Converter, soft starting method and device thereof, energy storage system and storage medium

Abstract

This application relates to a converter and its soft-start method and apparatus, energy storage system, and storage medium. The converter is used to connect to the power grid via a switch. The method includes: acquiring the grid voltage and the converter's output voltage when the switch is open; determining a virtual current based on the output voltage and the grid voltage; performing start-up control on the converter based on the virtual current; controlling the switch to close when the virtual current reaches zero; or controlling the switch to close when the virtual power reaches zero, wherein the virtual power is determined based on the virtual current; thus, the risk of overcurrent during the soft-start phase of the converter is avoided.

Description

Technical Field

[0001] This application relates to the field of power conversion technology, and in particular to a converter and its soft-start method and apparatus, energy storage system, and storage medium. Background Technology

[0002] During the grid-connected operation phase of a power conversion system (PCS), the PCS typically operates in current source mode.

[0003] In related technologies, during the soft start phase of the converter, the voltage source open-loop mode is usually adopted. That is, with the grid voltage as the reference, the grid voltage on both sides of the AC contactor and the converter output voltage are synchronized first, then the AC contactor is closed, and after the AC contactor is closed, the converter pulse is blocked, and then the current source mode is switched to restart.

[0004] However, in the soft-start phase of the converter in related technologies, the delay time of the AC contactor closing is difficult to obtain accurately. If the blocking pulse is delayed, it will lead to the risk of overcurrent. If the blocking pulse is blocked in advance, it will cause the AC contactor to generate an inrush current when it is energized. That is, both delayed and premature blocking of the pulse have the risk of overcurrent. Summary of the Invention

[0005] Therefore, it is necessary to provide a converter and its soft-start method and device, energy storage system and storage medium that can avoid overcurrent risks, in order to address the above-mentioned technical problems.

[0006] In a first aspect, this application provides a soft-start method for a converter, the converter being connected to a power grid via a switch, the method comprising:

[0007] When the switch is open, the grid voltage and the converter output voltage are obtained;

[0008] The virtual current is determined based on the output voltage and the mains voltage;

[0009] The converter is started up based on the virtual current;

[0010] When the virtual current reaches zero, the switch is controlled to close; or when the virtual power reaches zero, the switch is controlled to close, wherein the virtual power is determined based on the virtual current.

[0011] In one embodiment, determining the virtual current based on the output voltage and the grid voltage includes:

[0012] The difference between the output voltage and the mains voltage is determined, and the virtual current is obtained based on the ratio of the difference to a preset virtual impedance.

[0013] In one embodiment, the virtual power includes virtual active power and virtual reactive power;

[0014] The step of controlling the start-up of the converter based on the virtual current includes:

[0015] Based on the grid voltage and the virtual current, active and reactive power calculations are performed to obtain the virtual active power and the virtual reactive power.

[0016] Based on the virtual active power and the virtual reactive power, power outer loop closed-loop control is performed to obtain the first active current command value and the first reactive current command value.

[0017] Based on the first active current command value and the first reactive current command value, current inner loop closed-loop control is performed to obtain the first modulation wave;

[0018] The converter is started up based on the first modulation wave.

[0019] In one embodiment, the step of performing active and reactive power calculations based on the grid voltage and the virtual current to obtain the virtual active power and the virtual reactive power includes:

[0020] The grid voltage and the virtual current are both transformed from the three-phase stationary coordinate system to the synchronous rotating coordinate system to obtain the d-axis and q-axis components of the grid voltage and the virtual current.

[0021] The virtual active power is obtained by summing the product of the d-axis component of the grid voltage and the d-axis component of the virtual current, and the product of the q-axis component of the grid voltage and the q-axis component of the virtual current.

[0022] The virtual reactive power is obtained by multiplying the q-axis component of the grid voltage by the d-axis component of the virtual current, and by the difference between the product of the d-axis component of the grid voltage and the q-axis component of the virtual current.

[0023] In one embodiment, the method further includes:

[0024] When the switch is closed, the grid current is obtained;

[0025] The converter is controlled to connect to the grid based on the grid current.

[0026] In one embodiment, the grid-connection control of the converter based on the grid current includes:

[0027] Based on the grid voltage and the grid current, active and reactive power calculations are performed to obtain the actual active power and actual reactive power.

[0028] Based on the actual active power and the actual reactive power, perform power outer loop closed-loop control to obtain the second active current command value and the second reactive current command value.

[0029] Based on the second active current command value and the second reactive current command value, current inner loop closed-loop control is performed to obtain the second modulation wave;

[0030] The converter is controlled to connect to the grid based on the second modulation wave.

[0031] In one embodiment, the step of performing active and reactive power calculations based on the grid voltage and the grid current to obtain the actual active power and actual reactive power includes:

[0032] The grid voltage and the grid current are both transformed from the three-phase stationary coordinate system to the synchronous rotating coordinate system to obtain the d-axis and q-axis components of the grid voltage and the grid current.

[0033] The actual active power is obtained by summing the product of the d-axis component of the grid voltage and the d-axis component of the grid current, and the product of the q-axis component of the grid voltage and the q-axis component of the grid current.

[0034] The actual reactive power is obtained by multiplying the q-axis component of the grid voltage by the d-axis component of the grid current, and by the difference between the product of the d-axis component of the grid voltage and the q-axis component of the grid current.

