Conventional Three-phase Voltage Source Inverter Research Articles

Comprehensive Analysis and Evaluation of DC-Link Voltage and Current Ripples in Symmetric and Asymmetric Two-Level Six-Phase Voltage Source Inverters

Multiphase drives (MPD) in general and six-phase in particular have been gaining popularity in many industries, which calls for a proper multiphase inverter (MPI) design. For voltage source inverter (VSI)-fed drives, the knowledge of voltage and current stresses on the dc-link are imperative for input capacitor sizing. To this end, the voltage and current stresses on the dc-link capacitor in two-level six-phase VSIs are examined thoroughly in this article for two configurations of load/winding spatial distribution: symmetric and asymmetric. First, the harmonic spectrum of the input dc current of each inverter is analyzed in detail by benchmarking them against the conventional three-phase VSI, to precisely establish the dc-capacitor requirement reduction in six-phase counterparts. Second, analytical formulae for the dc-link capacitor voltage ripples are derived for both configurations. Third, simple formulae for dc-capacitor sizing for six-phase VSIs with different load configurations are provided. The accuracy of the derived formulae is verified by simulation and experimental testing at various power factors and modulation depth. It is found that six-phase VSI supplying symmetric and asymmetric loads reaps 10% and 7% lower dc-link current ripples, respectively. Hence, six-phase symmetric loads yield the smallest capacitor size.

Transformer-Less Cascaded Voltage Source Converter Based STATCOM

In this work, a transformer-less voltage source converter (VSC) based STATCOM is proposed with a combination of cascaded conventional three-phase voltage source inverters. This modular structure provides multilevel operation with reduced switch count and independent DC-link capacitors. The actual contribution of this paper is the transformer-less configuration of a conventional cascaded voltage source converter which provides reduced cost and volume as compared to other transformer-less converter configurations. The system provides reactive power compensation with better power quality when connected to the nonlinear power electronics load also. A simple control system is provided for balancing the Dc link capacitor voltage and reactive power compensation. The validation of the proposed model is analyzed with simulation using MATLAB/SIMULINK software and the results are obtained with different linear and nonlinear load configurations.

Grid-Connected Induction Motor Using a Floating DC-Link Converter Under Unbalanced Voltage Sag

This article proposes a series compensator with unbalanced voltage sag ride-through capability applied to grid-connected induction motors. A conventional three-phase voltage source inverter (VSI) is intended to regulate the motor voltages. The VSI is connected in series with the grid and a three-phase machine with open-ended windings. The proposed system is suitable for applications in which no frequency variation is required, like large pumps or fans. The VSI dc-link voltage operates as a floating capacitor through the energy minimized compensation (EMC) technique, in which there is no dc source or injection transformer. The motor load condition determines the minimum grid voltage positive component (sag severity) to keep EMC operation. Meanwhile, a voltage unbalance may increase the dc-link voltage requirements. A 1.5-hp four-pole induction motor has been used to verify the ride-through capability of the proposed compensator under grid voltage disturbances. A total harmonic distortion (THD) analysis of grid currents demonstrates that the proposed system provides low THD even if no passive filter is used. The operating principle, converter output voltage analysis, pulsewidth modulation technique, control strategy, and components ratings are discussed as well. Simulation and experimental results are presented to demonstrate the feasibility of the system.

Flying Capacitor-Assisted Two-Leg Inverter for Permanent Magnet Synchronous Motor Drive

This article proposes an inverter configuration for a high-power-density permanent magnet synchronous motor (PMSM) drive. The proposed inverter consists of a two-leg voltage source inverter (VSI) and a flying capacitor. The VSI and the capacitor are connected to two of the three-phase stator windings of the PMSM, sharing one phase. Although the VSI controls the motor torque or speed, the flying capacitor not only boosts the stator voltage above the dc link voltage through resonance with stator inductances but also mitigates power imbalance through a phase shift. Despite the use of a two-leg inverter, such a combination enables PMSM drive with the high power density and low torque ripple. Unlike conventional boost inverters, the voltage stress of the switches is maintained at the dc-link voltage regardless of the boost ratio. It also allows PMSMs to have higher power capability while using fewer active devices than conventional three-phase VSIs. This article presents the operating principle and area of the proposed PMSM drive. A control strategy that accurately controls average torque and speed while minimizing copper loss and limiting inverter voltage and torque ripple is also proposed. The performance of the proposed PMSM drive is demonstrated with both steady-state and transient experiments.

A STATCOM Based on a Three-Phase, Triple Inverter Modular Topology for Multilevel Operation

In this paper, a static synchronous compensator (STATCOM) is proposed in which a new modular structure with conventional three-phase voltage source inverters is used to multilevel operation. The inverters are connected to a transformer in an open-end winding configuration and with three independent DC links. In this structure, the inverters will be connected in a cascade configuration. Besides the multilevel operation, the system is also characterized by low required blocking voltages for switch ratings, since the proposed STATCOM can apply the double of the DC capacitor voltage to the transformer windings. The development of the control system for the proposed topology is also presented. The operation of the proposed topology and the performance of the developed control system will be tested through several simulation and experimental tests.

