A grid-connected converter transient power control method

Abstract

The application discloses a grid-connected converter instantaneous power control method, and belongs to the technical field of power electronic conversion, which comprises the following steps: extracting positive sequence components and negative sequence components of grid voltage and grid-connected current in a two-phase static orthogonal coordinate system; obtaining instantaneous positive sequence, negative sequence active power and reactive power components of the grid-connected converter; decomposing active power instructions and reactive power instructions into positive sequence active power instructions, negative sequence active power instructions, positive sequence reactive power instructions and negative sequence reactive power instructions according to three different control targets; adjusting the positive sequence active power, the negative sequence active power, the positive sequence reactive power and the negative sequence reactive power by using a closed-loop control circuit; and generating driving control signals of the grid-connected converter for grid-connected converter instantaneous power control. The method can improve the grid adaptability and following capacity of the grid-connected converter under the premise of ensuring the control effect.

Description

Technical Field

[0001] This application belongs to the field of power electronic converter technology, specifically relating to a method for instantaneous power control of a grid-connected converter. Background Technology

[0002] As the interface unit between new energy power generation systems and the power grid, the control performance of grid-connected converters directly affects the economy and reliability of wind power generation systems. Therefore, research on grid-connected converter control strategies has always been a key focus for many experts and scholars.

[0003] Existing instantaneous power control schemes for grid-connected converters include control schemes based on switching meters, predictive power control schemes, and control schemes based on extended instantaneous power theory. In these schemes, the use of switching meters results in an unpredictable switching frequency for the inverter, leading to an unpredictable harmonic spectrum in the grid-connected current and increasing the design complexity of the filter. Predictive power control schemes are susceptible to fluctuations in inverter parameters, exhibiting low robustness. Control schemes based on extended instantaneous power theory are primarily used when grid-connected converters operate at unity power factor, failing to meet the requirements for variable power factor operation of grid-connected converters. Summary of the Invention

[0004] Purpose of the invention: The purpose of this application is to provide a method for instantaneous power control of grid-connected converters, which overcomes the defects of existing control schemes and improves the grid adaptability and following capability of grid-connected converters while ensuring control effect.

[0005] Technical solution: The instantaneous power control method for a grid-connected converter described in this application includes:

[0006] Extract the positive-sequence and negative-sequence components of the grid voltage and the grid-connected current in a two-phase stationary orthogonal coordinate system.

[0007] The instantaneous positive-sequence active power component, instantaneous negative-sequence active power component, instantaneous positive-sequence reactive power component, and instantaneous negative-sequence reactive power component of the grid-connected converter are obtained.

[0008] According to the control objectives, the active power command and reactive power command of the grid-connected converter are decomposed into positive sequence active power command, negative sequence active power command, positive sequence reactive power command and negative sequence reactive power command; the control objectives include eliminating the negative sequence component in the grid-connected current, eliminating the second harmonic fluctuation in the active power, and eliminating the second harmonic fluctuation in the reactive power.

[0009] The positive-sequence active power, negative-sequence active power, positive-sequence reactive power, and negative-sequence reactive power are adjusted separately using a closed-loop control circuit.

[0010] The drive control signal of the grid-connected converter is generated for instantaneous power control of the grid-connected converter.

[0011] In some embodiments, the grid voltage is a three-phase grid voltage, the grid-connected current is a three-phase grid-connected current, and the grid-connected converter is a three-phase grid-connected converter.

[0012] In some embodiments, the grid-connected converter is a voltage source converter based on a two-level topology circuit, a voltage source converter based on a three-level topology circuit, or a voltage source converter based on a multi-level topology circuit.

[0013] In some embodiments, the positive-sequence component and the negative-sequence component are extracted using a positive-negative sequence decomposition algorithm; the positive-negative sequence decomposition algorithm includes processing the grid voltage and grid-connected current through a 3 / 2 coordinate transformation and a delay signal cancellation algorithm, respectively.

[0014] In some embodiments, the amplitude of the positive sequence component of the grid voltage The amplitude of the negative sequence component of the grid voltage Calculate using the following formula:

[0015]

[0016] In the formula, The positive-sequence component of the grid voltage is the α-axis component in the two-phase stationary orthogonal coordinate system. The positive-sequence component of the grid voltage is the β-axis component in the two-phase stationary orthogonal coordinate system. The negative sequence component of the grid voltage is the α-axis component in the two-phase stationary orthogonal coordinate system. The negative sequence component of the grid voltage is the β-axis component in the two-phase stationary orthogonal coordinate system.

