- Power Electronics Tutorial
- Power Electronics - Home
- Power Electronics - Introduction
- Power Electronics - Switching Devices
- Linear Circuit Elements
- Power Semiconductor Devices
- Silicon Controlled Rectifier
- Power Electronics - TRIAC
- Power Electronics - BJT
- Power Electronics - IGBT
- Power Electronics - MOSFET
- Solved Example
- Phase Controlled Converters
- Power Electronics - Pulse Converters
- Effect of Source Inductance
- Performance Parameters
- Reactive Power Control of Converters
- Power Electronics - Dual Converters
- Solved Example
- DC to DC Converters
- Power Electronics - Choppers
- Power Electronics - Control Methods
- Resonant Switching
- DC Converters Solved Example
- AC to DC Converters
- Single Phase AC Voltage Controllers
- Power Electronics - Cycloconverters
- Integral Cycle Control
- Power Electronics - Matrix Converters
- Solved Example
- Power Electronics Resources
- Power Electronics - Quick Guide
- Power Electronics - Useful Resources
- Power Electronics - Discussion
- Selected Reading
- UPSC IAS Exams Notes
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Power Electronics - Control Methods
In a converter, there are two basic methods of control used to vary the output voltage. These are −
- Time ratio control
- Current limit control
Time Ratio Control
In time ratio control, a constant k given by $\frac{T_{ON}}{T}$ is varied. The constant k is called duty ratio. Time ratio control can be achieved in two ways −
Constant Frequency
In this control method, the frequency (f = 1/T0N) is kept constant while the ON time T is varied. This is referred to as pulse width modulation (PWM).
Variable Frequency
In variable frequency technique, the frequency (f = 1/T) is varied while the ON time T is kept constant. This is referred to as the frequency modulation control.
Current Limit Control
In a DC to DC converter, the value of the current varies between the maximum as well as the minimum level for continuous voltage. In this technique, the chopper (switch in a DC to DC converter) is switched ON and then OFF to ensure that current is kept constant between the upper and lower limits. When the current goes beyond the maximum point, the chopper goes OFF.
While the switch is at its OFF state, current freewheels via the diode and drops in an exponential manner. The chopper is switched ON when the current reaches the minimum level. This method can be used either when the ON time T is constant or when the frequency (f=1/T).