Power conversion apparatus and control method therefor

Abstract

The present application provides a power conversion apparatus and a control method therefor. The power conversion apparatus comprises a first bridge arm, a second bridge arm, a transformer, and a controller. The first bridge arm comprises a first switch transistor and a second switch transistor, and the second bridge arm comprises a third switch transistor and a fourth switch transistor. The first bridge arm and the second bridge arm are connected in parallel, and the midpoint of the first bridge arm and the midpoint of the second bridge arm are respectively connected to two ends of a primary winding of the transformer or to two ends of a secondary winding; the first switch transistor is connected to the third switch transistor. The controller controls, according to a comparison result of the electrical data of the transformer to a threshold value, the power conversion apparatus to switch between a first working mode and a second working mode. Under the first working mode, the phase of the fourth switch transistor lags behind the first phase angle of the first switch transistor, and under the second working mode, the phase of the first switch transistor lags behind the second phase angle of the fourth switch transistor. Additionally, the transformer is thus generally not subjected to bias so as to protect the power conversion apparatus.

Description

Power conversion device and control method thereof

[0001] This application claims priority to the Chinese patent application filed with the State Intellectual Property Office of China on January 5, 2024, with application number 202410024605.8, and priority to the Chinese patent application entitled “Power conversion device and control method thereof”, all contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to the field of power supply technology, and in particular to a power conversion device and a control method thereof. Background Art

[0003] The dual active bridge (DAB) converter can achieve electrical isolation between input and output, and has the advantages of high power density and easy soft switching. It can meet the needs of various applications of DC voltage to DC voltage and DC voltage to AC voltage conversion. Therefore, DAB converters have been widely used.

[0004] Traditional DAB converters primarily employ the circuit structure shown in Figure 1a. As shown in Figure 1a, the DAB converter primarily comprises a low-voltage full-bridge, a transformer T, an inductor Lr, and a high-voltage full-bridge. The low-voltage full-bridge comprises a first and second parallel-connected arm, while the high-voltage full-bridge comprises a third and fourth parallel-connected arm. The first arm comprises switches S1 and S2 connected in series, the second arm comprises switches S3 and S4 connected in series, the third arm comprises switches S5 and S6 connected in series, and the fourth arm comprises switches S7 and S8 connected in series. The DAB converter shown in Figure 1a can be controlled by adjusting the switching frequency, the phase angle between the first and second arms (e.g., the phase difference between switches S1 and S4), the phase angle between the third and fourth arms (e.g., the phase difference between switches S5 and S8), and the phase angle between the third and first arms (e.g., the phase difference between switches S1 and S5). Exemplarily, when the phase angle between the third bridge arm and the fourth bridge arm is 0, the voltage and current waveform diagram of the DAB converter is shown in Figure 1b. The DAB converter outputs power by adjusting the switching frequency fs, the phase angle θ1 between the first bridge arm and the second bridge arm, and the phase angle θ3 between the third bridge arm and the first bridge arm.

[0005] In actual physical circuits, each component has a certain initial deviation. For example, the on-resistance of a switch is calibrated to xΩ, but the actual on-resistance can range from 80%*xΩ to 120%*xΩ. As shown in Figure 1c, the on-resistance of S1 in the DAB converter is increased by the bias resistance rbias. When the DAB converter shown in Figure 1c uses the switching frequency fs, the phase angle θ1 between the first and second bridge arms, the phase angle θ0 between the third and fourth bridge arms, and the phase angle θ3 between the third and first bridge arms, as shown in Figure 1b, the voltage and current waveforms of the DAB converter shown in Figure 1c are shown in Figure 1d. During the period t0 to t2, switch S1 is turned on. Due to the increase in the on-resistance of S1 by rbias and the negative current iLr of the inductor Lr, the primary voltage vp of the transformer T has a certain positive offset compared to the primary voltage vp shown in Figure 1b. During the period from t2 to t3 , the switch S1 is still turned on, and since the on-resistance of the switch S1 increases by rbias , the primary voltage vp of the transformer T also has a certain bias.

[0006] In summary, during the period from t0 to t3, i.e., the period when the switch S1 is turned on, the primary voltage vp of the transformer T has a certain positive bias as a whole. However, the transformer T is subjected to a unidirectional bias, which may cause the transformer T to saturate and fail to work. In severe cases, the DAB converter may fail to work and be damaged. Summary of the Invention

[0007] The present application provides a power conversion device and a control method thereof, which can substantially prevent the transformer from being subjected to bias, thereby achieving protection for the power conversion device.

[0008] In a first aspect, the present application provides a power conversion device for connecting to a DC power supply and a power grid or load to perform energy conversion. The power conversion device includes a first bridge arm, a second bridge arm, a transformer, and a controller. The transformer includes a primary winding and a secondary winding. The first bridge arm includes a first switching transistor and a second switching transistor connected in series, and the second bridge arm includes a third switching transistor and a fourth switching transistor connected in series. The first bridge arm is connected in parallel with the second bridge arm, and the midpoint of the first bridge arm and the midpoint of the second bridge arm are respectively connected to the two ends of the primary winding or the two ends of the secondary winding. The first switching transistor is connected to the third switching transistor. The controller is configured to control the phase of the first switching transistor to lag behind the phase of the fourth switching transistor by a second phase angle when the electrical data of the transformer is greater than a threshold and the phase of the fourth switching transistor lags behind the phase of the first switching transistor by a first phase angle; and to control the phase of the fourth switching transistor to lag behind the phase of the first switching transistor by the first phase angle when the electrical data of the transformer is less than or equal to the threshold and the phase of the first switching transistor lags behind the phase of the fourth switching transistor by the second phase angle. The first phase angle and the second phase angle are both greater than or equal to 0° and less than or equal to 180°, and the electrical data of the transformer includes the input voltage, input current, output voltage or output current of the transformer.

[0009] In this embodiment, when it is determined based on the electrical data of the transformer that the transformer has a voltage bias, the power conversion device controls itself to switch between a first working mode (i.e., the phase of the fourth switch tube lags behind the phase of the first switch tube by a first phase angle) and a second working mode (i.e., the phase of the first switch tube lags behind the phase of the fourth switch tube by a second phase angle), so that when the transformer has a voltage bias, the front-to-back relationship between the first bridge arm and the second bridge arm is swapped before and after the mode switching, so that the current waveform amplitude and shape of the inductor in the power conversion device remain unchanged before and after the mode switching, but the phase relative to the first bridge arm is different, so that the voltage bias borne by the transformer after the mode switching is opposite to the voltage bias borne by the transformer before the mode switching, thereby offsetting the voltage bias borne by the transformer before the mode switching, so as to avoid transformer saturation, thereby achieving protection for the power conversion device.

[0010] With reference to the first aspect, in a first possible implementation manner, the first phase angle is the same as the second phase angle.

[0011] In this embodiment, since the second phase angle is the same as the first phase angle, it means that the phase angle between the first bridge arm and the second bridge arm is always the same before and after the working mode is switched. Therefore, it can be ensured that the current waveform of the inductor does not change before and after the working mode of the power conversion device is switched, thereby not affecting the normal operation of the power conversion device.

[0012] In combination with the first aspect or the first possible implementation of the first aspect, in a second possible implementation, the power conversion device further includes a third bridge arm, wherein the midpoint of the first bridge arm and the midpoint of the second bridge arm are respectively connected to the ends of the primary winding, and the midpoint of the third bridge arm is connected to the secondary winding. Alternatively, the midpoint of the first bridge arm and the midpoint of the second bridge arm are respectively connected to the ends of the secondary winding, and the midpoint of the third bridge arm is connected to the primary winding. The third bridge arm includes a fifth switching tube and a sixth switching tube connected in series. The controller is used to control the phase of the first switching tube to lag behind the second phase angle of the fourth switching tube and the phase of the fifth switching tube to lag behind the fourth phase angle of the fourth switching tube when the electrical data of the transformer is greater than the threshold, the phase of the fourth switching tube lags behind the phase of the first switching tube by the first phase angle, and the phase of the fifth switching tube lags behind the phase of the first switching tube by the third phase angle; and to control the phase of the fourth switching tube to lag behind the first phase angle of the first switching tube and the phase of the fifth switching tube to lag behind the phase of the first switching tube by the third phase angle when the electrical data of the transformer is less than or equal to the threshold, the phase of the first switching tube lags behind the phase of the fourth switching tube by the second phase angle, and the phase of the fifth switching tube lags behind the phase of the fourth switching tube by the fourth phase angle.

[0013] In this embodiment, the power conversion device ensures that the master-slave relationship between the third bridge arm and the main bridge arm remains unchanged before and after the mode switch, thereby not affecting the normal operation of the power conversion device. The main bridge arm is the main bridge arm of the first bridge arm and the second bridge arm, and is the first bridge arm when the power conversion device is in the first operating mode and the second bridge arm when the power conversion device is in the second operating mode.

[0014] In combination with the second possible implementation of the first aspect, in a third possible implementation, the third phase angle is the same as the fourth phase angle.

[0015] In this embodiment, since the second phase angle is the same as the first phase angle, and the fourth phase angle is the same as the third phase angle, it means that before and after the working mode is switched, the phase angle between the first bridge arm and the second bridge arm is always the same, and the phase angle between the third bridge arm and the main bridge arm is always the same. Therefore, it can be ensured that the voltage waveform of the power conversion device does not change before and after the working mode of the power conversion device is switched, and the current waveform of the inductor does not change before and after the working mode of the power conversion device is switched, thereby not affecting the normal operation of the power conversion device.

[0016] In combination with the second possible implementation of the first aspect or the third possible implementation of the first aspect, in a fourth possible implementation, the power conversion device also includes an inductor, which is connected in series with the primary winding or the secondary winding between the midpoint of the first bridge arm and the midpoint of the second bridge arm, or the inductor is connected in series with the primary winding or the secondary winding and then connected to the midpoint of the third bridge arm.

[0017] In conjunction with the fourth possible implementation of the first aspect, in a fifth possible implementation, the power conversion device further includes a first resonant capacitor and a second resonant capacitor, wherein the first resonant capacitor and the second resonant capacitor are connected in series and then in parallel with the third bridge arm. The two ends of the primary winding are respectively connected to the midpoint of the first bridge arm and the midpoint of the second bridge arm, and the secondary winding and the inductor are connected in series between the midpoint of the third bridge arm and the midpoint of the capacitor, where the midpoint of the capacitor is the connection point between the first resonant capacitor and the second resonant capacitor.

[0018] In this embodiment, the first resonant capacitor, the second resonant capacitor and the inductor form a resonant circuit, so that the power conversion device is a resonant power conversion device, so that the current waveform of the inductor tends to a sine wave, which is beneficial to reducing the peak value of the current flowing through the switching tube in the power conversion device, and is beneficial to the switching tube in the power conversion device to achieve soft switching, so as to reduce the loss of the switching tube, thereby improving the efficiency of the power conversion device.

[0019] In combination with the fourth possible implementation of the first aspect, in a sixth possible implementation, the power conversion device also includes a first resonant capacitor and a second resonant capacitor, wherein the first resonant capacitor and the second resonant capacitor are connected in series and then in parallel with the third bridge arm; the primary winding and the inductor are connected in series between the midpoint of the first bridge arm and the midpoint of the second bridge arm, and the two ends of the secondary winding are respectively connected to the midpoint of the third bridge arm and the midpoint of the capacitor, and the midpoint of the capacitor is the connection point between the first resonant capacitor and the second resonant capacitor.

[0020] In this embodiment, the first resonant capacitor, the second resonant capacitor, and the inductor form a resonant circuit, making the power conversion device a resonant power conversion device. This allows the current waveform of the inductor to approach a sine wave, thereby reducing the peak current flowing through the switching tube in the power conversion device. This also facilitates soft switching of the switching tube in the power conversion device, thereby reducing switching tube losses and improving the efficiency of the power conversion device. Furthermore, in addition to being connected in series with the secondary winding, the inductor can also be connected in series with the primary winding, allowing for diverse power conversion device structures and high flexibility.

[0021] In combination with the fourth possible implementation of the first aspect, in a seventh possible implementation, the power conversion device also includes a first resonant capacitor and a second resonant capacitor, wherein the first resonant capacitor and the second resonant capacitor are connected in series and then in parallel with the third bridge arm; the two ends of the primary winding are respectively connected to the midpoint of the third bridge arm and the midpoint of the capacitor, and the secondary winding and the inductor are connected in series between the midpoint of the first bridge arm and the midpoint of the second bridge arm, and the midpoint of the capacitor is the connection point of the first resonant capacitor and the second resonant capacitor.

[0022] In this embodiment, the first resonant capacitor, the second resonant capacitor, and the inductor form a resonant circuit, making the power conversion device a resonant power conversion device. This allows the current waveform of the inductor to approach a sine wave, thereby reducing the peak current flowing through the switching tube in the power conversion device. This also facilitates soft switching of the switching tube in the power conversion device, reducing switching tube losses and thus improving the efficiency of the power conversion device. Furthermore, the third bridge arm can be connected to the primary winding in addition to the secondary winding, allowing for diverse power conversion device structures and high flexibility.

[0023] In combination with the fourth possible implementation of the first aspect, in an eighth possible implementation, the power conversion device also includes a first resonant capacitor and a second resonant capacitor, wherein the first resonant capacitor and the second resonant capacitor are connected in series and then in parallel with the third bridge arm; the primary winding and the inductor are connected in series between the midpoint of the third bridge arm and the midpoint of the capacitor, and the two ends of the secondary winding are respectively connected to the midpoint of the first bridge arm and the midpoint of the second bridge arm, and the midpoint of the capacitor is the connection point of the first resonant capacitor and the second resonant capacitor.

[0024] In this embodiment, the first resonant capacitor, the second resonant capacitor and the inductor form a resonant circuit, so that the power conversion device is a resonant power conversion device, so that the current waveform of the inductor tends to a sine wave, which is beneficial to reducing the peak value of the current flowing through the switching tube in the power conversion device, and is beneficial to the switching tube in the power conversion device to achieve soft switching, so as to reduce the loss of the switching tube, thereby improving the efficiency of the power conversion device.

