Power converter and energy storage system

Abstract

The invention provides a power converter and an energy storage system, and belongs to the technical field of power electronics. The power converter provided by the invention comprises an NPC three-level balance circuit, a current sampling circuit and a control circuit. Wherein the current sampling circuit can sample current which flows through the midpoint of a bus and flows through a clamping diode included in a first bridge arm in the NPC three-level balance circuit. The control circuit can determine that the clamping diode or the internal switching tube in the first bridge arm has a short-circuit fault if the current is detected to be large under the condition that the external switching tube in the first bridge arm is switched on or the internal switching tube in the first bridge arm is switched off. At the moment, the control circuit stops outputting the PWM signal to the NPC three-level balance circuit, so that each switching tube in the NPC three-level balance circuit is turned off, and the diffusion of the short-circuit fault can be avoided. Therefore, short-circuit protection of the NPC three-level balance circuit is realized, and fire caused by electric leakage of the NPC three-level balance circuit is avoided.

Description

Technical Field

[0001] The present application relates to the field of power electronics technology, and in particular to a power converter and an energy storage system. Background Art

[0002] A neutral point clamped (NPC) three-level balancing circuit is a power conversion circuit for balancing the energy of positive and negative bus capacitors (ie, bus capacitors connected to the positive bus and bus capacitors connected to the negative bus).

[0003] The NPC three-level balancing circuit generally includes: an upper bridge arm and a lower bridge arm connected to each other, the connection point of the upper bridge arm and the lower bridge arm is also called the bridge arm midpoint, and each bridge arm in the upper bridge arm and the lower bridge arm includes: a bus capacitor, an external switch tube, an internal switch tube and a clamping diode. The bus capacitor in the upper bridge arm and the bus capacitor in the lower bridge arm are connected in series between the positive bus and the negative bus, and the series node between the positive and negative bus capacitors is also called the bus midpoint. The external switch tube and the internal switch tube in the upper bridge arm are connected in sequence between the positive bus and the bridge arm midpoint, and the clamping diode in the upper bridge arm is connected to the bus midpoint and between the connection point of the external switch tube and the internal switch tube in the upper bridge arm. The external switch tube and the internal switch tube in the lower bridge arm are connected in sequence between the negative bus and the bridge arm midpoint, and the clamping diode in the lower bridge arm is connected to the bus midpoint and between the connection point of the external switch tube and the internal switch tube in the lower bridge arm. In addition, the NPC three-level balancing circuit also includes an inductor connected between the bus midpoint and the bridge arm midpoint. Among them, each external switch tube and each internal switch tube in the NPC three-level balancing circuit can be periodically turned on and off to balance the voltage on the positive and negative bus capacitors, that is, to balance the energy of the positive and negative bus capacitors.

[0004] However, due to factors such as abnormal voltage or overtemperature, the devices in the NPC three-level balancing circuit may fail (such as short circuit failure). If protection is not implemented in time, the short circuit failure will spread. In severe cases, it may even cause leakage in the NPC three-level balancing circuit and cause a fire. Summary of the invention

[0005] The present application provides a power converter and an energy storage system, which can solve the problem in the related art that the fault spreads due to the failure to implement protection against the short-circuit fault in time.

[0006] In a first aspect, a power converter is provided, which includes: a midpoint clamped NPC three-level balancing circuit, a current sampling circuit and a control circuit. The NPC three-level balancing circuit includes: a first bridge arm and a second bridge arm, and each of the first bridge arm and the second bridge arm includes: a clamping diode, an external switch tube and an internal switch tube. The current sampling circuit is used to: sample a first current flowing through the bus midpoint and the clamping diode in the first bridge arm, and the bus midpoint is the midpoint between the positive bus and the negative bus connected to the NPC three-level balancing circuit. The control circuit is used to: when the external switch tube in the first bridge arm is turned on, if the first current is greater than the first current threshold, stop outputting a pulse width modulation (PWM) signal to the NPC three-level balancing circuit; or, when the internal switch tube in the first bridge arm is turned off, if the first current is greater than the second current threshold, stop outputting a PWM signal to the NPC three-level balancing circuit. Wherein, the second current threshold is greater than or equal to the first current threshold.

[0007] It can be understood that when the external switch tube in the first bridge arm is turned on, or the internal switch tube is turned off, under normal circumstances, the current of the direct current provided by the direct current source will not flow through the clamping diode in the first bridge arm, that is, the current sampling circuit will not sample the first current flowing through the midpoint of the busbar and flowing through the clamping diode. Correspondingly, at this time, if the control circuit obtains the first current through the current sampling circuit, and the first current is large, it can be determined that the clamping diode or the internal switch tube in the first bridge arm has a short circuit fault. In addition, because the control circuit can stop outputting the PWM signal to the NPC three-level balancing circuit when the short circuit fault is detected, so that the NPC three-level balancing circuit stops working, the spread of the short circuit fault can be avoided, and the short circuit protection of the NPC three-level balancing circuit can be realized, so as to avoid the leakage of the NPC three-level balancing circuit and cause a fire.

[0008] In addition, for the first bridge arm, since the control circuit directly determines whether the clamping diode or the internal switch tube has a short-circuit fault based on the first current flowing through the clamping diode, the first current will not be directly affected by the half-bus voltage drop or dynamic load change, so the control circuit can quickly and reliably identify the occurrence of the short-circuit fault. Furthermore, the control circuit can implement protection against the short-circuit fault in a timely manner, and the protection effect is better.

[0009] Optionally, the current sampling circuit may include: a first sampling resistor, one end of which may be connected to the busbar midpoint, and the other end of which may be connected to the anode of the clamping diode in the first bridge arm.

[0010] That is, the first sampling resistor can be used to reliably sample the first current flowing through the midpoint of the busbar and through the clamping diode, and the structure of the current sampling circuit is simple.

[0011] Optionally, the current sampling circuit can also be used to: sample the second current flowing through the midpoint of the busbar and flowing through the clamping diode in the second bridge arm. The control circuit can also be used to: when the external switch tube in the second bridge arm is turned on, if the second current is greater than a third current threshold, stop outputting a PWM signal to the NPC three-level balancing circuit; or, when the internal switch tube in the second bridge arm is turned off, if the second current is greater than a fourth current threshold, stop outputting a PWM signal to the NPC three-level balancing circuit. The fourth current threshold can be greater than or equal to the third current threshold.

[0012] As with the first bridge arm, when the external switch tube in the second bridge arm is turned on, or the internal switch tube is turned off, under normal circumstances, the current of the DC power provided by the DC source will not flow through the clamping diode in the second bridge arm, that is, the current sampling circuit will not sample the second current flowing through the midpoint of the busbar and through the clamping diode. Correspondingly, at this time, if the control circuit obtains the second current through the current sampling circuit, and the second current is large, it can be determined that the clamping diode or the internal switch tube in the second bridge arm has a short circuit fault. In addition, because the control circuit can stop outputting the PWM signal to the NPC three-level balancing circuit when the short circuit fault is detected, so that the NPC three-level balancing circuit stops working, the spread of the short circuit fault can be avoided, and the short circuit protection of the NPC three-level balancing circuit can be realized, so as to avoid the leakage of the NPC three-level balancing circuit and cause a fire.

[0013] In addition, since the control circuit can also detect whether the clamping diode or the internal switch tube in the second bridge arm has a short-circuit fault and implement short-circuit protection for the short-circuit fault, the protection is more comprehensive and the protection effect is better. Moreover, for the second bridge arm, since the second current is also not directly affected by the half-bus voltage drop or dynamic load change, the control circuit can also quickly and reliably identify the occurrence of the short-circuit fault. Furthermore, the control circuit can implement protection for the short-circuit fault in a timely manner, and the protection effect is better.

