Power converter

Abstract

The invention provides a power converter, and belongs to the technical field of power electronics. The controller can control the fifth switch tube to be normally closed in the process that the second switch tube in the bridge arm is switched on and the first switch tube is periodically switched on and switched off, namely under the condition that current flows out of the bridge arm through the first switch tube and the second switch tube which are connected in series; and the fifth switch tube is connected between the bus midpoint and the series connection point of the first switch tube and the second switch tube, so that the short circuit of the positive direct current bus caused by the connection of the positive direct current bus and the bus midpoint when the first switch tube is short-circuited can be prevented.

Description

Technical Field

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

[0002] A power converter is a circuit used to convert direct current (DC) to alternating current (AC). In addition, a power converter usually includes a positive DC bus, a negative DC bus, and multiple switches connected between the positive DC bus and the negative DC bus. By controlling the on and off states of the multiple switches, the power converter can achieve DC and AC power conversion.

[0003] However, when a switch tube is short-circuited, the busbar will be short-circuited due to the switching of other switch tubes. Summary of the invention

[0004] A power converter is provided, which can solve the problem in the related art that a positive direct current bus and a negative direct current bus are prone to bus short circuit.

[0005] In the first aspect, a power converter is provided. The power converter includes: a bridge arm, a positive DC bus, a negative DC bus, a positive DC bus capacitor, a negative DC bus capacitor and a controller. Wherein: the bridge arm is used to convert the DC power of the photovoltaic module or the energy storage battery into AC power, and the bridge arm includes a first switch tube, a second switch tube, a third switch tube, a fourth switch tube, a fifth switch tube and a sixth switch tube. Wherein, the first switch tube, the second switch tube, the third switch tube and the fourth switch tube are connected in series between the positive DC bus and the negative DC bus in sequence, the fifth switch tube is connected between the series connection point of the first switch tube and the second switch tube and the sixth switch tube, and the sixth switch tube is connected between the series connection point of the third switch tube and the fourth switch tube and the fifth switch tube. The positive DC bus capacitor and the negative DC bus capacitor are connected in series between the positive DC bus and the negative DC bus, and the series connection point of the positive DC bus capacitor and the negative DC bus capacitor is the bus midpoint, and the bus midpoint is connected to the series connection point of the fifth switch tube and the sixth switch tube. The controller is used to control the fifth switch tube to remain turned off when the second switch tube is turned on and the first switch tube is periodically turned on and off.

[0006] Based on the connection mode of each switch tube, it can be known that in the process of the second switch tube being turned on and the first switch tube being periodically turned on and off, the current can flow out of the bridge arm through the first switch tube and the second switch tube, and the power converter can work in the positive half cycle and the current flows out of the working mode. At this time, by always controlling the fifth switch tube, which is a complementary switch tube to the first switch tube, to be turned off, the positive DC bus can be prevented from being connected to the bus midpoint, thereby preventing the positive DC bus from being short-circuited.

[0007] Optionally, the controller can be used to: when the second switch tube is turned on and the first switch tube is periodically turned on and off, and when the current flowing out of the bridge arm through the first switch tube and the second switch tube is greater than a first current threshold, control the fifth switch tube to remain turned off. The first current threshold is 5% to 10% of the rated current flowing out of the bridge arm.

[0008] That is, the controller can not only refer to the process of the second switch tube being turned on and the first switch tube being periodically turned on and off as a trigger condition to control the fifth switch tube to be normally turned off, but can also refer to the current size, and can control the fifth switch tube to be normally turned off only when the current is large during this process. In this way, it can prevent the current from reversing during the commutation process when the current is small, and can avoid the situation where the current cannot flow normally due to the fifth switch tube being normally turned off, thereby ensuring the normal operation of the power converter.

[0009] Optionally, the controller can also be used to: when the second switch tube is turned on and the first switch tube is periodically turned on and off, and when the first switch tube is short-circuited, first control the sixth switch tube to be turned on, then control the second switch tube to be turned off, and control the third switch tube, the fourth switch tube and the fifth switch tube to remain turned off.

[0010] When the first switch tube is short-circuited, the controller first controls the sixth switch tube to be turned on, then controls the second switch tube to be turned off, and controls the third switch tube, the fourth switch tube and the fifth switch tube to remain turned off, so that the current can flow out through the freewheeling diodes of the sixth switch tube and the third switch tube in sequence, thereby preventing the short circuit fault from spreading inside the power converter.

[0011] Optionally, the controller can also be used to: when the second switch tube is turned on and the first switch tube is periodically turned on and off, and when the first switch tube is short-circuited, first control the sixth switch tube to be turned on, then control the second switch tube to be turned off, and then control the third switch tube to be turned on, and control the fourth switch tube and the fifth switch tube to remain turned off.

[0012] When the first switch tube is short-circuited, the controller first controls the sixth switch tube to be turned on, then controls the second switch tube to be turned off, and then controls the third switch tube to be turned on, while controlling the fourth switch tube and the fifth switch tube to remain turned off. This allows the current to flow out through the sixth switch tube and the third switch tube in sequence, and also prevents the short-circuit fault from spreading inside the power converter.

[0013] Optionally, there may be multiple bridge arms, and the multiple bridge arms may be connected in parallel. The controller may also be used to: when a first switch tube included in any bridge arm among the multiple bridge arms is short-circuited, control all switch tubes included in other bridge arms except any bridge arm to be turned off.

[0014] When the first switch tube included in any bridge arm is short-circuited, the controller can prevent the short-circuit fault from spreading to other bridge arms by controlling all the switch tubes included in other bridge arms to turn off.