[0035] Secondly, this application also provides a converter soft-start device, wherein the converter is used to connect to the power grid via a switch, and the device includes:

[0036] A voltage acquisition module is used to acquire the grid voltage and the converter's output voltage when the switch is open;

[0037] The virtual calculation module is used to determine the virtual current based on the output voltage and the grid voltage;

[0038] A soft-start control module is used to control the start-up of the converter based on the virtual current, wherein the switch is closed when the virtual current reaches zero; or the switch is closed when the virtual power reaches zero, wherein the virtual power is determined based on the virtual current.

[0039] In one embodiment, the virtual calculation module is further configured to determine the difference between the output voltage and the grid voltage, and to obtain the virtual current based on the ratio of the difference to a preset virtual impedance.

[0040] In one embodiment, the virtual power includes virtual active power and virtual reactive power; the soft-start control module includes an active and reactive power calculation unit, a power outer loop closed-loop control unit, a current inner loop closed-loop control unit, and a start control unit;

[0041] The active and reactive power calculation unit is used to perform active and reactive power calculations based on the grid voltage and the virtual current to obtain the virtual active power and the virtual reactive power.

[0042] The power outer loop closed-loop control unit is used to perform power outer loop closed-loop control based on the virtual active power and the virtual reactive power to obtain the first active current command value and the first reactive current command value.

[0043] The current inner loop closed-loop control unit is used to perform current inner loop closed-loop control according to the first active current command value and the first reactive current command value to obtain the first modulation wave.

[0044] The start-up control unit is used to start the converter according to the first modulation wave.

[0045] In one embodiment, the active and reactive power calculation unit is further configured to transform both the grid voltage and the virtual current from a three-phase stationary coordinate system to a synchronous rotating coordinate system, thereby obtaining the d-axis and q-axis components of the grid voltage and the d-axis and q-axis components of the virtual current; and,

[0046] The virtual active power is obtained by summing the products of the d-axis components of the grid voltage and the virtual current, and the products of the q-axis components of the grid voltage and the virtual current; and...

[0047] The virtual reactive power is obtained by multiplying the q-axis component of the grid voltage by the d-axis component of the virtual current, and by the difference between the product of the d-axis component of the grid voltage and the q-axis component of the virtual current.

[0048] In one embodiment, the device further includes:

[0049] A current acquisition module is used to acquire the grid current when the switch is closed;

[0050] The grid connection control module is used to perform grid connection control on the converter according to the grid current.

[0051] In one embodiment, the grid-connected control module includes an active and reactive power calculation unit, a power outer loop closed-loop control unit, a current inner loop closed-loop control unit, and a grid-connected control unit;

[0052] The active and reactive power calculation unit is used to perform active and reactive power calculations based on the grid voltage and the grid current to obtain the actual active power and actual reactive power.

[0053] The power outer loop closed-loop control unit is used to perform power outer loop closed-loop control based on the actual active power and the actual reactive power to obtain the second active current command value and the second reactive current command value.

[0054] The current inner loop closed-loop control unit is used to perform current inner loop closed-loop control according to the second active current command value and the second reactive current command value to obtain the second modulation wave;

[0055] The grid-connected control unit is used to perform grid-connected control of the converter according to the second modulation wave.

[0056] Thirdly, this application also provides a converter, including a controller, which is used to implement the converter soft-start method provided in the first aspect above.

[0057] Fourthly, this application also provides an energy storage system, including the converter provided in the third aspect above.

[0058] Fifthly, this application also provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the converter soft-start method provided in the first aspect above.

[0059] The aforementioned converter, its soft-start method and apparatus, energy storage system, and storage medium, wherein the converter is connected to the power grid via a switch, such as a grid-connected switch, which is an AC contactor. By acquiring the grid voltage and converter output voltage on both sides of the switch when it is open, a virtual current is determined based on these voltages. Then, the converter is started based on this virtual current until the virtual current or virtual power reaches zero, i.e., when the converter output voltage and grid voltage are synchronized in phase and amplitude. At this point, the switch is closed, thus completing the soft start of the converter in current source mode. In this embodiment, since the converter completes the soft start in current source mode, and the converter also operates in current source mode during grid-connected operation, compared to related technologies, the converter does not require a blocking pulse to switch operating modes from the soft start stage to the grid-connected operation stage. For example, it does not require a blocking pulse to switch from voltage source open-loop mode to current source mode. This avoids overcurrent risks, eliminates limitations on switch closing delay time, and simplifies the soft start process. Attached Figure Description

[0060] To more clearly illustrate the technical solutions in the embodiments of this application or related technologies, the drawings used in the description of the embodiments of this application or related technologies will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0061] Figure 1 This is a schematic diagram of a converter grid connection scenario in one embodiment;

[0062] Figure 2 This is a flowchart illustrating a converter soft-start method in one embodiment;

[0063] Figure 3 This is a flowchart illustrating step S204 in one embodiment;

[0064] Figure 4 This is a flowchart illustrating step S206 in one embodiment;

[0065] Figure 5 This is a schematic diagram illustrating the control method of the converter in current source mode in one embodiment.

[0066] Figure 6 This is a flowchart illustrating step S402 in one embodiment;

[0067] Figure 7 This is a flowchart illustrating the converter soft-start method in one embodiment;

[0068] Figure 8 This is a flowchart illustrating step S704 in one embodiment;

[0069] Figure 9 This is a flowchart illustrating step S802 in one embodiment;

[0070] Figure 10 This is one of the structural block diagrams of a converter soft-start device in one embodiment;

[0071] Figure 11 This is a second structural block diagram of the converter soft-start device in one embodiment;

[0072] Figure 12 This is the third structural block diagram of the converter soft-start device in one embodiment;

[0073] Figure 13 This is the fourth structural block diagram of a converter soft-start device in one embodiment. Detailed Implementation

[0074] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0075] The converter soft-start method provided in this application embodiment can be executed by the converter's controller, which can be integrated inside the converter or located outside the converter. The converter includes energy storage converters, photovoltaic inverters, etc. The converter is connected to the power grid via a switch, such as a grid-connected switch, which is a contactor, and the contactor is an AC contactor. For example, see reference... Figure 1 The output of the converter is connected to one side of the AC contactor K1 via a filter circuit, and the other side of the AC contactor K1 is connected to the power grid. The filter circuit can be composed of circuit components such as capacitor C and inductor L. The filter circuit is used to filter the output voltage of the converter (referred to as the converter output voltage). The converter output voltage can be the AC voltage generated by the AC-DC conversion circuit inside the converter.

