JP2001112286A - Current detection device for brushless dc motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To readily detect current flowing in a brushless DC motor, without having to utilize voltage drop in a resistor or a MOSFET provided in a current path. SOLUTION: A current detection circuit 20 consists of a computing circuit computing detected voltage Vo (Vo=VB-V1-V2), based on the neutral point voltage V1 of a motor 2 detected by three resistors RO, rotation proportional voltage V2 which is proportional to a rotational speed N of the motor 2, and power supply voltage VB for motor driving supplied to an inverter 6. The rotation proportional voltage V2 is set at V2=(k.Φ/2).N with the characteristics of an F/V converter 10, and the resistance values of resistors R4, R5 (where (k) is an electromotive force constant and Φ is a magnetic flux amount acting on the armature winding.). As a result, motor current can be detected without motor current being passed through a resistor, and moreover a current detection circuit can be formed more easily than in the case where motor current is detected by the on-voltage of FET which constitutes the inverter 6.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current detecting device for detecting a current flowing in a three-phase brushless DC motor in which armature windings are △ -connected.

[0002]

2. Description of the Related Art Conventionally, 3 armature windings are connected by △.
The drive device of the phase brushless DC motor is configured, for example, as shown in FIG. The drive device shown in FIG. 3 is provided with a permanent magnet on the rotor, and three-phase (U, V, W) armature windings 2U, 2V, 2W wound on the stator side. It is for driving a two-phase brushless DC motor (hereinafter simply referred to as a motor) 2, and as a drive circuit,
Three transistors TR for connecting the connection points between the armature windings of each phase of the motor 2 to the positive side of the DC power supply 4 respectively
1, TR2, TR3, and 3 for connecting the connection points of the armature windings of each phase to the negative electrode side of the DC power supply 4 respectively.
An inverter 6 including the transistors TR4, TR5, and TR6 is provided.

Further, the motor 2 is provided with a rotation sensor 8 for generating a detection signal Vθ synchronized with the rotation of the motor 2, and further, the frequency (F) of the detection signal Vθ from the rotation sensor 8 is converted to a voltage (V F / V converter 1 that generates a speed signal Vn representing the rotation speed of the motor 2 by converting
0 is provided. The detection signal Vθ from the rotation sensor 8 and the speed signal Vn generated by the F / V converter 10 are input to the control circuit 12 together with an externally input command signal indicating the target speed of the motor 2. .

The control circuit 12 switches the energization to each of the armature windings 2U, 2V, and 2W according to the rotational position of the motor 2 obtained from the detection signal Vθ from the rotation sensor 8, and also controls the armature winding 2U. , 2V, and 2W, the speed signal Vn from the F / V converter 10 is controlled.
Is used to control the actual rotation speed of the motor 2 obtained by the above to a target speed. Specifically, the on / off state of each of the transistors TR1 to TR6 constituting the inverter 6 is controlled. For example, when energizing the U-phase armature winding 2U, the transistor TR1 connected to one end of the armature winding 2U is turned on, and the transistor TR connected to the other end is turned on.
6. Pulse width modulation (PWM) according to the amount of current to be passed through 6
By turning on and off with the applied PWM signal, the amount of current flowing through the armature winding 2U is controlled.

As described above, in the brushless DC motor driving device, the current flowing through each of the armature windings 2U, 2V, and 2W is PWM-controlled to control the rotation speed of the motor 2 to the target speed. When the motor 2 is locked or when an abnormality such as disconnection or short circuit occurs on the motor 2 side, an overcurrent flows to the motor 2 side via the inverter 6 and the motor 2 or the inverter 6 may be burned. .

Therefore, conventionally, as shown in FIG. 3, a current (motor current) supplied to the motor 2 via the inverter 6 is detected on a current path between the DC power supply 4 and the inverter 6. Current detection resistor (shunt resistor) R
s is provided, and the control circuit 12 stops energizing the motor 2 (in other words, controlling the inverter 6) when the voltage drop at the current detection resistor Rs becomes equal to or greater than the set value for overcurrent detection. I am trying to do it.

