Power conversion apparatus and control method therefor

Abstract

The invention provides a power conversion device and a control method thereof, and a controller in the power conversion device is used for controlling a first bridge arm and a second bridge arm when a power factor angle is larger than 0 and smaller than or equal to a first threshold value and a voltage phase angle of an initial modulation signal of the first bridge arm is located between a first voltage phase angle and a second voltage phase angle. Adjusting the common-mode voltage to gradually change and keeping the switching state of the first bridge arm unchanged; when the voltage phase angle is between the second voltage phase angle and the third voltage phase angle, adjusting the common-mode voltage to gradually change at a first change rate and enabling the first bridge arm to continuously switch the switching state; wherein the third voltage phase angle is equal to the voltage peak phase angle of the first bridge arm; the difference between the third voltage phase angle and the first voltage phase angle is positively correlated with the power factor angle. According to the power conversion equipment, when the DPWM is adopted as a modulation mode and the power factor angle is not equal to 0, the output current peak ripple can be reduced, and the generation of common-mode resonance can be reduced at the same time.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power electronics, and particularly relates to a power conversion device and a control method thereof. BACKGROUND

[0002] Modulation methods adopted by the power conversion device mainly include Sine Pulse Width Modulation (SPWM), Space Vector Pulse Width Modulation (SVPWM), Discontinuous Pulse Width Modulation (DPWM) and the like. In the SPWM and SVPWM, the switching tubes of the power conversion device act in each switching cycle, and the switching loss is large, while the DPWM can control the state of some switching tubes to remain unchanged (always on or always off) in a switching cycle, thereby reducing the switching loss. At the same time, the power conversion device can exchange reactive power with the power grid by adjusting the power factor angle of the output to be greater than 0, so as to help maintain the stability of the grid voltage.

[0003] However, when the power conversion device adopts the DPWM as the modulation method, a large common-mode resonance is usually generated inside the power conversion device, which can cause serious Electro Magnetic Interference (EMI) problems, and even cause damage to the devices of the power conversion device. At the same time, in the case that the power conversion device adopts the DPWM as the modulation method and the power factor angle of the output of the power conversion device is not equal to 0, the current peak value ripple of the output of the power conversion device is high, which leads to the degradation of the power quality provided to the power grid. Therefore, how to reduce the current peak value ripple of the output of the power conversion device and reduce the common-mode resonance generated inside the power conversion device when the power conversion device adopts the DPWM as the modulation method and the power factor angle of the output of the power conversion device is not equal to 0 is a technical problem that needs to be solved by the person skilled in the art. SUMMARY

[0004] The present application provides a power conversion device and a control method thereof, which can reduce the current peak value ripple of the output and reduce the common-mode resonance generated when the power conversion device adopts the DPWM as the modulation method and the power factor angle of the output is not equal to 0, and has strong applicability.

[0005] In a first aspect, the present application provides a power conversion device, a direct current end of the power conversion device being configured to be connected to a direct current source, an alternating current end of the power conversion device being configured to be connected to a power grid or a load; the power conversion device comprising a controller, a filter capacitor module, a three-phase power conversion bridge, a direct current bus, and a positive bus capacitor and a negative bus capacitor connected in series to a midpoint of the direct current bus; the direct current bus being connected between the direct current end and the three-phase power conversion bridge, the positive bus capacitor being connected to a positive pole of the direct current bus, the negative bus capacitor being connected to a negative pole of the direct current bus, the three-phase power conversion bridge being connected to the midpoint of the direct current bus through the filter capacitor module; the three-phase power conversion bridge comprising a first bridge arm, a second bridge arm and a third bridge arm; the controller is further configured to: in a case where a power factor angle of an output of the power conversion device is greater than 0 and less than or equal to a first threshold value, when a voltage phase angle of an initial modulation signal of the first bridge arm is located between a first voltage phase angle and a second voltage phase angle, adjusting a common-mode voltage of the three-phase power conversion bridge to gradually change and keeping the first bridge arm unchanged in switching state and the second bridge arm and the third bridge arm continuously switching in switching state; when the voltage phase angle of the initial modulation signal of the first bridge arm is located between the second voltage phase angle and a third voltage phase angle, adjusting the common-mode voltage to gradually change at a first change rate and keeping the first bridge arm, the second bridge arm and the third bridge arm continuously switching in switching state; wherein the third voltage phase angle is a voltage phase angle of the initial modulation signal of the first bridge arm when a voltage value of the initial modulation signal of the first bridge arm is equal to a voltage peak value of the initial modulation signal; a difference between the third voltage phase angle and the first voltage phase angle is positively correlated with the power factor angle, and an angle size of the second voltage phase angle is between the third voltage phase angle and the first voltage phase angle.

[0006] In the embodiment, since the power factor angle is equal to the phase difference between the voltage peak value of the initial modulation signal of the first bridge arm and the output current peak value, as the power factor angle increases or decreases, the phase difference between the voltage peak value of the initial modulation signal of the first bridge arm and the output current peak value will increase or decrease accordingly. Then, the controller can ensure that the output current of the first bridge arm is close to the current peak value between the third voltage phase angle and the first voltage phase angle, that is, the absolute value of the current output by the first bridge arm is relatively large, by adjusting the difference between the third voltage phase angle (that is, the voltage phase angle corresponding to the initial modulation signal of the first bridge arm equal to the voltage peak value) and the first voltage phase angle and positively correlating the difference with the power factor angle. At the same time, since the second voltage phase angle is located between the first voltage phase angle and the third voltage phase angle, the controller can control the first bridge arm to keep the switching state unchanged when the voltage phase angle of the initial modulation signal of the first bridge arm is located between the first voltage phase angle and the second voltage phase angle, by gradually changing the common-mode voltage and keeping the switching state of the first bridge arm unchanged, so as to reduce the current peak value ripple output by the first bridge arm. In addition, when the voltage phase angle of the initial modulation signal of the first bridge arm is located between the second voltage phase angle and the third voltage phase angle, the controller does not continue to control the first bridge arm to keep the switching state unchanged, because when the voltage phase angle of the initial modulation signal of the first bridge arm is close to the third voltage phase angle, the common-mode voltage may change abruptly. For example, when the voltage phase angle of the initial modulation signal of the first bridge arm is greater than the third voltage phase angle, the absolute value of the current output by the second bridge arm is relatively large, so the controller will adjust the common-mode voltage switching when the voltage phase angle of the initial modulation signal of the first bridge arm is equal to the third voltage phase angle, so as to control the second bridge arm to switch from continuously switching the switching state to keeping the switching state unchanged. In order to avoid common-mode resonance caused by the abrupt change of the common-mode voltage, the controller controls the common-mode voltage to change gradually at a first change rate between the second voltage phase angle and the third voltage phase angle, so as to control the common-mode voltage to change slowly. It can be seen that in the embodiment, the controller can reduce the current peak value ripple output by the first bridge arm, while reducing the risk of common-mode resonance generated inside the power conversion device, and has strong applicability.

[0007] In a possible implementation, the AC end of the power conversion device includes a first AC end, a second AC end and a third AC end, the first AC end is connected to the first bridge arm, the second AC end is connected to the second bridge arm, and the third AC end is connected to the third bridge arm; the voltage phase angle of the initial modulation signal of the first bridge arm is the same as the voltage phase angle of the AC power of the first AC end, the voltage phase angle of the initial modulation signal of the second bridge arm is the same as the voltage phase angle of the AC power of the second AC end, and the voltage phase angle of the initial modulation signal of the third bridge arm is the same as the voltage phase angle of the AC power of the third AC end.

[0008] In the embodiment, when the controller generates the pulse width modulation signal according to the initial modulation signal of each bridge arm to control the operation of each bridge arm, the voltage phase angle of the corresponding connected alternating end of each bridge arm can be equal to the voltage phase angle of the initial modulation signal. Therefore, the initial modulation signal of each bridge arm can be understood as the alternating current reference signal of the corresponding connected alternating end.

[0009] In a possible implementation, the difference between the third voltage phase angle and the first voltage phase angle is equal to the sum of the power factor angle output by the power conversion device and the second threshold value, and the difference between the second voltage phase angle and the third voltage phase angle is equal to the third threshold value.

[0010] In the embodiment, the controller can calculate the first voltage phase angle according to the third voltage phase angle, the power factor angle, and the second threshold value, and calculate the second voltage phase angle according to the third voltage phase angle and the third threshold value, which is simple and easy to implement.

[0011] In a possible implementation, when the power factor angle output by the power conversion device is greater than a fourth threshold value and less than or equal to a first threshold value, the difference between the third voltage phase angle and the first voltage phase angle is kept equal to the sum of the second threshold value and the fourth threshold value.

[0012] In the embodiment, when the power factor angle is greater than the fourth threshold value and less than or equal to the first threshold value, if the controller calculates the first voltage phase angle according to the third voltage phase angle, the power factor angle, and the second threshold value, and the initial modulation signal of the first bridge arm is located between the first voltage phase angle and the third voltage phase angle, the controller can not control the first bridge arm to keep the switch state unchanged, that is, the controller cannot control the first bridge arm to keep the switch state unchanged when the absolute value of the current output by the first bridge arm is relatively large. Therefore, when the power factor angle is greater than the fourth threshold value and less than or equal to the first threshold value, the controller adjusts the difference between the third voltage phase angle and the first voltage phase angle to keep it equal to the sum of the second threshold value and the fourth threshold value, so as to ensure that the voltage phase angle of the initial modulation signal of the first bridge arm is located between the second voltage phase angle and the first voltage phase angle, that is, the controller controls the first bridge arm to keep the switch state unchanged when the absolute value of the current output by the first bridge arm is relatively large, thereby reducing the current peak value ripple output by the first bridge arm.

[0013] In a possible implementation, the second threshold value is equal to 30 degrees, the third threshold value is equal to 10 degrees, and the fourth threshold value is equal to 30 degrees.

[0014] In the embodiment, when the power factor angle is less than or equal to 30 degrees, the controller adjusts the difference between the third voltage phase angle and the first voltage phase angle to be equal to the power factor angle plus 30 degrees, so that the absolute value of the current output by the first bridge arm between the first voltage phase angle and the third voltage phase angle is relatively large. When the power factor angle is greater than 30 degrees, the controller adjusts the difference between the third voltage phase angle and the first voltage phase angle to remain equal to 60 degrees, so that the first bridge arm can remain in the same switching state between the first voltage phase angle and the second voltage phase angle when the power factor angle is too large, and the reliability is high. Further, after determining the third voltage phase angle and the first voltage phase angle, the controller can adjust the difference between the second voltage phase angle and the third voltage phase angle to be equal to 10 degrees, and control each bridge arm to switch the switching state between the second voltage phase angle and the third voltage phase angle, so as to adjust the common-mode voltage to change gently at a first change rate. Since the difference between the second voltage phase angle and the third voltage phase angle is relatively small, the controller can reduce the common-mode resonance while making the voltage phase angle range in which the first bridge arm switches the switching state continuously relatively small, so as to avoid greatly increasing the switching loss. In addition, the controller can flexibly adjust the value of the third threshold according to the common-mode resonance and the switching loss. For example, when the third threshold increases, that is, the difference between the third voltage phase angle and the second voltage phase angle increases, the controller can adjust the common-mode voltage to change more gently, so that the common-mode resonance is reduced better. Conversely, when the third threshold decreases, the difference between the second voltage phase angle and the first voltage phase angle increases, and the controller can control the first bridge arm to remain in the same switching state in a larger voltage phase angle range, so that more switching loss is reduced.