[0015] In the second aspect, a power converter is provided. The power converter includes: a bridge arm, a positive DC bus, a negative DC bus, a positive DC bus capacitor, a negative DC bus capacitor and a controller. Wherein: the bridge arm is used to convert the DC power of the photovoltaic module or the energy storage battery into AC power, and the bridge arm includes a first switch tube, a second switch tube, a third switch tube, a fourth switch tube, a fifth switch tube and a sixth switch tube. Wherein, the first switch tube, the second switch tube, the third switch tube and the fourth switch tube are connected in series between the positive DC bus and the negative DC bus in sequence, the fifth switch tube is connected between the series connection point of the first switch tube and the second switch tube and the sixth switch tube, and the sixth switch tube is connected between the series connection point of the third switch tube and the fourth switch tube and the fifth switch tube. The positive DC bus capacitor and the negative DC bus capacitor are connected in series between the positive DC bus and the negative DC bus, and the series connection point of the positive DC bus capacitor and the negative DC bus capacitor is the bus midpoint, and the bus midpoint is connected to the series connection point of the fifth switch tube and the sixth switch tube. The controller is used to control the first switch tube to remain turned off when the second switch tube is turned on and the fifth switch tube is periodically turned on and off.

[0016] Based on the connection mode of each switch tube, it can be known that in the process of the second switch tube being turned on and the fifth switch tube being periodically turned on and off, the current can flow into the bridge arm through the second switch tube and the fifth switch tube, and the power converter can work in the positive half cycle and the current flows in the working mode. At this time, by always controlling the first switch tube, which is a complementary switch tube to the fifth switch tube, to be turned off, the positive DC bus can be prevented from being connected to the bus midpoint, and thus the positive DC bus can also be prevented from being short-circuited.

[0017] Optionally, the controller can be used to: when the second switch tube is turned on and the fifth switch tube is periodically turned on and off, and when the current flowing into the bridge arm through the second switch tube and the fifth switch tube is greater than a second current threshold, control the first switch tube to remain turned off. The second current threshold is 5% to 10% of the rated current flowing into the bridge arm.

[0018] That is, the controller can not only refer to the process of the second switch tube being turned on and the fifth switch tube being periodically turned on and off as a trigger condition to control the first switch tube to be normally turned off, but can also refer to the current size, and can control the first switch tube to be normally turned off only when the current is large during this process. In this way, it can prevent the current from reversing during the commutation process when the current is small, and can avoid the situation where the current cannot flow normally due to the first switch tube being normally turned off, thereby ensuring the normal operation of the power converter.

[0019] Optionally, the controller can also be used to: when the second switch tube is turned on and the fifth switch tube is periodically turned on and off, and when the fifth switch tube is short-circuited, control the second switch tube to remain turned on, and control the first switch tube, the third switch tube, the fourth switch tube and the sixth switch tube to remain turned off.

[0020] When the fifth switch tube is short-circuited, the controller controls the second switch tube to remain turned on and controls the first, third, fourth and sixth switch tubes to remain turned off, so that the current can flow through the second switch tube and the short-circuited fifth switch tube in sequence, thereby preventing the short-circuit fault from spreading inside the power converter.

[0021] Optionally, the controller can also be used to: when the second switch tube is turned on and the fifth switch tube is periodically turned on and off, and when the fifth switch tube is short-circuited, control the second switch tube to turn off, control the first switch tube and the fourth switch tube to remain turned off, and control the sixth switch tube and the third switch tube to turn on.

[0022] When the fifth switch tube is short-circuited, the controller controls the second switch tube to turn off, controls the first switch tube and the fourth switch tube to remain turned off, and controls the sixth switch tube and the third switch tube to turn on, so that the current can flow through the third switch tube and the sixth switch tube in sequence, and also prevents the short circuit fault from spreading inside the power converter.

[0023] Optionally, there may be multiple bridge arms, and the multiple bridge arms may be connected in parallel. The controller may also be used to: when the fifth switch tube included in any one of the multiple bridge arms is short-circuited, control all the switch tubes included in the other bridge arms except any one of the bridge arms to be turned off.

[0024] Similarly, when the fifth switch tube included in any bridge arm is short-circuited, the controller can control all the switch tubes included in other bridge arms to turn off, thereby preventing the short-circuit fault from spreading to other bridge arms.

[0025] In summary, the present application provides a power converter. Since the controller can control the fifth switch tube to be normally closed during the process in which the second switch tube in the bridge arm is turned on and the first switch tube is periodically turned on and off, that is, when the current flows out of the bridge arm through the first switch tube and the second switch tube connected in series, and since the first switch tube is connected to the positive DC bus, the fifth switch tube is connected between the bus midpoint and the series connection point of the first switch tube and the second switch tube, it can be prevented that when the first switch tube is short-circuited, the positive DC bus is connected to the bus midpoint to cause the bus short-circuit. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 is a schematic diagram of a working scenario of a power converter provided in an embodiment of the present application;

[0027] Figure 2 is a structural schematic diagram of a power converter provided in an embodiment of the present application;

[0028] Figure 3 is a schematic diagram of a working mode of a power converter provided in an embodiment of the present application;

[0029] Figure 4 is a schematic diagram of the structure of another power converter provided in an embodiment of the present application;

[0030] Figure 5 is a schematic diagram of another working mode of a power converter provided in an embodiment of the present application;

[0031] Figure 6 is a schematic diagram of a working process of a power converter provided in an embodiment of the present application;

[0032] Figure 7 This is a schematic diagram of the working timing of a power converter provided in an embodiment of the present application;

[0033] Figure 8 This is a schematic diagram of the working timing of another power converter provided in an embodiment of the present application. DETAILED DESCRIPTION

[0034] The power converter provided by the embodiment of the present application is described in detail below in conjunction with the accompanying drawings. First, the key terms involved in the embodiment of the present application are introduced.

[0035] Photovoltaic module: also known as photovoltaic panel, is a device used to convert solar energy into direct current electricity through the photovoltaic effect.

[0036] Energy storage battery: An electrochemical device that can store electrical energy and release it when needed.

[0037] Power grid: The whole composed of substations and transmission and distribution lines of various voltages in the power system, also known as the public power grid.

[0038] Box transformer: also known as box-type substation or box-type transformer, is an integrated power distribution equipment that can realize the conversion and distribution of electric energy.

