TWI818495B - Power converter and power conversion method using the same - Google Patents

Abstract

A power converter includes a voltage control unit, a current control unit and a hysteresis control unit. The voltage control unit is adapted to generate a first current command. The hysteresis control unit couples the voltage control unit with the current control unit and is adapted to, in the first mode, decouple the voltage control unit and the current control unit and generate a second current command to be transmitted to the current control unit when the detection current reaches the first threshold value, and couple the voltage control unit with the current control unit and transmit the first current command generated by the voltage control unit to the current control unit when the first current command reaches the second threshold, so as to convert the first mode of the power converter to a second mode. The current control unit is adapted to output a mode control signal according to the first current command and the second current command.

Description

Power converter and power conversion method using the same

The present invention relates to a power converter and a power conversion method using the same, and in particular, to a grid-connected dual-mode power converter and a power conversion method using the same.

It is known that during the mode switching process of a power converter, the switching path will oscillate at the conversion point (or "reversal point") between the two modes. This oscillation can easily cause the automatic control state equation to go out of control. Therefore, how to propose a new power converter to solve the problem of commutation oscillation is one of the efforts of those in this technical field.

Therefore, the present invention proposes a power converter and a power conversion method using the same, which can improve the aforementioned conventional problems.

An embodiment of the present invention provides a power converter. The power converter includes a voltage control unit, a current control unit and a hysteresis control unit. The voltage control unit is adapted to generate a first current command. The hysteresis control unit is coupled to the voltage control unit and the current control unit and is adapted to: in a first mode, when a detection current reaches a first threshold value, decouple the voltage control unit and the current control unit and generate a first transmitting the two current commands to the current control unit; and, when the first current command reaches a second threshold value, coupling the voltage control unit and the current control unit, and transmitting the first current command generated by the voltage control unit to the current control unit , to switch the power converter from a first mode to a second mode. Wherein, the current control unit is adapted to output a mode control signal according to the first current command and the second current command.

Another embodiment of the present invention provides a power conversion method. The power conversion method includes the following steps: a voltage control unit generates a first current command; in a first mode, when a detection current reaches a first threshold value, a hysteresis control unit uncouples the voltage control unit and a The current control unit generates a second current command and transmits it to the current control unit; and when the first current command reaches a second threshold, the hysteresis control unit couples the voltage control unit and the current control unit and transmits the command of the voltage control unit. The generated first current command is given to the current control unit to switch the power converter from the first mode to a second mode. Wherein, the current control unit is adapted to output a mode control signal according to the first current command and the second current command.

In order to have a better understanding of the above and other aspects of the present invention, examples are given below and are described in detail with reference to the accompanying drawings:

Please refer to Figures 1 to 4. Figure 1 is a schematic diagram of the power converter 100 according to an embodiment of the present invention. Figure 2 is a schematic diagram of the control body 120 of Figure 1. Figures 3A and 3B are Figure 1 is a system block diagram of the power supply mode switching of the power converter 100, and Figure 4 is a schematic diagram of the mode switching path of the power converter 100 of Figure 1.

As shown in FIGS. 1 and 4 , the power converter 100 includes a voltage control unit 111 , a current control unit 112 and a hysteresis control unit 113 . The voltage control unit 111 is adapted to generate the first current command . The hysteresis control unit 113 is coupled to the voltage control unit 111 and the current control unit 112 . The hysteresis control unit 113 is adapted to: (1). In the first mode, when a current is detected When the first threshold T1 is reached, the voltage control unit 111 and the current control unit 112 are decoupled and a second current command is generated. transmitted to the current control unit 112 (as shown in Figure 3A), and (2). When the first current command When the second threshold value T2 is reached, the voltage control unit 111 and the current control unit 112 are coupled, and the first current command generated by the voltage control unit 111 is transmitted. to the current control unit 111 (shown in FIG. 3B ) to switch the power converter 100 from the first mode to the second mode. The current control unit 112 is adapted to respond to the first current command and the second current command , output a mode control signal .

