Patent ID: 12261553

It should be understood that the appended drawings are not necessarily to scale, presenting a somewhat simplified representation of various preferred features illustrative of the basic principles of the disclosure. The specific design features of the present disclosure as disclosed herein, including, for example, specific dimensions, orientations, locations, and shapes will be determined in part by the particular intended application and use environment.

In the figures, reference numbers refer to the same or equivalent parts of the present disclosure throughout the several figures of the drawing.

DETAILED DESCRIPTION

Specific structural or functional descriptions presented in the embodiments of the present disclosure are only illustrative for the purpose of describing embodiments according to the concept of the present disclosure, and the embodiments according to the concept of the present disclosure may be implemented in various forms. In addition, the present disclosure should not be construed as being limited to the embodiments described herein, and should be understood to include all modifications, equivalents, and substitutes included in the spirit and scope of the present disclosure.

Meanwhile, in the present disclosure, even though terms such as “first”, “second”, etc. may be used to describe various elements, the elements are not limited by these terms. These terms are only used to distinguish one element from another. For example, within the scope not departing from the scope of the rights according to the concept of the present disclosure, a first element may be referred to as a second element, and similarly, the second element may be referred to as the first element.

When an element is referred to as being “coupled” or “connected” to another element, the element may be directly coupled or connected to the other element. However, it should be understood that another element may be present therebetween. In contrast, when an element is referred to as being “directly coupled” or “directly connected” to another element, it should be understood that there are no other elements therebetween. Other expressions for describing a relationship between elements, that is, expressions such as “between” and “immediately between” or “adjacent to” and “directly adjacent to”, should be interpreted similarly.

Like reference numerals refer to like elements throughout. The terminology used herein is for the purpose of describing the embodiments, and is not intended to limit the present disclosure. In the present specification, a singular expression includes the plural form unless the context clearly dictates otherwise. Referring to expressions “comprises” and/or “comprising” used in the specification, a mentioned component, step, operation, and/or element does not exclude the presence or addition of one or more other components, steps, operations, and/or elements.

Hereinafter, the present disclosure will be described in detail with reference to the accompanying drawings.

A motor may be controlled in various ways depending on the type of the motor and whether or not an inverter is used. For example, it is possible to use various control methods, such as voltage control, frequency control, voltage and frequency control, voltage duty control, vector control, etc. In case of a WFSM, in addition to rotating magnetic field control for motor rotation, control of field magnetic flux serving as main flux (DC control) needs to be accompanied.

When a normal conducting coil made of copper, aluminum, etc., is used in the WFSM, time constants of both the field coil and the armature coil are small. Therefore, the WFSM having the normal conducting coil may quickly reach a target current value. Since a response speed of current is fast, there is no need for special driving control when controlling a field current, and only a part lost by a resistance of the field coil after driving is compensated.

However, in case of the WFSM including a superconducting coil, resistivity is significantly small (approximately 7×10−23ohm-cm), and a time constant is large. Therefore, it takes a long time to reach a target current value, and control responsiveness deteriorates.

Accordingly, an object of the present disclosure is to provide a method of controlling a motor capable of improving a response of the motor, in particular, a response speed of the WFSM including the superconducting coil.

FIG.1is a simplified cross-sectional view of a WFSM1, andFIG.2is a block diagram of a control system of the WFSM1according to the present disclosure.

Referring toFIGS.1and2, the WFSM1is a motor in which a field coil12is wound around a rotor10and includes the rotor10and a stator20as other types of electric motors. The field coil12is wound around the rotor10, and an armature coil22is wound around the stator20.

Currents are respectively supplied to the rotor10and the stator20so that the rotor10can rotate by electromagnetic interaction between the rotor10and the stator20. The WFSM1may receive direct current from a DC source40by the field coil12through a slip ring30. Three-phase alternating current from an AC source50is supplied to the stator20through the armature coil22.

The WFSM1is controlled by a controller60. An output of the WFSM1may be controlled through control of a field current supplied to the field coil12. Specifically, since the output of the WFSM1is proportional to a field current and magnetic flux, and the magnetic flux is proportional to an armature current, the output of the WFSM1may be controlled through the field current and the armature current applied to the armature coil22and the field coil12, respectively. Accordingly, the controller60may determine the field current Ifapplied to the field coil12and the armature current Iaapplied to the armature coil22, so that determined values can be applied to the respective coils12,22. To this end, the controller60is configured to be able to control currents supplied to the field coil12and the armature coil22by the DC source40and the AC source50, respectively, as necessary.

