Control method for power conversion circuit, and inverter

Abstract

A control method for a power conversion circuit, and an inverter. The power conversion circuit comprises a driver, a bootstrap unit, an upper switch transistor, and a lower switch transistor. The method comprises: on the basis of the maximum loss of a bootstrap diode and the voltage of the bootstrap diode, obtaining a target duty cycle for turning on / off an upper switch transistor or a lower switch transistor; obtaining a half cycle on the basis of the target duty cycle and the voltage of a bootstrap capacitor, two half cycles forming one working cycle; and controlling a driver to drive the upper switch transistor to be turned on at the target duty cycle in a first half cycle of each working cycle and turned off in a second half cycle of each working cycle, and to drive the lower switch transistor to be turned off in the first half cycle of each working cycle and turned on at the target duty cycle in the second half cycle of each working cycle, such that the bootstrap capacitor is charged. Thus, damage to the bootstrap diode caused by excessive inrush current can be reduced.

Description

Control methods for power conversion circuits and inverters

[0001] This application claims priority to Chinese Patent Application No. 202411547325.1, filed on October 31, 2024, entitled "Control Method and Inverter for Power Conversion Circuit", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of power electronics technology, and in particular to a control method for a power conversion circuit and an inverter. Background Technology

[0003] Currently, in the half-bridge or full-bridge power conversion circuits of photovoltaic inverters, bootstrap circuits are typically used to power the high-side drive. Since the initial voltage of the bootstrap capacitor in the bootstrap circuit is 0V, the inrush current flowing through the bootstrap circuit can become excessive during its initial operation, easily damaging the bootstrap diodes and affecting their lifespan.

[0004] In related technologies, to reduce the damage to bootstrap diodes caused by excessive inrush current, methods such as connecting a current-limiting resistor in series in the bootstrap circuit or reducing the size of the bootstrap capacitor are commonly used. However, while the method of connecting a current-limiting resistor in series has a certain limiting effect on the peak value of the inrush current, it is still difficult to reduce the energy of the inrush current that causes damage to the bootstrap diode. Reducing the size of the bootstrap capacitor can reduce the inrush current, but it is easily limited by the operating environment of the bootstrap capacitor. For example, if the operating voltage of the bootstrap capacitor is lower than the high-side drive voltage, the high-side drive will not function properly. Summary of the Invention

[0005] Therefore, this application provides an auxiliary power supply and inverter with a relatively simple circuit structure, which can reduce costs.

[0006] In view of the above, it is necessary to provide a control method and inverter for a power conversion circuit, which can reduce the problem of excessive inrush current damaging the bootstrap diode when the bootstrap unit is working.

[0007] This application provides a control method for a power conversion circuit. The power conversion circuit includes a driver, a bootstrap unit, an upper switch, and a lower switch. The upper and lower switches are connected in series and are both connected to the driver. The power supply terminal of the driver is connected to the midpoint between the upper and lower switches through the bootstrap unit. The bootstrap unit includes a bootstrap capacitor and a bootstrap diode connected in series. The control method includes: obtaining a target duty cycle for the upper or lower switch based on the maximum loss of the bootstrap diode and the voltage of the bootstrap diode; obtaining a half-cycle based on the target duty cycle and the voltage of the bootstrap capacitor, with two half-cycles constituting one operating cycle; controlling the driver to drive the upper switch to conduct with the target duty cycle in the first half-cycle of each operating cycle and turn off in the second half-cycle of each operating cycle, and driving the lower switch to turn off in the first half-cycle of each operating cycle and conduct with the target duty cycle in the second half-cycle of each operating cycle, so as to charge the bootstrap capacitor.

[0008] In some embodiments, obtaining the target duty cycle for switching on or off the upper or lower switch based on the maximum loss of the bootstrap diode and the voltage of the bootstrap diode includes: 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 voltage drop of the bootstrap diode; obtaining the current of the bootstrap capacitor based on the voltage of the zero-state response of the bootstrap capacitor during charging; and obtaining the target duty cycle based on the correspondence and the current of the bootstrap capacitor.

[0009] In some embodiments, a half-cycle is obtained based on a target duty cycle and the voltage of the bootstrap capacitor, and two half-cycles constitute a working cycle, including: obtaining the voltage of the bootstrap capacitor based on the charging voltage of the bootstrap unit and the charging expectation coefficient.

[0010] In some embodiments, a current limiting unit is provided between the bootstrap diode and the bootstrap capacitor; the target duty cycle of the upper or lower switch is obtained based on the maximum loss of the bootstrap diode and the voltage of the bootstrap diode, and further includes obtaining the target duty cycle based on the switching frequency of the upper or lower switch and the resistance value of the current limiting unit.

[0011] In some embodiments, a half-cycle is obtained based on a target duty cycle and the voltage of the bootstrap capacitor, and two half-cycles constitute a duty cycle. The method further includes gradually increasing the target duty cycle to obtain multiple different duty cycles.

[0012] 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, a second upper switch, a first lower switch, and a second lower switch; the first upper switch and the first lower switch are connected in series and are both connected to the first driver, and the power supply terminal of the first driver is connected to the midpoint between the first upper switch and the first lower switch through the first bootstrap unit, the first bootstrap unit including a first bootstrap capacitor and a first bootstrap diode connected in series; the second upper switch and the second lower switch are connected in series and are both connected to the second driver, the power supply terminal of the second driver is connected to the midpoint between the second upper switch and the second lower switch through the second bootstrap unit, the second bootstrap unit including a second bootstrap capacitor and a second bootstrap diode connected in series; the first ... The control method for the power conversion circuit further includes: in a first time interval, controlling a first driver to drive a first upper switch to be turned on with a target duty cycle in the first half of each operating cycle and turned off in the second half of each operating cycle, and driving a first lower switch to be turned off in the first half of each operating cycle and turned on with a target duty cycle in the second half of each operating cycle, so as to charge the first bootstrap capacitor; in a second time interval, controlling a second driver to drive a second upper switch to be turned on with a target duty cycle in the first half of each operating cycle and turned off in the second half of each operating cycle, and driving a second lower switch to be turned off in the first half of each operating cycle and turned on with a target duty cycle in the second half of each operating cycle, so as to charge the second bootstrap capacitor; the second time interval is different from the first time interval and is continuous.