[0039] Power conversion system (PCS): A device used to achieve power conversion and control, which is a type of power converter. The power conversion here includes the conversion of direct current (DC) to alternating current (AC) and the conversion of alternating current (AC) to direct current (DC).

[0040] Inverter: A device used to convert direct current (DC) output by a DC source into alternating current (AC), which is a type of power converter. The DC source is, for example, a photovoltaic module, and accordingly, the inverter is also called a photovoltaic inverter.

[0041] ANPC circuit: A multi-level inverter topology that can be used in photovoltaic inverters and energy storage converters PCS to achieve conversion between direct current DC and alternating current AC. Common ANPC circuits include three-level ANPC circuits and five-level ANPC circuits. As the name implies, a three-level ANPC circuit refers to a circuit that can provide three levels (including positive level, zero level and negative level); a five-level ANPC circuit refers to a circuit that can provide five levels (including two positive levels, zero level and two negative levels).

[0042] Bus: The wiring that connects the power converter to the DC source. The DC source usually includes a positive pole and a negative pole. Correspondingly, the bus generally includes a positive DC bus (also called a positive bus) BUS+ connected to the positive pole and a negative DC bus (also called a negative bus) BUS- connected to the negative pole.

[0043] Wave blocking: A power converter usually includes a bridge arm and a controller, and the bridge arm includes multiple switch tubes. The controller can output a pulse-width modulation (PWM) signal to the switch tube in the bridge arm to control the on and off of the switch tube. The PWM signal is also called a PWM wave. Correspondingly, the controller outputting a PWM signal can refer to emitting a wave, and wave blocking refers to the controller stopping outputting a PWM wave.

[0044] Defensive PWM (DEPWM) modulation: A technology that improves the anti-interference ability and working reliability of the power converter by optimizing the generation and control strategy of PWM signals.

[0045] Taking the power converter including the ANPC circuit as an example, based on the above records, it can be known that the ANPC circuit usually includes multiple switch tubes, and the switch tubes are usually insulated gate bipolar transistors (IGBT), that is, IGBTs are mostly used as power semiconductor devices in the ANPC circuit. However, since IGBTs are mostly used in high-frequency, high-voltage or high-current scenarios when applied to ANPC circuits, the failure rate is relatively high, and the IGBTs at some positions are subjected to greater stress, so the failure rate is correspondingly higher. Here, the IGBTs at some positions are, for example, external switch tubes used for the DC connection bus in the photovoltaic inverter. In addition, the loss of the external switch tube is generally relatively large. All of these make the external switch tube prone to short-circuit failure. At this time, if other switch tubes are operated normally, serious faults such as bus short circuit will occur, and in severe cases, even the fault will spread. Of course, the switch tube can also be a metal-oxide-semiconductor field-effect transistor (MOSFET).

[0046] Based on this, the embodiment of the present application provides a DEPWM modulation method for a power converter, so as to avoid short-circuit faults by controlling the switch tube in the power converter, and can also detect short-circuit faults online and achieve safe wave blocking to achieve short-circuit protection. Optionally, the power converter may include a three-level ANPC circuit or a five-level ANPC circuit. The following embodiment is described by taking a three-level ANPC circuit as an example.

[0047] Figure 1 A possible scenario is shown in Figure 1. Figure 1 , the scenario includes a DC source, a power converter, a box transformer, a power grid and a load. The DC source may include a photovoltaic module and an energy storage battery. The power converter may include an inverter and an energy storage converter PCS. The DC source may provide direct current DC. The inverter in the power converter can convert the direct current DC provided by the photovoltaic module into alternating current AC and then send it to the power grid and load through the box transformer to supply power to the power grid and load. The energy storage converter PCS in the power converter can convert the direct current DC provided by the energy storage battery into alternating current AC and then send it to the power grid and load through the box transformer, or it can also convert the alternating current AC from the power grid into direct current DC and output it to the energy storage battery so that the energy storage battery can store electrical energy.

[0048] Figure 2 Schematic diagram of a power converter provided in an embodiment of the present application. Figure 2As shown, the power converter includes: a bridge arm 01, a positive DC bus BUS+, a negative DC bus BUS-, a positive DC bus capacitor C1, a negative DC bus capacitor C2 and a controller 02. Among them:

[0049] The bridge arm 01 is used to convert the direct current DC of the photovoltaic module or the energy storage battery into alternating current AC, and the bridge arm 01 includes a first switch tube T1, a second switch tube T2, a third switch tube T3, a fourth switch tube T4, a fifth switch tube T5 and a sixth switch tube T6. Among them, the first switch tube T1, the second switch tube T2, the third switch tube T3 and the fourth switch tube T4 are connected in series between the positive DC bus BUS+ and the negative DC bus BUS-, the fifth switch tube T5 is connected between the series connection point of the first switch tube T1 and the second switch tube T2 and the sixth switch tube T6, and the sixth switch tube T6 is connected between the series connection point of the third switch tube T3 and the fourth switch tube T4 and the fifth switch tube T5. The positive DC bus capacitor C1 and the negative DC bus capacitor C2 are connected in series between the positive DC bus BUS+ and the negative DC bus BUS-. The series connection point of the positive DC bus capacitor C1 and the negative DC bus capacitor C2 is the bus midpoint N, and the bus midpoint N is connected to the series connection point of the fifth switch tube T5 and the sixth switch tube T6.

[0050] Based on this, it can be known that the first switch tube T1 and the fourth switch tube T4 are the external switch tubes recorded above. The second switch tube T2 and the third switch tube T3 can be called internal switch tubes. The fifth switch tube T5 and the sixth switch tube T6 can be called clamping switch tubes. In addition, the bridge arm 01 can be divided into an upper half bridge arm connected between the positive DC bus BUS+ and the bus midpoint N, and a lower half bridge arm connected between the negative DC bus BUS- and the bus midpoint N. The first switch tube T1, the second switch tube T2 and the fifth switch tube T5 can be used as the external switch tube, the internal switch tube and the clamping switch tube in the upper half bridge arm, respectively, and the fourth switch tube T4, the third switch tube T3 and the sixth switch tube T6 can be used as the external switch tube, the internal switch tube and the clamping switch tube in the lower half bridge arm, respectively.