[0015] In a possible implementation, when the current phase angle output by the power conversion device leads the voltage phase angle, the first voltage phase angle leads the second voltage phase angle, and the second voltage phase angle leads the third voltage phase angle.

[0016] In the embodiment, when the current phase angle output by the power conversion device leads the voltage phase angle, the current peak value output by the first bridge arm leads the voltage peak value of the initial modulation signal, that is, when the absolute value of the current output by the first bridge arm is relatively large, the voltage phase angle of the initial modulation signal corresponding thereto leads the third voltage phase angle, and the range between the first voltage phase angle and the third voltage phase angle is the value range of the voltage phase angle of the initial modulation signal when the absolute value of the current output by the first bridge arm is relatively large. Therefore, the first voltage phase angle leads the third voltage phase angle. At the same time, since the second voltage phase angle is located between the first voltage phase angle and the third voltage phase angle, the second voltage phase angle also leads the third voltage phase angle.

[0017] In a possible implementation, in the case that the phase angle of the current output by the power conversion device lags behind the phase angle of the voltage, the first voltage phase angle lags behind the second voltage phase angle, and the second voltage phase angle lags behind the third voltage phase angle.

[0018] In the embodiment, in the case that the phase angle of the current output by the power conversion device lags behind the phase angle of the voltage, the peak value of the current output by the first bridge arm lags behind the peak value of the voltage of the initial modulation signal, that is, the voltage phase angle of the initial modulation signal corresponding to the case that the absolute value of the current output by the first bridge arm is relatively large lags behind the third voltage phase angle, and the range between the first voltage phase angle and the third voltage phase angle is the value range of the voltage phase angle of the initial modulation signal in the case that the absolute value of the current output by the first bridge arm is relatively large. Therefore, the first voltage phase angle lags behind the third voltage phase angle. Meanwhile, since the second voltage phase angle is between the first voltage phase angle and the third voltage phase angle, the second voltage phase angle also lags behind the third voltage phase angle.

[0019] In a possible implementation, the first threshold value is equal to 36.87 degrees.

[0020] In the embodiment, the controller can reduce the peak value of the current output by the first bridge arm and reduce the risk of common-mode resonance by adjusting the common-mode voltage in different voltage phase angle intervals of the first bridge arm when detecting that the power factor angle of the power conversion device is greater than 0 and less than or equal to 36.87 degrees, and the detection method is simple and has strong applicability.

[0021] In a possible implementation, in the case that the third voltage phase angle is the voltage phase angle of the initial modulation signal of the first bridge arm when the voltage of the initial modulation signal of the first bridge arm is equal to the positive peak value of the voltage of the initial modulation signal, and the phase angle of the current output by the power conversion device leads the phase angle of the voltage, when the controller adjusts the common-mode voltage to gradually change at a first change rate, the common-mode voltage satisfies:

[0022] Vcom = (1-2μ)-μVmin-(1-μ)Vmax

[0023]

[0024] wherein Vmax is the voltage of the initial modulation signal of the first bridge arm, Vmin is the voltage of the initial modulation signal of the second bridge arm, θ2 is the third voltage phase angle, θ3 is the second voltage phase angle, and θ is the voltage phase angle of the initial modulation signal of the first bridge arm.

[0025] In the embodiment, the controller can adjust the common-mode voltage to change at a first change rate according to Vmax, Vmin, θ2, θ3, and θ, and the calculation method is simple and easy to implement.

[0026] In a possible implementation, in a case where the third voltage phase angle is the voltage phase angle of the initial modulation signal of the first bridge arm when the voltage magnitude of the initial modulation signal of the first bridge arm is equal to the voltage negative peak value of the initial modulation signal, and the current phase angle output by the power conversion device leads the voltage phase angle, when the controller gradually changes the common-mode voltage at the first change rate, the common-mode voltage satisfies:

[0027] Vcom = (1 - 2μ) - μVmin - (1 - μ)Vmax

[0028]

[0029] wherein Vmax is the voltage magnitude of the initial modulation signal of the first bridge arm, Vmin is the voltage magnitude of the initial modulation signal of the second bridge arm, θ2 is the third voltage phase angle, θ3 is the second voltage phase angle, and θ is the voltage phase angle of the initial modulation signal of the first bridge arm.

[0030] In the embodiment, the controller can adjust the common-mode voltage to change at the first change rate according to Vmax, Vmin, θ2, θ3 and θ, and the calculation is simple and easy to implement.

[0031] In a possible implementation, in a case where the third voltage phase angle is the voltage phase angle of the initial modulation signal of the first bridge arm when the voltage magnitude of the initial modulation signal of the first bridge arm is equal to the voltage positive peak value of the initial modulation signal, and the current phase angle output by the power conversion device lags behind the voltage phase angle, when the controller gradually changes the common-mode voltage at the first change rate, the common-mode voltage satisfies:

[0032] Vcom = (1 - 2μ) - μVmin - (1 - μ)Vmax

[0033]

[0034] wherein Vmax is the voltage magnitude of the initial modulation signal of the first bridge arm, Vmin is the voltage magnitude of the initial modulation signal of the second bridge arm, θ2 is the third voltage phase angle, θ3 is the second voltage phase angle, and θ is the voltage phase angle of the initial modulation signal of the first bridge arm.

[0035] In the embodiment, the controller can adjust the common-mode voltage to change at the first change rate according to Vmax, Vmin, θ2, θ3 and θ, and the calculation is simple and easy to implement.

[0036] In a possible implementation, in a case where the third voltage phase angle is equal to the voltage phase angle of the initial modulation signal of the first bridge arm when the voltage magnitude of the initial modulation signal of the first bridge arm is equal to the voltage negative peak value of the initial modulation signal, and the current phase angle output by the power conversion device lags behind the voltage phase angle, when the controller adjusts the common-mode voltage to gradually change at a first change rate, the common-mode voltage satisfies:

[0037] Vcom=(1-2μ)-μVmin-(1-μ)Vmax

[0038]

[0039] wherein Vmax is the voltage magnitude of the initial modulation signal of the first bridge arm, Vmin is the voltage magnitude of the initial modulation signal of the second bridge arm, θ2 is the third voltage phase angle, θ3 is the second voltage phase angle, and θ is the voltage phase angle of the initial modulation signal of the first bridge arm.

[0040] In the embodiment, the controller can adjust the common-mode voltage to change at the first change rate according to Vmax, Vmin, θ2, θ3 and θ, and the calculation is simple and easy to implement.

[0041] In a second aspect, the application provides a control method of a power conversion device. The method is applied to the power conversion device. A direct current end of the power conversion device is used to connect a direct current source. An alternating current end of the power conversion device is used to connect a power grid or a load. The power conversion device comprises a filter capacitor module, a three-phase power conversion bridge, a direct current bus, a positive bus capacitor and a negative bus capacitor connected in series at a midpoint of the direct current bus. The direct current bus is connected between the direct current end and the three-phase power conversion bridge. The positive bus capacitor is connected to a positive pole of the direct current bus. The negative bus capacitor is connected to a negative pole of the direct current bus. The three-phase power conversion bridge is connected to the midpoint of the direct current bus through the filter capacitor module. The three-phase power conversion bridge comprises a first bridge arm, a second bridge arm and a third bridge arm. The method comprises the following steps.

[0042] detecting a power factor angle output by the power conversion device;

[0043] In a case where the power factor angle is greater than 0 and less than or equal to a first threshold value, when the voltage phase angle of the initial modulation signal of the first bridge arm is located between a first voltage phase angle and a second voltage phase angle, adjusting the common-mode voltage of the three-phase power conversion bridge to gradually change and keeping the switching state of the first bridge arm unchanged and the switching states of the second bridge arm and the third bridge arm continuously switched; when the voltage phase angle of the initial modulation signal of the first bridge arm is located between the second voltage phase angle and a third voltage phase angle, adjusting the common-mode voltage to gradually change at a first change rate and keeping the switching states of the first bridge arm, the second bridge arm and the third bridge arm continuously switched.

[0044] The third voltage phase angle is the voltage phase angle of the initial modulation signal of the first bridge arm when the voltage size of the initial modulation signal of the first bridge arm is equal to the voltage peak value of the initial modulation signal; the difference between the third voltage phase angle and the first voltage phase angle is positively correlated with the power factor angle; and the angle size of the second voltage phase angle is between the third voltage phase angle and the first voltage phase angle.

[0045] In a possible implementation, the AC end of the power conversion device includes a first AC end, a second AC end and a third AC end, the first AC end is connected to the first bridge arm, the second AC end is connected to the second bridge arm, and the third AC end is connected to the third bridge arm; the voltage phase angle of the initial modulation signal of the first bridge arm is the same as the voltage phase angle of the AC power of the first AC end, the voltage phase angle of the initial modulation signal of the second bridge arm is the same as the voltage phase angle of the AC power of the second AC end, and the voltage phase angle of the initial modulation signal of the third bridge arm is the same as the voltage phase angle of the AC power of the third AC end.

[0046] In a possible implementation, the difference between the third voltage phase angle and the first voltage phase angle is equal to the sum of the power factor angle output by the power conversion device and a second threshold value, and the difference between the second voltage phase angle and the third voltage phase angle is equal to a third threshold value.

[0047] In a possible implementation, when the power factor angle output by the power conversion device is greater than a fourth threshold value and less than or equal to a first threshold value, the difference between the third voltage phase angle and the first voltage phase angle remains equal to the sum of the second threshold value and the fourth threshold value.

[0048] In a possible implementation, the second threshold value is equal to 30 degrees, the third threshold value is equal to 10 degrees, and the fourth threshold value is equal to 30 degrees.

[0049] In a possible implementation, when the current phase angle output by the power conversion device leads the voltage phase angle, the first voltage phase angle leads the second voltage phase angle, and the second voltage phase angle leads the third voltage phase angle.

[0050] In a possible implementation, when the current phase angle output by the power conversion device lags the voltage phase angle, the first voltage phase angle lags the second voltage phase angle, and the second voltage phase angle lags the third voltage phase angle.

[0051] In a possible implementation, the first threshold value is equal to 36.87 degrees.

[0052] In a possible implementation, in a case where the third voltage phase angle is the voltage phase angle of the initial modulation signal of the first bridge arm when the voltage magnitude of the initial modulation signal of the first bridge arm is equal to the positive peak value of the initial modulation signal and the current phase angle output by the power conversion device leads the voltage phase angle, when the common-mode voltage gradually changes at the first change rate, the common-mode voltage satisfies:

[0053] Vcom = (1 - 2μ) - μVmin - (1 - μ)Vmax

[0054]

[0055] wherein Vmax is the voltage magnitude of the initial modulation signal of the first bridge arm, Vmin is the voltage magnitude of the initial modulation signal of the second bridge arm, θ2 is the third voltage phase angle, θ3 is the second voltage phase angle, and θ is the voltage phase angle of the initial modulation signal of the first bridge arm.

[0056] In a possible implementation, in a case where the third voltage phase angle is the voltage phase angle of the initial modulation signal of the first bridge arm when the voltage magnitude of the initial modulation signal of the first bridge arm is equal to the negative peak value of the initial modulation signal and the current phase angle output by the power conversion device leads the voltage phase angle, when the common-mode voltage gradually changes at the first change rate, the common-mode voltage satisfies:

[0057] Vcom = (1 - 2μ) - μVmin - (1 - μ)Vmax

[0058]

[0059] wherein Vmax is the voltage magnitude of the initial modulation signal of the first bridge arm, Vmin is the voltage magnitude of the initial modulation signal of the second bridge arm, θ2 is the third voltage phase angle, θ3 is the second voltage phase angle, and θ is the voltage phase angle of the initial modulation signal of the first bridge arm.

