The Research On The SVPWM Control Strategy Of NPC Three-Level Inverter

Multilevel converters have been widely used in high-voltage and high-power application fields. Among many of its modulation strategies, Space Vector Modulation has been one of the most popular research points. The main advantages of the strategy are the following: it provides larger under modulation range and offers significant flexibility to optimize switching waveforms; it is well suited for implementation on a digital computer; it has higher DC voltage utilization radio.The operation principle and basic components of three-level inverter system are studied as following points:1. This thesis have researched the topology of three-level-inverter, and discussed the principle of the three-level-inverter.2. The principle of the voltage vector modulating technique is studied based on the principle of two-level inverter. A Space Vector Modulation algorithm is proposed by using the nearest three vectors as reference voltage vector. The judging rules of the small sectors and the out voltage vector sequence and time are presented as well as the producing of the signals for SVPWM. The main factor which influences neutral-point voltage balance of three-level inverter is deeply studied. After analyzing the influence of different vector to neutral-point voltage, a theory which can realize the balance of neutral-point voltage is introduced.3. A mathematical model of the three-level inverter was set up. Based on the state feedback decoupling, the dual-close-loop control of DC motor is applied to three-level inverter. As a result, the three-level inverter has favorable dynamic and steady state performance, sinusoidal output current and unity power factor.4. This thesis simulates algorithm proposed with MATLAB. TMS320F2812 DSP is chose as the main controller to complete system software. With the algorithm, waveforms, which verify the proposed algorithm, were achieved on three-level inverter.