CN116914819A

CN116914819A - Power conversion device and photovoltaic energy storage system

Info

Publication number: CN116914819A
Application number: CN202310720456.4A
Authority: CN
Inventors: 向军; 张锐翔; 李罗; 陈富文; 糜晓宇
Original assignee: Huawei Digital Power Technologies Co Ltd
Current assignee: Huawei Digital Power Technologies Co Ltd
Priority date: 2023-06-16
Filing date: 2023-06-16
Publication date: 2023-10-20

Abstract

The application provides a power conversion device and a photovoltaic energy storage system. The power conversion device comprises a power conversion circuit, a balance bridge arm circuit, a positive bus and a negative bus; the balance bridge arm circuit is connected with the power conversion circuit through a positive bus and a negative bus; the balance bridge arm circuit comprises a first switch tube, a second switch tube, a first diode, a second diode, a first inductor and a second inductor, wherein the first switch tube is connected with a positive bus, the first switch tube and the second diode are connected with a first endpoint, the second diode is also connected with a negative bus, the first endpoint is connected with the first inductor, and the first inductor is also connected with the second endpoint with the power conversion circuit; the second end point is used for being connected with the midpoint of the bus; the second switch tube is connected with the negative bus, the second switch tube and the first diode are connected with the third endpoint, the first diode is also connected with the positive bus, the third endpoint is also connected with the second inductor, and the second inductor is also connected with the second endpoint. By adopting the embodiment of the application, the power loss can be reduced.

Description

Power conversion device and photovoltaic energy storage system

Technical Field

The application relates to the technical field of power electronics, in particular to a power conversion device and a photovoltaic energy storage system.

Background

With the increasing shortage of fossil energy and the increasing importance of people on environmental problems, new energy technologies represented by solar energy are rapidly developed. More and more household users and industrial and commercial users start to install the photovoltaic power generation system, and in order to improve the economy and stability of photovoltaic power generation, a matched photovoltaic energy storage system is also installed. An inverter is included in the photovoltaic energy storage system. The inverter is used for realizing the conversion of direct current and alternating current, and is widely used in the scenes of photovoltaic power generation, uninterrupted power supply, energy storage systems and the like.

In order to ensure that when an alternating current power grid connected with a load fails, the load can still work normally to improve the reliability and comfort of user electricity consumption, the photovoltaic energy storage system generally has off-grid operation capability. In off-grid operation, the inverter is required to provide more functions and higher power supply capability as a key device for converting the dc voltage and the ac voltage of the photovoltaic module and the battery. Therefore, in the existing off-grid operation scene, the working loss of the inverter is larger, namely the power loss is larger, and how to reduce the power loss of the inverter is a technical problem which needs to be solved by the technicians in the field.

Disclosure of Invention

The application provides a power conversion device and a photovoltaic energy storage system, which can reduce power loss.

In a first aspect, the present application provides a power conversion device comprising a power conversion circuit, a balancing bridge arm circuit, a positive bus, and a negative bus; the balance bridge arm circuit is connected with the power conversion circuit through the positive bus and the negative bus;

the balance bridge arm circuit comprises a first switch tube, a second switch tube, a first diode, a second diode, a first inductor and a second inductor, wherein the first end of the first switch tube is connected with the positive bus, the second end of the first switch tube and the cathode of the second diode are connected with a first endpoint, the anode of the second diode is connected with the negative bus, the first endpoint is connected with the first end of the first inductor, and the second end of the first inductor and the power conversion circuit are connected with a second endpoint; the second end point is used for being connected with the midpoint of the bus; the first end of the second switch tube is connected with the negative bus, the second end of the second switch tube and the anode of the first diode are connected with a third end point, the cathode of the first diode is connected with the positive bus, the third end point is connected with the first end of the second inductor, and the second end of the second inductor is connected with the second end point;

The power conversion circuit comprises a positive bus capacitor and a negative bus capacitor, wherein a first end of the positive bus capacitor is connected with the positive bus, a second end of the positive bus capacitor and a first end of the negative bus capacitor are connected with the second end point, and a second end of the negative bus capacitor is connected with the negative bus.

In a practical scenario of off-grid operation, the three-phase ac voltage output by the power conversion device may be provided to an ac load to supply power. While ac loads are mostly unbalanced loads, three-phase unbalance occurs during the power supply. The voltages of the positive bus capacitor and the negative bus capacitor in the power conversion device are not equal due to the three-phase imbalance. Therefore, in the scheme of the application, the first switching tube can be used for realizing excitation and follow current of the first inductor, and the second switching tube can be used for realizing excitation and follow current of the second inductor so as to balance the voltages of the positive bus capacitor and the negative bus capacitor and further balance the three-phase imbalance. During excitation of the first inductor, the second diode may be used to prevent current from the positive bus from flowing to the negative bus via the conductive first switching tube. Compared with the prior art that the current of the positive bus is prevented from flowing to the negative bus through the first switch tube which is conducted through the diode sealed in the second switch tube, the second diode can be realized as a diode with smaller reverse recovery loss such as a silicon carbide diode or a fast recovery diode, and the reverse recovery loss in the excitation process is smaller than that of the prior art sealed diode. In addition, the reverse recovery loss of the second diode is small, so that the current passing through the first switching tube is small when the first switching tube is conducted, and the turn-on loss of the first switching tube is small. So that the total loss is reduced, thereby reducing the power loss of the power conversion device. On the other hand, during excitation of the second inductor, the first diode may be used to prevent current of the positive bus from flowing to the negative bus via the conductive second switching tube. Similarly, the first diode may be implemented as a diode with smaller reverse recovery loss, such as a silicon carbide diode or a fast recovery diode, so that the reverse recovery loss in the excitation process is smaller than that of the existing diode with an inner package. In addition, since the reverse recovery loss of the first diode is small, the current passing through the second switching tube is small when the second switching tube is turned on, and thus the turn-on loss of the second switching tube is small. So that the total loss is reduced, thereby reducing the power loss of the power conversion device.

