An APF control method that can effectively attenuate background harmonic voltage

Abstract

The present invention belongs to the technical field of power grid harmonic suppression, and particularly relates to an APF control method that can effectively attenuate background harmonic voltage. First, the APF installed at the end of the distribution feeder collects the three-phase voltage signal of the busbar, and converts the three-phase voltage signal to a two-phase rotating coordinate system of the corresponding frequency according to the frequency of each harmonic to be suppressed, and extracts the harmonic component of the corresponding frequency through a low-pass filter; then, according to the relationship between the wavelength of the harmonic and the feeder length, it is determined whether to integrate or differentiate it and the gain. k L or k C The command current of APF is obtained by selecting the command current of APF; finally, the command current is subtracted from the actual output current of APF for closed-loop regulation, and a modulation signal is obtained after PWM modulation to control APF. The present invention can effectively suppress the oscillation amplification of background harmonic voltage on the distribution feeder, especially can effectively attenuate background harmonic voltage.

Description

Technical Field

[0001] The present invention belongs to the technical field of power grid harmonic suppression, and in particular relates to an APF control method that can effectively attenuate background harmonic voltage. Background Art

[0002] With the rapid development of power electronics technology, there are more and more nonlinear loads in the power grid, and the resulting harmonic problems are becoming increasingly serious. The commonly used current sensing parallel APF can compensate for most of the harmonic currents, but the background harmonic oscillation caused by the resonance between the feeder inductance and the reactive compensation capacitor in the power grid will seriously amplify these residual harmonics, resulting in serious node voltage distortion, which in turn threatens equipment and personal safety.

[0003] At present, for the propagation and oscillation amplification of background harmonic voltage, the effective and mainstream solutions are mostly based on RAPF (Resistive Active Power Filter), which originated from the voltage detection-based active power filter proposed by Japanese scholar Yasufumi Akagi. The main purpose of this type of APF is different from the conventional APF used to compensate for harmonic currents, but to suppress the background harmonic amplification caused by resonance. Yasufumi Akagi and other scholars analyzed the standing wave harmonics on the distribution feeder and found that when the virtual resistance value of the terminal RAPF is equal to the characteristic impedance of the feeder, the "whack-a-mole" effect can be eliminated and the harmonic oscillation on the entire feeder will be completely suppressed. After that, many improvement schemes based on RAPF were proposed, including gain self-adjustment scheme, multi-RAPF collaborative suppression scheme and RAPF installation location selection scheme.

[0004] Chinese invention patent CN 111541250 A discloses a local control method for a voltage-detecting APF, comprising: dividing the power grid into a plurality of control areas with the nodes where each voltage-detecting APF is located in the power grid as the center; obtaining the fluctuation range of the harmonic current injected by the harmonic pollution source in each control area and the preset local operation characteristics of the voltage-detecting APF; according to the fluctuation range and the local operation characteristics, taking the harmonic distortion of each node in the control area not exceeding the limit as a constraint condition, taking the minimum adjustment amount of each harmonic conductance as an objective function, determining the optimal harmonic conductance adjustment amount of the voltage-detecting APF in each control area; adjusting the conductance value of the voltage-detecting APF in each control area according to the optimal harmonic conductance adjustment amount, so as to control the voltage-detecting APF. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide an APF control method that can effectively attenuate background harmonic voltage.

[0006] In order to solve the above technical problems, the present invention provides an APF control method that can effectively attenuate background harmonic voltage, and an APF control method that can effectively attenuate background harmonic voltage, characterized in that it includes the following steps:

[0007] A. Detect the three-phase voltage signal u on the bus at the end of the distribution feeder, i.e. the APF installation location a 、u b 、u c ,The harmonic components in the voltage signal are separated through the synchronous rotating coordinate technology;

[0008] B. Determine the relationship between each harmonic and the feeder length, select the corresponding phase shift strategy for each harmonic voltage and calculate the optimal gain, and then add them together to obtain the APF command current;

[0009] C. Compare the command current calculated in the control scheme with the actual output current of the APF and make a difference. After the difference is proportionally controlled, PWM modulation is performed to obtain the drive signal of the three-phase bridge arm of the APF, thereby controlling the three-phase converter;

[0010] In the step B, specifically including

[0011] a. If the feeder length and the wavelength of a harmonic meet the following conditions

[0012]

[0013] In the formula, n is a positive integer, l is the length of the distribution feeder, and λ is the wavelength of the harmonic; then the left shift strategy, that is, the integral link, is used for the extracted harmonic voltage, and its optimal gain can be calculated by the following formula:

[0014]

[0015] Where β is the phase shift coefficient, MOD is the remainder function, and L0 is the distributed inductance per unit length of the feeder.

