Negative sequence current control and parameter optimization method in case of inaccurate orientation of negative sequence angle of power grid

Abstract

The invention discloses a negative-sequence current control and parameter optimization method for inaccurate orientation of a power grid negative-sequence angle of an energy storage converter, which comprises the following steps of: (1) sampling voltage and current by the energy storage converter, carrying out data processing, and then obtaining a negative-sequence current reference given value through a negative-sequence current control algorithm; (2) compensating a reference given value and a feedback value of the negative sequence current loop through active disturbance rejection control; and (3) optimizing PI controller parameters by using a particle swarm algorithm to obtain negative-sequence control voltage, and realizing accurate tracking control of negative-sequence current. According to the invention, negative sequence current control can be realized without knowing the negative sequence angle of the power grid, the system robustness is ensured, the problems of poor tracking effect of the PI controller and the like caused by manual parameter setting are avoided, and rapid convergence of a given value and a feedback value is ensured.

Description

Technical Field

[0001] This invention belongs to the field of energy storage converter control, specifically relating to a method for negative sequence current control and parameter optimization when the negative sequence angle orientation of an energy storage converter in the power grid is inaccurate. Background Technology

[0002] Under conditions of grid voltage imbalance or distortion, the phase-locked loop (PLL) of the power storage converter (PCS) may experience orientation inaccuracies. This can cause traditional control strategies based on the dq coordinate system to fail, particularly making it difficult to control the negative sequence current caused by the imbalance. Improper control of the negative sequence current not only causes AC current waveform distortion and increases losses, but also induces second-order ripple and power oscillations in the DC bus voltage, which may trigger protection mechanisms or damage equipment in severe cases.

[0003] Currently, the main methods for controlling negative-sequence current when PLL orientation is inaccurate include the dual-synchronous rotating coordinate system method, and the positive-negative sequence separation and PLL enhancement method based on delay signal cancellation. The core idea of ​​the dual-synchronous rotating coordinate system method is to simultaneously establish two synchronous rotating coordinate systems (positive-sequence and negative-sequence), with the negative-sequence synchronous rotating coordinate system rotating at an angular velocity of -ωt. In this coordinate system, the negative-sequence component behaves as a DC component and can be controlled by a PI controller. However, this method still relies on the accuracy of the PLL phase-locked loop. The positive-negative sequence separation and PLL enhancement method based on delay signal cancellation focuses on improving the orientation accuracy of the PLL itself under voltage imbalance / distortion, thus laying the foundation for subsequent traditional dq-based control (including negative-sequence control). It utilizes DSC technology to quickly and accurately separate the positive-sequence voltage component specifically for the PLL input; however, this method requires an additional separation algorithm (DSC), increasing complexity, and the dynamic response of the PLL itself is affected by the DSC stage. Summary of the Invention

[0004] This invention addresses the problems in existing technologies where inaccurate PLL orientation leads to the failure of traditional control based on the dq coordinate system, particularly the inability of the negative sequence current component to be effectively adjusted by the PI controller under an incorrect reference coordinate system, and the poor control effect caused by manually setting PI parameter values. The purpose is to provide a method for negative sequence current control and parameter optimization when the negative sequence angle orientation of the energy storage converter is inaccurate.

[0005] This invention is achieved through the following technical solution:

[0006] A method for negative sequence current control and parameter optimization when the negative sequence angle orientation of an energy storage converter in the power grid is inaccurate includes the following steps:

[0007] (I) The energy storage converter samples the voltage and current and processes the data, and then obtains the negative sequence current reference value through the negative sequence current control algorithm;

[0008] The sampling voltage and current of the energy storage converter are specifically: sampling grid-side phase voltage u a u b u c and the three-phase current i on the inverter side a i b i c ;

[0009] The data processing specifically includes the following steps:

[0010] (i) The grid-side phase voltage u a u b u c and the three-phase current i on the inverter side a i b i c After the abc / αβ coordinate transformation, the current i in the αβ coordinate system is obtained. α i β and voltage u in the αβ coordinate system α u β ;

