Electricity: motor control systems – Closed loop speed control system for dc motor with commutator – Field control – or field and armature control – by analog...
Reexamination Certificate
1999-09-14
2001-12-04
Nappi, Robert E. (Department: 2837)
Electricity: motor control systems
Closed loop speed control system for dc motor with commutator
Field control, or field and armature control, by analog...
C388S819000, C318S254100, C318S434000, C318S696000, C318S599000
Reexamination Certificate
active
06327424
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method of operating an electric motor controlled through power transistors and to a circuit for that purpose. The invention also relates to a function-generating control module for power transistors for this purpose, especially for a circulating pump motor for a heating system. More particularly, the invention relates to a method of modulating the pulse duration, also referred to herein as the pulse width or pulse length, of the voltage pulses used as control pulses for power transistors, generally under the control of a microprocessor and in a system in which the microprocessor can transfer data to an intermediate register and the register contents can be read out by a module which initiates the voltage pulses and based upon the register contents, determines the lengths or durations of those pulses. The invention also relates to a circuit for this purpose.
BACKGROUND OF THE INVENTION
Processes in which modulated pulses are used to control power transistors are referred to frequently as pulse duration or pulse width modulation (PWM) systems and can be used to control alternating current motors. In pulse width modulation, a control unit determines a duration of each of a succession of pulses which are applied as voltage pulses to control power transistors so that behind the power transistors, a correspondingly pulsed supply voltage is developed across the motor winding.
Since the motor winding has substantial inductivity, the high frequency alternating voltage can be smoothed to a more or less direct current. If the inductivity of the windings themselves are insufficient for this purposes, ahead of the motor terminals, a smoothing filter can be provided. The result is a direct current flow through the windings or a direct voltage applied across the winding. This direct current can be varied as to its level by modulation of the pulse width and the motor can be a dc motor.
The modulation of the pulse width can be so effected that in the motor windings an alternating current of comparatively low frequency can flow.
The pulse width modulation is effected utilizing a microprocessor which is connected to a module for generating the control signals for the power transistors (PWM module) by writing the pulse width of the next pulse to be generated as a value in a register. The PWM modules reads this value out and switches the power transistor on for the duration of the read value. If, based upon such PWM values, it is desirable to generate a curve, for example, in alternating voltage curve, the microprocessor must inscribe for each switching time a respective value in the register. As a result, a relatively large processor capacity or computer capacity is required so that the microprocessor can respond rapidly to load limits and the like. As soon as the limit is exceeded and the processor is no longer capable of resetting the register in the correct rhythm, the output of the PWM module and the resulting low frequency alternating current signal contain discontinuities. These can lead to electromagnetic failures or noise and require larger filters or additional filter components at considerable cost.
OBJECTS OF THE INVENTION
It is the principal object of the present invention to provide an improved method of pulse width modulation which can utilize smaller capacity processor or computer units, which can eliminate the need for expensive filters and which can insure optimum pulse sequences at high clocking rates and smooth current curves.
Another object of the invention is to provide an improved electronic circuit system for carrying out the process.
It is also an object of the invention to provide an improved circulating pump system for a hot water heating circulation which uses electronic commutation in a more efficient way than has been heretofore.
SUMMARY OF THE INVENTION
These objects and others which will become apparent hereinafter are attained, in accordance with the invention, in a method for modulating the duration of pulses for controlling power transistors which comprises the steps of:
(a) storing data with respect to sequences in a microprocessor;
(b) writing with the microprocessor data characteristic of a succession of pulses of at least one pulse sequence to an intermediate register;
(c) reading with a module connected to the intermediate register the contents thereof and based upon the data read from the intermediate register and characterizing the one pulse sequence:
(c1) initiating and applying to the power transistors a corresponding succession of transistor-control pulses,
(c2) limiting a duration of a first, starting one of the transistor-control pulses to a duration determined by data contents of the register, and
(c3) varying the durations of the remaining transistor-control pulses of the succession of transistor-control pulses to ultimately reach a final transistor-control pulse of the succession of transistor-control pulses in accordance with the data in the intermediate register.
A circuit in accordance with the invention can comprise:
a microprocessor for storing data with respect to pulse sequences;
an intermediate register connected to the microprocessor whereby the microprocessor can write data characteristic of a succession of pulses of at least one pulse sequence to the intermediate register; and
a module connected to the intermediate register for reading out the contents thereof and based upon data read from the intermediate register and characterizing the one pulse sequence:
initiating and applying to the power transistors a corresponding succession of transistor-control pulses,
limiting a duration of a first starting one of the transistor control pulses to a duration determined by data contents of the register, and
varying the durations of the remaining transistor-control pulses of the succession of transistor control pulses to ultimately reach a final transistor control pulse of the succession of transistor-control pulses in accordance with the data in the intermediate register.
More specifically, in the method aspects of the invention, for an electrocommuted DC motor utilized as a pump drive for a circulating pump for a heating system, the power to the electric motor is delivered through power transistors, at least one microprocessor is provided, an intermediate register is connected to the microprocessor and the contents of the intermediate register can be read out by a module which determines the lengths or durations of the voltage pulses based upon the register contents and initiates those voltage pulses which are applied to the power transistors to trigger them into conduction. The microprocessor inscribes data characterizing a plurality of pulse sequences into the intermediate register and the module reads the data from the intermediate register. Based upon the data read out, the module initiates a plurality of voltage pulses of variable length, the length or duration of the first or starting pulse and the variation of the lengths of the pulses following the starting pulse and up to and including the last pulse or final pulse are calculated from the data in the intermediate register.
The basic thought of the invention is that the PWM module is an intelligent module which based upon parameters drawn from the register can automatically control the width of the next pulse and therefore the pulse width modulation function. The PWM module can advantageously be a simple hardware component like a clock generator and/or counter so that a high pulse frequency and thus a high quality of modulation can be achieved.
An important advantage of the invention is that the “intelligent” PWM module can relieve the processor and thus eliminate the need for the processor to make specific pulse by pulse decisions as to the width of each succeeding pulse. The capacity of the microprocessor can be significantly reduced which can contribute to a corresponding reduction of the fabrication costs of the control unit. The process of the invention can be generally utilized for any purposes for which pulse width modulat
Dubno Herbert
Martin Edgardo San
Nappi Robert E.
Wilo GmbH
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