Study On Three-Level Statcom

In electric power system, the harmfulness to system because of lack of reactive power can not be ignored. STATCOM (Static Synchronous Compensator) is an important member of Flexible AC Transmission System, comparing with traditional reactive power compensation device, it not only decrease the volume and cost of the device, but also has faster response speed and more smooth regulating property. However, because of its electronic components withstand voltage and harmonic problem limit its application. Therefore, how to limit its harmonic and improve the reliability are in urgent need of solution.On the basis of thorough analysis on reactive power compensation device in existence, this paper study on three-level STATCOM. The device is use of neutral-point clamping method to divide the inverter circuit into positive,negative and zero three level, so that each component subject to the maximum voltage reduced to half of the traditional inverter circuit; Based on instantaneous reactive power theory, the detection circuit used i_p-i_q to detect reactive current, so that detect results are not effects of voltage frequency distortion, improving the accuracy of detection; Control strategy using space vector pulse width modulation (SVPWM) technology, it has merits of easy digital implementation, high utilization of DC voltage, low current harmonic, neutral-point potential control is easier to achieve.Take TMS320LF2407A as core, designed hardware and software of STATCOM control system. Three-phase voltage and three-phase current signal of system measured by voltage transformer and current transformer, then they pass voltage conditioning circuit and current conditioning circuit respectively, converted analog signals that A/D converter can accept. These analog signals enter controller after A/D converted. Controller calculates phase difference 5 between STATCOM output voltage and system voltage, and then put it into pulse generator. Pulse generator generate multipath pulse which changes with phase and pulse width of 5, these driving pulse to drive the opening and turn-off of IGBT, so that the device can generate reactive power that system required. Finishing such as signal detection and conditioning circuit, voltage zero-crossing detection circuit, the PLL hardware multiplier circuit, IGBT driver circuit, the main part of hardware circuit design and including such as main program, capture interrupt subroutine, ADC and PWM interrupt service subroutine main function modules software design.By theoretical analysis indicates that compared with two-level device, this device output voltage waveform harmonic small, high reliability; Simulation results show that compared with traditional reactive power compensation devices, this device with dynamic characteristics well, high accuracy compensation, with functions of reactive compensation and absorb excess reactive power of system to stable voltage.