Single phase to three phase converter capable of variable speed motor operation

Claim 2

Apparatus for converting a single phase AC input to a three phase AC output comprising: (a) a pair of single phase AC input terminals connected to a pair of input lines; (b) three output lines connectable to a three phase motor load; (c) an inverter circuit connected to the input lines to receive single phase AC power therefrom and having an output node connected to one of the output lines, the inverter circuit responsive to control signals to provide an AC output voltage at its output node; (d) a bi-directional switch responsive to a control signal connected between one of the input lines and a second of the output lines, the third output line connected to the other of the input lines; (e) control means, connected to monitor the voltage on the three output lines and the output current through the bi-directional switch and from the inverter circuit, for providing control signals to the bi-directional switch and the inverter circuit to provide output currents from the inverter circuit and through the bi-directional switch to the motor which have fundamental frequency components lower than the frequency of the AC input voltage on the input lines and at different phases whereby controlled start-up of a three phase AC motor connected to the output lines can be obtained.

Claim 3

The apparatus of claim 1 wherein the inverter circuit includes a pair of DC bus lines, a pair of capacitors connected together at a node and connected across the DC bus lines, the node between the capacitors connected to one of the input lines, a pair of rectifying diodes connected together at a node and connected across the DC bus lines, the node between the diodes connected to the other of the input lines, and two gate controlled switching devices connected together at the output node and connected across the DC bus lines, and wherein the control means controls the switching of the switching devices in the inverter circuit.

Claim 4

The apparatus of claim 2 wherein the gate controlled switching devices are power transistors.

Claim 5

The apparatus of claim 1 wherein the control means estimates the speed of a motor connected to the output lines from the measured output voltages and the inverter circuit and bi-directional switch currents and provides a controlled start-up of the motor by providing fundamental current components at increasing frequency on the output lines as the speed of the motor increases.

Claim 6

The apparatus of claim 1 wherein after a motor connected to the output lines has started up and approaches its rated speed, the control means controls the bi-directional switch to conduct constantly and controls the inverter to provide balanced three phase voltages across the three output lines.

Claim 7

The apparatus of claim 1 wherein the bi-directional switch is a triac.

Claim 8

The apparatus of claim 1 wherein the control means provides controlled start-up of a motor connected to the output lines by providing increasing frequency output current through the bi-directional switch and from the inverter circuit as the speed of the motor increases, and after start-up of the motor, the control means turns off the bi-directional switch and operates the inverter circuit to provide single phase power to the motor to drive the motor up to near rated speed, and then turns on the bi-directional switch to conduct constantly and controls the switching of the inverter circuit to provide balanced three phase output voltages on the three output lines.

Claim 9

The apparatus of claim 7 wherein after start-up of a motor connected to the output lines when the motor has reached at or near its rated speed, the control means operates the inverter circuit to provide a selected voltage level at the rated frequency to the motor and switches the bi-directional switch to provide a selected phase delay of conduction and a selected voltage level on the output line connected to the bi-directional switch at the rated frequency, such that the voltage applied to the motor at the three output lines at the rated frequency of the motor may be varied to control the motor speed and flux level.

Claim 10

Apparatus for converting a single phase AC input to a three phase AC output which is provided to a three phase induction motor comprising: (a) a pair of single phase AC input terminals connected to a pair of input lines; (b) three output lines connectable to the three phase motor load; (c) an inverter circuit connected to the input lines to receive single phase AC power therefrom and having an output node connected to one of the output lines, the inverter circuit including a pair of DC bus lines, a pair of capacitors connected together at a node and connected across the DC bus lines, the node between the capacitors connected to one of the input lines, a pair of rectifying diodes connected together at a node and connected across the DC bus lines, the node between the diodes connected to the other of the input lines, and two gate controlled switching devices connected together at the output node and connected across the DC bus lines; (d) a bi-directional switch responsive to a control signal connected between one of the input lines and a second of the output lines, the third output line connected to the other of the input lines; (e) control means, connected to monitor the voltage on the three output lines and the output current through the bi-directional switch and from the inverter circuit, for providing control signals to the bi-directional switch and the gate controlled switching devices of the inverter circuit to provide output currents from the inverter circuit and through the bi-directional switch to the motor which have fundamental frequency components lower than the frequency of the AC input voltage on the input lines and at different phases and at increasing frequency as the speed of the motor increases to provide controlled start-up of motor connected to the output lines, wherein after start-up of the motor, the control means turns off the bi-directional switch and controls the switching devices of the inverter circuit to provide single phase power of increasing frequency to the motor as the motor increases in speed until the speed of the motor is near its rated speed, and thereafter controls the bi-directional switch to conduct constantly and controls the switching devices of the inverter circuit to provide balanced three phase power to the motor at the rated frequency of the motor.

