Patent Application
20190180899
The present disclosure relates to permanent magnet synchronous generators (PMSGs). In particular, it relates to stator secondary windings to modify a permanent magnet (PM) field of PMSGs.
In a permanent magnet synchronous generator (PMSG), a permanent magnet (PM), which is mounted on a rotor coupled to a shaft of a machine, generates a constant magnet field. In the case of a short circuit fault, a fixed permanent magnet field strength will keep energizing the stator windings of the generator as long as the rotor rotates, thereby resulting in a continued and large short-circuit current until the machine completely stops. This continued and large short-circuit current can cause significant damage to the generator, potentially disabling the generator.
Currently, a conventional method used for generator short circuit protection is the employment of a line-installed circuit breaker of a thermal-magnetic type. The disadvantage of using this type of circuit breaker is that the thermal effect requires a relatively long time to activate. Additionally, this circuit breaker is also subject to malfunctioning. In both of these cases, the circuit breaker may fail to protect the generator.
As such, there is a need for an improved design for generator short circuit protection.
The present disclosure relates to a method, system, and apparatus for secondary windings to modify a permanent magnet (PM) field of a permanent magnet synchronous generator (PMSG). In one or more embodiments, a method for a permanent magnet synchronous generator (PMSG) comprises rotating a permanent magnet (PM) of the PMSG. The method further comprises generating, from the permanent magnet rotating, a permanent magnet field. In one or more embodiments, the permanent magnet field couples through a plurality of stator primary windings (SPW) of the PMSG. Also, the method comprises generating, by the stator primary windings, primary currents from the permanent magnet field. In addition, the method comprises drawing, by a plurality of stator secondary windings (SSW) of the PMSG, secondary currents from a power source. Further, the method comprises generating, by the stator secondary windings, a stator secondary winding magnetic field from the secondary currents. In one or more embodiments, the permanent magnet field and the stator secondary winding magnetic field together create an overall magnetic field for the PMSG.
In at least one embodiment, the stator secondary winding magnetic field counteracts, weakens, or strengthens the permanent magnet field. In some embodiments, the permanent magnet is mounted onto a rotor. In one or more embodiments, the primary currents are three-phase currents. In at least one embodiment, the power source is a three-phase power source (TPS). In some embodiments, the secondary currents are three-phase sinusoidal currents or three-phase quasi-sinusoidal currents.
In one or more embodiments, the power source comprises a controller, a plurality of switches, and a direct current (DC) power source. In some embodiments, the switches form an inverter. In at least one embodiment, the method further comprises comparing, by the controller, load currents to referenced maximum currents. In some embodiments, the method further comprises generating, by the controller, a plurality of pulse sequences, when the load currents are greater than the maximum currents. In one or more embodiments, the method further comprises switching, the plurality of switches, by using the pulse sequences to produce the secondary currents.
In at least one embodiment, a system for a permanent magnet synchronous generator (PMSG) comprises a permanent magnet (PM) of the PMSG to rotate and to generate a permanent magnet field. The system further comprises a plurality of stator primary windings (SPW), of the PMSG, to generate primary currents from the permanent magnet field. Also, the system comprises a plurality of stator secondary windings (SSW), of the PMSG, to draw secondary currents from a power source, and to generate a stator secondary winding magnetic field from the secondary currents. In one or more embodiments, the permanent magnet field and the stator secondary winding magnetic field together create an overall magnetic field for the PMSG.
In one or more embodiments, the controller is to compare load currents to maximum currents. In some embodiments, the controller is to generate a plurality of pulse sequences, when the load currents are greater than the maximum currents. In at least one embodiment, the plurality of switches is to be switched by using the pulse sequences to generate the secondary currents.
The features, functions, and advantages can be achieved independently in various embodiments of the present disclosure or may be combined in yet other embodiments.
These and other features, aspects, and advantages of the present disclosure will become better understood with regard to the following description, appended claims, and accompanying drawings where:
The methods and apparatus disclosed herein provide an operative system for secondary windings to modify a permanent magnet (PM) field of a permanent magnet synchronous generator (PMSG). In one or more embodiments, the system of the present disclosure allows for a design and control method of stator secondary windings (SSW) to modify the permanent magnet field of a permanent magnet synchronous generator. In particular, the disclosed system employs stator secondary windings within a permanent magnet synchronous generator. In at least one embodiment, the stator secondary windings generate a magnetic field to (1) counteract the permanent magnet field of the permanent magnet synchronous generator to provide protection to the generator from a short circuit (SC) fault. In some embodiments, the stator secondary windings generate a magnetic field to (2) weaken or (3) strengthen the permanent magnet field of the permanent magnet synchronous generator. Specifically, the stator secondary windings allow for the control of the permanent magnet main field flux linkage, in terms of both timing and value, for short circuit fault protection as well as for field weakening or strengthening.
