Advanced Materials Research Vols. 1070-1072

Abstract: This research presents a new adaptive speed controller for the brushless DC motor. Themethodology of model reference adaptive control is applied to a novel model of BLDC motor. Thisnovel model provides the possibility to compensate the torque ripples and load torque.

Abstract: In order to analyze the transient performance of the multiple three-phase synchronous motor (MTSM) operating at synchronous speed, according to the complex mathematical model and the stator inductance matrix feature of the MTSM, its complex equivalent circuit was studied, and the parameter formulas of this equivalent circuit are presented in the general form. The complex equivalent circuit of the MTSM proposed in this paper is formed by many reactance branches which contain an armature reactance of the one set of three-phase winding and several equivalent leakage reactances, and the equivalent leakage reactances are related to the stator currents.

Abstract: This paper proposes an induction motor variable frequency speed control system based on fuzzy-PI self-tuning. The system includes coordinate transformation modules, vector control modules, space vector pulse width modules, fuzzy-PI self-tuning speed regulator, excitation current and torque current PI regulator. Because the speed regulator controlled by the fuzzy-PI self-tuning has better control effect than traditional PI. The performance can be reflected by the shorter response time, smaller overshoot. In addition, when the load torque changes, the electromagnetic torque changes more smoothly and does not have large fluctuations.

Abstract: This paper takes the ship air-cooled AC generator with the radial ventilation system for example, establishes the mathematical model of a generator core and winding temperature by using an equivalent thermal circuit method and the temperature calculation method based on the operating parameters, analyzes the transfer function between the generator stator winding temperature rise and the phase voltage, phase current and reactive power, and finally verifies validity of the mathematical model by the experiment.

Abstract: In order to discuss the transient process of induction motors dynamic braking,analysis the impact of the brake resistance on the time, and then choose the best resistance.In Matlab / Simulink environment,based on motor simulation model,by repeatedly adjusting the rotor resistor, their impact on motor speed during braking time can be visually observed.By using the least squares method in Matlab, each discrete points of the resistor and the corresponding braking time can be fitted into continuous curve, resulting in the optimum braking resistor under the shortest brake time. With the optimum load resistance in the rotor, the motor brake fastest and more stable without fluctuations,and provide the theoretical guidance for other motor control and engineering.

Abstract: Aiming at the existing strong coupling problem of UPQC model in synchronous rotating coordinate system, in order to realize the control process easily and accomplish the complete decoupling, two-phase coordinate system α-β was introduced to the complete decoupling PI control of voltage and current compensation unit. According to the corresponding mathematical model, the topology map of voltage and current compensation unit was gained. Direct single closed-loop control method was used, meantime, parameter was set and the structure chart of PI control unit was designed. Finally, the effectiveness and feasibility of the control method is proved by Matlab/Smulink simulation and hardware experiment.

Abstract: Aim at solving the complex computation and complicated circuit of grid-connected converter, the sliding mode variable structure theory is introduced into its direct instantaneous power control. By analysis and modeling of three-phase grid-connected converter with an LCL-filter, sliding mode variable structure control is constructed with the active power and reactive power. The chattering is weakened by using the exponential reaching law. Cost of LCL grid-connected converter system is reduced at the same time when unit power factor and low harmonic distortion are realized. In order to increase the stability of the system, the virtual flux variable is integrated with the sliding-mode variable structure direct power control algorithm, and the improved first-order low pass filter virtual flux is used to remove the voltage sensor. By simulation, the effectiveness and feasibility of the control method is proved.

Abstract: SiC MOSFET, as a promising power semiconductor devices, has attracted attention from many laboratories and companies for its super performance in high temperature, high voltage and high frequency applications. To protect the devices from overvoltage induced by parasitic inductance in high frequency applications, snubber circuit is a must. In this paper, simulation of snubber circuit in a high frequency PWM inverter is invested, under different numbers of snubber circuit , parasitic parameters, different kinds of load and whether a SiC SBD exsits. Some useful conclusions are obtained to help design more perfect snubber circuit.

Abstract: Renewable energy are usually connected to the power grid through an inverter. As the penetration level of such inverter-based distribution generation resources increases, PCC point harmonics become an important concern for grid stability and power quality. In this paper, the PCC-point harmonics in a parallel-inverter-based photovoltaic station were measured and some significant characteristics of such harmonics were presented. These harmonics are stationary; the voltage and current waveforms are lower frequency, power correlation and inter-harmonic. And these harmonics are 3-phase symmetric and contain 3^rd and 6^th harmonic components. The transitions of the PCC harmonic occurrence and vanishing are instantaneous. The analysis indicates that the PCC harmonics are not produced by the resonances related to the linearities of PV inverters but the inverter nonlinearities are the primary reasons. The strategy to eliminate the PCC point harmonics are proposed in this study.

Abstract: Pulse modulation width (PWM) of multi-phase inverter is the key technologies of ships electrical propulsion. In this paper, theories and realization of space vector PWM (SVPWM) for five-phase inverter is analyzed. The proposed SVPWM adopts two adjacent large voltage vectors to composite the reference voltage vector and this method have advantages of easy to realize. Theoretical waveform and harmonics of five-phase inverter output voltages under the proposed control method are deduced. The analysis shows that there are very large third harmonics in the inverter output voltages and currents. The total harmonic distortion (THD) is large also, and changes small with the modulation index. Simulation and experiments certify the conclusions.