Power converter start-up control method, controller, and power conversion system

Abstract

A power converter start-up control method, a controller, and a power conversion system. The method comprises: acquiring a grid voltage corresponding to a power converter, an active power command, and a reactive power command (302); on the basis of the grid voltage, the active power command, and the reactive power command, calculating a target start-up interval and a current command (304), the target start-up interval being located between a first time threshold and a second time threshold; and starting, within the target start-up interval, the power converter according to the current command (306).

Description

Power converter start-up control method, controller and power conversion system

[0001] Related applications

[0002] This disclosure claims priority to Chinese patent application No. 2024119983643, filed on December 31, 2024, entitled "Power Converter Start-up Control Method, Controller and Power Conversion System", the entire contents of which are incorporated herein by reference. Technical Field

[0003] This disclosure relates to the field of power conversion technology, and in particular to a power converter start-up control method, controller, and power conversion system. Background Technology

[0004] A power converter is a power conversion device used to transform electrical energy from one form to another, enabling energy transmission and control under different power requirements. A power converter can convert DC power generated by DC power supply devices such as photovoltaic panels into AC power, which can then be fed into the power grid, enabling grid connection of DC power supply devices.

[0005] In scenarios such as power converter startup, grid connection high and low voltage ride-through, and power converter light load control, it is necessary to control the startup process of the power converter to ensure the reliability of the power converter startup. Summary of the Invention

[0006] Therefore, it is necessary to provide a power converter startup control method, controller, and power conversion system that can ensure the reliability of power converter startup in response to the above-mentioned technical problems.

[0007] In a first aspect, this disclosure provides a power converter startup control method, including:

[0008] Obtain the grid voltage, active power command, and reactive power command corresponding to the power converter;

[0009] The target start-up range and current command are calculated based on the grid voltage, active power command and reactive power command. The target start-up range is located between the first time threshold and the second time threshold.

[0010] The power converter is started according to the current command within the target start-up range.

[0011] In one embodiment, the current command includes an active current command and a reactive current command, wherein calculating the target start-up range and the current command based on the grid voltage, the active power command, and the reactive power command includes:

[0012] Determine the first and second time thresholds based on the instantaneous value or phase of the grid voltage;

[0013] The active current command is determined based on the active power command and the grid voltage.

[0014] The reactive current command is determined based on the reactive power command and the grid voltage.

[0015] In one embodiment, starting the power converter according to a current command within the target startup range includes:

[0016] If the reactive power indicated by the reactive power command is greater than the power threshold, the power converter is started in the target start-up range with the reactive current at zero.

[0017] The reactive current of the power converter is controlled according to the preset gradient step size to reach the target reactive current indicated by the reactive current command.

[0018] In one embodiment, starting the power converter according to a current command within the target startup range includes:

[0019] If the reactive power indicated by the reactive power command is less than or equal to the power threshold, the power converter is started in the target starting range according to the target reactive current indicated by the reactive current command.

[0020] In one embodiment, the target start-up range and current command are calculated based on the grid voltage, active power command, and reactive power command, including:

[0021] When the reactive power corresponding to the reactive power command is greater than the power threshold, the offset phase is determined according to the reactive power command and the active power command.

[0022] The first and second time thresholds are obtained based on the offset phase and the amplitude or phase of the grid voltage.

[0023] The active current command is determined based on the active power command and the grid voltage.

[0024] The reactive current command is determined based on the reactive power command and the grid voltage.

[0025] In one embodiment, the method further includes:

[0026] The active power command is obtained based on the maximum power point of the energy device corresponding to the power converter.

[0027] In one embodiment, the method further includes:

[0028] Active power commands are obtained based on the dispatching needs of the power grid system.

[0029] In one embodiment, the power converter includes a DC-side circuit, a transformer, and an AC-side circuit, wherein,

[0030] The DC-side circuit includes an actively driven full-bridge circuit;

[0031] The AC side circuit includes an actively driven bidirectional switching half-bridge circuit.

[0032] In one embodiment, the AC side circuit includes a resonant inductor, the instantaneous current values ​​of which are less than the current threshold at a first time threshold and a second time threshold.

[0033] Secondly, this disclosure also provides a controller. The controller is connected to a power converter; the controller includes a memory and a processor, the memory storing a computer program, and the processor executing the computer program to implement the steps of the method as described in the first aspect.

[0034] Thirdly, this disclosure also provides a power conversion system. The power conversion system includes a power converter and the controller provided in the second aspect above; wherein the power converter includes a DC-side circuit, a transformer, and an AC-side circuit, wherein the DC-side circuit includes an actively driven full-bridge circuit; and the AC-side circuit includes an actively driven bidirectional switching half-bridge circuit.