[0076] In one exemplary embodiment, reference is made to Figure 2 A converter soft-start method is provided, which may include the following steps S202~S206.

[0077] S202 acquires the grid voltage and the converter's output voltage when the switch is open.

[0078] The conditions for a converter to operate in grid-connected mode in current source mode include: the phase and amplitude of the converter output voltage are synchronized with the grid voltage, where phase synchronization means that the frequency is also synchronized.

[0079] When the grid-connected switch is open, the converter is not yet connected to the grid. Based on the conditions for grid-connected operation in current source mode, when the converter needs to be soft-started in current source mode, the converter output voltage Uinv and the grid voltage Ug located on both sides of the grid-connected switch when it is open can be obtained first. This prepares for synchronizing the phase and amplitude of the converter output voltage with the grid voltage. The converter output voltage and grid voltage can be obtained using conventional voltage acquisition methods in the art, such as through voltage detection equipment like voltage transformers. This application does not specifically limit the method used in this embodiment.

[0080] S204 determines the virtual current based on the output voltage and the mains voltage.

[0081] In the phase where the converter operates in grid-connected current source mode, it is typically controlled using a power outer-loop closed-loop control and a current inner-loop closed-loop control. Accordingly, during the converter's soft-start phase, a virtual electrical parameter value can be determined as the feedback value in the outer-loop closed-loop control. This constructs the soft-start phase of the converter in current source mode, enabling both outer-loop and inner-loop closed-loop control. This control method is then used to start the converter, ensuring that the phase and amplitude of the converter's output voltage are synchronized with the grid voltage.

[0082] Virtual electrical parameter values ​​can be determined based on the converter output voltage and grid voltage located on both sides of the grid-connected switch when the grid-connected switch is open. These electrical parameters can be, but are not limited to, power, voltage, and current. For example, virtual electrical parameter values ​​may include virtual current or virtual power, with the virtual power determined based on the virtual current; for instance, the virtual power can be determined based on the physical relationship between current and power, and on the virtual current and grid voltage.

[0083] S206 controls the converter's startup based on the virtual current, and closes the switch when the virtual current or virtual power reaches zero.

[0084] In this context, starting the converter based on virtual electrical parameter values ​​means using the control method described above to start the converter, thereby achieving synchronization between the converter's output voltage and the grid voltage in terms of phase and amplitude. When the virtual electrical parameter value reaches zero, such as when the virtual current or virtual power reaches zero, it indicates that the converter's output voltage and the grid voltage are synchronized in terms of phase and amplitude. At this point, the grid-connected switch can be closed. Once the grid-connected switch is fully closed, the converter's soft start in current source mode is completed, and it then directly enters the grid-connected operation phase in current source mode, during which power dispatching can be performed.

[0085] In this embodiment, since the converter completes soft start in current source mode, and the converter also operates in current source mode during grid-connected operation, the converter does not need to switch operating modes by blocking pulses from the soft start stage to the grid-connected operation stage, compared with related technologies. For example, it does not need to switch from voltage source open-loop mode to current source mode by blocking pulses, thereby avoiding overcurrent risks and not limiting the closing delay time of the grid-connected switch. At the same time, it simplifies the soft start process.

[0086] In one exemplary embodiment, the virtual electrical parameter value is a virtual current, referenced to... Figure 3 The step S204, which involves determining the virtual current based on the output voltage and the mains voltage, may include the following step S302.

[0087] S302 determines the difference between the output voltage and the mains voltage, and obtains the virtual current based on the ratio of this difference to the preset virtual impedance.

[0088] In this embodiment, the difference between the converter output voltage and the grid voltage can be determined as Uinv-Ug. This difference can then be used to assess the synchronization between the converter output voltage and the grid voltage. Furthermore, the virtual current can be determined based on the ratio of this difference to a preset virtual impedance. For example, the virtual current Ivir = (Uinv-Ug) / Rvir, where Rvir is the preset virtual impedance. The specific value of the preset virtual impedance can be preset according to the actual application. The specific value of the preset virtual impedance can affect the time required for the phase and amplitude of the converter output voltage and the grid voltage to reach synchronization. For example, in a three-phase system, the virtual current of phase A is Ivira = (Uinva - Uga) / Rvir, the virtual current of phase B is Ivirb = (Uinvb - Ugb) / Rvir, and the virtual current of phase C is Ivirc = (Uinvc - Ugc) / Rvir, where Uinva, Uinvb, and Uinvc are the output voltages of phases A, B, and C of the converter, respectively, and Uga, Ugb, and Ugc are the grid voltages of phases A, B, and C, respectively.

[0089] In one exemplary embodiment, virtual power includes virtual active power and virtual reactive power, combined with Figure 4 and Figure 5 The start-up control of the converter based on the virtual current in step S206 may include the following steps S402 to S408.

