Control method and system of three-phase three-level AC / DC converter

Abstract

The invention discloses a control method and system of a three-phase three-level AC / DC converter. A multi-parallel quasi-resonance PR control method based on time delay phase compensation is adopted in the main body control link, time delay is converted into fixed phases needing to compensate fundamental waves and high order, and the influence of time delay between sampling and output on the system is improved. Aiming at the frequency fluctuation condition of the power grid side, the real-time frequency of the power grid is updated in real time through DSOGI-FLL, a frequency value is transferred to a phase compensation link, the compensation link is calculated through a new frequency value, a new transfer function is obtained after new parameter values are calculated, the new transfer function is connected into a main body control link in series, and the self-adaptive adjustment effect is achieved.

Description

Technical Field

[0001] The present invention belongs to the field of AC-DC circuits and relates to a control method and system for an AC / DC converter, and in particular relates to a control method and system for a three-phase three-level AC / DC converter with improved PR and adaptive phase compensation. Background Art

[0002] The main charging equipment in the field of new energy vehicles has two topologies: single-phase and three-phase. The three-phase equipment draws power from the power grid in three phases, and has higher input and output power than the single-phase charging circuit. The main three-phase topologies are mainly two-level (mainly three-phase six-switch) and three-level (mainly Vienna and T-type three-level). Among them, the DC side of the three-level circuit has +V DC / 2, 0, -V DC / 2 three levels, which significantly reduce the voltage stress at both ends of the switching devices in the circuit, and have the effect and significance of reducing the cost for switch selection.

[0003] The main control logic of the T-type three-level circuit is concise and the circuit structure is simple. It is currently widely used in three-phase charging equipment for electric vehicles. Under the conditions of forward rectification and reverse off-grid inversion, the T-type three-level circuit is only powered by a single power supply, and generally adopts PI control to obtain a better control effect. Under grid-connected conditions, the three-wire T-type three-level circuit will cause the waveform quality of the grid-connected current to deteriorate due to the unbalanced midpoint potential. Generally, a PR control strategy is required to obtain a better control effect.

[0004] On the grid side, the network impedance of the power grid is not a pure resistive load, and the network impedance is generally regarded as an inductor and a resistor in series. The resistance part has little effect on the output stability of the grid-connected on-board charging equipment. When the inductance part changes, it will aggravate the phase margin reduction problem caused by the multiple parallel quasi-resonant PR control system itself, thereby causing system instability.

[0005] The traditional phase compensation method can perform fixed-frequency phase compensation for 3 / 5 / 7 times, or uniform compensation for the cutoff frequency. However, in a weak power grid environment, the frequency will fluctuate to a certain extent (47-52Hz), and the system cannot be adjusted adaptively. It is easy for the compensation link and the power grid frequency to not match, which will cause the control of the charging equipment to become unstable, affecting the safety of the equipment and users. Summary of the invention

[0006] In order to solve the problems and needs in the background technology, the present invention proposes a control method and system for a three-phase three-level AC / DC converter with improved PR and adaptive phase compensation. The present invention obtains real-time key information of the power grid through a sampling circuit, outputs key parameters of the phase compensation link through corresponding calculations by a calculation unit, reconstructs the control loop, realizes phase compensation under power grid fluctuations, improves the phase margin, enhances the stability of the control link, reduces the harmonic content of the grid-connected current on the grid side, and improves the success rate and quality of grid connection.

[0007] The technical solution of the present invention is as follows:

[0008] 1. A control method for a three-phase three-level AC / DC converter

[0009] Step 1: Obtain the voltage signal and current signal of the power grid;

[0010] Step 2: Calculate the α and β components of the current signal in the stationary coordinate system and the grid frequency according to the voltage signal and current signal of the grid, and reconstruct the α and β components of the three-phase current signal in the stationary coordinate system by using the multiple parallel quasi-resonant PR control method based on time delay phase compensation to obtain the reconstructed current α and β components;

[0011] Step 3: Selectively perform phase compensation on the reconstructed current α and β components according to the current grid frequency, then perform space vector inverse transformation on the final current α and β components to obtain the modulation wave signal, and then perform DPWM modulation on the modulation wave signal to obtain the duty cycle signal of the three-phase three-level AC / DC converter;

[0012] Step 4: Repeat steps 1 to 3 to continuously control the three-phase three-level AC / DC converter to achieve phase dynamic compensation and stability improvement.

