Control system and control method

Abstract

The present invention provides a control system (100, 200, 300) for controlling a single phase induction motor (150, 250) with a main winding (151, 251) and with an auxiliary winding (152, 252), the control system (100, 200, 300) comprising a first bidirectional switching element (101) and a second bidirectional switching element (102), wherein the first bidirectional switching element (101) is arranged between a phase supply input (103, 203) of the single phase induction motor (150, 250) and the main winding (151, 251) and wherein the second bidirectional switching element (102) is arranged electrically parallel to the main winding (151, 251), and a control unit (105, 205) coupled to the first bidirectional switching element (101) and the second bidirectional switching element (102).

Claims

1. A control system for controlling a single phase induction motor with a main winding and with an auxiliary winding, the control system comprising: a first bidirectional switching element and a second bidirectional switching element, wherein the first bidirectional switching element is arranged between a phase supply input of the single phase induction motor and the main winding and wherein the second bidirectional switching element is arranged electrically parallel to the main winding, a controller coupled to the first bidirectional switching element and the second bidirectional switching element, wherein the controller is configured to control in an alternating manner, during a positive half-wave of a supply voltage of the single phase induction motor the first bidirectional switching element to provide a positive current to the main winding and the second bidirectional switching element to provide a freewheeling current path for the positive current through the main winding, and wherein the controller is configured to control in the alternating manner, during a negative half-wave of the supply voltage of the single phase induction motor the first bidirectional switching element to provide a negative current to the main winding and the second bidirectional switching element to provide the freewheeling current path for the negative current through the main winding, further comprising a current sensor coupled to the controller and configured to sense an input current to the single phase induction motor at the phase supply input, wherein the controller is configured to drive the first bidirectional switching element and the second bidirectional switching element based on the sensed current, wherein the controller is configured to control the first bidirectional switching element and the second bidirectional switching element in the alternating manner based on a PWM scheme, wherein the controller is configured to determine a duty cycle for the PWM scheme based on the input current, wherein the controller comprises an integral controller configured for determining the duty cycle based on a difference between a reference current value and the input current, wherein the controller comprises a reference value determination unit configured to determine the reference current value based on a fixed current value and a variable feedback current value, wherein the controller is configured to determine the variable feedback current value based on the duty cycle, wherein the reference value determination unit is configured to determine the reference current value by adding the fixed current value to the variable feedback current value.

2. The control system according to claim 1, comprising an input filter circuit arranged between the phase supply input of the single phase induction motor and a neutral input of the single phase induction motor.

3. The control system according to claim 1, comprising a bypass switching element arranged between the phase supply input and the main winding.

4. The control system according to claim 1, comprising a running capacitor arranged between the phase supply input and the auxiliary winding.

5. The control system according to claim 1, wherein the first bidirectional switching element comprises two switching elements arranged in common emitter connection or common collector connection, and/or wherein the second bidirectional switching element comprises two switching elements arranged in common emitter connection or common collector connection; and/or wherein the first bidirectional switching element comprises two parallel reverse blocking transistors, and/or wherein the second bidirectional switching element comprises two parallel reverse blocking transistors.

6. The control system of claim 1, wherein the first bidirectional switching element comprises: a first transistor comprising a first gate terminal connected to the controller, a second terminal connected to the phase supply input, and a third terminal; a second transistor comprising a second gate terminal connected to the controller, a fourth terminal connected to the third terminal, and a fifth terminal connected to the main winding; a first diode that is configured to allow positive current flow through the first diode from the third terminal to the second terminal; and a second diode that is configured to allow positive current flow through the second diode from the fourth terminal to the fifth terminal.

7. The control system of claim 1, further comprising a switch, wherein the second bidirectional switching element comprises: a first transistor comprising a first gate terminal connected to the controller, a second terminal connected to the phase supply input via the switch, and a third terminal; a second transistor comprising a second gate terminal connected to the controller, a fourth terminal connected to the third terminal, and a fifth terminal connected to the main winding; a first diode that is configured to allow positive current flow through the first diode from the third terminal to the second terminal; and a second diode that is configured to allow positive current flow through the second diode from the fourth terminal to the fifth terminal.

8. The control system of claim 1, wherein the variable feedback current value is proportional to the duty cycle.

9. The control system of claim 1, wherein the integral controller is configured for determining the duty cycle by integrating over time a multiplicative product of (a) the difference between the reference current value and the input current and (b) a proportionality factor.

