JPH0795796A - Motor current detecting equipment - Google Patents

Abstract

PURPOSE:To detect with high accuracy driving current, which is chopper- controlled and flows from power supply to motor, and regenerative current, which flows from motor to power supply. CONSTITUTION:The motor current detecting equipment includes a shunt resistance Rs through which driving current If, flowing from a battery B to a motor M, and regenerative current Ir, flowing from the motor M to the battery B, are passed; an operational amplifier OP1 to which voltage produced in the shunt resistance Rs is to be input; and another operational amplifier OP2 to which the output voltage of the operational amplifier OP1 is to be input through a diode D6. The gain of the operational amplifier OP1 is equalized with that of the operational amplifier OP2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a motor current detecting device applicable to, for example, an electric power steering device in which a steering force of steering wheels of an automobile is assisted by a motor.

[0002]

2. Description of the Related Art Steering torque applied to steered wheels is detected, and a motor drive current determined in accordance with the detected torque is
An electric power steering device has been developed in which a direct current motor that assists the steering force is driven to drive the direct current motor, and the rotational force thereof assists the steering force.

A conventional motor current detecting device applied to such an electric power steering device is disclosed in, for example, Japanese Patent Application Laid-Open No. 4-
No. 251596. FIG. 5 is a schematic block diagram showing the configurations of a motor drive circuit and a motor current detection circuit in the electric power steering device. The positive electrode of the battery 48, whose negative electrode is grounded, is connected to the contact 49 of the relay,
It is grounded through a series circuit of a shunt resistor Rs for current detection and a motor drive circuit 47 in which switching elements 1UL, 1LL, 1UR, 1LR composed of FETs are bridge-connected. The motor drive circuit 47 is configured by connecting a series circuit of switch elements 1UL and 1LL and a series circuit of switch elements 1UR and 1LR in parallel. The DC motor 10 is interposed between the connection between the switch elements 1UL and 1LL and the connection between the switch elements 1UR and 1LR.

One terminal of the shunt resistor Rs has a positive input terminal + of the differential circuit 51 via the resistor Ra, a positive input terminal + of the differential circuit 52 via the resistor Re, and a differential input via the resistor Rf. It is connected to the negative input terminal-of the circuit 52. The other terminal of the resistor Rs is connected to the negative input terminal-of the differential circuit 51 via the resistor Rb. The positive input terminal + of the differential circuit 51 (52) is a resistor Rc.
It is connected to a predetermined power source Vr via (Rg). The negative input terminal-of the differential circuit 51 (52) is connected to its output terminal via the resistor Rd (Rh). The output terminal of the differential circuit 51 is connected to the negative input terminal − of the comparator 53 via the resistor Ri, and the output terminal of the differential circuit 52 is connected to the positive input terminal + of the comparator 53 via the resistor Rj.

The negative input terminal-of the comparator 53 has a resistor R
It is connected to its output terminal via a series circuit of k and the diode D ₁ . A diode D ₂ having a cathode connected to the negative input terminal − is interposed between the output terminal of the comparator 53 and the negative input terminal −. The connection between the resistor Rk and the anode of the diode D ₁ is connected to the predetermined power source Vr via the resistor Rl and grounded via the capacitor C ₁ . Constitute a peak hold circuit 54 by and resistance Rl and the capacitor C ₁ and. In addition, the differential circuit 51,52,
The motor current detection circuit 50 is configured by the comparator 53 and the peak hold circuit 54.

Next, the operations of the motor drive circuit 47 and the motor current detection circuit 50 will be described. When the motor 10 is rotated in the forward direction, the switching element 1UR and
1LL is turned off. And switch elements 1UL and 1LR
Is turned on while the PWM signal given from the gate drive circuit (not shown) is at H level, and turned off while the PWM signal is at L level. PWM that rotates the motor 10 forward
While the signal is at H level, the motor drive current flows through the shunt resistor Rs, the switch element 1UL, the motor 10 and the switch element 1LR. Also, while the PWM signal is at L level,
A regenerative current flows through the motor 10, the diode included in the switch element 1UR, the shunt resistor Rs, the relay contact 49, the battery 48, and the diode included in the switch element 1LL.