Since the hysteresis control unit 113 can decouple the voltage control unit 111 and the current control unit 112 at an appropriate time and transmit a current command different from the first The second current command to the current control unit 112, thereby changing the mode switching path of the power converter 100. For example, as shown in FIG. 4 , the mode switching path of the power converter 100 according to the embodiment of the present invention can avoid passing through or being too close to the origin O, thereby avoiding the occurrence of oscillation due to commutation.

As shown in Figure 1, the power flow of the power converter 100 is controlled by the current control unit 112 (through the mode control signal control), and the current command of the current control unit 112 is provided by the voltage control unit 111. Compared with controlling the power flow by the voltage control unit 111, the speed of controlling the power flow by the current control unit 112 is faster.

As shown in FIG. 1 , the power converter 100 further includes a controller 110 , a controller 120 and a user interface 130 . The aforementioned voltage control unit 111 , current control unit 112 and hysteresis control unit 113 may be configured in the controller 110 . In addition, the controller 110 further includes a switching signal generating unit 114, which can also be configured within the controller 110. The switching signal generating unit 114 can control the signal according to the mode A corresponding control signal P1 is generated to control the control body 120 to switch modes. In one embodiment, the switching signal generating unit 114 is, for example, a pulse width modulation (PWM) generating unit, the control signal P1 is, for example, a pulse width modulation signal, and the duty cycle of the pulse width modulation signal is The value can be determined according to the control signal Then, the mode switching is performed by controlling the control body 120.

At least one of the voltage control unit 111 , the current control unit 112 , the hysteresis control unit 113 and the switching signal generation unit 114 is, for example, software, firmware, or a physical circuit formed by a semiconductor process. At least two of the voltage control unit 111, the current control unit 112, the hysteresis control unit 113 and the switching signal generation unit 114 can be integrated into one unit. In addition, at least one of the voltage control unit 111 , the current control unit 112 , the hysteresis control unit 113 and the switching signal generation unit 114 may also be spatially separated from the controller 110 (but still electrically connected to the controller 110 ).

As shown in FIG. 1 , the user interface 130 can be coupled to the controller 110 . The user interface 130 can receive the control command S1 from the user and generate the corresponding voltage control command according to the control command S1 , voltage control command It may be transmitted to the controller 110, for example, to the voltage control unit 111 of the controller 110. In one embodiment, the user interface 130 can communicate with the controller 110 through an interface (not shown), where the interface is, for example, an RS422 to RS232 interface, but the embodiment of the present invention is not limited to this. In addition, as shown in FIG. 3A , the controller 110 adopts appropriate or even conventional automatic control according to the control loop (for example, a closed loop equation) formed by the voltage control unit 111 , the current control unit 112 and the hysteresis control unit 113 . Technical or automatic control state equations generate control signals close to or consistent with control instructions S1 . Although not stated, the error for the second current command and detection current The difference can be used in the control loop.

As shown in FIG. 2 , the control body 120 includes a first coupling terminal 120A and a second coupling terminal 120B. The first coupling terminal 120A can be coupled to the first mode system 10 that supports the first mode. The first mode The system 10 is, for example, a first power supply or a first load, and the second coupling terminal 120B can be coupled to the second mode system 20 that supports the second mode. The second mode system 20 is, for example, a second power supply or a second load. The first load is, for example, a power storage device, which is configured on a fixed object (such as a building, a charging pile, etc.), a movable device (such as an electric vehicle, etc.) or a portable device (such as a mobile power supply device, etc.) Battery. The second load is, for example, electronic devices such as home appliances and computers. In this embodiment, the first mode system 10 belongs to, for example, a local bus system (Local Bus System), for example, a DC side bus (DC BUS) of a distributed power generation end or a power storage end, and the second mode system 20 For example, it belongs to the Global Bus System, such as the AC BUS.

