Ramp Comparison Research Articles

Control of Multi-cell AC/DC and Cascaded H-bridge DC/AC-basedAC/DC/AC Converter

A single-phase two-stage AC/DC/AC converter topology is investigated in this paper, which involves multi-winding transformer-fed multi-cell AC/DC and cascaded H-bridge multi-level (CHBMLI) DC/AC converter stages. Both the converter stages utilize current control using the fixed and uniform switching methods, which simultaneously achieve the regulation of the DC link voltages of all the cells. The proposed control loop for the AC/DC converter stage uses a single-voltage sensor to control the DC link voltages of all the cells using self-voltage regulating property of the multi-winding transformer. This single-control loop uses the feedback of the instantaneous AC current at the primary of the transformer and any one of the DC link voltage to achieve the input AC current control and multiple DC link voltage control. The fixed frequency ramp comparison current control in AC/DC stage of the converter provides a uniform switching cycle among all the units. A phase-shifted multi-carrier PWM (PS-MCPWM)-based fixed frequency current control of the DC/AC converter comprising CHBMLI provides equal loading across all DC links of the AC/DC converter. The results are verified through PSCAD simulations and experimental results are obtained through the LabVIEW FPGA controller implemented for two-cell, five-level converter topology.

Design and Implementation of PID GA and Fuzzy logic Controllers for an Electrical Drive with Various Noise Disturbances

It is a great challenge for human being to keep up the constant speed in drive when external Noise disturbances occur due to fluctuations of power supply. In order to avoid these issues, PID controllers are intended using predictable method such as Ziegler Nichols method. But finest level is not obtained in transient and steady state. During the MATLAB Simulation, the error is present transient and steady state behavior in conventional PID controllers. Hence it is necessary to design a PID controller with Novel intelligent technique for speed control of drive like fuzzy and Genetic Algorithm. It considers error as fitness function which is to be minimized using various GA operators such as mutation etc. The Drive will be operated with different external noises like sinusoidal noise, Saw tooth noise and Ramp noise and comparison between PID, GA and Fuzzy PID will be presented and their performances are studied.

AN ADVANCED CURRENT CONTROLLER TECHNIQUE BASED ACTIVE POWER FILTER FOR POWER QUALITY IMPROVEMENT

Power Quality issues are becoming a major concern for today’s power system engineers. Large scale incorporation of non-linear loads has the potential to raise harmonic voltages and currents in an electrical distribution system to unacceptable high levels that can adversely affect the system. Active power filter (APF) based on power electronic technology is currently considered as the most competitive equipment for mitigation of harmonics and reactive power simultaneously. Instantaneous power theory is used for generation of reference current. This paper presents a comparative study of the performance of three current control strategies namely ramp comparison method, hysteresis current controller (HCC) and Adaptive hysteresis current controller(AHCC) and superiority of AHCC is established. Simulation results for all the method are presented using MATLAB/SIMULINK power system toolbox demonstrating the effectiveness of using adaptive hysteresis band.

Design of Single Phase Cyclo-Converter Using Cascaded Multilevel Inverter

This paper presents a single phase AC/DC/AC converter based on parallel AC/DC and cascaded multi-level DC/AC Converter. For a two-cell AC/DC/AC converter, two units of full-bridges are connected in parallel and two units of full-bridges are connected in cascade. It is proposed that instead of using two separate control loops of DC link voltages at the AC to DC conversion stage, only a single control loop with only one voltage sensor is proposed in this paper when two cells are equally loaded. It is also shown that by controlling only one cell DC link voltage, the other dc link voltage also gets controlled automatically. Use of simple and unipolar ramp comparison control at both the stages leads to fixed switching frequency operation of all the switches along with the improved quality of input current and output voltage as compared to simple PWM control. The simulation result for the proposed topology has been obtained through the MATLAB simulation studies, for a two-cell based parallel cum cascaded AC/DC/AC converter. The experimental verification of the proposed topology and control strategy has been obtained. Index Terms: AC/DC converter, DC/AC converter, AC/DC/AC Converter, Parallel Converter, Unipolar PWM.

