A cyclo converter (CCV) or a cyclo inverter is a device which basically converts a voltage(constant one), frequency(constant) AC waveform to another AC waveform at a frequency which is. this is done by synthesizing the output waveform from segments of the AC supply without an intermediate DC link. Cyclo Converters are of two types-:
1. circulating current type
2.blocking mode type
The high power products which are of commercial types are usually blocking mode type.
Three phase inverter
Three-phase inverters are used for variable-frequency drive applications and for high power applications such as HVDC power transmission. A three-phase inverter basically contains three single-phase inverter switches each connected to any of the load terminals. In a basic control scheme, the three-switch operation is coordinated and controlled in such a way that each switch operates at 60 degree in the fundamental o/p wavforme. After this a line to line o/p wave form is created which consists of six basic steps.
This waveform with a zero-voltage step in between the positive and negative sections of the square-wave such that the harmonics which are multiples of three are discarded as described above. if we apply carrier-based PWM techniques to the above six-step waveform then, the waveform shape is remained same.
Single Phase Inverter
Single Phase Full Bridge Converter
- Full bridge converter is a basic to convert dc to ac.
- An Ac o/p is produced from a DC i/p by closing and opening switches in an appropriate sequence.
- Four different states are classified which depends on the number of switches that are closed.
S1 & S2
S3 & S4
S1 & S3
S2 & S4
- Switches S1 and S4 should not be closed at the same time. it is advisable to close S2 and S3 in parallel
- if it is not connected so, then a short circuit can be encountered with the dc source.
- Real switches do not turn on or off immediately. Therefore the transition time of switching should be occupied in the control of switches.
- Overlap of switch “on” will cause short circuit (shoot-through fault) across the dc voltage source.
- Blanking time:- literally the blanking time is the total time that is used for switching.
- Transistor is operated in linear (active) mode.
- Here the o/p voltage is calculated as the multiplication of current as well resistance.
- The transistor can be modelled by an equivalent variable resistor as shown in figure.
- can only produce output at lower voltages from the input.
- It becomes of no use when the drop in voltage is extremely high and the current is high as heat dissipated is equal to the product of the output current and the voltage drop
Questions and answers.
Q1. what is a step up converter?
ans> It is a converter wherein the step up DC input voltage is equal or higher than DC output voltage. These types of converters uses controlled switches such as MOSFET etc.
Q2. what are the conditions for the working of step up converter?
ans> Inductor current should always be positive i.e continuous.
The power loss should be zero.
The circuit must be operable at steady state.