Pulse Width Modulation Current Source Research Articles

Input characteristics of variable modulation index controlled current source inverters

Standard PWM current source inverters (CSIs) usually operate at fixed modulation index. The proposed modified current source inverter (MCSI) can operate with most pulse width modulation (PWM) techniques and with a variable modulation index, since the DC link inductor current freewheels on itself and not through the CSI. The use of variable modulation index control results in faster response times with no penalty on input power factor as compared to other variable modulation index schemes. This paper confirms this by investigating the input characteristics of the MCSI as seen from the AC mains. The quality of the input AC line currents is examined, and a design procedure for the input filters is given. Power factor and efficiency are discussed. Results are compared to those of other current source inverter topologies. Experimental results obtained from a 5 kVA converter confirm the theoretical considerations.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A high performance current source inverter

A modified PWM (pulse width modulated) current source inverter (CSI) that can operate with varying modulation indices (including low modulation indices) is presented. Any standard VSI (voltage source inverter) PWM pattern can be used with this inverter. This feature is obtained without compromising the converter system efficiency and power factor, and at the cost of only one auxiliary switch. The added degree of freedom obtained through modulation index control allows instantaneous control of output current and results in a high-performance inverter system. Inverter steady-state performance equations have been derived, as well as design equations and guidelines. The feasibility and performance of the CSI are verified by simulation and experimental implementation on a 5 kVA system.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A new injection method for AC harmonic elimination by active power filter

An injection method for an active filter which eliminates the harmonics present in AC lines by injecting PWM harmonic compensating current is proposed. In the proposed method, the active filter produces a pulsewidth modulation (PWM) current that cancels the existing harmonics up to any order completely. To generate such PWM current, both inverter and DC current source is needed. The current source can be replaced by a large inductor without any external power source. This can be achieved by providing the inverter with rectifying capability because the inverter has the same circuit structure as the rectifier. Therefore, the proposed model of PWM injection current includes not only the harmonic components to suppress the existing harmonics up to any order, but also the fundamental one, to raise the inductor current to any desired value. The characteristics of the injection method are investigated through a digital computer simulation. Feasibility is proved by the experimental results.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>