[0017] In some embodiments, the instantaneous positive-sequence active power component, the instantaneous negative-sequence active power component, the instantaneous positive-sequence reactive power component, and the instantaneous negative-sequence reactive power component of the grid-connected converter are obtained using the following calculation formulas:

[0018]

[0019]

[0020] In the formula, p 01 p is the instantaneous positive-sequence active component. 02 Let q be the instantaneous negative-sequence active component. 01 Let q be the instantaneous positive-sequence reactive power component. 02 The instantaneous negative-sequence reactive power component;

[0021] The positive-sequence component of the grid-connected current is the α-axis component in the two-phase stationary orthogonal coordinate system. The positive-sequence component of the grid-connected current is the β-axis component in the two-phase stationary orthogonal coordinate system. The negative sequence component of the grid-connected current is the α-axis component in the two-phase stationary orthogonal coordinate system. The negative sequence component of the grid-connected current is the β-axis component in the two-phase stationary orthogonal coordinate system.

[0022] In some embodiments, the control target is switched in the following manner:

[0023] When the grid-connected converter takes output active power as the main control target, if the negative sequence imbalance of the grid voltage is less than the threshold value, the grid-connected converter operates to eliminate the negative sequence component in the grid current; if the negative sequence imbalance of the grid voltage is greater than the threshold value, the grid-connected converter operates to eliminate the second harmonic fluctuation in the active power.

[0024] When the grid-connected converter takes output reactive power as the main control objective, if the negative sequence imbalance of the grid voltage is less than the threshold value, the grid-connected converter operates to eliminate the negative sequence component in the grid current; if the negative sequence imbalance of the grid voltage is greater than the threshold value, the grid-connected converter operates to eliminate the second harmonic fluctuation in the reactive power.

[0025] When the grid-connected converter takes the output of three-phase symmetrical grid-connected current as the main control objective, the grid-connected converter operates in accordance with the method of eliminating the negative sequence component in the grid-connected current.

[0026] In some embodiments, the positive-sequence active power command, negative-sequence active power command, positive-sequence reactive power command, and negative-sequence reactive power command are calculated according to the following formulas in the process of eliminating the negative-sequence component in the grid-connected current:

[0027]

[0028] In the formula, P * Q is the active power command for the grid-connected converter. * The reactive power command for the grid-connected converter. The positive-sequence active power instruction. The negative-order active power instruction. The positive-sequence reactive power instruction. This refers to the negative-sequence reactive power instruction;

[0029] In the process of eliminating second harmonic fluctuations in active power, the positive-sequence active power command, negative-sequence active power command, positive-sequence reactive power command, and negative-sequence reactive power command are calculated according to the following formula:

[0030]

[0031] The first variable D1 and the second variable D2 are calculated using the following formula:

[0032]

[0033] In the process of eliminating second harmonic fluctuations in reactive power, the positive-sequence active power command, negative-sequence active power command, positive-sequence reactive power command, and negative-sequence reactive power command are calculated according to the following formula:

[0034]

[0035] In some embodiments, the active power command is issued by the upper-level controller or generated by the DC voltage control loop of the grid-connected converter, and the reactive power command is issued by the upper-level controller or directly set to 0.

[0036] In some embodiments, the closed-loop control loop includes adjusting the difference between the power command and the instantaneous power value via a controller, and adding a decoupling component.

[0037] In some embodiments, the difference includes: the difference between the positive-sequence active power command and the instantaneous positive-sequence active power component, the difference between the negative-sequence active power command and the instantaneous negative-sequence active power component, the difference between the positive-sequence reactive power command and the instantaneous positive-sequence reactive power component, and the difference between the negative-sequence reactive power command and the instantaneous negative-sequence reactive power component.

[0038] In some embodiments, the controller includes a proportional-integral controller or a proportional-integral-resonant controller.

[0039] In some embodiments, in the closed-loop control loop, the decoupling component of the positive-sequence active power command control loop is +ω. S Lq 01 The decoupling component of the negative-sequence active power command control loop is -ω. S Lq 02 The decoupling component of the positive-sequence reactive power command control loop is -ω. S Lp 01 The decoupling component of the negative-sequence reactive power command control loop is +ω. S Lp 02 ;

[0040] Where, ω S Where ω is the grid angular frequency, and L is the AC-side filter inductance value of the grid-connected converter.

[0041] In some embodiments, the reference voltage vector required for the grid-connected converter to achieve the control objective is extracted from the output of the closed-loop control loop; the output of the closed-loop control loop includes: the output of the positive-sequence active power command control loop, the output of the negative-sequence active power command control loop, the output of the positive-sequence reactive power command control loop, and the output of the negative-sequence reactive power command control loop.

[0042] In some embodiments, the method includes: extracting a reference voltage vector required for the grid-connected converter to achieve the control objective from the output of the closed-loop control loop using a voltage command calculation module;

[0043] The voltage command calculation module includes a positive sequence reference voltage vector calculation module, a negative sequence reference voltage vector calculation module, and a reference voltage vector calculation module;

[0044] The calculation formula of the positive sequence reference voltage vector calculation module is as follows:

[0045]

[0046] In the formula, and These are the α-axis and β-axis components of the positive-sequence reference voltage vector in the two-phase stationary orthogonal coordinate system, respectively. This is the output result of the positive sequence active power command control loop. This is the output result of the positive sequence reactive power command control loop;

[0047] The calculation formula of the negative sequence reference voltage vector calculation module is as follows:

[0048]

[0049] In the formula, and These are the α-axis and β-axis components of the negative-sequence reference voltage vector in the two-phase stationary orthogonal coordinate system, respectively. This is the output result of the negative-sequence active power command control loop. The output result of the negative sequence reactive power command control loop;

[0050] The calculation formula of the reference voltage vector calculation module is as follows:

[0051]

[0052] In the formula, and These are the α-axis and β-axis components of the reference voltage vector in the two-phase stationary orthogonal coordinate system, respectively.