[0007]

However, if the motor current is detected using the current detection resistor Rs provided in the current path between the DC power supply 4 and the inverter 6 as described above, the current detection resistor Rs , A power loss occurs in the current detection resistor Rs. If the resistance value is increased in order to increase the detection level of the motor current, there arises a problem that the power loss increases or the current detection resistor Rs generates heat.

On the other hand, as a method of detecting a motor current without providing a current detection resistor Rs on a current path through which the motor current flows, a switching transistor TR1 to TR6 constituting an inverter 6 includes a MOS transistor as shown in FIG.
It has also been considered that the motor current is detected by using a FET and detecting a drain-gate voltage (ON voltage) when the MOSFET is turned on.

That is, the armature windings 2U, 2
V, 2W include a transistor T constituting the inverter 6.
A current flows through R1 to TR6, and the on-voltage of the MOSFET is determined by the on-resistance of the MOSFET and the current flowing through the MOSFET.
By detecting the ON voltage, the motor current can be detected from the ON voltage.

However, in order to detect the motor current from the ON voltage of the MOSFET, the MOSFET whose ON voltage is to be detected must be switched in accordance with the rotation of the motor 2, and the MOSFET has a parasitic diode. The regenerative current flows through and the reverse voltage is generated,
The current detection circuit becomes complicated. In particular, in the drive circuit that performs PWM control of the motor current as described above, the MOSF
Since the ON voltage of the ET fluctuates, the current detection circuit becomes more complicated.

SUMMARY OF THE INVENTION The present invention has been made in view of such a problem, and the motor current can be simply reduced without using a voltage drop in a current detection resistor or MOSFET provided on a current path through which the motor current flows as in the prior art. It is an object of the present invention to provide a current detection device for a brushless DC motor that can detect a current.

[0012]

According to a first aspect of the present invention, there is provided a current detecting apparatus for rotating a three-phase brushless DC motor having armature windings connected via a drive circuit. This is for detecting the motor current flowing through each of the armature windings when the operation is performed, and includes neutral point voltage detection means, rotation proportional voltage generation means, and calculation means.

Here, the neutral point voltage detecting means is for detecting the neutral point voltage V1 of the brushless DC motor, one end of which is connected to a connection point between the armature windings of each phase. The ends are constituted by three resistors having the same resistance value connected to each other. That is, in a three-phase brushless DC motor in which armature windings are △ -connected, a neutral point does not physically exist as in a three-phase motor in which armature windings are star-connected (Y-connected). Therefore, in the present invention, by configuring the neutral point voltage detecting means as described above, the neutral point voltage V1 is obtained by using three resistors connected to the connection point between the armature windings of each phase. Is to be detected.

The rotation proportional voltage generating means generates a rotation proportional voltage V2 proportional to the rotation speed N of the brushless DC motor defined by the following equation (1) based on the detection signal from the rotation sensor. V2 = A · N (1) (where A is a proportional constant, so that when an electromotive force constant is k and a magnetic flux amount applied to the armature winding is Φ, A = k · Φ / 2. The calculation means includes a motor driving power supply voltage VB applied to the drive circuit of the brushless DC motor, a neutral point voltage V1 detected by the neutral point voltage detection means, and a rotation proportional voltage. Based on the rotation proportional voltage V2 generated by the generation means, a detection voltage Vo representing the motor current is calculated according to the following equation (2).

Vo = VB-V1-V2 (2) That is, the general expression representing the behavior of the DC motor is as follows: VM is the voltage applied to the motor, k is the electromotive force constant, and the amount of magnetic flux applied from the rotor to the armature winding. Is Φ, and the current flowing through the armature winding is Ia,
Assuming that the total resistance of the motor drive system including the armature winding is Ra, it can be described as the following equation (3).

VM = k ・ Φ ・ N + Ia ・ Ra (3) On the other hand, in a three-phase brushless DC motor, a voltage is applied to each winding via a drive circuit (the inverter circuit described above). The applied voltage VM cannot be directly detected. However, if the neutral point voltage of the three-phase brushless DC motor is V1 as described above, the voltage VM applied to the motor is equal to the neutral point voltage V1 and the power supply supplied to the drive circuit (the inverter circuit described above). From the voltage VB, the following equation
Can be described as (4).