The voltage at both terminals of the shunt resistor Rs is detected by the differential circuit 51. The voltage detected by the differential circuit 51 is input to the negative input terminal-of the comparator 53 and half-wave rectified. The differential circuit 52 compensates the offset voltage generated by the differential circuit 51 and the comparator 53. The voltage across the shunt resistor Rs half-wave rectified by the comparator 53 is given to the peak hold circuit 54 and held there. The output voltage V of the peak hold circuit 54 represents the current of the motor 10. Then, the current flowing through the motor 10 when the switch element is on and the current flowing through the motor 10 when the switch element is off are detected from the voltage across the shunt resistor Rs.

[0008]

As described above, the motor current detection device in the conventional electric power steering system has a peak detection voltage corresponding to the motor drive current flowing from the battery through the motor during the ON period of the switch element. Since it is output from the hold circuit, the accuracy of detecting the motor current is low, and the rotational force of the motor cannot be controlled with high accuracy by the detected voltage. Further, it is necessary to include the peak hold circuit, the offset voltage compensation circuit, and the differential circuit, which causes a problem that the circuit becomes complicated and becomes large in size.

In view of such a problem, the present invention provides a motor current detecting device which can detect both the motor drive current flowing from the battery to the motor and the regenerative current flowing from the motor to the battery with high accuracy and which can be constructed by a simple circuit. The purpose is to do.

[0010]

A motor current detecting device according to the present invention is a motor current detecting device for detecting a current of a motor driven by a chopper control of a motor drive circuit connected to a power source. A first current detecting means for detecting a current flowing to the motor; and a second current detecting means for detecting a current flowing from the motor to the power supply,
It is characterized in that the first current detection means and the second current detection means have the same gain.

[0011]

[Operation] When the motor drive current flows from the power supply to the motor,
The first current detection means and the second current detection means perform a non-inverting amplification operation as a whole, and the gain thereof is 1 + {(R ₂ + R ₃ ) /
R ₁ }. When regenerative current flows from the motor to the power supply,
The first current detection means operates as a buffer, the second current detection means performs an inverting amplification operation, and the gain thereof is − (R ₃ /
R ₂ ). The absolute value of the gain of the motor drive current and the regenerative current is 1 + {(R ₂ + R ₃ ) / R ₁ } = (R ₃
/ R ₂ ) is established, and the regenerative current is detected with the same accuracy as the motor drive current (however, R ₁ , R ₂ and R ₃ are resistance values). As a result, the motor drive current and the regenerative current can be detected with high accuracy using a simple circuit.

[0012]

The present invention will be described in detail below with reference to the drawings showing the embodiments thereof. FIG. 1 is a block diagram showing the configuration of a motor current detection device of an electric power steering device according to the present invention. The positive electrode of battery B with its negative electrode grounded is the FET
Is connected to one side terminal P of a motor drive circuit MD in which switching elements S ₁ , S ₂ , S ₃ and S ₄ are connected, and the other side terminal Q is grounded via a shunt resistor Rs for current detection. It is grounded. The motor drive circuit MD is configured by connecting a series circuit of switch elements S ₁ and S _{3 and} a series circuit of switch elements S ₂ and S ₄ in parallel.

A PWM (pulse width modulation) voltage for chopper controlling the switch elements is applied to the gates of the switch elements S ₁ , S ₂ , S ₃ , S ₄ from a gate control circuit (not shown). A direct current motor (hereinafter referred to as a motor) M is interposed between a connection portion between the switch elements S ₁ and S ₃ and a connection portion between the switch elements S ₂ and S _4, and the switch elements S ₁ , is rotated forward the motor M by turning on the S _4, and is adapted to reverse the motor M by turning on the device element S _2, S _3.

The connection between the shunt resistor Rs and the other terminal Q of the motor drive circuit MD is connected to the non-inverting input terminal + of the operational amplifier OP ₁ which is the first current detecting means via the resistor R ₀ . The inverting input terminal − of the operational amplifier OP ₁ has a resistor R ₁
Is connected to the output terminal through a diode D ₅ whose anode is connected to the inverting input terminal −. The output terminal of the operational amplifier OP ₁ is connected to the non-inverting input terminal + of the operational amplifier OP ₂ which is the second current detecting means via the diode D ₆ having the anode connected to the non-inverting input terminal +. It is grounded via R ₄ .