[0035] The aforementioned power converter startup control method, controller, and power conversion system include: acquiring the grid voltage, active power command, and reactive power command corresponding to the power converter; calculating the target startup interval and current command based on the grid voltage, active power command, and reactive power command, wherein the target startup interval is located between a first time threshold and a second time threshold; and starting the power converter according to the current command within the target startup interval. In this way, in various startup scenarios of the power converter, after receiving an external startup command or an internally determined startup command, the power converter is not started directly. Instead, the target startup range and current command are determined by tracking the grid voltage, active power command, and reactive power command. Within the target startup range, the power converter is started according to the current command. For example, a startup control device is set in the power converter. This startup control device includes two input terminals and two output terminals. One input terminal is used to input the grid voltage, and the other input terminal is used to input the active power command and reactive power command. One output terminal is used to output the target startup range, and the other output terminal is used to output the current command. The power converter starts based on the target startup range and current command output by the startup control device. Starting the power converter according to the current command within the target startup range can reduce the current surge of each switch in the power converter during startup, avoid damage to the switch, and improve the reliability of the power converter startup. Attached Figure Description

[0036] To more clearly illustrate the technical solutions in the embodiments or conventional technologies of this disclosure, the accompanying drawings used in the description of the embodiments or conventional technologies will be briefly introduced below. Obviously, the accompanying drawings described below are only embodiments of this disclosure. For those skilled in the art, other drawings can be obtained based on the disclosed drawings without creative effort.

[0037] Figure 1 is an application environment diagram of a power converter startup control method in one embodiment;

[0038] Figure 2 is an exemplary schematic diagram of the circuit topology of a power converter to which the power converter startup control method is applicable in one embodiment.

[0039] Figure 3 is a flowchart illustrating a power converter startup control method provided in one embodiment;

[0040] Figure 4 is an exemplary schematic diagram showing the relationship between the current waveform of the resonant inductor and the grid voltage waveform of a power converter provided in one embodiment;

[0041] Figure 5 is a schematic diagram of the input and output of a start-up control device provided in one embodiment;

[0042] Figure 6 is a flowchart illustrating the steps for obtaining the target start-up range and current command in one embodiment;

[0043] Figure 7 is a schematic diagram of the process of determining the first time threshold and the second time threshold based on the instantaneous value of the grid voltage in one embodiment;

[0044] Figure 8 is a flowchart illustrating the steps of starting the power converter according to the current command in the target start-up range in one embodiment.

[0045] Figure 9 is a flowchart illustrating the steps for obtaining the target startup range and current command in another embodiment. Detailed Implementation

[0046] The technical solutions of the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this disclosure, and not all embodiments. Based on the embodiments of this disclosure, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this disclosure.

[0047] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of this disclosure.

[0048] It is understood that the terms "first," "second," etc., as used herein may be used to describe various elements, but these elements are not limited by these terms. These terms are used only to distinguish one element from another. For example, without departing from the scope of this disclosure, a first resistor may be referred to as a second resistor, and similarly, a second resistor may be referred to as a first resistor. Both the first resistor and the second resistor are resistors, but they are not the same resistor.

[0049] It is understood that the term "connection" in the following embodiments should be understood as "electrical connection," "communication connection," etc., if the connected circuits, modules, units, etc., have electrical signal or data transmission with each other.

[0050] It is understood that the term "based on" as used in this disclosure is used to describe one or more factors that influence the determination, but does not exclude other factors that may influence the determination. For example, the phrase "determine A based on B" means that the determination of A can be based entirely or at least partially on factor B. That is, B is a factor that influences the determination of A, but does not exclude the fact that the determination of A is also based on C.

[0051] When used herein, the singular forms of “a,” “an,” and “the” may also include the plural forms unless the context clearly indicates otherwise. It should also be understood that the terms “comprising / including” or “having,” etc., specify the presence of the stated features, wholes, steps, operations, components, parts, or combinations thereof, but do not preclude the possibility of the presence or addition of one or more other features, wholes, steps, operations, components, parts, or combinations thereof. Meanwhile, the term “and / or” as used in this specification includes any and all combinations of the associated listed items.

[0052] In an exemplary embodiment, the provided power converter startup control method can be applied in the application environment shown in Figure 1, wherein the DC terminal of the power converter 102 is connected to the energy device 104, and the AC terminal of the power converter 102 is connected to the power grid system 106, for converting the DC power generated by the energy device 104 into AC power and transmitting it to the power grid system 106, thereby realizing grid-connected power generation of the energy device 104. For example, the energy device 104 may be a photovoltaic module.

