Working of Step-Down Chopper with RL Load
The circuit configuration depicts a step down chopper connected to a RL load with a fixed DC supply. Choppers are commonly employed to drive separately excited DC motors, where the motor’s armature is modeled as an RL-load , combining resistance and inductance in the context of a step-down chopper , two modes for the load current are possible due to the interaction of the chopper with the RL-load . They are:
- Continuous load current
- Discontinues load current
Continuous Load Current Mode
In the scenario of a high load inductance ,continuous load current is achieved in a step-down chopper system. During the chopper’s ON period (0 to δT) , the RL load connects to the circuit , causing the load voltage (VL) to track the source voltage(Vdc) , and load current rises to its maximum at t= δT. When the chopper switches OFF( δT to T), load voltage drops to zero, but the load current persists due to the load inductance , preventing sudden current changes . Thus once the chopper is turned OFF , the stored current in the load inductance freewheels through the free-wheeling diode D f , gradually decreasing to its lower limit as depicted in the waveforms.
Discontinues Load Current Mode
When the load inductance is small in a step-down chopper system , discontinuous load current results . During the chopper OFF period , the load voltage drops to zero and the load current starts decreasing . Subsequently , the load current reaches zero at a specific moment and stays at zero until the chopper is turned ON again(t=T) . This pattern repeats, creating a waveform for the load current that exhibits discontinuity . The small load inductance allows for a more rapid decrease in current during the OFF period , leading to the intermittent nature of the load current in this configuration.
Step Down Chopper
In power electronics, a chopper refers to a type of electronic switch that is used to control the flow of electrical power. It functions as a high-speed ON/OFF semiconductor switch that modulates the voltage or current in a circuit. A chopper is a static device that transforms a fixed DC input voltage into a variable DC output voltage. It acts as the DC counterpart(equivalent) of an AC transformer due to its similar behavior. These are also used in trolley cars, marine hoists, forklift trucks, and mine haulers. Future electric automobiles are likely to use choppers for their speed control and braking. The chopper system offers smooth control, high efficiency, fast response, and regeneration.
Table of Content
- What is Chopper?
- Classification of Chopper
- Construction and Components of Step-Down Chopper
- Step-Down Chopper with Low Pass Filter
- Advantages of Step Down Chopper
- Disadvantages of Step Down Chopper
- Applications of Step Down Chopper