[0013] In some embodiments, the control method for the power conversion circuit further includes: controlling the first driver to stop outputting a drive signal in a second time interval; and controlling the second driver to stop outputting a drive signal in a first time interval.

[0014] This application also provides an inverter, including: a power conversion circuit, the power conversion circuit including a driver, a bootstrap unit, an upper switching transistor and a lower switching transistor, the upper switching transistor and the lower switching transistor being connected in series and both connected to the driver, the power supply terminal of the driver being connected to the connection midpoint between the upper switching transistor and the lower switching transistor through the bootstrap unit, the bootstrap unit including a bootstrap capacitor and a bootstrap diode connected in series; a controller configured to: obtain a target duty cycle for switching the upper or lower switching transistor on and off based on the maximum loss of the bootstrap diode and the voltage of the bootstrap diode; obtain a half-cycle based on the target duty cycle and the voltage of the bootstrap capacitor, wherein two half-cycles constitute one operating cycle; control the driver to drive the upper switching transistor to conduct with the target duty cycle in the first half-cycle of each operating cycle and turn off in the second half-cycle of each operating cycle, and drive the lower switching transistor to turn off in the first half-cycle of each operating cycle and conduct with the target duty cycle in the second half-cycle of each operating cycle, so as to charge the bootstrap capacitor.

[0015] In some embodiments, the controller is further configured to gradually increase the target duty cycle to obtain multiple different duty cycles when a half-cycle is obtained based on the target duty cycle and the voltage of the bootstrap capacitor.

[0016] 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, a second upper switch, a first lower switch, and a second lower switch; the first upper switch and the first lower switch are connected in series and are both connected to the first driver, and the power supply terminal of the first driver is connected to the midpoint between the first upper switch and the first lower switch through the first bootstrap unit, the first bootstrap unit including a first bootstrap capacitor and a first bootstrap diode connected in series; the second upper switch and the second lower switch are connected in series and are both connected to the second driver, the power supply terminal of the second driver is connected to the midpoint between the second upper switch and the second lower switch through the second bootstrap unit, the second bootstrap unit including a second bootstrap capacitor and a second bootstrap diode connected in series; the first ... The controller is further configured to: in a first time interval, control a first driver to drive the first upper switch to be turned on with a target duty cycle in the first half of each operating cycle and turned off in the second half of each operating cycle, and drive the first lower switch to be turned off in the first half of each operating cycle and turned on with a target duty cycle in the second half of each operating cycle, so as to charge the first bootstrap capacitor; in a second time interval, control a second driver to drive the second upper switch to be turned on with a target duty cycle in the first half of each operating cycle and turned off in the second half of each operating cycle, and drive the second lower switch to be turned off in the first half of each operating cycle and turned on with a target duty cycle in the second half of each operating cycle, so as to charge the second bootstrap capacitor; the second time interval is continuous with but different from the first time interval. Compared with the prior art, this application has at least the following advantages:

[0017] 1. In this application, the on / off state of the upper or lower switching transistor 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. This reduces the inrush current generated when the bootstrap capacitor is charged and disperses the energy of the inrush current, thereby reducing the problem of excessive inrush current damaging the bootstrap diode.

[0018] 2. By gradually increasing the target duty cycle, different operating cycles can be obtained. Thus, when controlling the on / off state of the upper or lower switching transistor in different operating cycles, the charging time of the bootstrap capacitor gradually decreases as the target duty cycle gradually increases. This can improve the charging efficiency of the bootstrap capacitor while reducing the damage to the bootstrap diode caused by excessive inrush current.

[0019] 3. By controlling the first driver to stop outputting the drive signal in the second time interval and 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 stress problem of the switching transistor caused by narrow pulse hard switching in the full-bridge power conversion circuit. Attached Figure Description

[0020] Figure 1 is a characteristic curve of current and voltage during the charging process of the bootstrap capacitor in the bootstrap circuit of the prior art.

[0021] Figure 2 is a schematic diagram of the thermal effect of the bootstrap diode in the bootstrap circuit of the prior art during the bootstrap capacitor charging process.

[0022] Figure 3a is a schematic diagram of the structure and one working state of the half-bridge power conversion circuit according to an embodiment of this application;

[0023] Figure 3b is a schematic diagram of the structure of the half-bridge power conversion circuit according to an embodiment of this application and another operating state;

[0024] Figure 4 is a flowchart of the control method of the half-bridge power conversion circuit according to an embodiment of this application;

[0025] Figure 5 is a schematic diagram of a target duty cycle obtained by the control method of the power conversion circuit in an embodiment of this application;

[0026] Figure 6 is a current and voltage characteristic curve of the bootstrap capacitor charging process in the control method of the power conversion circuit corresponding to the embodiment of Figure 5 of this application.

[0027] Figure 7 is a schematic diagram of the thermal effect of the bootstrap diode during the bootstrap capacitor charging process in the control method of the power conversion circuit corresponding to the embodiment of Figure 5 of this application.

[0028] Figure 8 is a schematic diagram of another target duty cycle obtained by the control method of the power conversion circuit in an embodiment of this application;

[0029] Figure 9 is a schematic diagram of the structure of a full-bridge power conversion circuit according to an embodiment of this application;

[0030] Figure 10 is a flowchart of the control method of the full-bridge power conversion circuit according to an embodiment of this application;

[0031] Figure 11 is a schematic diagram of another target duty cycle obtained by the control method of the power conversion circuit in an embodiment of this application;

[0032] Figure 12 is a schematic diagram of the inverter structure according to an embodiment of this application.

[0033] Explanation of key 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.

[0034] The following detailed description, in conjunction with the accompanying drawings, will further illustrate this application. Detailed Implementation

[0035] In the description of the embodiments in this application, the words "exemplary," "or," and "for example" are used to indicate examples, illustrations, or descriptions. Any embodiment or design scheme described as "exemplary" or "for example" in the embodiments of this application should not be construed as being more preferred or advantageous than other embodiments or design schemes. Specifically, the use of the words "exemplary," "or," and "for example" is intended to present the relevant concepts in a specific manner.

[0036] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. The terminology used in this application's specification is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. It should be understood that, unless otherwise stated, " / " in this application means "or". For example, A / B can mean A or B. "And / or" in this application is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A alone, A and B simultaneously, and B alone. "At least one" refers to one or more. "More than one" refers to two or more. For example, at least one of a, b, or c can represent: a, b, c, a and b, a and c, b and c, and a, b, and c (seven cases).