As shown in FIG. 2 , the control body 120 further includes a switch 121 , a capacitor C1 , an inductor L1 , a capacitance detector 122 and an inductance detector 123 . The capacitor C1 and the capacitance detector 122 may be coupled to the side of the switch 121 that conforms to the first mode. The capacitance detector 122 can detect a capacitance voltage of the capacitor C1 (herein referred to as "detection voltage"). ”). The inductor L1 and the inductance detector 123 may be coupled to the side of the switch 121 that conforms to the second mode. The inductor detector 123 can detect an inductor current of the inductor L1 (herein referred to as "detection current"). ”). The switch 121 is coupled to the capacitor C1 and the inductor L1. The switch 121 can convert the power storage of the first mode system 10 into the power consumption of the second mode system 20 , or convert the power supply of the second mode system 20 into the power storage of the first mode system 10 . By switching between the two modes, the flexibility of electric energy application can be increased. For example, when the electric vehicle (first load) has idle power storage, the electric vehicle can feed the stored power back to the mains (second power supply) or to the load that supports the second mode (second load); when the electric vehicle needs to be charged At this time, the mains power can be used to power electric vehicles. In addition, the embodiment of the present invention does not limit the specific circuit structure of the switch 121, which may include any suitable circuit or conventional circuit that can perform AC and DC conversion.

In addition, although not shown, in one embodiment, the aforementioned detection voltage and detect current After being processed by the transparent amplifier and converter, it is then transmitted to the controller 110, where the amplifier is, for example, a differential amplifier, and the converter, for example, is an analog-to-Digital Converter (ADC).

In addition, the first mode is, for example, one of the DC mode and the AC mode, and the second mode is, for example, the other one of the DC mode and the AC mode. The DC mode is, for example, a Power Factor Correction (PFC) operation, and the AC mode is, for example, an inverter (Inverter) operation. The first mode of the embodiment of the present invention is a DC mode, and the second mode is an AC mode as an example. In addition, as shown in Figure 4, the first mode and the second mode are, for example, represented by the horizontal axis ( ) is the boundary, the area below the horizontal axis (negative value) in Figure 4 is defined as the first mode, and the area above the horizontal axis (positive value) is defined as the second mode.

The following describes the detailed process of switching from the first mode to the second mode.

Please refer to Figures 4 and 5 at the same time. Figure 5 illustrates a mode switching flow chart of the power converter 100 in Figure 1 . The horizontal axis in Figure 4 represents the first current command changes, and the vertical axis represents the detection current changes. In this embodiment, the detection current For example, it is the peak value of the inductor current of the inductor L1 in Figure 2, but it can also be the inductor current itself or the average value.

In step S110, as shown in Figures 3B and 4, at the operating point A1 (in the first mode), when the current is detected When the first threshold value T1 is not reached, the hysteresis control unit 113 changes the first current command generated by the voltage control unit 111 to transmitted to the current control unit 112. For example, the hysteresis control unit 113 does not process the voltage control unit 111 and simply converts the first current command to transmitted to the current control unit 112. first current command based on the voltage control command and detection voltage error depends; in other words, the first current command The value of can be based on the error And updated. For example, taking the control instruction S1 indicating switching from the first mode to the second mode, in response to the control instruction S1, the controller 110 can generate a voltage smaller than the detection voltage. voltage control command (Right now, ) to produce a positive (+) error . Error The positive value of represents a tendency to switch from the negative direction (the area below the horizontal axis in Figure 4) to the positive direction (the area above the horizontal axis in Figure 4).

In addition, the first threshold T1 is, for example, a preset ratio of the peak value of the full load current. The preset ratio is, for example, any integer between 1% and 10%, such as 5%, 6%, 7%, etc. Taking a power converter 100 with a rated power of 5 kilowatts (kW) and a voltage of 220 volts as an example, the full load current is 22.72 amps, and the peak value of the full load current is 32.12 amps. Taking the default ratio of 5% as an example, the obtained first threshold value T1 is -1.61 amps (the negative value is based on the negative value definition of the first mode).

