Lixiang Wei

Matrix converter topologies with reduced number of switches

A direct AC-to-AC converter commonly termed a matrix converter has a simple structure and many attractive features. However, the complexity of its conventional PWM strategy is prone to commutation failure, which is a factor that keeps it from being utilized in industry. This paper focuses on several alternative dual-bridge matrix topologies which do not possess this problem. First, these converters have the same characteristics as a conventional matrix converter, such as four-quadrant operation, unity input power factor, no DC-link capacitor, and high quality voltage/current waveforms. Second, the number of switches can be reduced thus reducing the cost. Third, the switches on the line side can turn on and off at zero current, they do not have any difficult commutation problems. Lastly, the complexity of the clamp circuit in these topologies can be greatly simplified thereby further reducing the cost. This paper introduces several topologies with a reduced number of switches and analyzes the characteristics of this converter family. Simulation and experimental results of a 9-switch topology are provided to verify its feasibility.

Analysis of PWM Frequency Control to Improve the Lifetime of PWM Inverter

Studies show that the power cycling mean time to failure (MTTF) of the insulated-gate bipolar transistor (IGBT) bond wire in an adjustable speed drive may be very short under some very common conditions. This paper proposes a switching frequency reduction method based on the junction temperature variation (ΔTj) of an inverter IGBT. It has the following advantages. First, it reduces the pulsewidth-modulation frequency under low-speed higher torque condition. Second, the inverter is started more smoothly and safely under higher command switching frequency and high-torque condition. Third, the overall MTTF of the inverter IGBT can be improved. The theory analysis, simulation, and experimental result are provided to show these advantages.

Investigation of dual-bridge matrix converter operating under unbalanced source voltages

The dual-bridge matrix converter concept has been gaining recognition as a promising circuit alternative in recent years. A direct feed-forward unbalance control method with power factor adjustment ability is developed for a 9-switch dual-bridge matrix converter system. It firstly detects the line side source voltages. Then, after adjusting the switching functions of only the line side converter, the system can provide balanced output voltage with slightly distortion of line side current. Analysis demonstrates that the output voltage capacity and power factor adjustability is limited under unbalanced conditions. Theory analysis, simulation and experimental results are presented to verify the effectiveness of this control method.

Analysis of IGBT Power Cycling Capabilities Used in Doubly Fed Induction Generator Wind Power System

The doubly fed induction generator (DFIG) is one of the most popular topologies applied in wind power systems. Its main advantage is to adjust the speed of a large system with much lower power converters. This is because its rotor-side converter (RSC) operates under slip frequency and it needs only to support slip power to the overall system. However, this slip frequency is much lower than the grid frequency, and insulated-gate bipolar transistors (IGBTs) in the RSC are susceptible to power cycling failures. This paper provides a method to analyze the power cycle capability of a DFIG power converter under wind power applications. Different current control methods, including minimal stator losses, minimal rotor losses, and minimal overall losses, are analyzed and compared. It is verified that the sizes of the IGBT must be selected appropriately to avoid earlier power cycling failures. Designing a wind power converter into the targeted system is critical for cost reduction without sacrificing the reliability of the whole system.

Evaluation of Power Semiconductors Power Cycling Capabilities for Adjustable Speed Drive

This paper analyzes the power cycling capability of semiconductor under various conditions for adjustable speed drive (ASD). An analysis is made that calculates the mean time to failure (MTTF) of the semiconductor under various conditions, including low speed operation capability, high speed thermal capability and overload capability. After that, the MTTF estimations of the IGBT under different heatsink design and different drive ratings are studied. This paper will show that the MTTF of the inverter may be very short under some very common operating conditions. Thus, it is prudent to size the drive properly in order to avoid earlier failure.

Analysis of Power Cycling Capability of IGBT Modules in a Conventional Matrix Converter

This paper analyzes the power cycling capability of IGBT modules in a conventional matrix converter used as a motor drive. The analysis is made under various condition for this topology, including low speed operation capability, high speed thermal and power cycle capability and etc. It was found that the power cycling mean time to failure (MTTF) of IGBT in a matrix converter is low when the input and output frequency is close to each other or when the output frequency of the converter is low. As a result, the chip size of the conventional matrix converter may be larger than the other candidates. In the end of the paper, some guidance of designing a matrix converter for long term reliabilities is also discussed.

Analysis of PWM frequency control to improve the lifetime of PWM inverter

Studies have shown that the power cycling Mean Time to Failure (MTTF) of the IGBT bond wire in an adjustable speed drive (ASD) may be very short under some very common conditions. This paper proposes a switching frequency reduction method based on junction temperature variation (ΔTj) of the inverter IGBT. It has the following advantages. Firstly, it only reduces the PWM frequency under low speed higher torque condition; secondly, the inverter can be started more smoothly and safely under higher command switching frequency and high torque condition. Thirdly, the overall MTTF of the inverter IGBT can be improved dramatically. Theory analysis, simulation and experimental result will be provided to show these advantages.

Junction Temperature Prediction of a Multiple-chip IGBT Module under DC Condition

This paper develops a thermal model for a six-pack insulated gate bipolar transistor (IGBT) power module operating as a three phase voltage source inverter. With this model, the temperature of each chip can be derived directly from the losses of the silicon chips and a thermal impedance matrix. The losses of each chip can be calculated through the voltage and current information of the power module. The impedance model can be easily transferred into a micro-processor to predict the online chip temperatures. It largely increases the temperature accuracy when the inverter operates at zero or low output frequency. Theory analysis, simulation and experimental results are provided to verify the effectiveness of this model

Robust voltage commutation of the conventional matrix converter

The three-phase AC-AC converter termed the matrix converter can provide high quality input/output waveforms and adjustable input power factor without any large energy storage component. However, it has not yet found much acceptance in industry. The main reason is that it requires a complicated commutation scheme to prevent input side short circuits and output side open circuits. This paper develops a new voltage commutation scheme for the conventional matrix converter. One advantage of this scheme is that it provides robust voltage commutations for the converter without sacrificing the quality of the line side current waveforms. The second advantage is that it needs the least information from the system than any algorithm yet reported. It only detects the line side synchronization angle which can have detection errors within /spl plusmn//spl pi//6 radians under unity input power factor to provide accurate commutation. The last advantage of this scheme is that it can provide easier shut down sequences for the system. Theoretical analysis, simulation and experimental results are provided to verify its effectiveness in the paper.

Mitigation of current harmonics for multi-pulse diode front end rectifier systems

18 pulse rectifier systems have been shown to be a cost effective harmonic solution in many industries where IEEE 519 is specified. However, multi-pulse rectifiers are susceptible to phase unbalance of the source voltage and preexisting harmonic voltages. A small amount of voltage unbalance can cause a large amount of current harmonic injected back to the input source. Consequently, a stricter preexisting voltage THD condition has to be specified for an 18 pulse rectifier to meet the IEEE 519 current harmonics requirement. This paper introduces a DC link passive filtering method to solve this problem. This method greatly reduces the current harmonics caused by the phase unbalance, the 5/sup th/, and the 7/sup th/ order voltage harmonics by adding several series LC resonant loops into the DC link. As a result, the proposed 18-pulse rectifier can still meet IEEE 519 under abnormal source voltage conditions of the AC line. Theory analysis, simulation and experimental result are provided in this paper to verify the effectiveness of this method.