Electricity: motive power systems – Induction motor systems – Primary circuit control
Patent
1984-06-29
1986-04-08
Smith, Jr., David
Electricity: motive power systems
Induction motor systems
Primary circuit control
318803, H02P 540
Patent
active
045815690
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
BACKGROUND OF THE INVENTION
This invention relates to an AC motor control apparatus in which the current loop of an AC motor such as an induction motor is in digital form.
The recent spread of microcomputers has made it possible to substitute a microcomputer for a variety of discrete circuits. This holds for the control circuit of an AC motor, particularly the velocity control loop of which has already been placed under the control of a microcomputer.
FIG. 1 is a block diagram of a conventional AC motor control circuit. In FIG. 1, numeral 1 denotes a three-phase AC motor such as one for rotating the spindle of a machine tool. Numeral 2 denotes a pulse generator for producing velocity pulses TSA in dependence upon the rotation of the AC motor 1. Numeral 3 designates an arithmetic unit comprising a computer and which is part of a control section for the motor 1. The arithmetic unit 3 senses the actual velocity RV of the AC motor 1 on the basis of the velocity pulses TSA from the pulse generator, and produces an amplitude command Id as well as U- and V-phase phase commands .theta.ud, .theta.vd in dependence upon the difference between the actual velocity and a commanded velocity CV. The arithmetic unit 3 is composed of a processor 30 for performing processing, a program memory 31 storing a control program, a data memory 32 for storing various data, input/output ports 33, 34, a counter 35, and an address/data bus 36 interconnecting these components. The processor 30, in accordance with the control program in the program memory 31, reads via the bus 36 a value recorded in the counter 35, which counts the velocity pulses TSA, obtains the actual velocity RV of the AC motor 1 from the difference between the read value and the previously read value the processor 30 then, calculates the amplitude command Id on the basis of the difference between the actual velocity and the commanded velocity CV issued by an external unit, and applies the amplitude command to the input/output port 33 through the bus 36. Further, in accordance with the control program, the processor 30 retrieves a phase conversion table in the data memory 32 on the basis of the value from the counter 35, reads the corresponding U- and V-phase phase commands .theta.ud and .theta.vd, respectively, and applies these commands to the input/output port 34 via the bus 36. In order to deliver current commands Iud, Ivd in the form of U- and V-phase sinusoidal signals to which motor excitation frequency wt has been applied, the phase conversion table is stored digitally in the form of numerical values representing each of the crest or peak values of the sinusoidal signals.
Numeral 4a denotes a digital/analog converter (DA circuit) for converting the digital amplitude command Id into an analog amplitude command Is. Numerals 4b, 4c denote multiplying-type digital/analog conversion circuits for converting the respective U- and V-phase current commands Iud, Ivd into analog quantities and for multiplying these analog quantities by the analog amplitude command Is to produce analog U- and V-phase current commands Iu, Iv, respectively. Numeral 5 designates a W-phase current forming circuit for forming a W-phase current command Iw from the analog U- and V-phase current commands Iu, Iv. Numeral 6 represents an operational amplifier for obtaining the difference between actual phase currents and the commanded currents Iu, Iv, Iw in the respective phases. The operational amplifier 6 is composed of an operational amplifier for calculating the difference between the commanded currents Iu, Iv, Iw in the respective phases, and the actual phase currents Iau, Iav, Iaw, respectively, and an arithmetic unit 10 for producing a W-phase phase current Iaw by adding Iav and Iau, which are sensed by current transformers 9r, 9s. Numeral 7 denotes a pulse-width modulating circuit, and numeral 8 an inverter controlled by an output signal from the pulse-width modulating circuit for providing a DC voltage derived from an externally provided three-phase AC power supply and a re
REFERENCES:
patent: 4364109 (1982-12-01), Okado et al.
patent: 4387421 (1983-06-01), Zach et al.
patent: 4409534 (1983-10-01), Bose
patent: 4419615 (1983-12-01), Muto et al.
Fujioka Yoshiki
Hirota Mitsuhiko
Fanuc Limited
Smith Jr. David
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