10. A control method for controlling a single phase induction motor with a main winding, with an auxiliary winding and with a running capacitor arranged between a phase supply input and the auxiliary winding, the control method comprising: providing in an alternating manner a positive current to the main winding and a freewheeling current path for the positive current through the main winding during a positive half-wave of a supply voltage of the single phase induction motor, and providing in the alternating manner a negative current to the main winding and the freewheeling current path for the negative current through the main winding during a negative half-wave of the supply voltage of the single phase induction motor, further comprising sensing an input current to the single phase induction motor at the phase supply input, wherein providing in the alternating manner the positive current to the main winding and the freewheeling current path for the positive current and providing in the alternating manner the negative current to the main winding and the freewheeling current path for the negative current is performed based on the input current, wherein providing in the alternating manner the positive current to the main winding and the freewheeling current path for the positive current and providing in the alternating manner the negative current to the main winding and the freewheeling current path for the negative current is performed based on a PWM scheme, wherein the PWM scheme is based on the input current, especially, wherein a duty cycle is determined with an integral controller based on a difference between a reference current value and the input current, and comprising determining the reference current value based on a fixed current value and a variable feedback current value, wherein the variable feedback current value is determined based on the duty cycle, wherein determining the reference current value comprises determining the reference current value by adding the fixed current value to the variable feedback current value.

11. The control method according to claim 10, comprising filtering an input voltage between the phase supply input of the single phase induction motor and a neutral input of the single phase induction motor.

12. The control method according to claim 10, wherein providing in the alternating manner the positive current to the main winding and the freewheeling current path for the positive current is performed with two switching elements arranged in common emitter connection or common collector connection or with two parallel reverse blocking transistors, and/or wherein providing in the alternating manner the negative current to the main winding and the freewheeling current path for the negative current is performed with two switching elements arranged in common emitter connection or common collector connection or with two parallel reverse blocking transistors.

13. The control method of claim 10, wherein the variable feedback current value is proportional to the duty cycle.

14. The control method of claim 10, wherein determining the duty cycle comprises integrating over time a multiplicative product of (a) the difference between the reference current value and the input current and (b) a proportionality factor.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) For a more complete understanding of the present invention and advantages thereof, reference is now made to the following description taken in conjunction with the accompanying drawings. The invention is explained in more detail below using exemplary embodiments which are specified in the schematic figures of the drawings, in which:

(2) FIG. 1 shows a block diagram of an embodiment of a control system according to the present invention;

(3) FIG. 2 shows a flow diagram of an embodiment of a control method according to the present invention;

(4) FIG. 3 shows a block diagram of another embodiment of a control system according to the present invention;

(5) FIG. 4 shows a block diagram of a control algorithm for use with an embodiment of a control system according to the present invention;

(6) FIG. 5 shows a diagram of variables in an embodiment of a control system according to the present invention; and

(7) FIG. 6 shows another diagram of variables in an embodiment of a control system according to the present invention.

(8) In the figures like reference signs denote like elements unless stated otherwise.

DETAILED DESCRIPTION OF THE DRAWINGS

(9) FIG. 1 shows a block diagram of an embodiment of a control system 100 for a single phase induction motor 150. The single phase induction motor 150 comprises a main winding 151 and an auxiliary winding 152. The single phase induction motor 150 is supplied with electrical energy via a single phase AC source, i.e. via an AC voltage. Such a voltage may for example comprise 230 V with a frequency of 50 Hz or 110 V with a frequency of 60 Hz. However, any other voltage level and frequency is also possible.

(10) The control system 100 comprises a first bidirectional switching element 101 and a second bidirectional switching element 102. The first bidirectional switching element 101 is arranged between a phase supply input 103 of the single phase induction motor 150 and the main winding 151. The second bidirectional switching element 102 is arranged electrically in parallel to the main winding 151. The ends of the second bidirectional switching element 102 and the main winding 151 that are not coupled to the first bidirectional switching element 101 are coupled to a neutral input 104. A control unit 105 is provided that is coupled to the first bidirectional switching element 101 and the second bidirectional switching element 102 for controlling the first bidirectional switching element 101 and the second bidirectional switching element 102 during a start-up phase of the single phase induction motor 150.

(11) The first bidirectional switching element 101 and the second bidirectional switching element 102 are switching elements that allow electrical current to flow in both directions, when they are actuated or controlled to be closed. This allows using the first bidirectional switching element 101 and the second bidirectional switching element 102 in AC applications, where the supply voltage comprises positive and negative voltage levels.

