SU584416A1 - Three-phase inverter for supplying zero-wire load - Google Patents

Description

one

The invention relates to the field of converter technology and can be used in power supply and electric drive systems of vehicles and industrial installations.

Three-phase inverters are known that convert a constant voltage to a three-phase alternating voltage, including key elements and output transformers 1-3. Such inverters can be made on three single-phase cells with a tap from the midpoint of the primary winding of the output transformer, three single-phase bridge or half-bridge cells, or according to a bridge circuit.

In cases where the inverter feeds a group of consumers, some of which are single-phase and creates a significant imbalance of load currents in phases, zero balancing of the load, usually connected to a common point of the secondary windings of the output transformers, is required for balancing the voltage. In this case, the phase voltage in the inverter circuits has a rectangular shape. Additional transformers or chokes are used to improve the shape of the phase output voltage curve.

The aim of the invention is to improve the shape of the output voltage curve. This is achieved by the fact that in the proposed inverter

On the cores of phase transformers additional windings are placed, connected between the zero point of the star of the secondary windings of phase transformers and the zero output of the load circuit.

FIG. 1 is a diagram of the described inverter, performed on three single-phase cells; in fig. 2 - the same, vypolnepny on the bridge circuit; in fig. Figures 3 and 4 show charts.

The inverter (see Fig. 1) is made on three single-phase cells, for example, with the midpoint of the primary winding of the output transformer. Each cell contains a group of controlled valves 1-b and an output transformer 7-9. The secondary windings W2 are connected by a star, the common point of which is connected to the neutral terminal O through the secondary windings through the additional windings WK of the output transformers connected by themselves consistently.

In the three-phase inverter (see Fig. 2), the control valves I-6 are connected in a bridge circuit, and the winding Wjv is made common (covers the cores of three transformers 7-9).

Inverter works as follows.

When switching valves 1-6 in the order inherent in three-phase inverters, on the windings of transformers 7-9 are formed

rectangular voltages UA, UB and Uc (see Fig. 3), mutually offset by 120 el. hail. The total voltage across the windings WN in the circuit of FIG. 1 or the voltage across the common winding WN in the circuit of FIG. 2 is UN UA- - rUB + Uc and has a rectangular triple frequency shape.

The phase output voltage of the UAO, t / Bo and Uco inverters is equal to the voltage difference across the windings Wz and WN, i.e. f / An t / At /, etc. The form of the phase voltage has an improved spectral composition - does not contain third and multiples of three harmonics.

The volume occupied by the winding is small, since it flows only around the unbalance current of the inverter loads.

If the converter cells of the circuit in FIG. 1 is made according to a bridge circuit, then the voltages of both A and B and L / C can be formed in the form of rectangles 150 wide in width. hail. (see Fig. 4). At the same time, the phase voltage has a three-step form, in which the third and multiple harmonics are absent and the 5- and 7-harmonics are significantly (3.73 times) reduced. This further reduces the weight and size of the output filter of the inverter. Performing a common winding Wff (see Fig. 2) reduces the weight of copper and the number of output terminals of the transformers. It is especially convenient to perform a common winding WN with toroidal cores of transformers.

invention formula

Claims (3)

1. A three-phase inverter for supplying a zero-output load, containing phase transformers, the primary windings of which are included in the output circuits of controllable valve cells, and the secondary ones are connected in star and connected to a load circuit, characterized in that, in order to improve the output voltage waveform , on the cores of transformers additional windings are included, connected between the star zero point and the zero output of the load circuit. 2. The inverter according to claim 1, characterized in that the additional windings are located on the core of the transformer of each phase and are connected together in a coherent manner. 3. The inverter according to claim 1, characterized in that the circuit formed by the additional windings covers the cores of all transformers. Information sources, taken into account in the examination 1. US patent number 3448366, CL. 321-5, 1969. 2. US patent number 3767996, cl. 321-9A, 1973. 3. Moin V.S. and Laptev N.N. Stabilized, bath transistor converters. M., “Energy, p. 154, fig. 5-18. Fig.Z II A U U U LT /.  . H / . H fchg