36results about How to "Small harmonic distortion" patented technology

The invention discloses a switching period optimizing space vector pulse width modulation method and a modulator. Average switching frequency is controlled through time windows of width adaptive regulation, and the switching periods in different time windows are mutually independent; switching periods in the same time window are correlated, optimizing rules between the switching periods by means of the time windows, switching period coefficients, modulation rates and phase angles control the switching periods, peak values of cluster harmonic waves in SVPWM can be significantly reduced, total harmonic distortion is greatly reduced, and the quality of output voltage is improved. The average switching frequency is controlled through the time windows of the width adaptive regulation, frequency ranges of a power switch tube is sufficiently utilized, and cost performance of a variable frequency system is improved. The modulator can sufficiently utilize flexible circuit customization characteristics of an FPGA, and integrates other circuits and algorithms of a speed regulating system into one FPGA; the speed for controlling software execution is improved, and guarantee is provided for application of the modulator in the variable-frequency speed control system.

The present application discloses a SVPWM control method, system and device for eliminating the dead zone effect, which are applied to NPC multilevel converters, including: obtaining three sub-vectors for synthesizing the target voltage vector, and determining the three sub-vectors The action time ratio and its corresponding switch state, and then according to the action time ratio and switch state, the initial comparison value of each phase in the three phases is obtained; according to the current direction of each phase in the three phases and the slope of the triangular carrier, use the preset Correction amount, correcting the initial comparison value to obtain the correction comparison value; comparing the correction comparison value of each of the three phases with the triangular carrier wave to obtain the corresponding comparison result; according to the comparison result of each phase, the phase is logically processed , to generate SVPWM pulses. The SVPWM pulse obtained by the invention can obtain a relatively ideal sine wave output voltage, the total harmonic distortion of the output current is obviously reduced, and the impact on the load or the power supply network is avoided.

The invention discloses a novel dead zone compensation method based on discontinuous pulse width modulation, which is characterized in that it includes the following steps: according to the sector where the target voltage vector is located and the respective polarities of the three-phase stator currents, the dead zone generated by the dead zone is obtained The voltage error of the three phases a, b, and c relative to the DC bus of the lower bridge arm; according to the voltage error, the respective phase voltage errors of the three phases a, b, and c caused by the dead zone and the tube voltage drop are obtained; the phase voltage error is carried out The equal-amplitude transformation of the three-phase stationary to the two-phase stationary coordinate system obtains the voltage error of the phase voltage in the two-phase stationary coordinate system; combined with the real-time rotor flux position angle, the phase voltage error in the two-phase rotating coordinate system is calculated; Perform voltage feed-forward compensation on the phase voltage; finally, according to the command voltage in the two-phase rotating coordinate system obtained after the voltage feed-forward compensation, as well as the rotor flux angle and the DC bus voltage, execute the DPWM modulation strategy; the invention can be widely used in AC Drive system and photovoltaic grid-connected system.

The invention discloses a control method for restraining point potential fluctuation in a three-level grid-connected inverter. The control method comprises the steps that firstly, signals of direct-current bus voltage are extracted from the two ends of a direct-current bus capacitor and the estimation value of point potential fluctuation in the direct-current bus capacitor is determined, wherein the signals of the direct-current bus voltage comprise the tracking value of the direct-current bus voltage and first-order and second-order differential signals; a nonlinear PI controller is used for controlling the difference between the reference value of the direct-current bus voltage and the actual value of the direct-current bus voltage; the estimation value of point potential fluctuation in the direct-current bus capacitor is used for compensating point potential fluctuation in the direct-current bus capacitor of the inverter to obtain the actual controlled quantity of the inverter. The control method lowers the unbalanced degree of point potentials in the direct-current capacitor of the three-level grid-connected inverter, reduces harmonic distortion of currents output by the inverter, improves the quality of electric energy output by the inverter; reduces voltage borne by an inverter switch device and prolongs the service life of the inverter switch device and the service life of a voltage-dividing capacitor; the robustness of a system is improved and negative influences on the system from non-measureable disturbance are resisted.

The invention discloses a specific harmonic elimination pulse width modulation control method and device for eliminating the dead zone effect, which are used for diode-clamped NPC multi-level converters, including current and voltage for NPC multi-level converters Closed-loop control, real-time calculation of voltage modulation ratio and real-time phase; query the preset switching angle storage table according to the voltage modulation ratio, and obtain a set of standard switching angles corresponding to the voltage modulation ratio; according to the output current direction and delay of the NPC multi-level converter The radian value of on-time conduction and the radian value of early turn-off are used to correct the standard switching angle, eliminate the dead zone effect in the standard switching angle, and obtain a set of corrected standard switching angles; based on the corrected standard switching angle, determine the real-time phase. According to the angle interval at the angle interval and the preset correspondence table, the driving pulse with dead zone corresponding to the real-time angle is obtained to drive the NPC multilevel converter. The invention can eliminate the influence of the dead zone effect on the driving pulse of the converter, and optimize the harmonic level of the converter.