The inverting input terminal-of the operational amplifier OP ₂ has a resistance R
_It is connected to the inverting input terminal − of the operational amplifier OP ₁ via _{2 and to} the output terminal of the operational amplifier OP ₂ via the resistor R ₃ . The output voltage Vo, which is the detected value of the motor drive current and the regenerative current flowing through the motor M, is output from the output terminal of the operational amplifier OP ₂ . In addition, parasitic diodes D ₁₁ , D ₁₂ , D ₁₃ , and D ₁₄ exist in the switch elements S ₁ , S ₂ , S ₃ , and S ₄ .

Next, the operation of the motor current detecting device configured as described above will be described. Now, the gate of the switching element S _1, S _4, the switch element S _1, S ₄ gives PWM voltages chopper control is turned on, the switch element S ₁ from the battery B, the motor M, the switch element S ₄ and the shunt resistance A motor drive current If indicated by a solid arrow flows through Rs. Further, while the switch elements S ₁ and S ₄ are off, the shunt resistance Rs, the parasitic diode D ₁₃ of the switch element S ₃ , the motor M, and the parasitic diode D of the switch element S ₂ are generated by the energy stored in the inductance of the motor. ₁₂ through to battery B, regenerative current I indicated by broken line arrow
r flows.

As a result, the shunt resistor Rs has an operational amplifier OP corresponding to the motor drive current If and the regenerative current Ir.
Input voltage Vi which should be input to ₁ is generated and operational amplifier OP ₁
Is input to the non-inverting input terminal + of. Then, the input voltage V generated in the shunt resistor Rs by the motor drive current If
i is Vi = If.multidot.Rs.gtoreq.0 (1), and the input voltage Vi generated in the shunt resistor Rs by the regenerative current Ir is Vi = -Ir.multidot.Rs <0 (2).

In this way, when the motor drive current is chopper controlled, bidirectional currents indicated by solid line arrows and broken line arrows flow in the shunt resistor Rs, so that these currents are detected with the same accuracy. , the gain 1 + operational amplifier _{OP 1 {(R 2 + R} 3) / R 1} and the operational amplifier OP ₂ gain (R ₃ / R ₂₎ and a _{1 + {(R 2 + R} 3) /
It is necessary to satisfy R ₁ } = (R ₃ / R ₂ ).

When the motor drive current If is flowing and the input voltage Vi is Vi ≧ 0, the motor current detection circuit operates as the circuit shown in FIG. 2 because the diode D ₅ becomes non-conductive. The operational amplifiers OP ₁ and OP ₂ collectively perform one non-inverting amplification operation. Then, the current i flowing through the resistor R _2
1 is i ₁ = (Vi / R ₁ ) = {(Vo −Vi) / (R ₂ + R ₃ )} (3) {Vo / (R ₂ + R ₃ )} = {Vi / (R ₂ + R) ₃ )} + (Vi / R ₁ ) ... (4), and Vo = [{1 + {(R ₂ + R ₃ ) / R ₁ }] · Vi ... (5), and the gain G is G = {. 1 + {(R ₂ + R ₃ ) / R ₁ } (6)

Next, the regenerative current Ir flows and the input voltage V
When i is Vi ≦ 0, the motor current detection circuit operates as the circuit shown in FIG. 3 because the diode D ₆ is non-conductive, and the operational amplifier OP ₁ serves as a buffer and the operational amplifier OP ₂ serves as a buffer.
Performs an inverting amplification operation using the input voltage Vi as an input. The resistor R ₂ current i ₂ flowing through _{the, i 2 = (- Vi)} / R 2 = Vo / R 3 ... (7) , and the output voltage Vo is _{Vo = - (R 3 / R} 2) · Vi> 0 … (8). Whereby the gain G of the operational amplifier OP ₂ is, G = - a _{(R 3 / R 2) ...} (9).

Thus, in the motor current detection circuit, [1 + {(R ₂ + R ₃ ) / R ₁ } for equalizing the absolute values of the bidirectional current gains of the motor drive current If and the regenerative current Ir. ] = (R ₃ / R ₂ ) is established. As a result, the motor drive current If and the regenerative current Ir can be detected with the same accuracy. Similar effects can be obtained by using analog switches for the diodes D ₅ and D ₆ and turning them on and off.