[0025] In conjunction with the fourth possible implementation manner of the first aspect, in a ninth possible implementation manner, the power conversion device further includes a fourth bridge arm, the fourth bridge arm being connected in parallel with the third bridge arm. Two ends of the primary winding are respectively connected to the midpoint of the first bridge arm and the midpoint of the second bridge arm, and the secondary winding and the inductor are connected in series between the midpoint of the third bridge arm and the midpoint of the fourth bridge arm.

[0026] In this embodiment, the power conversion device is applicable not only to a circuit structure with three bridge arms, but also to a circuit structure with four bridge arms, and has strong applicability.

[0027] In conjunction with the fourth possible implementation manner of the first aspect, in a tenth possible implementation manner, the power conversion device further includes a fourth bridge arm, the fourth bridge arm being connected in parallel with the third bridge arm. The primary winding and the inductor are connected in series between the midpoint of the first bridge arm and the midpoint of the second bridge arm, and the two ends of the secondary winding are connected to the midpoint of the third bridge arm and the midpoint of the fourth bridge arm, respectively.

[0028] In this embodiment, the power conversion device is applicable not only to a three-bridge-arm circuit structure but also to a four-bridge-arm circuit structure, thus providing strong applicability. Furthermore, the inductor can be connected in series with both the secondary winding and the primary winding, thus providing a diverse and highly flexible power conversion device.

[0029] In conjunction with the fourth possible implementation manner of the first aspect, in an eleventh possible implementation manner, the power conversion device further includes a fourth bridge arm, the fourth bridge arm being connected in parallel with the third bridge arm. Two ends of the primary winding are respectively connected to the midpoint of the third bridge arm and the midpoint of the fourth bridge arm, and the secondary winding and the inductor are connected in series between the midpoint of the first bridge arm and the midpoint of the second bridge arm.

[0030] In this embodiment, the power conversion device is applicable not only to a three-bridge-arm circuit structure but also to a four-bridge-arm circuit structure, thus providing strong applicability. Furthermore, the third bridge arm can be connected to both the secondary winding and the primary winding, thus providing a diverse and highly flexible power conversion device.

[0031] In conjunction with the fourth possible implementation manner of the first aspect, in a twelfth possible implementation manner, the power conversion device further includes a fourth bridge arm, the fourth bridge arm being connected in parallel with the third bridge arm. The primary winding and the inductor are connected in series between the midpoint of the third bridge arm and the midpoint of the fourth bridge arm, and the two ends of the secondary winding are connected to the midpoint of the first bridge arm and the midpoint of the second bridge arm, respectively.

[0032] In this embodiment, the power conversion device is applicable not only to a circuit structure with three bridge arms, but also to a circuit structure with four bridge arms, and has strong applicability.

[0033] In combination with any one of the ninth possible implementation manner of the first aspect to the twelfth possible implementation manner of the first aspect, in a thirteenth possible implementation manner, the power conversion device further includes a first resonant capacitor. The primary winding or the secondary winding, the inductor, and the first resonant capacitor are connected in series between the midpoint of the first bridge arm and the midpoint of the second bridge arm, or the primary winding or the secondary winding and the first resonant capacitor are connected in series between the midpoint of the first bridge arm and the midpoint of the second bridge arm, or the primary winding or the secondary winding, the inductor, and the first resonant capacitor are connected in series between the midpoint of the third bridge arm and the midpoint of the fourth bridge arm, or the primary winding or the secondary winding and the first resonant capacitor are connected in series between the midpoint of the third bridge arm and the midpoint of the fourth bridge arm.

[0034] In this embodiment, the first resonant capacitor and the inductor form a resonant circuit, making the power conversion device a resonant power conversion device. This allows the current waveform of the inductor to approach a sinusoidal wave, thereby reducing the peak current flowing through the switching tube in the power conversion device. This also facilitates soft switching of the switching tube in the power conversion device, thereby reducing switching tube losses and improving the efficiency of the power conversion device. Furthermore, in addition to being able to connect the first resonant capacitor and the inductor to the same winding of the transformer, the first resonant capacitor and the inductor can also be connected to two different windings of the transformer, allowing for diverse and highly flexible structures of the power conversion device.

[0035] In combination with any one of the fourth possible implementation manner of the first aspect to the thirteenth possible implementation manner of the first aspect, in a fourteenth possible implementation manner, the inductor includes a leakage inductance of a transformer.

[0036] In a second aspect, the present application provides a control method for a power conversion device, the method comprising: when the electrical data of the transformer is greater than a threshold and the phase of the fourth switch tube lags behind the phase of the first switch tube by a first phase angle, controlling the phase of the first switch tube to lag behind the phase of the fourth switch tube by a second phase angle; when the electrical data of the transformer is less than or equal to the threshold and the phase of the first switch tube lags behind the phase of the fourth switch tube by the second phase angle, controlling the phase of the fourth switch tube to lag behind the phase of the first switch tube by the first phase angle, wherein the first phase angle and the second phase angle are both greater than or equal to 0° and less than or equal to 180°, and the electrical data of the transformer include the input voltage, input current, output voltage or output current of the transformer. The method is applicable to a power conversion device, which is used to be connected between a DC power supply and a power grid or a load to perform energy conversion. The power conversion device includes a first bridge arm, a second bridge arm and a transformer. The transformer includes a primary winding and a secondary winding. The first bridge arm includes a first switching tube and a second switching tube connected in series. The second bridge arm includes a third switching tube and a fourth switching tube connected in series. The first bridge arm is connected in parallel with the second bridge arm, and the midpoint of the first bridge arm and the midpoint of the second bridge arm are respectively connected to the two ends of the primary winding or the two ends of the secondary winding; the first switching tube is connected to the third switching tube.

[0037] With reference to the second aspect, in a first possible implementation manner, the first phase angle is the same as the second phase angle.

[0038] In combination with the second aspect or the first possible implementation of the second aspect, in a second possible implementation, the power conversion device further includes a third bridge arm, wherein the midpoint of the first bridge arm and the midpoint of the second bridge arm are respectively connected to the ends of the primary winding, and the midpoint of the third bridge arm is connected to the secondary winding. Alternatively, the midpoint of the first bridge arm and the midpoint of the second bridge arm are respectively connected to the ends of the secondary winding, and the midpoint of the third bridge arm is connected to the primary winding. The third bridge arm includes a fifth switching tube and a sixth switching tube connected in series. The controller is used to control the phase of the first switching tube to lag behind the second phase angle of the fourth switching tube and the phase of the fifth switching tube to lag behind the fourth phase angle of the fourth switching tube when the electrical data of the transformer is greater than the threshold, the phase of the fourth switching tube lags behind the phase of the first switching tube by the first phase angle, and the phase of the fifth switching tube lags behind the phase of the first switching tube by the third phase angle; and to control the phase of the fourth switching tube to lag behind the first phase angle of the first switching tube and the phase of the fifth switching tube to lag behind the phase of the first switching tube by the third phase angle when the electrical data of the transformer is less than or equal to the threshold, the phase of the first switching tube lags behind the phase of the fourth switching tube by the second phase angle, and the phase of the fifth switching tube lags behind the phase of the fourth switching tube by the fourth phase angle.

[0039] In combination with the second possible implementation of the second aspect, in a third possible implementation, the third phase angle is the same as the fourth phase angle.

[0040] In combination with the second possible implementation of the second aspect or the third possible implementation of the second aspect, in a fourth possible implementation, the power conversion device also includes an inductor, which is connected in series with the primary winding or the secondary winding between the midpoint of the first bridge arm and the midpoint of the second bridge arm, or the inductor is connected in series with the primary winding or the secondary winding and then connected to the midpoint of the third bridge arm.

[0041] In conjunction with the fourth possible implementation of the second aspect, in a fifth possible implementation, the power conversion device further includes a first resonant capacitor and a second resonant capacitor, wherein the first resonant capacitor and the second resonant capacitor are connected in series and then in parallel with the third bridge arm. The two ends of the primary winding are respectively connected to the midpoint of the first bridge arm and the midpoint of the second bridge arm, and the secondary winding and the inductor are connected in series between the midpoint of the third bridge arm and the midpoint of the capacitor, where the midpoint of the capacitor is the connection point between the first resonant capacitor and the second resonant capacitor.

[0042] In combination with the fourth possible implementation of the second aspect, in a sixth possible implementation, the power conversion device also includes a first resonant capacitor and a second resonant capacitor, wherein the first resonant capacitor and the second resonant capacitor are connected in series and then in parallel with the third bridge arm; the primary winding and the inductor are connected in series between the midpoint of the first bridge arm and the midpoint of the second bridge arm, and the two ends of the secondary winding are respectively connected to the midpoint of the third bridge arm and the midpoint of the capacitor, and the midpoint of the capacitor is the connection point between the first resonant capacitor and the second resonant capacitor.

[0043] In combination with the fourth possible implementation of the second aspect, in a seventh possible implementation, the power conversion device also includes a first resonant capacitor and a second resonant capacitor, wherein the first resonant capacitor and the second resonant capacitor are connected in series and then in parallel with the third bridge arm; the two ends of the primary winding are respectively connected to the midpoint of the third bridge arm and the midpoint of the capacitor, and the secondary winding and the inductor are connected in series between the midpoint of the first bridge arm and the midpoint of the second bridge arm, and the midpoint of the capacitor is the connection point of the first resonant capacitor and the second resonant capacitor.

[0044] In combination with the fourth possible implementation of the second aspect, in an eighth possible implementation, the power conversion device also includes a first resonant capacitor and a second resonant capacitor, wherein the first resonant capacitor and the second resonant capacitor are connected in series and then in parallel with the third bridge arm; the primary winding and the inductor are connected in series between the midpoint of the third bridge arm and the midpoint of the capacitor, and the two ends of the secondary winding are respectively connected to the midpoint of the first bridge arm and the midpoint of the second bridge arm, and the midpoint of the capacitor is the connection point of the first resonant capacitor and the second resonant capacitor.

[0045] In conjunction with the fourth possible implementation manner of the second aspect, in a ninth possible implementation manner, the power conversion device further includes a fourth bridge arm, the fourth bridge arm being connected in parallel with the third bridge arm. Two ends of the primary winding are respectively connected to the midpoint of the first bridge arm and the midpoint of the second bridge arm, and the secondary winding and the inductor are connected in series between the midpoint of the third bridge arm and the midpoint of the fourth bridge arm.

[0046] In conjunction with the fourth possible implementation manner of the second aspect, in a tenth possible implementation manner, the power conversion device further includes a fourth bridge arm, the fourth bridge arm being connected in parallel with the third bridge arm. The primary winding and the inductor are connected in series between the midpoint of the first bridge arm and the midpoint of the second bridge arm, and the two ends of the secondary winding are connected to the midpoint of the third bridge arm and the midpoint of the fourth bridge arm, respectively.

[0047] In conjunction with the fourth possible implementation manner of the second aspect, in an eleventh possible implementation manner, the power conversion device further includes a fourth bridge arm, the fourth bridge arm being connected in parallel with the third bridge arm. Two ends of the primary winding are respectively connected to the midpoint of the third bridge arm and the midpoint of the fourth bridge arm, and the secondary winding and the inductor are connected in series between the midpoint of the first bridge arm and the midpoint of the second bridge arm.

[0048] In conjunction with the fourth possible implementation manner of the second aspect, in a twelfth possible implementation manner, the power conversion device further includes a fourth bridge arm, the fourth bridge arm being connected in parallel with the third bridge arm. The primary winding and the inductor are connected in series between the midpoint of the third bridge arm and the midpoint of the fourth bridge arm, and the two ends of the secondary winding are connected to the midpoint of the first bridge arm and the midpoint of the second bridge arm, respectively.

[0049] In combination with any one of the ninth possible implementation manner of the second aspect to the twelfth possible implementation manner of the second aspect, in a thirteenth possible implementation manner, the power conversion device further includes a first resonant capacitor. The primary winding or the secondary winding, the inductor, and the first resonant capacitor are connected in series between the midpoint of the first bridge arm and the midpoint of the second bridge arm, or the primary winding or the secondary winding and the first resonant capacitor are connected in series between the midpoint of the first bridge arm and the midpoint of the second bridge arm, or the primary winding or the secondary winding, the inductor, and the first resonant capacitor are connected in series between the midpoint of the third bridge arm and the midpoint of the fourth bridge arm, or the primary winding or the secondary winding and the first resonant capacitor are connected in series between the midpoint of the third bridge arm and the midpoint of the fourth bridge arm.

[0050] In combination with any one of the fourth possible implementation manner of the second aspect to the thirteenth possible implementation manner of the second aspect, in a fourteenth possible implementation manner, the inductor includes a leakage inductance of a transformer.

