Harmonic voltage control method and system based on harmonic current search

Abstract

The invention relates to a harmonic voltage control method and system based on harmonic current search, and the method comprises the steps: searching and determining a harmonic current set value iref of an active power filter (APF) capable of reducing the harmonic voltage of a power grid, and controlling the harmonic current output of the APF through a proportional resonance (PR) controller according to the harmonic current set value iref; the system comprises a harmonic current searching module and a harmonic current control module, the harmonic current searching module is responsible for searching an APF harmonic current set value capable of reducing power grid harmonic voltage, input parameters of the harmonic current searching module comprise a harmonic current step length delta I, power grid harmonic voltage Ugh and a maximum value Ughmax allowed by the power grid harmonic voltage, and an output parameter is an APF harmonic current set value iref; the harmonic voltage of the power grid is effectively controlled, and the stability and the electric energy quality of a power system are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of power system control, and in particular to a harmonic voltage control method and system based on harmonic current search. Background Art

[0002] In modern power systems, with the widespread application of nonlinear loads (such as power electronic equipment, arc furnaces, inverters, etc.), harmonic problems have become increasingly prominent. The generation of harmonic currents not only causes distortion of the grid voltage waveform, but may also cause equipment overheating, vibration, noise and other problems. In severe cases, it may even threaten the stable operation and power supply quality of the power system. Therefore, effective control of harmonics has become an important issue that needs to be urgently addressed in the field of power systems.

[0003] The active power filter (APF) achieves dynamic suppression of harmonics by real-time detection of harmonic currents in the power grid and generates reverse harmonic currents for compensation. APF has the advantages of good filtering effect and strong adaptability, but its performance depends to a large extent on the accuracy of harmonic current detection and control algorithms.

[0004] Although the existing harmonic current detection and control technology has made certain progress, it still faces many challenges in practical applications. For example, how to quickly and accurately search for the optimal harmonic current compensation value to achieve effective control of harmonic voltage is still a hot topic and difficulty in current research. Summary of the invention

[0005] The present invention provides a harmonic voltage control method and system based on harmonic current search, which determines the harmonic current control value of an active power filter (APF) through harmonic current search, and then accurately controls the harmonic current output of the APF, so as to achieve the purpose of effectively reducing the harmonic voltage in the power grid.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A harmonic voltage control method based on harmonic current search comprises the following steps:

[0008] S1, initialization: set the active power filter APF harmonic current setting value iref to the initial value;

[0009] S2, loop judgment: continuously judge whether the grid harmonic voltage Ugh exceeds the maximum allowed value Ughmax, if it exceeds, enter the search process;

[0010] S3, temporary value saving: save the current active power filter APF harmonic current setting value iref as a temporary value iref_temp;

[0011] S4, search attempt: try to search the temporary value i in turn ref_temp The increase amplitude is ΔI and the angle is Harmonic current As the new setting value of the new APF harmonic current, 90°, 180° or -90°, select U gh The reduced setting value is used as the final i ref ;

[0012] S5, comparison: set the harmonic current to the value i ref And the actual harmonic current i of the active power filter APF apf Make comparisons;

[0013] S6, control signal generation: input the difference of the comparison result into a proportional resonant PR controller to generate a control signal U for adjusting the APF harmonic current output hapf .

[0014] Furthermore, the control range of the harmonic current step length ΔI is 0.001 to 0.1 pu.

[0015] Furthermore, the resonance point of the proportional resonance PR controller is set according to the order of the harmonic voltage that needs to be controlled.

[0016] A harmonic voltage control system based on harmonic current search, comprising a harmonic current search module and a harmonic current control module, wherein the output end of the harmonic current search module is connected to the input end of the harmonic current control module, and the output end of the current control module is connected to the input end of an active power filter APF;

[0017] The harmonic current search module is used to search and determine the active power filter APF harmonic current setting value i that can reduce the harmonic voltage of the power grid. ref ;

[0018] The harmonic current control module is used to control the harmonic current output of the active power filter APF using a proportional resonance PR controller according to the harmonic current setting value iref output by the harmonic current search module.

[0019] Furthermore, the input parameters of the harmonic current search module include the harmonic current step length ΔI, the grid harmonic voltage U gh And the maximum value U allowed for the grid harmonic voltage ghmax .

