Power converter and control method thereof

Abstract

The invention provides a power converter and a control method thereof, and belongs to the technical field of power electronics. The power converter provided by the invention comprises a power conversion circuit and a controller. The controller can detect the peak value of the output current of the alternating current end of the power conversion circuit after controlling the direct current component change of the output voltage of the power conversion circuit. Moreover, the controller can adjust the change direction of the direct-current component of the output voltage of the power conversion circuit based on the change condition of the peak value of the output current, so as to suppress the peak value of the output current of the power conversion circuit at a lower level, thereby achieving the effective suppression of the bias current of a load carried by the power converter. According to the power converter provided by the invention, the magnetic bias current can be effectively suppressed without arranging a DCV sampling circuit, so that the power converter can be ensured to be relatively small in size, and relatively low in structural complexity and hardware cost.

Description

Technical Field

[0001] This application relates to the field of power electronics technology, and in particular to a power converter and its control method. Background Technology

[0002] When a power converter operates off-grid with an inductive load (such as a transformer), the DC bias voltage of the AC output voltage must be controlled within a certain range to avoid excessive bias current of the inductive load, which could damage the inductive load.

[0003] To control the DC bias voltage of the output voltage, power converters typically require a DC bias voltage (DCV) sampling circuit. This circuit samples the DC bias voltage in the output voltage and uses closed-loop regulation to suppress it at a low level, thereby minimizing the bias current of the inductive load. However, the DCV sampling circuit significantly increases the size, structural complexity, and hardware cost of the power converter. Summary of the Invention

[0004] This application provides a power converter and its control method, which can solve the technical problem that setting up a DCV sampling circuit in the power converter increases the size, structural complexity and hardware cost of the power converter.

[0005] In a first aspect, a power converter is provided, comprising: a power conversion circuit and a controller. The power conversion circuit includes a DC terminal and an AC terminal. The DC terminal is used to connect to a DC power supply, and the AC terminal is used to connect to a load. The power conversion circuit converts DC power from the DC power supply into AC power and outputs it to the load. The controller controls the DC component of the output voltage at the AC terminal to change sequentially along a first direction, a second direction, and a target direction. The first direction is the direction that increases or decreases the DC component of the output voltage, and the second direction is opposite to the first direction. If the change in the first peak value is less than the change in the second peak value, the target direction is the first direction; if the change in the first peak value is greater than or equal to the change in the second peak value, the target direction is the second direction or the direction that keeps the DC component of the output voltage constant. The first peak value change is the change in the peak value of the output current after the DC component of the output voltage changes along the first direction. The second peak value change is the change in the peak value of the output current after the DC component of the output voltage changes along the second direction.

[0006] In the solution provided in this application, the controller can detect the peak value of the output current at the AC terminal of the power conversion circuit after controlling the change in the DC component of the output voltage of the power conversion circuit. Furthermore, the controller can adjust the direction of change of the DC component of the output voltage of the power conversion circuit based on the change in the peak value of the output current, thereby suppressing the peak value of the output current of the power conversion circuit to a low level, and thus effectively suppressing the bias current of the load driven by the power converter. Since the power converter provided in this application can suppress the bias current without setting up a DCV sampling circuit, it can ensure that the power converter has a small size and low structural complexity and hardware cost.

[0007] In one possible implementation, the controller is configured to: after controlling the DC component of the output voltage to change sequentially along a first direction and a second direction, if the sum of the absolute values ​​of the first DC change and the second DC change is greater than a first threshold, then continue to control the DC component of the output voltage to change along a target direction. Here, the first DC change is the change in the DC component of the output current after the DC component of the output voltage changes along the first direction; the second DC change is the change in the DC component of the output current after the DC component of the output voltage changes along the second direction.

[0008] When a power converter operates off-grid and is connected to an inductive load, changes in the DC component of the output voltage will cause significant changes in the DC component of the output current. Therefore, when the controller detects that the sum of the absolute values ​​of the first and second DC changes exceeds a first threshold, it can determine that the load connected to the power converter includes an inductive load. In this case, to effectively suppress the bias current of the inductive load, the controller can continue to control the DC component of the output voltage to change in the target direction. Conversely, if the controller detects that the sum of the absolute values ​​of the first and second DC changes is not greater than the first threshold, it can determine that the load connected to the power converter does not include an inductive load, thus eliminating the need to further disturb the DC component of the output voltage.

[0009] In one possible implementation, the controller is configured to: after controlling the DC component of the output voltage to change sequentially along a first direction and a second direction, if the absolute value of the first DC change is greater than a second threshold or the absolute value of the second DC change is greater than the second threshold, then continue to control the DC component of the output voltage to change along a target direction. Wherein, the first DC change is the change in the DC component of the output current after the DC component of the output voltage changes along the first direction; the second DC change is the change in the DC component of the output current after the DC component of the output voltage changes along the second direction.

[0010] When the controller detects that the absolute value of either the first or second DC change is greater than a second threshold, it can determine that the load connected to the power converter includes an inductive load. In this case, to effectively suppress the bias current of the inductive load, the controller can continue to control the DC component of the output voltage to change along the target direction. Conversely, if the controller detects that the absolute values ​​of both the first and second DC changes are not greater than the second threshold, it can determine that the load connected to the power converter does not include an inductive load, and therefore there is no need to further disturb the DC component of the output voltage.

[0011] In one possible implementation, the controller is further configured to: after controlling the DC component of the output voltage to change along a target direction, if the change in the third peak value is greater than the change in the second peak value, then control the DC component of the output voltage to change along a second direction; if the change in the third peak value is less than or equal to the change in the second peak value, then control the DC component of the output voltage to change along a first direction. Wherein, the change in the third peak value is the change in the peak value of the output current after the DC component of the output voltage changes along the target direction.

[0012] In the solution provided in this application, the controller can further determine the next disturbance direction after the target direction based on the magnitude of the change in the peak value of the output current, thereby achieving continuous and accurate disturbance of the DC component of the output voltage and ensuring that the peak value of the output current gradually converges and decreases. Furthermore, if the change in the third peak value is less than or equal to the change in the second peak value, the controller, after controlling the DC component of the output voltage to change along the first direction, can again control the DC component of the output voltage to change sequentially along the second direction and the target direction. If the change in the third peak value is greater than the change in the second peak value, the controller, after controlling the DC component of the output voltage to change along the second direction, can again control the DC component of the output voltage to change along the first direction, and based on the magnitude of the change in the peak value of the output current caused by the two changes, continues to determine the next change direction of the DC component of the output voltage. Thus, the controller achieves cyclic adjustment of the DC component of the output voltage to ensure that the peak value of the output current, after gradually converging and decreasing, can be maintained at a small value, thereby suppressing the bias current of the inductive load to a low level.

[0013] In one possible implementation, the peak value of the output current is the sum of the absolute value of the negative half-cycle peak value and the positive half-cycle peak value of the output current.

[0014] Under different operating conditions, changes in the DC component of the output voltage at the AC terminal of the power conversion circuit may have different effects on the positive and negative half-cycle peak values ​​of the output current. For example, under certain operating conditions, after a change in the DC component of the output voltage, the change in the positive half-cycle peak value of the output current may differ from the change in the negative half-cycle peak value. Alternatively, only the positive or negative half-cycle peak value of the output current may change, while the other half-cycle peak value remains unchanged. Therefore, this application, by detecting the sum of the absolute value of the negative half-cycle peak value and the positive half-cycle peak value of the output current, can ensure that the change in the sum of these peak values ​​accurately reflects the impact of changes in the DC component of the output voltage on the output current, thereby reducing the probability of false disturbances to the DC component of the output voltage.

