A method for controlling power quality of energy storage converter

Abstract

The present invention provides a method for controlling the power quality of an energy storage converter. When the voltage state is abnormal, an impedance estimation method is used to estimate the impedance of the grid connection point line. A voltage control optimization algorithm is executed based on the obtained impedance information and voltage information to calculate the capacity for voltage control and perform voltage control. When the voltage state is normal or the converter has residual capacity for harmonic control after executing the voltage control optimization algorithm, the grid connection point line current is sampled, and its third and fifth harmonic amplitudes and phases are obtained through fast Fourier transform. After obtaining the effective value of the grid connection point voltage at the current moment, a harmonic control optimization algorithm is executed and harmonic control is performed. The strategy disclosed by the present invention improves the flexibility of power quality control of the energy storage converter and the capacity utilization rate of the energy storage converter.

Description

Technical Field

[0001] The present invention relates to the technical field of power systems, and in particular to a method for managing power quality of an energy storage converter. Background Art

[0002] The integration of large-scale power electronic equipment and renewable energy into distribution networks has led to severe harmonic pollution. The voltage fluctuations caused by power fluctuations and randomness have also deteriorated system voltage quality. Energy storage converters, with their fast four-quadrant power regulation capabilities, can rapidly support active and reactive power and balance load fluctuations. Once properly controlled, they can also perform the same active filtering functions as APFs, achieving comprehensive power quality management for low-voltage distribution networks.

[0003] Current research on using energy storage converters to manage power quality in distribution networks focuses primarily on the design of control strategies for energy storage converters. This approach involves dividing the converter's power quality management capacity into a fixed voltage management capacity and a harmonic management capacity. This power quality management solution is easy to implement, as it allocates two fixed capacities for voltage management and harmonic management, respectively. However, its problem lies in its limited flexibility: when the actual capacity required for voltage management exceeds the fixed allocated capacity, voltage management requirements may not be fully met. When the required capacity for voltage management is less than the fixed allocated capacity, the remaining capacity is not fully utilized for harmonic management, resulting in wasted capacity. Summary of the Invention

[0004] In response to the deficiencies of the prior art, the present invention provides a method for managing the power quality of an energy storage converter. The present invention optimizes the capacity allocation of the energy storage converter to improve the flexibility of the energy storage converter's power management and the capacity utilization of the energy storage converter.

[0005] The technical solution of the present invention is: a method for controlling the power quality of an energy storage converter, comprising the following steps:

[0006] S1) Obtaining the effective value information of the grid connection point voltage and judging the voltage status of the distribution network;

[0007] S2) When the voltage state is low voltage or overvoltage, use the impedance estimation method to estimate the line impedance of the grid connection point;

[0008] S3), first executing the voltage management optimization algorithm 1 based on the estimated impedance information and voltage information to calculate the active power and reactive power of the energy storage converter required for voltage management;

[0009] S4) Determine whether the energy storage converter has residual capacity based on the active power and reactive power of the energy storage converter calculated by the voltage management optimization algorithm 1; if there is no residual capacity, execute step S5);

[0010] If there is any remaining capacity, execute voltage management optimization algorithm 2 to calculate the active power and reactive power of the energy storage converter required for voltage management; then execute step S5);

[0011] S5) Calculate the capacity of the energy storage converter occupied by the active power and reactive power required for voltage control;

[0012] S6) When the voltage state is normal or after executing the voltage management optimization algorithm, determine whether the energy storage converter has remaining capacity for harmonic control; if so, execute step S7);

[0013] S7) Sample the grid connection point line current, obtain the amplitude and phase of the third harmonic and fifth harmonic of the grid connection point line current through fast Fourier transform, and obtain the effective value of the grid connection point voltage at the current moment, then execute the harmonic control optimization algorithm and start harmonic compensation.