Claim 11

Apparatus for converting a single phase AC input to a three phase AC output which is provided to a three phase induction motor comprising: (a) a pair of single phase AC input terminals connected to a pair of input lines; (b) three output lines connectable to the three phase motor load; (c) an inverter circuit connected to the input lines to receive single phase AC power therefrom and having an output node connected to one of the output lines, the inverter circuit including a pair of DC bus lines, a pair of capacitors connected together at a node and connected across the DC bus lines, the node between the capacitors connected to one of the input lines, a pair of rectifying diodes connected together at a node and connected across the DC bus lines, the node between the diodes connected to the other of the input lines, and two gate controlled switching devices connected together at the output node and connected across the DC bus lines; (d) a bi-directional switch responsive to a control signal connected between one of the input lines and a second of the output lines, the third output line connected to the other of the input lines; (e) control means, connected to monitor the voltage on the three output lines and the output current through the bi-directional switch and from the inverter circuit, for providing control signals to the bi-directional switch and the gate controlled switching devices of the inverter circuit to provide output currents from the inverter circuit and through the bi-directional switch to the motor which have fundamental frequency components lower than the frequency of the AC input voltage on the input lines and at different phases and at increasing frequency as the speed of the motor increases to provide controlled start-up of motor connected to the output lines, wherein after start-up of the motor, the control means turns off the bi-directional switch and controls the switching devices of the inverter circuit to provide single phase power of increasing frequency to the motor as the motor increases in speed until the speed of the motor is near its rated speed, and thereafter controls the bi-directional switch to conduct constantly and controls the switching devices of the inverter circuit to provide balanced three phase power to the motor at the rated frequency of the motor.

Claim 12

The apparatus of claim 9 wherein the control means estimates the motor speed from the measured output voltages and the inverter circuit and bi-directional switch currents and provides a controlled start-up of the motor by providing fundamental current components at increasing frequency as the speed of the motor increases.

Claim 13

The apparatus of claim 9 wherein the gate controlled switching devices are power transistors and the bi-directional switch is a triac.

Claim 14

The apparatus of claim 9 wherein after start-up of the motor when the motor has reached at or near its rated speed, the control means operates the switching devices of the inverter circuit to provide a selected voltage level at the rated frequency to the motor and to switch the bi-directional switch to provide a selected phase delay of conduction and a selected voltage level on the output line connected to the bi-directional switch at the rated frequency, such that the voltage applied to the motor at the three output lines at the rated frequency of the motor may be varied to control the motor speed and flux level.

Claim 15

Apparatus for converting a single phase AC input to a three phase AC output which is provided to a three phase induction motor, comprising: (a) a pair of single phase AC input terminals connected to a pair of input lines; (b) three output lines connectable to a three phase motor load; (c) an inverter circuit connected to the input lines to receive single phase AC power therefrom and having an output node connected to one of the output lines, the inverter circuit responsive to control signals to provide an AC output voltage at its output node; (d) a bi-directional switch responsive to a control signal connected between one of the input lines and a second of the output lines, the third output line connected to the other of the input lines; (e) control means, connected to monitor the voltage on the three output lines and the output current through the bi-directional switch and from the inverter circuit, for providing control signals to the bi-directional switch and the inverter circuit when the motor has reached at or near its rated speed to operate the inverter circuit to provide a selected voltage level at the rated frequency to the motor and to switch the bi-directional switch to provide a selected phase delay of conduction and a selected voltage level on the output line connected to the bi-directional switch at the rated frequency, such that the voltage applied to the motor at the three output lines at the rated frequency of the motor may be varied to control the motor speed and flux level.

Claim 16

Apparatus for converting a single phase AC input to a three phase AC output which is provided to a three phase induction motor, comprising: (a) a pair of single phase AC input terminals connected to a pair of input lines; (b) three output lines connectable to a three phase motor load; (c) an inverter circuit connected to the input lines to receive single phase AC power therefrom and having an output node connected to one of the output lines, the inverter circuit responsive to control signals to provide an AC output voltage at its output node; (d) a bi-directional switch responsive to a control signal connected between one of the input lines and a second of the output lines, the third output line connected to the other of the input lines; (e) control means, connected to monitor the voltage on the three output lines and the output current through the bi-directional switch and from the inverter circuit, for providing control signals to the bi-directional switch and the inverter circuit when the motor has reached at or near its rated speed to operate the inverter circuit to provide a selected voltage level at the rated frequency to the motor and to switch the bi-directional switch to provide a selected phase delay of conduction and a selected voltage level on the output line connected to the bi-directional switch at the rated frequency, such that the voltage applied to the motor at the three output lines at the rated frequency of the motor may be varied to control the motor speed and flux level.

Claim 17

The apparatus of claim 13 wherein the inverter circuit includes a pair of DC bus lines, a pair of capacitors connected together at a node and connected across the DC bus lines, the node between the capacitors connected to one of the input lines, a pair of rectifying diodes connected together at a node and connected across the DC bus lines, the node between the diodes connected to the other of the input lines, and two gate controlled switching devices connected together at the output node and connected across the DC bus lines, and wherein the control means controls the switching of the switching devices in the inverter circuit.

Claim 18

The apparatus of claim 14 wherein the gate controlled switching devices are power transistors and the bi-directional switch is a triac.

