JPH01126197A - Current detecting circuit for inverter device - Google Patents

Abstract

PURPOSE:To simplify a current detecting circuit and lower a cost, by switching the polarities of the current signals of respective arms based on the rotor position signal of a motor, and by detecting the respective phase current values of the motor. CONSTITUTION:By current detecting resistors 51, 52, 53, each current flowing to U, V, W-phases is detected as voltage signal, and the input of the current to the input terminals X, Y, Z of respective analog SW 71, 72, 73 is provided. The input of respective rotor position signals S, T, R to the respective control terminals A, B, C of the analog SW is provided. Then, the polarities of the current signals of respective arms are switched based on the rotor position signals S, T, R of a motor. By using inversion buffers 81, 82, a differential amplifier 84, and a buffer 83, and by taking the arithmetic sum of current signals, the respective phase current values of the motor are detected.

Description

[Detailed description of the invention] a. Industrial application field The present invention relates to a current detection circuit of an inverter device.

b. Prior Art The conventional technology will be explained using a three-phase inverter device using MOSFETs that controls a three-phase motor as an example.

FIG. 3 is an example of a circuit diagram showing the configuration of a conventional three-phase inverter device, which includes a DC main taIt, six switching elements 1) to 16.3-phase motors U and V.

It is composed of three loads 41, 42.43 and three current detection circuits 31, 32.33 corresponding to the W winding.

In this inverter device, in order to control the speed of the motor, it is necessary to control the current flowing through the motor, and therefore it is necessary to detect the current of each phase of the motor. The phase current Iu,
Iv and Iw are detected.

C0 Problems to be Solved by the Invention However, the current detection means in the conventional example has the following drawbacks. That is, since there is a large potential difference between the GND of the current detection section and the GN[l level of the current control circuit, these two circuits cannot be directly connected and must be electrically isolated. For this reason, an isolated amplifier was required, which was a major obstacle to making the device smaller and cheaper.
In view of this point, it is an object of the present invention to simplify the current detection circuit and thereby provide a small and inexpensive current detection circuit without using an isolated current detection circuit.

d. Means for solving the problem The above problem can be solved by using a DC main ta and a first ta connected in parallel to the DC main power supply. Second. a third switching circuit, an R signal and an S signal, which are signals corresponding to the motor rotation angle, have a period of 2π electrical angle, and have a mutual phase difference of π/3;
an encoder that generates a T signal, the R signal, the S signal,
The first signal is synchronized with the T signal. Second. In the current detection circuit of the inverter device for a three-phase motor, the current detection circuit includes a control circuit that sequentially controls the third switching circuit on and off. The first, second, . Third
a current detection resistor, an output terminal that conducts with the input side when the control signal is "L", and an H output terminal that conducts with the input side when the control signal is "H", and the input terminal is connected to the input side. 1. Second
．． The first . Second. a third single-pole double-throw switch; and a third single-pole double-throw switch; a first addition circuit that adds the output of the output terminal of the third single-pole double-throw switch and the output of the H output terminal of the second single-pole double-throw switch; a second adder circuit that adds the output of the H output terminal of the switch and the output of the second output terminal of the single-pole double-throw switch; and a second adder circuit that adds the output of the H output terminal of the switch and the output of the second adder circuit; 2
A subtraction circuit as an input, and the above-mentioned 1. Second. The above R signal and T signal are respectively applied to the control terminal of the third single-pole double-throw switch.

The problem has been solved by a current detection circuit for an inverter device, which is connected to the S signal and detects the output of the subtraction circuit as the inverter current.

For example, power? In an inverter device using l05FET, the power MOS of the switching element group (hereinafter referred to as lower arm) connected to the GND side of the inverter
A current detection resistor is inserted into each phase between the source terminal of the FET and GND, and the current signal of each phase is input to an analog circuit that is switched by the R, S, and T signals, which are the motor rotor position signals. .

This analog sh has one input circuit and two output circuits, an H terminal and an L terminal.
Or L#A child is selected. U phase terminal, ■ phase H
The terminal and the L terminal of the W phase are connected together and inputted to the inverting input terminal of the differential amplifier via a buffer. Similarly, the H terminal of the U phase, the L terminal of the ■ phase, and the H#i terminal of the W phase are connected together and inputted to the non-inverting terminal of the differential amplifier via a buffer.