[0014] Optionally, the current sampling circuit may include: a first sampling resistor and a second sampling resistor. One end of the first sampling resistor may be connected to the bus midpoint, and the other end of the first sampling resistor may be connected to the positive electrode of the clamping diode in the first bridge arm; one end of the second sampling resistor may be connected to the bus midpoint, and the other end of the second sampling resistor may be connected to the negative electrode of the clamping diode in the second bridge arm.

[0015] That is, in a possible implementation, a first sampling resistor and a second sampling resistor may be used to reliably sample the first current flowing through the bus midpoint and the clamping diode in the first bridge arm and the second current flowing through the bus midpoint and the clamping diode in the second bridge arm. That is, different sampling resistors may be used for sampling the first current and the second current, respectively. In this way, independent sampling of the first current and the second current may be achieved with high sampling accuracy.

[0016] Optionally, the current sampling circuit may include: a first sampling resistor, one end of which may be connected to the bus midpoint, and the other end of which may be connected to the anode of the clamping diode in the first bridge arm and the cathode of the clamping diode in the second bridge arm, respectively.

[0017] That is, in another possible implementation, a first sampling resistor can be used to reliably sample the first current flowing through the bus midpoint and the clamping diode in the first bridge arm, and reliably sample the second current flowing through the bus midpoint and the clamping diode in the second bridge arm. That is, the same sampling resistor can be shared for sampling the first current and the second current. In this way, the number of components required to be set can be simplified, saving costs.

[0018] Optionally, the power converter may further include: a first voltage sampling circuit. The first voltage sampling circuit may be used to: sample a first collector-emitter voltage between the collector and emitter of the external switch tube in the first bridge arm. The control circuit may also be used to: stop outputting a PWM signal to the NPC three-level balancing circuit if the first collector-emitter voltage is less than a first voltage threshold. The first voltage threshold may be less than a first half-bus voltage, and the first half-bus voltage may be a potential difference between the bus connected to the external switch tube in the first bridge arm and the midpoint of the bus in the positive bus and the negative bus.

[0019] It can be understood that, under normal circumstances, the first collector-emitter voltage of the external switch tube in the first bridge arm is generally not too small. If the first collector-emitter voltage of the external switch tube is much smaller than the potential difference between the busbar connected to the external switch tube and the busbar midpoint, the control circuit can determine that a short circuit fault occurs in the external switch tube in the first bridge arm at this time. In addition, since the control circuit can stop outputting PWM signals to the NPC three-level balancing circuit when the short circuit fault is detected, so that the NPC three-level balancing circuit stops working, the spread of the short circuit fault can be avoided, and the short circuit protection of the NPC three-level balancing circuit can be realized, so as to avoid the leakage of the NPC three-level balancing circuit and cause fire.

[0020] In addition, since the control circuit can also detect whether the external switch tube in the first bridge arm has a short-circuit fault and implement short-circuit protection for the short-circuit fault, the protection is more comprehensive and the protection effect is better. Moreover, for the first bridge arm, since the first collector-emitter voltage is also not directly affected by the half-bus voltage drop or dynamic load change, the control circuit can also quickly and reliably identify the occurrence of the short-circuit fault. Furthermore, the control circuit can implement protection for the short-circuit fault in a timely manner, and the protection effect is better.

[0021] Optionally, the power converter may further include: a second voltage sampling circuit. The second voltage sampling circuit may be used to: sample a second collector-emitter voltage between the collector and emitter of the external switch tube in the second bridge arm. The control circuit may also be used to: stop outputting a PWM signal to the NPC three-level balancing circuit if the second collector-emitter voltage is less than a second voltage threshold. The second voltage threshold may be less than a second half-bus voltage, and the second half-bus voltage may be a potential difference between the bus connected to the external switch tube in the second bridge arm and the midpoint of the bus in the positive bus and the negative bus.

[0022] As with the first bridge arm, under normal circumstances, the second collector-emitter voltage of the external switch tube in the second bridge arm is generally not too small. If the second collector-emitter voltage of the external switch tube is much smaller than the potential difference between the busbar connected to the external switch tube and the busbar midpoint, the control circuit can determine that a short circuit fault occurs in the external switch tube in the second bridge arm at this time. In addition, since the control circuit can stop outputting PWM signals to the NPC three-level balancing circuit when the short circuit fault is detected, so that the NPC three-level balancing circuit stops working, the spread of the short circuit fault can be avoided, and the short circuit protection of the NPC three-level balancing circuit can be realized, so as to avoid the leakage of the NPC three-level balancing circuit and cause fire.

[0023] In addition, since the control circuit can also detect whether the external switch tube in the second bridge arm has a short-circuit fault and implement short-circuit protection for the short-circuit fault, the protection is more comprehensive and the protection effect is better. Moreover, for the second bridge arm, since the second collector-emitter voltage is also not directly affected by the half-bus voltage drop or dynamic load change, the control circuit can also quickly and reliably identify the occurrence of the short-circuit fault. Furthermore, the control circuit can implement protection for the short-circuit fault in a timely manner, and the protection effect is better.

[0024] In a second aspect, a power converter is provided, which includes: an NPC three-level balancing circuit, a first voltage sampling circuit and a control circuit. The NPC three-level balancing circuit includes: a first bridge arm and a second bridge arm, and each of the first bridge arm and the second bridge arm includes: a clamping diode, an external switch tube and an internal switch tube. The first voltage sampling circuit is used to: sample the first collector-emitter voltage between the collector and the emitter of the external switch tube in the first bridge arm. The control circuit is also used to: if the first collector-emitter voltage is less than the first voltage threshold, stop outputting a PWM signal to the NPC three-level balancing circuit. Wherein, the first voltage threshold is less than the first half bus voltage, and the first half bus voltage is the potential difference between the bus connected to the external switch tube in the first bridge arm and the bus midpoint in the positive bus and the negative bus connected to the NPC three-level balancing circuit, and the bus midpoint is the midpoint between the positive bus and the negative bus.

[0025] Optionally, the power converter may further include: a second voltage sampling circuit. The second voltage sampling circuit may be used to: sample a second collector-emitter voltage between the collector and emitter of the external switch tube in the second bridge arm. The control circuit may also be used to: stop outputting a PWM signal to the NPC three-level balancing circuit if the second collector-emitter voltage is less than a second voltage threshold. The second voltage threshold may be less than a second half-bus voltage, and the second half-bus voltage may be a potential difference between the bus connected to the external switch tube in the second bridge arm and the midpoint of the bus in the positive bus and the negative bus.

[0026] In a third aspect, an energy storage system is provided, the energy storage system comprising: an energy storage battery, and a power converter as provided in the first aspect and the second aspect. The NPC three-level balancing circuit in the power converter is used to convert the direct current provided by the energy storage battery into alternating current.