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] 1) The harmonic current search module can accurately and automatically search and determine the optimal APF harmonic current setting value to effectively reduce the harmonic voltage in the power grid, and perform accurate grid harmonic voltage acquisition, efficient algorithm search and reliable APF control strategy;

[0022] 2) Through the use of the PR controller, the harmonic current control module can achieve precise control of harmonic currents of specific orders, improving the accuracy and efficiency of control. In addition, the resonance point of the PR controller can be flexibly set according to the harmonic voltage order to be controlled, so that the harmonic current control module can adapt to different power grid environments and requirements;

[0023] 3) Through the combination of search algorithm and PR controller, effective control of grid harmonic voltage is achieved, improving the stability and power quality of the power system. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a structural schematic diagram of the system of the present invention.

[0025] Figure 2 This is the harmonic current setting flow chart of the present invention.

[0026] Figure 3 This is the harmonic current search flow chart of the present invention.

[0027] Figure 4 This is a structural diagram of the harmonic current control described in the present invention.

[0028] Figure 5 It is a schematic diagram of the harmonic search process of the present invention. DETAILED DESCRIPTION

[0029] The specific implementation of the present invention will be further described below in conjunction with the accompanying drawings:

[0030] See Figure 1 , is a structural diagram of the system of the present invention. The present invention is a harmonic voltage control system based on harmonic current search, comprising a harmonic current search module, a harmonic current control module and an active power filter APF, wherein the output end of the harmonic current search module is connected to the input end of the harmonic current control module, and the output end of the current control module is connected to the input end of the active power filter APF.

[0031] A harmonic voltage control method based on harmonic current search, comprising searching and determining an active power filter APF harmonic current setting value i that can reduce the harmonic voltage of the power grid ref , according to the harmonic current setting value i output by the harmonic current search module ref , a proportional resonant PR controller is used to control the harmonic current output of the active power filter APF.

[0032] 1) Harmonic current search module: used to search and determine the active power filter APF harmonic current setting value i that can reduce the harmonic voltage of the power grid ref , wherein the input parameters of the harmonic current search module include the harmonic current step length ΔI, the grid harmonic voltage U gh And the maximum value U allowed for the grid harmonic voltage ghmax , the output parameter is the active power filter APF harmonic current setting value i ref .

[0033] The harmonic current step size ΔI is the current amplitude added to the harmonic current setting value of the active power filter APF during each current search process. Its function is to control the fineness and speed of the current search. When the current step size is 0.001pu, the search is more precise but the speed is slower; when the current step size is 0.1pu, the search speed is faster but the optimal solution may be missed.

[0034] The grid harmonic voltage U gh It is the harmonic voltage value obtained by collecting the grid voltage and analyzing it. It serves as the input of the current search and is used to evaluate the impact of the current active power filter APF harmonic current setting value on the grid harmonic voltage.

[0035] The maximum value U allowed for the harmonic voltage of the power grid ghmax , is the maximum harmonic voltage value allowed for power grid operation, and is an important parameter for power grid stability and safe operation of equipment. It serves as the termination condition of the search algorithm. When the power grid harmonic voltage drops below this value, the search process stops.

[0036] The active power filter APF harmonic current setting value i ref , which is obtained through the search algorithm and is used to control the set value of the APF harmonic current output. Its function is to serve as the input of the harmonic current control module to guide the active power filter APF to generate corresponding harmonic current to reduce the harmonic voltage in the power grid.

[0037] The harmonic current search module searches and determines the active power filter APF harmonic current setting value i that can reduce the harmonic voltage of the power grid. ref Including harmonic current setting and search process, the specific steps are as follows:

[0038] S1, initialization: set the active power filter APF harmonic current setting value i ref Set to initial value;

[0039] S2. Cyclic judgment: Continuously judge the grid harmonic voltage U gh Whether it exceeds the maximum value allowed U ghmax, if it exceeds, the search process will be entered;

[0040] S3, temporary value saving: save the current active power filter APF harmonic current setting value i ref is the temporary value i ref_temp ;

[0041] S4, search attempt: try to search the temporary value i in turn ref_temp Add the harmonic current ΔI∠φ with amplitude ΔI and angle φ as the new APF harmonic current setting value, where φ = 0°, 90°, 180° or -90°, that is, i ref =i ref_temp +ΔI∠φ, after each attempt, determine U gh Whether to reduce, if reduced, then use the i ref As the harmonic current setting value of the active power filter APF, and end this search; if U gh If it does not decrease, continue to try the next angle setting value;

[0042] S5, output result: the final determined active power filter APF harmonic current setting value i ref Output to the harmonic current control module.

