Constant frequency and narrowband variable frequency power system and method based on independent speed variable frequency generator

Abstract

The present invention relates to a constant frequency and narrowband variable frequency power system and method based on an independent speed variable frequency generator. A system may include an independent speed variable frequency (ISVF) generator configured to convert torque from a shaft into an AC power signal. The ISVF generator may have one or more pole pairs, and its equivalent shaft frequency is equal to the shaft frequency multiplied by the number of pole pairs. When the equivalent shaft frequency is less than a lower frequency limit, the generator control unit may set the generator output frequency of the ISVF generator to be equal to the lower frequency limit of the AC bus, when the equivalent shaft frequency is greater than an upper frequency limit, set the generator output frequency of the ISVF generator to be equal to the upper frequency limit of the AC bus, and when the equivalent shaft frequency is between the lower frequency limit and the upper frequency limit, set the generator output frequency of the ISVF generator to be equal to the equivalent shaft frequency.

Description

Technical Field

[0001] The present disclosure relates generally to the field of power distribution, and more particularly to constant frequency and narrowband power distribution based on independent speed variable frequency (ISVF) generators. Background Art

[0002] Induction generators may be used in power distribution systems such as aircraft and other vehicles to provide an alternating current (AC) power signal used by various AC loads. The AC loads typically have power frequency requirements that limit the AC power signal to a constant frequency or to a frequency band narrower than the typical operating frequency band of the prime mover (e.g., an engine).

[0003] In a typical power distribution system, to achieve a constant generator output frequency, a constant speed drive (or some other type of variable speed transmission) may be provided between the prime mover and the shaft of the generator. Constant speed drives may be complex, heavy, and / or bulky. Therefore, they may not be suitable for some applications, particularly for aircraft applications. Other disadvantages may exist. Summary of the invention

[0004] Disclosed herein are systems and methods that can overcome one or more disadvantages of typical power distribution systems. In an example, a system includes a prime mover configured to rotate a shaft. The system also includes an ISVF generator configured to convert torque from the shaft into an AC power signal, wherein the ISVF generator has one or more pole pairs, and wherein the equivalent shaft frequency is equal to the shaft frequency of the shaft multiplied by the number of pole pairs. The system includes an AC bus having a lower frequency limit and an upper frequency limit. The system also includes a generator control unit, which is configured to set the generator output frequency of the ISVF generator to be equal to the lower frequency limit when the equivalent shaft frequency is less than the lower frequency limit, set the generator output frequency of the ISVF generator to be equal to the upper frequency limit when the equivalent shaft frequency is greater than the upper frequency limit, and set the generator output frequency of the ISVF generator to be equal to the equivalent shaft frequency when the equivalent shaft frequency is greater than or equal to the lower frequency limit and less than or equal to the upper frequency limit.

[0005] In some examples, the generator control unit is configured to generate an excitation signal to control the ISVF generator, wherein the equivalent excitation frequency is equal to the excitation frequency of the excitation signal multiplied by the number of pole pairs. In such examples, setting the generator output frequency equal to the lower frequency limit includes setting the equivalent excitation frequency to the difference between the lower frequency limit and the equivalent shaft frequency, setting the generator output frequency equal to the upper frequency limit includes setting the equivalent excitation frequency of the excitation signal to the difference between the upper frequency limit and the equivalent shaft frequency, and setting the generator output frequency equal to the equivalent shaft frequency includes setting the equivalent excitation frequency of the excitation signal to zero.

[0006] In some examples, the system includes a coupling, which is disposed between the prime mover and the shaft and is configured to convert a second torque associated with the prime mover into a torque associated with the shaft. In some examples, the coupling includes a fixed ratio gear coupling, a belt, or a combination thereof. In some examples, the prime mover is configured to rotate the shaft without any constant speed drive device connected between them. In some examples, the system includes an AC load set electrically connected to the AC bus, wherein the frequency lower limit and the frequency upper limit are determined at least in part based on the operating requirements of the AC load set. In some examples, the system may include an AC-to-DC (AC / DC) converter electrically connected to the AC bus and a DC (DC) bus electrically connected to the AC / DC converter, wherein the AC / DC converter is configured to convert an AC power signal on the AC bus into a DC power signal on the DC bus. In some examples, the prime mover is an aircraft engine.

[0007] In an example, a method includes rotating a shaft using a prime mover. The method also includes converting torque from the shaft into an AC power signal using an ISVF generator, wherein the ISVF generator has one or more pole pairs, and wherein the equivalent shaft frequency is equal to the shaft frequency of the shaft multiplied by the number of pole pairs. The method also includes applying the AC power signal to an AC bus having a lower frequency limit and an upper frequency limit. The method also includes setting the generator output frequency of the ISVF generator to be equal to the lower frequency limit when the equivalent shaft frequency is less than the lower frequency limit. The method includes setting the generator output frequency of the ISVF generator to be equal to the upper frequency limit when the equivalent shaft frequency is greater than the upper frequency limit. The method also includes setting the generator output frequency of the ISVF generator to be equal to the equivalent shaft frequency when the equivalent shaft frequency is between the lower frequency limit and the upper frequency limit.