[0053] In some embodiments, the drive control signal is generated using a sectorless modulation algorithm;

[0054] The sectorless modulation algorithm includes: a sinusoidal pulse width carrier modulation algorithm suitable for two-level three-phase voltage source topologies, a sinusoidal pulse width modulation algorithm with third harmonic injection, and a sectorless space voltage vector modulation algorithm or a carrier modulation algorithm suitable for three-level three-phase voltage source topologies or a carrier modulation algorithm suitable for multi-level three-phase voltage source topologies.

[0055] Beneficial effects: Compared with the prior art, the instantaneous power control method for grid-connected converters in this application directly uses the instantaneous power of the grid-connected converter as the control object, eliminating the current control loop in the traditional control method, and improving the speed and accuracy of the grid-connected converter in responding to the power demand of the grid. By setting three different control targets, the method can select the appropriate control target according to the grid voltage imbalance and application, thereby improving the grid adaptability of the grid-connected converter. The entire process from the issuance of control commands to the generation of grid-connected converter drive control signals is executed in a two-phase stationary orthogonal coordinate system, without phase-locked loops and rotating coordinate transformations, saving a lot of trigonometric function calculations, simplifying the algorithm structure, improving the grid following capability of the grid-connected converter, saving a lot of hardware computing resources, and facilitating digital implementation. Attached Figure Description

[0056] The technical solution and other beneficial effects of this application will become apparent from the following detailed description of specific embodiments in conjunction with the accompanying drawings.

[0057] Figure 1 A schematic flowchart illustrating the instantaneous power control method for a grid-connected converter provided in an embodiment of this application;

[0058] Figure 2 This is a schematic diagram of the structure of the two-level converter in the embodiments of this application;

[0059] Figure 3 This is a schematic diagram of a three-level converter structure based on diode clamping in an embodiment of this application;

[0060] Figure 4 This application describes a modular multilevel converter based on a full-bridge module and / or a half-bridge module in its embodiments.

[0061] Figure 5 This application describes a delta converter based on H-bridge cascade in the embodiments of this application;

[0062] Figure 6 This is a schematic diagram illustrating one of the active power command generation processes of a grid-connected converter in an embodiment of this application.

[0063] Figure 7 When the control objective of eliminating the negative sequence component in the grid-connected current is adopted in the embodiments of this application, the dynamic and static characteristics of the grid-connected converter are as follows:

[0064] Figure 8 for Figure 7 Local curves of dynamic and static characteristics in the range of 2.8–3 seconds;

[0065] Figure 9 When the control objective of eliminating second harmonic fluctuations in active power is adopted in the embodiments of this application, the dynamic and static characteristics of the grid-connected converter are as follows;

[0066] Figure 10 for Figure 9 Local curves of dynamic and static characteristics in the range of 2.8–3 seconds;

[0067] Figure 11 When the control objective of eliminating second harmonic fluctuations in reactive power is adopted in the embodiments of this application, the dynamic and static characteristics of the grid-connected converter are as follows;

[0068] Figure 12 for Figure 11 Local curves of dynamic and static characteristics in the range of 2.8–3s. Detailed Implementation

[0069] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0070] The applicant found that current control strategies for grid-connected converters fall into two categories: grid voltage-oriented current closed-loop control and direct power control (DPC). In grid current closed-loop control, the active and reactive power injected into the grid by the grid-connected converter is indirectly regulated through the closed-loop control of the grid current after active-reactive power decomposition. Therefore, the dynamic and static characteristics of the active-reactive power output of the grid-connected converter heavily depend on the quality of the grid current control algorithm. Direct power control, based on instantaneous power theory, directly adjusts the inverter's output voltage vector according to the error between the instantaneous active-reactive power and the target value. The entire process does not include a current control loop. Furthermore, after the grid connection of renewable energy generation systems, power system dispatch mainly regulates the generation system by issuing active and reactive power commands. Therefore, adopting a direct power control strategy for grid-connected converters will have significant advantages.

[0071] Meanwhile, the applicant also discovered that, because the actual grid voltage is not ideally three-phase symmetrical, a certain degree of imbalance will persist, and significant three-phase voltage imbalance may occur when a grid fault occurs. When the grid-connected converter operates under an unbalanced grid, double-frequency fluctuations will occur in the DC-side voltage of the grid-connected converter and the power injected into the grid, which will cause distortion and a sharp increase in the grid-connected current, seriously affecting the grid-connected converter's input current quality and equipment safety, making the system unable to operate safely and reliably. At the same time, the design specifications for wind power converters require that grid-connected converters operate normally when the grid voltage imbalance is no greater than 4%, and can maintain grid-connected operation when the voltage imbalance is greater than 4% but less than 8%. Therefore, researching direct power control strategies for grid-connected converters under unbalanced grid voltage is of great significance.