[0013] In step 2, the α and β components of the current signal in the stationary coordinate system and the grid frequency are calculated based on the voltage signal and the current signal of the grid, specifically:

[0014] The grid frequency is obtained by processing the grid voltage signal through a frequency-locked loop, and the grid voltage vector phase is obtained by processing the grid voltage signal through a digital phase-locked loop; then, based on the obtained grid voltage vector phase, the grid current signal is transformed into a space vector to obtain the α and β components of the three-phase current signal in a stationary coordinate system.

[0015] The transfer function G of the multiple parallel quasi-resonant PR control method based on time delay phase compensation is PR (s) satisfies the following formula:

[0016]

[0017] Among them, k p and k r are the first and second control parameters respectively, n is the frequency generation coefficient, s is a complex variable in the complex plane, ω c is the cutoff frequency of the low-pass filter, θ is the phase compensation angle, ω o is the fundamental frequency of the power grid.

[0018] In step 3, phase compensation is selectively performed on the reconstructed current α and β components according to the current grid frequency, specifically:

[0019] The frequency deviation between the current grid frequency and the standard grid frequency is calculated. If the current frequency deviation is less than the preset deviation threshold, the current grid is a standard grid, and the reconstructed current α and β components are used as the final current α and β components; otherwise, it is an abnormal grid, and the adaptive phase compensation method is used to perform phase compensation on the reconstructed current α and β components, and the compensated current α and β components are obtained and used as the final current α and β components.

[0020] The transfer function G of the adaptive phase compensation method is n (s) satisfies the following formula:

[0021]

[0022] Among them, ω m is the center frequency, is the maximum compensation phase angle, γ is the proportional parameter, z and p are the parameters of the first and second compensation links.

[0023] 2. A control system for a three-phase three-level AC / DC converter

[0024] A power grid signal sampling unit, used to obtain voltage and current signals of the power grid;

[0025] The frequency-locked loop is used to process the voltage signal of the power grid and output the power grid frequency;

[0026] Phase-locked loop, used to process the voltage signal of the power grid and output the grid voltage vector phase;

[0027] A space vector transformation unit, used to perform space vector transformation on the current signal of the power grid based on the acquired power grid voltage vector phase, and output α and β components of the three-phase current signal in a stationary coordinate system;

[0028] A multiple parallel quasi-resonant PR controller is used to reconstruct the α and β components of the three-phase current signal in a stationary coordinate system, and output the reconstructed current α and β components;

[0029] A phase compensation selection unit, used to selectively perform phase compensation on the reconstructed current α and β components according to the current grid frequency, and output the final current α and β components;

[0030] A space vector inverse transformation unit is used to perform space vector inverse transformation on the final current α and β components and output a modulated wave signal;

[0031] The DPWM modulation unit is used to output a duty cycle signal of a three-phase three-level AC / DC converter after performing DPWM modulation according to the modulation wave signal.

[0032] The phase compensation selection unit specifically includes:

[0033] A frequency deviation judgment unit is used to calculate the frequency deviation between the current power grid frequency and the standard power grid frequency, and judge whether the current power grid is a standard power grid or an abnormal power grid according to the calculated frequency deviation, and use the reconstructed current α and β components of the standard power grid as the final current α and β components;

[0034] The phase compensation controller is used to perform phase compensation on the reconstructed current α and β components of the abnormal power grid to obtain the compensated current α and β components as the final current α and β components.

[0035] 3. A computer device

[0036] The device comprises a memory and a processor, wherein the memory stores a computer program, and the processor implements the steps of the control method of a three-phase three-level AC / DC converter when executing the computer program.

[0037] 4. A computer-readable storage medium

[0038] The medium stores a computer program, and when the computer program is executed by the processor, the steps of the control method of the three-phase three-level AC / DC converter are implemented.

[0039] 5. A computer program product

[0040] The product comprises a computer program / instruction, which, when executed by a processor, implements the steps of the control method of a three-phase three-level AC / DC converter.

[0041] The beneficial effects of the present invention are:

[0042] (1) Compared with the traditional grid-connected PI control strategy and ideal PR control: PI control has a good control effect only on DC quantities. In the AC / DC level control strategy, the system needs to be converted to the dq coordinate system and complex decoupling calculations are required, which increases the trigonometric function values ​​calculated by the calculation unit, increases the complexity and calculation time, and has higher cost requirements. Although the ideal PR controller can better track the fundamental signal of the center frequency than the PI control, due to its gain characteristics, it cannot output stability when the grid is offset.