FIG. 4 is a block diagram showing the configuration of another embodiment of the motor current detecting device according to the present invention. The positive electrode of the battery B whose negative electrode is grounded is connected to one terminal P of the motor drive circuit MD via a shunt resistor Rs.
One terminal of the shunt resistor Rs is connected to the non-inverting input terminal + of the operational amplifier OP ₁ via the resistor R ₂₀ , and the non-inverting input terminal + is grounded via the resistor R ₂₁ . The other terminal of the shunt resistor Rs is connected to the operational amplifier OP via the resistor R _22.
1 is connected to the inverting input terminal-and the inverting input terminal-
Is connected to its output terminal via a resistor R ₂₃ .

The output terminal of the operational amplifier OP ₁ is connected to the inverting input terminal − of the operational amplifier OP ₂ via the resistor R ₂₄ , and is connected to the non-inverting input terminal + of the operational amplifier OP ₂ via the resistor R ₂₅ . Inverting input terminal of the operational amplifier OP ₂ - it is connected to the output terminal via a resistor R _26, and outputs an output voltage Vo corresponding to the motor drive current and regenerative current from the output terminal. The non-inverting input terminal + of the operational amplifier OP ₂ is grounded via the analog switch ASW. The analog switch ASW is supplied with an on / off signal S corresponding to the motor drive current and the regenerative current. In this motor current detecting device, the operational amplifier OP ₁ operates as a differential amplifier circuit, and the operational amplifier OP ₂ performs full-wave rectification of the input voltage Vi ′ input to the operational amplifier OP ₂ by turning on / off the analog switch ASW.

When a current is flowing from the battery B to the motor drive circuit MD, that is, when the voltage Vi 'input to the operational amplifier OP ₂ is Vi'≥0, the analog switch ASW is turned off. Then, the output voltage Vo is Vo =
Vi '.

On the other hand, when the regenerative current is flowing from the motor drive circuit MD to the battery B, that is, when Vi '<0, the analog switch ASW is turned on. Therefore Vo =
The -vi '(provided that when R ₂₄ = R _26). In this way, the bidirectional current flowing through the shunt resistor Rs can be detected as the corresponding output voltage Vo.

Although the present embodiment has been described with respect to the case of the electric power steering apparatus, it is needless to say that the same effect can be obtained even in a DC motor used for other purposes.

[0027]

As described above in detail, according to the present invention, both the motor drive current flowing from the power source to the motor and the regenerative current flowing from the motor to the power source can be detected with high accuracy. Further, since the peak hold circuit and the offset voltage compensating circuit which are required in the related art are not required, the circuit is extremely simple and can be miniaturized.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a motor current detection device according to the present invention.

FIG. 2 is an operation explanatory diagram of an operational amplifier when a motor drive current is detected.

FIG. 3 is an operation explanatory diagram of an operational amplifier when detecting a regenerative current.

FIG. 4 is a block diagram showing the configuration of another embodiment of the motor current detection device.

FIG. 5 is a block diagram showing a conventional motor current detection device in an electric power steering device together with a motor drive circuit.

[Explanation of symbols] Rs shunt resistance D ₅ , D ₆ diode OP ₁ , OP ₂ operational amplifier M DC motor B battery S _{1 to} S ₄ switch element

Claims (5)

[Claims] 1. A motor current detection device for detecting a current of a motor in which a motor drive circuit connected to a power supply is driven by chopper control, and a first current detection means for detecting a current flowing from the power supply to the motor, A motor current detection device comprising: a second current detection means for detecting a current flowing from a motor to a power supply, wherein the first current detection means and the second current detection means have the same gain. 2. The motor current detection device according to claim 1, wherein operational amplifiers are used for the first current detection means and the second current detection means. 3. The motor current detection device according to claim 1, wherein the detection output of the first current detection means is configured to be input to the second current detection means via a diode. 4. The motor current detection device according to claim 1, wherein the gains of the first current detection means and the second current detection means are determined by a resistance value of a resistor connected to an operational amplifier. 5. The motor current according to claim 1, wherein the input terminal of the second current detection means is grounded through an opening / closing means that opens / closes according to a current flowing from the power source to the motor and a current flowing from the motor to the power source. Detection device.