Control of capacitor voltage of three phase five-level NPC voltage source inverter. Application to inductor motor drive.

One of the most important drawbacks of the three phase five-level NPC (Neutral Point Clamped) source voltage inverters(VSI) is the Neutral Point balance. As consequence, the capacitor voltages of the input DC voltage of the VSI are not equal. There are different ways to cope with this problem. In this paper, a simple solution that solves this balance is given. It is based on using of four three phase PWM voltage source rectifier with four clamping bridge to stabilize these Dc voltages. So, the authors propose to study the cascade constituted by four three phase PWM voltage source rectifiers-clamping bridge-filter-five-level NPC VSI-Induction machine. In the first part, we present a topology of five-level NCP VSI, and then we propose a model of this converter and an algebraic PWM strategy for the control. The second part presents the topology and the controlled model of three phase voltage source rectifier. We develop, also a PWM strategy to control this converter. In the third part, we study a high voltage cascade: Four PWM voltage source rectifiers-filter-five-level NPC VSI - Induction machine. In the last part of this paper, the authors study the stability problem of the input DC voltages of the five-level NPC VSI. As application, we study the performances drive of the three phase induction machine fed by this cascade. This drive system can find applications in great power and high voltage fields as electrical traction.