Direct current to alternating current converter and control method therefor

Abstract

The present application relates to a direct current to alternating current converter and a control method therefor. The direct current to alternating current converter comprises a plurality of first circuits, a second circuit and a control circuit, wherein first ends of the first circuits are respectively each connected to a direct current source, and second ends of the first circuits are connected in parallel or in series and then connected to the second circuit; the control circuit is communicatively connected to the first circuits and the second circuit; and the control circuit is adapted to control the first circuits and the second circuit on the basis of electrical signals at the first ends of the first circuits and an electrical signal at a second end of the second circuit. The present application enables the direct current to alternating current converter to maintain high energy conversion efficiency under different operating conditions, thereby reducing energy loss.

Description

DC-AC converters and their control methods Related applications

[0001] This application claims priority to Chinese patent application No. 2024115166427, filed on October 28, 2024, entitled "DC-AC converter and control method thereof", and Chinese patent application No. 2024115166323, filed on October 28, 2024, entitled "Control method, controller, storage medium and program product for power conversion system", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of converter technology, and in particular to a DC-AC converter and its control method. Background Technology

[0003] With the development of new energy technologies, the power conversion efficiency of DC-AC converters has become a very important research direction in the field of new energy. Summary of the Invention

[0004] Therefore, it is necessary to provide a DC-AC converter and its control method to address the above-mentioned technical problems. This method can make full use of various available DC sources, improve the availability and efficiency of energy utilization, and enable the DC-AC converter to maintain high energy conversion efficiency under different operating conditions, thereby reducing energy loss. Attached Figure Description

[0005] To more clearly illustrate the technical solutions in the embodiments or related technologies of this application, the accompanying drawings used in the description of the embodiments or related technologies will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0006] Figure 1a is a schematic diagram of one embodiment of a DC-AC converter;

[0007] Figure 1b is a second schematic diagram of the structure of a DC-AC converter in one embodiment;

[0008] Figure 2a is a third schematic diagram of the structure of a DC-AC converter in one embodiment;

[0009] Figure 2b is a schematic diagram of the structure of a DC-AC converter in one embodiment;

[0010] Figure 3a is a schematic diagram of the structure of a DC-AC converter in one embodiment;

[0011] Figure 3b is a schematic diagram of the DC-AC converter in one embodiment;

[0012] Figure 3c is a schematic diagram of the DC-AC converter in one embodiment;

[0013] Figure 4 is a schematic diagram of the structure of a DC-AC converter in one embodiment;

[0014] Figure 5a is a schematic diagram of the structure of a DC-AC converter in one embodiment;

[0015] Figure 5b is a schematic diagram of the structure of a DC-AC converter in one embodiment;

[0016] Figure 6 is an eleventh schematic diagram of the structure of a DC-AC converter in one embodiment;

[0017] Figure 7a is a schematic diagram of one embodiment of the high-frequency transformer coupling method;

[0018] Figure 7b is a second schematic diagram of the coupling method of the DC-AC converter in one embodiment;

[0019] Figure 8 is a schematic diagram of the primary side bridge arm circuit connected in series in one embodiment;

[0020] Figure 9a is a schematic diagram of one embodiment of the same-name terminal setting method;

[0021] Figure 9b is a second structural schematic diagram of the same-name terminal setting method in one embodiment;

[0022] Figure 10 is a flowchart illustrating the control method of a DC-AC converter in one embodiment;

[0023] Figure 11 is a flowchart illustrating the steps of inputting corresponding control signals to each first circuit and second circuit in one embodiment;

[0024] Figure 12a is one of the operation sequence diagrams of a plurality of first circuits in one embodiment;

[0025] Figure 12b is a second runtime sequence diagram of multiple first circuits in one embodiment;

[0026] Figure 13 is a flowchart illustrating the steps of inputting corresponding control signals to each of the first and second circuits in another embodiment;

[0027] Figure 14a is a schematic diagram of the structure of a DC-AC converter in one embodiment;

[0028] Figure 14b shows the signal waveforms on both sides of the high-frequency transformer in one embodiment;

[0029] Figure 14c shows one of the waveforms of the control signal in one embodiment;

[0030] Figure 14d shows a second waveform of the control signal in one embodiment;

[0031] Figure 15 is a flowchart illustrating the steps of controlling the first circuit and the second circuit in one embodiment;

[0032] Figure 16a is a schematic diagram of the signal sampling location in one embodiment;

[0033] Figure 16b is a waveform diagram of the DC source in one embodiment;

[0034] Figure 16c is a waveform diagram of the electrical signal at the second terminal of the second circuit when the output reactive power is zero in one embodiment;

[0035] Figure 16d is a waveform diagram of the electrical signal at the first terminal of the second circuit when the output reactive power is zero in one embodiment;

[0036] Figure 16e is a waveform diagram of the electrical signal at the second terminal of the second circuit when outputting inductive reactive power in one embodiment;

[0037] Figure 16f is a waveform diagram of the electrical signal at the first terminal of the second circuit when outputting inductive reactive power in one embodiment;

[0038] Figure 16g is a waveform diagram of the electrical signal at the second terminal of the second circuit when outputting capacitive reactive power in one embodiment;

[0039] Figure 16h is a waveform diagram of the electrical signal at the first terminal of the second circuit when outputting capacitive reactive power in one embodiment;

[0040] Figure 17 is a flowchart illustrating the control method of a DC-AC converter in one embodiment;

[0041] Figure 18 is a schematic diagram of the DC-AC converter in another embodiment;

[0042] Figure 19 is a flowchart illustrating the steps for determining control information for each first circuit in one embodiment;

[0043] Figure 20 is a flowchart illustrating the steps for determining control information for each first circuit in another embodiment;

[0044] Figure 21a is a schematic diagram of one of the current waveforms in one embodiment;

[0045] Figure 21b is a second schematic diagram of the current waveform in one embodiment;

[0046] Figure 21c is a schematic diagram of the current waveform in one embodiment;

[0047] Figure 21d is a schematic diagram of the current waveform in one embodiment;

[0048] Figure 21e is a schematic diagram of the current waveform in one embodiment;

[0049] Figure 21f is a schematic diagram of the current waveform in one embodiment;

[0050] Figure 21g is a schematic diagram of the current waveform in one embodiment;

[0051] Figure 21h is a schematic diagram of the current waveform in one embodiment;

[0052] Figure 21i is a schematic diagram of the current waveform in one embodiment;

[0053] Figure 21j is a schematic diagram of the current waveform in one embodiment. Detailed Implementation

[0054] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0055] It is understood that the terms "first," "second," etc., used herein may be used to describe various elements, but these elements are not limited by these terms. These terms are only used to distinguish one element from another. For example, without departing from the scope of this application, a first resistor may be referred to as a second resistor, and similarly, a second resistor may be referred to as a first resistor. Both the first resistor and the second resistor are resistors, but they are not the same resistor.

[0056] It is understood that the term "connection" as used in this application refers to a circuit / module / unit being directly or indirectly connected to another circuit / module / unit (or communicating directly or indirectly with another circuit / module / unit). If the connected circuits, modules, units, etc., have electrical signal or data transmission with each other, it should be understood as "electrical connection", "communication connection", etc.

[0057] It is understood that the term "based on" as used in this application is used to describe one or more factors that affect the determination, but does not exclude other factors that may affect the determination. For example, the phrase "determining A based on B" means that the determination of A can be based entirely or at least partially on factor B. That is, B is a factor that affects the determination of A, but does not exclude the determination of A from being based on C.

[0058] With the development of new energy technologies, the application of DC-AC converters is becoming increasingly widespread. A DC-AC converter is a power conversion device used to convert electrical energy from one form to another, enabling energy transmission and control under different power requirements. Power converters can be micro-inverters, energy storage converters, etc.

[0059] This application provides a DC-AC converter comprising multiple first circuits, one second circuit, and a control circuit. The first terminal of each first circuit is connected to a DC source, and the control circuit is adapted to control each first circuit and the second circuit based on electrical signals from the first terminal of each first circuit and electrical signals from the second terminal of the second circuit. In this application's embodiments, compared to a one-to-one connection between photovoltaic modules and the DC-AC converter (i.e., "one-to-one"), the DC-AC converter using this application's circuit topology can simultaneously connect multiple photovoltaic modules (i.e., "one-to-N"), reducing the number of DC-AC converters and lowering the overall system cost. Furthermore, the shared second circuit design further reduces device costs. Moreover, due to the reduced number of DC-AC converters, the installation process is simpler, and maintenance and management costs are correspondingly reduced, saving time and manpower. Simultaneously, the one-to-N DC-AC converter has higher power density and conversion efficiency, enabling more efficient conversion between DC and AC power. At least two first circuits can connect to multiple different DC sources, allowing the DC-AC converter to fully utilize various available DC sources, greatly improving energy availability and utilization efficiency, and enhancing the reliability and stability of the entire system. The control circuit precisely controls the electrical signals of each circuit, optimizing the DC-to-AC conversion process. This ensures the DC-AC converter maintains high energy conversion efficiency and reduces energy loss under various operating conditions. Furthermore, the precise control of the second circuit guarantees stable voltage, frequency, and waveform of the output AC power. This is crucial for applications connected to AC loads or grid-connected systems, ensuring normal load operation and preventing equipment damage due to power quality issues.

[0060] In an exemplary embodiment, as shown in Figures 1a and 1b, a DC-AC converter is provided. The DC-AC converter includes a plurality of first circuits 11, a second circuit 12, and a control circuit. The first terminal of each first circuit 11 is connected to a DC source, and the second terminals of each first circuit 11 are connected in parallel or series to the second circuit 12. The control circuit is communicatively connected to each first circuit 11 and the second circuit 12. The control circuit is adapted to control each first circuit 11 and the second circuit 12 based on electrical signals from the first terminals of each first circuit 11 and the second terminals of the second circuit 12. It should be noted that the connection relationship between the control circuit and each first circuit 11 and the second circuit 12 is not shown in the figures.

[0061] In this embodiment, the DC-AC converter includes a plurality of first circuits 11, a common second circuit 12, and a control circuit. A first terminal of each first circuit 11 is connected to a DC source. In some embodiments, the first terminals of two or more first circuits 11 are connected to different DC sources. For example, the DC-AC converter includes three first circuits 11, wherein two first circuits 11 are connected to a first DC source DC1, and another first circuit 11 is connected to a second DC source DC2; or, in another embodiment, the three first circuits 11 are respectively connected to the first DC source DC1, the second DC source DC2, and the third DC source DC3.

[0062] In one embodiment, the DC-AC converter includes two first circuits 11, which are respectively connected to two independent photovoltaic modules. That is, the first end of one first circuit 11 is connected to a DC source DC1, and the first end of the other first circuit 11 is connected to a DC source DC2.

[0063] The second ends of multiple first circuits 11 can be connected in parallel (Figure 1a) or in series (Figure 1b). The second end of each first circuit 11 is connected to the first end of a second circuit 12, and the second end of the second circuit 12 can be connected to an AC power grid or an AC load.

[0064] The control circuit is communicatively connected to each of the first circuits 11 and the second circuits 12. In practical applications, the control circuit acquires the electrical signals from the first terminals of each first circuit 11 and the second terminals of each second circuit 12. Based on the electrical signals from the first terminals of each first circuit 11 and the second terminals of each second circuit 12, the control circuit determines the corresponding control signals for each first circuit 11 and the second circuit 12. Then, the control signals are transmitted to the corresponding circuits to control the first circuits 11 and the second circuits 12, thereby achieving the function of converting DC to AC or vice versa.

[0065] The aforementioned DC source can be a photovoltaic module (PV) or an energy storage battery, etc.

[0066] A DC-AC converter is a power conversion device used to convert electrical energy from one form to another, enabling energy transmission and control under different power requirements. Examples of DC-AC converters include microinverters and energy storage converters.