[0060] In a possible implementation, in a case where the third voltage phase angle is the voltage phase angle of the initial modulation signal of the first bridge arm when the voltage magnitude of the initial modulation signal of the first bridge arm is equal to the positive peak value of the initial modulation signal and the current phase angle output by the power conversion device lags behind the voltage phase angle, when the common-mode voltage gradually changes at the first change rate, the common-mode voltage satisfies:

[0061] Vcom = (1 - 2μ) - μVmin - (1 - μ)Vmax

[0062]

[0063] Vmax, Vmin, θ2, θ3, θ, and Vcom are defined as follows: Vmax is the voltage size of the initial modulation signal of the first bridge arm; Vmin is the voltage size of the initial modulation signal of the second bridge arm; θ2 is the third voltage phase angle; θ3 is the second voltage phase angle; θ is the voltage phase angle of the initial modulation signal of the first bridge arm; and Vcom is the common-mode voltage.

[0064] In a possible implementation, in a case where the third voltage phase angle is equal to the voltage phase angle of the initial modulation signal of the first bridge arm when the voltage size of the initial modulation signal of the first bridge arm is equal to the negative peak value of the voltage of the initial modulation signal, and the current phase angle output by the power conversion device lags behind the voltage phase angle, when the common-mode voltage gradually changes at a first change rate, the common-mode voltage satisfies:

[0065] Vcom=(1-2μ)-μVmin-(1-μ)Vmax

[0066]

[0067] Vmax, Vmin, θ2, θ3, θ, and Vcom are defined as follows: Vmax is the voltage size of the initial modulation signal of the first bridge arm; Vmin is the voltage size of the initial modulation signal of the second bridge arm; θ2 is the third voltage phase angle; θ3 is the second voltage phase angle; θ is the voltage phase angle of the initial modulation signal of the first bridge arm; and Vcom is the common-mode voltage.

[0068] The beneficial effects of the scheme provided in the second aspect can refer to the description of the first aspect, which will not be repeated here. BRIEF DESCRIPTION OF DRAWINGS

[0069] Figure 1 An application scenario diagram of a grid-connected system provided in the present application is shown;

[0070] Figure 2 A frame diagram of a power conversion device provided in the present application is shown;

[0071] Figure 3 A signal change diagram of a power conversion device provided in the present application is shown;

[0072] Figure 4 Another signal change diagram of a power conversion device provided in the present application is shown;

[0073] Figure 5 Still another signal change diagram of a power conversion device provided in the present application is shown;

[0074] Figure 6 Still another signal change diagram of a power conversion device provided in the present application is shown;

[0075] Figure 7 Still another signal change diagram of a power conversion device provided in the present application is shown;

[0076] Figure 8 Another signal change schematic diagram of the power conversion device provided by the embodiment of the present application is provided as follows;

[0077] Figure 9 A flowchart of the control method of the power conversion device provided by the present application is provided as follows. DETAILED DESCRIPTION

[0078] The power conversion device provided by the present application is applied in a grid-connected system, which can be applied in different application scenarios, such as a light storage power supply application scenario, a wind storage power supply application scenario, a pure storage power supply application scenario, or other application scenarios, etc. The following takes the light storage power supply application scenario as an example for illustration.

[0079] Please refer to Figure 1 , Figure 1 An application scenario schematic diagram of the grid-connected system provided by the present application is provided as follows. In Figure 1 The grid-connected system includes a storage converter and a photovoltaic inverter in the light storage power supply scenario shown in the figure. The direct current end of the storage converter is connected to a storage battery, the alternating current end of the storage converter is connected to an alternating current bus of the grid-connected system, and the alternating current bus is also connected to a load and a power grid. The storage converter converts the direct current from the storage battery into alternating current and outputs it to the alternating current bus to supply power to the load and the power grid. Alternatively, the storage converter converts the alternating current from the power grid into direct current to charge the direct current source. The direct current end of the photovoltaic inverter is connected to a photovoltaic module, the alternating current end of the photovoltaic inverter is connected to the alternating current bus, and the photovoltaic inverter converts the direct current from the photovoltaic module into alternating current and outputs it to the alternating current bus to supply power to the load and the power grid. The storage converter and the photovoltaic inverter are both used to provide power conversion functions in the grid-connected system, and the storage converter and the photovoltaic inverter can be collectively referred to as a power conversion device. The storage battery and the photovoltaic module are both used to provide direct current to the power conversion device, and the storage battery and the photovoltaic module can be collectively referred to as a direct current source.

[0080] In actual applications, the grid-connected system can also be provided with a box-type transformer, which is used to adjust and distribute the input alternating current and then output it to adapt to the voltage requirements of different power transmission nodes. For example, the alternating current transmitted by the alternating current bus usually has a relatively high voltage amplitude, and therefore the power conversion device can transmit the alternating current to the box-type transformer for voltage boosting and then provide it to the alternating current bus. In addition, the alternating current transmitted by the alternating current bus can be stepped down by the box-type transformer and then provided to the load, or if the rated voltage amplitude of the load is adapted to the voltage amplitude of the alternating current transmitted by the alternating current bus, the alternating current bus can also directly supply power to the load. When the grid-connected switch is closed and the grid-connected system is in grid-connected operation, the alternating current transmitted by the alternating current bus can be stepped up by one or more box-type transformers and then output to the power grid. The specific setting position and number of the box-type transformer can be flexibly adjusted according to the actual application scenario, and the embodiments of the present application do not limit this.

[0081] It should be noted that, according to the number of power supply phases, the power grid can be divided into a single-phase power grid, a three-phase power grid or other multi-phase power grid. The three-phase power grid has the advantages of high transmission efficiency, large power support, flexible voltage, etc. In actual application, the power grid into which the grid-connected system is usually a three-phase power grid. In order to adapt to the three-phase power grid, the power conversion device of the grid-connected system is a three-phase power conversion device. Among them, the three-phase power conversion device contains a large number of switching tubes, and each switching tube has a large number of switching switches, which results in large switching loss of the three-phase power conversion device. Therefore, the three-phase power conversion device usually adopts DPWM as the modulation mode to reduce the switching loss. However, the conventional DPWM modulation mode has many limitations, which may cause large common-mode resonance in the three-phase power conversion device, and further cause serious EMI, and even cause device damage. In addition, in order to help maintain the stability of the power grid voltage, the three-phase power conversion device usually needs to have the ability of reactive power regulation, that is, the three-phase power conversion device needs to have the ability of exchanging reactive power with the power grid. For example, when the power grid voltage drops, the three-phase power conversion device outputs reactive power to the power grid, which can help to lift the power grid voltage. In the process of exchanging reactive power between the three-phase power conversion device and the power grid, the power factor angle of the three-phase power conversion device is greater than 0 (that is, the power factor PF is less than 1). It should be noted that, in the case that the power factor angle of the three-phase power conversion device is greater than 0, the current peak value ripple of the output of the power conversion device is high, which causes the power quality provided to the power grid to decrease. Usually, the power conversion device can reduce the current peak value ripple of the output by increasing the inductance of the internal filter inductor. However, the increase of the inductance of the filter inductor will reduce the power density of the power conversion device.

[0082] Based on this, the application provides a power conversion device, which can reduce the current peak value ripple of the output and reduce the generation of common-mode resonance in the case of adopting DPWM as the modulation mode and the output power factor angle not being equal to 0, and has strong applicability.

[0083] The above is only an example of the application scenario of the power conversion device provided by the application, and is not exhaustive. The application does not limit the application scenario.

[0084] The following content combines Figures 2 to 8 The specific implementation principle of the power conversion device provided by the embodiment of the application is introduced.

[0085] It should be noted that the power conversion device provided in this application embodiment can perform DC power inversion or AC power rectification. The working principle of reducing common-mode resonance during the inversion or rectification process is similar. For ease of explanation, the following description uses the working principle of the power conversion device during the inversion process as an example. The working principle of the power conversion device during the rectification process can be found in the following description, which will not be repeated in this application embodiment.

[0086] In this embodiment, the DC terminal of the power conversion device is connected to a DC source, and the AC terminal is connected to the power grid or a load. The power conversion device includes a three-phase power conversion bridge. This three-phase power conversion bridge is disposed between the DC terminal and the AC terminal of the power conversion device. The power conversion device controls the three-phase power conversion bridge to convert the DC power provided by the DC source into AC power and output it to the AC terminal, thereby realizing the supply of power to the power grid.

[0087] For example, please refer to Figure 2 , Figure 2 This is a schematic diagram of a frame of a power conversion device provided in an embodiment of this application. Figure 2 As shown, the DC terminals dc1 and dc2 of the power conversion device are connected to the positive and negative terminals of the DC source, respectively. The AC terminals ac1, ac2, and ac3 of the power conversion device are each connected to the power grid or load via a corresponding live wire. Inside the power conversion device, the input terminals of the three-phase power conversion bridge include input terminals i1 and i2. Input terminal i1 is connected to DC terminal dc1 via the positive terminal BUS+ of the DC bus, and input terminal i2 is connected to DC terminal dc2 via the negative terminal BUS- of the DC bus. The output terminals of the three-phase power conversion bridge include output terminals o1, o2, and o3. Output terminal o1 is connected to AC terminal ac1, output terminal o2 is connected to AC terminal ac2, and output terminal o3 is connected to AC terminal ac3. The power conversion device also includes a controller, which controls the three-phase power conversion bridge to convert the DC power provided by the DC source into AC power and output it to AC terminals ac1, AC terminals ac2, and AC terminals ac3, thereby providing three-phase AC power to the power grid. Among them, AC terminals ac1, ac2 and ac3 have the same AC frequency and the phase angle difference between them is equal to 120 degrees.

[0088] In the embodiment of the present application, the power conversion device further comprises a positive bus capacitor C1 and a negative bus capacitor C2. The positive bus capacitor C1 and the negative bus capacitor C2 are connected in series between the positive pole BUS+ and the negative pole BUS- of the DC bus, for absorbing the power fluctuation generated by the DC bus, thereby stabilizing the DC bus voltage. The series connection point of the positive bus capacitor C1 and the negative bus capacitor C2 is the DC bus midpoint N. The three-phase power conversion bridge can be connected to the DC bus midpoint N. In addition, the power conversion device further comprises a filter capacitor module, which is arranged between the output end of the three-phase power conversion bridge and the AC end of the power conversion device, for reducing the leakage current output by the AC end of the power conversion device. As shown in Figure 2 , the filter capacitor module comprises filter capacitors C1, C2 and C3. One end of the filter capacitor C1 is connected to the output end o1, and the other end of the filter capacitor C1 is connected to the DC bus midpoint N. The filter capacitor C1 can guide the leakage current output by the output end o1 to the DC bus midpoint N, thereby reducing the leakage current output by the power conversion device. Similarly, the filter capacitors C2 and C3 are arranged in a similar manner and have similar functions, which will not be described here. In addition, the power conversion device is also provided with a filter inductor, as shown in Figure 2 , the filter inductor is arranged between the output end of the three-phase power conversion bridge and the AC end of the power conversion device, for filtering high-frequency harmonics in the output voltage of the three-phase power conversion bridge. In addition, the power conversion device can also be provided with other functional modules according to the actual application scenario, which will not be described one by one in the embodiment of the present application.