[0090] S402 performs active and reactive power calculations based on grid voltage and virtual current to obtain virtual active power and virtual reactive power.

[0091] For example, refer to Figure 5During the soft-start phase of the converter in current source mode, when performing power outer loop closed-loop control on the converter, the virtual current can be used as the current feedback value. Then, based on the grid voltage and the virtual current, active and reactive power calculations are performed to obtain the virtual power. The virtual power includes virtual active power P1 and virtual reactive power Q1. The virtual power is used as the power feedback value, and the power command value is zero.

[0092] S404 performs closed-loop control of the power outer loop based on the virtual active power and virtual reactive power to obtain the first active current command value and the first reactive current command value.

[0093] For example, refer to Figure 5 In the soft-start phase of the converter current source mode, the power command value is zero, and the virtual active power P1 and virtual reactive power Q1 are used as power feedback values ​​to perform power outer loop closed-loop control, so as to obtain the current command value of the current inner loop closed-loop control. The current command value includes the first active current command value and the first reactive current command value.

[0094] S406, based on the first active current command value and the first reactive current command value, performs closed-loop control of the inner current loop to obtain the first modulation wave.

[0095] For example, refer to Figure 5 In the soft-start phase of the converter current source mode, the first modulation wave may include the active component Vq1 and the reactive component Vd1 of the first modulation wave in the synchronous rotating coordinate system dq. The active component Vq1 and the reactive component Vd1 of the first modulation wave can be transformed from the synchronous rotating coordinate system dq to the three-phase stationary coordinate system abc to obtain the first modulation wave Vabc1 in the three-phase stationary coordinate system abc.

[0096] S408 controls the start-up of the converter based on the first modulation wave.

[0097] For example, in the soft-start phase of the converter current source mode, the converter can be started and controlled according to the first modulation wave Vabc1 in the three-phase stationary coordinate system abc. This achieves "power outer loop closed-loop control + current inner loop closed-loop control" of the converter, thereby synchronizing the phase and amplitude of the converter output voltage with the grid voltage.

[0098] In one exemplary embodiment, reference is made to Figure 6 The step S402, which involves calculating active and reactive power based on the grid voltage and virtual current to obtain virtual active power and virtual reactive power, may include the following steps S602 to S606.

[0099] S602 transforms both the grid voltage and the virtual current from the three-phase stationary coordinate system to the synchronous rotating coordinate system, obtaining the d-axis and q-axis components of the grid voltage and the d-axis and q-axis components of the virtual current.

[0100] For example, the phase of the grid voltage can be obtained through a phase-locked loop, and then, with the phase of the grid voltage as a reference, both the grid voltage and the virtual current can be transformed from the three-phase stationary coordinate system to the synchronous rotating coordinate system, so that the d-axis component of the grid voltage is Ud, the q-axis component of the grid voltage is Uq, the d-axis component of the virtual current is Id1, and the q-axis component of the virtual current is Iq1.

[0101] S604. The virtual active power is obtained by summing the product of the d-axis component of the grid voltage and the d-axis component of the virtual current, and the product of the q-axis component of the grid voltage and the q-axis component of the virtual current.

[0102] For example, the virtual active power P1 = F * (Ud * Id1 + Uq * Iq1), where F is a preset equal amplitude coefficient, for example, F = 1.5. The preset equal amplitude coefficient is introduced to achieve synchronization between the amplitude of the converter output voltage and the grid voltage.

[0103] S606. The virtual reactive power is obtained by taking the product of the q-axis component of the grid voltage and the d-axis component of the virtual current, and the difference between the product of the d-axis component of the grid voltage and the q-axis component of the virtual current.

[0104] For example, the virtual reactive power Q1 = F * (-Ud * Iq1 + Uq * Id1).

[0105] Therefore, in this embodiment of the application, the soft-start stage in the converter current source mode involves the following steps:

[0106] When the switch is open, the grid voltage and converter output voltage are acquired. The difference between the converter output voltage and the grid voltage is determined to be Uinv-Ug. Based on the ratio of this difference to the preset virtual impedance, the virtual current Ivir=(Uinv-Ug) / Rvir is determined, and the virtual current is used as the current feedback value in the power outer loop closed-loop control.

[0107] A phase-locked loop (PLL) is used to obtain the phase of the grid voltage. Then, using the phase of the grid voltage as a reference, both the grid voltage and the virtual current are transformed from the three-phase stationary coordinate system to the synchronous rotating coordinate system. The d-axis component of the grid voltage is Ud, the q-axis component is Uq, the d-axis component of the virtual current is Id1, and the q-axis component is Iq1. The virtual active power P1 = F * (Ud * Id1 + Uq * Iq1) and the virtual reactive power Q1 = F * (-Ud * Iq1 + Uq * Id1) are calculated. The virtual active power and virtual reactive power values ​​are used as the power feedback values ​​in the power outer loop closed-loop control.

[0108] With the power command value at zero and virtual active power and virtual reactive power as power feedback values, power outer loop closed-loop control is performed to obtain the current command value for current inner loop closed-loop control. The current command value includes the first active current command value and the first reactive current command value.

[0109] Based on the first active current command value and the first reactive current command value, current inner loop closed-loop control is performed to obtain the first modulation wave. The first modulation wave may include the active component Vq1 and the reactive component Vd1 of the first modulation wave in the synchronous rotating coordinate system dq. The active component Vq1 and the reactive component Vd1 of the first modulation wave can be transformed from the synchronous rotating coordinate system dq to the three-phase stationary coordinate system abc to obtain the first modulation wave Vabc1 in the three-phase stationary coordinate system abc.

