Ultra-wideband power grid simulation method based on improved repetitive control

Abstract

The invention proposes an ultra-wideband power grid simulation method based on improved repetitive control, and the method comprises the steps: carrying out the reconstruction of a repetitive controller from an internal model and a compensator, and obtaining a self-adaptive control inner loop system matched with the compensator through deduction; secondly, a plurality of internal model branches considering the normal deviation of the power grid frequency are connected in parallel, delay parameters of each branch are accurately designed by using a fractional order delay filter, and improvement is performed by using a compensator, so that the requirement of ultra-wideband high-performance output of the power grid simulator is met.

Description

Technical Field

[0001] The invention belongs to the field of power grid simulator technology, and in particular to an ultra-wideband power grid simulation method based on improved repetitive control. Background Art

[0002] With the rapid development of distributed power generation, the problems such as harmonics and voltage imbalance caused by its integration into the power grid cannot be ignored. The operating state of the real power grid is uncontrollable and cannot provide various working conditions required for grid-connected equipment testing. Therefore, it is particularly important to study a power grid simulator that can accurately reproduce various working conditions of the power grid. For high-voltage and large-capacity power grid simulators, the control method is the key to reproducing high-quality output waveforms.

[0003] In traditional control methods, PI control is simple to implement and can track DC signals without error, but it cannot track harmonics without error. PR control can track harmonics without static error, but if the reference signal is a multi-frequency harmonic, multiple controllers need to be designed, which increases the design workload and system complexity. Beat-free control has fast dynamic response, but it requires high accuracy of the mathematical model of the controlled object and cannot suppress load disturbances and system parameter drift. Repetitive control can track sinusoidal signals without error, but its dynamic performance is poor and is affected by fundamental frequency offset. Summary of the invention

[0004] The invention proposes an ultra-wideband power grid simulation method based on improved repetitive control.

[0005] The technical solution to achieve the purpose of the present invention is: an ultra-wideband power grid simulation method based on improved repetitive control, comprising:

[0006] S1: Set the output voltage reference value and sample the voltage across the device under test to obtain the output voltage;

[0007] S2: Calculate the difference between the voltage reference value and the sampled output voltage;

[0008] S3: inputting the difference between the voltage reference value and the sampled output voltage into the improved multi-internal model fractional-order repetitive control module for processing to obtain a first output result;

[0009] S3: adding the first output result to the output voltage reference value and inputting the result into a Lyapunov-based adaptive control module to obtain a second output result;

[0010] S4: modulate the second output result as a modulation wave to obtain a turn-on signal of each switch tube in the cascaded H-bridge module, simulate the voltage across the device under test, and resample the voltage across the device under test to obtain the output voltage, and return to S2.

[0011] Preferably, the transfer function of the improved multi-internal model fractional-order repetitive control module is:

[0012] G rc (z) = G ml (z)S(z)

[0013] In the formula, G ml (z) is the transfer function of the multi-internal model, and S(z) is the transfer function of the compensator.

[0014] Preferably, the multi-inner mold structure is composed of five branches connected in parallel, specifically:

[0015]

[0016] In the formula, k i is the weight coefficient of the i-th branch, i = 1, 2, ..., 5, Q(z) is the internal model coefficient, N i is the delay coefficient of the ith branch.

[0017] Preferably, the delay parameter N is a non-integer and is obtained by using a fractional delay approximation scheme based on a finite impulse response filter. Then z -N Specifically:

[0018]

[0019] In the formula, M is the filter order, N d is the fractional part of the delay factor.

[0020] Preferably, the transfer function of the Lyapunov-based adaptive control module is determined as follows:

[0021] Based on the Lyapunov theorem, the adaptive control H(s) in the s domain is derived as:

[0022]

[0023] in, G is the delay link; ZOH (s) is a zero-order holder; the expressions of P(s) and P1(s) are:

[0024] P(s)=1 / (LCs 2 +rCs+1)

[0025] P1(s)=Cs / (LCs 2 +rCs+1)

[0026] In the formula, C is the filter capacitor; L is the filter inductor; r is the equivalent resistance.

[0027] a1(s), a2(s), and a3(s) are:

[0028]

[0029] In the formula, n=ρ+kk1, k, ρ, k1 are adaptive control parameters, They are the estimated values ​​of filter capacitor C, filter inductor L, and equivalent resistance r respectively;

[0030] will be continuous G ZOH (s), P(s), P1(s), a1(s), a2(s), a3(s) are discretized to obtain z -1 , P(z), P1(z), a1(z), a2(z), a3(z), and the transfer function H(z) of the Lyapunov-based adaptive control module in the discrete domain is obtained.

[0031] Preferably, the transfer function of the Lyapunov-based adaptive control module is specifically:

[0032]

[0033] Compared with the prior art, the present invention has the following significant advantages: compared with the existing control method, the present invention has faster dynamic response, higher steady-state accuracy and wider tracking harmonic frequency range.

[0034] The present invention is described in further detail below in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 is the power grid simulator topology.

