Patent ID: 12212184

DETAILED DESCRIPTION OF AN EMBODIMENT OF THE INVENTION

The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all embodiments of the invention are shown. This invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout.

Generators have many applications and are designed to meet requirements of different types of load as explained above. Loads connected to generators may be linear loads and/or non-linear loads. Examples of linear loads may include, but are not limited to, heaters, motors, transformers, or the like. Examples of non-linear loads may include, but are not limited to computer, Uninterruptable Power Supplies (UPSs), electronic equipment, variable frequency drives, or the like. Each of these loads may have different requirements and therefore generators used for each of these applications differ in configuration, size, and/or operation.

One application addressed in the present invention is to construct a generator that ultimately drives a stand-alone refrigeration unit or a refrigeration unit located in a truck, tractor, trailer, semi-trailer, or the like used to transport medical supplies, pharmaceutical products (e.g., medicines), perishable products (e.g., meat, dairy, poultry, seafood, or the like), chemical products, or the like. Such an application requires a generator that meets specific voltage, size, efficiency, and/or cost requirements in order to maintain a temperature at or below 6 degrees Celsius within the truck, trailer, semi-trailer, or the like. In particular, a generator used in such an application requires (i) a minimum voltage while starting an inductive load (e.g., induction motor) at or above ambient temperature, and (ii) an output voltage that does not exceed an upper voltage limit while being driven at full speed without any load current at or below ambient temperatures, while maintaining high efficiency under a specified full load running condition and keeping the overall cost and size of the generator low.

Conventional generators existing in such applications are designed using thicker and stronger magnets and/or high number of slots, thereby driving up the size and cost of the generators. Bulky generators that cost more are usually not desirable. As such, there exists a need for a generator that meets specific requirements of the predefined load (i.e., an induction motor that drives the refrigeration unit). The present invention discloses a novel generator that is structured to meet the specific voltage requirements while keeping the size and cost of the generator low and efficiency of the generator high.

FIG.1illustrates a block diagram100of a generator of the present invention that is designed and structured to meet requirements of a predefined load. As shown, generator120of the present invention is connected to a predefined load, where the predefined load is an induction motor130which is used to drive a refrigeration unit140. The generator120is driven by an engine110that controls the speed of the engine generator set to provide a frequency required by the predefined load. In one preferred embodiment of the present invention, the engine110is a diesel engine. The generator120is designed and structured to meet the requirements of a predefined load by relying at least in part on magnetic characteristics of steel that is used in the generator without having to use stronger and/or thicker magnets that are cost prohibitive.

FIG.2illustrates a B-H curve associated with steel to be used in the generator to meet requirements of the load, according to embodiments of the present invention. In some embodiments, to maintain the output voltage of the generator above a transient required voltage while starting the predefined load when at or above ambient temperature and to maintain the output voltage of the generator below an voltage upper limit when running with no load current at or below ambient temperatures, a grade type of steel is selected to construct the generator120such that the steel has (i) an apparent relative permeability below 500 for point210ofFIG.2and/or (ii) an apparent relative permeability above 10 for point220ofFIG.2. Relative apparent permeability is defined as the ratio of flux density (B) to the applied magnetic field strength (H). As shown, the region of delta B (ΔB) is defined as the difference between a minimum flux density (Bmin) (i.e., point210ofFIG.2) of the steel required to meet the transient voltage requirement while starting the predefined load when at or above ambient temperature and a maximum flux density Point (Bmax) (i.e., point220ofFIG.2) of the steel required to stay within the maximum output voltage of the generator when running with no load current at or below ambient temperatures.