[0110] The converter is started by controlling the first modulation wave in the three-phase stationary coordinate system, thus realizing the outer loop closed-loop control of the power and the inner loop closed-loop control of the current of the converter, thereby achieving synchronization of the phase and amplitude of the converter output voltage with the grid voltage.

[0111] When the virtual current or virtual power reaches zero, it indicates that the phase and amplitude of the converter output voltage are synchronized with the grid voltage. At this time, the grid connection switch can be closed. Once the grid connection switch is fully closed, the converter completes the soft start in current source mode and then directly enters the grid-connected operation stage in current source mode. During the grid-connected operation stage, power scheduling can be performed.

[0112] Since the converter completes soft start in current source mode, and the converter also operates in current source mode during grid-connected operation, compared with related technologies, the converter does not need to switch operating modes by blocking pulses from the soft start stage to the grid-connected operation stage. For example, it does not need to switch from voltage source open-loop mode to current source mode by blocking pulses. This avoids overcurrent risk, does not limit the closing delay time of the switch, and simplifies the soft start process.

[0113] The following embodiments of this application describe the grid connection phase in converter current source mode:

[0114] In one exemplary embodiment, reference is made to Figure 7 The soft-start method for the converter may also include the following steps S702~S704.

[0115] S702 obtains the grid current when the switch is closed.

[0116] S704 performs grid connection control of the converter based on the grid current.

[0117] For example, in combination Figure 1 and Figure 5 Once the grid connection switch is fully closed, the soft start of the converter in current source mode is completed. At this time, the current feedback value in the power outer loop closed-loop control of the converter can be switched from the virtual current Ivir to the grid current Ig by switching a switching switch s, thereby enabling grid-connected operation in current source mode.

[0118] In one exemplary embodiment, reference is made to Figure 8 The grid-connected control of the converter based on the grid current in step S704 may include the following steps S802~S808.

[0119] S802 performs active and reactive power calculations based on grid voltage and grid current to obtain the actual active power and actual reactive power.

[0120] For example, refer to Figure 5 During the grid-connected operation phase in the converter current source mode, the grid current is used as the current feedback value during the power outer loop closed-loop control of the converter. Then, based on the grid voltage and grid current, active and reactive power calculations are performed to obtain the actual power. The actual power includes the actual active power P2 and the actual reactive power Q2. The actual power is used as the power feedback value, and the power command value is the power dispatch value.

[0121] S804 performs closed-loop power control on the outer loop based on the actual active power and actual reactive power to obtain the second active current command value and the second reactive current command value.

[0122] For example, refer to Figure 5 During the grid-connected operation phase in the converter current source mode, the power dispatch value is used as the power command value, and the actual active power P2 and the actual reactive power Q2 are used as the power feedback values ​​to perform power outer loop closed-loop control, thereby obtaining the current command value of the current inner loop closed-loop control. The current command value includes the second active current command value and the second reactive current command value.

[0123] S806 performs closed-loop control of the inner current loop based on the second active current command value and the second reactive current command value to obtain the second modulation wave.

[0124] For example, refer to Figure 5 During the grid-connected operation phase in the converter current source mode, the second modulation wave may include the active component Vq2 and the reactive component Vd2 of the second modulation wave in the synchronous rotating coordinate system dq. The active component Vq2 and the reactive component Vd2 of the second modulation wave can be transformed from the synchronous rotating coordinate system dq to the three-phase stationary coordinate system abc to obtain the second modulation wave Vabc2 in the three-phase stationary coordinate system abc.

[0125] S808 performs grid connection control on the converter based on the second modulation wave.

[0126] For example, during the grid-connected operation phase in the converter current source mode, the converter can be started and controlled according to the second modulation wave Vabc2 in the three-phase stationary coordinate system abc. This achieves closed-loop control of the power outer loop and closed-loop control of the current inner loop of the converter, thereby realizing power dispatch.

[0127] In one exemplary embodiment, reference is made to Figure 9 Step S802, which involves calculating active and reactive power based on grid voltage and grid current to obtain actual active power and actual reactive power, may include the following steps S902 to S906.

[0128] S902 transforms both the grid voltage and grid current from the three-phase stationary coordinate system to the synchronous rotating coordinate system, obtaining the d-axis and q-axis components of the grid voltage and the grid current.

[0129] For example, the phase of the grid voltage can be obtained through a phase-locked loop, and then, with the phase of the grid voltage as a reference, both the grid voltage and the grid current can be transformed from the three-phase stationary coordinate system to the synchronous rotating coordinate system, so as to obtain the d-axis component of the grid voltage as Ud, the q-axis component of the grid voltage as Uq, the d-axis component of the grid current as Id2, and the q-axis component of the virtual current as Iq2.

[0130] S904. The actual active power is obtained by summing the products of the d-axis components of the grid voltage and the d-axis components of the grid current, and the products of the q-axis components of the grid voltage and the q-axis components of the grid current.

[0131] For example, the actual active power P2 = F * (Ud * Id2 + Uq * Iq2), where F is a preset equal amplitude coefficient, for example F = 1.5. The preset equal amplitude coefficient is introduced to achieve synchronization between the amplitude of the converter output voltage and the grid voltage.

[0132] S906: The actual reactive power is obtained by taking the product of the q-axis component of the grid voltage and the d-axis component of the grid current, and the difference between the product of the d-axis component of the grid voltage and the q-axis component of the grid current.

[0133] For example, the actual reactive power Q2 = F * (-Ud * Iq2 + Uq * Id2).

[0134] Therefore, in this embodiment of the application, the grid-connected operation phase in converter current source mode includes the following steps:

[0135] With the switch closed, obtain the grid voltage and grid current.

