Power converter and power system

Abstract

The invention relates to the technical field of power supplies, in particular to a power converter and a power system. According to the power converter, the input end of an inverter circuit is connected with a direct-current connecting end, the inverter circuit comprises a commutation bridge, the first output end of the commutation bridge is connected with the first end of a primary winding of a first transformer, and the second end of the primary winding is connected with the first end of an alternating-current connecting end; the second output end of the commutation bridge is connected with the second end of the AC connection end. A secondary winding of the first transformer is connected with the input end of the branch circuit, and the output end of the branch circuit is connected with the direct-current connecting end; the power converter is used for controlling the commutation bridge under a specified working condition so as to transmit alternating current of an alternating current source connected with the alternating current connecting end to the branch circuit through the first transformer; and the branch circuit is used for converting input alternating current into direct current and transmitting the direct current to the direct current connecting end. According to the circuit, reverse transmission of power from the alternating current connecting end to the direct current connecting end can be achieved, and reactive power support of the alternating current connecting end is provided through reverse transmission.

Description

Technical Field

[0001] This disclosure relates to the field of power supply technology, and in particular to a power converter and power system. Background Technology

[0002] Photovoltaic inverters play two core roles in photovoltaic (PV) power generation systems: maximum power point tracking (MPPT) of PV modules and grid-connected power generation. Common PV inverters include centralized inverters, string inverters, and microinverters. In low-power PV power generation scenarios, single-phase microinverters are increasingly widely used due to their ease of installation and maintenance, high power generation efficiency, and ability to achieve module-level safe shutdown. However, microinverters in related technologies often only transmit the power output from the PV system to the AC grid and cannot provide reactive power support to the AC grid. Summary of the Invention

[0003] This disclosure aims to at least partially address one of the technical problems in the related art. To this end, a first objective of this disclosure is to provide a power converter capable of reverse power transfer from an AC connection to a DC connection, thereby providing reactive power support to the AC connection via the reverse transfer.

[0004] The second objective of this disclosure is to propose an electric power system.

[0005] To achieve the above objectives, a first aspect of this disclosure provides a power converter, comprising: a DC connection terminal, an inverter circuit, a first transformer, a branch circuit, and an AC connection terminal; the input terminal of the inverter circuit is connected to the DC connection terminal, the inverter circuit includes a commutation bridge, the first output terminal of the commutation bridge is connected to the first end of the primary winding of the first transformer, and the second end of the primary winding is connected to the first end of the AC connection terminal; the second output terminal of the commutation bridge is connected to the second end of the AC connection terminal; the secondary winding of the first transformer is connected to the input terminal of the branch circuit, and the output terminal of the branch circuit is connected to the DC connection terminal; the power converter is used to control the commutation bridge under specified operating conditions to transmit AC power from the AC source connected to the AC connection terminal to the branch circuit through the first transformer; the branch circuit is used to convert the input AC power into DC power and transmit it to the DC connection terminal.

[0006] According to the power converter of this disclosure embodiment, the first output terminal of the commutation bridge is connected to the first terminal of the primary winding of the first transformer, and the second terminal of the primary winding is connected to the first terminal of the AC connection terminal. Under specified operating conditions, the commutation bridge transmits the AC power from the AC source connected to the AC connection terminal to the branch circuit through the first transformer. The branch circuit converts the input AC power into DC power and transmits it to the DC connection terminal. In this way, through the inverter circuit, the first transformer, and the branch circuit, reverse power transmission from the AC connection terminal to the DC connection terminal is realized, so as to provide reactive power support for the AC connection terminal through reverse transmission.

[0007] In some embodiments, the first transformer includes at least one secondary winding, wherein, in the case where the first transformer includes multiple secondary windings, at least two of the multiple secondary windings have opposite voltage polarities.

[0008] In some embodiments, when the first transformer includes a first secondary winding, the branch circuit includes: a first capacitor connected in parallel with a DC connection terminal; a first diode, the anode of the first diode being connected to a first terminal of the first secondary winding, the cathode of the first diode being connected to a first terminal of the first capacitor, and a second terminal of the first secondary winding being connected to a second terminal of the first capacitor.

[0009] In some embodiments, when the first transformer includes a second secondary winding and a third secondary winding, the branch circuit includes: a second capacitor connected in parallel with a DC connection terminal; a second diode and a third diode, wherein the anode of the second diode is connected to a first terminal of the second secondary winding, the anode of the third diode is connected to a first terminal of the third secondary winding, the cathodes of the second diode and the third diode are both connected to a first terminal of the second capacitor, and the second terminals of the second secondary winding and the third secondary winding are both connected to a second terminal of the second capacitor.

[0010] In some embodiments, the branch circuit further includes: a first switching transistor and a second switching transistor, wherein the first switching transistor is connected in series with a second diode, and the second switching transistor is connected in series with a third diode.

[0011] In some embodiments, the second switch is turned off when the AC current is in the positive half-cycle, and the first switch is turned off when the AC current is in the negative half-cycle.

[0012] In some embodiments, when the first transformer includes a first secondary winding, the branch circuit includes: a third capacitor connected in parallel with a DC connection terminal; a fourth diode, the anode of which is connected to a first terminal of the first secondary winding; a fifth diode, the anode of which is connected to a second terminal of the first secondary winding; a first inductor, the first terminal of which is connected to the cathodes of the fourth and fifth diodes respectively, the second terminal of which is connected to the first terminal of the third capacitor, and the second terminal of the first secondary winding is connected to the second terminal of the third capacitor.

[0013] In some embodiments, where the first transformer includes a second secondary winding and a third secondary winding, the branch circuit includes: a fourth capacitor connected in parallel with a DC connection terminal; a sixth diode and a seventh diode, the anode of the sixth diode being connected to a first terminal of the second secondary winding, and the anode of the seventh diode being connected to a first terminal of the third secondary winding; an eighth diode, the anode of the eighth diode being connected to a second terminal of both the second and third secondary windings; and a second inductor, the first terminal of the second inductor being connected to the cathodes of the sixth, seventh, and eighth diodes, the second terminal of the second inductor being connected to a first terminal of the fourth capacitor, and the second terminals of the second and third secondary windings being connected to the second terminals of the fourth capacitor.

[0014] In some embodiments, the branch circuit further includes a third switch and a fourth switch, wherein the third switch is connected in series with a sixth diode and the fourth switch is connected in series with a seventh diode.

[0015] In some embodiments, the fourth switch is turned off when the AC current is in the positive half-cycle, and the third switch is turned off when the AC current is in the negative half-cycle.

[0016] In some embodiments, the power converter is also used to control the commutation bridge under normal operating conditions to convert the DC power from the DC source connected to the DC connection terminal into AC power and deliver it to the AC connection terminal through the primary winding.

[0017] In some embodiments, the commutation bridge includes a fifth switch, a sixth switch, a seventh switch, and an eighth switch. The first ends of the fifth switch and the seventh switch are respectively the input ends of the commutation bridge. The second ends of the fifth switch and the first ends of the sixth switch are respectively connected to the first ends of the primary winding. The second ends of the seventh switch and the first ends of the eighth switch are respectively connected to the second ends of the AC connection terminal. The second ends of the sixth switch and the second ends of the eighth switch are respectively the third output ends of the commutation bridge.

[0018] In some embodiments, under specified operating conditions, the fifth and seventh switching transistors are respectively in the off state, and the sixth and eighth switching transistors are switched synchronously according to a first preset frequency; under normal operating conditions, the fifth and eighth switching transistors are switched on synchronously, the sixth and seventh switching transistors are switched on synchronously, and the sixth and eighth switching transistors are switched on alternately according to a second preset frequency.

[0019] In some embodiments, the first preset frequency is greater than the second preset frequency.

[0020] In some embodiments, the fifth and seventh switching transistors are thyristors, and the sixth and eighth switching transistors are MOSFETs or IGBTs.

[0021] In some embodiments, when the power factor of the power converter is less than 1 and greater than or equal to -1, the power converter is in a specified operating condition.

[0022] To achieve the above objectives, a second aspect of this disclosure provides a power system including the aforementioned power converter.

[0023] According to the power system of this disclosure, the aforementioned power converter can realize the reverse transmission of power from the AC connection terminal to the DC connection terminal, so as to provide reactive power support for the AC connection terminal through the reverse transmission.

[0024] Additional aspects and advantages of this disclosure will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this disclosure. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the power converter according to the first embodiment of the present disclosure;

[0026] Figure 2 This is a schematic diagram of a power converter that performs reverse power transmission during half a cycle of alternating current according to an embodiment of the present disclosure.