[0027] In summary, the present application provides a power converter and an energy storage system. In the solution provided by the present application, the power converter includes an NPC three-level balancing circuit, a current sampling circuit and a control circuit. Among them, the current sampling circuit can sample the current flowing through the bus midpoint and through the clamping diode included in the first bridge arm of the NPC three-level balancing circuit. The control circuit can determine that the clamping diode or the internal switch tube in the first bridge arm has a short circuit fault when the external switch tube in the first bridge arm is turned on or the internal switch tube is turned off. At this time, because the control circuit will stop outputting a PWM signal to the NPC three-level balancing circuit so that each switch tube in the NPC three-level balancing circuit is turned off, the spread of the short circuit fault can be avoided. Thus, short-circuit protection of the NPC three-level balancing circuit is achieved, and fire caused by leakage of the NPC three-level balancing circuit is avoided. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is a structural schematic diagram of an energy storage system provided in an embodiment of the present application;

[0029] Figure 2 It is a structural schematic diagram of a UPS power supply provided in an embodiment of the present application;

[0030] Figure 3 is a schematic diagram of the structure of a power converter provided in an embodiment of the present application;

[0031] Figure 4 is a schematic diagram of the structure of another power converter provided in an embodiment of the present application;

[0032] Figure 5 is a structural schematic diagram of another power converter provided in an embodiment of the present application;

[0033] Figure 6 is a structural schematic diagram of another power converter provided in an embodiment of the present application;

[0034] Figure 7 is a structural schematic diagram of another power converter provided in an embodiment of the present application;

[0035] Figure 8 is a structural schematic diagram of another power converter provided in an embodiment of the present application;

[0036] Fig. 9 is a structural schematic diagram of another power converter provided in an embodiment of the present application;

[0037] Fig.10 It is a structural schematic diagram of another power converter provided in an embodiment of the present application. DETAILED DESCRIPTION

[0038] The power converter and energy storage system provided by the embodiments of the present application are described in detail below in conjunction with the accompanying drawings. First, the key terms involved in the embodiments of the present application are introduced.

[0039] Bus: The wiring that connects the input end of the NPC three-level balanced circuit to the DC source. The DC source usually includes a positive pole and a negative pole. Correspondingly, the bus generally includes a positive bus BUS+ and a negative bus BUS-. The positive bus BUS+ is connected to the positive pole of the DC source, and the negative bus BUS- is connected to the negative pole of the DC source.

[0040] Half bus: The input end of the NPC three-level balanced circuit usually adopts the solution of series capacitors, that is, two bus capacitors are connected in series between the positive bus BUS+ and the negative bus BUS-, and the series node of the two bus capacitors is also called the bus midpoint. Half bus refers to the connection between the positive bus BUS+ or the negative bus BUS- and the bus midpoint. For example, the connection from the positive bus BUS+ to the bus midpoint can be called the positive half bus or the upper half bus, and the connection from the negative bus BUS- to the bus midpoint can be called the negative half bus or the lower half bus.

[0041] NPC three-level balancing circuit: a power electronic device used for energy conversion. By adding a midpoint clamp, the NPC three-level balancing circuit can output three different levels: positive level, negative level and zero level at the midpoint of the topology. Through the operation of the three-level topology, the unbalanced energy on the positive and negative busbars can be transmitted and adjusted until the energy on the positive and negative busbars is balanced, so that the energy of the positive and negative busbar capacitors is balanced.

[0042] Wave blocking: The energy storage system usually includes an inverter circuit and a control circuit. Among them, the control circuit can output a PWM signal to the inverter circuit to control the on and off of the switch tube in the inverter circuit and drive the inverter circuit to work. The PWM signal is also called a PWM wave. Correspondingly, the control circuit outputting a PWM signal can refer to emitting a wave, and wave blocking refers to the control circuit stopping outputting a PWM wave, thereby stopping the inverter circuit from working.

[0043] The NPC three-level balancing circuit provided in the embodiments of the present application is mostly used in energy storage systems. Figure 1 A schematic diagram of the structure of an energy storage system is shown. Figure 1 As shown, the energy storage system includes: an energy storage battery and a power converter (also called an energy storage power converter). The power converter may include an NPC three-level balancing circuit, and the NPC three-level balancing circuit in the power converter can be used to convert the direct current provided by the energy storage battery into alternating current. In addition, the NPC three-level balancing circuit in the power converter can also output the converted alternating current to a load or a power grid. Accordingly, in combination with Figure 1 It can also be seen that the power converter can be connected to the energy storage battery through the positive bus BUS+ and the negative bus BUS-, and the power converter can be connected to the load or the grid through the output terminal. In addition, as mentioned above, the NPC three-level balancing circuit in the power converter can also transmit and adjust the unbalanced energy on the positive and negative buses when performing voltage conversion until the energy on the positive and negative buses is balanced, so that the energy of the positive and negative bus capacitors is balanced.

[0044] It is understandable that the energy storage system refers to a device for storing electrical energy or other forms of energy, and its main function is to store electrical energy and release it when needed to supply electricity to a load or a power grid. Of course, the NPC three-level balancing circuit recorded in the embodiments of the present application is not limited to application in energy storage systems. For example, in some other embodiments, the NPC three-level balancing circuit can also be applied to a power generation system. A power generation system refers to a device for converting a form of energy (such as solar energy provided by a photovoltaic module) into electrical energy and then outputting it to a load or a power grid to supply electricity to the load or the power grid. Alternatively, in some other embodiments, the NPC three-level balancing circuit can also be applied to an inverter, a rectifier or an uninterruptible power supply (UPS), and is mostly designed in the form of a power supply device. An uninterruptible power supply is also called a UPS power supply, and a UPS power supply is mostly used in the field of data centers to provide electrical energy to loads in data centers.

[0045] For example, take the NPC three-level balancing circuit applied to UPS power supply as an example. Figure 2 FIG. 1 shows a schematic diagram of the structure of a UPS power supply. Figure 2 As shown, the UPS power supply may include multiple power modules, bypass modules and load terminals, and the power input of each power module includes AC input and DC input. The AC input is connected to the main input to receive power from the mains; the DC input is connected to the battery to receive power from the battery. The power input of the bypass module is connected to the bypass input to receive power from the generator. Figure 2 It can be seen that the power output of each power module and the power output of the bypass module are connected to the load terminal H, and the load terminal H is used to connect to the load. In addition, each power module includes a rectifier circuit (also called a rectifier), an inverter circuit (also called an inverter) and a DC conversion circuit (also called a DC converter). The rectifier circuit can be connected to the main input, the inverter circuit can be connected to the rectifier circuit and the load terminal H respectively, and the DC conversion circuit can be connected to the rectifier circuit, the inverter circuit and the battery respectively. Among them, the rectifier circuit can be used to rectify the DC power input from the main circuit and output it to the inverter circuit. The DC conversion circuit can be used to convert the DC power from the battery into DC power and output it to the inverter circuit. The inverter circuit may include an NPC three-level balancing circuit, and the NPC three-level balancing circuit in the inverter circuit can be used to convert the received DC power into AC power and output it to the load through the load terminal H. In addition, the inverter circuit can be connected to the rectifier circuit and the DC conversion circuit through the positive bus BUS+ and the negative bus BUS-. The NPC three-level balancing circuit in the inverter circuit can also transmit and adjust the unbalanced energy on the positive and negative bus bars during voltage conversion until the energy on the positive and negative bus bars is balanced, so that the energy of the positive and negative bus capacitors is balanced.

[0046] Furthermore, it is understandable that in the field of power electronics, the control circuit can periodically output PWM signals to the NPC three-level balancing circuit in units of switching cycles to control the on and off of the switch tube in the NPC three-level balancing circuit, so that the energy on the positive and negative buses connected to the NPC three-level balancing circuit is balanced. Furthermore, since the NPC three-level balancing circuit needs to have a bus balance of the upper and lower half buses (i.e., the voltage or current on the upper half bus and the lower half bus needs to be relatively balanced), the working reliability requirements of the components included in the NPC three-level balancing circuit are relatively high. Once a component fails, such as a short circuit failure of the switch tube in the NPC three-level balancing circuit, if protection is not implemented in time, the fault will spread, leading to serious consequences such as leakage, fire, and even injury.

