GB2231179A

GB2231179A - Device for controlling and regulating a direct-current electric motor

Info

Publication number: GB2231179A
Application number: GB9006862A
Authority: GB
Inventors: Andrea Nepote
Original assignee: Marelli Autronica SpA
Current assignee: Marelli Europe SpA
Priority date: 1989-03-31
Filing date: 1990-03-28
Publication date: 1990-11-07
Also published as: FR2646030A1; ES2021242A6; SE9001165D0; IT8967233A0; DE4010022A1; SE9001165L; IT1232074B; GB9006862D0

Description

1 DEVICE FOR CONTROLLING AND REGULATING A DIRECT-CURRENT ELECTRIC MOTOR 3

-1 X 1-7 el The present invention relates to a device for controlling and regulating a direct-current electric motor.

More specifically, the subject of the invention is a device including: a transistor whose collector-emitter path is intended to be connected in series with the armature winding of the motor, between the two poles of a direct-current voltage supply, a sensor adapted to provide a signal indicative of the current present in the collector-emitter path of the transistor, and a current-regulator circuit comprising an amplifier with a first input for a control signal, a second input connected to the current sensor, and an output connected to the transistor for regulating the current flowing in the collector-emitter path in dependence on the control signal and on the signal provided by the sensor.

Control and regulation devices of the aforesaid type are used, for example, for controlling the motors of electric fans in motor-vehicle airconditioning systems.

Irregular operation and, in particular, phenomena of instability and the establishment of high-frequency self -oscillations are often encountered in the control and regulation devices of the type indicated above produced up to now.

2 The object of the present invention is to provide a device of the type specified above which prevents the aforesaid problems.

This object is achieved according to the invention by means of a control and regulation device of the type specified above, the main characteristic of which lies in that fact that an integrating network is interposed between the second input and the output of the amplifier.

This solution involves a certain but acceptable reduction in the gain at high frequencies, whilst at low and very low frequencies, and particularly with a steady current, the gain remains very high.

Moreover, 'the solution according to the invention ensures extremely stable operation of the device even at high frequencies, actually eliminating the possibility of the establishment of self-oscillations.

One possible explanation of the origin of the problems of the prior-art devices and the effectiveness of the solution proposed may perhaps be the following.

The high-frequency instability and the establishment of self oscillations in the prior-art devices are perhaps due to the effect of stray capacitance between the terminals of the transistor, particularly between its base and its collector. The effect of this capacitance is to cause a rapid fall in gain at high frequencies with a "gradient" equal to or greater than 12dB per octave when the gain is approximately 1. According to the known Bode's criterion, this is the reason for the instability.

d 1 3 The integrating network introduced in the device according to the invention apparently prevents instability problems because it causes the insertion of a pole at the origin, that is, at a frequency f = 0, of the overall transfer characteristic of the device. This has the effect of reducing the gain at medium and high frequencies, but with a gradient of less than 12dB per octave with a unitary gain value, resulting in stable operation at these frequencies also.

One embodiment of the invention will now be more particularly described, purely by way of non-limiting example, with reference to the accompanying drawing which shows the circuit diagram of a device for controlling and regulating a direct-current electric motor according to the present invention.

With reference to the drawing, a direct-current electric motor, for example, the motor for driving an electric fan in an air-conditioning system, is indicated 1. The armature winding of the motor is arranged in series with the collector-emitter path of an npn-type transistor 2, between the two poles of a direct-current voltage supply 3 constituted, for example, by a battery.

A resistor 4 is situated between the emitter of the transistor 2 and earth and acts as a current sensor: in operation, the voltage across this resistor is substantially proportional to the current flowing in the armature winding of the motor 1.

An operational amplifier, indicated 5, has its non-inverting input 5a connected to the central contact of a voltage divider constituted by two resistors 6 and 4 7 between the output of a digital/analog converter 8 and earth. In a manner not shown, the digital/analog converter 8 receives digital signals from a micoprocessor for controlling the operation of the electric motor 1.

The output of the operational amplifier 5 is connected to the base of the transistor 2 through a protective diode 9.

A feedback resistor, indicated 10, is interposed between the emitter of the transistor 2 and the inverting input 5b of the amplifier 5.

According to the invention, a reactive integrating network is associated with the amplifier 5 and is constituted by a resistor 11 and a capacitor 12 connected in series between the inverting input 5b and the output of the amplifier.

In operation, the current flowing in the collector-emitter path of the transistor 2, and hence in the armature winding of the motor 1, is regulated in dependence on the amplitude of the analog signal applied to the input Sa of the amplifier 5 and on the signal applied to the inverting input 5b through the resistors 4 and 10, the latter signal being indicative of the current actually flowing in the armature winding of the motor.

The effect of the integrating circuit 11, 12 is substantially to introduce into the transfer characteristic of the entire circuit a pole at a frequency f = o, and a zero at a frequency f = 112pi.C.Rll, in which C is the capacitance of the 1 1 capacitor 12 and R 11 is the resistance of the resistor 11.

As stated above, the solution according to the invention ensures the absolute stability of the device, even at high frequencies.

Claims

6 CLAIMS

1. A device for controlling and regulating a direct-current electric motor, including a transistor whose collector-emitter path is intended to be connected in series with the armature winding of the motor, between the two poles of a direct-current voltage supply, a sensor adapted to provide a signal indicative of the current present in the collector- emitter path of the transistor, and a current-regulator circuit including an amplifier with a first input for a control signal, a second input connected to the current sensor, and an output connected to the transistor for regulating the current flowing in the collector-emitter path in dependence on the control signal and on the signal provided by the current sensor, in which an integrating network is interposed between the second input and the output of the amplifier.

2. A device according to Claim 1, in which the integrating circuit comprises a first resistor and a capacitor connected in series.

3. A device according to Claim 2, in which a second resistor is interposed between the current sensor and the second input of the amplifier.

4. A device for controlling and regulating a direct-current electric motor, substantially as herein described with reference to, and as shown in, the accompanying drawing.

1 Published 1990 atThe Patent office, State House, 6671 HigliHolborn. London WC1R4TP.Further copies maybe obtainedfrom. The Patent Mce. Sales Branch. St Mary Cray, Orpington, Kent BRS 3RD. Printed by Multiplex techniques ltd. St Mary Cray. Kent, Con. 1187