[0072] In view of this, embodiments of this application provide an instantaneous power control method for grid-connected converters, which is applicable to three-phase grid-connected converters.

[0073] In some embodiments, the instantaneous power control method for the grid-connected converter includes:

[0074] Extract the positive-sequence and negative-sequence components of the grid voltage and the grid-connected current in a two-phase stationary orthogonal coordinate system.

[0075] The instantaneous positive-sequence active power component, instantaneous negative-sequence active power component, instantaneous positive-sequence reactive power component, and instantaneous negative-sequence reactive power component of the grid-connected converter are obtained.

[0076] According to the control objectives, the active and reactive power commands of the grid-connected converter are decomposed into positive sequence active power commands, negative sequence active power commands, positive sequence reactive power commands, and negative sequence reactive power commands. The control objectives include eliminating the negative sequence component in the grid-connected current, eliminating the second harmonic fluctuation in the active power, and eliminating the second harmonic fluctuation in the reactive power.

[0077] The positive-sequence active power, negative-sequence active power, positive-sequence reactive power, and negative-sequence reactive power are adjusted separately using a closed-loop control circuit.

[0078] Generate drive control signals for the power transistors of the grid-connected converter.

[0079] In some embodiments, the instantaneous power control method for the grid-connected converter includes: acquiring grid voltage and grid-connected current.

[0080] In some embodiments, the instantaneous power control method for the grid-connected converter includes: acquiring three-phase grid voltage and three-phase grid-connected current.

[0081] In some embodiments, the instantaneous power control method for the grid-connected converter includes: extracting the positive-sequence component and negative-sequence component of the grid voltage and the positive-sequence component and negative-sequence component of the grid current in a two-phase stationary orthogonal coordinate system using a positive-negative-sequence decomposition algorithm.

[0082] In some embodiments, the instantaneous power control method for the grid-connected converter includes: decomposing the active and reactive power commands of the grid-connected converter into positive-sequence active power commands, negative-sequence active power commands, positive-sequence reactive power commands, and negative-sequence reactive power commands through a control command calculation module for positive and negative sequence active and reactive power. That is, in this embodiment, the control command calculation module for positive and negative sequence active and reactive power can decompose the active and reactive power commands of the grid-connected converter according to three different control objectives: eliminating the negative-sequence component in the grid-connected current, eliminating second-harmonic frequency fluctuations in the active power, and eliminating second-harmonic frequency fluctuations in the reactive power.

[0083] In some embodiments, to eliminate the negative sequence component in the grid-connected current, the positive sequence active power command, negative sequence active power command, positive sequence reactive power command, and negative sequence reactive power command can be calculated according to the following formula:

[0084]

[0085] In the formula, P * Q * These are the active power command and reactive power command for the grid-connected converter, respectively. This is a positive-order active instruction. This is a negative-order active instruction. This is a positive-sequence reactive power instruction. This is a negative-order reactive power instruction;

[0086] To eliminate second-harmonic fluctuations in active power, the positive-sequence active power command, negative-sequence active power command, positive-sequence reactive power command, and negative-sequence reactive power command can be calculated using the following formula:

[0087]

[0088] The magnitude of the positive sequence component of the grid voltage. This represents the magnitude of the negative sequence component of the grid voltage. Calculate using the following formula:

[0089]

[0090] Variables D1 and D2 are calculated using the following formula:

[0091]

[0092] To eliminate second-harmonic fluctuations in reactive power, the positive-sequence active power command, negative-sequence active power command, positive-sequence reactive power command, and negative-sequence reactive power command can be calculated using the following formula:

[0093]

[0094] In some embodiments, the instantaneous power control method for the grid-connected converter includes: using a control structure with four sets of closed-loop control loops combined with decoupling components to adjust the positive-sequence active power, negative-sequence active power, positive-sequence reactive power and negative-sequence reactive power respectively.

[0095] In some embodiments, the instantaneous power control method for the grid-connected converter includes: extracting a reference voltage vector required for the grid-connected converter to achieve a control target from the output results of four grid-connected control loops.

[0096] In some embodiments, the instantaneous power control method for the grid-connected converter includes: extracting the reference voltage vector required for the grid-connected converter to achieve the control target from the output results of four grid-connected control loops through a voltage command calculation module.