As previously mentioned above, in a PMSG, a permanent magnet, which is mounted on a rotor coupled to a shaft of a machine, generates a constant magnet field. In the case of a short circuit fault, the fixed permanent magnet field strength will keep energizing the stator windings (i.e. stator primary windings) of the generator as long as the rotor rotates, thereby resulting in a continued and large short-circuit current until the machine completely stops. This continued and large short-circuit current can cause significant damage to the generator, and potentially disable the generator.
A conventional method, currently used, for generator short circuit protection is the implementation of a line-installed circuit breaker of a thermal-magnetic type. The drawback of using this type of circuit breaker is that the thermal effect requires a relatively long time to activate. In addition, this circuit breaker is also subject to malfunctioning. In both of these cases, the circuit breaker may fail to protect the generator. The system of the present disclosure implements stator secondary windings (SSW) in a permanent magnet synchronous generator to generate a magnetic field to counteract the permanent magnet field of the generator to protect the generator from a short circuit fault.
In the following description, numerous details are set forth in order to provide a more thorough description of the system. It will be apparent, however, to one skilled in the art, that the disclosed system may be practiced without these specific details. In the other instances, well known features have not been described in detail so as not to unnecessarily obscure the system.
Embodiments of the present disclosure may be described herein in terms of functional and/or logical components and various processing steps. It should be appreciated that such components may be realized by any number of hardware, software, and/or firmware components configured to perform the specified functions. For example, an embodiment of the present disclosure may employ various integrated circuit components (e.g., memory elements, digital signal processing elements, logic elements, look-up tables, or the like), which may carry out a variety of functions under the control of one or more processors, microprocessors, or other control devices. In addition, those skilled in the art will appreciate that embodiments of the present disclosure may be practiced in conjunction with other components, and that the system described herein is merely one example embodiment of the present disclosure.
For the sake of brevity, conventional techniques and components related to generators, and other functional aspects of the system (and the individual operating components of the systems) may not be described in detail herein. Furthermore, the connecting lines shown in the various figures contained herein are intended to represent example functional relationships and/or physical couplings between the various elements. It should be noted that many alternative or additional functional relationships or physical connections may be present in an embodiment of the present disclosure.
The PMSG 100 also comprises a permanent magnet (PM) 130. The permanent magnet 130 is mounted onto a rotor (not shown) coupled to a shaft of a primary mover (e.g., a machine) (not shown). The permanent magnet 130 is depicted to be in the form of an elongated bar with a north end (labeled “N”) and a south end (labeled “S”). It should be noted that the permanent magnet 130 may be manufactured to be of various different shapes than an elongated bar as is depicted in
As the machine is operating, the rotor rotates in the direction of arrow 140 and, in turn, also rotates the permanent magnet 130 accordingly. The spinning of the permanent magnet 130 creates a fixed excitation magnetic field (e.g., a permanent magnet field) ({right arrow over (ψ)}PM). This fixed excitation magnetic field (e.g., a permanent magnet field) ({right arrow over (ψ)}PM) couples (i.e. radiates) through the coils of the stator primary windings 120, thereby causing the stator primary windings 120 to generate three-phase currents (e.g., primary currents) 110. It should be noted that the overall magnetic field (for the PMSG 100 comprises only the permanent magnet field ({right arrow over (ψ)}gen{right arrow over (ψ)}SSW).
In this figure, the PMSG 200 is circular in shape and comprises a plurality of bars 250. In this figure, the PMSG 200 comprises six (6) bars 250. It should be noted that in other embodiments, the PMSG 200 may comprise more or less bars 250 than the six bars 250 that are shown in
Also in this figure, Three (3) pairs of stator secondary windings (SSW) 260 are constructed on the six (6) bars 250 to form phase A winding (a-a′), phase B winding (b-b′), and phase C winding (c-c′). Each winding comprises two (2) coils (e.g., phase A winding comprises coil a and coil a′), and each coil can comprises multiple turns (though one (1) turn per coil is shown as an example in
Also, in
The PMSG 200 also comprises a permanent magnet (PM) 230. The permanent magnet 230 is mounted onto a rotor (not shown) coupled to a shaft of a primary mover (e.g., a machine) (not shown). In one or more embodiments, the machine may be a motor or engine of a vehicle, such as an airborne vehicle (e.g., an aircraft), a terrestrial vehicle (e.g., a truck or car), or a marine vehicle (e.g., a ship or boat). The permanent magnet 230 is depicted to be in the form of an elongated bar with a north end (labeled “N”) and a south end (labeled “S”). It should be noted that, in one or more embodiments, the permanent magnet 230 may be manufactured to be of various different shapes than an elongated bar as is depicted in
As the machine is operating, the rotor rotates in the direction of arrow 240 and, in turn, also rotates the permanent magnet 230 accordingly. The spinning of the permanent magnet 230 creates a fixed excitation magnetic field (e.g., a permanent magnet field) ({right arrow over (ψ)}PM). This fixed excitation magnetic field (e.g., a permanent magnet field) ({right arrow over (ψ)}PM) couples (i.e. radiates) through the coils of the stator primary windings 220, thereby causing the stator primary windings 220 to generate three-phase currents (e.g., primary currents) 210.