The invention discloses a large-scale electric vehicle cluster system based on MMC and its control method. The topology structure of the large-scale electric vehicle cluster system, calculate the virtual state of charge through the initial state of charge of each electric vehicle, the user-set dwell time and the expected state of charge, and determine the driving signal drive generated by each carrier signal according to the virtual state of charge sorting The sub-module where the corresponding electric vehicle is located realizes the differential control of the charging and discharging power of the electric vehicle connected to the sub-module according to user needs, and realizes three-phase power balance and unit power factor control on the grid side. The invention has high integration degree, high modularization degree, high efficiency, small harmonic distortion, low switching loss, strong fault tolerance capability, and independent control of the sub-modules in each phase bridge arm.

The invention belongs to the field of power converter control, and discloses a three-phase current transformer model prediction control method free from a voltage sensor. The method comprises the following steps: 1, sampling AC-side currents and DC-side voltages of a current transformer; 2, performing integration on network-side voltages of the current transformer under an alpha-beta coordinate system, then after a low-pass filtering link, together with power grid currents i<alpha> and i<beta>, observing AC network-side virtual magnetic linkages (phi<alpha>, phi<beta>); 3, according to the observed virtual magnetic linkages phi<alpha> and phi<beta>, reconstructing power grid voltages and calculating magnetic linkage space angles; 4, based on a voltage outer loop, by use of model prediction control, through a solving algorithm of secondary planning, calculating optical voltage instructions (v<d><*>,v<q><*>); and 5, obtaining driving signals of a power switch tube after the voltage instructions pass through dq / alpha beta and then is subjected to an SVPWM algorithm. According to the invention, under the condition that an AC-side voltage transducer is omitted, the provided current transformer model prediction control algorithm performs searching optimization by use of a secondary planning solving algorithm, such that the system reliability is improved, the computational complexity is reduced, the difficulty of parameter setting is reduced, and the realization is easy.

The invention discloses a seven-section type SVPWM (space vector pulse width modulation) method of a five-level inverter. The method mainly comprises the following steps of 1, judging a large sector; 2, normalizing the sector through conversion of a coordinate system; 3, determining a small sector of reference voltage vector and the type; 4, calculating the action time of three basic voltage vectors; 5, selecting the switching state with small common mode voltage generated by the three basic voltage vectors; 6, forming a seven-section type switching sequence according to the selected switching state; 7, utilizing the PWM pulse generated by the switching sequence to drive the five-level inverter. The method has the advantages that the accurate position of the reference voltage vector can be quickly determined, and the calculation formula of the action time of the basic voltage vector is uniform and simple; the harmonic distortion is decreased by the seven-section type switching sequence, the common mode voltage is reduced, and the outputted alternating current voltage is balanced and symmetric; the method is favorable for being popularized and applied to higher levels.

The invention discloses a fault-tolerant voltage equalization control method for a bidirectional AC-DC energy storage converter, the steps are as follows: step S1, constructing a switch state S i ; S2, get the output voltage U j with switch state S i S3, constructing the power quadratic prediction model; S4, calculating the predicted value of the DC side separation capacitor voltage difference; S5, constructing the value function g; S6, initializing; S7, collecting the grid voltage and output current; S8, calculating Output voltage U in the current switching state j ;S9, calculate the predicted power value for the first time; S10, calculate the predicted power value for the second time; S11, calculate the value function g; S12, compare the size of the value function g with the comparison variable m, and assign the minimum value to the comparison variable m ; S13, judge and output. The invention calculates the optimal voltage vector in advance by performing two-step prediction on the output power, effectively compensates the delay of the algorithm, and reduces the influence of the delay on system performance. After the delay compensation is added, when the sampling frequency is high, the present invention can significantly reduce power fluctuations and grid-connected current harmonic distortion.

The invention discloses a three-phase two-switch rectifier filter inductance and hysteresis loop control switching frequency design method, step 1, the inductance current of each phase on the converter side is in a critical continuous state under the required load, and the phase inductance current on the converter side is calculated The inductance value L of the inductor; step 2, calculate the time delay T of the low-pass filter used for inductor current filtering d ; Step 3, if the frequency is f s =1 / T s The time delay of the signal passing through the second-order low-pass filter is T d , the corresponding phase delay satisfies: According to the second-order low-pass filter, the corner frequency is ω s The phase delay of the signal then calculates the natural resonant angular frequency ω of the second-order low-pass filter n ; Step 4: Under the condition of filter delay, the switching frequency f of the actual converter s The natural resonant angular frequency f using a low-pass filter n . The invention helps to reduce the harmonic distortion of the grid-side current, improves the sinusoidal degree of the grid-side current, and provides an engineering design method for switching frequency design under current hysteresis control.