Chiller system with direct-drive switched reluctance motor

Abstract

A 3000-20000 rpm RS-SR motor (RS-SR) and adjustable speed drive (ASD), with a cooling and lubrication system that is independent of the existing chiller lubrication and refrigerant cooling circuits. Product is configured as a direct replacement for motor, starter (drive), and gearbox solutions historically and currently used by OEM's on chillers. Oil containment and low motor cavity pressure is achieved with Axial Carbon Ceramic seals. Using an inner shell suspended in an outer shell: a coolant path is created, and vibration is abated, as well as meeting pressure vessel requirements. These features enable precise qualification of product independent of the chiller system over range of speeds and loads on a calibrated test stand. Specific information derived from qualification tests enables integration of optimization subroutines into the ASD that improve efficiency and increase ability to operate at or near compressor surge boundary.

Claims

1. A chiller-compressor system utilizing a direct-drive, environmental regulated, semi-hermetic, switched reluctance motor/drive system (RS-SR Motor/Drive) having prequalification and pretested operating parameters comprising: a motor using an axial seal; a stator core of said motor bonded to an inner shell; and an Adjustable Speed Drive (ASD) regulating system performance, wherein said ASD is interconnected to a check valve/pressure relief valve, a super heat gas bypass control valve, a circulating super heat gas control valve, a pressure/temperature transducer, and a liner actuator on guide or pre-rotation vanes to optimize performance and predictive control of regulated circulating superheated gases, acceleration, and deceleration.

2. The RS-SR Motor/Drive as in claim 1 said inner shell suspended on each end in said outer shell to attenuate noise transmission from said stator core to said outer shell.

3. The RS-SR Motor/Drive as in claim 1 said ASD controlling said check valve/pressure relief valve as a means to release excess pressure in a heat exchanger to compressor intake.

4. The RS-SR Motor/Drive as in claim 1 said ASD controlling a normally closed said super heat gas bypass control valve as a means of adding super-heated gas to the circulating cooling circuit in the motor cavity.

5. The RS-SR Motor/Drive as in claim 1 said ASD controlling said circulating super-heat control valve as a means of regulating the pressure and temperature in the motor cavity.

6. The RS-SR Motor/Drive as in claim 1 said ASD with said pressure temperature transducer as means to verify pressure and temperature control of the motor cavity.

7. The RS-SR Motor/Drive as in claim 1 said ASD controlling optimum position of said linear actuator on guide or pre-rotation vanes based on known torques and speed of the said RS-SR Motor/Drive.

8. The RS-SR Motor/Drive of claim 1 said ASD controlling said acceleration and deceleration in either direction of rotation, wherein enabling adaptation to torque pulsations and reverse of rotation when operating near or at a surge condition.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1a illustrates existing technology in the typical configuration using a gearbox to increase the speed of the shaft connected to compressor impeller (or wheel).

(2) FIG. 1b illustrates proposed system that uses a direct drive RS-SR motor and drive system, with no gearbox, reduced footprint and typical control loop shown.

(3) FIG. 2 illustrates RS-SR motor Drive and Control Box

(4) FIG. 3 illustrates regulated, Semi-Hermetic, High-Speed Switched Reluctance Motor with Semi-isolated Cooling and Lube System.

(5) FIG. 4 illustrates typical Carbon Ceramic seal configuration being used to separate compressor operating environment from the RS-SR motor operating environment.

(6) FIG. 5 illustrates a typical assembly with the impeller attached to the drive end of the shaft. The objective of the figure is to demonstrate that the motor cavity is a contained environment separate from the refrigerant around the impeller and the ambient atmosphere outside the motor.

(7) FIG. 6 illustrates a method of regulating the pressure and temperature in the motor cavity.

(8) FIG. 7 illustrates the relationship between the inner and outer shells of the motor. A typical coolant flow path is also described.

(9) FIG. 8 illustrates the designed gap between the inner and out shell.

(10) FIG. 9 illustrates the major components needed to facilitate control of guide vanes (or pre rotation vanes) in conjunction with ASD interface.

(11) FIG. 10 illustrates a test configuration to facilitate full load testing and characterization of motor and drive.

(12) FIG. 11 illustrates a “Reference Numeral” table listing elements referenced in specification.

REFERENCE NUMERALS

(13) Refer to FIG. 11 in Drawings file.