[0043] The basic form of control of the present invention is a quasi-resonant PR control of multiple parallel connections. Quasi-resonant PR control increases the bandwidth near the center frequency. Although it reduces the gain of some fundamental frequencies (no longer infinite), it significantly improves the dynamic performance of steady-state output. At the same time, since component errors and limited word length need to be considered in digital implementation, quasi-resonant PR control is more in line with actual design and production needs than ideal PR control. On this basis, quasi-resonant PR controls for different center frequencies (fundamental, 3rd, 5th, 7th) are connected in parallel, which can suppress higher harmonics while controlling the fundamental output, and has a better effect of tracking sine waves, and can suppress midpoint voltage offset and DC bus double frequency interference, and obtain a grid-connected current with a lower harmonic content on the grid-connected side.

[0044] (2) In view of the phase compensation of time delay, the present invention proposes to reconstruct the control from the structure of quasi-resonant PR, and proposes a multiple parallel quasi-resonant PR control method based on time delay phase compensation. The reconstruction at the system level can visualize the problem of time delay through the transfer function, and analyze and study its impact on the system. The reconstructed PR control can directly compensate from the control loop, and there is no need to manually modify the grid voltage vector phase information of the digital part to perform manual compensation at the phase level. It has a better theoretical basis and effectively reduces the interference of the delay problem caused by the sampling, calculation and output of the digital circuit part on the grid connection and the complexity of product development.

[0045] (3) The present invention proposes adaptive phase compensation, which is mainly aimed at adaptive compensation for grid fluctuations. There are two main types of grid-side fluctuations: changes in grid-side impedance and changes in grid frequency. In the present invention, the adaptive phase compensation serves as compensation for the control system. When the grid-side impedance changes, it can improve the phase margin of the system and avoid control instability caused by system fluctuations, thereby causing equipment damage and reduced grid current quality. On the other hand, the adaptive phase compensation of the present invention can extract the current grid frequency according to the fluctuation of the grid frequency, automatically update it when calculating the phase compensation link parameters, and more accurately calculate the phase compensation link parameters required by the control system at this moment, thereby improving the stability of the system, reducing the high-order harmonic content of the grid current, and reducing the interference of grid changes on the quality of the grid current.

[0046] (4) Combined phase compensation strategy: The present invention integrates two common grid-connected phase problems, and realizes multi-dimensional phase compensation by reconstructing the quasi-resonant PR structure and series adaptive phase compensation. In use, when there is no significant change in the power grid (the power grid frequency does not fluctuate violently), delay compensation is used to reduce the impact of digital circuits on control, and the system stability is improved; in the case of power grid fluctuations, the adaptive phase compensation link is connected in series, and the precise power grid frequency is extracted in real time through the frequency-locked loop, and more accurate system parameters are calculated, thereby improving system stability and reducing the harmonic distortion rate of the grid-connected current. The combination of the two strategies reduces the computational redundancy of the DSP, reduces the computational cost, and more efficiently ensures the success of the grid-connected work. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 It is a three-wire T-type three-level circuit grid-connected topology diagram.

[0048] Figure 2 It is a control flow chart of multiple parallel quasi-resonant delay compensation control and adaptive phase compensation method.

[0049] Figure 3 This is the Bode comparison diagram of the PR control system before and after phase compensation based on time delay.

[0050] Figure 4 Schematic diagram of the DSOGI-FLL frequency-locked loop structure based on double generalized second-order integration.

[0051] Figure 5 The current inner loop control block diagram for adding an adaptive phase compensation link.

[0052] Figure 6 To add the Bode diagram comparison diagram before and after the adaptive phase compensation link.

[0053] Figure 7 The comparison diagram of grid-connected current before and after using the adaptive phase compensation link in the circuit simulation provided. DETAILED DESCRIPTION

[0054] The invention is described below with reference to the accompanying drawings and embodiments.