[0008] In some examples, the method includes generating an excitation signal to control an ISVF generator, wherein an equivalent excitation frequency is equal to an excitation frequency of the excitation signal multiplied by the number of pole pairs, wherein the step of setting the generator output frequency equal to a lower frequency limit includes setting the equivalent excitation frequency to a difference between the lower frequency limit and an equivalent shaft frequency, wherein the step of setting the generator output frequency equal to an upper frequency limit includes setting the equivalent excitation frequency of the excitation signal to a difference between the upper frequency limit and the equivalent shaft frequency, and wherein the step of setting the generator output frequency equal to the equivalent shaft frequency includes setting the equivalent excitation frequency of the excitation signal to zero.

[0009] In some examples, the method includes using a coupling to convert a second torque associated with the prime mover into a torque associated with the shaft. In some examples, the coupling includes a fixed ratio gear coupling, a belt, or a combination thereof. In some examples, the step of rotating the shaft is performed without any constant speed drive device being connected between the shaft and the prime mover. In some examples, the AC / DC converter is electrically connected to the AC bus, and wherein the DC bus is electrically connected to the AC / DC converter. In these examples, the method may include converting an AC power signal on the AC bus to a DC power signal on the DC bus at the AC / DC converter.

[0010] In an example, a system includes a prime mover configured to rotate a shaft. The system also includes an ISVF generator configured to convert torque from the shaft into an AC power signal, wherein the ISVF generator has one or more pole pairs, and wherein an equivalent shaft frequency is equal to the shaft frequency of the shaft multiplied by the number of pole pairs. The system also includes an AC bus and a generator control unit configured to generate an excitation signal to control the ISVF generator, wherein the equivalent excitation frequency is equal to the excitation frequency of the excitation signal multiplied by the number of pole pairs, and wherein the generator control unit maintains a constant generator output frequency by setting the equivalent excitation frequency equal to a difference between the constant generator output frequency and the equivalent shaft frequency.

[0011] In some examples, the system includes a coupler disposed between the prime mover and the shaft and configured to convert a second torque associated with the prime mover into a torque associated with the shaft, wherein the coupler includes a fixed ratio gear coupling, a belt, or a combination thereof. In some examples, the prime mover is configured to rotate the shaft without any constant speed drive device coupled therebetween. In some examples, the system includes an AC load set electrically connected to an AC bus, wherein a constant generator output frequency is determined based at least in part on an operational requirement of the AC load set. In some examples, the system includes an AC / DC converter electrically connected to the AC bus and a DC bus electrically connected to the AC / DC converter, wherein the AC / DC converter is configured to convert an AC power signal on the AC bus into a DC power signal on the DC bus. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 is a block diagram of an example of an independent speed variable frequency (ISVF) generator based power system.

[0013] Figure 2 It is a graph that relates the shaft frequency band to the equivalent shaft frequency band and the AC output signal frequency band.

[0014] Figure 3 It is a graph that relates the excitation frequency band to the equivalent excitation frequency band.

[0015] Figure 4 is a graph that depicts the power capability requirement of the excitation signal as a function of the frequency of the excitation signal.

[0016] Figure 5 is a set of graphs comparing the power requirements associated with a first configuration of an ISVF generator-based power system to a second configuration.

[0017] Figure 6 is a flow chart depicting an example of a power distribution method based on an ISVF generator.

[0018] Although the present disclosure is susceptible to various modifications and alternative forms, specific examples are shown in the drawings and will be described in detail herein. However, it should be understood that the present disclosure is not intended to be limited to the specific forms disclosed. On the contrary, the present invention is intended to cover all modifications, equivalents and substitutes that fall within the scope of the present disclosure. DETAILED DESCRIPTION

[0019] Reference Figure 1 , depicts an independent speed variable frequency (ISVF) generator-based power system 100. As described herein, the system 100 can be configured to generate and distribute power within a frequency band that is narrower than that generated using a typical induction generator for a given shaft speed range, without a constant speed drive or other type of transmission.

[0020] The system 100 may include a prime mover 102. For example, the prime mover 102 may be an aircraft engine or another type of vehicle engine. The prime mover 102 may be attached to a coupling 104. The coupling 104 may include a fixed gear ratio coupling, a belt coupling, or a combination thereof, and may be configured to convert a torque 129 from the prime mover 102 to a torque 130 on a shaft 106. The coupling 104 may differ from a constant speed device in that the torque transfer ratio of the coupling 104 may be fixed rather than variable. The shaft 106 may be attached to an ISVF generator 108. By using the ISVF generator 108 rather than a typical induction generator, the system 100 may omit any constant speed drive device between the prime mover 102 and the shaft 106.

[0021] The ISVF generator 108 may be configured to convert the torque 130 from the shaft 106 into an AC power signal 132. The ISVF generator 108 may generate the AC power signal 132 such that the frequency of the AC power signal 132 is independent of the shaft speed of the shaft 106. Examples of ISVF generators 108 that may be used with the system 100 are further described in U.S. Patent Application No. 15 / 819,919, filed on November 21, 2017, published as U.S. Patent Application Publication No. 2019 / 0158002 and entitled “Independent Speed ​​Variable Frequency Alternating Current Generator,” the contents of which are incorporated by reference in their entirety.