In addition, the WFSM1further includes a sensor70. The sensor70may include a magnetic flux sensor72, such as a Hall sensor, for measuring magnetic flux, a current sensor74for measuring current, and a torque sensor76for measuring the torque of the WFSM1. A value measured by the sensor70is transmitted to the controller60.

In the WFSM1, a coil is used instead of a permanent magnet to create magnetic flux in the rotor10, and the coil is wound around teeth of the rotor to generate field magnetic flux. As mentioned above, it takes a long time to reach a target current after the current is supplied to the field coil12formed of the superconducting wire when compared to a normal conducting coil.

A detailed description may be given in consideration of Equation 1. In general, a current i(t) flowing through a coil is charged by an inductance L component.

i⁡(t)=1L⁢∫v⁡(t)⁢dtEquation⁢1

Here, t denotes time and v(t) denotes voltage with respect to time.

A current applied to a resistor-inductor circuit is expressed as in Equation 2 below, where E denotes an electromotive force and R denotes resistance.

i⁡(t)=ER⁢(1-e-RL⁢t)Equation⁢2

Here, a time constant τ is given as in the following Equation 3.

τ=LREquation⁢3

That is, the resistivity is inversely proportional to the inductance L, and the time constant increases as the inductance L increases. Therefore, in case of the WFSM1including the superconducting coil, it takes a long time to reach the target current value.

Accordingly, the present disclosure can solve a problem of low responsiveness of the WFSM1having the superconducting coil by starting the WFSM1after at least a part or all of the field coil12is charged.

A description will be given of a control method of the WFSM1when the field coil12is completely charged 100% before the WFSM1is driven with reference toFIG.3.

At step S10, when a target speed ωt, which is a rotational speed targeted by the WFSM1, is less than or equal to a rated speed ωr, control according to the present embodiment is executed by the controller60.

When the target speed ωt, of the WFSM1is less than or equal to the rated speed ωr, the controller60causes the DC source40to charge the field coil12in a stopped state of the WFSM1at S12. As a non-limiting example, the DC source40may be a battery or a secondary battery.

In addition, the controller60verifies whether the field coil12is fully charged or charged 100%. To this end, the controller60determines whether current magnetic flux Φc, which is current field flux, has reached target magnetic flux Φtat S14. In some embodiments, the current magnetic flux Φcis measured by a magnetic flux sensor72provided in the WFSM1. In some embodiments, the current magnetic flux Φcmay be determined by the field current Ifmeasured by the current sensor74provided in the WFSM1. The controller60determines whether the current magnetic flux Φchas reached the target magnetic flux Φtbased on a measured value of at least one of the magnetic flux sensor72or the current sensor74.

When the current magnetic flux Φcdoes not reach the target magnetic flux Φt, the operation returns to S12so that the controller60causes the field coil12to be charged. When the current magnetic flux Φcgenerated in the field coil12is equal to or greater than the target magnetic flux Φt, the controller60drives the WFSM1and controls driving of the WFSM1at S16. When the current magnetic flux Φtreaches the target magnetic flux Φt, the WFSM1may generate rated torque Tr, and driving of the WFSM1may be controlled according to operating conditions.

Then the controller60determines whether the current magnetic flux Φcof the field coil12is maintained at the target magnetic flux Φtat S18. Specifically, the controller60determines whether the current magnetic flux Φcis equal to or greater than the target magnetic flux Φt. Even at this time, the current magnetic flux Φcof the field coil12may be determined by the measured value of the magnetic flux sensor72or the current sensor74.

The controller60determines whether the current magnetic flux Φcis following the target magnetic flux Φtwhile the WFSM1is being driven. When the current magnetic flux Φcis less than the target magnetic flux Φt, the controller60controls driving of the WFSM1while increasing the field current Ifat S19.

Conversely, when the current magnetic flux Φcis equal to or greater than the target magnetic flux Φtat step S18, the controller60checks the output of the WFSM1. That is, the controller60compares current torque Tcand a current speed ωcof the WFSM1with target torque Ttand the target speed ωr, respectively at S20. Specifically, the controller60determines whether the current torque Tcis equal to or greater than the target torque Tt, and the current speed ωcis substantially equal to the target speed ωt.

When the current torque Tcis less than the target torque Tt, and the current speed ωcis not the target speed ωt, the operation proceeds to a block A. As illustrated inFIG.4, the case where the current torque Tcis less than the target torque Ttmeans that the field coil12has not been charged 100%. Thus, the operation returns to S12, so that the controller60may cause the field coil12to be charged at S201. When the current torque Tcis equal to or greater than the target torque Tt, the controller60determines whether the current speed ωcis not equal to the target speed ωtat S203. In other words, when the current speed ωcis greater or less than the target speed ωt, the controller60controls a rotational speed through control of a load angle of the armature current Iaapplied to an armature coil Iaso that the current speed ωcreaches the target speed ωtat S205.