VM = 2 (VB-V1) (4) Then, this equation (4) is substituted into the above equation (3), and the motor current Ia is obtained using the power supply voltage VB and the neutral point voltage V1. The following equation (5) is derived when the calculation formula for the calculation is derived.

Ia = (VB−V1−k · Φ · N / 2) · 2 / Ra (5) In addition, the rotor of the three-phase brushless DC motor usually has
A permanent magnet is provided, the magnetic flux Φ applied from the rotor to the stator motor is constant, and the electromotive force coefficient k is also constant.

Therefore, the above equation (5) can be rewritten as the following equation (6), and the detection voltage Vo obtained by the arithmetic means according to the above equation (2) is proportional to the motor current Ia.
It can be seen that the motor current Ia can be detected from the detection voltage Vo. As described above, in the current detection device of the present invention, the rotation speed N obtained by the detection signal from the rotation sensor generally provided in the drive device of the three-phase brushless DC motor is obtained.
, The neutral point voltage V1 of the armature winding, and the power supply voltage VB, a detection voltage Vo representing the motor current Ia can be obtained. Since there is no need to provide a resistor, the motor current can be detected without causing problems such as an increase in power consumption and heat generation of the current detection resistor.

In order to detect the motor current (detection voltage), an arithmetic circuit capable of adding and subtracting each of the voltages VB, V1, V2 may be used.
Like the conventional device that calculates the motor current from the ON voltage of
Since there is no need to provide a complicated logic circuit, the device can be realized at low cost without complicating the device configuration and increasing the cost.

[0021]

Embodiments of the present invention will be described below. FIG. 1 is an electric circuit diagram showing the overall configuration of a brushless DC motor driving device according to an embodiment to which the present invention is applied.

The drive device of the present embodiment is, for example, a brushless DC motor for a blower, which is used for adjusting the amount of conditioned air blown into a vehicle interior by an air conditioner for a vehicle, by a target device designated by the control device for the air conditioner. It is for driving at a rotational speed. And in the driving device of the present embodiment,
The entire drive system, including the brushless DC motor, is configured in exactly the same way as the conventional device shown in FIG. 3, and differs from the conventional device shown in FIG.
FIG. 3 shows that the resistors R0 (three) having the same resistance value are connected to the connection points (three places) between U, 2V, and 2W, respectively.
Instead of the current detection resistor Rs shown in FIG.
Are provided.

Therefore, in the following description, in the present embodiment, the same components as those of the conventional device shown in FIG.
The same reference numerals as used in the description of the conventional device are given and the detailed description is omitted, and the above-described two points different from the conventional device shown in FIG. 3 will be described in detail.

First, the three resistors R0 are for detecting the neutral point voltage V1 of the motor 2. That is,
The motor 2 includes U, V, W phase armature windings 2U, 2V, 2
W is a three-phase brushless DC motor with a △ connection, and a neutral point does not physically exist unlike a motor in which armature windings 2U, 2V, and 2W are Y-connected. Therefore, in the present embodiment, a resistor R0 having the same resistance value is connected to a connection point between the windings of the armature windings 2U, 2V, and 2W, which are connected to each other. By connecting the ends to each other, a virtual neutral point of the motor 2 is created, and the voltage at the connection point is detected as the neutral point voltage V1. Incidentally, these three resistors R0 correspond to the neutral point voltage detecting means of the present invention.

On the other hand, the current detection circuit 20 is for generating a detection voltage Vo corresponding to the motor current in accordance with the above-mentioned equation (2), and is an operational amplifier constituting an addition / subtraction circuit as arithmetic means of the present invention. OP1 is mainly configured. Here, first, the non-inverting input terminal (+) of the operational amplifier OP1 is connected to the positive electrode of the DC power supply 4 via the resistor R1, and is connected to the negative electrode (ground) of the DC power supply 4 via the resistor R2. It is connected to the. For this reason, the voltage of the non-inverting input terminal (+) of the operational amplifier OP1 is obtained by dividing the power supply voltage VB supplied from the DC power supply 4 to the inverter 6 as a drive circuit by the resistors R1 and R2, “VB · R
2 / (R1 + R2) ".