[0014] Preferably, in step S2), if the current grid connection point voltage state is low voltage, the impedance estimation of the grid connection point line specifically includes the following steps:

[0015] S211) First, record the effective value of the current grid connection point voltage , then control the energy storage converter to output 20% to 25% of the rated capacity of reactive power, and record the effective value of the grid connection point voltage after the reactive power is output ; Then calculate the reactance of the grid connection point line according to formula (2) ,Right now:

[0016] (2)

[0017] Where, is the reactive power output by the energy storage converter; It is the effective value of the grid connection point voltage when no reactive power is output; is the effective value of the grid connection point voltage after reactive power is output;

[0018] S212) The energy storage converter stops outputting reactive power and records the effective value of the grid connection point voltage at the current moment again. Then control the energy storage converter to output 20% to 25% of the rated capacity of active power, and record the effective value of the grid connection point voltage after the active power is output. , and calculate the resistance of the grid connection point line according to formula (3) ;Right now:

[0019] (3)

[0020] Where, is the active power output by the energy storage converter; It is the effective value of the grid connection point voltage when no active power is output; is the effective value of the grid connection point voltage after the active power is output;

[0021] S213) Output the grid connection point impedance estimation result.

[0022] Preferably, in step S2), if the current grid connection point voltage state is overvoltage, the impedance estimation of the grid connection point line specifically includes the following steps:

[0023] S221) First, record the effective value of the current grid connection point voltage , then control the energy storage converter to absorb 20% to 25% of the rated capacity of reactive power, and record the effective value of the grid connection point voltage after absorbing the reactive power , and calculate the reactance of the grid connection point line according to formula (4) ,Right now:

[0024] ; (4)

[0025] Where, is the effective value of the grid connection point voltage when no reactive power is absorbed; It is the effective value of the grid connection point voltage after absorbing reactive power; It is the reactive power absorbed by the energy storage converter;

[0026] S222) The energy storage converter stops absorbing reactive power and records the effective value of the grid connection point voltage at the current moment again. Then control the energy storage converter to absorb 20% to 25% of the rated capacity of active power, and record the effective value of the grid connection point voltage after absorbing the active power. , calculate the resistance of the grid connection point line according to formula (5) ;Right now:

[0027] ; (5)

[0028] Where, It is the effective value of the grid connection point voltage when no active power is absorbed; It is the effective value of the grid connection point voltage after absorbing active power; is the active power absorbed by the energy storage converter;

[0029] S223) Output the grid connection point impedance estimation result.

[0030] As a preferred embodiment, in step S3), first obtain the effective value of the grid connection point voltage at the current moment, and then execute the voltage management optimization algorithm 1. The voltage management optimization algorithm 1 adopts the particle swarm optimization algorithm. If low voltage management is performed, the objective function Defined as:

[0031] ; (6)

[0032] Calculate the active power and reactive power corresponding to its maximum value through formula (6);

[0033] If overvoltage control is carried out, the objective function Defined as:

[0034] ; (7)

[0035] The active power and reactive power corresponding to the minimum value of the objective function are calculated by formula (7);

[0036] At the same time, the constraints of voltage management optimization algorithm 1 are defined as:

[0037] ; (8)

[0038] Where, The active power of the energy storage converter solved by the voltage management optimization algorithm 1; The reactive power of the energy storage converter solved by the voltage management optimization algorithm 1; , indicating low voltage status; , indicating overvoltage status; The effective value of the grid connection point voltage before executing the voltage management optimization algorithm 1; is the capacity of the energy storage converter.

[0039] As a preferred embodiment, in step S4), the criterion 1 is used for judgment in the low voltage state; if the judgment result is that there is no remaining capacity, the active power of the energy storage converter solved by the voltage management optimization algorithm 1 is and reactive power As a reference value, control the power output by the energy storage converter and execute step S5);

[0040] In the overvoltage state, the second criterion is used for judgment; if the judgment result is that there is no remaining capacity, the active power of the energy storage converter solved by the voltage management optimization algorithm 1 is and reactive power As a reference value, the power absorbed by the energy storage converter is controlled, and step S5 is executed).