[0047] Based on this, in some embodiments, the inductor current or half-bus voltage in the NPC three-level balancing circuit can be detected to determine whether a short-circuit fault occurs in a device in the NPC three-level balancing circuit, so as to perform necessary protection actions when a short-circuit fault occurs. The protection action may include controlling the NPC three-level balancing circuit to stop working to reduce the loss caused by the short-circuit fault. For example, it is usually determined that a short-circuit fault occurs in a device in the NPC three-level balancing circuit when the inductor current exceeds the current protection value or the half-bus voltage drops below the voltage protection value. However, when the half-bus is short-circuited and the load changes dynamically (that is, the power demand of the load changes dynamically), that is, when there is no short-circuit fault in the device, the half-bus voltage will drop normally and the inductor current will increase normally. Therefore, in order to prevent misprotection, the current protection value needs to be set higher and the voltage protection value needs to be set lower in this embodiment. This will often result in that when it is determined that a short-circuit fault occurs in a device and the protection action is implemented, multiple switching cycles have passed, that is, the switch tube in the NPC three-level balancing circuit has been turned on and off in multiple switching cycles, and the protection is delayed, and the protection time may reach the millisecond (ms) level or even the second (s) level. During this process, the short-circuit fault may have spread and the protection effect is poor.

[0048] The following describes the NPC three-level balancing circuit provided in the embodiment of the present application by taking the NPC three-level balancing circuit applied to an energy storage system as a part of a power converter in the energy storage system as an example.

[0049] The embodiment of the present application provides a power converter, which can implement short-circuit protection at the level of a single switching cycle, and the protection time can be shortened to the microsecond (us) level, that is, it can detect a short-circuit fault within the us level time and implement short-circuit protection in time, thereby preventing the short-circuit fault from spreading further, and the protection effect is good. Figure 3 and Figure 4As shown, the power converter includes: a neutral point clamped NPC three-level balancing circuit 01, a current sampling circuit 02 and a control circuit 03.

[0050] The NPC three-level balancing circuit 01 includes: a first bridge arm 011 and a second bridge arm 012, and each of the first bridge arm 011 and the second bridge arm 012 includes: a clamping diode, an external switch tube and an internal switch tube. Figure 3 In the figure, the clamping diode, the external switch tube and the internal switch tube included in the first bridge arm 011 are marked as D01, Q1 and Q2 respectively; the clamping diode, the internal switch tube and the external switch tube included in the second bridge arm 012 are marked as D02, Q3 and Q4 respectively.

[0051] It can be understood that the external switch tube refers to the switch tube directly connected to the positive bus BUS+ or the negative bus BUS-, and the internal switch tube refers to the switch tube directly connected to the midpoint of the bridge arm. That is, for each bridge arm in the first bridge arm 011 and the second bridge arm 012, the external switch tube and the internal switch tube can be connected in sequence between one of the positive bus BUS+ and the negative bus BUS- and the midpoint of the bridge arm. Among them, the bridge arm in which the external switch tube and the internal switch tube are connected in sequence between the positive bus BUS+ and the midpoint of the bridge arm can also be called the upper bridge arm; the bridge arm in which the external switch tube and the internal switch tube are connected in sequence between the negative bus BUS- and the midpoint of the bridge arm can also be called the lower bridge arm. In addition, for each bridge arm, the clamping diode can be connected between the bus midpoint N and the connection node between the external switch tube and the internal switch tube. Furthermore, in the upper bridge arm, the positive electrode of the clamping diode is connected to the bus midpoint N, and the negative electrode of the clamping diode is connected to the connection node of the external switch tube and the internal switch tube. In the lower bridge arm, the positive electrode of the clamping diode is connected to the connection node of the external switch tube and the internal switch tube, and the negative electrode of the clamping diode is connected to the bus midpoint N. And, refer to Figure 3 It can also be seen that the NPC three-level balancing circuit 01 can also include two bus capacitors C1 and C2 connected in series between the positive bus BUS+ and the negative bus BUS-, and an inductor L connected in series between the bus midpoint N and the bridge arm midpoint. The series node of the two bus capacitors C1 and C2 is the bus midpoint N.

[0052] For example, Figure 3 In the NPC three-level balancing circuit 01 shown, the external switch tube Q1 and the internal switch tube Q2 of the first bridge arm 011 are connected between the positive bus BUS+ and the midpoint of the bridge arm in sequence, and the external switch tube Q4 and the internal switch tube Q3 of the second bridge arm 012 are connected between the negative bus BUS- and the midpoint of the bridge arm in sequence, and Figure 3In the embodiment of the present application, the connection node between the external switch tube Q1 and the internal switch tube Q2 is identified as A, the midpoint of the bridge arm (i.e., the connection node between the internal switch tube Q2 and the internal switch tube Q3) is identified as B, and the connection node between the internal switch tube Q3 and the external switch tube Q4 is identified as C. Accordingly, in the embodiment of the present application, the first bridge arm 011 may refer to the upper bridge arm, and the second bridge arm 012 may refer to the lower bridge arm. On this basis, continue to refer to Figure 3 It can be seen that in the first bridge arm 011, the positive electrode of the clamping diode D01 can be connected to the bus midpoint N, and the negative electrode of the clamping diode D01 can be connected to the connection node A. In the second bridge arm 012, the positive electrode of the clamping diode D02 can be connected to the connection node C, and the negative electrode of the clamping diode D02 can be connected to the bus midpoint N. Of course, in some other embodiments, the first bridge arm 011 can also refer to the lower bridge arm, and the second bridge arm 012 can refer to the upper bridge arm. This embodiment of the present application is not limited to this.

[0053] Optionally, each of the external switch tube and the internal switch tube may generally be an insulated gate bipolar transistor (IGBT) or a metal-oxide-semiconductor field-effect transistor (MOSFET), and each switch tube may include a body diode connected between a collector and an emitter. Figure 3 In the figure, the body diodes of the external switch tube Q1 and the external switch tube Q4 are marked as D1 and D4, respectively, and the body diodes of the internal switch tube Q2 and the internal switch tube Q3 are marked as D2 and D3, respectively. Figure 3 The NPC three-level balancing circuit 01 of the structure shown is an I-type NPC three-level balancing circuit.

[0054] As described above, during the normal operation of the NPC three-level balancing circuit 01, the control circuit 03 can output a PWM signal to each switch tube therein in units of a switching cycle to control the switching of each switch tube in each switching cycle. Moreover, for each switch tube, when the potential of the PWM signal output by the control circuit 03 to the switch tube is a valid potential (e.g., a positive pulse), the switch tube can be turned on; when the potential of the PWM signal output by the control circuit 03 to the switch tube is an invalid potential (e.g., a zero pulse), the switch tube can be turned off. Furthermore, when all devices in the NPC three-level balancing circuit 01 are normal, when the external switch tube and the internal switch tube in each bridge arm are turned on, the current can flow through the current path of the external switch tube and the internal switch tube (referred to as current path 1); when the external switch tube in each bridge arm is turned off and the internal switch tube is turned on, the current can flow through the current path of the clamping diode and the internal switch tube (referred to as current path 2). Moreover, for the upper bridge arm, when the external switch tube is turned off and the internal switch tube is turned on, the current can flow through the clamping diode and the internal switch tube in sequence. For the lower bridge arm, when the external switch tube is turned off and the internal switch tube is turned on, the current can flow through the internal switch tube and the clamping diode in sequence.

