Three-phase Multilevel Voltage Source Inverter Research Articles

Combined use of the nearest vector selecting technique and low-frequency quarter-wave symmetric space vector PWM in control of three-phase multilevel voltage source inverter

The paper offers the problem’s solution of the three-phase multilevel voltage source inverter (MLVSI) control with low dynamic losses in power semiconductor switches. The proposed technique is based on a single approach that operates with values of the integer and fractional parts of the relative values of the reference delta voltages, and it allows combining the use of the space-vector control, choosing the nearest vector (SVC), with the low-frequency space-vector pulse-width modulation with the quarter-wave symmetry of the output voltages (QWS-SVPWM). Depending on the impedance kind of a generalized load, the integrated voltage harmonics factor (weighted THD) of the appropriate order is being minimized by applying one of the two mentioned modulation methods (SVC or QWS-SVPWM) for a current range of voltage amplitude modulation index. Like its components, the combined algorithm is suitable for MLVSI of any circuit configuration and any number of equal output voltage levels.

A Reduced Switch Five-Level VSI for High-Performance Vector Controlled PMSM Drive

This work presents the strategy for vector control of permanent magnet synchronous motor (PMSM) drive fed with a three-phase multi-level voltage source inverter for high performance. In the present work, the traditional 2-level inverter is replaced with a novel reduced switch 5-level inverter, and comparative analysis is done. The implementation of the five-level inverter improves the torque, stator current, and mechanical dynamics of the drive. Here PWM technique is employed to generate the gate pulses for switching devices in a planned sequence to obtain five-level output voltage. The 12 operating modes are defined for reduced switch 5-level inverter that produces voltages as 0, ±2Vdc/3, ±Vdc, ±4Vdc/3 with reduced total harmonics distortion (THD). The close-loop vector control of PMSM with developed five-level inverter is implemented to improve the performance of drive in terms of rise time, settling time, stator current harmonics. The overall system is developed in MATLAB/Simulink and investigations are done in different input command and loading conditions. An extensive simulation study and analysis of results reveal the potential of the present work. This work mainly focuses on the reduction of motor electromagnetic torque pulsations along with improved speed response.

Design and Implementation of a New Multilevel DC-Link Three-phase Inverter

This paper presents a new configuration for a three-phase multilevel voltage source inverter. The main bridge is built from a classical three-phase two-level inverter and three bidirectional switches. A variable DC-link employing two unequal DC voltage supplies and four switches is connected to the main circuit in such a way that the proposed inverter produces four levels in the output voltage waveform. In order to obtain the desired switching gate signals, the fundamental frequency staircase modulation technique is successfully implemented. Furthermore, the proposed structure is extended and compared with other types of multilevel inverter topologies. The comparison shows that the proposed inverter requires a smaller number of power components. For a given number of voltage steps N, the proposed inverter requires N/2 DC voltage supplies and N+12 switches connected with N+7 gate driver circuits, while diode clamped or flying capacitor inverters require N-1 DC voltage supplies and 6(N-1) switches connected with 6(N-1) gate driver circuits. A prototype of the introduced configuration has been manufactured and the obtained simulation and experimental results ensure the feasibility of the proposed topology and the validity of the implemented modulation technique.

A Generalized Three-Phase Multilevel Current-Source Inverter Topology

A generalized three-phase multilevel current-source inverter (MCSI) topology is proposed by implanting the generalized N-level current cells into a three-phase MCSI topology which is derived from the three-phase multilevel voltage-source inverter (MVSI) topology through dual conversion. In the generalized three-phase MCSI topology, each intermediate dc-link current level can be automatically balanced without adding any external circuits, thus a true multilevel structure is provided. Output current of each phase is independently modulated because of being supplied with two DC current-sources. This allows the wealth of existing knowledge relating to the operations, modulations and control strategies of multilevel VSI to be immediately applied to such multilevel CSI. Simulation results of 5-level and 7-level CSI systems are presented to verify the proposed three-phase MCSI topology.