What is Current Source Inverter (CSI)?
A Current Source Inverter (CSI) is a type of inverter where the input DC current is kept constant, unlike a Voltage Source Inverter where voltage is constant.
Circuit Diagram
Working Of Current Source Inverter
In current source inverter four thyristor T1, T2, T3 & T4 are used. This thyristor is called CSI stage. These thyristor is connected with DC input ‘E’ and inductor is connected in series. It is used to flow the constant current from input to AC load. Load is connected to output.
In first mode thyristor T1 and T2 conduct and in second mode thyristor T3 and T4 conduct. Voltage across the thyristor is input voltage.
During Positive Half Cycle
In first cycle when input is given, the DC current flows through thyristor T1 & T2. Thyristor T1 conducts and current flows through load (load current is output current). And when thyristor T2 will conduct. At that time thyristor T3 and T4 will not conduct. Thyristor T1 and T2 will work in positive half cycle.
T1, T2 on then output current is positive from 0 to T/2 and input current is equal to output current.
∴ Vin = Vo
During Negative Half Cycle
• In second half cycle thyristor T3 and T4 will conduct. The flow from thyristor T3 to load and then to thyristor T4, then source. When thyristor T3 and T4 will conduct at that time thyristor T1 and T2 are in reverse biased, they are not conducting the current.
At that time the output current is negative and output current is negative from T/2 to T. At that time output voltage is negative.
∴ Vin = −Vo
• T1, T2 on then output current positive from 0 to T/2,
∴ Vin = Vo
• T3, T4 on then output current negative from T/2 to T,
∴ Vin = −Vo
Output Waveform of CSI
Write a note on CSI
The current source inverter converts the input direct current into an alternating current. In a current source inverter, the input current remains constant but this current is adjustable. The current source inverter is also called fed inverter.
The output voltage of the inverter is independent of the load. The magnitude and nature of the load current depends on the nature of load impedance.