In one possible embodiment, the first switching tube, the first inductor, and the positive bus capacitor form a closed loop excited by the first inductor in response to the first switching tube being turned on; in response to the first switching tube being turned off, the first inductor, the negative bus capacitor, and the second diode form a closed loop, the second diode being configured to provide a freewheeling loop for current of the first inductor.

In the scheme, excitation and follow current of the first inductor can be realized by controlling the on-off of the first switching tube so as to balance the voltages of the positive bus capacitor and the negative bus capacitor and further balance the unbalanced three-phase condition. In the process of exciting the first inductor, compared with the prior art that the current of the positive bus is prevented from flowing to the negative bus through the conducted first switch tube by the diode sealed in the second switch tube, the current of the positive bus is prevented from flowing to the negative bus through the conducted first switch tube by the second diode. The second diode can be realized as a diode with smaller reverse recovery loss such as a silicon carbide diode or a fast recovery diode, so that the reverse recovery loss in the excitation process is smaller than that of the existing encapsulated diode. In addition, the reverse recovery loss of the second diode is small, so that the current passing through the first switching tube is small when the first switching tube is conducted, and the turn-on loss of the first switching tube is small. So that the total loss is reduced, thereby reducing the power loss of the power conversion device.

In one possible embodiment, the second switching tube, the negative bus capacitor and the second inductor form a closed loop excited by the second inductor in response to the second switching tube being turned on; the first diode is used for preventing the current of the positive bus from flowing to the negative bus through the second switch tube; and in response to the second switching tube being turned off, the second inductor, the first diode and the positive bus capacitor form a closed loop, and the first diode is used for providing a freewheeling loop for the current of the second inductor.

In the scheme, excitation and follow current of the second inductor can be realized by controlling the on-off of the second switching tube so as to balance the voltages of the positive bus capacitor and the negative bus capacitor and further balance the unbalanced three-phase condition. In the process of exciting the second inductor, compared with the existing method that the current of the positive bus is prevented from flowing to the negative bus through the conducted second switching tube by the diode sealed in the first switching tube, the method and the device prevent the current of the positive bus from flowing to the negative bus through the conducted second switching tube by the first diode. The first diode can be realized as a diode with smaller reverse recovery loss such as a silicon carbide diode or a fast recovery diode, so that the reverse recovery loss in the excitation process is smaller than that of the existing diode with the inner package. In addition, since the reverse recovery loss of the first diode is small, the current passing through the second switching tube is small when the second switching tube is turned on, and thus the turn-on loss of the second switching tube is small. So that the total loss is reduced, thereby reducing the power loss of the power conversion device.

In one possible embodiment, the power conversion device further includes a controller, where the controller is configured to turn on the first switching tube when the voltage of the positive bus capacitor is greater than the voltage of the negative bus capacitor;

the controller is further configured to turn off the first switching tube after the first switching tube is turned on for a first preset period of time.

In the scheme, the controller is used for sensing the voltage of the positive bus capacitor and the negative bus capacitor, and on-off control of the first switching tube is realized under the condition that the voltage of the positive bus capacitor is sensed to be larger than the voltage of the negative bus capacitor, so that timely voltage balance control can be realized, and the system performance is ensured.

In one possible embodiment, the power conversion device further includes a controller, and the controller is configured to turn on the second switching tube when the voltage of the negative bus capacitor is greater than the voltage of the positive bus capacitor;

the controller is further configured to turn off the second switching tube after the second switching tube is turned on for a second preset period of time.

In the scheme, the controller senses the voltage of the positive bus capacitor and the negative bus capacitor, and on-off control of the second switching tube is realized under the condition that the voltage of the negative bus capacitor is sensed to be larger than the voltage of the positive bus capacitor, so that timely voltage balance control can be realized, and the system performance is ensured.

In one possible embodiment, the first diode is a silicon carbide diode or a fast recovery diode; and/or, the second diode is a silicon carbide diode or a fast recovery diode.

In the above scheme, the first diode and/or the second diode may be a diode with smaller reverse recovery loss, such as a silicon carbide diode or a fast recovery diode, so that the reverse recovery loss in the excitation process is smaller than that of the diode sealed in the existing switching tube. In addition, the reverse recovery loss of the first diode and/or the second diode is small, so that the current passing through the switching tube when the corresponding switching tube is conducted is small, and the turn-on loss of the switching tube is small. So that the total loss is reduced, thereby reducing the power loss of the power conversion device.

In one possible embodiment, the first inductor and the second inductor are two independent inductors; alternatively, the first inductor is a first portion of a three-tap inductor, the second inductor is a second portion of the three-tap inductor, the first tap of the three-tap inductor is a first end of the first inductor, the second tap of the three-tap inductor is a first end of the second inductor, and the third tap of the three-tap inductor is a second end of the first inductor and a second end of the second inductor.

In the scheme, the first inductor and the second inductor are used in various modes, so that the specific implementation process is not limited by the specific form of the inductor device, and the application range and the application scene of the power conversion device provided by the application are enlarged.

In one possible implementation, the power conversion circuit is a two-level circuit or a three-level circuit.

In the scheme, the power conversion circuit is used and selected variously, so that the specific implementation process is not limited by the specific form of the power conversion circuit, and the application range and the application scene of the power conversion device are enlarged.

In a possible implementation manner, the power conversion device is an inverter, or an inverter circuit board, or an energy storage converter PCS, or a PCS circuit board.

In a possible embodiment, the first switching transistor and/or the second switching transistor is an insulated gate bipolar transistor IGBT or a metal-oxide semiconductor field effect transistor MOSFET.

In a possible embodiment, the second end point and the bus midpoint are configured to be connected to a neutral output of the power converter in an off-grid operation of the power converter.