[0037] It should also be noted that the terms "first" and "second" in the specification, claims and drawings of this application are used to distinguish similar objects, rather than to describe a specific order or sequence.

[0038] In half-bridge or full-bridge power conversion circuits, bootstrap circuits are typically used to power the high-side drive to reduce costs. A bootstrap circuit usually consists of a bootstrap capacitor, a bootstrap diode, and a bypass circuit, with the bootstrap capacitor and bootstrap diode connected in series. Figure 1 shows the current and voltage characteristic curves of the bootstrap capacitor charging process in a prior art bootstrap circuit. Referring to Figure 1, since the initial voltage of the bootstrap capacitor is 0V, during the initial operation of the bootstrap circuit, the voltage (U) of the bootstrap capacitor charges from 0V to the voltage after time ts, completing the charging process. This can result in an excessively large inrush current flowing through the bootstrap circuit; that is, the charging current (i) of the bootstrap capacitor exceeds the maximum current (Imax) that the bootstrap diode can withstand, easily damaging the bootstrap diode and thus affecting its lifespan.

[0039] Currently, bootstrap diodes are generally used in two ways: one is placed outside the integrated circuit (IC), and the other is integrated inside the IC. When the bootstrap diode is placed outside the IC, due to limitations in space and other factors, its current-carrying capacity is limited, and the inrush current is not easily excessive. When the bootstrap diode is placed inside the IC, due to limitations in the packaging process, its ability to withstand inrush current flowing through the bootstrap diode circuit is relatively low.

[0040] Figure 2 is a schematic diagram of the thermal effect of the bootstrap diode in a bootstrap circuit during the charging process of the bootstrap capacitor. Referring to Figure 2, during the initial operation of the bootstrap circuit, the voltage of the bootstrap capacitor continuously charges from 0V to the voltage after time ts. During this continuous process, the bootstrap diode is in the transient heating region, which can easily lead to continuous heating and overheating. If the inrush current is too large, it will cause excessive transient losses in the bootstrap diode, resulting in thermal failure. Simultaneously, the bonding wires inside the IC may melt due to the excessive energy of the inrush current. Alternatively, if the inrush current energy is too high, although it will not directly melt the bonding wires, it will cause drastic fluctuations in junction temperature. Prolonged exposure to such conditions can lead to solder layer fatigue and reduce the lifespan of the IC.

[0041] Therefore, in related technologies, to reduce the problem of excessive inrush current damaging the bootstrap diode, methods such as connecting a current-limiting resistor in series in the bootstrap circuit or reducing the size of the bootstrap capacitor are commonly used. However, while connecting a current-limiting resistor in series can limit the peak value of the inrush current to some extent, it is still difficult to reduce the energy of the inrush current that damages the bootstrap diode. Furthermore, the size of the current-limiting resistor is easily limited by voltage dips, so connecting a current-limiting resistor in series is not a good method. Reducing the size of the bootstrap capacitor can also reduce the inrush current, but it is easily limited by the operating environment of the bootstrap capacitor, such as the high-side drive voltage ripple. If the operating voltage of the bootstrap capacitor is lower than the high-side drive voltage, the high-side drive will not function properly. Therefore, reducing the size of the bootstrap capacitor is not a good way to solve the problem of excessive inrush current.

[0042] Therefore, this application provides a control method for a power conversion circuit and an inverter, which can reduce the problem of excessive inrush current damaging the bootstrap diode when the bootstrap unit is working.

[0043] The control method and inverter of the power conversion circuit provided in this application will be described in detail below with reference to Embodiment 1 and Embodiment 2.

[0044] Example 1:

[0045] Figure 3a is a schematic diagram of the structure and one working state of the half-bridge power conversion circuit 11 according to Embodiment 1 of this application; Figure 3b is a schematic diagram of the structure and another working state of the half-bridge power conversion circuit 11 according to Embodiment 1 of this application.

[0046] The control method for the power conversion circuit of this application can be applied to a half-bridge power conversion circuit 11, which can be used in an inverter for current or voltage power conversion. Referring to Figure 3a or 3b, the half-bridge power conversion circuit 11 may include a driver U0, a bootstrap unit 111, an upper switch SH, and a lower switch SL. The upper switch SH and the lower switch SL can be connected in series and are both connected to the driver U0. The first power supply terminal VCC1 of the driver U0 is connected to the midpoint between the upper switch SH and the lower switch 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 capacitors, inductors, or resistors, and other components or units used to constitute a complete power conversion circuit. This 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 used to constitute a complete power conversion circuit are not described in detail here.

[0047] In some embodiments, the upper switching transistor SH can be connected to the high-voltage bus HV. After the bootstrap unit 111 boosts the voltage, it can discharge to the high-voltage bus HV through the upper switching transistor SH. Therefore, the power conversion of the power conversion circuit can be controlled by controlling the upper switching transistor SH.

[0048] In some embodiments, the upper switch SH and the lower switch SL can be MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors), also known as metal-oxide-semiconductor field-effect transistors. Correspondingly, the driver U0 can include a gate driver. In other embodiments, the upper switch SH and the lower switch SL can also be other types of switching transistors, such as polysilicon transistors, insulated-gate bipolar transistors (IGBTs), and bipolar junction transistors (BJTs); the driver U0 can also be other types of drivers, such as a microcontroller with the same or similar function as the driver U0.

[0049] In the half-bridge power conversion circuit 11, the power supply Vcc is connected to the first terminal of the bootstrap capacitor CB through the bootstrap diode DB. The second terminal of the bootstrap capacitor CB is connected to the midpoint between the source of the upper switching transistor SH and the drain of the lower switching transistor SL, i.e., the source of the upper switching transistor SH and the drain of the lower switching transistor SL are connected, and the second terminal of the bootstrap capacitor CB is connected to either the source of the upper switching transistor SH or the drain of the lower switching transistor SL. The first power supply terminal VCC1 of the driver U0 is connected to the first terminal of the bootstrap capacitor CB. The first driving terminal Vo1 of the driver U0 is connected to the gate of the upper switching transistor SH. The second driving terminal Vo of the driver U0 is connected to the gate of the lower switching transistor SL. The first ground terminal GND1 of the driver U0 is connected to the second terminal of the bootstrap capacitor CB. The second ground terminal GND of the driver U0 is connected to the source of the lower switching transistor SL and 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. The second power supply terminal VCC of the driver U0 is connected to the power supply Vcc.