[0027] Figure 3 This is a schematic diagram of a power converter that performs reverse power transmission throughout the entire cycle of alternating current according to the first embodiment of this disclosure.

[0028] Figure 4 This is a schematic diagram of a power converter that performs reverse power transmission throughout the entire cycle of alternating current according to a second embodiment of the present disclosure.

[0029] Figure 5 This is a schematic diagram of a power converter that performs reverse power transmission during half a cycle of alternating current according to another embodiment of the present disclosure.

[0030] Figure 6 This is a schematic diagram of a power converter that performs reverse power transmission throughout the entire cycle of alternating current according to a third embodiment of the present disclosure.

[0031] Figure 7 This is a schematic diagram of a power converter that performs reverse power transmission throughout the entire cycle of alternating current according to the fourth embodiment of this disclosure.

[0032] Figure 8a This is a schematic diagram of the power converter according to the second embodiment of the present disclosure;

[0033] Figure 8b This is a schematic diagram of the power converter according to the third embodiment of the present disclosure;

[0034] Figure 8c This is a schematic diagram of the power converter according to the fourth embodiment of the present disclosure;

[0035] Figure 9a for Figure 8a A schematic diagram of the corresponding power converter that performs reverse power transmission throughout the entire cycle of alternating current;

[0036] Figure 9b for Figure 8b A schematic diagram of the corresponding power converter that performs reverse power transmission throughout the entire cycle of alternating current;

[0037] Figure 9c for Figure 8c A schematic diagram of the corresponding power converter that performs reverse power transmission throughout the entire cycle of alternating current;

[0038] Figure 10 for Figure 2 A schematic diagram of the specific circuit structure of the corresponding power converter;

[0039] Figure 11 for Figure 3 A schematic diagram of the specific circuit structure of the corresponding power converter;

[0040] Figure 12 for Figure 4 A schematic diagram of the specific circuit structure of the corresponding power converter;

[0041] Figure 13 for Figure 9b A schematic diagram of the specific circuit structure of the corresponding power converter;

[0042] Figure 14 This is a schematic diagram of the structure of a power system according to an embodiment of the present disclosure. Detailed Implementation

[0043] Embodiments of this disclosure are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain this disclosure, and should not be construed as limiting this disclosure.

[0044] The power converter and power system proposed in the embodiments of this disclosure are described below with reference to the accompanying drawings.

[0045] Figure 1 This is a schematic diagram of the structure of a power converter according to some embodiments of the present disclosure.

[0046] Reference Figure 1The power converter includes: DC connection terminals (A1, A2), inverter circuit 10, first transformer T1, branch circuit 20, and AC connection terminals (B1, B2).

[0047] The inverter circuit 10 has its input terminals connected to DC terminals (A1, A2). The inverter circuit 10 includes a commutation bridge 11. The first output terminal of the commutation bridge 11 is connected to the first terminal of the primary winding of the first transformer T1, and the second terminal of the primary winding is connected to the first terminal B1 of the AC terminal. The second output terminal of the commutation bridge 11 is connected to the second terminal B2 of the AC terminal. The secondary winding of the first transformer T1 is connected to the input terminal of the branch circuit 20, and the output terminal of the branch circuit 20 is connected to the DC terminals (A1, A2). The power converter is used to control the commutation bridge 11 under specified operating conditions to transmit the AC power from the AC source connected to the AC terminals (B1, B2) to the branch circuit 20 through the first transformer T1. The branch circuit 20 is used to convert the input AC power into DC power and transmit it to the DC terminals (A1, A2).

[0048] It should be noted that the DC connection terminals (A1, A2) are suitable for electrically connecting DC equipment such as energy storage capacitors (large capacitors) and energy storage devices of photovoltaic modules; the AC connection terminals (B1, B2) are suitable for connecting AC equipment such as AC power grids and AC loads.

[0049] When the power converter operates under specified conditions, the AC current forms an AC path with the primary winding and commutator bridge 11. The first transformer T1 couples the AC current from the primary winding to the secondary winding, and the secondary winding transmits the coupled AC current to the branch circuit 20. The branch circuit 20 converts the AC current from the secondary winding into DC current and transmits it to the DC connection terminals (A1, A2). Therefore, the power at the AC connection terminals (B1, B2) is transmitted to the DC connection terminals (A1, A2) through the commutator bridge 11, the first transformer T1, and the branch circuit 20, realizing reverse power transmission. Through reverse power transmission, the power at the AC connection terminals (B1, B2) can be stored at the DC connection terminals (A1, A2) to provide reactive power support for the AC connection terminals (B1, B2) or to store energy at the DC connection terminals (A1, A2).

[0050] For example, the DC connection terminals (A1, A2) are electrically connected to the energy storage capacitor of the photovoltaic module, and the AC connection terminals (B1, B2) are electrically connected to the AC power grid. When the power converter operates under specified conditions, it performs reverse power transmission, i.e., reactive power compensation (when reactive power compensation is required). At this time, the commutation bridge 11 can be controlled to operate, so that the power from the AC power grid is transmitted to the energy storage capacitor of the photovoltaic module for storage through the commutation bridge 11, the first transformer T1, and the branch circuit 20, thereby providing reactive power support to the AC power grid. Therefore, the power converter can realize the transmission of power from the AC power grid to the photovoltaic system to provide reactive power support to the AC power grid.

[0051] For example, the DC connection terminals (A1, A2) are electrically connected to the energy storage device, and the AC connection terminals (B1, B2) are electrically connected to the AC power grid. When the power converter operates under specified conditions, it performs reverse power transmission, i.e., reactive power compensation (when reactive power compensation is required). At this time, the commutation bridge 11 can be controlled to operate, so that the power from the AC power grid is transmitted to the energy storage device for storage through the commutation bridge 11, the first transformer T1, and the branch circuit 20, thereby providing reactive power support to the AC power grid or charging the energy storage device. Therefore, the power converter can realize the transmission from the AC power grid to the energy storage device to provide reactive power support to the AC power grid or charge the energy storage device.

[0052] In the above embodiments, the reverse power transmission from the AC connection terminal to the DC connection terminal can be realized through the commutation bridge, the first transformer and the branch circuit, so as to provide reactive power support for the AC connection terminal through reverse transmission to meet reactive power demand, or to charge the DC connection terminal through the AC connection terminal.

[0053] In some embodiments, the power converter is also used to control the commutation bridge 11 under normal operating conditions to convert the DC power from the DC source connected to the DC connection terminals (A1, A2) into AC power and deliver it to the AC connection terminals (B1, B2) through the primary winding.

[0054] When the power converter is operating under normal conditions, the inverter circuit 10 inverts the DC power from the DC connection terminals (A1, A2) into AC power and transmits it to the primary winding of the first transformer T1. At this time, the primary winding of the first transformer T1 acts as a filter inductor to filter the AC power output from the inverter circuit 10, and finally transmits it to the AC connection terminals (B1, B2), realizing forward power transmission. It should be noted that the branch circuit 20 does not work during this process.

[0055] For example, consider a DC connection (A1, A2) electrically connected to the energy storage capacitor of the photovoltaic module, and an AC connection (B1, B2) electrically connected to the AC power grid. When the photovoltaic module is connected to the grid, the power converter performs forward power transmission, i.e., normal operating condition. At this time, the inverter circuit 10 can be controlled to work, and the power of the photovoltaic module is transmitted to the AC power grid through the inverter circuit 10 and the primary winding of the first transformer T1. Then, the power converter performs reverse power transmission, i.e., designated operating condition. At this time, the commutation bridge 11 can be controlled to work, and the power of the AC power grid is transmitted to the energy storage capacitor of the photovoltaic module for storage through the commutation bridge 11, the first transformer T1 and the branch circuit 20, so as to realize reactive power support of the AC power grid.

[0056] In the above embodiments, the inverter circuit and the first transformer enable forward power transmission from the DC connection terminal to the AC connection terminal, and the commutation bridge, the first transformer, and the branch circuit enable reverse power transmission from the AC connection terminal to the DC connection terminal, thereby achieving bidirectional power transmission between AC and DC. Furthermore, in the process of achieving bidirectional power transmission, the number of components can be reduced because the commutation bridge is reused, thereby reducing the cost of the inverter.

[0057] In some embodiments, the first transformer T1 includes at least one secondary winding, wherein, in the case where the first transformer T1 includes multiple secondary windings, at least two of the multiple secondary windings have opposite voltage polarities.