[0055] Figure 1It is a three-wire T-type three-level circuit grid-connected topology, including twelve switch tubes S1, S2, S3, S4, S5, S6, S7, S8, S9, S10, S11, and S12, of which S1-S6 are IGBT power tubes and S7-S12 are Si-MOS power tubes. In the rectification direction only, S1-S6 can be replaced by diodes, that is, it is transformed into a VIENNA three-phase rectification topology. S1-S6 are called longitudinal tubes, and S7-S12 are called transverse tubes. Under grid-connected operation, the upper and lower tubes of the longitudinal tube are turned on in sequence according to the positive and negative half cycles of the grid voltage sine wave according to the power frequency cycle, and remain in a normally closed state when not turned on. Within half a cycle, the longitudinal tube and transverse tube that need to be turned on are complementary to each other according to the duty cycle output by the control loop. The control loop realizes the output current sine wave on the inverter side through real-time changes in the duty cycle, and realizes the inverter function and grid-connected function.

[0056] The present invention proposes a control method for a three-phase three-level AC / DC converter. Figure 2 As shown, specifically including:

[0057] When the control system of the three-phase three-level AC / DC converter receives the grid-connected signal from the host computer, the control system switches to the grid-connected state and starts up. The control flow of the grid-connected working mode of the three-phase three-level AC / DC converter is as follows:

[0058] Step 1: After entering the grid-connected state, obtain the three-phase voltage signal and three-phase current signal of the grid through differential sampling;

[0059] Step 2: Calculate the α and β components of the three-phase current signal in the stationary coordinate system and the grid frequency according to the voltage signal and current signal of the grid, and reconstruct the α and β components of the three-phase current signal in the stationary coordinate system by using the multiple parallel quasi-resonant PR control method based on time delay phase compensation to obtain the reconstructed current α and β components;

[0060] In step 2, the α and β components of the three-phase current signal in the stationary coordinate system and the grid frequency are calculated based on the voltage signal and current signal of the grid, specifically:

[0061] The grid frequency (i.e., grid fundamental frequency) is obtained by processing the grid voltage signal through the frequency-locked loop, and the grid voltage vector phase is obtained in real time after processing the grid voltage signal through the digital phase-locked loop; specifically: the three-phase phase-locked loop obtains the phase information of the grid voltage vector through the digital filtering and voltage control link of the grid voltage signal, which is used for the control loop to perform space vector transformation. The three-phase frequency-locked loop adopts a two-layer combination structure of DSOGI-FLL, in which the DSOGI link decomposes the positive and negative sequence of the three-phase voltage signal and generates an orthogonal signal, and the FLL link uses the orthogonal signal to calculate and obtain the grid frequency, which is used for recalculating the parameters in the subsequent adaptive compensation link.

[0062] Figure 4 The schematic diagram of the DSOGI-FLL frequency-locked loop structure based on double generalized second-order integral. The frequency-locked loop in the present invention serves as the part for obtaining the grid frequency. Its main purpose is to obtain the real-time grid frequency under grid fluctuations and provide it to the adaptive phase compensation link for adaptive calculation. The structure is mainly divided into two parts: the DSOGI orthogonal signal generation part and the FLL frequency-locked loop part.

[0063] DSOGI is a double generalized second-order integral structure. By performing space vector transformation on the three-phase voltage, the positive sequence fundamental frequency components of the α and β components in the stationary coordinate system are extracted. The orthogonal generator part is mainly used in the frequency locked loop. Its structure is based on the filtering link of the second-order generalized integral, which can meet the high quality requirements of the frequency locked loop for the signal. The transfer function of the DSOGI orthogonal generator is:

[0064]

[0065] Where V′ is the output signal that tracks the input signal V of the orthogonal generator, D(s) is its transfer function, qV′ is the output signal with a phase lag of 90° behind V′, Q(s) is its transfer function, q is the orthogonal operator, τ′ is the center frequency in the DSOGI link, and K is the proportional parameter in the link.

[0066] Figure 5 middle is the positive sequence part corresponding to the α and β components of the grid voltage, and its calculation formula is as follows:

[0067]

[0068]

[0069] Among them, the α and β components of the grid voltage V α 、V β Input DSOGI orthogonal generator, corresponding to obtain two sets of orthogonal signals, V′ α and qV′ α is a set of orthogonal signals, V′ β and qV′ β is a set of orthogonal signals. The signals with q in the expression are delayed by 90°, and q is the orthogonal operator.

[0070] The design of the FLL frequency-locked loop is based on the characteristics of being sensitive to frequency signal changes. The basic structure of the notch filter is selected, and its transfer function G q (s) is:

[0071]

[0072] Where ω′ is the center frequency of the frequency-locked loop, which is consistent with DSOGI. Since the basic structure of the notch filter has a gain of 0 at the center frequency, it is selected as the main structure of the FLL based on this characteristic. By performing a first-order linear approximation on the frequency-locked loop, a simplified model can be obtained and the corresponding proportional parameters can be calculated. The amount of calculation in the DSP is significantly reduced, and the overall efficiency of the frequency-locked loop is improved.