[0050] In some embodiments, the power supply Vcc can be the auxiliary power supply for the inverter.

[0051] In some embodiments, the bootstrap unit 111 may further include a bypass capacitor Cvcc, and an auxiliary power supply and a bootstrap diode DB may be connected to the first terminal of the bypass capacitor Cvcc, while the second terminal of the bypass capacitor Cvcc is grounded. Thus, the auxiliary power supply can power the bootstrap unit 111 through the bypass capacitor Cvcc.

[0052] In some embodiments, the bypass capacitor Cvcc may include an energy storage capacitor and a filter capacitor connected in parallel. Thus, the auxiliary power supply can simultaneously power the bootstrap unit 111 through the bypass capacitor Cvcc while filtering the energy, thereby improving the purity of the supplied energy.

[0053] In some embodiments, a current limiting unit may be provided between the bootstrap diode DB and the bootstrap capacitor CB, and the current limiting unit may include at least one current limiting resistor RB.

[0054] In the embodiments of this application, as shown by the dashed arrow in FIG3a, when the lower switch 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. As shown by the dashed arrow in FIG3b, when the lower switch SL of the half-bridge power conversion circuit 11 is turned off and the upper switch 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 SL and the upper switch SH are pulled to the high-voltage bus HV. In this case, the bootstrap capacitor CB can release the stored electrical energy to the high-voltage bus HV through the upper switch SH on the high-side through the first drive terminal Vo1 and the first ground terminal GND1 of the driver U0.

[0055] Figure 4 is a flowchart of the control method of the half-bridge power conversion circuit in Embodiment 1 of this application.

[0056] As mentioned above, since the initial voltage of the bootstrap capacitor is 0V, during the initial operation of the bootstrap circuit, the voltage of the bootstrap capacitor is charged from 0V, which can lead to excessive inrush current flowing through the bootstrap circuit. Therefore, a control method for the power conversion circuit is proposed. Referring to Figure 4, the control method applied to a half-bridge power conversion circuit may include:

[0057] Step S100: Obtain the target duty cycle for switching on or off the upper or lower switch based on the maximum loss of the bootstrap diode and the voltage of the bootstrap diode.

[0058] The maximum loss of a bootstrap diode refers to the maximum forward power loss of the bootstrap diode. When a forward current flows through a bootstrap diode, a voltage drop is generated in the forward voltage. The voltage drop and the power loss caused by the forward current constitute the forward power loss.

[0059] In some embodiments, the target duty cycle is related to the on / off frequency of the upper or lower switch. Since the conduction of the upper or lower switch includes pulse rise and fall times, in some embodiments, the target duty cycle is not less than the pulse width of the upper or lower switch. This reduces the likelihood of pulse loss during the conduction of the upper or lower switch.

[0060] Since the bootstrap capacitor and bootstrap diode are connected in series in the bootstrap unit, the current flowing through the bootstrap diode is the same as the current flowing through the bootstrap capacitor. During the charging process of the bootstrap capacitor, in order to reduce 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 correspondence with the maximum loss. Therefore, step S100 may also include: 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 voltage drop of the bootstrap diode. Among them, the 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 correspondence between the target duty cycle and the maximum loss of the bootstrap diode can be obtained by formula (1):

[0061] In equation (1), D is the target duty cycle; i is the bootstrap capacitor charging current; P max The maximum transient loss within the SOA (Safety Operation Area) range of the bootstrap diode is referred to here as the maximum loss; U e is the voltage drop across the bootstrap diode; f is the switching frequency of the upper or lower switching transistor.

[0062] As mentioned above, the target duty cycle is related to the switching frequency of the upper or lower switch. In some embodiments, the target duty cycle is also related to the resistance value of the current limiting unit. Therefore, step S100 may further include: obtaining the target duty cycle based on the switching frequency of the upper or lower switch and the resistance value of the current limiting unit. It can be understood that in the power conversion circuit of the inverter, the upper and lower switches are always alternately turned on, so step S100 may specifically refer to obtaining the target duty cycle based on the switching frequency of the lower switch and the resistance value of the current limiting unit.

[0063] In some embodiments, the switching frequency of the upper or lower switch is related to the circuit topology of the power conversion circuit. The switching frequency of the upper or lower switch can be a preset range value, for example, the switching frequency of the upper or lower switch can be set to 80kHz to 120kHz.

[0064] It is understandable that, since the initial voltage of the bootstrap capacitor is 0V, 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 conditions are zero (the system has no energy at the beginning). Therefore, the current of the bootstrap capacitor required in step S100 can be obtained based on the voltage of the zero-state response during charging. The charging voltage of the bootstrap capacitor can be obtained using equation (2):

[0065] Among them, V ccU is the input voltage of the auxiliary power supply, U is the charging voltage of the bootstrap capacitor, and t is the charging time. In equation (2), τ is a time constant used to represent the response speed of the bootstrap capacitor charging. It is equal to the product of the resistance of the current-limiting resistor and the capacitance of the bootstrap capacitor, i.e., τ = R. B *C B R B C is the resistance value of the current-limiting resistor. B This is the capacitance value of the bootstrap capacitor.

[0066] Differentiating equation (2) yields the charging current of the bootstrap capacitor, which can be obtained from equation (3):

[0067] As can be seen from the above, the target duty cycle is related to 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, this includes combining the correspondence between the target duty cycle and the maximum loss of the bootstrap diode, i.e., equation (1), with the charging current of the bootstrap capacitor, i.e., equation (3), to obtain the maximum limit of the target duty cycle, i.e., equation (4):

[0068] In equation (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, while the target duty cycle is negatively correlated with the switching frequency of the upper or lower switching transistor 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 switching frequency of the upper or lower switching transistor 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.

[0069] In addition, in Embodiment 1 of this application, the control method, when applied to a half-bridge power conversion circuit, may further include:

[0070] Step S200: Obtain the half-cycle based on the target duty cycle and the voltage of the bootstrap capacitor.

[0071] Two half-cycles constitute one working cycle. The bootstrap capacitor is charged through an auxiliary power supply, so the charging voltage of the bootstrap capacitor can be equal to the input voltage of the auxiliary power supply.