[0015] In one possible implementation, the power conversion circuit includes: an inverter bridge arm and an inverter inductor; the inverter bridge arm is connected between the positive and negative terminals of the DC terminal, the midpoint of the inverter bridge arm is connected to one end of the inverter inductor, and the other end of the inverter inductor is the AC terminal. The output current is the current flowing through the inverter inductor.

[0016] During normal operation of the power converter, the controller needs to detect and control the current flowing through the inverter inductor. Therefore, the power converter also includes a current sampling circuit located at the AC terminal of the power conversion circuit, which can sample the current flowing through the inverter inductor. In the solution provided in this application, the controller can reuse the existing current sampling circuit in the power converter to detect the output current of the power conversion circuit and adjust the DC component of the output voltage at the AC terminal of the power conversion circuit. Thus, there is no need to add an additional hardware sampling circuit to the power converter, thereby avoiding increasing the size, structural complexity, and hardware cost of the power converter.

[0017] Secondly, a control method for a power converter is provided. This control method controls the power converter as described in the first aspect, which includes a power conversion circuit. The control method can be executed by a controller in the power converter. The control method includes: controlling the DC component of the output voltage at the AC terminal of the power conversion circuit to change sequentially along a first direction, a second direction, and a target direction. The first direction is the direction that increases or decreases the DC component of the output voltage, and the second direction is opposite to the first direction. Furthermore, if the change in the first peak value is less than the change in the second peak value, the target direction is the first direction; if the change in the first peak value is greater than or equal to the change in the second peak value, the target direction is the second direction or the direction that keeps the DC component of the output voltage constant. The first peak value change is the change in the peak value of the output current after the DC component of the output voltage changes along the first direction. The second peak value change is the change in the peak value of the output current after the DC component of the output voltage changes along the second direction.

[0018] In one possible implementation, after controlling the DC component of the output voltage to change sequentially along a first direction and a second direction, controlling the DC component of the output voltage to change along a target direction includes: if the sum of the absolute values ​​of the first DC change and the second DC change is greater than a first threshold, then continuing to control the DC component of the output voltage to change along the target direction. Wherein, the first DC change is the change in the DC component of the output current after the DC component of the output voltage changes along the first direction, and the second DC change is the change in the DC component of the output current after the DC component of the output voltage changes along the second direction.

[0019] In one possible implementation, after controlling the DC component of the output voltage to change sequentially along a first direction and a second direction, controlling the DC component of the output voltage to change along a target direction includes: if the absolute value of the first DC change is greater than a second threshold or the absolute value of the second DC change is greater than the second threshold, then continuing to control the DC component of the output voltage to change along the target direction. Wherein, the first DC change is the change in the DC component of the output current after the DC component of the output voltage changes along the first direction, and the second DC change is the change in the DC component of the output current after the DC component of the output voltage changes along the second direction.

[0020] In one possible implementation, after controlling the DC component of the output voltage to change along the target direction, the control method further includes: if the change in the third peak value is greater than the change in the second peak value, then controlling the DC component of the output voltage to change along the second direction; if the change in the third peak value is less than or equal to the change in the second peak value, then controlling the DC component of the output voltage to change along the first direction. Wherein, the change in the third peak value is the change in the peak value of the output current after the DC component of the output voltage changes along the target direction.

[0021] In one possible implementation, the peak value of the output current is the sum of the absolute value of the negative half-cycle peak value and the positive half-cycle peak value of the output current.

[0022] In one possible implementation, the power conversion circuit includes an inverter bridge arm and an inverter inductor; the output current is the current flowing through the inverter inductor.

[0023] The control method and the technical effects of each implementation provided in the second aspect above can be referred to the power converter and the technical effects of each implementation provided in the first aspect above, and will not be repeated here.

[0024] In summary, this application provides a power converter and its control method. The power converter includes a power conversion circuit and a controller. The controller can detect the peak value of the output current at the AC terminal of the power conversion circuit after controlling the change in the DC component of the output voltage of the power conversion circuit. Furthermore, the controller can adjust the direction of change of the DC component of the output voltage of the power conversion circuit based on the change in the peak value of the output current, thereby suppressing the peak value of the output current of the power conversion circuit to a low level, and thus effectively suppressing the bias current of the load driven by the power converter. Since the power converter provided in this application can effectively suppress the bias current without setting up a DCV sampling circuit, it ensures that the power converter has a small size and low structural complexity and hardware cost. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the structure of a power converter provided in an embodiment of this application; Figure 2 This is a schematic diagram of another power converter provided in an embodiment of this application; Figure 3 This is a schematic diagram showing the change of the DC component of the output voltage of a power converter provided in an embodiment of this application; Figure 4 This is a flowchart of a control method for a power converter provided in an embodiment of this application; Figure 5 This is a flowchart of a bias current suppression algorithm provided in an embodiment of this application. Detailed Implementation

[0026] The power converter and its control method provided in the embodiments of this application are described in detail below with reference to the accompanying drawings. First, the key terms involved in the embodiments of this application are introduced.

[0027] Grid connection refers to the connection of a new energy power generation system (such as a photovoltaic power generation system, energy storage system, or photovoltaic-storage system) with an external power grid, through transmission lines to exchange electrical energy and interact with the external power grid, and to operate in coordination to meet electricity demand.

[0028] Off-grid: refers to the state in which a renewable energy power generation system operates independently without relying on the power grid. In the off-grid state, the power converter (such as an inverter) in the renewable energy power generation system can convert the direct current provided by photovoltaic modules or energy storage batteries into alternating current to supply power to the load.

[0029] Magnetizing bias current: The DC current component superimposed on the AC operating current of an inductive load (such as a transformer or inductor). Excessive magnetizing bias current can damage the inductive load.

[0030] Figure 1This is a schematic diagram of a power converter provided in an embodiment of this application. Figure 1 As shown, a power converter typically includes a bus capacitor C. bus1 and C bus2 DC / AC converter circuit, inverter inductor L a L b and L c Filter capacitor C a C b and C c The circuit includes relays and electromagnetic interference (EMI) filtering circuits. The DC / AC converter circuit's DC terminal is used to connect to a DC power source (such as photovoltaic modules or energy storage batteries) via a DC bus. This DC bus includes a positive bus and a negative bus, with a bus capacitor C. bus1 and C bus2 It is connected in series between the positive and negative buses of the DC bus. The AC terminal of the DC / AC converter circuit is connected to one end of the inverter inductor. The DC / AC converter circuit is used to convert the DC power from the DC power supply into AC power for output. The other end of the inverter inductor is connected to the power grid or load through a relay and an EMI filter circuit. For example, the AC terminal of the DC / AC converter circuit is a three-phase AC terminal, which is connected to the inverter inductor L. a L b and L c One end is connected to the corresponding filter capacitor C. a C b and C c One end is connected to the inverter inductor L a L b and L c The other end is connected to the corresponding filter capacitor C. a C b and C c The other end is connected to the midpoint of the busbar, which is the busbar capacitance C. bus1 and C bus2 The nodes connected in series.