[0053] In an exemplary embodiment, referring to FIG2, the power converter includes a DC-side current, a transformer, and an AC-side circuit, wherein the DC-side circuit includes an actively driven full-bridge circuit; and the AC-side circuit includes an actively driven bidirectional switching half-bridge circuit.

[0054] For example, as shown in Figure 2, the first bridge arm of the full-bridge circuit includes switching transistors Q1 and Q2, and the second bridge arm includes switching transistors Q3 and Q4. Points A and B are the load interfaces of the full-bridge circuit. r The transformer is used; the upper arm of the bidirectional switching half-bridge circuit is implemented based on a bidirectional switch composed of switching devices Q5 and Q6, and the lower arm is implemented based on a bidirectional switch composed of switching devices Q7 and Q8. The midpoint C of the arm is connected through the resonant inductor L. r Connected to transformer T r V dc This indicates the DC-side power supply voltage, V. ac This refers to the AC side grid voltage.

[0055] The switching transistor can also be called a power transistor. In this embodiment, the switching transistor can be implemented using, but is not limited to, MOS transistors (Metal-Oxide-Semiconductor Field-Effect Transistors) and IGBTs (Insulated Gate Bipolar Transistors).

[0056] For example, the upper bridge arm circuit and the resonant capacitor C p Correspondingly, the lower bridge arm circuit and the resonant capacitor C n Correspondingly, the resonant capacitor C p and resonant capacitor C n Series connection, filter capacitor C o and filter impedance Z g A filter circuit is formed. In other examples, the resonant capacitor in the AC side circuit can be configured differently than shown in Figure 2. For example, the AC side circuit includes one resonant capacitor, which, together with the resonant inductor L... r Series connection. The instantaneous current value of the resonant inductor described below in this disclosure can also be the resonant cavity current value. That is, the AC side circuit does not necessarily include the electronic component of the resonant inductor, but the resonant cavity current still exists, and the method of this disclosure can still be applied.

[0057] The power converter startup control provided in this disclosure is applicable to scenarios including, but not limited to, the following three scenarios:

[0058] Scenario 1: The scenario where the power converter starts from the shutdown state. In this scenario, the power converter needs to start the power generation operation after receiving the start command in order to generate electricity in the grid.

[0059] Scenario 2: When the power converter is operating in grid-connected power generation mode, it detects a sudden change in grid voltage. The converter first blocks the voltage surge to prevent damage from the sudden change in grid voltage. When the grid voltage returns to normal, the power converter restarts its operation. In some embodiments, Scenario 2 is referred to as the high-low voltage ride-through scenario.

[0060] Scenario 3: This is a light-load operation scenario for the power converter. In this scenario, the power converter operates for a certain period of time, then shuts down for another period before resuming operation. For example, the power converter first operates for 'a' frequency cycles, then shuts down for 'b' frequency cycles. Then, the power converter operates for 'a' frequency cycles, then shuts down for 'b' frequency cycles, and so on. The power converter starts up every 'a+b' frequency cycles to improve its operating efficiency, where 'a' and 'b' are integers greater than 1. In some embodiments, Scenario 3 is referred to as the burst mode scenario.

[0061] In an exemplary embodiment, referring to FIG3, the provided power converter startup control method is used in the power converter shown in FIG1. ​​As shown in FIG3, the method includes steps 302 to 306, wherein:

[0062] Step 302: Obtain the grid voltage, active power command, and reactive power command corresponding to the power converter.

[0063] In this context, obtaining the grid voltage corresponding to the power converter refers to the power converter's operating parameters for real-time tracking of the grid voltage; for example, the operating parameters include at least the phase of the grid voltage or the instantaneous value of the grid voltage.

[0064] In one possible implementation, the grid voltage can be obtained through a voltage sampling circuit; or through a current transformer and a resistor circuit.

[0065] The active power command is used to indicate the amount of active power that the power converter needs to provide after startup.

[0066] In one possible implementation, the active power command is determined by obtaining the active power command based on the maximum power point of the energy device corresponding to the power converter.

[0067] For example, the energy device is a photovoltaic module; under the current illumination environment, the photovoltaic module is controlled by maximum power point tracking (MPPT) to obtain the maximum power point of the photovoltaic module, and the active power of the power converter is determined based on the maximum power point.

[0068] In this possible implementation, determining the active power command based on the maximum power point of the energy device corresponding to the power converter can improve the grid connection efficiency of the power converter.

[0069] In one possible implementation, the active power command is determined through the following steps: obtaining the active power command based on the dispatching needs of the power grid system.

[0070] For example, the power converter receives the grid's dispatch instructions, determines the amount of active power to be provided based on the dispatch requirements indicated in the dispatch instructions, and obtains the active power instruction.

