AC Chopper Research Articles

Novel line conditioner with voltage up/down capability

In this paper, a novel pulsewidth-modulated line conditioner with fast output voltage control is proposed. The line conditioner is made up of an AC chopper with reversible voltage control and a transformer for series voltage compensation. In the AC chopper, a proper switching operation is achieved without the commutation problem. To absorb energy stored in line stray inductance, a regenerative DC snubber can be utilized which has only one capacitor without discharging resistors or complicated regenerative circuit for snubber energy. Therefore, the proposed AC chopper gives high efficiency and reliability. The output voltage of the line conditioner is controlled using a fast sensing technique of the output voltage. It is also shown via some experimental results that the presented line conditioner gives good dynamic and steady-state performance for high quality of the output voltage.

Steady State Analysis and Simulation of AC chopper Fed Capacitor-Run Induction Motors

This paper presents steady state analysis and simulation of single pulse width modulated ac chopper fed capacitor run induction motor for variable speed operation. The d-q axis model of the cpacitor run motor is used for simulation study. Experimental results are provided to validate the simulation study.

Three-phase unbalanced-voltage compensators

In this paper, three-phase unbalanced-voltage compensators using ac choppers are proposed. The proposed three-phase unbalanced-voltage compensators are made up of three single-phase ac choppers and transformers for unbalanced-voltage compensation and output voltage regulation. The proposed compensators use ac choppers which solve the commutation problem, limit the switch voltage stress to the maximum line voltage, and also raise efficiency using regenerative dc snubbers. Compared with previous unbalanced-voltage compensators that use complex voltage source inverters, the proposed unbalanced-voltage compensators use ac choppers and utilize source or output line voltages in 30° phase shift with the phase voltages as the input of the ac chopper. Then, the proposed compensators give high efficiency, fast dynamics, simple power circuit, and reduced control circuit. It is also shown via some simulation and experimental results that the presented unbalanced-voltage compensators give good dynamic and steady state performances.

AC chopper voltage controller-fed single-phase induction motor employing symmetrical PWM control technique

Due to the growing demand in improving the performance of motor drives, there is an increasing need to improve the quality and reliability of the drive circuit. AC-to-AC converter schemes using pulse width modulation (PWM) are proved to achieve substantial advantages over conventional line-commutated AC controllers. With the increasing availability and power capability of MOSFET's and IGBT's switches, PWM converters can efficiently and economically be used in low and medium power applications. However, such controllers have been applied only to control the voltage of passive R-L loads. In this paper, the performance characteristics of a symmetrical PWM AC chopper controller-fed single-phase induction motor drive are evaluated. The developed analysis is experimentally verified by an experimental verified mathematical model is used for this purpose.

Three-phase ideal phase shifter using AC choppers

A three-phase ideal phase shifter using pulse-width modulation (PWM) AC choppers is proposed. The ideal phase shifter is made up of three single-phase PWM AC choppers and transformers for series quadrature voltage injection. The proposed phase shifter uses PWM AC choppers to solve the commutation problem and produces phase shift without amplitude variation. In the PWM AC chopper, the required switching operation to solve the commutation problem is achieved using regenerative DC snubbers. Previous phase shifters have utilised the source voltage as the input to the tap changer, but the proposed phase shifter utilises, simultaneously, the output and source voltage as the input to the PWM AC chopper. The proposed phase shifter gives phase shift without amplitude variation, high efficiency, fast dynamics, high reliability, and significant reduction of the filter size. It is also shown via simulation and experimental results that the proposed ideal phase shifter gives good dynamic and steady state phase shift performances. Experimental results obtained on a 6 kVA AC chopper are discussed.

PWM buck-boost ac choppers for safe commutation

Novel pulse-width modulated (PWM) buck-boost ac choppers solving the commutation problem are proposed for single-phase and three-phase systems. The power circuits of the single-phase and three-phase buck-boost ac choppers use only two and three standard switch modules, respectively, and regenerative dc snubbers are attached directly to standard switch modules to absorb energy stored in line stray inductance. The switching policy for solving the commutation problem is achieved. Compared with previous buck-boost ac choppers, the switching loss is reduced and RC snubbers causing power loss are eliminated. The equivalent circuits of the proposed ac choppers are obtained and the power factor is derived from the equivalent circuits. The proposed ac chopper has the following advantages; improved power factor, low harmonics, sinusoidal input current, fast dynamics, high efficiency, high reliability, and significant reduction of the filter size. Experimental results show that the proposed scheme gives good steady-state performances of the ac chopper and that they coincide with the theoretical results.

