Single-phase and three-phase AC-AC converters are employed in variable speed drive, induction heating systems, and grid voltage compensation. They are direct frequency and voltage controllers having no intermediate power conversion stage. The frequency controllers govern the output frequency (low or high) in discrete steps as per the requirements. The voltage controllers only regulate the RMS value of the output voltage. The output voltage regulation is achieved on the basis of the various voltage control techniques such as phase-angle, on-off cycle, and pulse-width modulation (PWM) control. The power quality of the output voltage is directly linked with its control techniques. Voltage controllers implemented with a simple control technique have large harmonics in their output voltage. Different control techniques have various harmonics profiles in the spectrum of the output voltage. Traditionally, the evaluation of power quality concerns is based on the simulation platform. The validity of the simulated values depends on the selection of the period of a waveform. Any deficiency in the selection of the period leads to incorrect results. A mathematical analytical approach can tackle this issue. This becomes important to analytically analyze the harmonious contents generated by various switching control algorithms for the output voltage so that these results can be successfully used for power quality analysis and filtering of harmonics components through various harmonics suppression techniques. Therefore, this research is focused on the analytical computation of the harmonics coefficients in the output voltage realized through the various voltage and frequency control techniques. The mathematically computed results are validated with the simulation and experimental results.

Voltage sags and swells are the major problems of the power distribution system that arise due to uneven distribution of the single-phase and nonlinear loads. They severely degrade the power quality and may cause the failure of the equipment at the user’s side. The voltage sag and swell issues are compensated by operating the AC voltage controllers with bipolar voltage gain characteristics. In these converters, high switching voltage and current, and a large number of switching devices are the main issues that cause unwanted power losses and result in reduced efficiency of the system. High voltage stresses may cause device failure due to the increase in dv/dt rating. The large count of switching devices results in high cost and high conversion losses. So here, we propose a novel AC converter with fewer switching devices that reduces switching voltage and current to have low conversion losses. The amplitude of the output is governed through the direct PWM control (DPWM) of one switch that controls the switching state of the other switch indirectly called indirect PWM control switch (IDPWM). The detailed analysis of the proposed converter is carried out to compare its performance with the existing converters. MATLAB/Simulink environment-based simulation results are proved through the experimental results obtained by developing a hardware prototype.

In this research, a new single-phase direct AC-to-AC converter, operating in buck and boost mode, with a bipolar voltage gain, is proposed. The operation is accomplished through high frequency direct and indirect PWM control of a single switch with low voltage stresses. This reduces, not only the control effort, but also the switching losses. The low voltage stresses across the high frequency switches, reduce the dv/dt problem significantly without any loss and bulky voltage snubber arrangement. The operation, in its all-operating modes, has a low inductor ripple current and switching current. The proposed converter may be employed as an AC voltage restorer in a power distribution system to cope with the voltage sag and swell issues. The detailed analysis of the proposed converter is carried out in order to compare its performance with the existing converters. The simulation results obtained using the MATLAB/Simulink environment are verified through experimental results.

The suggested single‐phase ac‐to‐ac matrix converter operated with inverting and noninverting characteristics may solve the grid voltage swell and sag problem in power distribution system, respectively. It is also employed as a direct frequency changer for domestic induction heating. The output voltage is regulated through duty cycle control of high frequency direct PWM (DPWM) and indirect PWM (IDPWM) switching devices. The DPWM control switches control the switching states of IDPWM switching devices. The inverting and noninverting characteristics are achieved with low voltage stresses and hence low dv/dt across the high and low frequency‐controlled switches. This reduces their voltage rating and losses. The high voltage overshoot problem in frequency step‐up operation is also analyzed. The sliding mode (SM) controller is employed to solve this problem. Pulse selective approach determines the power quality of load voltage. The validity of the mathematically computed values is carried out by modelling the proposed topology in MATLAB/Simulink environment and through hardware results.

Induction heating (IH) is an environmentally friendly solution for heating and melting processes. The required high-frequency magnetic field is accomplished through frequency controllers. Direct frequency controllers (DFC) are preferred to dual converters as they have low conversion losses, compact size, and simple circuit arrangement due to low component count. Numerous frequency controllers with complex switching algorithms are employed in the induction heating process. They have a complicated circuit arrangement, and complex control as their switching sequences have to synchronize with source voltage that requires the zero-crossing detection of the input voltage. They also have a shoot-through problem and poor power quality. Therefore, this research proposes a novel frequency controller with a low count of six controlled switching devices without a zero-crossing detector (ZCD) having a simple control arrangement. The required switching signals are simply generated by using any pulse-width-modulated (PWM) generator. The performance of the proposed topology is verified through simulation results obtained using the MATLAB/Simulink environment and experimental setup.

Variable voltage and frequency are required to govern the torque-speed characteristics of many industrial drive systems. Traditionally, this is achieved with a power converting system implemented with multistage converters. This technology is based on rectifying AC power into DC and then DC into AC with an inverter circuit. The power quality concerns of both conversion stages are tackled by selecting high switching frequency PWM control and harmonics mitigation filters. Also, using a bulky DC-link capacitor is one of the big sources of low system reliability, so this approach increases the conversion losses, circuit, and control complications. The frequency step-down conversion is very attractive with direct AC-AC converters as it has a simple control and circuit structure, but these converters face poor power quality challenges once the output frequency is decreased with respect to an input. In these converters, the total harmonic distortion (THD) of the output voltage becomes very poor once the output frequency is reduced. The problem of high THD of the output is addressed in the power converting circuits implemented with line frequency multi-winding transformers. The required number of output winding and switching devices (diodes and thyristors) increases once the value of the output frequency is decreased. This will increase the overall volume, cost, and losses. The use of a bulky and costly line frequency transformer may be eliminated if AC voltage controllers have non-inverted and inverted voltage buck capabilities, such existing topologies either have complex control schemes or require a large number of operating devices. Therefore, in this research article, a new transformerless frequency step-down converter employing fewer devices is proposed. This approach is realized with a high-frequency controlled rectifier for the required voltage stabilization and a low-frequency inverter bridge for frequency control. Its validation is supported by the results attained from Simulink and practical-based prototypes.