Control method of power conversion circuit and inverter

Abstract

The invention provides a control method of a power conversion circuit and an inverter. The power conversion circuit comprises a driver, a bootstrap unit, an upper switch tube and a lower switch tube. The method comprises the steps of obtaining a target duty ratio of on-off of an upper switching tube or a lower switching tube according to the maximum loss of a bootstrap diode and the voltage of the bootstrap diode; half cycles are obtained according to the target duty ratio and the voltage of the bootstrap capacitor, and the two half cycles form a work cycle; and controlling the driver to drive the upper switch tube to be switched on at the target duty ratio in the first half period of each work period and to be switched off at the second half period of each work period, and driving the lower switch tube to be switched off at the first half period of each work period and to be switched on at the target duty ratio in the second half period of each work period, so as to charge the bootstrap capacitor. Therefore, the problem that the bootstrap diode is damaged due to overlarge impact current can be reduced.

Description

Technical Field

[0001] The present application relates to the field of power electronics technology, and in particular to a control method and an inverter for a power conversion circuit. Background Art

[0002] At present, in the half-bridge or full-bridge power conversion circuit of the photovoltaic inverter, a bootstrap circuit is usually used to power the high-side drive. Since the initial voltage of the bootstrap capacitor in the bootstrap circuit is 0V (volt), during the initial operation of the bootstrap circuit, the impact current flowing through the bootstrap circuit will be too large, which is easy to damage the bootstrap diode in the bootstrap circuit and affect the service life of the bootstrap diode.

[0003] In the related art, in order to reduce the problem of excessive impact current damaging the bootstrap diode, a method of connecting a current limiting resistor in series in the bootstrap circuit or reducing the capacitance of the bootstrap capacitor is usually adopted. However, although the method of connecting a current limiting resistor in series has a certain limiting effect on the peak value of the impact current, it is still difficult to reduce the energy of the impact current when it damages the bootstrap diode. Although the method of reducing the capacitance of the bootstrap capacitor can reduce the impact current, it is easily limited by the working environment of the bootstrap capacitor. For example, when the working voltage of the bootstrap capacitor is less than the high-side drive voltage, it will cause the high-side drive to fail to work normally. Summary of the invention

[0004] In view of the above, it is necessary to provide a control method of a power conversion circuit and an inverter, in which the problem of excessive impact current damaging the bootstrap diode can be reduced when the bootstrap unit is working.

[0005] The present application provides a control method for a power conversion circuit, wherein the power conversion circuit includes a driver, a bootstrap unit, an upper switch tube and a lower switch tube, wherein the upper switch tube and the lower switch tube are connected in series and are both connected to the driver, wherein the power supply end of the driver is connected to the connection midpoint between the upper switch tube and the lower switch tube through the bootstrap unit, and the bootstrap unit includes a bootstrap capacitor and a bootstrap diode connected in series; the control method includes: obtaining a target duty cycle of turning on and off the upper switch tube or the lower switch tube according to the maximum loss of the bootstrap diode and the voltage of the bootstrap diode; obtaining a half cycle according to the target duty cycle and the voltage of the bootstrap capacitor, wherein two half cycles constitute a working cycle; controlling the driver to drive the upper switch tube to turn on at the target duty cycle in the first half cycle of each working cycle and to turn off in the second half cycle of each working cycle, and to drive the lower switch tube to turn off in the first half cycle of each working cycle and to turn on at the target duty cycle in the second cycle of each working cycle, so as to charge the bootstrap capacitor.

[0006] In some embodiments, a target duty cycle of turning on and off the upper switch tube or the lower switch tube is obtained according to the maximum loss of the bootstrap diode and the voltage of the bootstrap diode, including: obtaining the correspondence between the target duty cycle and the maximum loss of the bootstrap diode based on the current of the bootstrap capacitor and the tube voltage drop voltage of the bootstrap diode; obtaining the current of the bootstrap capacitor based on the voltage of the zero-state response of the bootstrap capacitor when charging; and obtaining the target duty cycle based on the correspondence and the current of the bootstrap capacitor.

[0007] In some embodiments, a half cycle is obtained according to a target duty cycle and a voltage of a bootstrap capacitor, and two half cycles constitute a working cycle, including: obtaining the voltage of the bootstrap capacitor based on a charging voltage of the bootstrap unit and a charging expectation coefficient.

[0008] In some embodiments, a current limiting unit is set between the bootstrap diode and the bootstrap capacitor; the target duty cycle of the upper switch tube or the lower switch tube is obtained according to the maximum loss of the bootstrap diode and the voltage of the bootstrap diode, and it also includes: obtaining the target duty cycle according to the on-off frequency of the upper switch tube or the lower switch tube and the resistance value of the current limiting unit.

[0009] In some embodiments, a half cycle is obtained according to the target duty cycle and the voltage of the bootstrap capacitor, and two half cycles constitute a working cycle, and the method further includes: gradually increasing the target duty cycle to obtain a plurality of different working cycles.

[0010] In some embodiments, the power conversion circuit includes a first driver, a second driver, a first bootstrap unit, a second bootstrap unit, a first upper switch tube, a second upper switch tube, a first lower switch tube and a second lower switch tube; the first upper switch tube and the first lower switch tube are connected in series and are both connected to the first driver, the power supply end of the first driver is connected to the connection midpoint between the first upper switch tube and the first lower switch tube through the first bootstrap unit, and the first bootstrap unit includes a first bootstrap capacitor and a first bootstrap diode connected in series; the second upper switch tube and the second lower switch tube are connected in series and are both connected to the second driver, the power supply end of the second driver is connected to the connection midpoint between the second upper switch tube and the second lower switch tube through the second bootstrap unit, and the second bootstrap unit includes a second bootstrap capacitor and a second bootstrap diode connected in series; the first upper switch tube and the second upper switch tube are connected in series. The control method of the power conversion circuit also includes: in a first time interval, controlling the first driver to drive the first upper switch tube to be turned on at a target duty cycle in the first half of each working cycle and turned off in the second half of each working cycle, driving the first lower switch tube to be turned off in the first half of each working cycle and turned on at the target duty cycle in the latter period of each working cycle, so that the first bootstrap capacitor is charged; in a second time interval, controlling the second driver to drive the second upper switch tube to be turned on at a target duty cycle in the first half of each working cycle and turned off in the second half of each working cycle, driving the second lower switch tube to be turned off in the first half of each working cycle and turned on at the target duty cycle in the latter period of each working cycle, so that the second bootstrap capacitor is charged; the second time interval is different from and continuous with the first time interval.

[0011] In some embodiments, the control method of the power conversion circuit further includes: controlling the first driver to stop outputting the driving signal during the second time interval; and controlling the second driver to stop outputting the driving signal during the first time interval.

[0012] The present application also provides an inverter, including: a power conversion circuit, the power conversion circuit includes a driver, a bootstrap unit, an upper switch tube and a lower switch tube, the upper switch tube and the lower switch tube are connected in series and are both connected to the driver, the power supply end of the driver is connected to the connection midpoint between the upper switch tube and the lower switch tube through the bootstrap unit, the bootstrap unit includes a bootstrap capacitor and a bootstrap diode connected in series; a controller, configured to: obtain a target duty cycle for turning on and off the upper switch tube or the lower switch tube according to the maximum loss of the bootstrap diode and the voltage of the bootstrap diode; obtain a half cycle according to the target duty cycle and the voltage of the bootstrap capacitor, wherein two half cycles constitute a working cycle; control the driver to drive the upper switch tube to turn on at the target duty cycle in the first half cycle of each working cycle and turn off in the second half cycle of each working cycle, and drive the lower switch tube to turn off in the first half cycle of each working cycle and turn on at the target duty cycle in the second cycle of each working cycle, so as to charge the bootstrap capacitor.