[0067] In the above embodiments, the DC-AC converter includes multiple first circuits, each with its first terminal connected to a DC source. When one DC source fails, the others can continue to provide energy to the system, ensuring the continuous operation of the DC-AC converter and improving the reliability and stability of the entire system. The control circuit precisely controls the electrical signals of each circuit, optimizing the DC-to-AC and AC-to-DC conversion processes. This ensures the DC-AC converter maintains high energy conversion efficiency under different operating conditions, reducing energy loss. Furthermore, the precise control of the second circuits by the control circuit ensures that the output AC power has stable voltage, frequency, and waveform. This is crucial for applications connected to AC loads or integrated into the AC power grid, guaranteeing normal load operation and preventing equipment damage due to power quality issues. Additionally, the topology of the DC-AC converter provided in this application is easily upgraded and expanded. The number of first circuits can be conveniently increased to improve the input power and capacity of the DC-AC converter. This scalability allows the DC-AC converter to adapt to different application scenarios, from small independent power systems to large distributed energy networks.

[0068] In an exemplary embodiment, as shown in Figures 2a and 2b, each first circuit 11 includes a primary side bridge arm circuit 111, a high-frequency transformer T, a resonant circuit 112, and a secondary side bridge arm circuit 113.

[0069] In this embodiment, each first circuit 11 may include a primary-side bridge arm circuit 111, a high-frequency transformer T, a resonant circuit 112, and a secondary-side bridge arm circuit 113. The first terminal of each primary-side bridge arm circuit 111 is connected to a DC source. In one embodiment, the first terminals of at least two primary-side bridge arm circuits 111 are connected to different DC sources.

[0070] The resonant circuit 112 can be set on the primary side of the high-frequency transformer T or on the secondary side of the high-frequency transformer T.

[0071] As shown in Figure 2a, the resonant circuit 112 is disposed on the primary side of the high-frequency transformer T. The second end of each primary side bridge arm circuit 111 is connected to the first end of the resonant circuit 112, and the second end of the resonant circuit 112 is connected to the primary winding of the high-frequency transformer T. The secondary winding of the high-frequency transformer T is connected to the first end of the secondary side bridge arm circuit 113, and the second end of the secondary side bridge arm circuit 113 is connected to the second circuit 12.

[0072] As shown in Figure 2b, the resonant circuit 112 is located on the secondary side of the high-frequency transformer T. The first end of the primary side bridge arm circuit 111 is connected to the DC source; the second end of the primary side bridge arm circuit 111 is connected to the primary winding of the high-frequency transformer T; the resonant circuit 112 is located between the secondary winding of the high-frequency transformer T and the secondary side bridge arm circuit 113, and the second end of the secondary side bridge arm circuit 113 is connected to the second circuit 12. The high-frequency transformer T can achieve electrical isolation between the primary and secondary circuits.

[0073] The primary-side bridge arm circuit 111 described above may include one of an H-bridge circuit and a half-bridge circuit, and the secondary-side bridge arm circuit described above may include one of an H-bridge circuit and a half-bridge circuit. For example, the primary-side bridge arm circuit 111 of each first circuit 11 is an H-bridge circuit, and the secondary-side bridge arm circuit 113 is a half-bridge circuit; or, the primary-side bridge arm circuit 111 of each first circuit 11 is a half-bridge circuit, and the secondary-side bridge arm circuit 113 is an H-bridge circuit.

[0074] It should be noted that in high-power conversion scenarios, the secondary bridge arm circuit 113 is suitable for using an H-bridge circuit.

[0075] Taking Figure 2b as an example, the operation of the first circuit 11 may include: the primary-side bridge arm circuit 111 and the high-frequency transformer T convert the DC voltage output from the DC source, and transmit the converted AC voltage to the resonant circuit 112 and the secondary-side bridge arm circuit 113; the resonant circuit 112 can make the DC-AC converter operate in a resonant state, so that the current across the transformer approaches a sinusoidal current, thereby improving the conversion efficiency of the DC-AC converter. Furthermore, the switching transistors in the first circuit 11 can perform zero-voltage switching (ZVS) or zero-current switching (ZCS) through the resonant capacitor and / or resonant inductor. The secondary-side bridge arm circuit 113 shapes the converted voltage and transmits the shaped voltage to the second circuit 12.

[0076] The above embodiments provide various topologies for the first circuit, which can realize current conversion and current shaping functions, providing a basis for the second circuit to output AC current.

[0077] In one exemplary embodiment, the resonant circuit 112 can have various structures. In one such structure, as shown in FIG3a, the resonant circuit 112 includes a first resonant capacitor Cr1; the first terminal of the first resonant capacitor Cr1 is connected to the secondary winding of the high-frequency transformer T, and the second terminal of the first resonant capacitor Cr1 is connected to the secondary bridge arm circuit 113.

[0078] The first resonant capacitor Cr1 is placed between the secondary winding of the high-frequency transformer T and the secondary bridge arm circuit 113. The leakage inductance of the high-frequency transformer T serves as the resonant inductance Lr. The high-frequency transformer T and the first resonant capacitor Cr1 form a resonant circuit.

[0079] In another configuration, the resonant circuit 112 includes a resonant inductor Lr and a second resonant capacitor Cr2; the first end of the resonant circuit 112 is connected to the secondary winding of the high-frequency transformer T, and the second end of the resonant circuit 112 is connected to the secondary bridge arm circuit 113.

[0080] As shown in Figure 3b, the first end of the resonant inductor Lr is connected to the secondary winding of the high-frequency transformer T, and the second end of the resonant inductor Lr is connected to the secondary bridge arm circuit 113; the first end of the second resonant capacitor Cr2 is connected to the secondary winding of the high-frequency transformer T, and the second end of the second resonant capacitor Cr2 is connected to the secondary bridge arm circuit 113.

[0081] In the above structure, in addition to the leakage inductance of the high-frequency transformer T, a resonant inductor Lr is also separately provided. The high-frequency transformer T, the resonant inductor Lr and the second resonant circuit 112 form a resonant circuit.

[0082] Understandably, with the circuit structure shown in Figures 3a and 3b, the resonant capacitor is connected in series with the secondary side of the high-frequency transformer T. Under abnormal operating conditions, such as abnormal output power grid, overload, short circuit, etc., the instantaneous overvoltage or undervoltage on the resonant capacitor will not cause voltage stress on the switching transistor, which can significantly improve the system reliability.

[0083] In another configuration, the resonant circuit 112 includes two series-connected third resonant capacitors Cr3 and Cr4; the series circuit formed by the third resonant capacitor Cr3 and the fourth resonant capacitor Cr4 is connected in parallel with the secondary bridge arm circuit 113, and the common terminal of the third resonant capacitor Cr3 and the fourth resonant capacitor Cr4 is connected to the second terminal of the secondary side of the high-frequency transformer T.

[0084] As shown in Figure 3c, the first terminal of the third resonant capacitor Cr3 is connected to the secondary bridge arm circuit 113, the second terminal of the third resonant capacitor Cr3 is connected to the first terminal of the fourth resonant capacitor Cr4, and the second terminal of the fourth resonant capacitor Cr4 is connected to the secondary bridge arm circuit 113. The common terminal of the third resonant capacitor Cr3 and the fourth resonant capacitor Cr4 is connected to the second terminal of the secondary side of the high-frequency transformer T. The leakage inductance of the secondary side of the high-frequency transformer T, the third resonant capacitor Cr3, and the fourth resonant capacitor Cr4 form a resonant circuit.

[0085] In the above embodiment, the resonant capacitor is placed on the secondary side of the transformer, that is, on the AC side of the DC-AC converter. This is because the DC side voltage is usually much lower than the AC side voltage; for example, the DC side voltage range is 40V-60V, while the AC side voltage range is 220Vac-230Vac. This results in the DC side operating in a low-voltage, high-current state, while the AC side operates in a high-voltage, low-current state. If the resonant capacitor is placed on the DC side, two problems arise: first, the resonant capacitor has a low capacitance value and a large current, leading to difficulties in component selection, or even the absence of usable components; second, the resonant capacitor not only participates in the basic operation of the resonant circuit but also acts as an isolation capacitor to address the magnetic saturation problem of the high-frequency transformer. Because the DC side voltage is much lower than the AC side voltage, under the same component dispersion conditions, the AC volt-second value deviation of the high-frequency transformer is greater, making magnetic saturation more likely. Therefore, placing the resonant capacitor on the AC side can act as a DC blocking capacitor, effectively suppressing the magnetic saturation problem of the transformer. Simultaneously, the AC side current is small, reducing the current-carrying capacity requirement for the resonant capacitor and making component selection easier.

[0086] In an exemplary embodiment, as shown in FIG4, the second circuit 12 includes a first switch M1, a second switch M2, a third switch M3, and a fourth switch M4; the first terminal of the first switch M1 is connected to each of the first circuits 11, and the second terminal of the first switch M1 is connected to the first terminal of the second switch M2; the second terminal of the second switch M2 is connected to each of the first circuits 11; the first terminal of the third switch M3 is connected to each of the first circuits 11, and the second terminal of the third switch M3 is connected to the first terminal of the fourth switch M4; the second terminal of the fourth switch M4 is connected to each of the first circuits 11; the common terminal of the first switch M1 and the second switch M2 is adapted to be connected to the power grid or an AC load, and the common terminal of the third switch M3 and the fourth switch M4 is adapted to be connected to the power grid or an AC load; the first switch M1, the second switch M2, the third switch M3, and the fourth switch M4 are all bidirectional switches.

[0087] In this embodiment, the second circuit 12 can adopt an expanded circuit topology, which consists of four switching transistors, with the control terminal of each transistor connected to the control circuit. The control circuit determines the control signal for each switching transistor based on the DC voltage and / or DC current of the primary side bridge arm circuit 111, and the AC voltage and / or AC current of the common terminal of the first switching transistor M1 and the second switching transistor M2, and the common terminal of the third switching transistor M3 and the fourth switching transistor M4, and transmits the control signal to the corresponding switching transistor, thereby controlling the on / off state of each switching transistor and realizing the DC-AC conversion of the DC-AC converter.

[0088] Furthermore, the control circuit controls the on / off state of each switch in the second circuit 12, which can shape the current output by the first circuit 11 to produce a sinusoidal alternating current.

[0089] In the above embodiments, the second circuit adopts an expanded circuit topology, which includes four switching transistors. This simple topology reduces circuit cost. Furthermore, this topology can operate stably in the low-frequency range, adapting to different operating frequency requirements and effectively transmitting power while reducing energy loss during transmission. Additionally, this topology enables soft switching, which reduces switching losses, improves circuit efficiency, reduces electromagnetic interference, and lowers voltage and current stress on the switching devices, extending device lifespan and improving circuit reliability.

[0090] In one exemplary embodiment, the switching transistor of the second circuit 12 switches once per power frequency cycle, where the power frequency cycle refers to the frequency of the alternating current in the power grid, such as 50Hz or 60Hz. The switching frequency of the switching transistor in the first circuit 11 is higher than 30kHz, and preferably above the resonant frequency, such as 70kHz, 90kHz, 1MHz, 2MHz, etc.

[0091] In this embodiment, the switching transistor in the first circuit 11 operates at a high frequency. The switching frequency range varies depending on the type of switching transistor. For example, if the switching transistor in the first circuit 11 is a MOSFET, the switching frequency range is between 30kHz and 500kHz; if the switching transistor in the first circuit 11 is a gallium nitride (GaN) switching transistor, the switching frequency can reach the MHz level.

[0092] Meanwhile, the switching transistors in the second circuit 12 operate at low frequencies, meaning they switch only once per power frequency cycle. Therefore, the performance requirements for all the switching transistors in the second circuit are relatively low, allowing for the selection of lower-cost components.

[0093] In the above embodiments, the switching transistor of the second circuit operates at a low frequency, which can reduce switching losses and conduction losses, thereby reducing the power consumption of the DC-AC converter.

[0094] In an exemplary embodiment, as shown in FIG4, the second circuit 12 further includes a filter capacitor Cx; the first end of the filter capacitor Cx is connected to the first terminal of the first switching transistor M1, and the second end of the filter capacitor is connected to the second terminal of the second switching transistor M2.

[0095] In this embodiment of the application, the second circuit 12 may further include a filter capacitor Cx, which can filter out the interference signal output by the first circuit 11, thereby providing power quality.

[0096] In one exemplary embodiment, each of the first circuits 11 includes a primary-side bridge arm circuit 111, a high-frequency transformer T, and a resonant circuit 112. Based on this structure, the second circuit 12 may adopt other structures.

[0097] The primary side bridge arm circuit 111 can be an H-bridge circuit or a half-bridge circuit, and the resonant circuit 112 can be set on the primary side of the high-frequency transformer T or on the secondary side of the high-frequency transformer T.

