A control method and system for a three-phase three-level ac / dc converter

Abstract

The application discloses a control method and system of a three-phase three-level AC / DC converter. A multiple parallel quasi-resonant PR control method based on time delay phase compensation is adopted in the main control link of the application, the time delay is converted into a fixed phase which needs to be compensated for the fundamental wave and high-order, and the influence of the delay between sampling and output on the system is improved. In view of the frequency fluctuation of the power grid, the real-time frequency of the power grid is updated in real time through a DSOGI-FLL, and the frequency value is transferred to the phase compensation link. The compensation link calculates through the new frequency value, obtains a new transfer function after calculating new parameter values, is connected in series into the main control link, and the effect of adaptive adjustment is realized.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of AC-DC circuit, and particularly relates to a control method and system of a three-phase three-level AC / DC converter improved in PR and adaptive phase compensation. BACKGROUND

[0002] The charging equipment in the field of new energy vehicles mainly has single-phase and three-phase topologies. The three-phase equipment takes 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 topology mainly includes two-level (three-phase six-switch) and three-level (Vienna and T-type three-level) topologies. The DC side of the three-level circuit has three levels of +V DC / 2, 0, and -V DC / 2, which significantly reduces the voltage stress of the switching devices in the circuit and has a cost-reducing effect on the selection of switching devices.

[0003] The T-type three-level circuit has simple main control logic and circuit structure, and is widely used in three-phase charging equipment for electric vehicles. In the forward rectification and reverse off-grid inverter working conditions, only one side of the power supply is energized, and PI control can be used to obtain good control effect. In the grid-connected working condition, the three-wire T-type three-level circuit causes the waveform quality of the grid-connected current to decrease due to the unbalanced midpoint potential, and generally needs to adopt a PR control strategy to obtain better control effect.

[0004] For the grid side, the network impedance of the power grid is not a pure resistive load, and the network impedance is generally approximately regarded as a series connection of an inductance and a resistance. The resistance part has little effect on the output stability of the grid-connected vehicle charging equipment, and the inductance part will aggravate the phase margin reduction problem caused by the multiple parallel quasi-resonant PR control system itself when it changes, 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, but in a weak power grid environment, the frequency will fluctuate to a certain extent (47-52 Hz), and the system cannot adaptively adjust, which easily causes mismatch between the compensation link and the power grid frequency, thereby causing control instability of the charging equipment and affecting the safety of the equipment and users. SUMMARY

[0006] In order to solve the problems and needs in the background art, the present application proposes a control method and system of a three-phase three-level AC / DC converter with improved PR and adaptive phase compensation. The present application obtains real-time key information of the power grid through a sampling circuit, calculates the key parameters of the phase compensation link through the corresponding calculation of the calculation unit, reconstructs the control loop, realizes phase compensation under power grid fluctuation, 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.

[0007] The technical solutions of the present application are as follows:

[0008] One kind of control method of 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, 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 power grid, and obtain the reconstructed current α, β components by reconstructing the α, β components of the three-phase current signal in the stationary coordinate system respectively using the multiple parallel quasi-resonant PR control method based on time delay phase compensation;

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

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

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

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

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

[0016]

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

[0018] In step 3, the reconstructed current α, β components are selectively phase-compensated according to the current power grid frequency, specifically:

[0019] A frequency deviation between the current power grid frequency and a standard power grid frequency is calculated, and if the current frequency deviation is less than a preset deviation threshold, the current power grid is a standard power grid, and the reconstructed current α, β components are taken as the final current α, β components; otherwise, the current power grid is an abnormal power grid, and the reconstructed current α, β components are phase-compensated using an adaptive phase compensation method to obtain compensated current α, β components and take them as the final current α, β components.

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

[0021]

[0022] where ω m is a center frequency, is a maximum phase compensation angle, γ is a proportional parameter, and z and p are the first and second compensation link parameters.

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

[0024] A power grid signal sampling unit is configured to acquire voltage signals and current signals of the power grid.

[0025] A frequency-locked loop is configured to output a power grid frequency after processing the voltage signals of the power grid.

[0026] A phase-locked loop is configured to output a power grid voltage vector phase after processing the voltage signals of the power grid.

[0027] A space vector conversion unit is configured to perform space vector conversion on the current signals of the power grid based on the acquired power grid voltage vector phase, and output α, β components of the three-phase current signals in a stationary coordinate system.

