Active filter compensating voltage selective harmonic elimination pulse modulation control method

Abstract

The present application relates to a kind of active filter compensation voltage selective harmonic elimination pulse modulation control method, the method is as follows: using formula to solve grid voltage Fourier coefficient and nonlinear load current Fourier coefficient, on this basis, solve compensation voltage Fourier coefficient and establish mathematical compensation model, finally, solve compensation model and obtain switching angle, according to the switching angle obtained, the control pulse of corresponding width is generated.Using this method can avoid the carrier frequency band harmonic with high interference energy in the comparison method PWM APF system, ensure the premise of compensation effect, eliminate single-phase parallel APF conduction EMI at source, realize the power quality purification under the condition of intelligent power grid EMC standard.

Description

Technical Field

[0001] This invention belongs to the field of active filtering technology for power electronic equipment, and relates to a pulse width modulation control method for compensating voltage selective harmonic elimination in an active power filter. Background Technology

[0002] Driven by green and energy-saving awareness, smart grids, as an inevitable trend in power grid technology, have become a hot area of ​​development for countries worldwide. Ensuring power quality is a crucial foundation for smart grid construction. However, with the increasing use of high-power nonlinear and impulsive loads in power systems, power quality problems in smart grids persist and are becoming increasingly severe. APFs, as a primary means of addressing harmonic pollution in power quality, are widely used in smart grid construction. APFs can be connected to the smart grid in series or parallel. Compared to series-connected APFs, parallel-connected APFs have become a research focus due to their advantages such as higher efficiency, lower cost, and easier control. Conventional single-phase parallel-connected APFs use a PWM converter controlled by a comparator method to perform rectification and inversion functions, outputting compensation current to neutralize reactive and harmonic components in the nonlinear load current, thus ensuring power quality in the smart grid.

[0003] However, due to the inherent characteristics of the comparator-based PWM pulse containing two related time variables—the modulation wave period and the carrier period—the AC-side pulse voltage of the APF converter contains integer multiples of carrier frequency harmonics with high-energy interference. Simultaneously, the high-frequency operation of power switching devices transfers these high-energy interference harmonics to the frequency range of conducted EMI (9kHz-30MHz), causing the beneficial process of APF power grid purification to generate harmful carrier frequency conducted EMI, threatening the safe and stable operation of the smart grid. Currently, domestic and international research on APF conducted EMI suppression mainly focuses on hardware-based terminal filtering methods and software-based source suppression methods. Hardware-implemented EMI filters can effectively filter high-order harmonics in the converter output waveform, but they increase system cost and complexity. Software-implemented spread spectrum modulation technology can, to some extent, reduce EMI by expanding the carrier frequency harmonic spectrum of the APF, but it does not eliminate EMI. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide an active filter compensation voltage selective harmonic elimination pulse modulation control method. This method can eliminate single-phase parallel APF conducted EMI from the source while ensuring the compensation effect, and realize power quality purification under the EMC standard conditions of smart grid.

[0005] To solve the above-mentioned technical problems, the active filter compensation voltage selective harmonic elimination pulse modulation control method of the present invention is as follows: First, the Fourier coefficients of the grid voltage are solved separately. Nonlinear load Fourier coefficients The Fourier coefficients of the APF compensation voltage are obtained by combining the Fourier coefficients of the grid voltage and the Fourier coefficients of the nonlinear load; then, the APF SHEPWM compensation model is established and solved based on the Fourier coefficients of the APF compensation voltage to obtain the switching angle required for control, and control pulses of corresponding width are generated based on the obtained switching angle.

[0006] Solve for the Fourier coefficients of the grid voltage using equation (1);

[0007]

[0008] in, The Fourier coefficients of the grid voltage; n is the harmonic order; u s (t m ) represents the grid voltage signal u s (t) at t m The sampled value at time t m = mT / M, m = 1, 2, ..., M; T is the period of the measured signal; M is the number of equal parts of the period T of the measured signal.

[0009] Using Equation (2) for the Fourier coefficients of the nonlinear load current;

[0010]

[0011] in, i represents the Fourier coefficients of the nonlinear load current; l (t m ) represents the nonlinear load current signal i l (t) at t m The sampled value at time.

[0012] Solve for the Fourier coefficients of the APF compensation voltage using equation (3);

[0013]

[0014] Where L is the APF energy storage inductor; R L The internal resistance of the APF energy storage inductor is given by ω = 2π / T, where ω is the angular velocity.

[0015] The APF SHEPWM compensation model is as follows:

[0016]

[0017] Solving the APF SHEPWM compensation model yields the switching angle.

