AC Chopper Research Articles

Novel clamping modulation for three‐phase buck‐boost ac choppers

AbstractThree‐phase ac choppers feature output voltage amplitude controllability and enable more compact system realizations compared to autotransformers. For the practical realization advantageously standard power transistor with unipolar voltage blocking capability such as MOSFETs can be employed as a naturally resulting offset voltage between the grid and the input‐stage starpoint ensures purely positive power transistor voltages. This offset voltage is, however, not strictly defined and may drift to higher voltage values, resulting in high power transistor voltage stresses and finally a potential overvoltage breakdown. Traditionally, the offset voltage drift is prevented by introducing discharge resistors across the input‐stage capacitors which, however, results in substantial ohmic losses. This paper analyzes the offset voltage formation in ac choppers and proposes a novel clamping modulation scheme which ensures a strictly defined and minimum time‐varying offset voltage without need for discharge resistors. Theoretical analyses and circuit simulations are finally experimentally verified with a 400 V (rms, line‐to‐line) 50 Hz grid connected three‐phase buck‐boost ac chopper with 3 kW rated power.

Power quality improvement of PWM AC Chopper fed capacitor run induction motor using BFO, PSO and CSO Algorithm

This paper exhibits performance enhancement of PWM AC chopper fed capacitor run induction motor by using optimization algorithm. The PWM AC chopper utilizes enhanced asymmetrical pulse width modulation technique by incorporating four pulses in quarter cycle. The switching instants are obtained optimally by bacteria foraging optimization, particle swarm optimization and cuckoo search optimization algorithm. The power quality parameters considered in this paper are total harmonic distortion of current, total harmonic distortion of voltage, power factor and efficiency. The simulation result shows that proposed algorithm shows better performance compared to other optimization techniques.

Comparative Analysis of PWM AC Choppers with Different Loads with and Without Neural Network Application

In this paper, we focus on the "Artificial Neural Network (ANN) based PWM-AC chopper". This system is based on the PWM AC chopper-encouraged single-phase induction motor. The main purpose of this paper is to design and implement an ideal technique regarding speed control. Here analyzed PWM-based AC-AC converter with resistive load, R-L load and finally, the PWM AC chopper is fed to single phase induction for speed control. Using other soft computing and optimization techniques such as Artificial Neural Networks, Fuzzy Logic, Convolution algorithm, PSO, and Neuro Fuzzy can control the Speed. We used Artificial Neural Network to control the Speed of the PWM-AC Single phase induction motor drive. The Neural Network toolbox has been further used for getting desired responses. Neural system computer programs are executed in MATLAB. The performance of the proposed method of ANN system of PWM AC Chopper fed single phase induction motor drive is better than other traditional and base methods for controlling the Speed, based on the MOSFET.

Direct AC-AC Converter Based on Odd Symmetrical No-Differential AC Chopper Legs With Unipolar Modulation Strategy

Direct AC-AC Converter Based on Odd Symmetrical No-Differential AC Chopper Legs With Unipolar Modulation Strategy

Analysis of Interharmonics Generation in Induction Motors Driven by Variable Frequency Drives and AC Choppers

In modern power systems, interharmonics have emerged as noninteger frequency components that appear in current or voltage signals. Double-stage AC-DC-AC converters have been identified as a primary source of interharmonics. Previous studies have highlighted modulation techniques, filters, passive components, unbalanced conditions and DC link effects as relevant factors. However, the interaction between these factors and the inertial properties of induction motors has not been explored. This study assesses various types of AC drives, including variable frequency drives (VFDs) and soft starters (AC choppers), to investigate their interaction with machine inertial properties in interharmonic generation. The employed technique for time-frequency spectral analysis is the wavelet synchrosqueezed transform combined with a clustering method. This paper demonstrates that the interaction of the inertial properties of low-power induction motors with the variations of the switching frequencies of the VFDs, the filters used in the DC link and a soft start indirectly contribute to harmonic generation and potentially to interharmonics in the electrical grid and the outputs of the inverter.

