short-circuit fault occurs in the low-frequency power grid, the low-frequency circuit breaker interrupts the AC short-circuit current at the zero-crossing point of the AC current, thereby protecting the system.

[0041] In one specific embodiment, such as Figure 3 As shown, the wind turbine that outputs low-frequency electrical energy also includes: a low-frequency filter 7; the second end of the converter module 3 is connected to the grid-side circuit breaker 6 through the low-frequency filter.

[0042] Specifically, the low-frequency filter can be a passive filter or an active filter, which can reduce the distortion of low-frequency power output. During the modification process, the resonant frequency of the filter needs to be checked.

[0043] In one specific embodiment, such as Figure 4As shown, the converter module 3 includes: a generator-side converter module 31, a DC capacitor 32, and a grid-side converter module 33; the AC side of the generator-side converter module 31 is connected to the generator 2 through the generator-side circuit breaker 5, and the DC side of the generator-side converter module 31 is connected in parallel with the DC capacitor 32 and then connected to the DC side of the grid-side converter module 33; the AC side of the grid-side converter module 33 is connected to the grid-side circuit breaker 6 through a low-frequency filter.

[0044] Specifically, the grid-side converter module 33 actually includes a grid-side converter and its controller. Through the control function of its controller, it can synchronize with the low-frequency power grid and convert the electrical energy output by the generator 2 into stable low-frequency electrical energy, which is then sent out through the low-frequency power grid.

[0045] Specifically, the grid-side converter consists of power electronic switching devices and filters. The grid-side converter can be a two-level converter, a multi-level converter, or an AC-AC converter, depending on the capacity and voltage requirements. It should be able to achieve bidirectional power transmission.

[0046] Specifically, the grid-side converter filter can be an LC type filter, an LCL filter, or an active filter; in the conversion of power frequency wind turbines to low frequency wind turbines, the resonant frequency needs to be checked.

[0047] Specifically, the generator-side converter module includes the generator-side converter and its controller. The generator-side converter and grid-side converter topologies should be determined according to capacity and voltage requirements, and should be able to achieve bidirectional power transmission. The PWM waveform generated by the control system controls each switching device. The converter topology can be a two-level VSC topology, an MMC-based converter, or an M3C-based AC-AC frequency converter.

[0048] Specifically, the DC capacitor 32 can be either a regular capacitor or a supercapacitor. To ensure stable system operation under impulsive load conditions, a certain amount of energy storage batteries and supercapacitors are provided.

[0049] In one specific embodiment, the generator-side converter module 31 includes: a first converter and a second converter; the AC side of the first converter and the AC side of the second converter are both connected to the generator 2 through the generator-side circuit breaker 5, and the DC side of the first converter and the DC side of the second converter are connected in series and then connected in parallel with the DC capacitor 32.

[0050] For example, the machine-side converter uses a hybrid topology. The first converter can be a 6-pulse rectifier bridge, and the second converter can be a VSC-based converter connected in series. To achieve the change of the VSC DC voltage, the VSC adopts a full-bridge converter topology. The DC voltage relationship of the machine-side converter is as follows: where V... WT This represents the AC voltage amplitude of the wind turbine generator.

[0051]

[0052] The power flowing through the wind turbine generator's converter is determined by the DC voltage V of the rectifier bridge and the VSC itself. dc1 and V dc2 Divide the power equally. The total power flowing through the wind turbine is as follows, where k mppt It is the ratio of active power to DC voltage.

[0053] P = kmpptVdc1 (2)

[0054] That is, total power and V dc1 They are directly proportional, by adjusting V dc1 It can achieve smooth power delivery.

[0055] Wind turbine converters typically employ maximum power point tracking (MPPT) or maintain the DC capacitor voltage of 32V. Preferably, the grid-side converter controls the DC capacitor voltage of 32V, while the turbine-side full-bridge VSC handles its own DC voltage. Furthermore, as the wind power output increases, Vdc2 decreases, and the turbine-side converter control block diagram is as follows: Figure 6 As shown, Figure 6 China P mppt P represents the maximum power of the wind turbine. wt V represents the real-time power of the wind turbine. dcN DC voltage V dc The rated value, I sq I represents the real-time value of the q-axis DC current of the machine-side converter. sqref I is the reference value for the q-axis DC current of the machine-side converter. sd I represents the real-time value of the d-axis DC current of the machine-side converter. sdref This is the reference value for the d-axis DC current of the machine-side converter.