[0073] Based on the obtained grid voltage vector phase, the three-phase current signal of the grid is transformed into a space vector, that is, the three-phase current is transformed into a stationary coordinate system αβ to obtain the α and β components of the three-phase current signal in the stationary coordinate system.

[0074] The multiple parallel quasi-resonant PR control method based on time delay phase compensation specifically estimates the overall time delay based on the sampling, calculation, and output of the digital control part to obtain the amount of delayed time. According to the estimated amount of time, the multiple parallel quasi-resonant PR control method is reconstructed. In the process of the present invention, the reconstructed quasi-resonant PR control method (i.e., the multiple parallel quasi-resonant PR control method based on time delay phase compensation) will realize the phase compensation of the time delay at the system principle level. The reconstructed quasi-resonant PR control method specifically converts the time delay into a fixed phase that needs to be compensated for the fundamental and higher orders, and improves the impact of the delay between sampling and output on the system.

[0075] Specifically:

[0076] PR control is a control method for zero-error tracking of sinusoidal signals based on the inner membrane principle. Its transfer function is expressed as follows:

[0077]

[0078] On the basis of the ideal PR, a low-pass filter is used to replace the integrator (the second term in the above formula is replaced by the integrator structure), and the higher-order terms generated in the calculation are ignored. The fundamental wave, the third harmonic, the fifth harmonic, and the seventh harmonic (the main harmonic components of the power grid) are synchronously controlled in parallel, and the transfer function is:

[0079]

[0080] Among them, 2n+1 corresponds to the fundamental wave, the third harmonic, the fifth harmonic, and the seventh harmonic respectively when n is 0 / 1 / 2 / 3.

[0081] Taking into account the system delay caused by sampling and calculation, combined with the clock of the computing chip and the complexity of the terminal in the program, it is estimated that the system delay is basically in the range of 1.5τ0T-2ω0T, where T represents the switching period of the PWM wave output by the control system, and ω0 is the fundamental frequency of the power grid. The transfer function with total delay is:

[0082] Gdelay (s) = e -asT

[0083] The amplitude of the transfer function of the time delay is 1, and the phase gain is -aωT, where a corresponds to 1.5-2 in the system delay of 1.5ωT-2ωT. The time delay increases the phase lag of the control system as a whole, reduces the phase margin of the control system, and makes the system prone to instability.

[0084] In the transfer function of the system, at s = 0, the corresponding e is introduced jθ Compensation can offset the impact of delay.

[0085] Transfer function G of multiple parallel quasi-resonant PR control method based on time delay phase compensation PR (s) satisfies the following formula:

[0086]

[0087] Among them, k p and k r They are the first and second control parameters of the PR link, which are generally calculated based on the transfer function of the system or the experimental parameters of the actual machine. n is the frequency generation coefficient. 2n+1 corresponds to the fundamental wave, the third harmonic, the fifth harmonic, and the seventh harmonic when n is 0 / 1 / 2 / 3 respectively. s is a complex variable in the complex plane, which is used to describe the frequency response and stability of the dynamic system. ω c is the cutoff frequency of the low-pass filter, θ is the phase compensation angle, ω o is the fundamental frequency of the power grid.

[0088] Figure 3 The Bode phase diagram of the multiple parallel quasi-resonant PR control based on time delay phase compensation and the ordinary quasi-resonant PR control is compared. The multiple parallel quasi-resonant PR control system is compensated based on 25kHz sampling and switching frequency, and the PR control parameter is selected as k p =10, k r = 1000. It can be seen that the reconstructed PR control link compensates the phase of the control link and improves the phase margin compared with the original PR control, thereby reducing the impact of delay on system stability and output.