[0072] In practical applications, when the bootstrap capacitor is charged through the auxiliary power supply, the bootstrap capacitor is not fully charged to the same voltage value as the input voltage of the auxiliary power supply. For example, the bootstrap capacitor can be charged to a desired charging level, such as 80%, 90%, 100%, etc. That is, the voltage of the bootstrap capacitor is related to the desired charging level, and the desired charging level can be represented by a charging expectation coefficient. Therefore, step S200 may further include: obtaining the voltage of the bootstrap capacitor based on the charging voltage of the bootstrap unit and the charging expectation coefficient. The relationship between the voltage of the bootstrap capacitor, the charging expectation coefficient, and the charging duration can be expressed by equation (5):

[0073] where K is the desired voltage coefficient, 0 < K < 1. For example, if the bootstrap capacitor is expected to be charged to 90% of the input voltage V of the auxiliary power supply, K can be set to 0.9; t1 is the charging duration. cc of the auxiliary power supply, K can be set to 0.9; t1 is the charging duration.

[0074] 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:

[0075] Step S300: Control the driver to drive the upper switch tube to conduct with a 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 conduct with a target duty cycle in the second half cycle of each working cycle, so as to charge the bootstrap capacitor.

[0076] In some other embodiments, step S300 may also be: Control the driver to drive the lower switch tube to conduct with a 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 upper switch tube to turn off in the first half cycle of each working cycle and conduct with a target duty cycle in the second half cycle of each working cycle, so as to charge the bootstrap capacitor. In other words, the control order of the upper switch tube and the lower switch tube can be interchanged.

[0077] Figure 5 is a schematic diagram of a target duty cycle obtained in the control method of the power conversion circuit according to the first embodiment of the present application.

[0078] In some embodiments, as shown in Figure 5, multiple working cycles can form the charging duration t1 of the bootstrap capacitor. During the duration t1, the high-level pulse and the low-level pulse form a working cycle with a target duty cycle D. In addition, it can also be that during the duration t1, the high-level pulse and the low-level pulse form a working cycle with a target duty cycle D.

[0079] Figure 6 is a characteristic curve of current (i) and voltage (U) during the charging process of the bootstrap capacitor in the control method of the power conversion circuit corresponding to the embodiment of Figure 5 of this application; Figure 7 is a schematic diagram of the thermal effect of the bootstrap diode during the charging process of the bootstrap capacitor in the control method of the power conversion circuit corresponding to the embodiment of Figure 5 of this application.

[0080] As shown in Figures 1 and 6, during the duration t1, the switching on or off of the upper or lower switch is controlled by obtaining a target duty cycle related to the maximum loss of the bootstrap diode in the bootstrap unit. This allows the bootstrap capacitor of the bootstrap unit to be charged intermittently (i.e., the voltage (U) of the bootstrap capacitor increases in a stepwise manner as shown in Figure 6). This reduces the inrush current generated when the bootstrap capacitor is charging (i.e., as shown in Figure 6, due to the presence of parasitic inductance in the power conversion circuit, the current (i) of the bootstrap capacitor cannot jump from 0 to V). cc / R B Therefore, the current flowing through the bootstrap diode is within the maximum current (Imax) range that the bootstrap diode can withstand, and the energy of the surge current can be dispersed (as shown in Figure 7), which can reduce the problem of excessive surge current damaging the bootstrap diode. When the bootstrap diode is integrated into the IC, the situation of excessive surge current damaging the bootstrap diode can be reflected by obtaining the thermal shock parameters on the bonding line. Specifically, the thermal shock on the bonding line can be expressed by equation (6): I 2 t = 1 / 3i p 2 t = 0.5*i p *t*i p *2 / 3=ΔQ cB *i p *2 / 3 = C B *ΔV*i p *2 / 3 (6)

[0081] The bootstrap capacitor charging current can be represented as a triangular wave. t is the duration of a single pulse, which can be equal to the target duty cycle divided by the switching frequency of the transistor, i.e., t = D / f; ΔV is the voltage difference between the bootstrap capacitor before and after half a cycle (i.e., a single pulse); i p Peak value of triangular wave current when charging the bootstrap capacitor; ΔQ CB This represents the amount of charge transferred by the bootstrap capacitor before and after the end of a half-cycle.

[0082] It is understandable that the thermal shock parameters on the bonding line are related to the capacitance of the bootstrap capacitor, the voltage difference between the bootstrap capacitor before and after half-cycle operation, and the peak value of the triangular wave current during bootstrap capacitor charging. Therefore, ΔV and i can be reduced by adjusting the target duty cycle of the bootstrap capacitor charging. p This can indirectly reduce the thermal shock on the bonding line.

[0083] In addition, the transient loss of the bootstrap diode can be used to reflect the damage to the bootstrap diode caused by excessive inrush current. Specifically, the transient loss of the bootstrap diode can be expressed by equation (7):

[0084] Where P is the transient loss of the bootstrap diode; T is the duty cycle; and 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 during one duty cycle, the loss of the bootstrap diode is related to the current flowing through it and the voltage drop across it. Due to the forward conduction characteristic of the bootstrap diode, its voltage drop can be approximated as a constant voltage drop; therefore, equation (7) can be equivalent to:

[0085] As can be understood from equation (8), the transient loss of the bootstrap diode is also related to the capacitance of the bootstrap capacitor and the voltage difference between the bootstrap capacitor and the operating voltage of the bootstrap capacitor before and after half a cycle. Therefore, the transient loss of the bootstrap diode can be reduced by adjusting the target duty cycle of the bootstrap capacitor charging to reduce the voltage difference between the bootstrap capacitor and the operating voltage of the bootstrap capacitor before and after half a cycle.

[0086] Figure 8 is a schematic diagram of another target duty cycle obtained by the control method of the power conversion circuit in Embodiment 1 of this application.

[0087] To reduce the potential for prolonged bootstrap capacitor charging time caused by intermittent charging of the bootstrap capacitor when controlling the on / off state of the upper or lower switching transistor via a target duty cycle, as shown in Figure 8, in some embodiments, step S200 may further include: gradually increasing the target duty cycle to obtain multiple different operating cycles. That is, after the bootstrap capacitor is charged using a target duty cycle in one operating cycle, the target duty cycle used for charging the bootstrap capacitor in the next operating cycle may be larger than the target duty cycle used in the previous operating cycle or multiple previous operating cycles.