[0071] Step 304: Calculate the target start-up interval and current command based on the grid voltage, active power command, and reactive power command. The target start-up interval is located between the first time-limit threshold and the second time-limit threshold.

[0072] In order to reduce the drive loss of the switching transistors, a resonant circuit is set in the DC-AC conversion circuit of the power converter. The energy exchange between the resonant inductor and the resonant capacitor creates the conditions for soft switching operation of each switching transistor. However, at the moment when the power converter starts up, the energy exchange process has not yet been established, and it is impossible to create the conditions for soft switching operation with a small drive current for each switching transistor. At this time, the switching transistor will be subjected to the instantaneous current impact when the power converter starts up. If the starting current is large, the switching transistor may be damaged, resulting in a decrease in the operational reliability of the power converter.

[0073] In the absence of reactive power, the current amplitude of the resonant inductor of the power converter is positively correlated with the absolute value of the instantaneous grid voltage. Please refer to Figure 4(a) and Figure 4(b). The change in the amplitude of the current envelope of the resonant inductor is the same as the change in the amplitude of the instantaneous grid voltage. The larger the absolute value of the instantaneous grid voltage, the larger the amplitude of the current envelope of the resonant inductor; the smaller the absolute value of the instantaneous grid voltage, the smaller the amplitude of the current envelope of the resonant inductor. Near the zero-crossing point of the grid voltage, the absolute value of the instantaneous grid voltage is small, and the amplitude of the current envelope of the resonant inductor is also small. At the peak or trough of the grid voltage, the amplitude of the current envelope of the resonant inductor is large.

[0074] In the presence of reactive power, for example, the relationship between the amplitude of the current envelope of the resonant inductor of the power converter and the absolute value of the instantaneous value of the grid voltage is shown in Figures 4(a) and (c). Depending on the magnitude of reactive power and active power, there is a certain phase deviation between the waveform of the current envelope of the resonant inductor and the waveform of the grid voltage; that is, when the grid voltage is at its minimum, the amplitude of the current envelope of the resonant inductor is not necessarily at its minimum.

[0075] The startup of a power converter is a temporary state, requiring a relatively small current value. Excessive current can cause a significant current surge to the switching transistors. During startup, energy resides in the inductor and is transferred through it, manifesting as inductor current. Therefore, controlling the startup of the power converter based on the inductor current provides a more direct reflection of current and energy changes during startup, resulting in more precise control. In this embodiment, the reactive power state at the start-up of the power converter is determined based on the grid voltage, active power command, and reactive power command. The real-time state of the grid voltage is also determined, thereby identifying a target start-up interval that minimizes the amplitude of the resonant inductor current. When the reactive power is zero, the target start-up interval with a smaller inductor current amplitude can be determined based on the moment when the instantaneous grid voltage value is relatively small. When the reactive power is not zero, the target start-up interval can be determined based on the phase deviation at the moment when the instantaneous grid voltage value is relatively small. Alternatively, the reactive current can be initially set to zero based on the moment when the instantaneous grid voltage value is relatively small, and then adjusted to the required reactive current after start-up. This allows the power converter to start within a time interval with a smaller inductor current amplitude, reducing the current impact on the switching transistors during power converter startup and improving the reliability of power converter startup and operation.

[0076] The current command refers to the magnitude of the current required for the power converter to start up. The current command includes an active current command and a reactive current command. The active current command indicates the amount of current supplied by the power converter to the power grid system, while the reactive current command indicates the amount of current required by the power converter to power its internal components such as inductors and capacitors. For example, the AC current indicated in the current command is determined based on the combination of active and reactive currents. The power converter must operate according to the current magnitude indicated in the current command during startup.

[0077] Step 306: Start the power converter according to the current command in the target start-up range.

[0078] Specifically, the power converter is started according to the current magnitude indicated by the current command within the target start-up range.

[0079] The power converter startup control method provided in the above embodiments, in various startup scenarios of the power converter, after receiving an externally input startup command or an internally determined startup command, does not directly start the power converter. Instead, it determines the target startup range and current command by tracking the grid voltage, active power command, and reactive power command, and starts the power converter according to the current command within the target startup range. For example, referring to Figure 5, a startup control device is set in the power converter. The startup control device includes two input terminals and two output terminals. One input terminal is used to input the grid voltage, and the other input terminal is used to input the active power command and reactive power command. One output terminal is used to output the target startup range, and the other output terminal is used to output the current command. The power converter starts based on the target startup range and current command output by the startup control device. Starting the power converter according to the current command within the target startup range can reduce the current surge of each switch in the power converter during startup, avoid damage to the switch, and improve the reliability of the power converter startup.

