JPH04308420A - Motor controller - Google Patents

Abstract

PURPOSE:To detect an overcurrent by detecting the overcurrent by means of an FET having a wide linear relation between its drain current and drain-source voltage drop. CONSTITUTION:FETs Q'1-Q'6 are used as the transistors forming an inverter. The drain-source voltage drops VDS4-VDS6 of the FETs Q'1-Q'6 proportional to the first- to third-phase currents of a motor are detected in series with three switches AS1-AS3 which are turned on by a switch drive circuit SC at the FET conducting timing of a control circuit CONT. The detected voltage drops are compared with an overcurrent setting reference voltage VS by means of an error amplifier AMP and, when one of the voltage drops exceeds the set voltage, the occurrence of an overcurrent is discriminated and a drive signal distribution circuit CD is controlled. Irrespective of the phase of the overcurrent, the overcurrent is prevented by stopping the supply of a drive signal to the circuit CONT and turning off the FETs. Since no shunt nor Hall element is used, the circuit can be reduced in size and this motor controller can be constituted to a small size.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverter type motor control device using FETs, and particularly to an overcurrent control circuit.

0002

2. Description of the Related Art Conventionally, as a means for controlling the rotation of a multi-phase AC brushless motor using DC as a power source, a circuit having a circuit as shown in FIG. 5 has been widely used. This circuit uses an inverter circuit consisting of six transistors Q1 to Q6 and a control circuit CONT to convert direct current to alternating current, and controls the output voltage to control the rotation of the three-phase brushless motor M. In this case, it is required to prevent performance deterioration of the motor and transistors due to overload. Therefore, conventional measures have been taken to use a circuit that detects when the current in the motor circuit has entered the overcurrent region, and to immediately cut off the motor current by turning off all transistors Q1 to Q6 when an overcurrent occurs. For example, one of the typical methods is to connect a current shunt in series to the input circuit of a transistor inverter, and compare the detected voltage with the overcurrent setting reference voltage in an error amplifier to detect an overcurrent condition, and output the This is a current shunt system in which the control circuit CONT is controlled by the control circuit CONT to turn off all transistors Q1 to Q6. Another method, as shown in Fig. 6(a), is to use an iron core C that detects the current change in the input conductor L of the transistor inverter as a change in magnetic flux, and a resistance value change characteristic that is linearly proportional to the change in magnetic flux. A current detection device in which a magnetoresistive element H to be detected is inserted into a gap G of an iron core C is used, and this is shown in Fig. 6.
As shown in (b), the resistance R1 of the magnetoresistive element H and the resistance R
2, R3, constant voltage element DZ and error amplifier AMP
This is a so-called Hall element method that detects overcurrent conditions by forming a circuit consisting of the following.

0003

[Problems to be Solved by the Invention] However, in vehicles such as small mobile vehicles that use a motor as a drive source, where the mounting space for equipment is severely limited, peripheral circuits such as motor control circuits and overcurrent control circuits are required. There is a strong demand for devices to be made as compact as possible, but it is difficult to meet this demand with the above-mentioned shunt type or Hall element type. That is, although the control circuit and the error amplifier of the overcurrent control circuit can be made extremely compact using IC circuits, it is difficult to make the shunt and the Hall element small. In addition, in the case of the shunt type, I2R loss occurs, which is disadvantageous for vehicles with large drive power constraints, such as small mobile vehicles that use battery power as a motor drive source. Further, as a means of preventing the above-mentioned peripheral devices from increasing in size, it is conceivable to utilize the voltage drop between the collector and emitter of the transistor shown in FIG. However, as is well known, the base current IB
Collector-emitter voltage drop V with as a parameter
The relationship between CE and collector current IC has a non-linearity with a sharp rise as shown in FIG. Therefore, the collector current IC
Since the change in the collector-emitter voltage drop VCE with respect to the change in VCE is extremely small, it is difficult to detect an overcurrent condition.
There is a drawback that even if the motor current slightly exceeds a set overcurrent range, it is determined to be an overcurrent and the power supply to the motor is stopped. Therefore, even if this method can be made compact, it is difficult to put into practical use due to performance problems such as operational reliability.

