Harmonic compensation control method with adjustable parallel filter loop width

Abstract

The invention discloses a harmonic compensation control method capable of adjusting the loop width of a parallel filter. Specifically, a three-phase current passes through a hysteresis comparator and then is output to a drive circuit, the drive circuit passes through an inverter bridge arm and then is output to an alternating current inlet wire inductor as an alternating current, the alternating current inlet wire inductor as an output end feeds back an output end voltage through a Hall voltage sensor, and a direct current side of the inverter bridge arm also feeds back a bus voltage. The feedback of the output end voltage and the feedback of the direct current side bus voltage form loop width adjustment and are fed back to a hysteresis comparator, the hysteresis comparator is changed into a variable-loop-width hysteresis comparator, and meanwhile, an alternating current inlet wire inductor serving as the output end carries out feedback compensation on the output end current through a Hall current sensor to supply three-phase current. The method has the beneficial effects that the change of the instruction current signal can be accurately tracked in real time through the compensation current signal when the active filter adopts parallel filtering, and the dynamic performance of power quality harmonic compensation is improved.

Description

Technical Field

[0001] The present invention relates to the technical field related to power distribution networks, and in particular to a harmonic compensation control method with adjustable loop width of a parallel filter. Background Art

[0002] With the continuous increase in the penetration rate of microgrids, a large number of power electronic generating devices are connected to the distribution network. The operation of these devices can easily cause the distortion of the grid current and voltage waveforms, resulting in power quality problems such as harmonic pollution and reactive power loss in the distribution network. Power quality problems such as harmonics generated by nonlinear loads on the user side will also affect distributed power sources. As a comprehensive power quality regulation device, the power quality controller can be used to compensate for reactive power, harmonics, negative sequence current, etc. generated by nonlinear loads, and has become a research hotspot for many experts and scholars. For the distribution network harmonic detection method, it is mainly divided into Fourier transform method, wavelet transform method, harmonic detection algorithm based on instantaneous theory, adaptive filtering algorithm and other methods.

[0003] The Fourier transform method detects harmonic currents based on the discrete Fourier transform method and uses a triangular carrier comparison method for current tracking. The Fourier FFT algorithm is more suitable for loads that change slowly due to its delay, but it is difficult to be effective for microgrids with complex dynamic changes. The wavelet analysis method basically inherits all the advantages of the Fourier analysis method, but its disadvantage is that the amount of calculation is large. How to apply the wavelet transform to an asymmetric power system is an unresolved problem. According to an extensive and in-depth survey of existing literature, in the process of UPQC harmonic detection research, the most widely used method is based on instantaneous power theory, which now mainly includes the pq method and i p -i q Method.i p -i q This method is applicable to various situations such as grid voltage distortion and grid voltage asymmetry. Since various power devices in microgrids are easily affected by weather and other environmental factors, it is very easy to generate random, unstable, and fluctuating harmonic voltages, which increases the difficulty of harmonic control in distribution networks. For multivariable, nonlinear, time-varying control systems, traditional PI control parameters cannot be optimized as the state of the controlled object changes, resulting in poor control performance. Summary of the invention

[0004] The present invention aims to overcome the above-mentioned deficiencies in the prior art and provides a harmonic compensation control method with adjustable loop width of a parallel filter capable of improving the dynamic performance of power quality harmonic compensation.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A harmonic compensation control method with adjustable loop width of a parallel filter is specifically as follows: three-phase current is output to a drive circuit after passing through a hysteresis comparator, and the drive circuit is output as AC to an AC incoming line inductor after passing through an inverter bridge arm, and the AC incoming line inductor as an output end feeds back the output end voltage through a Hall voltage sensor, and the DC side of the inverter bridge arm also feeds back the bus voltage, and the feedback of the output end voltage and the feedback of the DC side bus voltage constitute loop width adjustment feedback to the hysteresis comparator, and the hysteresis comparator is changed into a variable loop width hysteresis comparator, and at the same time, the AC incoming line inductor as an output end feeds back the output end current through a Hall current sensor to compensate for the three-phase current.

[0007] Aiming at the problem that the current power quality controller adopts the traditional hysteresis control method to compensate the shortcoming of the fixed current signal following error, resulting in poor harmonic compensation performance, the present invention proposes a harmonic compensation method based on i p -i q Based on the method, a hysteresis control compensation strategy with variable loop width is adopted to ensure that the active filter can accurately track the changes of the command current signal in real time through the compensation current signal when using parallel filtering, thereby improving the dynamic performance of power quality harmonic compensation.