[0056] In one specific embodiment, such as Figure 7 As shown, the wind turbine that outputs low-frequency electrical energy also includes an energy harvesting system 8. The energy harvesting system 8 should have the ability to output power frequency and will provide electrical energy of a suitable voltage level to the internal load of the wind turbine.

[0057] Specifically, after the energy harvesting system 8 takes energy from the low-voltage side of the transformer 4, it outputs AC power of a preset frequency. The AC power of the preset frequency supplies power to AC loads, including the power frequency loads inside the wind turbine; and / or, after the energy harvesting system 8 takes energy from the DC capacitor 32, it outputs DC power, which supplies DC power.

[0058] Optionally, such as Figure 7As shown, the energy harvesting system 8 may include any one or a combination of several of the following: AC / AC converter, frequency multiplier transformer, DC / DC converter, and DC / AC converter; the AC / AC converter and the frequency multiplier transformer both extract energy from the low-voltage side of the transformer 4 and output AC power of a preset frequency; the DC / DC converter and the DC / AC converter both extract energy from the DC capacitor 32 and output DC power.

[0059] Specifically, the embodiments of the present invention utilize the function of frequency multiplier transformers to convert low frequencies into power frequencies, providing stable power to wind turbines and improving their ability to cope with internal impact loads. Compared with other types of energy harvesting systems, the energy harvesting system proposed in the embodiments of the present invention has the advantages of high power supply reliability, low cost and easy modification, and has broad application prospects.

[0060] In one specific embodiment, except Figure 7 The energy harvesting system 8 shown in this embodiment of the invention, which outputs low-frequency electrical energy, further includes: a composite energy harvesting system; the composite energy harvesting system harvests energy from the DC capacitor 32 and the low-voltage side of the transformer 4 respectively; the composite energy harvesting system is used to filter the low-frequency electrical energy output by the converter module 3; provides dynamic reactive power compensation when there is an AC short-circuit fault; and provides AC load power supply, including the power frequency load power supply inside the wind turbine.

[0061] Specifically, such as Figure 8 As shown, the composite energy harvesting system includes: coupling reactors (La, Lb, Lc), first electronic switches (Sa1, Sb1, Sc1), second electronic switches (Sa2, Sb2, Sc2), energy storage battery, rectifier VSC1, and inverter VSC2.

[0062] Specifically, the primary side of the coupling reactor is connected in series with the AC line; the AC side of the rectifier is connected to the secondary side of the coupling reactor through the first electronic switch, and the AC side of the rectifier is also connected to the AC line through the second electronic switch. The DC side of the rectifier is connected in parallel with the energy storage battery and then connected in series with the DC side of the inverter. The DC side of the inverter also draws energy from the DC capacitor 32, and the AC side of the inverter is connected to the AC load.

[0063] Specifically, the coupling reactor can be used as a filter reactor to filter out harmonics during normal operation; during AC short-circuit faults, by switching electronic switches, a dynamic voltage of ΔU is superimposed to promote fault recovery.

[0064] Specifically, the embodiments of the present invention are based on Figure 8 The topology of the hybrid energy harvesting system is shown below, and the operation method of the hybrid energy harvesting system is as follows:

[0065] (1) When the AC line is normal, the first electronic switch is open and the second electronic switch is closed. The rectifier uses the id-iq method to filter out harmonics (control method as follows). Figure 9 As shown), and maintains the DC voltage of the composite energy harvesting system, the inverter adopts AC voltage control to generate the AC voltage amplitude and frequency required for the AC load.

[0066] Specifically, Figure 9 Chinese V Fdref V Fqref V is the reference value for the AC voltage to be compensated. Fd V Fq I represents the actual value of the AC voltage to be compensated. 1d I 1q I represents the real-time value of the dq-axis current of the grid-side converter. 1dref I 1qref These are the reference values ​​for the dq axis current of the machine-side converter.

[0067] (2) When an AC voltage drop occurs, the first electronic switch closes and the second electronic switch opens. The composite energy harvesting system harvests energy from the DC capacitor 32 and maintains the DC voltage. The rectifier is connected to provide reactive power to the AC system.

[0068] based on Figure 7 , Figure 8 The wind turbine topology shown illustrates this process: once the grid AC voltage is established, the low-frequency circuit breaker is closed, and the low-frequency AC voltage charges transformer 4. Subsequently, the energy harvesting system draws energy from the low-frequency grid to charge the wind turbine's internal control system / yaw system and other loads. Then, the grid-side converter is unlocked and begins charging the DC-side capacitor to establish DC voltage. Finally, the turbine-side converter is unlocked. After the entire system starts up, the wind turbine begins outputting low-frequency electrical energy.

