A power conversion device and a control method for the power conversion device

Abstract

A power conversion device and a control method for the power conversion device are used to reduce the output voltage amplitude of the converter when a power grid fault is restored to ensure the safety of the device. The power conversion device includes: a controller and a converter, the controller is connected to the converter; the controller is used to detect the output voltage of the converter; the controller is used to reduce the active current output by the converter to a first current value and reduce the reactive current output by the converter to a second current value after the output voltage of the converter is less than a first threshold value, and when the output voltage of the converter rises to a value greater than a second threshold value, the second threshold value being greater than the first threshold value; the reactive current and active current output by the converter are adjusted according to a preset current adjustment rate until the active current is adjusted from the first current value to a target active current value, and the reactive current is adjusted from the second current value to a target reactive current value.

Description

Technical Field

[0001] The present application relates to the technical field of converters, and in particular to a power conversion device and a control method for the power conversion device. Background Art

[0002] Photovoltaic power generation is widely used as a clean renewable energy source. Photovoltaic power generation systems can convert light energy into electrical energy and output it to the grid. Generally, the inverter in the photovoltaic power generation system is connected to the grid-connected transformer, which converts the voltage output by the inverter into the grid voltage and outputs it to the grid.

[0003] When a fault occurs in the power grid, the grid voltage decreases. At this time, the converter needs to inject reactive current into the grid to support the grid voltage recovery. When the transmission impedance between the grid and the converter is large or the proportion of asynchronous energy contained in the grid is high, the converter output voltage presents weak grid characteristics. In this scenario, if a short circuit occurs in the grid, the converter will inject a certain amount of reactive current and active current into the grid. When the grid fault is restored, although the grid voltage has returned to normal, due to the detection delay, control delay and phase-locked dynamic process of the converter, the converter will still inject reactive current and active current into the grid for a period of time. This current will cause the voltage amplitude at both ends of the transmission impedance to increase, resulting in an increase in the output voltage of the converter. This large voltage may cause damage to some components and affect the normal operation of the equipment.

[0004] At present, a buffer circuit is often used between the converter and the power grid to weaken the converter output current, thereby reducing the converter output voltage amplitude. However, the buffer circuit method requires additional new devices under the current architecture, which increases system costs. Summary of the invention

[0005] The present application provides a power conversion device and a control method for the power conversion device, which can reduce the output voltage amplitude of the power conversion device when a power grid fault is restored to ensure the safety of the device.

[0006] In a first aspect, the present application provides a power conversion device, which can be connected to a new energy power generation system and a power grid respectively, and realize the grid connection of the new energy power generation system. Specifically, the power conversion device includes a controller and a converter, and the controller is connected to the converter.

[0007] Specifically, the controller is used to detect the output voltage of the converter. The controller is used to reduce the active current output by the converter to a first current value and reduce the reactive current output by the converter to a second current value after the output voltage of the converter is less than the first threshold value, and reduce the reactive current output by the converter to a second current value when the output voltage of the converter rises to a value greater than the second threshold value, wherein the second threshold value is greater than the first threshold value; and adjust the reactive current and active current output by the converter according to a preset current adjustment rate until the active current is adjusted from the first current value to the target active current value, and the reactive current is adjusted from the second current value to the target reactive current value. Wherein, the target reactive current value is within the reactive current value range output by the converter when the converter is operating normally, the target active current value is within the active current value range output by the converter when the converter is operating normally, and the first current value and the second current value are any values ​​within 50% of the reactive current value and the active current value range output by the converter when the converter is operating normally, respectively.

[0008] With the above power conversion device, when it is detected that the output voltage of the converter is less than the first threshold, it can be determined that the power grid connected to the power conversion device has a fault. In order to support the recovery of the power grid, the converter will output a large current. The output voltage of the converter continues to be detected. When it is detected that the output voltage of the converter rises to be greater than the second threshold, it is determined that the power grid fault has been recovered, and the reactive current and active current output by the converter are controlled to drop to the first current value and the second current value respectively, so as to avoid the large current output by the converter increasing the current amplitude flowing through the transmission impedance, thereby achieving the purpose of reducing the output voltage amplitude of the converter. Since the output current and output voltage amplitude of the converter are reduced, the safety of the converter and the devices connected to the converter is guaranteed.

[0009] In a possible implementation, the first current value and the second current value are greater than zero and less than or equal to 10% of the active current value and the reactive current value outputted by the converter when the converter is working normally.

[0010] By using the above power conversion device, the lower the amplitudes of the first current value and the second current value, the smaller the total output current of the converter, and the lower the current amplitude of the corresponding transmission impedance, thereby achieving the purpose of quickly reducing the output voltage of the converter.

[0011] In one possible implementation, the controller is specifically used to: adjust the reactive current or active current output by the converter according to different current adjustment rates until the active current value is adjusted from the first current value to the target active current value, and the reactive current is adjusted from the second current value to the target reactive current value.

[0012] By adopting the above power conversion device, the current adjustment rate of the active current or reactive current output by the converter can be controlled by utilizing the working requirements of the converter, thereby meeting the converter's requirements for output voltage and output current.

[0013] In one possible implementation, the controller is specifically used to: adjust the reactive current or active current output by the converter in multiple adjustment stages, wherein the current adjustment rate of each of the multiple adjustment stages is different, or the current adjustment rate of at least one of the multiple adjustment stages is different from the current adjustment rates of other adjustment stages, and the other adjustment stages are adjustment stages other than at least one of the multiple adjustment stages.