[0028] A plurality of parallel quasi-resonant PR controllers are configured to reconstruct the α, β components of the three-phase current signals in the stationary coordinate system respectively, and output reconstructed current α, β components.

[0029] The phase compensation selection unit is configured to selectively perform phase compensation on the reconstructed current alpha and beta components according to the current grid frequency, and output final current alpha and beta components.

[0030] The space vector inversion unit is configured to perform space vector inversion on the final current alpha and beta components, and output a modulation wave signal.

[0031] The DPWM modulation unit is configured to perform DPWM modulation on the modulation wave signal, and output a duty cycle signal of the three-phase three-level AC / DC converter.

[0032] The phase compensation selection unit specifically comprises:

[0033] The frequency deviation judgment unit is configured to calculate a frequency deviation between the current grid frequency and a standard grid frequency, and determine whether the current grid is a standard grid or an abnormal grid according to the calculated frequency deviation, and take the reconstructed current alpha and beta components of the standard grid as the final current alpha and beta components.

[0034] The phase compensation controller is configured to perform phase compensation on the reconstructed current alpha and beta components of the abnormal grid to obtain compensated current alpha and beta components, and take the compensated current alpha and beta components as the final current alpha and beta components.

[0035] Three, a computer device

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

[0037] Four, a computer readable storage medium

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

[0039] Five, a computer program product

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

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

[0042] (1) Compared with the traditional grid-connected PI control strategy and ideal PR control: PI control only has good control effect on direct current flow, needs to convert the system to dq coordinate system in the control strategy of AC / DC level, and needs to perform complex decoupling calculation, increases the calculation of trigonometric function value of 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 stably when the grid deviates.

[0043] The control basis of the application is multiple parallel quasi-resonant PR control. Quasi-resonant PR control increases the bandwidth near the center frequency, although it reduces the gain of part of the fundamental frequency (no longer infinite), but significantly improves the dynamic performance of the steady-state output. At the same time, due to the need to consider component errors and finite word length when digitally implemented, quasi-resonant PR control is more in line with actual design and production needs than ideal PR control. On this basis, the quasi-resonant PR control for different center frequencies (fundamental, 3 times, 5 times, 7 times) is connected in parallel, which can suppress high-order harmonics while controlling the fundamental output, has better effect of tracking sine wave, can suppress midpoint voltage deviation and DC bus double frequency interference, and obtains grid-connected current with lower harmonic content on the grid side.

[0044] (2) For the phase compensation of time delay, the application proposes to control reconstruction 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 time delay problem through the transfer function, and analyze and study the impact of the time delay problem on the system. The reconstructed PR control can directly compensate from the control loop, without the need to manually modify the grid voltage vector phase information of the digital part, and artificially compensate at the phase level, which has a better theoretical basis and effectively reduces the time delay problem caused by sampling, calculation and output of the digital circuit part, and the complexity of product research and development.

[0045] (3) The application proposes adaptive phase compensation, mainly for adaptive compensation of grid fluctuations. There are mainly two types of grid fluctuations: changes in grid impedance and changes in grid frequency. The adaptive phase compensation in the application, as a compensation of the control system, can improve the phase margin of the system when the grid impedance changes, and avoid control instability caused by system fluctuations, thereby causing equipment damage and reducing the quality of grid-connected current. On the other hand, the adaptive phase compensation of the application can extract the current grid frequency according to the fluctuation of the grid frequency, automatically update the phase compensation link parameters when calculating, 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-connected current, and reducing the interference of grid changes on the quality of the grid-connected current.

[0046] (4) Combined phase compensation strategy: The application integrates two common grid-connected phase problems, and realizes multi-dimensional phase compensation through the reconstruction of quasi-resonant PR structure and series adaptive phase compensation. In use, under the condition that the power grid does not change greatly (the power grid frequency does not fluctuate greatly), time delay compensation is adopted to reduce the influence of digital circuit on control, and the system stability is improved; in the case of power grid fluctuation, series adaptive phase compensation link is adopted, and accurate power grid frequency is extracted in real time through frequency-locked loop, and more accurate system parameters are calculated, so as to improve the system stability and reduce the grid current harmonic distortion rate. The strategy of combining the two reduces the calculation redundancy of DSP, reduces the calculation cost, and more efficiently ensures the success of grid-connected work. BRIEF DESCRIPTION OF DRAWINGS

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

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

[0049] Figure 3 It is a Bode comparison chart of PR control system before and after time delay-based phase compensation.