[0043] 2) Harmonic current control module: used to set the harmonic current setting value i according to the output of the harmonic current search module ref , using proportional resonant PR controller to control the harmonic current output of active power filter APF;

[0044] The input of the harmonic current control module includes: the set value i output by the harmonic current search module ref , the actual harmonic current i of the active power filter APF apf , the output is the control signal of the active power filter APF, which will directly act on the active power filter APF to adjust its harmonic current output, see Figure 4 , specifically including the following process:

[0045] P1. The harmonic current control module receives input parameters: receives the harmonic current setting value i output by the harmonic current search module. ref And the actual harmonic current i of the active power filter APF apf ;

[0046] P2, comparison: the harmonic current setting value i ref The actual harmonic current i apf Make comparisons;

[0047] P3, control signal generation: the difference of the comparison result is input into a proportional resonant PR controller to generate a control signal U for adjusting the APF harmonic current output hapf , which is used to further adjust the harmonic current output of the active power filter APF to achieve the purpose of reducing the harmonic voltage of the power grid.

[0048] The following examples are implemented on the premise of the technical solution of the present invention, and provide detailed implementation methods and specific operation processes, but the protection scope of the present invention is not limited to the following examples. The methods used in the following examples are conventional methods unless otherwise specified.

[0049] [Example 1]

[0050] The present invention discloses a harmonic voltage control system based on harmonic current search, comprising a harmonic current search module, a harmonic current control module and an active power filter APF, wherein the output end of the harmonic current search module is connected to the input end of the harmonic current control module, and the output end of the current control module is connected to the input end of the active power filter APF.

[0051] A harmonic voltage control method based on harmonic current search, comprising searching and determining an active power filter APF harmonic current setting value i that can reduce the harmonic voltage of the power grid ref , according to the harmonic current setting value i output by the harmonic current search module ref , a proportional resonant PR controller is used to control the harmonic current output of the active power filter APF.

[0052] The harmonic current search module is used to search and determine the active power filter APF harmonic current setting value i that can reduce the harmonic voltage of the power grid. ref , wherein the input parameters of the harmonic current search module include the harmonic current step length ΔI, the grid harmonic voltage U gh And the maximum value U allowed for the grid harmonic voltage ghmax , the output parameter is the active power filter APF harmonic current setting value i ref .

[0053] The harmonic current search module includes two control processes: harmonic current setting process and harmonic current search process. Figure 2 , Figure 3 shown.

[0054] Depend on Figure 2 The harmonic current setting process is as follows:

[0055] S1: Set the APF harmonic current to value i ref Set to 0;

[0056] S2: Determine the grid harmonic voltage Ugh Is it less than or equal to the maximum value U allowed by the grid harmonic voltage? ghmax , if U gh Less than or equal to U ghmax , execute S3, if U gh Greater than U ghmax , execute S4;

[0057] S3:i ref Remain unchanged, then return to continue executing S2;

[0058] S4: Execute the harmonic current search process to obtain i ref , then returns to continue executing S2.

[0059] Depend on Figure 3 The harmonic current search process is as follows:

[0060] S5: Set the APF harmonic current to value i ref Assign the temporary value i to the APF harmonic current setpoint ref_temp , i.e. i ref_temp =i ref , using i ref_temp Save the current before searching. ref Original value;

[0061] S6: First, set the APF harmonic current setting value to i ref =i ref_temp +ΔI∠0°; then determine the grid harmonic voltage U gh Whether to reduce; if U gh Decrease, then the output i ref =i ref_temp +ΔI∠0°, finally execute S9 to end this current search; if U gh If it does not decrease, execute S7;

[0062] S7: First, set the APF harmonic current setting value to i ref =i ref_temp +ΔI∠90°; then determine the grid harmonic voltage U gh Whether to reduce; if U gh Decrease, then the output i ref =i ref_temp +ΔI∠90°, finally execute S9 to end this current search; if U gh If it does not decrease, execute S8;

[0063] S8: First, set the APF harmonic current setting value to i ref =i ref_temp +ΔI∠180°; then determine the grid harmonic voltage U gh Whether to reduce; if Ugh Decrease, then the output i ref =i ref_temp +ΔI∠180°, finally execute S9 to end this current search; if U gh If there is no decrease, the output i ref =i ref_temp +ΔI∠-90°, finally execute S9 to end this current search;

[0064] S9: Output i ref .

[0065] Figure 5 This is a schematic diagram of the harmonic search process. That is, after each search, the current will increase by an amplitude of ΔI and an angle of φ (φ=0°, 90°, 180° or -90°) on the basis of the original control current. The φ value is determined by Figure 3 The harmonic current search process is obtained.

