Generalized PWM-Based Method for Multiphase Neutral-Point-Clamped Converters With Capacitor Voltage Balance Capability

Abstract

This paper presents a generalized PWM-based control algorithm for multiphase neutral-point-clamped (NPC) converters. The proposed algorithm provides a zero-sequence to be added to the reference voltages that contributes to improve the performance of the converter by: i) regulating the neutral-point (NP) current to eliminate/attenuate the low-frequency NP voltage ripples, ii) reducing the switching losses of the power semiconductors and iii) maximizing the range of modulation indices for linear operation mode. The control method is formulated following a carrier-based PWM approach. Hence, dealing with complex space-vector diagrams to solve the modulation problem for multiphase converters is avoided. The recursive approach means that it can be easily extended to n-phase converters without increasing the complexity and computational burden, making it especially attractive for digital implementation. The proposed method allows regulating the NP voltage without the need for external controllers; therefore, no parameter tuning is required. The algorithm has been tested in a four-leg NPC converter prototype performing as a three-and four-phase system and operating with balanced and unbalanced loads. Index TermsCarrier-based pulse-width modulation, multiphase multilevel converter, neutral-point-clamped converter, capacitor voltage balance.

Research on the Neutral-Point Voltage Balance for NPC Three-Level Inverters under Non-Ideal Grid Conditions

“…In Equations (12) and (13), I mp represents the amplitude of the positive-sequence grid currents, and ϕ ui is the phase difference between positive-sequence grid voltage and positive-sequence grid current. Substituting Equations 7and 11into Equation 6, v c can be derived as:…”

“…By substituting Equations (9), (10), (12), and (13) into Equation 14, the waveforms of v c under different grid conditions are shown in Figure 3, where C and I mp are normalized.…”

“…In [11], a proportional integral (PI) controller was used to modify the reference current to maintain the NP voltage balance. NP balance methods based on zero-sequence component injection were proposed in [12,13], which calculated the zero-sequence component in the switching period. Based on the average NP voltage model in a line cycle, the PI controllers were proposed for the NP voltage balance in some papers, and the PI parameters for the controllers were usually selected for the maximum output power condition [14,15].…”

Nonlinear Effects of Three-Level Neutral-Point Clamped Inverter on Speed Sensorless Control of Induction Motor

“…Induction motors are mechanically robust, low cost, simple to manufacture, highly reliable, and are suitable for high-voltage and high-power drive applications. At present, the high-voltage high-power motor drive device often adopts a three-level neutral-point clamped structure, which has the advantages of small loss, high efficiency, and small harmonics compared with a conventional two-level inverter [4,5]. Among all the control strategies of induction motors, vector control or field-oriented control is the most popular.…”

A Versatile Workbench Simulator: Five-phase Inverter and PMa-SynRM performance evaluation

“…Multi-phase machines can be used in many applications such as power traction, energy generation, and industrial applications among others. Some benefits of these machines are better fault tolerance, improved torque per ampere, more degrees of freedom, higher reliability, and improved distribution of power between the inverter phase legs, among others [7]- [9].…”