Jung-Sik Yim

A new architecture for offshore wind farms

Offshore wind farms using HVDC links can be positioned a large distance from shore, opening up new opportunities for wind generation. Conventional approaches using 60 Hz generators and transformers are not appropriate in such applications, as they are heavy and result in expensive and complex installation and maintenance issues. This paper proposes an alternative architecture for such wind farms, using permanent magnet generators, medium frequency transformers and simple power converters to realize a compact and light system. It is possible that in the long term, the proposed approach may prove attractive for land-based wind farms as well.

Modified Current Control Schemes for High-Performance Permanent-Magnet AC Drives With Low Sampling to Operating Frequency Ratio

These days, high-frequency permanent-magnet synchronous motors (PMSMs) are used in industry; their maximum synchronous frequency is higher than 1 kHz. However, the sampling and switching frequencies of the digital inverter that consists of the digital controller and pulsewidth-modulation voltage source inverters are limited due to the cost and efficiency reasons. As a result, the current regulation loop has some problems when the high-frequency PMSM runs around its maximum speed and the ratio of the sampling frequency over the synchronous frequency, F ratio = (f samp/fr), is small. In this paper, the problems of the current regulation loop caused by small F ratio in the high-frequency PMSM drive are carefully investigated. Two problems are discussed in this paper: the stability problem and the sampling error. In addition, solutions for the problems are developed; a complex proportional and integral controller with predicted active damping terms is developed to stabilize the current regulation loop, and a model-based error estimator is offered to compensate the sampling error. The developed solutions are verified by simulations and experiments.

Design of Speed Control Loop of A Variable Speed Diesel Engine Generator by Electric Governor

Electric governors are widely used in diesel engine applications. And a proportional, integral and derivative(PED) controllers runs the electric governor in order to control the engine speed. However, it is difficult to analyze the system stability due to the non-linear characteristics of the diesel engine, and as a result, the PID controller should be tuned by trial-and-error approach. In this paper, a locally linearized diesel engine model is proposed based on the experimentally obtained engine torque map, and the proposed model is verified by simulations and experiments. Through the simulations and experiments it is concluded that the proposed model can be used in the system analysis and so to determine the PID controller gains.

Sensorless position control of active magnetic bearings based on high frequency signal injection method

This paper proposes a novel method to estimate the position of suspended body that hovers due to the electromagnetic force. The position information of the suspended body can be extracted from the coil currents, which contain the high frequency components due to the injected high frequency voltage without any additional hardware. The control of coil currents and the position of suspended body is performed with the digital controller using DSP. The effectiveness of the position estimation and control strategy without displacement sensors has been verified by simulation and experimental results.

Sensorless position control of active magnetic bearings based on high frequency signal injection with digital signal processing

The high frequency signal injection method in the sensorless position control of active magnetic bearings (AMB), has some merits such in that there is no steady-state error in the estimated position and can control the amplitude of the signals used for position estimation. In this paper, a method to inject a high frequency signal and to process the signal to obtain the position of the rotor has been proposed. In this method, all the signal processing is done in the digital domain, and in contrast to the analog method, there is no offset nor are there any continuous tuning problems. The proposed method does not need additional hardware for signal injection and signal processing. The PWM inverter, which is used to regulate coil current, generates the injection signal, and the DSP, which is used to control the system, performs signal processing in a normal sampling cycle. The experimental results show reasonable performance with regard to the 4-degree-of-freedom control of rotor position, while rotating at 30,000 [r/min].

Sensorless vector control of super high speed turbo compressor

The goal of this paper is to control 118,000r/min turbo compressor driven by 12 kW, 2 pole surface mounted permanent magnet synchronous motor (SMPMSM) in a position sensorless mode. PLL-type observer is adopted for the angle and the speed estimation because of its simplicity and easy implementation. The analysis of the observer is described, and based on that analysis, the observer gains are set. Also, the experimental results to verify the analysis are shown.

Parallel operation of PWM inverters for high speed motor drive system

This paper describes a topology with a parallel operation of PWM inverters for high speed motor drive systems. High speed motors have been widely used in industries to reduce system size and improve power conversion efficiency. However, the high speed motors sometimes suffer from core losses caused by PWM current ripples; noting that the phase inductance, Ls, of a high speed motor is smaller than that of ordinary motors, it is significant that the current ripple generated by a Pulse Width modulation(PWM) inverter becomes noticeable in the high speed motor. In the proposed topology, three PWM inverters are connected in parallel through nine coupled inductors. Compared to the PWM current ripple of the conventional single inverter system, that of the proposed scheme can be conspicuously reduced without the voltage drop at the inductors. In this paper, a theoretical analysis of the output voltage of the proposed topology is presented, and then the validity of the proposed method is verified by experimental results.

A Study on Parallel Operation of PWM Inverters for High Speed and High Power Motor Drive System

High speed motors have been widely used in industries to reduce system size and improve power conversion efficiency. However, the high speed motors sometimes suffer from core losses caused by PWM current ripple; noting that the phase inductance, , of high speed motor is smaller than that of ordinary motors. In the proposed topology, three PWM inverters are connected in parallel through nine coupled inductors. Compared to the PWM current ripple of the conventional single inverter system, that of the proposed scheme can be conspicuously reduced without the voltage drop at the inductors. In this paper a theoretical analysis of the output voltage of the proposed topology is presented, and then the validity of the proposed method is verified by experimental results.

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.

Voltage Sag Ride-Through of Super High-Speed Turbo Compressor

Turbo compressors have been extensively used in the factory automation as a part of pneumatic manipulators. Authors developed a position sensorless super-high speed turbo compressor, and it has been installed and working at the industrial plants for years. But repeated failures have been reported at some specific sites. In this paper, the repeated failures are analyzed through experiments and theoretical approach and the remedy against the failures is proposed. Through the analysis, it is presented that there are current overshoots at the instances of voltage sags due to the time delay of dc-link voltage measurement, and the overshoots sometimes trip the inverter even after the voltage sags are cleared. And, the measurement circuit has been modified to reduce time delay. The proposed method has been applied to the failure sites, and the repeated failures have been disappeared.