[0014] In a possible implementation, the controller is specifically used to: adjust the reactive current output by the converter according to the same current adjustment rate or The active current is adjusted from the first current value to the target active current value, and the reactive current is adjusted from the second current value to the target reactive current value.

[0015] In a possible implementation, when the output voltage of the converter is less than a first threshold, low voltage ride-through occurs in the converter.

[0016] When the power conversion device is used, when a fault occurs in the power grid to which the power conversion device is connected, the output voltage of the converter drops and low voltage ride-through occurs. Therefore, the low voltage ride-through value at which the converter experiences low voltage ride-through can be used as the first threshold.

[0017] In a possible implementation manner, the second threshold is less than or equal to a minimum voltage value output by the converter when the converter works normally.

[0018] By adopting the above-mentioned power conversion device, when the power grid recovers after a fault, the output voltage of the converter rises rapidly, and the output voltage of the converter is suppressed by reducing the output current of the converter. The output voltage of the converter can be less than the minimum voltage value output when the converter is working normally as the power grid fault recovery moment, so as to realize the control of the output current of the converter in advance and reduce the output voltage amplitude of the converter 402.

[0019] In a second aspect, the present application provides a control method for a power conversion device, which can be applied to a power conversion device, and the power conversion device includes a controller and a converter. Specifically, the control method mainly includes the following steps: detecting the output voltage of the converter; after the output voltage of the converter is less than a first threshold value, when the output voltage of the converter rises to be greater than a second threshold value, reducing the active current output by the converter to a first current value, and reducing the reactive current output by the converter to a second current value, the second threshold value is greater than the first threshold value; adjusting the reactive current and active current output by the converter according to a preset current adjustment rate until the active current is adjusted from the first current value to a target active current value, and the reactive current is adjusted from the second current value to a target reactive current value, the target reactive current value is within the reactive current value range output by the converter when the converter is working normally, the target active current value is within the active current value range output by the converter when the converter is working normally, and the first current value and the second current value are any values ​​within 50% of the reactive current value and the active current value range respectively less than the reactive current value and the active current value range output by the converter when the converter is working normally.

[0020] By adopting the above control method, when it is detected that the output voltage of the converter is less than the first threshold value, it can be determined that the power grid connected to the power conversion device has a fault, and in order to support the recovery of the power grid, the converter will output a large current. Continue to detect the output voltage of the converter, and when it is detected that the output voltage of the converter rises to be greater than the second threshold value, it is determined that the power grid fault has been recovered, and the reactive current and active current output by the converter are controlled to drop to the first current value and the second current value respectively, so as to avoid the large current output by the converter increasing the current amplitude flowing through the transmission impedance, thereby achieving the purpose of reducing the output voltage amplitude of the converter. Since the output current and output voltage amplitude of the converter are reduced, the safety of the converter and the devices connected to the converter is guaranteed.

[0021] In a possible implementation, the first current value and the second current value are greater than zero and less than or equal to 10% of the active current value and the reactive current value outputted by the converter when the converter is working normally.

[0022] By adopting the above method, the lower the amplitudes of the first current value and the second current value, the smaller the total output current of the converter, and the lower the current amplitude of the corresponding transmission impedance, thereby achieving the purpose of quickly reducing the output voltage of the converter.

[0023] In one possible implementation, the reactive current and active current output by the converter are adjusted according to a preset current adjustment rate until the active current is adjusted from a first current value to a target active current value, and the reactive current is adjusted from a second current value to a target reactive current value, including: adjusting the reactive current or active current output by the converter according to different current adjustment rates until the active current value is adjusted from a first current value to a target active current value, and the reactive current is adjusted from a second current value to a target reactive current value.

[0024] By adopting the above method, the current adjustment rate of the active current or reactive current output by the converter can be controlled by utilizing the working requirements of the converter, thereby meeting the converter's requirements for output voltage and output current.

[0025] In one possible implementation, the reactive current or active current output by the converter is adjusted according to different current adjustment rates, including: adjusting the reactive current or active current output by the converter in multiple adjustment stages, wherein the current adjustment rates of each adjustment stage in the multiple adjustment stages are different, or the current adjustment rate of at least one adjustment stage in the multiple adjustment stages is different from the current adjustment rates of other adjustment stages, and the other adjustment stages are adjustment stages other than at least one adjustment stage in the multiple adjustment stages.

[0026] In one possible implementation, the reactive current and active current output by the converter are adjusted according to a preset current adjustment rate until the active current is adjusted from a first current value to a target active current value, and the reactive current is adjusted from a second current value to a target reactive current value, including: adjusting the reactive current or active current output by the converter according to the same current adjustment rate until the active current value is adjusted from a first current value to a target active current value, and the reactive current is adjusted from a second current value to a target reactive current value.

[0027] In a possible implementation, when the output voltage of the converter is less than a first threshold, low voltage ride-through occurs in the converter.

[0028] By adopting the above method, when a fault occurs in the power grid to which the power conversion device is connected, the output voltage of the converter drops and low voltage ride-through occurs, so the low voltage ride-through value at which the converter experiences low voltage ride-through can be used as the first threshold.

[0029] In a possible implementation, the second threshold is less than a minimum voltage output by the converter when the converter works normally.