(12) The control unit 105 that is coupled to the first bidirectional switching element 101 and the second bidirectional switching element 102 may e.g. be a microcontroller 105. It is understood, that any other type of control unit is also possible, such a control unit may comprise an ASIC, a FPGA, a CPLD or the like. The control unit 105 may comprise output ports that couple the control unit 105 to the first bidirectional switching element 101 and the second bidirectional switching element 102 to control the switching state of the first bidirectional switching element 101 and the second bidirectional switching element 102. Such outputs may e.g. be logic level outputs with voltage levels of 5 V, or e.g. 3.3 V. It is understood, that either the control unit 105 or the first bidirectional switching element 101 and the second bidirectional switching element 102 may comprise further circuitry, like e.g. resistors and transistors, that couples the control unit 105 to the first bidirectional switching element 101 and the second bidirectional switching element 102.

(13) For operating the single phase induction motor 150 the single phase induction motor 150 is started in a startup phase until it reaches its operating conditions, i.e. its operating speed or revolutions. In this startup phase the single phase induction motor 150 usually causes a high inrush current that puts a high load on the mains supply network.

(14) To lower the high inrush current, the control unit 105 may control the first bidirectional switching element 101 and the second bidirectional switching element 102 such that with the main winding 151 they form a type of buck-converter. This buck-converter will reduce the voltage over the main winding 151 and at the same time increase the current through the main winding 151 compared to the voltage and current at the phase supply input 103. With a respective control it is therefore possible to reduce or avoid the inrush current peaks and at the same time increase the current through the main winding 151 that is responsible for producing the starting torque in the single phase induction motor 150.

(15) To this end, the control unit 105 may alternatingly control during a positive half-wave of the input voltage at the phase supply input 103 the first bidirectional switching element 101 to provide a positive current to the main winding 151 and the second bidirectional switching element 102 to provide a freewheeling current path for the positive current through the main winding 151. This means that while the first bidirectional switching element 101 is closed, the second bidirectional switching element 102 is opened, and vice versa.

(16) During a negative half-wave of the input voltage at the phase supply input 103 the control unit 105 will control the first bidirectional switching element 101 to provide a negative current to the main winding 151, 251 and the second bidirectional switching element 102 to provide a freewheeling current path for the negative current through the main winding 151, 251. Again, this means that while the first bidirectional switching element 101 is closed, the second bidirectional switching element 102 is opened, and vice versa.

(17) The amount of current increase and voltage decrease in the main winding 151 compared to the phase supply input 103 may be controlled by the control unit 105 through the switching times of the first bidirectional switching element 101 and the second bidirectional switching element 102. The control unit 105 may e.g. perform a PWM based switching of the first bidirectional switching element 101 and the second bidirectional switching element 102. A specific control scheme will be described with regard to FIG. 5.

(18) After the single phase induction motor 150 reaches its operating conditions, i.e. after the startup phase, the control unit 105 may permanently open the first bidirectional switching element 101 and permanently close the second bidirectional switching element 102 for normal operation of the single phase induction motor 150. As may be seen in FIG. 3 a bypass for the first bidirectional switching element 101 is also possible.

(19) For sake of clarity in the following description of the method based FIG. 2 the reference signs used in the description of the apparatus based figures will be maintained.

(20) FIG. 2 shows a flow diagram of a control method for controlling a single phase induction motor 150, 250 with a main winding 151, 251, with an auxiliary winding 152, 252 and with a running capacitor arranged between a phase supply input 103, 203 and the auxiliary winding 152, 252.

(21) The control method comprises providing S1 in an alternating manner a positive current to the main winding 151, 251 and a freewheeling current path for the positive current through the main winding 151, 251 during a positive half-wave of a supply voltage of the single phase induction motor 150, 250, and providing S2 in an alternating manner a negative current to the main winding 151, 251 and a freewheeling current path for the negative current through the main winding 151, 251 during a negative half-wave of a supply voltage of the single phase induction motor 150, 250.

(22) Providing in an alternating manner a positive current to the main winding 151, 251 and a freewheeling current path for the positive current may e.g. be performed with two switching elements 210, 211 arranged in common emitter connection or common collector connection or with two parallel reverse blocking transistors. The same applies to providing in an alternating manner a negative current to the main winding 151, 251 and a freewheeling current path for the negative current. This may be performed with two switching elements 212, 213 arranged in common emitter connection or common collector connection or with two parallel reverse blocking transistors.