[0016] b. If the feeder length and the wavelength of a harmonic satisfy the following conditions

[0017]

[0018] In the formula, n is a positive integer, l is the length of the distribution feeder, and λ is the wavelength of the harmonic; then the right shift strategy should be used for the extracted harmonic voltage, that is, the differential link should be used, and its optimal gain can be calculated by the following formula:

[0019]

[0020] Where β is the phase shift coefficient, MOD is the remainder function, and C0 is the distributed capacitance per unit length of the feeder.

[0021] Preferably, in step A, specifically including

[0022]

[0023] In the formula, u a ,u b and u c is the three-phase voltage signal on the bus at the end of the distribution feeder, i.e., the location where the APF is installed, u d and u q They are the d-axis and q-axis components of the three-phase voltage signal in the two-phase rotating coordinate system after Park transformation;

[0024] Convert the voltage signal from the three-phase stationary coordinate system to the two-phase rotating coordinate system to obtain the dq axis component u d 、u q , where ω h =h*ω f ,ω f Obtained by a phase-locked loop;

[0025] For u d 、u q Perform low-pass filtering to extract its DC component

[0026]

[0027] In the formula, are the d-axis and q-axis DC components after low-pass filtering in the two-phase rotating coordinate system after Park transformation, u ha ,u hb and u hc It is the hth harmonic component of the three-phase voltage signal on the bus at the end of the distribution feeder, i.e., the location where the APF is installed;

[0028] The voltage signal is converted from the two-phase rotating coordinate system to the three-phase stationary coordinate system to obtain the hth harmonic component u ha 、u hb 、u hc , where ω h =h*ω f ,ω f Obtained by a phase-locked loop.

[0029] After adopting the above method, the present invention has the following beneficial effects:

[0030] 1. Due to the unique standing wave phase shift characteristics of this technical solution, the "whack-a-mole" effect in the traditional RAPF solution can be effectively avoided;

[0031] 2. By moving the antinode of the harmonic standing wave on the distribution feeder so that it is exactly at the beginning of the feeder, the harmonic voltage on the feeder will not be amplified, and the harmonic voltage in most areas will be effectively attenuated;

[0032] 3. Due to the independent control of each harmonic, the attenuation effect of all harmonic voltages can be optimized;

[0033] 4. The APF using this solution only needs to be installed at the end of the feeder, and the installation location is not demanding. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0035] Figure 1 This is a schematic diagram of the APF installation of the present invention;

[0036] Figure 2 is a control block diagram of the control scheme of the present invention;

[0037] Figure 3 This is a theoretical comparison diagram of the fifth harmonic voltage oscillation and suppression effect on the 11km feeder line of the present invention;

[0038] Figure 4 This is a theoretical comparison diagram of the seventh harmonic voltage oscillation and suppression effect on the 11km feeder line of the present invention;

[0039] Figure 5 This is a simulation comparison diagram of the fifth harmonic voltage oscillation and suppression effect on the 11km feeder line of the present invention;

[0040] Figure 6 This is a simulation comparison diagram of the seventh harmonic voltage oscillation and suppression effect on the 11km feeder line of the present invention. DETAILED DESCRIPTION

[0041] The present invention provides an APF control method that can effectively attenuate background harmonic voltage, and an APF control method that can effectively attenuate background harmonic voltage, characterized in that it includes the following steps:

[0042] A. Detect the three-phase voltage signal u on the bus at the end of the distribution feeder, i.e. the APF installation location a 、u b 、u c ,The harmonic components in the voltage signal are separated through the synchronous rotating coordinate technology;

[0043] B. Determine the relationship between each harmonic and the feeder length, select the corresponding phase shift strategy for each harmonic voltage and calculate the optimal gain, and then add them together to obtain the APF command current;

[0044] C. Compare the command current calculated in the control scheme with the actual output current of the APF and make a difference. After the difference is proportionally controlled, PWM modulation is performed to obtain the drive signal of the three-phase bridge arm of the APF, thereby controlling the three-phase converter.