[0051] In addition, reference Figure 2 It can be seen that the bridge arm 01 may also include a diode D (also called a freewheeling diode) correspondingly connected between the emitter and the collector of each switch tube. Figure 2 In the figure, the diodes connected between the two electrodes of the first switch tube T1 to the sixth switch tube T6 are marked as D1 to D6 respectively.

[0052] The controller 02 is used to control the fifth switch tube T5 to remain off when the second switch tube T2 is turned on and the first switch tube T1 is periodically turned on and off. That is, for the upper half bridge arm, the controller 02 can control the clamping switch tube to be normally off when the internal switch tube is turned on and the external switch tube is periodically turned on and off.

[0053] It is understandable that, combined with Figure 3 In one embodiment, when the second switch tube T2 is turned on and the first switch tube T1 is periodically turned on and off, the current can flow out of the bridge arm 01 through the first switch tube T1 and the second switch tube T2 in sequence. At this time, it can be considered that the power converter works in the positive half cycle and the current flows out of the working mode, and the power converter is used to convert direct current DC into alternating current AC.

[0054] In some embodiments, as described in the background, the first switch tube T1 and the fifth switch tube T5 in the bridge arm 01 are complementary switch tubes, that is, the external switch tube and the clamp switch tube in the upper half bridge arm are complementary switch tubes. When the first switch tube T1 is turned on, the fifth switch tube T5 is turned off; and when the first switch tube T1 is turned off, the fifth switch tube T5 is turned on. This will cause the positive DC bus BUS+ to be connected to the bus midpoint N due to the conduction of the fifth switch tube T5 when the first switch tube T1 is short-circuited, thereby causing the positive DC bus BUS+ to have a bus short circuit.

[0055] In the embodiment of the present application, continue to combine Figure 3 , because the controller 02 can always control the fifth switch tube T5, which is a complementary switch tube to the first switch tube T1, to be turned off when the second switch tube T2 is turned on and the first switch tube T1 is periodically turned on and off, it can ensure that even if the first switch tube T1 is short-circuited, the positive DC bus BUS+ and the bus midpoint N will not be connected through the fifth switch tube T5, thereby preventing the bus short circuit caused by the short circuit of the first switch tube T1. In this way, the fault diffusion efficiency of the switch tube short circuit can also be reduced, thereby reserving enough time to facilitate the detection of whether the first switch tube T1 is short-circuited.

[0056] In addition, by controlling the fifth switch tube T5 to be normally off, not only will the normal operation of the power converter not be affected, but the action of the fifth switch tube T5 can be reduced, thereby reducing the loss of the fifth switch tube T5.

[0057] It is understandable that, in the process of keeping the fifth switch tube T5 turned off, the diode D5 connected thereto can also be turned off. That is, in the embodiment of the present application, when the power converter operates in the positive half cycle and the current flows out in the working mode, that is, the external switch tube in the upper half bridge arm is periodically turned on and off and the internal switch tube is turned on, the clamp switch tube complementary to the external switch tube and the corresponding diode are controlled to be normally closed to prevent the positive DC bus BUS+ from being short-circuited. This method can also be called a DEPWM modulation.

[0058] It can also be understood that the controller 02 can output a PWM signal to the switch tube in units of switching cycles to control the periodic on and off of the switch tube, that is, to control the normal switching of the switch tube. Moreover, when the potential of the PWM signal output by the controller 02 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 controller 02 to the switch tube is an invalid potential (e.g., a zero pulse), the switch tube can be turned off. Alternatively, the controller 02 can also control the switch tube to be turned off by stopping the input of the PWM signal.

[0059] Optionally, the controller 02 can be used to: when the second switch tube T2 is turned on and the first switch tube T1 is periodically turned on and off, and when the current flowing out of the bridge arm 01 through the first switch tube T1 and the second switch tube T2 is greater than the first current threshold, control the fifth switch tube T5 to remain turned off.

[0060] Among them, the first current threshold value can be 5% to 10% of the rated current flowing out of the bridge arm, and the rated current can refer to the maximum current allowed to pass through the bridge arm when the power converter is working normally and the bridge arm can continue to operate stably. At this time, the current flows out of the bridge arm 01 through the first switch tube T1 and the second switch tube T2 in sequence. In addition, the first current threshold value can be a threshold value pre-set in the controller 02, and of course it can also be flexibly adjusted.

[0061] That is, the triggering condition for the controller 02 to control the fifth switch tube T5 to remain turned off includes not only the process that the second switch tube T2 is turned on and the first switch tube T1 is periodically turned on and off, but also the magnitude of the current flowing out of the bridge arm 01 in the process. When the current is large, the controller 02 will control the fifth switch tube T5 to remain turned off; otherwise, the controller 02 can control the fifth switch tube T5 to be turned on and off periodically, and control the fifth switch tube T5 and the first switch tube T1 to be turned on and off complementary to each other. In this way, when the current is small, the current can be prevented from reversing during the commutation process. At this time, if the fifth switch tube T5 is still controlled to be normally closed, the current will not flow normally, affecting the normal operation of the power converter. The embodiment of the present application can avoid current reversal by controlling the fifth switch tube T5 and the first switch tube T1 to be turned on and off complementary to each other when the current is small, thereby ensuring the normal operation of the power converter.

[0062] Of course, it is not limited to the process that the second switch tube T2 is turned on and the first switch tube T1 is periodically turned on and off, and the triggering is also based on the triggering condition of the current size to control the on and off of the fifth switch tube T5. For example, the triggering can also be realized by high-speed sampling of the current.