Nondifferential AC Choppers Based Identical Bipolar Buck–Boost AC–AC Converter Without Commutation Issue

This article proposes a new H-bridge structured bipolar pulsewidth modulation (PWM) buck–boost ac–ac converter based on the nondifferential ac choppers. The proposed converter can generate simple identical noninverting and inverting buck–boost voltage outputs by modulating one phase leg with single control duty ratio ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${d}_1$</tex-math></inline-formula> or <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${d}_2$</tex-math></inline-formula> ). It can also provide flexible identical noninverting and inverting buck–boost operations by modulating both phase legs with two control duty ratios ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${d}_1$</tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${d}_2$</tex-math></inline-formula> ). In the proposed topology, the use of nondifferential ac choppers eliminates the complementary switching of ac switches and related inductor open-circuit issue. Moreover, half the switching devices are configured as switching-cell units to avoid shoot-through occurrence due to accidental turn- <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</small> of complementary switches. Therefore, the proposed topology is free from commutation issue and can abolish PWM deadtimes to produce high-quality output with improved utilization of switch duty ratios. It also provides continuous input current and can perform normally with reactive loads. It has the potential to mitigate both voltage sags and swells (due to bipolar operation) when used as series voltage compensator; and unlike the existing nondifferential bipolar ac–ac converters, it can provide compensation for more intense voltage sags (of above 50%) as well. In-depth analysis of the proposed topology and hardware verifications are provided in this article.

A novel AC chopper integrated with active measurement of wideband impedance for wind power system

Large-scale wind farms are susceptible to oscillations like any other power systems with high penetration of power electronics, whose characteristics of wideband impedance hold the key to resolving this issue. However, due to the high cost of impedance measurements for power systems, computational modelling methods are usually used, accuracy of which is difficult to be verified. This paper proposes a novel AC chopper integrated with active measurement of wideband impedance (AIM-ACC), which can be slightly modified from the existing energy consuming devices in wind power systems. With the help of the proposed Reversed-phase Chirp Pulse Width Modulation (RC-PWM) signal, the AIM-ACC generates chopper current within a desired wide frequency band, avoiding the spectral shifting effects of sinusoidal voltages. Thus, the impedance characteristics of wind system are obtained by measuring the injected current and its corresponding voltage, with fast excitation time, good controllability and high accuracy. Finally, the verification of an experiment with single-phase branch and a simulation with the proposed AC chopper in wind power system was carried out for the effectiveness of the proposed method.

AC CHOPPER DESIGN AS UNIVERSAL MOTOR DRIVER BASED ON FUZZY LOGIC CONTROLLER

The electric motor has the function is converting electrical energy into mechanical energy. Based on supply, the electric motor is divided into two kinds of supply that are alternating current and direct current. The universal motor is an alternating current motor, the construction, and characteristics of a universal motor are the same as a direct current motor. Fuzzy Logic Controller is combined with AC Chopper circuit as a universal motor driver to control the motor universal speed at the stability of 1000 RPM and uses LM393 Optical Encoder sensor that will give a feedback signal to the fuzzy system as input. This research purpose is to implement AC Chopper as a universal motor driver to get more stable speed control combined with Fuzzy Logic Controller as feedback. In this study, the author uses the experimental method. With variable control are setpoint at 50% duty cycle and 1000 RPM speed reference of motor universal. Which is using 10 types of duty cycle values to get the average of driver efficiency and then using 2 kinds of load conditions for the controller test. The result of the driver test is to get speed control while without load condition has a period of 3 – 5 seconds to reach 1000 RPM. Then, when the load shedding condition has an overshoot value of up to 1193.33 RPM and reaches 1000 RPM in the range of 2 - 3 seconds. In this study, got the result of average driver efficiency is 85.41%.

