MXPA01004493A - Microturbine power generating system including a battery source for supplying startup power - Google Patents

Abstract

A microturbine power generating system (10) includes a battery source (46) for providing startup power. Dc power provided by the battery source (46) is converted to three-phase ac power, and the three-phase ac power is supplied to stator windings (36) of an electrical generator (16) of the system (10). The three-phase ac power causes the electrical generator (16) to operate as a starter motor. An up chopper (254) may be used to reduce the required voltage of the battery source (46). A down chopper (154) may be used to charge the battery source (46) during normal operation of the microturbine power generating system (10). The down chopper (154) can allow the battery source (46) to supply backup power in the event the electrical generator (16) experiences a failure.

Description

MICROTURBINE ENERGY GENERATING SYSTEM THAT INCLUDES A BATTERY SOURCE FOR FEEDING STARTING ENERGY BACKGROUND OF THE INVENTION The present invention relates, in general, to microturbine energy generating systems. More specifically, the present invention relates to a microturbine energy generating system that includes a battery source to provide starting energy. The United States Electrical Energy Research Institute (EPRI), which is the uniform research agency for domestic electrical installations, predicts that by 2006 up to 40% of all new generation of electric power could be provided by distributed generators. In many parts of the world, the lack of an electrical infrastructure (for example transmission and distribution lines), the commercialization of distributed generators will increase greatly since the central plants will not only cost more per kilowatt, but will also need expensive infrastructure installed to supply of energy to electricity consumers. In the United States and other countries that already have electrical infrastructure, small modular units for distributed generation of microturbine, multi-fuel will also allow electricity consumers to choose the most cost-effective electric service. Small modular units for the distributed multi-fuel microturbine generation could help mitigate the current "low voltage" and "nighttime blackouts" that are prevalent in many parts of the world. A concept of simple moving parts, simple to allow maintenance with few technical skills. The low general cost will allow acquisition in those parts of the world where capital is scarce.

For an example of a microturbine energy generating system see U.S. Patent No. 4,765,607 which is assigned to the assignee of the present invention. The microturbine energy generating system includes a turbine, a compressor and an electric generator, with each device including a rotating component (for example, a turbine wheel, a compressor wheel and a permanent magnet rotor). Starting the microturbine energy generating system can be problematic. It is possible to use a separate initiating motor to start the compressor until the microturbine power generating system is able to maintain combustion. In an alternative, the electric generator can be used to ignite the compressor during start-up, as described in co-pending patent application of US Ser. 08 / 995,462, filed December 19, 1997. A switch / initiator control is included to feed an excitation current to the stator windings of the electric generator, which in turn rotate the compressor until combustion is maintained. When using any approach, an external power source is needed to run the stator motor or to feed an excitation current to the stator windings of the electrical generator. US series No. 08 / 995,462 also describes a battery for powering the switch / initiator control. The battery has the size according to the requirements of the system. However, such a battery tends to have a high voltage. High voltage batteries are difficult and potentially dangerous to handle. Large, high-voltage batteries are also uncomfortable and, therefore, it is difficult to supply them in large quantities. This will create problems of mass production of the power generating systems of microturbines.

Battery allows the use of available batteries. The low-voltage batteries available are usually easier and safer to operate, and these are easier to achieve compared to high-voltage batteries. By controlling the recharge rate as a function of temperature, problems related to temperature can be reduced. According to still another aspect of the invention, the starting circuit includes a periodic down-switch to recharge the battery source during normal operation of the micro-turbine power generating system. This allows the battery source to be recharged conveniently.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a block diagram of a micrbine energy generating system according to the present invention, the system includes a battery source and a start control, Figure 2 is an illustration of a control alternative starter for the micrbine energy generating system, Figures 3 to 5 are illustrations of alternate battery sources and alternative start controls for the "micrbine energy generating system, and Figure 6 is a flow chart of a method for initiating the power generating system according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION Figure 1 shows a micrbine energy generating system 10 that includes a compressor 12, a turbine 14 and an integrated electric generator 16. For the embodiment shown in the drawings, the electric generator 16 is cantilevered of the compressor 12. The compressor 12, the turbine 14 and the electric generator 16 are normally ted by a single common arrow 18. Although the compressor 12, the turbine 14 and the electric generator 16 can be mounted to separate arrows, the use of the only common arrow 18 adds the compatability and reliability of the micrbine energy generating system 10. The arrow 18 can be supported by self-pressurized air bearings such as sheet bearings. The blade bearings eliminate the need for a separate bearing lubrication system and reduce the need for maintenance service. The blade bearings also reduce vibration, which reduces system maintenance.

