Young-Cheol Lim

Switched-Inductor Quasi-Z-Source Inverter

This paper deals with a new family of high boost voltage inverters called switched-inductor quasi-Z-source inverters (SL-qZSIs). The proposed SL-qZSI is based on the well-known qZSI topology and adds only one inductor and three diodes. In comparison to the SL-ZSI, for the same input and output voltages, the proposed SL-qZSI provides continuous input current, a common ground with the dc source, reduced the passive component count, reduced voltage stress on capacitors, lower shoot-through current, and lower current stress on inductors and diodes. In addition, the proposed SL-qZSI can suppress inrush current at startup, which might destroy the devices. This paper presents the operating principles, analysis, and simulation results, and compares them with those of the SL-ZSI. To verify the performance of the proposed converter, a laboratory prototype was constructed with 48 Vdc input and an ac output line-to-line voltage of 120 Vrms. The simulation and experimental results verified that the converter has high step-up inversion ability.

Single-Phase AC–AC Converter Based on Quasi-Z-Source Topology

This paper deals with a new family of single-phase ac-ac converters called single-phase quasi-Z-source ac-ac converters. The proposed converter inherits all the advantages of the traditional single-phase Z-source ac-ac converter, which can realize buck-boost, reversing, or maintaining the phase angle. In addition, the proposed converter has the unique features that the input voltage and output voltage share the same ground and the operation is in the continuous current mode. The operating principles of the proposed converter are described, and a circuit analysis is provided. In order to verify the performance of the proposed converter, a laboratory prototype was constructed with a voltage of 84 Vrms/60 Hz. The simulation and experimental results verified that the converter has a lower input current total harmonic distortion and higher input power factor in comparison with the conventional single-phase Z-source ac-ac converter.

A New Hybrid Random PWM Scheme

This paper proposes a new hybrid random pulsewidth modulation (PWM) scheme based on a TMS320LF2407 DSP, in order to disperse the acoustic switching noise spectra of an induction motor drive. The proposed random PWM pulses are produced through the logical comparison of a pseudorandom binary sequence (PRBS) bits with the PWM pulses corresponding to two random triangular carriers. For this reason, the PWM pulses of the proposed scheme possess the hybrid characteristics of the random pulse position PWM and the random carrier frequency PWM. In order to verify the validity of the proposed method, the simulations and experiments were conducted with a 1.5-kW three-phase induction motor under the 2.5-A load condition. The DSP generates the random numbers, the PRBS bits with a lead-lag random bit (8 bit) and the three-phase reference signals. Also, a frequency modulator MAX038 makes the randomized frequency triangular carrier (3 plusmn 1 kHz). From the results, the proposed scheme shows good randomization effects of the voltage, current, and acoustic noise of the motor as compared with conventional scheme (3 kHz).

Improved Trans-Z-Source Inverter With Continuous Input Current and Boost Inversion Capability

This paper deals with a new family of high boost voltage inverters that improve upon the conventional trans-Z-source and trans-quasi-Z-source inverters. The improved trans-Z-source inverter provides continuous input current and a higher boost voltage inversion capability. In addition, the improved inverter can suppress resonant current at startup, which might destroy the device. In comparison to the conventional trans-Z-source/-trans-quasi-Z-source inverters, for the same transformer turn ratio and input and output voltages, the improved inverter has a higher modulation index with reduced voltage stress on the dc link, lower current stress flow on the transformer windings and diode, and lower input current ripple. In order to produce the same input and output voltage with the same modulation index, the improved inverter uses a lower transformer turn ratio compared to the conventional inverters. Thus, the size and weight of the transformer in the improved inverter can be reduced. This paper presents the operating principles, analysis and simulation results, and compares them with those of the conventional trans-Z-source/-quasi-Z-source inverters. To verify the performance of the improved converter, a laboratory prototype was constructed based on a TMS320F2812 digital signal processor with 100 Vdc input and 115 Vrms output voltage.

TZ-Source Inverters

A new family of single-stage high-step-up boost voltage inverters based on transformers is proposed, called TZ-source inverters. By replacing two inductors in the classical Z-source inverter with two transformers, the proposed inverter produces a very high boost voltage gain when the turn ratio of the transformers is larger than 1. Compared to the trans-Z-source inverters, the proposed TZ-source inverter uses a lower transformer turn ratio, which reduces the transformers size and weight while producing the same output voltage gain. The extension of the proposed inverter topology to dc-link-type and embedded-type topologies is presented. The operating principles, analysis, and simulation results are shown. To verify the performance of the proposed TZ-source inverter, a laboratory prototype was constructed and operated with 60-V dc input. The simulation and experimental results verified that the converter has high-step-up inversion ability.