The inverting input terminal (-) of the operational amplifier OP1 is connected to the output terminal of the buffer BF1 via a resistor R3, and the buffer BF2 is connected via a resistor R6.
, And further connected to the output terminal of the operational amplifier OP1 via a resistor R7.

The buffer BF1 is for taking in the neutral point voltage V1 from the connection point of the three resistors R0, and has an input terminal connected to the connection point (virtual neutral point) of the three resistors R0. It is connected to the. A capacitor C0 having one end connected to the negative side (ground) of the DC power supply 4 is connected to the input path of the neutral point voltage V1 from the virtual neutral point to the input terminal of the buffer BF1. This is because the capacitor C0 absorbs the voltage change of the virtual neutral point caused by the rotation of the motor 2, and inputs a stable neutral point voltage V1 to the operational amplifier OP1.

On the other hand, the buffer BF2 is for taking in a rotation proportional voltage V2 proportional to the rotation speed N of the motor 2, and its input terminal is connected to the output terminal of the F / V converter 10 via a resistor R4. It is connected to the negative side (ground) of the DC power supply 4 via the resistor R5.

The resistors R4 and R5 convert the speed signal (voltage) Vn output from the F / V converter 10 into a divided voltage value "R5 / (R
4 + R5) "to generate a rotation proportional voltage V2 defined by the above-mentioned equation (1) in proportion to the rotation speed N of the motor 2, and together with the F / V converter 10, It functions as the rotation proportional voltage generation means of the present invention.

That is, the F / V converter 10 includes the rotation sensor 8
By converting the frequency (F) of the detection signal synchronized with the rotation of the motor 2 output from the motor 2 into a voltage (V),
Is generated, the speed signal Vn is proportional to the rotation speed N of the motor 2.

If the proportionality constant of the speed signal Vn with respect to the rotation speed N is a (that is, Vn = aN), the rotation proportional voltage defined by the above equation (1) is determined based on the speed signal Vn. In order to generate V2, from the above equation (1), V2 = A · N = (k · Φ / 2) · (Vn / a) = Vn ·
Since R5 / (R4 + R5), the resistance values of the resistors R4 and R5 are calculated by the following equation.
What is necessary is just to set as shown in (7).

R5 (R4 + R5) = (k · Φ) / (2 · a) (7) Therefore, in the present embodiment, the resistance values of the resistors R4 and R5 are set so as to satisfy the above equation (7). By setting, the voltage input to the operational amplifier OP1 via the buffer BF2 is set to the rotation proportional voltage V2 defined by the above equation (1).

Also, of the resistors R1, R2, R3, R6, and R7 connected to the operational amplifier OP1, the operational amplifier OP1
The resistance values of the resistors R1 and R2 connected to the non-inverting input terminal (+) are set such that “R2 = R1 / 2”.
The resistance values of the other resistors R3, R6, and R7 are set to the same resistance values as the resistor R1 (R1 = R3 = R6 = R7).

As a result, the output V from the operational amplifier OP1 is
o is: Vo = VB · R2 / (R1 + R2) + VB · R2 / (R
1 + R2) −V1 + VB · R2 / (R1 + R2) −V2 = 3 · VB · R2 / (R1 + R2) −V1−V2 = VB−V1−V2, and the detection voltage Vo corresponding to the above equation (2) is obtained. become.

The detection voltage Vo output from the operational amplifier OP1 is input to the control circuit 12, and the control circuit 12 monitors the overcurrent flowing through the motor 2 from the detection voltage Vo and sets the motor 2 at the target speed. The drive control protects the motor 2 and the inverter 6 from overcurrent.

The protection operation from the overcurrent by the control circuit 12 is executed, for example, as shown in FIG. That is, when some abnormality occurs on the motor 2 side and the motor current starts to increase, the detection voltage Vo increases accordingly.
By determining whether or not o exceeds a preset overcurrent determination voltage Vth, it is determined whether or not an overcurrent has flowed through the motor 2.