[0089] In the embodiment of the present application, the three-phase power conversion bridge specifically comprises a first bridge arm, a second bridge arm and a third bridge arm, and the first bridge arm, the second bridge arm and the third bridge arm are connected in parallel between the input end i1 and the input end i2 of the three-phase power conversion bridge. The midpoint of the first bridge arm is connected to the AC end ac1 of the power conversion device as the output end o1 of the three-phase power conversion bridge, the midpoint of the second bridge arm is connected to the AC end ac2 of the power conversion device as the output end o2 of the three-phase power conversion bridge, and the midpoint of the third bridge arm is connected to the AC end ac3 of the power conversion device as the output end o3 of the three-phase power conversion bridge. Figure 2 The positions of the first bridge arm, the second bridge arm and the third bridge arm shown in the figure can be exchanged, and the embodiment of the present application does not limit this. The controller converts the DC power into AC power and outputs it to the corresponding AC end through the control of the three bridge arms, so as to provide three-phase AC power to the power grid or the load. It should be noted that the implementation of the controller in controlling each bridge arm to convert DC power is similar, and for the sake of understanding, the following content will be described taking the first bridge arm as an example.

[0090] Specifically, to control the first bridge arm to convert the direct current into the alternating current, the controller first acquires an initial modulation signal of the first bridge arm. The initial modulation signal of the first bridge arm is used to represent an alternating current reference signal of the first alternating current end. According to the initial modulation signal of the first bridge arm, the controller can obtain a pulse width modulation (PWM) signal of the first bridge arm, and then control the first bridge arm to convert the direct current into the alternating current and output to the first alternating current end, and make the alternating current frequency, voltage phase angle of the first alternating current end equal to the frequency, voltage phase angle of the initial modulation signal of the first bridge arm. Further, to reduce the switching loss, the controller can control the first bridge arm to operate in a DPWM modulation mode. The purpose of DPWM is that in a switching period, there is always a bridge arm without switching action, thereby reducing the switching loss. To achieve this purpose, the controller injects a common mode voltage into the initial modulation signal, so that the superposition of the two signals can generate the real modulation signal of the bridge arm. In this way, by designing a common mode voltage, the modulation signal of any bridge arm can be clamped to +1 or -1 in at least one switching period. Therefore, when the modulation signal of the bridge arm is converted into a PWM signal, the switching tube can be controlled to remain in a state for a period of time. For example, the controller can first acquire a common mode voltage of the three-phase power conversion bridge, and superimpose the common mode voltage on the initial modulation signal of the first bridge arm to obtain a target modulation signal of the first bridge arm. The controller generates a PWM signal of the first bridge arm according to the target modulation signal of the first bridge arm to control the first bridge arm to remain in a switching state, thereby reducing the switching loss generated by the first bridge arm. At the same time, the controller superimposes the common mode voltage on the initial modulation signals of the second bridge arm and the third bridge arm in the same way to control the second bridge arm and the third bridge arm to continuously switch the switching state. It can be understood that since the line voltage of the alternating current provided by the first bridge arm, the second bridge arm and the third bridge arm to the power grid or the load is equal to the difference between the output voltages of different bridge arms, the common mode voltages injected into the initial modulation signals of the three bridge arms can be offset, and will not affect the alternating current waveform provided to the power grid or the load.

[0091] It should be noted that the switching frequency of the switching tube of the first bridge arm is high when the switching state of the first bridge arm is continuously switched. At this time, if the absolute value of the current output by the first bridge arm is large, the absolute value of the current flowing through the switching tube in the first bridge arm will also be large, thereby causing the current peak ripple output by the first bridge arm to be high. Therefore, in the embodiments of the present application, when the absolute value of the current output by the first bridge arm is large, the controller can control the first bridge arm to remain in a switching state, and the second bridge arm and the third bridge arm to continuously switch the switching state, so as to reduce the current peak ripple output by the first bridge arm.

[0092] For example, in some application scenarios, the power factor angle of the power conversion device is equal to 0 (i.e., the power factor PF is equal to 1). At this time, since the voltage and the current output by the power conversion device are in phase, and the voltage phase angle of the initial modulation signal of the first bridge arm is the same as the voltage phase angle of the power conversion device, and the current phase angle of the first bridge arm is the same as the current phase angle of the power conversion device, the voltage phase angle of the initial modulation signal of the first bridge arm is the same as the current phase angle of the first bridge arm. Then, when the voltage of the initial modulation signal of the first bridge arm approaches the voltage peak value, the output current of the first bridge arm also approaches the current peak value, i.e., the absolute value of the current output by the first bridge arm is relatively large. Therefore, when the voltage of the initial modulation signal of the first bridge arm approaches the voltage peak value, the controller controls the first bridge arm to keep the switching state unchanged, and controls the second bridge arm and the third bridge arm to continuously switch the switching state, so as to reduce the switching loss of the first bridge arm and reduce the current peak value ripple output by the first bridge arm.

[0093] In other application scenarios, the power factor angle of the power conversion device is greater than 0 (i.e., the power factor PF is less than 1). For example, when the grid voltage drops, the power conversion device adjusts the power factor angle to be greater than 0, so as to output reactive power to the grid, so that the grid voltage is raised under the action of the reactive current and the line impedance, thereby compensating for the drop of the grid voltage. It can be understood that when the power factor angle of the power conversion device is greater than 0, there is a phase difference between the voltage and the current output by the power conversion device, and there is a phase difference between the output current of the first bridge arm and the initial modulation signal of the first bridge arm. Then, when the absolute value of the current output by the first bridge arm is relatively large, the voltage of the initial modulation signal of the first bridge arm may not approach the voltage peak value. At this time, if the controller still controls the first bridge arm to keep the switching state unchanged and controls the second bridge arm and the third bridge arm to continuously switch the switching state when the voltage of the initial modulation signal of the first bridge arm approaches the voltage peak value, the first bridge arm cannot be controlled to keep the switching state unchanged when the absolute value of the current output by the first bridge arm is relatively large, thereby causing the current peak value ripple output by the first bridge arm to increase significantly.

[0094] In the embodiments of the present application, in order to control the current peak ripple of the first bridge arm in time when the power factor angle of the power conversion device is greater than 0 (i.e., the power factor PF is less than 1), the controller can detect the power factor angle of the power conversion device in real time during the operation of the power conversion device. It should be noted that in most application scenarios, the power factor angle of the power conversion device is less than or equal to a first threshold. Therefore, the power conversion device provided in the embodiments of the present application is mainly applied to scenarios in which the power factor angle is less than or equal to the first threshold. The specific value of the first threshold can be flexibly adjusted according to actual requirements. For example, the first threshold can be equal to 36.87 degrees (i.e., the power factor PF is equal to 0.8). As can be seen from the above, when the power factor angle of the power conversion device is greater than 0, the current peak ripple of the first bridge arm obviously increases. Therefore, the controller can control the current peak ripple of the first bridge arm in time when the power factor angle is greater than 0 and less than or equal to the first threshold (i.e., the power factor PF is less than 1 and greater than or equal to 0.8).

[0095] It can be understood that, as can be seen from the above, the controller controls the first bridge arm to keep the switching state unchanged when the absolute value of the current output by the first bridge arm is relatively large, which can reduce the current peak ripple output by the first bridge arm. Therefore, when the controller detects that the power factor angle is greater than 0 and less than or equal to the first threshold, the controller can first determine the specific value range of the voltage phase angle of the initial modulation signal of the first bridge arm corresponding to the case in which the absolute value of the current output by the first bridge arm is relatively large. The controller controls the first bridge arm to keep the switching state unchanged when the voltage phase angle of the initial modulation signal of the first bridge arm is located in the specific value range, so as to control the first bridge arm to keep the switching state unchanged when the absolute value of the current output by the first bridge arm is relatively large, thereby reducing the current peak ripple output by the first bridge arm.

[0096] Specifically, in order to determine the specific value range of the voltage phase angle of the initial modulation signal of the first bridge arm corresponding to the case in which the absolute value of the current output by the first bridge arm is relatively large, the controller first determines a third voltage phase angle of the first bridge arm according to the initial modulation signal of the first bridge arm. The third voltage phase angle is the voltage phase angle of the initial modulation signal of the first bridge arm when the voltage of the initial modulation signal of the first bridge arm reaches a voltage peak value. The difference between the third voltage phase angle and the voltage phase angle of the initial modulation signal of the first bridge arm when the current of the first bridge arm is equal to a current peak value (hereinafter referred to as the current peak phase angle of the first bridge arm) is equal to the power factor angle. Therefore, the controller can determine the current peak phase angle of the first bridge arm according to the power factor angle and the third voltage phase angle of the first bridge arm.

[0097] For example, in the case where the voltage output by the power conversion device lags behind the current, the changes of the initial modulation signal of the first bridge arm and the output current can be referred to as followsFigure 3 , Figure 3 A signal change schematic diagram of the power conversion device provided by the embodiment of the present application is shown. Figure 3 U1 represents the initial modulation signal of the first bridge arm, I1 represents the output current of the first bridge arm, θ3 represents the third voltage phase angle of the first bridge arm, i.e. when the voltage phase angle of U1 is equal to θ3, the voltage of U1 is equal to the voltage peak value. θa is the current peak value phase angle of the first bridge arm, i.e. when the voltage phase angle of U1 is equal to θa, the current of I1 is equal to the current peak value, and the difference between θa and θ3 is equal to the power factor angle Alternatively, in the case that the output voltage of the power conversion device leads the output current, the change of the initial modulation signal of the first bridge arm and the output current can refer to Figure 4 , Figure 4 Another signal change schematic diagram of the power conversion device provided by the embodiment of the present application is shown. Figure 4 U1 represents the initial modulation signal of the first bridge arm, I2 represents the output current of the first bridge arm, θ3 represents the third voltage phase angle of the first bridge arm, and θb is the current peak value phase angle of the first bridge arm, and the difference between θb and θ3 is equal to the power factor angle

[0098] It can be understood that when the voltage phase angle of the initial modulation signal of the first bridge arm is close to the current peak value phase angle, the absolute value of the output current of the first bridge arm is relatively large. Therefore, when the voltage phase angle of the initial modulation signal of the first bridge arm is close to the current peak value phase angle, the controller controls the first bridge arm to keep the switch state unchanged, which can effectively reduce the current peak value ripple of the output of the first bridge arm. In order to determine the specific value range of the voltage phase angle of the initial modulation signal of the first bridge arm when the voltage phase angle of the initial modulation signal of the first bridge arm is close to the current peak value phase angle, the controller determines the third voltage phase angle of the first bridge arm according to the current peak value phase angle of the first bridge arm after determining the current peak value phase angle of the first bridge arm. The third voltage phase angle is used to form the specific value range of the voltage phase angle with the first voltage phase angle. That is, when the voltage phase angle of the initial modulation signal of the first bridge arm is between the first voltage phase angle and the third voltage phase angle, the voltage phase angle of the initial modulation signal of the first bridge arm is close to the current peak value phase angle, i.e. the absolute value of the output current of the first bridge arm is relatively large.

[0099] In some feasible implementations, the controller can determine the first voltage phase angle of the first bridge arm based on the peak current phase angle of the first bridge arm and a second threshold. The second threshold can be understood as the maximum value of the difference between the voltage phase angle and the peak current phase angle of the initial modulation signal of the first bridge arm when the absolute value of the current output by the first bridge arm is relatively large. For example, this second threshold is equal to 30 degrees. That is, when the difference between the voltage phase angle and the peak current phase angle of the initial modulation signal of the first bridge arm is less than or equal to the second threshold, the absolute value of the current output by the first bridge arm is relatively large. Therefore, the controller can determine the first voltage phase angle of the first bridge arm based on the peak current phase angle and the second threshold, and the difference between the first voltage phase angle and the peak current phase angle is equal to the second threshold.