[0036] Figure 2 It is a schematic diagram of the ultra-wideband power grid simulation method based on improved repetitive control.

[0037] Figure 3 Discrete equivalent block diagram of an adaptive control system.

[0038] Figure 4 Schematic diagram of the internal model structure of multiple internal models fractional-order repetitive control.

[0039] Figure 5 This is a comparison chart of the FFT analysis of the harmonic tracking simulation output voltage waveform.

[0040] Figure 6 This is a comparison chart of harmonic tracking performance experimental results. DETAILED DESCRIPTION

[0041] The present invention proposes an ultra-wideband power grid simulation method based on improved repetitive control for a power grid simulator, wherein the power grid simulator includes three phases, each phase includes a transformer, a rectifier, a cascaded CLLC module and a cascaded H-bridge module connected in sequence, and each H-bridge module input end is connected to a DC voltage U dc , each H-bridge module includes two output ports. The first output port of the first H-bridge module is connected to one end of the equivalent resistor r, the other end of the equivalent resistor r is connected to one end of the filter inductor L, the other end of the filter inductor L is connected to the filter capacitor C and one end of the device under test; the second output port of the first H-bridge module is connected to the first output port of the next H-bridge module; the second output port of the next H-bridge module is connected to the first output port of the next H-bridge module, and so on; the second output port of the last H-bridge module is connected to the filter capacitor C and the other end of the device under test, such as Figure 1 shown.

[0042] The present invention includes two parts: outer loop improved multi-internal model fractional-order repetitive control and inner loop adaptive control based on Lyapunov. After the inner loop adaptive control strategy is controlled, the compensator S(z) in the outer loop repetitive control can be used for targeted design. At this time, the closed-loop frequency characteristics of the system basically meet the high-performance design requirements of zero phase shift and zero gain in the low and medium frequency bands and attenuation in the high frequency band. At the same time, the multi-internal model structure G in the outer loop improved repetitive control ml (z) The compensator S(z) can be used to introduce a proportional link to achieve an overall increase in the amplitude gain near the target harmonic, ensuring that the control system can achieve wide-range high-performance tracking of the target harmonic within the set fundamental frequency offset range.

[0043] like Figure 2 As shown, for the improved multi-internal model fractional-order repetitive control, the output voltage reference value v is first set ref , and sample the voltage across the device under test to obtain the output voltage v o , with v ref and v o The difference E is used as the input of the improved multi-internal model fractional order repetitive control module. The improved multi-internal model fractional order repetitive control module includes a multi-internal model structure G ml (z) and compensator structure S(z), which is expressed as:

[0044] G rc (z) = G ml (z)S(z)

[0045] The output result U and the reference voltage v obtained by improved multi-internal model fractional-order repetitive control ref The added v ref1 As the input of the inner loop Lyapunov-based adaptive control.

[0046] Furthermore, if Figure 4 As shown, the multi-inner module structure G in the outer ring ml (z) is composed of five branches connected in parallel, namely 48Hz, 49Hz, 50Hz, 51Hz and 52Hz branches, corresponding to the branches with subscripts 1 to 5. G ml The expression of (z) is as follows:

[0047]

[0048] Each branch includes a weight coefficient k, an internal model coefficient Q(z) and a delay coefficient N. The delay parameter N is a non-integer and is obtained by using a fractional delay approximation scheme based on a finite impulse response (FIR) filter. -N It can be written as:

[0049]

[0050] In the formula, int(N) is the integer part, N d is the decimal part. It is implemented by Lagrange linear interpolation, and the corresponding expression is:

[0051]

[0052] Filter coefficient D l According to Thiran's formula, we get:

[0053]

[0054] Where M is the filter order, which is a compromise between computational difficulty and approximation effect, and N d The best effect is when it approaches half of M.

[0055] Inner loop: For Lyapunov-based adaptive control, the closed-loop transfer function is:

[0056]

[0057] v ref1 The output result v1 is obtained by H(z) as the input of the inner loop control. v1 is used as the modulation wave and compared with the triangle wave to generate the switch tube drive signal to control the action of each switch tube in the cascade H-bridge module, and finally the output voltage v o simulation.

[0058] Furthermore, the discrete equivalent block diagram of the inner loop adaptive control system is shown in the attached figure. Figure 3 As shown. The adaptive control H(s) in the s domain is derived based on the Lyapunov theorem:

[0059]

[0060] in, G is the delay link due to actual sampling and calculation; ZOH (s) is a zero-order holder; the expressions of P(s) and P1(s) are:

[0061] P(s)=1 / (LCs 2 +rCs+1)

[0062] P1(s)=Cs / (LCs 2 +rCs+1)

[0063] a1(s), a2(s), and a3(s) are:

[0064]

[0065] In the formula, n=ρ+kk1. k, ρ, k1 are adaptive control parameters, all of which are positive real numbers. They are the estimated values ​​of C, L, and r, respectively, calculated by the projection algorithm.

[0066] will be continuous G ZOH (s), P(s), P1(s), a1(s), a2(s), a3(s) are discretized to obtain z -1 , P(z), P1(z), a1(z), a2(z), a3(z), and the transfer function H(z) of the Lyapunov-based adaptive control module in the discrete domain is obtained.