(23) The control method may comprise sensing the input current to the single phase induction motor 150, 250 at the phase supply input 103, 203. Providing in an alternating manner a positive current to the main winding 151, 251 and a freewheeling current path for the positive current and providing in an alternating manner a negative current to the main winding 151, 251 and a freewheeling current path for the negative current may then be performed based on the sensed current.

(24) Providing in an alternating manner a positive current to the main winding 151, 251 and a freewheeling current path for the positive current and providing in an alternating manner a negative current to the main winding 151, 251 and a freewheeling current path for the negative current may further be performed based on a PWM scheme. The PWM scheme may be based on the measured input current, wherein the duty cycle may be determined with an integral controller 320 based on a reference current value and based on the measured supply current. The reference current value may be determined based on a fixed current value and a variable feedback current value, wherein the variable feedback current value may be determined based on the current duty cycle.

(25) The control method may further comprise filtering an input voltage between the phase supply input 103, 203 of the single phase induction motor 150, 250 and a neutral input 104, 204 of the single phase induction motor 150, 250.

(26) FIG. 3 shows a block diagram of another control system 200 for controlling a single phase induction motor 250. The single phase induction motor 250 also comprises a main winding 251 and an auxiliary winding 252. The control system 200 is based on the control system 100 and also comprises a control unit 205 that controls switching elements. However, in the control system 200 the first bidirectional switching element and the second bidirectional switching element are not specifically referenced. Instead, the first bidirectional switching element and the second bidirectional switching element are each represented by two MOSFET-Transistors 210, 211 and 212, 213 in common emitter configuration. A single MOSFET-Transistor is a directional switching element that allows switching a current from the source to the drain with a voltage at the gate that is positive regarding the voltage at the source of the transistor. Current in the other direction may flow via the inherent diode of the MOSFET. Therefore, by arranging two MOSFETs in series with reverse polarity it is possible to controllably switch currents in both directions.

(27) It is understood, that instead of two MOSFETs in common emitter arrangement other arrangements may be provided. For example IGBTs may be used. Further, a common collector arrangement may be chosen. Further, reverse blocking transistors may be used in a parallel configuration. In addition, although only single MOSFETs 210, 211, 212, 213 are shown, it is understood that every one of the shown MOSFETs may be implemented as a parallel arrangement of two or more MOSFETs or IGBTs or other switching elements.

(28) In the control system 200 the control unit 205 individually controls the single MOSFETs 210, 211, 212, 213. During a positive half-wave of the input voltage, the control unit 205 will alternatingly control the MOSFETs 210, 212. During a negative-half wave of the input voltage, the control unit 205 will alternatingly control the MOSFETs 211, 213.

(29) The control system 200 also comprises a bypass switching element 216 that is arranged in parallel to the MOSFETs 210, 211. This bypass switching element 216 may be used to bypass the MOSFETs 210, 211 during a normal operation of the single phase induction motor 250.

(30) In addition, the single phase induction motor 250 also comprises an input filter 215 that filters the input voltage and current between the phase supply input 203 and the MOSFETs 210, 211. It can be seen that the bypass switching element 216 also bypasses the input filter 215.

(31) FIG. 4 shows a block diagram of a control algorithm for use with a control system 300. The output of the control algorithm is a duty cycle d from integral controller 320, that may be used by the control unit 105, 205 to control the first bidirectional switching element 101 and the second bidirectional switching element 102, e.g. the MOSFETs 210, 211, 212, 213.

(32) Integral controller 320 comprises a proportional element 323 that multiplies an input value with a proportionality factor K.sub.I. An integral element 324 or integrator than integrates over time the output of proportional element 323 to generate the duty cycle d.

(33) The input to integral controller 320 is generated from the difference of a reference current i.sub.Ref and an absolute value of a measured current ABS(i.sub.L), wherein i.sub.L is the current that flows into the single phase induction motor 150, 250 at the phase supply input 103, 203.

(34) The reference current i.sub.Ref is generated in a feedback loop that receives the duty cycle d. A proportional element 322 then multiplies the duty cycle d with factor K1. The output of proportional element 322 is then added to a fixed reference current value i.sub.RefFixed to generate the reference current i.sub.Ref.

(35) Possible values for i.sub.RefFixed, K1, and K.sub.i are: i.sub.RefFixed=17 A K1=34 A K.sub.i=120 1/As

(36) It is however understood, that these values are just exemplary values and that the respective values for specific applications may be determined e.g. experimentally or by simulation.

(37) FIG. 5 shows a diagram of currents over time in a control system 100, 200, 300 according to the present invention.