0004

OBJECTS OF THE INVENTION The present invention provides a circuit that is significantly smaller in size than the conventional shunt type or Hall element type, and also has excellent overcurrent control performance.

[0005]

[Means of the Invention for Solving the Problems] The present invention uses FETs in place of the transistors Q1 to Q6 constituting the inverter shown in FIG. It was revealed that by using the voltage drop between the drain and source during overcurrent detection, it becomes possible to effectively detect and control overcurrent without increasing the size of the device or using shunts. It has been done. That is, FET
When the gate voltage VG is taken as a parameter, the drain-source voltage drop VDS when the FET is on and the drain current ID have a linear proportional relationship over a wide range as shown in FIG. Moreover, since the slope is much gentler than that of a normal transistor, it is possible to obtain a sufficiently large change in drain-source voltage drop proportional to a change in drain current. Therefore, it is possible to provide a large difference between the control current region and the overcurrent region, so that overcurrent can be detected effectively.

The present invention was conceived based on the above. That is, as shown in FIG. 2, FETs Q1' to Q6' are used as transistors forming an inverter, and the drain and source of FETs Q1' to Q6' are proportional to the motor current of the first, second, and third phases of the motor M. The voltage drops VDS4, VDS5, VDS6 between the control circuit C
Three switches AS1 are turned on by the switch drive circuit SC in accordance with the conduction timing of the FET by the ONT.
, AS2, and AS3 in series. For example, this is compared with the overcurrent setting reference voltage VS in the error amplifier AMP, and the voltage drop VDS4 is
~ When VDS6 exceeds the set reference voltage, it is determined that there is an overcurrent, and the output generated at this time controls the drive signal distribution circuit CD, so that no matter which phase the overcurrent occurs, the control circuit C
This prevents overcurrent from flowing by stopping the supply of drive signals to the ONT and turning off all FETs. By doing the above, there is no need to use a current shunt or a Hall element as in the conventional case, so the overcurrent circuit can be made smaller, and the motor control device can be made smaller. Next, examples of the present invention will be described.

[0007]

Embodiment FIG. 3 is a circuit diagram of an embodiment of the present invention, and FIG. 4 is a waveform diagram for explaining its operation. In Figure 3, Q1'~Q
6' is a FET, Q1', Q4', Q2
' and Q5', and the sources and drains of Q3' and Q6' are connected in series, respectively. Also Q1', Q
The drains of Q2', Q3' are commonly connected and connected to the positive polarity of the DC power supply, and the drains of Q4', Q5' and Q6
' sources are commonly connected and connected to the negative polarity terminal of the DC power supply. M is a three-phase brushless motor, and its input terminals m1, m2, m3 are FETQ4', Q
5' and the drain of Q6'. Then, by the control circuit CONT, first FETQ3' and Q4 are
', then Q1' and Q5', then Q2' and Q6'...
Turn on the motor M in the following order to drive the motor M. T is a timing circuit, which includes three analog switches AS1,
AS2 and AS3 are formed, one end of each of which is connected to the drains of FETs Q4', Q5' and Q6', and the other end commonly connected via a current limiting resistor R of an overcurrent detection circuit described later. and FETQ4',
Q in synchronization with the gate drive signals of Q5' and Q6'.
4', Q5', and Q6' are each on-period by the timing signal sent from the control circuit CONT.
(d) Turns on as shown in (e) and (f), as shown in Fig. 4(a).
(b) As in (c), FETQ4', Q5', Q6
Figure 4 (g
) to the amplifier AMP. OI is an overcurrent detection circuit and is formed from the following parts. R is a summing resistor, AMP is an amplifier, and MD is an average value overcurrent detection circuit. Among these, R4, R5, and C are resistors and capacitors that obtain the average value of the output of the amplifier AMP, Q7 is a transistor, and DZ1 is a reference. A constant voltage element for setting the average voltage VS1, for example a Zener diode, R6 is a current limiting resistor, and Thy is a thyristor. PD is a peak value overcurrent detection circuit, and is formed from a constant voltage element for setting a reference peak value voltage VS2, for example, a Zener diode DZ2 and a current limiting resistor R7. CC is a drive circuit for the control circuit, and is composed of six signal distribution circuits, for example, gate ICs IC1 to IC6. The average value overcurrent detection circuit MD described above has an output obtained by smoothing the output of the amplifier AMP shown in FIG. (h
) Reference voltage V due to Zener diode DZ1 shown in
When S1 is exceeded, a current is passed through the gate of the thyristor Thy to turn it on. And this allows each gate I
When the input level of one terminal of C1 to IC6 becomes Low level, the drive signals q1 to q6 of the control circuit CONT applied to the other terminal are not accepted, and all FETs Q1' to Q6' are turned off. do. Furthermore, when the instantaneous value VP of the output of the amplifier AMP exceeds the reference voltage VS2 generated by the Zener diode DZ2 shown in FIG. 4(h), the peak overcurrent detection circuit PD turns on the thyristor Thy and controls the control circuit CONT. Drive signal q1
~q6 will not be accepted. and FETQ
1' to Q6' are all turned off to prevent overcurrent from flowing to the brushless motor M. Note that the average value or instantaneous value overcurrent detection circuit can be omitted if necessary.