[0098] In some embodiments, as shown in FIG5a, the second circuit includes a secondary bridge arm circuit 121, a first switch M1, a second switch M2, a third switch M3, and a fourth switch M4; the secondary bridge arm circuit 121 is connected to each of the first circuits 11; the first terminal of the first switch M1 is connected to the secondary bridge arm circuit 121, and the second terminal of the first switch M1 is connected to the first terminal of the second switch M2; the second terminal of the second switch M2 is connected to the secondary bridge arm circuit 121; the first terminal of the third switch M3 is connected to the secondary bridge arm circuit 121, and the second terminal of the third switch M3 is connected to the first terminal of the fourth switch M4; the second terminal of the fourth switch M4 is connected to the secondary bridge arm circuit 121; the common terminal of the first switch M1 and the second switch M2 is adapted to be connected to the power grid or an AC load, and the common terminal of the third switch M3 and the fourth switch M4 is adapted to be connected to the power grid or an AC load. The second circuit 12 also includes a filter capacitor Cx.

[0099] In the above structure, the first circuit 11, after being connected in parallel or series, is connected to the secondary bridge arm circuit 121 of the second circuit 12. The second circuit 12 also includes an expanded circuit topology, which consists of four switching transistors. The control electrode of each switching transistor is connected to the control circuit. The control circuit determines the control signal for each switching transistor based on the DC voltage and / or DC current of the primary bridge arm circuit 111, and the AC voltage and / or AC current of the common terminal of the first switching transistor M1 and the second switching transistor M2, and the common terminal of the third switching transistor M3 and the fourth switching transistor M4. The control signal is then transmitted to the corresponding switching transistor to control the on / off state of each switching transistor, thereby realizing the DC-AC conversion of the DC-AC converter.

[0100] Similarly, as shown in Figure 5b, the second circuit 12 also includes filter capacitors Cx1 and Cx2.

[0101] Understandably, since the second circuit 12 includes a secondary bridge arm circuit 121, multiple first circuits 11 can share the secondary bridge arm circuit 121, thereby simplifying the circuit topology and saving components. The second circuit also includes an expanded circuit topology, which can operate stably in the low-frequency range, adapt to different operating frequency requirements, and effectively transmit power, reducing energy loss during transmission.

[0102] In some embodiments, as shown in FIG6, the second circuit 12 includes a first capacitor C1, a second capacitor C2, a fifth switch M5, a sixth switch M6, a seventh switch M7, and an eighth switch M8; the first terminal of the first capacitor C1 is connected to the first terminal of the fifth switch M5, and the second terminal of the first capacitor C1 is connected to the first terminal of the second capacitor C2; the second terminal of the second capacitor C2 is connected to the second terminal of the eighth switch M8; the second terminal of the fifth switch M5 is connected to the first terminal of the sixth switch M6; the second terminal of the sixth switch M6 is connected to the first terminal of the seventh switch M7; the second terminal of the seventh switch M7 is connected to the first terminal of the eighth switch M8; the common terminal of the first capacitor C1 and the second capacitor C2 is connected to the first circuit 11; the common terminal of the sixth switch M6 and the seventh switch M7 is connected to the first circuit 11.

[0103] In this embodiment, the second circuit 12 includes a first capacitor C1, a second capacitor C2, a fifth switch M5, a sixth switch M6, a seventh switch M7, and an eighth switch M8. The first capacitor C1 and the second capacitor C2 are connected in series to form a first series circuit, and the fifth switch M5, the sixth switch M6, the seventh switch M7, and the eighth switch M8 form a second series circuit. The first series circuit and the second series circuit are connected in parallel, and the parallel connection can be connected to an AC power grid or an AC load.

[0104] The common terminal of the first capacitor C1 and the second capacitor C2 is connected to the first circuit 11, and the common terminal of the sixth switch M6 and the seventh switch M7 is connected to the first circuit 11.

[0105] The control electrodes of the fifth switch M5, the sixth switch M6, the seventh switch M7, and the eighth switch M8 are all connected to the control circuit. The control circuit controls the on / off state of each switch in the second circuit 12, which can shape the current output by the first circuit 11 to output a sinusoidal alternating current.

[0106] In the above embodiments, the second circuit adopts the aforementioned circuit topology, which includes four switching transistors. This simple topology not only improves device utilization but also reduces circuit cost and power consumption. Furthermore, it reduces the number of secondary bridge arm circuits in the first circuit, thereby reducing the number of devices in the DC-AC converter.

[0107] In Figures 1a-6, the high-frequency transformers in the multiple first circuits 11 are independent. In an exemplary embodiment, at least two high-frequency transformers T are coupled via magnetic cores. The coupling methods include full coupling as shown in Figure 7a and partial coupling as shown in Figure 7b.

[0108] In this embodiment, each first circuit 11 includes a high-frequency transformer T. These high-frequency transformers T can be set independently or coupled through a magnetic core. Magnetic core coupling of the high-frequency transformers allows for a more compact structure of the DC-AC converter, thereby saving space and meeting equipment design requirements.

[0109] In one exemplary embodiment, as shown in FIG8, the first ends of a plurality of primary-side bridge arm circuits 111 are connected in series.

[0110] In this embodiment of the application, among the multiple first circuits 11, the first ends of at least two primary side bridge arm circuits 111 can be connected in series, thereby changing the magnitude of the DC voltage and DC current input to the DC-AC converter, enabling the DC-AC converter to perform various power conversions and be applied to more scenarios.

[0111] In an exemplary embodiment, the first circuit 11 includes a first type of first circuit 11 and a second type of first circuit 11, as shown in FIG9a. In the first type of first circuit 11, the same-name terminals of the primary winding and the secondary winding of the high-frequency transformer T are correspondingly arranged, as shown in FIG9b. In the second type of first circuit 11, the same-name terminals of the primary winding and the opposite-name terminals of the secondary winding of the high-frequency transformer T are correspondingly arranged.

[0112] In high-frequency transformers, the same-name terminals refer to the terminals where the current flows into the two mutually inducting coils when the magnetic flux generated is in the same direction; conversely, the terminals where the current flows into the two coils and the magnetic flux is in different directions are called opposite-name terminals.

[0113] In this embodiment, the first circuit 11 can be divided into two categories based on the different positions of the same-name and different-name terminals of the high-frequency transformer T. In the first category of the first circuit 11, the same-name terminals of the primary winding and the secondary winding of the high-frequency transformer T are correspondingly arranged, and the different-name terminals of the primary winding and the secondary winding are correspondingly arranged. In the second category of the first circuit 11, the same-name terminals of the primary winding and the different-name terminals of the secondary winding of the high-frequency transformer T are correspondingly arranged, and the different-name terminals of the primary winding and the secondary winding are correspondingly arranged.

[0114] In the above embodiments, in the first type of first circuit, the corresponding terminals of the primary winding and the secondary winding of the high-frequency transformer are arranged to enhance each other's magnetic flux, reducing magnetic flux leakage and energy loss, and improving energy transmission efficiency. In the second type of first circuit, the corresponding terminals of the primary winding and the opposite terminals of the secondary winding of the high-frequency transformer are arranged to change the voltage phase relationship between the primary and secondary windings, thereby introducing a specific phase difference or signal transformation, enabling the DC-AC converter to achieve more conversion functions.

[0115] In an exemplary embodiment, as shown in FIG10, a control method for a DC-AC converter includes a plurality of first circuits and a second circuit; the first terminal of each first circuit is connected to a DC source, and the second terminal of each first circuit is connected to the second circuit in parallel or in series; taking the application of this method to the control circuit of a DC-AC converter as an example, it may include the following steps:

[0116] Step 201: Obtain the electrical signals of the first terminal of each first circuit and the electrical signals of the second terminal of each second circuit in the DC-AC converter.

[0117] The control circuit acquires electrical signals from the first terminal of the first circuit and electrical signals from the second terminal of the second circuit. The electrical signals from the first terminal of each first circuit and the second terminal of each second circuit include: the DC voltage of each first circuit, and the AC voltage and AC current of the second circuit; or, the DC voltage and DC current of each first circuit, and the AC voltage of the second circuit; or, the DC voltage and DC current of each first circuit, and the AC voltage and AC current of the second circuit.

[0118] Step 202: Input corresponding control signals to each first circuit and second circuit according to the electrical signals at the first terminal of each first circuit and the electrical signals at the second terminal of each second circuit.

[0119] The control circuit determines the control signal corresponding to each first circuit and the control signal corresponding to each second circuit based on the electrical signal at the first terminal of each first circuit and the electrical signal at the second terminal of each second circuit. Then, it transmits each control signal to the corresponding circuit to control the first circuit and the second circuit, thereby realizing the function of converting DC to AC or AC to DC.

[0120] In some embodiments, the control circuit acquires the DC voltage at the first terminal of each first circuit 11, the AC voltage and AC current at the second terminal of each second circuit 12, and controls each first circuit 11 and second circuit 12 according to the DC voltage of each first circuit 11 and the AC voltage and AC current of each second circuit 12.

[0121] Alternatively, the control circuit acquires the DC voltage and DC current at the first terminal of each first circuit 11 and the AC voltage at the second terminal of the second circuit 12, and controls each first circuit 11 and the second circuit 12 based on the DC voltage and DC current of each first circuit 11 and the AC voltage of the second circuit 12.

[0122] Alternatively, the control circuit acquires the DC voltage and DC current of the first terminal of each first circuit 11 and the AC voltage and AC current of the second terminal of the second circuit 12, and controls each first circuit 11 and the second circuit 12 according to the DC voltage and DC current of each first circuit 11 and the AC voltage and AC current of the second circuit 12.

[0123] Understandably, different signal combinations acquired by the control circuit can produce specific effects in different application scenarios, meeting the needs of various applications. Furthermore, the control circuit does not need to acquire signals from within the DC-AC converter; it only needs to acquire signals from both ends of the DC-AC converter, especially signals from the resonant circuit, to achieve control. Because the frequency of the resonant circuit current is very high, the requirements for the sampling device are very high. However, the embodiments of this application can accurately control the DC-AC converter to achieve DC-AC conversion based on the electrical signals from the first end of the first circuit and the second end of the second circuit, simplifying the signals that need to be acquired and reducing the difficulty and cost of signal acquisition.

[0124] In the above embodiments, the control circuit precisely controls each of the first and second circuits in the DC-AC converter based on the electrical signals at both ends of the DC-AC converter. This optimizes the DC-to-AC and AC-to-DC conversion processes, ensuring the DC-AC converter maintains high energy conversion efficiency under different operating conditions, reducing energy loss, and ensuring system reliability and efficiency. In off-grid photovoltaic power generation systems, the precise control of the first and second circuits by the control circuit ensures that the output AC power has stable voltage amplitude, frequency, and current quality, guaranteeing the normal operation of AC loads in the system and preventing equipment damage due to power quality issues. Furthermore, in grid-connected photovoltaic power generation systems, the precise control of the first and second circuits by the control circuit optimizes the quality of output voltage and current, significantly reducing the harmonic content of the AC output current.

[0125] In an exemplary embodiment, as shown in FIG11, the above embodiment of "inputting corresponding control signals to each first circuit and each second circuit according to the electrical signals at the first terminal of each first circuit and the electrical signals at the second terminal of the second circuit" may include the following steps:

[0126] Step 301: Determine the power of the DC source corresponding to each first circuit.

[0127] Since at least two of the first circuits in a DC-AC converter may be connected to different DC sources, the control circuit first determines the power of the DC source corresponding to each first circuit during the control process.

[0128] Step 302: Based on the power of the DC source corresponding to each first circuit, input corresponding control signals to each first circuit and second circuit to control the multiple first circuits to operate in turn.

[0129] The operating phase of each first circuit corresponds to the power of the DC source.

[0130] The control circuit determines the operating period of each first circuit based on the power of the DC source corresponding to each first circuit. For example, based on the power of the DC source corresponding to each first circuit, it determines that some first circuits operate continuously while others stop operating; or, it determines that some first circuits operate during the first power frequency cycle and stop operating during the second power frequency cycle, while others stop operating during the first power frequency cycle and operate during the second power frequency cycle.

[0131] After determining the operating mode of each first circuit, the control circuit generates control signals corresponding to each first circuit and control signals corresponding to each second circuit, and sends the corresponding control signals to each first circuit and each second circuit.

