## 1 Introduction
Along with this advantage, the other attractive feature in this category of converters is the ability of output voltage regulation. However, the current rating of the operating transistors has to be increased as there may be a problem of high current surges during the shoot-through period. The high-order component of the z-source arrangement slows down the dynamic response. However, z-source converters reported in [14; 15] have no facility to produce the non-inverted voltage buck operation. Therefore, these converters cannot compensate for the voltage sag problem with a depth level of less than 50%, which is one of the most occurring problems (more than 50%) in the power distribution system. This problem also increases the complication once the output pulses try to arrange themselves to govern the output frequency. The converters reported in [16; 17] can tackle the preceding problems. However, the main issue in these circuits is the requirement of a large number of operating devices that not only increase the overall volume but also lead to an increase in the system's overall cost. The variable speed drive system requires frequency control to govern the rotating speed of the motors. Some specific loads, such as steel rolling and grinding mills, only need speed control in some selected discrete levels. Here the required speed may be half, one-third, or one-fourth of the machine's rated speed. The control of the motor speed is directly linked with the frequency control. In this frequency control range, voltage control is mandatory; otherwise, it leads to the core saturation problem in the connected motors. In the motor speed control mechanism, the ratio of the motor's voltage to frequency should be kept constant to maintain magnetic flux constant. Otherwise, the magnetic core of the motor may be saturated and cause the burning of motors. The bipolar voltage-gain direct AC-AC converter is one of the attractive approaches for the load where the required speed regulation is in discrete levels or steps. These converters can produce output voltage with a controllable amplitude that can be in-phase or out of phase with respect to the input voltage. These features of the produced voltage enable the arrangement of the number of positive and negative half-cycles at the output with either polarity of the source voltage according to the required output frequency. Although the characteristics of this output are always in non-sinusoidal forms as it contains unwanted harmonics [18], they are still favorable in numerous fields, as described in [19; 20; 21]. The converter reported in [22] belongs to the category of symmetric voltage gain both for voltage in-phase and out-of-phase operation. In this circuit, the number of required active switches is eight, along with three capacitors and two inductors. The count of active switching devices and passive components is reduced in another symmetrical bipolar voltage gain converter [23], as shown in Figure 1. This circuit can govern the magnitude of the output voltage from zero voltage to the maximum value of the input voltage. Its output may be in-phase or out of phase, with input voltage ensuring the non-inverting and inverting operation. This circuit can effectively be used to vary the output frequency in discrete steps just by modifying the control signals. There is the use of six active switching devices and eight diodes. There is always the conduction of two transistors and two diodes to produce the required output. The number of gate control circuits is proportional to the number of active switching devices. The reduction in the use of switching transistors effectively compacts the overall circuit volume and cost. In existing circuits, the following are the main issues that need to be addressed for a reliable and efficient power conversion process. 1. There is the conduction of more switching devices or components that increases the conduction losses;
2.