Active power filter control method and system suitable for frequency fluctuations

Abstract

The application discloses a kind of active power filter control method and system suitable for frequency fluctuation, the decimal part of the sampling number is corrected using FIR filter based on Lagrange interpolation method, the bandwidth after frequency fluctuation is improved using variable bandwidth adjustment internal model control (VBAI) technology, effectively solve the problem that control effect is seriously reduced caused by the change of sampling number of traditional repetitive control caused by power grid frequency fluctuation, ensure the stability of control gain under frequency fluctuation.

Description

TECHNICAL FIELD

[0001] The present application relates to power electronic control technology, in particular to a control method and system of active power filter suitable for frequency fluctuation. BACKGROUND

[0002] Active power filter (APF) is a power quality key equipment for compensating grid harmonics, which can effectively control harmonic pollution. APF generally contains active elements whose output of inverter acts as power supply, through detecting load harmonic current and applying specific algorithm, the output voltage value of inverter can be controlled, to generate compensation current with same amplitude and complementary phase of harmonic current, so as to achieve the purpose of filtering. The most commonly used APF is shunt active power filter (SAPF). APF mainly includes main circuit, detection circuit, control circuit and drive circuit. For three-phase power distribution network, the main circuit is generally three-phase thyristor bridge circuit, the detection circuit is ip-iq detection based on instantaneous power method, the control circuit often adopts PR and hysteresis control, and the drive circuit includes SPWM and SVPWM modulation circuit. The control circuit involves the most core part of APF work, and is the most important link for APF to play filtering effect. At present, the research on APF control technology under stable grid frequency is relatively sufficient, but there are still few APFs that can achieve high stable control technology under industrial control change, especially under grid frequency fluctuation, resulting in defects such as incomplete filtering of harmonics and slow response of APF under frequency fluctuation.

[0003] Repeat control technology (RC) can achieve no-error tracking of periodic reference signal, and can be well applied in APF. The traditional repeat control technology such as Figure 1 As shown, can achieve efficient tracking control of periodic signal, and the core idea is internal model principle. The "internal model" in internal model principle refers to embedding mathematical dynamic model of external signal in feedback loop, and the "internal model" is the description of dynamic characteristics of external signal, and the so-called external signal includes input signal and disturbance signal. When the feedback path of a closed-loop control system is increased by an accurate "internal model", the control system can control the input signal and disturbance signal at the same time, and can achieve accurate tracking of input signal and elimination of disturbance signal.

[0004] From Figure 2Mathematical analysis shows that the "inner model" system has N poles, and all the N poles are located on the unit circle. According to the necessary and sufficient condition for stability of a discrete system, the poles located on the unit circle are critical stable poles, and the entire system is in a critical stable state. Once the load changes, the entire system is prone to instability, which is the reason why the typical repetitive control has poor robustness, especially when the grid frequency changes, which leads to a decrease in the effect of the entire APF. Figure 1 It is also shown that the repetitive control determines that there is a periodic hysteresis in the output signal from the basic structure, and this hysteresis cannot be avoided, which has a greater impact on the dynamic performance of the APF under varying conditions, especially when the grid frequency changes.

[0005] Based on this, some improved techniques are proposed, as follows:

[0006] The prior art indicates that a quadratic compensator C2(z) can be connected in series in the inner model part, which is generally a constant less than 1 or a low-pass filter to move the poles inward to the unit circle to improve the stability of the system, as shown in Figure 3 This scheme only improves the stability of the single-channel traditional repetitive control and cannot improve the stability of the repetitive control under grid frequency fluctuations, resulting in insufficient compensation and instability of the system.

[0007] In order to improve the response speed of the repetitive control, some research indicates that a PI controller can be connected in parallel to the entire system to improve the dynamic response, and increasing the proportional coefficient can achieve an increase in the dynamic response, as shown in Figure 4 .

[0008] The existing scheme has poor adaptability when facing grid frequency fluctuations. Specifically, after the grid frequency changes, the sampling frequency of the IRC will change, for example, when the sampling frequency is 10 kHz and the grid frequency fluctuates to 49.6 Hz, the sampling frequency N = 10k / 49.6 = 201.61. The IRC cannot control the decimal part of N, resulting in control with an integer multiple of the sampling frequency, which severely reduces the control effect. Figure 5 The amplitude-frequency characteristic of the control system is shown in the figure, and the green line at the 9th harmonic is taken as an example. When the IRC is normally working at the 9th harmonic, the frequency is 50*9 = 450 Hz, and the control gain is 35.38 dB. When the fundamental frequency decreases to 49.6 Hz, the 9th harmonic frequency is 49.6*9 = 446.4 Hz, and the gain decreases to 7.79 dB, which severely reduces the harmonic filtering effect. SUMMARY

[0009] The technical problems to be solved by the present application are to provide a frequency fluctuation applicable active power filter control method and system, to solve the problem of serious reduction of control effect caused by change of sampling number of traditional repetitive control due to power grid frequency fluctuation, and to ensure stable control gain under frequency fluctuation.