Switching technique for current-controlled AC-to-AC converters

The AC-to-AC converter called the matrix converter is very simple in structure and has powerful controllability. However, there are few practical applications, particularly in power electronics fields. The major reasons largely lie in the commutation problem and complexity of the control circuit. This paper proposes a novel commutation technique which is very simple to implement. This commutation scheme allows the deadtime to avoid current spikes of nonideal switches and, at the same time, establishes a current path of the inductive load to avoid voltage spikes. A switching technique of the matrix converter using a space-vector-modulation (SVM) based hysteresis current controller (HCC) is also proposed. The switching technique is implemented without any computational burden and is controlled with a simple control circuit. This technique utilizes advantages of the HCC and SVM technique. Simulation and experimental results obtained on a 5 kW single-phase AC chopper and an 11 kW three-phase to three-phase matrix converter are discussed.

Analysis, Simulation and Experimental Investigations on ac Chopper Fed Series Motor

AC voltage controllers employing phase controlled Triac or back to back connected SCRs are widely employed for the speed control of ac series motors in a number of applications. They are found to create some problems such as introduction of harmonics, poor supply power factor, interference to communication equipments and heating of the motor. Chopping technique employing PWM control strategy is found to overcome some of the problems associated with phase control. Hence, in this paper, an attempt is made to introduce ac chopper for the speed control of ac series motor. The switching angles of the ac chopper are controlled to get a smoother output waveform. AC chopper fed series motor is extensively analysed and its performance compared with that of the conventional controller. The drive system is simulated in SIMULINK and the performance observed. Experimental investigations are also carried out on a power MOSFET based ac chopper fed series motor to confirm the theoretical results.

PWM Controlled ac Power Supply based on ac Chopper Technology and Its Applications

Many studies of the ac power supply have been reported. There are ac chopper circuits in these reports. The ac chopper circuits are effective method for ac power control. But, the ac chopper does not apply to practical use because it has some problems that needs bi-directional switch and ac snubber.In this paper, I propose the novel PWM controlled ac power supply based on ac chopper technology. Proposed PWM controlled ac power supply can solve problems of devices and snubber circuits because this circuit uses bilateral switch circuit instead of bi-directional switch. This paper describes circuit configuration and operation of PWM controlled ac power supply, and explains ac voltage regulator and series voltage compensator for application example through experimental results.

Time Ratio Controlled Three-phase AC Chopper

A general switching method suitable to control three-phase AC chopper circuit is presented. Such a method can be used with different circuit configurations of the AC chopper. Detailed harmonic analysis of the AC chopper when controlled by the time ratio control (TRC) strategy is given. TRC has the advantages of linear control of the fundamental component of the output voltage and elimination of all harmonics of order less than the frequency ratio by two. Also, the control signal can be generated easily. Experimental results verifying the analysis are presented.

Automatic voltage regulator with fast dynamic speed

A novel automatic voltage regulator is proposed and analysed. The power circuit is made up of a pulse-width modulated (PWM) buck-boost AC chopper which uses only two standard switch modules. In the AC chopper, the commutation scheme allows dead-time to avoid current spikes from switching and at the same time establishes a current path in the inductor to avoid voltage spikes. The AC chopper uses regenerative DC snubbers attached directly to power semiconductor modules to absorb energy stored in stray line inductances. These DC snubbers enhance the conversion efficiency and feature a very simple structure consisting only of a capacitor. A fast peak voltage detector for fast output voltage control is also proposed. It is shown, via experimental results, that the proposed scheme gives good dynamic and steady-state performances for a high-quality output voltage.

A new configuration of single-phase symmetrical PWM AC chopper voltage controller

With the increased availability of power MOSFETs and insulated gate bipolar transistors, a new generation of simple choppers for AC inductive loads is foreseen. These new power semiconductors ease the use of forced commutations of thyristor switches to improve the supply power factor, even with highly inductive loads. The AC controllers with thyristor technology can be replaced by pulsewidth modulation (PWM) AC chopper controllers which have important advantages. In this paper, a symmetrical PWM AC chopper designed to operate with single-phase inductive loads with a reduced number of controlled switches is described. The operation as a variable voltage source of this converter is evaluated. This includes the conversion characteristics, harmonic generation, harmonic distortion factor, and input power factor. By digital simulation, these characteristics are investigated theoretically, and to correlate the measurements with theory, an experimental setup is presented to confirm the analytical analysis.

Artificial Neural Network for the Optimal Control of an AC Chopper Fed Induction Motor

A novel concept of application of artificial neural networks for the optimal control of an ac chopper fed induction motor is presented. The speed of the induction motor is controlled by controlling the switching angles of the ac chopper. The idea proposed in this paper is to use artificial neural network (ANN) as a non-linear signal converter, which accepts the reference value of the modulation index as input and outputs the values of the primary switching angles. The use of neural network as a controller makes it possible to vary the switching angles optimally such that the selected dominant lower order harmonics are eliminated and high quality output is obtained. Hence, this contributes to the improvement in overall system performance. The ANN based drive system is simulated using SIMULINK toolbox in MATLAB package and performance observed. The superiority of the neural network based controller over the conventional analog and microprocessor based controller is also discussed.