In summary, in the actual scenario of off-grid operation, the three-phase ac voltage output by the power conversion device may be provided to the ac load to supply power. While ac loads are mostly unbalanced loads, three-phase unbalance occurs during the power supply. The voltages of the positive bus capacitor and the negative bus capacitor in the power conversion device are not equal due to the three-phase imbalance. Therefore, in the scheme of the application, on one hand, excitation and follow current of the first inductor can be realized by controlling the on-off of the first switching tube so as to balance the voltages of the positive bus capacitor and the negative bus capacitor and further balance the unbalanced three-phase condition. In the process of exciting the first inductor, compared with the prior art that the current of the positive bus is prevented from flowing to the negative bus through the conducted first switch tube by the diode sealed in the second switch tube, the current of the positive bus is prevented from flowing to the negative bus through the conducted first switch tube by the second diode. Because the second diode is a diode with smaller reverse recovery loss such as a silicon carbide diode or a fast recovery diode, the reverse recovery loss in the excitation process is smaller than that of the existing diode with the inner seal. In addition, the reverse recovery loss of the second diode is small, so that the current passing through the first switching tube is small when the first switching tube is conducted, and the turn-on loss of the first switching tube is small. So that the total loss is reduced, thereby reducing the power loss of the power conversion device.

On the other hand, excitation and follow current of the second inductor can be realized by controlling on-off of the second switching tube so as to balance the voltages of the positive bus capacitor and the negative bus capacitor and further balance the unbalanced three-phase condition. In the process of exciting the second inductor, compared with the existing method that the current of the positive bus is prevented from flowing to the negative bus through the conducted second switching tube by the diode sealed in the first switching tube, the method and the device prevent the current of the positive bus from flowing to the negative bus through the conducted second switching tube by the first diode. Because the first diode is a diode with smaller reverse recovery loss such as a silicon carbide diode or a fast recovery diode, the reverse recovery loss in the excitation process is smaller than that of the existing diode with the inner seal. In addition, since the reverse recovery loss of the first diode is small, the current passing through the second switching tube is small when the second switching tube is turned on, and thus the turn-on loss of the second switching tube is small. So that the total loss is reduced, thereby reducing the power loss of the power conversion device.

In a second aspect, the present application provides a photovoltaic energy storage system comprising a power conversion device as described in any one of the first aspects above.

In a third aspect, the present application provides a power conversion device comprising a power conversion circuit, a balancing bridge arm circuit, a positive bus, and a negative bus; the balance bridge arm circuit is connected with the power conversion circuit through a positive bus and a negative bus;

the balance bridge arm circuit comprises a switching tube, a diode and an inductor, wherein the first end of the switching tube is connected with a positive bus, the second end of the switching tube is connected with a first end point, the first end point is connected with the first end point of the inductor, and the second end of the first inductor and the power conversion circuit are connected with a second end point; the second end point is used for being connected with the midpoint of the bus; the anode of the diode is connected with the negative bus, and the cathode of the diode is connected with the first endpoint;

the power conversion circuit comprises a positive bus capacitor and a negative bus capacitor, wherein a first end of the positive bus capacitor is connected with a positive bus, a second end of the positive bus capacitor and a first end of the negative bus capacitor are connected to a second endpoint, and a second end of the negative bus capacitor is connected with a negative bus.

In the scheme, the switching tube can be used for realizing excitation and follow current of the inductor so as to balance the voltages of the positive bus capacitor and the negative bus capacitor and further balance the unbalanced three-phase condition. During excitation of the inductor, the diode may be used to prevent current from the positive bus from flowing to the negative bus via the conductive switching tube. Compared with the prior art that the current of the positive bus is prevented from flowing to the negative bus through the on-state switching tube by the diode sealed in the switching tube, in the scheme, the diode can be realized as a diode with smaller reverse recovery loss such as a silicon carbide diode or a fast recovery diode, and the reverse recovery loss in the excitation process is smaller than that of the prior art sealed diode. In addition, the reverse recovery loss of the diode is small, so that the current passing through the switching tube is small when the switching tube is conducted, and the turn-on loss of the switching tube is small. So that the total loss is reduced, thereby reducing the power loss of the power conversion device.

In a fourth aspect, the present application provides a power conversion device, the power conversion device comprising a power conversion circuit, a balancing bridge arm circuit, a positive bus, and a negative bus; the balance bridge arm circuit is connected with the power conversion circuit through a positive bus and a negative bus;

the balance bridge arm circuit comprises a switching tube, a diode and an inductor, wherein the first end of the switching tube is connected with a negative bus, the second end of the switching tube and the anode of the diode are connected with a first end point, the cathode of the diode is connected with a positive bus, the first end point is connected with the first end of the inductor, and the second end of the inductor is connected with a second end point; the second end point is used for being connected with the midpoint of the bus;

Drawings

Fig. 1 and fig. 2 are schematic structural diagrams of a photovoltaic energy storage system according to an embodiment of the present application;

fig. 3 is a schematic diagram of an inverter circuit;

fig. 4 to 19 are schematic structural diagrams of a power conversion device according to an embodiment of the application.

Detailed Description

In the embodiments of the present application, "a plurality" means two or more. In the embodiment of the present application, "and/or" is used to describe the association relationship of the association object, and represents three relationships that may exist independently, for example, a and/or B may represent: a alone, B alone, or both a and B. Description modes such as "at least one (or at least one) of a1, a2, … … and an" adopted in the embodiment of the present application include a case where any one of a1, a2, … … and an exists alone, and also include a case where any combination of any plurality of a1, a2, … … and an exists alone; for example, the description of "at least one of a, b, and c" includes the case of a alone, b alone, a and b in combination, a and c in combination, b and c in combination, or a, b, and c in combination. In the embodiment of the application, the connection C and the connection D represent the circuit connection between the C and the D, which indicates that the electric signal transmission between the C and the D can be realized.

In various embodiments of the application, where terminology and/or descriptions of the various embodiments are consistent and may be referred to each other, unless specifically indicated as such and where logical conflict, features of different embodiments may be combined to form new embodiments in accordance with their inherent logical relationships.

In order to facilitate understanding of the embodiments of the present application, the following first describes techniques and terms related to the embodiments of the present application.