[0010] To solve the above technical problems, the technical solution of the present application is as follows: a frequency fluctuation applicable active power filter control method, comprising the following steps:

[0011] S1, detecting the harmonic current in the power distribution network and judging whether the harmonic current exists; if yes, entering step S2;

[0012] S2, calculating the current command value by using the harmonic current;

[0013] S3, modulating the current command value by SVPWM to obtain a switching signal, and using the switching signal to control the on-off of the active power filter switching tube;

[0014] Wherein,

[0015] The calculation formula of the current command value I ref is as follows: Wherein, I Lh is the detected harmonic current; G FVBAF (z) is the transfer function of the current tracking control link, D(z) is the disturbance signal, T(z) is the repetitive control compensator, G(z) is a constant, R(z) represents the detected harmonic current, G pi (z) is a PI controller;

[0016]

[0017] K 00 , K 01 , K 10 and K 11 are proportional coefficients, K Icc1 and K Icc2 represent the proportion of odd-even order bandwidth control, C2(z) is a quadratic compensator, N is the sampling number, and C2(z) is a quadratic compensator.

[0018] The present application uses the FIR filter (AIMSF technology) based on Lagrange interpolation method to correct the fractional part of the sampling number, effectively solves the problem of serious reduction of control effect caused by change of sampling number of traditional repetitive control due to power grid frequency fluctuation, and ensures stable control gain under frequency fluctuation.

[0019] Wherein, f sw represents the sampling frequency, fs is the fundamental frequency.

[0020] The secondary compensator C2(z) is a constant less than 1 or a low-pass filter.

[0021] w0 = 2π / T0.

[0022] K 00 and K 11 sum to 1.

[0023] After controlling the on-off of the active power filter switch tube by the switch signal, the method further comprises:

[0024] S4, continuously detecting the harmonic current, if the harmonic current does not exist, ending, if not, returning to S2.

[0025] In the application, T(z) = Kz n S(z), K is a proportional coefficient, z n is a phase lead element coefficient, S(z) is a filter element function, In the application, z n is a pure lead effect, in the implementation, z n is regarded as a constant, and the size of the lead is determined by n.

[0026] As an inventive concept, the application also provides an active power filter control system suitable for frequency fluctuation, comprising a memory, a processor and a computer program stored in the memory; the processor executes the computer program to realize the steps of the above method.

[0027] Compared with the prior art, the application has the beneficial effects that:

[0028] 1. The application effectively solves the problem of serious reduction of control effect caused by the change of sampling frequency of traditional repetitive control due to power grid frequency fluctuation, and ensures the stability of control gain under frequency fluctuation.

[0029] 2. The decoupling idea is used to divide the harmonic sampling into odd harmonic sampling and even harmonic sampling for parallel control, which can improve the response speed by 2 times under ideal conditions and improve the dynamic performance of the system under frequency fluctuation.

[0030] 3. When the power grid frequency fluctuates, the control bandwidth can be significantly increased, for example, the bandwidth of up to 50 harmonics

[0031] (50*50 = 2.5kHz) will be lifted, which improves the stability of the system and enables the APF to maintain good compensation effect when the power grid frequency changes. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1For the traditional IRC control inner model;

[0033] Figure 2 For the IRC control principle structure;

[0034] Figure 3 For the IRC control principle structure for improving dynamic performance;

[0035] Figure 4 For the parallel type APF principle structure diagram;

[0036] Figure 5 For the control gain analysis of repetitive control under frequency variation;

[0037] Figure 6 For the adaptive inner model sampling frequency control (AIMSF) principle diagram of embedding FIR filter in the forward channel of repetitive control;

[0038] Figure 7 For the gain after adopting the AIMSF technology;

[0039] Figure 8 For the decoupling principle diagram of the inner model;

[0040] Figure 9 For the principle diagram of the bandwidth control inner model improved by adding;

[0041] Figure 10 For the control principle diagram of Kicc to the control bandwidth;

[0042] Figure 11 For the circuit principle diagram of the embodiment of the application;

[0043] Figure 12 For the control principle diagram of the embodiment of the application;

