Reverse rotation of a motor configured for operation in a forward direction

There are disclosed herein various implementations of a method and a system enabling operation of a motor in reverse. Such a method includes applying a first drive signal to begin rotating the motor in a reverse direction, the first drive signal being applied for a predetermined period of time. The method also includes using a position sensor signal for the motor to control motor drive in the reverse direction when the motor reaches a predetermined reverse speed, and operating the motor in the reverse direction.

BACKGROUND

Background Art

Alternating current (AC) motors, such as single phase AC motors, are utilized in a wide variety of applications. For example, single phase AC motors may be used to rotate fans in large refrigeration units or freezers utilized to store and/or display perishable food products in a commercial setting. In applications requiring substantially continuous operation, high priority is typically placed on motor durability and efficiency. As a result, motors used to provide reliable temperature control for perishable goods may be configured and optimized for operation, i.e., rotation, in only one direction.

Under some circumstances, however, it may be desirable or advantageous to rotate a motor configured for operation in one direction, in reverse. For example, in commercial refrigeration applications, substantially constant rotation of a fan motor in one direction can result in the accumulation of dust or other debris on condenser coils of a refrigeration unit. Occasional reverse rotation of the fan motor may serve as an aid to purging such dust or debris from the condenser coils, resulting in more reliable and efficient cooling of the stored perishable goods.

SUMMARY

The present disclosure is directed to reverse rotation of a motor configured for operation in a forward direction, substantially as shown in and/or described in connection with at least one of the figures, and as set forth more completely in the claims.

DETAILED DESCRIPTION

FIG. 1shows flowchart100presenting an exemplary method enabling reverse rotation of a motor configured for operation in a forward direction, according to one implementation. It is noted that the method described by flowchart100may be utilized to enable reverse rotation of a wide variety of motor types. However, in the interests of conceptual clarity, the method of flowchart100will be described by reference to exemplary motor system200, shown byFIG. 2. In addition, some of the advantages enabled by the exemplary method of flowchart100will be further illustrated by reference toFIGS. 3A, 3B, and 3C.

FIG. 2shows exemplary system200enabling reverse rotation of motor260configured for operation in forward direction211, according to one implementation. System200includes motor260coupled to load262so as to drive load262. System200also includes motor controller202coupled to motor260. As shown byFIG. 2, motor controller202is configured to generate motor control signal250, as well as to provide drive signals220a/220and240a/240to motor260, and to receive position sensor signal232for motor260. Motor controller202may be implemented as an integrated circuit (IC), for example.

Also shown inFIG. 2are rotor210of motor260, forward direction of rotation211for rotor210(also referred to herein as “forward direction211”), reverse direction of rotation213for rotor210(also referred to herein as “reverse direction213”), and position sensor230for motor260. It is noted that althoughFIG. 2depicts position sensor230as being integrated with motor260, that representation is provided merely by way of example. In other implementations, position sensor230may be implemented as a separate feature of system200and be operatively coupled to motor260and motor controller202. In addition,FIG. 2shows two exemplary angular sectors of motor260, i.e., sectors I and II, in which rotor210may be positioned when motor260is stopped, and through which rotor210may rotate when motor260is in operation.

RegardingFIGS. 3A and 3B, respective graphs300A and300B show an exemplary relationship among position sensor signal332, the application of drive signals320a/320and340a/340, and motor current362drawn by a motor operated in reverse, according to one implementation.FIG. 3Cpresents graph300C show an exemplary relationship among position sensor signal332, the application of drive signals320and340, and motor current363drawn by a motor operated in reverse, according to another implementation. It is noted that drive signals320a/320and340a/340, and position sensor signal332, inFIGS. 3A, 3B, and 3Ccorrespond respectively to drive signals220a/220and240a/240, and position sensor signal232, inFIG. 2. It is further noted that motor current362inFIGS. 3A and 3B, and motor current363inFIG. 3C, are exemplary representations of a current drawn by motor260to drive load262when motor260is operated in reverse direction213, inFIG. 2.

Continuing to refer toFIGS. 2 and 3Awith further reference to flowchart100, inFIG. 1, flowchart100begins with identifying an angular orientation of motor260configured to operate in forward direction211(110). For example, motor260may be a single phase alternating current (AC) motor configured to drive load262, which may take the form of a fan utilized in a refrigeration unit or freezer for storing and/or displaying perishable goods in a commercial setting. As noted above, in such applications, in which substantially continuous operation may be required of motor260, high priority is typically placed on the durability and efficiency of motor260. As a result, motor260may be configured and optimized for operation, i.e., rotation, in forward direction211opposite reverse direction213, but not for operation in reverse direction213. For example, motor260may be configured to have a reluctance facilitating startup and efficient operation in forward direction211, while obstructing startup and resulting in substantially less efficient operation in reverse direction213.