[0097] Specifically, such as Figure 1 As shown, in some embodiments, three-phase grid voltage and three-phase grid-connected current are collected, and after undergoing 3 / 2 coordinate transformation and delay signal cancellation methods, the positive-sequence and negative-sequence components of the grid voltage and grid-connected current in a two-phase stationary orthogonal coordinate system are extracted. Based on instantaneous power theory and the definitions of positive-sequence and negative-sequence power components, the positive-sequence component p of the instantaneous active power is calculated. 01 and negative order component p 02 The positive-sequence component q of instantaneous reactive power 01 and negative order component q 02 The system's power command P * and Q * The control command calculation module for positive and negative sequence active and reactive power decomposes the power command into positive sequence active power command according to different control objectives. Negative-order active instructions Positive sequence reactive power instructions and negative sequence reactive power instructions Subsequently, closed-loop regulation is performed on each instruction and cross-decoupling terms are added to generate a reference voltage vector, which is then used to generate the drive control signal for the grid-connected converter through a sectorless modulation algorithm.

[0098] In some embodiments, the grid-connected converter is a voltage source converter based on a two-level topology circuit, a voltage source converter based on a three-level topology circuit, or a voltage source converter based on a multi-level topology circuit.

[0099] For details, please refer to Figure 2 , Figure 2 The present invention illustrates the structure of a two-level converter, which belongs to the category of voltage source converters based on two-level topology circuits. This structure can adopt the instantaneous power control method for grid-connected converters provided in the embodiments of this application.

[0100] Please see Figure 3 , Figure 3 The present invention illustrates the structure of a three-level converter based on diode clamping, which belongs to the category of voltage source converters based on three-level topology circuits. This structure can also adopt the instantaneous power control method for grid-connected converters provided in the embodiments of this application.

[0101] Please see Figure 4 , Figure 4 A modular multilevel converter based on a full-bridge module and / or a half-bridge module is shown, where 1 is a half-bridge module and 2 is a full-bridge module. It belongs to the category of voltage source converters based on multilevel topology circuits. This structure can also adopt the instantaneous power control method for grid-connected converters provided in the embodiments of this application.

[0102] Please see Figure 5 , Figure 5 An H-bridge cascaded angle converter is shown, where 2 is a full-bridge module, which belongs to the category of voltage source converter based on multi-level topology circuit. This structure can also adopt the instantaneous power control method for grid-connected converters provided in the embodiments of this application.

[0103] In some embodiments, the positive and negative sequence decomposition algorithm includes a 3 / 2 coordinate transformation and a delay signal cancellation (DSC) module. Specifically, in a two-phase stationary orthogonal coordinate system, the positive and negative sequence decomposition method of the three-phase grid voltage based on the delay signal cancellation algorithm is shown in the following equation. The positive and negative sequence decomposition method of the three-phase grid current can also be implemented according to the following equation, where T is the fundamental period:

[0104]

[0105] In some embodiments, the calculation formulas for the instantaneous positive-sequence active power component, instantaneous negative-sequence active power component, instantaneous positive-sequence reactive power component, and instantaneous negative-sequence reactive power component of the grid-connected converter are as follows:

[0106]

[0107]

[0108] In the formula, p 01 p is the instantaneous positive-sequence active component. 02 For the instantaneous negative-order active component, q 01 For the instantaneous positive-sequence reactive power component, q 02 This is the instantaneous negative-sequence reactive power component; This represents the α-axis component of the positive-sequence grid voltage in a two-phase stationary orthogonal coordinate system. Let β be the β-axis component of the grid voltage in a two-phase stationary orthogonal coordinate system with positive sequence components. This represents the α-axis component of the negative sequence component of the grid voltage in a two-phase stationary orthogonal coordinate system. This refers to the β-axis component of the negative sequence component of the grid voltage in a two-phase stationary orthogonal coordinate system. This represents the α-axis component of the positive-sequence component of the grid-connected current in a two-phase stationary orthogonal coordinate system. This represents the β-axis component of the positive-sequence component of the grid-connected current in a two-phase stationary orthogonal coordinate system. This represents the α-axis component of the negative sequence component of the grid-connected current in a two-phase stationary orthogonal coordinate system. This represents the β-axis component of the negative sequence component of the grid-connected current in a two-phase stationary orthogonal coordinate system.

[0109] In some embodiments, the three different control objectives of the instantaneous power control method for the grid-connected converter can be switched in the following manner:

[0110] When the grid-connected converter takes the output active power as the main control target, if the negative sequence imbalance of the grid voltage is less than the threshold value, the grid-connected converter operates to eliminate the negative sequence component in the grid current; if the negative sequence imbalance of the grid voltage is greater than the threshold value, the grid-connected converter operates to eliminate the second harmonic fluctuation in the active power.

[0111] When the grid-connected converter takes the output reactive power as the main control objective, if the negative sequence imbalance of the grid voltage is less than the threshold value, the grid-connected converter operates to eliminate the negative sequence component in the grid current; if the negative sequence imbalance of the grid voltage is greater than the threshold value, the grid-connected converter operates to eliminate the second harmonic fluctuation in the reactive power.

[0112] When the grid-connected converter takes the output of three-phase symmetrical grid-connected current as the main control objective, the grid-connected converter can operate to eliminate the negative sequence component in the grid-connected current, regardless of the value of the negative sequence imbalance of the grid voltage.