A Low-Cost DC Chopper With Coupling Transformer for Offshore Wind VSC-HVdc System

The dc chopper (DCC) is the key equipment of offshore wind voltage source converter based high-voltage direct current (VSC-HVdc) system. Combining the advantages of the ac chopper and the centralized DCC, a novel dc chopper with coupling transformer (CT-DCC) is proposed. The use of the coupling transformer can reduce the voltage on the concentrated resistor to eliminate the high-voltage wall bushing effectively. Compared with the traditional DCC, the cost of CT-DCC is reduced by 35% for ±400 kV/1100 MW offshore wind VSC-HVdc project. In addition, the application of the coupling transformer provides an opportunity for the introduction of freewheeling inductance, which greatly eliminates the interference of pulse-current generated by the existing DCC on dc-link voltage. Through system simulation, the peak value of the dc-link voltage during the fault ride through is 1.02 p.u., and the dc-link voltage ripple is only 1%–2%, which meets the system requirements. After the detailed analysis of the working principle and characteristics of CT-DCC, the control strategy and design principle are given. Furthermore, a prototype experiment of up to 10 kV/10 MW is conducted to verify the feasibility of CT-DCC.

Intelligent transformer tap controller for harmonic elimination in photovoltaic interfaced micro-grid network

The photovoltaic (PV) system is interfaced to the microgrid through an on-load tap changer (OLTC) transformer. Pulse width modulation (PWM) AC choppers are used to control these OLTC but create harmonics owing to their non-optimal firing angles. In this paper, Differential Evolution (DE) and Grey Wolf Optimizer (GWO) techniques are used for optimal control of an AC chopper to keep the harmonic distortion of voltage and current within limits. An IEEE-13 node network is adapted as a micro-grid with PV integration through transformers. The simulated results are validated by a laboratory set-up. A dSPACE experimental set-up is used for the real-time implementation of optimization algorithms. The results show that the DE gives firing angles that improve power quality, particularly a reduction in total harmonic distortion and improvement in the root mean square voltage profile. The research is particularly useful for the on-line power quality improvement in PV interfaced microgrid networks.

Performance Investigation of Synchronized Three-Phase AC Chopper-Based Controller for Small Hydrogeneration Systems

This article presents the design, development, and performance analysis of a three-phase synchronized ac chopper (SynACC)-based controller for small hydrogeneration systems. The three-phase SynACC-based controller is used to control the voltage and frequency of a three-phase self-excited induction generator (SEIG)-based small hydropower generation system. The SynACC-controlled dump load is connected at the point of common coupling across the consumer load that controls the system frequency and voltage using instantaneous power balancing method. The SynACC-based controller has synchronized the system frequency feedback-based pulsewidth modulated current delivered to the dump load with the SEIG output voltage in order to make the equal instantaneous currents and similar frequency spectrum of current in all the three phases of the dump load circuit. The equal instantaneous currents and similar frequency spectrum of currents in all the three phases of the dump load circuit significantly improve the system stability. That also improves the system efficiency by removing the multiple and fast fluctuating torque generation problem in three-phase SEIG-based small hydrogeneration systems. The SynACC controller improves the system power factor, since it reduces the reactive power demanded by the dump load circuit. The laboratory prototype of the scheme has been developed and detailed mathematical modeling along with the simulation and experimental results are presented in the article to validate the claims. The technique presented in this article may also be used to develop an improved power quality heating furnace system for chemical and process industry applications.

Calculation of the Voltage Unbalance Factor for High-Speed Railway Substations with V-Connection Scheme

In France, high-speed railway lines are powered by a 2 × 25 kV/50 Hz electrification system. The substations include two single-phase transformers connected to the high-voltage electrical transmission network on different pairs of phases according to a so-called “V-connection scheme”. In practice, due to the large variations in the power absorbed by the trains, this connection does not make it possible to satisfactorily limit the unbalance in the three-phase voltages. In order to correctly size a balancing system to be associated with the substation, it is necessary to calculate, with precision, the voltage unbalance factor as a function of the power drawn by the trains. In its first part, this paper presents modelling of the substation and proposes an algorithm which allows for the calculation of the upstream line voltage as a function of the power consumption at the secondary of the transformers. The voltage unbalance factor can then be determined over a long period of operation. In the second part of this paper, the same approach is applied with an unbalance-compensator based on Steinmetz circuits controlled by AC choppers. Finally, in both cases, the results of the calculations are validated by simulations performed with PLECS simulation software.