[0132] In some embodiments, multiple first circuits operate in turn, with the DC source being a photovoltaic module (PV). As shown in Figure 12a, the two first circuits connected to DC source PV1 and DC source PV2 operate and shut down in turn. Alternatively, the first circuit connected to DC source PV1, the first circuit connected to DC source PV2, and the first circuit connected to DC source PVn operate and shut down in turn. Furthermore, the operating periods can overlap to avoid the total power of the multiple first circuits not meeting the demand when operating in turn.

[0133] In this circuit, the control signals of multiple first circuits have the same frequency, but different phases as they run in turn.

[0134] In some embodiments, control signals of a plurality of first circuits are used to control the first type of first circuit to operate during the zero-crossing period of the AC current of the second circuit, the second type of first circuit to operate during the non-zero-crossing period of the AC current, and the power of the first type of first circuit is lower than the power of the second type of first circuit.

[0135] The power of the first circuit connected to the DC source PVn is lower than that of the first circuit connected to the DC source PV1. As shown in Figure 12b, the first circuit connected to the DC source PVn operates during the zero-crossing period of the AC current, while the first circuit connected to the DC source PV1 operates during the non-zero-crossing period.

[0136] In some embodiments, as shown in FIG12b, the first circuit connected to the DC source PVn operates during the zero-crossing period of the AC current, while the first circuit connected to the DC source PV1 operates continuously.

[0137] It should be noted that the running and shut-off periods of each first circuit can be carried out within half a power frequency cycle, or within one or more power frequency cycles, thereby ensuring that the output power of the second circuit is continuous.

[0138] In the above embodiments, the power of the DC source corresponding to each first circuit is determined; based on the power of the DC source corresponding to each first circuit, corresponding control signals are input to each first circuit and the second circuit, which allows multiple first circuits to operate in a hiccup mode in turn, thereby improving the efficiency of the DC-AC converter under light load. Because the first circuit handles a larger instantaneous power when it is working, the efficiency of each first circuit can be in an optimal state, thus improving the overall system efficiency.

[0139] In an exemplary embodiment, as shown in FIG13, the above embodiment of "inputting corresponding control signals to each first circuit and each second circuit according to the electrical signals of the first terminal of each first circuit and the electrical signals of the second terminal of the second circuit" may include the following steps:

[0140] Step 401: Based on the electrical signals of the first terminal of each first circuit and the electrical signals of the second terminal of the second circuit, obtain multiple control variables.

[0141] Step 402: Input corresponding control signals to each of the first and second circuits according to multiple control variables. Wherein, in the case where each of the first circuits of the DC-AC converter includes a primary-side bridge arm circuit, a high-frequency transformer, a resonant circuit, and a secondary-side bridge arm circuit, the multiple control variables include: the switching frequency of the switching transistors in each first circuit; the phase difference between each primary-side bridge arm circuit and its corresponding secondary-side bridge arm circuit; and the inner phase shift angle of each primary-side bridge arm circuit and / or the duty cycle of the switching transistor pulses of the primary-side bridge arm circuit. Wherein, in the case where each of the first circuits of the DC-AC converter includes a primary-side bridge arm circuit, a high-frequency transformer, and a resonant circuit, the multiple control variables include: the switching frequency of the switching transistors in each first circuit; the phase difference between each first circuit and the second circuit; and the inner phase shift angle of each primary-side bridge arm circuit and / or the duty cycle of the switching transistor pulses of the primary-side bridge arm circuit.

[0142] Precise control of resonant circuits has always been a significant technical challenge in the field of DC-AC converters. This application introduces multiple control parameters to increase the system's degrees of freedom, thereby enabling a more flexible, accurate, and efficient control strategy. This multi-control quantity design allows the DC-AC converter to better adapt to dynamic changes under complex operating conditions, improving the control accuracy and response capability of the resonant circuit.

[0143] For example, based on the electrical signals at the first terminal of each first circuit and the electrical signals at the second terminal of the second circuit, the switching frequency, outward phase shift angle, inward phase shift angle, and / or duty cycle of the switching devices in each first circuit are determined.

[0144] When each first circuit of the DC-AC converter includes a primary-side bridge arm circuit, a high-frequency transformer, a resonant circuit, and a secondary-side bridge arm circuit, the external phase shift angle is the phase difference between each primary-side bridge arm circuit and the corresponding secondary-side bridge arm circuit; when each first circuit of the DC-AC converter includes a primary-side bridge arm circuit, a high-frequency transformer, and a resonant circuit, the external phase shift angle is the phase difference between each first circuit and the second circuit.

[0145] The switching cycle can be determined based on the switching frequency; the time difference between the rising edge of the primary voltage and the rising edge of the secondary voltage of the high-frequency transformer can be determined based on the outer phase shift angle; the pulse width of the switching transistor in the primary bridge circuit can be determined based on the phase difference (inner phase shift angle) between the two half-bridge arms in the primary bridge arm circuit and / or the pulse duty cycle of the switching transistor in the primary bridge arm circuit.

[0146] In an exemplary embodiment, each primary-side bridge arm circuit includes two half-bridge arms, namely, the left bridge arm (switches Q11 and Q12) and the right bridge arm (switches Q13 and Q14) of the H-bridge. The pulse width of the switches in each primary-side bridge arm circuit can be determined by the phase difference between the two half-bridge arms and / or the pulse duty cycle of the switches in each primary-side bridge arm circuit. The following details how to implement multi-control variable control using a single-channel first circuit 11 as an example. It should be noted that the control method is the same for multiple-channel first circuits; the types of control variables used are the same, only the values ​​of the control variables differ.

[0147] Taking the circuit structure shown in Figure 14a as an example, using a multivariable control method, the control circuit will control the high-frequency pulse voltage across the high-frequency transformer T1 into the waveform shown in Figure 14b. The voltage Vpri1 across the primary winding of the high-frequency transformer T1 is a three-level pulse voltage, consisting of a positive voltage, a zero voltage, and a negative voltage, with equal amplitude and pulse width for both. The voltage Vsec1 across the secondary winding of the high-frequency transformer T1 is a two-level pulse voltage (duty cycle 50%), consisting of a positive voltage and a negative voltage, with equal amplitude and pulse width for both.

[0148] Ts is a switching cycle, obtained by taking the reciprocal of the switching frequency fs by the control circuit; Tsec is the pulse width (i.e., the duration of the high-level pulse) of the secondary voltage Vsec1 of the high-frequency transformer T1, which is 50% of the switching cycle Ts, meaning the voltage pulse width has a fixed 50% duty cycle; Tex is the time difference between the rising edge of the primary voltage Vpri1 and the rising edge of the secondary voltage Vsec1 of the high-frequency transformer T1, calculated by the control circuit based on the outer phase shift angle; Tpri is the pulse width of the primary voltage Vpri1 of the high-frequency transformer T1, calculated by the control circuit based on the duty cycle Din or the inner phase shift angle in.

[0149] As shown in Figure 14c, the control circuit determines that the control signals for switches Q11 and Q12 are complementary signals, and the control signals for switches Q13 and Q14 are also complementary signals. The duty cycle of the control signals is the duty cycle Din calculated by the control circuit. Here, the time converted from the duty cycle Din is equal to Tpri.

[0150] As shown in Figure 14d, the control circuit determines that the control signals for switches Q11 and Q12 are complementary signals, and the control signals for switches Q13 and Q14 are also complementary signals, with a fixed 50% duty cycle. The angle between the rising edges of the control signals for switches Q11 and Q13 is the inner phase shift angle in calculated by the control circuit. Here, the time obtained by converting the inner phase shift angle in is equal to Tpri, and the conversion relationship is Tpri = Ts * in / 360°.

[0151] Using the above method, the control signal for each first circuit can be determined based on multiple control variables of each first circuit, and the control signal for the second circuit can be determined based on the control signals of the multiple first circuits. Then, the corresponding control signals are input to each first circuit and the second circuit.

[0152] In the above embodiments, multiple control variables are obtained based on the electrical signals of the first terminal of each first circuit and the electrical signals of the second terminal of the second circuit. This enables precise monitoring and analysis of different circuits, thereby making the generation of control signals more accurate and better meeting the actual needs of DC-AC converters.

[0153] In an exemplary embodiment, as shown in FIG15, the following steps may also be included:

[0154] Step 501: Obtain scheduling instructions.

[0155] The dispatching instructions may include at least one of the following: active power dispatching instructions, reactive power dispatching instructions, power grid dispatching instructions, and manual dispatching instructions.

[0156] For example, in one embodiment, when a DC-AC converter is connected to a photovoltaic module, active power dispatch commands can control the voltage and current on the DC side of the DC-AC converter, ensuring the photovoltaic system continuously operates at its maximum active power point. In another embodiment, active power dispatch can also implement anti-reverse current functionality. When the photovoltaic module and DC-AC converter are grid-connected, this dispatch strategy ensures that all active power generated by the photovoltaic module and DC-AC converter is used to meet load demand. Specifically, the active power output of the DC-AC converter can dynamically match the power consumption of the load. Even if the DC-AC converter can operate at its maximum active power point, its output can still be limited or controlled to a preset active power value to prevent the AC power generated by the DC-AC converter from flowing back to the AC grid. This control strategy effectively ensures the stability and security of the power grid, meeting grid requirements.

[0157] Reactive power scheduling commands and grid dispatch commands can be commands issued by the power plant. Reactive power scheduling commands aim to control the reactive power output of the DC-AC converter. For example, a command might instruct the DC-AC converter to output 50W of reactive power, or simultaneously output 400W of active power and 100W of reactive power. Manual dispatch commands can be commands issued by users through mobile applications (APPs). These commands can control active and reactive power, as well as the start-up and shutdown status of the DC-AC converter. When the DC-AC converter is connected to an energy storage device, manual dispatch commands can also control the operating mode of the energy storage system, such as the start-up and shutdown or charging / discharging period control in self-consumption mode.

[0158] Step 502: Based on the scheduling instructions, the electrical signals at the first terminals of each first circuit, and the electrical signals at the second terminals of each second circuit, input the corresponding control signals to each first circuit and the second circuit.

[0159] The DC-AC converter can receive the maximum power point of the photovoltaic module generated by the internal control circuit or the external control circuit. The DC-AC converter can respond to the maximum power point and control each of the first circuit and the second circuit according to the electrical signal of the first terminal of each first circuit and the electrical signal of the second terminal of the second circuit, thereby outputting AC power corresponding to the maximum power point.

[0160] In some embodiments, the scheduling instructions include a maximum active power point scheduling instruction and a reactive power scheduling instruction; embodiments of this application may further include: obtaining a current signal and a voltage signal at the second terminal of the second circuit based on the maximum active power point scheduling instruction and the reactive power scheduling instruction; determining a control signal based on the current signal and voltage signal at the second terminal of the second circuit, and then inputting the corresponding control signal to each of the first circuit and the second circuit. The current signal and voltage signal at the second terminal of the second circuit include the amplitude, frequency, and phase of the current and voltage.

[0161] In some embodiments, the present application may further include: controlling the current direction between each first circuit 11 and second circuit 12 according to a scheduling instruction, so as to convert the DC current of the DC source DC into AC current and output it from the second circuit 12, or to convert the AC current input to the second circuit 12 into DC current and output it from the first circuit 11.

[0162] In conventional technologies, it is difficult to control reactive power in power conversion devices that include deployable inverters. However, the DC-AC converter provided in this application can control reactive power, stably output AC power, and allows for the control of reactive power and power factor to stabilize the power grid.

[0163] In this embodiment of the application, the control circuit can control the first circuit 11 and the second circuit 12 according to the scheduling command. When the current is input from the first circuit 11 and output from the second circuit 12, after the DC current of the DC source DC is input, the DC-AC converter converts the DC current into AC current under the control of the control circuit and outputs the AC current from the second circuit 12.

[0164] With current input from the second circuit 12 and output from the first circuit 11, after the AC current from the AC grid is input, the DC-AC converter, under the control of the control circuit, converts the AC current into DC current and outputs the DC current from the first circuit 11.

[0165] Understandably, a DC-AC converter, under the control of a control circuit, can achieve bidirectional conversion. It can not only use a DC source to supply power to an AC grid or AC load, but also use an AC grid to provide energy to a DC source so that the DC source can store energy.