[0011] (ii) Using a positive / negative order separation module based on a second-order generalized integrator (PNSS-SOGI) from i α i β and u α u β Separate the negative sequence current i in the αβ coordinate system αNeg i βNeg and negative sequence voltage u αNeg u βNeg ;

[0012] (iii) The negative sequence current i αNeg i βNeg and negative sequence voltage u αNeg u βNeg After αβ / dq coordinate transformation, the negative sequence current i in the dq coordinate system is obtained. dNeg i qNeg and negative sequence voltage u dNeg u qNeg ;

[0013] (iv) The negative sequence voltage u dNeg u qNeg The amplitude of the grid-side negative sequence voltage u is obtained using the amplitude calculation formula. gNegAmp ;

[0014] The formula for calculating the amplitude is:

[0015]

[0016] In the formula: u gNegAmp This represents the magnitude of the negative sequence voltage on the grid side, in units of μ. αNeg u βNeg The negative sequence voltage is given in the αβ coordinate system, and the unit is V.

[0017] The process of obtaining the negative sequence current reference value through the negative sequence current control algorithm specifically includes the following steps:

[0018] (i) Set the target value I of the negative sequence active current of the power grid. PNeg and the target value of negative sequence reactive current I QNeg Calculate the negative sequence active power P of the power grid. Neg and negative sequence reactive power Q Neg ;

[0019] The target value of negative sequence active current I of the power grid PNeg and the target value of negative sequence reactive current I QNeg The calculation formula is:

[0020]

[0021] In the formula: I PNeg The target value for negative sequence active current is expressed in A; I QNeg The target value for negative sequence reactive current is given in A; k PNeg k is the negative-sequence active current proportionality coefficient, dimensionless; QNeg The negative sequence reactive current proportionality coefficient, dimensionless; u gNegAmp I represents the magnitude of the negative sequence voltage on the grid side, in V. N This is the rated current of the energy storage converter, in amperes (A).

[0022] The negative sequence active power P of the power grid Neg and negative sequence reactive power Q Neg The calculation formula is:

[0023]

[0024] In the formula: P Neg Q represents negative-sequence active power, measured in W. Neg This refers to negative sequence reactive power, measured in W; u gNegAmp I represents the magnitude of the negative sequence voltage on the grid side, in V. PNeg The target value of negative sequence active current in the power grid, in A; I QNeg This represents the target value for negative sequence reactive current, in A.

[0025] (ii) Calculate the reference setpoint i of the negative sequence current control loop in the dq coordinate system. dNegRef i qNegRef;

[0026] The formula for calculating the reference setpoint of the negative sequence current control loop in the dq coordinate system is as follows:

[0027]

[0028] In the formula: i dNegRef i qNegRef The reference setpoint for the negative sequence current control loop in the dq coordinate system is given in A; u dNeg u qNeg P represents the negative sequence voltage in the dq coordinate system, in V. Neg Q represents the negative-sequence active power of the power grid, measured in W. Neg This represents negative sequence reactive power, measured in W.

[0029] The formula for calculating the reference setpoint of the negative sequence current control loop in the dq coordinate system is derived by using the negative sequence voltage u in the dq coordinate system. dNeg u qNeg The negative sequence active power P of the power grid Neg and negative sequence reactive power Q Neg The derivation is obtained by substituting into the following formula;

[0030]

[0031] In the formula P Neg Q represents negative-sequence active power, measured in W. Neg This refers to negative sequence reactive power, measured in W; u dNeg u qNeg The negative sequence voltage in the dq coordinate system is expressed in V; i dNeg i qNeg The negative sequence current is expressed in dq coordinates, in A.

[0032] (II) Compensate the reference setpoint and feedback value of the negative sequence current loop through active disturbance rejection control;

[0033] Specifically:

[0034] (Ⅱ-ⅰ) The negative sequence current i in the dq coordinate system dNeg i qNeg After obtaining the extended state observer (ESO) and perturbation compensation,

[0035] The mathematical expression for the extended state observer is:

[0036]

[0037] In the formula: e is the difference between the observer's estimate and the actual measurement; i d / qdq axis measured current value; β1 and β2 are the observer bandwidth and the velocity determining the disturbance estimation, respectively; z1 and z2 are the estimated current and the total disturbance, respectively; b0 is the control gain; α is the nonlinearity intensity; δ is the nonlinearity interval threshold of the fal function; v d / q This is the compensation value;

[0038] The mathematical expression for the disturbance compensation is:

[0039]

[0040] In the formula: v d / q inv The final inverter dq-axis compensation command value; v0 is the initial compensation value; b0 is the control gain; z2 is the total disturbance.