(14) All numerals defining features are three digit and bracketed as shown “(###)”. A list of features is referenced the brackets will be at each end of the list “(###, ###, & ###)”

Definitions

(15) Environmentally—when used in conjunction with “controlled” in this document means the pressure and temperature inside the motor cavity is regulated to the lowest safe pressure level that does not exceed a temperature that would put the motor winding or bearing oil at risk. The limit would base upon lower of the insulation class of windings and or breakdown temperature of the bearing oil. Qualified—when used with reference to test means the insulation system used in the motor has materials that have been tested to assure compatibility with the fluids being moved by the compressor. A typical test method to verify qualification might be UL 984a. “RS-SR” is an acronym for “Regulated Semi-hermetic—Switch Reluctance” for clarity. “CCS” is an acronym for “Carbon Ceramic Seal” with a coefficient of friction less than 0.15 and a wear life greater than 20 years at 50 meters per second and contact surface load of 0.4 mpa. “Motor Cavity”—the enclosure formed by the assembly of: the inner shell (210), opposite drive end bell (212), drive end bell (214), seal and shaft (802, 804, 806, 805, 402) and bearing end cap 220. Impeller Cavity—the space in the enclosure that contains the impeller that has a pressure that is not exceeded in the motor cavity. Space on impeller side of drive end bell as labeled in FIG. 3.

Description of the Preferred Embodiments

(16) The preferred embodiment of the RS-SR motor is as illustrated in FIG. 3, using “shell-in-a-shell” construction. Coolant is forced to circulate between the two shells (210 & 211) and around the shell circumference thereby removing motor losses as illustrated in FIGS. 7 & 8. The coolant at elevated temperature is pumped to a heat exchanger (614) thereby keeping rejected heat outside the equipment room. Primary heat removal path for losses in the rotor are down the shaft (402) and into the impeller (406). Auxiliary cooling, when needed, is provided by introducing superheated gas into the drive end of the motor and extracting hotter superheated gas from the opposite drive end of motor cavity (602), (612), (614), (619), (620). FIG. 3

(17) End bells on both ends of the motor (212, 214 & 220) in conjunction with inner shell (210) form a pressure vessel to prevent refrigerant loss in the event of seal failure. FIG. 5

(18) Outer shell (211) seals on both ends of inner shell (210) yielding a sealed coolant cavity; this allows any fluid with sufficient specific heat to be used as a motor coolant. (For example: heat losses may be carried off in the cooling tower wall instead of the working refrigerant as in traditional semi-hermetic motor. This will improve chiller system efficiency.) FIG. 7

(19) The preferred embodiment of the RS-SR drive is two-level topology as shown in FIG. 1b & 2; with electronic feedback loops to control chiller system behavior and efficiency(618, 601 & 604). (For example, the Guide Vanes.) FIGS. 1b, 3 & 9

(20) As shown in FIG. 4 & FIG. 5 high pressure gas on the Impeller (406) side of the “Drive End Bell” (214) pushes the carbon ceramic seal (802) into the axial sealing surface of the shaft (402). A second ceramic seal (809) on the inboard side of the “Drive End Bell” (214) creates a second bearer. Both seals are pre-loaded (806 & 809) to assure the seal fit does not become a leak path. The enclosure formed by both end bells (212, 214 & 220) and the “Inner Shell” (210) is a reduced pressure area at less than one atmosphere, but it also has significant strength to prevent a burst failure if the seals should fail.

(21) FIG. 3 & FIG. 6 show how the motor cavity temperature and pressure is controlled using small variable speed compressor acting as a vacuum pump (612) too: circulate superheated gas, reduce pressure in motor cavity, degas oil circulating in the bearing of the motor.

(22) Conventional semi-hermetic special purpose motors have liquid refrigerant dumped into the motor cavity and allow the spinning rotor to throw the liquid refrigerant around the inside of the unit. This requires hundreds of hours of qualification testing to identify potential hot spots to place the motor temperature sensors. The net result is typically a temperature gradient that easily varies by 100 degrees C., dependent upon where on the motor the temperature is measured. (The primary cooling path is through OD of the stator and supplemented by superheated gas in the motor cavity as needed. This yields smaller predicable gradients in the motor windings, which are the primary risk.)

(23) The result of conventional practice is significant fluid drag losses on the motor, that reduce the motor efficiency particularly at part load where the fluid drag losses stay near constant and reduce the power out to power in ratio.