Sliding mode control of a dynamic voltage restorer based on PWM AC chopper in three-phase three-wire systems

In this paper, a control system is presented based on sliding mode control (SMC) for a three-phase three-wire dynamic voltage restorer to compensate for voltage sag and swell. This dynamic voltage restorer (DVR) system includes an AC/AC converter in each phase without energy storage and DC link. The proposed controller has advantages such as robustness against parameter variations, guaranteed stability, implementation simplicity and fast dynamic response. The second-order generalized integrator (SOGI) based phase-locked-loop (PLL) is implemented in this controller to remove the voltage harmonics. It is worth mentioning that the SOGI-PLL operates independently for each phase that the variation of voltage asymmetric can be identified. The proposed control method can compensate the power quality problems such as voltage sag, swell, under voltage, and overvoltage at balanced and unbalanced conditions. The performance of the proposed method has been evaluated by simulations and experimental results.

SYNCHRONOUS AC CHOPPER FOR UNIVERSAL MOTOR SPEED CONTROL USING FUZZY LOGIC

The use of Universal type motors is very commonly used, both in daily life and in research activities. The universal motor can be used as prime mover generator PMSG (Permanent Magnet Synchronous Generator), which in its application there are obstacles, namely the difficulty of stabilizing the speed due to the influence of changes in the load connected to the PMSG, this affects the output voltage generated by the system. In this case, a speed stabilizer system is needed to stabilize the output voltage generated based on the load given to the system. AC Chopper is one of the circuits that can be applied in a speed control system that functions as an AC-AC voltage regulator which is the input of the Universal motor. Synchronous AC Chopper is one type of AC Chopper circuit which according to previous research has better performance in terms of efficiency than Basic AC Chopper. As for this control system, Fuzzy Mamdani logic is flexible and has a tolerance on existing data with control results having a settling time of ±15 seconds and an average efficiency of 84.99%.

Design and control of a single-phase voltage compensator based on an AC Chopper

Introduction: This paper is the result of the research “Design and control of single phase voltage compensator based on AC Chopper” developed in the AD-AF Academy of Viet Nam in 2019.&#x0D; Problem: This article develops power electronic devices based on AC chopper and provides solution for the voltage sag which is long-lasting and deep amplitude of fading at rural power grid.&#x0D; Objective: Improve the quality of the electricity system in rural Vietnam.&#x0D; Methodology: With the improvement of power system, power quality has become the major concern of user and grid companies. The Voltage sag has turned into the research priority because of the most frequently happening and great economic loss. Based on the rounded analysis of traditional voltage compensation devices, this article develops power electronic devices based on AC chopper and provides solution for the voltage sag which is long-lasting and deep amplitude of fading at rural power grid.&#x0D; Results: On the one hand, it reduces the cost and space of the device. On the other hand, it solves the short compensation time of UPS and DVR.&#x0D; Conclusion: The trial operation proves that this single-phase low-voltage compensation device has obvious compensation effect for most resistive loads and some inductive loads, less harmonic content, long continuous compensation time and stable performance.&#x0D; Originality: This compensation device integrates the advantages of UPS and DVR, and also solves their shortcomings and deficiencies.&#x0D; Limitations: The authors need to spend more time to the development and design three-phase low-voltage compensation device.

Improved Control Strategy for Three-Phase AC Choppers under Induction Motor Load (Dept.E)

This paper p resents a modified control strategy for controlling three-phase ac chopper under induction motor load. This modified strategy is known as Extinction Angle Control (EAC). This new strategy is compared with the Modified Phase Angle Control (MPAC) and Symmetrical Angle Control (SAC) to demonstrate its superior performance. These strategies are based on varying the stator ac voltage to control the speed of a three-phase induction motor. The proposed strategy is characterized by a higher power factor and a better total harmonic distortion compared with the other two strategies over the normal operating arrangement. Performance evaluation of the motor under the different switching strategies is demonstrated. The simulation of the system is carried out using a PSIM computer program. The simulation results are compared with the experimental results obtained from a laboratory prototype. The levels of harmonics in the supply currents and power factor are evaluated for different control strategies.