The output voltage of this differential amplifier corresponds to the current signal, and the PII
It becomes the current feedback signal of the M current control circuit and is compared with the current command to determine PW? 'l pulse is generated.

d. Operation The present invention detects the three currents flowing through each arm of the inverter using a resistor, and determines the polarity of the current signal of each arm as the rotor position signal (R, S) of the motor.

T), and the current value of each phase of the motor is detected by calculating the arithmetic sum of the current signals.

Furthermore, since one end of the detection resistor is connected to GNfl of the inverter circuit, GND of the current detection circuit and GND of the current control circuit can be made to have the same potential.

f. Embodiment FIG. 1 is a circuit diagram of a preferred embodiment of a current detection circuit for an inverter device according to the present invention, and FIG. 2 shows temporal changes in signals at the main points in FIG. 1.

It should be noted that members with corresponding reference numbers in FIG. 1 and FIG. 3 are the same or corresponding members.

FIG. 1 shows a three-phase PWM inverter using MOSFETs.

The six MOSFET groups are alternately turned on and off in a predetermined excitation sequence by a rotor position signal from an encoder 60 attached to the motor 40.

As shown in FIG. 2, the rotor position signal is a signal R2 signal S having a period of electrical angle π and a mutual phase difference of π/3.
, signal T.

The MO on the same arm uses PWM pulse signals output from the current control circuit to control the current flowing to the motor.
3F [! T is turned on and off alternately in the PIIM period. Now, consider the case where current is caused to flow from the U phase to the V phase by an excitation sequence. At this time, due to the excitation sequence command, M
O3FE↑1) and 14 and MO3FET12 and 1
3 is alternately turned on and off by the PWM signal.

The on/off ratio changes depending on the magnitude of the current command given to the inverter, and in this case, MO5F[! On period of Tll and 14 is 12 and 1
The on period is longer than that of No. 3.

Current detection resistors 51, 5 with resistance values R51, R52, R53
2.53, currents 1u and Iv flowing in U, V, and W phases
, I- respectively as voltage signals 1u x R51,Iv
Detected as X R52, Iw
Enter Y and Z. Control terminals A, B, and C of this analog S- are connected to rotor position signals S, T, and R, respectively.

The outputs XI, YO, and ZO of the analog S- are connected together and input to an inverting buffer 81, which is an adder circuit at the next stage. On the other hand, the analog outputs XO, Yl, and Zl are also connected together and input to an inverting buffer 82, which is another adder circuit.

The output of the inverting buffer 81 is connected to the inverting input terminal of the next-stage differential amplifier 84, which is a subtraction circuit, and also to the inverting buffer 82.
The outputs of are each connected to a non-inverting input terminal. The result is
When i, YO, and ZO are selected, the polarity of the signal remains unchanged, and when XO, Yl, and Zl are selected, the signal polarity is inverted. Note that the output of the differential amplifier 84 may be used directly as the current signal, but there is no problem even if an appropriate buffer 83 is further connected.

The circuit that calculates the difference between the sum of the outputs of the three analog switches, H and L output terminals, and the sum of the outputs of the H, L and H output terminals is not limited to the above example, but can also combine multiple operational amplifier circuits. It can be realized by using known techniques or with a single operational amplifier circuit.

MO3FET II and 14 are now turned on by the PWM signal,? Considering the case where l05FETs 12 and 13 are off, this is set as mode 1. At this time, DCti! The current from MO3FE714. It passes through the resistor 52 and returns to the power supply.

On the other hand, no current flows in the W phase (during this period, MO5FE
T15 and T16 are off), the voltage Vlv generated across the resistor 52 at this time is VIv = Iv x R52.

By the way, in this case, the R, S, T signal beams, and L.

Since it is L, the output terminals of S are xo, yo, and zo, and the current output formula is 1out = [uxR51+(-1vXR52)"-I
Since it is expressed by the relational expression VXR52, it ends up being rout ” -1v X I?52, that is, the detection voltage VIu of Iu is
1 and then input to the inverting input terminal of the differential amplifier 84, so the sign is not inverted as a result. However, the detection voltage Vv of Iv is inverted by the buffer 82 and then input to the inverting input terminal of the differential amplifier 84. Since it is input to the terminal, the sign of this voltage Vv will be inverted as a result.