(24) The described system in “FIG. 6” eliminates liquid refrigerant in the motor cavity and uses only superheated refrigerant in the motor cavity. This minimizes the range of temperatures in an operating unit, thereby reducing stresses on the motor windings caused by differential expansion. Yields a lower viscosity medium for the rotor to rotate in, increasing efficiency.

(25) FIG. 7 & FIG. 8 shows a shell-in-a-shell (210 & 211)construction provides a controlled cooling fluid path. FIG. 7 shows the ribs on both ends of inner stator shell (210), adjacent the end bells (212 & 214), are near line to line contact to facilitate a fluid seal and maintain a gap between inner (210) and outer (211) shells at the center rib locations as shown in FIG. 8. (In this example there are 5 center ribs.) FIG. 8 shows the gap between inner shell rib (210) and the outer shell (211) that reduces vibration transmission from stator core (216) to outer shell (211), making the unit much quieter. The ribs on the OD of the inner shell (210) shown in FIG. 7 serve the functions of: Stiffening the Inner Shell. Forming a convoluted path that facilities uniform heat removal. Increasing the surface area for removal of heat.

(26) FIG. 9 shows a linear actuator (604) with a position feedback loop (601) to drive controller (104) that enables “on the fly tuning” of “Guide Vane” (618) position to maximize efficiency of chiller system. Possible because precise speed, torque and efficiency of the motor is always known and the response time is reduced to microseconds. FIG. 2 shows a simple feedback loop between actuator (302) and ASD (104).

(27) FIG. 6 shows a sensor inside the motor cavity with a feed through (602) that communicates the current pressure and temperature conditions electronically to ASD (104). The ASD (104) then sends control information to the “Compressor/Vacuum pump” (214) to regulate the internal pressure and temperature.

(28) The ASD (214) sends control information to the “Control Valves” (619 & 620) to regulated flow of refrigerant into the motor cavity, thereby controlling motor temperature. The ASD optimizes temperature and pressure to maximize motor efficiency and assure motor life. Check Valve (616) opens to relieve excess superheated gas pressure and vents to compressor inlet. Control Valve (620) releases to allow flow of superheated gas through motor cavity. Control Valve (619) releases to provide supplemental superheated gas to the pressure to motor cooling circuit if needed.

(29) FIG. 3 the “Compressor/Vacuum pump” (612) assure bearing oil is degassed. Heat exchangers (610 & 614) are used to remove heat (motor losses) refrigerant circulating in motor cavity and the oil circulating in the bearings.

(30) FIG. 10 shows a simple test configuration like that used with a Commodity ODP, TEWAC or TEFC motor. Proposed RS-SR Motor Drive system makes full load testing of motor possible; there is no need for the chiller system components to support its operation, when completing a battery of standard tests.

CONCLUSION

(31) The RS-SR motor drive system is an evolution of the drive and motor used for centrifugal compressors. The product is manufactured as a direct replacement of motors and gearboxes yielding greater than 33% improvement in chiller efficiency over conventional motor and wye delta starters. (Greater than an 8% improvement over conventional motor and VFD systems.) The product is pre-tested and qualified to perform on legacy products and new OEM equipment. Construction with axial carbon ceramic seals facilitates: Operating the motor in a reduced pressure environment that reduces fluid drag losses. Separating the sleeve bearing oil from the primary chiller circuit to improve evaporator and condenser heat transfer. Circulation of superheated gasses to supplement the cooling of the motor. Independent load testing and qualification outside conventional chiller system. Construction with shell in a shell facilitates: Noise attenuation by suspending the motor core in the inner shell. Creation of a sealed coolant path that removes heat from the stator OD. Creation of a convoluted cooling path to assure effective uniform cooling. Creation of a sealed cavity that blocks escape of refrigerant to the atmosphere. Independent load testing and qualification outside conventional chiller system. Construction with ASD and related devices facilitates: Predictive control of motor cavity pressure and temperature based on load. Control of guide vanes to optimize performance based on motor loading. Operation on surge boundaries utilizing capabilities of ASD and RS-SR motor. Precise real time measurement of motor speed and power for refinement of system control features. Controlled acceleration and deceleration in either direction of rotation to facilitate adaptation to rapidly changing conditions common when operating at or near surge.