SU577626A1 - Transformerless inverter - Google Patents

Description

one

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

Inverters on key elements are known that are used to obtain a stepwise (close to sinusoidal) shape of the output voltage curve 1, 2, 3.

The closest to the invention proposed is an inverter made according to a bridge or half bridge circuit and powered from a source having intermediate leads connected via additional key elements.

The purpose of the invention is to reduce the voltage applied to the key elements while maintaining their total quantity and, consequently, increasing reliability.

This is achieved by the fact that each half-bridge arm is made of at least two serially connected main control keys, the connection point of which is connected to the corresponding power supply outlet through one of the additional control keys that are dioded in the opposite direction.

Figure 1 shows a diagram of a transformerless inverter in figure 2 shows the sequence of switching transistors in this circuit.

The inverter contains a chain of four consistently connected main controlled switches (transistors) 1,2,3,4, shunted by return diodes 5,6,7,8 and forming a half bridge. The intermediate points of this chain are connected via additional controlled keys (transistors) 9 and 10, shunted by diodes 11 and 12, with power supply taps. The switching sequence of the transistors in this circuit is shown in Fig. 2 to obtain the voltage UJ B of the transistors 1-4 to form a half-bridge, which, together with the capacitors

13 and 14 form a bridge, in the diagonal of which the load 15 is included.

The voltage tlj of the inverter power is applied to two OCHOBHte i transistors 1 and 2 or 3 and 4 connected in series, and to transistors 1

or 4, a voltage greater than the voltage Uj (U),) I cannot be applied, since otherwise a diode 11 or 12 is opened. For a better voltage distribution, transistors 9 (10) can also be opened.

A voltage is applied to transistors 9 and 10 as closely as possible to voltage Us, {Ui,). Consequently, in the proposed circuit, the transistors are applied voltage (almost twice) less than in the known one. Thanks to this, the reliability of the inverter operation (the margin of breakdown and peak power during the switching process increases) and its cost decreases the ability to use lower voltage and therefore cheaper transistors. The number of elements (transistors and diodes) in the known and proposed schemes are the same.

To obtain a three-phase inverter, three half bridges (see Fig. 1) are used, connected in parallel to the power supply circuits and controlled with a mutual offset of 120 °. If the power supply taps are performed with a ratio of 0.268 Ui, a three-step linear voltage form with a distortion coefficient of 16% and the highest of the 11th harmonics is 9%.

Claims (3)

1. Author's testimony of the USSR No. 260729, cl. H 02 M 7/52, 1967. 2. USSR author's certificate No. 316162, cl. H 02 M 7/52, 1970. 3. US patent 3391323, cl. 3121-5, 1968. / CV