[0031] When a power converter operates in grid-connected mode, its AC terminal is connected to the power grid; when operating off-grid, its AC terminal is connected to the load. For example, refer to... Figure 1When operating off-grid, the AC terminal of the power converter is connected to the load via a transformer. When the power converter operates off-grid with an inductive load (such as a transformer), if the DC bias voltage of the AC output voltage is high, the volt-second accumulation effect will cause the inductive load to become magnetized, resulting in a large magnetizing current. This large magnetizing current can damage the inductive load, or cause the power converter to exhibit overcurrent derating or overcurrent protection behavior, affecting its load-carrying capacity. Therefore, when operating off-grid, the power converter needs to have the ability to control the DC bias voltage of the output voltage within a certain range, thereby suppressing the magnetizing current to a small range.

[0032] Typically, power converters suppress the bias current of inductive loads by actively controlling the DC bias voltage of the output voltage. For example, such as... Figure 1 As shown, the power converter uses a DCV sampling circuit ( Figure 1 (Not shown in the image) The DC bias voltage of the three-phase AC output voltage is sampled respectively, denoted as , 、 After obtaining the sampling information from the DCV sampling circuit, the power converter typically uses a closed-loop regulator to control the DC component of the output voltage, keeping it within a very small range. Therefore, when the load contains inductive loads (such as transformer-type loads), no significant bias current is generated, and the power converter device has good adaptability to inductive loads.

[0033] The aforementioned DCV sampling circuit is a hardware circuit and generally includes a differential amplifier, which can be either an isolated operational amplifier or a non-isolated operational amplifier. However, because this differential amplifier needs to extract a weak differential-mode signal (tens of millivolts) from a large common-mode signal (hundreds of volts), an isolated operational amplifier is generally used to ensure voltage sampling accuracy. This significantly increases the size, structural complexity, and hardware sampling cost of the power converter.

[0034] This application provides a power converter that can effectively suppress the bias current of inductive loads (such as transformer-type loads) without increasing structural complexity or hardware cost, thereby improving product competitiveness without sacrificing the power converter's load adaptability. Figure 2As shown in the figure, the power converter provided in this application embodiment includes a power conversion circuit 10 and a controller 20. The controller 20 may include a digital signal processor (DSP). The power conversion circuit 10 includes a DC terminal and an AC terminal. The DC terminal is used to connect to a DC power supply, and the AC terminal is used to connect to a load. The power conversion circuit 10 converts the DC power from the DC power supply into AC power and outputs it to the load. The power converter provided in this application embodiment can be a photovoltaic inverter, and correspondingly, the DC power supply can be a photovoltaic module. Alternatively, the power converter can be a power conversion system (PCS), and correspondingly, the DC power supply can be an energy storage battery.

[0035] In this embodiment, the controller 20 is used to control the DC component of the output voltage at the AC terminal of the power conversion circuit 10 to change sequentially along a first direction, a second direction, and a target direction. For example, when the power converter is running off-grid, the controller 20 controls the DC component of the output voltage to change sequentially along the first direction, the second direction, and the target direction.

[0036] The DC component of the output voltage is also called the DC bias voltage. The first direction described above refers to the direction that increases or decreases the DC component of the output voltage, while the second direction is opposite to the first direction. Furthermore, if the first peak value changes... Less than the change in the second peak If the target direction is the first direction; if the change in the first peak value is... Greater than or equal to the change in the second peak The target direction is either the second direction or the direction that keeps the DC component of the output voltage constant. The first peak change... This represents the change in the peak value of the output current after the DC component of the output voltage changes along the first direction. The second peak value change... This represents the change in the peak value of the output current after the DC component of the output voltage changes along the second direction.

[0037] As described above, the controller 20 can first control the DC component of the output voltage at the AC terminal of the power conversion circuit 10 to change in two opposite directions, and after each change in the DC component of the output voltage, detect the change in the peak value of the output current. Then, the controller 20 can determine the target direction based on the magnitude of the change in the peak value of the output current detected twice, and continue to adjust the DC component of the output voltage according to the target direction.

[0038] The changes in the peak value of the output current mentioned above are all equal to the difference between the peak value of the output current after the change and the peak value of the output current before the change; that is, the changes are relative changes with positive and negative signs. Therefore, if the change in the peak value of the output current is less than 0, it indicates that the peak value of the output current has decreased; if the change in the peak value of the output current is greater than 0, it indicates that the peak value of the output current has increased.

[0039] In this embodiment, the adjustment range of the controller 20 when adjusting the DC component of the output voltage is a fixed value, that is, the change range of the DC component of the output voltage is a fixed value each time it changes. Therefore, during the process of the controller 20 adjusting the DC component of the output voltage, if there are no external interference factors affecting the peak value of the output current in the system, for example, if the load driven by the power converter does not change, then the aforementioned first peak value change amount... Change in the second peak They are equal in magnitude but opposite in sign. If external disturbances affect the peak value of the output current, such as changes in the load driven by the power converter, the change in the peak value of the output current caused by these external disturbances can be expressed as... After removing the influence of external interference factors, the change in the peak value of the output current caused by the change of the DC component of the output voltage along the first direction can be expressed as: .

[0040] If the actual change caused by the above is less than 0, that is This indicates that changing the DC component of the output voltage along the first direction can reduce the peak value of the output current, thereby reducing the bias current of the inductive load. Therefore, the controller 20 can determine the target direction as the first direction, that is, control the DC component of the output voltage to change along the first direction again, so that the peak value of the output current continues to decrease, thereby effectively suppressing the bias current of the inductive load.

[0041] If the actual change caused by the above is greater than or equal to 0, that is... This indicates that a change in the DC component of the output voltage along the first direction will cause the peak value of the output current to increase or remain unchanged. Therefore, the controller 20 can determine that the target direction is the second direction or the direction that remains unchanged. That is, the controller 20 can continue to control the DC component of the output voltage to change along the second direction, or control the DC component of the output voltage to remain unchanged, thereby controlling the peak value of the output current at a low level and thus effectively suppressing the bias current of the inductive load.

[0042] In this embodiment, the controller 20 can cyclically control the DC component of the output voltage of the power conversion circuit 10 to change sequentially along the first direction, the second direction and the target direction, so that the peak value of the output current of the power conversion circuit 10 gradually converges and decreases, thereby suppressing the bias current of the inductive load to a low level.

[0043] In summary, the power converter provided in this application embodiment allows the controller to detect the peak value of the output current at the AC terminal of the power conversion circuit after controlling the change in the DC component of the output voltage of the power conversion circuit. Furthermore, the controller can determine the direction of change of the DC component of the output voltage of the power conversion circuit based on the change in the peak value of the output current, thereby suppressing the peak value of the output current of the power conversion circuit to a low level and effectively suppressing the bias current of the load driven by the power converter. Since this power converter can effectively suppress the bias current without setting up a DCV sampling circuit, it ensures a small size and low structural complexity and hardware cost. Moreover, when determining the direction of change of the DC component of the output voltage of the power conversion circuit based on the change in the peak value of the output current, the controller can also remove the influence of external interference factors on the peak value of the output current. Therefore, accurate adjustment of the DC component of the output voltage can be achieved, thereby reliably suppressing the bias current.

[0044] In one possible implementation, such as Figure 2 As shown, the power conversion circuit 10 in the power converter includes a DC / AC conversion circuit 11 and an inverter inductor. The DC / AC conversion circuit 11 includes at least one phase inverter arm. This inverter arm is connected between the positive and negative terminals of the DC power of the power conversion circuit 10, i.e., between the positive and negative busbars. Furthermore, the midpoint of this inverter arm is connected to one end of the inverter inductor, and the other end of the inverter inductor is the AC terminal of the power conversion circuit 10. The output current is the current flowing through the inverter inductor.