[0089] Step 3: According to the current grid frequency, phase compensation is selectively performed on the reconstructed current α and β components, and then the final current α and β components are subjected to space vector inverse transformation to obtain the modulation wave signal, and then DPWM modulation is performed according to the modulation wave signal to obtain the duty cycle signal of the three-phase three-level AC / DC converter. The duty cycle of the switching device of the three-phase three-level AC / DC converter is adjusted by the duty cycle signal to realize the control of the main power circuit;

[0090] In step 3, phase compensation is selectively performed on the reconstructed current α and β components according to the current grid frequency, specifically:

[0091] The frequency deviation between the current grid frequency and the standard grid frequency (i.e. 50Hz) is calculated, and the frequency deviation is used to determine whether the grid fluctuates. Specifically, if the current frequency deviation is less than the preset deviation threshold, the current grid is a standard grid, and the reconstructed current α and β components are used as the final current α and β components; otherwise, it is an abnormal grid, and the phase compensation of the reconstructed current α and β components is performed using the series adaptive phase compensation method, and the compensated current α and β components are obtained and used as the final current α and β components.

[0092] Transfer function G of adaptive phase compensation method n (s) satisfies the following formula:

[0093]

[0094] Among them, ω m is the center frequency of the lead link, is the maximum compensation phase angle, γ is the proportional parameter, z and p are the first and second compensation link parameters that need to be calculated and determined.

[0095] The center frequency of the lead link is usually selected as the cutoff frequency or the highest harmonic frequency;

[0096] For the quasi-resonant PR control system with multiple parallel connections, the phase compensation link of the present invention sets the center frequency at the highest frequency in parallel, that is, the 7th resonance, that is:

[0097] ω m =7·ω

[0098] Wherein, ω is the fundamental frequency of the power grid, ω=2π·grid frequency.

[0099] When determining the maximum phase compensation angle, it is considered that the maximum phase compensation angle will increase the high-frequency gain of the control system and increase the high-order harmonic part of the system, so the value is generally less than 30°.

[0100] The current inner loop refers to the internal loop for controlling the current in the control system. Under rectification and inversion conditions, there will be a voltage outer loop for controlling the voltage. The present invention is only for grid-connected conditions, so only the current inner loop part exists in the control system.

[0101] The adaptive function of the present invention is mainly reflected in that when the power grid fluctuates, the fundamental frequency of the power grid is also changing, that is, the fundamental frequency ω of the power grid in the above formula is also updated in real time. Figure 4The three-phase frequency-locked loop in the system extracts the grid frequency by processing and calculating the grid voltage signal, and compares the obtained ω with the standard grid frequency 2π·50rad / s. When the deviation exceeds 0.5Hz, the new ω is assigned to the phase compensation link to recalculate z, p, and γ. After the corresponding parameters are calculated, they are connected in series to the current inner loop control loop for phase compensation.

[0102] Step 4: Repeat steps 1 to 3 to continuously control the three-phase three-level AC / DC converter to achieve phase dynamic compensation and stability improvement of the three-phase three-level AC / DC converter.

[0103] The present invention obtains real-time key information of the power grid through a sampling circuit, outputs key parameters of the phase compensation link after corresponding calculations by a computing unit, reconstructs the control loop, realizes phase compensation under power grid fluctuations, improves the phase margin, enhances the stability of the control link, reduces the harmonic content of the grid-connected current on the grid side, and improves the grid-connected success rate and grid-connected quality.

[0104] The present invention proposes a control system for a three-phase three-level AC / DC converter, the control system comprising:

[0105] A power grid signal sampling unit, used to obtain voltage and current signals of the power grid;

[0106] The frequency-locked loop is used to process the voltage signal of the power grid and output the power grid frequency;

[0107] Phase-locked loop, used to process the voltage signal of the power grid and output the grid voltage vector phase in real time;

[0108] A space vector transformation unit is used to perform space vector transformation on the three-phase current signal of the power grid based on the acquired power grid voltage vector phase, that is, to transform the three-phase current to a stationary coordinate system αβ, and output α and β components of the three-phase current signal in the stationary coordinate system;

[0109] A multiple parallel quasi-resonant PR controller is used to reconstruct the α and β components of the three-phase current signal in a stationary coordinate system, and output the reconstructed current α and β components;

[0110] A phase compensation selection unit, used to selectively perform phase compensation on the reconstructed current α and β components according to the current grid frequency, and output the final current α and β components;

[0111] A space vector inverse transformation unit is used to perform space vector inverse transformation on the final current α and β components and output a modulated wave signal;

[0112] The DPWM modulation unit is used to output a duty cycle signal of a three-phase three-level AC / DC converter after performing DPWM modulation according to the modulation wave signal.

