SU1679618A1 - Inverter phase switch - Google Patents

Description

The invention relates to power switching technology and allows you to increase the efficiency of the switch while simplifying it due to the fact that between the second terminals of the transistor switches 1, 2 parallel to the current-limiting chokes 5.6 are formed by additional diodes 7, 8 and 9 two chains, the diodes of which are included opposite in relation to the direction of the power source. In the first chain, a high-speed power diode 7 is used, in the second - pulsed diodes 8 and 9. The common point of the two diodes of the second chain is connected to the midpoint of a capacitive divider formed by shunt capacitors 10, 11 and connected between the tires of the power source. 3 il.

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The invention relates to a power switching technology and can be used in inverters of AC and DC drives, built on power transistors operating in the mode of pulse-width modulation.

The aim of the invention is to increase the efficiency of the switch and its simplification.

FIG. 1 is a circuit diagram of a switch; in fig. 2 and 3 are timing diagrams explaining the operation of the device.

The inverter phase switch contains two power transistor switches 1 and 2. The first switch 1, eashuntied by the power diode 3, is connected to the positive side of the power supply source by a collector circuit. A key 2, eashunted by a power diode 4. The emitter circuit is connected to the negative bus of the power source. Between the second terminals of the keys 1 and 2 and the switch output are included, respectively, the current-limiting chokes 5 and 6.

In the first diode chain connected in parallel to the chokes 5 and 6, one high-speed power diode 7 is used, in the second diode chain - pulsed diodes 8 and 9, the common point of which is connected to the common point of the capacitive divider on the high-frequency shunt capacitors 10 and 11 connected between the buses power supply. In the inverter (FIG. 1) there may be three switches (or more) if an AC motor or a valve motor is used, or two switches if a DC motor is used, which is adjustable from a bridge inverter.

The phase switch of the inverter operates as follows.

Consider, for example, the operation of a switch for the direction of current Ts. For the opposite direction of current 1g, everything happens in a similar way. Let the initial state correspond to the disabled key 1. There may be two cases. In one of them, by the time key 1 is turned on, the load current I flows only through the inductor 6 and the closing diode 4 (FIGS. 1 and 2). In another case (Fig. 3), at the moment of switching on the key 1, the load current 1.1 flows through two parallel circuits: across the choke 6 and across the choke 5 and the diode 7, and both components are summed up in the closing diode 4. The switching processes in the first case proceed as follows . At the moment Xo, a signal is given to turn on the power transistor

key 1 (Fig. 2a) and the key is turned on, the voltage of the 11ke of the power transistor decreases from the value of E _P qt to the value of 11 ke of us (fig. 26) and the rise of the collector current 1 _{to the} key 1 (fig. 2c), throttle 5 (fig. 2g) and a corresponding decrease in the current of the choke 6 (Fig. 2 h). The current through the closing choke 4 decreases (Fig. 2d).

At the moment of time Ho the key 1 and the current of the inductor 5, changing synchronously, become equal to the load current, and the currents of the inductor 6 and the closing diode 4 decrease to zero. Further, the current in the diode 4 changes direction to the opposite (Fig. 2d) and increases in the opposite direction.

Thus, the current in the inductor 6 also changes.

At the 8th instant of time x2, excess charges are absorbed at the base near the transition boundary of diode 4, and the current of the diode rapidly drops to zero. The potential build-up on diode 4 begins, therefore, the current of the inductor 6 begins to flow through diode 9 and recharge the capacitors 10 and 11. Moreover, the voltage on the capacitor 11 increases, and on the capacitor 10 decreases accordingly. The capacitor overcharge current (Fig. 2e), by throwing (by the magnitude of the reverse Current decay through diode 4), increases from zero and then varies sinusoidally upwards. The currents of key 1 and chokes 5 and 6 change accordingly. At time xs, capacitors 10 and 11 completely recharge, and the recharge current drops sharply to zero. The key current 1 decreases by the same amount. The current of the chokes 5 and 6 from this moment decreases synchronously in magnitude and by the time X4 the current of the choke 5 becomes equal to the load current, and the current of the choke 6 decreases to zero. The time moment X5 is the moment of the end of the control impulse and the cessation of the current through the switch 1. From this moment begins the increase in voltage Q _K e 1 (Fig. 26) and the corresponding decrease in voltage at the output of the circuit. The capacitors 10 and 11 are recharged by the load current in the opposite direction to the initial charging current (Fig. 2e). After the end of capacitor overcharge (xe), choke current 5 begins to flow through diode 7 and diode 4. From this point on, currents are redistributed between chokes 5 and 6. Choke current 5 decreases from a value equal to the load current to zero, and choke current 6 changes in antiphase - from 0 to the load current.

At the time χγ, all transitional

processes at shutdown end.

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The next cycle proceeds in a similar way. A similar course of transients is characteristic of classical schemes, the condition for the functioning of which is the complete completion of transients to the next cycle. In such schemes, the energy stored in the current-limiting chokes must be completely dissipated either inside the circuit or transferred to an external energy receiver. In the second case, with a high efficiency of the energy receiver, the efficiency of the entire cascade may also increase. If the energy receiver is resistive, the cascade efficiency is determined only by the level of losses determined by the amount of energy stored in the current-limiting chokes and the switching frequency of the power switches. The second mode of operation differs from the classical one in that by the time the key was turned on, the transients in the current-limiting chokes were not yet completed.

The specific level of losses, referred to the unit of power, at a fixed switching frequency can significantly decrease as compared with the first case, but the requirements for the power elements are higher here. So diode 7 should have a high speed. The diagrams corresponding to this case are shown in FIG. 3. A characteristic feature of this mode is that when the transistor switch 1 is turned on, a characteristic surge is observed at its current diagram at the time point z corresponding to the closing moment of diode 7. ' In order to reduce the losses at switching on, this power diode must be fast-acting with respect to the closing diodes 3 and 4. Further, the processes are basically the same as in the previous case.

Achieving a positive effect is provided by a significant simplification of the device, while acceptable conditions are met for switching the power switches for all switch operation modes and at the same time increasing the switch efficiency, which is provided both by eliminating resistive elements from the recharging circuit of reactive elements and using the second mode shown in FIG. 3

Claims (1)

Claim An inverter phase switch containing two transistor switches shunted by counter-connected corresponding diodes, shunt capacitors and additional diodes, the first terminals of the transistor switches connected to the positive and negative power supply buses, the second terminals of the transistor switches are connected to the output of the phase switch, respectively Inverter, characterized in that, in order to increase efficiency and simplify, between the second terminals of the transistor the keys in parallel with the current-limiting chokes include two chains, one of which contains <one additional diode and the other two series-connected additional diodes, with the indicated diodes opposed to the direction of the power source, the common connection point of the two additional diodes is connected to the midpoint connections of the first terminals of the shunt capacitors, the second terminals of which are connected to the corresponding power supply buses. 1679618