[0088] When controlling the on / off state of the upper or lower switching transistor during different operating cycles, the target duty cycle gradually increases, and the charging time of the bootstrap capacitor gradually decreases. This can improve the charging efficiency of the bootstrap capacitor while reducing the risk of damage to the bootstrap diode from excessive inrush current.

[0089] In some embodiments, the target duty cycle can be gradually increased over one charging duration of the bootstrap capacitor to obtain multiple different duty cycles. For example, during one charging duration of the bootstrap capacitor, there can be multiple duty cycles for charging the bootstrap capacitor. In the first duty cycle, the bootstrap capacitor uses the minimum target duty cycle. In the next duty cycle, the target duty cycle used for charging the bootstrap capacitor can be larger than that of the first duty cycle, and so on.

[0090] In other embodiments, referring to Figure 8, the target duty cycle can be gradually increased over multiple charging durations of the bootstrap capacitor to obtain multiple different duty cycles. For example, in multiple charging durations, such as t1, t2, t3, and t4, the target duty cycle D1% used by the bootstrap capacitor is the same and minimum in the first charging duration t1; the target duty cycle D2% used by the bootstrap capacitor during charging in the next charging duration t2 is the same and can be larger than that in the first charging duration t1; the target duty cycle D3% in the next duration t3 is larger than that in the previous one, and so on.

[0091] Example 2:

[0092] Figure 9 is a schematic diagram of the structure of the full-bridge power conversion circuit 12 in Embodiment 2 of this application.

[0093] The control method of the power conversion circuit of this application can also be applied to the full-bridge power conversion circuit 12. Referring to Figure 9, the 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 SH1, a second upper switch SH2, a first lower switch SL1, and a second lower switch SL2. The first upper switch SH1 and the first lower switch 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 midpoint between the first upper switch SH1 and the first lower switch 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 SH2 and the second lower switch 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 midpoint between the second upper switch SH2 and the second lower switch 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 SH1 and the second upper switch SH2 are connected. It should also be noted that the full-bridge power conversion circuit 12 includes at least other components or units such as capacitors, inductors or resistors to form a complete power conversion circuit. This 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 to form a complete power conversion circuit will not be described in detail here.

[0094] In some embodiments, the first upper switch SH1 and the second upper switch SH2 can be connected to the high-voltage bus HV. After the first bootstrap unit 121 and the second bootstrap unit 122 boost the voltage, they can discharge to the high-voltage bus HV through the first upper switch SH1 and the second upper switch SH2. This facilitates the power conversion of the power conversion circuit by controlling the upper switches.

[0095] In some embodiments, the load 200 may be connected to the midpoint between the first upper switch SH1 and the first lower switch SL1 and the midpoint between the second upper switch SH2 and the second lower switch SL2.

[0096] In some embodiments, the first upper switch SH1, the second upper switch SH2, the first lower switch SL1, and the second lower switch SL2 can be MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors). Correspondingly, the first driver U1 and the second driver U2 can include gate drivers. In other embodiments, the first upper switch SH1, the second upper switch SH2, the first lower switch SL1, and the second lower switch SL2 can also be other types of switching transistors, such as polysilicon transistors, insulated-gate bipolar transistors (IGBTs), and bipolar junction transistors (BJTs); the first driver U1 and the second driver U2 can also be other types of drivers, such as microcontrollers that have the same or similar functions as the first driver U1 or the second driver U2.

[0097] In the full-bridge power conversion circuit 12, the power supply Vcc is connected to the first terminal of the first bootstrap capacitor CB1 through the first bootstrap diode DB1. The second terminal of the first bootstrap capacitor CB1 is connected to the midpoint of the connection between the source of the first upper switch SH1 and the drain of the first lower switch SL1. That is, the source of the first upper switch SH1 is connected to the drain of the first lower switch SL1, and the second terminal of the first bootstrap capacitor CB1 is connected to either the source of the first upper switch SH1 or the drain of the first lower switch SL1. The first power supply terminal VCC1 of the first driver U1 is connected to the first terminal 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 SH1. The second driving terminal Vo of the first driver U1 is connected to the gate of the first lower switch SL1. The first ground terminal GND1 of the first driver U1 is connected to the second terminal 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 SL1 and 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. The second power supply terminal VCC of the first driver U1 is connected to the power supply Vcc.

[0098] In the full-bridge power conversion circuit 12, the power supply Vcc is also connected to the first terminal of the second bootstrap capacitor CB2 through the second bootstrap diode DB2. The second terminal of the second bootstrap capacitor CB2 is connected to the midpoint of the connection between the source of the second upper switch SH2 and the drain of the second lower switch SL2. That is, the source of the second upper switch SH2 is connected to the drain of the second lower switch SL2, and the second terminal of the second bootstrap capacitor CB2 is connected to either the source of the second upper switch SH2 or the drain of the second lower switch SL2. The first power supply terminal VCC1 of the second driver U2 is connected to the first terminal 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 SH2. The second driving terminal Vo of the second driver U2 is connected to the gate of the second lower switch SL2. The first ground terminal GND1 of the second driver U2 is connected to the second terminal 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 SL2 and 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. The second power supply terminal VCC of the second driver U2 is connected to the power supply Vcc.

[0099] In some embodiments, the power supply Vcc can be the auxiliary power supply for the inverter.

[0100] In some embodiments, the first bootstrap unit 121 may further include a first bypass capacitor Cvcc1, an auxiliary power supply and a first bootstrap diode may be connected to a first terminal of the first bypass capacitor Cvcc1, and a second terminal of the first bypass capacitor Cvcc1 is grounded. The second bootstrap unit 122 may further include a second bypass capacitor Cvcc2, an auxiliary power supply and a second bootstrap diode may be connected to a first terminal of the second bypass capacitor Cvcc2, and a second terminal of the second bypass capacitor Cvcc2 is grounded. Thus, the auxiliary power supply can power the first bootstrap unit 121 through the first bypass capacitor Cvcc1 and power the second bootstrap unit 122 through the second bypass capacitor Cvcc2.

[0101] In some embodiments, the first bypass capacitor Cvcc1 may include a capacitor for energy storage and a capacitor for filtering, wherein the energy storage capacitor and the filtering capacitor are connected in parallel. Thus, the auxiliary power supply can simultaneously power the first bootstrap unit 121 through the first bypass capacitor Cvcc1 and perform filtering, thereby improving the purity of the supplied energy.