[0113] In some embodiments, the active power command of the grid-connected converter can be issued by the upper-level controller or generated by the DC voltage control loop of the grid-connected converter, while the reactive power command of the grid-connected converter is usually issued by the upper-level controller or directly set to 0.

[0114] like Figure 6 As shown, in some embodiments, the active power command P of the grid-connected converter... * Inverter DC side voltage command The square of the actual DC bus voltage u dc The difference between the squares is generated after adjustment by the PI controller.

[0115] In some embodiments, the closed-loop control loop includes adjusting the difference between the power command and the instantaneous power value via a controller, and adding a decoupling component.

[0116] In some embodiments, the difference between the power command and the instantaneous power value includes: the difference between the positive-sequence active power command and the instantaneous positive-sequence active power component, the difference between the negative-sequence active power command and the instantaneous negative-sequence active power component, the difference between the positive-sequence reactive power command and the instantaneous positive-sequence reactive power component, and the difference between the negative-sequence reactive power command and the instantaneous negative-sequence reactive power component.

[0117] In some embodiments, the controller described above includes a proportional-integral controller or a proportional-integral-resonant controller.

[0118] In some embodiments, the closed-loop control loop includes four sets of control loops, and the decoupling component has different expressions in different control loops: the decoupling component of the positive-sequence active power command control loop is +ω. S Lq 01 The decoupling component of the negative-sequence active power command control loop is -ω. S Lq 02 The decoupling component of the positive-sequence reactive power command control loop is -ω. S Lp 01 The decoupling component of the negative-sequence reactive power command control loop is +ω. S Lp 02 ; where ω S Where is the grid angular frequency, L is the AC-side filter inductance value of the grid-connected converter, and p 01 p is the instantaneous positive-sequence active component. 02 For the instantaneous negative-order active component, q 01 For the instantaneous positive-sequence reactive power component, q 02 It is the instantaneous negative-sequence reactive component.

[0119] In some embodiments, the output of the closed-loop control loop includes: the output of the positive-sequence active power command control loop. Output result of negative sequence active power command control loop Output of the positive sequence reactive power command control loop Output result of negative sequence reactive power command control loop

[0120] In some embodiments, the reference voltage vector required for the grid-connected converter to achieve the control target is extracted from the output of the closed-loop control loop by the voltage command calculation module; the voltage command calculation module includes a positive sequence reference voltage vector calculation module, a negative sequence reference voltage vector calculation module, and a reference voltage vector calculation module.

[0121] The formula for calculating the positive sequence reference voltage vector is as follows:

[0122]

[0123] In the formula, and These are the α-axis and β-axis components of the positive-sequence reference voltage vector in a two-phase stationary orthogonal coordinate system, respectively.

[0124] The formula for calculating the negative sequence reference voltage vector is as follows:

[0125]

[0126] In the formula, and These are the α-axis and β-axis components of the negative sequence reference voltage vector in a two-phase stationary orthogonal coordinate system, respectively.

[0127] The calculation formula for the reference voltage vector calculation module is shown in the following equation.

[0128]

[0129] In the formula, and These are the α-axis and β-axis components of the reference voltage vector in a two-phase stationary orthogonal coordinate system, respectively.

[0130] In some embodiments, the instantaneous power control method for the grid-connected converter utilizes a sectorless modulation algorithm to generate drive control signals for the power transistors of the grid-connected converter. The sectorless modulation algorithm includes a sinusoidal pulse width carrier modulation algorithm (SPWM) suitable for two-level three-phase voltage source topologies, a sinusoidal pulse width modulation algorithm with third harmonic injection, and a sectorless space vector modulation algorithm (SVPWM), or a carrier modulation algorithm suitable for three-level three-phase voltage source topologies, or a carrier modulation algorithm suitable for multi-level three-phase voltage source topologies.

[0131] This application also provides specific experimental data for the instantaneous power control method of the grid-connected converter. The relevant parameters of the wind power grid-connected converter are: AC grid voltage rated at 690V, rated frequency at 50Hz, inverter rated capacity at 300kVA, AC side connected reactor at 1.0mH, DC side supporting capacitor at 3.0mF, DC side voltage target at 1100V, switching frequency at 3kHz, and the grid-connected converter operating at full power with a reactive power command of 0. When the A-phase grid voltage amplitude drops by 40%, the dynamic and static characteristics of the grid-connected converter are observed under three different control targets. Figures 7-8 , Figures 9-10 and Figures 11-12 As shown. Figures 7-8 The embodiment shown aims to eliminate negative sequence current in the grid-connected current. To make the curves in the figure clearer, Figure 8 for Figure 7 The curve after 2.8 seconds, Figures 9-10The embodiment shown aims to eliminate second harmonic fluctuations in active power. To make the curves in the figure clearer, Figure 10 for Figure 9 The curve after 2.8 seconds, Figures 11-12 The embodiment shown aims to eliminate second harmonic fluctuations in reactive power. To make the curves in the figure clearer, Figure 12 for Figure 11 The curve after 2.8 seconds. In each curve graph, from top to bottom, it represents the grid voltage e of phase A. sa / Grid-connected current i sa Three-phase grid-connected current i sa / i sb / i sc DC bus voltage u dc The instantaneous active power p and instantaneous reactive power q of the grid-connected converter output.