[0063] Optionally, in an optional implementation, the controller 02 can also be used to: when the second switch tube T2 is turned on and the first switch tube T1 is periodically turned on and off, and when the first switch tube T1 is short-circuited, first control the sixth switch tube T6 to be turned on, then control the second switch tube T2 to be turned off, and control the third switch tube T3, the fourth switch tube T4 and the fifth switch tube T5 to remain turned off.

[0064] Optionally, in another optional implementation, the controller 02 can also be used to: when the second switch tube T2 is turned on and the first switch tube T1 is periodically turned on and off, and when the first switch tube T1 is short-circuited, first control the sixth switch tube T6 to be turned on, then control the second switch tube T2 to be turned off, and then control the third switch tube T3 to be turned on, and control the fourth switch tube T4 and the fifth switch tube T5 to remain turned off.

[0065] That is, when the power converter is operating in the positive half cycle and the current is flowing out, the controller 02 can also detect whether the external switch tube in the upper half bridge arm is short-circuited. And once the external switch tube is short-circuited, the controller 02 can achieve short-circuit protection by controlling the on and off of other switch tubes. For example:

[0066] The controller 02 can control the on-off of other switch tubes according to the above optional implementation method. In this way, the current can be first introduced into the lower half bridge arm, and then flow out of the bridge arm through the clamp switch tube and the diode of the internal switch tube (i.e., T6 and D3) in the lower half bridge arm in sequence. That is, the current can be commutated from the external switch tube and the internal switch tube (i.e., T1 and T2) in the upper half bridge arm to the clamp switch tube and the diode of the internal switch tube in the lower half bridge arm to prevent the short circuit fault from spreading inside the power converter. Correspondingly, the internal switch tube in the upper half bridge arm and the external switch tube in the lower half bridge arm (i.e., T2 and T4) can respectively withstand the voltage of the positive DC bus BUS+ and the negative DC bus BUS- without overvoltage breakdown. Alternatively, the controller 02 can control the on-off of other switch tubes according to the above another optional implementation method. In this way, the current can be first introduced into the lower bridge arm, and then flow out of the bridge arm through the clamping switch tube and the internal switch tube in the lower bridge arm in sequence, which can also prevent the short circuit fault from spreading.

[0067] Optionally, the controller 02 may detect whether the first switch tube T1 is short-circuited based on the speed of change of the current flowing out of the bridge arm or the magnitude of the current. For example, the controller 02 may determine that the first switch tube T1 is short-circuited when the speed of change of the current flowing out of the bridge arm is greater than a speed threshold or the current is greater than a current threshold. Both the speed threshold and the current threshold here may be the maximum values ​​determined when the first switch tube T1 is not short-circuited, which may be pre-set in the controller 02, and of course may also be flexibly adjusted.

[0068] Alternatively, if Figure 4 As shown, the power converter may include multiple bridge arms 01 , and the multiple bridge arms 01 may be connected in parallel. Figure 4 The schematic diagram shows two bridge arms 01 connected in parallel. Based on this structure, the controller 02 can also be used to control the switching tubes (i.e., T1 to T6) included in other bridge arms 01 except any one bridge arm 01 to be turned off when the first switching tube T1 included in any one of the multiple bridge arms 01 is short-circuited. In this way, the short-circuit fault can be prevented from spreading to other bridge arms, thereby achieving safe wave blocking.

[0069] In summary, the embodiment of the present application provides a power converter. Since the controller can control the fifth switch tube to be normally closed when the second switch tube in the bridge arm is turned on and the first switch tube is periodically turned on and off, and since the first switch tube is connected to the positive DC bus, the fifth switch tube is connected between the bus midpoint and the series connection point of the first switch tube and the second switch tube, it is possible to prevent the positive DC bus from being connected to the bus midpoint when the first switch tube is short-circuited, thereby preventing the bus from being short-circuited due to the positive DC bus being connected to the bus midpoint.

[0070] The present application also provides a power converter. The structure of the power converter can refer to Figure 2 , which will not be described in detail here. The controller 02 is used to control the first switch tube T1 to remain off when the second switch tube T2 is turned on and the fifth switch tube T5 is periodically turned on and off. That is, for the upper half bridge arm, the controller 02 can also control the external switch tube to be normally off when the internal switch tube is turned on and the clamping switch tube is periodically turned on and off.

[0071] It is understandable that, combined with Figure 5 In one embodiment, when the second switch tube T2 is turned on and the fifth switch tube T5 is periodically turned on and off, the current can flow into the bridge arm 01 through the second switch tube T2 and the fifth switch tube T5 in sequence. At this time, it can be considered that the power converter works in the positive half cycle and the current flows in the working mode, and the power converter can be used to convert alternating current AC into direct current DC.

[0072] As mentioned above, in some embodiments, the first switch tube T1 and the fifth switch tube T5 in the bridge arm 01 are complementary switches. This will cause the positive DC bus BUS+ to be connected to the bus midpoint N due to the conduction of the first switch tube T1 when the fifth switch tube T5 is short-circuited, thereby causing the positive DC bus BUS+ to be short-circuited.

[0073] In the embodiment of the present application, continue to combine Figure 5, because the controller 02 can always control the first switch tube T1, which is a complementary switch tube to the fifth switch tube T5, to be turned off when the second switch tube T2 is turned on and the fifth switch tube T5 is periodically turned on and off, it can ensure that even if the fifth switch tube T5 is short-circuited, the positive DC bus BUS+ and the bus midpoint N will not be connected through the first switch tube T1, thereby preventing the bus short circuit caused by the short circuit of the fifth switch tube T5, and also reducing the fault diffusion efficiency of the switch tube short circuit, thereby reserving enough time to facilitate the detection of whether the fifth switch tube T5 is short-circuited. In addition, the action of the first switch tube T1 can also be reduced, thereby reducing the loss of the first switch tube T1.