[0058] Specifically, when the reverse power transmission requirement is low, such as when the application only needs to achieve a power factor of 0.8, the secondary winding of the first transformer T1 can be set to one. During reverse power transmission, the first transformer T1 can achieve reverse power transmission during the positive or negative half-cycle of the AC power provided at the AC connection terminals (B1, B2), depending on the design of the corresponding terminals of the first transformer T1.

[0059] When the reverse power transmission requirement is high, such as when the application scenario needs to be geared towards micro-storage applications, the secondary winding of the first transformer T1 can be set to two, and the polarities of these two secondary windings are opposite. That is, when the power is transmitted in reverse, regardless of whether the AC power provided by the AC connection terminals (B1, B2) is in the positive half-cycle or the negative half-cycle, there is a secondary winding in the first transformer T1 that can realize the reverse power transmission.

[0060] In the above embodiments, by configuring different secondary windings for the first transformer, different power reverse transmission requirements can be met.

[0061] In some embodiments, when the first transformer T1 includes a first secondary winding, the branch circuit 20 includes: a first capacitor C1 and a first diode D1, wherein the first capacitor C1 is connected in parallel with the DC connection terminals (A1, A2); the anode of the first diode D1 is connected to the first end of the first secondary winding, the cathode of the first diode D1 is connected to the first end of the first capacitor C1, and the second end of the first secondary winding is connected to the second end of the first capacitor C1.

[0062] For example, refer to Figure 2 When the first transformer T1 includes a secondary winding, such as a first secondary winding, the branch circuit 20 may include a first capacitor C1 and a first diode D1. The first terminal of the first capacitor C1 is electrically connected to the DC connection terminal A1, and the second terminal of the first capacitor C1 is electrically connected to the DC connection terminal A2; that is, the first capacitor C1 is connected in parallel with the DC connection terminals (A1, A2). The first diode D1 is connected in series with the first secondary winding and then in parallel with the first capacitor C1. Specifically, the anode of the first diode D1 is electrically connected to the first terminal of the first secondary winding, the cathode of the first diode D1 is electrically connected to the first terminal of the first capacitor C1, and the second terminal of the first secondary winding is electrically connected to the second terminal of the first capacitor C1.

[0063] In this example, the first end of the first secondary winding and the first end of the primary winding of the first transformer T1 are the same name. The first end of the primary winding of the first transformer T1 is electrically connected to the first output end of the commutation bridge 11. The second end of the primary winding of the first transformer T1 is electrically connected to the AC connection end B1. The AC connection end B2 is also electrically connected to the commutation bridge 11. In this way, reverse power transmission can be achieved during the positive half-cycle of the AC power provided by the AC connection ends (B1, B2).

[0064] Specifically, during forward power transmission, the inverter circuit 10 converts the DC power at the DC connection terminals (A1, A2) into AC power, and then filters the AC power through the primary winding of the first transformer T1 before finally transmitting it to the AC connection terminals (B1, B2). It should be noted that during this process, because the voltage difference across the primary winding of the first transformer T1 is small (i.e., the ripple voltage of the inverter circuit 10), the first diode D1 may fail to conduct due to reverse cutoff (i.e., the voltage polarity of the first secondary winding of the first transformer T1 is consistent with the voltage polarity of the DC devices at the DC connection terminals (A1, A2), and the reverse voltage across the first diode D1 is the sum of the two), or it may fail to conduct due to insufficient conduction voltage (i.e., the voltage polarity of the first secondary winding of the first transformer T1 is inconsistent with the voltage polarity of the DC devices at the DC connection terminals (A1, A2), but the voltage of the DC devices at the DC connection terminals (A1, A2) is higher than the voltage of the first secondary winding of the first transformer T1). In this case, the primary winding of the first transformer T1 is only used for filtering, and the first diode D1 is always in the cutoff state.

[0065] During reverse power transmission, in the positive half-cycle of the AC power supplied at the AC connection terminals (B1, B2), the first transformer T1 can be charged using AC power by controlling the commutator bridge 11. The first diode D1 is reverse-biased and its reverse voltage is the sum of the voltage of the first secondary winding of the first transformer T1 and the voltage of the DC equipment at the DC connection terminals (A1, A2). Then, the AC power is controlled to stop charging the first transformer T1, and the first secondary winding of the first transformer T1 freewheels through the first diode D1. The energy of the first transformer T1 is transferred to the first capacitor C1 and the DC equipment at the DC connection terminals (A1, A2) through the first diode D1. In the negative half-cycle of the AC power supplied at the AC connection terminals (B1, B2), based on the working principle, power cannot be transmitted in reverse.

[0066] It should be noted that by adjusting the same-name terminals of the first transformer T1, power can be transmitted in reverse during the negative half-cycle of the AC power supplied at the AC connection terminals (B1, B2), for example, by taking the second terminal of the first secondary winding of the first transformer T1 and the first terminal of the primary winding of the first transformer T1 as the same-name terminals.

[0067] In the above embodiments, the first transformer enables reverse power transmission during half a cycle of AC power, making it suitable for application scenarios with low power transmission requirements.

[0068] In some embodiments, when the first transformer T1 includes a second secondary winding and a third secondary winding, the branch circuit 20 includes: a second capacitor C2, a second diode D2, and a third diode D3, wherein the second capacitor C2 is connected in parallel with the DC connection terminals (A1, A2); the anode of the second diode D2 is connected to the first end of the second secondary winding, the anode of the third diode D3 is connected to the first end of the third secondary winding, the cathodes of the second diode D2 and the third diode D3 are both connected to the first end of the second capacitor C2, and the second ends of the second secondary winding and the third secondary winding are both connected to the second end of the second capacitor C2.

[0069] For example, refer to Figure 3In the case where the first transformer T1 includes two secondary windings, such as a second secondary winding and a third secondary winding, the branch circuit 20 may include a second capacitor C2, a second diode D2, and a third diode D3. The first terminal of the second capacitor C2 is electrically connected to the DC connection terminal A1, and the second terminal of the second capacitor C2 is electrically connected to the DC connection terminal A2; that is, the second capacitor C2 is connected in parallel with the DC connection terminals (A1, A2). The second diode D2 is connected in series with the second secondary winding and then in parallel with the second capacitor C2. Simultaneously, the third diode D3 is connected in series with the third secondary winding and then in parallel with the second capacitor C2. Specifically, the anode of the second diode D2 is electrically connected to the first terminal of the second secondary winding, the anode of the third diode D3 is electrically connected to the first terminal of the third secondary winding, the cathodes of the second diode D2 and the third diode D3 are respectively electrically connected to the first terminal of the second capacitor C2, and the second terminals of the second and third secondary windings are respectively electrically connected to the second terminal of the second capacitor C2.

[0070] In this example, the first end of the second secondary winding, the second end of the third secondary winding, and the first end of the primary winding of the first transformer T1 are the same-named ends. The first end of the primary winding of the first transformer T1 is electrically connected to the first output end of the commutation bridge 11, and the second end of the primary winding of the first transformer T1 is electrically connected to the AC connection end B1. The AC connection end B2 is also electrically connected to the commutation bridge 11. In this way, reverse power transmission can be achieved in both the positive and negative half-cycles of the AC power provided by the AC connection ends (B1, B2).

[0071] Specifically, during forward power transmission, the inverter circuit 10 converts the DC power at the DC connection terminals (A1, A2) into AC power, which is then filtered by the primary winding of the first transformer T1 before being transmitted to the AC connection terminals (B1, B2). Based on the foregoing analysis, during this process, the primary winding of the first transformer T1 is only used for filtering, while the second diode D2 and the third diode D3 remain in the off state.

[0072] During reverse power transmission, in the positive half-cycle of the AC power supplied at the AC connection terminals (B1, B2), the first transformer T1 can be charged using AC power by controlling the commutator bridge 11. The second diode D2 is reverse-biased and its reverse voltage is the sum of the reflected voltage of the second secondary winding of the first transformer T1 and the voltage of the DC equipment at the DC connection terminals (A1, A2). The third diode D3's reverse voltage is the difference between the reflected voltage of the third secondary winding and the voltage of the DC equipment at the DC connection terminals (A1, A2). When the turns ratio design of the first transformer T1 satisfies the requirements of the third secondary winding... When the reflected voltage is lower than the voltage of the DC equipment at the DC connection terminals (A1, A2), the third diode D3 will be in the reverse cutoff state. Then, the AC power is controlled to stop charging the first transformer T1. The second secondary winding of the first transformer T1 freewheels through the second diode D2. The energy of the first transformer T1 is transferred to the second capacitor C2 and the DC equipment at the DC connection terminals (A1, A2) through the second diode D2. At this time, the reverse voltage that the third diode D3 bears is twice the voltage of the DC equipment at the DC connection terminals (A1, A2), so the third diode D3 is in the reverse cutoff state.

