Electricity: motive power systems – Synchronous motor systems – Hysteresis or reluctance motor systems
Reexamination Certificate
2000-12-22
2002-04-02
Ro, Bentsu (Department: 2837)
Electricity: motive power systems
Synchronous motor systems
Hysteresis or reluctance motor systems
C318S254100, C318S432000, C388S906000
Reexamination Certificate
active
06366048
ABSTRACT:
BACKGROUND AND SUMMARY OF THE INVENTION
This application claims the priority of German Application 19961798.8, filed Dec. 22, 1999, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a method and an arrangement for regulating the phase current in a switched reluctance machine, whose stator windings in each phase are each connected to a DC chopper controller which is connected to a regulator which processes the control error between the required current value and the measured actual current value and applies pulse-width-modulated electrical pulses to the DC chopper controller.
An arrangement of the type described above is known (U.S. Pat. No. 5,754,024). The DC chopper controller in each phase of the known arrangement comprises a first series circuit of a switching transistor with a freewheeling diode, and a second series circuit of a freewheeling diode with a switching transistor. The switching transistor in the first series circuit is connected to the positive pole of a DC voltage source, and the switching transistor in the second series circuit is connected to the negative pole of the DC voltage source. The freewheeling diodes are reverse-biassed with respect to the polarity of the DC voltage source. The control electrodes of the switching transistors, which are IGBTs, are connected to a pulse-width modulator which has a first input connected to a clock generator, a second input connected to a comparator, and a third input to which an on/off signal is applied. The phase winding is arranged in series with a current sensor between the points where the switching transistors are connected to the freewheeling diodes. A first input of the comparator has a required current value applied to it, and a second input has the actual current value from the current sensor applied to it. The required current value and the on signal together with the off signal for the pulse-width modulator are determined as a function of the rotor position, measured by a sensor. The pulse-width modulator starts when it is intended to apply current to the respective winding, and stops when it is intended to stop current flowing in the winding once again.
German Patent DE 43 10 772 C2 discloses a method for regulating the phase current in a switched reluctance machine, whose stator windings in each phase are each connected to a DC chopper controller, which is connected to a regulator which processes the control error between the required current value and the measured actual current value and applies pulse-width-modulated electrical pulses to the DC chopper controller. In the case of the control circuit disclosed there, the control error between the required current value and the actual current value is supplied to a PI regulator.
European Patent EP 0 684 693 A2 discloses an arrangement for regulating the phase current of brushless DC machines and switched reluctance machines, in which the control error is determined from the required values and from actual current values obtained by sampling and equidistant intervals.
A three-point regulator with hysteresis is suitable for regulating the phase current in the reluctance machine. The output of the three-point regulator can assume three states, each of which can be associated with a switching state of a converter or DC chopper controller. The association with the “on, short-circuit” and “off” switching states of the current regulator allows the phase current to be regulated not only in motor operation but also in generator operation down to zero speed, without the three-point regulator needing to be switched. If the three-point regulator has identical switching thresholds when the reluctance machine is being operated as a motor and as a generator, this, in fact, results in a higher mean current value in generator operation than in motor operation. This effect can be minimized by hysteresis loops which are shifted one above the other. One advantage of a three-point regulator with hysteresis is its simple structure.
A disadvantage of the three-point regulator is that the converter switching frequency caused by the three-point regulator depends not only on the switching thresholds but also on the rate of current change in the machine winding, which in turn depends on the phase voltage, the winding resistance, the present current value, the phase inductance (which is dependent on the rotor position) and the rotation speed. Taking account of these influencing variables, the switching thresholds of the three-point regulator must be selected such that the maximum switching frequency of the power semiconductors in the converter is not exceeded. During operation of the reluctance machine, this results in switching frequencies which are well below the maximum switching frequency and are in the audible range. As a result the reluctance machine produces irritating noises.
The invention is based on the problem of specifying a method which can be matched flexibly to different situations that occur with reluctance machines, and an arrangement for regulating the current in phase windings of a switched reluctance machine, in which irritating noise from the reluctance machine, caused by the switching frequencies of the converter active devices is largely avoided and in which the phase currents can be set dynamically and quickly to the predetermined required values.
According to the invention, with regard to a method of the type described initially, the problem is solved by determining the control error from the required values and from actual current values obtained by sampling at equidistant intervals. Also a first manipulated variable is formed from the control error digitally using a proportional-integral characteristic, by linear superimposition of an integral element and a proportional element which is multiplied by the respective electrical angular position of the reluctance machine. Furthermore the first manipulated variable has a second manipulated variable superimposed on it linearly, which is formed as a pilot control value of a characteristic value by multiplication by the rotation speed, which characteristic value is read, as a function of the phase current and as a function of the electrical angular position of the rotor, from a characteristic map, which includes the derivative of the magnetic flux of the reluctance machine with regard to the electrical angular position, as a function of the electrical angular position of the rotor of the reluctance machine and as a function of the phase current. The method according to the invention allows the phase currents to be well regulated even at high rotation speeds and at high pulse-width-modulation frequencies, as well as allows for rapid changes in the induced phase voltage.
One preferred embodiment provides that characteristic values are stored in a table as a function of the electrical rotor angle positions. The characteristic values are determined from a data set with the magnetic flux values of the reluctance machine as a function of the electrical rotor angular position and of the phase currents by deriving the flux values with respect to the rotor angle, by division by a saturation current which is typical for the transition to the saturated magnetic state, and by forming the mean values of the respective rotor position. The pilot value is formed by multiplication of the characteristic value, which is read as a function of the measured electrical rotor angular position, by the rotation speed and the phase current. In this embodiment, relatively little memory capacity is required for storing the characteristic values. The approximate determination of the rotational voltage value for the pilot control is not a disadvantage, because the regulator can quickly compensate for a relatively small error between the required value and the actual value.
In one expedient embodiment, the control error at the time t
K
=k*T
A
is calculated using the following equation e (k)=w (k)−x (k) where e is the control error, W is the required current value, x is the actual
Crowell & Moring LLP
Daimler-Chrysler AG
Ro Bentsu
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