[0132] It is evident that this instantaneous power control method for grid-connected converters improves the speed and accuracy of the converter's response to grid power demand. By setting three different control objectives, the appropriate control objective can be selected based on the grid voltage imbalance and application scenario, thereby enhancing the grid adaptability of the converter. The entire process from the issuance of control commands to the generation of grid-connected converter drive control signals is executed in a two-phase stationary orthogonal coordinate system, improving the grid following capability of the converter, saving significant hardware computing resources, and facilitating digital implementation.

[0133] In the above embodiments, the descriptions of each embodiment have different focuses. For parts not described in detail in a certain embodiment, please refer to the relevant descriptions in other embodiments.

[0134] The above provides a detailed description of the instantaneous power control method for a grid-connected converter provided in the embodiments of this application, and uses specific examples to illustrate the principles and implementation methods of this application. The description of the above embodiments is only for the purpose of helping to understand the technical solutions and core ideas of this application. Those skilled in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or make equivalent substitutions for some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A method for instantaneous power control of a grid-connected converter, characterized in that, include: Extract the positive-sequence and negative-sequence components of the grid voltage and the grid-connected current in a two-phase stationary orthogonal coordinate system. The instantaneous positive-sequence active power component, instantaneous negative-sequence active power component, instantaneous positive-sequence reactive power component, and instantaneous negative-sequence reactive power component of the grid-connected converter are obtained. The instantaneous positive-sequence active power component is... The instantaneous negative-sequence active power component. The instantaneous positive-sequence reactive power component, The instantaneous negative-sequence reactive power component; According to the control objectives, the active power command and reactive power command of the grid-connected converter are decomposed into positive sequence active power command, negative sequence active power command, positive sequence reactive power command and negative sequence reactive power command; the control objectives include eliminating the negative sequence component in the grid-connected current, eliminating the second harmonic fluctuation in the active power, and eliminating the second harmonic fluctuation in the reactive power. The positive-sequence active power, negative-sequence active power, positive-sequence reactive power, and negative-sequence reactive power are adjusted separately using a closed-loop control circuit. In the closed-loop control loop, the decoupling component of the positive-sequence active power command control loop is: The decoupling component of the negative-sequence active power command control loop is The decoupling component of the positive-sequence reactive power command control loop is: The decoupling component of the negative sequence reactive power command control loop is ; in, The angular frequency of the power grid. L This refers to the AC-side filter inductance value of the grid-connected converter; The drive control signal of the grid-connected converter is generated for instantaneous power control of the grid-connected converter.

2. The instantaneous power control method for grid-connected converters according to claim 1, characterized in that, The grid-connected converter is a voltage source converter based on a two-level topology circuit, a voltage source converter based on a three-level topology circuit, or a voltage source converter based on a multi-level topology circuit.

3. The instantaneous power control method for grid-connected converters according to claim 1, characterized in that, The positive-sequence component and the negative-sequence component are extracted using a positive-negative sequence decomposition algorithm; the positive-negative sequence decomposition algorithm includes processing the grid voltage and grid-connected current through a 3 / 2 coordinate transformation and a delay signal elimination algorithm, respectively.

4. The instantaneous power control method for grid-connected converters according to claim 1, characterized in that, The amplitude of the positive sequence component of the grid voltage The amplitude of the negative sequence component of the grid voltage Calculate using the following formula: In the formula, The positive-sequence component of the grid voltage is the α-axis component in the two-phase stationary orthogonal coordinate system. The positive sequence component of the grid voltage in the two-phase stationary orthogonal coordinate system. β Axial components, The negative sequence component of the grid voltage in the two-phase stationary orthogonal coordinate system. α Axial components, The negative sequence component of the grid voltage in the two-phase stationary orthogonal coordinate system. β Axial components.

5. The instantaneous power control method for grid-connected converters according to claim 4, characterized in that, The instantaneous positive-sequence active power component, instantaneous negative-sequence active power component, instantaneous positive-sequence reactive power component, and instantaneous negative-sequence reactive power component of the grid-connected converter are obtained using the following calculation formulas: In the formula, The positive sequence component of the grid-connected current in the two-phase stationary orthogonal coordinate system. α Axial components, The positive sequence component of the grid-connected current in the two-phase stationary orthogonal coordinate system. β Axial components, The negative sequence component of the grid-connected current is defined in the two-phase stationary orthogonal coordinate system. α Axial components, The negative sequence component of the grid-connected current is defined in the two-phase stationary orthogonal coordinate system. β Axial components.