[0041] As a preferred method, in step S4), if there is any remaining capacity, the voltage management optimization algorithm 2 is executed to calculate the minimum capacity of the energy storage converter that can be used to manage the voltage to the normal range under low voltage or overvoltage conditions and the corresponding active power and reactive power; the voltage management optimization algorithm 2 adopts the particle swarm optimization algorithm; the objective function of the voltage management optimization algorithm 2 is and constraints are defined as:

[0042] ; (11)

[0043] ; (12)

[0044] Where, The active power of the energy storage converter solved by voltage management optimization algorithm 2; The reactive power of the energy storage converter solved by voltage management optimization algorithm 2; is the capacity of the energy storage converter;

[0045] In the low voltage state, the active power corresponding to the minimum capacity of the energy storage converter will be occupied and reactive power As a reference value, it controls the power output by the energy storage converter;

[0046] In the overvoltage state, the active power corresponding to the minimum capacity of the energy storage converter will be occupied and reactive power As a reference value, it controls the power absorbed by the energy storage converter.

[0047] As a preference, in step S5), when the energy storage converter has no remaining capacity, the active power and reactive power required for voltage management occupy the capacity of the energy storage converter. ;

[0048] When the energy storage converter has surplus capacity, the active power and reactive power required for voltage management occupy the capacity of the energy storage converter. ;Right now:

[0049] ; (13)

[0050] ; (14)

[0051] Where, The active power of the energy storage converter solved by the voltage management optimization algorithm 1; The reactive power of the energy storage converter solved by the voltage management optimization algorithm 1; , indicating low voltage status; , indicating overvoltage status; The active power of the energy storage converter solved by voltage management optimization algorithm 2; The reactive power of the energy storage converter solved by voltage management optimization algorithm 2.

[0052] As a preference, in step S7), the objective function of the harmonic control optimization algorithm is And the constraints are:

[0053] ; (16)

[0054] ; (17)

[0055] Where, is the third harmonic amplitude in the line current at the grid connection point; is the third harmonic compensation amount; is the fifth harmonic amplitude in the line current at the grid connection point; is the fifth harmonic compensation amount; The effective value of the grid connection point voltage before executing the harmonic control optimization algorithm; is the remaining capacity of the energy storage converter.

[0056] The beneficial effects of the present invention are:

[0057] 1. The present invention estimates the line impedance of the grid connection point through an impedance estimation method, executes a voltage management optimization algorithm based on the impedance information and the voltage effective value information, and performs a harmonic control optimization algorithm if there is surplus capacity, thereby improving the flexibility of the power quality management of the energy storage converter;

[0058] 2. When the capacity required for voltage management exceeds the allocated capacity, the present invention can meet the voltage management requirements through dynamic optimization allocation of capacity; when the capacity required for voltage management is less than the allocated capacity, the remaining capacity can be fully used for harmonic management through dynamic optimization allocation of capacity, thereby improving the utilization rate of the energy storage converter capacity. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] Figure 1 It is a flow chart of the method of the present invention;

[0060] Figure 2 Detailed flow diagram of the method of the present invention;

[0061] Figure 3 This is a schematic diagram of the power quality pollution source and energy storage converter connected to the distribution network structure according to an embodiment of the present invention. DETAILED DESCRIPTION

[0062] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings:

[0063] like Figure 1-2 As shown, this embodiment provides a method for managing power quality of an energy storage converter, comprising the following steps:

[0064] S1) Obtaining the effective value information of the grid connection point voltage and judging the voltage status of the distribution network;

[0065] When the controller of the energy storage converter obtains the effective value data of the grid connection point voltage, it determines the distribution network voltage status by the following formula, namely:

[0066] ; (1)

[0067] Where, It is the judgment result after the voltage value is judged; is the effective value of the current voltage at the grid connection point; is the effective value of the rated voltage; It is the maximum acceptable effective value of the fluctuating voltage.