[0136] A phase-locked loop (PLL) is used to obtain the phase of the grid voltage. Then, using the phase of the grid voltage as a reference, both the grid voltage and grid current are transformed from the three-phase stationary coordinate system to the synchronous rotating coordinate system. The d-axis component of the grid voltage is Ud, the q-axis component is Uq, the d-axis component of the grid current is Id2, and the q-axis component is Iq2. The actual active power P2 = F * (Ud * Id2 + Uq * Iq2) and the actual reactive power Q2 = F * (-Ud * Iq2 + Uq * Id2) are calculated and used as the power feedback values ​​in the power outer loop closed-loop control.

[0137] Using power dispatch value as power command value and actual active power and actual reactive power as power feedback values, power outer loop closed-loop control is performed to obtain current command value for current inner loop closed-loop control. The current command value includes the second active current command value and the second reactive current command value.

[0138] Based on the second active current command value and the second reactive current command value, current inner loop closed-loop control is performed to obtain the second modulation wave. The second modulation wave may include the active component Vq2 and the reactive component Vd2 of the second modulation wave in the synchronous rotating coordinate system dq. The active component Vq2 and the reactive component Vd2 of the second modulation wave can be transformed from the synchronous rotating coordinate system dq to the three-phase stationary coordinate system abc to obtain the second modulation wave Vabc2 in the three-phase stationary coordinate system abc.

[0139] The converter is controlled by the second modulation wave in the three-phase stationary coordinate system, thus realizing the outer loop control of power and the inner loop control of current of the converter, thereby achieving power dispatch.

[0140] Since the converter completes soft start in current source mode, and the converter also operates in current source mode during grid-connected operation, compared with related technologies, the converter does not need to switch operating modes by blocking pulses from the soft start stage to the grid-connected operation stage. For example, it does not need to switch from voltage source open-loop mode to current source mode by blocking pulses. This avoids overcurrent risk, does not limit the closing delay time of the switch, and simplifies the soft start process.

[0141] It should be understood that although the steps in the flowcharts of the embodiments described above are shown sequentially according to the arrows, these steps are not necessarily executed in the order indicated by the arrows. Unless explicitly stated herein, there is no strict order restriction on the execution of these steps, and they can be executed in other orders. Moreover, at least some steps in the flowcharts of the embodiments described above 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 some of the steps or stages of other steps.

[0142] Based on the same inventive concept, this application also provides a converter soft-start device for implementing the converter soft-start method described above. The solution provided by this device is similar to the solution described in the above method; therefore, the specific limitations in one or more embodiments of the converter soft-start device provided below can be found in the limitations of the converter soft-start method described above, and will not be repeated here.

[0143] In one exemplary embodiment, such as Figure 10 As shown, a converter soft-start device is provided for soft-start control of a converter. The converter is connected to the power grid via a grid-connected switch. The device includes:

[0144] The voltage acquisition module 1010 is used to acquire the grid voltage and the output voltage of the converter when the switch is open;

[0145] Virtual computing module 1020 is used to determine virtual current based on the output voltage and the grid voltage;

[0146] The soft-start control module 1030 is used to control the start-up of the converter based on the virtual current, wherein the switch is closed when the virtual current reaches zero; or the switch is closed when the virtual power reaches zero, wherein the virtual power is determined based on the virtual current.

[0147] In an exemplary embodiment, the virtual calculation module 1020 is further configured to determine the difference between the output voltage and the grid voltage, and obtain the virtual current based on the ratio of the difference to a preset virtual impedance.

[0148] In one exemplary embodiment, reference is made to Figure 11The virtual power includes virtual active power and virtual reactive power; the soft start control module 1030 includes an active and reactive power calculation unit 1131, a power outer loop closed-loop control unit 1132, a current inner loop closed-loop control unit 1133, and a start control unit 1134.

[0149] The active and reactive power calculation unit 1131 is used to perform active and reactive power calculations based on the grid voltage and the virtual current to obtain the virtual active power and the virtual reactive power.

[0150] The power outer loop closed-loop control unit 1132 is used to perform power outer loop closed-loop control based on the virtual active power and the virtual reactive power to obtain the first active current command value and the first reactive current command value.

[0151] The current inner loop closed-loop control unit 1133 is used to perform current inner loop closed-loop control according to the first active current command value and the first reactive current command value to obtain the first modulation wave.

[0152] The start control unit 1134 is used to start the converter according to the first modulation wave.

[0153] In an exemplary embodiment, the active and reactive power calculation unit 1131 is further configured to transform both the grid voltage and the virtual current from a three-phase stationary coordinate system to a synchronous rotating coordinate system, thereby obtaining the d-axis and q-axis components of the grid voltage and the d-axis and q-axis components of the virtual current; and,

[0154] The virtual active power is obtained by summing the products of the d-axis components of the grid voltage and the virtual current, and the products of the q-axis components of the grid voltage and the virtual current; and...

[0155] The virtual reactive power is obtained by multiplying the q-axis component of the grid voltage by the d-axis component of the virtual current, and by the difference between the product of the d-axis component of the grid voltage and the q-axis component of the virtual current.

[0156] In one exemplary embodiment, reference is made to Figure 12 The converter soft starter also includes:

[0157] The current acquisition module 1210 is used to acquire the grid current when the switch is closed;

[0158] The grid connection control module 1220 is used to perform grid connection control on the converter according to the grid current.