The air entering the admission of the compressor 12 is compressed. The compressed air exiting from an outlet of the compressor 12 is circulated through the side passages of cold air 20 in a recuperator 22. Within the recuperator 22, the compressed air absorbs heat from the heat of the turbine's waste gases. The heated, compressed air exiting the cold side of the recuperator 22 is supplied to a combustor 24. The use of the recuperator 22 for heating the compressed air reduces fuel consumption. The fuel is also fed to the combustor 24. It is possible to use gaseous or liquid fuel. In gaseous fuel mode, it is possible to use any suitable gaseous fuel. Fuel alternatives include diesel, torch gas, off-gas, gasoline, naphtha, propane, JP-8, methane, natural gas and other synthetic gases. The flow of the fuel to the combustor 24 is regulated by a flow regulating valve 26. The fuel is injected into the combustor 24 by means of an injection nozzle 28. Within the combustor 24, the fuel and compressed air are mixed and burned by a lighter 27 in an exothermic reaction. The hot, expanding gases that result from combustion in the combustor 24 are directed to an intake nozzle 30 of the turbine 14. The hot, expanding gases resulting from the combustion are expanded through the turbine 14, creating by this means the energy of the turbine. The energy of the turbine, in turn, drives the compressor 12 and the electric generator 16. The exhaust gas of the turbine is circulated through hot exhaust side passages 32 in the recuperator 22. Inside the recuperator 22, the heat of the Exhaust gas from the turbine is transferred to the compressed air in the cold lateral passages of air 20. In this form, some of the combustion heat is recovered and used to raise the temperature of the compressed air before combustion. Before releasing part of its heat, the exhaust gas exits from the recuperator 22. In a preferred embodiment, the generator 16 is a brushless permanent magnetless, two-pole (TPTL), ring-wound machine with a permanent magnet r 34 and stator windings 36. The r 34 is attached to the arrow 18. When the r 34 tes by the energy of the turbine generated by the ting turbine 14, an alternating current is induced in the stator windings 36. The speed of the turbine 14 can vary according to the demands of external energy placed in the power generating system of microturbine 10. Variations in the speed of the turbine will produce a variation in the frequency of the alternating current generated by the electric generator 16. The energy ac is rectified to energy by a rectifier 38, and the energy of is converted into fixed frequency ac energy by a fixed frequency electronic inverter by an electronic inverter solid state 40 (hereinafter the "main" investor 40). The use of the rectifier 38 and the main inverter 40 allows ample flexibility in determining the service of the electrical installation that is to be provided by the power generating system of the present invention. Because it is possible to select any inverter, the frequency of ac power can be selected by the consumer. In the modes that provide direct use of the ac energy at uncontrolled frequencies [sic], the rectifier 38 and the main inverter 40 are eliminated. A regulator 42 regulates the speed of the turbine by controlling the amount of fuel flowing to the combustor 24. The regulator 42 uses detector signals generated by the group of detectors 44 to determine external demands on the microturbine energy generating system 10 and then regulates the fuel valve 26 accordingly. The group of detectors 44 includes one or more detectors such as turbine speed sensors and different temperature and pressure detectors for measuring the operating temperatures and pressures in the microturbine power generating system 10. A battery source 46 and a starter control 48 are included for starting the microturbine power generating system 10. The starter control 48 includes a link of 50 and a solid-state inverter 52 (hereinafter the "second" inverter 52). The battery source 46 feeds the energy from a high voltage to the link of 50. The phrase "battery source", when used herein, means one or more cells or any other convenient means for feeding electrical current. If a group of two or more cells is used, they are connected by electrical means. Other means for feeding the electric current include, for example, capacitors or ultracapacitors and other devices for energy storage. During start-up, the regulator 42 commands the transistors of the second inverter 52 to turn on and off and by this means convert the energy from the link of 50 to the three-phase ac power. The three-phase ac power that is fed to the stator windings 36 of the electric generator 16 causes the electric generator 16 to function as a starter motor. By controlling the modulation frequency of the transistors in the second inverter 