[0030] By adopting the above method, when the power grid recovers after a fault, the output voltage of the converter rises rapidly, and the output voltage of the converter is suppressed by reducing the output current of the converter. The output voltage of the converter can be less than the minimum voltage value output when the converter is working normally as the power grid fault recovery moment, so as to control the output current of the converter in advance and reduce the output voltage amplitude of the converter 402. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 A schematic diagram of a grid-connected renewable energy power generation system provided in an embodiment of the present application;

[0032] Figure 2 A schematic diagram of a waveform of an output voltage of a converter provided in an embodiment of the present application;

[0033] Figure 3 A schematic diagram of the structure of a buffer circuit provided in an embodiment of the present application;

[0034] Figure 4 A schematic diagram of a power conversion device provided in an embodiment of the present application Figure 1 ;

[0035] Figure 5 A schematic diagram of a power conversion device provided in an embodiment of the present application Figure 2 ;

[0036] Figure 6 A schematic diagram of a converter output voltage waveform provided in an embodiment of the present application;

[0037] Figure 7 A flow chart of a control method for a power conversion device provided in an embodiment of the present application. DETAILED DESCRIPTION

[0038] The embodiments of the present application will be described in detail below with reference to the accompanying drawings.

[0039] The specific operating method in the method embodiment can also be applied to the device embodiment or the system embodiment. It should be noted that in the description of this application, "multiple" only refers to "two or more". "And / or" describes the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / ", unless otherwise specified, generally indicates that the previous and subsequent associated objects are in an "or" relationship. In addition, it should be understood that in the description of this application, words such as "first" and "second" are only used to distinguish the purpose of description, and cannot be understood as indicating or implying relative importance, nor can they be understood as indicating or implying order.

[0040] It should be noted that in the embodiments of the present application, "connection" can be an electrical connection or a communication connection. The electrical connection between two electrical components can be a direct or indirect connection between the two electrical components. For example, A and B are connected, which can be either A and B directly connected, or A and B are indirectly connected through one or more other electrical components, such as A and B are connected, or A and C are directly connected, C and B are directly connected, and A and B are connected through C.

[0041] It should be noted that the switch in the embodiment of the present application may be one or more of various types of switch devices such as a relay, a metal oxide semiconductor field effect transistor (MOSFET), a bipolar junction transistor (BJT), an insulated gate bipolar transistor (IGBT), a gallium nitride field effect transistor (GaN), a silicon carbide (SiC) power tube, etc., and the embodiment of the present application will not list them one by one. Each switch device may include a first electrode, a second electrode and a control electrode, wherein the control electrode is used to control the conduction or disconnection of the switch device. When the switch device is turned on, current can be transmitted between the first electrode and the second electrode of the switch device, and when the switch device is turned off, current cannot be transmitted between the first electrode and the second electrode of the switch device. Taking MOSFET as an example, the control electrode of the switch device is the gate, the first electrode of the switch device may be the source of the switch device, the second electrode may be the drain of the switch device, or the first electrode may be the drain of the switch device, and the second electrode may be the source of the switch device.

[0042] With the development of new energy, the proportion of electricity generated by new energy power generation systems in the power grid is increasing. Among them, the electricity generated by new energy power generation systems can be transmitted to the power grid through grid-connected devices. Figure 1 The figure shows the schematic diagram of the grid connection of the new energy power generation system. Figure 1 , the new energy power generation system is connected to the converter, the grid-connected transformer and the power grid in sequence. Among them, the converter can convert the direct current generated by the new energy power generation system into alternating current, and output the alternating current to the grid-connected transformer. The grid-connected transformer can regulate the voltage of the alternating current output by the converter, and then output the regulated alternating current to the power grid through the transmission line. It should be noted that the grid-connected transformer can also realize the electrical isolation between the new energy power generation system and the power grid.

[0043] It should be understood that the new energy power generation system proposed in this application can be but is not limited to a photovoltaic power generation system, a wind power generation system or a hydroelectric power generation system.

[0044] There is a first impedance on the transmission line between the grid-connected transformer and the grid, there is a second impedance on the grid-connected transformer, and a third impedance which is the sum of the first impedance and the second impedance represents the transmission impedance between the converter and the grid.

[0045] For actual use, see Figure 2As shown, in the process of transmitting the electric energy generated by the new energy power generation system to the power grid, if the power grid fails at time t1, such as a short circuit fault, the converter will inject reactive current into the power grid to support the power grid voltage recovery. When the power grid fault is restored at time t2, the power grid voltage returns to normal value, but due to the detection delay, control delay and phase-locked dynamic process of the converter, the converter will still inject reactive current and active current into the power grid for a period of time. This current will be superimposed with the current generated by the inductive impedance and pass through the transmission impedance, resulting in an increase in the amplitude of the current flowing through the transmission impedance. At this time, the current will need to be delayed until time t3 to recover to a normal value. During this time period, the output voltage of the output converter is the sum of the power grid voltage and the voltage generated when the current flows through the transmission impedance, and the output end of the converter is in a high voltage state. Before the current flowing through the transmission impedance returns to normal current, the converter and the new energy power generation system connected to the converter may be damaged due to the high voltage.

[0046] It should be noted that when the power grid fails, the output voltage of the converter drops and the converter experiences low voltage ride-through. At this time, the output voltage of the converter is less than the low voltage ride-through threshold. In order to maintain the connection between the converter and the power grid, the converter needs to output a large current for current compensation. When the power grid fault is restored, due to the superposition of the converter output current and the inductive impedance follow-up, the output port of the converter rises significantly, and the output voltage of the converter is greater than or equal to the high voltage ride-through threshold. When the power grid is operating normally, the converter is in a normal state. At this time, the reactive current output by the converter is the target reactive current value, and the active current output by the converter is the target active current value.