[0159] In one exemplary embodiment, reference is made to Figure 13The grid-connected control module 1220 includes an active and reactive power calculation unit 1131, a power outer loop closed-loop control unit 1132, a current inner loop closed-loop control unit 1133, and a grid-connected control unit 1134.

[0160] The active and reactive power calculation unit 1131 is also used to perform active and reactive power calculations based on the grid voltage and the grid current to obtain the actual active power and the actual reactive power.

[0161] The power outer loop closed-loop control unit 1132 is also used to perform power outer loop closed-loop control based on the actual active power and the actual reactive power to obtain the second active current command value and the second reactive current command value.

[0162] The current inner loop closed-loop control unit 1133 is also used to perform current inner loop closed-loop control according to the second active current command value and the second reactive current command value to obtain the second modulation wave;

[0163] The grid-connected control unit 1134 is also used to perform grid-connected control of the converter according to the second modulation wave.

[0164] In an exemplary embodiment, the active and reactive power calculation unit 1131 is further configured to transform both the grid voltage and the grid current from a three-phase stationary coordinate system to a synchronous rotating coordinate system, thereby obtaining the d-axis and q-axis components of the grid voltage and the grid current; and,

[0165] The actual active power is obtained by summing the product of the d-axis component of the grid voltage and the d-axis component of the grid current, and the product of the q-axis component of the grid voltage and the q-axis component of the grid current.

[0166] The actual reactive power is obtained by multiplying the q-axis component of the grid voltage by the d-axis component of the grid current, and by the difference between the product of the d-axis component of the grid voltage and the q-axis component of the grid current.

[0167] The converter soft-start device and converter soft-start method provided in this application belong to the same inventive concept, can solve the same technical problems, and achieve the same technical effects. Repeated content will not be repeated.

[0168] Each module in the aforementioned converter soft-start device can be implemented entirely or partially through software, hardware, or a combination thereof. These modules can be embedded in the processor of a computer device in hardware form or independent of it, or stored in the memory of a computer device in software form, so that the processor can call and execute the operations corresponding to each module.

[0169] In one exemplary embodiment, a converter is provided, which may include a controller. The controller includes a processor, memory, input / output (I / O) interfaces, and a communication interface. The processor, memory, and I / O interfaces are connected via a system bus, and the communication interface is connected to the system bus via the I / O interfaces. The processor of the controller provides computing and control capabilities. The memory of the controller includes a non-volatile storage medium and internal memory. The non-volatile storage medium stores an operating system, computer programs, and a database. The internal memory provides an environment for the operation of the operating system and computer programs in the non-volatile storage medium. The database of the controller stores data. The I / O interfaces of the controller are used for exchanging information between the processor and external devices. The communication interface of the controller is used for communicating with external terminals via a network connection. When the computer program is executed by the processor, it implements the converter soft-start method provided in any of the above embodiments.

[0170] Those skilled in the art will understand that the structure of the controller described above is only a partial structure related to the solution of this application, and does not constitute a limitation on the controller to which the solution of this application is applied. A specific controller may include more or fewer components, or combine certain components, or have different component arrangements.

[0171] In one exemplary embodiment, a converter is provided, including a memory and a processor, wherein the memory stores a computer program, and the processor executes the computer program to implement the converter soft-start method provided in any of the above embodiments.

[0172] The converter and converter soft-start method provided in the embodiments of this application belong to the same inventive concept, can solve the same technical problems, and achieve the same technical effects. Repeated content will not be repeated here.

[0173] In one exemplary embodiment, an energy storage system is provided, which includes an energy storage battery and a converter provided in any of the above embodiments.

[0174] The energy storage system and the converter soft-start method provided in this application belong to the same inventive concept, can solve the same technical problems, and achieve the same technical effects. Repeated content will not be repeated here.

[0175] In one exemplary embodiment, a computer-readable storage medium is provided having a computer program stored thereon, which, when executed by a processor, constitutes the converter soft-start method provided in any of the above embodiments.

[0176] 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 above methods. Any references to memory, databases, or other media used in the embodiments provided in this application can include at least one of non-volatile memory 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 application 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 application may be general-purpose processors, central processing units, graphics processing units, digital signal processors, programmable logic devices, quantum computing-based data processing logic devices, artificial intelligence (AI) processors, etc., and are not limited to these.

[0177] 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 application.

[0178] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of this 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 application, and these all fall within the protection scope of this application. Therefore, the protection scope of this application should be determined by the appended claims.

Claims

1. A soft-start method for a converter, characterized in that, The converter is used to connect to the power grid via a switch, and the method includes: When the switch is open, the grid voltage and the converter output voltage are obtained; The virtual current is determined based on the output voltage and the mains voltage; The converter is started up based on the virtual current; When the virtual current reaches zero, the switch is controlled to close; or when the virtual power reaches zero, the switch is controlled to close, wherein the virtual power is determined based on the virtual current.

2. The method according to claim 1, characterized in that, Determining the virtual current based on the output voltage and the grid voltage includes: The difference between the output voltage and the mains voltage is determined, and the virtual current is obtained based on the ratio of the difference to a preset virtual impedance.

3. The method according to claim 1 or 2, characterized in that, The virtual power includes virtual active power and virtual reactive power; The step of controlling the start-up of the converter based on the virtual current includes: Based on the grid voltage and the virtual current, active and reactive power calculations are performed to obtain the virtual active power and the virtual reactive power. Based on the virtual active power and the virtual reactive power, power outer loop closed-loop control is performed to obtain the first active current command value and the first reactive current command value. Based on the first active current command value and the first reactive current command value, current inner loop closed-loop control is performed to obtain the first modulation wave; The converter is started up based on the first modulation wave.