[0018] Based on the switching angle Generate control pulses to control the power converter to generate compensation current i c This can filter out any harmonic current introduced by nonlinear loads.

[0019] The aforementioned active filter compensation voltage selective harmonic cancellation pulse modulation control method is implemented through a SHEPWM APF compensation system; the SHEPWM APF compensation system includes a grid power supply, a control system, an isolation drive module, an APF energy storage inductor Lc, and a nonlinear load; the control system solves for the Fourier coefficients of the grid voltage. Nonlinear load Fourier coefficients The APF compensation voltage Fourier coefficient is obtained by combining the Fourier coefficients of the grid voltage and the nonlinear load; then, the APF SHEPWM compensation model is established and solved based on the APF compensation voltage Fourier coefficient to obtain the switching angle required for control; the isolation drive module generates control pulses based on the switching angle.

[0020] The nonlinear load is a 5th harmonic source, and the control system solves for the switching angles α1, α3, and α5 according to the following formula;

[0021]

[0022] The main advantages of this invention are:

[0023] (1) The power switching device does not need to introduce a high-frequency carrier during the control pulse generation process, which can eliminate integer multiples of the carrier frequency band harmonics with high interference energy.

[0024] (2) The number of switching angles based on SHEPWM technology depends on the essential characteristic of the amount of controlled frequency domain information, which can effectively reduce the switching frequency of the power components of the converter to reduce switching losses.

[0025] (3) It can accurately calculate the switching angle of the power element in the converter, control the converter to generate compensation current to filter out any harmonic current introduced by nonlinear load, and realize the improvement of power quality of smart grid.

[0026] (4) Based on the principle of intelligent algorithm, a combined solution method with shared software resources is designed to realize real-time output of APFSHEPWM pulses, control the power converter to generate compensation current, and neutralize the reactive and harmonic currents introduced by nonlinear loads. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the SHEPWM APF compensation system.

[0028] Figure 2 This is a flowchart of the process for solving the switching angle in this invention;

[0029] Figure 3 This is a simulation diagram of the compensation current for verifying the switching angle obtained in step S5.

[0030] Figure 4 It is the change in time-domain information of the compensation current;

[0031] Figure 5 It is the change in frequency domain information of the compensation current;

[0032] Figure 6 It is a SHEPWM APF open-loop control system model built using Matlab Simulink;

[0033] Figure 7 The time-domain waveform obtained after compensating for the third harmonic and the first nine harmonics of the power grid in the simulation results;

[0034] Figure 8 It is the frequency domain waveform obtained after compensating for the third harmonic and the first nine harmonics of the power grid in the simulation results. Detailed Implementation

[0035] like Figure 1 As shown, the SHEPWM APF compensation system includes the grid power supply u s The system involves nonlinear loads and a SHEPWM APF, where the SHEPWM APF comprises a control system, an isolation drive module, and a power converter. The control system generates corresponding SHEPWM control signals based on information such as the harmonics to be compensated and the power supply, and then uses the isolation drive module to control the power converter to generate the compensation current i. c This achieves compensation for the current to be compensated.

[0036] like Figure 2 As shown, the active filter compensation voltage selective harmonic elimination pulse modulation control method of the present invention is as follows: First, the Fourier coefficients of the grid voltage and the Fourier coefficients of the nonlinear load are solved respectively. Then, the Fourier coefficients of the APF compensation voltage are solved by combining the Fourier coefficients of the grid voltage and the Fourier coefficients of the nonlinear load. Next, an APF SHEPWM compensation model is established and solved based on the Fourier coefficients of the APF compensation voltage to obtain the switching angle required for control. Based on the obtained switching angle, a control pulse of corresponding width is generated.

[0037] The present invention specifically includes the following steps:

[0038] S1: Solve for the Fourier coefficients of the grid voltage using equation (1), as shown in Table 1.

[0039]

[0040] in, The Fourier coefficients of the grid voltage; n is the harmonic order; u s(t m ) represents the grid voltage signal u s (t) at t m The sampled value at time t m = mT / M, m = 1, 2, ..., M; T = 20 ms is the period of the measured signal; M = 200 is the number of equal parts of the period T of the measured signal.

[0041] Table 1 shows the Fourier coefficients of the grid voltage obtained according to equation (1).

[0042] Table 1. Fourier Coefficients of Grid Voltage

[0043]

[0044] S2: Solve for the Fourier coefficients of the nonlinear load current using equation (2), as shown in Table 2.

[0045]

[0046] in, i represents the Fourier coefficients of the nonlinear load current; l (t m ) represents the nonlinear load current signal i l (t) at t m The sampled value at time.