[0050] Figure 4 It is a DSOGI-FLL frequency-locked loop structure schematic diagram based on double generalized second-order integral.

[0051] Figure 5 It is a current inner loop control block diagram with adaptive phase compensation link.

[0052] Figure 6 It is a Bode chart comparison chart before and after adding adaptive phase compensation link.

[0053] Figure 7 It is a grid-connected current comparison chart before and after the adaptive phase compensation link provided by the circuit simulation. DETAILED DESCRIPTION

[0054] The application will be described below in combination with the drawings and examples.

[0055] Figure 1The three-wire T-type three-level circuit grid-connected topology comprises twelve switch tubes S1, S2, S3, S4, S5, S6, S7, S8, S9, S10, S11 and S12, wherein S1-S6 are IGBT power tubes, and S7-S12 are Si-MOS power tubes. In the rectifying direction only, S1-S6 can be replaced by diodes, that is, converted into a VIENNA three-phase rectifier topology. S1-S6 are referred to as longitudinal tubes, and S7-S12 are referred to as transverse tubes. In the grid-connected operation, the upper and lower tubes of the longitudinal tubes are sequentially turned on according to the positive and negative half cycles of the grid voltage sine wave in the power frequency cycle, and remain off when not turned on. In a half cycle, the longitudinal tubes and the transverse tubes that need to be turned on are turned on complementarily according to the duty cycle output by the control loop. The control loop realizes the output of a sine wave on the inverter side through the real-time change of the duty cycle, and realizes the inverter function and the grid-connected function.

[0056] The application provides a control method of a three-phase three-level AC / DC converter, as shown in the accompanying drawings, and specifically comprises the following steps: Figure 2

[0057] When the control system of the three-phase three-level AC / DC converter receives the grid-connected signal of the upper computer, the control system is converted into the grid-connected state and started. The control flow of the grid-connected operation mode of the three-phase three-level AC / DC converter is as follows:

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

[0059] Step 2: The alpha and beta components of the three-phase current signals in the stationary coordinate system and the grid frequency are calculated according to the voltage signals and the current signals of the power grid, the alpha and beta components of the three-phase current signals in the stationary coordinate system are reconstructed by using a multiple parallel quasi-resonant PR control method based on time delay phase compensation, and the reconstructed current alpha and beta components are obtained;

[0060] In step 2, the alpha and beta components of the three-phase current signals in the stationary coordinate system and the grid frequency are calculated according to the voltage signals and the current signals of the power grid, and specifically:

[0061] The grid frequency (i.e. the grid fundamental frequency) is obtained by processing the voltage signals of the power grid through a lock frequency loop, and the phase of the voltage vector of the power grid is obtained in real time by processing the voltage signals of the power grid through a digital lock phase loop. Specifically: the three-phase lock phase loop obtains the phase information of the voltage vector of the power grid through digital filtering and a voltage control link of the voltage signals of the power grid, and is used for space vector transformation in the control loop. The three-phase lock frequency loop adopts a two-layer combined structure of DSOGI-FLL, wherein the DSOGI link decomposes the positive and negative sequences of the three-phase voltage signals and generates orthogonal signals, and the FLL link obtains the grid frequency through calculation of the orthogonal signals, and is used for re-calculation of 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 integration. The frequency-locked loop acts as a part of acquiring the power grid frequency in the application, and its main purpose is to acquire the real-time power grid frequency under power grid fluctuation and provide adaptive calculation for the adaptive phase compensation link. The structure is mainly divided into two parts: the DSOGI quadrature signal generator part and the FLL frequency-locked loop part.

[0063] The DSOGI is a double generalized second-order integration structure, which extracts the positive sequence fundamental frequency component of the α and β components in the stationary coordinate system through space vector transformation of the three-phase voltage. The quadrature generator part is mainly adopted in the frequency-locked loop, and its structure is based on the filter link of the second-order generalized integration, which can meet the high quality requirements of the frequency-locked loop for signals. The transfer function of the DSOGI quadrature generator is:

[0064]

[0065] wherein V' is the output signal of the tracking quadrature generator input signal V, D(s) is the transfer function thereof, qV' is the output signal of the phase lag V' 90°, Q(s) is the transfer function thereof, q is the quadrature operator, τ' is the center frequency in the DSOGI link, and K is the proportional parameter in the link.