[0068] S2) When the voltage state is low voltage or overvoltage, use the impedance estimation method to estimate the line impedance of the grid connection point;

[0069] If the current grid connection point voltage state is low voltage, the impedance estimation of the grid connection point line specifically includes the following steps:

[0070] S211) First, record the effective value of the current grid connection point voltage , then control the energy storage converter to output 20% to 25% of the rated capacity of reactive power, and record the effective value of the grid connection point voltage after the reactive power is output ; Then calculate the reactance of the grid connection point line according to formula (2) ,Right now:

[0071] (2)

[0072] Where, is the reactive power output by the energy storage converter; It is the effective value of the grid connection point voltage when no reactive power is output; is the effective value of the grid connection point voltage after reactive power is output;

[0073] S212) The energy storage converter stops outputting reactive power and records the effective value of the grid connection point voltage at the current moment again. Then control the energy storage converter to output 20% to 25% of the rated capacity of active power, and record the effective value of the grid connection point voltage after the active power is output. , and calculate the resistance of the grid connection point line according to formula (3) ;Right now:

[0074] (3)

[0075] Where, is the active power output by the energy storage converter; It is the effective value of the grid connection point voltage when no active power is output; is the effective value of the grid connection point voltage after the active power is output;

[0076] S213) Output the grid connection point impedance estimation result.

[0077] If the current grid connection point voltage state is overvoltage, the impedance estimation of the grid connection point line specifically includes the following steps:

[0078] S221) First, record the effective value of the current grid connection point voltage , then control the energy storage converter to absorb 20% to 25% of the rated capacity of reactive power, and record the effective value of the grid connection point voltage after absorbing the reactive power , and calculate the reactance of the grid connection point line according to formula (4) ,Right now:

[0079] ; (4)

[0080] Where, is the effective value of the grid connection point voltage when no reactive power is absorbed; It is the effective value of the grid connection point voltage after absorbing reactive power; It is the reactive power absorbed by the energy storage converter;

[0081] S222) The energy storage converter stops absorbing reactive power and records the effective value of the grid connection point voltage at the current moment again. Then control the energy storage converter to absorb 20% to 25% of the rated capacity of active power, and record the effective value of the grid connection point voltage after absorbing the active power. , calculate the resistance of the grid connection point line according to formula (5) ;Right now:

[0082] ; (5)

[0083] Where, It is the effective value of the grid connection point voltage when no active power is absorbed; It is the effective value of the grid connection point voltage after absorbing active power; is the active power absorbed by the energy storage converter;

[0084] S223) Output the grid connection point impedance estimation result.

[0085] S3) Execute the voltage management optimization algorithm 1 based on the estimated impedance information and voltage information to calculate the active power and reactive power of the energy storage converter required for voltage management; the details are as follows:

[0086] First, obtain the effective value of the grid connection point voltage at the current moment, and then execute the voltage management optimization algorithm 1. The voltage management optimization algorithm 1 adopts the particle swarm optimization algorithm. If low voltage management is performed, the objective function Defined as:

[0087] ; (6)

[0088] Calculate the active power and reactive power corresponding to its maximum value through formula (6);

[0089] If overvoltage control is carried out, the objective function Defined as:

[0090] ; (7)

[0091] The active power and reactive power corresponding to the minimum value of the objective function are calculated by formula (7);

[0092] At the same time, the constraints of voltage management optimization algorithm 1 are defined as:

[0093] ; (8)

[0094] Where, The active power of the energy storage converter solved by the voltage management optimization algorithm 1; The reactive power of the energy storage converter solved by the voltage management optimization algorithm 1; , indicating low voltage status; , indicating overvoltage status; The effective value of the grid connection point voltage before executing the voltage management optimization algorithm 1; is the capacity of the energy storage converter.

