Closed-loop DC-link Voltage Balancing Algorithm for a Four-level π-type Converter

Abstract

A four-level π-type converter is a Neutral Point Clamped (NPC) multilevel converter topology for low/medium voltage applications. As the inherent issue with this topology, the DC-link capacitor voltage balancing is challenging, especially when it operates as a single-end inverter/rectifier with unity power factor. This paper proposes a closed-loop DC-link voltage balancing algorithm of a π-type converter that is effective and simple to implement. In principle, this approach is based on Redundant Level Modulation (RLM). The RLM utilizes additional voltage levels in each switching window to gain extra controllability of the DC-link capacitor voltages without affecting the average output voltage. An algorithm based on mathematical and logical operations is developed to utilize RLM to achieve the closed-loop voltage balancing. The proposed control method is effective over the full modulation index (M = 0 ~ 1.15) and full power factor range (cos φ = 0 ~ 1). The algorithm is implemented in a test rig, and the experiment confirms its effectiveness.

Carrier-based Closed-loop DC-link Voltage Balancing Algorithm for Four Level NPC Converters Based on Redundant Level Modulation

“…The proposed approach does not require any changes on the modulator block because it only manipulates the modulating waves. A detailed block diagram of the control scheme can be found in [22]. Moreover, the proposed algorithm involves only analytical expressions and logical operations without requiring any mandatory PI/PID controllers, which is similar to the algorithm in [7] for three-level converters.…”

“…As the contribution, this paper proposes a carrier-based closed-loop voltage balancing algorithm for a four-level NPC converter that is simple to implement and effective over full operating conditions. The proposed approach features the following merits: The proposed approach was firstly brought up in the conference paper [22] and further improved by combining it with conventional ZSI approach to form a hybrid scheme in this paper. The rest of the paper is organized as follows.…”

Opportunities, Challenges, and Potential Solutions in the Application of Fast-Switching SiC Power Devices and Converters

“…This is also the case for four-level or higher level neutral point clamped (NPC) converters or other simplified topologies. The virtual space vector modulation [105] or redundant level modulation [106] however can achieve dc-link capacitor voltage balancing at the cost of an increased number of switching actions and consequent increased switching loss. Given that wide-bandgap (e.g.…”

A Fast Multilevel SVPWM Method Based on the Imaginary Coordinate With Direct Control of Redundant Vectors or Zero Sequence Components

“…This can also be perceived as part of the middle level '1' being split into levels '2' and '0', equivalently. The corresponding modulation schemes are 'virtual vector modulation' or 'redundant level modulation' [18,19]. Although the method in Fig.1 (b) can achieve neutral point voltage balancing, the drawback of this method is increased harmonics and increased switching losses due to more switching actions [20].…”

“…The total number of layers (l) that can be selected to be added can be worked out as follows. First, the total number of vectors at the three vertexes can be calculated by u aCeil and u aFloor were given in (18) and (19). i=0, 1, 2 represents the three vertexes.…”