[0074] It is understandable that, in the process of keeping the first switch tube T1 turned off, the diode D1 connected thereto can also be turned off. That is, in the embodiment of the present application, when the power converter operates in the positive half cycle and the current flows in the working mode, that is, the clamp switch tube in the upper half bridge arm is periodically turned on and off and the internal switch tube is turned on, the external switch tube complementary to the clamp switch tube and the corresponding diode are controlled to be normally closed to prevent the positive DC bus BUS+ from being short-circuited. This control method can also be called a DEPWM modulation.

[0075] Optionally, the controller 02 can be used to: when the second switch tube T2 is turned on and the fifth switch tube T5 is periodically turned on and off, and when the current flowing into the bridge arm 01 through the second switch tube T2 and the fifth switch tube T5 is greater than the second current threshold, control the first switch tube T1 to remain turned off.

[0076] The second current threshold may be 5% to 10% of the rated current flowing into the bridge arm 01. For the description of the rated current and the current threshold, reference may be made to the description of the first current threshold, which will not be repeated here. The second current threshold may be the same as or different from the first current threshold.

[0077] That is, the triggering condition for the controller 02 to control the first switch tube T1 to remain turned off includes not only the process that the second switch tube T2 is turned on and the fifth switch tube T5 is periodically turned on and off, but also the magnitude of the current flowing into the bridge arm 01 during the process. When the current is large, the controller 02 will control the first switch tube T1 to remain turned off; otherwise, the controller 02 can control the first switch tube T1 to be turned on and off periodically, and control the first switch tube T1 and the fifth switch tube T5 to be turned on and off complementary. In this way, it can also prevent the current from reversing during the commutation process when the current is small, thereby affecting the normal operation of the power converter.

[0078] Optionally, in the first embodiment, the controller 02 can also be used to: when the second switch tube T2 is turned on and the fifth switch tube T5 is periodically turned on and off, and when the fifth switch tube T5 is short-circuited, control the second switch tube T2 to remain turned on, and control the first switch tube T1, the third switch tube T3, the fourth switch tube T4 and the sixth switch tube T6 to remain turned off.

[0079] Optionally, in the second embodiment, the controller 02 can also be used to: when the second switch tube T2 is turned on and the fifth switch tube T5 is periodically turned on and off, and when the fifth switch tube T5 is short-circuited, control the second switch tube T2 to turn off, control the first switch tube T1 and the fourth switch tube T4 to remain turned off, and control the sixth switch tube T6 and the third switch tube T3 to turn on.

[0080] That is, in the working mode where the power converter works in the positive half cycle and the current flows in, the controller 02 can also detect whether the clamp switch tube in the upper half bridge arm is short-circuited. And once the clamp switch tube is short-circuited, the controller 02 can achieve short-circuit protection by controlling the on and off of other switches. For example:

[0081] The controller 02 can control the on and off of other switch tubes according to the first embodiment described above. In this way, the current can flow through the internal switch tube and the clamp switch tube (i.e., T2 and T5) in the upper half bridge arm in sequence, preventing the short circuit fault from spreading inside the power converter. Alternatively, the controller 02 can control the on and off of each other switch tube according to the second embodiment described above. In this way, the current can be introduced into the lower half bridge arm and flow through the internal switch tube and the clamp switch tube (i.e., T3 and T6) in the lower half bridge arm in sequence, also preventing the short circuit fault from spreading.

[0082] Of course, it is not limited to the above-mentioned method. For example, the controller 02 can also control all the switch tubes in the upper half bridge arm where the short circuit occurs to be turned off, that is, while controlling the external switch tube (i.e., T1) in the upper half bridge arm to remain turned off, the internal switch tube (i.e., T2) in the upper half bridge arm is also controlled to be turned off, so that the current flows through the diode and the clamp switch tube (i.e., D2 and T5) of the internal switch tube in the upper half bridge arm in sequence. Alternatively, the internal switch tube (i.e., T2) in the upper half bridge arm can also be controlled to remain turned on, and the internal switch tube and the clamp switch tube (i.e., T3 and T6) in the lower half bridge arm can be controlled to be turned on at the same time, so that the current flows through the internal switch tube and the clamp switch tube (i.e., T2 and T3) in the upper half bridge arm in sequence, and flows through the internal switch tube and the clamp switch tube (i.e., T3 and T6) in the lower half bridge arm in sequence. This can prevent the short circuit fault from spreading.

[0083] Optionally, the controller 02 can also determine that the fifth switch tube T5 is short-circuited when the speed of change of the current flowing into the bridge arm is greater than the speed threshold or the current is greater than the current threshold. The speed threshold and the current threshold here can both be the maximum values ​​determined when the fifth switch tube T5 is not short-circuited, which can be pre-set in the controller 02 and can also be flexibly adjusted.

[0084] Optionally, in Figure 4 Based on the structure, the controller 02 can also be used to: when the fifth switch tube T5 included in any bridge arm 01 among the multiple bridge arms 01 is short-circuited, control all the switch tubes included in other bridge arms 01 except any bridge arm 01 to be turned off. In this way, the short circuit fault can be prevented from spreading to other bridge arms, thereby achieving safe wave blocking.

[0085] In summary, the embodiment of the present application provides a power converter. Since the controller can control the first switch tube to be normally off when the second switch tube in the bridge arm is turned on and the fifth switch tube is periodically turned on and off, and since the first switch tube is connected to the positive DC bus, and the fifth switch tube is connected between the bus midpoint and the series connection point of the first switch tube and the second switch tube, it is possible to prevent the positive DC bus from being short-circuited with the bus midpoint when the fifth switch tube is short-circuited, thereby preventing a short circuit.

[0086] It can be understood that the above embodiments are all based on the upper half bridge arm included in the power converter, the power converter works in the positive half cycle and the current flows in or out of the working mode as an example of protection control mode. Since the lower half bridge arm has the same structure as the upper half bridge arm, it can be known that for the lower half bridge arm, the power converter works in the negative half cycle and the current flows in or out of the working mode, the controller 02 can perform the same control to prevent the negative DC bus BUS- from being short-circuited due to the short circuit of the switch tube, and to prevent the spread of the short circuit fault when the switch tube is short-circuited, which will not be repeated here.