[0051] It should be understood that the implementation and beneficial effects of the above-mentioned aspects of the present application can be referenced to each other. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] FIG1a is a schematic structural diagram of a DAB converter provided by the prior art;

[0053] FIG1b is a schematic diagram of voltage and current waveforms of a DAB converter provided by the prior art;

[0054] FIG1c is a schematic structural diagram of a DAB converter with bias provided in the prior art;

[0055] FIG1d is a schematic diagram of voltage and current waveforms of a DAB converter with bias provided by the prior art;

[0056] FIG2 is a schematic diagram of an application scenario of the power conversion device provided by the present application;

[0057] FIG3a is a schematic structural diagram of a power conversion device provided by the present application;

[0058] FIG3 b is another schematic structural diagram of the power conversion device provided by the present application;

[0059] FIG3c is another schematic structural diagram of the power conversion device provided by the present application;

[0060] FIG3 d is another schematic structural diagram of the power conversion device provided by the present application;

[0061] FIG4 is another schematic structural diagram of the power conversion device provided by the present application;

[0062] FIG5 is a schematic diagram of voltage and current waveforms of a power conversion device provided by the present application;

[0063] FIG6a is another schematic structural diagram of the power conversion device provided by the present application;

[0064] FIG6 b is another schematic structural diagram of the power conversion device provided by the present application;

[0065] FIG6c is another schematic structural diagram of the power conversion device provided by the present application;

[0066] FIG6 d is another schematic structural diagram of the power conversion device provided by the present application;

[0067] FIG6e is another schematic structural diagram of the power conversion device provided by the present application;

[0068] FIG7 is another schematic structural diagram of the power conversion device provided by the present application;

[0069] FIG8 is another schematic diagram of voltage and current waveforms of the power conversion device provided by the present application;

[0070] FIG9 is another schematic diagram of voltage and current waveforms of the power conversion device provided by the present application;

[0071] FIG10a is another schematic structural diagram of the power conversion device provided by the present application;

[0072] FIG10b is another schematic structural diagram of the power conversion device provided by the present application;

[0073] FIG10c is another schematic structural diagram of the power conversion device provided by the present application;

[0074] FIG10d is another schematic structural diagram of the power conversion device provided by the present application;

[0075] FIG10e is another schematic structural diagram of the power conversion device provided by the present application;

[0076] FIG11a is another schematic structural diagram of the power conversion device provided by the present application;

[0077] FIG11b is another schematic structural diagram of the power conversion device provided by the present application;

[0078] FIG12a is another schematic structural diagram of the power conversion device provided by the present application;

[0079] FIG12b is another schematic structural diagram of a power conversion device provided by the present application;

[0080] FIG13 is a flow chart of a control method for a power conversion device provided by the present application;

[0081] FIG14 is another flow chart of the control method of the power conversion device provided in the present application. DETAILED DESCRIPTION

[0082] The power conversion device provided in this application can be applied to various application fields such as energy storage power generation, photovoltaic power generation, new energy smart microgrid, power transmission and distribution, etc. The power conversion device provided in this application can be an inverter, a power storage converter (Power Conversion System, PCS), an uninterruptible power supply (Uninterrupted Power Supply, UPS), etc., and is applicable to different application scenarios, such as photovoltaic power supply scenarios, energy storage power supply scenarios, photovoltaic and storage hybrid power supply scenarios, UPS power supply scenarios, etc. The photovoltaic power supply scenario is used as an example for explanation below.

[0083] Refer to Figure 2, which is a schematic diagram of an application scenario of the power conversion device provided by the present application. In the photovoltaic power supply scenario, the power conversion device provided by the present application is the DAB converter shown in Figure 2, which includes a first bridge arm, a second bridge arm, a third bridge arm, a fourth bridge arm, a transformer T, an inductor Lr and a controller. The transformer T includes a primary winding Lp and a secondary winding Ls. The input end of the DAB converter is connected to the photovoltaic module, and the output end is connected to the AC power grid or household appliances. Among them, the first bridge arm is composed of a switch tube S1 and a switch tube S2 connected in series, the second bridge arm is composed of a switch tube S3 and a switch tube S4 connected in series, the third bridge arm is composed of a switch tube S5 and a switch tube S6 connected in series, and the fourth bridge arm is composed of a switch tube S7 and a switch tube S8 connected in series. The first bridge arm and the second bridge arm are connected in parallel at the input end of the DAB converter, and the midpoint of the first bridge arm (i.e., the connection point of the switch tubes S1 and S2) and the midpoint of the second bridge arm (i.e., the connection point of the switch tubes S3 and S4) are respectively connected to the two ends of the primary winding Lp. The secondary winding Ls and inductor Lr are connected in series between the midpoint of the third bridge arm (i.e., the junction of switches S5 and S6) and the midpoint of the fourth bridge arm (i.e., the junction of switches S7 and S8). The third and fourth bridge arms are connected in parallel at the output of the DAB converter. Optionally, the first bridge arm comprises switches S5 and S6 connected in series, the second bridge arm comprises switches S7 and S8 connected in series, the third bridge arm comprises switches S1 and S2 connected in series, and the fourth bridge arm comprises switches S3 and S4 connected in series.

[0084] After the DAB converter begins operation, the controller in the DAB converter inverts the DC power at the DAB converter's input into AC power by adjusting the switching frequency in the bridge arms and the phase angles between the four bridge arms, thereby providing power to various types of electrical devices, such as an AC grid or a load. During the process of the DAB converter supplying power to the electrical devices, the controller controls the phase of switch S1 to lag behind the phase of switch S4 by a second phase angle if the electrical data of transformer T (such as input voltage, input current, output voltage, or output current) is greater than a threshold and the phase of switch S4 lags behind the phase of switch S1 by a first phase angle. Furthermore, the controller controls the phase of switch S4 to lag behind the phase of switch S1 by the first phase angle if the electrical data of transformer T is less than or equal to the threshold and the phase of switch S1 lags behind the phase of switch S4 by the second phase angle. The first phase angle and the second phase angle are both greater than or equal to 0° and less than or equal to 180°. Thus, when a voltage bias occurs in the transformer T, the DAB converter offsets the voltage bias borne by the transformer T by controlling itself to switch between the first working mode (i.e., the phase of the switch tube S4 lags behind the phase of the switch tube S1 by a first phase angle) and the second working mode (the phase of the switch tube S1 lags behind the phase of the switch tube S4 by a second phase angle).

[0085] It can be understood that when a voltage bias occurs in the transformer T, the DAB converter controls itself to switch between the first operating mode and the second operating mode, so that the front-to-back relationship between the first bridge arm and the second bridge arm when the voltage bias occurs in the transformer T is swapped before and after the mode switching, so that the amplitude and shape of the current waveform of the inductor Lr remain unchanged before and after the mode switching, but the phase relative to the first bridge arm is different, so that the voltage bias borne by the transformer T after the mode switching is opposite to the voltage bias borne by the transformer T before the mode switching, thereby offsetting the voltage bias borne by the transformer T before the mode switching, avoiding saturation of the transformer T, and thus protecting the DAB converter.

[0086] The above is only an example of the application scenarios of the power conversion device provided by this application, and is not an exhaustive list. This application does not limit the application scenarios.

[0087] The working principle of the power conversion device provided in this application is illustrated below with reference to Figures 3a to 12b.

[0088] Referring to FIG3a , FIG3a is a schematic diagram of the structure of a power conversion device provided in the present application. As shown in FIG3a , the power conversion device 1 is used to connect between a DC power supply and a power grid or load to perform energy conversion. The power conversion device 1 includes a first bridge arm 11, a second bridge arm 12, a transformer 13, and a controller 14. The transformer 13 includes a primary winding Lp and a secondary winding Ls. The input end of the power conversion device 1 includes input terminals in11 and in12, which are respectively connected to the positive and negative poles of the DC power supply. The DC power supply includes a photovoltaic module or a battery cluster. The output end of the power conversion device 1 includes output terminals out11 and out12, which are respectively connected to the AC power grid or load. The first bridge arm 11 and the second bridge arm 12 are connected in parallel between the input terminals in11 and in12. The midpoint of the first bridge arm 11 and the midpoint of the second bridge arm 12 are respectively connected to the two ends of the primary winding Lp, such as the same-name end and the opposite-name end of the primary winding Lp. The first bridge arm 11 includes a switch tube S1 and a switch tube S2 connected in series, and the midpoint of the first bridge arm 11 is the connection point between the switch tubes S1 and S2. The second bridge arm 12 includes a switch tube S3 and a switch tube S4 connected in series, and the midpoint of the second bridge arm 12 is the connection point between the switch tubes S3 and S4. Among them, the switch tube in each of the above-mentioned bridge arms can be a controllable switch tube, such as a metal-oxide-semiconductor field-effect transistor (MOSFET), a bipolar junction transistor (BJT), an insulated gate bipolar transistor (IGBT), etc. The power conversion device 1 also includes an inductor Lr, which is connected in series with the secondary winding Ls. Optionally, the inductor Lr can also be connected in series with the primary winding Lp. For details, please refer to the power conversion device 1 shown in Figure 3b. As shown in FIG3 b , the inductor Lr and the primary winding Lp are connected in series between the midpoint of the first bridge arm 11 and the midpoint of the second bridge arm 12 .

[0089] Optionally, the first bridge arm 11 and the second bridge arm 12 can also be connected to the secondary winding Ls, please refer to the power conversion device 1 shown in Figure 3c for details. As shown in Figure 3c, the first bridge arm 11 and the second bridge arm 12 are connected in parallel between the output terminals out11 and out12 of the power conversion device 1. The midpoint of the first bridge arm 11 and the midpoint of the second bridge arm 12 are respectively connected to the two ends of the secondary winding Ls, such as the opposite-name end and the same-name end of the secondary winding Ls. The power conversion device 1 also includes an inductor Lr, which is connected in series with the primary winding Lp. Optionally, the inductor Lr can also be connected in series with the secondary winding Ls, please refer to the power conversion device 1 shown in Figure 3d for details. As shown in Figure 3d, the inductor Lr is connected in series with the secondary winding Ls between the midpoint of the first bridge arm 11 and the midpoint of the second bridge arm 12.

[0090] It should be noted that the inductor Lr in the present application may be the leakage inductance of the transformer 13 or an inductor independent of the transformer 13 , and the present application does not impose any limitation on this.

[0091] In one embodiment, after the power conversion device 1 is in operation, the controller 14 controls the power conversion device 1 to be in the first operating mode or the second operating mode. Thereafter, the controller 14 starts to detect the electrical data of the transformer 13, and controls the power conversion device 1 to switch between the first operating mode and the second operating mode based on the electrical data of the transformer 13. The electrical data of the transformer 13 includes the input voltage, input current, output voltage, or output current of the transformer 13. In the first operating mode, the phase of the switch tube S4 lags behind the phase of the switch tube S1 by a first phase angle, that is, the turn-on time of the switch tube S4 lags behind the turn-on time of the switch tube S1, and the phase difference between the phase of the switch tube S4 at the initial turn-on time and the phase of the switch tube S1 at the initial turn-on time is the first phase angle. Optionally, the first phase angle may also be the phase angle at which the phase of switch S3 lags behind the phase of switch S2, i.e., the turn-on time of switch S3 lags behind the turn-on time of switch S2, and the phase difference between the phase of switch S3 at the initial turn-on time and the phase of switch S2 at the initial turn-on time is the first phase angle. In the second operating mode, the phase of switch S1 lags behind the phase of switch S4 by a second phase angle, i.e., the turn-on time of switch S1 lags behind the turn-on time of switch S4, and the phase difference between the phase of switch S1 at the initial turn-on time and the phase of switch S4 at the initial turn-on time is the second phase angle. Optionally, the second phase angle may also be the phase angle at which the phase of switch S2 lags behind the phase of switch S3, i.e., the turn-on time of switch S2 lags behind the turn-on time of switch S3, and the phase difference between the phase of switch S2 at the initial turn-on time and the phase of switch S3 at the initial turn-on time is the second phase angle. The first phase angle and the second phase angle are both greater than or equal to 0° and less than or equal to 180°.

[0092] Specifically, when the power conversion device 1 is in the first operating mode and the electrical data of the transformer 13 is greater than a threshold, the controller 14 controls the power conversion device 1 to switch to the second operating mode. The controller 14 also controls the power conversion device 1 to switch to the first operating mode when the power conversion device 1 is in the second operating mode and the electrical data of the transformer 13 is less than or equal to the threshold. This ensures that when a voltage offset occurs in the transformer 13, the controller 14 controls the power conversion device 1 to switch between the first and second operating modes to offset the voltage offset experienced by the transformer 13.

[0093] In an embodiment of the present application, when a voltage bias occurs in the transformer 13, the power conversion device 1 controls itself to switch between the first working mode and the second working mode, so that when a voltage bias occurs in the transformer 13, the front-to-back relationship between the first bridge arm 11 and the second bridge arm 12 is swapped before and after the mode switching, so that the current waveform amplitude and shape of the inductor Lr before and after the mode switching remain unchanged, but the phase relative to the first bridge arm 11 is different, so that the voltage bias borne by the transformer 13 after the mode switching is opposite to the voltage bias borne by the transformer 13 before the mode switching, thereby offsetting the voltage bias borne by the transformer 13 before the mode switching, so as to avoid saturation of the transformer 13, thereby achieving protection for the power conversion device 1.

[0094] Since the power conversion device 1 eliminates the voltage bias borne by the transformer 13 in the same manner regardless of whether the inductor Lr in the power conversion device 1 is connected in series with the primary winding Lp or the secondary winding Ls, for the sake of convenience, the working principle of the power conversion device 1 is introduced below by taking the inductor Lr connected in series with the secondary winding Ls as an example.

[0095] For example, refer to Figure 4, which is another structural schematic diagram of the power conversion device provided by the present application. As shown in Figure 4, compared with the power conversion device 1 shown in Figure 3a, the power conversion device 1 shown in Figure 4 also includes a third bridge arm 15 and a fourth bridge arm 16. Among them, the third bridge arm 15 and the fourth bridge arm 16 are connected in parallel between the output terminals out11 and out12 of the power conversion device 1, and the secondary winding Ls and the inductor Lr are connected in series between the midpoint of the third bridge arm 15 and the midpoint of the fourth bridge arm 16. The third bridge arm 15 is composed of a switch tube S5 and a switch tube S6 connected in series, and the midpoint of the third bridge arm 15 is the connection point of the switch tubes S5 and S6. The fourth bridge arm 16 is composed of a switch tube S7 and a switch tube S8 connected in series, and the midpoint of the fourth bridge arm 16 is the connection point of the switch tubes S7 and S8. Optionally, the power conversion device 1 further includes an input capacitor Cl and an output capacitor Ch, the input capacitor Cl is connected between the input terminals in11 and in12 of the power conversion device 1 , and the output capacitor Ch is connected between the output terminals out11 and out12 of the power conversion device 1 .

