SU1651218A1 - Pickup of load current of bridge inverter - Google Patents

Abstract

The invention relates to a converter technique and can be used in AC electric drives with frequency-current control to control the load current. In order to increase the accuracy of the conversion in the low-current region in the asymmetrical switching mode, the I7 key and the logical block 16 are entered into it. The signals of the control unit 15 close the keys 1-4 of the bridge inverter 9 so that it can be symmetrical (the keys 1, 4 or 2 are closed and 3) or unbalanced load operation mode 11. In symmetric mode, the current flows through only one of the shunts (12 or 14), in the asymmetrical mode (either key 3 or 4 is closed), the current of power supply 10 flows through both shunts simultaneously, therefore the key 17 block 16 in this section In this case, the operational amplifier 20 with resistors 13, 18, 19, and 2 converts the signal of shunt 12 only. Diodes 5–8 protect the bridge inverter 9, 2, or 6 volts. I

Description

The invention relates to a converter technique and can be used in AC electric drives with frequency-current control to control the load current.

The aim of the invention is to improve the accuracy of conversion in the field of small currents in the asymmetrical switching mode.

Fig, 1 shows a block diagram of the current sensor; figure 2 is an embodiment of a logical block.

, The current sensor contains keys 1-4 and diodes 5-8, which form a bridge inverter H, with the first conclusions

keys 1 and 2 and the cathodes of diodes 5 and 6 are combined and connected to the positive terminal 10 of the power supply, the negative terminal of which is connected. with the bus, the second output of key 1 is connected to the anode and cathode of diodes 5 and 7, respectively, and the first outputs of key 3 and load 11, the second output of load 11 is connected to the second output of key 2, the first output of key 4 and the anode and cathode of diode 6 and 8 respectively, the anode of the diode 7 is connected to the second output of the key 3, the first output of the shunt 12 and the first output of the resistor 13, the first output of the shunt 14

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connected to the anode of the diode 8 and the second output of the key 4, the second outputs of the shunts 12 and 14 are combined and connected to the common bus, the four outputs of the control unit 15 are connected to the corresponding control inputs of the keys 1-4 and the inputs of the logic unit 16, the output of which is connected to the control Key 17, the first terminal of the shunt 14 is connected to the first terminal of the resistor 18, the second terminal of the resistor 13 is connected to the second terminal of the resistor 19 and the inverting input of the operational amplifier 20, the non-inverting input of which is connected to the first terminals of the resistor 21 and the key and 17 and the second terminal of the resistor 18, the output of the operational amplifier 20 is connected to the first terminal of the 1H resistor and is the current sensor output 22, the second terminals of the resistor 21 and the switch 17 are connected to a common bus. Operational amplifier 20 and resistors 13, 18, 19 and 21 form the sum of the mountains.

Logic block 16 contains the elements OR NOT 24-26 and the inverter 27, wherein the two inputs of the element OR NOT 24 and the two inputs of the element TRI-NOT 5 are corresponding to the logic block 16, the output of which is the output of the element OR-NOT 26, whose char input is connected to the output of an OR-NOT 24 element, the output of an OR-NOT 25 element through an inverter 27 is connected to the second input of the OR-NOT 26 element.

The device works as follows.

The control unit 15 provides a symmetrical and asymmetrical mode of operation of the bridge inverter 9. With a symmetrical mode of operation, the rapid increase in the load current 13 reaches ™ with the closure of the keys J and 4, and the decay - with the closure of the keys 2 and 3. In both cases, the load current 11 flows through one of shunts 12 or 14. With an asymmetrical mode of operation, the flow of current in the positive direction is ensured by closing the key 4, - in negative - by closing the key 3. The load current then flows simultaneously in both shunts 12 and 14 (the currents in them are equal),

A high level of control signals from the outputs of the control unit 15 corresponds to a closed state

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keys 1–4 of the bridge inverter 9. the same applies to the output signal of logic unit 16, which ensures the closure of the key 17 while the load current 1 1 flows through shunts 12 and 14.

Suppose that switches 1 and 4 are closed, the current flows through only one of the shunts (through shunt 14), so the key 17 is open, the useful signal from the shunt 14 goes to resistor 18 and is outputted at output 22. At the input of resistor 13, zero signal.

If only key 4 is closed, the current flows through the load stored in load 11 (for example, in the inductance of an electric motor) through the circuit: load 11, key 4, shunts 12 and 14 (diode 7, second load terminal 11. Key 17 by logic block I6 with This is closed and there is no signal at the non-inverted input of opamp 20, so there is no error in the output signal.

If keys 2 and 3 are closed, current flows only through shunt 12, key

17 is open, but at the input of the resistor

18 zero signal.

If only key 3 is closed, then under the action of energy stored in load 11, the current flows again through shunts 12 and 14 at the same time, but key 17 is closed, therefore one

excluded from signals i

At the output of the OR-NOT 26 element, the control signal will be high only when both inputs are low at its inputs.

Claims (1)

Invention Formula ; The load current sensor of the bridge inverter, containing four keys, the first terminals of the first and second keys; whose combined and connected to the cathodes of the first and second diodes and the positive output of the power source, the negative output of which is connected to the common bus, the second output of the first key is connected to the first output of the third key, the anode and cathode of the first and third diodes, respectively, and the first load terminal, the second output which is connected to the anode by the cathode of the second and fourth 51 diodes respectively, the second output of the second key and the first output of the fourth key, the second output of the third key is connected to the anode of the third diode and the first output of the first shunt, four resistors and an operational amplifier, the non-inverting input of which is connected to the first output of the first resistor, the second output of which is connected to the common bus, the first output of the second resistor is the output of the current sensor and is connected to the output of the operational amplifier, the inverting input of which is connected to the second terminals of the second and third resistor a second fourth switch terminal is connected to the anode of the fourth diode and the first terminal of the second Gaunt, second terminals of the shunt are combined and connected to a common mud, control inputs of all Clue 0 21 five 86 whose connections are connected to the corresponding outputs of the control unit, which means that, in order to improve the accuracy of the conversion in the low-current region in the asymmetrical switching mode, a fifth key and a logic unit are added to the current sensor whose four inputs are connected to the corresponding outputs of the control unit, the output of the logic unit is connected to the control input of the fifth key, the first output of which is connected to the first output of the first resistor and the second output of the fourth resistor, the first outputs of the third and h tvertogo resistors are connected to first terminals of the first and second shunts respectively, the second terminal of the fifth switch is connected to the common bus. FIG. one FIG. 2