[0102] 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 simultaneously power the second bootstrap unit 122 through the second bypass capacitor Cvcc2 and perform filtering, thereby improving the purity of the supplied energy.

[0103] In the embodiments of this application, referring to the working principle of the half-bridge power conversion circuit, when the first lower switch 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 SL1 of the full-bridge power conversion circuit 12 is turned off and the first upper switch SH1 on the high side is turned on, the first ground terminal GND1 of the first driver U1 and the midpoint of the connection between the first lower switch SL1 and the first upper switch SH1 are pulled to the high-voltage bus HV. In this case, the first bootstrap capacitor CB1 can release the stored electrical energy to the high-voltage bus HV through the first upper switch SH1 on the high side via the first drive terminal Vo1 and the first ground terminal GND1 of the first driver U1.

[0104] When the second lower switch SL2 is turned on, the auxiliary power supply can charge the second bootstrap capacitor CB2 via the second bypass capacitor Cvcc2 and the second bootstrap diode DB2. When the second lower switch SL2 of the full-bridge power conversion circuit 12 is turned off and the second upper switch SH2 on the high side is turned on, the first ground terminal GND1 of the second driver U2 and the midpoint of the connection between the second lower switch SL2 and the second upper switch SH2 are pulled to the high-voltage bus HV. In this case, the second bootstrap capacitor CB2 can release the stored electrical energy to the high-voltage bus HV through the second upper switch SH2 on the high side via the first drive terminal Vo1 and the first ground terminal GND1 of the second driver U2.

[0105] Figure 10 is a flowchart of the control method of the full-bridge power conversion circuit according to Embodiment 2 of this application; Figure 11 is a schematic diagram of another target duty cycle obtained by the control method of the power conversion circuit according to an embodiment of this application.

[0106] Please refer to Figure 10. The control method applied to a full-bridge power conversion circuit includes:

[0107] Step S100: Obtain the target duty cycle for switching on or off the upper or lower switch based on the maximum loss of the bootstrap diode and the voltage of the bootstrap diode.

[0108] Step S200: Obtain the half-cycle based on the target duty cycle and the voltage of the bootstrap capacitor.

[0109] Step S301: In the first time interval, control the first driver to drive the first upper switch to be turned on with 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 to be turned off in the first half of each working cycle and turned on with a target duty cycle in the second half of each working cycle, so as to charge the first bootstrap capacitor.

[0110] Step S302: In the second time interval, control the second driver to drive the second upper switch to be turned on with the 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 to be turned off in the first half of each working cycle and turned on with the target duty cycle in the second half of each working cycle, so as to charge the second bootstrap capacitor.

[0111] 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 interleaved, 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, the next second time interval is adjacent to the previous first time interval, and so on.

[0112] In some embodiments, step S301 may further include: controlling the first driver to stop outputting a drive signal during a second time interval. Step S302 may further include: controlling the second driver to stop outputting a drive signal during a first time interval. Referring to Figure 11, the first time interval may be the duration t1 of the bootstrap capacitor charging, and the second time interval may be the duration t2 of the bootstrap capacitor charging. Taking the control of the first and second lower switching transistors as an example, during duration t1, the first lower switching transistor can be switched on and off with a target duty cycle D, and the drive of the second switching transistor can be blocked (i.e., the output drive signal can be stopped); during duration t2, the second lower switching transistor can be switched on and off with a target duty cycle D, and the drive of the first switching transistor can be blocked (i.e., the output drive signal can be stopped).

[0113] In some embodiments, stopping the output drive signal may mean disabling the current or voltage output at the signal output terminal, or outputting a low level to keep the switching transistor continuously off.

[0114] It is understood that the difference between the full-bridge power conversion circuit of Embodiment 2 and the half-bridge power conversion circuit of Embodiment 1 lies in the number of bridge arms. Specifically, as shown in Figures 3a, 3b, and 9, the full-bridge power conversion circuit is equivalent to a combination of two half-bridge power circuits. Correspondingly, as shown in Figures 4 and 10, the difference in the control method of the power conversion circuit is that when applied to the full-bridge power conversion circuit, it is equivalent to interleaving the control of two half-bridge power conversion circuits, while the control of a single bridge arm in the control steps is basically the same as the control method applied to the half-bridge power conversion circuit. Therefore, when the control method of the power conversion circuit of this application is applied to the full-bridge power conversion circuit, the method for obtaining the target duty cycle and the beneficial effects of the control method on the first bootstrap diode or the second bootstrap diode are basically the same as when applied to the half-bridge power conversion circuit, and will not be elaborated further here.

[0115] In addition, the full-bridge power conversion circuit may suffer from switching transistor stress caused by narrow-pulse hard switching. By using steps S301 and S302, 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 switching transistor stress caused by narrow-pulse hard switching in the full-bridge power conversion circuit.

[0116] In summary, in this embodiment, by obtaining a target duty cycle related to the maximum loss of the bootstrap diode in the bootstrap unit to control the on / off state of the upper or lower switch, the bootstrap capacitor of the bootstrap unit can be charged intermittently. This reduces the inrush current generated during the charging of the bootstrap capacitor and disperses the energy of the inrush current, thus reducing the problem of excessive inrush current damaging the bootstrap diode. By gradually increasing the target duty cycle to obtain different operating cycles, the charging time of the bootstrap capacitor gradually decreases when controlling the on / off state of the upper or lower switch in different operating cycles, thereby improving the charging efficiency of the bootstrap capacitor while reducing the damage to the bootstrap diode caused by excessive inrush current. By controlling the first driver to stop outputting the drive signal in the second time interval and controlling the second driver to stop outputting the drive signal in the first time interval, the charging of the first and second bootstrap capacitors can be alternately controlled in the full-bridge power conversion circuit, reducing the stress problem of the switching transistors caused by narrow pulse hard switching in the full-bridge power conversion circuit.

[0117] Figure 12 is a schematic diagram of the inverter structure according to an embodiment of this application.

[0118] Please refer to Figure 12. This application also provides an inverter 100, including: a power conversion circuit 1 and a controller 2.

[0119] The power conversion circuit 1 can 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 can be either the half-bridge power conversion circuit or the full-bridge power conversion circuit of any of the above embodiments.

[0120] The controller 2 can be a microcontroller unit (MCU) or a digital signal processor (DSP). The controller 2 is electrically connected to the power conversion circuit 1, and the controller 2 can execute the control method of any of the above embodiments to control the power conversion circuit 2.