A Switched-Capacitor-Voltage-Doubler Based Boost Inverter for Common-Mode Voltage Reduction

In this paper, a modified three-phase two-level voltage source inverter is proposed. By combining the conventional three-phase H-bridge inverter with a switched-capacitor-voltage-doubler network, the DC-link voltage of the proposed inverter is double with respect to the input DC voltage. As a result, the output voltage of the proposed inverter can be higher than the input DC voltage. Furthermore, a common-mode voltage (CMV) of the proposed inverter can be reduced through controlling the two additional switches based on the space vector pulse-width modulation. Compared to the existing modulations and topologies, the variation in CMV can only be up to 16.6% of DC-link voltage. Furthermore, the voltage stress across additional switches and diodes is equal to half of DC-link voltage. Mathematical analysis, operating principles, and comparison of the proposed three-phase two-level voltage source inverter with the conventional three-phase voltage source inverters are presented. The simulation results based on PLECS software verify a good performance of the proposed inverter. Finally, a laboratory prototype based on a TMS320F280049 DSP is developed and experimental tests are carried out to validate the effectiveness of the proposed three-phase inverter topology.

Comprehensive Modelling and and Experimental Testing of Fault Detection and Management of a Non-Redundant Fault-Tolerant VSI

This paper presents an investigation and a comprehensive analysis on fault operations in a conventional three-phase voltage source inverter. After an introductory section dealing with power converter reliability and fault analysis issues in power electronics, a generalized switching function accounting for both healthy and faulty conditions and an easy and feasible method to embed fault diagnosis and reconfiguration within the control algorithm are introduced. The proposed system has simple and compact implementation. Experimental results operating both at open- and closed-loop current control, obtained using a test bench realized using a dSPACE system and the fault-tolerant inverter prototype demonstrate that the proposed solution is effective and feasible and makes all faults easily managed by the controller itself.

SVM Procedure for $n$-Phase VSI With Low Harmonic Distortion in the Overmodulation Region

Space vector modulation (SVM) technique has become a standard method for the impression of voltage references in conventional three-phase voltage source inverters. The method is nowadays used in multiphase (more than three) drives, where linear and overmodulation regions are covered only for the five-phase case. This work proposes a general SVM procedure for linear and overmodulation regions in <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$n$</tex></formula> -phase drives (being <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$n$</tex></formula> any odd number, <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$n &gt; 3$</tex></formula> ) and simplifies the extension of SVM to the multiphase case. The proposed method achieves the reference voltage at the fundamental frequency while reducing introduced harmonic components in the overmodulation region compared to previous proposals.

Three-Phase Hybrid Multilevel Inverter Based on Half-Bridge Modules

A novel three-phase hybrid multilevel converter is proposed for medium-voltage applications. The converter employs a conventional three-phase voltage source inverter (VSI) linking series connected half-bridge modules at each phase. With the proposed connection, a large portion of energy can be processed by the VSI by employing a single multi-pulse rectifier, while smaller power shares are processed within the half-bridge modules. Thus, the requirements for galvanically insulated dc sources are reduced. Modularity is naturally achieved. A modulation scheme for a four-level version is proposed and analyzed in detail. This scheme allows unidirectional power flow in all dc sources and, consequently, enables diode bridges to be employed in the rectification input stage for unidirectional applications.

Three-Phase Power Quality Compensator Under the Unbalanced Sources and Nonlinear Loads

A three-phase voltage-source inverter for a power quality compensator under the unbalanced mains and nonlinear loads is proposed to provide balanced three-phase source current and improve input power factor. The proposed converter is based on the conventional three-phase voltage-source inverter with three additional ac power switches to achieve three-level pulsewidth modulation. The voltage stress of three ac power switches is clamped to half the dc-link voltage. The balanced reference mains currents are estimated using the dc-bus voltage and load currents. A proportional-integral voltage controller is used in the outer loop to compensate the switching losses of the voltage-source inverter. To perform the integrated power quality compensation, a hysteresis current control scheme is adopted to track the balanced line current command in phase with mains voltage. Three voltage levels are generated on the ac terminal of the proposed inverter. Computer simulation and experimental results are provided to verify the effectiveness of the proposed control scheme.

An Investigation of a Control Method for Fault-Mode Inverters to Drive Induction Motors

In this paper, a control method in fault-mode for three-phase voltage source inverters to drive AC motors is proposed. The proposed method does not require any additional switching devices and specially constructed motors with an external terminal of the neutral point. Thus, this method can be easily applied to conventional three-phase voltage source inverters. When the one leg of the inverters is lost by a trouble in the switching devices, the turn-on signals for the switching devices are removed. Then, the corresponding phase of the motor is connected to the neutral point of the DC link divided by the two series-connected DC smoothing capacitors. In this connection, the switching devices in the remaining two phases of the inverter can apply sinusoidal line-to-line voltage to produce the three-phase balanced currentin the motor. To realize the proposed method, a method to compensate the voltage fluctuation of the DC neutral point must be developed. The effectiveness of the proposed control strategy for the fault-mode three-phase voltage source inverters has been confirmed by the experimental results employing a test system.

A novel dynamic voltage restorer and its unbalanced control strategy based on space vector PWM

A novel dynamic voltage restorer which is composed of a conventional three-phase voltage source inverter and an emitter follower is presented in this paper to reduce the adverse effects on sensitive loads caused by three-phase supply voltage unbalance in distribution systems. The adverse effect caused by the negative sequence component of the supply voltage can be eliminated and the load voltage magnitude can be restored to specified value by using the three-phase voltage-source inverter. The emitter follower is capable of eliminating the adverse effect caused by the zero sequence component of the supply voltage. An unbalanced control strategy based on space vector PWM is presented to realize the fast dynamic response of the dynamic voltage restorer. Feasibility of this method is verified by digital simulation.