# Power Electronics Control Methods - Power Electronics

## What is the use of control methods in power electronics?

Converter will have two basic methods of control which are used for differentiating the output voltage and they are

• Time ratio control
• Current limit control

## Time Ratio Control

In time ratio control, a constant k given by TON/T will be varied and it is known as duty ratio. Time ratio control can be accomplished in two ways

## Constant Frequency

In this control method, the frequency (f = 1/T0N) will be kept constant whereas the ON time T will be varied and this known as pulse width modulation (PWM).

## Variable Frequency

In variable frequency technique, frequency (f = 1/T) will be varied whereas the ON time T will be kept constant and this is known as the frequency modulation control.

## Current Limit Control

In a DC to DC converter, value of the current will be varying among the maximum as well as the minimum level for nonstop voltage. In this technique, chopper (switch in a DC to DC converter) will be switched ON and then OFF to make sure that the current is kept steady between the upper and lower limits. When the current reaches the maximum point, the chopper goes OFF.

Whereas the switch will be at its OFF state, current freewheels via the diode and will drop in an exponential manner. Chopper will be switched ON when the current reaches the minimum level. This method will be used either when the ON time T is constant or when the frequency (f=1/T).

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