COMPARISON OF CURRENT CONTROL METHODS ON CARRIER BASED VSI-PWM INVERTER DRIVES FROM LINE POWER QUALITY ASPECT

This paper describes simulation result of two methods in current controlling for carrier based VSI-PWM inverter: hysteresis and ramp comparison control. The simulation useful in selection of ASDs and generally–converter, from power quality point of view. Simulation result show that both ramp comparison and hysteresis control methods gives difference characteristic on line voltage and line current. A ramp comparison method is better in form of lower effect on line current distortion compare with hysteresis control method. Meanwhile, for line voltage distortion, hysteresis control seen better.

A novel DSP-based current-controlled PWM strategy for single phase grid connected inverters

The three major approaches for current-regulated inverters are ramp comparison, hysteresis control, and predictive current control. From these three, predictive current control offers the potential for achieving more precise current control with minimum distortion and harmonic noise. But, the predictive method is difficult to implement and needs more computational burden. The traditional predictive current controller has a poor performance under component parameter variations, and is less robust to filters inductance mismatch. A robust predictive current control strategy was proposed and studied. Both simulations and experimental results show that the proposed method is much more robust to parameter mismatch than the traditional one.

Implementation of programmed modulated carrier HCC based on analytical solution for uniform switching of voltage source inverters

An analytical basis is established in this paper for a programmed function of known amplitude to be added to the feedback path of a hysteresis current controller (HCC) in a static power inverter. Improper amplitude and slope of the carrier waveform in a modulated carrier HCC frequently encounter the problem of sudden high frequency switching. Though intuitive approaches exists to tackle the problem practically, proper analytical basis has not been established so far. This paper deals with solving the problem analytically, so that implementation of such scheme for an inverter operation can be done systematically and accurately. A theoretical model of programmed ramp comparison HCC (PRCHCC) is developed in this paper that defines a carrier waveform based on inverter supply voltage, load parameters and reference current waveform. The parameters of the carrier waveform of PRCHCC can be deterministically predicted for uniform switching frequency operation. Simulation and experimental results highlights the potential of the proposed model for uniform switching at all operating conditions.

Simulation and analysis of brushless DC motor drives using hysteresis, ramp comparison and predictive current control techniques

The brushless DC motor with a permanent magnet rotor is considered for the present study. Because of the special structure of the motor, it produces a trapezoidal back electromotive force (EMF). The applied current waveform is rectangular-shaped. Non-ideal effects in the trapezoidal back EMF and motor currents generate a pulsating torque. The reduction of the torque ripple is important from a speed and position control point of view. In the present paper a brushless dc motor drive is simulated and analyzed using hysteresis, ramp comparison and predictive current control schemes. By comparing the results obtained using these techniques, advantages and disadvantages of each technique and its range of applications are discussed.

PWM INVERTER FED INDUCTION MOTORS LOSSES EVALUATION

ABSTRACT In this paper the authors deal with the problems concerning the steady state losses evaluation in medium power industrial induction motors supplied by PWM inverter. They present a method based on the no-load and short circuit tests. This technique seems to be very useful for the good obtained results and because it is quite similar to the standard no-load and short circuit tests used with sinusoidal voltage supply. The method is based on some simple hypothesis that have been verified during the experimental tests by means of mathematical models. As a consequence, it is possible to compare the no-load and the short circuit tests under sinusoidal and PWM inverter supply considering the same rms fundamental voltage. The method has been applied to a 7.5 kW induction motor supplied by a prototype PWM Voltage Source Inverter (VSI) modulated with a ramp comparison technique at a 1 kHz switching frequency. The obtained results could be utilized in order to define some design criteria and the derating for...

Current Control of VSI-PWM Inverters

The inherent limitations of commanding voltages and currents in a three-phase load with an inverter are examined. An overview of several current controllers described in the literature is presented, and computer simulations are used to compare performance. A switching diagram is developed which reveals some of the operating characteristics of hysteresis controllers. For ramp comparison controllers, a frequency transfer function analysis is used to predict the line currents and provide some insight into the compensation required to reduce the current errors.

Novel Control Schemes for 3-Phase Zero Voltage Switching

The use of phase-locked loop (PLL) in 3-? zero voltage switching (ZVS) by sensing 1 ? is brought out. The burst and proportional control schemes for 3-? ZVS using off-the-shelf integrated circuits (IC's) are described. The schemes explained employ zero voltage synchronous switching for both steady-state operation and starting. The proportional control scheme uses a voltage controlled monostable in contrast to the present method of ramp comparison with the control voltage. The experimental results are given for a time base of 8 cycles for proportional-type control with resistive loads.