As shown in Figures 3B and 4, in the first switching path SW1 from the operating point A1 to the operating point A2, the first current command generated by the voltage control unit 112 The value continues to be updated. For example, the first current command It gradually changes from a negative value with a large amplitude to a negative value with a smaller amplitude, so that the detection current With the first current command Reduce the amplitude (the trend of change from negative value to positive value direction).

In step S120, as shown in Figures 3A and 4, at the operating point A2 (in the first mode), when the current is detected When the first threshold T1 is reached, the hysteresis control unit 113 decouples the voltage control unit 112 and the current control unit 110 and generates a second current command. , and transmits the second current command to the current control unit 112. Since the voltage control unit 112 and the current control unit 110 are decoupled, the current control unit 110 is not controlled by the voltage control unit 112, for example, the first current command generated by the voltage control unit 111 Not transmitted to current control unit 112.

As shown in Figures 3A and 4, in the second switching path SW2 from the operating point A2 to the operating point A3, the voltage control unit 112 is not affected by decoupling and does not change the first current command. In the generation mode, the updated first current command is still continuously generated. , but is not transmitted to the current control unit 112 . In the second switching path SW2, the second current command generated by the hysteresis control unit 113 The amplitude (Amplitude) is a constant, so that the detection current The value remains constant. In the second switching path SW2, when the first current command When the second threshold T2 is not reached, the hysteresis control unit 113 continues to transmit the second current command. to the current control unit 112.

In step S130, as shown in Figures 3B and 4, at the operating point A3 (in the first mode), when the first current command When reaching the second threshold T2 (reaching the operating point A3), the hysteresis control unit 113 re-couples the voltage control unit 111 and the current control unit 112, and transmits the first current command generated by the voltage control unit 111 Transmitted to the current control unit 111 to switch the power converter 100 from the first mode to the second mode. After the voltage control unit 111 and the current control unit 112 are re-coupled, the hysteresis control unit 113 does not generate the second current command. , nor transmit a signal to the current control unit 112; in other words, the hysteresis control unit 113 does not control the current control unit 112. In one embodiment, the second threshold T2 may be a certain proportion of the current rating indicated in the specifications of the power converter 100, such as any integer between 1% and 10%, such as 5%, 6%, 7% etc.

As shown in Figures 3B and 4, in the third switching path SW3 from the operating point A3 to the operating point A4, the detection current Between the first threshold T1 and the third threshold T3, the first current command generated by the voltage control unit 111 The value is roughly constant. In detail, since the occurrence time of the third switching path SW3 is quite short, the first current command The change in is not significant, so it can be regarded as a constant.

As shown in Figures 3B and 4, at the operating point A4 (in the second mode), when the current is detected When reaching the third threshold value T3, the hysteresis control unit 113 continues to transmit the first current command generated by the voltage control unit 111. transmitted to the current control unit 112. The third threshold T3 is determined in a manner similar to or the same as the first threshold T1. For example, the third threshold T3 is a preset ratio of the peak value of the full load current. The preset ratio is, for example, any integer between 1% and 10%, such as 5%, 6%, 7%, etc. Taking the power converter 100 with a rated power of 5 kW and a voltage of 220 volts as an example, the full load current is 22.72 amps, and the peak value of the full load current is 32.12 amps. Taking the default ratio of 5% as an example, the obtained third threshold value T3 is +1.61 amps (the positive value is based on the positive value definition of the second mode).

As shown in Figures 3B and 4, in the fourth switching path SW4 from the operating point A4 to the operating point A5 (in the second mode), when the current is detected When it is greater than the third threshold T3, the first current command generated by the voltage control unit 111 The values are continuously updated. For example, the first current command It gradually changes from a positive value with a small amplitude to a positive value with a larger amplitude, so that the detection current With the first current command Increase the amplitude (increase the transmission power in the positive direction).