[0041] (Ⅱ-ⅱ) Set the reference setpoint i of the negative sequence current control loop in the dq coordinate system. dNegRef i qNegRef Obtained through nonlinear error feedback

[0042] The mathematical expression for the nonlinear error feedback is:

[0043]

[0044] In the formula: v0 is the initial compensation value; k v α is the dynamic response speed coefficient; δ is the nonlinear intensity; δ is the nonlinear interval threshold of the fal function; k d To suppress high-frequency noise figure; e is the difference between the observer estimate and the actual measurement;

[0045] (II-III) Comparison and The difference is then input into the PI controller;

[0046] (III) The particle swarm optimization algorithm optimizes the PI controller parameters to obtain the negative sequence control voltage and realizes accurate tracking control of the negative sequence current.

[0047] Specifically, the following steps are included:

[0048] (III-I) Randomly initialize k p k i And its velocity, and calculate the fitness of each particle;

[0049] (III-II) Update position by tracking individual best (pbest) and group best (gbest);

[0050] The expression for the update rule is:

[0051]

[0052] In the formula: Let be the velocity of the i-th particle when the iteration number is k+1; Let be the velocity of the i-th particle when the iteration number is k. This represents the position of the i-th particle when the iteration number is k+1. pbest represents the position of the i-th particle when the iteration number is k. i The optimal tracking value for the i-th particle is: x is the particle's position; i is the i-th particle; k is the number of iterations; v is the particle's velocity; ω is the inertia weight, ranging from 0.4 to 0.9; c1 and c2 are learning factors, set to 2.0; r1 and r2 are random numbers, ranging from [0,1].

[0053] (III-III) If the current fitness is better than the tracking individual best (pbest) or the group best (gbest), then replace it; finally, terminate when the maximum number of iterations is reached or gbest converges;

[0054] (Ⅲ-ⅳ) The error value of the active disturbance rejection control output is given to the particle swarm optimization algorithm k p k i After the PI controller with parameters is applied, the negative sequence control voltage u in the αβ coordinate system is obtained through dq / αβ coordinate transformation. αβNeg .

[0055] The beneficial effects of this invention are:

[0056] This invention provides a method for negative sequence current control and parameter optimization when the negative sequence angle orientation of an energy storage converter is inaccurate. Negative sequence current control can be achieved without knowing the grid's negative sequence angle. First, voltage and current are sampled and processed. A negative sequence current reference setpoint is obtained through a negative sequence current control algorithm. Active disturbance rejection control ensures system robustness by dynamically compensating for the setpoint and feedback value in real time. Particle swarm optimization optimizes the PI controller parameters, avoiding problems such as poor PI controller tracking caused by manually setting parameters, and ensuring rapid convergence of the setpoint and feedback value. Attached Figure Description

[0057] Figure 1 This is a schematic diagram of the energy storage converter topology and data processing principle of the present invention;

[0058] Figure 2 This is a block diagram of the negative sequence current and parameter optimization control of the present invention;

[0059] Figure 3 This is a flowchart of the particle swarm optimization algorithm for optimizing the PI parameters of the negative-order current loop in this invention;

[0060] Figure 4 This is the phase voltage waveform of the power grid under asymmetrical fault according to the present invention;

[0061] Figure 5 The per-unit value u of the negative sequence voltage amplitude of the power grid in this invention. gNegAmp_pu Negative sequence active current I of the power grid PNeg and negative sequence reactive current I QNeg The actual value;

[0062] Figure 6 The negative sequence control voltage u of this invention αβNeg Waveform diagram.