[0045] Preferably, in step A, specifically including

[0046]

[0047] In the formula, u a ,u b and u c is the three-phase voltage signal on the bus at the end of the distribution feeder, i.e., the location where the APF is installed, u d and u q They are the d-axis and q-axis components of the three-phase voltage signal in the two-phase rotating coordinate system after Park transformation;

[0048] Convert the voltage signal from the three-phase stationary coordinate system to the two-phase rotating coordinate system to obtain the dq axis component u d 、u q , where ω h =h*ω f ,ω f Obtained by a phase-locked loop;

[0049] For u d 、u q Perform low-pass filtering to extract its DC component

[0050]

[0051] In the formula, are the d-axis and q-axis DC components after low-pass filtering in the two-phase rotating coordinate system after Park transformation, u ha ,u hb and u hc It is the hth harmonic component of the three-phase voltage signal on the bus at the end of the distribution feeder, i.e., the location where the APF is installed;

[0052] The voltage signal is converted from the two-phase rotating coordinate system to the three-phase stationary coordinate system to obtain the hth harmonic component u ha 、u hb 、u hc , where ω h =h*ω f ,ω f Obtained by a phase-locked loop.

[0053] Preferably, in step B, specifically including

[0054] a. If the feeder length and the wavelength of a harmonic meet the following conditions

[0055]

[0056] In the formula, n is a positive integer, l is the length of the distribution feeder, and λ is the wavelength of the harmonic; then the left shift strategy, that is, the integral link, is used for the extracted harmonic voltage, and its optimal gain can be calculated by the following formula:

[0057]

[0058] Where β is the phase shift coefficient, MOD is the remainder function, and L0 is the distributed inductance per unit length of the feeder.

[0059] b. If the feeder length and the wavelength of a harmonic satisfy the following conditions

[0060]

[0061] In the formula, n is a positive integer, l is the length of the distribution feeder, and λ is the wavelength of the harmonic; then the right shift strategy should be used for the extracted harmonic voltage, that is, the differential link should be used, and its optimal gain can be calculated by the following formula:

[0062]

[0063] Where β is the phase shift coefficient, MOD is the remainder function, and C0 is the distributed capacitance per unit length of the feeder.

[0064] like Figure 1 As shown, the APF using this solution needs to be installed at the end of the feeder, and only the voltage signal u at the installation location needs to be collected. abc It is used to extract the harmonic components and the output current of APF for current closed-loop regulation. In the figure, R0 and L0 are the resistance and inductance of the distribution feeder, respectively, and C0 is the reactive compensation capacitor.

[0065] like Figure 2 As shown, before applying this solution, it is necessary to determine the phase shift strategy corresponding to each harmonic according to the specific working conditions (using left shift or right shift) and calculate the optimal control gain k L and k C . Then, the harmonic components in the voltage at the installation point are extracted through the synchronous rotating coordinate system, and different phase shift strategies and gains are used for each harmonic component and then added to obtain the command current of the APF. Finally, the output current of the APF is closed-loop regulated and PWM modulated to obtain the drive signal of the APF. In order to maintain the stability of the DC side voltage of the APF, a DC side voltage loop is added to the control strategy.

[0066] like Figure 3 and 4As shown, taking the suppression of the 5th and 7th harmonic voltage oscillation amplification on an 11km distribution feeder as an example, theoretical analysis shows that the 5th and 7th harmonic voltages will be amplified in certain areas of the feeder. When the mainstream RAPF scheme is used, the harmonic voltage oscillation is completely suppressed, but the 5th and 7th harmonic voltages cannot be effectively attenuated. When the standing wave phase shift control scheme in the present invention is used, the harmonic voltage will not be amplified on the entire feeder, and the 5th and 7th harmonic voltages in most areas are effectively attenuated. It can be seen that the suppression effect of the scheme in the present invention is significantly better than that of the mainstream RAPF scheme.