Also, during operation, the stator primary windings 220 generate three-phase currents (e.g., primary currents) 210 for power distribution. The stator secondary windings 260 of the PMSG 200 draw three-phase currents (e.g., secondary currents) 270 from a power source (e.g., refer to 300 of
The three-phase currents (e.g., secondary currents) 270 are specially tuned three-phase sinusoidal currents (e.g., refer to
It should be noted that if the PMSG 200 is manufactured to comprise more or less bars 250 than the six bars 250 that are shown in
During operation of the three-phase power source 300, while the voltage source 330 supplies voltage, the controller 310 commands the plurality of switches 320 to switch. The switching of the plurality of switches 320 produces three-phase currents (e.g., secondary currents) 270 that are drawn by the stator secondary windings 260 of the PMSG 200. The three-phase currents (e.g., secondary currents) 270 comprises three sinusoidal currents (refer to
During operation of the PMSG 200 (refer to
The right column of the table shows how a stator secondary winding magnetic field ({right arrow over (ψ)}SSW), which is equal in size and opposite in phase than the permanent magnet field ({right arrow over (ψ)}PM) (i.e. {right arrow over (ψ)}SSW=−{right arrow over (ψ)}PM), counteracts the permanent magnet field ({right arrow over (ψ)}PM) such that the overall magnetic field ({right arrow over (ψ)}gen) of the PMSG 200 is equal to zero (0) (i.e. {right arrow over (ψ)}gen={right arrow over (ψ)}PM+{right arrow over (ψ)}SSW=0).
The specific example given in the formulas below shows how to calculate the three-phase currents (e.g., the secondary currents) 270 drawn by the stator secondary windings 260 to cause the stator secondary windings 260 to generate magnetic field ({right arrow over (ψ)}SSW) that counteracts the magnetic field ({right arrow over (ψ)}PM) generated by the permanent magnet 230 for short circuit protection.
The magnetic flux created by permanent magnet 230:
=|
|∠(θ1)
|| is constant, and is determined by the PM material and generated construction.
θ1 is measurable.
The magnetic flux created by stator secondary windings 260:
=|IAMP|∠(θ2)
=|IAMP|∠(θ2−120)
=|IAMP|∠(θ2−240)
=k·(
+
+
)=k·|IAMP|∠(90+θ2)
Where, k is constant, determined by generator material and construction.
To completely counteract :
|∠(90+θ2)=|
|∠(180+θ1)
Therefore:
Finally, the controller 310, of the three-phase power source 300, will command the plurality of switches (e.g., six switches) 320, of the three-phase power source 300, to inject three-phase currents (e.g., secondary currents) 270 into the stator secondary windings 260 of the PMSG 200 using following equations, together referred to as Equation 1:
It should be noted that the formulas above (with slight modifications) may be used to calculate the three-phase currents (e.g., secondary currents) 270 to be drawn by the stator secondary windings 260 to cause the stator secondary windings 260 to generate a magnetic field (ψSSW) that adds to or subtracts from the magnetic field ({right arrow over (ψ)}PM) generated by the permanent magnet 230 for magnetic field strengthening or weakening, respectively.
Referring to
Also, during operation, secondary sensors (e.g., current transducers) 660 sense the three-phase currents (e.g., secondary currents) 270 drawn by the stator secondary windings 260. The secondary sensors 660 then generate secondary current signals (ISSW) (i.e. measurements of the secondary currents) 670 based on the sensed three-phase currents (e.g., secondary currents) 270.
While the voltage source 330 supplies voltage, during operation, the controller receives the primary current signals (Iload) 610 from the primary sensors (e.g., current transducers) 620, receives the secondary current signals (ISSW) 670 from the secondary sensors (e.g., current transducers) 660, and receives the rotor position angle θ of the permanent magnet 230.