[0044] Figure 13 For the filtering effect of FVBAF-RC-APF under the standard working condition (50Hz) of the embodiment of the application; (a) before filtering, (b) after filtering, (c) current waveform before and after filtering;

[0045] Figure 14 For the filtering effectiveness analysis under power distribution network frequency fluctuation; (a) compensation effect of IRC-APF at 49.5Hz, (b) compensation effect of FVBAF-RC-APF at 49.5Hz;

[0046] Figure 15 For the filtering effectiveness analysis under power distribution network frequency fluctuation; (a) f L =49.5Hz grid side current THD analysis, (b) f H =50.05Hz grid side current THD analysis;

[0047] Figure 16This is the compensated grid current when simulating grid frequency fluctuations; (a) simulated grid frequency is 49.5 Hz, (b) simulated grid frequency is 50.5 Hz;

[0048] Figure 17 This is the FVBAF-RC-APF workflow diagram. DETAILED DESCRIPTION

[0049] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0050] Example 1

[0051] The embodiment of the present invention designs a parallel active power filter, which mainly includes a harmonic current detection link, a current tracking control link, a PWM switch drive link and a current conversion main circuit link. Figure 11 As shown. The main converter circuit is a full-bridge circuit with parallel energy storage elements on the DC side. Because the working state of the circuit will change between inversion and rectification, it is called a converter. The principle of the parallel APF is: first, the harmonic current on the load side is sampled through the harmonic current detection link to extract the load harmonic current. The current tracking control link obtains the compensation instruction current according to the load harmonic current value and the DC side capacitor voltage value, and compares the current with the actual output current of the converter for control. The control technology adopts the variable bandwidth adaptive sampling frequency repetitive control technology (VBAF-RC) proposed in the embodiment of the present invention to obtain PWM control signal pulses to control the on and off of the main circuit switch tube. At this time, the converter acts as an inverter and outputs a compensation current that is equal to the harmonic current in magnitude and opposite in phase to achieve harmonic cancellation.

[0052] The embodiment of the present application proposes a variable bandwidth adjustment internal model control (VBAI) cascade adaptive internal model sampling frequency control (AIMSF) technology, namely, a variable bandwidth adaptive sampling frequency repetitive control technology (VBAF-RC), which is specifically described as follows:

[0053] 1、Based on the Lagrange interpolation method, the finite impulse response filter (FIR) is commonly used in some filter design scenarios with irregular frequency response requirements, such as multi-band filters or filters with special frequency response shapes. The fractional part of the sampling frequency is a typical form of special frequency response, so the filter can be used to correct the sampling frequency.

[0054] Figure 6 The adaptive internal model sampling frequency control technology (AIMSF) represents embedding the FIR filter into the repetitive control forward channel. The FIR filter is cascaded into the forward channel of the control system to correct the gain. Taking the 9th harmonic as an example, Figure 7 The blue line in the amplitude-frequency curve is the gain after the adaptive internal model sampling frequency control technology (AIMSF) is used. It obviously clamps the weak gain of 7.79 dB to 35 dB, ensuring the stability of the control gain under frequency fluctuation.

[0055] When the grid frequency changes, especially when the grid frequency decreases, the introduction of the adaptive internal model sampling frequency control technology (AIMSF) will cause the cycle delay of the internal model to become longer, and the PI controller parameters used by IRC to adjust the dynamic performance will not be in the original optimal state. Macroscopically, it reflects that the dynamic performance of the entire system becomes slower when the frequency fluctuates. Using the decoupling idea, the harmonic sampling is divided into odd harmonic sampling and even harmonic sampling for simultaneous parallel control. Because the parallel sampling frequency is reduced by half, the response speed can be doubled under ideal conditions, as shown in Figure 8 .

[0056] Further research shows that the adaptive internal model sampling frequency control technology (AIMSF) also has a serious attenuation at higher harmonic frequencies and when the grid frequency is too large. The embodiment of the present application proposes a variable bandwidth adjustment internal model control (VBAI) technology, which forcibly increases the gain of IRC at the harmonic frequency, namely, widens the control bandwidth. The increased control structure is as follows: Figure 9As shown, the increased structure can be considered as a "special inner mode", which is essentially to control RC by RC itself. The transfer function of the structure is analyzed, and the internal control coefficient (K Iccn , n = 0, 1) is introduced, and the width of the gain bandwidth can be dynamically adjusted by adjusting KIccn, and the control structure is as shown in Figure 10 .