52, the regulator 42 can vary the frequency of the ac power fed to the stator windings 36. The frequency of the ac energy starts at a low frequency as can be 2 Hz, and then it goes up (that is, it increases). The rise of the frequency of ac energy causes the speed of the turbine to rise. Although the electric generator 16 is being operated as a starter, the regulator 42 is checking one or more parameters that indicate whether the system 10 can maintain combustion. For example, the regulator 42 could monitor the speed of the turbine. Once the regulator 42 determines that the microturbine energy generating system 10 can maintain combustion (for example, the turbine speed reaches a threshold), the regulator 42 interrupts the supply of ac power from the inverter 40 to the stator windings 36 and turn on the fuel and the lighter 27. Once the electric generator 16 is able to generate electrical power, the regulator 42 enables the rectifier 38 and the main inverter 40 to convert the output of the electric generator 16 to a fixed frequency ac power. The rectifier 38 and the main inverter 40 are enabled, in the manner shown in the drawings, by connecting the inputs of the rectifier 38 to the terminals of the electric generator 16 through a first circuit breaker 47. The first circuit breaker 47 is shown for Illustrative In practice, the rectifier 38 and the main inverter 40 can be enabled by other means. The battery source 46 has a voltage that can be monitored by the electric generator 16. The actual voltage will depend in part on the counter electromotive force generated by the electric generator 16 during start-up. As an exemplary embodiment, a high-voltage battery is used such as a single sealed lead-acid battery with 192 two-volt cells in series to produce a nominal voltage of approximately 400 volts. A 46 battery source is available from Ha Ker Energy Products, located in Arnsburg, Missouri. Figure 2 shows an alternative start control 148. The start control 148 includes a link of 50, the second inverter 52 and a downward periodic switch 154. During the normal operation of the power generating system of microturbine 10, the downward periodic switch 154 draws some of the current to an output of the rectifier 38 and uses this current to charge the battery source 46. The descending periodic switch 154 includes a circuit breaker 156 which is controlled by the regulator 42. Since the voltage at the rectifier output of 38 will normally be greater than the battery voltage, the circuit breaker 156 of the descending periodic switch 154 is modulated by the width of the pulse by the regulator 42 so that the average voltage across the battery source 46 can properly charge the source 46. The descending periodic switch 154 also includes a diode 158 and an inductor 160. The inductor 1 60 serves as a current filter which limits the rate of current increase while the circuit breaker 156 of the descending periodic switch is closed. The diode 158 provides a path for the inductor current while the circuit breaker 156 of the descending periodic switch is open. Thus, the descending periodic switch 154 allows the high voltage battery source 46 to be conveniently charged. Circuit breaker 156 of the descending periodic switch is modulated in a duty cycle or fixed utilization factor. For example, in a preferred embodiment, the circuit breaker 156 of the descending periodic switch is modulated with a utilization factor of 80% to allow a 400 volt battery to be charged by a rectifier 38 with an output voltage of 500 vdc. However, in the alternative embodiments, a more elaborate scheme is used to control the charging rate of the battery source 46. For example, the battery source 46 is charged at a rate that is a function of the parameters such as temperature of the battery, the charging current and the battery voltage. The signals indicating these parameters can be generated by the group of detectors 44. While the source of the battery 46 is being charged, the regulator 42 checks these parameters to regulate the recharge rate. The regulator 42 begins to modulate the circuit breaker 156 at a fixed utilization factor. Meanwhile, the regulator 42 also checks the charging current to ensure that the charging current does not exceed a threshold. If the load current exceeds a threshold, the regulator 42 reduces the utilization factor until the current falls below the threshold. While the battery source 46 is being recharged, the regulator 42 also checks the temperature and voltage of the battery. The regulator 42 stops recharging the battery source 46 when the battery source 46, at a certain temperature, it reaches a certain battery voltage. It is possible to measure the temperature of the battery inside the battery case. The charging current can be measured by a current detector attached to an upper conductor within the battery source 46.