[0063] For those skilled in the art, other related figures can be obtained from the above figures without any creative effort. Detailed Implementation

[0064] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0065] Example 1

[0066] An example verification is conducted using an asymmetrical fault in a 690V AC power grid system. Figure 4 The phase voltage waveforms during grid asymmetric faults are presented. During grid asymmetric faults, the energy storage converter should absorb an appropriate amount of negative-sequence dynamic reactive current to prevent the grid asymmetry from worsening. The specific steps for negative-sequence current control and parameter optimization methods when the grid negative-sequence angle orientation of the energy storage converter is inaccurate are as follows:

[0067] (I) Energy storage converter topology and data processing schematic diagram as follows Figure 1 As shown, the phase voltage u on the sampling network side a u b u c Inverter-side three-phase current i a i b i c After the abc / αβ coordinate transformation, we get i α i β and u α u β Subsequently, the negative sequence current i in the αβ coordinate system is separated by a positive-negative sequence separation module based on a second-order generalized integrator (PNSS-SOGI). αNeg i βNeg and negative sequence voltage u αNeg u βNeg After further αβ / dq coordinate transformation, the negative sequence current i in the dq coordinate system can be obtained. dNeg i qNeg and negative sequence voltage u dNeg u qNeg Negative sequence voltage u αβNegThe negative sequence voltage amplitude u is obtained through the amplitude calculation formula. gNegAmp .

[0068] (II) Setting the negative sequence active current I of the power grid PNeg and negative sequence reactive current I QNeg The target value is then used to calculate the negative-sequence active power P of the power grid. Neg and negative sequence reactive power Q Neg .

[0069] The formula for calculating the target value is:

[0070]

[0071] In the formula: I PNeg The target value of negative sequence active current in the power grid, in A; I QNeg The target value for negative sequence reactive current of the power grid, in A; u gNegAmp_pu I represents the per-unit value of the negative sequence voltage amplitude of the power grid, in V. N For, the unit is A;

[0072] (III) Calculate the reference setpoint i of the negative sequence current control loop in the dq coordinate system. dNegRef i qNegRef . will u dNeg u qNeg and P Neg Q Neg Substituting into the formula, we can derive i dNegRef i qNegRef i dNegRef i qNegRef The calculation formula is:

[0073]

[0074] In the formula: u gNegAmp_pu This represents the per-unit value of the negative sequence voltage amplitude of the power grid, in units of ;

[0075] (IV) Compensate the reference setpoint and feedback value of the negative sequence current loop through active disturbance rejection control. Figure 2 The control block diagram of active disturbance rejection control is given, i dNeg i qNeg After obtaining the extended state observer (ESO) and perturbation compensation, i dNegRef i qNegRef Obtained through nonlinear error feedback Subsequently and The error is then fed into the PI controller after comparison.

[0076] (V) Optimize the PI parameters using the particle swarm optimization algorithm. Figure 3A flowchart of the particle swarm optimization algorithm for optimizing the PI parameters of the negative-sequence current loop is given. First, k is randomly initialized. p k i The system calculates the fitness of each particle based on its velocity and the swarm optimization algorithm. Then, it updates the position by tracking the individual best (pbest) and swarm best (gbest). If the current fitness is better than pbest or gbest, it is replaced. Finally, the process terminates when the maximum number of iterations is reached or gbest converges. The error value output by the active disturbance rejection control is fed into the particle swarm optimization algorithm. p k i After the PI controller with parameters is applied, the negative sequence control voltage u in the αβ coordinate system is obtained through dq / αβ coordinate transformation. αβNeg .

[0077] (VI) with Figure 4 Taking the phase voltage waveform of the asymmetrical fault grid shown as an example, simulation verification is performed. The negative sequence control voltage u obtained after the above working process is... αβNeg like Figure 5 As shown, the per-unit value of the negative sequence voltage amplitude of the power grid is u. gNegAmp_pu Negative sequence active current I of the power grid PNeg and negative sequence reactive current I QNeg The actual value is as follows Figure 6 As shown, this invention can achieve precise tracking and control of negative sequence current, proving the effectiveness and feasibility of this invention.

[0078] The method of this invention does not require a phase-locked loop (PLL) to directional grid negative sequence angle. By setting target values ​​for grid-side negative sequence active current and negative sequence reactive current, and based on the negative sequence current control algorithm, the negative sequence control current in the dq coordinate system can be output. The given value and feedback value are compensated by active disturbance rejection control and compared. At the same time, the negative sequence current loop PI parameters are optimized by particle swarm optimization algorithm to ensure the negative sequence current control effect.