[0057] In Figure 9 , a bandwidth control channel is connected in parallel to each of the odd harmonic control channel and the even harmonic control channel, i.e. odd bandwidth control and even bandwidth control, to form a four-mode composite repetitive control link. The four modules are essentially a modification of the inner mode, i.e. adding a "special inner mode" to achieve the purpose of RC controlling RC. Each of the four channels has an odd-even control coefficient, the odd control coefficient K0 = K 00 + K 01 , and the even control coefficient K1 = K 11 + K 10 , wherein K 01 and K 10 also act together with the internal control coefficients K ICC1 and K ICC2 to control the bandwidth width of the odd frequency and the even frequency.

[0058] Kicc1 and Kicc2 represent the proportion of odd-even bandwidth control. In order to maintain the stability of the system, Kicc1 or Kicc2 should be greater than 0.5. If the value of Kicc is continuously increased, the bandwidth between the odd and even harmonics will also increase, and when Kicc tends to infinity, the gain of the entire frequency band will even present a straight line, i.e. the bandwidth is infinite, of course, at this time, the control effect is also lost.

[0059] K00, K01, K11 and K10 in the above formula represent the proportion coefficients of the three channels. K00 and K10 respectively determine the filtering proportion of the odd harmonic and the even harmonic. When the content of the odd harmonic is greater than that of the even harmonic, K00 > K10 can be allowed. Generally, the sum of K00 and K10 is 1. K01 and K10 respectively determine the bandwidth width proportion of the odd harmonic and the even harmonic, and can also affect the gain size. When K01 > K0, the gain of the odd harmonic increases, and the gain at the even harmonic is weakened. When K01 >> K10, the even harmonic will even no longer have positive gain.

[0060] Figure 10As shown in the control bandwidth variation when Kicci and Kicci2 are equal and vary according to 10, 2.5 and 1.0, it is obvious that the control bandwidth at the frequency point will increase significantly with the increase of Kicci, the bandwidth within up to 50th harmonic (50*50=2.5 kHz) will be lifted, and the whole system bandwidth will increase, greatly improving the stability when the frequency fluctuates. As shown in (a) and (b) in FIG. 1, if the values of K01 or K10 are changed, the bandwidth control strength of Kicci and Kicci2 can be realized. When K01=1 and K10=20, the odd-order bandwidth is narrowed and the even-order bandwidth is widened. Figure 10

[0061] In combination with the above improvements, the complete core circuit design diagram proposed by the embodiment of the present application is shown in FIG. 2, and the corresponding complete core control technology, i.e. the principle structure diagram of the four-mode bandwidth variable type adaptive sampling frequency type repetitive control technology (FVBAF-RC) is shown in FIG. 3. Figure 11 Figure 12

[0062] Figure 12 ​​​The control principle structure of four-mode variable bandwidth adaptive sampling frequency type repetitive control technology (FVBAF-RC) is shown. The four-mode variable bandwidth adaptive sampling frequency type repetitive control technology has four forward channels of repetitive control "inner mode", the channel where K00 and K01 are located jointly constitutes odd harmonic control, and the channel where K10 and K11 are located jointly constitutes even harmonic control. When the input signal R(z) of the system enters, the PI control link first responds to the signal and controls the signal for the first time. After delaying for half a fundamental period, the repetitive control "inner mode" starts to work, and each channel contains specific links. C2(z) is a quadratic compensator, which is generally a constant less than 1 or a low-pass filter, and is used to stabilize the poles of the "inner mode" control link. FIR is a finite impulse response filter based on Lagrange linear interpolation, which is used to track the decimal part of the sampling frequency caused by the frequency deviation. Kicc is the harmonic bandwidth control coefficient, and the relative size of Kicc1 or Kicc2 can be adjusted to increase or decrease the bandwidth at odd or even frequencies. When Kicc1>Kicc2, the bandwidth at the odd frequency is increased, and when Kicc1<Kicc2, the bandwidth at the even frequency is increased. The value of Kicc in other channels is mainly to resist the excessive change of the peak gain. T(z) is a repetitive control compensator, which is mainly used to compensate the amplitude-frequency and phase-frequency characteristics of the control object G(z) to meet the zero gain and zero phase shift of the system, so its composition generally includes proportional link, phase lead link and filter link, etc. D(z) is a disturbance signal, which is generally directly added to the output signal C(z), and then the output signal is transmitted back to the input signal through the negative feedback link, and the value of the deviation signal E(z) is continuously adjusted to approach 0 to realize the stable control of the input signal. Through the continuous control of the PI controller and the FVBAF-RC controller, the input signal can be well tracked and controlled in less than 10 fundamental periods.