[0047] Table 2 shows the Fourier coefficients of the nonlinear load current obtained according to equation (2).

[0048] Table 2 Fourier coefficients of nonlinear load current

[0049]

[0050] S3: Combine equations (1) and (2) to obtain the results, and use equation (3) to solve for the Fourier coefficients of the APF compensation voltage, as shown in Table 3.

[0051]

[0052] in, R is the Fourier coefficient of the nonlinear load current; L is the inductance value of the APF energy storage inductor Lc; R L Let Lc be the internal resistance of the APF energy storage inductor, and ω = 2π / T be the angular velocity.

[0053] Table 3 shows the Fourier coefficients of the APF compensation voltage obtained by substituting Tables 1 and 2 into equation (3).

[0054] Table 3 Fourier coefficients of APF compensation voltage

[0055]

[0056] S4: Combine the results obtained from equation (3) to establish the APF SHEPWM compensation model, as shown in equation (4).

[0057]

[0058]

[0059] Among them, e dc The DC-side voltage of the APF converter (power converter); n max For the maximum harmonic order, α n Let n be the angle of the switch.

[0060] S5: Solve equation (4) to obtain the switching angle.

[0061] S6: Control system output switching angle As the SHEPWM control signal, the isolation drive module generates control pulses based on the SHEPWM control signal, which in turn controls the power converter to generate a compensation current i. c .

[0062] To make the technical solution and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings, specific embodiments and a specific example.

[0063] Example 1

[0064] When e dc =350V, L=3.6mH, R L =0.1Ω, U s =311V, At that time, the nonlinear load is set to a 390uF capacitor C. f With a resistor R of 100 / 18Ω f After being connected in parallel with the 4mH inductor coil L f The series-connected 5th harmonic sources are shown in Table 4.

[0065] Table 4 Frequency Domain Information of Nonlinear Load Current

[0066]

[0067] S1: Solve for the Fourier coefficients of the grid voltage using equation (1), as shown in Table 1.

[0068]

[0069] in, The Fourier coefficients of the grid voltage; n is the harmonic order; u s (t m ) represents the grid voltage signal u s (t) at tm The sampled value at time t m = mT / M, m = 1, 2, ..., M; T = 20 ms is the period of the measured signal; M = 200 is the number of equal parts of the period T of the measured signal.

[0070] Table 5 shows the Fourier coefficients of the grid voltage obtained according to equation (1).

[0071] Table 5 Fourier Coefficients of Grid Voltage

[0072]

[0073]

[0074] S2: The Fourier coefficients of the nonlinear load current are obtained using equation (2), as shown in Table 2.

[0075]

[0076] in, i represents the Fourier coefficients of the nonlinear load current; l (t m ) represents the nonlinear load current signal i l (t) at t m The sampled value at time.

[0077] Table 6 shows the Fourier coefficients of the nonlinear load current obtained according to equation (2).

[0078] Table 6 Fourier coefficients of nonlinear load current

[0079]

[0080] S3: Combine equations (1) and (2) to obtain the results, and use equation (3) to solve for the Fourier coefficients of the APF compensation voltage, as shown in Table 3.

[0081]

[0082] in, R is the Fourier coefficient of the nonlinear load current; L is the inductance value of the APF energy storage inductor Lc; R L Let Lc be the internal resistance of the APF energy storage inductor, and ω = 2π / T be the angular velocity.

[0083] Table 7 shows the Fourier coefficients of the APF compensation voltage obtained by substituting Tables 1 and 2 into equation (3).

[0084] Table 7 Fourier coefficients of APF compensation voltage

[0085]

[0086] S4: Combine the results obtained from equation (3) to establish the APF SHEPWM compensation model, as shown in equation (4).

[0087]

[0088]

[0089] Among them, e dc n is the DC-side voltage of the APF converter. max This represents the maximum harmonic order.

[0090] Based on equation (4), the APF SHEPWM compensation model matrix is ​​established by substituting the result obtained from equation (3), and equation (5) is obtained.

[0091]

[0092] S5: Solve equation (5) to obtain the switching angle.

[0093] Table 8 shows the six switching angles obtained by solving equation (5) using an artificial neural network algorithm written in MATLAB m language, which are used to eliminate the first five harmonics.

[0094] Table 8 Switching Angles (SHEPWM1-SHEPWM6)

[0095]

[0096] A verification simulation model was built using MATLAB-Simulink software, such as... Figure 3 The switching angles in Table 8 are input into the simulation model, and after processing, control pulse signals of corresponding widths are generated. Under the control of the control pulse signals, a compensation current i is generated. c The time-frequency domain information of the compensation current is as follows: Figure 4 , 5 .