[0047] In order to eliminate the problem of high current and high voltage output by the converter, a buffer circuit is currently often used at the output end of the converter, such as Figure 3 As shown in FIG. 1 , a possible schematic diagram of a buffer circuit is shown. Figure 3 The buffer circuit is composed of filter components such as filter capacitors and filter inductors. These filter components can filter out high-frequency signals on the transmission line to eliminate the peak values ​​of AC voltage and current, thereby suppressing the output voltage and output current amplitude of the converter. However, this method of suppressing current and voltage requires adding additional components to the grid-connected architecture of the new energy power generation system, which increases the grid-connected cost of the new energy power generation system.

[0048] In view of this, an embodiment of the present application provides a power conversion device and a control method for the power conversion device, which are used to reduce the output voltage amplitude of the converter when a power grid fault is restored to ensure the safety of the device.

[0049] See also Figure 4As shown, a power conversion device provided in an embodiment of the present application is provided. The power conversion device 400 is connected to a grid-connected inverter and a new energy power generation system, respectively, and is used to output the electric energy of the new energy power generation system to a grid connected to the grid-connected inverter, thereby realizing the grid connection of the new energy power generation system. Specifically, the power conversion device 400 includes a controller 401 and a converter 402.

[0050] The controller 401 is connected to the converter 402. The controller 401 is used to detect the output voltage of the converter 402; after the output voltage of the converter 402 is less than the first threshold value, when the output voltage of the converter 402 rises to be greater than the second threshold value, the controller 401 is used to reduce the active current output by the converter 402 to the first current value, and reduce the reactive current output by the converter 402 to the second current value; according to the preset current adjustment rate, the reactive current and the active current output by the converter 402 are adjusted until the active current is adjusted from the first current value to the target active current value, and the reactive current is adjusted from the second current value to the target reactive current value.

[0051] Among them, the target reactive current value is within the range of reactive current values ​​output by the converter 402 when it is working normally, the target active current value is within the range of active current values ​​output by the converter when it is working normally, the second threshold is greater than the first threshold, and the first current value and the second current value are any values ​​within 50% of the range of reactive current value and active current value output by the converter when it is working normally, respectively.

[0052] It should be noted that when a fault occurs in the power grid, the output voltage of the converter 402 decreases and low voltage crossing occurs. Therefore, the controller 401 can use the low voltage crossing value of the converter 402 as the first threshold, that is, when the controller 401 detects that the output voltage of the converter 402 is less than the first threshold, it can be determined that a fault occurs in the power grid and low voltage crossing occurs in the converter 402.

[0053] It should be noted that when the power grid fault is restored, the output voltage of the converter 402 will rise rapidly due to the inductive impedance flow and the large current output by the converter 402. In order to determine the power grid fault recovery moment as soon as possible and suppress the output voltage of the converter 402, the second threshold used to control the output current adjustment moment of the converter 402 can be set to be greater than the first threshold and less than or equal to the minimum voltage value output when the converter 402 is working normally. Since the second threshold is less than the minimum voltage value output when the converter 402 is working normally, the controller 401 can adjust the converter output current in the early stage of power grid fault recovery before the output voltage of the converter 402 rises significantly, so as to suppress the output voltage of the converter 402.

[0054] It should be understood that since the second threshold is less than the minimum voltage value output by the converter 402 when it is working normally, the controller 401 can control the output current of the converter 402 to decrease before the output voltage of the converter 402 rises significantly, and the output voltage amplitude of the converter 402 increases.

[0055] With the power conversion device 400 provided by the present application, when the output voltage of the converter 402 is less than the first threshold, the controller 401 can determine that the power grid has failed and the converter 402 has low voltage ride-through. When the output voltage of the converter 402 is detected to rise to a value greater than the second threshold, it can be determined that the power grid fault has been restored. In order to prevent the large current output by the converter 402 from increasing the amplitude of the current flowing through the transmission impedance, the active current output by the converter 402 can be reduced to a first current value, and the reactive current output by the converter 402 can be reduced to a second current value, thereby reducing the current amplitude flowing through the transmission impedance between the power grid and the converter 402. When the current amplitude flowing through the transmission impedance decreases, the voltage difference across the transmission impedance decreases, and the output voltage amplitude of the converter 402 decreases, thereby ensuring the safety of the power conversion device 400 and the devices connected to the power conversion device 400. Then gradually adjust the active current value and reactive current value output by the converter 402 until the active current and reactive current values ​​are restored to the target active current value and target reactive current value when the converter 402 is working normally. During the output current adjustment of the converter 402, the electric energy stored in the inductive impedance is gradually consumed, and the current amplitude on the transmission impedance gradually decreases. Therefore, when the output current of the converter 402 is restored to the target active current value and target reactive current value, the output voltage of the converter 402 can be restored to the output voltage when the converter 402 is working normally, and the converter 402 can work normally.

[0056] It should be understood that when the controller 401 reduces the active current output by the converter 402 to a first current value, and reduces the reactive current output by the converter 402 to a second threshold value, the current value of the total current output by the converter 402 is less than the current value transmitted on the power grid, which can accelerate the consumption rate of the electric energy stored in the inductive impedance, thereby accelerating the decrease rate of the voltage amplitude across the transmission impedance. The converter output voltage can quickly recover to the output voltage when the converter 402 is operating normally, thereby ensuring the safety of the converter 402 and the devices connected to the converter 402.

[0057] It should be understood that when it is determined that the power grid fault has been restored, the active current output by the converter 402 is reduced to a first current value, and the reactive current output by the converter 402 is reduced to a second current value. The smaller the amplitudes of the first current value and the second current value are, the smaller the amplitude of the total output current of the converter 402 is, the lower the amplitude of the current flowing through the transmission impedance is, and the lower the output voltage amplitude of the converter 402 is.

