System and method for controlling neutral point voltage balance with low frequency oscillation suppression function

Abstract

The invention discloses a system and a method for controlling neutral point voltage balance with a low frequency oscillation suppression function. The system comprises a multi-level inverter and a digital processing control module, wherein the digital processing control module comprises a sampling unit, a closed-loop control unit and a digital pulse width modulation (DPWM) unit; the output end of the DPWM unit is connected to each switching tube of the bridge arm of each phase of the multi-level inverter. The method comprises the following steps: in each switching period, the sampling unit acquires a direct-current bus voltage signal of the multi-level inverter, and a three-phase voltage signal and a three-phase current signal both output by the multi-level inverter, respectively; the acquired signals are processed by the closed-loop control unit to obtain three-phase modulating waves; the three-phase modulating waves are processed by the DPWM unit to obtain a pulse width modulation control signal which is used for controlling the working state of the switching tube of each phase of the multi-level inverter by virtue of a drive circuit. The system and the method are capable of suppressing the low frequency oscillation of the neutral point voltage of the direct-current bus of the multi-level inverter and realizing the neutral point voltage balance.

Description

technical field [0001] The invention belongs to the field of control technology in power electronic conversion technology, in particular to a mid-point voltage balance control system and method with low-frequency oscillation suppression function. Background technique [0002] In recent years, multilevel inverters have been widely used in high-voltage, medium-to-high-power conversion occasions; their circuit topology and control methods have become a research hotspot today. Compared with the two-level inverter, the multi-level inverter has many advantages such as low voltage stress of the switching tube, low electromagnetic noise, and low harmonic distortion rate of the output voltage. [0003] The topology of multilevel inverters can be roughly divided into three categories: diode-clamped, cascaded, and flying-capacitor-type, of which the most widely used is the diode-clamped inverter. Taking the three-level inverter as an example, the three-level diode-clamped inverter can...

AI Technical Summary

Problems solved by technology

For example: Literature 1 (Wang Xinyu, He Yingjie, Liu Jinjun. The control mechanism of mid-point voltage balance on the DC side of three-level inverters injected into zero-sequence component SPWM modulation[J]. Journal of Electrotechnical Society, 2011,26(5):71- 77.) The mid-point voltage control is realized by injecting 6 times the zero-sequence component into the three-phase modulation wave control command voltage, but this method is relatively complicated, and it is controlled based on a power frequency cycle, which is similar to the method based on the switching cycle. ratio, the adjustment time is too long; Document 2 (Song Wenxiang, Chen Guocheng, etc. A three-level space vector modulation method with midpoint potential balance function and its realization [J]. Chinese Electrical Engineering, 2006, 26 (12 ):96-100.) On the basis of the traditional seven-segment SVPWM control method that does not have the function of midpoint voltage balance adjustment, a new SVPWM that combines thirteen-segment, nine-segment, and seven-segment hybrid modulation is proposed The control method controls the midpoint voltage. It selects the modulation mode in intervals within a power frequency cycle. In the thirteen-segment modulation mode, the switching tube operates 12 times in each switching cycle, and in the nine-segment modulation mode, each switch The periodic switching tube operates 8 times, so the average switching loss of this hybrid modulation method is greatly increased compared with the traditional seven-segment SVPWM control method

Document 3 (Cheng Shanmei, Wang Dan, Xia Litao, Wan Shuyun. Research on Discontinuous Space Vector Pulse Width Modulation [J], Servo Technology, 2002,36(4):37-40.) mainly studies several discontinuous The space vector pulse width modulation strategy is aimed at a certain phase in a certain area within the power frequency cycle, thereby reducing switching losses, but this control method does not have the ability to control the midpoint voltage balance

[0005] To sum up, the traditional SVPWM, DPWMx, and SPWM control methods generally do not have the ability to adjust the midpoint voltage balance, and the traditional DPWMx method keeps a certain phase of the switch in a continuous interval within the power frequency cycle, so it can reduce Switching loss, but in the non-action area of ​​the switch, the ripple of the inverter output inductor current increases, the longer the time in the non-action area, the larger the ripple, which will inevitably affect the harmonic characteristics of the output current

Images