As shown inFIG.2, a knee region of the B-H curve is a portion of the curve where the relative apparent permeability starts to rapidly change out of saturation with decreasing flux density (B). In the region of the B-H curve that is above the knee region, the steel used in the generator is in a high degree of saturation. If the flux density (B) of the steel is at point220(Bmax) when the generator is running with no load at or below ambient temperatures, then while starting the predefined load, current is drawn by the predefined load, thereby potentially causing the point210(Bmin) to drop below the knee region of the B-H curve and the generated voltage may drop below the limit required to start the induction motor, which is not desirable. Therefore, it is important for Bminto stay as high on the B-H curve as possible while still having the Bmaxnot to cause a voltage to exceed the maximum voltage limit of the generator. In other words, the region of delta B (ΔB) should be minimized, which is possible when the Bminis high on the knee region of the B-H curve, that is below a relative apparent permeability limit. The highly saturated condition of the steel minimizes the change in flux density (B) between the hot generator, transient loaded condition and the cold generator no load current condition, thereby keeping the generator within the specified voltage limits. In some embodiments, a grade type of steel is selected such that the relative apparent permeability of the steel is below 500 and above 10 to meet the voltage requirements of the predefined load.

FIG.3Aillustrates B-H curves of different grades of steel, according to an embodiment of the present invention. As shown, the curve310illustrates the B-H curve for M470-50A grade electrical steel and the curve320illustrates the B-H curve for M210-35A grade electrical steel. As shown, the Bmax(i.e., point314associated with curve310and point324associated with curve320) and Bmin(i.e., point312associated with curve310and point322associated with curve320) value for both the curves310and320is the same. Therefore, both grade steels have the same delta B (ΔB) such that both grade steels will meet the voltage requirements of the predefined load. However, the magnetic field strength (H) required to achieve the Bminand Bmaxvalues in M210-35A grade electrical steel is higher than the M470-50A grade electrical steel. If the M210-35A grade electrical steel is selected for designing and constructing the generator, a higher grade magnet or a longer magnet in the direction of magnetization with higher field strength is required, thereby driving up the cost of the generator.

FIG.3Billustrates relative apparent permeability curves of different grades of steel, according to an embodiment of the present invention. As shown, curve330is the relative apparent permeability curve for M470-50A grade electrical steel, curve340is the relative apparent permeability curve for M1000-65A grade electrical steel, and curve350is the relative apparent permeability curve for M210-35A grade electrical steel. For a given magnetic polarization, the relative apparent permeability curves of different grades of steel shown inFIG.3Bmeet the flux density requirements of the predefined load described inFIG.2. As mentioned above, any of the different grades of steel shown inFIG.3Bmay be used in the generator120. Typically, higher grade electrical steels cost more and have lower losses when compared with lower grade electrical steels that cost less. The M210-35A grade electrical steel is a higher grade steel when compared with the M470-50A grade electrical steel and the M1000-65A grade electrical steel. As explained inFIG.3A, the amount of field strength (H) required for the M210-35A grade electrical steel is higher than the M470-50A grade electrical steel to achieve the required Bmaxand Bminvalues. Although a higher grade steel is desirable because of lower losses, the cost of the higher grade steel and the additional magnet volume required by the higher grade steel can be prohibitive. The overall cost of the generator is balanced based on selection criteria explained inFIGS.3A and3B. In one preferred embodiment, M470-50A grade electrical steel is used in the generator120of the present invention to meet the cost requirements and the voltage requirements of the predefined load.

FIG.4illustrates a cross sectional view of the generator120, according to an embodiment of the present invention. In some embodiments, the generator120is a three-phase generator. The generator120that is designed and constructed to meet the predefined load requirements, comprises at least a rotor assembly500and a stator600. In some embodiments of the present invention, the generator120is a permanent magnet generator, where the generator120comprise one or more permanent magnets. The generator120may be an ‘n’ pole generator, where ‘n’ presents the number of poles. The number of poles ‘n’ are selected based on the frequency requirements of the predefined load and/or the speed of the rotor500.

In a preferred embodiment of the present invention, the permanent magnet generator120is a four-pole generator comprising four sets of permanent magnets510a,510b,510c, and510dthat are placed inside the rotor assembly500. In some embodiments, the sets of permanent magnets510a,510b,510c, and510dmay be rare earth magnets. The sets of permanent magnets510a,510b,510c, and510dmay be pre-magnetized magnets that create persistent magnetic field with a predefined magnetic field intensity within the generator. The sets of permanent magnets510a,510b,510c, and510dare selected in conjunction with the grade type of steel selected for the generator.