[0058] Optionally, in order to reduce the output voltage amplitude of the converter 402, the first current value and the second current value are greater than zero and greater than or equal to 10% of the active current value and the reactive current value output when the converter is working normally.

[0059] During specific use, in order to achieve the maximum suppression effect of the output voltage of the converter 402, the present application preferably uses values ​​close to zero as the first current value and the second current value.

[0060] In practical applications, the power conversion device 400 can be fixed on the renewable energy power generation system. In another implementation, the power conversion device 400 can also be set in a flexible and detachable form, that is, a fixed interface is provided on the power conversion device 400 to achieve the connection between the power conversion device 400 and the renewable energy power generation system, and the connection between the power conversion device 400 and the grid-connected transformer. In this case, the power conversion device 400 can be regarded as a device independent of the renewable energy power generation system.

[0061] In a possible implementation, the new energy power generation system can also supply power to the power conversion device 400 .

[0062] It should be understood that if the controller 401 and the converter 402 in the power conversion device 400 are powered directly by the new energy power generation system, the voltage output by the new energy power generation system may be difficult to meet the power supply voltage requirements of the controller 401 and the converter 402. Therefore, a voltage converter may be connected between the new energy power generation system and the power conversion device 400. The voltage converter regulates the voltage output by the new energy power generation system to output a power supply voltage that can be used by the controller 401 and the converter 402.

[0063] See also Figure 5 , Figure 5 The schematic diagram of the structure of the power conversion device 400 provided in the embodiment of the present application is shown. In the present application, the power conversion device 400 includes a controller 401 and a converter 402. The controller 401 may include a voltage sensor 4011 and a processor 4012.

[0064] The voltage sensor 4011 in the controller 401 is a device for detecting the output voltage of the converter 402. The voltage sensor 4011 is connected to the output end of the converter 402 and the processor 4012 respectively, and is used to detect the output voltage of the converter 402 and output the detected voltage to the processor 4012.

[0065] In one example, when the output end of the converter 402 outputs three-phase alternating current, the input end of the voltage sensor 4011 can be a three-phase AC end, which is respectively connected to the three phase lines of the output end of the converter 402 for outputting three-phase alternating current. The voltage sensor 4011 receives the amplitude of the three-phase alternating current output by the output end of the converter 402 through the three-phase AC end, thereby detecting the output voltage of the converter 402.

[0066] In another example, when the output end of the converter outputs three-phase alternating current, the input end of the voltage sensor 4011 can be three single-phase AC ends, each of which is respectively connected to a phase line of the converter 402. The inductance sensor 4011 receives the voltage on each phase line of the converter 402 through the three single-phase input ends, thereby obtaining the amplitude of the three-phase alternating current output by the output end of the converter 402, thereby detecting the output voltage of the converter 402.

[0067] In a possible implementation, when the voltage sensor 4011 detects the three-phase AC power output by the converter, the voltage value of one phase of the three-phase AC power can be used as the output voltage of the converter 402 , and the output voltage of the converter 402 can be output to the processor 4012 .

[0068] In one example, in order to reduce the detection cost of the voltage sensor 4011, the voltage sensor 4011 can directly detect the alternating current transmitted on one of the phase lines at the output end of the converter 402, and use the detected alternating current as the output voltage of the converter 402, and output it to the processor 4012. The other two phase lines at the output end of the converter 402 do not undergo voltage detection.

[0069] In another example, in order to ensure the detection accuracy of the converter 4011, when the voltage sensor 4011 detects the three-phase AC power output by the converter, the average value of the three-phase AC power can be used as the output voltage of the converter 402, and the output voltage of the converter 402 can be output to the processor 4012.

[0070] In actual use, the voltage sensor 4011 may adopt an existing structure, such as a Hall sensor, wherein the voltage detection end of the Hall sensor is connected to the output end of the converter 402 , and the signal output end of the Hall sensor is connected to the processor 4012 .

[0071] It should be noted that the amplitude of the three-phase alternating current outputted from the output end of the converter 402 is relatively high, and the higher the voltage amplitude detected by the inductance sensor 4011, the higher the cost of the voltage sensor 4011 and the processor 4012 for processing the voltage detected by the voltage sensor 4011. In order to reduce the cost of the controller 401, a step-down module may be connected between the voltage sensor 4011 and the output end of the converter 402. The first end of the step-down module is connected to the output end of the converter 402, and the second end of the step-down module is connected to the voltage sensor 4011. The step-down module may step down the output voltage of the converter 402, and output the reduced voltage to the voltage sensor 4011 for detection. Among them, the step-down module may adopt an existing step-down device, such as a resistor or a step-down circuit, which is not limited in this application.

[0072] It should be noted that since the step-down module performs a proportional step-down process on the output voltage of the converter 402, when the subsequent processor 4012 receives the output voltage of the converter 402 output by the voltage sensor 4011, it needs to proportionally restore the voltage output by the voltage sensor 4011 to obtain the output voltage value of the converter 402.

[0073] The processor 4012 is a device for controlling the output current of the converter 402. The first end of the processor 4012 is connected to the voltage sensor 4011, and the second end of the processor 4012 is connected to the converter 402. The processor 4012 determines that a fault occurs in the power grid after the output voltage of the converter 402 is less than the first threshold. When the output voltage of the converter 402 rises to be greater than the second threshold, it is determined that the power grid fault is restored. In order to prevent the large current output by the converter 402 from increasing the current amplitude flowing through the transmission impedance, the active current output by the converter 402 is reduced to a first current value, and the reactive current output by the converter 402 is reduced to a second current value, and the reactive current and the active current output by the converter are adjusted according to a preset current adjustment rate until the active current is adjusted from the first current value to a target active current value, and the reactive current is adjusted from the second current value to a target reactive current value.