[0045] For example, refer to Figure 2 Taking a three-phase power converter as an example, the DC / AC conversion circuit 11 includes a three-phase inverter bridge arm, and the power conversion circuit 10 includes three inverter inductors L. a L b and L c The midpoint of the three-phase inverter bridge arm is connected to the three inverter inductors L. a L b and L c One end is connected to the corresponding three inverter inductors L a L b and L c The other end forms the three-phase AC terminal of the power conversion circuit 10.

[0046] During normal operation of the power converter, the controller 20 needs to detect and control the output current (such as the current flowing through the inverter inductor) at the AC terminal of the power conversion circuit 10. Therefore, the power converter also includes a current sampling circuit located at the AC terminal of the power conversion circuit 10. This current sampling circuit may include, for example, a Hall current sensor, or it may also include a digital current integrator. In the solution provided in this application embodiment, the controller 20 can reuse the existing current sampling circuit in the power converter to detect the output current at the AC terminal of the power conversion circuit 10 and adjust the DC component of the output voltage at the AC terminal of the power conversion circuit 10. Thus, there is no need to add an additional hardware sampling circuit to the power converter, thereby avoiding increasing the size, structural complexity, and hardware cost of the power converter.

[0047] In the embodiments of this application, for a three-phase power converter, such as Figure 2 As shown, the controller 20 can detect the output current of each phase AC terminal in the three-phase AC terminals of the power conversion circuit 10, that is, detect the current flowing through the inverter inductor L. a Output current I a Flowing through inverter inductor L b Output current I b and flowing through inverter inductor L c Output current I c Furthermore, the controller 20 can control the DC component change of the output voltage of the corresponding AC phase based on the change in the peak value of the output current of each AC phase. That is, for each AC phase of the power conversion circuit 10, the controller 20 can independently adjust the DC component of the output voltage of that AC phase using the scheme provided in the embodiments of this application, so that the peak value of the output current of that AC phase is smaller.

[0048] In this embodiment, the controller 20 adjusts the DC component of the output voltage once along a first direction or a second direction, which can also be referred to as perturbing the DC component of the output voltage once. Furthermore, the controller 20 can periodically adjust the DC component of the output voltage according to a fixed adjustment period, where each adjustment period is also called a beat. For example, the duration of each adjustment period can be 100 milliseconds (ms), 200 ms, or 500 ms. Correspondingly, the controller 20's adjustment of the DC component of the output voltage once can also be referred to as perturbing the DC component of the output voltage once. Furthermore, the adjustment magnitude of the controller 20 each time it adjusts the DC component of the output voltage can also be called the DC component adjustment step size Dcv_step or perturbation step size. For example, the adjustment step size Dcv_step can be from 0.1 volts (V) to 0.3V.

[0049] Figure 3This is a schematic diagram illustrating the change of the DC component of the output voltage of a power converter provided in an embodiment of this application. Figure 3 In the diagram, the horizontal axis represents time t, and the vertical axis represents the DC component Dcv of the output voltage at the AC terminal of the power conversion circuit 10. The explanation will take the first direction as the direction that increases the DC component of the output voltage, the second direction as the direction that decreases the DC component of the output voltage, and the first direction as the target direction. Figure 3 As shown, the controller 20 can increase the DC component of the output voltage by the adjustment step size Dcv_step at time t0, decrease the DC component of the output voltage by the adjustment step size Dcv_step at time t1, and then increase the DC component of the output voltage by the adjustment step size Dcv_step again at time t2. The interval between time t1 and time t0 is equal to the interval between time t2 and time t1, and both are equal to the aforementioned adjustment period.

[0050] In this embodiment, the controller 20 can first detect the peak value of the current output current each time it adjusts the DC component of the output voltage, and then adjust the DC component of the output voltage after detecting the peak value of the output current. That is, the controller 20 can periodically detect the peak value of the output current according to the above adjustment cycle, and the controller 20 can subtract the peak value of the output current detected each time from the peak value of the output current detected in the previous time to obtain the change in the peak value of the output current.

[0051] Continue with Figure 3 For example, controller 20 can detect the peak value of the output current at time t0. Then, the DC component of the output voltage is increased by the adjustment step size Dcv_step. Furthermore, the controller 20 can detect the peak value of the output current at time t1. Then, the DC component of the output voltage is reduced by the adjustment step size Dcv_step. Similarly, the controller 20 can detect the peak value of the output current at time t2. And based on the change of the first peak Less than the change in the second peak At time t2, the DC component of the output voltage is increased by the adjustment step size Dcv_step. The change in the first peak value... satisfy: The change in the second peak satisfy: .

[0052] In one possible implementation, the controller 20 pre-stores a reference value Dcv_ref for the DC component of the output voltage at the AC terminal of the power conversion circuit 10. This reference value Dcv_ref is also called the command value, and its initial value can be 0. During the operation of the power converter, the controller 20 can control the DC component of the output voltage at the AC terminal of the power conversion circuit 10 to maintain it at the reference value Dcv_ref. Accordingly, the controller 20 can adjust the DC component of the output voltage at the AC terminal of the power conversion circuit 10 by adjusting the reference value Dcv_ref.

[0053] In one possible implementation, the peak value of the output current refers to the sum of the absolute value of the negative half-cycle peak value and the positive half-cycle peak value of the output current. For example, the controller 20 can detect the positive half-cycle peak value of the output current (also called the positive half-wave load current peak value) and record this peak value as the first observed current. Furthermore, the controller 20 can detect the absolute value of the negative half-cycle peak value of the output current (also called the negative half-wave load current peak value) and record this absolute value as the second observed current. The sum of the first and second observed currents is recorded as the third observed current. In this embodiment, the peak value Ipeak of the output current can refer to this third observed current.

[0054] Under different operating conditions, the change in the DC component of the output voltage at the AC terminal of the power conversion circuit 10 may have different effects on the positive and negative half-cycle peak values ​​of the output current. For example, under certain operating conditions, after the DC component of the output voltage changes, the change in the positive half-cycle peak value of the output current may differ from the change in the negative half-cycle peak value, or only the positive or negative half-cycle peak value of the output current may change, while the other half-cycle peak value remains unchanged. Therefore, by using the aforementioned third observed current as the peak value Ipeak of the output current in this embodiment, it is possible to ensure that the change in the peak value Ipeak of the output current accurately reflects the impact of the change in the DC component of the output voltage on the output current, thereby reducing the probability of false disturbances to the DC component of the output voltage.

[0055] In this embodiment, the controller 20 can also detect the DC component Idc of the output current, and after each change in the DC component of the control output voltage, detect the change in the DC component Idc of the output current. When the load connected to the power converter has no inductive load, for example, when the load connected to the power converter is a half-wave load, or when the power factor (PF) of the power converter is 1 and it is connected to a full-wave purely resistive (R) load, the change in the DC component of the output current caused by the change in the DC component of the output voltage (i.e., a single disturbance of the DC component of the output voltage) is the magnitude of the change in the DC component of the output current. The change will be very small. At this point, to avoid algorithm malfunctions, the controller 20 will no longer disturb the DC component of the output voltage. When the load connected to the power converter includes an inductive load, the change in the DC component of the output voltage will cause a change in the DC component of the output current. If the voltage is relatively large, the controller 20 can continue to disturb the DC component of the output voltage.

