Types of Step Down Cycloconverter
Two types of Step Down Cycloconveters are
- Mid Point Step Down Cycloconverter
- Bridge-Type Step Down Cycloconverter
Mid Point Step Down Cycloconverter
A step down cycloconverter does not require forced commutation . It requires phase controlled converters connected as shown . During positive half cycle terminal A is positive with respect to o , P1 is triggered at ωt = π , positive output voltage appears across load and load current starts building up. At ωt = π , supply and load voltages are zero. After ωt = π, P1 is reverse biased. As load current is continues , P1 is not turned off at ωt = π . When P2 is triggered in sequence at ωt = π + α , reverse voltage appears across P1 , it is therefore turned off by natural commutation. When P1 is commutated , load current has built up to a value equal to RR as shown in waveforms.
With the turning on of P2 at ωt = π + α , output voltage is again positive as it was with P1 on. At ωt =2 π + α, when P1 is again turned on, P2 is naturally commutated and load current through P1 builds up beyond RS as shown. At the end of four positive half cycles of output voltage, load current is RU. When N2 is now triggered after P2 , load is subjected to a negative voltage cycle and load current decreases from positive RU to negative AB as shown . Now N2 is commutated and N1 is gated at 5 π + α . Load current becomes more negative than AB at 6 π + α , this is because with N1 on , load voltage is negative. For negative half cycles of output voltage , current is as shown. The positive group of voltage and current wave consists off our pulses and same is true for negative group of wave. One positive group of pulses along with one negative group of identical pulses constitute one cycle for the load voltage and load current. The supply voltage has, however gone through four cycles. The output frequency is :
f0 = fs /4
Bridge-Type Step Down Cycloconverter
During positive half cycle P1 P2 and N1 N2 are forward biased. At ωt = π , SCRs P1 P2 are turned on. Therefore, output voltage follows the positive envelope of supply voltage V0 = Vs . At ωt = π, SCRs P1 P2 are turned on. Therefore, output voltage follows the positive envelope of supply voltage V0 = Vs . Because of the load inductor P1 P2 still conduct up to ωt = π + α . At ωt = π + α, P3 P4 are triggered and P1 P2 are naturally commutated. Therefore, output voltage follows the positive envelope of supply voltage V0 = -Vs .
After four positive half cycles of output voltage , i.e., at ωt =4 π , P1 P2 and N1 N2 are forward biased. At ωt =4 π + α , P3 P4 are naturally commutated and N1 N2 are turned on. Therefore, output voltage follows the negative envelope of supply voltage V0 = -Vs . At ωt =5 π + α, N1 N2 are naturally commutated and N3 N4 are turned on. Therefore, output voltage follows the negative envelope of supply voltage V0 = Vs . The supply voltage has, however gone through four cycles. The output frequency is , therefore f0 = fs/4 .
Cycloconverters
Cycloconverters are power electronic devices designed to convert electric power directly from one frequency to another, typically without the need for an intermediate DC link. Additionally, they are employed in specialized systems where precise control of output frequency and low harmonic distortion are crucial. However, challenges include complexity in control strategies and the presence of harmonics in the output waveform, requiring careful design and control for optimal performance. A cycloconverter is thus a one-stage frequency changer. The fundamental principle of a cycloconverter involves breaking down the input AC power into smaller segments and reassembling them to form the desired output frequency.
In this Article, We will be going through Cycloconverter in power electronics, We will go through what is a Cycloconverter, its Type with its Construction, and its Characteristics, At last, we will conclude our Article with Some Solved Examples and FAQs.
Table of Content
- Cycloconverter
- Types
- Construction and Components
- Characteristics
- Advantages
- Disadvantages
- Applications
- Solved Example