As shown in Figures 3B and 4, in the fourth switching path SW4, when the current is detected When the operating point A5 is not reached, the hysteresis control unit 113 changes the first current command generated by the voltage control unit 111 to transmitted to the current control unit 112. For example, the hysteresis control unit 113 does not process the voltage control unit 111 and simply converts the first current command to transmitted to the current control unit 112. first current command based on the voltage control command and detection voltage error Depends. As shown in Figure 3B, the controller 110 can continuously generate a voltage smaller than the detection voltage. voltage control command (Right now, ) to produce a positive (+) error . In the fourth switching path SW4, the error A positive value indicates a continuous trend in the positive direction (the area above the horizontal axis in Figure 4). When detecting current When the operating point A5 is reached, the power flow reversal is completed.

The process of switching from the second mode to the first mode is similar to the aforementioned switching process from the first mode to the second mode. The following is explained using Figures 3 and 4 as examples.

As shown in Figures 3B and 4, in the operating point A5 (in the second mode), when the current is detected When the third threshold value T3 is not reached, the hysteresis control unit 113 transmits the first current command to the current control unit 112. first current command based on the voltage control command and detection voltage error Depends. Taking the control instruction S1 indicating switching from the second mode to the first mode as an example, in response to the control instruction S1, the controller 110 can generate a voltage greater than the detection voltage. voltage control command (Right now, ), to produce a negative (-) error . Error The negative value of represents the trend of switching from the positive direction (the area above the horizontal axis in Figure 4) to the negative direction (the area below the horizontal axis in Figure 4).

As shown in Figures 3B and 4, in the fifth switching path SW5 from the operating point A5 to the operating point A4 (in the second mode), the first current command generated by the voltage control unit 112 The value continues to be updated. For example, the first current command It gradually changes from a positive value with a large amplitude to a positive value with a smaller amplitude, so that the detection current With the first current command Reduce the amplitude (the trend of change from the positive value direction to the negative value direction).

As shown in Figures 3A and 4, at the operating point A4 (in the second mode), when the current is detected When the third threshold value T3 is reached, the hysteresis control unit 113 decouples the voltage control unit 112 and the current control unit 110 and generates a second current command. , and transmits the second current command to the current control unit 112. Since the voltage control unit 112 and the current control unit 110 are decoupled, the current control unit 110 is not controlled by the voltage control unit 112, for example, the first current command generated by the voltage control unit 111 Not transmitted to current control unit 112.

As shown in Figures 3A and 4, in the sixth switching path SW6 from the operating point A4 to the operating point A6, the voltage control unit 112 is not affected by decoupling and does not change the first current command. In the update mode, the updated first current command is still continuously generated. , but is not transmitted to the current control unit 112 . In the sixth switching path SW6, the second current command generated by the hysteresis control unit 113 The amplitude of is a constant, so that the detection current The value remains constant. In the sixth switching path SW6, when the first current command When the fourth threshold T4 is not reached, the hysteresis control unit 113 continues to transmit the second current command. to the current control unit 112. The determination method of the fourth threshold value T4 is the same as the aforementioned second threshold value T2, and will not be described again here.

As shown in Figures 3B and 4, in the operating point A6 (in the second mode), when the first current command When reaching the fourth threshold T4 (reaching the operating point A6), the hysteresis control unit 113 re-couples the voltage control unit 111 and the current control unit 112, and converts the first current command generated by the voltage control unit 111 Transmitted to the current control unit 111 to switch the power converter 100 from the second mode to the first mode. After the voltage control unit 111 and the current control unit 112 are re-coupled, the hysteresis control unit 113 does not generate the second current command. , nor transmit a signal to the current control unit 112; in other words, the hysteresis control unit 113 does not control the current control unit 112.