[0055] That is, under normal circumstances, that is, when no short-circuit fault occurs in each device, for each bridge arm, when the external switch tube in the bridge arm is turned on, the current will not flow through the current path 2, and will not flow through the clamping diode in the bridge arm. If there is still current flowing through the clamping diode in the bridge arm at this time, it can be known that the clamping diode in the bridge arm may have a short-circuit fault. And, for each switch tube, when the switch tube is turned off, the current will not flow through the switch tube. If there is still current flowing through the switch tube at this time, it can be known that the switch tube may have a short-circuit fault. For example, for the internal switch tube in each bridge arm, when the internal switch tube is turned off, the current will not flow through the current path 2, and will not flow through the clamping diode and the internal switch tube in the bridge arm. If the protection action for the short-circuit fault is not implemented in time, once the short-circuit fault spreads, it will cause damage to the NPC three-level balancing circuit 01, and may cause a fire in severe cases.

[0056] And continue to refer to Figure 4 It can be seen that the power converter provided in the embodiment of the present application further includes a current sampling circuit 02 and a control circuit 03 .

[0057] The current sampling circuit 02 is used to sample the first current I1 flowing through the bus midpoint N and the clamping diode D01 in the first bridge arm 011. The bus midpoint N is the midpoint between the positive bus BUS+ and the negative bus BUS- connected to the NPC three-level balancing circuit 01. That is, the current sampling circuit 02 can at least sample the current between the bus midpoint N and the clamping diode included in one of the upper bridge arm and the lower bridge arm. For example, in the structure where the first bridge arm 011 is the upper bridge arm, combined with Figure 3 and Figure 4 It can be seen that the current sampling circuit 02 can be used to sample the current between the bus midpoint N and the positive electrode of the clamping diode D01.

[0058] The control circuit 03 is used for:

[0059] When the external switch tube Q1 in the first bridge arm 011 is turned on, if the first current I1 is greater than the first current threshold, the pulse width modulation PWM signal is stopped from being output to the NPC three-level balancing circuit 01 .

[0060] or,

[0061] When the internal switch tube Q2 in the first bridge arm 011 is turned off, if the first current I1 is greater than the second current threshold, the PWM signal is stopped from being output to the NPC three-level balancing circuit 01 .

[0062] Accordingly, the control circuit 03 may be connected to the current sampling circuit 02 to obtain the first current I1 sampled by the current sampling circuit 02. The control circuit 03 may be, for example, a micro controller unit (MCU).

[0063] Combined with the above records, it can be known that when the control circuit 03 controls the external switch tube Q1 in the first bridge arm 011 to turn on, under normal circumstances, the current will not flow through the current path 2, that is, it will not flow through the clamping diode D01 in the first bridge arm 011. At this time, if the current sampling circuit 02 can still sample the current flowing through the bus midpoint N and the clamping diode D01, and at the same time detect that the current is greater than the first current threshold, the control circuit 03 can determine that the clamping diode D01 has a short circuit fault. When the control circuit 03 controls the internal switch tube Q2 in the first bridge arm 011 to turn off, under normal circumstances, the current will not flow through the current path 2, that is, it will not flow through the clamping diode D01 in the first bridge arm 011 to the internal switch tube Q2 and then flow through the internal switch tube Q2. At this time, if the current sampling circuit 02 can still sample the current flowing through the bus midpoint N and the clamping diode D01, that is, it samples that there is still current flowing through the clamping diode D01 and the internal switch tube Q2 in sequence, and at the same time detects that the current is greater than the second current threshold, then the control circuit 03 can determine that the internal switch tube Q2 has a short circuit fault. That is, Figure 4 In the structure shown, the control circuit 03 can at least detect whether the clamping diode D01 in the first bridge arm 011 and the internal switch tube Q2 have a short circuit fault.

[0064] In the embodiment of the present application, the control circuit 03 can stop outputting PWM signals to each switch tube in the NPC three-level balancing circuit 01, i.e., perform a wave blocking operation, when detecting a short-circuit fault in the clamping diode D01 in the first bridge arm 011 or a short-circuit fault in the internal switch tube Q2 in the first bridge arm 011. Thus, the NPC three-level balancing circuit 01 can stop working, thereby avoiding the spread of the short-circuit fault and realizing short-circuit protection for the NPC three-level balancing circuit 01.

[0065] Of course, in some other embodiments, when a short circuit occurs in any device in the NPC three-level balancing circuit 01, the control circuit 03 can also directly shut down the device to which the power converter belongs to achieve short circuit protection. In addition, the control circuit 03 can also issue an alarm prompt to remind the user that the NPC three-level balancing circuit 01 has a short circuit fault, so that the user can actively cut off the power in time to achieve short circuit protection. That is, the short circuit protection action is not limited to the wave blocking operation.

[0066] Among them, the first current threshold and the second current threshold can both be current thresholds pre-stored in the control circuit 03 or can be flexibly designed according to actual conditions, and the second current threshold is greater than or equal to the first current threshold. That is, the current threshold used to indicate that the clamping diode D01 has a short-circuit fault can be relatively small, and the current threshold used to indicate that the internal switch tube Q2 has a short-circuit fault can be relatively large. For example, the first current threshold can be approximately 30 amperes (A), and the second current threshold can be approximately 80A. It can be understood that because the response time of the diode is usually faster than the switch tube, by setting the first current threshold to be less than the second current threshold, short-circuit protection can be implemented in time for the short-circuit fault of the clamping diode D01, preventing the short-circuit current from flowing to the internal switch tube and causing the internal switch tube Q2 to fail, and the protection effect is better.

[0067] In addition, in the embodiment of the present application, since the control circuit 03 directly detects whether a short-circuit fault occurs in the clamping diode or the internal switch tube based on the current flowing through the bus midpoint N and the clamping diode in the bridge arm, the current is not directly affected by the half-bus voltage drop and the dynamic load change. Therefore, compared with the above-mentioned embodiment, which determines whether a short-circuit fault occurs by detecting that the inductor current exceeds the current protection value or the half-bus voltage drops below the voltage protection value, the current threshold does not need to be set higher. Furthermore, the control circuit 03 can identify the short-circuit fault and implement the protection action within one switching cycle, and the protection time can reach the microsecond level, thereby reliably avoiding the further spread of the short-circuit fault caused by the long short-circuit time, and the protection effect is better.

[0068] In summary, an embodiment of the present application provides a power converter. The power converter includes an NPC three-level balancing circuit, a current sampling circuit and a control circuit. Among them, the current sampling circuit can sample the current flowing through the bus midpoint and through the clamping diode included in the first bridge arm of the NPC three-level balancing circuit. The control circuit can determine that the clamping diode or the internal switch tube in the first bridge arm has a short circuit fault when the external switch tube in the first bridge arm is turned on or the internal switch tube is turned off. At this time, because the control circuit stops outputting a PWM signal to the NPC three-level balancing circuit so that each switch tube in the NPC three-level balancing circuit is turned off, the spread of the short circuit fault can be avoided. As a result, short-circuit protection of the NPC three-level balancing circuit is achieved, and fire caused by leakage of the NPC three-level balancing circuit is avoided.

[0069] Alternatively, if Figure 5 As shown, in the embodiment of the present application, the current sampling circuit 02 can also be used to: sample the second current I2 flowing through the bus midpoint N and the clamping diode D02 in the second bridge arm 012. That is, the current sampling circuit 02 can also sample the current between the bus midpoint N and the clamping diode included in the upper bridge arm and the other bridge arm in the upper bridge arm. In other words, the current sampling circuit 02 can sample the current between the bus midpoint N and the clamping diode in each bridge arm. For example, in the structure where the first bridge arm 012 is the lower bridge arm, combined with Figure 5 It can be seen that the current sampling circuit 02 can be used to sample the current between the bus midpoint N and the cathode of the clamping diode D02.

