Brushless direct current (BLDC) motors are becoming more prevalent in industries that typically did not use BLDC motors. For example, the need for increased efficiency in the heating, ventilating, and air conditioning market has led to the use of BLDC motors for powering the blower. BLDC motors can include a rotor having a plurality of magnetic poles (e.g., a plurality of poles produced with permanent magnets) of alternating polarity disposed on a surface of a rotor core, and a stator that receives electrical power and produces a magnetic field in response thereto. The magnetic field of the stator interacts with a magnetic field of the rotor to cause movement of the rotor.
Standard operating conditions for heating, ventilating, and/or air conditioning systems (collectively referred to herein as HVAC systems) generally vary over relatively short periods of time. It is typically preferred to adjust the cooling and heating cycles, among other parameters, of the HVAC systems as conditions vary. For example, some thermostats are configured to generate a signal indicative of a cooling requirement. In response to the signal generated by the thermostat, the motor of the HVAC system operates a fan or a blower.
Conventional HVAC applications often utilize multi-tapped permanent split capacitor (PSC) type motors. In general, a multi-tapped PSC motor is a motor that has a multi-tapped main winding where all or part of the main winding is coupled in parallel with an auxiliary starting winding that is coupled in series with a capacitor. Such multi-tapped PSC motors are used in HVAC applications, such as furnace blower and air handler applications, because the multi-tapped winding can produce variable output torque and, therefore, variable output speed for the purpose of delivering different amounts of air flow for different applications. For example, one tap setting may provide a relatively low amount of air flow for air circulation when there is no heating or cooling activity. Another tap setting could increase the air flow when cooling is desired. By using multiple taps, various operating states can be established for a tapped PSC motor, such as heating, cooling, and air. In general, each tap point on the multi-tapped PSC motor is coupled to an input line and relays are energized in response to control signals from, for example, a thermostat to energize one of the tap points at any given time.
Blower motors used in residential HVAC systems traditionally use PSC motors. These motors generally have two independent power connections to accommodate heating or cooling modes of operation. The heating or cooling power inputs are normally connected to different winding taps in the PSC motor to provide somewhat different operating speeds for the blower in the respective modes of operation. More than two sets of taps can be designed into the PSC motor, allowing the OEM or installer to select the operating speed by appropriate connection of the taps to the respective heating and cooling power connections. The energizing of these AC power connections to the motor is controlled by activation of a temperature switch and a relay driven from the thermostat.