Electricity: motive power systems – Induction motor systems – Primary circuit control
Patent
1985-12-12
1987-10-27
Smith, Jr., David
Electricity: motive power systems
Induction motor systems
Primary circuit control
318805, 318798, H02P 540
Patent
active
047032456
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a method and apparatus for controlling a synchronous motor in response to a PWM (Pulse Width Modulation) signal generated from a command input and a position signal of a rotating magnetic field and, more particularly, to a method and apparatus for controlling a permanent magnet synchronous motor having improved output torque characteristics.
FIG. 1 shows a conventional PWM control apparatus for a permanent magnet synchronous motor. Reference symbol E denotes a 3-phase power source. Reference numeral 3 denotes a rectifying circuit; 4, a transistor inverter; and 1, a transistor PWM control circuit. Reference symbol M denotes a permanent magnet synchronous motor. Reference numeral 2 denotes a rotor position detector, such as a pulse encoder, for detecting the position of a rotor in the permanent magnet synchronous motor M. The transistor PWM control circuit 1 compares a reference speed V0 with a present speed Vs of the rotor, which is obtained by processing a rotor position S detected by the rotor position detector 2. Transistors TA to TF in the transistor inverter 4 are turned on/off to control currents flowing through the U, V, and W phase windings of the permanent magnetic synchronous motor, thereby controlling the rotating speed of the motor. A typical arrangement of the transistor PWM control circuit 1 is illustrated in FIG. 2. Referring to FIG. 2, reference numeral 5 denotes a signal processor for calculating a voltage VS, representing the present rotor speed, in accordance with the rotor position detection output S; 6 and 7, ROMs for storing U and W phase command values corresponding to rotor positions, such that the resultant vector of currents flowing in the U, V, and W phases has a phase perpendicular to the main flux of a magnetic field generated by the rotor; and 8, a differential amplifier for amplifying the difference between the voltage V0, representing the speed command, and the voltage VS, representing the present speed from the signal processor 5, and generating an amplified difference signal. Reference numeral 9 denotes a filter which decreases gain at high frequencies and increases gain at low frequencies, and which clamps peak voltage with Zener diodes ZD. Reference numerals 10 and 11 denote multiplying digital/analog (D/A) converters. The multiplying D/A converter 10 multiplies an output voltage VE, which represents the difference between the speed command V0 and the present speed VS and which is generated by the filter 9, by the U command value read out from the ROM 6. Similarly, the multiplying D/A converter 11 multiplies the output voltage VE by the W command read out from the ROM 7. The multiplying D/A converters 10 and 11 generate U and W phase current commands RTC and TTC, respectively. Reference numeral 12 denotes an adder for adding the U and W phase current commands RTC and TTC, and generating a V phase current command STC which is shifted from the U and W phases by 120.degree.. Reference numerals 13 and 14 denote detectors for detecting currents Iu and Iw flowing through the U and W armature windings of the synchronous motor M. Reference numeral 15 denotes an adder for adding the U and W phase currents IR and IT detected by the U and W phase current detectors 13 and 14 to calculate a V phase current IS. Reference numerals 16, 17, and 18 denote circuits for supplying the current command voltages representing the currents to be fed to the U, V, and W armature windings. The circuits 16, 17, and 18 have an identical arrangement except for input signals supplied to the respective circuits. The circuit 16 comprises an operational amplifier 19 for amplifying the difference between the U phase current command RTC and the present U phase detection current IR, and a low-pass filter 20 for transmitting only the frequency component of the reference carrier wave, which is output from the operational amplifier 19. The circuit 17 receives the V phase current command STC and the present current IS, and the circuit 18 receives the W
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Kobayashi Toshio
Sakamoto Keiji
Fanuc Ltd
Smith Jr. David
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