FIG.6Aillustrates a stator600of the generator, according to an embodiment of the present invention. The stator600comprises a stator core610as illustrated inFIG.6B, according to an embodiment of the present invention. The stator600comprises one or more stator coils630placed in one or more stator slots620of the stator core610. In some embodiments, an optimum number of the one or more stator slots selected for the generator are 36 based on the generator size and inductance requirements associated with the predefined load. In some embodiments, the number of the one or more stator slots selected for the generator120may be lower or higher than 36. However, increase in the number of the one or more stator slots increases the losses of the generator for a given size of the generator. The stator core630comprises one or more laminated sheets made from the preselected steel. In some embodiments, the outside diameter of the stator is between 253 mm and 342 mm. In a preferred embodiment, the optimum outside diameter of the stator is 297.23 mm. In some embodiments, the length of the stator lamination stack is between 145 mm and 196 mm. In a preferred embodiment, the optimum length of the stator lamination stack is 170.66 mm. The relative apparent permeability induced in the preselected steel of the generator is dependent on the outside diameter of the stator500, the length of the stator500, the magnetic field produced by the permanent magnets510a,510b,510c, and510dand series turns per phase of the generator.

FIG.6Aillustrates a stator600of the generator, according to an embodiment of the present invention. The stator600comprises a stator core610as illustrated inFIG.6B, according to an embodiment of the present invention. The stator600comprises one or more stator coils630placed in one or more stator slots620of the stator core610. In some embodiments, an optimum number of the one or more stator slots selected for the generator are 36 based on the generator size and inductance requirements associated with the predefined load. In some embodiments, the number of the one or more stator slots selected for the generator120may be lower or higher than 36. However, increase in the number of the one or more stator slots increases the losses of the generator for a given size of the generator. The stator core630comprises one or more laminated sheets made from the preselected steel. In some embodiments, the outside diameter of the stator is between 253 mm and 342 mm. In a preferred embodiment, the optimum outside diameter of the stator is 297.23 mm. In some embodiments, the length of the stator lamination stack is between 145 mm and 196 mm. In a preferred embodiment, the optimum outside diameter of the stator lamination stack is 170.66 mm. The relative apparent permeability induced in the preselected steel of the generator is dependent on the outside diameter of the stator500, the length of the stator500, the magnetic field produced by the permanent magnets510a,510b,510c, and510dand series turns per phase of the generator.

The generator120does not comprise any control or regulating mechanism to control the output of the generator, which reduces the overall size and cost of the generator120. Instead, the generator120is designed such that the output voltage produced by the generator120meets the voltage requirements of the predefined load based on the magnetic field produced by the permanent magnets510a,510b,510c, and510d, magnetic characteristics of the preselected steel, the internal temperature of the generator which is in turn dependent on the ambient temperature, demagnetizing field resulting from the current drawn by the predefined load, size of the generator, number of series turns per phase in the generator, and inductance of the generator.

The magnetic field produced by the preselected permanent magnets510a,510b,510c, and510dof a predefined field strength causes the preselected steel to reach a level of saturation beyond the knee of the B-H curve. Once the level of saturation beyond the knee of the B-H curve is reached, even a significant change in the magnetic field strength does not cause a lot of change in the flux density of the preselected steel, thereby causing a very small change in the output voltage of the generator120. After the preselected steel reaches the saturation region that is above the knee of the B-H curve, the demagnetizing field from the current drawn by the predefined load and the internal temperature of the generator120control the output voltage of the generator120to meet the voltage requirements of producing an output voltage that is above a transient required voltage to start the predefined load when at or above ambient temperature and to maintain the output voltage below a voltage upper limit when running with no load current at or below ambient temperatures.

Additionally, the size of the generator and the type of permanent magnets are interdependent on each other which have an effect on the output voltage of the generator. If the size of the generator selected is large, the amount of magnetic flux passing through the steel (i.e., flux density (B)) of the generator is greater, thereby not requiring a magnet with higher field strength (H). In some embodiments, the size of the generator is based on the application associated with the generator. For example, the size of the generator to be used in a truck may vary from that of a generator designed for a small trailer. In addition to this interdependency, inductance of the generator is interdependent on the number of series turns per phase of the generator. If the number of series turns per phase used in the generator is higher, the inductance of the generator is high and vice versa. The number of series turns per phase are selected such that the inductance of the generator is not too high, since higher inductance lowers the total magnetic flux within the magnetic circuit of the generator because of the demagnetizing field from the current drawn by the predefined load.