[0073] It should be noted that the working principle of the negative half-cycle of the AC power supplied at the AC connection terminals (B1, B2) can be referred to the working principle of the positive half-cycle, which will not be elaborated here.

[0074] In the above embodiments, by setting two secondary windings in the first transformer, reverse power transmission can be achieved throughout the entire cycle of AC power, which is suitable for application scenarios with high power transmission requirements.

[0075] In some embodiments, refer to Figure 4 The branch circuit 20 also includes: a first switch Q1 and a second switch Q2, the first switch Q1 being connected in series with the second diode D2, and the second switch Q2 being connected in series with the third diode D3.

[0076] It should be noted that, based on the foregoing analysis, during reverse power transmission, in the positive half-cycle of the AC power supplied at the AC connection terminals (B1, B2), the reverse voltage across the third diode D3 is the difference between the reflected voltage of the third secondary winding and the voltage of the DC equipment at the DC connection terminals (A1, A2). To keep the third diode D3 in the off state, the turns ratio of the first transformer T1 needs to ensure that the reflected voltage of the third secondary winding is lower than the voltage of the DC equipment at the DC connection terminals (A1, A2). However, an excessively high turns ratio will cause excessive stress on some components of the multiplexed commutator bridge 11, making the circuit design difficult. Therefore, the second switch Q2 can be connected in series with the third diode D3. By controlling the second switch Q2, the stress requirements on the components can be reduced, thus simplifying the circuit design.

[0077] Similarly, by connecting the second diode D2 in series with the first switch Q1, the stress requirements on the device can be reduced and the circuit design difficulty can be decreased by controlling the first switch Q1.

[0078] In the above embodiments, by setting two secondary windings in the first transformer, reverse power transmission can be achieved throughout the AC power cycle, which is suitable for application scenarios with high power transmission requirements. At the same time, by using series switching transistors, the stress requirements on the devices can be reduced, and the circuit design difficulty can be reduced.

[0079] In some embodiments, when the AC current is in the positive half-cycle, the second switch Q2 is turned off; when the AC current is in the negative half-cycle, the first switch Q1 is turned off.

[0080] Specifically, based on the above analysis, it can be seen that during the positive half-cycle of the AC power supplied at the AC connection terminals (B1, B2), the third diode D3 is in the off state. Therefore, controlling the second switch Q2 to turn off can reduce the stress requirements on the device and reduce the difficulty of circuit design. During the negative half-cycle of the AC power supplied at the AC connection terminals (B1, B2), the second diode D2 is in the off state. Therefore, controlling the first switch Q1 to turn off can reduce the stress requirements on the device and reduce the difficulty of circuit design.

[0081] In some embodiments, when the first transformer T1 includes a first secondary winding, the branch circuit 20 includes: a third capacitor C3, a fourth diode D4, a fifth diode D5, and a first inductor L1, wherein the third capacitor C3 is connected in parallel with the DC connection terminals (A1, A2); the anode of the fourth diode D4 is connected to the first end of the first secondary winding; the anode of the fifth diode D5 is connected to the second end of the first secondary winding; the first end of the first inductor L1 is connected to the cathode of the fourth diode D4 and the cathode of the fifth diode D5, respectively; the second end of the first inductor L1 is connected to the first end of the third capacitor C3; and the second end of the first secondary winding is connected to the second end of the third capacitor C3.

[0082] For example, refer to Figure 5In the case where the first transformer T1 includes a secondary winding, such as a first secondary winding, the branch circuit 20 may include a third capacitor C3, a fourth diode D4, a fifth diode D5, and a first inductor L1. Specifically, the first terminal of the third capacitor C3 is electrically connected to the DC connection terminal A1, and the second terminal of the third capacitor C3 is electrically connected to the DC connection terminal A2; that is, the third capacitor C3 is connected in parallel with the DC connection terminals (A1, A2). The fourth diode D4 is connected in series with the first secondary winding and then in parallel with the fifth diode D5. Specifically, the anode of the fourth diode D4 is electrically connected to the first terminal of the first secondary winding, the cathode of the fourth diode D4 is electrically connected to the cathode of the fifth diode D5, and the second terminal of the first secondary winding is electrically connected to the anode of the fifth diode D5. The first terminal of the first inductor L1 is connected to the cathode of the fifth diode D5, the second terminal of the first inductor L1 is connected to the first terminal of the third capacitor C3, and the second terminal of the first secondary winding is connected to the second terminal of the third capacitor C3; that is, the first inductor L1 and the third capacitor C3 are connected in series.

[0083] In this example, the first end of the first secondary winding and the second end of the primary winding of the first transformer T1 are the same name. The first end of the primary winding of the first transformer T1 is electrically connected to the first output end of the commutation bridge 11, and the second end of the primary winding of the first transformer T1 is electrically connected to the AC connection end B1. The AC connection end B2 is also electrically connected to the commutation bridge 11. In this way, reverse power transmission can be achieved during the positive half-cycle of the AC power provided by the AC connection ends (B1, B2).

[0084] Specifically, during forward power transmission, the inverter circuit 10 converts the DC power at the DC connection terminals (A1, A2) into AC power, and then filters the AC power through the primary winding of the first transformer T1 before finally transmitting it to the AC connection terminals (B1, B2). It should be noted that during this process, because the voltage difference across the primary winding of the first transformer T1 is small (i.e., the ripple voltage of the inverter circuit 10), the fourth diode D4 may fail to conduct due to reverse cutoff (i.e., the voltage polarity of the first secondary winding of the first transformer T1 is consistent with the voltage polarity of the DC devices at the DC connection terminals (A1, A2), and the reverse voltage across the fourth diode D4 is the sum of the two), or it may fail to conduct due to insufficient conduction voltage (i.e., the voltage polarity of the first secondary winding of the first transformer T1 is inconsistent with the voltage polarity of the DC devices at the DC connection terminals (A1, A2), but the voltage of the DC devices at the DC connection terminals (A1, A2) is higher than the voltage of the first secondary winding of the first transformer T1). In this case, the primary winding of the first transformer T1 is only used for filtering, and the fourth diode D4 is always in the cutoff state.

[0085] During reverse power transmission, in the positive half-cycle of the AC power supplied at the AC connection terminals (B1, B2), the commutator bridge 11 can be controlled to first charge the first transformer T1 using AC power. The first secondary winding of the first transformer T1 freewheels through the fourth diode D4, and the energy of the first transformer T1 is transferred to the third capacitor C3 and the DC devices at the DC connection terminals (A1, A2) via the fourth diode D4 and the first inductor L1. Then, the AC power is controlled to stop charging the first transformer T1, and the fourth diode D4 is reverse-biased and cut off. In the negative half-cycle of the AC power supplied at the AC connection terminals (B1, B2), based on the working principle, power cannot be transmitted in reverse.

[0086] In the above embodiments, the first transformer enables reverse power transmission during half a cycle of AC power, making it suitable for application scenarios with low power transmission requirements.

[0087] In some embodiments, when the first transformer T1 includes a second secondary winding and a third secondary winding, the branch circuit 20 includes: a fourth capacitor C4, a sixth diode D6, a seventh diode D7, an eighth diode D8, and a second inductor L2, wherein the fourth capacitor C4 is connected in parallel with the DC connection terminals (A1, A2); the anode of the sixth diode D6 is connected to the first end of the second secondary winding, and the anode of the seventh diode D7 is connected to the first end of the third secondary winding; the anode of the eighth diode D8 is connected to the second end of the second secondary winding and the second end of the third secondary winding, respectively; the first end of the second inductor L2 is connected to the cathode of the sixth diode D6, the cathode of the seventh diode D7, and the cathode of the eighth diode D8, respectively; the second end of the second inductor L2 is connected to the first end of the fourth capacitor C4; and the second ends of the second secondary winding and the second ends of the third secondary winding are connected to the second end of the fourth capacitor C4, respectively.