[0095] S4), judging whether the energy storage converter has residual capacity according to the active power and reactive power of the energy storage converter calculated by the voltage management optimization algorithm 1; if there is no residual capacity, executing step S5), specifically as follows:

[0096] In the low voltage state, the criterion 1 is used for judgment; if the judgment result is that there is no remaining capacity, the active power of the energy storage converter solved by the voltage management optimization algorithm 1 is and reactive power As a reference value, control the power output by the energy storage converter and execute step S5);

[0097] In the overvoltage state, the second criterion is used for judgment; if the judgment result is that there is no remaining capacity, the active power of the energy storage converter solved by the voltage management optimization algorithm 1 is and reactive power As a reference value, control the power absorbed by the energy storage converter, and execute step S5); wherein:

[0098]

[0099] Where, is the effective value of the rated voltage; is the maximum acceptable effective value of the fluctuating voltage; The effective value of the grid connection point voltage before executing the voltage management optimization algorithm 1; The active power of the energy storage converter solved by the voltage management optimization algorithm 1; The reactive power of the energy storage converter solved by the voltage management optimization algorithm 1; , indicating low voltage status; , indicating an overvoltage state.

[0100] If there is any remaining capacity, the voltage management optimization algorithm 2 is executed to calculate the active power and reactive power of the energy storage converter required for voltage management; then step S5 is executed); specifically as follows:

[0101] If there is any remaining capacity, the voltage management optimization algorithm 2 is executed to calculate the minimum capacity of the energy storage converter and the corresponding active power and reactive power that can be used to manage the voltage to the normal range under low voltage or overvoltage conditions; the voltage management optimization algorithm 2 adopts the particle swarm optimization algorithm; the objective function of the voltage management optimization algorithm 2 is and constraints are defined as:

[0102] ; (11)

[0103] ; (12)

[0104] Where, The active power of the energy storage converter solved by voltage management optimization algorithm 2; The reactive power of the energy storage converter solved by voltage management optimization algorithm 2; is the capacity of the energy storage converter;

[0105] In the low voltage state, the active power corresponding to the minimum capacity of the energy storage converter will be occupied and reactive power As a reference value, it controls the power output by the energy storage converter;

[0106] In the overvoltage state, the active power corresponding to the minimum capacity of the energy storage converter will be occupied and reactive power As a reference value, it controls the power absorbed by the energy storage converter.

[0107] S5) Calculate the capacity of the energy storage converter occupied by the active power and reactive power required for voltage management; the details are as follows:

[0108] When the energy storage converter has no remaining capacity, the active power and reactive power required for voltage management occupy the capacity of the energy storage converter. ;

[0109] When the energy storage converter has surplus capacity, the active power and reactive power required for voltage management occupy the capacity of the energy storage converter. ;Right now:

[0110] ; (13)

[0111] ; (14)

[0112] Where, The active power of the energy storage converter solved by the voltage management optimization algorithm 1; The reactive power of the energy storage converter solved by the voltage management optimization algorithm 1; , indicating low voltage status; , indicating overvoltage status; The active power of the energy storage converter solved by voltage management optimization algorithm 2; The reactive power of the energy storage converter solved by voltage management optimization algorithm 2.

[0113] S6) When the voltage state is normal or after executing the voltage management optimization algorithm, it is determined whether the energy storage converter has any remaining capacity that can be used for harmonic management; the remaining capacity of the energy storage converter The calculation formula is:

[0114] ; (15)

[0115] Where, ;when When it is displayed, it means there is no remaining capacity. for ;when When , it indicates that there is remaining capacity; for ;

[0116] When the remaining capacity of the energy storage converter When it is greater than 0, execute step S7).