As further noted above, however, under some circumstances it may be desirable or advantageous to operate motor260in reverse direction213. For example, in commercial refrigeration applications, substantially constant rotation of motor260in forward direction211opposite reverse direction213can result in the accumulation of dust or other debris on condenser coils of the refrigeration unit or freezer served by load262. Occasional and selective operation of motor260in reverse direction213may advantageously facilitate the purging of such dust or debris from the condenser coils, resulting in more reliable and efficient cooling of the stored perishable goods.

Identification of the angular orientation of motor260(110) may correspond to identification of the angular position of rotor210, such as a rest position of rotor210when motor260and rotor210are stopped. Identification of the angular position of rotor210may be performed by motor controller202, through use of position sensor signal232/332. Position sensor signal232/332may be received by motor controller202from position sensor230, which may be a Hall sensor, for example, as known in the art, in which case position sensor signal232/332is provided as a Hall sensor signal. As shown byFIG. 3A, position sensor signal332may be substantially a square wave capable of having one of a HIGH or a LOW value, and including falling edges332aand rising edges332bcorresponding to transitions from HIGH to LOW and LOW to HIGH, respectively. Referring toFIG. 2, the state of position sensor signal232/332, i.e., HIGH or LOW may be used by motor controller202to identify whether rotor210is positioned within sector I or sector II of motor260. According to the example implementation shown byFIGS. 2 and 3A, prior to time t0inFIG. 3A, the angular orientation of motor260is such that rotor210is positioned in sector I, as indicated by position sensor signal232/332being HIGH.

Continuing to refer toFIGS. 2 and 3Ain combination withFIG. 1, flowchart100continues with applying first drive signal220a/320afor predetermined period of time t1to begin rotating motor260in reverse direction213opposite forward direction211(120). Application of first drive signal220a/320amay be performed by motor controller202. In one implementation, for example, first drive signal220a/320amay be applied as a pulse-width modulation (PWM) signal, in which the modulated drive signal is applied for predetermined period of time t1.

As noted above, motor260may be configured to have a reluctance which, while facilitating startup and efficient operation in forward direction211, obstructs startup in reverse direction213. As a result, the process utilized to startup motor260in forward direction211typically will not be effective in starting motor260in reverse direction213in which motor260has not been configured to operate. Consequently, the present inventive approach to enabling reverse rotation of motor260includes application of first drive signal220a/320afor predetermined period of time t1in order to overcome the reluctance of motor260to reverse operation. In other words, first drive signal220a/320amay be used to apply a “kick start” to motor260in reverse direction213.

It is noted that the duration of predetermined period of time t1may vary considerably depending on the type and specifications of motor260, as well as the characteristics of load262. With respect to the exemplary implementation discussed above, in which motor260is a single phase AC motor used to rotate a fan in a refrigeration unit or freezer, first drive signal220a/320amay be a PWM signal having a frequency of approximately ten kilohertz (10 kHz), and predetermined period of time t1may be a period of approximately 100 milliseconds (100 ms). Moreover, first drive signal220a/320amay be a PWM signal having a substantially constant, i.e., non-varying, duty cycle.

Application of first drive signal220a/320amay be based on the angular orientation of motor260prior to time t0. For example, in implementations in which motor260is a single phase AC motor, drive signals may be applied to motor260along one of two perpendicular drive phases, for example, one of a “U phase” and a “V phase”, as known in the art. Motor controller202may be configured to utilize the angular orientation of motor260identified previously to determine which of the motor phases, e.g., U phase or V phase, should receive first drive signal220a/320a. Such a determination may be performed by motor controller202in order to apply the most effective driving signal for initiating rotation of rotor210in reverse direction213.

Flowchart100continues with sensing a change in the angular orientation of motor260in reverse direction213after application of first drive signal220a/320a(130). Sensing of the change in angular orientation of motor260may correspond to sensing a change in the angular position of rotor210in reverse direction213, and may be performed by motor controller202, through use of position sensor signal232/332. As described above, according to the example implementation shown byFIGS. 2 and 3A, prior to time t0inFIG. 3A, the angular orientation of motor260was such that rotor210was positioned in sector I, as indicated by HIGH position sensor signal232/332.

A change in the angular orientation of motor260in reverse direction213after application of first drive signal220a/320amay correspond to rotor210rotating in reverse direction213into sector II, which corresponds in turn to a transition in position sensor signal232/332from HIGH to LOW. Thus sensing of the change in angular orientation of motor260in reverse direction213may be performed by motor controller202through detection of falling edge332aof position sensor signal232/332.

Flowchart100continues with applying second drive signal240a/340abased on the change in angular orientation of motor260to continue rotating motor260in reverse direction213(140). Application of second drive signal240a/340amay be performed by motor controller202. As explained above, in implementations in which motor260is a single phase AC motor, drive signals may be applied to motor260along one of two perpendicular drive phases, for example, one of a “U phase” and a “V phase”. Motor controller202may be configured to utilize the change in angular orientation of motor260identified previously as a trigger to change the phase of application of the drive signal. For example, where first drive signal220a/320ais applied to the U phase of motor260, second drive signal240a/340ais applied to the perpendicular V phase of motor260in response to falling edge332aof position sensor signal332.