A single-phase PWM current source type converter coupled with an ac chopper

A current source type converter can easily generate a sinusoidal current on the ac side by employing a PWM strategy. In the converter system for a single-phase supply, however, the dc current pulsates because the dc output voltage of the converter contains an ac component with twice the ac supply frequency. The dc current pulsations cause the ac current waveform to be distorted. Although the use of a dc reactor with large inductance reduces the dc current pulsations, the size and the weight of converter equipment including a dc reactor is large. Two-phase rectification using two full-bridge converters and a converter system with an ac chopper circuit has been proposed for elimination of the dc pulsations. In these converters, the number of switching devices comprising the circuit will unavoidably increase. To solve this problem, we propose a novel single-phase current source type converter coupled with an ac chopper circuit and the PWM method. In this circuit, two switching devices in the main bridge are used to form an ac chopper bridge with two added devices and a capacitor. This paper gives the experimental and theoretical waveforms and the steady-state characteristics. The results prove that a smooth dc current and a sinusoidal ac current are obtained, and that a great reduction of the dc inductance can be achieved by using the proposed converter. © 1998 Scripta Technica. Electr Eng Jpn, 123(3): 36–45, 1998

A microprocessor-based Load voltage control using an AC chopper

Pulse width Modulated (PWM) control technique for an a-c choppers using harmonic elimination method is proposed. The firing switching instants of a-c chopper for the proposed technique is derived theoretically. By using a microprocessor as a controller, makes it possible to store the firing switching instants time as a look-up table for different load voltage values. Two MOSFET's are used as an a-c chopper. Experimental results verifying the simulation analysis of the a-c chopper fed static (R-L) load and dynamic load (1-ph. induction motor). The proposed strategy is low cost, simplified, and control effective.

Step-up/down AC voltage regulator using transformer with tap changer and PWM AC chopper

A step-up/down AC voltage regulator is proposed, in which a tap-changing transformer and a pulsewidth modulation (PWM) AC chopper are combined. The proposed regulator can step up or down the output voltage to input voltage. Also, the proposed regulator restrains more harmonics of output voltage compared to the conventional PWM regulator. The input current flows continuously in the proposed regulator, while it flows discontinuously in the conventional PWM regulator. Through digital simulation, several characteristics are investigated theoretically and then compared with those of conventional schemes. Practical verification of the theoretical predictions is presented to confirm the capabilities of the proposed regulator.

A PWM buck-boost AC chopper solving the commutation problem

A novel pulsewidth modulation buck-boost AC chopper using regenerative DC snubbers is proposed and analyzed. Compared to the previous buck-boost AC choppers, AC snubbers causing power loss are eliminated using regenerative DC snubbers. Experimental results show that the proposed scheme gives good steady-state performance of the AC chopper, which coincides with the theoretical results.

Novel PWM line conditioner with fast output voltage control

A novel pulse-width modulated (PWM) line conditioner with fast output voltage control is proposed. The line conditioner is made up of a PWM AC chopper and a transformer for series voltage compensation. In the PWM AC chopper, a proper switching operation for solving the commutation problem is achieved. Power semiconductor modules which are commercially available can be used in this circuit and regenerative DC snubbers are attached directly to power semiconductor modules to absorb the energy stored in line stray inductance. These regenerative DC snubbers have a very simple structure consisting of a capacitor only with no discharging resistors or complicated regenerative circuit for snubber energy. Therefore the proposed AC chopper gives high efficiency and high reliability. The output voltage of the line conditioner is controlled using rapid sensing of the output voltage. The optimal gains of the controller giving an output with small overshoot and adequate damping are designed using the time-weighted quadratic performance index. It is also shown using simulation and experimental results that the proposed line conditioner gives good dynamic and steady state performances with high quality output voltage.

Microcontroller-based apparatus for control of three-phase APWM and SPWM AC chopper

A novel, intelligent and flexible microcontroller-based apparatus is described to control single/three-phase symmetrical PWM (SPWM) or asymmetrical PWM (APWM)AC chopper, which offers a superior performance. The optimized PWM techniques improve the input power factor, eliminate the harmonics up to a specified order and also enable linear control of the fundamental component of the output voltage and current. The SPWM or APWM switching patterns at the specified phase angle of output fundamental voltage are obtained by the Newton–Raphson method and are implemented by the microcontroller. Through digital simulation several characteristics are investigated and compared. A prototype of the control apparatus has been built and tested. Practical verification of the theoretical predictions is presented to confirm the capabilities of the new apparatus.

Ac chopper with harmonics elimination and phase control

AbstractA switching strategy for the A C chopper is presented. With this strategy, it is possible to control the phase angle of the output voltage, besides the possibility of controlling the output voltage magnitude. Furthermore, selected lower order harmonics can be eliminated. Profiles of switching angles of the proposed technique are given. Theoretical analysis of the performance of the A C chopper under this strategy along with experimental results verifying the analysis is detailed.