Khiem Nguyen-Duy

Improvement of Matrix Converter Drive Reliability by Online Fault Detection and a Fault-Tolerant Switching Strategy

The matrix converter system is becoming a very promising candidate to replace the conventional two-stage ac/dc/ac converter, but system reliability remains an open issue. The most common reliability problem is that a bidirectional switch has an open-switch fault during operation. In this paper, a matrix converter driving a speed-controlled permanent-magnet synchronous motor is examined under a single open-switch fault. First, a new fault-detection method is proposed using only the motor currents. Second, a novel fault-tolerant switching strategy is presented. By treating the matrix converter as a two-stage rectifier/inverter, existing modulation techniques for the inverter stage can be reused, whereas the rectifier stage is modified by control to counteract the fault. However, the proposed techniques require no additional hardware devices or circuit modifications to the matrix converter. Experimental results show that the proposed method can maintain the motor speed with a maximum ripple of 2%-a fivefold improvement over the uncompensated system. The proposed method therefore offers a very economical and effective solution for the matrix converter fault tolerance problem.

Minimization of the transformer inter-winding parasitic capacitance for modular stacking power supply applications

In an isolated power supply, the inter-winding parasitic capacitance plays a vital role in the mitigation of common mode noise currents created by fast voltage transient responses. The lower the transformer inter-winding capacitance, the more immune the power supply is to fast voltage transient responses. This requirement is even more critical for modular stacking applications in which multiple power supplies are stacked. This paper addresses the issue by presenting a detailed analysis and design of an unconventional isolated power supply that uses a ring core transformer with a very low inter-winding parasitic capacitance of 10 pF. Considering its output power of 300 W, this approach yields about 0.033 pF/W inter-winding capacitance over output power, approximately thirty times lower than existing approaches in the literature. This makes the converter a suitable solution for modular stacking of fast voltage switching applications. Mathematical derivation of the inter-winding capacitance and experiments are carried out to prove the validity of the approach.

High Dynamic Performance Nonlinear Source Emulator

As research and development of renewable and clean energy based systems is advancing rapidly, the nonlinear source emulator (NSE) is becoming very essential for testing of maximum power point trackers or downstream converters. Renewable and clean energy sources play important roles in both terrestrial and nonterrestrial applications. However, most existing NSEs have only been concerned with simulating energy sources in terrestrial applications, which may not be fast enough for testing of nonterrestrial applications. In this paper, a high-bandwidth NSE is developed that is able to simulate the behaviors of a typical nonlinear source under different critical conditions that can happen during their operations. The proposed 200-W NSE, which consists of a fourth-order output filter buck converter and a novel nonlinear small-signal reference generator, can quickly react not only to an instantaneous change in the input source but also to a load step between nominal and open circuit. Moreover, all of these operation modes have a very fast settling time of only 10 μs, which is hundreds of times faster than that of existing works. This attribute allows for higher speed and a more efficient maximum power point tracking algorithm. The proposed NSE, therefore, offers a superior dynamic performance among devices of the same kind.

Design of a 300-W Isolated Power Supply for Ultrafast Tracking Converters

This paper presents the design of a medium-power-rating isolated power supply for ultrafast tracking converters and MOS-gate driver circuits in medium- and high-voltage applications. The key feature of the design is its very low circuit input-to-output parasitic capacitance, which maximizes its immunity from noise due to fast changes in voltage. The converter is a voltage-controlled current source, utilizing a transformer with extremely low interwinding parasitic capacitance, which is achieved by separating the windings by a significant distance. Experimental measurements show that an overall circuit input-to-output parasitic capacitance of 10 pF in a 300-W prototype can be achieved. The circuit input-to-output capacitance per watt is therefore 30 times lower than that of existing approaches. A mathematical model of the interwinding capacitance of the proposed transformer, circuit analysis, and experimental results are provided to prove the feasibility of the converter.

A Review on the Implementation of Nonlinear Source Emulators

Renewable energy sources are playing an important role in industry as green sources of energy to reduce carbon dioxide emissions. They possess electrically nonlinear voltage-current characteristics. In the test and development of the downstream converters that utilize these renewable types of energy, the practice of using nonlinear source emulators instead of the real nonlinear sources has gained a lot of interest. Different methods of implementing nonlinear source emulators have been reported in the literature, but no paper exists reviewing and assessing them from different technical points of view. This paper provides a review of the implementation of existing nonlinear source emulators. Their configurations are redrawn as block diagrams and their circuit operations are discussed. Different industrial emulators are also briefly reviewed concerning their features.

A fault-tolerant modulation method to counteract the double open-switch fault in matrix converter drive systems without redundant power devices

This paper studies the double open-switch fault issue occurring within the conventional matrix converter driving a three-phase permanent-magnet synchronous motor system and proposes a fault-tolerant solution by introducing a revised modulation strategy. In this switching strategy, the rectifier-stage modulation is adjusted based on the knowledge of the switching logics of the inverter-stage and the operating input voltage sectors. However, the proposed fault-tolerant method does not rely on the assist of any redundant power devices or any reconfiguration of the matrix converter circuit by means of using redundant physical connections. It is shown that different locations of the double open switch affect the availability of the revised modulation. The steady state absolute speed error achieved with the proposed method is 4% of the nominal speed. Experimental results are performed to demonstrate the efficacy of the proposed methods.

Loss performance analysis of an isolated power supply for ultrafast tracking converters

This paper presents the loss performance analysis of an isolated power supply that is designed for ultra-fast tracking converters. The results of the analysis provide insights into the operation of the proposed power supply, how each physical component contributes to the total loss, and how its efficiency may be further improved.