[0080] For example, in Scenario 1, the power converter starts from the off state. After receiving the start-up command from the outside, the power converter does not start emitting waves directly. Instead, it calculates the target start-up range and current command based on the acquired grid voltage, active power command, and reactive power command. The power converter starts according to the current command within the target start-up range. This avoids the possibility that direct start-up may occur when the instantaneous value of the grid voltage is large, which could lead to a large current in the resonant inductor and damage to the switching transistors. The power converter start-up control method provided in this embodiment can improve the reliability of the power converter start-up.

[0081] For example, in Scenario 2, after the power converter detects that the grid voltage has returned to normal during a high-low voltage ride-through scenario, it does not directly start transmitting power. Instead, based on the acquired grid voltage, active power command, and reactive power command, it calculates the target start-up interval and current command. Within the target start-up interval, it starts the power converter according to the current command. This avoids the situation where the grid voltage is detected to have returned to normal, and the grid voltage is at a moment with a large instantaneous value. If the power converter is started directly at this moment, it would cause a large current in the resonant inductor, which could damage the switching transistors. The power converter start-up control method provided in this embodiment can improve the reliability of the power converter start-up.

[0082] For example, in scenario three, the power converter operates in burst mode. The power converter determines the target start-up time and current command based on the grid voltage, active power command, and reactive power command. The power converter selects the time when the instantaneous value of the grid voltage is relatively small to minimize the current of the resonant inductor, reduce the current impact on each switch at the start-up time of the power converter, and improve the reliability of the power converter start-up.

[0083] In an exemplary embodiment, the start-up control device of the power converter start-up control method is located outside the power converter, that is, independent of the power converter. The start-up control device controls the power converter to start based on the target start-up range and current command obtained by the power converter start-up control method shown in FIG3.

[0084] In an exemplary embodiment, the provided power converter startup control method includes an active current command and a reactive current command. This embodiment relates to the process of calculating the target startup range and the current command based on the grid voltage, active power command, and reactive power command. Referring to Figure 6, this process includes:

[0085] Step 602: Determine the first time threshold and the second time threshold based on the instantaneous value or phase of the grid voltage.

[0086] Specifically, by tracking the instantaneous value or phase of the grid voltage, the time interval with the smaller instantaneous value of the grid voltage is calculated, and the interval value is used as the first time threshold and the second time threshold. The first time threshold corresponds to a moment on the first side of the grid voltage zero-crossing point, and the second time threshold corresponds to a moment on the second side of the grid voltage zero-crossing point, with the first and second sides representing the two sides of the grid voltage zero-crossing point. The target start-up interval is a start-up interval that includes the grid voltage zero-crossing point.

[0087] In one possible implementation, a first time threshold and a second time threshold are determined based on the instantaneous value of the grid voltage. Specifically, based on the correspondence between the instantaneous value of the grid voltage and the amplitude of the inductor current, it is determined that when the absolute value of the instantaneous grid voltage is less than the voltage threshold U, the current impact on the switching transistor during power converter startup is relatively small. The first time threshold T1 and the second time threshold T2 are determined by tracking the magnitude and changes of the instantaneous grid voltage and the voltage threshold u0. For example, referring to Figure 7, the instantaneous values ​​corresponding to two adjacent sampling times t1 and t2 are u1 and u2, respectively. Since u1 is less than u2, and both u1 and u2 are greater than 0, it is determined that the grid voltage is currently in a positive half-cycle. The first time threshold T1 and the second time threshold T2 are calculated using the sampling time t1, the corresponding instantaneous value u1, the power frequency period of the grid voltage, and the voltage threshold u0.

[0088] In one possible implementation, a first time threshold and a second time threshold are determined based on the phase of the grid voltage. Specifically, the first time threshold T1 and the second time threshold T2 are determined based on tracking the phase of the grid voltage; based on the relationship between the instantaneous value and phase of the grid voltage, a first phase interval and a second phase interval corresponding to the startup time that minimizes the current impact on the switching transistor can be determined; by tracking the phase of the grid voltage, the phase of the grid voltage at the current sampling time, the power frequency period of the grid voltage, and the endpoint phase of the first or second phase interval are determined, and the first time threshold T1 and the second time threshold T2 are calculated. For example, the first phase interval... In The value ranges from 168° to 177°. The value range is from 183° to 192°, and is optional. The value range is 170° or 175°; The value range is 185° or 190°; the second phase interval In The value ranges from 348° to 357°. The value range is from 3° to 12°, and is optional. The value ranges from 350° to 355°. The value ranges from 5° to 10°.