[0056] In a first possible implementation, the controller 20 is configured to: after controlling the DC component of the output voltage to change sequentially along a first direction and a second direction, if the sum of the absolute values ​​of the first and second DC changes is greater than a first threshold, then continue to control the DC component of the output voltage to change along a target direction. If the sum of the absolute values ​​of the first and second DC changes is not greater than the first threshold, then the controller 20 can maintain the DC component of the output voltage unchanged. Here, the first DC change is the change in the DC component of the output current after the DC component of the output voltage changes along the first direction, and the second DC change is the change in the DC component of the output current after the DC component of the output voltage changes along the second direction.

[0057] As mentioned earlier, when the power converter operates off-grid and is connected to an inductive load, changes in the DC component of the output voltage will cause significant changes in the DC component of the output current. Therefore, when the controller 20 detects that the sum of the absolute values ​​of the first and second DC changes is greater than a first threshold, it can determine that the load connected to the power converter includes an inductive load. In this case, to effectively suppress the bias current of the inductive load, the controller 20 can continue to control the DC component of the output voltage to change along the target direction. Conversely, if the controller 20 detects that the sum of the absolute values ​​of the first and second DC changes is not greater than the first threshold, it can determine that the load connected to the power converter does not include an inductive load, and therefore there is no need to further disturb the DC component of the output voltage.

[0058] In a second possible implementation, the controller 20 is configured to: after controlling the DC component of the output voltage to change sequentially along a first direction and a second direction, if the absolute value of the first DC change is greater than a second threshold or the absolute value of the second DC change is greater than the second threshold, then continue to control the DC component of the output voltage to change along a target direction. If the absolute value of the first DC change is not greater than the second threshold, and the absolute value of the second DC change is not greater than the second threshold, then the controller 20 can maintain the DC component of the output voltage unchanged. Here, the first DC change is the change in the DC component of the output current after the DC component of the output voltage changes along the first direction, and the second DC change is the change in the DC component of the output current after the DC component of the output voltage changes along the second direction.

[0059] As mentioned earlier, when the power converter operates off-grid and is connected to an inductive load, a single change (i.e., a single disturbance) in the DC component of the output voltage will cause a significant change in the DC component of the output current. Therefore, the controller 20 can also determine that the load connected to the power converter includes an inductive load when it detects that the absolute value of the first DC change or the absolute value of the second DC change is greater than a second threshold. In this case, in order to effectively suppress the bias current of the inductive load, the controller 20 can continue to control the DC component of the output voltage to change along the target direction. Conversely, if the controller 20 detects that the absolute values ​​of both the first and second DC changes are not greater than the second threshold, it can determine that the load connected to the power converter does not include an inductive load, and therefore there is no need to further disturb the DC component of the output voltage.

[0060] In this embodiment, the first threshold is greater than the second threshold; for example, the first threshold can be twice the second threshold. Furthermore, the first and second thresholds can be determined based on the adjustment step size Dcv_step. For example, both the first and second thresholds are proportional to the adjustment step size Dcv_step. Since the DC impedance of the inductive load is close to 0 and much less than 1 ohm (Ω) when the load driven by the power converter includes an inductive load, the first and second thresholds can be greater than Dcv_step / 1Ω. For example, assuming the adjustment step size Dcv_step of the DC component of the output voltage is 0.3V, the first and second thresholds can be greater than 0.3A.

[0061] In this embodiment, when adjusting the DC component of the output voltage, the controller 20 can first detect the DC component of the current output current, and then adjust the DC component of the output voltage after detecting the DC component of the output current. That is, the controller 20 can periodically detect the DC component of the output current according to the above adjustment cycle, and the controller 20 can subtract the DC component of the output current detected each time from the DC component of the output current detected in the previous time to obtain the change in the DC component of the output current.

[0062] Continue with Figure 3 For example, controller 20 can detect the peak value of the output current at time t0. and the DC component of the output current Then, the DC component of the output voltage is increased by the adjustment step size Dcv_step. Furthermore, the controller 20 can detect the peak value of the output current at time t1. and the DC component of the output current Then, the DC component of the output voltage is reduced by the adjustment step size Dcv_step. Similarly, the controller 20 can detect the peak value of the output current at time t2. and the DC component of the output current Furthermore, the controller 20 is able to base its response on the change in the first peak value. Less than the change in the second peak And the first DC change The absolute value and the second DC change If the sum of the absolute values ​​of the values ​​exceeds the first threshold, at time t2, the DC component of the output voltage is increased by the adjustment step size Dcv_step. Here, the first DC change... satisfy: Second DC change satisfy: .

[0063] In one possible implementation, the controller 20 is further configured to: after the DC component of the control output voltage changes along the target direction, if the third peak value changes... Greater than the change in the second peak If the DC component of the control output voltage changes along the second direction, then the change in the third peak value... Less than or equal to the change in the second peak Then the DC component of the control output voltage changes along the first direction. Among them, the change in the third peak value... This represents the change in the peak value of the output current after the DC component of the output voltage changes along the target direction.

[0064] In this embodiment, the controller 20 can also determine the next disturbance direction after the target direction based on the magnitude of the change in the peak value of the output current, so as to achieve continuous and accurate disturbance of the DC component of the output voltage, thereby ensuring that the peak value of the output current can gradually converge and decrease.

[0065] In this embodiment, if the target direction is the first direction, then after removing the influence of external interference factors, the change in the peak value of the output current caused by the change of the DC component of the output voltage along the second direction can be expressed as: If the target direction is to keep the DC component of the output voltage constant, then the change in the third peak value... This refers to the change in the peak value of the output current introduced by external interference factors. Correspondingly, after removing the influence of external interference factors, the change in the peak value of the output current actually caused by the change in the DC component of the output voltage along the second direction can be expressed as: .

[0066] If the actual change caused by the above is less than 0, that is This indicates that the change of the DC component of the output voltage along the second direction reduces the peak value of the output current, thereby reducing the bias current of the inductive load. Therefore, the controller 20 can again control the change of the DC component of the output voltage along the second direction to reduce the peak value of the output current, thereby suppressing the bias current of the inductive load. If the actual change is greater than or equal to 0, i.e. This indicates that a change in the DC component of the output voltage along the second direction will cause the peak value of the output current to increase or remain unchanged. Therefore, the controller 20 can adjust the DC component of the output voltage in the opposite direction, i.e., in the first direction, to reduce the peak value of the output current and thus suppress the bias current of the inductive load.

[0067] In one possible implementation, if the target direction is the second direction, the controller 20 is further configured to: after the DC component of the control output voltage changes along the target direction, if the third peak value changes... If the value is less than 0, the DC component of the control output voltage continues to change along the second direction; if the change in the third peak value is less than 0... If the value is greater than 0, the DC component of the control output voltage changes along the first direction. That is, after the controller 20 controls the DC component of the output voltage to change along the second direction, if the peak value of the output current decreases, the controller 20 continues to adjust the DC component of the output voltage in the same direction; if the peak value of the output current increases, the controller 20 adjusts the DC component of the output voltage in the opposite direction. Furthermore, if the change in the third peak value... If the value is 0, then the controller 20 can control the DC component of the output voltage to change along either the first direction or the second direction.