[0022] The ISVF generator 108 may have one or more pole pairs 109 . Figure 1 The ISVF generator 108 is depicted as having two pole pairs 109 (i.e., four poles). However, more or less than two pole pairs are possible and consistent with the present disclosure. The number of pole pairs 109 can act as a multiplier between the frequency of the shaft 106 and the frequency of the AC power signal 132. Therefore, the shaft 106 can be associated with an equivalent shaft frequency that is equal to the shaft frequency of the shaft 106 multiplied by the number of pole pairs 109.

[0023] The system 100 may include a generator control unit (GCU) 110. The generator control unit 110 may be configured to generate an excitation signal 134 to control the ISVF generator 108. The ISVF generator 108 may use the excitation signal 134 to generate a rotating magnetic flux at a rotor of the ISVF generator 108, resulting in a frequency of the AC power signal 132 that is an algebraic sum of a frequency of the shaft 106 and a frequency of the excitation signal 134. The number of pole pairs 109 of the ISVF generator 108 may also affect the contribution of the excitation signal 134 to the AC power signal 132. Therefore, the equivalent excitation frequency of the excitation signal 134 may be equal to the excitation frequency of the excitation signal 134 multiplied by the number of pole pairs 109.

[0024] The ISVF generator 108 may be coupled to an AC bus 112. An AC load set 114 may be coupled to the AC bus 112 and configured to receive power from the AC bus 112. The AC load set 114 may have operating requirements such that the AC load set 114 is adapted to operate within an operating frequency band having a lower frequency limit and an upper frequency limit. The operating frequency band may be narrower than an operating frequency band associated with the prime mover 102.

[0025] AC / DC converter 116 may be coupled to AC bus 112. AC / DC converter 116 may be configured to convert AC power signal 132 to DC power signal 136 and use DC power signal 136 to power DC bus 118. A set of DC loads 120 may be coupled to DC bus 118.

[0026] A direct current to alternating current (DC / AC) converter 122 may be coupled to the DC bus 118. The DC / AC converter 122 may be configured to convert a DC power signal 136 to a second AC power signal 134 to power the second AC bus 124. A set of AC loads 126 may be coupled to the second AC bus 124. The second set of AC loads 126 may have different operating frequency and voltage requirements than the set of AC loads 114. In some examples, the second set of AC loads 126 corresponds to motor loads (e.g., for actuating a flight surface, etc.).

[0027] During operation, the generator control unit 110 may be configured to control the ISVF generator 108 to generate an AC power signal 132 that falls within a frequency band having a lower frequency limit and an upper frequency limit, which frequency band is narrower than the frequency band generated using a typical induction generator for a given shaft speed range. In a first configuration, to achieve the frequency band, the generator control unit 110 may be configured to set the generator output frequency of the ISVF generator 108 equal to the lower frequency limit in response to the equivalent shaft frequency (e.g., the shaft frequency multiplied by the number of pole pairs 109) being less than the lower frequency limit. The generator control unit 110 may be configured to set the generator output frequency of the ISVF generator 108 equal to the upper frequency limit in response to the equivalent shaft frequency being greater than the upper frequency limit. In response to the equivalent shaft frequency being greater than or equal to the lower frequency limit and less than or equal to the upper frequency limit, the generator control unit 110 may be configured to set the generator output frequency of the ISVF generator 108 equal to the equivalent shaft frequency. In a second configuration, the generator control unit 110 may simply maintain a constant generator output frequency, rather than narrowing the frequency band.

[0028] A benefit of the system 100 is that by narrowing the frequency range of the AC power signal using the rotational frequency range of the ISVF generator 108 relative to the shaft, the system 100 can omit complex, heavy, and / or bulky equipment (e.g., a constant speed drive) between the shaft and the ISVF generator 108. Another benefit is that the generator control unit 110 can limit the generator output frequency to a constant generator output frequency corresponding to the operating requirements of the AC load set 114. Another benefit is that in the case where the AC bus 112 can support a frequency band range, by making the generator output frequency 504 (shown in FIG. 1 ) Figure 5 ) is narrowed to a range having a lower frequency limit and an upper frequency limit, the load equipment can be lighter and less complex due to the favorable operating conditions of the narrow frequency band as described herein. Other benefits and advantages may exist.

[0029] Figure 2 and Figure 3 Depicted are the concepts of an equivalent shaft frequency 210 and an equivalent excitation frequency 308. These frequencies depend on the number of pole pairs 109 associated with the ISVF generator 108. In the case where only one pole pair is present, the equivalent shaft frequency 210 and the equivalent excitation frequency 308 are equal to the shaft frequency 208 and the excitation frequency 306, respectively.

[0030] Reference Figure 2 , depicts a graph relating shaft frequency band 202 to equivalent shaft frequency band 204 and AC output signal frequency band 206. Figure 2 As shown, shaft frequency 208 may fall within shaft frequency band 202. Shaft frequency 208 may represent the frequency at which a prime mover (e.g., prime mover 102) rotates a shaft (e.g., shaft 106). Shaft frequency band 202 may be limited between a lower shaft frequency limit 214 representing the lowest operating frequency at which the prime mover will rotate the shaft and an upper shaft frequency limit 216 representing the highest operating frequency at which the prime mover will rotate the shaft. For illustrative purposes, Figure 2 The lower shaft frequency limit 214 is depicted as 100 Hz and the upper shaft frequency limit 216 is depicted as 300 Hz.