[0096] In one embodiment, after the power conversion device 1 is in operation, the controller 14 adjusts the switching frequency of the switches in each bridge arm, the phase angle between the first bridge arm 11 and the second bridge arm 12, the phase angle between the third bridge arm 15 and the fourth bridge arm 16, and the phase angle between the first bridge arm 11 and the third bridge arm 15, so that the power conversion device 1 is in the first operating mode or the second operating mode, thereby controlling the output power of the power conversion device 1. The phase angle between the first bridge arm 11 and the second bridge arm 12 is the phase difference between the two diagonally located switches in the first bridge arm 11 and the second bridge arm 12, such as the phase difference between the phase of the switch S1 at the initial turn-on time and the phase of the switch S4 at the initial turn-on time. The phase angle between the third bridge arm 15 and the fourth bridge arm 16 is the phase difference between the two diagonally located switches in the third bridge arm 15 and the fourth bridge arm 16, such as the phase difference between the phase of the switch S5 at the initial turn-on time and the phase of the switch S8 at the initial turn-on time. The phase angle between the first bridge arm 11 and the third bridge arm 15 is the phase difference between the phase of any switch tube in the first bridge arm 11 and the phase of any switch tube in the third bridge arm 15, such as the phase difference between the phase of the switch tube S1 at the initial turn-on time and the phase of the switch tube S5 at the initial turn-on time, or the phase difference between the phase of the switch tube S2 at the initial turn-on time and the phase of the switch tube S6 at the initial turn-on time, or the phase difference between the phase of the switch tube S1 at the initial turn-on time and the phase of the switch tube S6 at the initial turn-on time, or the phase difference between the phase of the switch tube S2 at the initial turn-on time and the phase of the switch tube S5 at the initial turn-on time.

[0097] In the first operating mode, the phase of switch S4 lags behind the phase of switch S1 by a first phase angle, and the phase of switch S5 lags behind the phase of switch S1 by a third phase angle. In the second operating mode, the phase of switch S1 lags behind the phase of switch S4 by a second phase angle, and the phase of switch S5 lags behind the phase of switch S4 by a fourth phase angle. The phase of switch S5 lags behind the phase of switch S1 by a third phase angle, meaning that the turn-on time of switch S5 lags behind the turn-on time of switch S1, and the phase difference between the phase of switch S5 at the initial turn-on time and the phase of switch S1 at the initial turn-on time is the third phase angle. Optionally, the third phase angle may also be the phase angle at which the phase of switch S6 lags behind the phase of switch S2, or the phase angle at which the phase of switch S6 lags behind the phase of switch S1, or the phase angle at which the phase of switch S5 lags behind the phase of switch S2. The phase of switch S5 lags behind the phase of switch S4 by a fourth phase angle, i.e., the turn-on time of switch S5 lags behind the turn-on time of switch S4, and the phase difference between the phase of switch S5 at the initial turn-on time and the phase of switch S4 at the initial turn-on time is the fourth phase angle. Optionally, the fourth phase angle may be the phase angle at which the phase of switch S5 lags behind the phase of switch S3, the phase angle at which the phase of switch S6 lags behind the phase of switch S3, or the phase angle at which the phase of switch S6 lags behind the phase of switch S4. In addition, the range of the third phase angle and the range of the fourth phase angle are both 0° to 360°.

[0098] For a better understanding, the following describes a specific implementation method for eliminating the voltage bias borne by the transformer 13 in the power conversion device 1, in combination with the voltage and current waveform diagrams shown in Figure 1d and Figure 5, taking the on-resistance of the switch tube S1 as an example, with the bias resistance rbias increased and the phase angle between the third bridge arm 15 and the fourth bridge arm 16 as 0.

[0099] In one embodiment, as shown in FIG1d , during a switching cycle of the power conversion device 1 , the controller 14 controls the initial turn-on time of switch S4 to lag behind the initial turn-on time of switch S1 , and controls the phase difference between the phase of switch S4 at the initial turn-on time and the phase of switch S1 at the initial turn-on time to be θ1, so that the phase of switch S4 lags behind the phase of switch S1 by a first phase angle θ1. Furthermore, the controller 14 controls the initial turn-on time of switch S5 to lag behind the initial turn-on time of switch S1 , and controls the phase difference between the phase of switch S5 at the initial turn-on time and the phase of switch S1 at the initial turn-on time to be a third phase angle θ3, so that the phase of switch S5 lags behind the phase of switch S1 by a third phase angle θ3. Simultaneously, the controller 14 controls switches S5 and S8 to be simultaneously turned on or off, so that the phase angle between the third bridge arm 15 and the fourth bridge arm 16 is 0. Consequently, the power conversion device 1 is placed in the first operating mode.

[0100] Specifically, the power conversion device 1 is in a switching cycle in the first operating mode (i.e., the period from t0 to t6 as shown in FIG1d). At time t0, the controller 14 controls the switches S1, S3, S5, and S8 to be in the on state, and controls the switches S2, S4, S6, and S7 to be in the off state. During the period from t0 to t1, the switching state of each switch in the four bridge arms remains the same as that at time t0. If the on-resistance of the switch S1 does not increase the bias resistance rbias, the primary voltage vp (i.e., the voltage across the primary winding Lp) and the secondary voltage vs (i.e., the voltage across the secondary winding Ls) of the transformer 13 are both 0, and the voltage vr between the midpoint of the third bridge arm 15 and the midpoint of the fourth bridge arm 16 is vh. Therefore, the voltage borne by the inductor Lr can be obtained as vs-vr=-vh, so that the current iLr of the inductor Lr continues to decrease. However, after the bias resistor rbias is added to the on-resistance of the switch tube S1, since the switch tube S1 is in the on state during the period t0 to t1 and the current iLr of the inductor Lr is negative, the primary voltage vp of the transformer 13 has a positive bias during the period t0 to t1 as shown in Figure 1d.

[0101] At time t1, the controller 14 controls switches S1 and S3 to remain in the on state, switches S2 and S4 to remain in the off state, switches S5 and S8 to the off state, and switches S6 and S7 to the on state. During the period from t1 to t2, the switching state of each switch in the four bridge arms remains the same as at time t1. If the on-resistance of switch S1 does not increase the bias resistance rbias, the primary voltage vp and the secondary voltage vs of the transformer 13 are both 0, and the voltage vr between the midpoint of the third bridge arm 15 and the midpoint of the fourth bridge arm 16 is -vh. Therefore, the voltage borne by the inductor Lr can be obtained as vs-vr=vh, so that the current iLr of the inductor Lr begins to increase continuously. However, after the bias resistor rbias is added to the on-resistance of the switch tube S1, since the switch tube S1 is in the on state during the period t1 to t2 and the current iLr of the inductor Lr is negative, the primary voltage vp of the transformer 13 has a positive bias during the period t1 to t2 as shown in Figure 1d.

[0102] At time t2, controller 14 controls switches S1, S6, and S7 to remain in the on state, switches S2, S5, and S8 to remain in the off state, switches S3 to the off state, and switches S4 to the on state. During the period from t2 to t3, the switching state of each switch in the four bridge arms remains the same as at time t2. If the on-resistance of switch S1 is not increased by bias resistance rbias, the primary voltage vp of transformer 13 is vl, the secondary voltage vs of transformer 13 is n*vl, and the voltage vr between the midpoint of the third bridge arm 15 and the midpoint of the fourth bridge arm 16 is -vh. Therefore, the voltage across inductor Lr is vs-vr=n*vl+vh, resulting in the current iLr of inductor Lr continuously increasing from a negative value to a positive value. However, after the bias resistance rbias is added to the on-resistance of the switch S1, since the switch S1 is still in the on state during the period from t2 to t3, the primary voltage vp of the transformer 13 also has the bias shown in FIG. 1d during the period from t2 to t3.

[0103] At time t3, controller 14 controls switch S1 to switch to the off state, switches S2 to switch to the on state, and controls switches S3, S5, and S8 to remain in the off state, and switches S4, S6, and S7 to remain in the on state. During the period from t3 to t4, the switching state of each switch in the four bridge arms remains the same as at time t3. The primary voltage vp and the secondary voltage vs of transformer 13 are both 0. The voltage vr between the midpoint of the third bridge arm 15 and the midpoint of the fourth bridge arm 16 is -vh. As a result, the voltage across inductor Lr is vs-vr=vh, resulting in a continuous increase in the current iLr of inductor Lr. Since switch S1 is in the off state during this period, the primary voltage vp of transformer 13 is not biased during the period from t3 to t4.

[0104] At time t4, controller 14 controls switches S1 and S3 to remain in the off state, switches S2 and S4 to remain in the on state, switches S5 and S8 to both switch to the on state, and switches S6 and S7 to both switch to the off state. During the period t4 to t5, the switching state of each switch in the four bridge arms remains the same as at time t4. The primary voltage vp and secondary voltage vs of transformer 13 are both 0. The voltage vr between the midpoint of the third bridge arm 15 and the midpoint of the fourth bridge arm 16 is vh. As a result, the voltage across inductor Lr is vs-vr=-vh, and the current iLr of inductor Lr begins to decrease continuously. Since switch S1 is in the off state during this period, the primary voltage vp of transformer 13 does not have a bias during the period t4 to t5.

[0105] At time t5, controller 14 controls switches S1, S6, and S7 to remain in the off state, switches S2, S5, and S8 to remain in the on state, switches S3 to the on state, and switches S4 to the off state. During the period t5 to t6, the switching state of each switch in the four bridge arms remains the same as at time t5. The primary voltage vp of transformer 13 is -vl, the secondary voltage vs of transformer 13 is -n*vl, and the voltage vr between the midpoint of the third bridge arm 15 and the midpoint of the fourth bridge arm 16 is vh. As a result, the voltage across inductor Lr is vs-vr=-n*vl-vh, resulting in the current iLr of inductor Lr continuously decreasing from a positive value to a negative value. Since switch S1 is in the off state during this period, the primary voltage vp of transformer 13 is not biased during the period t5 to t6.

[0106] After the power conversion device 1 controls itself to be in the first operating mode based on the control timing of the switch tube in Figure 1d, the controller 14 detects the electrical data of the transformer 13. When the electrical data of the transformer 13 is greater than the threshold, it indicates that the primary voltage vp of the transformer 13 has a positive bias, and the controller 14 controls the power conversion device 1 to switch from the first operating mode to the second operating mode. The electrical data of the transformer 13 includes input voltage, input current, output voltage, or output current. When the electrical data of the transformer 13 is input voltage, the threshold is the first threshold; when the electrical data of the transformer 13 is input current, the threshold is the second threshold; when the electrical data of the transformer 13 includes input voltage and input current, the threshold includes the first threshold and the second threshold; when the electrical data of the transformer 13 is output voltage, the threshold is the third threshold; when the electrical data of the transformer 13 is output current, the threshold is the fourth threshold; when the electrical data of the transformer 13 includes output voltage and output current, the threshold includes the third threshold and the fourth threshold. This application does not limit the size of the above four thresholds. Specifically, the controller 14 controls the power conversion device 1 to switch from the first working mode to the second working mode when the input voltage of the transformer 13 is greater than the first threshold value and / or the input current of the transformer 13 is greater than the second threshold value. Optionally, the controller 14 controls the power conversion device 1 to switch from the first working mode to the second working mode when the output voltage of the transformer 13 is greater than the third threshold value and / or the output current of the transformer 13 is greater than the fourth threshold value. The specific values ​​of the above four thresholds can be adaptively adjusted based on the actual working conditions. For example, the above four thresholds are all 0. In addition, the voltage (such as input voltage, output voltage) or current (such as input current, output current) of the transformer used to determine whether the transformer 13 is biased in this application can be an instantaneous value, an effective value or an absolute value, etc., and this application does not impose any restrictions on this.

[0107] The specific control method of the controller 14 controlling the power conversion device 1 to switch to the second working mode is as follows:

[0108] As shown in FIG5 , during a switching cycle of the power conversion device 1, the controller 14 controls the initial turn-on time of switch S1 to lag behind the initial turn-on time of switch S4, and controls the phase difference between the phases of switch S1 at the initial turn-on time and switch S4 at the initial turn-on time to be θ2, so that the phase of switch S1 lags behind the phase of switch S4 by a second phase angle θ2. Furthermore, the controller 14 controls the initial turn-on time of switch S5 to lag behind the initial turn-on time of switch S4, and controls the phase difference between the phases of switch S4 at the initial turn-on time and switch S5 at the initial turn-on time to be a fourth phase angle θ4, so that the phase of switch S5 lags behind the phase of switch S4 by a fourth phase angle θ4. Simultaneously, the controller 14 controls switches S5 and S8 to be turned on and off simultaneously, so that the phase angle between the third bridge arm 15 and the fourth bridge arm 16 is 0. Thus, the power conversion device 1 is in the second operating mode.

[0109] Specifically, during a switching cycle (i.e., the period t0 to t6 shown in FIG5 ) of the power conversion device 1 in the second operating mode, at time t0, the controller 14 controls the switches S2, S4, S5, and S8 to be in the on state, and controls the switches S1, S3, S6, and S7 to be in the off state. During the period t0 to t1, the switching state of each switch in the four bridge arms remains the same as at time t0, the primary voltage vp and the secondary voltage vs of the transformer 13 are both 0, and the voltage vr between the midpoint of the third bridge arm 15 and the midpoint of the fourth bridge arm 16 is vh, so that the voltage borne by the inductor Lr can be obtained as vs-vr=-vh, so that the current iLr of the inductor Lr continues to decrease. Since the switch S1 is in the off state during this period, the primary voltage vp of the transformer 13 will not be biased during the period t0 to t1.

