Myoungho Kim

A dual-phase-shift control strategy for dual-active-bridge DC-DC converter in wide voltage range

This paper analyzes the dual-phase-shift (DPS) control strategy for a dual-active-bridge (DAB) converter in whole operation range. The DPS has two degree of freedom to control the transferring power, which can improve the performance of the DAB converter than single-phase-shift (SPS) control strategy. This paper derives the reactive power, the rms and the peak current flowing on the transformer and the zero-voltage-switching (ZVS) condition according to the operating conditions. Using this analysis and simulation results, a suitable control strategy for DAB converter is obtained. Experiments are performed to verify the proposed control strategy and to compare with the conventional SPS control strategy. The experimental results show that the proposed method can enhance the overall efficiency and expand the ZVS operation range.

Compensation of Current Measurement Error for Current-Controlled PMSM Drives

Accurate measurement of phase current is crucial in a current-controlled PMSM drive system. Current measurement error directly deteriorates torque control performance. This paper analyzes effects of the current measurement error on the phase current and the output voltage of the current controller. Based on the analysis, a compensation method is proposed. It compensates the offset error and the scaling error separately without any additional hardware but using the output voltage reference of the current controller. The proposed method can be applied to general current-controlled PMSM drives in whole operation range. Experimental results verify the effectiveness of the proposed compensation method.

A New Universal Isolated Converter for Grid Connection

This paper proposes an isolated universal-link ac-ac power converter suitable for grid connection. The proposed power converter can have multiple ports to connect various loads or electric energy sources, and the configuration can be arranged according to the situation. The proposed power converter does not need to employ the large interface inductor at input side and the huge electrolytic capacitor at dc link. Moreover, it utilizes high-frequency transformers for the galvanic isolation instead of bulky line-frequency transformers. These characteristics of the proposed power converter result in the reduction of the system volume and weight remarkably. The proposed power converter is the modular structure, and an H-bridge works as a basic module of the converter. By stacking the modules, the power converter can be adapted to the high-voltage grid and the various types of loads and/or sources. This paper addresses the structure of the proposed power converter and the fundamental principle of power flow. The operation of the proposed converter is verified by both computer simulations and experimental results with a laboratory-level prototype system.

An enhanced sensorless control method for PMSM in rapid accelerating operation

This paper presents an enhanced sensorless method to estimate rotor position for PMSM. The proposed method is based on the estimation of the back-EMF using a state observer. The conventional sensorless methods based on back-EMF estimation has problem of model discordance to the real motor model in electrical or mechanical dynamic state. An analysis is performed to verify how this problem deteriorates the estimation performance in the dynamic situations. Proposed method modifies state observer to match to the real motor model even in a fast accelerating situation. In order to verify feasibility of the proposed method, experimental results in a steady state and a dynamic state are presented.

An AC/DC power conversion based on Series-connected Universal Link converter

This paper presents a novel AC/DC power converter topology for the future energy conversion network. The proposed Series-connected Universal Link (SUL) converter transfers the power via the high frequency transformers and single phase full bridge converters. The shape of input AC source current is sinusoidal without PWM switching of the input side converter. Thanks to the reduced reactive components and high frequency transformer, the proposed converter can increase the power density and the efficiency significantly. It is expected that the SUL converter can be easily adapted to various renewable energy sources and energy storage system. Experimental results with prototype show the effectiveness of the proposed power converter topology.

A stator turn-fault detection method for inverter-fed IPMSM with high-frequency current injection

This paper presents a turn-fault detection method for inverter-fed Interior Permanent Magnet Synchronous Machines(IPMSMs) using high-frequency current injection when the motor is at standstill. When the motor is stopped, the fault current which flows in the faulty turns and the phase currents can be expressed with the injected phase current and the mutual inductance between each phase winding and the faulty turns. Because of the turn-fault, the injected high frequency currents cause different losses according to the direction of the injection. The proposed detection method exploits the difference of the losses of each case to diagnose the turn-fault. Experimental results are provided to verify the proposed detection method. The resultant loss pattern agrees well with that of the electrical model and shows reasonable sensitivity to the turn-fault. Two-turn fault among 27 turns of a phase winding of the motor under test has been detected easily with existing hardware of the drive system.

Condition monitoring of DC-link capacitors in drive system for electric vehicles

This paper proposes an online DC-link capacitor condition monitoring scheme for electric vehicles. Capacitance of both electrolytic and metallized polypropylene film (MPPF) capacitors decreases as the capacitors deteriorates, so that the proposed scheme utilizes the capacitance as the parameter of diagnosis of the DC-link capacitor. Every time the drive system of electric vehicles is turned on and off, the DC-link capacitor is diagnosed by estimating its capacitance. In order to estimate the capacitance, the DC-link capacitor is discharged through the traction motor, and its capacitance is estimated from its voltage and current information. The voltage and current of the DC-link capacitor can be acquired using existing sensors, and no additional hardware is required. During the discharge of the DC-link capacitor, the current flowing through the DC-link capacitor is regulated by a controller which uses relationship between currents of the DC-link capacitor and that of the traction motor. Experimental results show that the capacitance has been estimated within 2% error bound..

Compensation of current measurement error for current-controlled PMSM drives

Accurate measurement of phase current is crucial in a current-controlled permanent-magnet synchronous machine (PMSM) drive system. Current measurement error directly deteriorates torque control performance. This paper analyzes effects of the current measurement error on the phase current and the output voltage of the current controller. Based on the analysis, a compensation method is proposed. The proposed method compensates the offset and scaling errors separately without any additional hardware but using the commanded voltage reference of the current controller. The proposed method can be applied to general current-controlled PMSM drives in the whole operation range. Experimental results verify the effectiveness of the proposed compensation method.

Implementation of super high-speed permanent magnet synchronous machine drive

This paper proposes the control algorithm for a Surface Mounted Permanent Magnet Synchronous Motor(SMPMSM) drive system running at 116,000 r/min. Hall sensors are employed to measure the rotor position, and a speed observer is used to enhance the dynamic performance of the drive system. And in order to extend the output power capacity in the high-speed operating region, a flux-weakening controller, integrated with an anti-windup controller, is implemented. Through the simulations and experiments, it is validated that both high speed operation and fast acceleration has achieved with the proposed methods.

Modeling and Controller Design for a SEries-Connected Output Universal Link Converter

This paper conducts modeling and controller design for a SEries-connected Output Universal Link (SEOUL) converter. The SEOUL converter was proposed to interface multiple distributed power sources to the grid with a reduced amount of reactive components. It employs a high-frequency (HF) transformer instead of a bulky line-frequency transformer like solid-state transformers (SSTs). In addition, it does not use a large dc-link capacitor at the input side and reduces the size of the input filter. This is inherently possible due to its original operating characteristic. The input phase current is not actively controlled but synthesized indirectly by HF power transfer between input and output sides of the SEOUL converter. Therefore, it is important to properly control the HF power transfer part, on which this paper focuses. An analytic model is developed, and a control strategy is proposed based on the model with a decoupling control method. The developed model and the proposed control method were verified by experiments.