Implementation of PWM AC chopper controller for capacitor run induction motor drive via bacterial foraging optimization algorithm

&lt;p&gt;This paper focuses on design of closed-loop control for pulse width modulated AC chopper controlled capacitor run induction motor drive engaging enriched optimization algorithm based on foraging of bacteria. Capacitor run induction motor is a non-linear device and its parameter varies under different functional point of the system. A linearized increment model for PWM AC chopper is illustrated for a particular functional point of the drive. The conventional method does not provide acceptable performance under different load conditions. Bacteria foraging optimization technique categorizes accurate control parameters for the superlative dynamic response under unit step load variations. Field Programmable Gate Array is implemented practically for a particular functional point of the drive to exhibit accurate performance. Experimental and simulated results are obtained to authenticate the effectiveness of the optimized controller.&lt;/p&gt;&lt;p&gt; &lt;/p&gt;

Analysis and Control of Wireless Motor Drives With a Single Inverter in Primary Side

In motor drives supplied through wireless power transfer (WPT) systems, a high frequency inverter and a low frequency one are commonly used in the primary and secondary sides of the system, respectively. This arrangement causes reduced reliability and efficiency, and high cost. Besides, using an electrolyte isolator like big dc capacitor, shorten the system lifetime. This capacitor is usually located in parallel with the motor drive system. So, the capacitor fail leads to a total system failure. In this article, a multi-functional single inverter used in the primary side dispatch as the high-frequency ac power via a magnetic link as well as driving an induction motor without any extra inverter in the secondary side. This is obtained by using a simple AC chopper in the secondary side as a wave shaping convertor. In this way, the desirable ac power can efficiently be injected into the motor whereas the WPT system efficiency is improved by up to 5%. The modeling and mathematical analysis of the proposed wireless drive are presented. Also, the performance of the drive under an open-loop V/F control system is verified by simulation and experimental results. AC/AC converters, electric vehicles, wireless motor drives, wireless power transfer.

An Improved Bipolar-Type AC–AC Converter Topology Based on Nondifferential Dual-Buck PWM AC Choppers

A novel single-phase pulsewidth modulation (PWM) direct ac-ac converter based on two-level nondifferential dual-buck ac chopper legs with inverting and noninverting operations is first proposed in this article. It has the ability to resolve both voltage sag and swell problems at the same time when used as distributed flexible voltage conditioner. Compared to the traditional ac-ac converter, it has much enhanced system reliability thanks to no shoot-through problems even when all switches of each ac chopper legs are turned on, and therefore, the PWM dead time is not needed leading to improve the utilization of the duty cycles. Only half of the switches in the proposed converter is switched at high frequency during a switching period at most, which significantly reduces the total switching loss. In particularly, the converter has two greatest advantages that it retains the common sharing ground of the input and output and has the same buck/boost operation process for noninverting and inverting modes. In order to fully testify the performance of the proposed converter, a 500-W experimental prototype is built and tested at different conditions.

The calculation method of optimized AC choppers capacity in islanded MMC-HVDC system

In order to ensure the safety of renewable energy generation integration system through islanded MMC-HVDC, the AC choppers with the same capacity as sending end converter station are equipped in current projects. However, considering the actual operation needs, it is not necessary to equip so many AC choppers. The optimal capacity of the AC choppers can be calculated according to the most serious fault. The calculated capacity can meet two requirements. One is the renewable energy generation units just start to cut off when the DC voltage reaches the overvoltage limit value. Another one is to minimize the cost and floor area of the AC choppers. It can ensure that the converter station devices is not be damaged in the condition of lowest economic cost. A three-terminal and a four-terminal renewable energy generation integration system through islanded MMC-HVDC are built in PSCAD, which verifies the correctness of the theoretical analysis.