As shown in Figures 3B and 4, in the seventh switching path SW7 from the operating point A6 to the operating point A2, the detection current Between the third threshold value T3 and the first threshold value T1, the first current command generated by the voltage control unit 111 The value is roughly constant. In detail, since the occurrence time of the seventh switching path SW7 is quite short, the first current command The change in is not significant, so it can be regarded as a constant.

As shown in Figures 3B and 4, in the operating point A2 (in the first mode), when the current is detected When reaching the fourth threshold value T4, the hysteresis control unit 113 continues to transmit the first current command generated by the voltage control unit 111. transmitted to the current control unit 112.

As shown in Figures 3B and 4, in the eighth switching path SW8 from the operating point A2 to the operating point A1 (in the first mode), when the current is detected When it is greater than the first threshold T1, the first current command generated by the voltage control unit 111 The values are continuously updated. For example, the first current command It gradually changes from a negative value with a small amplitude to a negative value with a larger amplitude, so that the detection current With the first current command Increase the amplitude (increase the transmission power in the negative direction).

As shown in Figures 3B and 4, in the eighth switching path SW8, when the current is detected When the operating point A1 is not reached, the hysteresis control unit 113 changes the first current command generated by the voltage control unit 111 to transmitted to the current control unit 112. For example, the hysteresis control unit 113 does not process the voltage control unit 111 and simply converts the first current command to transmitted to the current control unit 112. first current command based on the voltage control command and detection voltage error Depends. As shown in Figure 3B, the controller 110 can continuously generate a voltage greater than the detection voltage. voltage control command (Right now, ), to produce a negative (-) error . In the eighth switching path SW8, the error The negative value of represents a trend that continues to change in the negative direction (the area below the horizontal axis in Figure 4). When detecting current Reaching the operating point A1 indicates completion of switching, or completion of power conversion.

In summary, embodiments of the present disclosure provide a power converter and a power conversion method using the same. The hysteresis control unit can selectively decouple the voltage control unit and the current control unit and change the current command so that the switching path avoids the reversal point. (For example, the origin in Figure 4) to avoid commutation oscillation, thereby preventing the controller of the automatic control equation from running out of control.

In summary, although the present invention has been disclosed above through embodiments, they are not intended to limit the present invention. Those with ordinary knowledge in the technical field to which the present invention belongs can make various modifications and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention shall be determined by the appended patent application scope.

100: Power converter 10: First mode system 20: Second mode system 110: Controller 111: Voltage control unit 112: Current control unit 113: Hysteresis control unit 114: Switching signal generation unit 120: Controller 120A: First coupling terminal 120B: Second coupling terminal 121: Switch 122: Capacitance detector 123: Inductance detector 130: User interface A1~A6: Operating point C1: Capacitor :Mode control signal L1:Inductor O:Origin :First current command :Second current command :Detect current :Voltage control command , :error : Detection voltage P1: Control signal S1: Control command SW1~SW8: Switching path T1: First threshold T2: Second threshold T3: Third threshold T4: Fourth threshold

Figure 1 is a schematic diagram of a power converter according to an embodiment of the present invention. Figure 2 shows a schematic diagram of the control body in Figure 1. Figures 3A and 3B illustrate the system block diagram of the power supply mode switching of the power converter in Figure 1. Figure 4 is a schematic diagram of the mode switching path of the power converter in Figure 1. Figure 5 illustrates the mode switching flow chart of the power converter in Figure 1 .

