Applied Power Electronics: Rectifiers, Choppers, Regulators

Applied Power Electronics: Rectifiers, Choppers, Regulators

Carlo Joseph Makdisie (Tishreen University, Syria) and Marah Fadl Mariam (Tishreen University, Syria)
DOI: 10.4018/978-1-7998-1230-2.ch018

Abstract

Most of the electric machines had a conventional design for speed –control. Previously, the speed regulation of these motors was done via traditional or mechanical contacts, for example: inserting resistors to the armature circuit or controlling the excited circuit of DC motor, and other methods of control. These classical methods, however, lead to non-linearity in mechanical or electromechanical characteristics [ω= f(M) or ω= f(I)], which in turn lead to increased power losses as the result of the non-soft regulation of speed, as well as the great inertia of classical control methods that rely on mechanical and electromagnetic devices.
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Background

In this chapter, the recent classification of rectifiers, converters, and regulators are explained. Empowering this chapter with MATLAB / Simulink simulation, and thorough representation of each circuit's eave forms, and the equations representing each one.

The electronics revolution began when the silicon transistor was invented, and then the invention of the Thyristor in 1956, which was developed and produced commercially. Since then, the power electronics have been deployed in many industrial applications and the importance of their development has increased with the continuous progress in computer science, microelectronics and advanced control systems of production lines in order to deal with high capacities of transferred power, control it and increase the efficiency . Nowadays, power electronic converters are used in every factory, facility, or industrial device, as well as domestic apparatus, such as vacuum cleaners, blenders, mixers, blending devices.

The speed equation for a DC motor is given by the following basic relationship:

It is clear from the previous equation, that the speed is varied or regulated by either changing the magnetic flux (978-1-7998-1230-2.ch018.m02 - the 978-1-7998-1230-2.ch018.m03 current), the applied voltage 978-1-7998-1230-2.ch018.m04 or changing the resistance of the armature circuit 978-1-7998-1230-2.ch018.m05.

The important question which is highlighted: Why the speed control is required? What is the goal?

If the speed exceeds the required limit, this will lead to distortion of the productive parts (ie, poor productivity), so they do not meet the required specifications. If the speed is less than the required value, this will lead to decreasing the efficiency of the actuator machine, which effects directly on productivity, cost and other factors. Therefore the use of power electronics converters is necessary to control the speed of the driven machine and set it at a suitable value for the accuracy of the production process.

There is also another purpose to use the power electronics converter; as an interface between the power supply and the load, and provide small size- weight efficiency, supply quality, control requirements.

Depending on the function of power electronics converters, they are divided into several main types:

  • 1.Rectifiers: and it is divided into two types:

    • a.

      Uncontrolled Rectifiers.

    • b.

      Controlled Rectifiers.

These circuits of both types convert the AC voltage into DC value, either constant /fixed (Uncontrolled) or variable (controlled).

Key Terms in this Chapter

Voltage regulator: is a system designed to automatically maintain a constant voltage level. A voltage regulator may use a simple feed-forward design or may include negative feedback. It may use an electromechanical mechanism, or electronic components.

Power electronics: is the technology associated with the efficient conversion, control and conditioning of electric power by static means from its available input form into the desired electrical output form.

Rectifier: is an electrical device that converts alternating current, which periodically reverses direction, to direct current, which flows in only one direction.

Chopper: is a basically static power electronics device which converts fixed DC voltage/power to variable DC voltage or power. It is nothing but a high-speed switch which connects and disconnects the load from source at a high rate to get variable or chopped voltage at the output.

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