The invention relates to a controller for a motor with and without a power factor correction circuit, and particularly, a controller that recalculates the maximum power provided to the motor.
A motor is designed to operate in a specific temperature range at a rated output power and input voltage. Operation beyond the maximum specified temperature for an extended period of time may cause damage to or failure of the controller (inverter) motor. In addition, variation in the input voltage affects the maximum power that can be drawn from the motor at the maximum specified operating temperature.
In order to enable the motor system to operate at higher temperatures and higher speeds, the invention provides a system that reduces the operating power of the motor when operating above the maximum specified temperature and below the rated voltage at maximum specified temperature without turning off the motor. The system does so by determining a maximum current limit based on certain operating conditions, effectively de-rating (i.e., calculating a lower current limit) the system to operate under conditions beyond the normal operating parameters and at the same time protecting against overheating of the electrical components.
In one embodiment, the invention provides a system of limiting current to a motor. The system comprises of a motor and a controller. The controller includes a processor and memory. The controller is configured to monitor the speed of the motor, the input voltage of the controller, and the temperature of the controller enclosure. The controller then determines a maximum current limit for the motor based on the monitored speed when the motor speed is below a speed threshold. If, however, the motor speed is above a threshold, the controller determines a maximum current limit for the motor based on the temperature of the controller enclosure.
In another embodiment the invention provides a method of limiting current to a motor, the method comprises monitoring the speed of a motor, the input voltage of the controller, and the temperature of the controller enclosure. The method further comprises determining a maximum current limit for the motor based on the monitored speed when the motor speed is below a speed threshold and determining a maximum current limit for the motor based on the temperature inside the controller enclosure when the motor speed is above the speed threshold.
Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings.
Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways.
The controller 105 is connected to a motor 125. The motor 125 is a permanent magnet, brushless Permanent Magnet Synchronous (PMS) motor. The PMS motor 125 includes a stator and a permanent magnet rotor. The motor 125 can further comprise of a programmable device (not pictured), such as a microcontroller, a digital signal processor, or a similar controller having a processor and memory. The programmable device of the PMS motor uses software stored in the memory to control the electronic commutator. Although motor 125 in
In the motor system 100, the controller 105 is separate from the on-board programmable device that controls the operation of the motor. However, in other embodiments, the controller 105 replaces the on-board programmable device and both controls the operation of the motor 125 and de-rates (or limits) the power to the motor 125.
In operation, the controller 105 de-rates (or limits) the power to the motor 125 by determining a maximum current limit at which the motor 125 may operate. Depending on the current operational condition of the motor 125, the maximum current limit is determined based on the speed of the motor 125, the temperature of the controller 105, or a combination of the input (or mains) voltage of the controller 105 and the temperature of the controller 105.
As illustrated in
The controller 105 determines if the speed of the motor 125 is above or below a predetermined speed threshold (step 220). If the speed is below the threshold, the maximum current limit is determined based only on the speed of the motor 125 and that maximum current limit is used (step 230). In this implementation, the maximum current limit based on the speed of the motor 125 is determined based on a current limit profile. A current limit profile, as illustrated in
If, however, the speed of the motor is above the speed threshold (step 220), the controller 105 determines if the temperature of the controller 105 is above or below a predetermined temperature threshold (step 235). If the temperature is below the threshold, the maximum current limit is again determined based on the speed of the motor 125 and that maximum current limit is used (step 230).
If the temperature of the controller 105 exceeds the temperature threshold (step 235), the controller 105 determines if the input voltage of the controller 105 is above or below a predetermined voltage threshold (step 245). If the input voltage is above the threshold, the maximum current limit is determined using a first formula based on the temperature of the controller 105 (step 250). In particular, the controller 105 calculates a de-rated maximum current limit using the following formula:
iq
where iq
The maximum current limit is then determined based only on the speed of the motor 125 (step 255). The controller 105 then determines whether the determined maximum current limit based on speed or the determined maximum current limit based on temperature is lower (step 260). If the determined maximum current limit based on speed is lower, then the maximum current limit based on speed is used (step 265). If the determined maximum current limit based on temperature is lower, then the maximum current limit based on temperature is used (step 270).
If the input voltage of the controller 105 is below the voltage threshold (step 245), the maximum current limit is determined using a second formula based on both the temperature and the input voltage (step 275). In particular, the controller 105 calculates a de-rated maximum current limit using the following formula:
iq
Again, iq
The maximum current limit is then determined based only on the speed of the motor 125 (step 280). The controller 105 then determines whether the determined maximum current limit based on speed or the determined maximum current limit based on temperature and input voltage is lower (step 285). If the determined maximum current limit based on speed is lower, then the maximum current limit based on speed is used (step 265). If the determined maximum current limit based on temperature and input voltage is lower, then the maximum current limit based on temperature and input voltage is used (step 290).
Thus, the invention provides, among other things, a system for de-rating (or limiting) the maximum power to be provided to a variable speed motor to enable operation of the motor beyond the normal operating parameters for the motor system. The maximum current limit is calculated by different methods depending on the speed and other operating conditions. Various features and advantages of the invention are set forth in the following claims.
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Number | Date | Country | |
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20130106334 A1 | May 2013 | US |