SU575751A1 - Transistor inverter - Google Patents

Description

(54) TRANSISTOR INVERTER

The invention relates to the field of technology converters and can be used in power supply and electric drive systems for transformerless conversion of high dc voltage to alternating voltage. Usually, bridge inverters powered by a high voltage (200-400 volts) use a series connection of transistors in each arm, which are switched synchronously under the action of the control voltage 1. The output voltage in such inverters is square and obtaining a sinusoid at the output includes a capacitor. In other bridge inverters with an improved qbopMoA output voltage curve, the output clips are connected to intermediate power supply taps via additional transistors and diodes 2. In these inverters, an increased voltage is applied to the transistors and they are closest to the invention. The purpose of the invention is to improve the spectral composition of the output voltage. This pell is achieved by the fact that the connection points of transistors connected in series in each arm of the inverter are connected via leads to an output for connecting the midpoint of the power source. FIG. 1 shows a transistor inverter circuit; FIG. 2 - diagrams of voltages on its main elements. The inverter consists of a three-phase bridge on transistors 1-12, in each arm of which two transistors are connected in series. The transistors are controlled from the master oscillator 13 through a control circuit 14. distributing and shaping the impulses ав ав av, 1 ни with the required duration and sequence shown in FIG. 2. The connection points of each pair of transuzzles through diodes 15-20 are connected to an output for connecting the midpoint of the inverter's power source (zero point source between these points in each; i.e. equalization resistors 21, 22 are turned on. 23. The circuit works as follows. The transistors switch in accordance with the timing diagram shown (for two phases) in Fig. 2 as voltages Ui - i8 (a solid line means the open state of the transistor.) Medium transistors 2–3, b – 7, 10–11 are open for 210 e. hail, and closed for 150 e. extreme

transistors, on the contrary, open 150 e. hail, and closed 210 e. hail.

In this order, the switching of transistors in the interval O-30 and 150-180 el. hail, when transistors 2 and 3 are open, the potential of the point “A relative to the point“ O is zero, and in the interval 30-150 el. degrees, when transistors 1 and 2 are open, this potential is equal to half the voltage of the power supply. Consequently, the voltage at the output terminal of the inverter relative to the zero point of the source has the form of a voltage U; yo and U go (Fig. 2), and the difference of these voltages forms a two-step linear output voltage,. The spectral composition of the voltage is significantly better than that of conventional three-phase bridge inverters, namely: the distortion coefficient is 18% instead of 32%, the harmonic is 5.5% instead of 20%, the seventh harmonic is 3.6% instead of 14%, and t .d ..

For operation on active-inductive load, the inverter, as in conventional circuits, has a reverse diode bridge (not shown in Fig. 1).

The voltage equalization at closed transistors is ensured by diodes 15-20 in cases when the reverse current of the extreme transistors is less than average, and the resistors 21, 22, 23 in the opposite case. In contrast to the prototype, the number of equalizing resistors is halved, and the power dissipated in them is reduced, since only the difference between the reverse current of the outer transistor and the middle transistor passes through the resistors 21, 22, 23.

In addition to the one shown in FIG. 1 voltage equalization by resistors can

all other known methods and schemes are used.

To further improve the shape of the output voltage curve, it is proposed to introduce an additional converter cell, the secondary windings of the output transformer 24 of which are connected in series with the extreme transistors. The voltage on these windings is chosen to be 0.0386 Ur, where Un is the supply voltage, and has a sixfold frequency, due to the switching of cell transistors 25-28 at that frequency.

The voltages and phi are modulated at the top, and the voltage. B becomes three-step (see dashed line in Fig. 2), has a SOI of 15.5 and it completely excludes the fifth, the seventh, the seventeen, nineteen-thirteen, etc. harmonics.

Claims (2)

1. FRG, patent .Vo 1244941, class 21 d2 12/03, 1960. 2. United States, patent Nb 339123, class. 321-5. 1965. ABOUT & ig. one lv h f B rf 7 t  g