Electricity: motive power systems – Switched reluctance motor commutation control
Reexamination Certificate
2000-07-19
2002-04-02
Ip, Paul (Department: 2837)
Electricity: motive power systems
Switched reluctance motor commutation control
C318S434000, C318S375000, C318S376000
Reexamination Certificate
active
06366038
ABSTRACT:
TECHNICAL FIELD
The present invention generally realtes to electric motor control techniques and more particularly relates to a method and circuit arrangement for generating a pulse-width modulated actuating signal for a d.c. actuator.
BACKGROUND OF THE INVENTION
Electrical direct current actuators, which have a distinct low-pass behavior with respect to the electrical or electromagnetic subsystem, are frequently used in electronic control and regulation devices. Typical examples of such actuators are d.c. motors or electromagnets, for example of the kind applied for actuating an electric parking brake or an electrohydraulic pressure generator or for the external control of an electromechanically actuated brake-force booster.
In order to minimize the power losses when controlling such electric d.c. actuators, the associated power amplifiers usually are controlled by a pulse-width modulated actuating signal in the kHz frequency range. The associated pulse-width modulator consists of a saw-tooth voltage generator which generates a saw-tooth shaped signal with the specified, constant kHz frequency and a maximum amplitude that is equal to the value of a reference voltage and a comparator that compares the saw-tooth signal with the value of a continuous actuating signal derived from the control circuit and fluctuating between a maximum and minimum value. When a d.c. motor is the actuator, the actuating signal, for example, is the armature voltage to set the desired torque of the motor. The reference voltage corresponds to the nominal value of the supply voltage; when this is used in a motor vehicle, the supply voltage generally is equal to the battery voltage of the vehicle electric system.
Furthermore, the comparator of the pulse-width modulator is designed in such a way that it supplies a binary switching signal for at least one switch arranged in the d.c. circuit of the actuator when the saw-tooth signal is below the actuating signal and uses this to generate a pulse-width modulated actuating signal with a pulse width representing the value of the continuous actuating signal and a pulse amplitude corresponding to the supply voltage within a specified pulse duty factor. Due to the low-pass behavior for the electric or electromagnetic subsystem of the actuator, a medium continuous actuator current of a specified size for activating the actuator according to the specifications from the control system adjusts itself.
The principle of the mode of functioning of such a pulse-width modulator is shown in FIG.
4
. Section A shows the course of the continuous actuating signal U
A
in relation to time. When a d.c. motor is the actuator this actuating signal U
A
, for example, is the armature voltage of the motor. The size of the actuating signal is determined in a superior control module, e.g. a microprocessor, in such a way that the d.c. actuator is activated with the necessary, desired actuating value.
Section B shows the form of the saw-tooth signal with respect to the actuating signal U
A
, with the maximum amplitude of the saw-tooth signal being equal to the reference voltage (U
Ref
) which—when applied in a motor vehicle—usually corresponds to the battery voltage of the vehicle electric system U
Bat,N
with the nominal value U
Bat,N
=12 Volt.
The pulse-width modulator generates a binary switching signal for at least one switch arranged in the d.c. circuit of the d.c. actuator, depending on whether the saw-tooth signal lies below or above the actuating signal U
A
.
FIG. 5
shows two typical actuators and their d.c. circuits, which are operated by the supply voltage, in the example shown by the battery voltage of the motor vehicle. Part A shows a d.c. motor M for a bidirectional movement, for example for actuating an electric parking brake. Four switches S
1
to S
4
are shown, which symbolically represent the associated power transistors that are controlled by the mentioned switching signal PWM and a negated switching signal PWM.
Part B shows the control of an electromagnet, for example in the external actuation of an electromechanically actuated brake-force booster, by means of switch S that is switched by the mentioned switching signal.
The ON duration T
ein
and the OFF duration T
aus
of the switches is shown in Part C of FIG.
4
. This diagram shows the pulse-width modulated actuating signal which leads to a medium actuator current (not shown) having the specified size in the d.c. circuits of the actuators due to the mentioned low-pass behavior.
For the derivation, in particular for calculating the continuous actuating signal, as well as for the configuration of the pulse-width modulator it is generally assumed that the supply voltage to be switched by the pulse-width modulator for activating the actuator, in the example the battery voltage of the vehicle electric system U
Bat
, is always constant and corresponds to the nominal value of the battery voltage U
Bat,N
=12 Volt. Thus, the same pulse duty factor p=T
ein
/T always is obtained for a defined actuating signal U
A
. In this connection, the time T stands for the period of the saw-tooth signal. Assuming that the supply voltage U
Bat
that is to be switched corresponds to its nominal value U
Bat,N
, the following correlation then applies for the actuating signal U
A
:
U
A
=P·U
Bat
=P·U
Bat,N
(1)
For determining the pulse duty factor p, especially on a microcontroller, the nominal value of the supply voltage U
Bat,N
that is to be switched is taken as the basis. If the actually switched supply voltage U
Bat
does not correspond to its nominal value U
Bat,N
, as was assumed for calculating the pulse duty factor p, then the pulse duty factor p and, hence, the pulse width will remain constant; however, the pulse amplitude will deviate from its nominal value, namely Ubat,N. Due to Gl. (1), therefore, a voltage value U
A
deviating from the specified value U
A
results in the actuator circuit on average, and the actuator is actually controlled with this.
Consequently, the actuating value of a superior control system is not realized exactly in this case, since the actuator is controlled with a value differing from the actuating signal. This leads to a deterioration of the control quality which becomes more and more serious as the actual supply voltage deviates increasingly from the nominal voltage. In individual cases, the control circuit may not be able to set a specified value or may tend to exhibit instabilities.
The object of the invention is to design the above-mentioned circuit arrangement for generating a specified pulse-width modulated actuating signal for a d.c. actuator in such a way that the pulse duty factor is adapted to the actual value of the supply voltage, wherein such circuit has a pulse-width modulator consisting of a saw-tooth voltage generator that generates a relatively high-frequency saw-tooth signal with a constant frequency and a maximum amplitude that is equal to the value of the supply voltage serving as the reference voltage as well as a comparator, to which the saw-tooth signal and a continuous actuating signal having a predefined size can be applied as input signals and which is designed in such a way that it supplies a first binary switching signal for at least one switch that is arranged in the d.c. circuit of the actuator connected to the supply direct voltage when the saw-tooth voltage is below the actuating signal and it supplies a second negated binary switching signal when the saw-tooth voltage is above the actuating signal and which uses this to generate a pulse-width modulated actuating signal with a pulse width representing the value of the continuous actuating signal and a pulse amplitude corresponding to the supply voltage within a specified pulse duty factor.
This object is achieved by a method according to the invetion in that the actual value of the supply voltage is determined and the pulse duty factor is adapted to the actual value of the supply voltage.
For this purpose, preferably a nominal value of the supply voltage is divided by the a
Continental Teves AG & Co. OHG
Rader & Fishman & Grauer, PLLC
LandOfFree
Method and circuit for generating a pulse-width modulated... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and circuit for generating a pulse-width modulated..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and circuit for generating a pulse-width modulated... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2904328