Static transformers of direct current to the alternating one.

Static converter is a semiconductor converter of DC 28.5 V in single phase alternating current with voltage of 115V and frequency 400 Hz, or three-phase alternating current with linear voltage 36 or 208 V and frequency 400 Hz. Capacities of static converters are up to 10 kVA and are limited with the characteristics of transistors, that are used in power circuits.

In civil aviation aircraft there are static converters of series ПОС and ПТС set. Name of the converter is decoded as follows: П - converter; O - single phase; T - three-phase; C - static. The number that stands after distinguishing mark indicates the output power in VA. The main elements of the single-phase converter (Fig. 4.6) is K converter, I inverter and filters: Ф_вх input and output Ф_вих. Converter is designed to convert DC (20... 30 V) in an adjusted constant voltage (50... 70 V). By varying of the output voltage of the converter we can maintain the output voltage of the converter to be constant at the moment of changing its load current or input voltage. This function is automatically performed by the voltage regulator of the converter.

Fig. 4.6

The inverter is designed to convert DC to AC with frequency of 400 Hz. Inverter is the most often performed as a bridge circuit (Fig. 4.7). Transistors operate in the key mode, and are switched on in pairs: VT1, VT4 and VT3, VT2. As a result, the current of the primary winding of the transformer changes its direction every half-period, and bipolar rectangular pulses are listed at the output winding of the transformer.

Fig. 4.7

The sequence of switching transistors' pairs and the duration of their state of being switched on are defined with pulses of control which are supplied to the base of transistors from the independent control circuit. Inventors of this way of control of power transistors are called inverters with independent excitation.