[0013] In some embodiments, the controller is further configured to: when a half cycle is obtained according to the target duty cycle and the voltage of the bootstrap capacitor, gradually increase the target duty cycle to obtain a plurality of different working cycles.

[0014] In some embodiments, the power conversion circuit includes a first driver, a second driver, a first bootstrap unit, a second bootstrap unit, a first upper switch tube, a second upper switch tube, a first lower switch tube and a second lower switch tube; the first upper switch tube and the first lower switch tube are connected in series and are both connected to the first driver, the power supply end of the first driver is connected to the connection midpoint between the first upper switch tube and the first lower switch tube through the first bootstrap unit, and the first bootstrap unit includes a first bootstrap capacitor and a first bootstrap diode connected in series; the second upper switch tube and the second lower switch tube are connected in series and are both connected to the second driver, the power supply end of the second driver is connected to the connection midpoint between the second upper switch tube and the second lower switch tube through the second bootstrap unit, and the second bootstrap unit includes a second bootstrap capacitor and a second bootstrap diode connected in series; the first upper switch tube and the first Two upper switch tubes are connected; the controller is also configured to: in a first time interval, control the first driver to drive the first upper switch tube to be turned on at a target duty cycle in the first half of each working cycle and turned off in the second half of each working cycle, and drive the first lower switch tube to be turned off in the first half of each working cycle and turned on at the target duty cycle in the latter period of each working cycle, so that the first bootstrap capacitor is charged; in a second time interval, control the second driver to drive the second upper switch tube to be turned on at a target duty cycle in the first half of each working cycle and turned off in the second half of each working cycle, and drive the second lower switch tube to be turned off in the first half of each working cycle and turned on at the target duty cycle in the latter period of each working cycle, so that the second bootstrap capacitor is charged; the second time interval is continuous and different from the first time interval.

[0015] Compared with the prior art, this application has at least the following advantages: 1. In the present application, the on and off of the upper switch tube or the lower switch tube is controlled by obtaining a target duty cycle related to the maximum loss of the bootstrap diode in the bootstrap unit, so that the bootstrap capacitor of the bootstrap unit can be charged intermittently, thereby reducing the impact current generated when the bootstrap capacitor is charged, and at the same time dispersing the energy of the impact current, which can reduce the problem of excessive impact current damaging the bootstrap diode.

[0016] 2. Different working cycles are obtained by gradually increasing the target duty cycle. When the on and off of the upper switch tube or the lower switch tube is controlled in different working cycles, the charging time of the bootstrap capacitor is gradually reduced due to the gradual increase in the target duty cycle. The charging efficiency of the bootstrap capacitor can be improved while reducing the damage to the bootstrap diode caused by excessive impact current.

[0017] 3. By controlling the first driver to stop outputting the driving signal in the second time interval; controlling the second driver to stop outputting the driving signal in the first time interval, the charging of the first bootstrap capacitor and the second bootstrap capacitor can be alternately controlled in the full-bridge power conversion circuit, thereby reducing the switch tube stress problem caused by narrow pulse width hard switching in the full-bridge power conversion circuit. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a characteristic curve diagram of current and voltage in the charging process of a bootstrap capacitor in a bootstrap circuit in the prior art.

[0019] Figure 2 The present invention is a schematic diagram of the thermal effect of a bootstrap diode in a bootstrap circuit in the prior art during the charging process of a bootstrap capacitor.

[0020] Figure 3 It is a schematic diagram of the structure and one working state of a half-bridge power conversion circuit according to an embodiment of the present application.

[0021] Figure 4 It is a schematic diagram of the structure of a half-bridge power conversion circuit and another working state of an embodiment of the present application.

[0022] Figure 5 It is a flow chart of a control method of a half-bridge power conversion circuit according to an embodiment of the present application.

[0023] Figure 6 It is a schematic diagram of a target duty cycle obtained in the control method of the power conversion circuit in an embodiment of the present application.

[0024] Figure 7 This application Figure 6 A characteristic curve diagram of current and voltage during the charging process of the bootstrap capacitor in the control method of the power conversion circuit of the corresponding embodiment.

[0025] Figure 8 This application Figure 6 Schematic diagram of thermal effect of bootstrap diode during charging process of bootstrap capacitor in control method of power conversion circuit of corresponding embodiment.

[0026] Fig. 9 It is a schematic diagram of another target duty cycle obtained in the control method of the power conversion circuit in an embodiment of the present application.

[0027] Fig.10 It is a schematic diagram of the structure of a full-bridge power conversion circuit according to an embodiment of the present application.

[0028] Fig.11 It is a flow chart of a control method of a full-bridge power conversion circuit according to an embodiment of the present application.

[0029] Fig.12It is a schematic diagram of another target duty cycle obtained in the control method of the power conversion circuit in the embodiment of the present application.

[0030] Fig.13 It is a schematic diagram of the structure of the inverter according to an embodiment of the present application.

[0031] Description of main component symbols: 100. Inverter; 1. Power conversion circuit; 11. Half-bridge power conversion circuit; 111. Bootstrap unit; 12. Full-bridge power conversion circuit; 121. First bootstrap unit; 122. Second bootstrap unit; 2. Controller; 200. Load.

[0032] The following specific implementation methods will further illustrate the present application in conjunction with the above-mentioned drawings. DETAILED DESCRIPTION

[0033] In the description of the embodiments of the present application, words such as "exemplary", "or", "for example" and the like are used to indicate examples, illustrations or descriptions. Any embodiment or design described as "exemplary" or "for example" in the embodiments of the present application should not be interpreted as being more preferred or more advantageous than other embodiments or designs. Specifically, the use of words such as "exemplary", "or", "for example" and the like is intended to present related concepts in a concrete manner.

[0034] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by technicians in the technical field in this application. The terms used in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application. It should be understood that, unless otherwise specified in this application, " / " means or. For example, A / B can represent A or B. "And / or" in this application is only a description of the association relationship of associated objects, indicating that three relationships can exist. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. "At least one" means one or more. "Multiple" means two or more than two. For example, at least one of a, b or c can represent: a, b, c, a and b, a and c, b and c, a, b and c seven situations.

[0035] It should also be noted that the terms "first" and "second" in the specification, claims and drawings of the present application are used to distinguish similar objects rather than to describe a specific order or sequence.

[0036] In a half-bridge or full-bridge power conversion circuit, a bootstrap circuit is usually used to power the high-side driver in order to reduce costs. The bootstrap circuit is usually composed of a bootstrap capacitor, a bootstrap diode, and a bypass circuit, wherein the bootstrap capacitor and the bootstrap diode are connected in series. Figure 1This is a characteristic curve of current and voltage during the charging process of the bootstrap capacitor in the bootstrap circuit in the prior art. Please refer to Figure 1 As shown, since the initial voltage of the bootstrap capacitor is 0V (volts), during the initial operation of the bootstrap circuit, the voltage of the bootstrap capacitor ( U ) is charged from 0V (volts) to the voltage after ts, and the charging is completed. The surge current flowing through the bootstrap circuit will be too large, that is, the charging current of the bootstrap capacitor ( i ) exceeds the maximum current that the bootstrap diode can withstand ( Imax ), which can easily damage the bootstrap diode in the bootstrap circuit and thus shorten the service life of the diode.

