AC inverter drive

An improved drive for controlling the speed of an AC induction motor, the stator winding of which is energized by a variable frequency, variable voltage inverter, the inverter providing a voltage to the stator winding of the motor, the magnitude of which is determined by a magnitude of a first input signal to the inverter, the inverter causing the voltage to be applied to the stator winding at a frequency determined by a magnitude of a second input signal to the inverter, the energization of the stator winding causing a rotating field to be established in the motor, slip appearing in the motor as the difference between the speed of the rotating field and the speed of a rotor of the motor, said drive comprising:

• a first conductor means (131) couplable to the inverter for supplying the first input signal to the inverter;
• a second conductor (133) couplable to the inverter for applying the second input signal to the inverter;
• a speed sensor (134) couplable to the motor rotor for providing a signal indicative of the speed of the motor rotor;
• a speed reference signal source providing a signal corresponding to a desired speed of the motor;
• a speed regulating amplifier (110) receiving the signals from said speed sensor and said speed reference signal source and having an output providing a speed error signal;
• means for selecting a portion of said speed error signal to form a first output signal providing slip limit to said drive;
• slip determining means (126) responsive to the speed of the motor rotor and the energization frequency of the stator winding for providing a signal indicative of the slip appearing in the motor;
• a slip regulating amplifier (118) receiving said first output signal and the slip signal from said slip determining means and providing a second output signal;
• a summing amplifier (124) receiving said motor rotor speed signal from said speed sensor and said second output signal of said slip regulating amplifier and providing an third output signal for forming said first input signal in said first conductor means and comprising said second input signal in said second conductor,
• an absolute value circuit (128) in said first conductor means for said output signal of said summing amplifier;
• low speed boost means coupled to said first conductor means for adding a low speed boost signal to the signal in said first conductor means, the magnitude of said low speed boost signal not exceeding that required to provide proper no-load excitation to the stator winding of the motor;
• and
• load boost signal means, said load boost signal means having an input coupled to the output of said speed regulating amplifier, an absolute value circuit, means for selecting a portion of said speed error signal of said speed regulating amplifier to form a load boost signal, and an output coupled to said first conductor means for adding said load boost signal to the signal in said first conductor means.

An improved drive for controlling the operative condition of an AC induction motor, the stator winding of which is energized by a variable frequency, variable voltage power supply, the power supply providing a voltage to the stator winding of the motor, the magnitude of which is determined by a characteristic of a first input signal to the power supply, the power supply causing the voltage to be applied to the stator winding at a frequency determined by a characteristic of a second input signal to the power supply, the energization of the stator winding causing a rotating field to be established in the motor, slip appearing in the motor as the difference between the speed of the rotating field and the speed of a rotor of the motor, said drive comprising:

• a first conductor means (131) couplable to the power supply for supplying the first input signal to the power supply;
• a second conductor (133) couplable to the power supply for applying the second input signal to the power supply;
• a speed sensor (134) couplable to the motor rotor for providing a signal indicative of the speed of the motor rotor;
• a speed reference signal source providing a signal corresponding to a desired speed of the motor;
• a speed regulating amplifier (110) receiving the signals from said speed sensor and said speed reference signal source and having an output providing a speed error signal;
• slip determining means (126) responsive to the speed of the motor rotor and the energization frequency of the stator winding for providing a signal indicative of the slip appearing in the motor;
• and
• a slip regulating amplifier (118) receiving the speed error signal from said speed regulating amplifier and the slip signal from said slip determining means and providing an output signal, said output signal forming said first input signal in said first conductor means and comprising said second input signal in said second conductor.

An improved drive for controlling the speed of an AC induction motor, the stator winding of which is energized by a variable frequency, variable voltage inverter, the inverter providing a voltage to the stator winding of the motor, the magnitude of which is determined by a magnitude of a first input signal to the inverter, the inverter causing the voltage to be applied to the stator winding at a frequency determined by a magnitude of a second input signal to the inverter, the energization of the stator winding causing a rotating field to be established in the motor, slip appearing in the motor as the difference between the speed of the rotating field and the speed of a rotor of the motor, said drive comprising:

• a first conductor means (131) couplable to the inverter for supplying the first input signal to the inverter;
• a second conductor (133) couplable to the inverter for applying the second input signal to the inverter;
• a speed sensor (134) couplable to the motor rotor for providing a signal indicative of the speed of the motor rotor;
• a speed reference signal source providing a signal corresponding to a desired speed of the motor;
• a speed regulating amplifier (110) receiving the signals from said speed sensor and said speed reference signal source and having an output providing a speed error signal;
• means for selecting a portion of said speed error signal to form a first output signal providing slip limit to said drive;
• slip determining means (126) responsive to the speed of the motor rotor and the energization frequency of the stator winding for providing a signal indicative of the slip appearing in the motor;
• and
• a slip regulating amplifier (118) receiving said first output signal and the slip signal from said slip determining means and providing a second output signal, said second output signal forming said first input signal in said first conductor means and comprising said second input signal in said second conductor,
• an absolute value circuit (128) in said first conductor means for said second output signal;
• low speed boost means coupled to said first conductor means for adding a low speed boost signal to the signal in said first conductor means, the magnitude of said low speed boost signal not exceeding that required to provide proper no-load excitation to the stator winding of the motor;
• and
• load boost signal means, said load boost signal means having an input coupled to the output of said speed regulating amplifier, an absolute value circuit, means for selecting a portion of said speed error signal of said speed regulating amplifier to form a load boost signal, and an output coupled to said first conductor means for adding said load boost signal to the signal in said first conductor means.