[0067] like Figure 5 and 6 As shown, taking the suppression of the 5th and 7th harmonic voltage oscillation amplification on an 11km distribution feeder as an example, the simulation results show that the 5th and 7th harmonic voltages will be amplified in certain areas of the feeder. When the mainstream RAPF scheme is used, the harmonic voltage oscillation is completely suppressed, but the 5th and 7th harmonic voltages cannot be effectively attenuated. When the standing wave phase shift control scheme in the present invention is used, the harmonic voltage will not be amplified on the entire feeder, and the 5th and 7th harmonic voltages in most areas are effectively attenuated. It can be seen that the suppression effect of the scheme in the present invention is significantly better than that of the mainstream RAPF scheme.

[0068] Compared with the traditional RAPF scheme, the present invention can not only suppress the oscillation amplification of the background harmonic voltage, but also effectively attenuate the background harmonic voltage, and the suppression effect is better. The present invention treats the background harmonic voltage oscillation from a completely new perspective. Due to its unique standing wave phase shift suppression mechanism, the "whack-a-mole" effect existing in the traditional RAPF suppression can be avoided.

[0069] The implementation described above is only a description of the preferred implementation mode of the present invention, and does not limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solution of the present invention by ordinary technicians in this field should fall within the protection scope determined by the claims of the present invention.

Claims

1. An APF control method that can effectively attenuate background harmonic voltage, characterized in that: The following steps are included: A. Detect the three-phase voltage signal u on the bus at the end of the distribution feeder, i.e. the APF installation location a 、u b 、u c ,The harmonic components in the voltage signal are separated through the synchronous rotating coordinate technology; B. Determine the relationship between each harmonic and the feeder length, select the corresponding phase shift strategy for each harmonic voltage and calculate the optimal gain, and then add them together to obtain the APF command current; C. Compare the command current calculated in the control scheme with the actual output current of the APF and make a difference. After the difference is proportionally controlled, PWM modulation is performed to obtain the drive signal of the three-phase bridge arm of the APF, thereby controlling the three-phase converter; In the step B, specifically comprising a. If the feeder length and the wavelength of a harmonic meet the following conditions In the formula, n is a positive integer, l is the length of the distribution feeder, and λ is the wavelength of the harmonic; then the left shift strategy, that is, the integral link, is used for the extracted harmonic voltage, and its optimal gain can be calculated by the following formula: Where β is the phase shift coefficient, MOD is the remainder function, and L0 is the distributed inductance per unit length of the feeder. b. If the feeder length and the wavelength of a harmonic satisfy the following conditions In the formula, n is a positive integer, l is the length of the distribution feeder, and λ is the wavelength of the harmonic; then the right shift strategy should be used for the extracted harmonic voltage, that is, the differential link should be used, and its optimal gain can be calculated by the following formula: Where β is the phase shift coefficient, MOD is the remainder function, and C0 is the distributed capacitance per unit length of the feeder.

2. The APF control method for effectively attenuating background harmonic voltage according to claim 1, characterized in that: In the step A, specifically including In the formula, u a ,u b and u c is the three-phase voltage signal on the bus at the end of the distribution feeder, i.e., the location where the APF is installed, u d and u q They are the d-axis and q-axis components of the three-phase voltage signal in the two-phase rotating coordinate system after Park transformation; Convert the voltage signal from the three-phase stationary coordinate system to the two-phase rotating coordinate system to obtain the dq axis component u d 、u q , where ω h =h*ω f ,ω f Obtained by a phase-locked loop; For u d 、u q Perform low-pass filtering to extract its DC component In the formula, are the d-axis and q-axis DC components after low-pass filtering in the two-phase rotating coordinate system after Park transformation, u ha ,u hb and u hc It is the hth harmonic component of the three-phase voltage signal on the bus at the end of the distribution feeder, i.e., the location where the APF is installed; The voltage signal is converted from the two-phase rotating coordinate system to the three-phase stationary coordinate system to obtain the hth harmonic component u ha 、u hb 、u hc , where ω h =h*ω f ,ω f Obtained by a phase-locked loop.

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