[0066] Figure 5 In The positive sequence part corresponding to the α and β components of the power grid voltage is calculated according to the following formula:

[0067]

[0068]

[0069] wherein the α and β components V α and V β of the power grid voltage are input into the DSOGI quadrature generator, and two sets of quadrature signals V' α and qV' α are obtained. β and qV' β are a set of quadrature signals, and the signals with q in the expression are signals lagging 90°, and q is the quadrature operator.

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

[0071]

[0072] Where ω' is the center frequency of the frequency-locked loop element, consistent with the DSOGI. Since the basic structure of the notch filter reduces the gain to 0 at the center frequency, it is selected as the main structure of the FLL according to this characteristic. A first-order linear approximation is made to the frequency-locked loop, a simplified model is obtained, and the corresponding proportional parameters are calculated, so that the operation amount 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 signals of the grid are subjected to space vector transformation, i.e. the three-phase currents are transformed to the stationary coordinate system αβ to obtain the α and β components of the three-phase current signals in the stationary coordinate system.

[0074] The multiple-parallel quasi-resonant PR control method based on time delay phase compensation is specifically to estimate the overall time delay of sampling, calculation and output of the digital control part to obtain the time amount of the delay. According to the estimated time amount, the multiple-parallel quasi-resonant PR control method is reconstructed. In the process of the present application, 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 fixed phases that need to be compensated for the fundamental wave and high-order waves, and improves the influence of the delay between sampling and output on the system.

[0075] Specifically:

[0076] The PR control is a control method for tracking a sinusoidal signal without error based on the inner membrane principle, and its transfer function expression form is as follows:

[0077]

[0078] Based on 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 high-order terms generated in the calculation are ignored, and the fundamental wave, the 3rd harmonic wave, the 5th harmonic wave and the 7th harmonic wave (main harmonic components of the grid) are controlled in parallel, and the transfer function is:

[0079]

[0080] Where 2n+1 corresponds to the fundamental wave, the 3rd harmonic wave, the 5th harmonic wave and the 7th harmonic wave when n is 0 / 1 / 2 / 3 respectively.

[0081] Considering the system time delay caused by sampling and calculation, combined with the clock of the calculation chip and the complexity of the program terminal, it is estimated that the system time delay is basically in the range of 1.5τ0T-2ω0T, T represents the switching period of the PWM wave output by the control system, and ω0 is the fundamental wave frequency of the grid. The transfer function with total time 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 1.5ωT-2ωT. The time delay increases the phase lag of the overall control system, reduces the phase margin of the control system, and causes the system to be prone to instability.

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

[0085] The transfer function G PR (s) of the multiple parallel quasi-resonant PR control method based on time delay phase compensation

[0086]

[0087] Where, k p and k r are the first and second control parameters of the PR element, respectively, which are generally calculated according to the transfer function of the system or obtained from the experimental parameters of the actual machine, n is the frequency generation coefficient, 2n+1 corresponds to the fundamental wave, 3rd harmonic, 5th harmonic, and 7th harmonic when n is 0 / 1 / 2 / 3, respectively, s is a complex variable in the complex plane, used to describe the frequency response, stability, etc. of a dynamic system, ω c is the cutoff frequency of the low-pass filter, θ is the phase compensation angle, and ω o is the fundamental frequency of the power grid.

[0088] Figure 3 The Bode phase diagram of the quasi-resonant PR control of multiple parallel based on time delay phase compensation and the ordinary quasi-resonant PR control is compared. The quasi-resonant PR control of multiple parallel based on time delay phase compensation is compensated based on a 25kHz sampling and switching frequency, and the control parameters of PR are selected as k p =10 and k r =1000. It can be seen that the reconstructed PR control element compensates for the phase of the control element compared to the original PR control, improves the phase margin, and thus reduces the influence of time delay on the stability and output of the system.