[0117] S7) Sampling the grid connection point line current, obtaining the amplitude and phase of the third harmonic and fifth harmonic of the grid connection point line current through fast Fourier transform, and obtaining the effective value of the grid connection point voltage at the current moment, then executing the harmonic control optimization algorithm and starting harmonic compensation;

[0118] In this embodiment, the objective function of the harmonic control optimization algorithm is And the constraints are:

[0119] ; (16)

[0120] ; (17)

[0121] Where, is the third harmonic amplitude in the line current at the grid connection point; is the third harmonic compensation amount; is the fifth harmonic amplitude in the line current at the grid connection point; is the fifth harmonic compensation amount; The effective value of the grid connection point voltage before executing the harmonic control optimization algorithm; is the remaining capacity of the energy storage converter.

[0122] Figure 3 The energy storage converter of this embodiment is used to manage power, which includes power quality pollution sources, energy storage converters and distribution network voltage sources. . Among them, the power quality pollution sources are represented by new energy sources such as photovoltaics. New energy sources such as photovoltaics increase the DC voltage through a DC-DC boost circuit and then connect to the inverter to achieve grid connection, thereby providing power to the grid. However, the randomness of its power leads to voltage fluctuations at the grid connection point, and photovoltaics introduce harmonic pollution when connected to the grid through power electronic equipment such as inverters. The energy storage converter below is the main body of power management. It also increases the DC voltage through a DC-DC boost circuit and then connects to the inverter for grid connection. By giving active command value, reactive command value and harmonic current compensation command, PI control + bipolar modulation is used to control the current corresponding to the inverter switch output, thereby achieving voltage management and harmonic management. In the figure L and L 1 are the power quality pollution source and the filter inductance before the energy storage converter is connected to the grid; the grid connection point line impedance estimated in the present invention is Figure 3 in The main goal of achieving power management is Figure 3 Grid-connected point voltage Effective value and grid connection point line current harmonics in .

[0123] The above embodiments and descriptions are only for explaining the principles and best embodiments of the present invention. Without departing from the spirit and scope of the present invention, the present invention may be subject to various changes and improvements, which shall fall within the scope of the invention to be protected.

Claims

1. A method for controlling the power quality of an energy storage converter, characterized in that: The steps include: S1) Obtaining the effective value information of the grid connection point voltage and judging the voltage status of the distribution network; S2) When the voltage state is low voltage or overvoltage, the impedance of the grid connection point line is estimated using the impedance estimation method; S3) Execute the voltage management optimization algorithm 1 based on the estimated impedance information and voltage information to calculate the active power and reactive power of the energy storage converter required for voltage management; the details are as follows: First, obtain the effective value of the grid connection point voltage at the current moment, and then execute the voltage management optimization algorithm 1. The voltage management optimization algorithm 1 adopts the particle swarm optimization algorithm. If low voltage management is performed, the objective function Φ low1 (P 1_o1 ,Q 1_o1 ) is defined as: The objective function Φ is calculated by formula (6): low1 (P 1_o1 ,Q 1_o1 ) Active power and reactive power corresponding to the maximum value; If overvoltage control is carried out, the objective function Φ high1 (P 2_o1 ,Q 2_o1 ) is defined as: The objective function Φ is calculated by formula (7) high1 (P 2_o1 ,Q 2_o1 ) Active power and reactive power corresponding to the minimum value; At the same time, the constraints of voltage management optimization algorithm 1 are defined as: Where, P i_o1 The active power of the energy storage converter solved by the voltage management optimization algorithm 1; Q i_o1 The reactive power of the energy storage converter solved by the voltage management optimization algorithm 1; where i = 1, represents the low voltage state; i = 2, represents the overvoltage state; U pcc is the effective value of the grid connection point voltage before executing the voltage management optimization algorithm 1; S pcs is the capacity of the energy storage converter; X1 is the reactance of the grid connection point line at low voltage; X2 is the reactance of the grid connection point line at overvoltage; S4), judging whether the energy storage converter has residual capacity according to the active power and reactive power of the energy storage converter calculated by the voltage management optimization algorithm 1; if there is no residual capacity, executing step S5); If there is any remaining capacity, the voltage management optimization algorithm 2 is executed to calculate the active power and reactive power of the energy storage converter required for voltage management; then step S5 is executed; specifically as follows: If there is any remaining capacity, the voltage management optimization algorithm 2 is executed to calculate the minimum capacity of the energy storage converter and the corresponding active power and reactive power that can be used to manage the voltage to the normal range under low voltage or overvoltage conditions; the voltage management optimization algorithm 2 adopts the particle swarm optimization algorithm; the objective function Φ2(P o2 ,Q o2 ) and the constraints are defined as: Where, P o2 The active power of the energy storage converter solved by the voltage management optimization algorithm 2; Q o2 The reactive power of the energy storage converter solved by the voltage management optimization algorithm 2; S pcs is the capacity of the energy storage converter; In the low voltage state, the active power P corresponding to the minimum capacity of the energy storage converter will be occupied. o2 and reactive power Q o2 As a reference value, it controls the power output by the energy storage converter; In the overvoltage state, the active power P corresponding to the minimum capacity of the energy storage converter will be occupied o2 and reactive power Q o2 As a reference value, it controls the power absorbed by the energy storage converter; S5) Calculate the capacity of the energy storage converter occupied by the active power and reactive power required for voltage management; S6), when the voltage state is normal or after executing the voltage management optimization algorithm, determine whether the energy storage converter has remaining capacity for harmonic management; if so, execute step S7); S7) Sample the grid connection point line current, obtain the amplitude and phase of the third harmonic and fifth harmonic of the grid connection point line current through fast Fourier transform, and obtain the effective value of the grid connection point voltage at the current moment, then execute the harmonic control optimization algorithm and start harmonic compensation.