[0067] The present invention derives an adaptive control inner loop system that matches the compensator; secondly, multiple inner model branches that take into account the normal deviation of the power grid frequency are connected in parallel, and each branch uses a fractional-order delay filter to accurately design the delay parameters, and uses the compensator to improve them, so as to achieve the requirements of ultra-wideband high-performance output of the power grid simulator.

[0068] Further simulation and experimental analysis are carried out to analyze the advantages of the control method proposed in the present invention.

[0069] The FFT analysis results of the harmonic tracking output voltage corresponding to the conventional repetitive control and the improved high-performance repetitive control proposed by the present invention are shown in the attached figure. Figure 5As shown. When the fundamental frequency is 50Hz, both the traditional repetitive control and the improved high-performance repetitive control can achieve good tracking of the given harmonic signal. When the fundamental frequency deviates from 50Hz, the steady-state tracking performance of the traditional repetitive control for the harmonics decreases significantly, and the control proposed in the present invention can still track the given harmonic signal well. It is proved that the tracking performance of the control proposed in the present invention for harmonics in the frequency range of 48Hz to 52Hz is significantly better than that of the traditional repetitive control.

[0070] The experimental results of harmonic tracking performance comparison of different control methods are shown in the attached figure. Figure 6 As shown. The calculated average harmonic tracking errors of the traditional repetitive control and the improved high-performance repetitive control for the fundamental wave of 50Hz are 1.73% and 2.25% respectively, indicating that the harmonic tracking effects of the improved high-performance repetitive control and the traditional repetitive control for the power frequency are similar; at the same time, when the fundamental waves are 48Hz, 49Hz, 51Hz and 52Hz, the average harmonic tracking errors of the traditional repetitive control and the improved high-performance repetitive control are 22.93% and 5.15% respectively. The results show that compared with the traditional repetitive control, the improved high-performance repetitive control has a wider control bandwidth and has a higher harmonic tracking accuracy when the given voltage frequency deviates from the power frequency.

Claims

1. An ultra-wideband power grid simulation method based on improved repetitive control, characterized in that: include: S1: Set the output voltage reference value and sample the voltage across the device under test to obtain the output voltage; S2: Calculate the difference between the voltage reference value and the sampled output voltage; S3: inputting the difference between the voltage reference value and the sampled output voltage into the improved multi-internal model fractional-order repetitive control module for processing to obtain a first output result; S3: adding the first output result to the output voltage reference value and inputting the result into a Lyapunov-based adaptive control module to obtain a second output result; S4: modulate the second output result as a modulation wave to obtain a conduction signal of each switch tube in the cascaded H-bridge module, simulate the voltage across the device under test, and resample the voltage across the device under test to obtain the output voltage, and return to S2.

2. The ultra-wideband power grid simulation method based on improved repetitive control according to claim 1, characterized in that: The transfer function of the improved multi-internal model fractional-order repetitive control module is: G rc (z)=G ml (z)S(z) In the formula, G ml (z) is the transfer function of the multi-internal model, and S(z) is the transfer function of the compensator.

3. The ultra-wideband power grid simulation method based on improved repetitive control according to claim 2, characterized in that: The multi-inner mold structure consists of five branches connected in parallel, specifically: In the formula, k i is the weight coefficient of the i-th branch, i = 1, 2, ..., 5, Q(z) is the internal model coefficient, N i is the delay coefficient of the ith branch.

4. The ultra-wideband power grid simulation method based on improved repetitive control according to claim 3 is characterized in that: The delay parameter N is a non-integer and is obtained by using a fractional delay approximation scheme based on a finite impulse response filter. Then z -N Specifically: In the formula, M is the filter order, N d is the fractional part of the delay factor.

5. The ultra-wideband power grid simulation method based on improved repetitive control according to claim 1, characterized in that: The transfer function of the Lyapunov-based adaptive control module is determined as follows: Based on the Lyapunov theorem, the adaptive control H(s) in the s domain is derived as: in, G is the delay link; ZOH (s) is a zero-order holder; the expressions of P(s) and P1(s) are: P(s)=1 / (LCs 2 +rCs+1) P1(s)=Cs / (LCs 2 +rCs+1) In the formula, C is the filter capacitor; L is the filter inductor; r is the equivalent resistance. a1(s), a2(s), and a3(s) are: In the formula, n=ρ+kk1, k, ρ, k1 are adaptive control parameters, They are the estimated values ​​of filter capacitor C, filter inductor L, and equivalent resistance r respectively; will be continuous G ZOH (s), P(s), P1(s), a1(s), a2(s), a3(s) are discretized to obtain z -1 , P(z), P1(z), a1(z), a2(z), a3(z), and the transfer function H(z) of the Lyapunov-based adaptive control module in the discrete domain is obtained.

6. The ultra-wideband power grid simulation method based on improved repetitive control according to claim 5, characterized in that: The transfer function of the adaptive control module based on Lyapunov is:

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