1. Switching on loss: the semiconductor switching device is powered by power loss from off (or off) to on.

2. Turn-off loss: the semiconductor switching device is powered by power loss from on to off.

3. On-state loss: power loss generated when the semiconductor switching device is turned on.

4. Diode conduction loss: the diode is turned on in the forward direction.

5. Diode reverse recovery loss: the power loss generated during the reverse recovery of the diode.

6. Grid connection: and (3) connecting with the power grid, namely accessing the power grid for power exchange.

7. Off-grid: and a state that the system is disconnected from the power grid and independently supplies power to the load.

8. Combining point: for a distributed power supply with a booster station, the grid connection point is a high-voltage side bus or node of the distributed power supply booster station. For a distributed power supply without a booster station, the grid connection point is a summary point of the output of the distributed power supply to a power grid. The grid connection point is the connection point of the power supply to the power grid.

9. Unbalanced load: refers to an ac load in which a three-phase imbalance occurs during the process of supplying power to the load. In particular, the alternating current load is supplied with power by three-phase alternating current. When the currents of the three phases are not identical, namely, the currents of the A phase, the B phase and the C phase are not equal, the three phases are unbalanced. The three-phase imbalance causes the current on the neutral or neutral (simply referred to as the N-line) to be non-zero.

Embodiments of the present application are described below by way of example with reference to the accompanying drawings.

Referring illustratively to fig. 1, a schematic structural diagram of a photovoltaic energy storage system is shown. The photovoltaic energy storage system 100 includes a power conversion device 120. The photovoltaic module 110 is connected to the power conversion device 120. The photovoltaic module 110 is used to convert solar energy into electrical energy. The power conversion device 120 is configured to convert the electric energy into power and output the power to the grid 200 or output the power to the ac load 300 for supplying power. The power conversion device 120 outputs electric energy to the power grid 200, i.e. grid-connected operation. The power conversion device 120 outputs electric energy to the ac load 300 only, i.e. off-grid operation.

The photovoltaic module 110 may be, for example, a solar photovoltaic panel, or may be a string type photovoltaic module composed of a solar photovoltaic panel and an optimizer, or may be a photovoltaic module composed of a solar photovoltaic panel and a module controller, or the like. The embodiment of the present application does not limit the specific composition structure of the photovoltaic module 110.

The power conversion device 120 may be an inverter or an energy storage converter (power conversion system, PCS), for example. Optionally, the power conversion device 120 may further include a circuit unit such as a DC/DC converter.

It will be appreciated that in one possible implementation, the photovoltaic energy storage system 100 described above is not limited to including the power conversion device 120. For example, see fig. 2.

As shown in fig. 2 (a), the photovoltaic energy storage system 100 may also include an off-grid controller 130 and an energy storage device 140. Illustratively, the on-grid and off-grid controller 130 is configured to implement selective control of on-grid operation and off-grid operation. Illustratively, the off-grid controller 130 may be implemented separately as an off-grid control box. Alternatively, the off-grid controller 130 may be packaged in a cabinet or box with the power conversion device 120, as described above, for example, and embodiments of the application are not limited in this regard. The energy storage device 140 may be used to store electrical energy. For example, after the photovoltaic module 110 converts solar energy into electrical energy, the power conversion device 120 may perform power conversion on the electrical energy and store the electrical energy in the energy storage device 140.

For example, in fig. 2 (a), after the dc power output by the energy storage device 140 and/or the photovoltaic module 110 is converted into ac power by the power conversion device 120, if the off-grid controller 130 controls to connect to the power grid 200, the ac power is output to the power grid 200. Alternatively, if the off-grid controller 130 controls the off-grid operation, i.e., disconnects from the grid 200, the ac power may be output to the ac load 300 to power the ac load.

As shown in fig. 2 (b), the photovoltaic energy storage system 100 may further include a low voltage power distribution cabinet 170, an energy storage device 140, an energy storage converter 150, and a transformer 160. In the photovoltaic energy storage system 100, the power conversion device 120 performs power conversion on the electric energy, and then distributes the electric energy through the low-voltage power distribution cabinet 170, and outputs the electric energy to the power grid 200 or the ac load 300 for supplying power. This output powers the ac load 300, i.e., off-grid operation is achieved to power the ac load 300.

In addition, the energy storage device 140 may be used to store electrical energy. For example, after the photovoltaic module 110 converts solar energy into electric energy, the power conversion device 120 may convert the electric energy into power, and then process the power through the transformer 160 and the energy storage converter 150 to store the power into the energy storage device 140. The specific processing of the transformer 160 and the energy storage converter 150 is not limited by the embodiment of the present application. For example, the electrical energy stored in the energy storage device 140 may also be supplied to the power grid 200 and/or the ac load 300. For example, the electric energy stored in the energy storage device 140 is inverted into ac power by the energy storage converter 150, processed by the transformer 160, distributed by the low-voltage power distribution cabinet 170, and then output to the power grid 200 or the ac load 300 for supplying power. It is to be understood that the description herein is intended as an example, and is not to be taken as limiting the embodiments of the application.

Illustratively, the energy storage device 140 may be a battery cluster or may be an energy storage cabinet including a battery cluster, or the like. One or more batteries may be included in a battery cluster, either in series or in parallel. The battery may include, for example, a lithium ion battery (e.g., a lithium iron phosphate battery or a ternary lithium battery), a lead acid battery (or lead acid battery), or a sodium battery, etc., and the specific type of battery is not particularly limited by the present application.

It will be appreciated that the system architecture shown in fig. 1 and 2 above is merely an example, and that the system architecture may include more or fewer devices or units in a specific implementation, and embodiments of the present application are not limited in this respect.

Illustratively, in the actual scenario of off-grid operation, the ac load 300 is mostly an unbalanced load, i.e., a three-phase imbalance occurs during the process of supplying the ac load 300, resulting in a non-zero current on the neutral line. The unbalance of the three phases can cause the adverse effects of overlarge voltage variation range, insufficient power supply, excessive loss and the like, and the danger of shortening the service life and even burning out can also occur to loads. Therefore, in order to balance this three-phase imbalance, the power conversion device 120 needs to provide a neutral point for the ac load 300 that can be refluxed. Accordingly, the inverter circuit for implementing the inverter function in the power conversion device 120 may be a three-phase four-leg inverter circuit, and the neutral point for providing the reflux to the ac load 300 may be a midpoint of the fourth leg. For ease of understanding, one possible three-phase four-leg inverter circuit schematic is shown, with exemplary reference to fig. 3.