[0070] The control circuit 03 can also be used for:

[0071] When the external switch tube Q4 in the second bridge arm 012 is turned on, if the second current I2 is greater than the third current threshold, the PWM signal is stopped from being output to the NPC three-level balancing circuit 01 .

[0072] or,

[0073] When the internal switch tube Q3 in the second bridge arm 012 is turned off, if the second current I2 is greater than the fourth current threshold, the PWM signal is stopped from being output to the NPC three-level balancing circuit 01 .

[0074] As with the first bridge arm 011, combined with the above records, it can be known that when the control circuit 03 controls the external switch tube Q4 in the second bridge arm 012 to turn on, under normal circumstances, the current will not flow through the current path 2, that is, it will not flow through the clamping diode D02 in the second bridge arm 012. At this time, if the current sampling circuit 02 can still sample the current flowing through the bus midpoint N and the clamping diode D02, and at the same time detect that the current is greater than the third current threshold, the control circuit 03 can determine that the clamping diode D02 has a short circuit fault. When the control circuit 03 controls the internal switch tube Q3 in the second bridge arm 012 to turn off, under normal circumstances, the current will not flow through the current path 2, that is, it will not flow through the internal switch tube Q3 in the second bridge arm 012 to the clamping diode D02 and then flow through the clamping diode D02. At this time, if the current sampling circuit 02 can still sample the current flowing through the bus midpoint N and the clamping diode D02, that is, it samples that there is still current flowing through the internal switch tube Q3 and the clamping diode D02 in sequence, and at the same time detects that the current is greater than the fourth current threshold, then the control circuit 03 can determine that the internal switch tube Q3 has a short circuit fault. That is, Figure 5 In the structure shown, the control circuit 03 can also detect whether the clamping diode D02 in the second bridge arm 012 and the internal switch tube Q3 have a short circuit fault.

[0075] Furthermore, in the embodiment of the present application, the control circuit 03 can stop outputting PWM signals to each switch tube in the NPC three-level balancing circuit 01, i.e., perform a wave blocking operation, when detecting a short-circuit fault in the clamping diode D02 in the second bridge arm 012 or a short-circuit fault in the internal switch tube Q3 in the second bridge arm 012. Thus, the spread of the short-circuit fault can be avoided, and short-circuit protection of the NPC three-level balancing circuit 01 can be achieved.

[0076] Among them, the third current threshold and the fourth current threshold can also be current thresholds pre-stored in the control circuit 03 or can be flexibly designed according to actual conditions, and the fourth current threshold can be greater than or equal to the third current threshold. That is, with the magnitude relationship between the first current threshold and the second current threshold, the current threshold used to indicate that the clamping diode D02 has a short-circuit fault can be relatively small, and the current threshold used to indicate that the internal switch tube Q3 has a short-circuit fault can be relatively large. Of course, the third current threshold and the first current threshold can be the same or different, and the fourth current threshold and the second current threshold can be the same or different. For example, the third current threshold can also be about 30A, and the fourth current threshold can also be about 80A. Similarly, it can be understood that because the response time of the diode is usually faster than the switch tube, by setting the third current threshold to be less than the fourth current threshold, short-circuit protection can be implemented in time for the short-circuit fault of the clamping diode D02, and the protection effect is better.

[0077] By setting the control circuit 03, short-circuit protection is also performed on the short-circuit faults of the clamping diode D02 and the internal switch tube Q3 in the second bridge arm 012, that is, short-circuit protection is performed on the short-circuit faults of the clamping diode and the internal switch tube included in each bridge arm, so that the protection is more comprehensive and the protection effect is better.

[0078] Optionally, as a possible implementation: Figure 6 As shown, the current sampling circuit 02 may include: a first sampling resistor R1.

[0079] One end of the first sampling resistor R1 can be connected to the busbar midpoint N, and the other end of the first sampling resistor R1 can be connected to the positive electrode of the clamping diode D01 in the first bridge arm 011 and the negative electrode of the clamping diode D02 in the second bridge arm 012, respectively. Correspondingly, the first bridge arm 011 can refer to the upper bridge arm, and the second bridge arm 012 can refer to the lower bridge arm. Of course, when the first bridge arm 011 is the lower bridge arm and the second bridge arm 012 is the upper bridge arm, the other end of the first sampling resistor R1 can be connected to the negative electrode of the clamping diode D01 in the first bridge arm 011 and the positive electrode of the clamping diode D02 in the second bridge arm 012, respectively. The following embodiments are similar and will not be described one by one.

[0080] Based on this structure, the first sampling resistor R1 can be used to sample both the first current I1 and the second current I2. That is, in this possible implementation, the current sampling circuit 02 can be configured to include a sampling resistor, or it can be considered that the sampling of the first current and the second current share the same sampling resistor.

[0081] Alternatively, as another possible implementation: Figure 7As shown, the current sampling circuit 02 may include: a first sampling resistor R1 and a second sampling resistor R2.

[0082] One end of the first sampling resistor R1 may be connected to the busbar midpoint N, and the other end of the first sampling resistor R1 may be connected to the anode of the clamping diode D01 in the first bridge arm 011 .

[0083] One end of the second sampling resistor R2 may be connected to the busbar midpoint N, and the other end of the second sampling resistor R2 may be connected to the cathode of the clamping diode D02 in the second bridge arm 012 .

[0084] Based on this structure, the first sampling resistor R1 can be used to sample the first current I1, and the second sampling resistor R2 can be used to sample the second current I2. That is, in another possible implementation, the current sampling circuit 02 can be configured to include two sampling resistors, or it can be considered that different sampling resistors are used for sampling the first current and the second current.

[0085] Understandably, relatively Figure 7 The structure shown, Figure 6 The structure shown in the figure can reduce the number of components required and save costs by setting a common sampling resistor to sample the first current I1 and the second current I2. Figure 6 The structure shown, Figure 7 The structure shown can achieve independent sampling of the first current I1 and the second current I2 by separately using different sampling resistors to sample the first current I1 and the second current I2, with high sampling accuracy.

[0086] Optionally, in Figure 6 On the basis of Figure 8 FIG. 2 shows a schematic diagram of the structure of another power converter. Figure 7 On the basis of Fig. 9 FIG. 2 shows a schematic diagram of the structure of another power converter. Figure 8 and Fig. 9 It can be seen that in the embodiment of the present application, the power converter may further include: a first voltage sampling circuit 04 .

[0087] The first voltage sampling circuit 04 can be used to sample a first collector-emitter voltage VCE1 between the collector and emitter of the external switch tube Q1 in the first bridge arm 011. The first collector-emitter voltage VCE1 can refer to a potential difference between the collector and emitter of the external switch tube Q1.

[0088] The control circuit 03 may also be configured to stop outputting the PWM signal to the NPC three-level balancing circuit 01 if the first collector-emitter voltage VCE1 is less than a first voltage threshold.

[0089] Correspondingly, the control circuit 03 may also be connected to the first voltage sampling circuit 04 to obtain the first collector-emitter voltage VCE1 sampled by the first voltage sampling circuit 04 .