[0088] For example, refer to Figure 6In the case where the first transformer T1 includes two secondary windings, such as a second secondary winding and a third secondary winding, the branch circuit 20 may include a fourth capacitor C4, a sixth diode D6, a seventh diode D7, an eighth diode D8, and a second inductor L2. Specifically, the first terminal of the fourth capacitor C4 is electrically connected to the DC connection terminal A1, and the second terminal of the fourth capacitor C4 is electrically connected to the DC connection terminal A2; that is, the fourth capacitor C4 is connected in parallel with the DC connection terminals (A1, A2). The sixth diode D6 is connected in series with the second secondary winding and then in parallel with the eighth diode D8. Simultaneously, the seventh diode D7 is connected in series with the third secondary winding and then in parallel with the eighth diode D8. Specifically, the anode of the sixth diode D6 is electrically connected to the first terminal of the first secondary winding, and the cathode of the sixth diode D6 is electrically connected to the cathode of the eighth diode D8. The anode of the seventh diode D7 is electrically connected to the first terminal of the first secondary winding, and the cathode of the seventh diode D7 is electrically connected to the cathode of the eighth diode D8. The second terminal of the first secondary winding is electrically connected to the anode of the eighth diode D8. The first end of the second inductor L2 is connected to the cathode of the eighth diode D8, the second end of the second inductor L2 is connected to the first end of the fourth capacitor C4, and the second end of the first secondary winding is connected to the second end of the fourth capacitor C4, that is, the second inductor L2 and the fourth capacitor C4 are connected in series.

[0089] In this example, the first end of the second secondary winding, the second end of the third secondary winding, and the second end of the primary winding of the first transformer T1 are terminals with the same name. The first end of the primary winding of the first transformer T1 is electrically connected to the first output terminal of the commutation bridge 11, and the second end of the primary winding of the first transformer T1 is electrically connected to the AC connection terminal B1. The AC connection terminal B2 is also electrically connected to the commutation bridge 11. In this way, reverse power transmission can be achieved in both the positive and negative half-cycles of the AC power provided by the AC connection terminals (B1, B2).

[0090] Specifically, during forward power transmission, the inverter circuit 10 converts the DC power at the DC connection terminals (A1, A2) into AC power, which is then filtered by the primary winding of the first transformer T1 before being transmitted to the AC connection terminals (B1, B2). Based on the foregoing analysis, during this process, the primary winding of the first transformer T1 is only used for filtering, and the sixth diode D6 and the seventh diode D7 are always in the off state.

[0091] During reverse power transmission, during the positive half-cycle of the AC power supplied at the AC connection terminals (B1, B2), the commutator bridge 11 can be controlled to first charge the first transformer T1 using AC power. The second secondary winding of the first transformer T1 freewheels through the sixth diode D6. The energy of the first transformer T1 is transferred to the fourth capacitor C4 and the DC equipment at the DC connection terminals (A1, A2) through the sixth diode D6 and the first inductor L1. The seventh diode D7 is reverse cut off, and the reverse voltage it bears is the sum of the reflected voltage of the third secondary winding of the first transformer T1 and the voltage of the DC equipment at the DC connection terminals (A1, A2). Then, the AC power is controlled to stop charging the first transformer T1, the sixth diode D6 is reverse cut off, and the reverse voltage of the seventh diode D7 is the difference between the reflected voltage of the third secondary winding and the voltage of the DC equipment at the DC connection terminals (A1, A2). When the turns ratio design of the first transformer T1 satisfies that the reflected voltage of the third secondary winding is lower than the voltage of the DC equipment at the DC connection terminals (A1, A2), the seventh diode D7 will be in the reverse cut-off state.

[0092] It should be noted that the working principle of the negative half-cycle of the AC power supplied at the AC connection terminals (B1, B2) can be referred to the working principle of the positive half-cycle, which will not be elaborated here.

[0093] In the above embodiments, by setting two secondary windings in the first transformer, reverse power transmission can be achieved throughout the entire cycle of AC power, which is suitable for application scenarios with high power transmission requirements.

[0094] In some embodiments, refer to Figure 7 The branch circuit 20 also includes: a third switch Q3 and a fourth switch Q4, with the third switch Q3 connected in series with the sixth diode D6, and the fourth switch Q4 connected in series with the seventh diode D7.

[0095] Similarly, in branch circuit 20, as follows Figure 6 In the circuit shown, to keep the seventh diode D7 in the off state, the turns ratio of the first transformer T1 needs to ensure that the reflected voltage of the third secondary winding is lower than the voltage of the DC devices at the DC connection terminals (A1, A2). Therefore, a high turns ratio can lead to excessive stress on some components of the multiplexed commutator bridge 11, making the circuit design difficult. Therefore, a fourth switch Q4 can be connected in series with the seventh diode D7. By controlling the fourth switch Q4, the stress requirements on the components can be reduced, thus simplifying the circuit design.

[0096] Similarly, by controlling the third switch Q3 in series with the sixth diode D6, the stress requirements on the devices can be reduced, thus simplifying the circuit design.

[0097] In the above embodiments, by setting two secondary windings in the first transformer, reverse power transmission can be achieved throughout the AC power cycle, which is suitable for application scenarios with high power transmission requirements. At the same time, by using series switching transistors, the stress requirements on the devices can be reduced, and the circuit design difficulty can be reduced.

[0098] In some embodiments, when the AC current is in the positive half-cycle, the fourth switch Q4 is turned off; when the AC current is in the negative half-cycle, the third switch Q3 is turned off.

[0099] Specifically, based on the above analysis, it can be seen that during the positive half-cycle of the AC power supplied at the AC connection terminals (B1, B2), the seventh diode D7 is in the off state. Therefore, controlling the fourth switch Q4 to turn off can reduce the stress requirements on the devices and reduce the difficulty of circuit design. During the negative half-cycle of the AC power supplied at the AC connection terminals (B1, B2), the sixth diode D6 is in the off state. Therefore, controlling the third switch Q3 to turn off can reduce the stress requirements on the devices and reduce the difficulty of circuit design.

[0100] In one optional embodiment, there are multiple inverter circuits 10, multiple first transformers T1, and multiple branch circuits 20. The multiple inverter circuits 10, multiple first transformers T1, and multiple branch circuits 20 correspond one-to-one. Each inverter circuit 10 is electrically connected to the AC connection terminal through a corresponding commutation bridge 11 and first transformer T1. There are one or more DC connection terminals. When there is only one DC connection terminal, the DC side of each inverter circuit 10 and the DC side of each branch circuit 20 are electrically connected to the DC connection terminal. When there are multiple DC connection terminals, the DC side of each inverter circuit 10 is electrically connected to different DC connection terminals, and the DC side of each branch circuit 20 is electrically connected to at least one of the multiple DC connection terminals.

[0101] For example, refer to Figure 8a The DC connection terminals (A1, A2) include one (A1 and A2), the DC side of two inverter circuits 10 and 10', the commutation bridge 11 is electrically connected to the first transformer T1, the commutation bridge 11' is electrically connected to the first transformer T1', and the DC sides of the two branch circuits 20 and 20' are both electrically connected to the DC connection terminals (A1 and A2).

[0102] Reference Figure 8b The DC connection terminals include two (A1 and A2, A1' and A2'). The DC side of the inverter circuit 10 is electrically connected to the DC connection terminals (A1 and A2), and the DC side of the inverter circuit 10' is electrically connected to the DC connection terminals (A1' and A2'). At the same time, the commutation bridge 11 is electrically connected to the first transformer T1, the commutation bridge 11' is electrically connected to the first transformer T1', and the DC sides of the branch circuits 20 and 20' are both electrically connected to the DC connection terminals (A1 and A2).

[0103] Reference Figure 8c The DC connection terminals include two (A1 and A2, A1' and A2'). The DC side of the inverter circuit 10 is electrically connected to the DC connection terminals (A1 and A2), and the DC side of the inverter circuit 10' is electrically connected to the DC connection terminals (A1' and A2'). At the same time, the DC side of the branch circuit 20 is electrically connected to the DC connection terminals (A1 and A2), and the DC side of the branch circuit 20' is electrically connected to the DC connection terminals (A1' and A2').

[0104] It should be noted that in the above example, the voltage polarities of the secondary windings of the first transformers in multiple branch circuits can be the same or different. When they are the same, reverse power transmission can be achieved during the positive or negative half-cycle of the AC power provided at the AC connection terminal; when they are different, reverse power transmission can be achieved during the entire cycle of the AC power provided at the AC connection terminal.

[0105] Furthermore, when there are multiple first transformers T1, each first transformer T1 includes a secondary winding, and at least two of the multiple first transformers T1 have secondary windings with opposite voltage polarities.