4. The method according to claim 3, characterized in that, The step of performing active and reactive power calculations based on the grid voltage and the virtual current to obtain the virtual active power and the virtual reactive power includes: The grid voltage and the virtual current are both transformed from the three-phase stationary coordinate system to the synchronous rotating coordinate system to obtain the d-axis and q-axis components of the grid voltage and the d-axis and q-axis components of the virtual current. The virtual active power is obtained by summing the product of the d-axis component of the grid voltage and the d-axis component of the virtual current, and the product of the q-axis component of the grid voltage and the q-axis component of the virtual current. The virtual reactive power is obtained by multiplying the q-axis component of the grid voltage by the d-axis component of the virtual current, and by the difference between the product of the d-axis component of the grid voltage and the q-axis component of the virtual current.

5. The method according to claim 1 or 2, characterized in that, The method further includes: When the switch is closed, the grid current is obtained; The converter is controlled to connect to the grid based on the grid current.

6. The method according to claim 5, characterized in that, The grid-connected control of the converter based on the grid current includes: Based on the grid voltage and the grid current, active and reactive power calculations are performed to obtain the actual active power and actual reactive power. Based on the actual active power and the actual reactive power, perform power outer loop closed-loop control to obtain the second active current command value and the second reactive current command value. Based on the second active current command value and the second reactive current command value, current inner loop closed-loop control is performed to obtain the second modulation wave; The converter is controlled to connect to the grid based on the second modulation wave.

7. The method according to claim 6, characterized in that, The step of performing active and reactive power calculations based on the grid voltage and grid current to obtain the actual active power and actual reactive power includes: The grid voltage and the grid current are both transformed from the three-phase stationary coordinate system to the synchronous rotating coordinate system to obtain the d-axis and q-axis components of the grid voltage and the grid current. The actual active power is obtained by summing the product of the d-axis component of the grid voltage and the d-axis component of the grid current, and the product of the q-axis component of the grid voltage and the q-axis component of the grid current. The actual reactive power is obtained by multiplying the q-axis component of the grid voltage by the d-axis component of the grid current, and by the difference between the product of the d-axis component of the grid voltage and the q-axis component of the grid current.

8. A soft-start device for a converter, characterized in that, The converter is used to connect to the power grid via a switch, and the device includes: A voltage acquisition module is used to acquire the grid voltage and the converter's output voltage when the switch is open; The virtual calculation module is used to determine the virtual current based on the output voltage and the grid voltage; A soft-start control module is used to control the start-up of the converter based on the virtual current, wherein the switch is closed when the virtual current reaches zero; or the switch is closed when the virtual power reaches zero, wherein the virtual power is determined based on the virtual current.

9. The apparatus according to claim 8, characterized in that, The virtual calculation module is also used to determine the difference between the output voltage and the grid voltage, and to obtain the virtual current based on the ratio of the difference to a preset virtual impedance.

10. The apparatus according to claim 8 or 9, characterized in that, The virtual power includes virtual active power and virtual reactive power; the soft-start control module includes an active and reactive power calculation unit, a power outer loop closed-loop control unit, a current inner loop closed-loop control unit, and a start control unit. The active and reactive power calculation unit is used to perform active and reactive power calculations based on the grid voltage and the virtual current to obtain the virtual active power and the virtual reactive power. The power outer loop closed-loop control unit is used to perform power outer loop closed-loop control based on the virtual active power and the virtual reactive power to obtain the first active current command value and the first reactive current command value. The current inner loop closed-loop control unit is used to perform current inner loop closed-loop control according to the first active current command value and the first reactive current command value to obtain the first modulation wave. The start-up control unit is used to start the converter according to the first modulation wave.

11. The apparatus according to claim 10, characterized in that, The active and reactive power calculation unit is also used to transform the grid voltage and the virtual current from the three-phase stationary coordinate system to the synchronous rotating coordinate system to obtain the d-axis and q-axis components of the grid voltage and the d-axis and q-axis components of the virtual current. as well as, The virtual active power is obtained by summing the product of the d-axis component of the grid voltage and the d-axis component of the virtual current, and the product of the q-axis component of the grid voltage and the q-axis component of the virtual current. as well as, The virtual reactive power is obtained by multiplying the q-axis component of the grid voltage by the d-axis component of the virtual current, and by the difference between the product of the d-axis component of the grid voltage and the q-axis component of the virtual current.

12. The apparatus according to claim 8 or 9, characterized in that, The device further includes: A current acquisition module is used to acquire the grid current when the switch is closed; The grid connection control module is used to perform grid connection control on the converter according to the grid current.

13. The apparatus according to claim 12, characterized in that, The grid-connected control module includes an active and reactive power calculation unit, a power outer loop closed-loop control unit, a current inner loop closed-loop control unit, and a grid-connected control unit. The active and reactive power calculation unit is used to perform active and reactive power calculations based on the grid voltage and the grid current to obtain the actual active power and actual reactive power. The power outer loop closed-loop control unit is used to perform power outer loop closed-loop control based on the actual active power and the actual reactive power to obtain the second active current command value and the second reactive current command value. The current inner loop closed-loop control unit is used to perform current inner loop closed-loop control according to the second active current command value and the second reactive current command value to obtain the second modulation wave; The grid-connected control unit is used to perform grid-connected control of the converter according to the second modulation wave.

14. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by the processor, it implements the soft-start method of the converter as described in any one of claims 1 to 7.

15. A converter, characterized in that, Includes a controller for performing the soft-start method for the converter as described in any one of claims 1-7.

16. An energy storage system, characterized in that, Including the converter as described in claim 15.

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