[0090] The first voltage threshold may be less than the first half bus voltage, and the first half bus voltage may be the potential difference between the bus connected to the external switch tube Q1 in the first bridge arm 011 and the bus midpoint N in the positive bus BUS+ and the negative bus BUS-. Figure 8 and Fig. 9 In the structure where the first bridge arm 011 is the upper bridge arm and the external switch tube Q1 is connected to the positive bus BUS+, the first half-bus voltage can be the potential difference between the positive bus BUS+ and the bus midpoint N, and the first half-bus voltage is also called the positive half-bus voltage. The first voltage threshold can also be a voltage threshold pre-stored in the control circuit 03 or can be flexibly designed according to actual conditions. For example, the first half-bus voltage can generally be about 300 volts (V), and the voltage range of the first voltage threshold can be about 50V to 100V, such as the first voltage threshold can be 80V. When the first collector-emitter voltage VCE1 of the external switch tube Q1 is less than the first voltage threshold, that is, much less than the first half-bus voltage, the control circuit 03 can determine that the external switch tube Q1 has a short circuit fault. That is, Figure 8 and Fig. 9 In the structure shown, the control circuit 03 can also detect whether the external switch tube Q1 in the first bridge arm 011 has a short circuit fault.

[0091] In the embodiment of the present application, the control circuit 03 can stop outputting PWM signals to each switch tube in the NPC three-level balancing circuit 01, i.e., perform a wave blocking operation, when detecting a short-circuit fault in the external switch tube Q1 in the first bridge arm 011. Thus, the spread of the short-circuit fault can be avoided, and short-circuit protection of the NPC three-level balancing circuit 01 can be achieved. In addition, by setting the control circuit 03 to also perform short-circuit protection on the short-circuit fault of the external switch tube Q1 included in the first bridge arm 011, the protection is more comprehensive and the protection effect is better.

[0092] Optionally, continue to refer to Figure 8 and Fig. 9 It can be seen that in the embodiment of the present application, the power converter may further include: a second voltage sampling circuit 05 .

[0093] The second voltage sampling circuit 05 can be used to sample a second collector-emitter voltage VCE2 between the collector and emitter of the external switch tube Q4 in the second bridge arm 012. The second collector-emitter voltage VCE2 can refer to a potential difference between the collector and emitter of the external switch tube Q4.

[0094] The control circuit 03 may also be configured to stop outputting the PWM signal to the NPC three-level balancing circuit 01 if the second collector-emitter voltage VCE2 is less than a second voltage threshold.

[0095] Correspondingly, the control circuit 03 may also be connected to the second voltage sampling circuit 05 to obtain the second collector-emitter voltage VCE2 sampled by the second voltage sampling circuit 05 .

[0096] The second voltage threshold may be less than the second half bus voltage, and the second half bus voltage may be the potential difference between the bus connected to the external switch tube Q4 in the second bridge arm 012 and the bus midpoint N in the positive bus BUS+ and the negative bus BUS-. Figure 8 and Fig. 9 In the structure where the second bridge arm 012 is the lower bridge arm and the external switch tube Q4 is connected to the negative bus BUS-, the second half-bus voltage can be the potential difference between the negative bus BUS- and the bus midpoint N, and the second half-bus voltage is also called the negative half-bus voltage. The second voltage threshold can also be a voltage threshold pre-stored in the control circuit 03 or can be flexibly designed according to actual conditions. Moreover, the second voltage threshold and the first voltage threshold can be the same or different. For example, the second half-bus voltage can generally be approximately 300V, and the voltage range of the second voltage threshold can be approximately 50V to 100V, such as the second voltage threshold can be 80V. When the first collector-emitter voltage VCE2 of the external switch tube Q4 is less than the second voltage threshold, that is, much less than the second half-bus voltage, the control circuit 03 can determine that the external switch tube Q4 has a short circuit fault. That is, Figure 8 and Fig. 9 In the structure shown, the control circuit 03 can also detect whether the external switch tube Q4 in the second bridge arm 012 has a short circuit fault.

[0097] In the embodiment of the present application, the control circuit 03 can stop outputting PWM signals to each switch tube in the NPC three-level balancing circuit 01, i.e., perform a wave blocking operation, when detecting a short-circuit fault in the external switch tube Q4 in the second bridge arm 012. Thus, the spread of the short-circuit fault can be avoided, and short-circuit protection of the NPC three-level balancing circuit 01 can be achieved. In addition, by setting the control circuit 03, short-circuit protection is also performed on the short-circuit fault of the external switch tube Q4 included in the second bridge arm 012, that is, short-circuit protection is performed on the short-circuit fault of the external switch tube included in each bridge arm, so that the protection is more comprehensive and the protection effect is better.

[0098] Similarly, in the embodiment of the present application, since the control circuit 03 directly detects whether the external switch tube has a short circuit fault based on the collector-emitter voltage of the external switch tube, the voltage is not directly affected by the half-bus voltage drop and dynamic load changes. Therefore, compared with the above embodiment, which determines whether a short circuit fault occurs by detecting that the inductor current exceeds the current protection value or the half-bus voltage drops below the voltage protection value, the voltage threshold does not need to be set lower. Furthermore, the control circuit 03 can identify the short circuit fault and implement the protection action within one switching cycle, and the protection time can reach the microsecond level, thereby reliably avoiding the further spread of the short circuit fault caused by the long short circuit time, and the protection effect is better.

[0099] Optionally, each of the first voltage sampling circuit 04 and the second voltage sampling circuit 05 may include an operational amplifier to reliably sample the collector-emitter voltage of the external switch tube.

[0100] Based on the foregoing records, it can be known that in the power converter provided by the embodiment of the present application, for the first bridge arm and the second bridge arm, the current sampling circuit and the control circuit can be set to cooperate with each other to quickly detect the short-circuit fault of the clamping diode and the internal switch tube in at least one bridge arm, and short-circuit protection can be implemented in time for the short-circuit fault. And, the voltage sampling circuit and the control circuit can also be set to cooperate with each other to quickly detect the short-circuit fault of the external switch tube in at least one bridge arm, and short-circuit protection can be implemented in time for the short-circuit fault. The protection time is short, the protection effect is good, and the protection is more comprehensive.

[0101] Optionally, as mentioned above, the NPC three-level balancing circuit 01 is not limited to use in power converters, but can also be used in rectifiers or uninterruptible power supplies (UPS), also known as UPS power supplies, and is mostly designed in the form of power supply equipment.

[0102] In summary, an embodiment of the present application provides a power converter. The power converter includes an NPC three-level balancing circuit, a current sampling circuit and a control circuit. Among them, the current sampling circuit can sample the current flowing through the bus midpoint and through the clamping diode included in the first bridge arm of the NPC three-level balancing circuit. The control circuit can determine that the clamping diode or the internal switch tube in the first bridge arm has a short circuit fault when the external switch tube in the first bridge arm is turned on or the internal switch tube is turned off. At this time, because the control circuit stops outputting a PWM signal to the NPC three-level balancing circuit so that each switch tube in the NPC three-level balancing circuit is turned off, the spread of the short circuit fault can be avoided. As a result, short-circuit protection of the NPC three-level balancing circuit is achieved, and fire caused by leakage of the NPC three-level balancing circuit is avoided.

[0103] The present application also provides a power converter. Fig.10 As shown, the power converter includes: an NPC three-level balancing circuit 01 , a first voltage sampling circuit 04 and a control circuit 03 .

[0104] The NPC three-level balancing circuit 01 includes: a first bridge arm 011 and a second bridge arm 012 , and each of the first bridge arm 011 and the second bridge arm 012 includes: a clamping diode, an external switch tube and an internal switch tube.

[0105] The first voltage sampling circuit 04 is used to sample a first collector-emitter voltage VCE1 between the collector and emitter of the external switch tube Q1 in the first bridge arm 011 .

