Control of stirling cooler displacement by pulse width modulation of drive motor voltage

A method for controlling the amplitude of the motor drive voltage applied to a reciprocating electrical motor driving a load at a selected operating frequency and period, the method comprising:

• (a) applying a pulse train voltage to the motor during one-half of its operating period, the pulse train having a pulse repetition frequency which is a harmonic of the motor's operating frequency;
• (b) applying the complement of said pulse train voltage to the motor during the other half of its operating period;
• and
• (c) modulating the duty cycle of the first pulse train voltage and therefore its complement to control the amplitude of the Fourier component of motor drive voltage at the operating frequency.

A method for controlling the amplitude of the motor drive voltage applied to a reciprocating electrical motor driving a load at a selected operating frequency, the method comprising:

• (a) generating a pulse train at a harmonic of the selected operating frequency;
• (b) generating a square wave at the operating frequency;
• (c) generating a series of pulses in synchronism with said pulse train, said series of pulses having a controllably variable modulated width;
• (d) generating the complement of the series of modulated pulses;
• (e) applying the series of modulated pulses to the motor during one-half of the motor's operating cycle and applying the complement of the series of modulated pulses to the motor during the other half cycle;
• and
• (f) controllably varying said modulated width to control the voltage applied to the motor at the operating frequency.

A circuit for controlling the amplitude of the motor drive applied to a reciprocating electrical motor driving a load at a selected operating frequency, the control circuit comprising:

• (a) oscillator circuit means for generating a pulse train at a frequency which is harmonic of said operating frequency;
• (b) circuit means for generating a square wave at said operating frequency;
• (c) a pulse generating circuit means for generating modulated width pulses having its input connected to the output of said oscillator circuit means and having a control signal input for controlling the pulse width of the pulses at the output of the pulse generating circuit means;
• (d) an exclusive OR circuit means having one input connected to the output of the square wave generating circuit means and the other input connected to receive the pulse width modulated pulses for inverting modulated width pulses to provide a complementary output during half of each operating frequency cycle;
• and
• (e) a power switching circuit means having its input connected to the output of the exclusive OR circuit means and its output connected to said motor for switching the voltage applied to the motor in response to said modulated width pulses.