In the three-phase four-leg inverter circuit shown in fig. 3, A, B, C and N represent output terminals of a-phase, B-phase, C-phase, and N-line currents, respectively. The main body inverter circuit portion of the circuit includes three legs, such as typical T-shaped three-level legs (as shown in fig. 3). And the fourth bridge arm is a two-level balanced bridge arm, and the N line of the user load can flow back to the middle point (as the point D in the figure 3) of the fourth bridge arm, so that the condition of unbalanced load work of the user is met. And a filter inductor can be added between the middle point of the fourth bridge arm and the N line, so that the harmonic wave is reduced, and the inductance volume of three phases of the output end A, B, C of the inverter circuit is reduced.

The fourth bridge arm comprises two switching tubes, and when the three-phase unbalance occurs, the zero sequence control of load voltage and/or current is realized by controlling the on-off of the two switching tubes so as to inhibit the three-phase unbalance state. And the power loss of the two switching tubes is larger when the two switching tubes work, so that the power loss of the whole inverter circuit is increased. In order to reduce power loss of an inverter circuit, the embodiment of the application provides a power conversion device.

Referring to fig. 4, a schematic diagram of a power conversion apparatus 400 according to an embodiment of the present application is shown. As shown in fig. 4, the power conversion device includes a power conversion circuit 401, a balance arm circuit 402, a positive Bus (bus+) and a negative Bus (Bus-). The balanced bridge arm circuit 402 is connected to the power conversion circuit 401 through the positive bus and the negative bus.

The balanced bridge arm circuit 402 includes a first switching tube Q1, a second switching tube Q2, a first diode D1, a second diode D2, a first inductance Lp1, and a second inductance Lp2. The first end of the first switching tube Q1 is connected to the positive bus, and the second end of the first switching tube Q1 and the cathode of the second diode D2 are connected to the first terminal T1. The anode of the second diode D2 is connected to the negative bus bar. The first terminal T1 is connected to a first terminal of the first inductor Lp1, and a second terminal of the first inductor Lp1 and the power conversion circuit 401 are connected to a second terminal T2. The second terminal T2 is adapted to be connected to the busbar midpoint Tc. The first end of the second switching tube Q2 is connected with the negative bus. The second end of the second switch tube Q2 and the anode of the first diode D1 are connected to the third terminal T3, and the cathode of the first diode D1 is connected to the positive bus. The third terminal T3 is connected to the first terminal of the second inductor Lp2, and the second terminal of the second inductor Lp2 is connected to the second terminal T2.

The power conversion circuit 401 includes a positive bus capacitance Cp, a negative bus capacitance Cn, and a main body power conversion module 4011. The first end of the positive bus capacitor Cp is connected to the positive bus. The second end of the positive bus capacitor Cp and the first end of the negative bus capacitor Cn are connected to a bus midpoint Tc, which is connected to the second end T2. The second end of the negative bus capacitor Cn is connected to the negative bus. The main body power conversion module 4011 is connected to a positive bus and a negative bus.

The power conversion device 400 further includes a three-phase voltage output terminal and a neutral line output terminal. As shown in fig. 4, a_out represents an a-phase output terminal, b_out represents a B-phase output terminal, c_out represents a C-phase output terminal, and n_out represents a neutral line output terminal. The three-phase voltage output terminal and the neutral line output terminal are connected to the main body power conversion module 4011. The main power conversion module 4011 is a main circuit for implementing an inversion function, and the main circuit may include a three-leg inverter circuit, and the description will be omitted herein.

In the power conversion device 400, in order to equalize the three-phase imbalance, the neutral line output terminal n_out is also connected to the second terminal T2 and the bus bar midpoint Tc, as shown in fig. 4. If the three-phase imbalance causes the voltages of the positive bus capacitor Cp and the negative bus capacitor Cn to be unequal, the voltages of the two capacitors can be balanced by controlling the on/off of the first switching tube Q1 and the second switching tube Q2 in the balanced bridge arm circuit 402. Specific equalization implementations are described in detail below and are not described in detail herein.

The first switching transistor Q1 and/or the second switching transistor Q2 may be, for example, a silicon carbide Diode (SIC Diode), or a Diode with a small reverse recovery loss such as a fast recovery Diode (Fast Recovery Diode, FRD).

The first and/or second switching transistors Q1 and Q2 may be, for example, insulated gate bipolar transistors (Insulated Gate Bipolar Transistor, IGBTs), or may be, for example, metal-Oxide-semiconductor field effect transistors (MOSFETs), or may be other types of transistors, as the embodiments of the present application are not limited in this respect.

The first inductance Lp1 and the second inductance Lp2 shown in fig. 4 are independent two inductances. In another possible implementation, the first inductor Lp1 may be part of a three-tap inductor, and the second inductor Lp2 may be another part of the three-tap inductor, as illustrated in fig. 5. In fig. 5, the inductance L is the three-tap inductance. The first tap of the three-tap inductor is the first end of the first inductor Lp 1. I.e. the first tap is connected to the first terminal T1. The second tap of the three-tap inductor is the first end of the second inductor Lp 2. I.e. the second tap is connected to the third terminal T3. The third tap of the three-tap inductor is the second end of the first inductor Lp1 and the second end of the second inductor Lp 2. I.e. the third tap is connected to the second terminal T2. The third tap of the three-tap inductor may be disposed at an intermediate point between the first tap and the second tap, or may be disposed at any position between the first tap and the second tap, specifically, may be disposed according to practical applications, and the embodiment of the present application is not limited thereto.