(38) In the diagram three regions are marked. The first region 1 comprises currents that are higher than 10 A. The second region 2 comprises currents between 10 A and −10 A. Finally, the third region 3 comprises currents that are lower than −10 A.

(39) The currents shown are the current i.sub.Main, i.e. the current through the main winding, and the current i.sub.2, i.e. the current that flows into the input filter 215 of the control system 200.

(40) In the diagram it can be seen, that the current i.sub.Main comprises a sinusoidal shape. This means that the main winding is supplied with a sinusoidal current. The current reaches levels in region 1 and region 3 that are over the limits of the second region 2.

(41) In contrast, the current that flows into the input filter is controlled such that it stays within the limits of region 2.

(42) It can be seen in the diagram of FIG. 5 that with the present invention the inrush current to the single phase induction motor may be limited, while at the same time driving the main winding with a full sinusoidal current.

(43) FIG. 6 shows a diagram of currents and a diagram of the duty cycle in a control system according to the present invention.

(44) The current diagram shows the reference current i.sub.Ref the supply current i.sub.supply and the current in the main winding i.sub.Main. The supply current i.sub.supply is the current that is measured as input value to the controller shown in FIG. 4 and may also be referenced as i.sub.L.

(45) The lower diagram shows the duty cycle that the controller of FIG. 4 generates for the respective currents as shown in the upper diagram.

(46) According to the controller schematic as shown in FIG. 4 the duty cycle is zero, when the absolute value of the supply current i.sub.supply is lower than the fixed reference current value i.sub.RefFixed. This is the operation in region 2 as shown in FIG. 5. When the duty cycle d is zero, the reference current i.sub.Ref equals the fixed reference current i.sub.RefFixed, in this case exemplarily 17 A.

(47) Once the supply current i.sub.supply exceeds the reference current i.sub.Ref, the error signal in the controller increases and the integral controller will gradually increase the duty cycle. While the duty cycle increases, the variable reference current i.sub.RefVariable will increase proportionally and the value of i.sub.Ref will also increase. While the duty cycle increases, it can be seen that the supply current i.sub.supply follows the limit set by the reference current i.sub.Ref. It can also be seen, that the amplitude of the current i.sub.supply is gradually limited, giving a rather round shape without sharp corners. This will produce less harmonics in the supply current i.sub.supply and will reduce the torque pulsations.

(48) Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a variety of alternate and/or equivalent implementations exist. It should be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration in any way. Rather, the foregoing summary and detailed description will provide those skilled in the art with a convenient road map for implementing at least one exemplary embodiment, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope as set forth in the appended claims and their legal equivalents. Generally, this application is intended to cover any adaptations or variations of the specific embodiments discussed herein.

(49) The present invention provides a control system (100, 200, 300) for controlling a single phase induction motor (150, 250) with a main winding (151, 251) and with an auxiliary winding (152, 252), the control system (100, 200, 300) comprising a first bidirectional switching element (101) and a second bidirectional switching element (102), wherein the first bidirectional switching element (101) is arranged between a phase supply input (103, 203) of the single phase induction motor (150, 250) and the main winding (151, 251) and wherein the second bidirectional switching element (102) is arranged electrically parallel to the main winding (151, 251), a control unit (105, 205) coupled to the first bidirectional switching element (101) and the second bidirectional switching element (102), wherein the control unit (105, 205) is configured to control in an alternating manner during a positive half-wave of a supply voltage of the single phase induction motor (150, 250) the first bidirectional switching element (101) to provide a positive current to the main winding (151, 251) and the second bidirectional switching element (102) to provide a freewheeling current path for the positive current through the main winding (151, 251), and wherein the control unit (105, 205) is configured to control in an alternating manner during a negative half-wave of a supply voltage of the single phase induction motor (150, 250) the first bidirectional switching element (101) to provide a negative current to the main winding (151, 251) and the second bidirectional switching element (102) to provide a freewheeling current path for the negative current through the main winding (151, 251). Further, the present invention provides a respective control method.

LIST OF REFERENCE SIGNS

(50) 100, 200, 300 control system 101 first bidirectional switching element 102 second bidirectional switching element 103, 203 phase supply input 104, 204 neutral input 105, 205 control unit 210, 211, 212, 213 switching element 215 input filter 216 bypass switching element 320 integral controller 321 reference value determination unit 322, 323 proportional element 324 integral element 325 summing point 326 difference point 327 measurement input 150, 250 single phase induction motor 151, 251 main winding 152, 252 auxiliary winding S1, S2 method steps