[0113] The phase compensation selection unit specifically includes:

[0114] A frequency deviation judgment unit is used to calculate the frequency deviation between the current power grid frequency and the standard power grid frequency, and judge whether the current power grid is a standard power grid or an abnormal power grid according to the calculated frequency deviation, and use the reconstructed current α and β components of the standard power grid as the final current α and β components;

[0115] The phase compensation controller is used to perform phase compensation on the reconstructed current α and β components of the abnormal power grid to obtain the compensated current α and β components as the final current α and β components.

[0116] The present invention provides a computer device, comprising a memory and a processor, wherein the memory stores a computer program, and the processor implements the steps of a control method for a three-phase three-level AC / DC converter when executing the computer program.

[0117] The present invention provides a computer-readable storage medium on which a computer program is stored. When the computer program is executed by a processor, the steps of a control method for a three-phase three-level AC / DC converter are implemented.

[0118] The present invention provides a computer program product, comprising a computer program / instruction, which implements the steps of a control method for a three-phase three-level AC / DC converter when executed by a processor.

[0119] In the experimental simulation, according to the actual working conditions, considering the compensation range of a single leading compensation link, the maximum phase compensation angle is 10°-30°. The present invention selects an angle of 25° as the maximum phase compensation angle. The frequency is selected as the frequency of the highest harmonic, and the current grid fundamental frequency value is obtained through DSOGI-FLL for calculation. The following example uses the grid fundamental frequency of 50Hz for demonstration. There are:

[0120]

[0121]

[0122] The calculation can be obtained:

[0123] z=1400.79

[0124] p=3451.92

[0125] γ can be calculated based on the compensation frequency (for example, 7·2π·50rad / s), and |G n (jω m )|=1, we can calculate:

[0126]

[0127] When the above parameters are working in the actual machine, they are recalculated according to the real-time frequency acquisition of ω, which can maintain the system stability more accurately.

[0128] Figure 6 To increase the Bode diagram comparison before and after the adaptive phase compensation link. Figure 5 The overall transfer function generated by the current loop structure and circuit structure shown (an LC filter circuit is connected between the three-phase three-level ACDC converter and the power grid, L is the filter inductor, and C is the filter capacitor) is:

[0129]

[0130] Among them, L includes L1 filter inductor and L g The grid-side inductance is one of the factors affecting the system change when the grid-side impedance changes, which may cause system instability and is one of the design premises of the present invention.

[0131] The open-loop transfer function of the system is connected in series with the adaptive phase compensation link G n By comparing the before and after (s), we can see that the phase margin after compensation is significantly improved. The phase margin at the 7th harmonic frequency and the cutoff frequency is maintained at 45° or above, which improves the system stability and avoids the possibility of system instability caused by power grid fluctuations, thereby causing damage to hardware circuits and other problems.

[0132] Figure 7 The circuit simulation provided is a comparison diagram of the grid-connected current before and after the adaptive phase compensation link is used. The design of the present invention is simulated and verified as an example, and the reference value of the controlled grid-connected current amplitude is 12A. According to the comparison of the grid-connected current before and after the series adaptive phase compensation link, it can be seen that the current distortion rate of the grid-connected current is reduced from 2.8% to 2.4%, and the waveform quality is improved, reflecting the improvement effect of the present invention on system stability and the optimization effect on the grid-connected current.

[0133] In view of the frequency fluctuation on the power grid side, the present invention updates the real-time frequency of the power grid through DSOGI-FLL in real time, and transfers the frequency value to the phase compensation link. The compensation link calculates through the new frequency value, and after calculating the new parameter values, the transfer function is regained and connected in series to the main control link to achieve the effect of adaptive regulation.

[0134] Finally, it should be noted that the above embodiments and explanations are only used to illustrate the technical solution of the present invention rather than to limit it. Those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the spirit and scope disclosed in the technical solution of the present invention, which should be included in the scope of protection of the claims of the present invention.

Claims

1. A control method for a three-phase three-level AC / DC converter, characterized in that: include: Step 1: Obtain the voltage signal and current signal of the power grid; Step 2: Calculate the α and β components of the current signal in the stationary coordinate system and the grid frequency according to the voltage signal and current signal of the grid, and reconstruct the α and β components of the three-phase current signal in the stationary coordinate system by using the multiple parallel quasi-resonant PR control method based on time delay phase compensation to obtain the reconstructed current α and β components; Step 3: Selectively perform phase compensation on the reconstructed current α and β components according to the current grid frequency, then perform space vector inverse transformation on the final current α and β components to obtain the modulation wave signal, and then perform DPWM modulation on the modulation wave signal to obtain the duty cycle signal of the three-phase three-level AC / DC converter; Step 4: Repeat steps 1 to 3 to continuously control the three-phase three-level AC / DC converter to achieve phase dynamic compensation and stability improvement.