Illustratively, the power conversion apparatus 400 may further include a controller, which may be used to control the on-off of the first switching tube Q1 and the second switching tube Q2. Alternatively, the controller may be independent of the power conversion device 400, and then the controller may be connected to the power conversion device 400 to perform on-off control of a switching tube in the power conversion device 400. It is to be understood that the description herein is intended as an example, and is not to be taken as limiting the embodiments of the application.

Illustratively, the power conversion apparatus 400 may further include a detection module for detecting whether the three-phase imbalance occurs. The specific detection method can refer to any method capable of realizing three-phase unbalance detection, and the embodiment of the application is not limited to the method. Alternatively, the detection module may be independent of the power conversion device 400, and then the detection module feeds back the detection result to the power conversion device 400 by being connected to the power conversion device 400, for example. Alternatively, the detection module may be independent of the power conversion device 400, and then, the detection module feeds back the detection result to the controller by being connected to the controller, so that the controller realizes on-off control of the switching tube in the power conversion device 400 based on the detection result. It is to be understood that the description herein is intended as an example, and is not to be taken as limiting the embodiments of the application.

Based on the above description, the three-phase imbalance may cause the voltages of the positive bus capacitor Cp and the negative bus capacitor Cn to be unequal. In one possible embodiment, if the three phases are unbalanced, the voltage of the positive bus capacitor Cp is greater than the voltage of the negative bus capacitor Cn. Then, the positive bus capacitor Cp can be charged to the negative bus capacitor Cn by controlling the on-off of the first switching tube Q1 to equalize the voltages of the two capacitors, thereby equalizing the three-phase imbalance.

In a specific implementation, the charging of the positive bus capacitor Cp to the negative bus capacitor Cn may be achieved by exciting and freewheeling the above-mentioned first inductance Lp 1. First, an implementation procedure for exciting the first inductance Lp1 will be described, and an exemplary description will be made below with reference to fig. 6 or fig. 7.

As shown in fig. 6 or 7, in the case where the voltage of the positive bus capacitor Cp is greater than the voltage of the negative bus capacitor Cn, the first switching tube Q1 may be controlled to be turned on. The first switching tube Q1, the first inductance Lp1, and the positive bus capacitor Cp are formed as a closed loop in which the first inductance Lp1 is excited (see an inductance excitation loop shown in fig. 6 or 7). At this time, the positive bus capacitor Cp is in a discharge state, and the first inductance Lp1 is in an excited state. The excitation state of the first inductor Lp1 is that the first inductor Lp1 stores energy. The discharging current of the positive bus capacitor Cp flows from the first end of the positive bus capacitor Cp through the positive bus, the first switching tube Q1 and the first inductor Lp1 back to the second end of the positive bus capacitor Cp. In addition, during the excitation of the first inductor Lp1, the second diode D2 is used to prevent the current of the positive bus from flowing to the negative bus through the first switching tube Q1.

Based on the above description, the power loss generated in the process of exciting the first inductance Lp1 is: p1=eonq1+eco_q1+err_d2. Wherein eon_q1 represents the on-loss of the first switching transistor Q1, econ_q1 represents the on-loss of the first switching transistor Q1, err_d2 represents the reverse recovery loss of the second diode D2.

The following describes an implementation procedure for freewheeling the first inductor Lp1, which is exemplarily described with reference to fig. 8 or 9.

As shown in fig. 8 or 9, after exciting the first inductor Lp1 for the first preset period of time, the first switching tube Q1 is turned off. The first preset duration may be, for example, a duration corresponding to a preset duty cycle of a circuit duty cycle in the power conversion apparatus 400, or may be a preset duration, etc. Illustratively, the preset duty cycle may be, for example, 50%, 40%, 30%, or the like, which is not limited by the embodiment of the present application. After the first switching transistor Q1 is turned off, the first inductor Lp1 starts to charge the negative bus capacitor Cn. The first inductance Lp1, the negative bus capacitor Cn, and the second diode D2 form a closed loop (see the inductive freewheel loop shown in fig. 8 or 9). I.e. the second diode D2 is used to provide a freewheeling circuit for the current of the first inductor Lp 1. At this time, the first inductance Lp1 is in a discharge freewheel state, and the negative bus capacitor Cn is in a charge state. The charging current of the negative bus capacitor Cn flows from the second end of the first inductor Lp1 through the negative bus capacitor Cn, the negative bus and the second diode D2 back to the first end of the first inductor Lp 1.

Based on the above description, the power loss generated in the process of freewheeling the first inductor Lp1 is: p2=eoff_q1+eco n_d2. Wherein eoff_q1 represents the turn-off loss of the first switching transistor Q1, and econ_d2 represents the forward turn-on loss of the second diode D2.

Based on the above description, the total loss p=p1+p2 throughout the process of charging the positive bus capacitance Cp to the negative bus capacitance Cn. I.e., p=eonq1+econq1+err_d2+eoff_q1+econ_d2. In the process of exciting the first inductor Lp1, compared with the existing method of preventing the current of the positive bus from flowing to the negative bus through the first switch tube Q1 by the diode sealed in the second switch tube Q2, in the embodiment of the application, because the second diode D2 is a diode with smaller reverse recovery loss such as a silicon carbide diode or a fast recovery diode, the reverse recovery loss of the err_d2 is smaller than that of the existing diode sealed in the prior art. In addition, since the reverse recovery loss of the second diode D2 is small, the current passing through the first switching tube Q1 is small when the first switching tube Q1 is turned on, and thus the turn-on loss eon_q1 of the first switching tube Q1 becomes small. It can be seen that err_d2 and eon_q1 reduce the above P1, i.e., the total loss P, thereby reducing the power loss of the above power conversion device 400.

In another possible embodiment, if the three phases are unbalanced, the voltage of the negative bus capacitor Cn is greater than the voltage of the positive bus capacitor Cp. Then, the negative bus capacitor Cn may be charged to the positive bus capacitor Cp by controlling the on-off of the second switching tube Q2 to equalize the voltages of the two capacitors, thereby equalizing the three-phase imbalance.