[0069] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A wind turbine generator that outputs low-frequency electrical energy, characterized in that, include: Wind turbines, generators, converter modules, transformers, machine-side circuit breakers, grid-side circuit breakers, low-frequency filters for filtering electrical noise, and composite energy harvesting systems, among which... The wind turbine, generator, converter module, and transformer are connected in series and then connected to the low-frequency power grid. The converter module is used to convert the electrical energy output by the generator into low-frequency electrical energy; The transformer is used to boost the voltage of the low-frequency electrical energy and then transmit it to the low-frequency power grid; The generator is connected to the first end of the converter module via the machine-side circuit breaker; The second end of the converter module is connected to the transformer via the grid-side circuit breaker; The generator-side circuit breaker is used to connect and disconnect the electrical energy on the line between the generator and the converter module; the grid-side circuit breaker is used to connect and disconnect the converter module and the transformer. The second end of the converter module is connected to the grid-side circuit breaker through the low-frequency filter; Machine-side converter module, DC capacitor and grid-side converter module; The AC side of the generator-side converter module is connected to the generator through the generator-side circuit breaker, and the DC side of the generator-side converter module is connected in parallel with the DC capacitor and then connected to the DC side of the grid-side converter module. The AC side of the grid-side converter module is connected to the grid-side circuit breaker through the low-frequency filter; The composite energy harvesting system draws energy from the DC capacitor and the low-voltage side of the transformer, respectively; the composite energy harvesting system is used to filter the low-frequency electrical energy output by the converter module; to provide dynamic reactive power compensation when there is an AC short-circuit fault on the output side of the grid-side converter module; and to output AC electrical energy after drawing energy from the DC capacitor so that the composite energy harvesting system can supply power to the AC load. The composite energy harvesting system includes: a coupling reactor, a first electronic switch, a second electronic switch, a rectifier, and an inverter; the primary side of the coupling reactor is connected in series with the AC line of the low-voltage side of the transformer to harvest energy from the low-voltage side of the transformer; the DC side of the inverter harvests energy from the DC capacitor, and the AC side of the inverter is connected to the AC load; the AC side of the rectifier is connected to the secondary side of the coupling reactor through the first electronic switch, and the AC side of the rectifier is also connected to the AC line through the second electronic switch; the DC side of the rectifier is connected in parallel with the energy storage battery and then in series with the DC side of the inverter.

2. The wind turbine generator for outputting low-frequency electrical energy according to claim 1, characterized in that, The machine-side converter module includes: First converter and second converter; The AC side of the first converter and the AC side of the second converter are both connected to the generator through the machine-side circuit breaker. The DC side of the first converter and the DC side of the second converter are connected in series and then connected in parallel with the DC capacitor.

3. The wind turbine generator for outputting low-frequency electrical energy according to claim 1, characterized in that, Also includes: Energy harvesting system; The energy harvesting system extracts energy from the low-voltage side of the transformer and outputs AC power of a preset frequency so that the energy harvesting system can provide AC power of the preset frequency to the AC load. And / or, the energy harvesting system harvests energy from the DC capacitor and outputs DC power so that the energy harvesting system supplies power to the DC load.

4. The wind turbine generator for outputting low-frequency electrical energy according to claim 3, characterized in that, The energy harvesting system includes: Any one or a combination of several of the following: AC / AC converter, frequency multiplier transformer, DC / DC converter, and DC / AC converter; The AC / AC converter and the frequency multiplier transformer both draw energy from the low-voltage side of the transformer and output AC power of a preset frequency. The DC / DC converter draws power from the DC capacitor and outputs DC power, while the DC / AC converter draws power from the DC capacitor and outputs AC power.

5. The wind turbine generator for outputting low-frequency electrical energy according to claim 1, characterized in that, When the AC line is normal, the first electronic switch is open and the second electronic switch is closed. The rectifier uses the id-iq method to filter out harmonics and maintain the DC voltage of the composite energy harvesting system. The inverter uses AC voltage control to generate the AC voltage amplitude and frequency required for the AC load. When an AC voltage drop occurs, the first electronic switch closes and the second electronic switch opens. The composite energy harvesting system draws energy from the DC capacitor and maintains the DC voltage. The rectifier is connected to provide reactive power to the AC system.

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