[0074] It should be understood that, since the processor 4012 reduces the output current of the converter 402 when the grid fault is restored, the current amplitude flowing through the transmission impedance is reduced, thereby reducing the output voltage amplitude of the converter 402. In addition, when the active current output by the converter 402 is the first current value, and the reactive current output by the converter 402 is the second current value, the total current value output by the converter is less than the current value of the transmission impedance, which can speed up the decline of the grid current, and the time for the output voltage of the converter 402 to recover to the output voltage value when the converter 402 is working normally is less than 100%. Figure 2 The time interval between t2 and t3.

[0075] In actual use, the converter 402 may be composed of components such as a switch tube, a diode, an inductor, and a capacitor. The working state of the converter may be achieved by adjusting the working states of these components (such as the switch tube).

[0076] In the present application, the adjustment of the working state of the above-mentioned device can be achieved through the processor 4012.

[0077] In actual use, the processor 4012 can be connected to the control electrode of the switch in the connected converter 402, and by providing a driving signal to the switch in the converter 402, it can control the turn-on time and turn-on duration of the switch tube, thereby adjusting the working state of the converter 402 and adjusting the output current of the converter 402.

[0078] Specifically, if the switch in the converter 402 is a MOS, the processor 4012 can be connected to the gate of the MOS tube to adjust the output current of the converter 402 by controlling the on-off of the MOS tube; if the switch in the converter 402 is a BJT, the processor can be connected to the base of the BJT to adjust the output current of the converter 402 by controlling the on-off of the BJT.

[0079] In specific implementation, the processor 4012 can be any one of a microcontroller unit (MCU), a central processing unit (CPU), a field programmable gate array (FPGA), and a digital signal processor (DSP). Of course, the specific form of the processor 4012 is not limited to the above examples.

[0080] In actual use, the processor 4012 can use multiple methods to adjust the output current of the converter 402. The following is a detailed description of the method in which the processor 4012 adjusts the output current of the converter.

[0081] In one possible implementation, when the output voltage of the converter 402 rises to be greater than the second threshold, the processor 4012 in the controller 401 adjusts the reactive current or active current output by the converter according to different current adjustment rates until the active current value is adjusted from the first current value to the target active current value, and the reactive current is adjusted from the second current value to the target reactive current value.

[0082] In specific implementation, the reactive current or active current output by the converter is adjusted in multiple adjustment stages.

[0083] Optionally, the current adjustment rate of each adjustment stage in the multiple adjustment stages is different.

[0084] It should be understood that when the current adjustment rate of each adjustment stage in a plurality of adjustment stages is different, the current difference between two consecutive time points in each adjustment stage is different.

[0085] Optionally, a current adjustment rate of at least one adjustment stage among the multiple adjustment stages is different from current adjustment rates of other adjustment stages, wherein the other adjustment stages are adjustment stages other than the at least one adjustment stage among the multiple adjustment stages.

[0086] It should be understood that when the current adjustment rates corresponding to the multiple adjustment stages are set, the adjustment rates corresponding to the adjustment stages are different, and the output current adjustment time of the converter 402 is different, which is specifically set according to the working requirements of the converter 402. For example, the withstand voltage value of the converter 402 is small, and the output voltage of the converter 402 needs to be reduced to the output voltage when the converter 402 is working normally as soon as possible. The current adjustment rate of the initial adjustment stage of the multiple adjustment stages can be increased, so that the converter 402 can be quickly reduced. For another example, if multiple precision devices are connected to the converter 402, and the output voltage of the converter 402 cannot drop quickly, the current adjustment rate of the multiple adjustment stages can be reduced, and the output voltage of the converter 402 can be slowly reduced to the output voltage when the converter 402 is working normally.

[0087] In another possible implementation, when the output voltage of the converter 402 rises to be greater than the second threshold, the processor 4012 in the controller 401 adjusts the reactive current or active current output by the converter at the same current adjustment rate until the active current value is adjusted from the first current value to the target active current value, and the reactive current is adjusted from the second current value to the target reactive current value.

[0088] It should be understood that when the processor 4012 adjusts the reactive current or active current output by the converter according to the same current adjustment rate, the active current or reactive current output by the converter 402 can change evenly.

[0089] It should be noted that the processor 4012's various current adjustment rate schemes for adjusting the active current and reactive current output by the converter 402 can all reduce the output voltage amplitude of the converter 402 and speed up the speed at which the converter 402 output current returns to a normal value, but the current adjustment duration is different.

[0090] Combine the following Figure 6 , taking the example that the controller 401 adjusts the reactive current and the active current output by the converter according to the same current, the change process of the output voltage of the converter 402 is described.

[0091] See also Figure 6As shown, when the power grid fails at time T1, the output voltage of the converter 402 drops below the first threshold, and the converter 402 has a low voltage ride-through. In order to support the recovery of the power grid, the controller converter 402 will inject reactive current into the power grid, so the converter 402 increases the total output current after time T1. When the power grid fault is restored, due to the inductive impedance preventing current mutation and the converter 402 detection delay problem, the voltage amplitude across the transmission impedance rises, and the output voltage of the converter 402 gradually rises. When the output voltage of the converter is detected to rise to the second threshold at time T2, the active current output by the converter 402 is controlled to be reduced to the first current value, and the reactive current output by the converter 402 is controlled to be reduced to the second current value. At this time, the total current output by the converter 402 is reduced. When the converter 402 after adjusting the current outputs the output current to the power grid, the total current amplitude on the transmission impedance decreases, and the output voltage amplitude of the corresponding converter 402 decreases. Since the output current of the converter is less than the current value transmitted on the transmission impedance, the total output current of the converter will accelerate the decreasing speed of the current on the transmission impedance, and adjust the active current value and the reactive current value at the same current rate until the reactive current value is the target reactive current value and the active current is the target active current value. At this time, the output current of the converter 402 is restored to the current range output by the converter 402 when the converter 402 is working normally, and the output voltage of the converter 402 is restored to the voltage range output by the converter 402 when the converter 402 is working normally.