[0166] In the above embodiments, a scheduling instruction is obtained; based on the scheduling instruction, the electrical signals at the first terminals of each first circuit, and the electrical signals at the second terminals of the second circuit, corresponding control signals are input to each first circuit and the second circuit. This embodiment, by combining scheduling instructions with electrical signals, enables more precise control of each circuit, improving system operating efficiency. Furthermore, in scenarios where multiple first circuits work collaboratively, it can better balance the load and optimize performance.

[0167] In one exemplary embodiment, the DC-AC converter is capable of generating active power and reactive power.

[0168] Active power refers to the power actually used to do work. It converts direct current (DC) energy into alternating current (AC) energy and transmits it to the load to meet the load's active power requirements. Reactive power, on the other hand, is the power used to establish magnetic and electric fields. Although it does not directly do work, it plays an important role in AC power systems. DC-AC converters may generate reactive power during energy conversion due to the presence of components such as inductors and capacitors.

[0169] In this embodiment of the application, after the DC-AC converter receives the reactive power dispatch command issued by the upper layer, the control circuit obtains the electrical signals of the first terminal of each first circuit 11 and the electrical signals of the second terminal of the second circuit 12, processes and calculates these signals to obtain the control signals of each first circuit 11 and the second circuit 12, and sends each control signal to the corresponding circuit.

[0170] Figure 16a shows the sampling positions of the electrical signals at the first terminal of the first circuit 11, the first terminal of the second circuit 12, and the second terminal of the second circuit 12. Figure 16b shows the waveforms of the DC voltage Vdc1 of DC source DC1 and the DC voltage Vdc2 of DC source DC2. The two DC voltages can be provided by photovoltaic modules or other DC sources such as energy storage batteries.

[0171] Figure 16c shows the waveforms of AC voltage Vac and AC current iac at the second terminal of the second circuit 12 when the output reactive power of the DC-AC converter is zero. Figure 16d shows the waveforms of DC voltage Vdc3 and DC current idc at the first terminal of the second circuit 12 when the output reactive power of the DC-AC converter is zero.

[0172] As shown in Figure 16c, within one complete power frequency cycle, the AC voltage Vac of the second circuit 12 crosses zero at times t0, t1, and t2; in the interval [t0, t1], the polarity of the AC voltage Vac is positive; in the interval [t1, t2], the polarity of the AC voltage Vac is negative. The AC current iac at the second terminal of the second circuit 12 is synchronized with the AC voltage Vac, with no phase difference, and also crosses zero at times t0, t1, and t2; in the interval [t0, t1], the polarity of the AC current iac at the second terminal of the second circuit 12 is positive; in the interval [t1, t2], the polarity of the AC current iac at the second terminal of the second circuit 12 is negative.

[0173] As shown in Figure 16d, the DC voltage Vdc3 at the first terminal of the second circuit 12 is synchronized with the AC voltage Vac at the second terminal of the second circuit 12, with no phase difference, and both cross zero at times t0, t1, and t2. In the interval [t0, t1], the polarity of the DC voltage Vdc3 at the first terminal of the second circuit 12 is positive; in the interval [t1, t2], the polarity of the DC voltage Vdc3 at the first terminal of the second circuit 12 is also positive. The DC current idc at the first terminal of the second circuit 12 is synchronized with the AC current iac at the second terminal of the second circuit 12, with no phase difference, and both cross zero at times t0, t1, and t2. In the interval [t0, t1], the polarity of the DC current idc at the first terminal of the second circuit 12 is positive; in the interval [t1, t2], the polarity of the DC current idc at the first terminal of the second circuit 12 is also positive.

[0174] Figure 16e shows the AC voltage Vac and AC current iac waveforms at the second terminal of the second circuit 12 when the DC-AC converter outputs inductive reactive power. Figure 16f shows the DC voltage Vdc3 and current idc waveforms at the first terminal of the second circuit 12 when the DC-AC converter outputs inductive reactive power.

[0175] As shown in Figure 16e, within one complete power frequency cycle, the AC voltage Vac crosses zero at times t0, t2, and t4; in the interval [t0, t2], the polarity of the AC voltage Vac is positive; in the interval [t2, t4], the polarity of the AC voltage Vac is negative. The AC current iac at the second terminal of the second circuit 12 lags behind the AC voltage Vac, that is, the AC current iac and the AC voltage Vac are out of sync and have a phase difference, crossing zero at times t1 and t3; in the interval [t0, t1], the polarity of the AC current iac at the second terminal of the second circuit 12 is negative; in the interval [t1, t2], the polarity of the AC current iac at the second terminal of the second circuit 12 is positive; in the interval [t2, t3], the polarity of the AC current iac at the second terminal of the second circuit 12 is positive; in the interval [t3, t4], the polarity of the AC current iac at the second terminal of the second circuit 12 is negative.

[0176] As shown in Figure 16f, the DC voltage Vdc3 at the first terminal of the second circuit 12 is synchronized with the AC voltage Vac, with no phase difference, and crosses zero simultaneously at times t0, t2, and t4. In the interval [t0, t2], the polarity of the DC voltage Vdc3 at the first terminal of the second circuit 12 is positive; in the interval [t2, t4], the polarity of the DC voltage Vdc3 at the first terminal of the second circuit 12 is also positive. The DC current idc at the first terminal of the second circuit 12 and the AC current iac at the second terminal of the second circuit 12 cross zero simultaneously at times t1 and t3. In the interval [t0, t1], the polarity of the DC current idc at the first terminal of the second circuit 12 is negative; in the interval [t1, t2], the polarity of the DC current idc at the first terminal of the second circuit 12 is positive; in the interval [t2, t3], the polarity of the DC current idc at the first terminal of the second circuit 12 is negative; in the interval [t3, t4], the polarity of the DC current idc at the first terminal of the second circuit 12 is positive.

[0177] As shown in Figures 16e and 16f, in the interval [t0, t2], the DC current idc at the first terminal of the second circuit 12 and the AC current iac at the second terminal of the second circuit 12 have the same amplitude and the same polarity; in the interval [t2, t4], the DC current idc at the first terminal of the second circuit 12 and the AC current iac at the second terminal of the second circuit 12 have the same amplitude but opposite polarities.

[0178] Figure 16g shows the AC voltage Vac and AC current iac waveforms at the second terminal of the second circuit 12 when the DC-AC converter outputs capacitive reactive power. Figure 16h shows the DC voltage Vdc3 and current idc waveforms at the first terminal of the second circuit 12 when the DC-AC converter outputs capacitive reactive power.

[0179] As shown in Figure 16g, within one complete power frequency cycle, the AC voltage Vac at the second terminal of the second circuit 12 crosses zero at times t0, t2, and t4; in the interval [t0, t2], the polarity of the AC voltage Vac is positive; in the interval [t2, t4], the polarity of the AC voltage Vac is negative. The AC current iac at the second terminal of the second circuit 12 leads the AC voltage Vac, and is asynchronous, with a phase difference, crossing zero at times t1 and t3; in the interval [t0, t1], the polarity of the AC current iac at the second terminal of the second circuit 12 is positive; in the interval [t1, t2], the polarity of the AC current iac at the second terminal of the second circuit 12 is negative; in the interval [t2, t3], the polarity of the AC current iac at the second terminal of the second circuit 12 is negative; in the interval [t3, t4], the polarity of the AC current iac at the second terminal of the second circuit 12 is positive.

[0180] As shown in Figure 16h, the DC voltage Vdc3 at the first terminal of the second circuit 12 is synchronized with the AC voltage Vac, with no phase difference, and crosses zero simultaneously at times t0, t2, and t4. In the interval [t0, t2], the polarity of the DC voltage Vdc3 at the first terminal of the second circuit 12 is positive; in the interval [t2, t4], the polarity of the DC voltage Vdc3 at the first terminal of the second circuit 12 is also positive. The DC current idc at the first terminal of the second circuit 12 and the AC current iac at the second terminal of the second circuit 12 cross zero simultaneously at times t1 and t3. In the interval [t0, t1], the polarity of the DC current idc at the first terminal of the second circuit 12 is positive; in the interval [t1, t2], the polarity of the DC current idc at the first terminal of the second circuit 12 is negative; in the interval [t2, t3], the polarity of the DC current idc at the first terminal of the second circuit 12 is positive; in the interval [t3, t4], the polarity of the DC current idc at the first terminal of the second circuit 12 is negative.

[0181] As shown in Figures 16g and 16h, in the interval [t0, t2], the DC current idc at the first terminal of the second circuit 12 and the AC current iac at the second terminal of the second circuit 12 have the same amplitude and the same polarity; in the interval [t2, t4], the DC current idc at the first terminal of the second circuit 12 and the AC current iac at the second terminal of the second circuit 12 have the same amplitude but opposite polarities.

[0182] In the above embodiments, the DC-AC converter can generate both active and reactive power, thus it can be applied to various scenarios. Generating active power can drive AC loads, such as enabling motors to operate normally. In distributed energy systems, such as solar photovoltaic power generation and wind power generation, the DC-AC converter can convert DC power into AC power and integrate it into the AC grid, achieving efficient utilization of renewable energy. Generating reactive power can maintain power system stability. For example, the DC-AC converter can quickly adjust reactive power output according to system needs, dynamically compensating for reactive power in the AC grid and effectively improving power quality.

[0183] In related technologies, DC-AC converters can be constructed from single-channel converters. These single-channel converters employ a hiccup mode to improve conversion efficiency during low-power operation. However, during hiccup operation, the single-channel converter cannot continuously output AC power.

[0184] To address the aforementioned problems, this application provides a control method for a DC-AC converter. The DC-AC converter used in this method includes multiple first circuits and a shared second circuit. The input terminals of each first circuit are connected to a DC source, and at least two first circuits are connected to different DC sources. For example, the DC-AC converter may include three first circuits, with two first circuits connected to a first DC source and the other connected to a second DC source; or, the three first circuits may be connected to a first DC source, a second DC source, and a third DC source, respectively. Furthermore, the output terminals of the multiple first circuits are connected in parallel and to the second circuit. The method includes acquiring operating data of the multiple first circuits; determining control information for each first circuit based on the operating data in response to a trigger signal; and controlling at least two first circuits to operate in a hiccup mode based on the control information, and continuously outputting a target AC current through the second circuit. The technical solution provided by this application allows the DC-AC converter to operate in a corresponding hiccup mode based on the operating data of the first circuits. This not only reduces the power loss of the DC-AC converter and improves its conversion efficiency, but also allows for continuous output of AC current through superposition of the currents output by the multiple first circuits and rectification by the second circuit. Furthermore, at least two first circuits are connected to different DC sources. Depending on the output power of the different DC sources, different control methods can be used to control the DC-AC converter, enabling the DC-AC converter to have multiple power conversion modes, such as a hiccup mode, which is suitable for more application scenarios.

[0185] In a plurality of first circuits, at least two of the first circuits are connected to different DC sources, and the output capacity (maximum output power) of the different DC sources is different. Therefore, the active power setpoint of the first circuits connected to different DC sources needs to be different. For example, the output power of DC source DC1 is greater than the output power of DC source DC2, that is, the output capacity of DC source DC1 is higher than that of DC source DC2. Therefore, the active power setpoint of the first circuit connected to DC source DC1 can be higher than that connected to DC source DC2.

[0186] Existing technologies primarily target single-input systems, where the input source is a single DC source. The system contains n first circuits, all connected to the same DC source, with each first circuit carrying 1 / n of the power. When the system includes two first circuits, each first circuit carries half the power of the DC source. The blocking and generating phases of each first circuit alternate, easily achieving symmetrical hiccup mode control, which can be accomplished by simply interleaving the operation of each first circuit.

[0187] This application addresses systems with multiple independent voltage source inputs, where different modules are not simply connected in parallel. The operation of each first circuit is limited by its corresponding input power, significantly increasing the difficulty of control. Existing technologies employ fixed symmetrical hiccup patterns primarily suitable for single-input, single-output scenarios; however, this application dynamically adjusts the hiccup pattern control strategy based on the corresponding operating data of the first circuit, optimizing the overall system performance and efficiency.

[0188] In one exemplary embodiment, there is no energy buffer capacitor at the connection point of each of the first and second circuits.

