Circuit and method for power efficiency improvement of induction motors
First Claim
1. In a power control system equipped with a microcomputer consisting of a separate ROM and RAM memory and a microprocessor to execute instructions and an AC induction motor, an electronic circuit for improving power efficiency, comprising:
- power controller means for making induction current free-wheeling and for controlling source voltage input to maintain an optimum state in accordance with loading by performing alternating PWM chopping;
zero-crossing detector means for generating a zero crossing signal of a definite pulse width at zero crossing points of an alternating voltage waveform;
starting protector means for preventing destruction of a device by bypassing starting current through an induction motor during an initial transient state;
relay controller means for controlling said starting protector means to bypass said starting current for a specified period of time during an initial start-up;
combination logic means for combining said zero crossing signal with a PWM waveform to produce first output signals;
coupling buffer means for controlling and buffering said first output signals from said combination logic means to provide second output signals;
base driver means for controlling said power controller means with said second output signals from said coupling buffer means;
current/voltage converter means for detecting load current of said induction motor and converting said load current to voltage;
digital/analog converter means adapted to convert digital reference data into analog values;
a comparator to compare said voltage converted in said current/voltage converter means with said analog value of said digital/analog converter means; and
a microprocessor coupled to receive said zero crossing signal, provide a transient state indicating signal to said relay controller means, receive a comparison signal provided by said comparator means by comparing said voltage converted in said current/voltage converter means with said analog value, provide and periodically vary on the basis of said comparison signal provided by said comparator means the value of said digital reference data to said digital/analog converter means, and provide said PWM waveform to said combination logic means in response to reception of said zero crossing signal.
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Abstract
A circuit and method to improve power efficiency of AC induction motors is described for adopting an AC PWM chopper method in power input controls. For a period of several seconds after initially supplying power source voltage, the starting voltage is bypassed by a relay switch to prevent malfunctioning of devices.
A PWM waveform is provided by a microcomputer and it is combined with a zero crossing signal of the power source voltage. The combined signal is controlled and buffered by photo couplers, by which power source voltage is controlled with transistors of a power controller unit.
A current flow through the motor is detected and store into memory of the microcomputer. In a next sequence, another PWM waveform is provided to again detect other current flow through the motor and its detected value is compared with the previous value store in the memory. These sequences are repeated to search for a minimum current value according to variation of loading on the motor.
18 Citations
18 Claims
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1. In a power control system equipped with a microcomputer consisting of a separate ROM and RAM memory and a microprocessor to execute instructions and an AC induction motor, an electronic circuit for improving power efficiency, comprising:
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power controller means for making induction current free-wheeling and for controlling source voltage input to maintain an optimum state in accordance with loading by performing alternating PWM chopping; zero-crossing detector means for generating a zero crossing signal of a definite pulse width at zero crossing points of an alternating voltage waveform; starting protector means for preventing destruction of a device by bypassing starting current through an induction motor during an initial transient state; relay controller means for controlling said starting protector means to bypass said starting current for a specified period of time during an initial start-up; combination logic means for combining said zero crossing signal with a PWM waveform to produce first output signals; coupling buffer means for controlling and buffering said first output signals from said combination logic means to provide second output signals; base driver means for controlling said power controller means with said second output signals from said coupling buffer means; current/voltage converter means for detecting load current of said induction motor and converting said load current to voltage; digital/analog converter means adapted to convert digital reference data into analog values; a comparator to compare said voltage converted in said current/voltage converter means with said analog value of said digital/analog converter means; and a microprocessor coupled to receive said zero crossing signal, provide a transient state indicating signal to said relay controller means, receive a comparison signal provided by said comparator means by comparing said voltage converted in said current/voltage converter means with said analog value, provide and periodically vary on the basis of said comparison signal provided by said comparator means the value of said digital reference data to said digital/analog converter means, and provide said PWM waveform to said combination logic means in response to reception of said zero crossing signal. - View Dependent Claims (3, 4, 5, 6, 7, 8, 9, 11)
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2. An efficiency improvement process for an induction motor in which PWM data is memorized for optimum controlled voltage according to variation of loading on said induction motor, load current value through said induction motor is detected, zero-crossing points of an AC input source voltage are detected, and by setting up starting delay time during an initial state and comparing said detected load current value of the induction motor with memorized reference data, said motor is consequently operated in an optimum state, comprising:
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controlling a relay to protect devices by bypassing starting current through said motor for a specified period of time during an initial starting state; applying an initial voltage to said induction motor by cutting off said relay for a few seconds and generating a PWM waveform in said controlling step; detecting a first value representing load current through said induction motor, converting the load current to voltage, and storing the voltage into memory; detecting a second value representing load current through said induction motor by providing a PWM waveform decreased by one step; comparing said first and second values; repeating said first value detecting step if said first value detected in said first value detecting step is larger than said second value detected in said second value detecting step, and detecting a third value representing load current by providing a PWM waveform having a voltage decreased by one step after checking elapse of a specified period of time if said first and second values are equal; comparing said third current value detected with said current value stored in memory, and if equal, then repeating said second value detecting step, if said stored current value is larger than said third value, then repeating said first value detecting step, and if said stored value is smaller than said third value, then increasing voltage by one step where instant variation of load current is checked; determining if said detected value of said first value is smaller than said detected value of said second value, then detecting a fourth value representing a load current through said induction motor after providing a PWM waveform having a voltage increased by one step; comparing said fourth detected value with said stored value, and if said fourth detected value is smaller than said stored value, then increasing said voltage by one step, and if equal or larger, then repeating said second value detecting step.
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10. A power control system, comprising:
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power controller means connectable between an alternating current induction motor and a source of alternating electrical voltage exhibiting an alternative voltage waveform, for controlling application of said alternating electrical voltage from the the source to the motor in dependence upon characteristics of a plurality of control signals; zero crossing detector means for generating a zero crossing signal having distinct logical states each exhibiting a pulse width coinciding in duration with duration of said alternating voltage waveform between zero crossing points; comparator means for detecting electrical current flowing between said power controller means and the motor, and for generating a comparison signal by comparing a first voltage proportional to said electrical current and a second voltage obtained from reference data; processor means storing PWM data defining PWM waveforms corresponding to each said second voltage obtained from said reference data, coupled to receive said zero crossing signal, to receive said comparison signal, and to provide said reference data to said comparator means on the basis of the value of said comparison signal, for in response to reception of said zero crossing signal, providing to said comparator means and periodically varying on the basis of said comparison signal, and value of said second voltage obtained from said reference data, and for in response to reception of said zero crossing signal, generating a PWM waveform from said PWM data corresponding to the value of said second voltage obtained from said reference data when said comparison signal is generated by said comparator means; and logic means connected between said power controller means and said processor means, for receiving said zero crossing signal and said PWM waveform and providing to said power controller means a first control signal exhibiting a first logic state in response to the occurrence of a first logical state of said zero crossing signal, a second control signal exhibiting a second logic state in response to the absence of said first logical signal of said zero crossing signal, a first PWM waveform as a third control signal, and a second PWM waveform as a fourth control signal. - View Dependent Claims (12, 13, 14, 15, 16, 17, 18)
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Specification