Midpoint voltage balance control system and method with low frequency oscillation suppression function

Abstract

The invention discloses a mid-point voltage balance control system and method with low-frequency oscillation suppression function. The system includes a multilevel inverter and a digital processing control module, wherein the digital processing control module includes a sequentially connected sampling unit, a closed-loop control unit and a DPWM pulse width modulation unit; the output of the DPWM pulse width modulation unit is driven by The circuit is connected to each switching tube of each phase bridge arm of the multi-level inverter. The method is as follows: in each switching period, the sampling unit separately collects the DC bus voltage signal of the multi-level inverter, the three-phase voltage signal and the three-phase current signal output by the multi-level inverter; the collected signals are passed through The closed-loop control unit processes the three-phase modulation wave; the three-phase modulation wave is processed by the DPWM pulse width modulation unit to obtain the pulse width modulation control signal, and the signal controls the working state of each phase switch tube of the multi-level inverter through the drive circuit. The invention can suppress the low-frequency oscillation of the midpoint voltage of the DC bus bar of the multilevel inverter and realize the midpoint 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...

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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

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