[0037] At present, there are generally two ways to connect the bootstrap diode, one is to place it outside the IC (integrated circuit), and the other is to integrate it inside the IC. When the bootstrap diode is placed outside the IC, due to various factors such as space size, the bootstrap diode has limited current resistance and the impact current is not easy to be too large. When the bootstrap diode is placed inside the IC, due to the limitation of the packaging process, the bootstrap diode has a small impact current resistance capacity flowing through the bootstrap diode circuit.

[0038] Figure 2 This is a schematic diagram of the thermal effect of the bootstrap diode in the bootstrap circuit in the prior art during the charging process of the bootstrap capacitor. Figure 2 As shown in the figure, during the initial operation of the bootstrap circuit, the voltage of the bootstrap capacitor is continuously charged from 0V (volts) to the voltage after the ts moment. During this continuous process, the bootstrap diode is in the transient heating zone, which may cause the bootstrap diode to continue to heat up, and then cause the bootstrap diode to overheat. If the impact current is too large, it will cause the bootstrap diode to have excessive transient losses, and then cause the diode to fail thermally. At the same time, the bonding wire inside the IC will also be directly blown due to the excessive impact current energy. In another case, although the impact current energy is too large, it will not cause the bonding wire to be directly blown, but it will cause the junction temperature to fluctuate violently. If this situation continues for a long time, it will also cause the solder layer to fatigue and reduce the service life of the IC.

[0039] Therefore, in the related art, in order to reduce the problem of excessive impact current damaging the bootstrap diode, a method of connecting a current limiting resistor in series in the bootstrap circuit or reducing the capacitance of the bootstrap capacitor is usually adopted. However, although the method of connecting a current limiting resistor in series has a certain limiting effect on the peak value of the impact current, it is still difficult to reduce the energy when the impact current damages the bootstrap diode. And the size of the current limiting resistor is easily limited by the voltage drop, so the current limiting resistor in series is not a good method. Although the method of reducing the capacitance of the bootstrap capacitor can also reduce the impact current, it is easily limited by the working environment of the bootstrap capacitor, for example, it is limited by the high-side drive voltage wave. If the working voltage of the bootstrap capacitor is less than the high-side drive voltage, it will cause the high-side drive to not work normally. Therefore, reducing the capacitance of the bootstrap capacitor is not a good method to solve the problem of excessive impact current.

[0040] To this end, the present application provides a control method for a power conversion circuit and an inverter, wherein when a bootstrap unit is working, the problem of excessive surge current damaging the bootstrap diode can be reduced.

[0041] The control method of the power conversion circuit and the inverter provided by the present application are described in detail below in combination with Embodiment 1 and Embodiment 2.

[0042] Embodiment 1: Figure 3 It is a schematic diagram of the structure and one working state of the half-bridge power conversion circuit 11 of the first embodiment of the present application; Figure 4 It is a schematic diagram of the structure and another working state of the half-bridge power conversion circuit 11 according to an embodiment of the present application.

[0043] The control method of the power conversion circuit of the present application can be applied to a half-bridge power conversion circuit 11, and the half-bridge power conversion circuit 11 can be used in an inverter to perform current or voltage power conversion. Figure 3 or Figure 4 , the half-bridge power conversion circuit 11 may include a driver U0, a bootstrap unit 111, an upper switch SH and a lower switch tube SL. The upper switch tube SH and the lower switch tube SL may be connected in series and both connected to the driver U0. The first power supply terminal VCC1 of the driver U0 is connected to the connection midpoint between the upper switch tube SH and the lower switch tube SL through the bootstrap unit 111. The bootstrap unit 111 includes a bootstrap capacitor CB and a bootstrap diode DB connected in series. It should be noted that the half-bridge power conversion circuit 11 also includes at least other components or units such as capacitors, inductors or resistors for constituting a complete power conversion circuit. The present application aims to reduce the problem of overcurrent damage to the bootstrap diode by improving the power conversion circuit control method. Therefore, other components or units for constituting a complete power conversion circuit are not described in detail here.

[0044] In some embodiments, the upper switch tube SH can be connected to the high voltage bus HV, and the bootstrap unit 111 can discharge to the high voltage bus HV through the upper switch tube SH after bootstrapping. Therefore, the power conversion of the power conversion circuit can be controlled by controlling the upper switch tube SH.

[0045] In some embodiments, the upper switch tube SH and the lower switch tube SL may be MOS tubes, namely MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor, MOSFET) tubes, the full name of which is Metal-Oxide Semiconductor Field-Effect Transistor, or MOSFET for short. Accordingly, the driver U0 may include a gate driver. In other embodiments, the upper switch tube SH and the lower switch tube SL may also be other types of switch tubes, such as polysilicon tubes, back cathode field effect transistors (Insulate-Gate Bipolar Transistor, IGBT) and bipolar junction transistors (Bipolar junction transistor, BJT), etc.; the driver U0 may also be other types of drivers, such as a microcontroller with the same or similar functions as the driver U0.

[0046] In the half-bridge power conversion circuit 11, the power supply Vcc is connected to the first end of the bootstrap capacitor CB through the bootstrap diode DB, the second end of the bootstrap capacitor CB is connected to the connection midpoint of the source of the upper switch tube SH and the drain of the lower switch tube SL, that is, the source of the upper switch tube SH is connected to the drain of the lower switch tube SL, and the second end of the bootstrap capacitor CB is connected to the source of the upper switch tube SH or the drain of the lower switch tube SL. The first power supply terminal VCC1 of the driver U0 is connected to the first end of the bootstrap capacitor CB, the first driving terminal Vo1 of the driver U0 is connected to the gate of the upper switch tube SH, the second driving terminal Vo of the driver U0 is connected to the gate of the lower switch tube SL, the first ground terminal GND1 of the driver U0 is connected to the second end of the bootstrap capacitor CB, the second ground terminal GND of the driver U0 is connected to the source of the lower switch tube SL and is grounded together, the high configuration terminal HI and the low level terminal LI of the driver U0 are connected to the controller of the power conversion circuit, and the second power supply terminal VCC of the driver U0 is connected to the power supply Vcc.

[0047] In some embodiments, the power source Vcc may be an auxiliary power source for the inverter.

[0048] In some embodiments, the bootstrap unit 111 may further include a bypass capacitor Cvcc, the auxiliary power supply and the bootstrap diode DB may be connected to a first end of the bypass capacitor Cvcc, and a second end of the bypass capacitor Cvcc is grounded. Thus, the auxiliary power supply may power the bootstrap unit 111 through the bypass capacitor Cvcc.

[0049] In some embodiments, the bypass capacitor Cvcc may include a storage capacitor and a filter capacitor, which are connected in parallel. Thus, the auxiliary power supply can filter while supplying energy to the bootstrap unit 111 through the bypass capacitor Cvcc, thereby improving the purity of the supplied energy.

[0050] In some embodiments, a current limiting unit may be disposed between the bootstrap diode DB and the bootstrap capacitor CB, and the current limiting unit may include at least one current limiting resistor RB.

[0051] In the embodiments of the present application, Figure 3 As shown by the dotted arrow in the middle, when the lower switch tube SL is turned on, the auxiliary power supply can charge the bootstrap capacitor CB through the bypass capacitor Cvcc via the bootstrap diode DB and the current limiting resistor RB. Figure 4 As shown by the dotted arrow, when the lower switch tube SL of the half-bridge power conversion circuit 11 is turned off and the upper switch tube SH on the high side is turned on, the first ground terminal GND1 of the driver U0 and the connection midpoint between the lower switch tube SL and the upper switch tube SH are pulled to the high-voltage bus HV. In this case, the bootstrap capacitor CB can release the stored electric energy through the upper switch tube SH on the high side to the high-voltage bus HV through the first driving terminal Vo1 and the first ground terminal GND1 of the driver U0.