[0110] At time t1, controller 14 controls switches S2 and S4 to remain in the on state, switches S1 and S3 to remain in the off state, switches S5 and S8 to the off state, and switches S6 and S7 to the on state. During the period t1 to t2, the switching state of each switch in the four bridge arms remains the same as at time t1. The primary voltage vp and secondary voltage vs of transformer 13 are both 0. The voltage vr between the midpoint of the third bridge arm 15 and the midpoint of the fourth bridge arm 16 is -vh. As a result, the voltage across inductor Lr is vs-vr=vh, causing the current iLr of inductor Lr to begin to increase continuously. Since switch S1 is in the off state during this period, the primary voltage vp of transformer 13 does not have a bias during the period t1 to t2.

[0111] At time t2, controller 14 controls switches S4, S6, and S7 to remain in the on state, switches S3, S5, and S8 to remain in the off state, switches S2 to the off state, and switches S1 to the on state. During the period from t2 to t3, the switching state of each switch in the four bridge arms remains the same as at time t2. If the on-resistance of switch S1 is not increased by bias resistance rbias, the primary voltage vp of transformer 13 is vl, the secondary voltage vs of transformer 13 is n*vl, and the voltage vr between the midpoint of the third bridge arm 15 and the midpoint of the fourth bridge arm 16 is -vh. Therefore, the voltage across inductor Lr is vs-vr=n*vl+vh, resulting in the current iLr of inductor Lr continuously increasing from a negative value to a positive value. However, after the bias resistance rbias is added to the on-resistance of the switch tube S1 , since the switch tube S1 is in the on state during the period from t2 to t3 , the primary voltage vp of the transformer 13 has a bias as shown in FIG. 5 during the period from t2 to t3 .

[0112] At time t3, the controller 14 controls the switch S4 to switch to the off state, controls the switch S3 to switch to the on state, controls the switches S2, S5, and S8 to remain in the off state, and controls the switches S1, S6, and S7 to remain in the on state. During the period from t3 to t4, the switching state of each switch in the four bridge arms remains the same as at time t3. If the on-resistance of the switch S1 does not increase the bias resistance rbias, the primary voltage vp and the secondary voltage vs of the transformer 13 are both 0, and the voltage vr between the midpoint of the third bridge arm 15 and the midpoint of the fourth bridge arm 16 is -vh. Therefore, the voltage borne by the inductor Lr can be obtained as vs-vr=vh, so that the current iLr of the inductor Lr continues to increase. However, after the bias resistor rbias is added to the on-resistance of the switch tube S1, since the switch tube S1 is in the on state during the period t3 to t4 and the current iLr of the inductor Lr is positive, the primary voltage vp of the transformer 13 has a negative bias during the period t3 to t4 as shown in Figure 1d.

[0113] At time t4, the controller 14 controls switches S2 and S4 to remain in the off state, switches S1 and S3 to remain in the on state, switches S5 and S8 to both switch to the on state, and switches S6 and S7 to both switch to the off state. During the period from t4 to t5, the switching state of each switch in the four bridge arms remains the same as at time t4. If the on-resistance of switch S1 does not increase the bias resistance rbias, the primary voltage vp and the secondary voltage vs of the transformer 13 are both 0, and the voltage vr between the midpoint of the third bridge arm 15 and the midpoint of the fourth bridge arm 16 is vh. As a result, the voltage borne by the inductor Lr can be obtained as vs-vr=-vh, so that the current iLr of the inductor Lr begins to continuously decrease. However, after the bias resistor rbias is added to the on-resistance of the switch tube S1, since the switch tube S1 is in the on state during the period t4 to t5 and the current iLr of the inductor Lr is positive, the primary voltage vp of the transformer 13 also has a negative bias during the period t4 to t5 as shown in FIG. 5 .

[0114] At time t5, controller 14 controls switches S4, S6, and S7 to remain in the off state, switches S3, S5, and S8 to remain in the on state, switches S2 to the on state, and switches S1 to the off state. During the period t5 to t6, the switching state of each switch in the four bridge arms remains the same as at time t5. The primary voltage vp of transformer 13 is -vl, the secondary voltage vs of transformer 13 is -n*vl, and the voltage vr between the midpoint of the third bridge arm 15 and the midpoint of the fourth bridge arm 16 is vh. As a result, the voltage across inductor Lr is vs-vr=-n*vl-vh, resulting in the current iLr of inductor Lr continuously decreasing from a positive value to a negative value. Since switch S1 is in the off state during this period, the primary voltage vp of transformer 13 is not biased during the period t5 to t6.

[0115] It can be understood that when the power conversion device 1 is in the first working mode and the primary voltage vp of the transformer 13 has a positive bias, the power conversion device 1 controls itself to switch to the second working mode, so that when the power conversion device 1 is in the second working mode, the primary voltage vp of the transformer 13 has a negative bias, thereby offsetting the positive bias of the primary voltage vp of the transformer 13, thereby avoiding saturation of the transformer 13, and avoiding the situation where the transformer 13 fails to work and damages the power conversion device 1, thereby protecting the power conversion device 1.

[0116] After the power conversion device 1 controls itself to the second operating mode based on the control timing of the switch tube in Figure 5, the controller 14 detects the electrical data of the transformer 13. If the electrical data of the transformer 13 is less than or equal to a threshold, indicating that the primary voltage vp of the transformer 13 has a negative bias, the controller 14 controls the power conversion device 1 to switch from the second operating mode to the first operating mode. The electrical data of the transformer 13 includes input voltage, input current, output voltage, or output current. For a detailed description of the thresholds, please refer to the corresponding description of the embodiment of the power conversion device 1 switching from the first operating mode to the second operating mode, which will not be repeated here. Specifically, the controller 14 controls the power conversion device 1 to switch from the second operating mode to the first operating mode when the input voltage of the transformer 13 is less than or equal to a first threshold and / or the input current of the transformer 13 is less than or equal to a second threshold. Optionally, the controller 14 controls the power conversion device 1 to switch from the second operating mode to the first operating mode when the output voltage of the transformer 13 is less than or equal to a third threshold and / or the output current of the transformer 13 is less than or equal to a fourth threshold.

[0117] It can be understood that when the power conversion device 1 is in the second working mode and the primary voltage vp of the transformer 13 has a negative bias, the power conversion device 1 controls itself to switch to the first working mode, so that when the power conversion device 1 is in the first working mode, the primary voltage vp of the transformer 13 has a positive bias, thereby offsetting the negative bias of the primary voltage vp of the transformer 13, thereby avoiding saturation of the transformer 13, and avoiding the situation where the transformer 13 fails to work and damages the power conversion device 1, thereby protecting the power conversion device 1.

[0118] It should be noted that the second phase angle θ2 shown in FIG5 is the same as the first phase angle θ1 shown in FIG1d, and the fourth phase angle θ4 shown in FIG5 is the same as the third phase angle θ3 shown in FIG1d. Since the second phase angle θ2 is the same as the first phase angle θ1, and the fourth phase angle θ4 is the same as the third phase angle θ3, it means that before and after the operating mode is switched, the phase angle between the first bridge arm 11 and the second bridge arm 12 is always the same, and the phase angle between the third bridge arm 15 and the main bridge arm is always the same. Therefore, it is ensured that the voltage waveform of the power conversion device 1 (such as the voltage waveforms of vp and vr) does not change before and after the operating mode of the power conversion device 1 is switched, and the current waveform of the inductor Lr does not change before and after the operating mode of the power conversion device 1 is switched, thereby not affecting the normal operation of the power conversion device 1. Among them, the main bridge arm is the main bridge arm of the first bridge arm 11 and the second bridge arm 12. When the power conversion device 1 is in the first operating mode, it is the first bridge arm 11, and when the power conversion device 1 is in the second operating mode, it is the second bridge arm 12.

[0119] Optionally, the power conversion device 1 shown in FIG4 may further include a first resonant capacitor, as specifically described in FIG6a . As shown in FIG6a , the power conversion device 1 further includes a first resonant capacitor Cr1 , wherein the first resonant capacitor Cr1 , the inductor Lr and the secondary winding Ls are connected in series at the midpoint of the third bridge arm 15 and the midpoint of the fourth bridge arm 16 . The first resonant capacitor Cr1 and the inductor Lr form a resonant circuit, making the power conversion device 1 a resonant power conversion device, thereby making the current waveform of the inductor Lr in the power conversion device 1 shown in FIG6a tend to be sinusoidal, thereby facilitating the reduction of the peak value of the current flowing through the switch tube in the power conversion device 1 and facilitating the soft switching of the switch tube in the power conversion device 1 to reduce the loss of the switch tube, thereby improving the efficiency of the power conversion device 1 . In addition, for the other parts of the voltage and current schematic diagram of the power conversion device 1 shown in FIG6a , except for the current waveform of the inductor Lr, please refer to the description of the corresponding parts in the voltage and current schematic diagram of the power conversion device 1 shown in FIG4 , and will not be repeated here. Optionally, the first resonant capacitor Cr1 and the inductor Lr in the power conversion device 1 shown in FIG6a may also be connected to two different windings of the transformer 13, respectively. For details, please refer to the power conversion device 1 shown in FIG6b. As shown in FIG6b, the first resonant capacitor Cr1 and the primary winding Lp are connected in series between the midpoint of the first bridge arm 11 and the midpoint of the second bridge arm 12, and the inductor Lr and the secondary winding Ls are connected in series between the midpoint of the third bridge arm 15 and the midpoint of the fourth bridge arm 16.

[0120] Optionally, the inductor Lr in the power conversion device 1 shown in Figure 4 can also be connected in series with the primary winding Ls, specifically referring to the power conversion device 1 shown in Figures 6c to 6e. As shown in Figure 6c, the inductor Lr and the primary winding Lp are connected in series between the midpoint of the first bridge arm 11 and the midpoint of the second bridge arm 12, and the two ends of the secondary winding Ls are connected to the midpoint of the third bridge arm 15 and the midpoint of the fourth bridge arm 16, respectively. Optionally, the power conversion device 1 shown in Figure 6c can also include a first resonant capacitor, specifically referring to the power conversion device 1 shown in Figure 6d. As shown in Figure 6d, the power conversion device 1 also includes a first resonant capacitor Cr1, and the first resonant capacitor Cr1, the inductor Lr and the primary winding Ls are connected in series between the midpoint of the first bridge arm 11 and the midpoint of the second bridge arm 12. Among them, the first resonant capacitor Cr1 and the inductor Lr form a resonant circuit, making the power conversion device 1 a resonant power conversion device, so that the current waveform of the inductor Lr in the power conversion device 1 shown in Figure 6d tends to be a sine wave, which is beneficial to reducing the peak value of the current flowing through the switch tube in the power conversion device 1 and facilitating the soft switching of the switch tube in the power conversion device 1 to reduce the switch tube loss, thereby improving the efficiency of the power conversion device 1. Optionally, the first resonant capacitor Cr1 in the power conversion device 1 shown in Figure 6d can also be connected to two different windings of the transformer 13 with the inductor Lr respectively, as shown in Figure 6e. As shown in Figure 6e, the inductor Lr and the primary winding Lp are connected in series between the midpoint of the first bridge arm 11 and the midpoint of the second bridge arm 12, and the first resonant capacitor Cr1 and the secondary winding Ls are connected in series between the midpoint of the third bridge arm 15 and the midpoint of the fourth bridge arm 16.

[0121] In an embodiment of the present application, when the primary voltage vp of the transformer 13 is biased, the power conversion device 1 controls itself to switch from the first working mode to the second working mode, or from the second working mode to the first working mode, so that when the primary voltage vp of the transformer 13 is biased, the front-to-back relationship between the first bridge arm 11 and the second bridge arm 12 is swapped before and after the mode switching, so that the bias borne by the primary voltage vp of the transformer 13 after the mode switching is opposite to the bias borne by the primary voltage vp of the transformer 13 before the mode switching, thereby offsetting the bias borne by the primary voltage vp of the transformer 13 before the mode switching, so as to avoid saturation of the transformer 13, thereby achieving protection for the power conversion device 1.

[0122] For example, see Figure 7, which is another structural diagram of the power conversion device provided by the present application. As shown in Figure 7, compared with the power conversion device 1 shown in Figure 4, the first bridge arm 11 and the second bridge arm 12 are connected in parallel between the output terminals out11 and out12 of the power conversion device 1, and the third bridge arm 15 and the fourth bridge arm 16 are connected in parallel between the input terminals in11 and in12 of the power conversion device 1. Here, for the description of the connection relationship between the transformer 13 and the inductor Lr, please refer to the description of the corresponding part in the power conversion device 1 shown in Figure 4, which will not be repeated here.

[0123] In one embodiment, after the power conversion device 1 is in operation, the controller 14 adjusts the switching frequency of the switches in each bridge arm, the phase angle between the first bridge arm 11 and the second bridge arm 12, the phase angle between the third bridge arm 15 and the fourth bridge arm 16, and the phase angle between the first bridge arm 11 and the third bridge arm 15, so as to place the power conversion device 1 in the first operating mode or the second operating mode, thereby controlling the output power of the power conversion device 1. In the first operating mode, the phase of the switch S4 lags behind the phase of the switch S1 by a first phase angle, and the phase of the switch S5 lags behind the phase of the switch S1 by a third phase angle. In the second operating mode, the phase of the switch S1 lags behind the phase of the switch S4 by a second phase angle, and the phase of the switch S5 lags behind the phase of the switch S4 by a fourth phase angle.

[0124] For a better understanding, the following describes a specific implementation method for the power conversion device 1 to eliminate the voltage bias borne by the transformer 13, in combination with the voltage and current waveform diagrams shown in Figures 8 and 9, still taking the on-resistance of the switch tube S1 as an example, in which the bias resistance rbias is increased and the phase angle between the third bridge arm 15 and the fourth bridge arm 16 is 0.