Further, in this mode, the current does not flow through the U-phase current detection resistor 51 and is detected only by the V-phase detection resistor 52, so that the polarity is reversed and finally detected.

Next, consider a case where MO3FETs 12 and 13 are turned on and MO3FETs II and 14 are turned off by the PWM signal, and this is set as mode 2. In this mode 2, the internal diode 92.93 of MO3FET 12.13 is turned on to maintain the current for a certain period of time for continuity of the motor current. In Iu, the current flow route is from the power supply GND to the resistor 51. MO5F! ! 712 internal diode 92. Pass through the U-phase coil to the neutral point, Iv is the V-phase coil, MO5F[! It circulates to the positive terminal of the power supply 1 via the internal diode 93 of T13.

In this case as well, no current flows in the W phase, and the current in this mode only flows in the U phase detection resistor 51, and the direction is opposite to Iv, resulting in Vlu = -1uxR51, and finally rout -Vlu --1u Further, the same can be considered in other excitation sequence modes.

g. Effects of the Invention Thus, according to the present invention, the following effects can be achieved, and it can greatly contribute to the field concerned.

1. Current detection can be easily and inexpensively performed using a resistor, analog or OP-amp.

2. The current flowing through the coil can always be detected in any mode of the inverter.

3. Since one end of the detection resistor is connected to the GND of the inverter device, the GND of the current detection circuit and the GND of the current control circuit can be made to have the same potential.

4. Even though the current route changes depending on whether PWM is turned on or off, current detection can be performed accurately and easily in any mode.

[Brief explanation of the drawing]

Figure 1 shows the current detection of the inverter device according to the present invention;
The figure shows an example of a current detection circuit for an inverter device according to the prior art. 1)-16...Power MO5FET. 31-33...Insulated current detection circuit, 40...Motor, 41-43...Motor winding, 51-5
3... Current detection resistor, 60... Encoder, 71-
73...Analog SW, 81-82...Inversion buffer, 83...Buffer, 84...Differential amplifier, 91-96...MO5FET built-in diode. Patent applicant: Oriental Motor Co., Ltd. (and 2 others)
given name)

Claims (3)

[Claims] (1) A DC main power supply, first, second, and third switching circuits connected in parallel to the DC main power supply, and a signal corresponding to the motor rotation angle with a period of 2π electrical angle. an encoder that sequentially generates an R signal, an S signal, and a T signal with a phase difference of π/3, and the first, second, and third switching circuits that sequentially operate in synchronization with the R signal, S signal, and T signal. In the current detection circuit of a three-phase motor inverter device including a control circuit that performs intermittent control, the first, second, and third
first, second, and third current detection resistors each provided in series with each switching circuit between the switching circuit and the ground point, and an L output terminal that conducts with the input side when the control signal is "L". and an H output terminal that is electrically connected to the input side when the control signal is "H", the input terminals of which are coupled to the switching circuit side terminal points of the first, second, and third current detection resistors, respectively. , add the outputs of the L output terminals of the second and third single-pole double-throw switches, the first and third single-pole double-throw switches, and the output of the H output terminal of the second single-pole double-throw switch. a first addition circuit; a second addition circuit that adds the outputs of the H output terminals of the first and third single-pole double-throw switches and the output of the L output terminal of the second single-pole double-throw switch; a subtraction circuit having two inputs, the output of the first addition circuit and the output of the second addition circuit, and the R signal applied to the control terminals of the first, second, and third single-pole double-throw switches, respectively A current detection circuit for an inverter device, wherein a T signal and an S signal are connected, and the output of the subtraction circuit is detected as an inverter current. (2) The first, second, and third switching circuits each consist of two MOSFETs connected in series, and M
A current detection circuit for an inverter device according to claim 1, wherein the midpoint of the OSFET is a circuit connected to a motor winding. (3) The current detection circuit for an inverter device according to claim (1), wherein the single-pole double-throw switch is an analog switch.