[0068] In this embodiment, after controlling the DC component of the output voltage to change along the target direction, the controller 20 can continue to cyclically control the DC component of the output voltage to change sequentially along three directions (such as the first direction, the second direction, and the target direction). Furthermore, in the next cycle, the initial direction of change of the DC component of the output voltage can be based on the aforementioned third peak value change. Second peak change The magnitude is determined, or based on the change in the third peak. Whether it is greater than 0 is determined. Specifically, if the change in the third peak value... Greater than the change in the second peak Or the change in the third peak If the value is less than 0, then in the next cycle, the first change direction of the DC component of the output voltage will be the second direction. Accordingly, in this next cycle, the controller 20 can control the DC component of the output voltage to change sequentially along the second and first directions, and then determine the target direction for the next cycle based on the magnitude of the change in the peak value of the output current caused by the two changes. If the third peak value change... Not greater than the change in the second peak value Or the change in the third peak If the value is greater than 0, then in the next cycle, the initial direction of change of the DC component of the output voltage will still be the first direction. Accordingly, in the next cycle, the controller 20 can continue to control the DC component of the output voltage to change sequentially along the first direction, the second direction, and the target direction.

[0069] For example, such as Figure 3 As shown, the controller 20 can detect the peak value of the current output current at time t3 in the next cycle. And calculate the change in the third peak. : Assuming the change in the third peak... Not greater than the change in the second peak value , then Figure 3 As shown, at time t3 of the next cycle, the controller 20 can again increase the adjustment step size Dcv_step of the DC component of the output voltage, meaning that the first change direction of the DC component of the output voltage in the next cycle is still in the direction of increase. Then, at time t4 of the next cycle, the controller 20 can decrease the adjustment step size Dcv_step of the DC component of the output voltage, and at time t5, increase the adjustment step size Dcv_step of the DC component of the output voltage.

[0070] In one possible implementation, the controller 20 is further configured to: after the DC component of the control output voltage changes along the target direction, if the third peak value changes... Greater than the change in the second peak If the absolute value of the second DC change is greater than the second threshold, then the DC component of the control output voltage changes along the second direction. The controller 20 is also configured to: if the third peak change... Less than or equal to the change in the second peak Alternatively, if the absolute value of the second DC change is less than or equal to the second threshold, the DC component of the control output voltage changes along the first direction.

[0071] In one possible implementation, such as Figure 2 As shown, the power converter also includes an EMI filter circuit 30 and a relay 40. Inverter inductor L a Lb and L c The other end is connected to one end of the relay 40 through the EMI filter circuit 30, and the other end of the relay 40 is used to connect to the power grid and / or the load.

[0072] In summary, this application provides a power converter including a power conversion circuit and a controller. The controller can detect the peak value of the output current at the AC terminal of the power conversion circuit after controlling the change in the DC component of the output voltage of the power conversion circuit. Furthermore, the controller can adjust the direction of change of the DC component of the output voltage of the power conversion circuit based on the change in the peak value of the output current, thereby suppressing the peak value of the output current of the power conversion circuit to a low level, and thus effectively suppressing the bias current of the load driven by the power converter. Since the power converter provided in this application does not require a DCV sampling circuit to effectively suppress the bias current, it ensures a small size and low structural complexity and hardware cost.

[0073] This application also provides a control method for a power converter. This control method can be applied to the power converter provided in the above embodiments and can be executed by the controller 20 in the power converter. Figure 4 As shown, the control method includes: Step 101: Control the DC component of the output voltage at the AC terminal of the power conversion circuit to change sequentially along the first direction, the second direction, and the target direction.

[0074] Wherein, the first direction is the direction that increases or decreases the DC component of the output voltage, and the second direction is opposite to the first direction; furthermore, if the change in the first peak value is less than the change in the second peak value, the target direction is the first direction; if the change in the first peak value is greater than or equal to the change in the second peak value, the target direction is the second direction or the direction that keeps the DC component of the output voltage unchanged. The change in the first peak value is the change in the peak value of the output current after the DC component of the output voltage changes along the first direction, and the change in the second peak value is the change in the peak value of the output current after the DC component of the output voltage changes along the second direction.

[0075] In a first possible implementation, in step 101 above, after the DC component of the output voltage is controlled to change sequentially along the first direction and the second direction, the process of controlling the DC component of the output voltage to change along the target direction may include: if the sum of the absolute value of the first DC change and the absolute value of the second DC change is greater than a first threshold, then the DC component of the output voltage is controlled to change along the target direction.

[0076] Wherein, the first DC change is the change in the DC component of the output current after the DC component of the output voltage changes along the first direction; the second DC change is the change in the DC component of the output current after the DC component of the output voltage changes along the second direction.

[0077] In a second possible implementation, in step 101 above, after controlling the DC component of the output voltage to change sequentially along the first direction and the second direction, the process of controlling the DC component of the output voltage to change along the target direction may include: if the absolute value of the first DC change is greater than the second threshold or the absolute value of the second DC change is greater than the second threshold, then continue to control the DC component of the output voltage to change along the target direction.

[0078] Wherein, the first DC change is the change in the DC component of the output current after the DC component of the output voltage changes along the first direction; the second DC change is the change in the DC component of the output current after the DC component of the output voltage changes along the second direction.

[0079] In one possible implementation, continue to refer to Figure 4 Following step 101 above, the control method further includes: Step 102: If the change in the third peak value is greater than the change in the second peak value, then control the DC component of the output voltage to change along the second direction.

[0080] Step 103: If the change in the third peak value is less than or equal to the change in the second peak value, then control the DC component of the output voltage to change along the first direction. The change in the third peak value is the change in the peak value of the output current after the DC component of the output voltage changes along the target direction.

[0081] In one possible implementation, the peak value of the output current is the sum of the absolute value of the negative half-cycle peak value and the positive half-cycle peak value of the output current.

[0082] In one possible implementation, the power conversion circuit includes an inverter bridge arm and an inverter inductor; the output current is the current flowing through the inverter inductor.

[0083] Figure 5 This is a flowchart of a bias current suppression algorithm provided in an embodiment of this application. Figure 5 As shown, the algorithm for suppressing the bias current can be a cyclic algorithm, with each cycle consisting of three steps: pre-disturbance, confirmation, and tracking. Specifically, if step=0, the pre-disturbance operation is performed; if step=1, the confirmation operation is performed; and if step=2, the tracking operation is performed. Figure 5In this algorithm, `Dcv_ref` is the reference value for the DC component of the output voltage, and its initial value is 0. `Dcv_step` is the adjustment step size for the DC component of the output voltage. `D` is the adjustment direction for the DC component of the output voltage, where `D=1` indicates that the adjustment direction is to increase the DC component of the output voltage, and `D=-1` indicates that the adjustment direction is to decrease the DC component of the output voltage. In the first loop of this suppression algorithm, the adjustment direction `D` in the pre-disturbance operation can be a default initial value, which can be 0 or 1; this embodiment does not limit this. After executing one loop, in the pre-disturbance operation of the next loop, as... Figure 5 As shown, the value of the adjustment direction D can be determined based on the magnitude of the peak change in output current Bck generated by the confirmation operation and the peak change in output current Trk generated by the tracking operation in the previous cycle.