[0125] In one embodiment, as shown in FIG8 , during a switching cycle of the power conversion device 1 , the controller 14 controls the initial turn-on time of switch S4 to lag behind the initial turn-on time of switch S1, and controls the phase difference between the phases of switch S1 at the initial turn-on time and switch S4 at the initial turn-on time to be θ1, so that the phase of switch S4 lags behind the phase of switch S1 by a first phase angle θ1. Furthermore, the controller 14 controls the initial turn-on time of switch S6 to lag behind the initial turn-on time of switch S1, and controls the phase difference between the phases of switch S1 at the initial turn-on time and switch S6 at the initial turn-on time to be a third phase angle θ3, so that the phase of switch S6 lags behind the phase of switch S1 by a third phase angle θ3. Simultaneously, the controller 14 controls switches S5 and S8 to be simultaneously turned on or off, so that the phase angle between the third bridge arm 15 and the fourth bridge arm 16 is 0. Consequently, the power conversion device 1 is placed in the first operating mode.

[0126] Specifically, the power conversion device 1 is in a switching cycle in the first working mode (i.e., the period from t0 to t6 as shown in FIG8 ). At time t0, the controller 14 controls the switches S1, S3, S6, and S7 to be in the on state, and controls the switches S2, S4, S5, and S8 to be in the off state. During the period from t0 to t1, the switching state of each switch in the four bridge arms remains the same as that at time t0. If the on-resistance of the switch S1 does not increase the bias resistance rbias, the primary voltage vp of the transformer 13 is vl, the secondary voltage vs of the transformer 13 is n*vl, and the voltage vr between the midpoint of the first bridge arm 11 and the midpoint of the second bridge arm 12 is 0. Therefore, the voltage borne by the inductor Lr can be obtained as vs-vr=n*vl, so that the current iLr of the inductor Lr continues to increase. However, after the bias resistance rbias is added to the on-resistance of the switch tube S1, since the switch tube S1 is in the on state during the period from t0 to t1, the voltage vr between the midpoint of the first bridge arm 11 and the midpoint of the second bridge arm 12 has a certain positive bias during the period from t0 to t1.

[0127] At time t1, the controller 14 controls switches S1 and S3 to remain in the on state, switches S2 and S4 to remain in the off state, switches S5 and S8 to both switch to the on state, and switches S6 and S7 to both switch to the off state. During the period from t1 to t2, the switching state of each switch in the four bridge arms remains the same as at time t1. If the on-resistance of switch S1 does not increase the bias resistance rbias, the primary voltage vp of transformer 13 is -vl, the secondary voltage vs of transformer 13 is -n*vl, and the voltage vr between the midpoint of the first bridge arm 11 and the midpoint of the second bridge arm 12 is 0. As a result, the voltage borne by inductor Lr is vs-vr=-n*vl, so that the current iLr of inductor Lr begins to continuously decrease. However, after the bias resistance rbias is added to the on-resistance of the switch tube S1, since the switch tube S1 is in the on state during the period from t1 to t2, the voltage vr between the midpoint of the first bridge arm 11 and the midpoint of the second bridge arm 12 has a certain positive bias during the period from t1 to t2.

[0128] At time t2, controller 14 controls switches S1, S5, and S8 to remain in the on state, switches S2, S6, and S7 to remain in the off state, switches S3 to the off state, and switches S4 to the on state. During the period from t2 to t3, the switching state of each switch in the four bridge arms remains the same as at time t2. If the on-resistance of switch S1 does not increase the bias resistance rbias, the primary voltage vp of transformer 13 is -vl, the secondary voltage vs of transformer 13 is -n*vl, and the voltage vr between the midpoint of the first bridge arm 11 and the midpoint of the second bridge arm 12 is vh. As a result, the voltage across inductor Lr is vs-vr=-n*vl-vh, causing the current iLr of inductor Lr to continuously decrease from a positive value to a negative value. However, after the bias resistance rbias is added to the on-resistance of the switch tube S1, since the switch tube S1 is still in the on state during the period from t2 to t3, the voltage vr between the midpoint of the first bridge arm 11 and the midpoint of the second bridge arm 12 also has a certain bias during the period from t2 to t3.

[0129] At time t3, controller 14 controls switch S1 to switch to the off state, switches S2 to switch to the on state, and controls switches S3, S6, and S7 to remain in the off state, and switches S4, S5, and S8 to remain in the on state. During the period from t3 to t4, the switching state of each switch in the four bridge arms remains the same as at time t3, the primary voltage vp of transformer 13 is -vl, the secondary voltage vs of transformer 13 is -n*vl, and the voltage vr between the midpoint of the first bridge arm 11 and the midpoint of the second bridge arm 12 is 0. Therefore, the voltage borne by inductor Lr can be obtained as vs-vr=-n*vl, so that the current iLr of inductor Lr continues to decrease. Since switch S1 is in the off state during this period, the voltage vr between the midpoint of the first bridge arm 11 and the midpoint of the second bridge arm 12 does not have any offset during the period from t3 to t4.

[0130] At time t4, controller 14 controls switches S1 and S3 to remain in the off state, switches S2 and S4 to remain in the on state, switches S5 and S8 to the off state, and switches S6 and S7 to the on state. During the period from t4 to t5, the switching state of each switch in the four bridge arms remains the same as at time t4. The primary voltage vp of transformer 13 is vl, the secondary voltage vs of transformer 13 is n*vl, and the voltage vr between the midpoint of the first bridge arm 11 and the midpoint of the second bridge arm 12 is 0. Therefore, the voltage borne by inductor Lr can be calculated as vs-vr=n*vl, and the current iLr of inductor Lr begins to increase continuously. Since switch S1 is in the off state during this period, the voltage vr between the midpoint of the first bridge arm 11 and the midpoint of the second bridge arm 12 does not have an offset during the period from t4 to t5.

[0131] At time t5, controller 14 controls switches S1, S5, and S8 to remain in the off state, switches S2, S6, and S7 to remain in the on state, switches S3 to the on state, and switches S4 to the off state. During the period t5 to t6, the switching states of each switch in the four bridge arms remain the same as at time t5. The primary voltage vp of transformer 13 is vl, the secondary voltage vs of transformer 13 is n*vl, and the voltage vr between the midpoint of the first bridge arm 11 and the midpoint of the second bridge arm 12 is -vh. Therefore, the voltage across inductor Lr is vs-vr=n*vl+vh, resulting in the current iLr of inductor Lr continuing to increase from a negative value to a positive value. Since switch S1 is in the off state during this period, the voltage vr between the midpoint of the first bridge arm 11 and the midpoint of the second bridge arm 12 is not biased during the period t5 to t6.

[0132] After the power conversion device 1 is controlled to be in the first operating mode based on the control timing of the switch tube in Figure 8, the controller 14 detects the electrical data of the transformer 13. If the electrical data of the transformer 13 is greater than a threshold, indicating that the secondary voltage vs of the transformer 13 has a positive bias, the controller 14 controls the power conversion device 1 to switch from the first operating mode to the second operating mode. The electrical data of the transformer 13 includes input voltage, input current, output voltage, or output current. For a detailed description of the thresholds, please refer to the corresponding description of the embodiment of the power conversion device 1 switching from the first operating mode to the second operating mode shown in Figure 4, and will not be repeated here. Specifically, the controller 14 controls the power conversion device 1 to switch from the first operating mode to the second operating mode when the input voltage of the transformer 13 is greater than a first threshold and / or the input current of the transformer 13 is greater than a second threshold. Optionally, the controller 14 controls the power conversion device 1 to switch from the first operating mode to the second operating mode when the output voltage of the transformer 13 is greater than a third threshold and / or the output current of the transformer 13 is greater than a fourth threshold. Exemplarily, all four of the above thresholds are 0.

[0133] The specific control method of the controller 14 controlling the power conversion device 1 to switch to the second working mode is as follows:

[0134] As shown in FIG9 , during a switching cycle of the power conversion device 1 , the controller 14 controls the initial turn-on time of switch S1 to lag behind the initial turn-on time of switch S4, and controls the phase difference between the phases of switch S1 at the initial turn-on time and switch S4 at the initial turn-on time to be θ2, so that the phase of switch S1 lags behind the phase of switch S4 by a second phase angle θ2. Furthermore, the controller 14 controls the initial turn-on time of switch S6 to lag behind the initial turn-on time of switch S4, and controls the phase difference between the phases of switch S4 at the initial turn-on time and switch S6 at the initial turn-on time to be a fourth phase angle θ4, so that the phase of switch S6 lags behind the phase of switch S4 by a fourth phase angle θ4. Simultaneously, the controller 14 controls switches S5 and S8 to be turned on and off simultaneously, so that the phase angle between the third bridge arm 15 and the fourth bridge arm 16 is 0. Thus, the power conversion device 1 is in the second operating mode.

[0135] Specifically, during a switching cycle (i.e., the period t0 to t6 shown in FIG9 ) in the second operating mode of the power conversion device 1, at time t0, the controller 14 controls the switches S2, S4, S6, and S7 to be in the on state, and controls the switches S1, S3, S5, and S8 to be in the off state. During the period t0 to t1, the switching state of each switch in the four bridge arms remains the same as at time t0, the primary voltage vp of the transformer 13 is vl, the secondary voltage vs of the transformer 13 is n*vl, and the voltage vr between the midpoint of the first bridge arm 11 and the midpoint of the second bridge arm 12 is 0, so that the voltage borne by the inductor Lr can be obtained as vs-vr=n*vl, so that the current iLr of the inductor Lr continues to increase. Since the switch S1 is in the off state during this period, the voltage vr between the midpoint of the first bridge arm 11 and the midpoint of the second bridge arm 12 will not be biased during the period t0 to t1.

[0136] At time t1, controller 14 controls switches S2 and S4 to remain in the on state, switches S1 and S3 to remain in the off state, switches S5 and S8 to both switch to the on state, and switches S6 and S7 to both switch to the off state. During the period from t1 to t2, the switching state of each switch in the four bridge arms remains the same as at time t1, the primary voltage vp of transformer 13 is -vl, the secondary voltage vs of transformer 13 is -n*vl, and the voltage vr between the midpoint of the first bridge arm 11 and the midpoint of the second bridge arm 12 is 0. Therefore, the voltage borne by inductor Lr can be obtained as vs-vr=-n*vl, so that the current iLr of inductor Lr begins to continuously decrease. Since switch S1 is in the off state during this period, the voltage vr between the midpoint of the first bridge arm 11 and the midpoint of the second bridge arm 12 does not have any offset during the period from t1 to t2.

[0137] At time t2, controller 14 controls switches S4, S5, and S8 to remain in the on state, switches S3, S6, and S7 to remain in the off state, switches S2 to the off state, and switches S1 to the on state. During the period from t2 to t3, the switching state of each switch in the four bridge arms remains the same as at time t2. If the on-resistance of switch S1 does not increase the bias resistance rbias, the primary voltage vp of transformer 13 is -vl, the secondary voltage vs of transformer 13 is -n*vl, and the voltage vr between the midpoint of the first bridge arm 11 and the midpoint of the second bridge arm 12 is vh. As a result, the voltage across inductor Lr is vs-vr=-n*vl-vh, causing the current iLr of inductor Lr to continuously decrease from a positive value to a negative value. However, after the bias resistance rbias is added to the on-resistance of the switch tube S1, since the switch tube S1 is in the on state during the period from t2 to t3, the voltage vr between the midpoint of the first bridge arm 11 and the midpoint of the second bridge arm 12 has a certain bias during the period from t2 to t3.

[0138] At time t3, the controller 14 controls the switch S4 to switch to the off state, controls the switch S3 to switch to the on state, controls the switches S2, S6, and S7 to remain in the off state, and controls the switches S1, S5, and S8 to remain in the on state. During the period from t3 to t4, the switching state of each switch in the four bridge arms remains the same as the switching state at time t3. If the on-resistance of the switch S1 does not increase the bias resistance rbias, the primary voltage vp of the transformer 13 is -vl, the secondary voltage vs of the transformer 13 is -n*vl, and the voltage vr between the midpoint of the first bridge arm 11 and the midpoint of the second bridge arm 12 is 0. As a result, the voltage borne by the inductor Lr can be obtained as vs-vr=-n*vl, so that the current iLr of the inductor Lr continues to decrease. However, after the bias resistor rbias is added to the on-resistance of the switch tube S1, since the switch tube S1 is in the on state during the period from t3 to t4 and the current iLr of the inductor Lr is negative, the voltage vr between the midpoint of the first bridge arm 11 and the midpoint of the second bridge arm 12 has a certain negative bias during the period from t3 to t4.

[0139] At time t4, controller 14 controls switches S2 and S4 to remain in the off state, switches S1 and S3 to remain in the on state, switches S5 and S8 to the off state, and switches S6 and S7 to the on state. During the period from t4 to t5, the switching state of each switch in the four bridge arms remains the same as at time t4. If the on-resistance of switch S1 does not increase the bias resistance rbias, the primary voltage vp of transformer 13 is vl, the secondary voltage vs of transformer 13 is n*vl, and the voltage vr between the midpoint of the first bridge arm 11 and the midpoint of the second bridge arm 11 is 0. Therefore, the voltage borne by inductor Lr can be obtained as vs-vr=n*vl, so that the current iLr of inductor Lr begins to increase continuously. However, after the bias resistor rbias is added to the on-resistance of the switch tube S1, since the switch tube S1 is in the on state during the period from t4 to t5 and the current iLr of the inductor Lr is negative, the voltage vr between the midpoint of the first bridge arm 11 and the midpoint of the second bridge arm 12 also has a certain negative bias during the period from t4 to t5.

[0140] At time t5, controller 14 controls switches S4, S5, and S8 to remain in the off state, switches S3, S6, and S7 to remain in the on state, switches S2 to the on state, and switches S1 to the off state. During the period t5 to t6, the switching states of each switch in the four bridge arms remain the same as at time t5. The primary voltage vp of transformer 13 is vl, the secondary voltage vs of transformer 13 is n*vl, and the voltage vr between the midpoint of the first bridge arm 11 and the midpoint of the second bridge arm 12 is -vh. Therefore, the voltage across inductor Lr is vs-vr=n*vl+vh, resulting in the current iLr of inductor Lr continuing to increase from a negative value to a positive value. Since switch S1 is in the off state during this period, the voltage vr between the midpoint of the first bridge arm 11 and the midpoint of the second bridge arm 12 is not biased during the period t5 to t6.

