载波移相调制死区时间对模块化多电平换流器的影响研究

分析了死区时间对模块化多电平换流器单个子模块的影响,得出了以下结论:桥臂电流大于零时,子模块从投入状态转向切除状态会产生正极性的死区电压;桥臂电流小于零时,子模块从切除状态转向投入状态会产生负极性的死区电压。分析了死区电压对模块化多电平换流器理想基波电压的影响,推导了输出死区基波电压等效幅值、实际输出电压基波幅值及角度偏移量的公式,得出了以下结论:直流侧电压一定时,死区电压对模块化多电平换流器的影响与载波比、死区时间和输出电压与电流的相位差有关,与投入模块数无关;提高电压调制度和降低死区时间可有效降低死区时间对模块化多电平换流器的影响。仿真结果验证了上述结论的有效性。

Synthesis Scheme for Low Power Designs Under Timing Constraints

To minimize the power consumption with resources operating at multiple voltages a time-constrained algorithm is presented.The input to the scheme is an unscheduled data flow graph (DFG),and timing or resource constraints.Partitioning is considered with scheduling in the proposed algorithm as multiple voltage design can lead to an increase in interconnection complexity at layout level.That is,in the proposed algorithm power consumption is first reduced by the scheduling step,and then the partitioning step takes over to decrease the interconnection complexity.The time-constrained algorithm has time complexity of O(n 2),where n is the number of nodes in the DFG.Experiments with a number of DSP benchmarks show that the proposed algorithm achieves the power reduction under timing constraints by an average of 46 5%.

Modular High-Power Electronics for a High-Speed MLC Flywheel Energy Storage System

The operation of a motor drive for high-power, high-speed applications, especially for the permanent-magnet synchronous AC motors with regeneration capability is presented. Power system utilizes a SVHPWM （space-vector-based hybrid pulse width modulation） for a reduced harmonic distortion and switching loss. Associated electromagnetic interference mitigation and cooling requirements are significantly reduced. Voltage source inverter drives a three-phase MLC200 flywheel. The modularity of the proposed topology also simplifies overall system design and manufacturability. The system topology and control strategy are discussed. Simulation results are presented to illustrate the harmonic distortion and switching loss reduction and reduced line current ripple.

Improvement on Switching Characteristics and Switching Losses of IGBT by ZVS-PWM

Absrtact: The principle of ZVS - PWM inverting circuit is first described by means of inverting welder supply. The contrastive study is made on switching characte -ristics and switching losses of IGBT between ZVS - PWM and hard - switching.

Spectral Calculation of the Output Voltage of an Inverter with Bipolar Pulse Width Modulation

Converters with pulse width modulation are used for connections between the direct current （DC） and alternating current （AC） networks, e.g., in uninterrupted power supply systems, AC electromotor drives, for powering induction furnaces, in audio technique. Spectrum of signals sampled by pulse amplitude modulation and output voltage spectrum of the converter with pulse width modulation have similar properties. Spectrum of signals sampled by pulse amplitude modulation contains a harmonic of frequency equal to the frequency of the modulating signal and the harmonics of frequencies equal to the sum of frequency of the modulating signal and multiples of the sampling frequency. The output voltage spectrum of the converter with bipolar pulse width modulation contains harmonic of frequency equal to the frequency of the modulating signal and harmonics of frequencies equal to sum of the frequency of the modulating signal and multiples of the frequency of the carrier signal. It also contains harmonics of frequencies equal to the sum of the multiples of the frequency of the modulating signal and the multiples of the carrier signal. The comparison analysis was carried out for the harmonics of the output voltage of the converter with bipolar pulse width modulation in time domain. The dependency of the amplitudes and frequency spectrum on the wave forms of the carrier signal and modulating signal was shown. Similarity of the output voltage spectrum of the converter and signal spectrum sampled by the pulse width modulation was also shown. Key words： Output voltage converter with bipolar pulse width modulation, spectral analysis, Fourier series, carrier signal, reference signal.

High-Power-Factor Adjustable Speed Drive Using Diode Clamped Multilevel Inverter

This paper presents a new approach to alleviate the harmonics and to enhance the power factor of the ASD （adjustable speed drive）. A conventional ASD with 2-level PWM （pulse width modulation） inverters generate high dv/dt and high frequency common mode voltages which are harmful for the drive applications. It reduces the motor bearings life and conducted EMI （electro magnetic interference） deteriorates the insulation. In this paper, a diode clamped multilevel （3-level） inverter is used to perform dual task. It generates HF （high frequency） current to be injected at the input of the three-phase front-end rectifier thereby improving the harmonic spectra and the power factor. It also drives the induction motor. The salient feature of this paper is that it does not require separate converters for improving power factor and to drive induction motor. Furthermore, inverter switches operate with ZVS （zero voltage switching）, thus reducing the switching losses substantially, The voltage stress of the switches also has been reduced to half of the conventional 2-level converter. The inverter is operated with SPWM （sinusoidal pulse width modulation） technique. The simulation results for a prototype of 2.2 kW are presented.

Dynamic voltage regulation and power export in a distribution system using distributed generation

The major aim of power quality(PQ) enhancing techniques is to maintain a specified voltage magnitude at a desired frequency for sensitive loads irrespective of faults on the power distribution network.The dynamic voltage restorer(DVR) is a device used to mitigate voltage sags to regulate load voltage.This paper presents a mathematical model for leading series voltage injection to mitigate sags thereby achieving the improvement of the utility power factor as well as power sharing between the DVR and utility.The power sharing will be as per requirement to compensate the sags considering the available distributed generation(DG).The approach of mitigating voltage sags using the concept of leading series voltage injection is suitable for those locations where phase shift in the voltage will not cause any problem.The MATLAB/SIMULINK SimPowerSystem toolbox has been used to obtain simulation results to verify the proposed mathematical model.