[0052] Figure 5 It is a flow chart of a control method of a half-bridge power conversion circuit according to the first embodiment of the present application.

[0053] As mentioned above, since the initial voltage of the bootstrap capacitor is 0V (volts), during the initial operation of the bootstrap circuit, the voltage of the bootstrap capacitor is charged from 0V (volts), and the impact current flowing through the bootstrap circuit will be too large. Therefore, a control method for a power conversion circuit is proposed, please refer to Figure 5 , when applied to a half-bridge power conversion circuit, the control method may include: Step S100: obtaining a target duty cycle of turning on and off the upper switch tube or the lower switch tube according to the maximum loss of the bootstrap diode and the voltage of the bootstrap diode.

[0054] The maximum loss of the bootstrap diode refers to the maximum forward power loss of the bootstrap diode. When a forward current flows through the bootstrap diode, a voltage drop of the forward voltage is generated. The power loss caused by the voltage drop of the forward voltage and the forward current is the forward power loss.

[0055] In some embodiments, the target duty cycle is related to the on-off frequency of the upper switch tube or the lower switch tube. Since the upper switch tube or the lower switch tube includes a pulse rise time and a pulse fall time when it is turned on, in some embodiments, the target duty cycle is not less than the pulse width of the upper switch tube or the lower switch tube. In this way, the loss of the pulse driving the upper switch tube or the lower switch tube to turn on can be reduced.

[0056] Since the bootstrap capacitor and the bootstrap diode are in series in the bootstrap unit, the current flowing through the bootstrap diode is the same as the current of the bootstrap capacitor. During the charging process of the bootstrap capacitor, in order to reduce the damage to the bootstrap diode, the loss of the bootstrap diode should not exceed the maximum loss, that is, the loss of the bootstrap diode during the charging process of the bootstrap capacitor should have a certain corresponding relationship with the maximum loss. Therefore, step S100 may also include: obtaining the corresponding relationship between the target duty cycle and the maximum loss of the bootstrap diode based on the current of the bootstrap capacitor and the tube voltage drop of the bootstrap diode. Among them, the tube voltage drop of the bootstrap diode is the voltage drop of the bootstrap diode, the current of the bootstrap capacitor is the charging current of the bootstrap capacitor, and the corresponding relationship between the target duty cycle and the maximum loss of the bootstrap diode can be obtained by formula (1): (1) In formula (1), D is the target duty cycle; i is the charging current of the bootstrap capacitor; P max It is the maximum transient loss within the SOA (Safety Operation Area) of the bootstrap diode, referred to here as the maximum loss; U e is the voltage drop of the bootstrap diode; f It is the on-off frequency of the upper switch tube or the lower switch tube.

[0057] As described above, the target duty cycle is related to the on-off frequency of the upper switch tube or the lower switch tube. In other embodiments, the target duty cycle is also related to the resistance of the current limiting unit. Therefore, step S100 may also include: obtaining the target duty cycle according to the on-off frequency of the upper switch tube or the lower switch tube and the resistance of the current limiting unit. It can be understood that in the power conversion circuit of the inverter, the upper switch tube and the lower switch tube are always turned on alternately, so step S100 may specifically refer to obtaining the target duty cycle according to the on-off frequency of the lower switch tube and the resistance of the current limiting unit.

[0058] In some embodiments, the on-off frequency of the upper switch tube or the lower switch tube is related to the circuit topology of the power conversion circuit. The on-off frequency of the upper switch tube or the lower switch tube can be a preset range value, for example, the on-off frequency of the upper switch tube or the lower switch tube can be set to 80kHz to 120kHz.

[0059] It can be understood that since the initial voltage of the bootstrap capacitor is 0V (volts), the charging voltage of the bootstrap capacitor can be given by the zero-state response. The zero-state response refers to the system response caused by the input signal when the initial condition is zero (the system has no energy at the beginning). Therefore, the current of the bootstrap capacitor required for step S100 can be obtained based on the voltage of the zero-state response when the bootstrap capacitor is charged. The charging voltage of the bootstrap capacitor can be obtained by formula (2): (2) in, V cc is the input voltage of the auxiliary power supply, U is the charging voltage of the bootstrap capacitor, t is the charging time. In formula (2), τ is a time constant used to indicate the response speed of the bootstrap capacitor charging, which is equal to the product of the resistance of the current limiting resistor and the capacitance of the bootstrap capacitor, that is, , R B is the resistance of the current limiting resistor, C B is the capacitance value of the bootstrap capacitor.

[0060] By taking the derivative of equation (2), we can obtain the charging current of the bootstrap capacitor, which can be obtained through equation (3): (3) From the above content, it can be known that the target duty cycle is related to the correspondence between the maximum loss of the bootstrap diode and the current of the bootstrap capacitor. In order to reduce the loss of the bootstrap diode, the target duty cycle should be limited by the correspondence between the maximum loss of the bootstrap diode and the current of the bootstrap capacitor. Therefore, step S100 may also include: obtaining the target duty cycle based on the correspondence between the target duty cycle and the maximum loss of the bootstrap diode and the current of the bootstrap capacitor. Specifically, the correspondence between the target duty cycle and the maximum loss of the bootstrap diode, that is, in equation (1), is combined with the charging current of the bootstrap capacitor, that is, equation (3), and the maximum limit of the target duty cycle is obtained, that is, equation (4): (4) In formula (4), it can be understood that the target duty cycle is positively correlated with the voltage drop of the bootstrap diode and the response speed of the bootstrap capacitor charging, and is negatively correlated with the on-off frequency of the upper switch tube or the lower switch tube and the maximum loss of the bootstrap diode. That is, when the voltage drop of the bootstrap diode is larger, the maximum limit of the target duty cycle is higher, the target duty cycle that can be set is larger, and the response speed of the bootstrap capacitor charging is faster; when the on-off frequency of the upper switch tube or the lower switch tube is higher, the maximum limit of the target duty cycle is lower, and the target duty cycle that can be set is smaller; when the maximum loss of the bootstrap diode is larger, the maximum limit of the target duty cycle is lower, and the target duty cycle that can be set is lower.

[0061] In addition, in the first embodiment of the present application, when the control method is applied to a half-bridge power conversion circuit, it may further include: Step S200: obtaining a half cycle according to the target duty cycle and the voltage of the bootstrap capacitor.

[0062] Two half cycles constitute one working cycle. The bootstrap capacitor is charged by the auxiliary power supply, so the charging voltage value of the bootstrap capacitor can be equal to the input voltage value of the auxiliary power supply.

[0063] In practical applications, when the bootstrap capacitor is charged by the auxiliary power supply, the bootstrap capacitor is not fully charged to a voltage value that is the same as the input voltage value of the auxiliary power supply. For example, the bootstrap capacitor can be charged to a desired charging degree, such as 80%, 90%, 100%, etc., that is, the voltage of the bootstrap capacitor is related to the desired charging degree, and the desired charging degree can be represented by the desired charging coefficient. Therefore, step S200 may also include: obtaining the voltage of the bootstrap capacitor based on the charging voltage of the bootstrap unit and the desired charging coefficient. Among them, the relationship between the voltage of the bootstrap capacitor, the desired charging coefficient and the duration of charging can be represented by formula (5): (5) in, K is the expected voltage coefficient, 0< K <1, for example, the bootstrap capacitor is expected to charge to the input voltage of the auxiliary power supply V cc 90% of K =0.9; t1 is the duration of charging.

