Cai Zhiyuan

Magnetic field calculation and dynamic behavior analyses of the permanent magnetic actuator

Due to its great advantages, the permanent magnetic actuator for a vacuum circuit breaker drew great attention from engineers all over the world. We present the magnetic field and dynamic behavior analyses for the permanent magnetic actuator using finite element method associated with parametrization, for calculating the displacement of the moving parts and the supply current when the actuator is DC voltage supplied or capacitor supplied. In this analysis, the magnetic, electric and mechanical phenomena are coupled and some curves reflecting the dynamic behavior obtained. In addition, the comparison of dynamic behavior between DC voltage supplied and capacitor discharge supplied is drawm.

Reduction of disturbance effects and sustained oscillation using multi-sensor fusion in a flexible link system

In this work, a general set of routines for multi-sensor fusion applied to a flexible link control system to reduce the effects of disturbance and the sustained oscillation in steady state is proposed. Since disturbance signals are tend to be introduced to control systems, it is necessary to rely on multi-sensor fusion to improve control performance in spite of disturbance. Multi-sensor fusion for a control system is considered as a sequence of making decisions for a combination of sensor data to make a proper control input in uncertain conditions of disturbance effects on sensors and the system. The proposed method is applied to a typical flexible link control system in which reduction of oscillation is obtained using a pair of photo sensors at the tip of the link. Since environmental light conditions affect the control performance critically, an accelerometer is used in addition to the existing photo sensors to overcome the difficulties. Also, the magnitude of sustained oscillation in steady state can be reduced by multi-sensor data fusion of various degrees of sensor resolution.

Monitor of electrical endurance of vacuum circuit breaker's contacts

This paper discusses an approach to the monitoring of the electrical endurance of a vacuum circuit breakers contacts, and gives the measurement circuit and signal processing method used.

Industrial Computer Control System for power frequency insulation Test with Testing Voltage Waveform Analysis

A power frequency insulation testing system of industrial computer-based on control, measurement and protection with testing voltage waveform analysis supplied the voltage from a testing transformer is presented. The whole testing process of power frequency withstanding voltage, breakdown and partial discharge test for high voltage electrical equipment can been automatically performed according to the testing criterion or the initialization defined by an user. The band-pass characteristic of combination wavelet is adopted to analyze testing voltage harmonics in the power frequency insulation test by the Matlab simulation. The simulation results demonstrate that the proposed scheme detects exactly harmonics of any frequency, and filters effectively the harmonics interference in testing voltage. The hardware configuration and software design of the system are proposed, and the measurement of testing voltage is mainly described in the tested equipment flashing-over. The industrial computer control system has been used successfully on some worksite for two years

Optimal placement for hybrid energy in micro-grid

Reasonable control of multiple energy forms for load power supply can effectively improve economy and reliability of micro-grid(MG) operation, however, up till now, these two problems of siting hybrid energy systems(HEMS) and scheduling them have been separately solved. In order to bring its flexible power supply capacity into fully play, this paper put forward an algorithm to optimally solve the problem of allocation and schedule of multiple hybrid photovoltaic (PV)-diesel distributed generation (DG) in distribution systems. Firstly, an energy control method of HEMS was present to improve efficiency and flexibility of MG operation; Secondly, an optimization problem was formulated considering not only to reduce the total investment, operation maintenance cost, network loss caused by imported power from the transmission grid, and un-served load in case of emergency, but also to maximize the excess generated power by the HEMS that may be injected into the distribution network.; Finally, an improved artificial bee colony (ABC)based on particle swarm optimization(PSO) was put forward to increase convergence speed. Simulation results based on IEEE - 33 and PG&E - 69 systems show that the presented control method can improve the economy of MG operation and reliability significantly.

New reactive islanding detected method for micro-grid

Islanding detection is an important technique for micro-grid connected/isolated control. Traditional passive island detection reliability is bad, while active method have negative influence on power quality, so a new method based on chaotic property was proposed. The main reasons of chaos phenomenon during micro-grid conversion process in both connected/isolated operation modes are studied in this paper. Chaos theory is applied to reconstruct the phase space of voltage waveform in the micro-grid conversion process. At the same time, the maximum Lyapunov exponents of the voltage waveform are extracted. The results prove that typical chaos phenomenon occurs during the conversion process. And finally, the simulations of micro-grid isolated detection are carried out in the platform of RTLAB, proved the islanding detection is effective based on the chaotic characteristics. Through introducing the chaos characteristics of connected/isolated micro-grid, blind areas of the island detection can be decreased, improve the accuracy and reliability of the island detection.

A novel approach to calculate the loss of inverter power device and design of water-cooled radiator

This paper puts forward an analytic method to calculate the power device loss of VFD (variable-frequency drive) and the temperature rise of water-cooled radiator. Detailed analysis and design for the loss of power devices, the temperature rise at inlets and outlets of water-cooled radiator, the temperature rise of convection heat transfer of cooling, the temperature rise of heat conduction of water cooling plate, power device internal thermal resistance and the highest temperature system are made. This paper designs a water-cooled radiator based on theoretical analysis, the evaluation for water-cooled radiator thermal performance is made and the simulation results validate the validity of the proposed scheme.

A Novel Restoring Over-voltage Protection Equipment for Power Frequency Insulation Experiments

A protection equipment of restoring over-voltage is presented based on theoretical analysis when a flashover of tested equipment occurs in power frequency insulation experiments, to which the testing voltage is applied from a testing transformer. The main circuit of protection equipment is a group of fast power electronics switches reversely paralleled on the side of testing transformers primary winding. The control part is mainly composed of input circuit, amplifier, electrical level comparator, timer, forming pulse circuit and strong trigger. In the interest of enhancing the anti-interference capability and reliability of restoring over-voltage protection equipment, the techniques of the potential suspension, shield, analogical isolation, photoelectric isolation, signal conversion, optical cable transmission and so on are adopted. When the flashover or breakdown of tested equipment occurs, the fast power electronics switches of protection equipment make the primary winding be a short circuit and secondary winding be power off. This equipment can effectively restrain the repeated flashovers and the restoring over-voltages on tested equipment. The restoring over-voltage protection equipment has been used successfully on some site two years

Breaking capacity test of vacuum circuit breaker using synthetic test circuit with current zero forecast

In order to test the breaking capacity of vacuum circuit breakers, it is needed to accurately control the synthetic test circuit so as to satisfy the test criterion. For the asymmetry breaking current, it is difficulty to ignite accurately the sphere gaps ahead before zero in an appointed time so as to turn on the arc prolonging current circuit and high voltage circuit. As a result, once asleep the synthetic testing would be unsuccessful. In this paper the synthetic test circuit with current zero forecast is presented. Based on the discussion of the digital signal processing technology, the control circuit has been set up, and the experiment shows a good agreement with the predictions.

An intelligent circuit breaker with synchronous closing function based on DSP

An intelligent circuit breaker with synchronous closing function based on DSP is presented in this paper. By which, the filtering algorithm based on Fourier algorithm is adopted in order to estimate the optimal reclosing angle so as to weaken the instantaneous current during reclosing circuit Based on the discussion of the digital signal processing technology, the hardware circuit has been set up and the software has been programmed. And the simulation results show a good agreement with the predictions.