The descending periodic switch 154 also allows the battery source 46 to supply power directly to the main inverter 40. If, for example, the electrical generator 16 experiences a fault and can not generate electrical power, the regulator 42 closes the circuit breaker 156 and commands to the main inverter 40 modulate the energy of the battery to produce a fixed frequency ac power. Thus, the downward periodic switch 154 also allows the battery source 46 to provide a back-up power supply. Figure 3 shows an alternative battery source 246 and another starting control (third) 248. Instead of providing a high voltage, the alternative battery source 246 provides a low voltage. The low voltage source 246 includes a single 48-volt battery or four 12-volt batteries connected in series. 12-volt batteries, in an exemplary fashion, are car batteries that are commonly available in opposition to large, high-voltage batteries. The low voltage source 246 alone does not provide sufficient voltage for the electric generator motor 16 during start-up. However, the third start control 248 includes a top periodic switch 254 that raises the voltage from the low voltage source 246 to a level that is capable of motorizing [sic] the electric generator 16. The upward periodic switch 254 raises the voltage by a factor between 5 and 15. For example, the upward periodic switch 254 can raise the 48 volts of the low voltage source 246 to a voltage of 400 volts. The high voltage is converted into a three-phase ac power to motorize the electric generator 16 during start-up. The rising periodic switch 254 includes a capacitor 256, a circuit breaker 258, an inductor 260 and a diode 262. At the start of the start, the regulator 42 modulates the amplitude of the breaker pulse of the rising periodic switch 258 causing the breaker of the periodic switch 258 open and close When the upstream breaker 258 circuit breaker closes, the battery power is stored in the upstream periodic switch inductor 260. When the upstream breaker switch 258 is opened, the power is transferred from the upstream breaker inductor 260 to the capacitor of the rising periodic switch 256. The diode of the rising periodic switch 262 prevents the capacitor 256 from being discharged while the circuit breaker of the rising periodic switch 258 is closed. The regulator 42 controls the charging rate of the capacitor of the rising periodic switch 256. The riser switch 258 can be modulated for a utilization factor which allows the capacitor of the rising periodic switch 256 to be charged rapidly when the voltage is low across the capacitor of the rising periodic switch 256. The breaker of the periodic switch rises FIG. 258 can be modulated to a utilization factor that allows the capacitor 256 to be charged at a slow charge rate when the voltage across the capacitor of the rising periodic switch 256 is high. The slow charge of the capacitor of the rising periodic switch 256 allows the components (e.g., diode 262 and inductor 260) to be economical in size. By reducing the size of the component reduces the cost and problems related to temperature such as thermal cooling and inefficiency of the components. Figure 4 shows a low voltage battery source 346 and an initiator controller 348 including a 50 link, an inverter 52 and a bi-directional periodic switch 354. The bi-directional periodic switch 254 provides the functionality of the up-and-down periodic switch 254 and the descending periodic switch 154. Thus, the bi-directional periodic switch 354 raises the voltage of the low-voltage battery source 346 and applies the high voltage on the link of 50. The second inverter 52 converts the energy into the 50-link in energy ac three-phase for starting. During the normal operation of the microturbine energy generating system 10, the bidirectional periodic switch 354 uses the output power of the rectifier to charge the low voltage battery source 346. A utilization factor of 10%, for example, reducing a rectified voltage from 500 volts to approximately 50 volts to charge a battery 48 volts. In the event that the electric generator 16 experiences a fault during normal operation, the bidirectional time switch 354 connects the battery source 346 to the inputs of the main inverter 40 to provide backup power. Figure 5 shows another embodiment of the present invention. The shunts 435A, 435B, 435C in the windings 436A, 436B, 436C of the stator windings 436 are carried out of the electrical machine 416. The shunts 435A, 435B, 435C allow an inverter 452 and a low voltage battery source 446 motorize the electric generator 416. The low-voltage battery source 446 can be used because the counter electromotive force is lower in the leads 435A, 435B, 435C than in the terminals 437A, 437B, 437C of the electric generator 416. Figure 6 shows a generalized method for the use of a battery in conjunction with a microturbine energy generating system. During the start-up of the microturbine energy generating system, the energy is received from the battery source (block 500). If a high voltage battery is used, the power is received directly from the battery. If a low voltage battery is used, the battery voltage rises, or, in the alternative, a stator winding of the electrical generator is derived and derivative voltage is provided. The energy of the battery is converted into polyphase AC energy during the start-up of the microturbine energy generating system (block 502), and the polyphase ac power is supplied to the stator windings of the electric generator (block 504). The polyphase AC energy causes the electric generator to function as an initiating motor during the start-up of the power generating system. At about the same time that the microturbine energy generating system can maintain combustion, the supply of the polyphase energy to the stator windings is interrupted (block 506). Once the electric generator is capable of producing electrical power, the output of the electric generator can be rectified and modulated to produce fixed frequency ac power (block 508). The fixed frequency ac power is placed on a power grid for consumer use, or is used directly without the grid. For the embodiment shown in the drawings, the rectified output of the electric generator is also subjected to the periodic downward switch and used to charge the power source (block 510). In the event that the electric generator fails, the battery power can be supplied to the main inverter, which modulates the battery power to provide fixed frequency backup power (block 512). The backup power can be placed in a power grid for consumer use, or the backup power can be used directly without the grid.