[0064] In addition, in the first embodiment of the present application, when the control method is applied to a half-bridge power conversion circuit, it may further include: Step S300: Control the driver to drive the upper switch tube to be turned on at a target duty cycle in the first half of each working cycle and turned off in the second half of each working cycle, and drive the lower switch tube to be turned off in the first half of each working cycle and turned on at a target duty cycle in the second half of each working cycle, so that the bootstrap capacitor is charged.

[0065] In some other embodiments, step S300 may also be: controlling the driver to drive the lower switch tube to turn on at the target duty cycle in the first half of each working cycle and turn off in the second half of each working cycle, driving the upper switch tube to turn off in the first half of each working cycle and turn on at the target duty cycle in the second half of each working cycle, so that the bootstrap capacitor is charged. In other words, the control order of the upper switch tube and the lower switch tube can be switched to each other.

[0066] Figure 6 It is a schematic diagram of a target duty cycle obtained in the control method of the power conversion circuit of the first embodiment of the present application.

[0067] In some embodiments, see Figure 6 As shown, multiple working cycles can form a duration t1 for controlling the charging of the bootstrap capacitor. During the duration t1, a high level pulse forms a working cycle with a target duty cycle D and a low level pulse. In addition, during the duration t1, a high level pulse and a low level pulse can form a working cycle with a target duty cycle D.

[0068] Figure 7 This application Figure 6 The current ( i ),Voltage( U ) characteristic curve diagram; Figure 8 This application Figure 6 Schematic diagram of thermal effect of bootstrap diode during charging process of bootstrap capacitor in control method of power conversion circuit of corresponding embodiment.

[0069] Combination Figure 1 and Figure 7 As shown, during the duration t1, the on-off of the upper switch tube or the lower switch tube is controlled by obtaining a target duty cycle related to the maximum loss of the bootstrap diode in the bootstrap unit, so that the bootstrap capacitor of the bootstrap unit can be intermittently charged (i.e. Figure 7 The voltage of the bootstrap capacitor is shown as U ) increases in a step-shaped manner), thereby reducing the inrush current generated when charging the bootstrap capacitor (i.e. Figure 7 As shown in Figure 2, due to the presence of parasitic inductance in the power conversion circuit, the current of the bootstrap capacitor ( i ) cannot jump from 0 to V cc / R B , so the current flowing through the bootstrap diode is within the maximum current that the bootstrap diode can withstand ( Imax ) range), and at the same time, the energy of the impulse current can be dispersed (i.e. Figure 8As shown in the figure), the problem of excessive impact current damaging the bootstrap diode can be reduced. When the bootstrap diode is integrated into the IC, the situation of excessive impact current damaging the bootstrap diode can be reflected by obtaining the thermal impact parameter on the bonding wire. Specifically, the thermal impact on the bonding wire can be expressed by formula (6): (6) Among them, the bootstrap capacitor charging current can be equivalent to a triangular wave. t is the duration of a single pulse, which can be equal to the target duty cycle divided by the on-off frequency of the following switch tube, that is, t= D / f ; ΔV is the voltage difference between the bootstrap capacitor before and after the half-cycle (i.e. single pulse) operation; i p is the peak value of the triangular wave current when charging the bootstrap capacitor; Δ Q CB is the amount of charge transferred from the bootstrap capacitor before and after the end of the half cycle.

[0070] It can be understood that the thermal shock parameters on the bonding wire are related to the capacitance of the bootstrap capacitor, the voltage difference of the bootstrap capacitor before and after the half-cycle operation, and the peak value of the triangular wave current when the bootstrap capacitor is charged. Therefore, the target duty cycle of the bootstrap capacitor charging can be adjusted to reduce Δ V and i p , which can indirectly reduce the thermal shock on the bonding line.

[0071] In addition, the situation where the bootstrap diode is damaged by excessive impact current can also be reflected by obtaining the transient loss of the bootstrap diode. Specifically, the transient loss of the bootstrap diode can be expressed by formula (7): (7) in, P is the transient loss of the bootstrap diode; T is the working cycle; i is the current flowing through the bootstrap diode, which is equal to the charging current of the bootstrap capacitor. It can be understood that in one working cycle, the loss of the bootstrap diode is related to the current flowing through the bootstrap diode and the voltage drop of the bootstrap diode. Due to the forward conduction characteristic of the bootstrap diode, the voltage drop of the bootstrap diode can be approximately equivalent to a constant voltage drop, so equation (7) can be equivalent to: (8) It can be understood that from equation (8), the transient loss of the bootstrap diode is also related to the capacitance of the bootstrap capacitor and the voltage difference of the bootstrap capacitor before and after the half-cycle operation. Therefore, the voltage difference of the bootstrap capacitor before and after the half-cycle operation can be reduced by adjusting the target duty cycle of the bootstrap capacitor charging, thereby reducing the transient loss of the bootstrap diode.

[0072] Fig. 9 It is a schematic diagram of another target duty cycle obtained in the control method of the power conversion circuit of the first embodiment of the present application.

[0073] In order to reduce the intermittent charging of the bootstrap capacitor of the bootstrap unit by controlling the on / off of the upper switch tube or the lower switch tube through the target duty cycle, the charging time of the bootstrap capacitor may be prolonged. Fig. 9 As shown, in some embodiments, step S200 may further include: gradually increasing the target duty cycle to obtain a plurality of different working cycles. That is, after the bootstrap capacitor is charged with the target duty cycle in one working cycle, the target duty cycle used when charging the bootstrap capacitor in the next working cycle may be greater than the target duty cycle used in the previous working cycle or the previous multiple working cycles.

[0074] When the on and off of the upper switch tube or the lower switch tube is controlled in different working cycles, as the target duty cycle gradually increases, the charging time of the bootstrap capacitor gradually decreases, which can improve the charging efficiency of the bootstrap capacitor while reducing the damage to the bootstrap diode caused by excessive impact current.

[0075] In some embodiments, the target duty cycle can be gradually increased during a charging duration of the bootstrap capacitor to obtain multiple different duty cycles. For example, during a charging duration of the bootstrap capacitor, there can be multiple duty cycles for charging the bootstrap capacitor, in which the bootstrap capacitor uses the smallest target duty cycle in the first duty cycle, and in the next duty cycle, the target duty cycle used when charging the bootstrap capacitor can be larger than the first duty cycle, and the next duty cycle can be larger than the previous one, and so on.

[0076] In some other embodiments, see Fig. 9 , the target duty cycle can be gradually increased in multiple charging durations of the bootstrap capacitor to obtain multiple different working cycles. For example, in multiple charging durations, such as t1, t2, t3, and t4, all target duty cycles D1% used by the bootstrap capacitor in the first charging duration t1 are the same and the smallest, the target duty cycle D2% used when charging the bootstrap capacitor in the next charging duration t2 is the same and can be larger than the first charging duration t1, and the target duty cycle D3% of the next duration t3 is larger than the previous one, and so on.

[0077] Embodiment 2: Fig.10 It is a structural diagram of the full-bridge power conversion circuit 12 of the second embodiment of the present application.

