Motor control circuit

A circuit for controlling the power provided to an induction load by a converter comprising:

• (a) ramping voltage generating circuit means for generating a voltage output signal which provides a first voltage signal for a first selected time period, a linear ramping voltage signal which changes from a first voltage level to a second voltage level at a substantially constant rate over a second selected time period, and the second voltage signal;
• (b) voltage-controlled oscillating circuit means connected to and substantially controlled by the ramping voltage generating circuit means for generating a pulse signal having a first, lower frequency substantially corresponding to the first voltage signal generated by the ramping voltage generating circuit means for a time corresponding to the first selected period of time, a linearly increasing frequency which increases from the first, lower frequency to a second higher frequency at a rate substantially proportionate to the rate at which the ramping voltage generating circuit means voltage output signal changes from the first voltage signal to the second voltage signal, and a second, higher frequency substantially corresponding to the second, voltage signal generated by the ramping voltage generating circuit means;
• and
• (c) constant-pulse-width circuit means connected to the voltage-controlled oscillating circuit means output for generating a control signal to a circuit providing AC power to the induction load such that the waveform provided across the induction load by the circuit providing the AC power has a substantially constant pulse-width, a frequency substantially proportionate to the frequency of the signal generated by the voltage-controlled oscillating circuit means and a substantially constant peak voltage.

A control circuit for controlling the activation of an induction motor comprising:

• (a) a thermostat, connected to monitor an external temperature, and connected in series between a first end of the induction motor and a power source for providing a closed circuit connection between the induction motor and the power source when the temperature detected by the thermostat is within a preselected range and an open circuit between the induction motor and the power source when the temperature detected by the thermostat is within a preselected range and an open circuit between the induction motor and the power source when the temperature detected by the thermostat is within a second range;
• (b) first voltage generating circuit means connected to the thermostat and induction motor for generating a first voltage signal when the thermostat provides a closed circuit connection;
• (c) a second voltage generating circuit means connected to the thermostat for providing a second voltage signal when the thermostat provides an open circuit connection;
• and
• (d) voltage comparator means, connected to receive the first and second voltage signals, for generating a first control signal when the first voltage signal is received and a second control signal when the second voltage is received;
• (e) control means, connected to said voltage comparator means, for activating the induction motor power source upon receipt of the first voltage signal.

A circuit for controlling an induction load powered by a DC source comprising:

• (a) a converter circuit means for receiving DC power and providing AC power to the induction load, said converter circuit means including means for switching the connection of the DC power across the induction load to provide a first positive voltage signal across the induction load, second substantially null voltage across the induction load a third negative voltage across the induction load, and a fourth substantially null voltage across both ends of the induction load, said second and fourth substantially null voltages provided by providing a conductive path between one of the two wires providing the DC power and both ends of the induction load;
• (b) converter circuit control means for providing a periodic control signal to said converter circuit means for switching said converter circuit means to alternately provide a positive voltage, first null voltage, negative voltage, and second null voltage across said induction load;
• and
• (c) start winding activation circuit means for the single phase induction load comprising:
• (i) ramp voltage generating circuit means for generating a voltage output signal which provides a first voltage signal for a first selected time period, a ramping voltage signal which increases at a constant rate from the first, voltage signal to a second, higher voltage signal over a second selected time period;
• (ii) voltage-controlled oscillating circuit means connected to and substantially controlled by the ramp generating circuit means for generating a pulse signal at a first, lower frequency substantially corresponding to the first, lower voltage signal generated by the ramp voltage generating circuit means, an increasing frequency which increases from the first, lower frequency to a second, higher frequency at a rate substantially proportionate to the rate at which the ramp voltage generating circuit means output voltage changes from the first voltage signal to the second voltage signal, and a second, higher frequency substantially corresponding to the second, higher voltage signal generated by the ramp voltage generating circuit means;
• and
• (iii) constant-pulse-width circuit means connected to the voltage-controlled oscillating circuit means output for generating a control signal to the converter circuit means such that the signal provided across the induction load by the converter circuit means has a substantially constant pulse-width, a frequency substantially proportionate to the frequency of the signal generated by the voltage controlled oscillating circuit means and a substantially constant peak voltage.

A temperature control circuit for an induction motor load power circuit comprising:

• (a) a thermostat means, connected to monitor an external temperature, and connected in series with the induction motor load and a power supply and having first, open and second, closed, states corresponding to off and on settings;
• (b) a first and second current source means electrically interconnected with said thermostat means such that the current source means are connected in parallel when said thermostat means in one of the first and second states;
• (c) a comparator means having an input interconnected to said first and second current source means, such that a first voltage is detected by the comparator means when said thermostat means is in one of the first and second states and a second voltage is detected by the comparator when said thermostat means is in the other of the first and second states;
• (d) control means interconnected to the output of said comparator means for activating the induction motor load power circuit when the first voltage is detected by the comparator;
• and
• (e) control means for sensing the rising DC bus voltage which is indicative of loss of induction motor load on DC converter due to the opening of the thermostat.

A method for starting an induction motor having a start winding, comprising the steps of:

• (a) controlling the pulse-width of an AC signal provided to the induction motor to maintain a substantially constant pulse-width;
• (b) controlling the amplitude of the AC signal provided to the induction motor to maintain a substantially constant peak amplitude;
• (c) providing the controlled AC signal to the induction motor at a first, lower frequency for a predetermined period of time;
• (d) activating the start winding of the induction motor during the predetermined period of time, wherein activating step (d) occurs substantially simultaneously with providing step (c);
• (e) linearly ramping the frequency of the controlled AC signal such that the frequency of the controlled AC signal being applied to the induction motor increases linearly from the first, lower frequency to a second, higher frequency, wherein linearly ramping step (e) occurs after the predetermined period of time of steps (c) and (d);
• and
• (f) providing the controlled AC signal to the induction motor at the second, higher frequency.