Selection of the grade type of the steel, a number of the plurality of stator slots, outside diameter of stator lamination to meet the voltage requirements of the load, length of the stator lamination stack to meet the voltage requirements of the load, a number of the plurality of permanent magnets for placing within the rotor, magnetic polarization associated with the plurality of permanent magnets, size of the generator, number of series turns per phase of the generator, and inductance of the generator have an effect on the output voltage of the generator. One or more of these selections are based on the requirements (e.g., voltage requirements, size requirements, cost requirements, efficiency requirements, power requirements, or the like) of the predefined load. As explained above, one or more of these selections may be interdependent on each other which drive the overall cost, size, and output of the generator.

FIG.7illustrates a configuration of the generator ofFIG.1, according to an embodiment of the present invention. In a first preferred embodiment of the present invention, the generator120comprises a stator600comprising at least a stator core610with a plurality of stator slots and a plurality of stator coils. The stator core610comprises stator lamination stack that is made of steel. In the first preferred embodiment of the present invention, the generator120comprises a rotor further comprising (i) a rotor core, where the rotor core comprises a rotor lamination stack made of the steel, and (ii) a plurality of permanent magnets510for establishing a rotating magnetic field within the generator120. The generator120according to the first preferred embodiment of the present invention is structured to meet a hot generator, high current, transient loaded minimum voltage working point requirement by maintaining relative apparent permeability of the steel below a first limit and to meet a cold generator, no load current, working point maximum voltage limit requirement.

FIG.8illustrates a configuration of the generator ofFIG.1, according to an embodiment of the present invention. In a second preferred embodiment of the present invention, the generator120comprises a generator magnetic circuit800, where the generator magnetic circuit comprises at least in part a preselected steel. The generator120according to the second preferred embodiment of the present invention is structured to meet a hot generator, high current, transient loaded minimum voltage working point requirement by maintaining relative apparent permeability of the steel below a first limit and to meet a cold generator, no load current, working point maximum voltage limit requirement.

FIG.9illustrates a process flow900of constructing the generator ofFIG.1, according to an embodiment of the present invention. As shown in block910of the process flow900, the method of constructing the generator comprises providing a stator comprising at least a stator core with a plurality of stator slots and a plurality of stator coils, wherein the stator core comprises a stator lamination stack made of steel. As shown in block920of the process flow900, the method of constructing the generator comprises providing a rotor comprising (i) a rotor core, where the rotor core comprises a rotor lamination stack made of the steel, and (ii) a plurality of permanent magnets for establishing a rotating magnetic field within the generator. The generator constructed based on the process flow900meets a hot generator, high current, transient loaded minimum voltage working point requirement by maintaining relative apparent permeability of the steel below a first limit and meets a cold generator, no load current, working point maximum voltage limit requirement.

FIG.9illustrates a process flow900of constructing the generator ofFIG.1, according to an embodiment of the present invention. As shown in block910of the process flow900, the method of constructing the generator comprises providing a stator comprising at least a stator core with a plurality of stator slots and a plurality of stator coils, wherein the stator core comprises a stator lamination stack made of steel. As shown in block920of the process flow900, the method of constructing the generator comprises providing a rotor comprising (i) a rotor core, where the rotor core comprises a rotor lamination stack made of the steel, and (ii) a plurality of permanent magnets for establishing a rotating magnetic field within the generator. The generator constructed based on the process flow900meets a hot generator, high current, transient loaded minimum voltage working point requirement by maintaining relative apparent permeability of the steel below a first limit and meets a cold generator, no load current working point, maximum voltage limit requirement.

Many modifications and other embodiments of the inventions set forth herein will come to mind to one skilled in the art to which these inventions pertain having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the inventions are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation. In addition, where possible, any terms expressed in the singular form herein are meant to also include the plural form and/or vice versa. As used herein, “at least one” shall mean “one or more” and these phrases are intended to be interchangeable. Accordingly, the terms “a” and/or “an” shall mean “at least one” or “one or more,” even though the phrase “one or more” or “at least one” is also used herein.