Bingsen Wang

Survey on Reliability of Power Electronic Systems

With wide-spread application of power electronic systems across many different industries, their reliability is being studied extensively. This paper presents a comprehensive review of reliability assessment and improvement of power electronic systems from three levels: 1) metrics and methodologies of reliability assessment of existing system; 2) reliability improvement of existing system by means of algorithmic solutions without change of the hardware; and 3) reliability-oriented design solutions that are based on fault-tolerant operation of the overall systems. The intent of this review is to provide a clear picture of the landscape of reliability research in power electronics. The limitations of the current research have been identified and the direction for future research is suggested.

A Systematic Topology Evaluation Methodology for High-Density Three-Phase PWM AC-AC Converters

This paper presents a systematic evaluation approach of three-phase pulsewidth-modulated (PWM) AC-AC converter topologies for high-density applications. All major components and subsystems in a converter are considered and the interdependence of all the constraints and design parameters is systematically studied. The key design parameters, including switching frequency, modulation scheme, and passive values, are selected by considering their impacts on loss, harmonics, electromagnetic interference (EMI), control dynamics and stability, and protection. The component selection criteria as well as the physical design procedures are developed from the high-density standpoint. The concept of using the same inductor for harmonic suppression and EMI filtering is introduced in the design. With the proposed methodology, four converter topologies, a back-to-back voltage source converter (BTB-VSC), a nonregenerative three-level boost (Vienna-type) rectifier plus voltage source inverter (NTR-VSI), a back-to-back current source converter (BTB-CSC), and a 12-switch matrix converter, are analyzed and compared for high specific power using SiC devices. The evaluation results show that with the conditions specified in this paper, BTB-VSC and NTR-VSI have considerably lower loss, resulting in higher specific power than BTB-CSC and the matrix converter. The proposed methodology can be applied to other topologies with different comparison metrics and can be a useful tool for high-density topology selection.

Dynamic Voltage Restorer Utilizing a Matrix Converter and Flywheel Energy Storage

A new series power conditioning system using a matrix converter with flywheel energy storage is proposed to cope with voltage sag problem. Previous studies have highlighted the importance of providing adequate energy storage in order to compensate for deep voltage sags of long durations in weak systems. With the choice of flywheel as a preferred energy storage device, the proposed solution utilizes a single ac/ac power converter for the grid interface as opposed to a more conventional ac/dc/ac converter, leading to higher power density and increased system reliability. The paper develops the dynamic model for the complete system including the matrix converter in dual synchronous reference frames coupled to the flywheel- machine and the grid, respectively. The dynamic model is used to design a vector control system that seamless integrates functions of compensating load voltage and managing energy storage during voltage sag and idling modes. The numerical simulation results and experimental results from a laboratory-scale hardware prototype are presented to verify system performance.

Operation and control of a dynamic voltage restorer using transformer coupled H-bridge converters

The dynamic voltage restorer (DVR) as a means of series compensation for mitigating the effect of voltage sags has become established as a preferred approach for improving power quality at sensitive load locations. Meanwhile, the cascaded multilevel type of power converter topology has also become a workhorse topology in high power applications. This paper presents the detailed design of a closed loop regulator to maintain the load voltage within acceptable levels in a DVR using transformer coupled H-bridge converters. The paper presents system operation and controller design approaches, verified using computer simulations, and a laboratory scale experimental prototype.

A single-phase current source solar inverter with reduced-size DC link

This paper presents a new current source converter topology that is primarily intended for single-phase photovoltaic (PV) applications. In comparison against the existing PV inverter technology, the salient features of the proposed topology are: a) the low frequency (double of line frequency) ripple that is common to single-phase inverter has been eliminated; b) the absence of low frequency ripple enables significantly reduced-size passive components to achieve necessary stiffness; and c) improved maximum-power-point-tracking performance is readily achieved due to the tightened current ripple even with reduced-size passive components. This paper presents the proposed topology and its working principle backed up with numerical verifications.

A Carrier Based PWM Algorithm for Indirect Matrix Converters

In this paper, the indirect matrix converter is systematically studied with the single-pole-multiple-pole representation. A carrier based PWM algorithm is developed in two steps. First, the continuous modulation functions for all the throws are derived based on the desired sinusoidal input currents. Then the switching functions are derived from the modulation functions with focus on the zero current commutation. The proposed PWM algorithm is verified by numerical simulation and hardware experimentation on a laboratory prototype matrix converter.

Comparative Evaluation of Direct Torque Control Strategies for Permanent Magnet Synchronous Machines

This paper presents a comprehensive evaluation of several direct torque control (DTC) strategies for permanent magnet synchronous machines (PMSMs), namely DTC, model predictive DTC, and duty ratio modulated DTC. Moreover, field-oriented control is also included in this study. The aforementioned control strategies are reviewed and their control performances are analyzed and compared. The comparison is carried out through simulation, finite-element analysis, and experimental results of a PMSM fed by a two-level voltage source inverter. With the intent to fully reveal the advantages and disadvantages of each control strategy, critical evaluation has been conducted on the basis of several criteria: Torque ripple, stator flux ripple, switching frequency of inverter, steady-state control performance, dynamic response, machine losses, parameter sensitivity, algorithm complexity, and stator current total harmonic distortion.

Unity Power Factor Control for Three-Phase Three-Level Rectifiers Without Current Sensors

Three-level rectifiers with reduced number of switches (such as the Vienna rectifier) to improve the input power quality of rectifier systems have been receiving wide interest in the past years. In this paper, a new carrier-based pulsewidth-modulation control algorithm is proposed for such converters to eliminate the low-frequency harmonics in the line current while achieving unity power factor at the rectifier input terminals. The operating constraints of the Vienna rectifier with the carrier-based modulation strategy are examined carefully, and the proposed control algorithm ensures that appropriate voltage/current directional constraints are met. A promising cost-reduction opportunity can be seen with the elimination of input current sensing to operate the Vienna rectifier. The control algorithm is verified via Saber simulation and experimental results.

DSP-controlled, space-vector PWM, current source converter for STATCOM application

Abstract Basic operational concepts of the single current source converter (CSC)-based STATCOM are studied in this paper. The space vector modulation scheme is adopted to control switching functions of the CSC. Capitalizing on anticipated new switch technology, the reduced-size LC filter is examined and design guidance is given. A filter current compensation method to reduce the error between command and response current is proposed under steady-state operation condition by use of phasor analysis. A loss compensation control is introduced that allows operation without a charging converter to maintain a desired value of current through the dc inductor. A DSP-based lab model is built to validate the concepts of the space vector modulated STATCOM and the control scheme proposed in this paper. The experimental results are satisfactory in that a low distortion line current results for steady-state operation.

Analysis and Experimental Verification of a Fault-Tolerant HEV Powertrain

This paper presents a fault-tolerant powertrain topology for series hybrid electric vehicles (SHEVs). The introduction of a redundant phase-leg that is shared by three converters in a standard SHEV powertrain allows us to maximize the reliability improvement with minimal part-count increase. Therefore, the cost increase is kept to minimum as well. The new topology features fast response in fault detection and isolation, and postfault operation at rated power throughput. Two implementations of the fault-tolerant design are presented in conjunction with elaborated discussion of the operating principles, control schemes, and fault diagnostic methods. The substantially improved reliability over standard SHEV powertrains is demonstrated by analysis of the Markov reliability model. Time-domain simulation based on a Saber model has been conducted and the results have verified the feasibility and performance of the proposed SHEV drive system. A scaled-down laboratory prototype has been built and the experimental results further validate the robust fault detection/isolation scheme and uncompromised postfault performance.