[0141] It can be understood that when the power conversion device 1 is in the first working mode and the voltage vr between the midpoint of the first bridge arm and the midpoint of the second bridge arm is positively biased, if the inductor Lr is kept transmitting consistent power, vr will cause the secondary voltage vs to also be positively biased through the inductor current iLr. The power conversion device 1 controls itself to switch to the second working mode, so that when the power conversion device 1 is in the second working mode, the voltage vr between the midpoint of the first bridge arm and the midpoint of the second bridge arm is negatively biased, and the secondary voltage vs is also negatively biased, thereby offsetting the positive bias of the secondary voltage vs of the transformer 13, thereby avoiding saturation of the transformer 13, and avoiding the situation where the transformer 13 fails to work and damages the power conversion device 1, thereby protecting the power conversion device 1.

[0142] After the power conversion device 1 controls itself to the second operating mode based on the control timing of the switch tube in Figure 9, the controller 14 detects the electrical data of the transformer 13. If the electrical data of the transformer 13 is less than or equal to a threshold, indicating that the secondary voltage vs of the transformer 13 has a negative bias, the controller 14 controls the power conversion device 1 to switch from the second operating mode to the first operating mode. The electrical data of the transformer 13 includes input voltage, input current, output voltage, or output current. For a detailed description of the thresholds, please refer to the corresponding description of the embodiment of the power conversion device 1 switching from the first operating mode to the second operating mode shown in Figure 4, which will not be repeated here. Specifically, the controller 14 controls the power conversion device 1 to switch from the second operating mode to the first operating mode when the input voltage of the transformer 13 is less than or equal to a first threshold and / or the input current of the transformer 13 is less than or equal to a second threshold. Optionally, the controller 14 controls the power conversion device 1 to switch from the second operating mode to the first operating mode when the output voltage of the transformer 13 is less than or equal to a third threshold and / or the output current of the transformer 13 is less than or equal to a fourth threshold.

[0143] It can be understood that when the power conversion device 1 is in the second working mode and the secondary voltage vs of the transformer 13 has a negative bias, the power conversion device 1 controls itself to switch to the first working mode, so that when the power conversion device 1 is in the first working mode, the secondary voltage vs of the transformer 13 has a positive bias, thereby offsetting the negative bias of the secondary voltage vs of the transformer 13, thereby avoiding saturation of the transformer 13, and avoiding the situation where the transformer 13 fails to work and damages the power conversion device 1, thereby protecting the power conversion device 1.

[0144] It should be noted that the second phase angle θ2 shown in FIG9 is the same as the first phase angle θ1 shown in FIG8, and the fourth phase angle θ4 shown in FIG9 is the same as the third phase angle θ3 shown in FIG8. Here, regarding the beneficial effects of the second phase angle θ2 being the same as the first phase angle θ1, the beneficial effects of the fourth phase angle θ4 being the same as the third phase angle θ3, and the value ranges of the first phase angle θ1 and the second phase angle θ2, please refer to the description of the corresponding parts in the power conversion device 1 shown in FIG4, and no further details are given here.

[0145] Optionally, the power conversion device 1 shown in FIG7 may further include a first resonant capacitor. For details, please refer to the power conversion device 1 shown in FIG10a. As shown in FIG10a, the power conversion device 1 further includes a first resonant capacitor Cr1. The first resonant capacitor Cr1, the inductor Lr, and the secondary winding Ls are connected in series at the midpoint of the first bridge arm 11 and the midpoint of the second bridge arm 12. The first resonant capacitor Cr1 and the inductor Lr form a resonant circuit, making the power conversion device 1 a resonant power conversion device. As a result, the current waveform of the inductor Lr in the power conversion device 1 shown in FIG10a tends to be sinusoidal, which is beneficial for reducing the peak value of the current flowing through the switch tube in the power conversion device 1 and is beneficial for the switch tube in the power conversion device 1 to achieve soft switching, thereby reducing the switch tube loss and improving the efficiency of the power conversion device 1. In addition, for the other parts of the voltage and current schematic diagram of the power conversion device 1 shown in FIG10a, except for the current waveform of the inductor Lr, please refer to the description of the corresponding parts in the voltage and current schematic diagram of the power conversion device 1 shown in FIG7, and will not be repeated here. Optionally, the first resonant capacitor Cr1 and the inductor Lr in the power conversion device 1 shown in FIG10a may also be connected to two different windings of the transformer 13, respectively. For details, please refer to the power conversion device 1 shown in FIG10b. As shown in FIG10b, the first resonant capacitor Cr1 and the primary winding Lp are connected in series between the midpoint of the third bridge arm 15 and the midpoint of the fourth bridge arm 16, and the inductor Lr and the secondary winding Ls are connected in series between the midpoint of the first bridge arm 11 and the midpoint of the second bridge arm 12.

[0146] Optionally, the inductor Lr in the power conversion device 1 shown in Figure 7 can also be connected in series with the primary winding Ls. For details, please refer to the power conversion device 1 shown in Figures 10c to 10e. As shown in Figure 10c, the inductor Lr and the primary winding Lp are connected in series between the midpoint of the third bridge arm 15 and the midpoint of the fourth bridge arm 16, and the two ends of the secondary winding Ls are connected to the midpoint of the first bridge arm 11 and the midpoint of the second bridge arm 12 respectively. Optionally, the power conversion device 1 shown in Figure 10c can also include a first resonant capacitor. For details, please refer to the power conversion device 1 shown in Figure 10d. As shown in Figure 10d, the power conversion device 1 also includes a first resonant capacitor Cr1, and the first resonant capacitor Cr1, the inductor Lr and the primary winding Ls are connected in series between the midpoint of the third bridge arm 15 and the midpoint of the fourth bridge arm 16. Among them, the first resonant capacitor Cr1 and the inductor Lr form a resonant circuit, making the power conversion device 1 a resonant power conversion device, so that the current waveform of the inductor Lr in the power conversion device 1 shown in Figure 10d tends to be a sine wave, which is beneficial to reducing the peak value of the current flowing through the switch tube in the power conversion device 1 and facilitating the soft switching of the switch tube in the power conversion device 1 to reduce the switch tube loss, thereby improving the efficiency of the power conversion device 1. Optionally, the first resonant capacitor Cr1 in the power conversion device 1 shown in Figure 10d can also be connected to two different windings of the transformer 13 with the inductor Lr respectively, as shown in Figure 10e. As shown in Figure 10e, the inductor Lr and the primary winding Lp are connected in series between the midpoint of the third bridge arm 15 and the midpoint of the fourth bridge arm 16, and the first resonant capacitor Cr1 and the secondary winding Ls are connected in series between the midpoint of the first bridge arm 11 and the midpoint of the second bridge arm 12.

[0147] In an embodiment of the present application, when the secondary voltage vs of the transformer 13 is biased, the power conversion device 1 controls itself to switch between the first working mode and the second working mode, so that when the secondary voltage vs of the transformer 13 is biased, the front-to-back relationship between the first bridge arm 11 and the second bridge arm 12 is swapped before and after the mode switching, so that the bias borne by the secondary voltage vs of the transformer 13 after the mode switching is opposite to the bias borne by the secondary voltage vs of the transformer 13 before the mode switching, thereby offsetting the bias borne by the secondary voltage vs of the transformer 13 before the mode switching, so as to avoid saturation of the transformer 13, thereby achieving protection for the power conversion device 1.

[0148] Furthermore, the control method for eliminating bias in the primary voltage vp of transformer 13 in power conversion device 1 shown in FIG4 is also applicable to the power conversion device 1 shown in FIG11a and FIG11b. As shown in FIG11a, power conversion device 1 includes a first bridge arm 11, a second bridge arm 12, a transformer 13, a controller 14, a third bridge arm 15, an inductor Lr, a first resonant capacitor Cr1, and a second resonant capacitor Cr2. Third bridge arm 15 includes a series-connected switch S5 and a switch S6, each consisting of two MOSFETs connected in reverse series. Third bridge arm 15 is connected in parallel between output terminals out11 and out12 of power conversion device 1. The first resonant capacitor Cr1 is connected in series with the second resonant capacitor Cr2, and then connected in parallel with the third bridge arm 15. The inductor Lr and the secondary winding Ls are connected in series between the midpoint of the third bridge arm 15 and the midpoint of the capacitor, which is the junction of the first resonant capacitor Cr1 and the second resonant capacitor Cr2. Here, for the connection relationship between the first bridge arm 11, the second bridge arm 12 and the transformer 13 in the power conversion device 1 shown in Figure 11a, please refer to the description of the corresponding part in the power conversion device 1 shown in Figure 4, and no further details will be given here. Optionally, the inductor Lr in the power conversion device 1 shown in Figure 11a can also be connected in series with the primary winding Lp. For details, please refer to the power conversion device 1 shown in Figure 11b. As shown in Figure 11b, the inductor Lr and the primary winding Lp are connected in series between the midpoint of the first bridge arm 11 and the midpoint of the second bridge arm 12, and the two ends of the secondary winding Ls are respectively connected to the midpoint of the third bridge arm 15 and the midpoint of the capacitor.

[0149] The control method for eliminating the bias in the secondary voltage vs of transformer 13 in the power conversion device 1 shown in FIG7 is also applicable to the power conversion device 1 shown in FIG12a and FIG12b. As shown in FIG12a, the power conversion device 1 includes a first bridge arm 11, a second bridge arm 12, a transformer 13, a controller 14, a third bridge arm 15, an inductor Lr, a first resonant capacitor Cr1, and a second resonant capacitor Cr2. The third bridge arm 15 includes a series-connected switch S5 and a switch S6, each consisting of two MOSFETs connected in reverse series. The third bridge arm 15 is connected in parallel between the input terminals in11 and in12 of the power conversion device 1. The first resonant capacitor Cr1 is connected in series with the second resonant capacitor Cr2, and then connected in parallel with the third bridge arm 15. The inductor Lr and the primary winding Lp are connected in series between the midpoint of the third bridge arm 15 and the midpoint of the capacitor, which is the connection point between the first resonant capacitor Cr1 and the second resonant capacitor Cr2. The first bridge arm 11 and the second bridge arm 12 are connected in parallel between the output terminals out11 and out12 of the power conversion device 1, and the two ends of the secondary winding Ls are respectively connected to the midpoint of the first bridge arm 11 and the midpoint of the second bridge arm 12. Optionally, the inductor Lr in the power conversion device 1 shown in Figure 12a can also be connected in series with the secondary winding Ls. For details, please refer to the power conversion device 1 shown in Figure 12b. As shown in Figure 12b, the inductor Lr and the secondary winding Ls are connected in series between the midpoint of the first bridge arm 11 and the midpoint of the second bridge arm 12, and the two ends of the primary winding Lp are respectively connected to the midpoint of the third bridge arm 15 and the midpoint of the capacitor.

[0150] It should be noted that the control method for eliminating the voltage bias borne by the transformer 13 provided in the present application is also applicable to the circuit structure in which the first bridge arm 11 and the second bridge arm 12 are interchanged and / or the third bridge arm 15 and the fourth bridge arm 16 are interchanged in the power conversion device 1 shown in Figures 3a to 12b.

[0151] See Figure 13, which is a flow chart of a control method for a power conversion device provided by the present application. The control method for a power conversion device provided by an embodiment of the present application is applicable to the power conversion device 1 shown in Figures 3a to 12b. The control method for a power conversion device may include the following steps:

[0152] S101, controlling a power conversion device to be in a first operating mode or a second operating mode.

[0153] In the first operating mode, the phase of the fourth switch lags behind the phase of the first switch by a first phase angle, and in the second operating mode, the phase of the first switch lags behind the phase of the fourth switch by a second phase angle, and both the first phase angle and the second phase angle are greater than or equal to 0° and less than or equal to 180°. Exemplarily, the first phase angle is the same as the second phase angle.

[0154] Optionally, in the first operating mode, the phase of the fourth switching transistor lags behind the phase of the first switching transistor by a first phase angle, and the phase of the fifth switching transistor lags behind the phase of the first switching transistor by a third phase angle. In the second operating mode, the phase of the first switching transistor lags behind the phase of the fourth switching transistor by a second phase angle, and the phase of the fifth switching transistor lags behind the phase of the fourth switching transistor by a fourth phase angle. Exemplarily, the first phase angle is the same as the second phase angle, and the third phase angle is the same as the fourth phase angle.

[0155] S102 , controlling the power conversion device to switch between a first operating mode and a second operating mode according to a comparison result of the electrical data of the transformer and a threshold value.

[0156] In an optional implementation, when the power conversion device is in the first operation mode and the electrical data of the transformer is greater than a threshold, the power conversion device is controlled to switch to the second operation mode.

[0157] In another optional embodiment, when the power conversion device is in the second working mode and the electrical data of the transformer is less than or equal to a threshold, the power conversion device is controlled to switch to the first working mode.

[0158] In a specific implementation, more operations performed by the power conversion device in the control method of the power conversion device provided in this application can be referred to the implementation method performed by the power conversion device 1 shown in Figures 3a to 12b, which will not be repeated here.

[0159] In an embodiment of the present application, when a voltage bias occurs in the transformer, the power conversion device controls itself to switch between the first working mode and the second working mode, so that the front-to-back relationship between the first bridge arm and the second bridge arm when the voltage bias occurs in the transformer is swapped before and after the mode switching, so that the amplitude and shape of the current waveform of the inductor before and after the mode switching remain unchanged, but the phase relative to the first bridge arm is different, so that the voltage bias borne by the transformer after the mode switching is opposite to the voltage bias borne by the transformer before the mode switching, thereby offsetting the voltage bias borne by the transformer before the mode switching, so as to avoid transformer saturation, thereby achieving protection for the power conversion device.