[0063] The four-mode variable bandwidth adaptive sampling frequency type repetitive control technology has four forward channels of repetitive control "inner mode", the channel where K 00 The channel where K 01 The channel where K 10 The channel where K 11 When the input signal R(z) of the system enters, the PI control link first responds to the signal and controls the signal for the first time. After delaying for half a fundamental period, the repetitive control "inner mode" starts to work, and each channel contains specific links. C2(z) is a quadratic compensator, which is generally a constant less than 1 or a low-pass filter, and is used to stabilize the poles of the "inner mode" control link.

[0064] FIR is a finite impulse response filter based on Lagrange linear interpolation, which is used to track the decimal part of the sampling frequency caused by the frequency deviation. K IccK is the harmonic bandwidth control coefficient, by adjusting K Icc1 or the relative size of K Icc2 , the increase and decrease of odd and even harmonic bandwidth can be realized, when K Icc1 >K Icc2 , the bandwidth at the odd frequency increases, when K Icc1 <K Icc2 , the bandwidth at the even frequency increases. The value of K Icc in other channels except the odd and even harmonic bandwidth control channels is mainly to resist the excessive change of peak gain. T(z) is a repetitive control compensator, mainly to compensate the amplitude and phase characteristics of the control object G(z) to meet the zero gain and zero phase shift of the system, so its composition generally includes proportional link, phase lead link and filter link, etc.

[0065] D(z) is a disturbance signal, generally directly added to the output signal C(z), and then the output signal is transmitted back to the input signal through the negative feedback link, and the value of the deviation signal E(z) is continuously adjusted to approach 0 to realize the stable control of the input signal. Through the continuous control of PI controller and FVBAF-RC controller, good tracking control of the input signal can be achieved in less than 10 fundamental periods.

[0066] The transfer function expression of the FVBAF-RC control link shown in Fig. Figure 12 is

[0067]

[0068] In formula (1), K 00 , K 01 , K 10 and K 11 represent the proportional coefficients of the four channels, K Icc1 and K Icc2 represent the proportion of odd and even harmonic bandwidth control, C2(z) is a quadratic compensator, and N is the sampling number of repetitive control, and its calculation formula is

[0069]

[0070] In formula (2), f sw represents the sampling frequency, and f s is the fundamental frequency.

[0071] In the continuous time domain, when the quadratic compensator C2(z) approaches 1, the transfer function of the odd and even harmonic control link can be expressed as

[0072]

[0073] The Taylor expansion of formula (3) is obtained as

[0074]

[0075] In formula (4), T0 is the fundamental period, w0 is the angular frequency of the fundamental signal, and they satisfy the relationship w0 = 2π / T0. It can be found from formula (4) that the FVBAF-RC controller has poles at the direct current or integer multiples of the fundamental frequency, and the gain at all odd harmonics and even harmonics is infinite, which can theoretically achieve zero-error tracking control of all harmonics.

[0076] K 00 and K 11 respectively determine the filtering proportion of odd harmonics and even harmonics respectively, when the content of odd harmonics is greater than that of even harmonics, K 00 > K 11 , generally, the sum of K 00 and K 11 is 1. When K 11 = 0, the even bandwidth control is invalid, and the system is equivalent to a pure odd harmonic control link.

[0077] K 01 and K 10 respectively determine the bandwidth proportion of odd harmonics and even harmonics, and can also affect the gain size, when K 01 > K 10 , the gain of odd harmonics increases, and the gain at even harmonics is weakened, when K 01 >> K 10 , even harmonics no longer have positive gain.

[0078] Formula (5) gives the transfer function expansion of the traditional IRC, and formula (4) can be seen that the error convergence speed of the FVBAF-RC control is half of the IRC under ideal conditions.

[0079]

[0080] The error transfer function of the system can be obtained from Figure 12

[0081]

[0082] G FVBAF (z) in formula (6) is the transfer function of the four-mode bandwidth variable adaptive sampling frequency type repetitive control link expressed in formula (1), R(z) represents the input signal, D(z) is the disturbance signal, T(z) is the repetitive control compensator, and G(z) is the control object. Therefore, the characteristic polynomial of the system is

[0083] Δ = 1 + [G pi (z) + G FVBAF ​(z)G(z) (7)

[0084] Assume

[0085]

[0086] Formula (8) can be actually understood as an equivalent control model when only the PI controller acts, and the FVB AF-RC controller does not act. Then formula (7) can be expressed as

[0087] Δ = [1 + G pi (z)G(z)] · [1 + G FVBAF (z)T(z)G s (z)] (9)

[0088] Therefore, the condition for the FVBAF-RC system to satisfy stability is that all solutions of formula (10) are within the unit circle, which is the stability condition of the system.