In a specific implementation, the charging of the positive bus capacitor Cp by the negative bus capacitor Cn may be achieved by exciting and freewheeling the above-mentioned second inductance Lp 2. First, a process for realizing the excitation of the second inductance Lp2 will be described, and an exemplary description will be given below with reference to fig. 10 or 11.

As shown in fig. 10 or 11, in the case where the voltage of the negative bus capacitor Cn is greater than the voltage of the positive bus capacitor Cp, the second switching tube Q2 may be controlled to be turned on. The second switching tube Q2, the negative bus bar capacitance Cn, and the second inductance Lp2 are formed as a closed loop in which the second inductance Lp2 is excited (see an inductance excitation loop shown in fig. 10 or 11). At this time, the negative bus capacitor Cn is in a discharge state, and the second inductor Lp2 is in an excited state. The excitation state of the second inductor Lp2 is the energy storage of the second inductor Lp 2. The discharge current of the negative bus capacitor Cn flows from the first end of the negative bus capacitor Cn through the bus midpoint Tc, the second inductance Lp2, the second switching tube Q2 and the negative bus back to the second end of the negative bus capacitor Cn. In addition, during the excitation of the second inductor Lp2, the first diode D1 is used to prevent the current of the positive bus from flowing to the negative bus through the second switching tube Q2.

Based on the above description, the power loss generated in the process of exciting the second inductance Lp2 is: p3=eon_q2+eco_q2+err_d1. Wherein eon_q2 represents the on-loss of the second switching transistor Q2, econ_q2 represents the on-loss of the second switching transistor Q2, err_d1 represents the reverse recovery loss of the first diode D1.

The following describes an implementation procedure for freewheeling the second inductor Lp2, which is exemplarily described with reference to fig. 12 or fig. 13.

As shown in fig. 12 or fig. 13, after the second inductor Lp2 is excited for the second preset period of time, the second switching tube Q2 is turned off. The second preset duration may be, for example, a duration corresponding to a preset duty cycle of a circuit duty cycle in the power conversion apparatus 400, or may be a preset duration, etc. Illustratively, the preset duty cycle may be, for example, 50%, 40%, 30%, or the like, which is not limited by the embodiment of the present application. After the second switching transistor Q2 is turned off, the second inductor Lp2 starts to charge the positive bus capacitor Cp. The second inductance Lp2, the first diode D1, and the positive bus capacitor Cp form a closed loop (see the inductive freewheel loop shown in fig. 12 or fig. 13). I.e. the first diode D1 is used to provide a freewheeling circuit for the current of the second inductance Lp 2. At this time, the second inductance Lp2 is in a discharge freewheel state, and the positive bus capacitor Cp is in a charge state. The charging current of the positive bus capacitor Cp flows from the first end of the second inductor Lp2 through the first diode D1, the positive bus and the positive bus capacitor Cp, and then returns to the second end of the second inductor Lp2 through the bus midpoint Tc and the second end T2.

Based on the above description, the power loss generated in the process of freewheeling the second inductor Lp2 is: p4=eoff_q2+eco n_d1. Wherein eoff_q2 represents the turn-off loss of the second switching transistor Q2, and econ_d1 represents the forward turn-on loss of the first diode D1.

Based on the above description, the total loss P' =p3+p4 throughout the process of charging the negative bus capacitor Cn with the negative bus capacitor Cn. I.e., P' =eonq2+econq2+err_d1+eoff_q2+econ_d1. In the process of exciting the second inductor Lp2, compared with the existing method of preventing the current of the positive bus from flowing to the negative bus through the second switch tube Q2 by the diode sealed in the first switch tube Q1, in the embodiment of the application, since the first diode D1 is a diode with smaller reverse recovery loss such as a silicon carbide diode or a fast recovery diode, the reverse recovery loss of the err_d1 is smaller than that of the existing diode sealed in the prior art. In addition, since the reverse recovery loss of the first diode D1 is small, the current passing through the second switching tube Q2 is small when the second switching tube Q2 is turned on, and thus the turn-on loss eon_q2 of the second switching tube Q2 becomes small. It can be seen that err_d1 and eon_q2 reduce the above P3, i.e., the total loss P' is reduced, thereby reducing the power loss of the above power conversion device 400.

In one possible implementation, the power conversion circuit 401 shown in fig. 4 to 12 may be a two-level circuit or a three-level circuit. For example, if the main power conversion module 4011 is a two-level inverter circuit (for example, see fig. 14 for an example), the voltage output by the main power conversion module 4011 has only two levels. Then, the three-phase voltage output from the power conversion circuit 401 is also only two levels, and the power conversion circuit 401 is a two-level circuit.

Alternatively, for example, if the main power conversion module 4011 is a three-level inverter circuit (for example, see fig. 15 for an example), that is, the voltage output by the main power conversion module 4011 has only three levels. Then, the three-phase voltage outputted from the power conversion circuit 401 is also only three levels, and the power conversion circuit 401 is a three-level circuit.

It should be understood that the two-level inverter circuit shown in fig. 14 is merely an example, and is not limited to the embodiment of the present application. In a specific implementation, the main power conversion module 4011 may be a two-level inverter circuit with other topologies, which is not limited by the embodiment of the present application. Similarly, the three-level inverter circuit shown in fig. 15 is merely an example, and is not limited to the embodiment of the present application. In a specific implementation, the main power conversion module 4011 may be a three-level inverter circuit with other topologies, which is not limited by the embodiment of the present application.

In addition, in a specific implementation, the power conversion circuit 401 may also be a circuit with more level outputs, such as a four-level output or a five-level output, which is not limited by the embodiment of the present application.

The power conversion apparatus 400 provided in the foregoing embodiment of the present application may be implemented as an inverter, or may be implemented as an inverter circuit board, or may be implemented as an energy storage converter, or may be implemented as an apparatus or device such as an energy storage converter circuit board. The embodiment of the present application does not limit the specific form of the apparatus or device that the power conversion apparatus 400 may be used to implement.

In addition, the power conversion device 400 provided by the embodiment of the application can be applied to a photovoltaic energy storage system. For example, the power conversion device 400 may be the power conversion device 120 shown in fig. 1 or fig. 2.