[0079] The method of this invention avoids the failure of traditional control based on the dq coordinate system caused by the inaccuracy of PLL orientation. In particular, under the wrong reference coordinate system, the negative sequence current component cannot be effectively adjusted by the PI controller. Furthermore, the PI parameter optimization through particle swarm optimization avoids the problem of poor control effect caused by manually setting the PI parameter value.

[0080] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for controlling and optimizing negative-sequence current and parameters when the negative-sequence angle orientation of a power grid is inaccurate, characterized in that: Includes the following steps: (I) The energy storage converter samples the voltage and current and processes the data, and then obtains the negative sequence current reference value through the negative sequence current control algorithm; (II) Compensate the reference setpoint and feedback value of the negative sequence current loop through active disturbance rejection control; (III) The particle swarm optimization algorithm optimizes the PI controller parameters to obtain the negative sequence control voltage and realizes accurate tracking control of the negative sequence current.

2. The method for controlling and optimizing negative sequence current and parameters when the negative sequence angle orientation of the power grid is inaccurate, as described in claim 1, is characterized in that: The energy storage converter sampling voltage and current includes the sampling grid-side phase voltage u. a u b u c and the three-phase current i on the inverter side a i b i c .

3. The method for controlling and optimizing negative-sequence current and parameters when the negative-sequence angle orientation of the power grid is inaccurate, as described in claim 1, is characterized in that: The data processing in step (I) specifically includes the following steps: (i) The grid-side phase voltage u a u b u c and the three-phase current i on the inverter side a i b i c After abc / αβ coordinate transformation, we get i α i β and u α u β ; (ii) Using a positive / negative order separation module based on a second-order generalized integrator, from i αβ and u αβ Separate the negative sequence current i in the αβ coordinate system αNeg i βNeg and negative sequence voltage u αNeg u βNeg ; (iii) The negative sequence current i αNeg i βNeg and negative sequence voltage u αNeg u βNeg After αβ / dq coordinate transformation, the negative sequence current i in the dq coordinate system is obtained. dNeg i qNeg and negative sequence voltage u dNeg u qNeg ; (iv) The negative sequence voltage u dNeg u qNeg The amplitude of the grid-side negative sequence voltage u is obtained using the amplitude calculation formula. gNegAmp .

4. The method for controlling and optimizing negative sequence current and parameters when the negative sequence angle orientation of the power grid is inaccurate, as described in claim 3, is characterized in that: The formula for calculating the amplitude is: In the formula: u gNegAmp This represents the magnitude of the negative sequence voltage on the grid side, in units of μ. αNeg u βNeg This represents the negative sequence voltage in the αβ coordinate system, expressed in V.

5. The method for controlling and optimizing negative-sequence current and parameters when the negative-sequence angle orientation of the power grid is inaccurate, as described in claim 1, is characterized in that: The step (I) of obtaining the negative sequence current reference value through the negative sequence current control algorithm specifically includes the following steps: (i) Set the target value I of the negative sequence active current of the power grid. PNeg and the target value of negative sequence reactive current I QNeg Calculate the negative sequence active power P of the power grid. Neg and negative sequence reactive power Q Neg ; (ii) Calculate the reference setpoint i of the negative sequence current control loop in the dq coordinate system. dNegRef i qNegRef .

6. The method for controlling and optimizing negative sequence current and parameters when the negative sequence angle orientation of the power grid is inaccurate, as described in claim 5, is characterized in that: The target value I of the negative sequence active current of the power grid PNeg and the target value of negative sequence reactive current I QNeg The calculation formula is: In the formula: I PNeg This represents the target value for negative sequence active current, in A. I QNeg The target value for negative sequence reactive current is given in A; k PNeg k is the negative-sequence active current proportionality coefficient, dimensionless; QNeg This is the negative sequence reactive current proportionality coefficient, which is dimensionless. u gNegAmp I represents the magnitude of the negative sequence voltage on the grid side, in V. N This is the rated current of the energy storage converter, in amperes (A). The negative sequence active power P of the power grid Neg and negative sequence reactive power Q Neg The calculation formula is: In the formula: P Neg Q represents negative-sequence active power, measured in W. Neg This refers to negative sequence reactive power, measured in W; u gNegAmp I represents the magnitude of the negative sequence voltage on the grid side, in V. PNeg This represents the target value of the negative-sequence active current of the power grid, in A. I QNeg This represents the target value for negative sequence reactive current, expressed in amperes (A).