[0089]

[0090] Substituting the stability condition into formula (1) and formula (8) for mathematical analysis, it can be obtained that the coupling relationship between parameters should satisfy the following formula

[0091]

[0092] K RC in formula (11) represents the total equivalent gain of repetitive control, represents the cosine value of the phase angle of the system, represents the modulus value of the equivalent control model G s (z). According to the stability condition, the parameter design of the aforementioned FVBAF-RC transfer function is performed, and the amplitude-frequency response and phase-frequency curve of the equivalent control object can be obtained by substituting the appropriate control parameters. It can be obtained from the graph that the gain of the control object in the medium and low frequency band is very close to 0 dB, and there is no obvious phase lag, and in the high frequency band, there is a relatively high negative gain. At this time, although the phase has a large lead, the influence on the system is small due to the serious gain attenuation, and the comprehensive control effect is good.

[0093] The difficulty of the embodiment of the present application is that the bandwidth at the odd and even specific frequencies in the four-mode bandwidth variable adaptive sampling frequency repeat control technology (FVBAF-RC) is difficult to widen, so the traditional IRC control is difficult to maintain the original control gain when the power grid frequency changes, thereby affecting the control effect. The bandwidth control structure proposed in the embodiment of the present application is designed on the basis of the "inner mode" structure unique to the repeat control, which can maintain good control of the periodic signal, and through the adjustment of the simple inner control coefficient, the simple and convenient bandwidth adjustment can be realized.

[0094] Figure 12 The meanings of the symbols involved in the embodiment of the present application are shown in the following table 1.

[0095] Table 1: meanings of each part of the current tracking control link

[0096]

[0097]

[0098] Figure 12 The transfer function shown in the embodiment of the present application is:

[0099]

[0100] The above-mentioned relationship between the output signal and the input signal can be obtained by multiplying the input signal R(z) by the above-mentioned transfer function to obtain the output signal C(z), and the formula can represent all properties of the current tracking control link proposed in the embodiment of the present application.

[0101] The mathematical relationship of each link is further described as follows:

[0102]

[0103] Figure 12 The flow of the embodiment of the present application is briefly introduced as follows:

[0104] ① The detected harmonic current is taken as an input signal and enters the negative feedback calculation with the output signal of the last period (initially 0) to obtain a deviation signal E(z), which is sent to step ②;

[0105] ② E(z) is sent to the FVBAF-RC control link, and a preliminary command signal Y(z) (main command signal) is obtained through the control link and sent to step ③;

[0106] ③The preliminary command signal Y(z) passes through a repetitive control compensator T(z), and the obtained signal is added to another command signal (non-main command signal, which can be ignored) obtained through a PI controller, and the two signals jointly act on the controlled object and are added to other disturbance signals to obtain a final control current command value, which is output to a driving circuit and is simultaneously fed back to the initial control stage (before the deviation signal) again, and the end condition of the feedback is that the deviation signal is 0. In actual operation, it is impossible for the deviation to reach 0, so the control will continue to be carried out.

[0107] Simulation experiment based on the Matlab / Simulink platform

[0108] The simulation parameters are shown in Table 2.

[0109] Table 2 Complete simulation circuit diagram

[0110]

[0111]

[0112] Figure 13 It is shown that, when the grid frequency is 50 Hz, the compensation effect of the designed FVBAF-RC-APF on the grid-side current. At 0.4 s, the grid frequency fluctuates from 50 Hz to 49.5 Hz. As can be seen from the figure, the APF reduces the load-side harmonic from THDi=21.44% to about 2.31% in less than 10 working periods (10*1 / 50 s), and operates stably under standard working conditions.

[0113] Figure 14 It is shown that, when the grid frequency is 50 Hz, the compensation effect of the designed FVBAF-RC-APF on the grid-side current. At 0.4 s, the grid frequency fluctuates from 50 Hz to 49.5 Hz. As can be seen from the figure, the APF reduces the load-side harmonic from THDi=21.44% to about 2.31% in less than 10 working periods (10*1 / 50 s), and operates stably under standard working conditions. Figure 14 As can be seen from (a) of FIG. 10, when the grid frequency decreases from 50 Hz to 49.5 Hz at 0.3 s, the response time of the IRC-APF becomes longer, and the control effect becomes worse, THDi increases from the original stable compensation of 3.56% to 9.18%, which exceeds the upper limit of 5% specified in the national standards such as “Power Quality: Public Grid Harmonics (GB / T 14549-1993)”, “Power Quality: Public Grid Interharmonics (GB / T 24337-2009)” and “Grid Operation Guidelines (GB / T 31464-2015)”, and the effect of harmonic filtering is relatively poor. Figure 14 As can be seen from (b) of FIG. 10, the FVBAF-RC-APF designed in the embodiment of the application can still ensure stable compensation within 10 working periods under the condition of frequency fluctuation, and the harmonic THDi decreases to 3.57, which only increases by 1.26%, and has a good compensation effect.