[0084] like Figure 5 As shown, in the pre-disturbance operation of the first loop of the suppression algorithm, i.e., when step=0, the controller 20 can adjust the reference value Dcv_ref of the DC component of the output voltage according to the initial value of the adjustment direction D: Dcv_ref + = D Dcv_step. It can be understood that if D=1, it means increasing the reference value Dcv_ref by Dcv_step; if D=-1, it means decreasing the reference value Dcv_ref by Dcv_step. Afterwards, controller 20 performs the step++ operation, which increments the value of step by 1.

[0085] At this point, step=1, and controller 20 performs a confirmation operation. In this confirmation operation, controller 20 can first acquire the peak change Pre and the DC change generated by the pre-disturbance operation. PreIdc. The peak value change Pre satisfies: Pre = Ip - Ip_pre, where Ip is the current peak value of the output current, and Ip_pre is the peak value of the output current in the previous cycle, i.e., the peak value of the output current before the DC component adjustment of the output voltage. DC change amount. PreIdc satisfies: PreIdc = Idc - Idc_pre, where Idc is the DC component of the current output current, and Idc_pre is the DC component of the output current in the previous cycle, i.e., the DC component of the output current before the DC component of the output voltage was adjusted. This is achieved by obtaining the peak change Pre and the DC change generated by the pre-disturbance operation. After PreIdc, controller 20 can set Ip_pre=Ip and Idc_pre=Idc to continue acquiring the peak change Bck and DC change generated by the confirmation operation in the next tracking operation. BckIdc. (Continue to refer to...) Figure 5 After completing the parameter acquisition and configuration, controller 20 can readjust the reference value Dcv_ref of the DC component of the output voltage: Dcv_ref - = D Dcv_step. That is, the controller 20 can change the reference value Dcv_ref of the DC component of the output voltage by Dcv_step in the opposite direction to that in the pre-disturbance operation (i.e., the direction of -D). Afterwards, the controller 20 performs the step++ operation again, that is, increments the value of step by 1.

[0086] At this point, step=2, and controller 20 performs a tracking operation. In this tracking operation, controller 20 can first acquire the peak change Bck and DC change generated by the confirmation operation. BckIdc. Wherein, the peak change Bck satisfies: Bck = Ip - Ip_pre, DC change. BckIdc satisfies: BckIdc = Idc - Idc_pre. Afterwards, controller 20 can set Ip_pre = Ip and Idc_pre = Idc to continue acquiring the peak change Trk generated by the tracking operation in the next cycle of pre-disturbance operation. After completing the above parameter acquisition and configuration, controller 20 can first determine whether the DC change is greater than a preset threshold. For example, controller 20 can determine the DC change... The absolute value of PreIdc and the DC change Does the sum of the absolute values ​​of BckIdc exceed the first threshold Ith? Figure 5 In this context, Abs represents the absolute value. If the sum of the absolute values ​​of the two DC changes is not greater than the first threshold Ith, the controller 20 can determine that the power converter is not connected to an inductive load, and therefore can keep the reference value Dcv_ref of the DC component of the output voltage unchanged. If the sum of the absolute values ​​of the two DC changes is greater than the first threshold Ith, the controller 20 can determine that the power converter is connected to an inductive load, and therefore can continue to judge the magnitudes of the peak changes Pre and Bck to determine the direction of adjustment of the DC component of the output voltage during tracking operation.

[0087] It is understandable that the mean values ​​of the peak change Pre and Bck are... This reflects the change in the peak output current introduced by external disturbances, such as the change in the load itself during a single disturbance. After removing the influence of this external disturbance, the actual change in the peak output current caused by the pre-disturbance operation can be expressed as: If the actual change is less than 0, that is... Then the controller 20 can determine that the pre-disturbance operation can reduce the peak value of the output current, therefore, if Figure 5 As shown, the controller 20 can again adjust the reference value Dcv_ref of the DC component of the output voltage according to the adjustment direction in the pre-disturbance operation: Dcv_ref + = D Dcv_step. If the actual change caused by the above is not less than 0, that is... If the pre-disturbance operation fails to reduce the peak value of the output current, then the controller 20 can determine that the pre-disturbance operation has failed to reduce the peak value of the output current. Figure 5 As shown, controller 20 can maintain the reference value Dcv_ref of the DC component of the output voltage unchanged. Alternatively, controller 20 can also adjust the reference value Dcv_ref of the DC component of the output voltage according to the adjustment direction in the confirmation operation: Dcv_ref - = D Dcv_step. After that, as... Figure 5 As shown, controller 20 resets the value of step to 0. Controller 20 can then enter the next loop and execute the pre-disturbance operation in the next loop.

[0088] Continue to refer to Figure 5 In the next cycle of pre-disturbance operation, controller 20 can first acquire the peak change Trk generated by the tracking operation in the previous cycle, which satisfies: Pre = Ip - Ip_pre. Then, controller 20 can set Ip_pre = Ip and Idc_pre = Idc to continue acquiring the peak change Pre and DC change generated by the pre-disturbance operation in the next confirmation operation. PreIdc. Since the tracking operation in the previous cycle may not have adjusted the DC component of the output voltage, the controller 20 does not need to acquire the change in the DC component of the output current in the pre-disturbance operation of the next cycle. Of course, the controller 20 can also acquire the change in the DC component generated by the tracking operation in the previous cycle, but this embodiment does not limit this. Then, as... Figure 5 As shown, controller 20 can compare the magnitudes of peak change Trk and Bck, and detect DC change. Is the absolute value of BckIdc greater than the second threshold? Ith.

[0089] Understandably, in the previous tracking operation, if the controller 20 again adjusts the DC component of the output voltage according to the adjustment direction in the pre-disturbance operation, then... It can reflect the change in the peak value of the output current actually caused by the confirmation operation in the previous cycle. In the previous tracking operation, if the controller 20 keeps the DC component of the output voltage constant, the peak value change Trk can reflect the change in the peak value of the output current introduced by external interference factors. It can reflect the change in the peak value of the output current actually caused by the confirmed operation in the previous cycle.

[0090] If the actual change caused by the above is less than 0, that is, if And DC change The absolute value of BckIdc is greater than the second threshold. If Ith indicates that the power converter is connected to an inductive load, and the confirmation operation in the previous cycle reduced the peak output current. Based on this, in the pre-disturbance operation of the next cycle, the controller 20 can use the adjustment direction of the confirmation operation in the previous cycle as the pre-disturbance direction. That is, as... Figure 5 As shown, the controller 20 can be set to adjust the direction. This means setting the adjustment direction D to be opposite to the adjustment direction of the pre-disturbance operation in the previous cycle, and adjusting the reference value Dcv_ref of the DC component of the output voltage according to the new adjustment direction. Afterwards, the controller 20 executes the step++ operation, which increments the value of step by 1, and performs the confirmation operation in the next cycle.

[0091] If the actual change caused by the above is not less than 0, that is, if or DC change The absolute value of BckIdc is not greater than the second threshold. If Ith, it indicates that the confirmation operation in the previous cycle failed to reduce the peak value of the output current. Based on this, in the pre-disturbance operation of the next cycle, the controller 20 can use the adjustment direction of the pre-disturbance operation in the previous cycle as the pre-disturbance direction. That is, as... Figure 5 As shown, controller 20 can continue to adjust the reference value Dcv_ref of the DC component of the output voltage according to the adjustment direction of the pre-disturbance operation in the previous cycle. Then, controller 20 executes the step++ operation, which increments the value of step by 1, and performs the confirmation operation in the next cycle.