As discussed above, motor260may have a reluctance that obstructs startup and operation in reverse direction213. Consequently, the present inventive approach to enabling reverse rotation of motor260may include one or more additional drive signal applications, such as application of second drive signal240a/340ain order to overcome the reluctance of motor260to reverse operation. In other words, second drive signal240a/340ais used to continue the process of “kick starting” motor260in reverse direction213.

Like first drive signal220a/320a, second drive signal240a/340amay be applied for a predetermined period of time, e.g., predetermined period of time t2. In some implementations, t1and t2may be substantially equal. Thus, in some implementations, first drive signal220a/320aand second drive signal240a/340amay be applied for predetermined period of time t1. In addition, like first drive signal220a/320a, in some implementations, second drive signal240a/340amay be applied as a PWM signal. Moreover, second drive signal240a/340amay be a PWM signal having a substantially constant duty cycle.

Flowchart100continues with using position sensor signal232/332for motor260to control motor drive in reverse direction213when motor260reaches a predetermined reverse speed (150). Use of position sensor signal232/332to control motor drive in reverse direction213may be performed by motor controller202.

The predetermined reverse speed at which motor controller203uses position sensor signal232/332to control motor drive in reverse direction213may vary considerably, based, for example, on motor260, load262, and the particular application for which motor260and load262are utilized. As shown by graph300A, inFIG. 3A, according to the present implementation, motor260reaches such a predetermined reverse speed after application of first and second drive signals220a/320aand240a/340a. However, in other implementations, more, or fewer, initial drive signal applications may be required to kick start motor260in reverse direction213. For example, in some implementations, second drive signal240a/340aand/or first drive signal220a/320amay be applied one or more additional times before motor260reaches the predetermined reverse speed.

As shown inFIGS. 3A and 3B, subsequent to application of respective first and second drive signals220a/320aand240a/340a, motor controller202may be configured to utilize falling edges332aand rising edges332bof position sensor signal332to trigger transitions between drive signals320and340. For example, where drive signals320are applied to the U phase of motor260in response to rising edges332bof position sensor signal332, drive signals340are applied to the perpendicular V phase of motor260in response to falling edges332aof position sensor signal332. It is noted that drive signals320and340may be PWM signals having a substantially constant duty cycle.

Flowchart100concludes with operating motor260in reverse direction213(160). In one implementation, motor controller202can be configured to use position sensor signal232/332to generate motor control signal250for driving motor260in reverse direction213. For example, as shown byFIGS. 3A and 3B, and as described above, motor controller202can generate motor control signal250according to the transitions of position sensor signal232/332. However, as noted above, motor260is configured for operation in forward direction211opposite reverse direction213. Consequently, motor260may perform inefficiently operated in reverse direction213, as shown by motor current362, which includes undesirable periodic motor current spikes362aand362b.

Graph300C, inFIG. 3C, depicts operation of motor260in reverse direction213, according to another implementation.FIG. 3Ccorresponds in general to reverse operation of motor260during the time interval represented inFIG. 3B. That is to say,FIG. 3Cshows another implementation for operating motor260in reverse direction213(160) after startup in reverse direction213. As shown inFIG. 3C, the transitioning between application of drive signals320and340produced by motor control signal250does not coincide with falling edges332aand rising edges332bof position sensor signal332. As further shown inFIG. 3C, the transitions between drive signals320and340produced by motor control signal250are phase shifted by some amount352from rising edge332b(and falling edge332a) of position sensor signal332. It is reiterated that drive signals320and340may be PWM signals having a substantially constant duty cycle.

Phase shifting of position sensor signal332to generate motor control signal250may be performed by motor controller202. The amount352by which the transitions between drive signals320and340are phase shifted from position sensor signal332will typically depend on the specifications of motor260, which may be ascertained in advance of operating motor260in reverse direction213. As a result, the amount352of phase shift applied by motor controller202to generate motor control signal250may be predetermined so as to reduce or substantially eliminate motor current spikes362aand362b, inFIG. 3B. Consequently, the implementation shown inFIG. 3Cenables motor260to have improved efficiency motor current363when operated in reverse direction213. In other words, in one implementation, using position sensor signal232/332to control motor drive in reverse direction213(150) includes phase shifting position sensor signal232/332to generate motor control signal250for driving motor260in reverse direction213.

Thus, by applying a first drive signal for a predetermined period of time, the implementations disclosed in the present application provide a kick start for startup in reverse of a motor configured for operation in a forward direction. In addition, by using a position sensor signal of the motor to generate a motor control signal for driving the motor in reverse, the implementations disclosed herein enable operation of the motor in reverse. Moreover, by phase shifting the position sensor signal to generate the motor control signal, the present application discloses a solution enabling enhanced efficiency by the motor when operated in reverse.