[0114] The THD analysis of the FVBAF-RC-APF designed in the embodiment of the present invention is performed when the grid frequency decreases to 49.5 Hz and increases to 50.5 Hz. Figure 15 When the grid frequency drops to 49.5 Hz, the steady-state current THDi is only 2.47%, and when the grid frequency rises to 50.5 Hz, the steady-state current THDi is only 2.13%, indicating that the APF designed in this embodiment of the present invention has good adaptability to grid frequency fluctuations.

[0115] The FVBAF-RC-APF designed in the embodiment of the present invention was simulated by a physical experiment on the RT-LAB platform to further verify its applicability in engineering applications. Figure 15 As shown in the figure, the simulated grid frequency is reduced to 49.5Hz and increased to 50.5Hz by the simulated grid generator. At this time, the grid side current after FVBAF-RC-APF filtering is as follows: Figure 16 As shown in the figure, regardless of whether the grid frequency is rising or falling, the grid-side current sinusoidality detected by the oscilloscope is good, indicating that the invented FVBAF-RC-APF has good applicability to wide frequency fluctuations in practical applications, high system operation stability, and certain production application value.

[0116] As mentioned above, the grid harmonic current under frequency fluctuation can be compensated stably and efficiently. Specifically, after using the embodiment of the present invention, the APF system can stably reduce the harmonic THD value of the grid current and ensure that the sinusoidality of the current waveform is at a high level.

[0117] Variable bandwidth adaptive sampling frequency repetitive control (VBAF-RC) technology has the following advantages:

[0118] 1. Adapting to grid frequency fluctuations: A Lagrange interpolation-based FIR filter (AIMSF technology) corrects the fractional portion of the sampling count, effectively addressing the severe degradation of control effectiveness caused by changes in the sampling count of traditional repetitive control due to grid frequency fluctuations. This ensures stable control gain under frequency fluctuations. For example, when the grid frequency fluctuates from 50Hz to 49.6Hz, the gain of traditional control technology drops significantly at the ninth harmonic. However, the use of AIMSF technology can clamp the gain back to a higher level, ensuring effective filtering of harmonics.

[0119] 2. Improve the dynamic performance of the system: Using the decoupling concept, harmonic sampling is divided into odd harmonic sampling and even harmonic sampling for parallel control. Under ideal conditions, the response speed can be increased by 2 times, improving the dynamic performance of the system during frequency fluctuations.

[0120] 3. Enhanced system stability: The variable bandwidth adjustment inner model control (VBAI) technique increases the special inner model structure, uses RC to re-control RC itself, and introduces an inner control coefficient to adjust the gain bandwidth width. When the grid frequency fluctuates, the control bandwidth can be significantly increased, such as the bandwidth within up to 50 harmonics (50*50=2.5kHz) will be lifted, which improves the stability of the system and enables the APF to maintain good compensation effect when the grid frequency changes. For example, when the grid frequency fluctuates within 50Hz±0.5Hz, the technique can enable the APF to stably compensate the grid harmonic current, reduce the harmonic THD value of the grid current, and ensure that the sinusoidal degree of the current waveform is at a high level.

[0121] 4. Flexible control mode: By adjusting the inner control coefficient, odd control coefficient, and even control coefficient, etc. parameters, the control of different frequency harmonics can be simply and conveniently realized, including the adjustment of filtering ratio, bandwidth width ratio, and gain size, to adapt to different grid operating conditions and load characteristics.

[0122] Embodiment 2

[0123] Embodiment 2 of the present application provides a terminal device corresponding to the above-mentioned embodiment 1. The terminal device can be a processing device for a client, such as a mobile phone, a notebook computer, a tablet computer, a desktop computer, etc., to execute the method of the above-mentioned embodiment.

[0124] The terminal device of the present embodiment includes a memory, a processor, and a computer program stored on the memory; the processor executes the computer program on the memory to realize the steps of the method of embodiment 1.