[0106] For example, refer to Figure 9a The first terminal of the secondary winding of the first transformer T1 and the first terminal of the primary winding of the first transformer T1 are of the same name, and the second terminal of the secondary winding of the first transformer T1' and the first terminal of the primary winding of the first transformer T1' are of the same name. Therefore, the voltage polarities of the secondary windings of the first transformer T1 and the secondary windings of the first transformer T1' are opposite. If branch circuit 20 performs reverse power transmission during the positive half-cycle of the AC current supplied at the AC connection terminal, then branch circuit 20' performs reverse power transmission during the negative half-cycle of the AC current supplied at the AC connection terminal. The circuit structures of branch circuits 20 and 20' can be... Figure 2 The branch circuit 20 has the same structure as the branch circuit 20 in the diagram. Thus, power reverse transmission throughout the entire cycle can be achieved without active switching switches such as the first switch Q1 and the second switch Q2. The circuit structures of branch circuits 20 and 20' can also be... Figure 5 The branch circuit 20 in the middle has the same structure, so that power reverse transmission can be achieved throughout the whole cycle without active switching switches such as the third switch Q3 and the fourth switch Q4.

[0107] Reference Figure 9b The circuit structures of branch circuits 20 and 20' are similar to... Figure 9aThe structure is the same as shown. In this example, power reverse transfer from the AC connection terminals (B1 and B2) to the DC connection terminals (A1 and A2) can be achieved throughout the entire cycle without active switching switches (such as the first switch Q1 and the second switch Q2, or the third switch Q3 and the fourth switch Q4).

[0108] Reference Figure 9c The circuit structures of branch circuits 20 and 20' are similar to... Figure 9a The structure shown is the same. In this example, power can be transferred in reverse to the DC connection terminals (A1 and A2) in one half-cycle and in reverse to the DC connection terminals (A1' and A2') in the other half-cycle.

[0109] In some embodiments, refer to Figures 10-13 The commutation bridge 11 includes: a fifth switch Q5, a sixth switch Q6, a seventh switch Q7, and an eighth switch Q8. The first end of the fifth switch Q5 and the first end of the seventh switch Q7 are the input terminals of the commutation bridge 11, the second end of the fifth switch Q5 and the first end of the sixth switch Q6 are connected to the first end of the primary winding, the second end of the seventh switch Q7 and the first end of the eighth switch Q8 are connected to the second end of the AC connection terminal B2, and the second end of the sixth switch Q6 and the second end of the eighth switch Q8 are the third output terminals of the commutation bridge 11.

[0110] In one optional embodiment, the inverter circuit 10 further includes a voltage conversion module 12, which includes a flyback voltage conversion circuit, a forward voltage conversion circuit, a push-pull voltage conversion circuit, a bridge circuit, or a resonant circuit. That is, in this disclosure, a variety of different voltage conversion circuits can be applied.

[0111] For example, refer to Figures 10-13 The voltage conversion module 12 includes: a fifth capacitor C5, a second transformer T2, a ninth switch Q9, a ninth diode D9, and a sixth capacitor C6. The fifth capacitor C5 is connected in parallel with the DC connection terminals (A1, A2). The first terminal of the primary winding of the second transformer T2 is electrically connected to the first terminal of the fifth capacitor C5. The second terminal of the primary winding of the second transformer T2 is electrically connected to the second terminal of the fifth capacitor C5 through the ninth switch Q9. The anode of the ninth diode D9 is electrically connected to the first terminal of the secondary winding of the second transformer T2. The cathode of the ninth diode D9 is electrically connected to the first terminal of the sixth capacitor C6 and the commutation bridge 11, respectively. The second terminal of the secondary winding of the second transformer T2 is electrically connected to the other terminal of the sixth capacitor C6 and the commutation bridge 11, respectively. In this example, the first terminal of the secondary winding of the second transformer T2 and the second terminal of the primary winding of the second transformer T2 are of the same name.

[0112] For ease of explanation, the following example illustrates the connection between the DC connection terminals (A1, A2) and the photovoltaic module (PV), and the AC connection terminals (B1, B2) and the AC power grid.

[0113] Reference Figure 10 During forward power transmission (i.e., the photovoltaic module PV transmits power to the AC grid), the ninth switch Q9 is first turned on, allowing the photovoltaic module PV to charge the second transformer T2, while the ninth diode D9 is in the off state. Then, the ninth switch Q9 is turned off, and the second transformer T2 freewheels through the ninth diode D9, transferring energy from the second transformer T2 to the sixth capacitor C6, the primary winding of the first transformer T1, and the AC grid. The fifth switch Q5, the seventh switch Q7, the sixth switch Q6, and the eighth switch Q8 only serve as power frequency commutation devices.

[0114] It should be noted that during forward power transmission, the voltage difference across the primary winding of the first transformer T1 is relatively small (i.e., the ripple voltage of the sixth capacitor C6). Therefore, the first diode D1 may not conduct due to reverse cutoff (i.e., the voltage polarity of the secondary winding of the first transformer T1 is the same as the voltage polarity of the photovoltaic module PV, and the reverse voltage across the first diode D1 is the sum of the two), or it may not conduct due to insufficient conduction voltage (the voltage polarity of the secondary winding of the first transformer T1 is different from the voltage polarity of the photovoltaic module PV, but the voltage of the photovoltaic module PV is higher than the voltage of the secondary winding of the first transformer T1). Therefore, the primary winding of the first transformer T1 is only used for filtering, and the first diode D1 is always in the cutoff state.

[0115] In other words, during forward power transmission, the grid-connected output power can be controlled by adjusting the on / off time of the ninth switch Q9. The commutator bridge 11 only functions to reverse the polarity, converting the sine wave output by the voltage conversion module 12 into a sine wave for transmission to the AC grid. In this operating mode, for the first transformer T1, the voltage difference in its primary winding is relatively small. This voltage is further reduced after being referred to the secondary winding. Therefore, regardless of the polarity, this voltage difference is insufficient to turn on the first diode D1 in the secondary winding. The secondary winding of the first transformer T1 is essentially open-circuited, serving only as a filter.

[0116] During reverse power transmission (i.e., the AC grid transmits power to the photovoltaic module PV for reactive power compensation), the ninth switch Q9, the fifth switch Q5, and the seventh switch Q7 are always in the off state.

[0117] During the positive half-cycle of the AC power Vg supplied by the AC grid, the sixth switch Q6 and the eighth switch Q8 are first turned on, charging the first transformer T1. The first diode D1 is reverse-biased and its reverse voltage is the sum of the reflected voltage of the secondary winding of the first transformer T1 and the voltage of the photovoltaic module PV. Then, the sixth switch Q6 and the eighth switch Q8 are turned off, and the first transformer T1 freewheels through the first diode D1. The energy of the first transformer T1 is transferred to the first capacitor C1 and the photovoltaic module PV through the first diode D1. During the negative half-cycle of the AC power Vg supplied by the AC grid, based on the working principle, power transfer cannot occur.

[0118] In other words, during the reverse power transmission, in the positive half-cycle of the AC current, the ninth switch Q9 and the upper switch of the commutation bridge 11 are both in the off state, and the lower switch of the commutation bridge 11 is in a high-frequency on / off state. By turning on the lower switch of the commutation bridge 11, the AC grid charges the first transformer T1, and by turning off the lower switch of the commutation bridge 11, the energy stored in the first transformer T1 is transmitted to the photovoltaic module PV.

[0119] Thus, the reverse transmission of power in half a power frequency cycle of the AC power grid can be achieved through the first transformer T1, the sixth switch Q6, the eighth switch Q8, the first diode D1, and the first capacitor C1, which is suitable for application scenarios with low power requirements.

[0120] Reference Figure 11 When power is transmitted in the forward direction (i.e., the photovoltaic module (PV) transmits power to the AC grid), its working principle is the same as... Figure 10 The examples shown are the same, so they will not be repeated here.

[0121] During reverse power transmission (i.e., the AC grid transmits power to the photovoltaic module PV for reactive power compensation), the ninth switch Q9, the fifth switch Q5, and the seventh switch Q7 are always in the off state.