When the current torque Tcand the current speed ωcreach the target torque Ttand the target speed ωt, respectively, the controller60determines whether the current torque Tcfalls within a preset range at S22. The preset range means that the current torque Tcis greater than or equal to the target torque Ttand is less than or equal to a certain ratio q of the target torque Tt. As a non-limiting example, the certain ratio q may be 1.03.

When the current torque Tcis not within the preset range, the controller60reduces the armature current Iaat S23. Then the operation returns to step S18. When the current torque Tcexceeds the set range due to load fluctuation during driving of the WFSM1, the armature current Iais controlled for control thereof.

When the current torque Tcis within the preset range, the controller60determines whether the current magnetic flux Φcis maintained at the target magnetic flux ωtor more at S24.

When the current magnetic flux Φcis maintained at the target magnetic flux Φtor more, the controller60continues to drive the WFSM1at S26. That is, since an operating state of the WFSM1is changed by an instantaneous load change, the current torque Tcand the current speed ωcare continuously fed back to drive the WFSM1. Alternatively, when the target speed ωtexceeds the rated speed ωrduring driving of the WFSM1, the WFSM1is controlled according to a high-speed operation control flowchart ofFIG.6.

Conversely, upon determining in step S24that the current magnetic flux Φcdoes not reach the target magnetic flux Φt, the controller60increases the field current Ifat S25.

A description will be given of a control method of the WFSM1when the field coil12is partially charged, for example, to a value between approximately 60 to 99.9%, with reference toFIG.5.

At step S300, first, when the target speed ωtof the WFSM1is equal to or less than the rated speed ωr, control according to the present embodiment is executed by the controller60.

When the target speed ωtof the WFSM1is less than or equal to the rated speed ωr, the controller60causes the DC source40to charge the field coil12in a stopped state of the WFSM1at S302. In this instance, the field coil12is only partially charged. For example, the field coil12is charged to 80%.

Then the controller60determines whether the current magnetic flux Φchas reached a preset ratio p of the target magnetic flux Φtat S304. The controller60compares the current magnetic flux Φcwith the target magnetic flux Φtto verify whether the field coil12is charged. The ratio p may be 0.6 to 0.99. For example, when the field coil12is charged to 80%, the ratio p may be 0.8. Here, as for the current magnetic flux Φc, a measurement value of at least one of the magnetic flux sensor72or the current sensor74may be similarly used.

When the current magnetic flux Φcdoes not reach the preset ratio p of the target magnetic flux Φt, the operation returns to step S302, and the controller60causes the field coil12to be charged. On the other hand, when the current magnetic flux Φcis greater than or equal to the preset ratio p of the target magnetic flux Φt, the controller60drives the WFSM1, and since only a portion is charged, an insufficient output of the WFSM1is compensated for with the armature current Ia(S306). That is, an output shortfall of the WFSM1is compensated through the armature current Ia. As for a current applied to the WFSM1, a value measured through a shunt resistor is input to the controller60. Accordingly, the torque and output of the WFSM1may be calculated based on parameters, such as a current value measured through the shunt resistor, and resistance and inductance set in the controller60. In this way, the output shortfall may be determined.

At step S308, the controller60compares the current torque Tcand the current speed ωcwith the target torque Ttand the target speed ωt, respectively, to determine whether a target output has been reached (S20). Specifically, the controller60determines whether the current torque Tcis equal to or greater than the target torque Tt, and the current speed ωcis the target speed ωt.

When the current torque Tcis less than the target torque Tt, or the current speed ωcis not the target speed ωt, the controller60increases both the field current Ifand the armature current Ia, and the operation returns to step S306(S309).

When the current torque Tcis equal to or greater than the target torque Tt, and the current speed ωcis the target speed ωt, the controller60determines whether the current magnetic flux Φchas reached the target magnetic flux ωt(S310).

When the current magnetic flux Φcis less than the target magnetic flux Φt, the controller60increases the field current Ifat S311. Conversely, when the current magnetic flux Φcis equal to or greater than the target magnetic flux Φt, the controller60determines whether the current torque Tcfalls within a preset range at S312. The preset range means that the current torque Tcis greater than or equal to the target torque Tt and is less than or equal to a certain ratio q of the target torque Tt. As a non-limiting example, the certain ratio q may be 1.03.