[0125] In some implementations, the memory can be a high-speed random access memory (RAM: Random Access Memory), and can also include a non-volatile memory, such as at least one disk memory.

[0126] In other implementations, the processor can be a central processing unit (CPU), a digital signal processor (DSP), or various types of general-purpose processors, without limitation.

[0127] Embodiment 3

[0128] Embodiment 3 of the present application provides a computer readable storage medium corresponding to the above-mentioned embodiment 1, which stores computer programs / instructions. When the computer programs / instructions are executed by the processor, the steps of the method of embodiment 1 are realized.

[0129] The computer readable storage medium can be a tangible device that can retain and store instructions for use by an instruction execution device. The computer readable storage medium can be, for example, but is not limited to, an electronic storage device, a magnetic storage device, an optical storage device, an electromagnetic storage device, a semiconductor storage device, or any combination thereof.

[0130] Those skilled in the art will appreciate that embodiments of the present application can be devised for a method, a system, or a computer program product. Accordingly, the present application can take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present application can take the form of a computer program product on one or more computer readable storage media (including, but not limited to, disk storage, CD-ROMs, optical storage devices, etc.) embodying computer readable program code thereon. Embodiments of the present application can be implemented in various computer languages including, but not limited to, Java, JavaScript, and the like.

[0131] The present application is described in reference to the flowchart illustrations and / or block diagrams according to the embodiments of the application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general purpose computer, special purpose computer, embedded processing system or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart illustrations and / or block diagrams block or blocks. Figure 1 one or more functions specified in the flowchart illustrations and / or block diagrams block or blocks. Figure 1 means for carrying out each of the

[0132] These computer program instructions can also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart illustrations and / or block diagrams block or blocks. Figure 1 one or more functions specified in the flowchart illustrations and / or block diagrams block or blocks. Figure 1 means for carrying out each of the

[0133] While the preferred embodiments of the application have been described, additional variations and modifications can be made to the embodiments by those skilled in the art once they learn of the basic inventive concepts. Therefore, the appended claims are intended to cover all such modifications and variations as fall within the true scope of the application.

[0134] Obviously, many modifications and variations of the present application are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims and their equivalents, the application can be practiced otherwise than as specifically described.

Claims

1. A control method for an active power filter suitable for frequency fluctuations, characterized in that: The following steps are involved: S1. Detect the harmonic current in the distribution network and determine whether there is harmonic current; If yes, go to step S2; S2. Calculating a current command value using the harmonic current; S3, modulating the current command value through SVPWM to obtain a switching signal, and using the switching signal to control the on and off of the active power filter switch; in, The current command value I ref The calculation formula is: Among them, I Lh is the detected harmonic current; G FVBAF (z) is the transfer function of the current tracking control link, D(z) is the disturbance signal, T(z) is the repetitive control compensator, G(z) is a constant, R(z) represents the input signal, G pi (z) is the PI controller, z is the complex frequency variable of the active power filter; K 00 , K 01 , K 10 and K 11 Represents the proportional coefficient of the four channels, K 00 With K 01 The channels together constitute odd harmonic control, K 10 With K 11 The channels together constitute the even harmonic control, K Icc1 and K Icc2 Represents the proportion of odd and even bandwidth control, by adjusting K Icc1 or K Icc2 The relative size of the odd and even bandwidth can be increased or decreased. When K Icc1 >K Icc2 When K Icc1 <K Icc2 When , the bandwidth at the even frequency increases, C2(z) is a quadratic compensator, N is the number of sampling times, and C2(z) is a quadratic compensator.

2. The active power filter control method applicable to frequency fluctuation according to claim 1, characterized in that: Among them, f sw represents the sampling frequency, f s is the fundamental frequency.

3. The active power filter control method applicable to frequency fluctuation according to claim 1, characterized in that: The quadratic compensator C2(z) is a constant less than 1 or a low-pass filter.

4. The active power filter control method applicable to frequency fluctuation according to claim 1, characterized in that: After using the switch signal to control the on and off of the active power filter switch tube, the method further includes: S4. Continue to detect harmonic current. If harmonic current does not exist, end; if not, return to S2.

5. The active power filter control method applicable to frequency fluctuation according to claim 1, characterized in that: T(z)=Kz n S(z), K is the proportional coefficient, z n is the phase advance link coefficient, S(z) is the filter link function, 6. An active power filter control system suitable for frequency fluctuations, comprising a memory, a processor, and a computer program stored in the memory; characterized in that: The processor executes the computer program to implement the steps of the method according to any one of claims 1 to 5.

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