[0189] In existing technologies, a large energy buffer is needed to reduce output fluctuations caused by hiccups; therefore, energy buffer capacitors are typically used. However, the selection and size of energy buffer capacitors increase the complexity of circuit design, and they also increase the cost and power loss of the inverter.

[0190] The DC-AC converter and control method provided in this application embodiment have relatively low output fluctuations even when one or more first circuits operate in hiccup mode. Therefore, in this application embodiment, no energy buffer capacitor is provided at the connection between each first circuit and the second circuit.

[0191] Since there are no energy buffer capacitors at the connection points of the first and second circuits, the effect of smoothing ripple can be achieved. Furthermore, the absence of energy buffer capacitors can reduce the design difficulty of the circuit and reduce the cost and power loss of the DC-AC converter.

[0192] It should be noted that when the first circuit is running in hiccup mode, the controller can control the primary side bridge arm circuit and / or the secondary side bridge arm circuit to shut down during a preset period of time, thereby achieving the shutdown of the entire first circuit during the preset period of time.

[0193] When the first circuit operates in hiccup mode, if the primary side bridge arm circuit is shut down during a preset time period, the controller will control the first switch M1, the second switch M2, the third switch M3 and the fourth switch M4 to be turned off during the preset time period.

[0194] The primary side bridge arm circuit consists of four switching transistors. By controlling the switching transistors to turn on and off, the direction of the current flowing into the high-frequency transformer can be controlled, and the first circuit can be turned off during a preset period of time. This allows the first circuit to operate in hiccup mode, thereby reducing the power loss of the DC-AC converter and improving the power conversion efficiency of the DC-AC converter.

[0195] The second circuit consists of four switching transistors. By controlling the switching transistors to turn on and off, the superimposed current of multiple first circuits can be shaped. When one or more first circuits are running in hiccup mode, the second circuit can reduce output fluctuations and can also continuously output a target AC current with a sine wave waveform throughout the entire cycle.

[0196] In an exemplary embodiment, as shown in FIG17, a control method for a DC-AC converter is provided. Taking the application of this method to the control circuit of a DC-AC converter as an example, it may include the following steps:

[0197] Step 601: Obtain the operating data of multiple first circuits.

[0198] The operating data of the first circuit includes at least one of the following: input voltage, input current, input power, output voltage, output current, output power, and operating power.

[0199] A DC-AC converter can be equipped with multiple sensors, each collecting different operating data. For example, a voltage sensor located at the input of the first circuit can collect the input voltage of the first circuit; a current sensor located at the input of the first circuit can collect the input current of the first circuit; a voltage sensor located at the output of the first circuit can collect the output voltage of the first circuit; and a current sensor located at the output of the first circuit can collect the output current of the first circuit.

[0200] The controller can acquire operating data such as input voltage, input current, output voltage, and output current from different sensors. It can also calculate the operating power of the first circuit based on the input voltage, input current, output voltage, output current, and the output power of the DC source.

[0201] It should be noted that the methods for obtaining runtime data are not limited to the examples above. In practical applications, the controller can also use other methods to obtain runtime data.

[0202] Step 602: In response to the trigger signal, determine the control information of each first circuit based on the operating data of the multiple first circuits.

[0203] The trigger signal is the signal that triggers the DC-AC converter to operate in hiccup mode.

[0204] When the DC-AC converter does not receive a trigger signal, it operates in non-hiccup mode. Upon receiving a trigger signal, it analyzes the operating data of multiple first circuits in response to the trigger signal, and determines the operating state and duration of the first circuit operating in hiccup mode, as well as the operating mode of the first circuit not operating in hiccup mode, based on the analysis results. The control information for each first circuit is then obtained by summarizing the above information.

[0205] Step 603: Based on the control information of each first circuit, control at least two first circuits to operate in hiccup mode and make the second circuit continuously output the target AC current.

[0206] After determining the control information of each first circuit, control commands are output to each first circuit according to the control information, so that at least two first circuits operate in hiccup mode, and the superimposed current of multiple first circuits can be shaped by the second circuit to form the target alternating current.

[0207] In the above embodiments, operating data of multiple first circuits are acquired; in response to a trigger signal, control information for each first circuit is determined based on the operating data of the multiple first circuits; based on the control information of each first circuit, at least two first circuits are controlled to operate in a hiccup mode, and the second circuit continuously outputs the target AC current. The technical solution provided by this application embodiment allows the DC-AC converter to be controlled to operate in a corresponding hiccup mode based on the operating data of the first circuits. This not only reduces the power loss of the DC-AC converter and improves its conversion efficiency, but also allows the current output from multiple first-stage circuits to be continuously output as AC current through superposition and rectification by the second circuit.

[0208] In an exemplary embodiment, "controlling at least two first circuits to operate in hiccup mode" in the above embodiment may include: controlling at least one first circuit to be turned off or to operate in a low-power state during a first preset period of time.

[0209] The first preset time period can be of any length; or, the first preset time period can be one or more half-AC cycles, and the preset time period of each first circuit can be different. Optionally, the first preset time periods of some first circuits can overlap.

[0210] Taking the DC-AC converter in Figure 18 as an example, controlling at least one first circuit to be shut down or to operate in a low-power state during a first preset time period can include: the first circuit controlling the output current Io1 shutting down every half AC cycle; and the first circuits controlling the output current Io2 and the output current Io3 operating at low power throughout the entire cycle. Alternatively, the first circuit controlling the output current Io1 shutting down in half an AC cycle t1 and operating at low power in half AC cycles t2 and t3; the first circuit controlling the output current Io2 shutting down in half an AC cycle t2 and operating at low power in half AC cycles t1 and t3; and the first circuit controlling the output current Io3 shutting down in half an AC cycle t3 and operating at low power in half AC cycles t1 and t2. Alternatively, the first circuit controlling the output current Io1 is turned off during half-AC cycles t1 and t2, and operates at low power during half-AC cycle t3; the first circuit controlling the output current Io2 is turned off during half-AC cycles t2 and t3, and operates at low power during half-AC cycle t1; and the first circuit controlling the output current Io3 is turned off during half-AC cycles t1 and t3, and operates at low power during half-AC cycle t2.

[0211] It should be noted that the hiccup operation mode of each first circuit is not limited to the above example and can be set according to the actual situation.

[0212] In the above embodiments, at least one first circuit is preferably directly turned off during a preset time period. This is because switching losses and conduction losses exist during the switching process of the switching transistor. By controlling at least one first circuit to be turned off during the first preset time period, these losses can be reduced, allowing the system to operate in a higher efficiency range.

[0213] In one exemplary embodiment, the method further includes: determining the duration of a first preset time period based on the operating data of each first circuit; and increasing the duration of the first preset time period when the operating data of the first circuit decreases.

[0214] The duration of each first circuit's shutdown or low-power operation is determined based on its operating data. Understandably, the controller can detect the output power of the DC source connected to each first circuit, or detect the operating power of each first circuit, to determine the operating data of the first circuit; if the operating data of a first circuit is determined to be decreasing, the duration of the first circuit's shutdown or low-power operation can be increased.

[0215] Increasing the time for the first circuit to be turned off or to operate at low power can be achieved by increasing the turn-off time of the switching transistor in the first circuit.

[0216] In the above embodiments, when the operating data of the first circuit is low, increasing the duration of the first circuit's shutdown or low-power operation allows for more efficient storage of energy from the input source. By extending the preset time period, the switching transistors in the DC-AC converter switch less frequently, reducing switching losses. Simultaneously, reducing losses from frequent switching helps decrease device heating and improve system durability. Appropriately extending the energy storage time reduces fluctuations in output voltage and current, resulting in a smoother output. During energy release, since the energy has been effectively pre-stored, the output efficiency of the DC-AC converter is improved, thereby reducing overall energy loss. Dynamically adjusting the length of the preset time period can further improve system efficiency.

[0217] In one exemplary embodiment, "controlling at least two first circuits to operate in hiccup mode" in the above embodiment includes controlling at least two first circuits to turn off in turn during the zero-crossing period.

[0218] The zero-crossing period includes the zero-crossing point of the output AC voltage of the DC-AC converter. Optionally, the zero-crossing period may include a zero-crossing phase of ±10°.

[0219] Taking the DC-AC converter in Figure 18 as an example, controlling at least two first circuits to turn off alternately during the zero-crossing period can include: the first circuit controlling the output current Io1 turning off during the zero-crossing period, and the first circuits controlling the output currents Io2 and Io3 operating at low power throughout the entire cycle. Alternatively, as shown in Figure 21c, the first circuit controlling the output current Io1 turning off during the zero-crossing period t0 and operating at low power during the non-zero-crossing period, and the first circuit controlling the output current Io2 turning off during the zero-crossing period t0' and operating at low power during the non-zero-crossing period. Alternatively, the first circuit controlling the output current Io1 turning off during the zero-crossing period t0, and the first circuit controlling the output current Io2 turning off during the zero-crossing period t0'.

[0220] It should be noted that the hiccup operation mode of each first circuit is not limited to the above example and can be set according to the actual situation.

[0221] In the above embodiments, at least two first circuits alternately turn off during the zero-crossing period. Compared to a scheme where only one first circuit turns off during the zero-crossing period, the alternating shutdown of the two first circuits can effectively distribute the losses of the switching transistor, thereby extending the lifespan of the switching transistor. Furthermore, this design also helps to achieve a more uniform load distribution, optimize system performance, and improve overall reliability.

[0222] In an exemplary embodiment, the operating state and corresponding operating duration of each first circuit can be determined based on the operating data of multiple first circuits.

[0223] In an exemplary embodiment, the states of the first circuit include high-power operation, low-power operation, and off; the duration of each state is N half-AC cycles, where N is a positive integer and can be variable.

[0224] Based on the above principles, it is possible to determine whether each first circuit operates at high power, low power, or is off, as well as the duration of high power operation, low power operation, and off operation.

[0225] The operating status of each first circuit corresponds to its operating data. In one embodiment, if the operating power of a first circuit is low, the high-power operating time of that first circuit is short, and the low-power operating or shutdown time is long. If the operating data of a first circuit is high, the high-power operating time of that first circuit is long, and the low-power operating or shutdown time is short.

[0226] In the above embodiments, the operating status and operating time of each first circuit are determined based on the operating data of each first circuit. The hiccup control method can be dynamically adjusted in a timely manner according to the actual operating power of the first circuit or the output of the DC source connected to the first circuit, so as to ensure stable system operation, improve conversion efficiency, and reduce system losses.

[0227] In an exemplary embodiment, as shown in FIG19, the "determining control information of each first circuit based on the operating data of multiple first circuits" in the above embodiment may include the following steps:

[0228] Step 701: Determine the power distribution of each first circuit within a second preset time period based on the operating data of the multiple first circuits.

[0229] Within a second preset time period, the sum of the distributed power of all the first circuits reaches the target power of the DC-AC converter. The second preset time period can be each half-AC cycle of the target AC current, or multiple half-AC cycles of the target AC current. The second preset time period can be each t1 time period, each t2 time period, or two t1 time periods and two t2 time periods. The distributed power is positively correlated with the current magnitude. Within each half-AC cycle, the sum of the distributed power of all the first circuits reaches the target power of the DC-AC converter, and the trend of the sum of the distributed power is the same as the trend of the superimposed current.

[0230] After acquiring the operating data of each first circuit, the controller analyzes and calculates the operating data of multiple first circuits. For example, it substitutes the operating data into a preset formula for calculation and interpolates the calculation results according to the parameters of the operating point preset by the first circuit. This allows the real-time processing power of multiple first circuits to be redistributed when at least one first circuit is running in hiccup mode. The redistributed power enables the second circuit to continuously provide the required output without being affected by hiccup mode.

[0231] Step 702: Determine the control information of each first circuit based on the power distribution of each first circuit within a preset time period.

[0232] After determining the power allocation, based on the power allocation of each first circuit in the preset time period, it is determined whether each first circuit is turned off in the preset time period, as well as the current magnitude and power magnitude in the preset time period, to obtain the control information of the first circuit.

[0233] As shown in Figure 21a, the first circuit with an output current of Io1 is in operation throughout each half-AC cycle, and the output current decreases every half-AC cycle. The first circuit with an output current of Io2 is turned off once every half-AC cycle.