In another possible implementation, the power conversion apparatus 400 may be implemented as the structure shown in fig. 16 and 17, for example. That is, the circuit structure mainly considers the control of voltage balance in the case that the voltage of the positive bus capacitor is larger than that of the negative bus capacitor. Specific description of excitation and freewheeling of the first inductor Lp1 may refer to the foregoing related descriptions of fig. 6 and fig. 8, which are not repeated herein.

In another possible implementation, the power conversion apparatus 400 may be implemented as the structure shown in fig. 18 and 19, for example. That is, the circuit structure mainly considers the control of voltage balance in the case that the voltage of the negative bus capacitor is larger than that of the positive bus capacitor. Specific description of excitation and freewheeling of the second inductor Lp2 may refer to the foregoing description related to fig. 10 and fig. 12, which is not repeated herein.

In summary, the power conversion device 400 provided by the embodiment of the present application can reduce the power loss of the whole circuit by reducing the reverse recovery loss of the diode and the turn-on loss of the switching tube in the process of balancing the three-phase output in the off-grid operation scene, thereby realizing the energy-saving operation of the circuit.

The terms "first," "second," and the like in this disclosure are used for distinguishing between similar elements or items having substantially the same function and function, and it should be understood that there is no logical or chronological dependency between the terms "first," "second," and "n," and that there is no limitation on the amount and order of execution. It will be further understood that, although the following description uses the terms first, second, etc. to describe various elements, these elements should not be limited by the terms. These terms are only used to distinguish one element from another element.

It should also be understood that, in the embodiments of the present application, the sequence number of each process does not mean that the execution sequence of each process should be determined by the function and the internal logic, and should not limit the implementation process of the embodiments of the present application.

It will be further understood that the terms "comprises" and/or "comprising," when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.

It should be further appreciated that reference throughout this specification to "one embodiment," "an embodiment," "one possible implementation" means that a particular feature, structure, or characteristic described in connection with the embodiment or implementation is included in at least one embodiment of the present application. Thus, the appearances of the phrases "in one embodiment" or "in an embodiment," "one possible implementation" in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

Finally, it should be noted that: the above embodiments are only for illustrating the technical solution of the present application, and not for limiting the same; although the application has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some or all of the technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit of the application.

Claims

1. The power conversion device is characterized by comprising a power conversion circuit, a balance bridge arm circuit, a positive bus and a negative bus; the balance bridge arm circuit is connected with the power conversion circuit through the positive bus and the negative bus;

the balance bridge arm circuit comprises a first switch tube, a second switch tube, a first diode, a second diode, a first inductor and a second inductor, wherein the first end of the first switch tube is connected with the positive bus, the second end of the first switch tube and the cathode of the second diode are connected with a first end point, the anode of the second diode is connected with the negative bus, the first end point is connected with the first end of the first inductor, and the second end of the first inductor and the power conversion circuit are connected with a second end point; the second end point is used for being connected with the midpoint of the bus; the first end of the second switching tube is connected with the negative bus, the second end of the second switching tube and the anode of the first diode are connected with a third end point, the cathode of the first diode is connected with the positive bus, the third end point is connected with the first end of the second inductor, and the second end of the second inductor is connected with the second end point;

2. The power conversion device according to claim 1, wherein the first switching tube, the first inductor, and the positive bus capacitor form a closed loop excited by the first inductor in response to the first switching tube being turned on; in response to the first switching tube being turned off, the first inductor, the negative bus capacitor and the second diode form a closed loop, and the second diode is used for providing a freewheeling loop for the current of the first inductor.

3. The power conversion device according to claim 1 or 2, characterized in that in response to the second switching tube being turned on, the second switching tube, the negative bus capacitor and the second inductor form a closed loop excited by the second inductor; in response to the second switching tube being turned off, the second inductor, the first diode and the positive bus capacitor form a closed loop, and the first diode is used for providing a freewheeling loop for the current of the second inductor.

4. A power conversion device according to any one of claims 1-3, further comprising a controller for turning on the first switching tube in case the voltage of the positive bus capacitor is greater than the voltage of the negative bus capacitor;

the controller is also used for turning off the first switching tube after the first switching tube is turned on for a first preset time period.

5. A power conversion device according to any one of claims 1-3, further comprising a controller for turning on the second switching tube in case the voltage of the negative bus capacitor is greater than the voltage of the positive bus capacitor;

the controller is also used for turning off the second switching tube after the second switching tube is turned on for a second preset time period.

6. The power conversion device according to any one of claims 1 to 5, wherein the first diode is a silicon carbide diode or a fast recovery diode; and/or the second diode is a silicon carbide diode or a fast recovery diode.

7. The power conversion device according to any one of claims 1-6, wherein the first inductor is a first portion of a three-tap inductor, the second inductor is a second portion of the three-tap inductor, a first tap of the three-tap inductor is a first end of the first inductor, a second tap of the three-tap inductor is a first end of the second inductor, and a third tap of the three-tap inductor is a second end of the first inductor and is a second end of the second inductor.

8. The power conversion device according to any one of claims 1 to 7, wherein the power conversion circuit is a two-level circuit or a three-level circuit.

9. The power conversion device according to any one of claims 1-8, characterized in that the power conversion device is an inverter, or an inverter circuit board, or an energy storage converter PCS, or a PCS circuit board.

10. The power conversion device according to any of claims 1-9, wherein the first switching tube and/or the second switching tube is an insulated gate bipolar transistor, IGBT, or a metal-oxide semiconductor field effect transistor, MOSFET.

11. A power conversion device according to any one of claims 1-10, characterized in that the second end point and the bus midpoint are adapted to be connected to the neutral output of the power conversion device in an off-grid operation of the power conversion device.

12. A photovoltaic energy storage system, characterized in that the photovoltaic energy storage system comprises an energy storage device and a power conversion device, the energy storage device is connected with the power conversion device, and the power conversion device is the power conversion device according to any one of claims 1-11.