When the current torque Tcis not within the preset range, the controller60reduces the armature current Iaat S313. That is, when the current torque Tcis increased out of the set range, the controller60controls the armature current Iaso that the current torque Tcis controlled. Then, the operation returns to step S308.

When the current torque Tcis within the preset range, the controller60determines whether the current magnetic flux Φcis maintained at the target magnetic flux Φtor more in step S314.

When the current magnetic flux Φcis less than the target magnetic flux Φt, the controller60increases the field current Ifat S315, and the operation returns to step S310. Upon determining that the current magnetic flux Φcis maintained at the target magnetic flux Φtor more, the controller60may determine again whether the current torque Tcis equal to or greater than the target torque Tt, and the current speed ωcis approximately equal to the target speed ωtat S316.

When the current torque Tcand the current speed ωcfail to reach the target torque Ttand the target speed ωt, respectively, the controller60may increase the field current Ifas necessary by returning to step S310.

When the current torque Tcand the current speed ωcreach the target torque Ttand the target speed ωt, respectively, the controller60continues to drive the WFSM1at S26. That is, since an operating state of the WFSM1is changed by an instantaneous load change, the current torque Tcand the current speed ωcare continuously fed back to drive the WFSM1. Alternatively, when the target speed ωtexceeds the rated speed ωrduring driving of the WFSM1, the WFSM1is controlled according to a high-speed operation control flowchart ofFIG.6.

When the target speed ωtchanges and exceeds the rated speed ωrduring driving of the WFSM1according toFIGS.3to5, high-speed control illustrated inFIG.6may be applied.

When the WFSM1is operated in excess of the rated speed ωrat S500, the controller60determines whether the WFSM1needs field-weakening operation at S502. Referring toFIG.7, a relationship between a rotational speed and torque of the WFSM1is illustrated. Up to the rated speed ωrof the WFSM1, 100% of the ability of the field is utilized, and a voltage of the battery or the DC source40may be used as the maximum value. However, after the rated speed ωr, induced voltage increases while the rotational speed increases, making it difficult to increase the speed due to limitations of the voltage of the DC source40. In order to increase the speed, the induced voltage is reduced by weakening the current magnetic flux Φcof the field. As the induced voltage decreases, a downward curve is created as the torque decreases. That is, the magnetic field flux is lowered to generate a desired speed in a region exceeding the rated speed ωr, and such operation of the motor is referred to as the field-weakening operation.

When the target speed ωtexceeds the rated speed ωr, according to a current speed request, and the WFSM1is driven, the field-weakening operation is performed. In this case, the controller60reduces the field current Ifso that the current magnetic flux Φcof the field is reduced at S504.

And the controller60determines the torque and speed at S506. Specifically, when the current torque Tcis equal to or greater than the target torque Tt, and the current speed ωcsatisfies the target speed ωt, the controller60continuously receives feedback of the current torque Tcand the current speed ωc, and drives the WFSM1at S508.

On the other hand, when the current torque Tcis less than the target torque Tt, or the current speed ωcis not the target speed ωt, weak magnetic flux is controlled through control of a current phase angle (S507). Weak magnetic flux control is a method of reducing a voltage by canceling magnetic flux generated in the field coil12of the rotor10when a current is applied to the armature coil22wound around the stator20with phase angle control. Due to time constant characteristics of the superconducting coil, a rate of change of magnetic flux during field-weakening control is significantly slow. The present disclosure may rapidly satisfy the required speed and torque by concurrently controlling the weak magnetic flux for fast response.

According to the present disclosure, by charging the field coil of the motor including the superconducting coil and then starting the motor, the required output may be immediately provided. In addition, the specifications of the inverter may be lowered by applying a current for creating magnetic flux required for the field before starting the motor.

In addition, according to the present disclosure, even when the field coil is charged at a certain rate instead of being fully charged, a target output may be provided through the armature current control, so that a start-up time may be reduced.

According to the present disclosure, there are provided a motor, particularly, a motor capable of providing a required output immediately by improving responsiveness of a WFSM in which a superconducting coil is used, and a method of controlling the same.

Effects of the present disclosure are not limited to those described above, and other effects not mentioned herein will be clearly recognized by those skilled in the art from the above description.

The present disclosure described above is not limited by the above-described embodiments and the accompanying drawings, and it will be apparent to those of ordinary skill in the art to which the present disclosure pertains that various substitutions, modifications, and changes are possible without departing from the technical idea of the present disclosure.