[0097] Following the steps for solving the six switching angles, the first four switching angles (SHEPWM1-SHEPWM4) are solved as shown in Table 9, and the first twelve switching angles (SHEPWM1-SHEPWM12) are shown in Table 10. An open-loop control system Simulink simulation model is then built using MATLAB-Simulink software. Figure 6 The third harmonic and the first eleventh harmonics generated by the nonlinear load are eliminated respectively. The grid-side current i is obtained after eliminating the first three and first eleven harmonics. s Comparison Figure 7 and Figure 8 .

[0098] Table 9 Switching Angles (SHEPWM1-SHEPWM4)

[0099]

[0100] Table 10 Switching Angles (SHEPWM1-SHEPWM12)

[0101]

[0102] observe Figure 7 , Figure 8 After compensation, the time-domain waveform of the grid-side current tends to be sinusoidal as the harmonic control order increases. An APF employing computational SHEPWM technology can accurately compensate for harmonics introduced by nonlinear loads, achieving controllable current frequency domain information.

[0103] This invention belongs to the field of active power filter technology for power electronic equipment. It proposes an active power filter (APF) compensation voltage selective harmonic elimination pulse width modulation (SHEPWM) control method. Starting from the APF compensation current model and the source of conducted electromagnetic interference (EMI), it obtains a precise control signal through high-precision spectrum analysis. This avoids the carrier frequency band harmonics with high interference energy in the comparison-based pulse width modulation (PWM) APF system. Under the premise of ensuring the compensation effect, it eliminates conducted EMI in single-phase parallel APF at the source, realizing power quality purification under the electromagnetic compatibility (EMC) standard conditions of smart grids.

[0104] This invention provides an APF compensation voltage SHEPWM control method. Starting from the APF compensation model and the source of conducted EMI, it obtains a precise control signal through a high-precision spectrum analysis method, avoiding the carrier frequency harmonics with high interference energy in the comparator-based PWM APF system. Under the premise of ensuring the compensation effect, it eliminates the conducted EMI of single-phase parallel APF at the source, and realizes power quality purification under the EMC standard conditions of smart grid.

Claims

1. A method for active filter compensation voltage selective harmonic elimination pulse modulation control, characterized in that... The method is as follows: First, solve for the Fourier coefficients of the grid voltage. , Nonlinear load Fourier coefficients , The APF compensation voltage Fourier coefficient is obtained by combining the Fourier coefficients of the grid voltage and the Fourier coefficients of the nonlinear load; then, the APF SHEPWM compensation model is established and solved based on the APF compensation voltage Fourier coefficients to obtain the switching angle required for control; and control pulses of corresponding width are generated based on the obtained switching angle. Solve for the Fourier coefficients of the grid voltage using equation (1); （1） in, , The Fourier coefficients of the grid voltage; For harmonic order; For grid voltage signal exist The sampled value at time 10:

00. , ; The period of the measured signal; The period of the measured signal The number of equal parts; Using Equation (2) for the Fourier coefficients of the nonlinear load current; （2） in, , The Fourier coefficients of the nonlinear load current; Nonlinear load current signal exist The sampled value at time; Solve for the Fourier coefficients of the APF compensation voltage using equation (3); （3） in, , The Fourier coefficients of the nonlinear load current; For APF energy storage inductor; The internal resistance of the APF energy storage inductor is... Angular velocity; The APF SHEPWM compensation model is as follows: （4） in, This refers to the DC-side voltage of the APF converter. The maximum harmonic order; Solving the APF SHEPWM compensation model yields the switching angle. .

2. The active filter compensation voltage selective harmonic elimination pulse modulation control method according to claim 1, characterized in that... This method is implemented through a SHEPWM APF compensation system; the SHEPWM APF compensation system includes a grid power supply, a control system, an isolation drive module, an APF energy storage inductor Lc, and a nonlinear load; the control system solves for the Fourier coefficients of the grid voltage. , Nonlinear load Fourier coefficients , The APF compensation voltage Fourier coefficient is obtained by combining the Fourier coefficients of the grid voltage and the Fourier coefficients of the nonlinear load; then, the APF SHEPWM compensation model is established and solved based on the APF compensation voltage Fourier coefficients to obtain the switching angle required for control; the isolation drive module generates control pulses based on the switching angle. The nonlinear load is a 5th harmonic source, and the control system calculates the switching angle according to the following formula. ; 。

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