6. The instantaneous power control method for grid-connected converters according to claim 1, characterized in that, The control target is switched in the following manner: When the grid-connected converter takes output active power as the main control target, if the negative sequence imbalance of the grid voltage is less than the threshold value, the grid-connected converter operates to eliminate the negative sequence component in the grid current; if the negative sequence imbalance of the grid voltage is greater than the threshold value, the grid-connected converter operates to eliminate the second harmonic fluctuation in the active power. When the grid-connected converter takes output reactive power as the main control objective, if the negative sequence imbalance of the grid voltage is less than the threshold value, the grid-connected converter operates to eliminate the negative sequence component in the grid current; if the negative sequence imbalance of the grid voltage is greater than the threshold value, the grid-connected converter operates to eliminate the second harmonic fluctuation in the reactive power. When the grid-connected converter takes the output of three-phase symmetrical grid-connected current as the main control objective, the grid-connected converter operates in accordance with the method of eliminating the negative sequence component in the grid-connected current.

7. The instantaneous power control method for grid-connected converters according to claim 4, characterized in that, In the process of eliminating the negative sequence component in the grid-connected current, the positive sequence active power command, negative sequence active power command, positive sequence reactive power command, and negative sequence reactive power command are calculated according to the following formula: In the formula, This refers to the active power command for the grid-connected converter. This refers to the reactive power command of the grid-connected converter. The positive-sequence active power instruction. The negative-order active power instruction. The positive-sequence reactive power instruction. This refers to the negative-sequence reactive power instruction; In the process of eliminating second harmonic fluctuations in active power, the positive-sequence active power command, negative-sequence active power command, positive-sequence reactive power command, and negative-sequence reactive power command are calculated according to the following formula: First variable D 1. Second variable D 2. Calculate using the following formula: In the process of eliminating second harmonic fluctuations in reactive power, the positive-sequence active power command, negative-sequence active power command, positive-sequence reactive power command, and negative-sequence reactive power command are calculated according to the following formula: 。 8. The instantaneous power control method for grid-connected converters according to claim 1, characterized in that, The active power command is issued by the upper-level controller or generated by the DC voltage control loop of the grid-connected converter, and the reactive power command is issued by the upper-level controller or directly set to 0.

9. The instantaneous power control method for grid-connected converters according to claim 1, characterized in that, The closed-loop control circuit includes adjusting the difference between the power command and the instantaneous power value through the controller, and adding a decoupling component.

10. The instantaneous power control method for a grid-connected converter according to claim 9, characterized in that, The difference includes: the difference between the positive-sequence active power command and the instantaneous positive-sequence active power component, the difference between the negative-sequence active power command and the instantaneous negative-sequence active power component, the difference between the positive-sequence reactive power command and the instantaneous positive-sequence reactive power component, and the difference between the negative-sequence reactive power command and the instantaneous negative-sequence reactive power component.

11. The instantaneous power control method for a grid-connected converter according to claim 9, characterized in that, The controller includes a proportional-integral controller or a proportional-integral-resonant controller.

12. The instantaneous power control method for grid-connected converters according to claim 1, characterized in that, The reference voltage vector required for the grid-connected converter to achieve the control target is extracted from the output of the closed-loop control loop; the output of the closed-loop control loop includes: the output of the positive-sequence active power command control loop, the output of the negative-sequence active power command control loop, the output of the positive-sequence reactive power command control loop, and the output of the negative-sequence reactive power command control loop.

13. The instantaneous power control method for grid-connected converters according to claim 4, characterized in that, include: The voltage command calculation module extracts the reference voltage vector required for the grid-connected converter to achieve the control target from the output of the closed-loop control loop. The voltage command calculation module includes a positive sequence reference voltage vector calculation module, a negative sequence reference voltage vector calculation module, and a reference voltage vector calculation module; The calculation formula of the positive sequence reference voltage vector calculation module is as follows: In the formula, and The positive sequence reference voltage vectors are respectively in the two-phase stationary orthogonal coordinate system. α Axial components and β Axial components, This is the output result of the positive sequence active power command control loop. This is the output result of the positive sequence reactive power command control loop; The calculation formula of the negative sequence reference voltage vector calculation module is as follows: In the formula, and The negative sequence reference voltage vectors are respectively in the two-phase stationary orthogonal coordinate system. α Axial components and β Axial components, This is the output result of the negative-sequence active power command control loop. The output result of the negative sequence reactive power command control loop; The calculation formula of the reference voltage vector calculation module is as follows: In the formula, and The reference voltage vectors are respectively in the two-phase stationary orthogonal coordinate system. α Axial components and β Axial components.

14. The instantaneous power control method for a grid-connected converter according to claim 1, characterized in that, The drive control signal is generated using a sectorless modulation algorithm; The sectorless modulation algorithm includes: a sinusoidal pulse width carrier modulation algorithm suitable for two-level three-phase voltage source topologies, a sinusoidal pulse width modulation algorithm with third harmonic injection, and a sectorless space voltage vector modulation algorithm or a carrier modulation algorithm suitable for three-level three-phase voltage source topologies or a carrier modulation algorithm suitable for multi-level three-phase voltage source topologies.

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