[0092] The converter 402 is a device for realizing the grid connection of the new energy power generation system. The input end of the converter 402 is connected to the new energy power generation system, and the output end of the converter 402 is connected to the grid through the grid-connected transformer. The converter 402 can convert the direct current output by the new energy power generation system into alternating current, and output the electric energy in the form of alternating current to the grid through the grid-connected transformer.

[0093] In the embodiment of the present application, the converter 402 used to realize the grid connection of the new energy power generation system can be an isolated voltage conversion device, or a non-isolated voltage conversion device. For example, an existing H-bridge drive circuit is used as the converter 402 to invert the direct current output by the new energy power generation system. In the specific implementation, the structure of the converter 402 is not specifically limited in this application.

[0094] Based on the same inventive concept, the embodiment of the present application also provides a control method for a power conversion device, which is applied to the power conversion device. The power conversion device may include a converter and a controller connected to the converter. The execution subject of the control method for the power conversion device provided in the embodiment of the present application may be the above controller. Figure 7 , the method specifically comprises the following steps:

[0095] Step 701: Detect the output voltage of the converter.

[0096] Step 702: after the output voltage of the converter is less than the first threshold, when the output voltage of the converter rises to be greater than the second threshold, reduce the active current output by the converter to the first current value, and reduce the reactive current output by the converter to the second current value, wherein the first threshold is less than the second threshold.

[0097] Specifically, when it is determined that the output voltage of the converter is greater than or equal to the set value, the drive signal of the switch tube in the converter is adjusted so that the reactive current output by the converter is a first threshold value and the active current output by the converter is a second threshold value.

[0098] Step 703, adjusting the reactive current and active current output by the converter according to the preset current adjustment rate until the active current is adjusted from the first current value to the target active current value, and the reactive current is adjusted from the second current value to the target reactive current value. The target reactive current value is within the reactive current value range output by the converter when the converter is operating normally, the target active current value is within the active current value range output by the converter when the converter is operating normally, and the first current value and the second current value are any values ​​within 50% of the reactive current value and the active current value range output by the converter when the converter is operating normally, respectively.

[0099] In a possible implementation, the first current value and the second current value are greater than zero and less than or equal to 10% of the active current value and the reactive current value outputted by the converter when the converter is working normally.

[0100] In one possible implementation, the reactive current and active current output by the converter are adjusted according to a preset current adjustment rate until the active current is adjusted from a first current value to a target active current value, and the reactive current is adjusted from a second current value to a target reactive current value, including: adjusting the reactive current or active current output by the converter according to different current adjustment rates until the active current value is adjusted from a first current value to a target active current value, and the reactive current is adjusted from a second current value to a target reactive current value.

[0101] In one possible implementation, the reactive current or active current output by the converter is adjusted according to different current adjustment rates, including: adjusting the reactive current or active current output by the converter in multiple adjustment stages, wherein the current adjustment rates of each adjustment stage in the multiple adjustment stages are different, or the current adjustment rate of at least one adjustment stage in the multiple adjustment stages is different from the current adjustment rates of other adjustment stages, and the other adjustment stages are adjustment stages other than at least one adjustment stage in the multiple adjustment stages.

[0102] In one possible implementation, the reactive current and active current output by the converter are adjusted according to a preset current adjustment rate until the active current is adjusted from a first current value to a target active current value, and the reactive current is adjusted from a second current value to a target reactive current value, including: adjusting the reactive current or active current output by the converter according to the same current adjustment rate until the active current value is adjusted from a first current value to a target active current value, and the reactive current is adjusted from a second current value to a target reactive current value.

[0103] In a possible implementation, when the output voltage of the converter is less than a first threshold, low voltage ride-through occurs in the converter.

[0104] In a possible implementation, the second threshold is less than a minimum voltage output by the converter when the converter works normally.

[0105] Specifically, the structure of the power conversion device and the process of the controller adjusting the output current of the converter can be seen in Figures 4 to 6 As shown, this application will not be repeated here.

[0106] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0107] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0108] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process in the computer or other programmable device. Figure 1 A process or multiple processes and / or boxes Figure 1The steps for the functions specified in one or more boxes.

[0109] Obviously, those skilled in the art can make various changes and modifications to the present application without departing from the scope of the present application. Thus, if these modifications and variations of the present application fall within the scope of the claims of the present application and their equivalents, the present application is also intended to include these modifications and variations.