[0078] The control method of the power conversion circuit of the present application can also be applied to the full-bridge power conversion circuit 12. Fig.10The full-bridge power conversion circuit 12 includes a first driver U1, a second driver U2, a first bootstrap unit 121, a second bootstrap unit 122, a first upper switch tube SH1, a second upper switch tube SH2, a first lower switch tube SL1, and a second lower switch tube SL2. The first upper switch tube SH1 and the first lower switch tube SL1 are connected in series and are both connected to the first driver U1. The first power supply terminal VCC1 of the first driver U1 is connected to the connection midpoint between the first upper switch tube SH1 and the first lower switch tube SL1 through the first bootstrap unit 121. The first bootstrap unit 121 includes a first bootstrap capacitor CB1 and a first bootstrap diode DB1 connected in series; the second upper switch tube SH2 and the second lower switch tube SL2 are connected in series and are both connected to the second driver U2. The first power supply terminal VCC1 of the second driver U2 is connected to the connection midpoint between the second upper switch tube SH2 and the second lower switch tube SL2 through the second bootstrap unit 122. The second bootstrap unit 122 includes a second bootstrap capacitor CB2 and a second bootstrap diode DB2 connected in series; the first upper switch tube SH1 and the second upper switch tube SH2 are connected. It should also be noted that the full-bridge power conversion circuit 12 also includes at least other components or units such as capacitors, inductors or resistors for forming a complete power conversion circuit. The present application aims to reduce the problem of overcurrent damage to the bootstrap diode by improving the power conversion circuit control method. Therefore, other components or units for forming a complete power conversion circuit are not described in detail here.

[0079] In some embodiments, the first upper switch tube SH1 and the second upper switch tube SH2 can be connected to the high-voltage bus HV, and the first bootstrap unit 121 and the second bootstrap unit 122 can be discharged to the high-voltage bus HV through the first upper switch tube SH1 and the second upper switch tube SH2 after bootstrapping. This facilitates the power conversion of the power conversion circuit by controlling the upper switch tubes.

[0080] In some embodiments, the load 200 may be connected to a connection midpoint between the first upper switch tube SH1 and the first lower switch tube SL1 and a connection midpoint between the second upper switch tube SH2 and the second lower switch tube SL2 .

[0081] In some embodiments, the first upper switch tube SH1, the second upper switch tube SH2, the first lower switch tube SL1 and the second lower switch tube SL2 may be MOS tubes, i.e., MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor, MOSFET) tubes, the full name of which is Metal-Oxide Semiconductor Field-Effect Transistor, or MOSFET for short. Accordingly, the first driver U1 and the second driver U2 may include gate drivers. In other embodiments, the first upper switch tube SH1, the second upper switch tube SH2, the first lower switch tube SL1 and the second lower switch tube SL2 may also be other types of switch tubes, such as polysilicon tubes, back cathode field effect tubes (Insulate-Gate Bipolar Transistor, IGBT) and bipolar junction transistors (Bipolar Junction Transistor, BJT), etc.; the first driver U1 and the second driver U2 may also be other types of drivers, such as a microcontroller having the same or similar functions as the first driver U1 or the second driver U2.

[0082] In the full-bridge power conversion circuit 12, the power supply Vcc is connected to the first end of the first bootstrap capacitor CB1 through the first bootstrap diode DB1, and the second end of the first bootstrap capacitor CB1 is connected to the connection midpoint of the source of the first upper switch tube SH1 and the drain of the first lower switch tube SL1, that is, the source of the first upper switch tube SH1 is connected to the drain of the first lower switch tube SL1, and the second end of the first bootstrap capacitor CB1 is connected to the source of the first upper switch tube SH1 or the drain of the first lower switch tube SL1. The first power supply terminal VCC1 of the first driver U1 is connected to the first end of the first bootstrap capacitor CB1, the first driving terminal Vo1 of the first driver U1 is connected to the gate of the first upper switch tube SH1, the second driving terminal Vo of the first driver U1 is connected to the gate of the first lower switch tube SL1, the first ground terminal GND1 of the first driver U1 is connected to the second end of the first bootstrap capacitor CB1, the second ground terminal GND of the first driver U1 is connected to the source of the first lower switch tube SL1 and is grounded together, the high configuration terminal HI and the low level terminal LI of the first driver U1 are connected to the controller of the power conversion circuit, and the second power supply terminal VCC of the first driver U1 is connected to the power supply Vcc.

[0083] In the full-bridge power conversion circuit 12, the power supply Vcc is also connected to the first end of the second bootstrap capacitor CB2 through the second bootstrap diode DB2, and the second end of the second bootstrap capacitor CB2 is connected to the connection midpoint of the source of the second upper switch tube SH2 and the drain of the second lower switch tube SL2, that is, the source of the second upper switch tube SH2 is connected to the drain of the second lower switch tube SL2, and the second end of the second bootstrap capacitor CB2 is connected to the source of the second upper switch tube SH2 or the drain of the second lower switch tube SL2. The first power supply terminal VCC1 of the second driver U2 is connected to the first end of the second bootstrap capacitor CB2, the first driving terminal Vo1 of the second driver U2 is connected to the gate of the second upper switch tube SH2, the second driving terminal Vo of the second driver U2 is connected to the gate of the second lower switch tube SL2, the first ground terminal GND1 of the second driver U2 is connected to the second end of the second bootstrap capacitor CB2, the second ground terminal GND of the second driver U2 is connected to the source of the second lower switch tube SL2 and is grounded together, the high configuration terminal HI and the low level terminal LI of the second driver U2 are connected to the controller of the power conversion circuit, and the second power supply terminal VCC of the second driver U2 is connected to the power supply Vcc.

[0084] In some embodiments, the power source Vcc may be an auxiliary power source for the inverter.

[0085] In some embodiments, the first bootstrap unit 121 may further include a first bypass capacitor Cvcc1, the auxiliary power supply and the first bootstrap diode may be connected to the first end of the first bypass capacitor Cvcc1, and the second end of the first bypass capacitor Cvcc1 is grounded. The second bootstrap unit 122 may further include a second bypass capacitor Cvcc2, the auxiliary power supply and the second bootstrap diode may be connected to the first end of the second bypass capacitor Cvcc2, and the second end of the second bypass capacitor Cvcc2 is grounded. Thus, the auxiliary power supply may supply energy to the first bootstrap unit 121 through the first bypass capacitor Cvcc1, and supply energy to the second bootstrap unit 122 through the second bypass capacitor Cvcc2.

[0086] In some embodiments, the first bypass capacitor Cvcc1 may include a capacitor for energy storage and a capacitor for filtering, and the capacitor for energy storage and the capacitor for filtering are connected in parallel. Thus, the auxiliary power supply can filter while supplying energy to the first bootstrap unit 121 through the first bypass capacitor Cvcc1, thereby improving the purity of the supplied energy.

[0087] In some embodiments, the second bypass capacitor Cvcc2 may include a capacitor for energy storage and a capacitor for filtering. Thus, the auxiliary power supply can filter while supplying energy to the second bootstrap unit 122 through the second bypass capacitor Cvcc2, thereby improving the purity of the supplied energy.

[0088] In the embodiment of the present application, referring to the working principle of the half-bridge power conversion circuit, when the first lower switch tube SL1 is turned on, the auxiliary power supply can charge the first bootstrap capacitor CB1 through the first bypass capacitor Cvcc1 via the first bootstrap diode DB1. When the first lower switch tube SL1 of the full-bridge power conversion circuit 12 is turned off and the first upper switch tube SH1 on the high side is turned on, the first ground terminal GND1 of the first driver U1 and the connection midpoint between the first lower switch tube SL1 and the first upper switch tube SH1 are pulled to the high-voltage bus HV. In this case, the first bootstrap capacitor CB1 can release the stored electric energy to the high-voltage bus HV through the first driving terminal Vo1 and the first ground terminal GND1 of the first driver U1 through the first upper switch tube SH1 on the high side.