[0089] Step 604: Determine the active current command based on the active power command and the grid voltage.

[0090] Specifically, based on the active power indicated by the active power command, the effective value of the grid voltage, and the power factor of the inverter, the active current at startup of the power converter is determined, and the active current command is obtained.

[0091] Step 606: Determine the reactive current command based on the reactive power command and the grid voltage.

[0092] Specifically, based on the reactive power magnitude indicated by the active power command, the effective value of the grid voltage, and the load power of the inverter, the reactive current magnitude corresponding to the power converter is determined, and the reactive current command is obtained.

[0093] The reactive power of the power converter can be zero or non-zero, depending on the internal settings of the power converter.

[0094] In one possible implementation, when the reactive power of the power converter is zero or close to zero; for example, when the reactive power of the power converter is less than the power threshold, the output voltage and output current of the power converter can be considered to be in phase, and the current envelope of the resonant inductor and the grid voltage are in phase.

[0095] In this implementation, when the reactive power indicated by the reactive power command is less than or equal to the power threshold, the process of starting the power converter in the target start-up interval according to the current command includes: starting the power converter in the target start-up interval according to the target reactive current indicated by the reactive current command.

[0096] When the reactive power indicated by the reactive power command is less than or equal to the power threshold, the calculated target reactive current is equal to or close to zero.

[0097] In one possible implementation, when the reactive power of the power converter is greater than or equal to the power threshold, the power converter outputs both active and reactive current. It can be assumed that the output voltage and output current of the power converter are out of phase, and there is a phase deviation between the current envelope of the resonant inductor and the grid voltage. Referring to Figure 8, in this implementation, the process of starting the power converter according to the current command within the target start-up range includes steps 802 to 804, wherein:

[0098] Step 802: If the reactive power indicated by the reactive power command is greater than the power threshold, start the power converter in the target start-up range with zero reactive current.

[0099] In cases where the reactive power indicated by the reactive power command is greater than the power threshold, the value of the target reactive current indicated by the determined reactive current command is not zero. If the power converter is started directly according to the target reactive current, there may still be a problem of excessive current at the start-up time. This embodiment starts the power converter with zero reactive current to avoid excessive current in the power converter at the start-up time, which could damage the switching transistors.

[0100] Step 804: Control the reactive current of the power converter according to the preset gradient step size to reach the target reactive current indicated by the reactive current command.

[0101] After the power converter starts up, the reactive current of the power converter is gradually increased to the target reactive current according to a preset gradient step size Δi. This ensures the reliable operation of the switching transistors while meeting the reactive power command requirements of the power converter. For example, Δi is used as the reactive current control target of the power converter; when the reactive current of the power converter reaches Δi, 2×Δi is used as the reactive current control target; when the reactive current of the power converter reaches 2×Δi, 3×Δi is used as the reactive current control target, and so on, until the reactive current of the power converter reaches the target reactive current indicated by the reactive current command.

[0102] For example, if the target reactive current is 2A, the reactive current control target of the power converter is increased by 0.1A step size from 0A to 2A, ensuring the reliability of the switching transistor operation.

[0103] In an exemplary embodiment, referring to Figure 9, this embodiment relates to the process of calculating the target start-up range and current command based on the grid voltage, active power command, and reactive power command when the reactive power corresponding to the reactive power command is greater than the power threshold. As shown in Figure 9, this process includes steps 902 to 908, wherein:

[0104] Step 902: When the reactive power corresponding to the reactive power command is greater than the power threshold, determine the offset phase based on the reactive power command and the active power command.

[0105] Among them, when the reactive power indicated by the reactive power command is greater than the power threshold, there is a phase deviation between the envelope phase of the current envelope of the resonant inductor and the voltage phase of the grid voltage, as shown in Figure 4(a) and (c); the offset phase obtained by the magnitude of the reactive power indicated by the reactive power command and the active power indicated by the active power command is the aforementioned phase deviation.

[0106] Step 904: Based on the offset phase and the amplitude or phase of the grid voltage, obtain the first time threshold and the second time threshold.

[0107] Specifically, the initial start-up interval is determined based on the amplitude or phase of the grid voltage, and the first and second time thresholds of the target start-up interval are obtained based on the initial start-up interval and the offset phase.

[0108] In one possible implementation, the reactive power type indicated by the reactive power command is inductive reactive power type, and the initial start-up interval is shifted backward by the time corresponding to the offset phase according to the timing sequence to obtain the target start-up interval.

[0109] In one possible implementation, the reactive power type indicated by the reactive power command is inductive reactive power type, and the initial start-up interval is shifted forward by the time corresponding to the offset phase according to the timing sequence to obtain the target start-up interval.