7. The method for controlling and optimizing negative-sequence current and parameters when the negative-sequence angle orientation of the power grid is inaccurate, as described in claim 5, is characterized in that: The formula for calculating the reference setpoint of the negative sequence current control loop in the dq coordinate system is as follows: In the formula: i dNegRef i qNegRef The reference setpoint for the negative sequence current control loop in the dq coordinate system is given in A; u dNeg u qNeg P represents the negative sequence voltage in the dq coordinate system, in V. Neg Q represents the negative-sequence active power of the power grid, measured in W. Neg This represents negative sequence reactive power, measured in W.

8. The method for controlling and optimizing negative-sequence current and parameters when the negative-sequence angle orientation of the power grid is inaccurate, as described in claim 1, is characterized in that: Step (II) specifically includes the following steps: (Ⅱ-ⅰ) The negative sequence current i in the dq coordinate system dNeg i qNeg After obtaining the extended state observer and perturbation compensation (Ⅱ-ⅱ) Set the reference setpoint i of the negative sequence current control loop in the dq coordinate system. dNegRef i qNegRef Obtained through nonlinear error feedback (II-III) Comparison and The difference is then input into the PI controller.

9. The method for controlling and optimizing negative-sequence current and parameters when the negative-sequence angle orientation of the power grid is inaccurate, as described in claim 8, is characterized in that: The mathematical expression for the extended state observer is: In the formula: e is the difference between the observer's estimate and the actual measurement; i d / q denoted as dq-axis measured current value; β1 and β2 are the observer bandwidth and the velocity determining the disturbance estimation, respectively; z1 and z2 are the estimated current and the total disturbance, respectively; b0 is the control gain; α is the nonlinearity intensity; δ is the threshold value for the nonlinear interval of the fal function; v d / q This is the compensation value; The mathematical expression for the disturbance compensation is: In the formula: v d / q inv The final inverter dq-axis compensation command value; v0 is the initial compensation value; b0 is the control gain; z2 is the total disturbance. The mathematical expression for the nonlinear error feedback is: In the formula: v0 is the initial compensation value; k v α is the dynamic response speed coefficient; α is the nonlinear intensity; δ is the threshold value for the nonlinear interval of the fal function; k d To suppress high-frequency noise; e is the difference between the observer estimate and the actual measurement.

10. The method for controlling and optimizing negative-sequence current and parameters when the negative-sequence angle orientation of the power grid is inaccurate, as described in claim 1, is characterized in that: Step (III) specifically includes the following steps: (III-I) Randomly initialize k p k i And its velocity, and calculate the fitness of each particle; (III-II) Update position by tracking individual best (pbest) and group best (gbest); The expression for the update rule is: In the formula: Let be the velocity of the i-th particle when the iteration number is k+1; Let be the velocity of the i-th particle when the iteration number is k. This represents the position of the i-th particle when the iteration number is k+1. pbest represents the position of the i-th particle when the iteration number is k. i The optimal tracking value for the i-th particle is: x is the particle's position; i is the i-th particle; k is the number of iterations; v is the particle's velocity; ω is the inertia weight, ranging from 0.4 to 0.9; c1 and c2 are learning factors, set to 2.0; r1 and r2 are random numbers, ranging from [0,1]. (III-III) If the current fitness is better than the tracking individual optimal or the group optimal, then replace it; finally, terminate when the maximum number of iterations or the group optimal convergence is reached; (Ⅲ-ⅳ) The error value of the active disturbance rejection control output is given to the particle swarm optimization algorithm k p k i After the PI controller with parameters is applied, the negative sequence control voltage u in the αβ coordinate system is obtained through dq / αβ coordinate transformation. αβNeg .

Images