[0031] The equivalent shaft frequency band 204 may be equal to the number of pole pairs of an ISVF generator (eg, the ISVF generator 108) multiplied by the shaft frequency band 202. Figure 2 In the example of , there may be two pole pairs, so that if the shaft frequency 208 is about 175 Hz, the equivalent shaft frequency 210 is about 350 Hz. Similarly, the equivalent shaft frequency lower limit 218 may be about 200 Hz, and the equivalent shaft frequency upper limit 220 may be about 600 Hz. Although Figure 2 The example of considers two pole pairs, but any number of pole pairs may be used.

[0032] Although a typical induction motor will generally generate an AC power signal having a frequency that falls within the equivalent shaft frequency band 204, an ISVF generator (e.g., the ISVF generator 108) may be controlled by an excitation signal (e.g., the excitation signal 134) to generate a narrower AC output signal frequency band 206. For example, the AC output signal frequency band 206 may have a lower frequency limit 222 that is greater than the equivalent shaft frequency lower limit 218. Likewise, the AC output signal frequency band 206 may have an upper frequency limit 224 that is less than the equivalent shaft frequency upper limit 220. Thus, the AC output signal frequency band 206 may be limited to meet the operating requirements of the AC load.

[0033] Reference Figure 3, depicts a graph relating an excitation frequency band 302 to an equivalent excitation frequency band 304. An excitation signal (e.g., excitation signal 134) may be applied to a field winding on a rotor of an ISVF generator (e.g., ISVF generator 108) to effectively increase or decrease the frequency of an output power signal. The excitation signal may have an excitation frequency 306 that falls within the excitation frequency band 302. Since the number of pole pairs associated with the ISVF generator affects the output frequency, the equivalent excitation frequency band 304 may be equal to the excitation frequency band 302 multiplied by the number of pole pairs. Likewise, the equivalent excitation frequency 308 may be equal to the excitation frequency 306 multiplied by the number of pole pairs.

[0034] In a single-pole-pair system, the generator output frequency can be the algebraic sum of the shaft frequency and the excitation frequency:

[0035] f Gen =f Shaft +f Excit

[0036] For systems with multiple pole pairs, both the shaft frequency and the excitation frequency can be multiplied by the number of pole pairs (PP):

[0037] f Gen =(f Shaft +f Excit )·PP

[0038] where f Shaft *PP is the equivalent shaft frequency, f Excit *PP is the equivalent excitation frequency.

[0039] Reference Figure 4 , graph 400 depicts the power capacity requirement S of the excitation signal Excit The frequency of the excitation signal f Excit 402. Although Figure 4 The description in FIG. 4 is applicable to a single pole pair system, but one of ordinary skill in the art will appreciate that, with the benefit of this application, these concepts can be extended to multiple pole pairs. As shown in graph 400, as the frequency f Excit Moving away from zero, the excitation signal may require more power S Excit In order to maintain a constant power output of the ISVF generator. Analysis shows that this relationship can be roughly represented by a conic section curve as shown. When the excitation frequency f Excit When the shaft speed is zero (meaning the shaft speed is equal to the generator output frequency), the excitation signal only needs to provide enough power to compensate for the power loss in the rotor winding (for example, y0). When the generator shaft speed is lower than the generator output frequency, the excitation frequency f Excit is positive. In this case, the excitation source provides apparent power to the stator winding. When the generator shaft speed is higher than the generator output frequency, the excitation frequency f Excitis negative. In this case, the excitation source draws apparent power from the generator shaft. (excitation frequency f Excit The greater the deviation between the rated output frequency of the generator, the greater the power capacity S of the excitation signal. Excit But the higher.

[0040] Reference Figure 5 , a first graph 500 depicts power requirements associated with a first configuration of system 100 and is compared to a second graph 550 depicting power requirements associated with a second configuration of system 100. The first configuration may correspond to a constant frequency output and the second configuration may correspond to a narrowed frequency band output.

[0041] As shown in the first graph 500, the generator control unit (e.g., the generator control unit 110) may maintain a constant generator output frequency 504. This may be performed by setting the equivalent excitation frequency 308 equal to the difference between the constant generator output frequency 504 and the equivalent shaft frequency 210. In other words, the generator output frequency 504 may be equal to the algebraic sum of the shaft frequency 208 and the excitation frequency 306:

[0042] F Gen =f Shaft (t)+f Excit (t)

[0043] To maintain a constant generator output frequency 504, the excitation frequency 306 may be set to zero when the shaft frequency 208 is equal to the generator output frequency 504, may be set to a positive value when the shaft frequency 208 is less than the generator output frequency 504, and may be set to a negative value when the shaft frequency 208 is greater than the generator output frequency 504:

[0044] If f Shaft (t) = F Gen , then f Excit (t) = 0

[0045] If f Shaft (t)<F Gen , then f Excit (t)>0

[0046] If f Shaft (t)>F Gen , then f Excit (t)<0

[0047] When considering the pole pairs associated with the ISVF generator, the generator output frequency 504 may be determined as:

[0048] F Gen =(f Shaft (t)+f Excit (t)) ·PP

[0049] To maintain a constant generator output frequency 504, the equivalent excitation frequency 308 may be set to zero when the equivalent shaft frequency 210 is equal to the generator output frequency 504, may be set to a positive value when the equivalent shaft frequency 210 is less than the generator output frequency 504, and may be set to a negative value when the equivalent shaft frequency 210 is greater than the generator output frequency 504:

[0050] If (f Shaft (t))·PP=F Gen , then (f Excit (t))·PP=0

[0051] If (f Shaft (t))·PP<F Gen , then (f Excit (t))·PP>0

[0052] If (f Shaft (t))·PP>F Gen , then (f Excit (t))·PP<0

[0053] As shown in the first graph 500, as the shaft frequency shifts away from the generator output frequency 504, more power is allocated to the excitation signal. In order to provide power for the frequency range between the equivalent shaft frequency lower limit 218 and the equivalent shaft frequency upper limit 220, a relatively high power 506 may be used. Therefore, when the shaft frequency range is relatively narrow, the constant generator output frequency configuration depicted in the first graph 500 may be appropriate. For engines that utilize a wider shaft frequency range, the configuration depicted in the second graph 550 may be more appropriate.

[0054] As shown in the second graph 550, the generator control unit (eg, the generator control unit 110) may maintain the generator output frequency 502. The generator output frequency 502 may be maintained between the lower frequency limit 222 and the upper frequency limit 224, rather than being constant:

[0055] F min ≤F Gen ≤F max

[0056] If the shaft frequency 208 is between the lower frequency limit 222 and the upper frequency limit, the generator output frequency 502 may be set equal to the shaft frequency 208 by setting the excitation frequency 306 of the excitation signal to zero. If the shaft frequency 208 is less than the lower frequency limit 222, the generator output frequency 502 may be set equal to the lower frequency limit 222 by setting the excitation frequency 306 to the difference between the lower frequency limit 222 and the shaft frequency 208. If the shaft frequency 208 is greater than the upper frequency limit 224, the generator output frequency 502 may be set equal to the upper frequency limit 224 by setting the excitation frequency 306 of the excitation signal to the difference between the upper frequency limit 224 and the shaft frequency 208:

[0057] If F min ≤f Shaft (t)≤F max , then f Excit (t) = 0

[0058] If f Shaft (t)≤F min , then f Excit (t) = F min -f Shaft (t)

[0059] If f Shaft (t)≥F max , then f Excit (t) = F max -f Shaft (t)

[0060] When considering the pole pairs associated with the ISVF generator, if the equivalent shaft frequency 210 is between the lower frequency limit 222 and the upper frequency limit, the generator output frequency 502 may be set equal to the equivalent shaft frequency 210 by setting the equivalent excitation frequency 308 of the excitation signal to zero. If the equivalent shaft frequency 210 is less than the lower frequency limit 222, the generator output frequency 502 may be set equal to the lower frequency limit 222 by setting the equivalent excitation frequency 308 to the difference between the lower frequency limit 222 and the equivalent shaft frequency 210. If the equivalent shaft frequency 210 is greater than the upper frequency limit 224, the generator output frequency 502 may be set equal to the upper frequency limit 224 by setting the equivalent excitation frequency 308 of the excitation signal to the difference between the upper frequency limit 224 and the equivalent shaft frequency 210:

[0061] If F min ≤(f Shaft (t))·PP≤F max , then (f Excit (t))·PP=0

[0062] If (f Shaft (t))·PP≤F min , then (fExcit (t))·PP=F min -(f Shaft (t)) ·PP

[0063] If (f Shaft (t))·PP≥F max , then (f Excit (t))·PP=F max -(f Shaft (t)) ·PP

[0064] As shown in the second graph 550, as the shaft frequency shifts away from the generator output frequency 502, more constant power is allocated to the excitation signal while the shaft frequency is between the lower frequency limit 222 and the upper frequency limit 224. Therefore, a relatively low power 508 can be used for the same shaft frequency range. When the shaft frequency range is relatively wide and the AC load is capable of operating at a frequency between the lower frequency limit 222 and the upper frequency limit 224, the narrowband generator output frequency configuration depicted in the second graph 550 may be appropriate.

[0065] Reference Figure 6 , depicts an example of an ISVF generator-based power distribution method 600. The method 600 may include, at 602, rotating a shaft using a prime mover. For example, the prime mover 102 may be used to rotate the shaft 106.

[0066] The method 600 may also include, at 604, converting the torque from the shaft into an AC power signal using an ISVF generator, wherein the ISVF generator has one or more pole pairs, and wherein the equivalent shaft frequency is equal to the shaft frequency of the shaft multiplied by the number of pole pairs. For example, the torque 130 from the shaft 106 may be converted into the AC power signal 132 using the ISVF generator 108.