[0110] In one possible implementation, the process of determining the initial start-up range based on the magnitude or phase of the grid voltage can be referred to the relevant process in the embodiment corresponding to Figure 6, and will not be repeated here.

[0111] Step 906: Determine the active current command based on the active power command and the grid voltage.

[0112] Step 908: Determine the reactive current command based on the reactive power command and the grid voltage.

[0113] Compared to the embodiment shown in Figure 8, this embodiment starts the power converter directly according to the active and reactive currents calculated by the active and reactive power commands when starting the power converter according to the current command in the target start-up range. There is no need to start the power converter with zero reactive current first and then gradually adjust the reactive current to the target reactive current.

[0114] In one exemplary embodiment, the instantaneous values ​​of the resonant cavity current in the AC side circuit at a first time threshold and a second time threshold are less than the current threshold. In one possible implementation, referring to FIG2, the AC side circuit of the power converter to which the power converter control method is applicable includes a resonant inductor Lr. The instantaneous values ​​of the current in the resonant inductor Lr at the first time threshold and the second time threshold are less than the current threshold.

[0115] The current threshold refers to a current value close to zero. For example, the current threshold is less than 0.1A.

[0116] In an exemplary embodiment, a power converter startup control method is provided, which is used in the power converter shown in FIG1. ​​The power converter includes a DC-side circuit, a transformer, and an AC-side circuit, wherein the DC-side circuit includes an actively driven full-bridge circuit; and the AC-side circuit includes an actively driven bidirectional switching half-bridge circuit. The method includes steps S1 to S7, wherein:

[0117] Step S1: Obtain the grid voltage, active power command, and reactive power command corresponding to the power converter.

[0118] Optionally, the active power command can be obtained based on the maximum power point of the energy device corresponding to the power converter.

[0119] Optionally, active power commands can be obtained based on the dispatching needs of the power grid system.

[0120] Step S2: Determine the first time threshold and the second time threshold based on the instantaneous value or phase of the grid voltage.

[0121] Step S3: Determine the active current command based on the active power command and the grid voltage.

[0122] Step S4: Determine the reactive current command based on the reactive power command and the grid voltage.

[0123] Step S5: If the reactive power indicated by the reactive power command is greater than the power threshold, start the power converter in the target start-up range with zero reactive current.

[0124] Step S6: Control the reactive current of the power converter according to the preset gradient step size to reach the target reactive current indicated by the reactive current command.

[0125] Step S7: If the reactive power indicated by the reactive power command is less than or equal to the power threshold, start the power converter in the target start-up range according to the target reactive current indicated by the reactive current command.

[0126] It should be understood that although the steps in the flowcharts of the above embodiments are shown sequentially according to the arrows, these steps are not necessarily executed in the order indicated by the arrows. Unless otherwise expressly stated herein, there is no strict order restriction on the execution of these steps; they can be executed in other orders, or multiple steps can be executed simultaneously. Moreover, at least some steps in the flowcharts of the above embodiments may include multiple steps or multiple stages. These steps or stages are not necessarily completed at the same time, but can be executed at different times. The execution order of these steps or stages is not necessarily sequential, but can be performed alternately or in turn with other steps or at least a portion of the steps or stages of other steps.

[0127] It is understood that the term "based on" as used in this disclosure is used to describe one or more factors that influence the determination, but does not exclude other factors that may influence the determination. For example, the phrase "determine A based on B" means that the determination of A can be based entirely or at least partially on factor B. That is, B is a factor that influences the determination of A, but does not exclude the fact that the determination of A is also based on C.

[0128] This disclosure also provides a controller connected to a power converter; the controller includes a memory and a processor, the memory storing a computer program, and the processor executing the computer program to implement the steps in the above method embodiments.

[0129] This disclosure also provides a power conversion system, which includes a power converter and a controller provided in the foregoing embodiments; wherein the power converter includes a DC-side circuit, a transformer and an AC-side circuit, wherein the DC-side circuit includes an actively driven full-bridge circuit; and the AC-side circuit includes an actively driven bidirectional switching half-bridge circuit.

[0130] In one embodiment, a computer device is also provided, including a memory and a processor, wherein the memory stores a computer program, and the processor executes the computer program to implement the steps in the above method embodiments.

[0131] In one embodiment, a computer-readable storage medium is provided having a computer program stored thereon that, when executed by a processor, implements the steps in the above method embodiments.

[0132] In one embodiment, a computer program product is provided, including a computer program that, when executed by a processor, implements the steps in the above method embodiments.