When an overcurrent is determined (at time t)
1), after temporarily stopping the motor control and elapse of a predetermined time,
Restart motor control. In other words, in this case, the motor 2 may return to a normal state and the motor control may be performed normally. After the overcurrent determination, the motor control is stopped for a predetermined time and the motor control is restarted. is there.

Further, even if the motor control is temporarily stopped and then resumed, the motor 2 does not return to the normal state, and an overcurrent may flow. Therefore, the detection voltage Vo and the overcurrent determination voltage Vth are maintained. Is performed based on the overcurrent. And
When the overcurrent is determined again after the restart of the motor control, the motor control is stopped for a predetermined time and then restarted.

Even if the motor control is repeatedly stopped and restarted, the motor 2 does not return to normal,
If the overcurrent is repeatedly determined, the motor 2 can be determined to be completely out of order. Therefore, when the overcurrent is determined, the number of determinations is counted, and the count value reaches a predetermined value. Then (time t2), it is determined that the motor 2 has completely failed, and execution of the motor control is prohibited, and the user is notified of that (motor failure).

As described above, in this embodiment, the power supply voltage VB for driving the motor supplied from the DC power supply 4 to the inverter 6 and the neutral point voltage VB of the brushless DC motor 2
1 and a rotation proportional voltage V proportional to the rotation speed N of the motor 2
2, a motor current flowing through the brushless DC motor 2 is detected by using a current detection circuit 20 that generates a detection voltage Vo from the motor.

Therefore, as in the conventional device shown in FIG. 3, the current detection resistor Rs
Need not be provided, it is possible to reduce power loss caused by motor current detection. Further, since the motor current can be detected without using a heating element that generates heat when the motor current flows, such as the current detection resistor Rs, the temperature of the entire driving device does not increase due to the heat generated by the element. Control can be executed stably.

Further, the current detection circuit 20 itself is provided by the above (2)
Since it can be configured by a simple arithmetic circuit (addition / subtraction circuit) that performs an operation according to the equation, the current detection circuit is compared with the case where the motor current is detected from the ON voltage of the transistor (MOSFET) forming the inverter 6. 20 can be simplified and realized at low cost.

[Brief description of the drawings]

FIG. 1 is an electric circuit diagram illustrating a configuration of an entire driving device for a brushless DC motor according to an embodiment.

FIG. 2 is a time chart illustrating an overcurrent protection operation by a control circuit according to the embodiment.

FIG. 3 is an electric circuit diagram illustrating a configuration of a whole brushless DC motor driving device.

[Explanation of symbols]

2 ... brushless DC motor, 2U, 2V, 2W ... armature winding, 4 ... DC power supply, 6 ... inverter, 8 ... rotation sensor, 10 ... F / V converter, 12 ... control circuit, 20 ... current detection circuit, BF1, BF2: buffer, OP1: operational amplifier, C0: capacitor, R0 to R7: resistor.

Claims (1)

[Claims] 1. A three-phase brushless DC motor in which armature windings of each phase are △ -connected, wherein a motor current flowing through each of the armature windings when the motor is rotationally driven via a drive circuit. A current detection device for detecting, wherein one end is connected to a connection point between the armature windings of each phase,
The other end is composed of three resistors connected to each other and having the same resistance value.
A neutral point voltage detecting means for detecting the neutral point voltage V1 of the motor; and a rotation of the brushless DC motor defined by the following equation (1) based on a detection signal from a rotation sensor for detecting the rotation of the brushless DC motor. A rotation proportional voltage generating means for generating a voltage V2 proportional to the speed N; V2 = A · N (1) (where A is a proportional constant, the electromotive force constant is k, the amount of magnetic flux applied to the armature winding, Is set to be A = k · Φ / 2, where Φ is Φ) Power supply voltage VB for motor drive applied to the drive circuit
Based on the neutral point voltage V1 detected by the neutral point voltage detection means and the rotation proportional voltage V2 generated by the rotation proportional voltage generation means, a detection voltage Vo representing the motor current, A current detecting device for a brushless DC motor, comprising: arithmetic means for calculating according to the following equation (2); and Vo = VB-V1-V2 (2).