[0122] During the positive half-cycle of the AC power Vg supplied by the AC grid, the sixth switch Q6 and the eighth switch Q8 can be controlled to be in the conducting state first, and the AC grid charges the first transformer T1. The second diode D2 is reverse cut off, and the reverse voltage it bears is the sum of the reflected voltage of the secondary winding of the first transformer T1 and the voltage of the photovoltaic module PV. The reverse voltage of the third diode D3 is the difference between the reflected voltage of the secondary winding of the first transformer T1 and the voltage of the photovoltaic module PV. By designing the turns ratio of the first transformer T1 so that the reflected voltage of the secondary winding of the first transformer T1 is lower than the voltage of the photovoltaic module PV, the third diode D3 can be reverse cut off. Then, the sixth switch Q6 and the eighth switch Q8 are controlled to be disconnected, and the first transformer T1 freewheels through the second diode D2. The energy of the first transformer T1 is transferred to the second capacitor C2 and the photovoltaic module PV through the second diode D2. At this time, the third diode D3 is reverse cut off, and the reverse voltage it bears is twice the voltage of the photovoltaic module PV.

[0123] During the negative half-cycle of the AC power Vg supplied by the AC grid, the sixth switch Q6 and the eighth switch Q8 can be controlled to be in the conducting state first, and the AC grid charges the first transformer T1. The third diode D3 is reverse cut off, and the reverse voltage it bears is the sum of the reflected voltage of the secondary winding of the first transformer T1 and the voltage of the photovoltaic module PV. The reverse voltage of the second diode D2 is the difference between the reflected voltage of the secondary winding of the first transformer T1 and the voltage of the photovoltaic module PV. By designing the turns ratio of the first transformer T1 so that the reflected voltage of the secondary winding of the first transformer T1 is lower than the voltage of the photovoltaic module PV, the second diode D2 can be reverse cut off. Then, the sixth switch Q6 and the eighth switch Q8 are controlled to be disconnected, and the first transformer T1 freewheels through the third diode D3. The energy of the first transformer T1 is transferred to the second capacitor C2 and the photovoltaic module PV through the third diode D3. At this time, the second diode D2 is reverse cut off, and the reverse voltage it bears is twice the voltage of the photovoltaic module PV.

[0124] Thus, through the first transformer T1, the sixth switch Q6, the eighth switch Q8, the second diode D2, the third diode D3, and the second capacitor C2, reverse power transmission throughout the entire power frequency cycle of the AC power grid can be achieved, making it suitable for applications with high power requirements.

[0125] Reference Figure 12 Considering Figure 10 In the example shown, when implementing reverse power transmission throughout the entire power frequency cycle, it is necessary to ensure that the turns ratio of the first transformer T1 is such that the reflected voltage of its secondary winding is lower than the voltage of the photovoltaic module PV to prevent overcurrent, thereby causing the corresponding diode to be reverse cut off. However, in the positive half-cycle, an excessively high turns ratio will cause excessive stress on the sixth switch Q6, and in the negative half-cycle, an excessively high turns ratio will cause excessive stress on the eighth switch Q8, making the circuit difficult to design.

[0126] Based on this, the second diode D2 is connected in series with the first switch Q1 (such as an IGBT or MOSFET), and the third diode D3 is connected in series with the second switch Q2 (such as an IGBT or MOSFET). During the positive half-cycle of the AC power Vg provided by the AC grid, the second switch Q2 is turned off, and the reverse power is transmitted through the secondary winding connected in series with the second diode D2; during the positive half-cycle of the AC power Vg provided by the AC grid, the first switch Q1 is turned off, and the reverse power is transmitted through the secondary winding connected in series with the third diode D3.

[0127] Thus, through the first transformer T1, the sixth switch Q6, the eighth switch Q8, the second diode D2, the third diode D3, and the second capacitor C2, reverse power transmission throughout the entire power frequency cycle of the AC power grid can be achieved, which is suitable for application scenarios with high power requirements. At the same time, through the first switch Q1 and the second switch Q2, the stress requirements on the sixth switch Q6 and the eighth switch Q8 can be reduced.

[0128] Reference Figure 13 Using two such Figure 10 The branch circuit 20 and the two first transformers T1 shown form a power converter that can transmit power in reverse throughout the entire power frequency cycle without the need to add active switching devices, such as the first switch Q1 and the second switch Q2.

[0129] During reverse power transmission (i.e., the AC grid transmits power to the photovoltaic module PV1 for reactive power compensation), the ninth switch Q9, the fifth switch Q5, and the seventh switch Q7 are always in the off state.

[0130] During the positive half-cycle of the AC power Vg provided by the AC grid, the sixth switch Q6 and the eighth switch Q8 are switched on and off at high frequency. The reverse power is transmitted through the secondary winding connected in series with the first diode D1. At the same time, the sixth switch Q6' and the eighth switch Q8' remain in the off state, and the secondary winding connected in series with the first diode D1' does not participate in the reverse power transmission.

[0131] During the negative half-cycle of the AC power Vg provided by the AC grid, the sixth switch Q6' and the eighth switch Q8' are controlled to switch on and off at high frequency. The reverse power is transmitted through the secondary winding connected in series with the first diode D1'. At the same time, the sixth switch Q6 and the eighth switch Q8 remain in the off state, and the secondary winding connected in series with the first diode does not participate in the reverse power transmission.

[0132] It should be noted that, Figure 13In the example, photovoltaic modules PV1 and PV2 can be the same photovoltaic module or different photovoltaic modules. Branch circuits 20 and 20' can be connected to the same photovoltaic module or different photovoltaic modules. When the power converter performs reverse power transmission, the sixth switch Q6 and the eighth switch Q8 can be controlled to remain in the off state, and then the fifth switch Q5 and the seventh switch Q7 can be controlled. In this way, the fifth switch Q5, the seventh switch Q7, the primary winding of the first transformer T1, and the AC current Vg can also form an AC path.

[0133] In some embodiments, under specified operating conditions, the fifth switch Q5 and the seventh switch Q7 are respectively in the off state, and the sixth switch Q6 and the eighth switch Q8 are switched synchronously according to a first preset frequency; under normal operating conditions, the fifth switch Q5 and the eighth switch Q8 are switched on synchronously, the sixth switch Q6 and the seventh switch Q7 are switched on synchronously, and the sixth switch Q6 and the eighth switch Q8 are switched on alternately according to a second preset frequency.

[0134] Specifically, when the power converter performs reverse power transmission, the upper transistor of the commutation bridge 11 needs to remain off, that is, the fifth switch Q5 and the seventh switch Q7 remain off. The lower transistor of the commutation bridge 11 needs to switch synchronously according to the first preset frequency to couple the AC current of the primary winding of the first transformer T1 to the secondary winding of the first transformer T1, that is, the sixth switch Q6 and the eighth switch Q8 switch synchronously according to the first preset frequency. When the power converter performs forward power transmission, the commutation bridge 11 only serves the function of polarity reversal. When the fifth switch Q5 and the eighth switch Q8 are on and the sixth switch Q6 and the seventh switch Q7 are off, the AC current output by the commutation bridge 11 is the positive half-cycle. When the fifth switch Q5 and the eighth switch Q8 are off and the sixth switch Q6 and the seventh switch Q7 are on, the AC current output by the commutation bridge 11 is the negative half-cycle.

[0135] In some embodiments, the first preset frequency is greater than the second preset frequency.

[0136] Understandably, because the sixth switch Q6 and the eighth switch Q8 need to couple the electrical energy of the primary winding of the first transformer T1 to the complex winding in order to provide reactive power support to the AC connection terminals (B1, B2) or charge the DC connection terminals (A1, A2) through reverse transmission, the sixth switch Q6 and the eighth switch Q8 need to switch quickly, so the first preset frequency is faster; while under normal operating conditions, the commutator bridge 11 needs to generate AC current with the same frequency as the AC current connected to the AC connection terminals (B1, B2), so the second preset frequency is slower.

[0137] In some embodiments, the fifth switch Q5 and the seventh switch Q7 are thyristors, and the sixth switch Q6 and the eighth switch Q8 are MOSFETs or IGBTs.

[0138] Specifically, since the fifth switch Q5 and the seventh switch Q7 remain off under specified operating conditions, they can be unidirectional conducting devices. Therefore, the fifth switch Q5 and the seventh switch Q7 are thyristors, and the sixth switch Q6 and the eighth switch Q8 are MOSFETs or IGBTs, respectively. Similarly, if the sixth switch Q6 and the eighth switch Q8 remain off under specified operating conditions, while the fifth switch Q5 and the seventh switch Q7 switch synchronously, then the sixth switch Q6 and the eighth switch Q8 can be thyristors, and the fifth switch Q5 and the seventh switch Q7 can be MOSFETs or IGBTs, respectively.