[0160] Referring to FIG14, FIG14 is another flow chart of the control method of the power conversion device provided by the present application. The control method of the power conversion device provided by the embodiment of the present application is applicable to the power conversion device 1 shown in FIG3a to FIG12b. The control method of the power conversion device may include the following steps:

[0161] S201, controlling the power conversion device to be in a first operating mode.

[0162] In the first operating mode, the phase of the fourth switch tube lags behind the phase of the first switch tube by a first phase angle, and the first phase angle is greater than or equal to 0° and less than or equal to 180°. Optionally, in the first operating mode, the phase of the fourth switch tube lags behind the phase of the first switch tube by the first phase angle, and the phase of the fifth switch tube lags behind the phase of the first switch tube by a third phase angle.

[0163] After the power conversion device is in the first operating mode, step S202 is executed.

[0164] S202, detecting electrical data of the transformer.

[0165] The electrical data of the transformer includes the input voltage, input current, output voltage or output current of the transformer.

[0166] S203: Determine whether the electrical data of the transformer is greater than a threshold.

[0167] Specifically, if the electrical data of the transformer is greater than the threshold, the power conversion device executes step S204. Otherwise, the power conversion device executes step S202.

[0168] S204: Control the power conversion device to switch to the second operating mode.

[0169] Specifically, when the phase of the fourth switch lags behind the phase of the first switch by a first phase angle in the first operating mode, the phase of the first switch lags behind the phase of the fourth switch by a second phase angle in the second operating mode. When the phase of the fourth switch lags behind the phase of the first switch by a first phase angle and the phase of the fifth switch lags behind the phase of the first switch by a third phase angle in the first operating mode, the phase of the first switch lags behind the phase of the fourth switch by a second phase angle and the phase of the fifth switch lags behind the phase of the fourth switch by a fourth phase angle in the second operating mode. The second phase angle is greater than or equal to 0° and less than or equal to 180°.

[0170] After the power conversion device is in the second operating mode, step S205 is executed.

[0171] S205: Detect electrical data of the transformer.

[0172] S206: Determine whether the electrical data of the transformer is less than or equal to a threshold.

[0173] Specifically, if the electrical data of the transformer is less than or equal to the threshold, the power conversion device executes step S201. Otherwise, the power conversion device executes step S205.

[0174] In a specific implementation, more operations performed by the power conversion device in the control method of the power conversion device provided in this application can be referred to the implementation method performed by the power conversion device 1 shown in Figures 3a to 12b, which will not be repeated here.

[0175] In an embodiment of the present application, when a voltage bias occurs in the transformer, the power conversion device controls itself to switch between the first working mode and the second working mode, so that the front-to-back relationship between the first bridge arm and the second bridge arm when the voltage bias occurs in the transformer is swapped before and after the mode switching, so that the amplitude and shape of the current waveform of the inductor before and after the mode switching remain unchanged, but the phase relative to the first bridge arm is different, so that the voltage bias borne by the transformer after the mode switching is opposite to the voltage bias borne by the transformer before the mode switching, thereby offsetting the voltage bias borne by the transformer before the mode switching, so as to avoid transformer saturation, thereby achieving protection for the power conversion device.

[0176] The above are only specific embodiments of the present application, but the scope of protection of this application is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in this application should be included in the scope of protection of this application. Therefore, the scope of protection of this application should be based on the scope of protection of the claims.

Claims

1. A power conversion device, which is used to connect between a DC power supply and a power grid or a load for energy conversion, is characterized in that, The power conversion device includes a first bridge arm, a second bridge arm, a transformer, and a controller. The transformer includes a primary winding and a secondary winding. The first bridge arm includes a first switch and a second switch connected in series. The second bridge arm includes a third switch and a fourth switch connected in series, where: The first bridge arm is connected in parallel with the second bridge arm. The midpoints of the first bridge arm and the second bridge arm are respectively connected to both ends of the primary winding or both ends of the secondary winding; the first switch is connected to the third switch; The controller is configured to control the phase of the first switch to lag the phase of the fourth switch by a second phase angle when the electrical data of the transformer is greater than a threshold value and the phase of the fourth switch lags the phase of the first switch by a first phase angle; When the electrical data of the transformer is less than or equal to the threshold value and the phase of the first switch lags the phase of the fourth switch by the second phase angle, control the phase of the fourth switch to lag the phase of the first switch by the first phase angle, where the first phase angle and the second phase angle are both greater than or equal to 0° and less than or equal to 180°, and the electrical data of the transformer includes the input voltage, input current, output voltage, or output current of the transformer.

2. The power conversion device according to claim 1, characterized in that, The first phase angle is the same as the second phase angle.

3. The power conversion device according to claim 1 or 2, characterized in that, The power conversion device further includes a third bridge arm. The midpoints of the first bridge arm and the second bridge arm are respectively connected to both ends of the primary winding, and the midpoint of the third bridge arm is connected to the secondary winding; or, the midpoints of the first bridge arm and the second bridge arm are respectively connected to both ends of the secondary winding, and the midpoint of the third bridge arm is connected to the primary winding; the third bridge arm includes a fifth switch and a sixth switch connected in series; The controller is configured to control the phase of the first switch to lag the phase of the fourth switch by a second phase angle and the phase of the fifth switch to lag the phase of the fourth switch by a fourth phase angle when the electrical data of the transformer is greater than a threshold value, the phase of the fourth switch lags the phase of the first switch by a first phase angle, and the phase of the fifth switch lags the phase of the first switch by a third phase angle; When the electrical data of the transformer is less than or equal to the threshold value, the phase of the first switch lags the phase of the fourth switch by the second phase angle, and the phase of the fifth switch lags the phase of the fourth switch by the fourth phase angle, control the phase of the fourth switch to lag the phase of the first switch by the first phase angle and the phase of the fifth switch to lag the phase of the first switch by the third phase angle.

4. The power conversion device according to claim 3, characterized in that The third phase angle is the same as the fourth phase angle.

5. The power conversion device according to claim 3 or 4, characterized in that, The power conversion device further includes an inductor. The inductor is connected in series with the primary winding or the secondary winding between the midpoints of the first bridge arm and the second bridge arm, or the inductor is connected in series with the primary winding or the secondary winding and then connected to the midpoint of the third bridge arm.

6. The power conversion device according to claim 5, characterized in that The power conversion device further includes a first resonant capacitor and a second resonant capacitor. Wherein, the first resonant capacitor and the second resonant capacitor are connected in series and then connected in parallel with the third bridge arm; both ends of the primary winding are respectively connected to the midpoint of the first bridge arm and the midpoint of the second bridge arm, and the secondary winding is connected in series with the inductor between the midpoint of the third bridge arm and the midpoint of the capacitor, and the midpoint of the capacitor is the connection point of the first resonant capacitor and the second resonant capacitor.

7. The power conversion device according to claim 5, characterized in that, The power conversion device further includes a first resonant capacitor and a second resonant capacitor. Wherein, the first resonant capacitor and the second resonant capacitor are connected in series and then connected in parallel with the third bridge arm; the primary winding is connected in series with the inductor between the midpoint of the first bridge arm and the midpoint of the second bridge arm, and both ends of the secondary winding are respectively connected to the midpoint of the third bridge arm and the midpoint of the capacitor, and the midpoint of the capacitor is the connection point of the first resonant capacitor and the second resonant capacitor.

8. The power conversion device according to claim 5, characterized in that, The power conversion device further includes a first resonant capacitor and a second resonant capacitor. Wherein, the first resonant capacitor and the second resonant capacitor are connected in series and then connected in parallel with the third bridge arm; both ends of the primary winding are respectively connected to the midpoint of the third bridge arm and the midpoint of the capacitor, and the secondary winding is connected in series with the inductor between the midpoint of the first bridge arm and the midpoint of the second bridge arm, and the midpoint of the capacitor is the connection point of the first resonant capacitor and the second resonant capacitor.

9. The power conversion device according to claim 5, characterized in that, The power conversion device further includes a first resonant capacitor and a second resonant capacitor. Wherein, the first resonant capacitor and the second resonant capacitor are connected in series and then connected in parallel with the third bridge arm; the primary winding is connected in series with the inductor between the midpoint of the third bridge arm and the midpoint of the capacitor, and both ends of the secondary winding are respectively connected to the midpoint of the first bridge arm and the midpoint of the second bridge arm, and the midpoint of the capacitor is the connection point of the first resonant capacitor and the second resonant capacitor.

10. The power conversion device according to claim 5, characterized in that, The power conversion device further includes a fourth bridge arm, and the fourth bridge arm is connected in parallel with the third bridge arm; both ends of the primary winding are respectively connected to the midpoint of the first bridge arm and the midpoint of the second bridge arm, and the secondary winding is connected in series with the inductor between the midpoint of the third bridge arm and the midpoint of the fourth bridge arm.

11. The power conversion device according to claim 5, characterized in that, The power conversion device further includes a fourth bridge arm, and the fourth bridge arm is connected in parallel with the third bridge arm; the primary winding is connected in series with the inductor between the midpoint of the first bridge arm and the midpoint of the second bridge arm, and both ends of the secondary winding are respectively connected to the midpoint of the third bridge arm and the midpoint of the fourth bridge arm.

12. The power conversion device according to claim 5, characterized in that, The power conversion device further includes a fourth bridge arm, and the fourth bridge arm is connected in parallel with the third bridge arm; both ends of the primary winding are respectively connected to the midpoint of the third bridge arm and the midpoint of the fourth bridge arm, and the secondary winding is connected in series with the inductor between the midpoint of the first bridge arm and the midpoint of the second bridge arm.

13. The power conversion device according to claim 5, characterized in that, The power conversion device further includes a fourth bridge arm, and the fourth bridge arm is connected in parallel with the third bridge arm; the primary winding and the inductor are connected in series between the midpoints of the third bridge arm and the fourth bridge arm, and the two ends of the secondary winding are respectively connected to the midpoints of the first bridge arm and the second bridge arm.

14. The power conversion device according to any one of claims 10-13, characterized in that, The power conversion device further includes a first resonant capacitor. Wherein, the primary winding or the secondary winding, the inductor and the first resonant capacitor are connected in series between the midpoints of the first bridge arm and the second bridge arm, or the primary winding or the secondary winding is connected in series with the first resonant capacitor between the midpoints of the first bridge arm and the second bridge arm, or the primary winding or the secondary winding, the inductor and the first resonant capacitor are connected in series between the midpoints of the third bridge arm and the fourth bridge arm, or the primary winding or the secondary winding is connected in series with the first resonant capacitor between the midpoints of the third bridge arm and the fourth bridge arm.

15. The power conversion device according to any one of claims 5-14, characterized in that, The inductor includes the leakage inductance of the transformer.

16. A control method for a power conversion device, characterized in that, The method includes: When the electrical data of the transformer is greater than the threshold and the phase of the fourth switching tube lags behind the phase of the first switching tube by a first phase angle, controlling the phase of the first switching tube to lag behind the phase of the fourth switching tube by a second phase angle; When the electrical data of the transformer is less than or equal to the threshold and the phase of the first switching tube lags behind the phase of the fourth switching tube by the second phase angle, controlling the phase of the fourth switching tube to lag behind the phase of the first switching tube by the first phase angle, where both the first phase angle and the second phase angle are greater than or equal to 0° and less than or equal to 180°. The electrical data of the transformer includes the input voltage, input current, output voltage or output current of the transformer; the method is applicable to the power conversion device, which is used to connect between a DC power supply and a power grid or a load for energy conversion. The power conversion device includes a first bridge arm, a second bridge arm and the transformer. The transformer includes a primary winding and a secondary winding. The first bridge arm includes the first switching tube and the second switching tube connected in series, and the second bridge arm includes the third switching tube and the fourth switching tube connected in series. Wherein, the first bridge arm is connected in parallel with the second bridge arm, and the midpoints of the first bridge arm and the second bridge arm are respectively connected to the two ends of the primary winding or the two ends of the secondary winding; the first switching tube is connected to the third switching tube.

17. The method according to claim 16, wherein The first phase angle is the same as the second phase angle.

18. The method according to claim 16 or 17, characterized in that, The power conversion device further includes a third bridge arm. The midpoints of the first bridge arm and the second bridge arm are respectively connected to the two ends of the primary winding, and the midpoint of the third bridge arm is connected to the secondary winding; or the midpoints of the first bridge arm and the second bridge arm are respectively connected to the two ends of the secondary winding, and the midpoint of the third bridge arm is connected to the primary winding; the third bridge arm includes the fifth switching tube and the sixth switching tube connected in series. When the electrical data of the transformer is greater than the threshold and the phase of the fourth switching tube lags behind the phase of the first switching tube by a first phase angle, controlling the phase of the first switching tube to lag behind the phase of the fourth switching tube by a second phase angle includes: When the electrical data of the transformer is greater than the threshold, the phase of the fourth switching tube lags behind the phase of the first switching tube by a first phase angle, and the phase of the fifth switching tube lags behind the phase of the first switching tube by a third phase angle, controlling the phase of the first switching tube to lag behind the phase of the fourth switching tube by a second phase angle and the phase of the fifth switching tube to lag behind the phase of the fourth switching tube by a fourth phase angle; When the electrical data of the transformer is less than or equal to the threshold and the phase of the first switching tube lags behind the phase of the fourth switching tube by the second phase angle, controlling the phase of the fourth switching tube to lag behind the phase of the first switching tube by the first phase angle includes: When the electrical data of the transformer is less than or equal to the threshold, the phase of the first switching tube lags behind the phase of the fourth switching tube by the second phase angle, and the phase of the fifth switching tube lags behind the phase of the fourth switching tube by the fourth phase angle, controlling the phase of the fourth switching tube to lag behind the phase of the first switching tube by the first phase angle and the phase of the fifth switching tube to lag behind the phase of the first switching tube by the third phase angle.

19. The method according to claim 18, characterized in that, The third phase angle is the same as the fourth phase angle.

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