Middle point voltage control device and method based on modulation wave interval division

Abstract

The invention discloses a middle point voltage control device and method based on modulation wave interval division. The device comprises a three-level inverter, a digital processing control module and a driving circuit, wherein the digital processing control module comprises a sampling unit, a closed-loop control unit, a sine pulse width modulation unit, a modulation wave interval division unit and a zero-sequence component calculation unit. The method comprises steps that an offset angle of a zero-crossing point after adding a zero-sequence component to a three-phase modulation signal is calculated; the modulation wave interval is divided, and the zero-sequence component required to suppress the midpoint voltage fluctuation is calculated; the sign of the zero sequence component is determined through comparing instantaneous voltages of upper and lower capacitors of the DC side; the zero-sequence component is added to the three-phase modulation signal and is then processed by the sinepulse width modulation unit to acquire a pulse width modulation control signal, and a switch tube of the three-level inverter is controlled by the driving circuit for operation. The device is advantaged in that hardware cost is low, accurate control is realized, the application scope is wide, the midpoint voltage fluctuation can be effectively inhibited, and the distortion rate of the network current is reduced.

Description

technical field [0001] The invention belongs to the technical field of control in power electronic conversion technology, in particular to a midpoint voltage control device and method based on division of modulation wave intervals. Background technique [0002] The NPC three-level inverter has been widely used in medium and high power applications due to its mature topology, low voltage withstand of switching devices, and low output harmonic content. However, due to the inherent characteristics of the NPC three-level inverter, the DC side of the inverter will have a problem of midpoint voltage fluctuation. At present, there are three main solutions to the problem of midpoint voltage fluctuation on the DC side of the three-level inverter: (1) Use an independent DC voltage source to supply power to the DC side capacitor; (2) Externally connect the midpoint balance control circuit; (3) ) using a specific midpoint voltage control method; because the first two methods will incre...

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Problems solved by technology

However, in actual situations, grid faults will lead to unbalanced three-phase voltages on the grid side. In the state of unbalanced three-phase voltages, the amplitude of midpoint voltage fluctuations will increase, and the frequency will be three times that of when three-phases are balanced. The frequency becomes power frequency, and contains odd harmonic components such as 3rd, 5th, and 7th, which brings difficulties to the control of the midpoint voltage

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