Thus, a microturbine energy generating system is described which includes a battery source to provide power and a start circuit to convert the energy from ac to energy. The battery source is, alternatively, a high-voltage battery or a low-voltage battery. The required voltage of the battery source can be reduced by the use of a periodic rising switch. The amplitude of the pulse modulating the rising periodic switch as a function of temperature can reduce the problems related to temperature. The necessary battery voltage is, alternatively, reduced by supplying power to the shunts in the stator windings of the electric generator. The reduction of the voltage required in the battery source allows the use of batteries that are commercially available. Low-voltage batteries, commonly available, are usually simpler and safer to operate and are easier to get compared to high-voltage batteries. The battery can be recharged during the normal operation of the microturbine energy generating system by using a periodic down-switch. The periodic downward switch allows the battery source to be recharged conveniently. The periodic down-cycle switch can also allow the battery source to supply backup power output if the electrical generator experiences failure. The battery source can instead be used in combination with a bidirectional periodic switch, which provides the functionality of the periodic up-switch and the down-cycle periodic switch. The invention having now been described in detail, those skilled in the art will recognize alternative embodiments that do not deviate from the present invention. Thus, the invention is not limited to the specific modalities described above, but may be considered in accordance with the scope and spirit of the following clauses.

Claims (8)

1. A microturbine energy generating system (10) comprises: a compressor (12) including a compressor wheel; a turbine (14) for converting gaseous heat energy into mechanical energy, the turbine includes a turbine wheel; an electric generator (15) for converting the mechanical energy produced by the turbine into electrical energy, the electric generator includes a rotor (34) and a stator (36), the rotor being mechanically coupled to the turbine wheel and the wheel of the turbine. compressor, the ac generator providing ac power during the normal operation of the microturbine energy generating system; a battery source (46) to provide the power of; a starting circuit (48) including an upward periodic switch (254) for raising the voltage of the battery source, and an inverter (52) for converting the energy of the rising periodic switch to ac power, the ac power being supplied to the stator during the start of the system, whereby the ac power causes the electric generator to rotate the wheels of the turbine and the compressor during start-up; a rectifier (38) for rectifying the ac energy generated by the electric generator; and means (154) for using the rectified energy to charge the battery source during the normal operation of the microturbine energy generating system.

2. The system of claim 1, wherein the battery source includes a single battery to provide power to the starting circuit. The system of claim 1, wherein the rising periodic switch includes a power storage unit that can be modulated at the pulse amplitude (256, 258, 260, 262) to store the energy from the battery source (246), and wherein the other system comprises a regulator (42) for modulating the amplitude of the drive of the storage unit to raise the voltage. The system of claim 1, wherein the recarriage means includes a periodic down-switch (154), responsive to rectified power, to provide the energy at a reduced voltage to the battery source. The system of claim 1, wherein the battery source is recharged as a function of the battery voltage, current and temperature of the battery. The system of claim 1, further comprising a second inverter (40) for converting the rectified energy into ac power and placing the ac power in an output grid, and wherein the recharging means further includes the means (156, 158, 160) to connect the battery to the second inverter when the electrical generator experiences failure, whereby the energy provided by the battery is converted into ac power by the second inverter and placed on the power grid. The system of claim 1, wherein a bidirectional periodic switch (354) loads the battery source (346) during normal operation and raises the voltage provided by the power source during start-up, a bidirectional periodic switch output providing the energy of the starting circuit. The system of claim 1, wherein the inverter (452) is connected to the leads (435A, 435B, 435C) in the windings (436A, 436B, 436C) of the stator (436). zí, it.íi »Sr, - tt.