[0067] The method 600 may also include, at 606 , converting a second torque associated with the prime mover to a torque associated with the shaft using the coupling. For example, the second torque 129 may be converted to the torque 130 using the coupling 104 .

[0068] The method 600 may further include, at 608 , generating an excitation signal to control the ISVF generator, wherein an equivalent excitation frequency is equal to an excitation frequency of the excitation signal multiplied by the number of pole pairs. For example, the generator control unit 110 may generate the excitation signal 134 .

[0069] The method 600 may further include applying an AC power signal to an AC bus having a lower frequency limit and an upper frequency limit at 610 . For example, the AC power signal 132 may be applied to the AC bus 112 .

[0070] The method 600 may include, at 612, setting the generator output frequency of the ISVF generator to be equal to the lower frequency limit when the equivalent shaft frequency is less than the lower frequency limit. Setting the generator output frequency of the ISVF generator to be equal to the lower frequency limit may include, at 614, setting the equivalent excitation frequency to the difference between the lower frequency limit and the equivalent shaft frequency.

[0071] The method 600 may further include, at 616, setting the generator output frequency of the ISVF generator to be equal to the upper frequency limit when the equivalent shaft frequency is greater than the upper frequency limit. Setting the generator output frequency to be equal to the upper frequency limit may include, at 618, setting the equivalent excitation frequency of the excitation signal to be equal to the difference between the upper frequency limit and the equivalent shaft frequency.

[0072] Method 600 may include, at 620, setting a generator output frequency of the ISVF generator to be equal to the equivalent shaft frequency when the equivalent shaft frequency is between a lower frequency limit and an upper frequency limit. Setting the generator output frequency to be equal to the equivalent shaft frequency includes, at 622, setting the equivalent excitation frequency of the excitation signal to zero.

[0073] A benefit of method 600 is that by narrowing the frequency range of the AC power signal using the rotational frequency range of the ISVF generator relative to the shaft, complex, heavy and / or bulky equipment (eg, a constant speed drive) between the shaft and the ISVF generator may be omitted.Other advantages may exist.

[0074] Furthermore, the present disclosure includes examples according to the following clauses, and thus it is noted that the protection scope is provided by the claims.

[0075] Clause 1. A system comprising: a prime mover configured to rotate a shaft; an independent speed variable frequency (ISVF) generator configured to convert torque from the shaft into an alternating current (AC) power signal, wherein the ISVF generator has one or more pole pairs and wherein an equivalent shaft frequency is equal to the shaft frequency of the shaft multiplied by the number of pole pairs; an AC bus having a lower frequency limit and an upper frequency limit; and a generator control unit configured to: set a generator output frequency of the ISVF generator to be equal to the lower frequency limit when the equivalent shaft frequency is less than the lower frequency limit; set the generator output frequency of the ISVF generator to be equal to the upper frequency limit when the equivalent shaft frequency is greater than the upper frequency limit; and set the generator output frequency of the ISVF generator to be equal to the equivalent shaft frequency when the equivalent shaft frequency is greater than or equal to the lower frequency limit and less than or equal to the upper frequency limit.

[0076] Clause 2. A system according to clause 1, wherein the generator control unit is configured to generate an excitation signal to control the ISVF generator, wherein the equivalent excitation frequency is equal to the excitation frequency of the excitation signal multiplied by the number of pole pairs, wherein setting the generator output frequency equal to a lower frequency limit includes setting the equivalent excitation frequency to the difference between the lower frequency limit and the equivalent shaft frequency, wherein setting the generator output frequency equal to an upper frequency limit includes setting the equivalent excitation frequency of the excitation signal to the difference between the upper frequency limit and the equivalent shaft frequency, and wherein setting the generator output frequency equal to the equivalent shaft frequency includes setting the equivalent excitation frequency of the excitation signal to zero.

[0077] Clause 3. The system of clause 1, further comprising: a coupling disposed between the prime mover and the shaft and configured to convert a second torque associated with the prime mover into a torque associated with the shaft.

[0078] Clause 4. The system of clause 3, wherein the coupling comprises a fixed ratio gear coupling, a belt, or a combination thereof.

[0079] Clause 5. The system of any one of clauses 1 to 4, wherein the prime mover is configured to rotate the shaft without any constant speed drive coupled therebetween.

[0080] Clause 6. The system of any of clauses 1 to 5, further comprising: a set of AC loads electrically connected to the AC bus, wherein the lower frequency limit and the upper frequency limit are determined based at least in part on operational requirements of the set of AC loads.

[0081] Clause 7. A system according to any one of clauses 1 to 6, the system further comprising: an alternating current to direct current (AC / DC) converter electrically connected to an AC bus; and a direct current (DC) bus electrically connected to the AC / DC converter, wherein the AC / DC converter is configured to convert an AC power signal on the AC bus into a DC power signal on the DC bus.

[0082] Clause 8. The system of any one of Clauses 1 to 7, wherein the prime mover is an aircraft engine.