Acoustic Noise/Vibration Reduction of a Single-Phase SRM Using Skewed Stator and Rotor

This paper presents a single-phase switched reluctance motor (SRM) with skewed stator and rotor so that the acoustic noise and vibration have been significantly reduced. The motor has the same skew angle for both stator and rotor laminations. The main source of acoustic noise and vibration is the rapid change of radial magnetic force along the air gap between the stator and rotor poles. Since the radial force (RF) is most intensified on the stator yoke near the salient poles, the abrupt change of the RF can be mitigated by skewing the stator and/or rotor laminations. Therefore, the RF can be more distributed throughout the stator core, and in turn, the peak value of the RF is reduced. In this paper, the distribution of the RF with respect to the skew angles is analyzed through the finite-element method simulation to design a single-phase SRM with the significantly reduced vibration and noise. Based on the simulation results, prototype motors with three different skew angles (0°, 30°, and 64°) have been constructed and tested, validating that the proposed design is effective in mitigating acoustic noise and vibration.

A Single-Phase Z-Source Buck–Boost Matrix Converter

This paper proposes a new type of converter called a single-phase Z-source buck-boost matrix converter. The converter can buck and boost with step-changed frequency, and both the frequency and the voltage can be stepped up or stepped down. In addition, the converter employs a safe-commutation strategy to conduct along a continuous current path, which results in the elimination of voltage spikes on switches without the need for a snubber circuit. The operating principles of the proposed single-phase Z-source buck-boost matrix converter are described, and a circuit analysis is provided. To verify the performance of the proposed converter, a laboratory prototype was constructed with a voltage of 40 Vrms/60 Hz and a passive RL load. The simulation and the experimental results verified that the converter can produce an output voltage with three different frequencies 120, 60, and 30 Hz, and that the amplitude of the output voltage can be bucked and boosted.

A Modified Single-Phase Quasi-Z-Source AC–AC Converter

A modified single-phase quasi-Z-source ac-ac converter is proposed in this paper. The proposed converter has the main features in that the output voltage can be bucked or boosted and be both in-phase and out-of-phase with the input voltage. The input voltage and output voltage share the same ground, the size of a converter is reduced, and it operates in a continuous current mode. A safe-commutation strategy for the modified single-phase quasi-Z-source ac-ac converter is used instead of a snubber circuit. The operating principles and a steady-state analysis are presented. A laboratory prototype, tested using a resistive load, a passive load, and a nonlinear load, was constructed that used an input voltage of 70 Vrms /60 Hz in order to verify the performance of the modified single-phase quasi-Z-source ac-ac converter. The experimental results verified that the converter has a lower input current total harmonic distortion, a higher input power factor, and a higher efficiency in comparison to a conventional single-phase Z-source ac-ac converter. In addition, the experimental results show that the use of the safe-commutation strategy is a significant improvement, as it makes it possible to avoid voltage spikes on the switches.

A Class of Quasi-Switched Boost Inverters

A switched boost inverter (SBI) can replace a Z-source inverter (ZSI) in low-power applications because it has one less LC pair than the ZSI. This paper presents a class of quasi-SBIs (qSBIs) that offers several advantages when compared with a conventional SBI, including reducing the voltage stress on the capacitor, increasing the boost voltage factor, and improving input current profiles. Operating principles, steady-state analysis, and comparisons with conventional inverters are presented. A prototype based on a TMS320F28335 digital signal processor is built to verify the operating principle of the proposed qSBIs.

A Comparison Between Single-Phase Quasi-

The properties of a single-phase quasi Z-source inverter (qZSI) and a single-phase quasi-switched boost inverter (qSBI), both of which are single-stage buck-boost inverters, are investigated and compared. For the same operating conditions, qSBI has the following advantages over qZSI: 1) Three capacitors are saved; 2) the current rating on both of its switches and diodes is lower; 3) its boost factor is higher with an equivalent parasitic effect; and 4) its efficiency is higher. However, qSBI has one more active switch and one more diode than Z-source/ qZSIs. In addition, the capacitor voltage stress of qSBI is higher than that of qZSI. The dc and ac component circuit analysis, impedance design with low-frequency and high-frequency ripples, component stresses, and power loss calculation are presented. A prototype based on a TMS320F28335 DSP is built in order to compare the operating principle of qSBI and qZSI.