Patent Application
20160056622
The field of the disclosure relates generally to motors, and more particularly, to a thermal protection device and methods for protecting a motor.
At least some known electric motors include thermal protection devices configured to terminate operation of the motor in response to thermal overload conditions, which could result in permanent damage to the motor and/or associated equipment. A thermal overload, such as an excessively high winding or rotor temperature, may occur as a result of a locked rotor, a high mechanical load, a supply overvoltage, a high ambient temperature, and/or some combination of these conditions. Such thermal protection devices are typically coupled between a motor power supply and the motor windings to protect against excessive heat buildup in the windings as current flows therethrough. As current flows and heats the windings, current also flows through the thermal protection device, causing it to heat up. When the thermal protection device reaches a pre-determined temperature, the device opens or “trips” and disconnects the windings from the motor circuit to prevent damage to the motor. As the thermal protection device cools, it eventually closes or “resets” and completes the motor circuit to energize the windings. As current flows through the thermal protection device and the windings, heat generated by the current flowing through the device causes the thermal protector to trip and again open the circuit, and as the thermal protector device cools it again resets and closes the circuit. Hence the thermal protector device cycles motor power on and off to prevent overheating of the motor in use.
Moreover, the spacing between the motor windings and the electronic control board of the motor may cause large temperature differentials, resulting in an inaccurate temperature sensing. An on-winding motor protection device interrupts power and accurately reacts to excessive temperatures. Most commercially available on-winding motor protectors are rated for low (less than about 600V) AC voltages or very low (less than about 50V) DC voltages. Many electronic motor controls utilize power switching to rapidly switch the DC voltage very fast to create an effective AC power. Such switched DC voltages exceed the power ratings of most commercially available thermal protectors.
In one aspect, a thermal protection device is described. The thermal protection device is electrically coupled between a power supply and a gate drive circuit for driving the motor. The thermal protection device is configured to disconnect the power supply from the gate drive circuit when a temperature measured by the thermal protection device exceeds a threshold temperature value.
In another aspect, a method of protecting a motor is provided. The method includes electrically coupling a thermal protection device between a power supply and a gate drive circuit for driving the motor. The method also describes disconnecting, using the thermal protection device, the power supply from the gate drive circuit when a temperature measured by the thermal protection device exceeds a threshold temperature value.
In another aspect, a motor controller configured to be coupled to a motor is provided. The motor controller includes a gate drive circuit and a thermal protection device. The gate drive circuit is configured to receive power from a power supply and output a switching signal. The thermal protection device electrically coupled between the power supply and the gate drive circuit. The thermal protection device is configured to disconnect the power supply from the gate drive circuit when a temperature measured by the thermal protection device exceeds a threshold temperature value.
In the exemplary embodiment, rotor 18 is mounted on and keyed to shaft 20 journaled for rotation in conventional bearings 22. Bearings 22 are mounted in bearing supports 24 integral with a first end member 26 and a second end member 28. End members 26 and 28 have inner facing sides 30 and 32 between which stationary assembly 12 and rotatable assembly 16 are located. Each end member 26 and 28 has an outer side 34 and 36 opposite its inner side 30 and 32. Additionally, second end member 28 has an aperture 38 for shaft 20 to extend through outer side 34.
In the exemplary embodiment, rotor 12 includes a ferromagnetic core 40 and is rotatable within stator 14. Segments 42 of permanent magnet material, each providing a relatively constant flux field, are secured, for example, by adhesive bonding to rotor core 40. Segments 42 are magnetized to be polarized radially in relation to rotor core 40 with adjacent segments 42 being alternately polarized as indicated. While magnets on rotor 18 are illustrated for purposes of disclosure, it is contemplated that other rotors having different constructions and other magnets different in number, construction, and flux fields may be utilized with such other rotors within the scope of the invention.
Stationary assembly 15 includes a plurality of winding stages 44 adapted to be electrically energized to generate an electromagnetic field. Stages 44 are coils of wire wound around teeth 46 of laminated stator core 14. Winding terminal leads 48 are brought out through an aperture 50 in first end member 26 terminating in a connector 52. While stationary assembly 12 is illustrated for purposes of disclosure, it is contemplated that other stationary assemblies of various other constructions having different shapes and with different number of teeth may be utilized within the scope of the invention.