[0234] In the above embodiments, the power allocation of each first circuit within a preset time period is determined based on the operating data of multiple first circuits; and the control information of each first circuit is determined based on the power allocation of each first circuit within the preset time period. In the technical solution of this application embodiment, the power is redistributed to each first circuit based on the target power required by the DC-AC converter, which allows the total power of the DC-AC converter to meet the demand. Moreover, during hiccup mode operation, the shut-off first circuits do not generate power loss, or their power loss is reduced. Therefore, the overall power loss of the DC-AC converter can be reduced. With the total power meeting the demand and power loss reduced, the power conversion efficiency of the DC-AC converter can be improved.

[0235] In an exemplary embodiment, as shown in FIG20, the second preset time period includes multiple half-AC cycles. In the above embodiment, "determining the control information of each first circuit according to the power distribution of each first circuit within the preset time period" may include the following steps:

[0236] Step 801: Divide the first circuits according to the power distribution of each first circuit in each half-AC cycle to obtain at least two types of first circuits.

[0237] After determining the power allocation of each first circuit in each half-AC cycle, multiple first circuits can be assigned to first circuits of different control types according to the magnitude of the power allocation, thereby adopting different control methods for different types of first stages.

[0238] For example, the first circuit operating in hiccup mode is classified as a first type of first circuit, and the first circuit not operating in hiccup mode is classified as a second type of first circuit. Alternatively, the first circuit operating in hiccup mode during the first half of the AC cycle is classified as a first type of first circuit, and the first circuit operating in hiccup mode during the second half of the AC cycle is classified as a second type of first circuit.

[0239] It should be noted that, based on the power distribution of multiple first circuits, more control types of first circuits can be classified, not limited to the first type of first circuit and the second type of first circuit mentioned above.

[0240] Step 802: Determine the control information of each type of first circuit based on the power distribution of each type of first circuit in each half-AC cycle.

[0241] Taking at least two types of first circuits, including a first type of first circuit and a second type of first circuit, as an example, after determining the power distribution of the first type of first circuit in each half-AC cycle, the control information of the first type of first circuit can be obtained based on this power distribution, determining whether the first type of first circuit is turned off in each half-AC cycle, and the current and power magnitudes in each half-AC cycle. Similarly, after determining the power distribution of the second type of first circuit in each half-AC cycle, the control information of the second type of first circuit can be obtained based on this power distribution, determining whether the second type of first circuit is turned off in each half-AC cycle, and the current and power magnitudes in each half-AC cycle.

[0242] Taking at least two types of first circuits, including first type first circuit, second type first circuit and third type first circuit, as an example, after determining the power distribution of each type of first circuit in each half-AC cycle, the control information of first type first circuit, second type first circuit and third type first circuit can be obtained based on the power distribution, such as whether first type first circuit, second type first circuit and third type first circuit are turned off in each half-AC cycle, and the current magnitude and power magnitude in each half-AC cycle.

[0243] In some embodiments, at least one of the at least two types of first circuits operates during each half-AC cycle. Understandably, if at least one type of first circuit operates during each half-AC cycle, the sum of the output currents of the multiple first circuits will remain greater than 0, meaning there is always current input to the second circuit, thus ensuring that the second circuit can output a continuous current.

[0244] In the above embodiments, at least two types of first circuits are obtained by dividing them according to the power allocation of each first circuit in each half-AC cycle; control information for each type of first circuit is determined according to the power allocation of each type of first circuit in each half-AC cycle. In the technical solution of this application embodiment, the control type is divided according to the redistributed power, which can accurately control each first circuit, thereby greatly improving the power conversion efficiency of the DC-AC converter.

[0245] Taking the DC-AC converter in Figure 18 as an example, the control method provided in this application can be used to control the current (Io1, Io2, Io3) in the first circuit to the current waveforms shown in Figures 21a-21j.

[0246] As shown in Figure 21a, the first circuit with output current Io1 operates at high power in half AC cycle t1 and at low power in half AC cycle t2. The first circuit with output current Io2 is turned off in half AC cycle t1 and operates at low power in half AC cycle t2.

[0247] As shown in Figure 21b, the first circuit for output current Io1 is turned off in half of the AC cycle t1 and operates at high power in half of the AC cycle t2; the first circuit for output current Io2 operates at high power in half of the AC cycle t1 and is turned off in half of the AC cycle t2.

[0248] As shown in Figure 21c, the first circuit of the output current Io1 is turned off during the zero-crossing period t0, operates at the first power during the zero-crossing period t0', and operates at the second power during the non-zero-crossing period; the first circuit of the output current Io2 operates at the third power during the zero-crossing period t0, is turned off during the zero-crossing period t0', and operates at the fourth power during the non-zero-crossing period.

[0249] As shown in Figure 21d, the first circuit for output current Io1 is turned off in half AC cycle t1 and runs in half AC cycles t2 and t3. The first circuit for output current Io2 runs in half AC cycle t1 and is turned off in half AC cycles t2 and t3.

[0250] As shown in Figure 21e, the first circuit with output current Io1 operates at low power during half-AC cycles t1 and t4, and at high power during half-AC cycles t2, t3, and t5. The first circuit with output current Io2 operates at low power during half-AC cycles t1 and t4, and is turned off during half-AC cycles t2, t3, and t5.

[0251] As shown in Figure 21f, the first circuit with output current Io1 operates at low power during the full cycle t1, the first circuit with output current Io2 operates at low power during half AC cycle t1 and is turned off during half AC cycle t2, and the first circuit with output current Io3 is turned off during half AC cycle t1 and operates at low power during half AC cycle t2.

[0252] As shown in Figure 21g, the first circuit with output current Io1 operates at low power during the entire cycle t1, the first circuit with output current Io2 operates at low power during half-AC cycles t1 and t2 and is turned off during half-AC cycle t3, and the first circuit with output current Io3 is turned off during half-AC cycles t1 and t2 and operates at low power during half-AC cycle t3.

[0253] As shown in Figure 21h, the first circuit for output current Io1 is turned off in half AC cycles t1 and t3, and operates at low power in half AC cycle t2. The first circuit for output current Io2 operates at low power in half AC cycle t1, and is turned off in half AC cycles t2 and t3. The first circuit for output current Io3 is turned off in half AC cycles t1 and t2, and operates at low power in half AC cycle t3.

[0254] As shown in Figure 21i, the first circuit for output current Io1 operates at low power during half-AC cycles t1 and t2 and is turned off during half-AC cycle t3. The first circuit for output current Io2 operates at low power during half-AC cycles t1 and t3 and is turned off during half-AC cycle t2. The first circuit for output current Io3 is turned off during half-AC cycle t1 and operates at low power during half-AC cycles t2 and t3.

[0255] As shown in Figure 21j, the first circuit for output current Io1 operates at low power during half-AC cycles t1-t5 and is turned off during half-AC cycle t6. The first circuit for output current Io2 is turned off during half-AC cycles t1 and t2 and operates at low power during half-AC cycles t3-t6. The first circuit for output current Io3 operates at low power during half-AC cycles t1, t2, and t6 and is turned off during half-AC cycles t3-t5.

[0256] The above embodiments provide a variety of hiccup operation modes, which enable the DC-AC converter to achieve a variety of conversion functions and adapt to a variety of application scenarios.

[0257] In some embodiments, the waveform of the output current of each first circuit 11 is a wavy wave during the operation period; the waveform of the superimposed current of multiple first circuits 11 is a wavy wave throughout the entire cycle, and the peak value of each wavy wave is the same; the output current of the second circuit 12 is a sine wave throughout the entire cycle.

[0258] As shown in Figure 21a, the waveform of the output current Io1 of the first circuit 11 is a flat wave in each cycle, and the waveform of the output current Io2 of the first circuit 11 is a flat wave during the operating period, while the current and voltage values ​​are constant at 0 during the off period. The waveform of the superimposed current Ii of multiple first circuits 11 is a flat wave throughout the entire cycle, and the peak value of each flat wave is the same. The second circuit 12 shapes the superimposed current Ii, and the resulting output current is a sine wave throughout the entire cycle.

[0259] In an exemplary embodiment, the conditions for generating the trigger signal include at least one of the following: the operating data of one or more first circuits is lower than a preset data threshold; the power conversion rate of one or more first circuits is lower than a preset conversion rate threshold; and the output power of the second circuit is lower than a preset power threshold.

[0260] In this embodiment, after acquiring the operating data of multiple first circuits, the controller compares the operating data of each first circuit with a preset data threshold. If the operating data of one or more first circuits is lower than the preset data threshold, it is determined that the DC-AC converter can operate in hiccup mode. For example, if the output current of one of the first circuits is lower than a preset current threshold, then that first circuit can operate in hiccup mode.

[0261] Alternatively, the controller calculates the power conversion rate of each first circuit based on the operating data. If the power conversion rate of one or more first circuits is lower than the preset conversion rate threshold, it indicates that the power conversion system is operating in a low-efficiency range. At this time, the conversion efficiency is low and the energy consumption is high. Therefore, it is determined that the DC-AC converter can be operated in hiccup mode.

[0262] Alternatively, the controller calculates the output power of the second circuit. If the output power of the second circuit is lower than the preset power threshold, it indicates that the power converted by the DC-AC converter has not met the requirements, and then it is determined that the DC-AC converter can operate in hiccup mode.

[0263] It should be noted that the conditions for generating the trigger signal are not limited to the examples above. In practical applications, other conditions can also be used to generate the trigger signal.

[0264] In the above embodiments, the conditions for generating the trigger signal include at least one of the following: the operating data of one or more first circuits is lower than a preset data threshold; the power conversion rate of one or more first circuits is lower than a preset conversion rate threshold; and the output power of the second circuit is lower than a preset power threshold. This application provides various conditions for generating the trigger signal, enabling the DC-AC converter to operate in hiccup mode under various conditions, thereby improving the power conversion rate of the DC-AC converter.

[0265] It should be understood that although the steps in the flowcharts of the embodiments described above are shown sequentially according to the arrows, these steps are not necessarily executed in the order indicated by the arrows. Unless explicitly stated herein, there is no strict order restriction on the execution of these steps, and they can be executed in other orders. Moreover, at least some steps in the flowcharts of the embodiments described above may include multiple steps or multiple stages. These steps or stages are not necessarily completed at the same time, but can be executed at different times. The execution order of these steps or stages is not necessarily sequential, but can be performed alternately or in turn with other steps or at least some of the steps or stages of other steps.

[0266] In an exemplary embodiment, a control circuit is provided. The control circuit includes a processor, a memory, an input / output interface (I / O), and a communication interface. The processor, memory, and I / O are connected via a system bus, and the communication interface is connected to the system bus via the I / O. The processor of the control circuit provides computational and control capabilities. The memory of the control circuit includes a non-volatile storage medium and internal memory. The non-volatile storage medium stores an operating system, computer programs, and a database. The internal memory provides an environment for the operation of the operating system and computer programs in the non-volatile storage medium. The database of the control circuit stores control data for a DC-AC converter. The I / O interface of the control circuit is used for exchanging information between the processor and external devices. The communication interface of the control circuit is used for communication with an external terminal via a network connection. When the computer program is executed by the processor, it implements a control method for a DC-AC converter.

[0267] Those skilled in the art will understand that the above structure does not constitute a limitation on the control circuit applied thereto by the present application. The control circuit may include more or fewer components than shown in the figure, or combine certain components, or have different component arrangements.

[0268] In one exemplary embodiment, a non-transitory computer-readable storage medium including instructions is also provided, such as a memory including instructions that can be executed by a processor of an electronic device to perform the above-described method. For example, the non-transitory computer-readable storage medium may be a ROM, random access memory (RAM), CD-ROM, magnetic tape, floppy disk, and optical data storage device, etc.

[0269] In one exemplary embodiment, a computer program product is also provided, which, when executed by a processor, can implement the above-described methods. The computer program product includes one or more computer instructions. When these computer instructions are loaded and executed on a computer, some or all of the above-described methods can be implemented, wholly or partially, according to the processes or functions described in the embodiments of this application.