[0089] Step 3: selectively phase-compensate the reconstructed current α, β components according to the current grid frequency, then perform spatial vector inverse transformation on the final current α, β components to obtain a modulation wave signal, then perform DPWM modulation on the modulation wave signal to obtain the duty cycle signal of the three-phase three-level AC / DC converter, and adjust the duty cycle of the switching devices of the three-phase three-level AC / DC converter through the duty cycle signal to realize control of the main power circuit;

[0090] In step 3, the reconstructed current alpha and beta components are selectively phase compensated according to the current grid frequency, specifically:

[0091] A frequency deviation between the current grid frequency and the standard grid frequency (i.e. 50 Hz) is calculated, and the frequency deviation is used to determine whether the grid is fluctuating. Specifically, if the current frequency deviation is less than a preset deviation threshold, the current grid is a standard grid, and the reconstructed current alpha and beta components are taken as the final current alpha and beta components; otherwise, it is an abnormal grid, and the reconstructed current alpha and beta components are phase compensated using the series adaptive phase compensation method to obtain compensated current alpha and beta components and take them as the final current alpha and beta components.

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

[0093]

[0094] Where ω m is the center frequency of the lead element, is the maximum phase compensation angle, gamma is the proportional parameter, z and p are the first and second compensation element parameters to be calculated and determined.

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

[0096] For multiple parallel quasi-resonant PR control systems, the phase compensation element of the present application sets the center frequency at the highest frequency of the parallel, i.e. the 7th harmonic, i.e.

[0097] ω m = 7·ω

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

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

[0100] The current inner loop refers to the internal loop in the control system that controls the current. In rectification and inversion conditions, there is a voltage outer loop that controls the voltage. The present application is only for grid-connected conditions, so there is only the current inner loop part in the control system.

[0101] The adaptive function in the present application mainly manifests as: when the grid fluctuates, the fundamental frequency of the grid also changes, i.e. the fundamental frequency of the grid ω in the above formula is also updated in real time. At this time, Figure 4The three-phase frequency-locked loop link in the control system is used for extracting the grid frequency through the processing and calculation of the grid voltage signal, and the obtained omega is compared with the standard grid frequency 2pi*50 rad / s. When the deviation exceeds 0.5 Hz, the new omega is assigned to the phase compensation link to re-calculate z, p and gamma, and the corresponding parameters are obtained and connected in series into the current inner loop control circuit to perform phase compensation.

[0102] Step 4: Steps 1-3 are repeated to continuously control the three-phase three-level AC / DC converter, so as to realize phase dynamic compensation and stability improvement of the three-phase three-level AC / DC converter.

[0103] The application obtains real-time key information of the grid through the sampling circuit, performs corresponding calculation through the calculation unit, outputs key parameters of the phase compensation link, reconfigures the control loop, realizes phase compensation under grid fluctuation, improves phase margin, enhances the stability of the control link, reduces the harmonic content of the grid-side grid-connected current, and improves the grid-connected success rate and grid-connected quality.

[0104] The application provides a control system of a three-phase three-level AC / DC converter, and the control system comprises:

[0105] A grid signal sampling unit is configured to obtain voltage signals and current signals of the grid.

[0106] A frequency-locked loop is configured to output a grid frequency after processing the voltage signals of the grid.

[0107] A phase-locked loop is configured to output a grid voltage vector phase in real time after processing the voltage signals of the grid.

[0108] A space vector conversion unit is configured to perform space vector conversion on the three-phase current signals of the grid based on the obtained grid voltage vector phase, that is, convert the three-phase current into the stationary coordinate system αβ, and output α and β components of the three-phase current signals in the stationary coordinate system.

[0109] A plurality of parallel quasi-resonant PR controllers are configured to reconfigure the α and β components of the three-phase current signals in the stationary coordinate system respectively, and output the reconfigured current α and β components.

[0110] A phase compensation selection unit is configured to selectively perform phase compensation on the reconfigured 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 conversion unit is configured to perform space vector inverse conversion on the final current α and β components, and output a modulation wave signal.

[0112] A DPWM modulation unit is configured to perform DPWM modulation on the modulation wave signal, and output a duty cycle signal of the three-phase three-level AC / DC converter.

[0113] The phase compensation selection unit specifically comprises:

[0114] A frequency deviation judging unit is configured to calculate a frequency deviation between the current grid frequency and the standard grid frequency, and judge whether the current grid is a standard grid or an abnormal grid according to the calculated frequency deviation, and take the reconstructed current alpha and beta components of the standard grid as the final current alpha and beta components.