[0106] The control circuit 03 is also used to: if the first collector-emitter voltage VCE1 is less than a first voltage threshold, stop outputting a PWM signal to the NPC three-level balancing circuit 01, wherein the first voltage threshold is less than a first half-bus voltage, and the first half-bus voltage is a potential difference between a bus connected to the external switch tube Q1 in the first bridge arm 011 and a bus midpoint N in the positive bus BUS+ and the negative bus BUS- connected to the NPC three-level balancing circuit 01, and the bus midpoint is the midpoint between the positive bus BUS+ and the negative bus BUS-.

[0107] Optionally, continue to refer to Fig.10 It can be seen that the power converter may further include: a second voltage sampling circuit 05 .

[0108] The second voltage sampling circuit 05 is used to sample a second collector-emitter voltage VCE2 between the collector and emitter of the external switch tube Q4 in the second bridge arm 012 .

[0109] The control circuit 03 is also used to stop outputting the PWM signal to the NPC three-level balancing circuit 01 if the second collector-emitter voltage VCE2 is less than a second voltage threshold, wherein the second voltage threshold is less than a second half-bus voltage, and the second half-bus voltage is the potential difference between the bus connected to the external switch tube Q4 in the second bridge arm 012 and the bus midpoint N among the positive bus BUS+ and the negative bus BUS-.

[0110] That is, in one embodiment, the power converter may at least be provided with a voltage sampling circuit to cooperate with the control circuit to quickly detect a short-circuit fault of an external switch tube in at least one bridge arm, and implement short-circuit protection in a timely manner for the short-circuit fault.

[0111] It can be understood that since the power converter has basically the same implementation method and technical effects as the power converter described in the above embodiments, for the purpose of brevity, the implementation method and technical effects of the power converter will not be repeatedly described here.

[0112] In the embodiments of the present application, the terms "first", "second" and "third" are used for descriptive purposes only and should not be understood as indicating or implying relative importance. The term "at least one" means one or more, and "plurality" means two or more.

[0113] The above is only an optional implementation of the present application, but the protection scope of the present application is not limited thereto. Any technician familiar with the technical field can easily think of various equivalent modifications or replacements within the technical scope disclosed in the present application, and these modifications or replacements should be included in the protection scope of the present application. Therefore, the protection scope of the present application shall be based on the protection scope of the claims.

Claims

1. A power converter, characterized in that: The power converter comprises: a mid-point clamped NPC three-level balancing circuit, a current sampling circuit and a control circuit; The NPC three-level balancing circuit comprises: a first bridge arm and a second bridge arm, and each of the first bridge arm and the second bridge arm comprises: a clamping diode, an external switch tube and an internal switch tube; The current sampling circuit is used to: sample a first current flowing through a bus midpoint and through a clamping diode in the first bridge arm, wherein the bus midpoint is a midpoint between a positive bus and a negative bus connected to the NPC three-level balancing circuit; The control circuit is used for: When the external switch tube in the first bridge arm is turned on, if the first current is greater than a first current threshold, then the pulse width modulation (PWM) signal is stopped from being output to the NPC three-level balancing circuit; or, When the internal switch tube in the first bridge arm is turned off, if the first current is greater than a second current threshold, the PWM signal is stopped from being output to the NPC three-level balancing circuit, wherein the second current threshold is greater than or equal to the first current threshold.

2. The power converter according to claim 1, characterized in that: The current sampling circuit comprises: a first sampling resistor; One end of the first sampling resistor is connected to the midpoint of the busbar, and the other end of the first sampling resistor is connected to the anode of the clamping diode in the first bridge arm.

3. The power converter according to claim 1, characterized in that: The current sampling circuit is also used to: sample a second current flowing through the midpoint of the busbar and through the clamping diode in the second bridge arm; The control circuit is also used for: When the external switch tube in the second bridge arm is turned on, if the second current is greater than a third current threshold, then stop outputting the PWM signal to the NPC three-level balancing circuit; or, When the internal switch tube in the second bridge arm is turned off, if the second current is greater than a fourth current threshold, the PWM signal is stopped from being output to the NPC three-level balancing circuit, wherein the fourth current threshold is greater than or equal to the third current threshold.

4. The power converter according to claim 3, characterized in that: The current sampling circuit comprises: a first sampling resistor and a second sampling resistor; One end of the first sampling resistor is connected to the midpoint of the busbar, and the other end of the first sampling resistor is connected to the positive electrode of the clamping diode in the first bridge arm; One end of the second sampling resistor is connected to the midpoint of the busbar, and the other end of the second sampling resistor is connected to the cathode of the clamping diode in the second bridge arm.

5. The power converter according to claim 3, characterized in that: The current sampling circuit comprises: a first sampling resistor; One end of the first sampling resistor is connected to the midpoint of the busbar, and the other end of the first sampling resistor is respectively connected to the anode of the clamping diode in the first bridge arm and the cathode of the clamping diode in the second bridge arm.

6. The power converter according to any one of claims 1 to 5, characterized in that: The power converter further includes: a first voltage sampling circuit; The first voltage sampling circuit is used to: sample a first collector-emitter voltage between a collector and an emitter of an external switch tube in the first bridge arm; The control circuit is also used to stop outputting the PWM signal to the NPC three-level balancing circuit if the first collector-emitter voltage is less than a first voltage threshold, wherein the first voltage threshold is less than a first half-bus voltage, and the first half-bus voltage is the potential difference between the bus connected to the external switch tube in the first bridge arm and the midpoint of the bus in the positive bus and the negative bus.

7. The power converter according to any one of claims 1 to 6, characterized in that: The power converter further includes: a second voltage sampling circuit; The second voltage sampling circuit is used to: sample a second collector-emitter voltage between the collector and emitter of the external switch tube in the second bridge arm; The control circuit is also used to stop outputting the PWM signal to the NPC three-level balancing circuit if the second collector-emitter voltage is less than a second voltage threshold, wherein the second voltage threshold is less than a second half-bus voltage, and the second half-bus voltage is the potential difference between the bus connected to the external switch tube in the second bridge arm and the midpoint of the bus in the positive bus and the negative bus.

8. A power converter, characterized in that: The power converter comprises: an NPC three-level balancing circuit, a first voltage sampling circuit and a control circuit; The NPC three-level balancing circuit comprises: a first bridge arm and a second bridge arm, and each of the first bridge arm and the second bridge arm comprises: a clamping diode, an external switch tube and an internal switch tube; The first voltage sampling circuit is used to: sample a first collector-emitter voltage between a collector and an emitter of an external switch tube in the first bridge arm; The control circuit is also used to: stop outputting the PWM signal to the NPC three-level balancing circuit if the first collector-emitter voltage is less than a first voltage threshold, wherein the first voltage threshold is less than a first half-bus voltage, and the first half-bus voltage is the potential difference between the bus connected by the external switch tube in the first bridge arm and the midpoint of the bus, among the positive bus and the negative bus connected to the NPC three-level balancing circuit, and the bus midpoint is the midpoint between the positive bus and the negative bus.

9. The power converter according to claim 8, characterized in that: The power converter further includes: a second voltage sampling circuit; The second voltage sampling circuit is used to: sample a second collector-emitter voltage between the collector and emitter of the external switch tube in the second bridge arm; The control circuit is also used to stop outputting the PWM signal to the NPC three-level balancing circuit if the second collector-emitter voltage is less than a second voltage threshold, wherein the second voltage threshold is less than a second half-bus voltage, and the second half-bus voltage is the potential difference between the bus connected to the external switch tube in the second bridge arm and the midpoint of the bus in the positive bus and the negative bus.

10. An energy storage system, characterized in that: The energy storage system comprises: an energy storage battery, and a power converter as claimed in any one of claims 1 to 9; The NPC three-level balancing circuit in the power converter is used to convert the direct current provided by the energy storage battery into alternating current.

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