Power electronics consist of various converter circuits such as AC to AC converter, AC to DC converter, DC to AC converter, cycloconverter, and so on. These converter circuits are frequently used in various electronic circuits and electronics projects for converting one form of electrical energy into another form of electrical another or electrical energy with different ratings in the same form. Here, in this article, let us discuss in detail about AC to AC converter circuit diagram and its working. But, primarily we must know what is an AC to AC converter.
AC to AC Converter
These types of power electronic converters are used to convert the alternating current waveforms of specific magnitude and specific frequency into alternating current waveforms with different magnitude and different frequency, as the signal remains AC, hence this converter is termed as AC to AC converter. To operate a few devices and machines we require some specific voltage with specific frequency which can be obtained using AC to AC converters. By regulating AC power using the AC to AC converter we can regulate the speed of induction motors. There are different types of AC to AC converters which are classified based on different criteria.
Types of AC to AC Converters
- DC link based AC to AC Converter
- Matrix Converter
These AC to AC converters are again classified into various types such as step up cycloconverters, step down cycloconverters, single phase to single phase cycloconverters, three phase to single phase cycloconverters, three phase to three phase cycloconverters, envelope cycloconverters, phase controlled cycloconverters, CSI converters, VSI converters, sparse matrix converters, very sparse matrix converters, ultra sparse matrix converters, and hybrid matrix converters. Let us discuss about a simple AC to AC converter circuit diagram in this article along with practical application of AC to AC converter.
Simple AC to AC Converter
Thyristor based single phase to single phase cycloconverter can be considered as a Simple AC to AC converter circuit diagram. The frequency of AC power can be changed using cycloconverters and these cyclconverters can also be used to change AC power magnitude in specific applications. Typically, AC to AC converter consists of DC link which increases the cost of system, reduces the efficiency in the conversion process. So, AC to AC converter without DC links such as cyclconverters are preferred for converting AC to AC power.
The working of simple AC to AC converter can be easily understood with above figure. The frequency of the input signal can be varied by varying the triggering pulse to the thyrsitors which are connected to form an AC to AC converter as shown in the figure below. The frequency of the signal can be stepped up or stepped down depending on the requirement using cycloconverters.
Simple AC to AC Converter Circuit Diagram
The simple AC to AC converter circuit diagram is shown in the above figure which is termed as single phase to single phase cycloconverter. It consists of two limbs, one limb is for positive half cycle and other limb for the negative half cycle of the power supply. Hence, they are called as negative limb (N-converter) and positive limb (P-converter) which consists of four thyrsitors in each of these limbs. The frequency of the input signal is varied by applying triggering pulse to these thyrsitors of AC to AC converter appropriately. Thus, by varying the triggering pulse we can vary the output power frequency.
Practical Application of Simple AC to AC Converter
Single phase induction motor speed control using thyrsitors is a practical application of simple AC to AC converter. In this project, the speed of induction motor can be regulated at three different speeds which can be obtained by three different frequencies. These three output frequencies are achieved by using single to single phase cycloconverter which is one of the types of AC to AC converter.
The block diagram of single phase induction motor speed control using AC to AC converter is shown in the above figure which consists of various blocks. These blocks include power supply block which is used for providing power supply to project kit. The microcontroller block with 8051 microcontroller interfaced with AC to AC converter through the Opto-isolator. There are slide switches which are interfaced with microcontroller and are used for selecting the mode (F, F/2, and F/3). The motor can be made to operate at three speeds by selecting the appropriate mode using these slide switches.
Based on the selected mode, the microcontroller gives triggering pulse to the thyrsitors of AC to AC converter and thus, the output power frequency is varied. Based on the speed vs frequency relation of motor, the speed of induction motor is controlled.
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