[0087] Optionally, the power converter may further include a current detection circuit, so that the controller 02 can detect the current through the current detection circuit. The current detection circuit may be a Hall element. The controller 02 may be a microcontroller unit (MCU).

[0088] For example, take the power converter working in the positive half cycle as an example, that is, for the upper half bridge arm, Figure 6 A schematic diagram of the working process of a power converter is shown in FIG. Figure 6As shown, when the power converter operates in the positive half cycle, the controller 02 can first determine whether the current flows out of the bridge arm or into the bridge arm. If the current does not flow out of the bridge arm, the controller 02 can control the clamp switch tube T5 in the upper half bridge arm to switch normally (that is, periodically on and off), and at the same time control the external switch tube T1 in the upper half bridge arm to be normally closed. If the current flows out of the bridge arm, the controller 02 can further determine whether the absolute value |i| of the current i is greater than the first current threshold ith. If |i|>ith, the controller 02 can control the external switch tube T1 in the upper half bridge arm to switch normally, and control the clamp switch tube T5 in the upper half bridge arm to be normally closed. Otherwise, the controller 02 can control the external switch tube T1 and the clamp switch tube T5 in the upper half bridge arm to complement each other. In this way, when the current is large, the clamp switch tube T5 can be controlled to be normally closed to avoid short circuit of the positive DC bus BUS+, and prevent current reversal, so as to avoid affecting the normal operation of the power converter. Afterwards, it is possible to continue to detect whether the external switch tube T1 in the upper half bridge arm is short-circuited, and when the external switch tube T1 is short-circuited, the Figure 7 The timing shown is to avoid the spread of short-circuit faults, achieve short-circuit protection, and ensure safe wave blocking. Figure 6 In the above table, Y indicates that the judgment result is yes, and N indicates that the judgment result is no.

[0089] refer to Figure 7 , at this time the current can be a positive value + greater than 0. Flg can be a short circuit flag, which is used to mark whether the external switch tube T1 in the upper half bridge arm is short-circuited.

[0090] When the external switch tube T1 in the upper half bridge arm is not short-circuited, the potential of Flg can be a low potential. At this time, the controller 02 can normally send waves to the external switch tube T1 in the upper half bridge arm, that is, normally output PWM signals, so that the external switch tube T1 is periodically turned on and off, and can output a signal of effective potential to the internal switch tube T2 in the upper half bridge arm, so that the internal switch tube T2 is turned on, and can also output a signal of invalid potential to the clamp switch tube T5 in the upper half bridge arm, so that the clamp switch tube T5 is always closed. In this way, the positive DC bus BUS+ can be prevented from being short-circuited due to the short circuit of the external switch tube T1. In this process, the controller 02 can output invalid potential signals to the external switch tube T4, the internal switch tube T3 and the clamp switch tube T6 in the lower half bridge arm, so that each switch tube in the lower half bridge arm is turned off.

[0091] When the external switch tube T1 in the upper half bridge arm is short-circuited, the short-circuit flag Flg can be set to a high potential. At this time, the controller 02 can output a valid potential signal to the clamp switch tube T6 in the lower half bridge arm after a period of time ΔT1, so that the clamp switch tube T6 is turned on, and then after a period of time ΔT2, it outputs an invalid potential signal to the internal switch tube T2 in the upper half bridge arm, so that the internal switch tube T2 is turned off, and then after a period of time ΔT3, it outputs a valid potential signal to the internal switch tube T3 in the lower half bridge arm, so that the internal switch tube T3 is turned on. In this way, the current can be commutated to the lower half bridge arm, and flow out through the clamp switch tube T6 and the internal switch tube T3 in the lower half bridge arm in turn, avoiding the spread of the short circuit fault.

[0092] For example, Figure 8 Another timing diagram is also shown by taking the working mode where the power converter works in the positive half cycle and the current flows into the bridge arm as an example. Figure 8 , at this time the current can be a negative value - less than 0. And Flg is also a short circuit flag, which is used to mark whether the clamp switch tube T5 in the upper half bridge arm is short-circuited.

[0093] When the clamp switch tube T5 in the upper half bridge arm is not short-circuited, the potential of Flg can be a low potential. At this time, the controller 02 can normally send waves to the clamp switch tube T5 in the upper half bridge arm, so that the clamp switch tube T5 is periodically turned on and off, and can output a signal of effective potential to the internal switch tube T2 in the upper half bridge arm, so that the internal switch tube T2 is turned on, and can also output a signal of invalid potential to the external switch tube T1 in the upper half bridge arm, so that the external switch tube T1 is always off. In this way, the positive DC bus BUS+ can be prevented from being short-circuited due to the short circuit of the clamp switch tube T5. In this process, the controller 02 can output invalid potential signals to the external switch tube T4, the internal switch tube T3 and the clamp switch tube T6 in the lower half bridge arm, so that each switch tube in the lower half bridge arm is turned off.

[0094] When the clamp switch tube T5 in the upper half bridge arm is short-circuited, the short-circuit flag Flg can be set to a high potential. At this time, the controller 02 can continue to output a valid potential signal to the internal switch tube T2 in the upper half bridge arm, so that the internal switch tube T2 remains turned on, and can output an invalid potential signal to the external switch tube T1 in the upper half bridge arm, and the external switch tube T4, the internal switch tube T3 and the clamp switch tube T6 in the lower half bridge arm, so that the external switch tube T1 in the upper half bridge arm and each switch tube in the lower half bridge arm remain turned off. In this way, the current can flow through the internal switch tube T2 and the clamp switch tube T3 in the upper half bridge arm in sequence, avoiding the spread of the short circuit fault.