[0100] For example, such as Figure 3 and Figure 4 As shown, θt2 is the second threshold, and θ1 is the first voltage phase angle of the first bridge arm. The controller calculates θ1 based on the peak current phase angle (θa or θb) of the first bridge arm and θt2. For example, in Figure 3 In this case, the voltage output of the power conversion device lags behind the current, so θ1 equals θa minus θt2. Figure 4 In the process, the voltage output of the power conversion device leads the current, so θ1 equals θa plus θt2. Obviously, when the voltage phase angle of the initial modulation signal U1 of the first bridge arm is within θ1 to θ3, the current output by the first bridge arm (I1 or I2) is close to the current peak value, that is, the absolute value of the current output by the first bridge arm is relatively large.

[0101] In some feasible implementations, as described above, the difference between the peak current phase angle and the third voltage phase angle of the first bridge arm is equal to the power factor angle, and the difference between the first voltage phase angle and the peak current phase angle of the first bridge arm is equal to the second threshold. Therefore, the difference between the first voltage phase angle and the third voltage phase angle of the first bridge arm is equal to the sum of the power factor angle and the second threshold, meaning the difference between the first voltage phase angle and the third voltage phase angle is positively correlated with the power factor angle. Thus, after obtaining the second threshold, the power factor angle, and the third voltage phase angle of the first bridge arm, the controller can directly calculate the first voltage phase angle of the first bridge arm based on these parameters, without first calculating the peak current phase angle of the first bridge arm.

[0102] In some possible embodiments, specifically, in the case that the voltage output by the power conversion device lags behind the current, the first voltage phase angle of the first bridge arm leads the third voltage phase angle, and the first voltage phase angle of the first bridge arm is equal to the third voltage phase angle minus the power factor angle minus the second threshold value. In the case that the voltage output by the power conversion device leads the current, the first voltage phase angle of the first bridge arm lags behind the third voltage phase angle, and the first voltage phase angle of the first bridge arm is equal to the third voltage phase angle plus the power factor angle plus the second threshold value.

[0103] For example, as shown in FIG. 3, in the case that the voltage output by the power conversion device lags behind the current, the second threshold value is equal to θt2, the power factor angle is equal to θp, and the third voltage phase angle of the first bridge arm is equal to θ3, the controller can calculate the first voltage phase angle θ1 of the first bridge arm to be equal to θ3 minus θp minus θt2. Figure 3 Alternatively, as shown in FIG. 4, in the case that the voltage output by the power conversion device lags behind the current, the second threshold value is equal to θt2, the power factor angle is equal to θp, and the third voltage phase angle of the first bridge arm is equal to θ3, the controller can calculate the first voltage phase angle θ1 of the first bridge arm to be equal to θ3 plus θp plus θt2. Alternatively, as shown in FIG. 4, in the case that the voltage output by the power conversion device lags behind the current, the second threshold value is equal to θt2, the power factor angle is equal to θp, and the third voltage phase angle of the first bridge arm is equal to θ3, the controller can calculate the first voltage phase angle θ1 of the first bridge arm to be equal to θ3 plus θp plus θt2. Figure 4 Alternatively, as shown in FIG. 4, in the case that the voltage output by the power conversion device lags behind the current, the second threshold value is equal to θt2, the power factor angle is equal to θp, and the third voltage phase angle of the first bridge arm is equal to θ3, the controller can calculate the first voltage phase angle θ1 of the first bridge arm to be equal to θ3 plus θp plus θt2.

[0104] In some possible embodiments, the controller calculates the first voltage phase angle of the first bridge arm according to the second threshold value, the power factor angle, and the third voltage phase angle of the first bridge arm, and gradually changes the common-mode voltage of the three-phase power conversion bridge when it is detected that the voltage phase angle of the initial modulation signal of the first bridge arm is between the first voltage phase angle and the third voltage phase angle, so that the common-mode voltage and the initial modulation signal of the first bridge arm are superimposed to keep the switch state of the first bridge arm unchanged. However, in the case that the power factor angle of the power conversion device is relatively large, when the voltage phase angle of the initial modulation signal of the first bridge arm is between the first voltage phase angle and the third voltage phase angle, the controller gradually changes the common-mode voltage of the three-phase power conversion bridge cannot keep the switch state of the first bridge arm unchanged, but keep the switch state of the second bridge arm or the third bridge arm unchanged. Then, the controller cannot keep the switch state of the first bridge arm unchanged when the absolute value of the current output by the first bridge arm is relatively large, so as to reduce the current peak ripple of the first bridge arm. Therefore, in the case that the power factor angle is relatively large, the embodiments of the present application can calculate the first voltage phase angle of the first bridge arm in other ways to adjust the angle range of the control of keeping the switch state of the first bridge arm unchanged, so as to keep the switch state of the first bridge arm unchanged when the absolute value of the current output by the first bridge arm is relatively large.

[0105] ​​​It should be noted that the controller can calculate the first voltage phase angle in other ways when the power factor angle is greater than the fourth threshold value and less than or equal to the first threshold value. The fourth threshold value can be understood as the maximum value of the power factor angle output by the power conversion device when the controller calculates the first voltage phase angle according to the second threshold value, the power factor angle and the third voltage phase angle, and adjusts the common-mode voltage between the first voltage phase angle and the third voltage phase angle to keep the switching state of the first bridge arm unchanged. For example, the fourth threshold value is equal to 30 degrees. That is, when the power factor angle is greater than the fourth threshold value, and the controller calculates the first voltage phase angle of the first bridge arm according to the second threshold value, the power factor angle and the third voltage phase angle, if the voltage phase angle of the initial modulation signal of the first bridge arm is between the first voltage phase angle and the third voltage phase angle, the controller cannot keep the switching state of the first bridge arm unchanged by adjusting the common-mode voltage. Therefore, the controller needs to calculate the first voltage phase angle in other ways.

[0106] In some possible embodiments, when the power factor angle is greater than the fourth threshold value and less than or equal to the first threshold value, the controller can calculate the first voltage phase angle according to the fourth threshold value, the second threshold value and the third voltage phase angle. The difference between the third voltage phase angle of the first bridge arm and the first voltage phase angle is equal to the sum of the second threshold value and the fourth threshold value. Therefore, when the power factor angle is greater than the fourth threshold value and less than or equal to the first threshold value, the difference between the first voltage phase angle and the third voltage phase angle remains unchanged.

[0107] For example, assuming that the fourth threshold value is equal to 30 degrees, the second threshold value is equal to 30 degrees, and the first threshold value is equal to 36.87 degrees. When the controller detects that the power factor angle output by the power conversion device is equal to 35 degrees, and the voltage output by the power conversion device lags behind the current, the power factor angle is greater than 30 degrees (the fourth threshold value) and less than 36.87 degrees (the first threshold value). In order to accurately control the first bridge arm to keep the switching state unchanged when the absolute value of the output current is relatively large, the controller calculates the first voltage phase angle of the first bridge arm to be equal to the third voltage phase angle minus 30 degrees (the fourth threshold value) minus 30 degrees (the second threshold value). Alternatively, when the voltage output by the power conversion device leads the current, the controller calculates the first voltage phase angle of the first bridge arm to be equal to the third voltage phase angle plus 30 degrees plus 30 degrees. Further, when the voltage phase angle of the initial modulation signal of the first bridge arm is between the first voltage phase angle and the third voltage phase angle, the controller can keep the switching state of the first bridge arm unchanged by gradually changing the common-mode voltage, thereby reducing the current peak ripple output by the first bridge arm.

[0108] In some possible embodiments, when the voltage phase angle of the initial modulation signal of the first bridge arm is between the first voltage phase angle and the third voltage phase angle, the controller can adjust the gradual change of the common-mode voltage according to the initial modulation signal of the first bridge arm, so that the first bridge arm keeps the switching state unchanged. Specifically, the common-mode voltage can be equal to 1 minus the voltage magnitude of the initial modulation signal of the first bridge arm, or the common-mode voltage can be equal to -1 minus the voltage magnitude of the initial modulation signal of the first bridge arm.

[0109] Similarly, the controller can obtain the first voltage phase angle and the third voltage phase angle of the second bridge arm or the third bridge arm, and when the voltage phase angle of the initial modulation signal of the second bridge arm or the third bridge arm is between the first voltage phase angle and the third voltage phase angle of the second bridge arm or the third bridge arm, the controller can adjust the gradual change of the common-mode voltage to control the second bridge arm or the third bridge arm to keep the switching state unchanged, thereby reducing the current peak ripple of the output of the second bridge arm or the third bridge arm. As can be seen from the above, there is a 120-degree phase difference between the output currents of the bridge arms, and therefore, at different times, the bridge arm with a larger absolute value of the output current is different. Therefore, the controller needs to switch the common-mode voltage of the three-phase power conversion bridge to control different bridge arms to keep the switching state unchanged at different times. For example, when the bridge arm with a larger absolute value of the output current is switched from the first bridge arm to the second bridge arm, the controller adjusts the switching of the common-mode voltage to control the first bridge arm to switch from keeping the switching state unchanged to continuously switching the switching state, and to control the second bridge arm to switch from continuously switching the switching state to keeping the switching state unchanged.

[0110] Specifically, in the embodiments of the present application, when the voltage phase angle of the initial modulation signal of each bridge arm is equal to the third voltage phase angle of the bridge arm, the bridge arm with larger output current absolute value will switch. For example, taking the first bridge arm as an example, in the case that the voltage output by the power conversion device lags behind the current, it can be known from the above that the first voltage phase angle of the first bridge arm leads the third voltage phase angle. When the initial modulation signal of the first bridge arm is between the first voltage phase angle and the third voltage phase angle, the first bridge arm outputs current with larger absolute value, and the controller gradually changes the common-mode voltage to control the first bridge arm to keep the switch state unchanged. When the voltage phase angle of the initial modulation signal of the first bridge arm is greater than the third voltage phase angle, the second bridge arm outputs current with larger absolute value, and thus the controller needs to adjust the common-mode voltage to switch when the voltage phase angle of the initial modulation signal of the first bridge arm is equal to the third voltage phase angle, so as to control the second bridge arm to keep the switch state unchanged. Alternatively, in the case that the voltage output by the power conversion device leads the current, it can be known from the above that the third voltage phase angle of the first bridge arm leads the first voltage phase angle. When the initial modulation signal of the first bridge arm is less than the third voltage phase angle, the third bridge arm outputs current with larger absolute value, and the controller gradually changes the common-mode voltage to control the third bridge arm to keep the switch state unchanged. When the voltage phase angle of the initial modulation signal of the first bridge arm is greater than the third voltage phase angle, the first bridge arm outputs current with larger absolute value, and thus the controller needs to adjust the common-mode voltage to switch when the voltage phase angle of the initial modulation signal of the first bridge arm is equal to the third voltage phase angle, so as to control the first bridge arm to keep the switch state unchanged. In general, when the voltage phase angle of the initial modulation signal of each bridge arm is equal to the third voltage phase angle of the bridge arm, the bridge arm with larger output current absolute value will switch, and thus the controller will adjust the common-mode voltage to switch.