[0115] A phase compensation controller is configured to perform phase compensation on the reconstructed current alpha and beta components of the abnormal grid to obtain compensated current alpha and beta components and take the compensated current alpha and beta components as the final current alpha and beta components.

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

[0117] The present application provides a computer readable storage medium, which stores a computer program, and the computer program implements the steps of the control method of the three-phase three-level AC / DC converter when executed by a processor.

[0118] The present application provides a computer program product comprising a computer program / instruction, which implements the steps of the control method of the 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 lead compensation link, the maximum phase compensation angle is 10°-30°, and the present application selects 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 examples take 50Hz as the grid fundamental frequency for demonstration.

[0120]

[0121]

[0122] The calculation is as follows:

[0123] z=1400.79

[0124] p=3451.92

[0125] γ can be calculated according to the compensation frequency (for example, 7·2π·50 rad / s), and |G n (jω m )|=1, and the calculation is as follows:

[0126]

[0127] The above parameters are recalculated according to the real-time frequency of ω during the actual machine operation, so that the system stability can be more accurately maintained.

[0128] Figure 6 In order to increase the Bode diagram contrast before and after the adaptive phase compensation link, according to Figure 5 The overall transfer function generated by the current loop structure and the circuit structure (LC filter circuit connected between the three-phase three-level ACDC converter and the power grid, L is the filter inductance, and C is the filter capacitance) is:

[0129]

[0130] Among them, L includes L1 filter inductance and L g The grid-side inductance is one of the influencing factors causing system changes when the grid-side impedance changes, which can cause system instability, and is one of the design premises of the present application.

[0131] The open-loop transfer function of the overall system is compared before and after the series adaptive phase compensation link G n (s), and it can be seen that the phase margin after compensation is obviously improved, the phase margin at the 7th harmonic frequency and the cutoff frequency is maintained at 45° and above, the system stability is improved, the possibility of system instability caused by grid fluctuation is avoided, and problems such as damage to hardware circuit are avoided.

[0132] Figure 7 In order to provide the grid-connected current comparison chart before and after the adaptive phase compensation link of the circuit simulation, according to the simulation verification of the design of the present application, the controlled grid-connected current amplitude reference value 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, which reflects the improvement effect of the present application on the system stability and the optimization effect on the grid-connected current.

[0133] The present application is aimed at the case of grid-side frequency fluctuation, and the real-time frequency of the grid is updated in real time through the DSOGI-FLL, and the frequency value is transferred to the phase compensation link, the compensation link is calculated through the new frequency value, the transfer function is obtained again after the new parameter value is calculated, and the adaptive adjustment effect is realized.

[0134] Finally, it should be explained that the above examples and explanations are only used to illustrate the technical solutions of the present application, but not to limit it. Those skilled in the art should understand that the technical solutions of the present application can be modified or replaced equivalently without departing from the spirit and scope of the technical solutions disclosed by the present application, and they should be covered in the protection scope of the claims of the present application.

Claims

1. A control method of a three-phase three-level AC / DC converter, characterized by, The method comprises the following steps: Step 1: obtaining voltage signals and current signals of the power grid; Step 2: obtain the components of the current signal in the stationary coordinate system and the grid frequency according to the voltage signal and the current signal of the power grid, and reconstruct the current components in the stationary coordinate system using a multiple parallel resonant PR control method based on time delay phase compensation 、 Step 3: obtain the reconstructed current components after reconstructing the three-phase current signals in the stationary coordinate system 、 , 、 ​ The transfer function of the multiple parallel quasi-resonant PR control method based on time delay phase compensation satisfies the following formula: wherein and are first and second control parameters, respectively, is a frequency generation coefficient, is a complex variable in the complex plane, is a cut-off frequency of a low-pass filter, is a phase compensation angle, is a grid fundamental frequency; Step 3: Selectively adjust the reconstructed current according to the current grid frequency. , Phase compensation is performed on the components, and then the final current is adjusted. , The components are subjected to inverse space vector transformation to obtain the modulation wave signal. Then, the modulation wave signal is subjected to DPWM modulation to obtain the duty cycle signal of the three-phase three-level AC / DC converter. Step 4: repeating steps 1-3 to continuously control the three-phase three-level AC / DC converter to realize phase dynamic compensation and stability improvement.