A comparator 600 of the controller 310 compares the primary current signals (Iload) 610 to predetermined maximum currents (Imax) to determine if Iload 610 is greater than Imax. If the comparator 600 determines that Iload 610 is not greater than Imax, this determination indicates that the PMSG 200 is not experiencing a short circuit fault 400, and the comparator outputs a signal (e.g., a “0” signal) to switch a switch 620 of the controller 310 to a “No” position (e.g., a first position). After the switch 620 is switched to the “No” position, at least one processor(s) (not shown) of the controller 310 causes the controller 310 to do nothing (i.e. zero) 610 other than to simply repeat the process of the comparator 600 comparing the primary current signals (Iload) 610 to predetermined maximum currents (Imax) to determine if Iload 610 is greater than Imax.
However, if the comparator 600 determines that Iload 610 is greater than Imax, this indicates that the PMSG 200 is experiencing a short circuit fault 400, and the comparator outputs a signal (e.g., a “1” signal) to switch the switch 620 to a “Yes” position (i.e. a second position). After the switch 620 is switched to the “Yes” position, the processor(s) of the controller 310 uses the formulas in Equation 1 above along with the rotor position angle θ of the permanent magnet 230 to calculate three-phase currents (e.g., calculated secondary currents) to be drawn by the stator secondary windings 260 to cause the stator secondary windings 260 to generate a magnetic field (ψSSW) that counteracts the magnetic field ({right arrow over (ψ)}PM) generated by the permanent magnet 230 for short circuit protection.
It should be noted that although the functional diagram of
Then, a subtractor 630 of the controller 310 subtracts the secondary current signals (ISSW) 670 received from the secondary sensors (e.g., current transducers) 660 from the calculated three-phase currents (e.g., the calculated secondary currents) to obtain the difference (i.e. a difference value) between the currents. Then, the difference value is inputted into a proportional-integral-derivative controller (PID) 640. The PID 640 applies an accurate and responsive correction to the difference value to generate a corrected difference value. The corrected difference value is then inputted into a pulse width modulation (PWM) generator 650. The PWM generator 650 uses the corrected difference value to generate a pulse sequence for each of the switches of the plurality of switches 320 (e.g., to generate a total of six (6) pulse sequences, one for each of the six switches). Then, the controller 310 outputs the pulse sequences.
Then, the pulse sequences are inputted into the plurality of switches 320. The pulses sequences command the plurality of switches 320 to switch. The switching of the plurality of switches 320 modulates the signal to produce three-phase currents (e.g., secondary currents) 270. The three-phase currents (e.g., secondary currents) 270 are drawn by the stator secondary windings 260 of the PMSG 200. The three-phase currents (e.g., secondary currents) 270 injected into the stator secondary windings 260 create a rotating magnetic field that couples with the stator primary windings 220 to produce a stator secondary winding magnetic field ({right arrow over (ψ)}SSW). The stator secondary winding magnetic field ({right arrow over (ψ)}SSW) counteracts the permanent magnet field ({right arrow over (ψ)}PM) for short circuit protection.
It should be noted that in other embodiments, the stator secondary winding magnetic field ({right arrow over (ψ)}SSW) may be less than or greater than in size and equal in phase to the permanent magnet field ({right arrow over (ψ)}PM) to strengthen the permanent magnet field ({right arrow over (ψ)}PM), as well as the overall magnetic field ({right arrow over (ψ)}gen) of the PMSG 200.
Although particular embodiments have been shown and described, it should be understood that the above discussion is not intended to limit the scope of these embodiments. While embodiments and variations of the many aspects of the invention have been disclosed and described herein, such disclosure is provided for purposes of explanation and illustration only. Thus, various changes and modifications may be made without departing from the scope of the claims.
Where methods described above indicate certain events occurring in certain order, those of ordinary skill in the art having the benefit of this disclosure would recognize that the ordering may be modified and that such modifications are in accordance with the variations of the present disclosure. Additionally, parts of methods may be performed concurrently in a parallel process when possible, as well as performed sequentially. In addition, more parts or less part of the methods may be performed.
Accordingly, embodiments are intended to exemplify alternatives, modifications, and equivalents that may fall within the scope of the claims.
Although certain illustrative embodiments and methods have been disclosed herein, it can be apparent from the foregoing disclosure to those skilled in the art that variations and modifications of such embodiments and methods can be made without departing from the true spirit and scope of the art disclosed. Many other examples of the art disclosed exist, each differing from others in matters of detail only. Accordingly, it is intended that the art disclosed shall be limited only to the extent required by the appended claims and the rules and principles of applicable law.