Motor 10 further includes an enclosure 54 which mounts on the rear portion of motor 10 to enclose control system 11 for motor 10 within enclosure 54. Control system 11 includes a plurality of electronic components 58 and a connector (not shown) mounted on a component board 60, such as a printed circuit board. Control system 11 applies a voltage to one or more of winding stages 44 at a time for commutating winding stages 44 in a preselected sequence to rotate rotatable assembly 16 about an axis of rotation.
Connecting elements 62 include a plurality of bolts that pass through bolt holes 64 in a second end member 28, bolt holes 66 in core 14, bolt holes 68 in a first end member 26, and bolt holes 70 in enclosure 54. Connecting elements 62 are adapted to urge second end member 28 and enclosure 54 toward each other thereby supporting first end member 26, stationary assembly 12, and rotatable assembly 16 therebetween. Additionally, a housing 72 is positioned between first end member 26 and second end member 28 to facilitate enclosing and protecting stationary assembly 12 and rotatable assembly 16.
In the exemplary embodiment, control system 11 includes at least one computing device 74, for example a microcontroller or a microprocessor, configured to control output signals from control system 11 for controlling the operating characteristics of motor 10. Control system 11 also includes a gate drive circuit 76 electrically coupled to and configured to control at least one power switch 78 based on instructions received from computing device 74.
In the exemplary embodiment, motor 10 further includes at least one thermal protection device 80 positioned adjacent to at least one of winding stages 44 and electrically coupled between a power supply (not shown) and to control system 11. Because protection devices configured for high voltage operation (i.e., greater than about 100V) are costly and uneconomical, thermal protection device 80 is configured for low voltage operation (i.e., less than about 600V AC or less than about 50V DC). Thermal protection device 80 is configured to sense a temperature of winding stage 44 and disconnect control system 11 from its power supply when the temperature exceeds a predefined threshold, as described in more detail herein.
Motor 10 may include any even number of rotor poles and the number of stator poles are a multiple of the number of rotor poles. For example, the number of stator poles may be based on the number of phases. In one embodiment (not shown), a three-phase motor 10 includes six rotor pole pairs and stator poles.
In the exemplary embodiment, a power supply 212 is coupled to gate drive circuit 204 and to microcontroller 210. Power supply 212 is internal to motor assembly 200 and derives a DC voltage from an AC input power source (not shown). Power supply 212 is a low-voltage power supply configured to provide a low DC voltage (i.e., less than 50V) to gate drive circuit 204. Microcontroller 210 retrieves stored programming data from a memory, and based on the power output by power supply 212, transmits control signals to gate drive circuit 204. Gate drive circuit 204 uses the control signals from microcontroller 210 to apply the low DC voltage to power switches 206. By switching the low DC voltage rapidly using power switches 206, gate drive circuit 204 generates a high DC voltage (i.e., larger than 50V), or an effective AC voltage, that operates electric motor 208.
In the exemplary embodiment, thermal protection device 202 is coupled between power supply 212 and gate drive circuit 204. Thermal protection device 202 is a temperature responsive device that is physically positioned adjacent to a winding 214 of electric motor 208 and is responsive to heat generated by current flowing through thermal protection device 202 and winding 214. Thermal protection device 202 is configured for 50 volt DC rated operation. Thermal protection device 202 includes a first conductor 216, an internal switch 218, and a second conductor 220. First conductor 216 is coupled to an output of power supply 212. Internal switch 218 includes a first side 222 coupled to first conductor 216 and a second side 224 coupled to second conductor 220. Second conductor 220 is coupled to second side 224 and to an input 226 of gate drive circuit 204. In one embodiment, internal switch 218 is a metallic material that electrically couples first conductor 216 to second conductor 220. The metallic material is configured to melt at a predetermined temperature, causing first conductor 216 to become uncoupled from second conductor 220.
