Research On Diode-Clamped Three-Level Inverter PWM Control Scheme For Inductive Machine

On the basis of sufficient argumentation of the three-level SVPWM algorithm, a neutral-point potential balancing with narrow-pulse elimination algorithm without current sensor is proposed, and dead time is compensated at the same time. The result of simulation and test verified that this algorithm is simple to be carried out, harmonics in output waveform are small, neutral-point potential can be controlled fairly well, and narrow pulse problem is solved as well. Furthermore, output torque is strengthened in low frequency for the successful dead-time compensation. All of these were achieved on a diode-clamped three-level model inverter developed with TMS320LF2407A DSP.The directed ideal for designation of feed-forward carrier-less PWM over-modulation is abstracted. On the basis of this ideal, 4 new over-modulation schemes were developed. Among of them, SMN1 is the simplest one and characteristic of accurate control of fundamental component of output. Over-modulation based on two mode limit trajectory method is extended to single mode. And by doing this, a uniform expression for calculation of reference vector, which can produce an output with the desired fundamental component, is obtained in the whole nonlinear region. This is valuable for both practice and theory. 9 over-modulation schemes, 4 of which are developed by this paper, were analyzed and compared uniformly. All of these 9 schemes were extended to diode-clamped three-level inverter, and experiment was carried out on it.Methods for accurate calculation of various index associated with harmonic characteristic of PWM waveform is developed with PWMVECTOR matrix. Indexes for evaluation of PWM waveform are studied systematically. A fact that the physical meaning of WTHD is just current THD is point out. By extending the ideal of WTHD, new harmonic-loss reflecting index LWTHD is brought forward. In addition, a new harmonic-torque reflecting index TTHD is brought forward too.The reasonable and universality of HDDF are explained with the aid of analytical expression and numerical calculation of harmonic of PWM waveform, and the relationship between HDDF and WTHD is find. It is clarified that PWM method can be evaluated and compared with regard to harmonic current if only the frequency spectrum satisfy the "shift" and "disperse" phenomenon.All of indexes mentioned in this paper except TTHD are calculated for the developed three-level SVPWM, and the result is compared with that of two popular two-level PWM methods.The three-level SVPWM method is compared with two popular two-level PWM methods with the aid of HDDF, and the relationships of switching frequency of them under same condition are calculated.