[0083] Clause 9. A method comprising: rotating a shaft using a prime mover; converting torque from the shaft into an alternating current (AC) power signal using an independent speed variable frequency (ISVF) generator, wherein the ISVF generator has one or more pole pairs, and wherein an equivalent shaft frequency is equal to the shaft frequency of the shaft multiplied by the number of pole pairs; applying the AC power signal to an AC bus having a lower frequency limit and an upper frequency limit; setting a generator output frequency of the ISVF generator to be equal to the lower frequency limit when the equivalent shaft frequency is less than the lower frequency limit; setting the generator output frequency of the ISVF generator to be equal to the upper frequency limit when the equivalent shaft frequency is greater than the upper frequency limit; and setting the generator output frequency of the ISVF generator to be equal to the equivalent shaft frequency when the equivalent shaft frequency is between the lower frequency limit and the upper frequency limit.

[0084] Clause 10. The method according to clause 9, further comprising: generating an excitation signal to control the ISVF generator, wherein the equivalent excitation frequency is equal to the excitation frequency of the excitation signal multiplied by the number of pole pairs, wherein the step of setting the generator output frequency equal to the lower frequency limit includes setting the equivalent excitation frequency to the difference between the lower frequency limit and the equivalent shaft frequency, wherein the step of setting the generator output frequency equal to the upper frequency limit includes setting the equivalent excitation frequency of the excitation signal to the difference between the upper frequency limit and the equivalent shaft frequency, and wherein the step of setting the generator output frequency equal to the equivalent shaft frequency includes setting the equivalent excitation frequency of the excitation signal to zero.

[0085] Clause 11. The method of clause 9, further comprising: using a coupling to convert a second torque associated with the prime mover into a torque associated with the shaft.

[0086] Clause 12. The method of clause 11, wherein the coupling comprises a fixed ratio gear coupling, a belt, or a combination thereof.

[0087] Clause 13. The method of any of clauses 9 to 12, wherein the step of rotating the shaft is performed without any constant speed drive coupled between the shaft and the prime mover.

[0088] Clause 14. A method according to any one of clauses 9 to 13, wherein an alternating current to direct current (AC / DC) converter is electrically connected to an AC bus, and wherein a direct current (DC) bus is electrically connected to the AC / DC converter, the method further comprising: converting an AC power signal on the AC bus into a DC power signal on the DC bus at the AC / DC converter.

[0089] Clause 15. The method of any one of clauses 9 to 14, wherein the prime mover is an aircraft engine.

[0090] Clause 16. A system comprising: a prime mover configured to rotate a shaft; an independent speed variable frequency (ISVF) generator configured to convert torque from the shaft into an alternating current (AC) power signal, wherein the ISVF generator has one or more pole pairs and wherein an equivalent shaft frequency is equal to the shaft frequency of the shaft multiplied by the number of pole pairs; an AC bus; and a generator control unit configured to generate an excitation signal to control the ISVF generator, wherein the equivalent excitation frequency is equal to the excitation frequency of the excitation signal multiplied by the number of pole pairs, and wherein the generator control unit maintains a constant generator output frequency by setting the equivalent excitation frequency equal to a difference between the constant generator output frequency and the equivalent shaft frequency.

[0091] Clause 17. The system according to clause 16, further comprising: a coupling disposed between the prime mover and the shaft and configured to convert a second torque associated with the prime mover into a torque associated with the shaft, wherein the coupling comprises a fixed ratio gear coupling, a belt, or a combination thereof.

[0092] Clause 18. The system of any of clauses 16 to 17, wherein the prime mover is configured to rotate the shaft without any constant speed drive coupled therebetween.

[0093] Clause 19. The system of any of Clauses 16 to 18, further comprising: a set of AC loads electrically connected to the AC bus, wherein the constant generator output frequency is determined based at least in part on operational requirements of the set of AC loads.

[0094] Clause 20. A system according to any one of clauses 16 to 19, the system further comprising: an alternating current to direct current (AC / DC) converter electrically connected to an AC bus; and a direct current (DC) bus electrically connected to the AC / DC converter, wherein the AC / DC converter is configured to convert an AC power signal on the AC bus into a DC power signal on the DC bus.

[0095] Although various examples have been shown and described, the disclosure is not limited thereto, but is to be construed as including all such modifications and changes as would be apparent to those skilled in the art.

Claims

1. An electric power system (100) based on an independent speed variable frequency (ISVF) generator, the electric power system comprising: a prime mover (102) configured to rotate a shaft (106); an independent speed variable frequency (ISVF) generator (108) configured to convert a torque (130) from the shaft (106) into an alternating current (AC) power signal (132), wherein the ISVF generator (108) has one or more pole pairs (109), and wherein an equivalent shaft frequency (210) is equal to a shaft frequency (208) of the shaft (106) multiplied by the number of pole pairs (109); an AC bus (112) having a lower frequency limit (222) and an upper frequency limit (224); and A generator control unit (110), the generator control unit being configured to: When the equivalent shaft frequency (210) is less than the frequency lower limit (222), setting the generator output frequency (502) of the ISVF generator (108) to be equal to the frequency lower limit (222); When the equivalent shaft frequency (210) is greater than the upper frequency limit (224), setting the generator output frequency (502) of the ISVF generator (108) to be equal to the upper frequency limit (224); and When the equivalent shaft frequency (210) is greater than or equal to the lower frequency limit (222) and less than or equal to the upper frequency limit (224), the generator output frequency (502) of the ISVF generator (108) is set equal to the equivalent shaft frequency (210).