[0133] It should be noted that the user information (including but not limited to user device information, user personal information, etc.) and data (including but not limited to data used for analysis, data stored, data displayed, etc.) involved in this disclosure are all information and data authorized by the user or fully authorized by all parties, and the collection, use and processing of the relevant data must comply with relevant regulations.

[0134] Those skilled in the art will understand that all or part of the processes in the methods of the above embodiments can be implemented by a computer program instructing related hardware. The computer program can be stored in a non-volatile computer-readable storage medium, and when executed, it can include the processes of the embodiments of the methods described above. Any references to memory, databases, or other media used in the embodiments provided in this disclosure can include at least one of non-volatile and volatile memory. Non-volatile memory can include read-only memory (ROM), magnetic tape, floppy disk, flash memory, optical memory, high-density embedded non-volatile memory, resistive random access memory (ReRAM), magnetic random access memory (MRAM), ferroelectric random access memory (FRAM), phase change memory (PCM), graphene memory, etc. Volatile memory can include random access memory (RAM) or external cache memory, etc. By way of illustration and not limitation, RAM can take many forms, such as Static Random Access Memory (SRAM) or Dynamic Random Access Memory (DRAM). The databases involved in the embodiments provided in this disclosure may include at least one type of relational database and non-relational database. Non-relational databases may include, but are not limited to, blockchain-based distributed databases. The processors involved in the embodiments provided in this disclosure may be general-purpose processors, central processing units, graphics processing units, digital signal processors, programmable logic devices, quantum computing-based data processing logic devices, etc., and are not limited to these.

[0135] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0136] The embodiments described above are merely illustrative of several implementations of this disclosure, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this disclosure, and these all fall within the scope of protection of this disclosure. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A power converter start-up control method, wherein, The method includes: Obtain the grid voltage, active power command, and reactive power command corresponding to the power converter; The target start-up interval and current command are calculated based on the grid voltage, active power command and reactive power command, and the target start-up interval is located between the first time threshold and the second time threshold. The power converter is started according to the current command in the target start-up range.

2. The method according to claim 1, wherein, The current command includes an active current command and a reactive current command, wherein the calculation of the target start-up range and current command based on the grid voltage, active power command, and reactive power command includes: The first time threshold and the second time threshold are determined based on the instantaneous value or phase of the grid voltage; The active current command is determined based on the active power command and the grid voltage; The reactive current command is determined based on the reactive power command and the grid voltage.

3. The method according to claim 1 or 2, wherein, The step of starting the power converter according to the current command in the target start-up range includes: If the reactive power indicated by the reactive power command is greater than the power threshold, the power converter is started in the target start-up range with the reactive current being zero. The reactive current of the power converter is controlled according to a preset gradient step size to reach the target reactive current indicated by the reactive current command.

4. The method according to any one of claims 1-3, wherein, The step of starting the power converter according to the current command in the target start-up range includes: If the reactive power indicated by the reactive power command is less than or equal to the power threshold, the power converter is started in the target start-up range according to the target reactive current indicated by the reactive current command.

5. The method according to any one of claims 1-4, wherein, The current command includes an active current command and a reactive current command, wherein the calculation of the target start-up range and current command based on the grid voltage, active power command, and reactive power command includes: When the reactive power corresponding to the reactive power command is greater than the power threshold, the offset phase is determined according to the reactive power command and the active power command. The first time threshold and the second time threshold are obtained based on the offset phase and the amplitude or phase of the grid voltage; The active current command is determined based on the active power command and the grid voltage; The reactive current command is determined based on the reactive power command and the grid voltage.

6. The method according to any one of claims 1-5, wherein, The method further includes: The active power command is obtained based on the maximum power point of the energy device corresponding to the power converter.

7. The method according to any one of claims 1-6, wherein, The method further includes: The active power command is obtained based on the scheduling requirements of the power grid system.

8. The method according to any one of claims 1-7, wherein, The power converter includes a DC-side circuit, a transformer, and an AC-side circuit, wherein... The DC-side circuit includes an actively driven full-bridge circuit; The AC side circuit includes an actively driven bidirectional switching half-bridge circuit.

9. The method according to claim 8, wherein, The instantaneous values ​​of the resonant cavity current in the AC side circuit are less than the current threshold at the first and second time thresholds.

10. A controller, wherein, The controller is connected to the power converter; the controller includes a memory and a processor, the memory storing a computer program, and the processor executing the computer program to implement the steps of the method according to any one of claims 1 to 9.

11. A power conversion system, wherein, The system includes a power converter and a controller as described in claim 10; wherein... The power converter includes a DC-side circuit, a transformer, and an AC-side circuit. The DC-side circuit includes an actively driven full-bridge circuit, and the AC-side circuit includes an actively driven bidirectional switching half-bridge circuit.

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