[0089] When the second lower switch tube SL2 is turned on, the auxiliary power supply can charge the second bootstrap capacitor CB2 through the second bypass capacitor Cvcc2 via the second bootstrap diode DB2. When the second lower switch tube SL2 of the full-bridge power conversion circuit 12 is turned off and the second upper switch tube SH2 on the high side is turned on, the first ground terminal GND1 of the second driver U2 and the connection midpoint between the second lower switch tube SL2 and the second upper switch tube SH2 are pulled to the high-voltage bus HV. In this case, the second bootstrap capacitor CB2 can release the stored electric energy to the high-voltage bus HV through the first driving terminal Vo1 and the first ground terminal GND1 of the second driver U2 through the second upper switch tube SH2 on the high side.

[0090] Fig.11 is a flow chart of a control method of a full-bridge power conversion circuit according to a second embodiment of the present application; Fig.12 It is a schematic diagram of another target duty cycle obtained in the control method of the power conversion circuit in the embodiment of the present application.

[0091] See also Fig.11 , the control method when applied to a full-bridge power conversion circuit includes: Step S100: obtaining a target duty cycle of turning on and off the upper switch tube or the lower switch tube according to the maximum loss of the bootstrap diode and the voltage of the bootstrap diode.

[0092] Step S200: obtaining a half cycle according to the target duty cycle and the voltage of the bootstrap capacitor.

[0093] Step S301: In a first time interval, control the first driver to drive the first upper switch tube to be turned on at a target duty cycle in the first half of each working cycle and to be turned off in the second half of each working cycle, and drive the first lower switch tube to be turned off in the first half of each working cycle and to be turned on at a target duty cycle in the second half of each working cycle, so that the first bootstrap capacitor is charged.

[0094] Step S302: In the second time interval, control the second driver to drive the second upper switch tube to be turned on at the target duty cycle in the first half of each working cycle and to be turned off in the second half of each working cycle, and drive the second lower switch tube to be turned off in the first half of each working cycle and to be turned on at the target duty cycle in the second half of each working cycle, so as to charge the second bootstrap capacitor.

[0095] The second time interval is different from and continuous with the first time interval. In some embodiments, multiple second time intervals and multiple first time intervals can be interlaced, that is, the first first time interval is adjacent to the first second time interval, the next first time interval is adjacent to the first second time interval, and the next second time interval is adjacent to the previous first time interval, and so on.

[0096] In some embodiments, step S301 may further include: controlling the first driver to stop outputting the driving signal during the second time interval. Step S302 may further include: controlling the second driver to stop outputting the driving signal during the first time interval. Fig.12 As shown, the first time interval may be the duration t1 of charging the bootstrap capacitor, and the second time interval may be the duration t2 of charging the bootstrap capacitor. Taking the control of the first lower switch tube and the second lower switch tube as an example, during the duration t1, the first lower switch tube may be controlled to be on and off with the target duty cycle D, and the drive of the second switch tube may be blocked (i.e., the output drive signal is stopped); during the duration t2, the second lower switch tube may be controlled to be on and off with the target duty cycle D, and the drive of the first switch tube may be blocked (i.e., the output drive signal is stopped).

[0097] In some embodiments, stopping outputting the driving signal may refer to prohibiting the current or voltage output of the signal output terminal, or outputting a low level so that the switch tube is continuously turned off.

[0098] It can be understood that the difference between the circuit structure of the full-bridge power conversion circuit of the second embodiment of the present application and the half-bridge power conversion circuit of the first embodiment lies in the number of bridge arms, which is specifically determined by Figure 3 , Figure 4 and Fig.10 It can be seen that the full-bridge power conversion circuit is equivalent to the combination of two half-bridge power circuits. Figure 5 and Fig.11It can be seen that the difference in the control method of the power conversion circuit is that when applied to a full-bridge power conversion circuit, it is equivalent to interleaving control of two half-bridge power conversion circuits, and the control of a single bridge arm in the control step is basically the same as the control method when applied to a half-bridge power conversion circuit. Therefore, when the control method of the power conversion circuit of the present application is applied to a full-bridge power conversion circuit, the way of obtaining the target duty cycle and the beneficial effect of the control method on the first bootstrap diode or the second bootstrap diode are basically the same as when applied to a half-bridge power conversion circuit, and will not be repeated here.

[0099] In addition, the full-bridge power conversion circuit may have a switch tube stress problem caused by a narrow pulse width hard switch. Through steps S301 and S302, the first bootstrap capacitor and the second bootstrap capacitor can be alternately controlled to charge in the full-bridge power conversion circuit, thereby reducing the switch tube stress problem caused by the narrow pulse width hard switch in the full-bridge power conversion circuit.

[0100] In summary, in the embodiment of the present application, the on-off of the upper switch tube or the lower switch tube is controlled by obtaining the target duty cycle related to the maximum loss of the bootstrap diode in the bootstrap unit, so that the bootstrap capacitor of the bootstrap unit can be charged intermittently, thereby reducing the impact current generated when the bootstrap capacitor is charged, and dispersing the energy of the impact current, which can reduce the problem of excessive impact current damaging the bootstrap diode. Different working cycles are obtained by gradually increasing the target duty cycle, thereby controlling the on-off of the upper switch tube or the lower switch tube in different working cycles. Since the target duty cycle gradually increases, the charging time of the bootstrap capacitor is gradually reduced at this time, and the charging efficiency of the bootstrap capacitor can be improved while reducing the impact current from damaging the bootstrap diode. By controlling the first driver to stop outputting the drive signal in the second time interval; controlling the second driver to stop outputting the drive signal in the first time interval, the charging of the first bootstrap capacitor and the second bootstrap capacitor can be alternately controlled in the full-bridge power conversion circuit, which can reduce the switch tube stress problem caused by the narrow pulse width hard switch in the full-bridge power conversion circuit.

[0101] Fig.13 It is a schematic diagram of the structure of the inverter according to an embodiment of the present application.

[0102] See also Fig.13 The present application also provides an inverter 100 , comprising: a power conversion circuit 1 and a controller 2 .

[0103] The power conversion circuit 1 may be a half-bridge power conversion circuit or a full-bridge power conversion circuit. The half-bridge power conversion circuit or the full-bridge power conversion circuit may be the half-bridge power conversion circuit or the full-bridge power conversion circuit of any of the above embodiments.

[0104] The controller 2 may be a microcontroller unit (MCU) or a digital signal processor (DSP). The controller 2 is electrically connected to the power conversion circuit 1 and may execute the control method of any of the above embodiments to control the power conversion circuit 2.

[0105] In some embodiments, the controller 2 can output a control signal to the driver of any of the above embodiments to control the driver to drive the switch tube to work. In other embodiments, the controller 2 can directly serve as the driver of any of the above embodiments to control the driver to drive the switch tube to work.

[0106] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present application and are not intended to limit it. Although the present application has been described in detail with reference to the preferred embodiments, a person of ordinary skill in the art should understand that the technical solution of the present application may be modified or replaced by equivalents without departing from the spirit and scope of the technical solution of the present application.