2. The control method of a three-phase three-level AC / DC converter according to claim 1, characterized in that: In step 2, the α and β components of the current signal in the stationary coordinate system and the grid frequency are calculated based on the voltage signal and the current signal of the grid, specifically: The grid frequency is obtained by processing the grid voltage signal through a frequency-locked loop, and the grid voltage vector phase is obtained by processing the grid voltage signal through a digital phase-locked loop; then, based on the obtained grid voltage vector phase, the grid current signal is transformed into a space vector to obtain the α and β components of the three-phase current signal in a stationary coordinate system.

3. The control method of a three-phase three-level AC / DC converter according to claim 1, characterized in that: The transfer function G of the multiple parallel quasi-resonant PR control method based on time delay phase compensation is PR (s) satisfies the following formula: Among them, k p and k r are the first and second control parameters respectively, n is the frequency generation coefficient, s is a complex variable in the complex plane, ω c is the cutoff frequency of the low-pass filter, θ is the phase compensation angle, ω o is the fundamental frequency of the power grid.

4. The control method of a three-phase three-level AC / DC converter according to claim 1, characterized in that: In step 3, phase compensation is selectively performed on the reconstructed current α and β components according to the current grid frequency, specifically: Calculate the frequency deviation between the current grid frequency and the standard grid frequency. If the current frequency deviation is less than the preset deviation threshold, the current grid is a standard grid, and the reconstructed current α and β components are used as the final current α and β components. Otherwise, it is an abnormal power grid. After phase compensation of the reconstructed current α and β components using an adaptive phase compensation method, the compensated current α and β components are obtained and used as the final current α and β components.

5. The control method of a three-phase three-level AC / DC converter according to claim 1, characterized in that: The transfer function G of the adaptive phase compensation method is n (s) satisfies the following formula: Among them, ω m is the center frequency, is the maximum compensation phase angle, γ is the proportional parameter, z and p are the parameters of the first and second compensation links.

6. A control system for a three-phase three-level AC / DC converter, characterized in that: include: A power grid signal sampling unit, used to obtain voltage and current signals of the power grid; The frequency-locked loop is used to process the voltage signal of the power grid and output the power grid frequency; Phase-locked loop, used to process the voltage signal of the power grid and output the grid voltage vector phase; A space vector transformation unit, used to perform space vector transformation on the current signal of the power grid based on the acquired power grid voltage vector phase, and output α and β components of the three-phase current signal in a stationary coordinate system; A multiple parallel quasi-resonant PR controller is used to reconstruct the α and β components of the three-phase current signal in a stationary coordinate system, and output the reconstructed current α and β components; A phase compensation selection unit, used to selectively perform phase compensation on the reconstructed current α and β components according to the current grid frequency, and output the final current α and β components; A space vector inverse transformation unit is used to perform space vector inverse transformation on the final current α and β components and output a modulated wave signal; The DPWM modulation unit is used to output a duty cycle signal of a three-phase three-level AC / DC converter after performing DPWM modulation according to the modulation wave signal.

7. A control system for a three-phase three-level AC / DC converter according to claim 6, characterized in that: The phase compensation selection unit specifically includes: A frequency deviation judgment unit is used to calculate the frequency deviation between the current power grid frequency and the standard power grid frequency, and judge whether the current power grid is a standard power grid or an abnormal power grid according to the calculated frequency deviation, and use the reconstructed current α and β components of the standard power grid as the final current α and β components; The phase compensation controller is used to perform phase compensation on the reconstructed current α and β components of the abnormal power grid to obtain the compensated current α and β components as the final current α and β components.

8. A computer device comprising a memory and a processor, wherein the memory stores a computer program, wherein: When the processor executes the computer program, the steps of the control method of a three-phase three-level AC / DC converter as claimed in any one of claims 1 to 5 are implemented.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the control method of a three-phase three-level AC / DC converter as claimed in any one of claims 1 to 5 are implemented.

10. A computer program product comprising a computer program / instructions, characterized in that When the computer program / instruction is executed by a processor, the steps of the control method of a three-phase three-level AC / DC converter as claimed in any one of claims 1 to 5 are implemented.

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