2. The power quality management method of an energy storage converter according to claim 1, characterized in that: In step S2), if the current grid connection point voltage state is low voltage, the impedance estimation of the grid connection point line specifically includes the following steps: S211), first record the current grid point voltage effective value U 11 , then control the energy storage converter to output 20% to 25% of the rated capacity of reactive power, and record the grid connection point voltage RMS value U after the reactive power is output 12 Then calculate the reactance X1 of the grid connection point line according to formula (2), that is: Where ΔQ1 is the reactive power output by the energy storage converter; U 11 is the effective value of the grid connection point voltage when no reactive power is output; U 12 is the effective value of the grid connection point voltage after reactive power is output; S212), the energy storage converter stops outputting reactive power, and records the effective value of the grid connection point voltage U at the current moment again. 21 Then control the energy storage converter to output 20% to 25% of the rated capacity of active power, and record the grid connection point voltage RMS U after the active power is output. 22 , and calculate the resistance R1 of the grid connection point line according to formula (3); that is: Where ΔP1 is the active power output by the energy storage converter; U 21 is the effective value of the grid connection point voltage when no active power is output; U 22 is the effective value of the grid connection point voltage after the active power is output; S213) Output the grid connection point impedance estimation result.

3. The power quality management method of an energy storage converter according to claim 2, characterized in that: In step S2), if the current grid connection point voltage state is overvoltage, the impedance estimation of the grid connection point line specifically includes the following steps: S221) First, record the current grid point voltage effective value U 31 , then control the energy storage converter to absorb 20% to 25% of the rated capacity of reactive power, and record the grid connection point voltage RMS value U after absorbing the reactive power 32 , and calculate the reactance X2 of the grid connection point line according to formula (4), that is: Where U 31 is the effective value of the grid connection point voltage when no reactive power is absorbed; U 32 is the effective value of the grid connection point voltage after absorbing reactive power; ΔQ2 is the reactive power absorbed by the energy storage converter; S222), the energy storage converter stops absorbing reactive power and records the effective value of the grid connection point voltage U at the current moment again. 41 , then control the energy storage converter to absorb 20% to 25% of the rated capacity of active power, and record the grid connection point voltage RMS U after absorbing the active power 42 , calculate the resistance R2 of the grid connection point line according to formula (5); that is: Where U 41 is the effective value of the grid connection point voltage when no active power is absorbed; U 42 is the effective value of the grid connection point voltage after absorbing active power; ΔP2 is the active power absorbed by the energy storage converter; S223) Output the grid connection point impedance estimation result.