[0121] In some embodiments, controller 2 may output control signals to the driver of any of the above embodiments to control the driver to drive the switching transistor. In other embodiments, controller 2 may directly function as the driver of any of the above embodiments to control the driver to drive the switching transistor.

[0122] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit it. Although this application has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of this application without departing from the spirit and scope of the technical solutions of this 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 switching transistor, and a lower switching transistor. The upper and lower switching transistors are connected in series and both are connected to the driver. The power supply terminal of the driver is connected to the midpoint between the upper and lower switching transistors through the bootstrap unit. The bootstrap unit includes a bootstrap capacitor and a bootstrap diode connected in series. The control method includes: The target duty cycle for switching on or off the upper or lower switch is obtained based on the maximum loss of the bootstrap diode and the voltage of the bootstrap diode. A half-cycle is obtained based on the target duty cycle and the voltage of the bootstrap capacitor, and two half-cycles constitute one working cycle. The driver controls the upper switch to turn on with the target duty cycle in the first half of each operating cycle and turn off in the second half of each operating cycle, and controls the lower switch to turn off in the first half of each operating cycle and turn on with the target duty cycle in the second half of each operating cycle, so as to charge the bootstrap capacitor.

2. The control method for the power conversion circuit according to claim 1, characterized in that, The step of obtaining the target duty cycle for switching on or off the upper or lower switch based on the maximum loss of the bootstrap diode and the voltage of the bootstrap diode includes: The relationship between the target duty cycle and the maximum loss of the bootstrap diode is obtained based on the current of the bootstrap capacitor and the voltage drop across the bootstrap diode. The current of the bootstrap capacitor is obtained based on the voltage of the zero-state response of the bootstrap capacitor during charging. The target duty cycle is obtained based on the correspondence and the current of the bootstrap capacitor.

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

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

5. The control method for the power conversion circuit according to claim 1, characterized in that, The step of obtaining a half-cycle based on the target duty cycle and the voltage of the bootstrap capacitor, wherein two half-cycles constitute one operating cycle, further includes: Gradually increase the target duty cycle to obtain multiple different work cycles.

6. The control method for 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, a second upper switch, a first lower switch, and a second lower switch. The first upper switch and the first lower switch are connected in series and are both connected to the first driver. The power supply terminal of the first driver is connected to the midpoint between the first upper switch and the first lower switch through the first bootstrap unit. The first bootstrap unit includes a first bootstrap capacitor and a first bootstrap diode connected in series. The second upper switch and the second lower switch are connected in series and are both connected to the second driver. The power supply terminal of the second driver is connected to the midpoint between the second upper switch and the second lower switch through the second bootstrap unit. The second bootstrap unit includes a second bootstrap capacitor and a second bootstrap diode connected in series. The first upper switch transistor and the second upper switch transistor are connected; The control method for the power conversion circuit also includes: In the first time interval, the first driver is controlled to drive the first upper switch to be turned on with the target duty cycle in the first half of each working cycle and turned off in the second half of each working cycle, and to drive the first lower switch to be turned off in the first half of each working cycle and turned on with the target duty cycle in the second half of each working cycle, so as to charge the first bootstrap capacitor. In the second time interval, the second driver is controlled to drive the second upper switch to be turned on with the target duty cycle in the first half of each working cycle and turned off in the second half of each working cycle, and to drive the second lower switch to be turned off in the first half of each working cycle and turned on with the target duty cycle in the second half of each working cycle, so as to charge the second bootstrap capacitor; the second time interval is different from the first time interval and is continuous.

7. The control method for the power conversion circuit according to claim 6, characterized in that, The control method for the power conversion circuit also includes: Control the first driver to stop outputting drive signals during the second time interval; The second driver is controlled to stop outputting drive signals during the first time interval.

8. An inverter, characterized in that, include: A power conversion circuit includes a driver, a bootstrap unit, an upper switch transistor, and a lower switch transistor. The upper switch transistor and the lower switch transistor are connected in series and are both connected to the driver. The power supply terminal of the driver is connected to the midpoint between the upper switch transistor and the lower switch transistor through the bootstrap unit. The bootstrap unit includes a bootstrap capacitor and a bootstrap diode connected in series. The controller is configured as follows: The target duty cycle for switching on or off the upper or lower switch is obtained based on the maximum loss of the bootstrap diode and the voltage of the bootstrap diode. A half-cycle is obtained based on the target duty cycle and the voltage of the bootstrap capacitor, wherein two half-cycles constitute one working cycle. The driver controls the upper switch to turn on with the target duty cycle in the first half of each operating cycle and turn off in the second half of each operating cycle, and controls the lower switch to turn off in the first half of each operating cycle and turn on with the target duty cycle in the second half of each operating cycle, so as to charge the bootstrap capacitor.

9. The inverter according to claim 8, characterized in that, The controller is also configured to gradually increase the target duty cycle to obtain multiple different operating cycles when a half-cycle is obtained based on the target duty cycle and the voltage of the bootstrap capacitor.

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, a second upper switch, a first lower switch, and a second lower switch. The first upper switch and the first lower switch are connected in series and are both connected to the first driver. The power supply terminal of the first driver is connected to the midpoint between the first upper switch and the first lower switch through the first bootstrap unit. The first bootstrap unit includes a first bootstrap capacitor and a first bootstrap diode connected in series. The second upper switch and the second lower switch are connected in series and are both connected to the second driver. The power supply terminal of the second driver is connected to the midpoint between the second upper switch and the second lower switch through the second bootstrap unit. The second bootstrap unit includes a second bootstrap capacitor and a second bootstrap diode connected in series. The first upper switch transistor and the second upper switch transistor are connected; The controller is also configured to: In the first time interval, the first driver is controlled to drive the first upper switch to be turned on with the target duty cycle in the first half of each working cycle and turned off in the second half of each working cycle, and to drive the first lower switch to be turned off in the first half of each working cycle and turned on with the target duty cycle in the second half of each working cycle, so as to charge the first bootstrap capacitor. In the second time interval, the second driver is controlled to drive the second upper switch to be turned on with the target duty cycle in the first half of each working cycle and turned off in the second half of each working cycle, and to drive the second lower switch to be turned off in the first half of each working cycle and turned on with the target duty cycle in the second half of each working cycle, so as to charge the second bootstrap capacitor. The second time interval is different from the first time interval and is continuous.

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