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

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 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 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.