JP2007082382A - Motor drive - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a motor drive in which breakage of at least one resistive element can be detected in an overcurrent protection circuit employing resistive elements. <P>SOLUTION: In parallel with two resistive elements R1 and R2 connected with the earthing side of an inverter circuit 14, a resistive element 30 for detecting breakage and the photodiode 34 of a photocoupler 32 are connected and the phototransistor 36 of the photocoupler 32 is connected with the control circuit 20 of the inverter circuit 14. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a motor drive device driven by an inverter circuit.

  The brushless DC motor is driven by an inverter circuit. In order to prevent the motor current flowing through the inverter circuit from becoming an abnormal value due to overload, an overcurrent protection circuit is provided (see, for example, Patent Document 1).

As the structure of this overcurrent protection circuit, for example, as shown in FIG. 4, two resistance elements R1 and R2 are connected to the wiring on the ground terminal side of the inverter circuit 102 to which the brushless DC motor 100 is connected. When the current flowing from the other ends of the two resistance elements R1 and R2 connected in parallel becomes equal to or higher than the reference value, the overcurrent protection circuit 104 determines that the current is overcurrent.
JP 2002-186272 A

  Chip resistors are used as the resistance elements R1 and R2 in the overcurrent protection circuit 104 as described above. When the brushless DC motor 100 is molded, the two chip resistors R1 and R2 are attached to the wiring board embedded in the mold resin. Therefore, the chip resistors R1 and R2 are easily damaged.

  When both the two resistance elements R1 and R2 are damaged, the current from the overcurrent protection circuit 104 does not flow, so that it can be determined immediately when a no-load test is performed. However, if one of the two chip resistors is damaged, it cannot be determined even in a no-load test, and the control circuit 106 cannot determine that the overcurrent protection circuit 104 is destroyed. .

  This principle will be described with reference to the graphs of FIGS.

  The horizontal axis of the graph in FIG. 2 is the torque T, the vertical axis is the motor current I, the horizontal axis of the graph in FIG. 3 is the torque T, and the vertical axis is the rotational speed N. In both FIGS. 2 and 3, when the resistance elements R1 and R2 are normal, a solid line is shown, and when one is damaged, a dotted line is shown. As shown by the dotted line, when T = 0, that is, when there is no load, even if two resistance elements are normal, even if one resistance element is destroyed, the value is the same. The abnormality cannot be determined.

  Therefore, in view of the above problems, the present invention provides a motor drive device that can detect the destruction of at least one resistive element even when at least one resistive element is destroyed in an overcurrent protection circuit using the resistive element.

  The invention according to claim 1 is a motor, an inverter circuit that supplies a drive current to the motor, a control circuit that controls the inverter circuit based on a speed command signal, and a motor current that detects a motor current of the inverter circuit In the motor drive device having the detection means, the motor current detection circuit is configured such that one end of each of the n (n> 1) resistance elements connected in parallel is connected to the ground terminal side wiring of the inverter circuit, The other end of the n resistance elements is connected to a current comparison circuit, a breakdown detection circuit is connected in parallel with the n resistance elements, and the current comparison circuit is configured to output a motor current value from the n resistance elements. When the value exceeds a reference value, a stop signal is output, and the breakdown detection circuit includes a breakdown detection resistance element and a photocoupler, and the breakdown detection resistance element and the photocoupler Are connected in series, the breakdown detection resistance element and the phototransistor are connected in parallel with the n resistance elements, the photocoupler of the photocoupler is connected to the control circuit, the control circuit, The motor driving device is characterized in that the motor is stopped by a breakdown detection signal from the phototransistor.

  The invention according to claim 2 is the motor drive device according to claim 1, wherein n = 2.

  The invention according to claim 3 is the motor drive device according to claim 1, wherein the breakdown detection signal from the phototransistor stops the speed command signal.

  The invention according to claim 4 is the motor drive device according to claim 1, wherein the motor is a brushless DC motor.

  According to the present invention, when at least one of the n resistance elements is destroyed, a current flows through the destruction resistance element, the phototransistor of the photocoupler is turned on, and the destruction detection signal is sent to the control circuit. Is output. The control circuit stops the motor when this destruction detection signal is detected.

  Hereinafter, a driving device 12 for a motor 10 according to an embodiment of the present invention will be described with reference to FIG. The motor 10 is a three-phase brushless DC motor.

(1) Configuration of Driving Device 12 of Motor 10 The driving device 12 will be described based on the block diagram of FIG.

  The drive device 12 includes an inverter circuit 14, an overcurrent protection circuit 16, an overcurrent detection circuit 18, a control circuit 20, a rectifier circuit 22, and a breakdown detection circuit 24.

  The inverter circuit 14 outputs a drive current to the three-phase stator winding of the motor 10 and constitutes a full bridge circuit in which three circuits in which two FETs are connected in series are connected in parallel. . In the inverter circuit 14, the power from the AC power supply 26 is rectified by the rectifier circuit 22, and the rectified power is supplied to the inverter circuit 14.

  The control circuit 20 is composed of a microcomputer, and performs PWM control of the inverter circuit 14 so that the rotational speed of the motor 10 matches the speed command signal S based on the speed command signal S input from the outside. That is, six control signals output from the control circuit 20 are input to the gate terminals of the six FETs 14 of the inverter circuit 14, and the number of rotations of the motor 10 is controlled by turning on / off the six FETs. ing. In this case, in order to detect the number of rotations of the motor 10, three Hall ICs 28 are provided in the vicinity of the rotor of the motor 10, and the control circuit 20 operates the motor based on the position detection signals from the three Hall ICs 28. The current rotational speed of 10 is detected, and feedback control is performed so as to match the speed command signal S.