[0111] It should be noted that in some application scenarios, when the controller adjusts the common-mode voltage switching to make the bridge arm that keeps the switch state unchanged switch, the common-mode voltage changes greatly in an instant, resulting in that the common-mode voltage contains more high-order harmonics. Further, the common-mode voltage is injected into the three-phase power conversion bridge and is output through the output end of the three-phase power conversion bridge. Since the output end of the three-phase power conversion bridge is connected to the DC bus midpoint through a filter capacitor module, the high-order harmonics in the common-mode voltage output by the three-phase power conversion bridge generates common-mode resonance through the filter capacitor module, thereby causing EMI inside the power conversion device, and even causing damage to the devices of the power conversion device. Therefore, in the embodiments of the present application, when the voltage phase angle of the initial modulation signal of each bridge arm is close to the third voltage phase angle of the bridge arm, that is, when the common-mode voltage is about to switch, the controller can adjust the common-mode voltage to gradually change at a first change rate to avoid sudden change of the common-mode voltage at the time of switching, thereby reducing the high-order harmonics in the common-mode voltage output by the three-phase power conversion bridge, and further reducing the risk of common-mode resonance inside the power conversion device. Taking the first bridge arm as an example, the controller can determine the second voltage phase angle of the first bridge arm according to the third voltage phase angle of the first bridge arm. The second voltage phase angle is used to constitute the specific value range of the voltage phase angle of the initial modulation signal of the first bridge arm when adjusting the common-mode voltage to gradually change at the first change rate with the third voltage phase angle. When the voltage phase angle of the initial modulation signal of the first bridge arm is between the second voltage phase angle and the third voltage phase angle, the controller adjusts the common-mode voltage to gradually change at the first change rate, which can avoid sudden change of the common-mode voltage.

[0112] In some possible implementation manners, specifically, the controller can calculate the second voltage phase angle of the first bridge arm according to the third voltage phase angle of the first bridge arm and the third threshold value, and the difference between the third voltage phase angle and the second voltage phase angle is equal to the third threshold value. It can be understood that the controller can flexibly adjust the specific value of the third threshold value according to the requirements of the actual application scenario. For example, the third threshold value is equal to 10 degrees.

[0113] In some possible implementation manners, in the case that the current output by the power conversion device leads the voltage, when the voltage phase angle of the initial modulation signal of the first bridge arm is equal to the third voltage phase angle, if the voltage size of the initial modulation signal of the first bridge arm is equal to the positive peak value of the voltage, the controller can calculate the common-mode voltage according to the following formula (1) to make the common-mode voltage gradually change at the first change rate when the voltage phase angle of the initial modulation signal of the first bridge arm is between the second voltage phase angle and the third voltage phase angle. The formula (1) satisfies:

[0114] Vcom=(1-2μ)-μVmin-(1-μ)Vmax

[0115]

[0116] wherein Vcom is the common-mode voltage, Vmax is the voltage magnitude of the initial modulation signal of the first bridge arm, Vmin is the voltage magnitude of the initial modulation signal of the second bridge arm, θ3 is the third voltage phase angle, θ2 is the second voltage phase angle, and θ is the voltage phase angle of the initial modulation signal of the first bridge arm.

[0117] In some possible embodiments, in the case that the current output by the power conversion device leads the voltage, when the voltage phase angle of the initial modulation signal of the first bridge arm is equal to the third voltage phase angle, if the voltage magnitude of the initial modulation signal of the first bridge arm is equal to the negative peak value of the voltage, the controller can calculate the common-mode voltage according to the following formula (2) to make the common-mode voltage gradually change at the first change rate when the voltage phase angle of the initial modulation signal of the first bridge arm is between the second voltage phase angle and the third voltage phase angle. The formula (2) satisfies:

[0118] Vcom = (1 - 2μ) - μVmin - (1 - μ)Vmax

[0119]

[0120] wherein Vcom is the common-mode voltage, Vmax is the voltage magnitude of the initial modulation signal of the first bridge arm, Vmin is the voltage magnitude of the initial modulation signal of the second bridge arm, θ3 is the third voltage phase angle, θ2 is the second voltage phase angle, and θ is the voltage phase angle of the initial modulation signal of the first bridge arm.

[0121] In some possible embodiments, in the case that the current output by the power conversion device lags behind the voltage, when the voltage phase angle of the initial modulation signal of the first bridge arm is equal to the third voltage phase angle, if the voltage magnitude of the initial modulation signal of the first bridge arm is equal to the positive peak value of the voltage, the controller can calculate the common-mode voltage according to the following formula (3) to make the common-mode voltage gradually change at the first change rate when the voltage phase angle of the initial modulation signal of the first bridge arm is between the second voltage phase angle and the third voltage phase angle. The formula (3) satisfies:

[0122] Vcom = (1 - 2μ) - μVmin - (1 - μ)Vmax

[0123]

[0124] wherein Vcom is the common-mode voltage, Vmax is the voltage magnitude of the initial modulation signal of the first bridge arm, Vmin is the voltage magnitude of the initial modulation signal of the second bridge arm, θ3 is the third voltage phase angle, θ2 is the second voltage phase angle, and θ is the voltage phase angle of the initial modulation signal of the first bridge arm.

[0125] In some possible embodiments, in the case that the current output by the power conversion device lags behind the voltage, when the voltage phase angle of the initial modulation signal of the first bridge arm is equal to the third voltage phase angle, if the voltage magnitude of the initial modulation signal of the first bridge arm is equal to the negative peak value of the voltage, the controller can calculate the common-mode voltage according to the following formula (4) to make the common-mode voltage gradually change at the first change rate when the voltage phase angle of the initial modulation signal of the first bridge arm is between the second voltage phase angle and the third voltage phase angle. The formula (4) satisfies:

[0126] Vcom = (1-2μ)-μVmin-(1-μ)Vmax

[0127]

[0128] wherein Vcom is the common-mode voltage, Vmax is the voltage magnitude of the initial modulation signal of the first bridge arm, Vmin is the voltage magnitude of the initial modulation signal of the second bridge arm, θ3 is the third voltage phase angle, θ2 is the second voltage phase angle, and θ is the voltage phase angle of the initial modulation signal of the first bridge arm.

[0129] For the convenience of understanding, the following content is combined with Figures 5 to 8 to illustrate by way of example. Figures 5 to 8 The signal change schematic diagram of the power conversion device provided by the embodiments of the present application is shown in the following figure. When the current output by the power conversion device lags behind the voltage, the signal changes of the power conversion device can be referred to Figure 5 . In Figure 5 , U1 represents the initial modulation signal of the first bridge arm, Vcom represents the common-mode voltage, θ1, θ2 and θ3 represent the first voltage phase angle, the second voltage phase angle and the third voltage phase angle of the first bridge arm respectively, and θt3 represents the third threshold value. When the voltage phase angle of U1 is between θ1 and θ2, the absolute value of the current output by the first bridge arm is relatively large, and the controller gradually changes Vcom to control the first bridge arm to keep the switching state unchanged, and the second bridge arm and the third bridge arm to continuously switch the switching state, so as to reduce the current peak value ripple output by the first bridge arm. When the voltage phase angle of U1 is between θ2 and θ3, Vcom is about to switch, and the controller gradually changes Vcom at the first change rate to control the first bridge arm, the second bridge arm and the third bridge arm to continuously switch the switching state, and to reduce the high-order resonance in the common-mode voltage output by the three-phase power conversion bridge. Similarly, please refer to Figure 6 , Figure 6In the diagram, U1 and U2 represent the initial modulation signals of the first and second bridge arms, respectively; Vcom represents the common-mode voltage; θ1, θ2, and θ3 represent the first, second, and third voltage phase angles of the second bridge arm, respectively; and θt3 represents the third threshold. When the voltage phase angle of U2 is between θ1 and θ2, the controller gradually adjusts Vcom to reduce the peak current ripple of the second bridge arm output. When the voltage phase angle of U2 is between θ2 and θ3, the controller gradually adjusts Vcom at a first rate of change, which can reduce higher-order resonances in the common-mode voltage of the three-phase power converter bridge output. Similarly, please refer to [link to relevant documentation]. Figure 7 , Figure 7 In this diagram, U1, U2, and U3 represent the initial modulation signals of the first, second, and third bridge arms, respectively; Vcom represents the common-mode voltage; θ1, θ2, and θ3 represent the first, second, and third voltage phase angles of the third bridge arm, respectively; and θt3 represents the third threshold. When the voltage phase angle of U3 is between θ1 and θ2, the controller gradually adjusts Vcom to keep the third bridge arm in a constant switching state while the first and second bridge arms continuously switch their switching states, thereby reducing the peak current ripple of the third bridge arm output. When the voltage phase angle of U3 is between θ2 and θ3, the controller gradually adjusts Vcom at a first rate of change to reduce higher-order resonances in the common-mode voltage output of the three-phase power converter bridge.

[0130] Similarly, when the current output by the power conversion device lags behind the voltage, the changes in various signals of the power conversion device can be found in [reference needed]. Figure 8 .exist Figure 8 In this context, U1 represents the initial modulation signal of the first bridge arm, Vcom represents the common-mode voltage, θ1, θ2, and θ3 represent the first, second, and third voltage phase angles of the first bridge arm, respectively, and θt3 represents the third threshold. The specific implementation of the controller is the same as described above. Figures 6 to 7 The specific implementation methods are similar, and will not be described in detail here.

[0131] In general, in the embodiments of the present application, when the power factor angle is less than or equal to 30 degrees, the controller adjusts the difference between the third voltage phase angle and the first voltage phase angle to be equal to the power factor angle plus 30 degrees, which can ensure that the absolute value of the current output by the first bridge arm between the first voltage phase angle and the third voltage phase angle is relatively large. At the same time, since the second voltage phase angle is located between the first voltage phase angle and the third voltage phase angle, the controller can control the first bridge arm to keep the switching state unchanged when the voltage phase angle of the initial modulation signal of the first bridge arm is located between the first voltage phase angle and the second voltage phase angle by gradually changing the common-mode voltage and keeping the switching state of the first bridge arm unchanged, so as to reduce the current peak ripple output by the first bridge arm. When the power factor angle is greater than 30 degrees, the controller adjusts the difference between the third voltage phase angle and the first voltage phase angle to remain equal to 60 degrees, which can ensure that the first bridge arm keeps the switching state unchanged between the first voltage phase angle and the second voltage phase angle when the power factor angle is too large, and has strong reliability. Further, after determining the third voltage phase angle and the first voltage phase angle, the controller can adjust the difference between the second voltage phase angle and the third voltage phase angle to be equal to 10 degrees, and control each bridge arm to keep switching the switching state between the second voltage phase angle and the third voltage phase angle, so as to adjust the common-mode voltage to change gently at a first change rate. Since the difference between the second voltage phase angle and the third voltage phase angle is relatively small, the controller can reduce the common-mode resonance while keeping the voltage phase angle range of the first bridge arm switching the switching state unchanged, thereby avoiding a large increase in switching loss. In addition, the controller can flexibly adjust the value of the third threshold according to the common-mode resonance and the switching loss. For example, when the third threshold increases, i.e., the difference between the third voltage phase angle and the second voltage phase angle increases, the controller can adjust the common-mode voltage to change more gently, thereby making the common-mode resonance reduction effect better. Conversely, when the third threshold decreases, the difference between the second voltage phase angle and the first voltage phase angle increases, and the controller can control the first bridge arm to keep the switching state unchanged in a larger voltage phase angle range, thereby reducing more switching loss.

[0132] Please refer to Figure 9 , Figure 9 A flowchart of a control method of a power conversion device provided by the present application is shown. The control method of the power conversion device provided by the embodiments of the present application is applicable to Figures 2 to 8 the controller in the corresponding specific embodiments. Specifically, the control method of the power conversion device can include the following steps:

[0133] S101, detecting the power factor angle of the power conversion device.