100:Power converter

110:Controller

111: Voltage control unit

112:Current control unit

113: Hysteresis control unit

114:Switch signal generation unit

120: Controller

130:User interface

D _cmd : mode control signal

I _{L,cmd 1} : first current command

I _{L,cmd 2} : second current command

I _L : detection current

V _bus,cmd : voltage control command

I _L,err : error

V _bus : detection voltage

P1: control signal

S1: Control command

Claims (18)

A power converter including: a voltage control unit adapted to generate a first current command; a current control unit; and A hysteresis control unit couples the voltage control unit and the current control unit and is suitable for: In a first mode, when a detected current reaches a first threshold, decouple the voltage control unit and the current control unit and generate a second current command to transmit to the current control unit; and When the first current command reaches a second threshold value, the voltage control unit and the current control unit are coupled, and the first current command generated by the voltage control unit is transmitted to the current control unit to convert the power supply The converter switches from the first mode to a second mode; Wherein, the current control unit is adapted to output a mode control signal according to the first current command and the second current command. The power converter as claimed in claim 1, wherein the hysteresis control unit is more suitable for: In the first mode, when the detected current does not reach the first threshold, the first current command generated by the voltage control unit is transmitted to the current control unit. The power converter of claim 1, wherein when the first current command reaches the second threshold, the amplitude of the second current command generated by the hysteresis control unit is constant, and the detection current maintains constant. The power converter of claim 1, wherein when the first current command does not reach the second threshold, the voltage control unit continues to update the first current command. The power converter as claimed in claim 1, wherein the hysteresis control unit is more suitable for: When the first current command does not reach the second threshold, the second current command is continuously transmitted to the current control unit. The power converter of claim 1, wherein when the detection current is between the first threshold and a third threshold, the voltage control unit generates the constant first current command. The power converter as claimed in claim 4, wherein the hysteresis control unit is more suitable for: When the detected current reaches a third threshold, the first current command generated by the voltage control unit is transmitted to the current control unit. The power converter of claim 6, wherein when the detection current is greater than the third threshold, the voltage control unit continues to update the first current command. As for the power converter described in claim 1, the hysteresis control unit is more suitable for: In the second mode, when the detection current reaches a third threshold, decouple the voltage control unit and the current control unit and generate the second current command to transmit to the current control unit; and When the first current command reaches a fourth threshold value, the voltage control unit and the current control unit are coupled, and the first current command generated by the voltage control unit is transmitted to the current control unit to convert the power supply The converter switches from the second mode to the first mode. A power conversion method including: a voltage control unit generates a first current command; In a first mode, when a detected current reaches a first threshold, a hysteresis control unit decouples the voltage control unit and a current control unit and generates a second current command to transmit to the current control unit; When the first current command reaches a second threshold, the hysteresis control unit couples the voltage control unit and the current control unit and transmits the first current command generated by the voltage control unit to the current control unit, to switch the power converter from the first mode to a second mode; Wherein, the current control unit is adapted to output a mode control signal according to the first current command and the second current command. The power conversion method as described in claim 10 further includes: In the first mode, when the detected current does not reach the first threshold, the hysteresis control unit transmits the first current command generated by the voltage control unit to the current control unit. The power conversion method as described in claim 10 further includes: When the first current command reaches the second threshold, the amplitude of the second current command generated by the hysteresis control unit is constant, and the detection current remains constant. The power conversion method as described in claim 10 further includes: When the first current command does not reach the second threshold, the voltage control unit continues to update the first current command. The power conversion method as described in claim 10 further includes: When the first current command does not reach the second threshold, the hysteresis control unit continues to transmit the second current command to the current control unit. The power conversion method as described in claim 10 further includes: When the detected current is between the first threshold and a third threshold, the voltage control unit generates a constant first current command. The power conversion method as described in claim 13 further includes: When the detected current reaches a third threshold, the hysteresis control unit transmits the first current command generated by the voltage control unit to the current control unit. The power conversion method as described in claim 15 further includes: When the detected current is greater than the third threshold, the voltage control unit continues to update the first current command. The power conversion method as described in claim 10 further includes: In the second mode, when the detected current reaches a third threshold, the hysteresis control unit decouples the voltage control unit and the current control unit and generates the second current command to transmit to the current control unit; as well as When the first current command reaches a fourth threshold, the hysteresis control unit couples the voltage control unit and the current control unit and transmits the first current command generated by the voltage control unit to the current control unit, to switch the power converter from the second mode to the first mode.

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