2. The control method of a three-phase three-level AC / DC converter according to claim 1, characterized by, In step 2, the stator coordinate system current signal components and the grid frequency are calculated based on the grid voltage signal and the current signal, specifically: , ​ The grid frequency is obtained by processing the voltage signal of the grid through a frequency-locked loop, and the grid voltage vector phase is obtained by processing the voltage signal of the grid through a digital phase-locked loop; then, based on the obtained grid voltage vector phase, the current signal of the grid is subjected to space vector transformation to obtain the 、 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 by, In step 3, the reconstructed current is selectively phase-compensated according to the current grid frequency, specifically: , component is phase-compensated. a frequency deviation between the current grid frequency and a standard grid frequency is calculated, and if the current frequency deviation is smaller than a pre-set deviation threshold, the current grid is a standard grid, and the reconstructed current , component is used as the final current , component; Otherwise, it is considered an abnormal power grid, and an adaptive phase compensation method is used to adjust the reconstructed current. , After phase compensation of the components, the compensated current is obtained. , The component and as the final current. , Quantity.

4. The control method of a three-phase three-level AC / DC converter according to claim 3, characterized by, Transfer function of the adaptive phase compensation method satisfies the following equation: wherein is a center frequency, is a maximum phase compensation angle, is a proportional parameter, are first and second compensation element parameters.

5. A control system for a three-phase three-level AC / DC converter, characterized by The method comprises the following steps: A power grid signal sampling unit is configured to obtain voltage signals and current signals of the power grid; A frequency-locked loop is configured to output a power grid frequency after processing the voltage signals of the power grid; A phase-locked loop is configured to output a power grid voltage vector phase after processing the voltage signals of the power grid; The space vector conversion unit is configured to perform space vector conversion on the current signal of the power grid based on the obtained phase of the power grid voltage vector, and output the three-phase current signal in the stationary coordinate system , component. Multiple parallel quasi-resonant PR controllers are used to process three-phase current signals in a stationary coordinate system. , The components are reconstructed separately, and the reconstructed current is output. , Quantity; The multiple parallel quasi-resonant PR controllers specifically comprise: The current signal in the stationary coordinate system is calculated according to the voltage signal and the current signal of the power grid 、 The three-phase current signals in the stationary coordinate system are reconstructed by using a multiple parallel resonant PR control method based on time delay phase compensation, respectively 、 The reconstructed current 、 components are obtained. The transfer function of the multiple parallel quasi-resonant PR control method based on time delay phase compensation satisfies the following formula: wherein and are first and second control parameters, respectively, is a frequency generation coefficient, is a complex variable in the complex plane, is a cut-off frequency of a low-pass filter, is a phase compensation angle, is a grid fundamental frequency; A phase compensation selection unit is used to selectively adjust the reconstructed current according to the current grid frequency. , Phase compensation is performed on the components to output the final current. , Quantity; a space vector inverter unit for performing a space vector inversion on the final current , components to output a modulation wave signal A DPWM modulation unit is configured to output duty cycle signals of the three-phase three-level AC / DC converter after DPWM modulation according to a modulation wave signal.

6. A control system for a three-phase three-level AC / DC converter as claimed in claim 5, characterised in that, The phase compensation selection unit specifically comprises: The frequency deviation judgment unit is used to calculate the frequency deviation between the current power grid frequency and the standard power grid frequency, and to determine whether the current power grid is a standard power grid or an abnormal power grid based on the calculated frequency deviation. It then reconstructs the current from the standard power grid. , The component is the final current. , Quantity; a phase compensation controller for phase compensating the reconstructed current of the abnormal power grid , to obtain a compensated current , component and as the final current , component. 7.A computer device, comprising a memory and a processor, wherein the memory stores a computer program, and the computer device is configured to perform the method according to any one of claims 1-6 when the computer program is executed by the processor. The processor executes the computer program to realize the steps of the control method of the three-phase three-level AC / DC converter according to any one of claims 1 to 4.

8. A computer-readable storage medium having stored thereon a computer program, characterized in that, The computer program is executed by the processor to realize the steps of the control method of the three-phase three-level AC / DC converter according to any one of claims 1 to 4.

9. A computer program product comprising computer programs / instructions, characterized in that, The computer program / instructions are executed by the processor to realize the steps of the control method of the three-phase three-level AC / DC converter according to any one of claims 1 to 4.

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