Hybrid modulation strategy for eliminating low‐frequency NP voltage oscillations in NPC using redistribution of NTV duty ratios

Abstract

Neutral point (NP) clamped (NPC) inverters produce low-frequency NP voltage oscillations when modulated with nearest three-vector (NTV) methods for certain loading conditions. Non-NTV modulations can address these oscillations at the expense of increased switching frequency, output voltage distortion and complexity. This study presents a new generalised algorithm to implement hybrid modulation strategies which can also eliminate NP voltage oscillations using a combination of the aforementioned methods. The proposed algorithm avoids abrupt changeover between the two modulations and ensures minimum contribution of non-NTV operation and hence its drawbacks. Moreover, the algorithm is computationally efficient compared with its counterparts, since it only uses redistributed NTV duty ratios to generate NTV and non-NTV modulations instead of using two separate complex algorithms which result in increased computational burden. A non-NTV method called selected three-vector (STV) modulation is chosen to perform the detailed analysis of above proposed algorithm for hybrid NTV-STV modulation. Additionally, a simplified STV (SSTV) is derived to develop a new hybrid NTV-SSTV modulation strategy which further reduces losses and complexity compared with the hybrid NTV-STV modulation, without affecting the performance of NPC. The proposed algorithm and the derived hybrid modulation strategy are validated using simulation and experimental results.

Two methods to control neutral‐point voltage fluctuation for a hybrid VIENNA rectifier

“…On the basis of analysing a large number of references about neutral‐point fluctuation control in the three‐level converter, the forms and reasons of neutral‐point voltage unbalance can be categorised as shown in Fig. 3 [12–15].…”

Two methods for controlling three‐time fundamental frequency neutral‐point voltage oscillation in a hybrid VIENNA rectifier

“…Based on the analysis of a large number of references about the neutral-point fluctuation control of three-level converter, the form and cause of neutral-point voltage unbalance can be summarised as Fig. 3 [20][21][22][23].…”

Double‐step model predictive direct power control with delay compensation for three‐level converter

“…By combining (1), (8) and 10, the cost function of the distance between ṽ and the six short vectors v si (i = 1-6) is defined as…”

“…The primary advantages of these converters are high-efficiency power conversion and low-input current harmonic. In industrial applications, diode neutral point clamped (NPC) converters [2,3,[6][7][8], active NPC converters [9,10], and T-type NPC (TNPC) converters [11,12] are three typical 3L converters. Since the power switches of the TNPC converter have a less conductive loss and an equal loss distribution [11,12], it is considered to illustrate the proposed approach in this work.…”