4. The power quality control method for an energy storage converter according to claim 1, characterized in that: In step S4), the criterion 1 is used for judgment in the low voltage state; if the judgment result is that there is no remaining capacity, the active power P of the energy storage converter solved by the voltage management optimization algorithm 1 is 1_o1 and reactive power Q 1_o1 As a reference value, control the power output by the energy storage converter and execute step S5); In the overvoltage state, the second criterion is used for judgment; if the judgment result is that there is no remaining capacity, the active power P of the energy storage converter solved by the voltage management optimization algorithm 1 is 2_o1 and reactive power Q 2_o1 As a reference value, the power absorbed by the energy storage converter is controlled, and step S5 is executed.

5. The power quality control method of an energy storage converter according to claim 4, characterized in that: In step S4), the expressions of the criterion 1 and criterion 2 are: Criterion 1: Criterion 2: Where U N is the rated voltage RMS value; ΔU is the maximum acceptable voltage fluctuation RMS value; U pcc is the effective value of the grid connection point voltage before executing the voltage management optimization algorithm 1; P i_o1 The active power of the energy storage converter solved by the voltage management optimization algorithm 1; Q i_o1 The reactive power of the energy storage converter solved by the voltage management optimization algorithm 1; where i=1 indicates a low voltage state; i=2 indicates an overvoltage state.

6. The method for controlling power quality of an energy storage converter according to claim 1, wherein: In step S5), when the energy storage converter has no remaining capacity, the active power and reactive power required for voltage management occupy the capacity of the energy storage converter S1. i_voltage ; When the energy storage converter has surplus capacity, the active power and reactive power required for voltage management occupy the capacity of the energy storage converter S2 voltage ;Right now: Where, P i_o1 The active power of the energy storage converter solved by the voltage management optimization algorithm 1; Q i_o1 The reactive power of the energy storage converter solved by the voltage management optimization algorithm 1; where i = 1, it indicates low voltage state; i = 2, it indicates overvoltage state; P o2 The active power of the energy storage converter solved by the voltage management optimization algorithm 2; Q o2 The reactive power of the energy storage converter solved by voltage management optimization algorithm 2.

7. The method for controlling power quality of an energy storage converter according to claim 6, wherein: In step S6), if the voltage state is normal or after executing the voltage management optimization algorithm, the remaining capacity Sk of the energy storage converter is calculated. remain ,Right now: Sk remain =S pcs -Sk voltage ; (15) Where, k = 1, 2; when k = 1, it means there is no remaining capacity, Sk voltage S1 i_voltage ; When k = 2, it means there is remaining capacity; Sk voltage S2 voltage ; When the remaining capacity of the energy storage converter Sk remain When it is greater than 0, execute step S7).

8. The method for controlling power quality of an energy storage converter according to claim 7, wherein: In step S7), the objective function Φ2(I′ h3 ,I′ h5 ) and the constraints are: Φ2(I′ h3 ,I′ h5 )=(I h3 -I′ h3 ) 2 +(I h5 -I′ h5 ) 2 ; (16) Where, I h3 is the third harmonic amplitude in the line current at the grid connection point; I′ h3 is the third harmonic compensation amount; I h5 is the fifth harmonic amplitude in the line current at the grid connection point; I′ h5 is the fifth harmonic compensation amount; U pcc1 Sk is the effective value of the grid connection point voltage before executing the harmonic control optimization algorithm; remain is the remaining capacity of the energy storage converter.

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