[0110] In the above embodiments, it can be implemented in whole or in part by software, hardware, firmware or any combination thereof. When implemented by software, it can be implemented in whole or in part in the form of a computer program product. The computer program product includes one or more computer instructions. When the computer program instructions are loaded and executed on a computer, the process or function described in the embodiment of the present invention is generated in whole or in part. The computer can be a general-purpose computer, a special-purpose computer, a computer network, or other programmable device. The computer instructions can be stored in a computer-readable storage medium, or transmitted from one computer-readable storage medium to another computer-readable storage medium. For example, the computer instructions can be transmitted from a website site, computer, server or data center by wired (e.g., coaxial cable, optical fiber, digital subscriber line (DSL)) or wireless (e.g., infrared, wireless, microwave, etc.) mode to another website site, computer, server or data center. The computer-readable storage medium can be any available medium that a computer can access or a data storage device such as a server or data center that includes one or more available media integrated. The available medium can be a magnetic medium (e.g., a floppy disk, a hard disk, a tape), an optical medium (e.g., a DVD), or a semiconductor medium (e.g., a solid state disk (SSD)), etc.

Claims

1. A power conversion device, comprising a controller and a converter, characterized in that: The controller is connected to the converter; The controller is used to detect the output voltage of the converter; The controller is configured to, after the output voltage of the converter is less than a first threshold, reduce the active current output by the converter to a first current value, and reduce the reactive current output by the converter to a second current value when the output voltage of the converter rises to be greater than a second threshold, wherein the second threshold is greater than the first threshold; Adjust the reactive current and active current output by the converter according to a preset current adjustment rate until the active current is adjusted from the first current value to a target active current value, and the reactive current is adjusted from the second current value to a target reactive current value, the target reactive current value is within a range of reactive current values ​​output by the converter when the converter is working normally, the target active current value is within a range of active current values ​​output by the converter when the converter is working normally, and the first current value and the second current value are any values ​​within 50% of the range of reactive current values ​​and active current values ​​output by the converter when the converter is working normally, respectively; The second threshold is less than or equal to a minimum voltage value output by the converter when the converter is working normally.

2. The power conversion device according to claim 1, characterized in that: The first current value and the second current value are greater than zero and less than or equal to 10% of the active current value and the reactive current value outputted by the converter when the converter is working normally.

3. The power conversion device according to claim 1 or 2, characterized in that: The controller is specifically used for: The reactive current or active current output by the converter is adjusted according to different current adjustment rates until the active current value is adjusted from the first current value to the target active current value, and the reactive current is adjusted from the second current value to the target reactive current value.

4. The power conversion device according to claim 3, characterized in that: The controller is specifically used for: The reactive current or active current output by the converter is adjusted in multiple adjustment stages, wherein the current adjustment rates of each of the multiple adjustment stages are different, or the current adjustment rate of at least one of the multiple adjustment stages is different from the current adjustment rates of other adjustment stages, and the other adjustment stages are adjustment stages other than the at least one adjustment stage in the multiple adjustment stages.

5. The power conversion device according to claim 1 or 2, characterized in that: The controller is specifically used for: The reactive current or active current output by the converter is adjusted at the same current adjustment rate until the active current value is adjusted from the first current value to the target active current value, and the reactive current is adjusted from the second current value to the target reactive current value.

6. The power conversion device according to claim 1, characterized in that: When the output voltage of the converter is less than the first threshold, low voltage ride-through occurs in the converter.

7. A control method for a power conversion device, characterized in that: Applied to a power conversion device, the power conversion device includes a controller and a converter, and the method includes: detecting an output voltage of the converter; After the output voltage of the converter is less than the first threshold, when the output voltage of the converter rises to be greater than a second threshold, reducing the active current output by the converter to a first current value, and reducing the reactive current output by the converter to a second current value, wherein the second threshold is greater than the first threshold; Adjust the reactive current and active current output by the converter according to a preset current adjustment rate until the active current is adjusted from the first current value to a target active current value, and the reactive current is adjusted from the second current value to a target reactive current value, the target reactive current value is within a range of reactive current values ​​output by the converter when the converter is working normally, the target active current value is within a range of active current values ​​output by the converter when the converter is working normally, and the first current value and the second current value are any values ​​within 50% of the range of reactive current values ​​and active current values ​​output by the converter when the converter is working normally, respectively; The second threshold is less than the minimum voltage output by the converter when the converter is working normally.

8. The method according to claim 7, characterized in that The first current value and the second current value are greater than zero and less than or equal to 10% of the active current value and the reactive current value outputted by the converter when the converter is working normally.

9. The method according to claim 7 or 8, characterized in that The step of adjusting the reactive current and the active current output by the converter according to a preset current adjustment rate until the active current is adjusted from the first current value to the target active current value, and the reactive current is adjusted from the second current value to the target reactive current value, comprises: The reactive current or active current output by the converter is adjusted according to different current adjustment rates until the active current value is adjusted from the first current value to the target active current value, and the reactive current is adjusted from the second current value to the target reactive current value.

10. The method according to claim 9, characterized in that The step of adjusting the reactive current or active current output by the converter according to different current adjustment rates includes: The reactive current or active current output by the converter is adjusted in multiple adjustment stages, wherein the current adjustment rates of each of the multiple adjustment stages are different, or the current adjustment rate of at least one of the multiple adjustment stages is different from the current adjustment rates of other adjustment stages, and the other adjustment stages are adjustment stages other than the at least one adjustment stage in the multiple adjustment stages.

11. The method according to claim 7 or 8, characterized in that The step of adjusting the reactive current and the active current output by the converter according to a preset current adjustment rate until the active current is adjusted from the first current value to the target active current value, and the reactive current is adjusted from the second current value to the target reactive current value, comprises: The reactive current or active current output by the converter is adjusted at the same current adjustment rate until the active current value is adjusted from the first current value to the target active current value, and the reactive current is adjusted from the second current value to the target reactive current value.

12. The method according to claim 7, characterized in that When the output voltage of the converter is less than the first threshold, low voltage ride-through occurs in the converter.

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