[0270] Those skilled in the art will understand that all or part of the processes in the methods of the above embodiments can be implemented by a computer program instructing related hardware. The computer program can be stored in a non-volatile computer-readable storage medium, and when executed, it can include the processes of the embodiments of the above methods. Any references to memory, databases, or other media used in the embodiments provided in this application can include at least one of non-volatile and volatile memory. Non-volatile memory can include read-only memory (ROM), magnetic tape, floppy disk, flash memory, optical memory, high-density embedded non-volatile memory, resistive random access memory (ReRAM), magnetic random access memory (MRAM), ferroelectric random access memory (FRAM), phase change memory (PCM), graphene memory, etc. Volatile memory can include random access memory (RAM) or external cache memory, etc. By way of illustration and not limitation, RAM can take many forms, such as Static Random Access Memory (SRAM) or Dynamic Random Access Memory (DRAM). The databases involved in the embodiments provided in this application may include at least one type of relational database and non-relational database. Non-relational databases may include, but are not limited to, blockchain-based distributed databases. The processors involved in the embodiments provided in this application may be general-purpose processors, central processing units, graphics processing units, digital signal processors, programmable logic devices, quantum computing-based data processing logic devices, etc., and are not limited to these.

[0271] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0272] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of this application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this application should be determined by the appended claims.

Claims

1. A DC-AC converter, wherein, The DC-AC converter includes multiple first circuits, a second circuit, and a control circuit; the first terminal of each first circuit is connected to a DC source, and the second terminal of each first circuit is connected to the second circuit in parallel or in series; the control circuit is communicatively connected to each first circuit and the second circuit. The control circuit is adapted to control each of the first circuits and the second circuits according to the electrical signal of the first terminal of each of the first circuits and the electrical signal of the second terminal of the second circuit.

2. The DC-AC converter according to claim 1, wherein, Each of the first circuits includes a primary-side bridge arm circuit, a high-frequency transformer, a resonant circuit, and a secondary-side bridge arm circuit; the first terminal of the primary-side bridge arm circuit is connected to the DC source; The second end of the primary side bridge arm circuit is connected to the primary winding of the high-frequency transformer; The resonant circuit is located on the secondary side of the high-frequency transformer.

3. The DC-AC converter according to claim 2, wherein, The resonant circuit includes a first resonant capacitor; a first terminal of the first resonant capacitor is connected to the secondary winding of the high-frequency transformer, and a second terminal of the first resonant capacitor is connected to the secondary bridge arm circuit. Alternatively, the resonant circuit includes a resonant inductor and a second resonant capacitor connected in series; the first end of the resonant circuit is connected to the secondary winding of the high-frequency transformer, and the second end of the resonant circuit is connected to the secondary bridge arm circuit. Alternatively, the resonant circuit includes two series-connected third and fourth resonant capacitors; the series circuit formed by the third and fourth resonant capacitors is connected in parallel with the secondary bridge arm circuit, and the common terminal of the third and fourth resonant capacitors is connected to the secondary winding of the high-frequency transformer.

4. The DC-AC converter according to claim 2, wherein, The second circuit includes a first switch, a second switch, a third switch, and a fourth switch; The first terminal of the first switching transistor is connected to each of the first circuits, and the second terminal of the first switching transistor is connected to the first terminal of the second switching transistor. The second terminal of the second switching transistor is connected to each of the first circuits; The first terminal of the third switch is connected to each of the first circuits, and the second terminal of the third switch is connected to the first terminal of the fourth switch. The second terminal of the fourth switching transistor is connected to each of the first circuits; The common terminal of the first and second switching transistors is adapted to be connected to the power grid or AC load, and the common terminal of the third and fourth switching transistors is adapted to be connected to the power grid or AC load; the first, second, third, and fourth switching transistors are all bidirectional switching transistors. In the second circuit, the switching transistor switches once per power frequency cycle, while the switching frequency of the switching transistor in the first circuit is higher than 30kHz.

5. The DC-AC converter according to claim 1, wherein, Each of the first circuits includes a primary-side bridge arm circuit, a high-frequency transformer, and a resonant circuit.

6. The DC-AC converter according to claim 5, wherein, The second circuit includes a secondary bridge arm circuit, a first switch, a second switch, a third switch, and a fourth switch; The secondary side bridge arm circuit is connected to each of the first circuits; The first terminal of the first switching transistor is connected to the secondary bridge arm circuit, and the second terminal of the first switching transistor is connected to the first terminal of the second switching transistor. The second terminal of the second switching transistor is connected to the secondary bridge arm circuit; The first terminal of the third switch is connected to the secondary bridge arm circuit, and the second terminal of the third switch is connected to the first terminal of the fourth switch. The second terminal of the fourth switching transistor is connected to the secondary bridge arm circuit. The common terminal of the first and second switching transistors is adapted to be connected to the power grid or AC load, and the common terminal of the third and fourth switching transistors is adapted to be connected to the power grid or AC load.

7. The DC-AC converter according to claim 5, wherein, The second circuit includes a first capacitor, a second capacitor, a fifth switch, a sixth switch, a seventh switch, and an eighth switch; The first terminal of the first capacitor is connected to the first electrode of the fifth switching transistor, and the second terminal of the first capacitor is connected to the first terminal of the second capacitor. The second terminal of the second capacitor is connected to the second terminal of the eighth switch transistor; The second terminal of the fifth switch is connected to the first terminal of the sixth switch; The second terminal of the sixth switch is connected to the first terminal of the seventh switch; The second terminal of the seventh switch is connected to the first terminal of the eighth switch. The common terminal of the first capacitor and the second capacitor is connected to each of the first circuits; The common terminal of the sixth and seventh switches is connected to each of the first circuits.

8. The DC-AC converter according to any one of claims 2-7, wherein, At least two high-frequency transformers are coupled via magnetic cores; the coupling methods include full coupling and partial coupling. The first ends of the multiple primary bridge arm circuits are connected in series; The first circuit includes a first type of first circuit and a second type of first circuit. In the first type of first circuit, the same-name terminals of the primary winding and the secondary winding of the high-frequency transformer are correspondingly set. In the second type of first circuit, the same-name terminals of the primary winding and the opposite-name terminals of the secondary winding of the high-frequency transformer are correspondingly set.

9. A control method for a DC-AC converter, wherein, Applied to the DC-AC converter according to any one of claims 1-8; the method includes: Acquire the electrical signals of the first terminal of each of the first circuits and the electrical signals of the second terminal of each of the second circuits in the DC-AC converter; Based on the electrical signals at the first terminal of each first circuit and the electrical signals at the second terminal of each second circuit, corresponding control signals are input to each first circuit and the second circuit. The electrical signals at the first terminal of each of the first circuits and the electrical signals at the second terminal of each of the second circuits include: The DC voltage at the first terminal of the first circuit, and the AC voltage and AC current at the second terminal of the second circuit; or, The DC voltage and DC current at the first terminal of the first circuit, and the AC voltage at the second terminal of the second circuit; or, The DC voltage and DC current at the first terminal of the first circuit, and the AC voltage and AC current at the second terminal of the second circuit.

10. The method according to claim 9, wherein, The step of inputting corresponding control signals to each of the first circuits and the second circuits based on the electrical signals at the first terminal of each of the first circuits and the electrical signals at the second terminal of each of the second circuits includes: Determine the power of the DC source corresponding to each of the first circuits; Based on the power of the DC source corresponding to each first circuit, corresponding control signals are input to each first circuit and the second circuit to control the multiple first circuits to operate in turn; wherein, the operating stage of each first circuit is related to the power of the DC source; Among them, multiple control signals of the first circuit are used to control the first type of first circuit to operate during the zero-crossing period of the AC power of the second circuit, the second type of first circuit to operate during the non-zero-crossing period of the AC power, and the power of the first type of first circuit is lower than the power of the second type of first circuit.

11. The method according to claim 9, wherein, The step of inputting corresponding control signals to each of the first circuits and the second circuits based on the electrical signals at the first terminal of each of the first circuits and the electrical signals at the second terminal of each of the second circuits includes: Based on the electrical signals at the first terminal of each of the first circuits and the electrical signals at the second terminal of each of the second circuits, multiple control variables are obtained; According to the plurality of control variables, corresponding control signals are input to each of the first circuit and the second circuit; Wherein, in the case that each of the first circuits of the DC-AC converter includes a primary-side bridge arm circuit, a high-frequency transformer, a resonant circuit, and a secondary-side bridge arm circuit, the plurality of control variables include: The switching frequency of the switching transistors in each of the first circuits; The phase difference between each of the primary-side bridge arm circuits and the corresponding secondary-side bridge arm circuits; and, The inner phase shift angle of each primary bridge arm circuit and / or the duty cycle of the switching transistor pulse of the primary bridge arm circuit; When each of the first circuits in the DC-AC converter includes a primary-side bridge arm circuit, a high-frequency transformer, and a resonant circuit, the plurality of control variables include: The switching frequency of the switching transistors in each of the first circuits; The phase difference between each of the first and second circuits; and, The inner phase shift angle of each primary bridge arm circuit and / or the duty cycle of the switching transistor pulse of the primary bridge arm circuit; Each of the primary side bridge arm circuits includes two half-bridge arms; The inner phase shift angle of the primary side bridge arm circuit includes the phase difference between the two half-bridge arms.

12. The method according to any one of claims 9-11, wherein, The method further includes: Obtain scheduling instructions; According to the scheduling instructions, the electrical signals at the first terminals of each of the first circuits, and the electrical signals at the second terminals of the second circuits, corresponding control signals are input to each of the first circuits and the second circuits. The dispatching instructions include at least one of active power dispatching instructions, reactive power dispatching instructions, power grid dispatching instructions, and manual dispatching instructions.

13. The method according to claim 12, wherein, The scheduling instructions include reactive power scheduling instructions; the step of inputting corresponding control signals to each of the first circuits and the second circuits according to the scheduling instructions, the electrical signals at the first terminals of each of the first circuits, and the electrical signals at the second terminals of the second circuits includes: According to the reactive power dispatching instruction, the current signal and voltage signal at the second terminal of the second circuit are obtained; The control signal is determined based on the current signal and voltage signal at the second terminal of the second circuit.

14. The method according to claim 12, wherein, The step of inputting corresponding control signals to each of the first and second circuits according to the scheduling instruction, the electrical signals at the first terminals of each of the first circuits, and the electrical signals at the second terminals of the second circuits includes: The scheduling instructions control the current direction between the first circuit and the second circuit to convert the DC current of the DC source into AC current and output it from the second circuit, or to convert the AC current input to the second circuit into DC current and output it from the first circuit.

15. A control method for a DC-AC converter, wherein, The control method, applied to the DC-AC converter according to any one of claims 1-8, comprises: Obtain operational data from multiple of the first circuits; In response to a trigger signal, control information for each of the first circuits is determined based on the operating data of the plurality of first circuits; Based on the control information of each of the first circuits, at least two of the first circuits are controlled to operate in hiccup mode, and the second circuit is made to continuously output the target AC current.

16. The method according to claim 15, wherein, The control of at least two of the first circuits to operate in hiccup mode includes: Control at least one of the first circuits to be turned off or to operate in a low-power state during a first preset time period; Alternatively, at least two of the first circuits may be controlled to turn off alternately during the zero-crossing period, which includes the zero-crossing point of the output AC voltage of the DC-AC converter.

17. The method according to claim 15 or 16, wherein, Determining the control information of each of the first circuits based on the operating data of the plurality of first circuits includes: The operating status and corresponding operating duration of each first circuit are determined based on the operating data of multiple first circuits. The states of the first circuit include high-power operation, low-power operation, and off. The operating duration of each state is N half-AC cycles, where N is a positive integer and can vary.

18. The method according to claim 15 or 16, wherein, Determining the control information of each of the first circuits based on the operating data of the plurality of first circuits includes: Based on the operating data of multiple first circuits, the power allocation of each first circuit within a second preset time period is determined; wherein, the sum of the power allocation of all first circuits within the second preset time period reaches the target power of the DC-AC converter. Based on the power distribution of each of the first circuits during the second preset time period, the control information of each of the first circuits is determined.

19. The method according to claim 18, wherein, The second preset time period includes multiple half-AC cycles. Determining the control information for each of the first circuits based on the power distribution within the second preset time period includes: Based on the power distribution of each of the first circuits in each half-AC cycle, at least two types of first circuits are obtained; Based on the power distribution of each type of first circuit in each half-AC cycle, the control information of each type of first circuit is determined, wherein at least one type of first circuit operates in each half-AC cycle.

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