[0066] The harmonic current control module is used to control the harmonic current setting value i according to the output of the harmonic current search module. ref , a proportional resonant PR controller is used to control the harmonic current output of the active power filter APF.

[0067] [Example 2]

[0068] In an actual power system, the method of the present invention is applied to a 10kV distribution network, in which there are a large number of nonlinear loads, such as frequency converters, arc furnaces, etc. These loads generate significant harmonic currents, resulting in serious distortion of the grid voltage waveform. In order to improve the power quality, we deployed a harmonic voltage control system based on the method of the present invention.

[0069] This system has the same structure as Example 1, a harmonic voltage control method based on harmonic current search, and implementation of the harmonic current search module:

[0070] S1. Initialization: Initialize the harmonic current setting value iref of APF to 0A.

[0071] S2, cycle judgment: through real-time monitoring of the grid voltage, and using the FFT algorithm to analyze the grid harmonic voltage Ugh, set the maximum value U of the grid harmonic voltage allowed ghmax 2% of the rated voltage (i.e. 200V, assuming the rated voltage is 10kV), when U gh When it exceeds 200V, the harmonic current search process is started.

[0072] S3, temporary value saving: save the current i ref The value (initial 0A) is saved as a temporary value i ref_temp .

[0073] S4, search attempt: Set the harmonic current step length ΔI to 0.5A, and try to search for i ref_temp Increase the harmonic current of ΔI∠0°, ΔI∠90°, ΔI∠180°, and ΔI∠-90°. After each attempt, observe the grid harmonic voltage U gh The change of U gh Therefore, this setting value is used as the new i ref .

[0074] 5. Output results: The final determined i ref The value is output to the harmonic current control module.

[0075] Implementation of harmonic current control module:

[0076] P1, input: receive the i output by the harmonic current search module ref value (in this case, the current value corresponding to ΔI∠90°) and the actual harmonic current i of the APF apf .

[0077] P2, comparison: i ref with i apf Compare and get the difference.

[0078] P3, control signal generation: The difference is input into the PR controller, and the resonance point of the PR controller is set to the frequency corresponding to the 5th harmonic to be controlled. The PR controller outputs the control signal U hapf , used to adjust the harmonic current output of APF.

[0079] P4, APF adjustment: APF is adjusted according to U hapf The signal adjusts its harmonic current output to offset the 5th harmonic current in the power grid.

Claims

1. A harmonic voltage control method based on harmonic current search, characterized in that: The steps include: S1, initialization: set the active power filter APF harmonic current setting value i ref Set to initial value; S2. Cyclic judgment: Continuously judge the grid harmonic voltage U gh Whether it exceeds the maximum allowed value U ghmax , if it exceeds, the search process will be entered; S3, temporary value saving: save the current active power filter APF harmonic current setting value i ref is the temporary value i ref_temp ; S4, search attempt: try to search for temporary value i in turn ref_temp Add a harmonic current ΔI∠φ with an amplitude of ΔI and an angle of φ as the new setting value of the harmonic current of the active power filter APF, where φ = 0°, 90°, 180° or -90°, and select U gh The reduced setting value is used as the final i ref ; S5, comparison: set the harmonic current to the value i ref And the actual harmonic current i of the active power filter APF apf Make comparisons; S6, control signal generation: input the difference of the comparison result into a proportional resonant PR controller to generate a control signal U for adjusting the APF harmonic current output hapf .

2. A harmonic voltage control method based on harmonic current search according to claim 1, characterized in that: The control range of the step length ΔI of the harmonic current is 0.001 to 0.1 pu.

3. The harmonic voltage control method based on harmonic current search according to claim 1 is characterized in that: The resonance point of the proportional resonant PR controller is set according to the order of harmonic voltage that needs to be controlled.

4. A control system for a harmonic voltage control method based on harmonic current search according to any one of claims 1 to 3, characterized in that: It includes a harmonic current search module and a harmonic current control module, wherein the output end of the harmonic current search module is connected to the input end of the harmonic current control module, and the output end of the current control module is connected to the input end of the active power filter APF; The harmonic current search module is used to search and determine the active power filter APF harmonic current setting value i that can reduce the harmonic voltage of the power grid. ref ; The harmonic current control module is used to control the harmonic current output of the active power filter APF using a proportional resonance PR controller according to the harmonic current setting value iref output by the harmonic current search module.

5. A harmonic voltage control system based on harmonic current search according to claim 4, characterized in that: The input parameters of the harmonic current search module include the harmonic current step length ΔI, the grid harmonic voltage U gh And the maximum value U allowed for the grid harmonic voltage ghmax .

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