[0008] As a preferred embodiment, the specific principle process is as follows:

[0009] According to the output characteristics of the hysteresis comparator, when the current passes through the AC line inductor, it takes one cycle to pulsate once. The switching cycle time T is the sum of the current rise time and the current fall time. The expression formula is as follows:

[0010]

[0011] Where: t up is the current rise time, u dc is the DC bus voltage, t down is the current falling time, L is the output AC line inductance, u0 is the output voltage feedback value, and h is the loop width value; according to the above formula, the switching frequency f is:

[0012]

[0013] According to the above switching frequency formula, the following formula is obtained:

[0014]

[0015] Take f = F, according to the above formula, the calculation formula of the ring width link is as follows:

[0016] h=h d -Δh

[0017] h d = k1 udc

[0018] Δh=k2·u o 2

[0019]

[0020] Where: Δh is the AC component of the loop width, h d is the DC component of the loop width, F is the switching frequency value, k1 is the coefficient of the DC component of the loop width, and k2 is the coefficient of the AC component of the loop width; through the above calculation, the variable loop width h signal value can be obtained.

[0021] As a preferred embodiment, when the current passes through the AC line inductor, there is an error between the actual current and the ideal sinusoidal current, that is, the error value Δi c , and the loop width h is the loop width AC component minus the loop width DC component, and the error value Δi c The loop width h output by the variable loop width link is calculated and judged, and the comparison result is output as a PWM signal. The specific comparison process is as follows:

[0022] (1) When Δi c <-h, PWM signal outputs high level, and the actual compensation current value increases;

[0023] (2) When -h<Δi c <h, PWM signal output remains unchanged;

[0024] (3) When Δi c >h, the PWM signal outputs a low level and the actual compensation current value decreases.

[0025] As a preference, the error value Δi c The actual compensation current must be within the required range of the loop width h so that the actual compensation current can track the compensation current signal and the output waveform is infinitely close to the compensation current waveform.

[0026] The beneficial effect of the present invention is that through the variable loop width hysteresis control compensation strategy, it is ensured that the active filter can accurately track the change of the command current signal in real time through the compensation current signal when parallel filtering is adopted, thereby improving the dynamic performance of power quality harmonic compensation. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a flow chart of the method of the present invention. DETAILED DESCRIPTION

[0028] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments.

[0029] The hysteresis control method is a PWM control technology commonly used in engineering control and is widely used in power quality management and control. However, the loop width h of the traditional hysteresis comparator is fixed, and the current following error is also fixed. In order to make the actual compensation current output have an effect on the command current, reduce the difference between the two, and make the compensation effect better, the traditional hysteresis control method can no longer meet such requirements. Therefore, the present invention proposes a hysteresis comparator to improve the parallel filter voltage compensation control and harmonic control method with adjustable loop width. The principle is as follows Figure 1 shown.

[0030] Different from the traditional hysteresis method, Figure 1 The voltage feedback and bus voltage feedback are added to form the loop width adjustment link, so that the loop width of the hysteresis comparator becomes a variable. Compared with the traditional hysteresis comparison method, the above improvement changes the traditional hysteresis comparator fixed loop width into a variable loop width hysteresis comparator. The basic principle process of the present invention is described as follows:

[0031] A harmonic compensation control method with adjustable loop width of a parallel filter, specifically: the three-phase current is output to the drive circuit after passing through a hysteresis comparator, and the drive circuit is output as AC to the AC incoming line inductor after passing through the inverter bridge arm. The AC incoming line inductor as the output end feeds back the output end voltage through a Hall voltage sensor, and the DC side of the inverter bridge arm also feeds back the bus voltage. The feedback of the output end voltage and the feedback of the DC side bus voltage constitute the loop width adjustment feedback to the hysteresis comparator, and the hysteresis comparator is changed into a variable loop width hysteresis comparator. At the same time, the AC incoming line inductor as the output end feeds back the output end current through a Hall current sensor to compensate for the three-phase current. The specific principle process is as follows,

[0032] According to the output characteristics of the hysteresis comparator, when the current passes through the AC line inductor, it takes one cycle to pulsate once. The switching cycle time T is the accumulation of the current rise time and the current fall time. The expression formula is as follows:

[0033]

[0034] Where: t up is the current rise time, u dc is the DC bus voltage, t down is the current falling time, L is the output AC line inductance, u0 is the output voltage feedback value, and h is the loop width value; according to the above formula, the switching frequency f is:

[0035]

[0036] According to the above switching frequency formula, the following formula is obtained:

[0037]

[0038] Take f = F, according to the above formula, the calculation formula of the ring width link is as follows:

[0039] h=h d -Δh

[0040] h d = k1·u dc

[0041] Δh=k2·u o 2

[0042]

[0043] Where: Δh is the AC component of the loop width, h d is the DC component of the loop width, F is the switching frequency value, k1 is the coefficient of the DC component of the loop width, and k2 is the coefficient of the AC component of the loop width. Through the above calculation, the variable loop width h signal value can be obtained. Figure 1 It can be seen that the error value Δi c is the error between the actual current and the ideal sinusoidal current. Theoretically, it is the superposition state of DC current and AC current. Since the loop width h is the loop width AC component minus the loop width DC component, the error value Δi c Can be compared with the ring width; the error value Δi c The loop width h output by the variable loop width link is calculated and judged, and the comparison result is output as a PWM signal. The specific comparison process is as follows:

[0044] (1) When Δi c <-h, PWM signal outputs high level, and the actual compensation current value increases;

[0045] (2) When -h<Δi c <h, PWM signal output remains unchanged;

[0046] (3) When Δi c >h, the PWM signal outputs a low level and the actual compensation current value decreases.

[0047] Among them, the error value Δi c The actual compensation current must be within the required range of the loop width h so that the actual compensation current tracks the compensation current signal and the output waveform is infinitely close to the compensation current waveform, ensuring that the real-time compensation effect of the PAPF (parallel active filter) is more perfect.

[0048] In summary, the present invention aims to solve the problem that the current power quality controller adopts the traditional hysteresis control method to compensate for the shortcomings of the fixed current signal following error, resulting in poor harmonic compensation performance. p -i qBased on the method, a hysteresis control compensation strategy with variable loop width is adopted to ensure that the active filter can accurately track the changes of the command current signal in real time through the compensation current signal when using parallel filtering, thereby improving the dynamic performance of power quality harmonic compensation.

Claims

1. A harmonic compensation control method with adjustable loop width of a parallel filter, characterized in that: Specifically, the three-phase current is output to the drive circuit after passing through the hysteresis comparator. The drive circuit is output as AC to the AC incoming line inductor after passing through the inverter bridge arm. The AC incoming line inductor as the output end feeds back the output end voltage through the Hall voltage sensor, and the DC side of the inverter bridge arm also feeds back the bus voltage. The feedback of the output end voltage and the feedback of the DC side bus voltage constitute the loop width adjustment feedback to the hysteresis comparator, and the hysteresis comparator is changed into a variable loop width hysteresis comparator. At the same time, the AC incoming line inductor as the output end feeds back the output end current through the Hall current sensor to compensate for the three-phase current.

2. The harmonic compensation control method with adjustable loop width of a parallel filter according to claim 1 is characterized in that: The specific principle process is as follows: According to the output characteristics of the hysteresis comparator, when the current passes through the AC line inductor, it takes one cycle to pulsate once. The switching cycle time T is the accumulation of the current rise time and the current fall time. The expression formula is as follows: Where: t up is the current rise time, u dc is the DC bus voltage, t down is the current falling time, L is the output AC line inductance, u0 is the output voltage feedback value, and h is the loop width value; according to the above formula, the switching frequency f is: According to the above switching frequency formula, the following formula is obtained: Take f = F, according to the above formula, the calculation formula of the ring width link is as follows: h=h d -Δh h d =k1·u dc Δh=k2·u o 2 Where: Δh is the AC component of the loop width, h d is the DC component of the loop width, F is the switching frequency value, k1 is the coefficient of the DC component of the loop width, and k2 is the coefficient of the AC component of the loop width; through the above calculation, the variable loop width h signal value can be obtained.

3. The harmonic compensation control method with adjustable loop width of a parallel filter according to claim 1 or 2, characterized in that: When the current passes through the AC line inductor, there is an error between the actual current and the ideal sinusoidal current, that is, the error value Δi c , and the loop width h is the loop width AC component minus the loop width DC component, and the error value Δi c The loop width h output by the variable loop width link is calculated and judged, and the comparison result is output as a PWM signal. The specific comparison process is as follows: (1) When Δi c <-h, PWM signal output high level, the actual compensation current value increases; (2) When -h<Δi c <h, PWM signal output remains unchanged; (3) When Δi c >h, the PWM signal outputs a low level and the actual compensation current value decreases.

4. The harmonic compensation control method with adjustable loop width of a parallel filter according to claim 3 is characterized in that: Error value Δi c The actual compensation current must be within the required range of the loop width h so that the actual compensation current can track the compensation current signal and the output waveform is infinitely close to the compensation current waveform.

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