2. The power system according to claim 1, wherein: The generator control unit (110) is configured to generate an excitation signal (134) to control the ISVF generator (108), wherein an equivalent excitation frequency (308) is equal to an excitation frequency (306) of the excitation signal multiplied by the number of pole pairs (109), wherein setting the generator output frequency (502) to be equal to the frequency lower limit (222) includes setting the equivalent excitation frequency (308) to be the difference between the frequency lower limit (222) and the equivalent shaft frequency (210), wherein setting the generator output frequency (502) to be equal to the upper frequency limit (224) includes setting the equivalent excitation frequency (308) of the excitation signal to be equal to the difference between the upper frequency limit (224) and the equivalent shaft frequency (210), and Wherein, setting the generator output frequency (502) equal to the equivalent shaft frequency (210) includes setting the equivalent excitation frequency (308) of the excitation signal to zero.

3. The power system according to claim 1, further comprising: A coupling (104) is disposed between the prime mover (102) and the shaft (106) and is configured to convert a second torque (129) associated with the prime mover (102) into a torque (130) associated with the shaft (106).

4. The power system according to claim 3, wherein: The coupling (104) comprises a fixed ratio gear coupling, a belt or a combination thereof.

5. The power system according to any one of claims 1 to 4, wherein: The prime mover (102) is configured to rotate the shaft (106) without any constant speed drive device coupled between the prime mover and the shaft.

6. The power system according to any one of claims 1 to 4, further comprising: A set of AC loads (114) electrically connected to the AC bus (112), wherein the lower frequency limit (222) and the upper frequency limit (224) are determined based at least in part on operational requirements of the set of AC loads (114).

7. The power system according to any one of claims 1 to 4, further comprising: an alternating current to direct current (AC / DC) converter (116) electrically connected to the AC bus (112); as well as A direct current (DC) bus (118) is electrically connected to the AC / DC converter (116), wherein the AC / DC converter (116) is configured to convert the AC power signal (132) on the AC bus (112) into a DC power signal (136) on the DC bus (118).

8. The power system according to any one of claims 1 to 4, wherein: The prime mover (102) is an aircraft engine.

9. A method for power distribution based on an independent speed variable frequency (ISVF) generator, the method comprising the following steps: Using a prime mover (102) to rotate a shaft (106); Converting the torque (130) from the shaft (106) into an alternating current (AC) power signal (132) using an independent speed variable frequency (ISVF) generator (108), wherein the ISVF generator (108) has one or more pole pairs (109), and wherein an equivalent shaft frequency (210) is equal to the shaft frequency (208) of the shaft (106) multiplied by the number of pole pairs (109); applying the AC power signal (132) to an AC bus (112) having a lower frequency limit (222) and an upper frequency limit (224); When the equivalent shaft frequency (210) is less than the frequency lower limit (222), setting the generator output frequency (502) of the ISVF generator (108) to be equal to the frequency lower limit (222); When the equivalent shaft frequency (210) is greater than the upper frequency limit (224), setting the generator output frequency (502) of the ISVF generator (108) to be equal to the upper frequency limit (224); and When the equivalent shaft frequency (210) is between the lower frequency limit (222) and the upper frequency limit (224), the generator output frequency (502) of the ISVF generator (108) is set equal to the equivalent shaft frequency (210).

10. The method according to claim 9, further comprising: generating an excitation signal (134) to control the ISVF generator (108), wherein an equivalent excitation frequency (308) is equal to the excitation frequency (306) of the excitation signal multiplied by the number of pole pairs (109), The step of setting the generator output frequency (502) to be equal to the frequency lower limit (222) includes setting the equivalent excitation frequency (308) to be the difference between the frequency lower limit (222) and the equivalent shaft frequency (210), The step of setting the generator output frequency (502) to be equal to the upper frequency limit (224) includes setting the equivalent excitation frequency (308) of the excitation signal to be equal to the difference between the upper frequency limit (224) and the equivalent shaft frequency (210), and The step of setting the generator output frequency (502) to be equal to the equivalent shaft frequency (210) includes setting the equivalent excitation frequency (308) of the excitation signal to zero.

11. The method according to claim 9, further comprising: A second torque (129) associated with the prime mover (102) is converted into a torque (130) associated with the shaft (106) using a coupling (104).

12. The method according to claim 11, wherein: The coupling (104) comprises a fixed ratio gear coupling, a belt or a combination thereof.

13. The method according to any one of claims 9 to 12, wherein: The step of rotating the shaft (106) is performed without any constant speed drive device coupled between the shaft (106) and the prime mover (102).

14. The method according to any one of claims 9 to 12, wherein: An alternating current (AC / DC) converter (116) is electrically connected to the AC bus (112), and a direct current (DC) bus (118) is electrically connected to the AC / DC converter (116), the method further comprising: The AC power signal (132) on the AC bus (112) is converted to a DC power signal (136) on the DC bus (118) at the AC / DC converter (116).

15. The method according to any one of claims 9 to 12, wherein: The prime mover (102) is an aircraft engine.

Images