Single-phase AC Chopper Research Articles

Power Factor Improvement and Voltage Harmonics Reduction in Pulse Width Modulation AC Chopper Using Bee Colony Optimization

This paper presents a new pulse width modulation (PWM) switching technique for a single phase AC chopper. In the proposed technique, the switching frequency is fixed and the optimal PWM switching angles are obtained by using bee colony optimization. This process can improve the input power factor and reduce the total harmonic distortion of the output voltage. The performance of the proposed technique is compared with that of the conventional PWM through the simulation and experimental results.

Direct AC-AC Step-Down Single-Phase Converter with Improved Performances

The paper presents two high-performance single-phase AC chopper circuits which perform AC-AC bidirectional direct conversion;one of them contains resistive loads and the other one is for inductive loads. It includes useful equations for chopper design. The correctfunctioning is tested by simulation.DOI: http://dx.doi.org/10.5755/j01.eee.18.10.1305

New Topologies for Static Reactive Power Compensator Based on PWM AC Choppers

Nowadays, static reactive power control is widely used in electrical power networks. The former solution based on Thyristor Controlled Reactors is progressively replaced by PWM Voltage Source Inverters. The first solution is quite simple but requires bulky shunt passive filters whereas the second solution shows higher semiconductor losses and requires a significant cooling system. In this paper, the authors present new topologies which show a good compromise in comparison to the classical solutions. Single phase AC Choppers are used to achieve controlled impedances (capacitive or inductive) at the fundamental frequency and thus adjust the reactive power level. This concept is applied for medium or high power applications and multi-converter structures based on step down or step up AC choppers are proposed. An example of design concerning reactive power compensation in a 25 kV/50 Hz AC traction line is presented. Finally, experimental results obtained for a 1.2 MVAR prototype demonstrate the feasibility of these novel topologies.

A Novel Single-Phase Soft-Switching AC Chopper Without Auxiliary Switches

A single-phase soft-switched series-resonant ac chopper without auxiliary switches is presented. The presented single-phase ac chopper is configured by a series-resonant conversion without cycloconversion and auxiliary switches. The presented single-phase ac chopper is a series resonator with four main switches to configure adaptively the resonant voltage robes. The output sinusoidal voltage is synthesized by a series of sinusoidal amplitude quasi-sinusoidal pulses following the input voltage amplitude. The presented single-phase ac chopper is operated by frequency modulation with a constant-on time control. Waveform syntheses for the output sinusoidal voltage are clearly derived. A typical design example of a 600 W single-phase soft-switching ac chopper is examined to assess the system performance. The power efficiency is over 92% when the output power is at maximum output rated power. The total harmonic distortion when the output power is at maximum output rated power is 0.949%.

Induction Motor Drive System using V-connection AC Chopper.

This paper proposes a novel induction motor drive system using a three-phase V-connection ac chopper that consists of two single-phase ac choppers. There are three new topics proposed in this paper. Firstly, this paper proves that the three-phase V-connection ac chopper can be operated properly only if the input and the output voltages are in synchronism . Secondly, a novel commutation method for ac chopper isproposed. The proposed commutation method combines the load current commutation and the input voltage commutation. Therefore, by applying the proposed commutation method, voltage and current surge around zero crossing of the input voltage and the load current do not occur. Thirdly, a novel high effciency control method for induction motor is proposed. The proposed control method does not require d-axis and q-axis current components, but uses only the magnitude ofthe primary current. The whole control system has a very simple structure. These new topics are confirmed by experimental results on a 750W general-purpose induction motor.

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.

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.

Asymmetrical PWM technique with harmonic elimination and power factor control in AC choppers

This paper describes the asymmetrical pulse width modulated (APWM) control technique for single phase AC choppers, which improves the input power factor and eliminates the harmonics of the output voltage up to a specified order. This technique also enables linear control of the fundamental component of the output voltage. The APWM switching patterns at the specified phase angle are obtained by the Newton-Raphson method and can be implemented by a one-chip microprocessor. Theoretical comparisons are made with conventional PWM technique and the computed performance indicates the superiority of the proposed APWM technique. Practical verification of the theoretical predictions is presented to conform the capabilities of the new technique. >