Three Level Inverter And Its Control For High-Power AC Motor Drive

As the general-purpose frequency inverter, High-voltage and High-power AC motor drive technology is also very important for energy conservation and reducing environment pollution to realize Low Carbon Economy. Due to the low component voltage stress, low harmonic component, high quality waveforms and good EMC performance, multilevel converter is widely used in High-power AC motor drive occations. Some research on Diode-Clamped three level inverter and its application for AC motor drive is done in this paper, listed as follows:Two modulation algorithms are discussed in this paper: Space Vector PWM (SVPWM) and Selected Harmonic Elimination PWM (SHEPWM). Issues studied about SVPWM are: the SVPWM theory, implementing steps, causes of the neutral point potential variation and the controlling algorithm; while issues studied about SHEPWM are: the SHE theory, the set and solution of nonlinear equations, and deep research is done on two specific solution methods, studies on the convergence of solution space and multiple solutions are also done. Simulational and experimental verification of the SVPWM and SHEPWM algorithms are implemented and compared.The accurate motor parameter is very important to the performance and reliability of a high performance vector-controlled AC drive system. The off-line identification of motor parameter based on three level inverter driving system is discussed in this paper. DC test, single phase locked-rotor test and no-load test are implemented by giving specific excitation signals. The motor parameters are calculated by the tested voltage and current combined with the motor equivalent circuit, simulation and experiment verified the theory.As the rotor time constant is variable with the running time of the motor, on-line rotor time constant identification is carried out both in vector controlled systems with and without speed encoder. Deep research is done on the problem of identificating the rotor speed and rotor time constant simultaneously. As they are coupled, simultaneous rotor speed and rotor time constant identification is realized in this paper by superimposing AC components on the field current command.Hardware designing of an AC motor drive system with a 500KW three level inverter is given. The power circuit, bus bar, radiator, sampling circuit, Fiber Optic Isolated High-power IGBT drivers, and structure design is analyzed. Deep research is done on the IGBT driver, an improved method is proposed to eliminate problems like too-frequent resets and too-short fault signal maintain time.