Claims

1. A control method for a power conversion circuit, characterized in that: The power conversion circuit includes a driver, a bootstrap unit, an upper switch tube and a lower switch tube, the upper switch tube and the lower switch tube are connected in series and are both connected to the driver, the power supply end of the driver is connected to the connection midpoint between the upper switch tube and the lower switch tube through the bootstrap unit, and the bootstrap unit includes a bootstrap capacitor and a bootstrap diode connected in series; the control method includes: obtaining a target duty cycle of turning on and off the upper switch tube or the lower switch tube according to the maximum loss of the bootstrap diode and the voltage of the bootstrap diode; obtaining a half cycle according to the target duty cycle and the voltage of the bootstrap capacitor, and two half cycles constitute a working cycle; controlling the driver to drive the upper switch tube to turn on at the target duty cycle in the first half cycle of each working cycle and turn off in the second half cycle of each working cycle, and drive the lower switch tube to turn off in the first half cycle of each working cycle and turn on at the target duty cycle in the second cycle of each working cycle, so that the bootstrap capacitor is charged.

2. The control method of the power conversion circuit according to claim 1, characterized in that: The target duty cycle of turning on and off the upper switch tube or the lower switch tube is obtained according to the maximum loss of the bootstrap diode and the voltage of the bootstrap diode, including: obtaining the corresponding relationship between the target duty cycle and the maximum loss of the bootstrap diode based on the current of the bootstrap capacitor and the tube drop voltage of the bootstrap diode; obtaining the current of the bootstrap capacitor based on the voltage of the zero-state response of the bootstrap capacitor when charging; and obtaining the target duty cycle based on the corresponding relationship and the current of the bootstrap capacitor.

3. The control method of the power conversion circuit according to claim 2, characterized in that: The step of obtaining a half cycle according to the target duty cycle and the voltage of the bootstrap capacitor, wherein two half cycles constitute a working cycle, includes obtaining the voltage of the bootstrap capacitor based on the charging voltage of the bootstrap unit and the expected charging coefficient.

4. The control method of the power conversion circuit according to claim 1, characterized in that: A current limiting unit is arranged between the bootstrap diode and the bootstrap capacitor; the target duty cycle of turning on and off the upper switch tube or the lower switch tube is obtained according to the maximum loss of the bootstrap diode and the voltage of the bootstrap diode, and also includes: obtaining the target duty cycle according to the on-off frequency of the upper switch tube or the lower switch tube and the resistance value of the current limiting unit.

5. The control method of the power conversion circuit according to claim 1, characterized in that: The step of obtaining a half cycle according to the target duty cycle and the voltage of the bootstrap capacitor, wherein two half cycles constitute a working cycle, further comprises: gradually increasing the target duty cycle to obtain a plurality of different working cycles.

6. The control method of the power conversion circuit according to claim 1, characterized in that: The power conversion circuit includes a first driver, a second driver, a first bootstrap unit, a second bootstrap unit, a first upper switch tube, a second upper switch tube, a first lower switch tube and a second lower switch tube; the first upper switch tube and the first lower switch tube are connected in series and are both connected to the first driver, the power supply end of the first driver is connected to the connection midpoint between the first upper switch tube and the first lower switch tube through the first bootstrap unit, and the first bootstrap unit includes a first bootstrap capacitor and a first bootstrap diode connected in series; the second upper switch tube and the second lower switch tube are connected in series and are both connected to the second driver, the power supply end of the second driver is connected to the connection midpoint between the second upper switch tube and the second lower switch tube through the second bootstrap unit, and the second bootstrap unit includes a second bootstrap capacitor and a second bootstrap diode connected in series; the first upper switch tube and the second upper switch tube connection; the control method of the power conversion circuit also includes: in a first time interval, controlling the first driver to drive the first upper switch tube to be turned on at the target duty cycle in the first half cycle of each working cycle and turned off in the second half cycle of each working cycle, driving the first lower switch tube to be turned off in the first half cycle of each working cycle and turned on at the target duty cycle in the second cycle of each working cycle, so that the first bootstrap capacitor is charged; in a second time interval, controlling the second driver to drive the second upper switch tube to be turned on at the target duty cycle in the first half cycle of each working cycle and turned off in the second half cycle of each working cycle, driving the second lower switch tube to be turned off in the first half cycle of each working cycle and turned on at the target duty cycle in the second cycle of each working cycle, so that the second bootstrap capacitor is charged; the second time interval is different from and continuous with the first time interval.

7. The control method of the power conversion circuit according to claim 6, characterized in that: The control method of the power conversion circuit further includes: controlling the first driver to stop outputting the driving signal in the second time interval; and controlling the second driver to stop outputting the driving signal in the first time interval.

8. An inverter, characterized in that: include: A power conversion circuit, the power conversion circuit comprising a driver, a bootstrap unit, an upper switch tube and a lower switch tube, the upper switch tube and the lower switch tube are connected in series and are both connected to the driver, the power supply end of the driver is connected to the connection midpoint between the upper switch tube and the lower switch tube through the bootstrap unit, the bootstrap unit comprises a bootstrap capacitor and a bootstrap diode connected in series; a controller, configured to: obtain a target duty cycle of turning on and off the upper switch tube or the lower switch tube according to the maximum loss of the bootstrap diode and the voltage of the bootstrap diode; obtain a half cycle according to the target duty cycle and the voltage of the bootstrap capacitor, wherein two half cycles constitute a working cycle; control the driver to drive the upper switch tube to turn on at the target duty cycle in the first half cycle of each working cycle and turn off in the second half cycle of each working cycle, and drive the lower switch tube to turn off in the first half cycle of each working cycle and turn on at the target duty cycle in the second cycle of each working cycle, so as to charge the bootstrap capacitor.

9. The inverter according to claim 8, characterized in that: The controller is further configured to: when a half cycle is obtained according to the target duty cycle and the voltage of the bootstrap capacitor, gradually increase the target duty cycle to obtain a plurality of different working cycles.

10. The inverter according to claim 8, characterized in that: The power conversion circuit includes a first driver, a second driver, a first bootstrap unit, a second bootstrap unit, a first upper switch tube, a second upper switch tube, a first lower switch tube and a second lower switch tube; the first upper switch tube and the first lower switch tube are connected in series and are both connected to the first driver, the power supply end of the first driver is connected to the connection midpoint between the first upper switch tube and the first lower switch tube through the first bootstrap unit, and the first bootstrap unit includes a first bootstrap capacitor and a first bootstrap diode connected in series; the second upper switch tube and the second lower switch tube are connected in series and are both connected to the second driver, the power supply end of the second driver is connected to the connection midpoint between the second upper switch tube and the second lower switch tube through the second bootstrap unit, and the second bootstrap unit includes a second bootstrap capacitor and a second bootstrap diode connected in series; the first upper switch tube and the second upper switch tube are connected; the controller is further configured to: in a first time interval, control the first driver to drive the first upper switch tube to turn on at the target duty cycle in the first half cycle of each working cycle and turn off in the second half cycle of each working cycle, and drive the first lower switch tube to turn off in the first half cycle of each working cycle and turn on at the target duty cycle in the second cycle of each working cycle, so that the first bootstrap capacitor is charged; In a second time interval, controlling the second driver to drive the second upper switch tube to be turned on at the target duty cycle in the first half of each working cycle and turned off in the second half of each working cycle, and driving the second lower switch tube to be turned off in the first half of each working cycle and turned on at the target duty cycle in the second half of each working cycle, so that the second bootstrap capacitor is charged; The second time interval is different from and continuous with the first time interval.

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