[0134] It can be understood that in some application scenarios, when the power factor angle is not equal to 0, the current peak value ripple output by the first bridge arm in the power conversion device can be significantly increased. In order to control the current peak value ripple output by the first bridge arm in time, the power conversion device can detect the output power factor angle.

[0135] The specific implementation of S101 can refer to the implementation of the controller in the above Figures 2 to 8 The specific implementation of S101 can refer to the implementation of the controller in the above

[0136] S102, in the case that the power factor angle is greater than 0 and less than or equal to the first threshold value, when the voltage phase angle of the initial modulation signal of the first bridge arm is located between the first voltage phase angle and the second voltage phase angle, the common mode voltage of the three-phase power conversion bridge is adjusted to gradually change and make the first bridge arm keep the switching state unchanged, and the second bridge arm and the third bridge arm continue to switch the switching state; when the voltage phase angle of the initial modulation signal of the first bridge arm is located between the second voltage phase angle and the third voltage phase angle, the common mode voltage is adjusted to gradually change at a first change rate and make the first bridge arm, the second bridge arm and the third bridge arm continue to switch the switching state.

[0137] It can be understood that, since the power factor angle is equal to the phase difference between the voltage peak value of the initial modulation signal of the first bridge arm and the output current peak value, as the power factor angle increases or decreases, the phase difference between the voltage peak value of the initial modulation signal of the first bridge arm and the output current peak value will increase or decrease accordingly. Then, the power conversion device can ensure that, between the third voltage phase angle and the first voltage phase angle, the output current of the first bridge arm is close to the current peak value, that is, the absolute value of the current output by the first bridge arm is relatively large, by adjusting the difference between the third voltage phase angle (that is, the voltage phase angle corresponding to the initial modulation signal of the first bridge arm when the voltage peak value is equal) and the first voltage phase angle and the power factor angle is positively correlated. At the same time, since the second voltage phase angle is located between the first voltage phase angle and the third voltage phase angle, when the voltage phase angle of the initial modulation signal of the first bridge arm is located between the first voltage phase angle and the second voltage phase angle, the power conversion device controls the common-mode voltage to gradually change and keeps the switching state of the first bridge arm unchanged, so as to control the first bridge arm to keep the switching state unchanged when the absolute value of the output current is relatively large, thereby reducing the current peak value ripple output by the first bridge arm. In addition, when the voltage phase angle of the initial modulation signal of the first bridge arm is located between the second voltage phase angle and the third voltage phase angle, the power conversion device does not continue to control the first bridge arm to keep the switching state unchanged, because when the voltage phase angle of the initial modulation signal of the first bridge arm is close to the third voltage phase angle, the common-mode voltage may change suddenly. In order to avoid common-mode resonance caused by sudden change of the common-mode voltage, the power conversion device controls the common-mode voltage to gradually change at a first change rate between the second voltage phase angle and the third voltage phase angle, so as to control the common-mode voltage to change slowly. It can be seen that, in the embodiment of the present application, the power conversion device can reduce the current peak value ripple output by the first bridge arm, while reducing the risk of generating common-mode resonance, and has strong applicability.

[0138] In an optional embodiment, the AC end of the power conversion device includes a first AC end, a second AC end and a third AC end, the first AC end is connected to the first bridge arm, the second AC end is connected to the second bridge arm, and the third AC end is connected to the third bridge arm; the voltage phase angle of the initial modulation signal of the first bridge arm is the same as the voltage phase angle of the AC power of the first AC end, the voltage phase angle of the initial modulation signal of the second bridge arm is the same as the voltage phase angle of the AC power of the second AC end, and the voltage phase angle of the initial modulation signal of the third bridge arm is the same as the voltage phase angle of the AC power of the third AC end.

[0139] It can be understood that, when the power conversion device generates the pulse width modulation signal according to the initial modulation signal of each bridge arm to control the operation of each bridge arm, the voltage phase angle of the AC end corresponding to each bridge arm can be made equal to the voltage phase angle of the initial modulation signal. It can be seen that, the initial modulation signal of each bridge arm can be understood as the AC power reference signal of the corresponding AC end.

[0140] In an optional embodiment, the difference between the third voltage phase angle and the first voltage phase angle is equal to the sum of the power factor angle output by the power conversion device and the second threshold value, and the difference between the second voltage phase angle and the third voltage phase angle is equal to the third threshold value.

[0141] It can be understood that the power conversion device can calculate the first voltage phase angle according to the third voltage phase angle, the power factor angle and the second threshold value, and can calculate the second voltage phase angle according to the third voltage phase angle and the third threshold value, and the calculation is simple and easy to implement.

[0142] In an optional embodiment, when the power factor angle output by the power conversion device is greater than a fourth threshold value and less than or equal to the first threshold value, the difference between the third voltage phase angle and the first voltage phase angle is kept equal to the sum of the second threshold value and the fourth threshold value.

[0143] It can be understood that when the power factor angle is greater than the fourth threshold value and less than or equal to the first threshold value, if the power conversion device calculates the first voltage phase angle according to the third voltage phase angle, the power factor angle and the second threshold value, and the initial modulation signal of the first bridge arm is located between the first voltage phase angle and the third voltage phase angle, the first bridge arm can not be controlled to keep the switching state unchanged, that is, it is not possible to control the first bridge arm to keep the switching state unchanged when the absolute value of the current output by the first bridge arm is relatively large. Therefore, when the power factor angle is greater than the fourth threshold value and less than or equal to the first threshold value, the power conversion device adjusts the difference between the third voltage phase angle and the first voltage phase angle to keep it equal to the sum of the second threshold value and the fourth threshold value, so as to ensure that the voltage phase angle of the initial modulation signal of the first bridge arm is located between the second voltage phase angle and the first voltage phase angle, that is, the first bridge arm keeps the switching state unchanged when the absolute value of the current output by the first bridge arm is relatively large, thereby reducing the current peak ripple output by the first bridge arm.

[0144] In an optional embodiment, the second threshold value is equal to 30 degrees, the third threshold value is equal to 10 degrees, and the fourth threshold value is equal to 30 degrees.

[0145] It can be understood that, in the case that the power factor angle is less than or equal to 30 degrees, the controller adjusts the difference between the third voltage phase angle and the first voltage phase angle to be equal to the power factor angle plus 30 degrees, which can ensure that the absolute value of the current output by the first bridge arm between the first voltage phase angle and the third voltage phase angle is relatively large. In the case that the power factor angle is greater than 30 degrees, the controller adjusts the difference between the third voltage phase angle and the first voltage phase angle to remain equal to 60 degrees, which can ensure that the first bridge arm remains in the same switching state between the first voltage phase angle and the second voltage phase angle when the power factor angle is too large, and the reliability is strong. Further, after determining the third voltage phase angle and the first voltage phase angle, the controller can adjust the difference between the second voltage phase angle and the third voltage phase angle to be equal to 10 degrees, and control each bridge arm to continuously switch the switching state between the second voltage phase angle and the third voltage phase angle, so as to adjust the common-mode voltage to change gently at a first change rate. Since the difference between the second voltage phase angle and the third voltage phase angle is relatively small, the controller can reduce the common-mode resonance while making the voltage phase angle range in which the first bridge arm continuously switches the switching state relatively small, thereby avoiding a large increase in switching loss. In addition, the controller can flexibly adjust the value of the third threshold according to the common-mode resonance and the switching loss. For example, when the third threshold increases, that is, the difference between the third voltage phase angle and the second voltage phase angle increases, the controller can adjust the common-mode voltage to change more gently, thereby making the common-mode resonance reduction effect better. Conversely, when the third threshold decreases, the difference between the second voltage phase angle and the first voltage phase angle increases, and the controller can control the first bridge arm to remain in the same switching state in a larger voltage phase angle range, thereby reducing more switching loss.

[0146] In an optional embodiment, in the case that the current phase angle output by the power conversion device leads the voltage phase angle, the first voltage phase angle leads the second voltage phase angle, and the second voltage phase angle leads the third voltage phase angle.

[0147] It can be understood that, in the case that the current phase angle output by the power conversion device leads the voltage phase angle, the current peak value output by the first bridge arm leads the voltage peak value of the initial modulation signal, that is, the voltage phase angle of the initial modulation signal corresponding to the case that the absolute value of the current output by the first bridge arm is relatively large leads the third voltage phase angle, and the range between the first voltage phase angle and the third voltage phase angle is the value range of the voltage phase angle of the initial modulation signal in the case that the absolute value of the current output by the first bridge arm is relatively large. Therefore, the first voltage phase angle leads the third voltage phase angle. At the same time, since the second voltage phase angle is located between the first voltage phase angle and the third voltage phase angle, the second voltage phase angle also leads the third voltage phase angle.

[0148] In an optional embodiment, the first voltage phase angle lags behind the second voltage phase angle, and the second voltage phase angle lags behind the third voltage phase angle, in the case that the current phase angle of the power conversion device output lags behind the voltage phase angle.

[0149] It can be understood that, in the case that the current phase angle of the power conversion device output lags behind the voltage phase angle, the current peak value of the first bridge arm output lags behind the voltage peak value of the initial modulation signal, that is, the voltage phase angle of the initial modulation signal corresponding to the case that the absolute value of the current output by the first bridge arm is relatively large lags behind the third voltage phase angle, and the range between the first voltage phase angle and the third voltage phase angle is the value range of the voltage phase angle of the initial modulation signal in the case that the absolute value of the current output by the first bridge arm is relatively large. Therefore, the first voltage phase angle lags behind the third voltage phase angle. Meanwhile, since the second voltage phase angle is between the first voltage phase angle and the third voltage phase angle, the second voltage phase angle also lags behind the third voltage phase angle.

[0150] In an optional embodiment, the first threshold value is equal to 36.87 degrees.

[0151] It can be understood that, when the power factor angle of the power conversion device output is greater than 0 and less than or equal to 36.87 degrees, the power conversion device can reduce the current peak value of the first bridge arm output and reduce the risk of common-mode resonance by adjusting the common-mode voltage in different voltage phase angle intervals of the first bridge arm, and the detection method is simple and has strong applicability.

[0152] In an optional embodiment, in the case that the third voltage phase angle is the voltage phase angle of the initial modulation signal of the first bridge arm when the voltage of the initial modulation signal of the first bridge arm is equal to the positive peak value of the voltage of the initial modulation signal, and the current phase angle of the power conversion device output leads the voltage phase angle, when the common-mode voltage gradually changes at the first change rate, the common-mode voltage satisfies:

[0153] Vcom=(1-2μ)-μVmin-(1-μ)Vmax

[0154]

[0155] wherein Vmax is the voltage of the initial modulation signal of the first bridge arm, Vmin is the voltage of the initial modulation signal of the second bridge arm, θ2 is the third voltage phase angle, θ3 is the second voltage phase angle, and θ is the voltage phase angle of the initial modulation signal of the first bridge arm.

[0156] It can be understood that the power conversion device can adjust the common-mode voltage to change at the first change rate according to Vmax, Vmin, θ2, θ3 and θ, and the calculation method is simple and easy to implement.

[0157] In an alternative embodiment, when the third voltage phase angle is the voltage phase angle of the initial modulation signal of the first bridge arm at which the voltage magnitude of the initial modulation signal of the first bridge arm is equal to the negative peak value of the voltage of the initial modulation signal, and the current phase angle output by the power conversion device leads the voltage phase angle, when the common-mode voltage gradually changes at the first change rate, the common-mode voltage satisfies:

[0158] Vcom = (1 - 2μ) - μVmin - (1 - μ)Vmax

[0159]

[0160] wherein Vmax is the voltage magnitude of the initial modulation signal of the first bridge arm, Vmin is the voltage magnitude of the initial modulation signal of the second bridge arm, θ2 is the third voltage phase angle, θ3 is the second voltage phase angle, and θ is the voltage phase angle of the initial modulation signal of the first bridge arm.