[0008]

As is clear from the above, in the present invention, overcurrent is detected using a FET that has a wide linear relationship between the drain current and the voltage drop between the drain and source. Since overcurrent is effectively detected without using a circuit, the overcurrent control circuit and the motor control circuit can be made compact.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between drain-source voltage drop and drain current of an FET.

FIG. 2 is a basic circuit diagram of the present invention.

FIG. 3 is a circuit diagram of an embodiment of the present invention.

FIG. 4 is a waveform diagram for explaining the operation of an embodiment of the present invention.

FIG. 5 is a schematic diagram of a conventional motor control device.

FIG. 6 is an explanatory diagram of a Hall element for overcurrent detection.

FIG. 7 is a diagram showing the relationship between collector-emitter voltage drop and collector current of a transistor.

[Explanation of symbols]

Q1 to Q6 Transistor CONT Control circuit M Brushless motor L Motor connection conductor C Iron core G Gap H Magnetoresistive element R1, R2, R3 Resistance DZ Constant voltage element Q1' to Q6' FET AS1, AS2, AS3 Analog switch S
C Switch drive circuit CC Control circuit drive circuit OI Overcurrent detection circuit R Current limiting resistor AMP Amplifier MD Average value overcurrent detection circuit R4, C, R5 Resistor forming the smoothing circuit, capacitor Q7 Transistor DZ1 Constant voltage element R7 Current limiting Resistor PD Instantaneous value overcurrent detection circuit DZ2 Constant voltage element CC Control circuit drive circuit IC1 to IC6 Signal distribution circuit Thy Thyristor

Claims (1)

[Claims] 1. A motor control device that controls the rotation of an AC multi-phase brushless motor using a DC power supply using an inverter made up of a transistor and its control circuit, wherein an FET is used as the transistor, and the FE
an analog switch circuit that is turned on in accordance with the conduction timing of T and sequentially detects the drain-source voltage drop of the FET proportional to each phase current of the brushless motor only when the FET is on; and an instantaneous voltage when the FET is on. an overcurrent detection circuit that sends out an output when the voltage drop, average voltage drop, or both exceed the overcurrent setting reference voltage level, and the output of this overcurrent detection circuit causes the control circuit to stop receiving drive signals. A motor control device comprising: a drive circuit for the control circuit that turns off all of the FETs.