In the exemplary embodiment, thermal protection device 202 increases in temperature according to motor winding 214 temperature. Internal switch 218 opens when motor winding 214 temperature exceeds the threshold temperature value to disconnect the power supply from the gate drive circuit. When an operating temperature of thermal protection device 202 exceeds a predetermined threshold, thermal protection device 202 transitions from an ON (closed) state to an OFF (open) state. When in the ON state, an electrical circuit through from power supply 212 to gate drive circuit 204 is completed through thermal protection device 202, thereby enabling gate drive circuit 204 to provide power to power switches 206. When in the OFF state, the electrical circuit is broken between power supply 212 and gate drive circuit 204 through thermal protection device 202 to prevent damage to electric motor 208 due to overheating of winding 214. Without power from power supply 212, gate drive circuit 204 cannot turn on power switches 206 and electric motor 208 shuts down.
In the exemplary embodiment, thermal protection device 202 is an automatic reset device such that as thermal protection device 202 cools in the OFF state, thermal protection device 202 resets and completes the circuit between power supply 212 and gate drive circuit 20. Thus, thermal protection device 202 cycles motor power on and off by cycling between the ON and OFF states, respectively. In an alternative embodiment, thermal protection device 202 is a one-shot device that does not reset once entering the OFF state.
In some embodiments, motor assembly 200 includes a second thermal protection device 228 that is electrically coupled to second side 224 of internal switch 218 and an input of gate drive circuit 204. Second thermal protection device 228 is a temperature responsive device that is physically positioned adjacent to power switches 206 and is responsive to heat generated by current flowing through second thermal protection device 228 and power switches 206. Second thermal protection device 228 operates similarly to thermal protection device 202 and may be used alone or in combination with thermal protection device 202.
The thermal protection devices and methods described herein may be implemented using computer programming or engineering techniques including computer software, firmware, hardware or any combination or subset thereof, wherein the technical effect may include at least one of: (a) electrically coupling a thermal protection device between a power supply and a gate drive circuit for driving the motor; and (b) disconnecting, using the thermal protection device, the power supply from the gate drive circuit when a temperature measured by the thermal protection device exceeds a threshold temperature value.
The term processor, as used herein, refers to central processing units, microprocessors, microcontrollers, reduced instruction set circuits (RISC), application specific integrated circuits (ASIC), logic circuits, and any other circuit or processor capable of executing the functions described herein.
As used herein, an element or step recited in the singular and preceded with the word “a” or “an” should be understood as not excluding plural elements or steps, unless such exclusion is explicitly recited. Furthermore, references to “example implementation” or “one implementation” of the present disclosure are not intended to be interpreted as excluding the existence of additional implementations that also incorporate the recited features.
As compared to known thermal protection devices and methods for protecting a motor, the thermal protection devices and methods described herein facilitate coupling/uncoupling a low DC voltage power supply of an electric motor to a gate drive circuit of the electric motor. Rather than coupling/uncoupling a high DC voltage output from the power switches to the motor windings with a thermal protector as in known systems, which typically exceeds the power rating of the thermal protector or necessitates the use of a larger, more costly thermal protector, the thermal protection device described herein enable uncoupling of the low DC voltage supply from the gate drive circuit before the DC voltage is switched to a high DC voltage for driving the motor. The thermal protection device is positioned adjacent a motor winding and opens an internal switch when motor winding temperature exceeds a predetermined threshold value to protect the motor from excessive winding temperatures. When the temperature lowers below the predetermined threshold value, the thermal protection device recouples the low DC voltage power supply to the gate drive circuit to resume motor operation. Accordingly, the thermal protection device provides a low-cost method for protecting a motor from excessive winding temperatures while operating at the proper voltage rating, resulting in safer operation for a user.
Exemplary embodiments of systems and methods for protecting a motor are described herein. The systems and methods described herein are not limited to the specific embodiments described herein, but rather, components of the systems and/or steps of the methods may be utilized independently and separately from other components and/or steps described herein.
This written description uses examples to provide details on the disclosure, including the best mode, and also to enable any person skilled in the art to practice the disclosure, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the disclosure is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.