[0139] In some embodiments, when the power factor of the power converter is less than 1 and greater than or equal to -1, the power converter is in a specified operating condition.

[0140] The power factor of a power converter is the ratio of active power to apparent power, reflecting the energy conversion efficiency of a power system. When the power factor is between -1 and 1 (excluding 1), the power converter exhibits reactive power, resulting in low energy utilization. Therefore, reactive power support can be provided to the AC connection terminal or the DC connection terminal can be charged through reverse transmission, thereby improving energy utilization.

[0141] It should be noted that when the energy storage device is connected to the DC connection terminal, if the power converter needs to charge the energy storage device, the power factor is -1.

[0142] In summary, the power converter according to the embodiments of this disclosure can realize the forward transmission of power from the DC connection terminal to the AC connection terminal through the inverter circuit and the primary winding of the first transformer, and realize the reverse transmission of power from the AC connection terminal to the DC connection terminal through the commutation bridge, the first transformer and the branch circuit, so as to provide reactive power support for the AC connection terminal or charge the DC connection terminal through the reverse transmission. It has multiple implementation methods and is suitable for different application scenarios and needs. Moreover, the bidirectional power transmission is achieved by reusing the commutation bridge, the circuit structure is simple, the number of components used is reduced, and the cost of the inverter can be effectively reduced.

[0143] In some embodiments, an electric power system is also provided.

[0144] Figure 14 This is a schematic diagram of the structure of a power system according to some embodiments of the present disclosure.

[0145] Reference Figure 14 The power system 200 includes the aforementioned power converter 100.

[0146] It should be noted that the power system 200 includes, but is not limited to, photovoltaic systems, energy storage systems, photovoltaic-storage-charging systems, microgrid systems, etc., but no specific restrictions are made here.

[0147] According to the power system of the present disclosure, the aforementioned power converter can not only realize the forward transmission of power from the DC connection terminal to the AC connection terminal, but also realize the reverse transmission of power from the AC connection terminal to the DC connection terminal, so as to provide reactive power support for the AC connection terminal through the reverse transmission.

[0148] It should be noted that, in the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this disclosure. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0149] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this disclosure, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0150] In this disclosure, unless otherwise expressly specified and limited, the terms "installation," "electrical connection," "connection," "fixation," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct electrical connection or an indirect electrical connection through an intermediate medium; they can refer to the internal connection of two components or the interaction between two components, unless otherwise expressly limited. Those skilled in the art can understand the specific meaning of the above terms in this disclosure according to the specific circumstances.

[0151] Although embodiments of the present disclosure have been shown and described above, it is to be understood that the above embodiments are exemplary and should not be construed as limiting the present disclosure. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present disclosure.

Claims

1. A power converter, characterized in that, include: DC connection terminal, inverter circuit, first transformer, branch circuit and AC connection terminal; The input terminal of the inverter circuit is connected to the DC connection terminal. The inverter circuit includes a commutation bridge. The first output terminal of the commutation bridge is connected to the first terminal of the primary winding of the first transformer, and the second terminal of the primary winding is connected to the first terminal of the AC connection terminal. The second output terminal of the commutation bridge is connected to the second terminal of the AC connection terminal. The secondary winding of the first transformer is connected to the input terminal of the branch circuit, and the output terminal of the branch circuit is connected to the DC connection terminal. The power converter is used to control the commutation bridge under specified operating conditions so as to transmit the AC power from the AC source connected to the AC connection terminal to the branch circuit through the first transformer. The branch circuit is used to convert the input AC power into DC power and deliver it to the DC connection terminal.

2. The power converter according to claim 1, characterized in that, The first transformer includes at least one secondary winding, wherein, in the case where the first transformer includes multiple secondary windings, at least two of the multiple secondary windings have opposite voltage polarities.

3. The power converter according to claim 2, characterized in that, When the first transformer includes a first secondary winding, the branch circuit includes: A first capacitor is connected in parallel with the DC connection terminal; The first diode has its anode connected to the first end of the first secondary winding, its cathode connected to the first end of the first capacitor, and its second end connected to the second end of the first secondary winding.

4. The power converter according to claim 2, characterized in that, In the case where the first transformer includes a second secondary winding and a third secondary winding, the branch circuit includes: The second capacitor is connected in parallel with the DC connection terminal; The second diode and the third diode are connected in the following ways: the anode of the second diode is connected to the first end of the second secondary winding, the anode of the third diode is connected to the first end of the third secondary winding, the cathodes of the second diode and the third diode are both connected to the first end of the second capacitor, and the second ends of the second secondary winding and the third secondary winding are both connected to the second end of the second capacitor.

5. The power converter according to claim 4, characterized in that, The branch circuit further includes: a first switching transistor and a second switching transistor, wherein the first switching transistor is connected in series with the second diode, and the second switching transistor is connected in series with the third diode.

6. The power converter according to claim 5, characterized in that, When the alternating current is in the positive half-cycle, the second switch is turned off; When the alternating current is in the negative half-cycle, the first switch is turned off.

7. The power converter according to claim 2, characterized in that, When the first transformer includes a first secondary winding, the branch circuit includes: The third capacitor is connected in parallel with the DC connection terminal; The fourth diode, wherein the anode of the fourth diode is connected to the first end of the first secondary winding; The fifth diode, wherein the anode of the fifth diode is connected to the second end of the first secondary winding; The first inductor has its first end connected to the cathode of the fourth diode and the cathode of the fifth diode, respectively. The second end of the first inductor is connected to the first end of the third capacitor, and the second end of the first secondary winding is connected to the second end of the third capacitor.

8. The power converter according to claim 2, characterized in that, In the case where the first transformer includes a second secondary winding and a third secondary winding, the branch circuit includes: A fourth capacitor is connected in parallel with the DC connection terminal; A sixth diode and a seventh diode, wherein the anode of the sixth diode is connected to the first end of the second secondary winding, and the anode of the seventh diode is connected to the first end of the third secondary winding; The eighth diode, wherein the anode of the eighth diode is connected to the second end of the second secondary winding and the second end of the third secondary winding, respectively; The second inductor has its first end connected to the cathodes of the sixth diode, the seventh diode, and the eighth diode, respectively. The second end of the second inductor is connected to the first end of the fourth capacitor. The second ends of the second secondary winding and the third secondary winding are respectively connected to the second end of the fourth capacitor.

9. The power converter according to claim 8, characterized in that, The branch circuit further includes a third switch and a fourth switch, wherein the third switch is connected in series with the sixth diode and the fourth switch is connected in series with the seventh diode.

10. The power converter according to claim 9, characterized in that, When the alternating current is in the positive half-cycle, the fourth switch is turned off; When the alternating current is in the negative half-cycle, the third switch is turned off.

11. The power converter according to any one of claims 1-10, characterized in that, The power converter is also used to control the commutation bridge under normal operating conditions to convert the DC power from the DC source connected to the DC connection terminal into AC power, and to transmit it to the AC connection terminal through the primary winding.

12. The power converter according to claim 11, characterized in that, The commutation bridge includes a fifth switch, a sixth switch, a seventh switch, and an eighth switch. The first ends of the fifth switch and the seventh switch are respectively the input ends of the commutation bridge. The second ends of the fifth switch and the first ends of the sixth switch are respectively connected to the first ends of the primary winding. The second ends of the seventh switch and the first ends of the eighth switch are respectively connected to the second ends of the AC connection terminal. The second ends of the sixth switch and the second ends of the eighth switch are respectively the third output ends of the commutation bridge.

13. The power converter according to claim 12, characterized in that, Under the specified operating conditions, the fifth and seventh switching transistors are respectively in the off state, and the sixth and eighth switching transistors switch synchronously according to the first preset frequency; Under normal operating conditions, the fifth and eighth switching transistors are turned on simultaneously, the sixth and seventh switching transistors are turned on simultaneously, and the sixth and eighth switching transistors are turned on alternately according to a second preset frequency.

14. The power converter according to claim 13, characterized in that, The first preset frequency is greater than the second preset frequency.

15. The power converter according to claim 12, characterized in that, The fifth and seventh switching transistors are thyristors, and the sixth and eighth switching transistors are MOSFETs or IGBTs.

16. The power converter according to claim 1, characterized in that, When the power factor of the power converter is less than 1 and greater than or equal to -1, the power converter is in the specified operating condition.

17. An electric power system, characterized in that, Includes the power converter according to any one of claims 1-16.

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