[0092] Understandable Figure 5 In the flowchart of the suppression algorithm shown, the peak change Pre is the first peak change mentioned above, the peak change Bck is the second peak change mentioned above, and the peak change Trk is the third peak change mentioned above. The DC change PreIdc is the first DC change mentioned above, and the DC change BckIdc is the second DC change mentioned above.

[0093] refer to Figure 5 It can be seen that the controller 20 can repeatedly execute the above-mentioned pre-disturbance, confirmation, and tracking operations to gradually reduce the peak value of the output current, thereby effectively suppressing the bias current of the inductive load. Furthermore, during the cyclic execution of the above suppression algorithm, the DC component of the output voltage and the DC component of the output current at the AC terminal of the power conversion circuit 10 both exhibit a decaying convergence trend of N steps. Here, N can be an integer greater than or equal to 2. Assuming N=2, the DC component of both the output voltage and the output current will show a trend of changing twice in one direction and then changing once in the opposite direction. For example, the DC component of both the output voltage and the DC component of the output current will decrease twice and then increase once. Or, as... Figure 3 As shown at times t2, t3, and t4, the DC components of both the output voltage and the output current increase twice and then decrease once. Alternatively, the DC components of both the output voltage and the output current cycle according to the pattern of first direction, second direction, remain unchanged, second direction, first direction, remain unchanged, first direction, second direction, remain unchanged...

[0094] The control method provided in the above embodiments has essentially the same implementation method and technical effect as the power converter described in the foregoing embodiments. Therefore, for the sake of brevity, the implementation method and technical effect of the control method of the power converter will not be described again here.

[0095] In the embodiments of this application, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance. The term "at least one" refers to one or more, and "multiple" refers to two or more.

[0096] In the embodiments of this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0097] The above description is merely an optional implementation of this application, but the scope of protection of this application is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in this application, and these modifications or substitutions should all be covered within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A power converter, characterized in that, The power converter includes: a power conversion circuit and a controller; The power conversion circuit includes a DC terminal and an AC terminal. The DC terminal is used to connect to a DC power supply, and the AC terminal is used to connect to a load. The power conversion circuit is used to convert the DC power from the DC power supply into AC power and then output it to the load. The controller is used to control the DC component of the output voltage of the AC terminal to change sequentially along the first direction, the second direction and the target direction; Wherein, the first direction is the direction that increases or decreases the DC component of the output voltage, and the second direction is opposite to the first direction; and, if the change in the first peak value is less than the change in the second peak value, then the target direction is the first direction; if the change in the first peak value is greater than or equal to the change in the second peak value, then the target direction is the second direction or the direction that keeps the DC component of the output voltage unchanged. The first peak value change is the change in the peak value of the output current after the DC component of the output voltage changes along the first direction, and the second peak value change is the change in the peak value of the output current after the DC component of the output voltage changes along the second direction.

2. The power converter according to claim 1, characterized in that, The controller is used for: After controlling the DC component of the output voltage to change sequentially along the first direction and the second direction, if the sum of the absolute value of the first DC change and the absolute value of the second DC change is greater than the first threshold, then the DC component of the output voltage is controlled to change along the target direction. Wherein, the first DC change is the change in the DC component of the output current after the DC component of the output voltage changes along the first direction, and the second DC change is the change in the DC component of the output current after the DC component of the output voltage changes along the second direction.

3. The power converter according to claim 1, characterized in that, The controller is used for: After controlling the DC component of the output voltage to change sequentially along the first direction and the second direction, if the absolute value of the first DC change is greater than the second threshold or the absolute value of the second DC change is greater than the second threshold, then the DC component of the output voltage is controlled to change along the target direction. Wherein, the first DC change is the change in the DC component of the output current after the DC component of the output voltage changes along the first direction, and the second DC change is the change in the DC component of the output current after the DC component of the output voltage changes along the second direction.

4. The power converter according to any one of claims 1 to 3, characterized in that, The controller is also used for: After controlling the DC component of the output voltage to change along the target direction, if the change in the third peak value is greater than the change in the second peak value, then the DC component of the output voltage is controlled to change along the second direction. If the change in the third peak value is less than or equal to the change in the second peak value, then the DC component of the output voltage is controlled to change along the first direction; The third peak change is the change in the peak value of the output current after the DC component of the output voltage changes along the target direction.

5. The power converter according to any one of claims 1 to 4, characterized in that, The peak value of the output current is the sum of the absolute value of the negative half-cycle peak value and the positive half-cycle peak value of the output current.

6. The power converter according to any one of claims 1 to 5, characterized in that, The power conversion circuit includes: an inverter bridge arm and an inverter inductor; the inverter bridge arm is connected between the positive and negative terminals of the DC terminal, the midpoint of the inverter bridge arm is connected to one end of the inverter inductor, and the other end of the inverter inductor is the AC terminal; The output current is the current flowing through the inverter inductor.

7. A control method for a power converter, characterized in that, The power converter includes a power conversion circuit, and the control method includes: The DC component of the output voltage at the AC terminal of the power conversion circuit is controlled to change sequentially along the first direction, the second direction, and the target direction; Wherein, the first direction is the direction that increases or decreases the DC component of the output voltage, and the second direction is opposite to the first direction; and, if the change in the first peak value is less than the change in the second peak value, then the target direction is the first direction; if the change in the first peak value is greater than or equal to the change in the second peak value, then the target direction is the second direction or the direction that keeps the DC component of the output voltage unchanged. The first peak value change is the change in the peak value of the output current after the DC component of the output voltage changes along the first direction, and the second peak value change is the change in the peak value of the output current after the DC component of the output voltage changes along the second direction.

8. The control method according to claim 7, characterized in that, After controlling the DC component of the output voltage to change sequentially along the first direction and the second direction, controlling the DC component of the output voltage to change along the target direction includes: If the sum of the absolute values ​​of the first DC change and the second DC change is greater than the first threshold, then the DC component of the output voltage is controlled to change along the target direction. Wherein, the first DC change is the change in the DC component of the output current after the DC component of the output voltage changes along the first direction, and the second DC change is the change in the DC component of the output current after the DC component of the output voltage changes along the second direction.

9. The control method according to claim 7, characterized in that, After controlling the DC component of the output voltage to change sequentially along the first direction and the second direction, controlling the DC component of the output voltage to change along the target direction includes: If the absolute value of the first DC change is greater than the second threshold or the absolute value of the second DC change is greater than the second threshold, then the DC component of the output voltage is controlled to change along the target direction. Wherein, the first DC change is the change in the DC component of the output current after the DC component of the output voltage changes along the first direction, and the second DC change is the change in the DC component of the output current after the DC component of the output voltage changes along the second direction.

10. The control method according to any one of claims 7 to 9, characterized in that, After controlling the DC component of the output voltage to change along the target direction, the control method further includes: If the change in the third peak value is greater than the change in the second peak value, then the DC component of the output voltage is controlled to change along the second direction; If the change in the third peak value is less than or equal to the change in the second peak value, then the DC component of the output voltage is controlled to change along the first direction; The third peak change is the change in the peak value of the output current after the DC component of the output voltage changes along the target direction.

11. The control method according to any one of claims 7 to 10, characterized in that, The peak value of the output current is the sum of the absolute value of the negative half-cycle peak value and the positive half-cycle peak value of the output current.

12. The control method according to any one of claims 7 to 11, characterized in that, The power conversion circuit includes an inverter bridge arm and an inverter inductor; the output current is the current flowing through the inverter inductor.

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