  In the overcurrent detection circuit 18, one end of each of the two resistance elements R1 and R2 is connected to the ground side of the inverter circuit 14, and the resistance elements R1 and R2 are connected in parallel. The other ends of the resistance elements R1 and R2 connected in parallel are connected to the overcurrent protection circuit 16. The overcurrent protection circuit 16 outputs a stop signal to the control circuit 20 when the motor current flowing from the resistance elements R1 and R2 connected in parallel becomes a reference value or more. The overcurrent protection circuit 16 is configured by a comparator, and a reference voltage is applied to one end of the comparator and compared with the voltages from the two resistance elements R1 and R2.

(2) Configuration of Destruction Detection Circuit 24 Next, the configuration of the destruction detection circuit 24 will be described.

  The breakdown detection circuit 24 includes a breakdown detection resistance element 30 and a photocoupler 32. As shown in FIG. 1, the breakdown detection resistance element 30 and the photodiode 34 of the photocoupler 32 are connected in series, and one end of the breakdown detection resistance element 30 is connected to the ground-side wiring of the inverter circuit 14. That is, it is connected in parallel with the two resistance elements R1, R2. In order to prevent destruction of the photodiode 34, the diode 38 is connected to the wiring on the ground side of the inverter circuit 14 in the direction opposite to the direction of the photodiode 34.

  The phototransistor 36 of the photocoupler 32 is connected to the input wiring 40 to which the speed command signal S is input, and the other end is grounded. Thus, when the phototransistor 36 is turned on, the speed command signal S flows to the ground side and does not flow to the control circuit 20.

(3) Operation State of Destruction Detection Circuit 24 Next, the operation state of the destruction detection circuit 24 will be described.

  When the two resistance elements R1 and R2 are both in a normal state, the motor current flows through the resistance elements R1 and R2 to the overcurrent protection circuit 16, and when an overload occurs due to overload, A stop signal is output from the current protection circuit 16, and the motor 10 stops.

  In this case, no current flows through the breakdown detection resistance element 30, and no current flows through the photodiode 34. Therefore, the phototransistor 36 is not turned on, and the speed command signal S is input to the control circuit 20.

  On the other hand, when one of the two resistance elements R1 and R2 is destroyed for some reason, the motor current flows through the non-destructed resistance element and the current is also supplied to the breakdown detection resistance element 30. Flows through the photodiode 34, and the phototransistor 36 is turned on. Therefore, since the speed command signal S is not input, the control circuit 20 determines that the resistance element has been destroyed and stops the motor 10.

  As described above, when the two resistance elements R1 and R2 are normal, no current flows through the breakdown detection resistance element 30, and when one resistance element is destroyed, no current flows through the breakdown detection resistance element 30. In order to make it flow, the following relationship is necessary. However, X is the resistance value of the breakdown detecting resistance element 30, I is the current value when the motor current is overcurrent, and Io is the minimum operating current of the photodiode 34.

X = R1 * R2 * (I-Io) / {(R1 + R2) * I2}

Even when the two resistance elements R1 and R2 are both destroyed, a current flows through the destruction detection resistance element 30, so that the motor 10 can be stopped.

  As described above, in the driving device 12 according to the present embodiment, when even one of the two resistance elements R1 and R2 is broken, it can be detected and the motor 10 can be stopped. it can.

(4) Modification 1
In the above-described embodiment, the speed command signal S is stopped when the phototransistor 36 is turned on. However, the present invention is not limited to this, and the structure may be such that a breakdown detection signal is output to the control circuit 20 when the phototransistor 36 is turned on. .

(5) Modification 2
In the above embodiment, the two resistance elements R1 and R2 are used. However, the present invention is not limited to this, and a structure in which three or more resistance elements are connected in parallel may be used.

  Further, the motor current may be detected using a single resistance element.

  The present embodiment is suitable for a motor driving device used in an air conditioner, a water heater, a dishwasher, an air cleaner, and the like.

It is a block diagram of the drive device of the motor which shows one Embodiment of this invention. It is a graph which shows the relationship between a torque and an electric current. It is a graph which shows the relationship between a torque and rotation speed. It is a block diagram of the drive device of the motor of a prior art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Motor 12 Drive apparatus 14 Inverter circuit 16 Overcurrent protection circuit 18 Overcurrent detection circuit 20 Control circuit 24 Destruction detection circuit 30 Destruction detection resistance element 32 Photocoupler 34 Photodiode 36 Phototransistor

Claims (4)

A motor,
An inverter circuit for supplying a drive current to the motor;
A control circuit for controlling the inverter circuit based on a speed command signal;
Motor current detection means for detecting the motor current of the inverter circuit;
In a motor drive device having
The motor current detection circuit is
One end of n (n> 1) resistance elements connected in parallel is connected to the ground terminal side wiring of the inverter circuit,
The other end of the n resistance elements is connected to a current comparison circuit,
A breakdown detection circuit is connected in parallel with the n resistance elements;
The current comparison circuit outputs a stop signal when a motor current value from the n resistance elements exceeds a reference value,
The breakdown detection circuit includes a breakdown detection resistance element and a photocoupler, wherein the breakdown detection resistance element and the phototransistor of the photocoupler are connected in series, and the breakdown detection resistance element and the phototransistor include the n number of breakdown transistors. Connected in parallel with a resistive element, the phototransistor of the photocoupler is connected to the control circuit,
The control circuit stops the motor in response to a breakdown detection signal from the phototransistor. The motor driving device according to claim 1, wherein n = 2. The motor driving apparatus according to claim 1, wherein the breakdown detection signal from the phototransistor stops the speed command signal. The motor driving apparatus according to claim 1, wherein the motor is a brushless DC motor.

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