[0161] It can be understood that the power conversion device can adjust the common-mode voltage to change at the first change rate according to Vmax, Vmin, θ2, θ3 and θ, and the calculation is simple and easy to implement.

[0162] In an alternative embodiment, when the third voltage phase angle is the voltage phase angle of the initial modulation signal of the first bridge arm at which the voltage magnitude of the initial modulation signal of the first bridge arm is equal to the positive peak value of the voltage of the initial modulation signal, and the current phase angle output by the power conversion device lags behind the voltage phase angle, when the common-mode voltage gradually changes at the first change rate, the common-mode voltage satisfies:

[0163] Vcom = (1 - 2μ) - μVmin - (1 - μ)Vmax

[0164]

[0165] wherein Vmax is the voltage magnitude of the initial modulation signal of the first bridge arm, Vmin is the voltage magnitude of the initial modulation signal of the second bridge arm, θ2 is the third voltage phase angle, θ3 is the second voltage phase angle, and θ is the voltage phase angle of the initial modulation signal of the first bridge arm.

[0166] It can be understood that the power conversion device can adjust the common-mode voltage to change at the first change rate according to Vmax, Vmin, θ2, θ3 and θ, and the calculation is simple and easy to implement.

[0167] In an optional embodiment, when the third voltage phase angle is equal to the voltage phase angle of the initial modulation signal of the first bridge arm, and the current phase angle output by the power conversion device lags behind the voltage phase angle, and when the common-mode voltage gradually changes at a first change rate, the common-mode voltage satisfies:

[0168] Vcom=(1-2μ)-μVmin-(1-μ)Vmax

[0169]

[0170] wherein Vmax is the voltage size of the initial modulation signal of the first bridge arm, Vmin is the voltage size of the initial modulation signal of the second bridge arm, θ2 is the third voltage phase angle, θ3 is the second voltage phase angle, and θ is the voltage phase angle of the initial modulation signal of the first bridge arm.

[0171] It can be understood that the power conversion device can adjust the common-mode voltage to change at a first change rate according to Vmax, Vmin, θ2, θ3 and θ, and the calculation is simple and easy to implement.

[0172] The above merely provides a specific implementation of the present application, but the protection scope of the present application is not limited thereto, and any person skilled in the art can easily think of changes or replacements within the technical scope disclosed by the present application, which should be covered by the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the above claims.

Claims

1. A power conversion device, characterized in that, The DC terminal of the power conversion device is used to connect to a DC source, and the AC terminal of the power conversion device is used to connect to the power grid or a load. The power conversion device includes a controller, a filter capacitor module, a three-phase power conversion bridge, a DC bus, and a positive bus capacitor and a negative bus capacitor connected in series at the midpoint of the DC bus. The DC bus is connected between the DC terminal and the three-phase power conversion bridge. The positive bus capacitor is connected to the positive terminal of the DC bus, and the negative bus capacitor is connected to the negative terminal of the DC bus. The three-phase power conversion bridge is connected to the midpoint of the DC bus through the filter capacitor module. The three-phase power conversion bridge includes a first bridge arm, a second bridge arm, and a third bridge arm. The controller is further configured to: When the power factor angle output by the power conversion device is greater than 0 and less than or equal to a first threshold, when the voltage phase angle of the initial modulation signal of the first bridge arm is between the first voltage phase angle and the second voltage phase angle, the common-mode voltage of the three-phase power conversion bridge is gradually changed, so that the first bridge arm remains in a switching state, while the second bridge arm and the third bridge arm continuously switch switching states; when the voltage phase angle of the initial modulation signal of the first bridge arm is between the second voltage phase angle and the third voltage phase angle, the common-mode voltage is gradually changed at a first rate of change, so that the first bridge arm, the second bridge arm, and the third bridge arm continuously switch switching states. Wherein, the third voltage phase angle is the voltage phase angle of the initial modulation signal of the first bridge arm when the voltage magnitude of the initial modulation signal of the first bridge arm is equal to the voltage peak value of the initial modulation signal; the difference between the third voltage phase angle and the first voltage phase angle is positively correlated with the power factor angle, and the angle of the second voltage phase angle is between the third voltage phase angle and the first voltage phase angle.

2. The power conversion device according to claim 1, characterized in that, The AC terminals of the power conversion device include a first AC terminal, a second AC terminal and a third AC terminal. The first AC terminal is connected to the first bridge arm, the second AC terminal is connected to the second bridge arm and the third AC terminal is connected to the third bridge arm. The voltage phase angle of the initial modulation signal of the first bridge arm is the same as the voltage phase angle of the AC power at the first AC terminal, the voltage phase angle of the initial modulation signal of the second bridge arm is the same as the voltage phase angle of the AC power at the second AC terminal, and the voltage phase angle of the initial modulation signal of the third bridge arm is the same as the voltage phase angle of the AC power at the third AC terminal.

3. The power conversion device according to claim 1, characterized in that, The difference between the third voltage phase angle and the first voltage phase angle is equal to the sum of the power factor angle output by the power conversion device and the second threshold, and the difference between the second voltage phase angle and the third voltage phase angle is equal to the third threshold.

4. The power conversion device according to claim 3, characterized in that, When the power factor angle output by the power conversion device is greater than the fourth threshold and less than or equal to the first threshold, the difference between the third voltage phase angle and the first voltage phase angle remains equal to the sum of the second threshold and the fourth threshold.

5. The power conversion device according to claim 4, characterized in that, The second threshold is equal to 30 degrees, the third threshold is equal to 10 degrees, and the fourth threshold is equal to 30 degrees.

6. The power conversion device according to any one of claims 1 to 5, characterized in that, When the current phase angle output by the power conversion device leads the voltage phase angle, the first voltage phase angle leads the second voltage phase angle, and the second voltage phase angle leads the third voltage phase angle.

7. The power conversion device according to any one of claims 1 to 5, characterized in that, When the current phase angle output by the power conversion device lags behind the voltage phase angle, the first voltage phase angle lags behind the second voltage phase angle, and the second voltage phase angle lags behind the third voltage phase angle.

8. The power conversion device according to any one of claims 1 to 7, characterized in that, The first threshold is equal to 36.87 degrees.

9. The power conversion device according to any one of claims 1 to 8, characterized in that, When the third voltage phase angle is equal to the voltage phase angle of the initial modulation signal of the first bridge arm, and the current phase angle output by the power conversion device leads the voltage phase angle, when the controller adjusts the common-mode voltage to gradually change at a first rate of change, the common-mode voltage satisfies: Vcom=(1-2μ)-μVmin-(1-μ)Vmax Where Vmax is the voltage magnitude of the initial modulation signal of the first bridge arm, and Vmin is the voltage magnitude of the initial modulation signal of the second bridge arm. The third voltage phase angle, The second voltage phase angle, The voltage phase angle of the initial modulation signal of the first bridge arm.

10. The power conversion device according to any one of claims 1 to 9, characterized in that, When the third voltage phase angle is equal to the voltage phase angle of the initial modulation signal of the first bridge arm, and the current phase angle output by the power conversion device leads the voltage phase angle, when the controller adjusts the common-mode voltage to gradually change at a first rate of change, the common-mode voltage satisfies: Vcom=(1-2μ)-μVmin-(1-μ)Vmax Where Vmax is the voltage magnitude of the initial modulation signal of the first bridge arm, and Vmin is the voltage magnitude of the initial modulation signal of the second bridge arm. The third voltage phase angle, The second voltage phase angle, The voltage phase angle of the initial modulation signal of the first bridge arm.

11. The power conversion device according to any one of claims 1 to 10, characterized in that, When the third voltage phase angle is equal to the voltage phase angle of the initial modulation signal of the first bridge arm, and the current phase angle output by the power conversion device lags behind the voltage phase angle, and the controller adjusts the common-mode voltage to gradually change at a first rate of change, the common-mode voltage satisfies: Vcom=(1-2μ)-μVmin-(1-μ)Vmax Where Vmax is the voltage magnitude of the initial modulation signal of the first bridge arm, and Vmin is the voltage magnitude of the initial modulation signal of the second bridge arm. The third voltage phase angle, The second voltage phase angle, The voltage phase angle of the initial modulation signal of the first bridge arm.

12. The power conversion device according to any one of claims 1 to 11, characterized in that, When the third voltage phase angle is equal to the voltage phase angle of the initial modulation signal of the first bridge arm, and the current phase angle output by the power conversion device lags behind the voltage phase angle, and the controller adjusts the common-mode voltage to gradually change at a first rate of change, the common-mode voltage satisfies: Vcom=(1-2μ)-μVmin-(1-μ)Vmax Where Vmax is the voltage magnitude of the initial modulation signal of the first bridge arm, and Vmin is the voltage magnitude of the initial modulation signal of the second bridge arm. The third voltage phase angle, The second voltage phase angle, The voltage phase angle of the initial modulation signal of the first bridge arm.

13. A control method for a power conversion device, the method being applied to the power conversion device, wherein the DC terminal of the power conversion device is used to connect to a DC source, and the AC terminal of the power conversion device is used to connect to a power grid or a load; the power conversion device includes a filter capacitor module, a three-phase power conversion bridge, a DC bus, and a positive bus capacitor and a negative bus capacitor connected in series at the midpoint of the DC bus; the DC bus is connected between the DC terminal and the three-phase power conversion bridge, the positive bus capacitor is connected to the positive terminal of the DC bus, the negative bus capacitor is connected to the negative terminal of the DC bus, and the three-phase power conversion bridge is connected to the midpoint of the DC bus through the filter capacitor module; the three-phase power conversion bridge includes a first bridge arm, a second bridge arm, and a third bridge arm, characterized in that... The method includes: Detect the power factor angle output by the power conversion device; When the power factor angle is greater than 0 and less than or equal to the first threshold, if the voltage phase angle of the initial modulation signal of the first bridge arm is between the first voltage phase angle and the second voltage phase angle, the common-mode voltage of the three-phase power conversion bridge is gradually changed, so that the first bridge arm remains in a switching state while the second and third bridge arms continuously switch switching states; if the voltage phase angle of the initial modulation signal of the first bridge arm is between the second and the third voltage phase angle, the common-mode voltage is gradually changed at a first rate of change, so that the first, second, and third bridge arms continuously switch switching states. Wherein, the third voltage phase angle is the voltage phase angle of the initial modulation signal of the first bridge arm when the voltage magnitude of the initial modulation signal of the first bridge arm is equal to the voltage peak value of the initial modulation signal; the difference between the third voltage phase angle and the first voltage phase angle is positively correlated with the power factor angle, and the angle of the second voltage phase angle is between the third voltage phase angle and the first voltage phase angle.

14. The method according to claim 13, characterized in that, The difference between the third voltage phase angle and the first voltage phase angle is equal to the sum of the power factor angle output by the power conversion device and the second threshold, and the difference between the second voltage phase angle and the third voltage phase angle is equal to the third threshold.

15. The method according to claim 14, characterized in that, When the power factor angle output by the power conversion device is greater than the fourth threshold and less than or equal to the first threshold, the difference between the third voltage phase angle and the first voltage phase angle remains equal to the sum of the second threshold and the fourth threshold.

Images