Claim 19

Apparatus for converting a single phase AC input to a three phase AC output comprising: (a) a pair of single phase AC input terminals connected to a pair of input lines; (b) three output lines connectable to a three phase motor load; (c) an inverter circuit connected to the input lines to receive single phase AC power therefrom and having an output node connected to one of the output lines, the inverter circuit including a pair of DC bus lines, a pair of capacitors connected together at a node and connected across the DC bus lines, the node between the capacitors connected to one of the input lines, a pair of rectifying diodes connected together at a node and connected across the DC bus lines, the node between the diodes connected to the other of the input lines, and two gate controlled switching devices connected together at the output node and connected across the DC bus lines; (d) a bi-directional switch responsive to a control signal connected between one of the input lines and a second of the output lines, the third output line connected to the other of the input lines; (e) control means, connected to monitor the voltage on the three output lines and the output current through the bi-directional switch and from the inverter circuit, for providing control signals to the bi-directional switch and the inverter circuit switching devices to provide output currents from the inverter circuit and through the bi-directional switch to the motor which have fundamental frequency components lower than the frequency of the AC input voltage on the input lines and at different phases whereby controlled start-up of a three phase AC motor connected to the output lines can be obtained.

Claim 20

Apparatus for converting a single phase AC input to a three phase AC output comprising: (a) a pair of single phase AC input terminals connected to a pair of input lines; (b) three output lines connectable to a three phase motor load; (c) an inverter circuit connected to the input lines to receive single phase AC power therefrom and having an output node connected to one of the output lines, the inverter circuit including a pair of DC bus lines, a pair of capacitors connected together at a node and connected across the DC bus lines, the node between the capacitors connected to one of the input lines, a pair of rectifying diodes connected together at a node and connected across the DC bus lines, the node between the diodes connected to the other of the input lines, and two gate controlled switching devices connected together at the output node and connected across the DC bus lines; (d) a bi-directional switch responsive to a control signal connected between one of the input lines and a second of the output lines, the third output line connected to the other of the input lines; (e) control means, connected to monitor the voltage on the three output lines and the output current through the bi-directional switch and from the inverter circuit, for providing control signals to the bi-directional switch and the inverter circuit switching devices to provide output currents from the inverter circuit and through the bi-directional switch to the motor which have fundamental frequency components lower than the frequency of the AC input voltage on the input lines and at different phases whereby controlled start-up of a three phase AC motor connected to the output lines can be obtained.

Claim 21

The apparatus of claim 16 wherein the control means estimates the speed of a motor connected to the output lines from the measured output voltages and the inverter circuit and bi-directional switch currents and provides a controlled start-up of the motor by providing fundamental current components at increasing frequency on the output lines as the speed of the motor increases.

Claim 22

The apparatus of claim 16 wherein the gate controlled switching devices are power transistors and the bi-directional switch is a triac.

Claim 23

The apparatus of claim 16 wherein after a motor connected to the output lines has started up and approaches its rated speed, the control means controls the bi-directional switch to conduct constantly and controls the inverter circuit to provide balanced three phase voltages across the three output lines.

Claim 24

The apparatus of claim 17 wherein, after start-up of the motor, the control means turns off the bi-directional switch and operates the inverter circuit to provide single phase power to the motor to drive the motor up to near rated speed, and then turns on the bi-directional switch to conduct constantly and controls the switching of the inverter circuit to provide balanced three phase output voltages on the three output lines.

Claim 27

The method of claim 21 wherein the phase angle between the fundamental component of the current passed through the bi-directional switch and the fundamental component of the current from the inverter circuit is 2π/3.

Claim 28

The method of claim 21 including the additional steps of: (1) determining the speed of the motor; (2) increasing the frequency of the fundamental current passed through the bi-directional switch and the current from the inverter circuit as the speed of the motor increases to drive the motor up in speed from a start to a selected speed.

Claim 29

The method of claim 23 wherein, after the motor has reached the selected speed, turning off the bi-directional switch so that no current is passed therethrough, and switching the switching devices of the inverter to provide single phase power through the inverter circuit to the motor at a frequency which increases as the speed of the motor increases.

Claim 30

The method of claim 24 wherein, after the motor has reached a speed near its rated speed, then: (1) turning on the bi-directional switch so that it conducts constantly; and (2) switching the switching devices of the inverter to provide balanced three phase voltages to the motor at the rated frequency of the motor.

Claim 31

The method of claim 24 wherein, after the motor has reached a speed at or near its rated speed, then: (1) switching the bi-directional switch at the rated frequency of the motor to provide power to the motor at a selected voltage and phase angle, (2) switching the switching devices of the inverter circuit at the rated frequency of the motor to provide power to the motor at a selected voltage and a selected phase angle with respect to the phase angle of the voltage provided through the bi-directional switch; (3) then, changing the point of conduction of the bi-directional switch on each cycle of the single phase AC input power and the switching of the switching devices of the inverter to change the level of the voltage provided to the motor at its rated frequency to control the speed and flux level of the motor.