[0095] In addition, Figure 4 Based on the structure, combined Figure 7and combination Figure 8 When a switch short circuit occurs in any bridge arm, the controller 02 can also stop outputting PWM signals to other bridge arms, that is, blocking the waves for other bridge arms to prevent the short circuit fault from spreading to other bridge arms and achieve safe blocking.

[0096] Optionally, Figure 7 and Figure 8 In the figure, the effective potential is a high potential relative to the invalid potential, and a high potential is used to indicate the blocking of other bridge arms.

[0097] Understandably, Figure 7 and Figure 8 All of them are schematic illustrations of a working sequence. That is, as mentioned above, the controller 02 can also implement short-circuit protection through other control methods, and the corresponding sequence is no longer shown here.

[0098] 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.

[0099] The above is only an optional implementation of the present application, but the driving 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 driving scope of the present application. Therefore, the driving scope of the present application should be based on the driving scope of the claims.

Claims

1. A power converter, characterized in that: The power converter comprises: a bridge arm, a positive DC bus, a negative DC bus, a positive DC bus capacitor, a negative DC bus capacitor and a controller, wherein: The bridge arm is used to convert direct current of a photovoltaic module or an energy storage battery into alternating current, and the bridge arm includes a first switch tube, a second switch tube, a third switch tube, a fourth switch tube, a fifth switch tube and a sixth switch tube, wherein the first switch tube, the second switch tube, the third switch tube and the fourth switch tube are sequentially connected in series between the positive DC bus and the negative DC bus, the fifth switch tube is connected between the series connection point of the first switch tube and the second switch tube and the sixth switch tube, and the sixth switch tube is connected between the series connection point of the third switch tube and the fourth switch tube and the fifth switch tube; the positive DC bus capacitor and the negative DC bus capacitor are connected in series between the positive DC bus and the negative DC bus, the series connection point of the positive DC bus capacitor and the negative DC bus capacitor is the bus midpoint, and the bus midpoint is connected to the series connection point of the fifth switch tube and the sixth switch tube; The controller is used to control the fifth switch tube to remain turned off when the second switch tube is turned on and the first switch tube is periodically turned on and off.

2. The power converter according to claim 1, characterized in that: The controller is used to control the fifth switch tube to remain turned off when the second switch tube is turned on and the first switch tube is periodically turned on and off, and when the current flowing out of the bridge arm through the first switch tube and the second switch tube is greater than a first current threshold, wherein the first current threshold is 5% to 10% of the rated current flowing out of the bridge arm.

3. The power converter according to claim 1 or 2, characterized in that: The controller is also used to: when the second switch tube is turned on and the first switch tube is periodically turned on and off, and when the first switch tube is short-circuited, first control the sixth switch tube to be turned on, then control the second switch tube to be turned off, and control the third switch tube, the fourth switch tube and the fifth switch tube to remain turned off.

4. The power converter according to claim 1 or 2, characterized in that: The controller is also used to: when the second switch tube is turned on and the first switch tube is periodically turned on and off, and when the first switch tube is short-circuited, first control the sixth switch tube to be turned on, then control the second switch tube to be turned off, then control the third switch tube to be turned on, and control the fourth switch tube and the fifth switch tube to remain turned off.

5. The power converter according to claim 3 or 4, characterized in that: The number of the bridge arms is multiple, and the multiple bridge arms are connected in parallel; The controller is also used for controlling all the switch tubes included in the other bridge arms except any one bridge arm to be turned off when the first switch tube included in any one bridge arm among the multiple bridge arms is short-circuited.

6. A power converter, characterized in that: The power converter comprises: a bridge arm, a positive DC bus, a negative DC bus, a positive DC bus capacitor, a negative DC bus capacitor and a controller, wherein: The bridge arm is used to convert direct current of a photovoltaic module or an energy storage battery into alternating current, and the bridge arm includes a first switch tube, a second switch tube, a third switch tube, a fourth switch tube, a fifth switch tube and a sixth switch tube, wherein the first switch tube, the second switch tube, the third switch tube and the fourth switch tube are sequentially connected in series between the positive DC bus and the negative DC bus, the fifth switch tube is connected between the series connection point of the first switch tube and the second switch tube and the sixth switch tube, and the sixth switch tube is connected between the series connection point of the third switch tube and the fourth switch tube and the fifth switch tube; the positive DC bus capacitor and the negative DC bus capacitor are connected in series between the positive DC bus and the negative DC bus, the series connection point of the positive DC bus capacitor and the negative DC bus capacitor is the bus midpoint, and the bus midpoint is connected to the series connection point of the fifth switch tube and the sixth switch tube; The controller is used to control the first switch tube to remain turned off during the process in which the second switch tube is turned on and the fifth switch tube is periodically turned on and off.

7. The power converter according to claim 6, characterized in that: The controller is used to: control the first switch tube to remain turned off when the second switch tube is turned on and the fifth switch tube is periodically turned on and off, and when the current flowing into the bridge arm through the second switch tube and the fifth switch tube is greater than a second current threshold, wherein the second current threshold is 5% to 10% of the rated current flowing into the bridge arm.

8. The power converter according to claim 6 or 7, characterized in that: The controller is also used to: when the second switch tube is turned on and the fifth switch tube is periodically turned on and off, and when the fifth switch tube is short-circuited, control the second switch tube to remain turned on, and control the first switch tube, the third switch tube, the fourth switch tube and the sixth switch tube to remain turned off.

9. The power converter according to claim 6 or 7, characterized in that: The controller is also used to: when the second switch tube is turned on and the fifth switch tube is periodically turned on and off, and when the fifth switch tube is short-circuited, control the second switch tube to turn off, control the first switch tube and the fourth switch tube to remain turned off, and control the sixth switch tube and the third switch tube to turn on.

10. The power converter according to claim 8 or 9, characterized in that: The number of the bridge arms is multiple, and the multiple bridge arms are connected in parallel; The controller is also used for: when the fifth switch tube included in any one of the multiple bridge arms is short-circuited, controlling all the switch tubes included in other bridge arms except the any one bridge arm to be turned off.

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