The simple base circuit of one phase buck-boost voltage controller is showed in fig. 1. The circuit also contains an input LC-low-pass filter.
The principle of operation of a voltage controller is similar to the operation of a buck-boost DC-DC converter . During the switch-on the input transistors T1, T2 the energy is accumulated in the input inductor L. During the swith-on the output transistors T3, T4 the energy from inductor L is passed in the output capacitor C and the load. The output voltage can be controled by a change of a correlation of state switch-on and switch-off.
By the further development were created the multi-cell circuits of voltage controllers , when each phase is formed by parallel connection with an input and output of several similar accumulative cells, with the appropriate shift of the control. The properties of the multi-cell voltage controller are deduced from the properties of one cell, the analysis approach of that is given below. The multi-cell voltage controller is characterized by the smaller installed power of elements, by the better quality of input and output energy and has more rigid external characteristics, than one-cell is in the fig. 1.
The creation of multiphase voltage controllers is also possible. In such circuits instead of the bidirectional transistors, as in fig. 1, it is possible to use the transistor with the inverse diode. The example of a three-phase controller is showed in fig. 2.
Fig. 2 Fig. 3
In case of availability of all ends of a multiphase load and source (in autonomous systems) it is possible to reduce an amount of transistors up to two, using diode bridges, as shown in fig. 3.
On the basis of any voltage controller is possible to construct AC-DC the converter, the example is shown in fig. 4. The dc voltage can be regulated from zero up to values ??considerably exceeding standard voltages of classic diode rectifiers.
The buck-boost cycloconverter is formed from the transistor cycloconverter, loaded on accumulative inductor, with an output part of a buck-boost voltage controller, showed in fig. 2, that gives the circuit in fig. 5. The three-phase input voltages of a main, current of accumulative inductor L and voltage on accumulative capacitor C of one phase are showed in fig. 6.
Fig. 5 Fig. 6
Fig. 7 Fig. 8
The blocks of the voltage source invertors (VSI) are included sequentially with the diode rectifiers, ensure to control their inputs and, accordingly, output voltages. The invertors are controled so that their voltage and current are moved on 90 degree. An active power does not pass through VSI, therefore there is no source of energy in their dc link. Thus one cell of the converter gives a current which is lagging behind the voltage of a main (fig. 8, diagram 1), and second - the same ladding one (fig. 8, diagram 2). As a result the current of an input source will be in-phase with the voltage, as is showed in fig. 8, diagram 3.