Dong-Seok Hyun

An improved stator flux estimation for speed sensorless stator flux orientation control of induction motors

This paper proposes a programmable low pass filter (LPF) to estimate stator flux for speed sensorless stator flux orientation control of induction motors. The programmable LPF is developed to solve the DC drift problem associated with a pure integrator and an analog LPF with fixed pole. The pole of the programmable LPF is located far from the origin in order to decrease the time constant as speed increases. The programmable LPF has the phase and the magnitude compensator to exactly estimate stator flux in a wide speed range. So, the drift problem is much improved and the stator flux is exactly estimated in the wide speed range. The validity of the proposed programmable LPF is verified by speed sensorless vector control of a 2.2 kW three-phase induction motor.

A novel PWM scheme for a three-level voltage source inverter with GTO thyristors

This paper presents a new PWM scheme for a three-level GTO inverters based on space voltage vectors. By this PWM method, the harmonic components of the output voltage can be minimised by avoiding the minimum pulse width limitation problem of the GTO and voltage balancing of DC link capacitors can also be kept. The principle of the PWM method and the voltage vector selection procedure are described in detail. Computer simulation and experimental results verify that the proposed PWM control scheme is suitable for high power and high voltage three-level GTO inverters applied to induction motor drives.<<ETX>>

A Power-Control Scheme With Constant Switching Frequency in Class-D Inverter for Induction-Heating Jar Application

In this paper, a simple power-control scheme for a constant-frequency class-D inverter with variable duty cycle at constant frequency is proposed. It is more suitable and acceptable for high-frequency induction-heating (IH) jar applications. The proposed control scheme has the advantages of not only wide power-regulation range but also ease of output-power control. In addition, it can achieve stable and efficient zero-voltage switching in the whole load range. The control principles of the proposed method are described in detail, and the validity is verified through the simulated and experimental results on the 42.8-kHz insulated gate bipolar transistor for an IH rated on 1.6 kW with constant-frequency variable power

A new simplified space-vector PWM method for three-level inverters

In this paper, a newly developed simplified space vector PWM (SVPWM) method for three-level inverter is presented. The space vector diagram of the three-level inverter is simplified into that of a two-level inverter. So the selection of switching sequence and the calculation of the dwelling time is done as conventional two-level SVPWM method. The control of DC link neutral-point potential is easy to implement. The proposed SVPWM method can be applied to the multi-level inverter. The validity of the new SVPWM method is verified by simulation and experiment with a three-level IGBT inverter.

An improved carrier-based SVPWM method using leg voltage redundancies in generalized cascaded multilevel inverter topology

The carrier-based space vector pulse width modula- tion (SVPWM), which is considered as simple and efficient PWM technology, can be also used in multilevel inverters. The method was originally designed for the two-level inverter and developed to the diode-clamped multilevel inverter structure. However it may be noted that it also cause bad switch utilization in cascaded mul- tilevel inverter. This paper introduces an improved carrier-based SVPWM scheme, which is fully suitable for cascaded multilevel in- verter topologies because it can achieve the optimized switch uti- lization through the redistribution of the triangular carrier waves considering leg voltage redundancies while having the advantages of the conventional carrier-based SVPWM. Using experimental re- sults, the superior performance of new PWM method is shown.

Half-bridge series resonant inverter for induction heating applications with load-adaptive PFM control strategy

This paper presents an effective control scheme incorporated in a voltage-fed half-bridge series resonant inverter for induction heating applications, which is based upon a load-adaptive tuned frequency tracking control strategy using a PLL (phase locked loop) and its peripheral control circuit. The proposed control strategy ensures stable operation characteristics of the overall inverter system and ZVS (zero voltage switching) operation in spite of sensitive load parameters variations as well as power regulation, especially for nonmagnetic heating loads. The operating principle and the design procedure of the inverter system with the proposed control scheme are described. Also, simulation results and performance characteristics in the steady-state are shown as compared with experimental results for a prototype induction cooking system rated at 1.2 kW.

A new n-level high voltage inversion system

This paper deals with a new multilevel high-voltage source inverter with gate-turn-off (GTO) thyristors. Recently, a multilevel approach seemed to be the best suited for implementing high-voltage power conversion systems because it leads to a harmonic reduction and deals with safe high-power conversion systems independent of the dynamic switching characteristics of each power semiconductor device. A conventional multilevel inverter has some problems; voltage unbalance between DC-link capacitors and larger blocking voltage across the inner switching devices. To solve these problems, the novel multilevel inverter structure is proposed.

A symmetric carrier technique of CRPWM for voltage balance method of flying-capacitor multilevel inverter

This paper presents a simple carrier symmetric method for the voltage balance of flying capacitors in flying-capacitor multilevel inverters. The carrier-redistribution pulsewidth-modulation (CRPWM) method was reported as a solution for the voltage balance but it has a drawback at the transition of voltage level. To achieve the voltage balance of flying capacitors, the utilization of each carrier must be balanced during a half-cycle of the switching period such as phase-shifted PWM. However, the CRPWM method causes the fluctuation of flying-capacitor voltages because the balanced utilization of carriers is not achieved. Moreover, it does not consider that the load current change has an influence on flying-capacitor voltages by assuming that the current flows into the load. Therefore, the charging and discharging quantities of flying-capacitor voltages do not become zero during the switching period. To overcome the drawbacks of CRPWM, it is modified by the technique where carriers of each band are disposed of symmetrically at every fundamental period. Firstly, the CRPWM method is reviewed and the theory on voltage balance of flying capacitors is analyzed. The proposed method is introduced and is verified through simulation and experimental results.

The analysis of conduction and switching losses in multi-level inverter system

The multi-level inverter system is very promising in AC drives, when both reduced harmonic content and high power are required. But, as the output voltage level increase, the number of using the semiconductor device is increased. In case of multi-level inverter system, the loss of semiconductor devices cannot be analyzed by conventional methods. The reason is that the loss of each the semiconductor device is different from one another unlike 2-level and the diode clamped inverter system needs extra clamping diode. In this paper, a simple and accurate method of computing conduction and switching loss is proposed for multi-level inverter system. The validity of the proposed method is proven for 3-level and 4-level diode clamped inverter system.

Comparison of single-sensor current control in the DC link for three-phase voltage-source PWM converters

This paper presents a technique for reconstructing converter line currents using the information from a single current sensor in the DC link of a converter and comparative evaluation of the performance of single sensor control techniques in the DC link for voltage-source pulsewidth modulation (V-S PWM) converters. When 3/spl phi/ input currents cannot be reconstructed, three methods to acquire the DC-link current are compared. Two of them are methods of modifying the switching state (I, II), and another is a method of using the predictive state observer. Also, compensation of sampling delay, and a simultaneous sample value of input currents in the center of a switching period are included. Suitable criteria for the comparison are identified, and the differences in the performance of these methods are investigated through experimental results for a typical V-S PWM converter rated at 10 kVA.