Abstract:
A serial interface circuit electrically connected to a controller to control an electric motor. The interface circuit includes a controller circuit and a motor circuit. The controller circuit includes a transmitter and a receiver circuit, and the motor circuit includes a transmitter circuit and a receiver circuit. The interface interrogates the motor to acquire status and diagnostic information by receiving commands from the controller, adjusts a voltage level to a desired level, outputs the voltage signal to command and control the motor, and receives a voltage response from the motor.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates generally to electrical motors, and more particularly to a digital communications link to control and interrogate a variable speed motor used in air moving systems. 
     Electronically commutated motors (ECMs) are used in a wide variety of applications because they are more efficient than known standard induction motors. ECMs include the efficiency and speed control advantages of a DC motor and minimize the disadvantages of DC motors, e.g., carbon brush wear, short life span, and noise. In Heating, Ventilation and Air Conditioning (HVAC) systems, as well as, known commercial air distributions systems, ECMs automatically adjust blower speed to meet a wide range of airflow requirements. Known ECMs use microprocessor technology to control fan speed, torque, air flow, and energy consumption. 
     Conventional blower motors are designed to operate at one speed, however, variable speed ECMs can operate at a wide range of speeds. Variable speed in an ECM is important because blowers need to adjust speed to deliver the airflow needed by the HVAC system. 
     Known ECMs have various modes of operation, and external control circuits determine an operating point of the ECM. In one mode of operation, Pulse Width Modulation (PWM) signals are transmitted to the electrical interface to control motor speed, motor torque and airflow produced by the motor. The operating point of the ECM is determined by an internal microprocessor control circuit that directly responds to a status of various control input lines. 
     SUMMARY OF THE INVENTION 
     Methods and apparatus for interfacing an electronically commutated motor to an HVAC system controller are described. In one aspect of the invention, the method includes an interface circuit coupled to the system controller and the electric motor and includes the steps of receiving commands from the controller, adjusting a voltage to a desired level, outputting the voltage signal through a motor control circuit to control the electric motor, receiving a voltage from the electric motor, and transmitting the received voltage to the controller. 
     In another aspect of the invention, an HVAC system includes an electronically commutated motor electrically coupled to the interface circuit, which is electrically connected to the system controller. The HVAC system receives commands from the controller, adjusts a voltage to a desired level, outputs the voltage signal through a motor control circuit to control the electric motor, receives a voltage from the electric motor through the motor control circuit, and transmits the received voltage to the controller. 
     In another aspect of the invention, the interface circuit is electrically connected to the HVAC controller and the electronically commutated motor. The interface circuit includes a controller circuit and a motor control circuit. The controller circuit includes a transmitter circuit and a receiver circuit, and the controller circuit interfaces with the HVAC controller. The motor control circuit includes a transmitter circuit having a first optocoupler and a receiver circuit having a second optocoupler. The motor control circuit interfaces with the electronically commutated motor. After receiving commands from the HVAC controller, the interface circuit adjusts a level of the voltage signal to a desired level, outputs an electrical signal through the first optocoupler, and receives an electrical response from the electronically commutated motor through the second optocoupler. The interface circuit in addition to controlling the electronically commutated motor, interrogates the electronically commutated motor to acquire status and diagnostic information. 
     As a result, a cost-effective and reliable electrical interface circuit, including a motor circuit and a receiver circuit, to electrically couple a controller to an electronically commutated motor is provided. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an exemplary embodiment of a system block diagram. 
         FIG. 2  is an exemplary embodiment of a schematic diagram of a controller interface circuit. 
         FIG. 3  is an exemplary embodiment of a schematic diagram of a motor control circuit. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is an exemplary system block diagram  10  of an electrical interface circuit  12  connected to a HVAC system  14  and a controller  16 , which is connected to a thermostat  18 . HVAC system  14  includes an electronically commutated motor  20  (ECM) including a microcontroller  22 . In one embodiment, ECM  20  is a variable speed ECM. Interface circuit  12  includes a controller interface circuit  24  and a motor control interface circuit  26 . Motor control interface circuit  26  is connected to microcontroller  22  within ECM  20 . HVAC system  14  communicates with ECM  20  through controller interface circuit  24  via a serial communications link  28 , e.g., a shielded cable. In another embodiment, controller interface circuit  24  communicates with motor control interface circuit  26  via a wireless digital communications link (not shown). In yet another embodiment, control interface circuit  24  communicates with motor control interface circuit  26  using wireless technology, e.g., infrared and RF technology (not shown). Interface circuit  12  receives information from controller  16  as to a specific torque, speed, or airflow ECM  20  is to be set based on a desired temperature from thermostat  18 . In one embodiment, interface circuit  12  is a digital interface. 
       FIG. 2  is an exemplary embodiment of a schematic diagram for controller interface circuit  24 . Controller interface circuit  24  includes a transmit circuit  30  and a receive circuit  32 . Controller transmit circuit  30  includes a Tx terminal  34  connected to a resistor  36  that is connected to a node  38 . Node  38  is connected to a base  40  of transistor  42 . Node  38  is also connected to a resistor  44  that is connected to an emitter  46  of transistor  42 . A power supply  47  is connected to emitter  46  of transistor  42 . A collector  48  of transistor  42  is connected to a TxOut terminal  50 . 
     Controller receive circuit  32  includes a power terminal  52  and a RxIN terminal  54 . RxIN terminal  54  is connected to a resistor  56  that is connected to a node  58 . Resistor  60  is connected between node  58  and a node  62 . Node  62  is connected to power terminal  52  and power supply  47 . Node  62  is connected to an emitter  64  of transistor  66  and node  58  is connected a base  68  of transistor  66 . A collector  70  of transistor  66  is connected to a node  72  that is connected to a resistor  74  and a Rx terminal  76 . Resistor  74  is tied to a node  78  that is tied to ground, a ground terminal  80 , and a common terminal  82 . 
     Of course, controller interface circuit  24  is not limited to practice in HVAC system  10  and can be utilized in connection with many other types and variations of controllers, besides controller  16  (shown in  FIG. 1 ). 
       FIG. 3  is an exemplary embodiment of a schematic diagram for motor control interface circuit  26 . Motor control interface circuit  26  includes a receive circuit  90  and a transmit circuit  92 . Motor receive circuit  90  includes a terminal RxIN  94  connected to a resistor  96 . Resistor  96  is connected to a node  98 . Resistor  100  is connected between node  98  and a node  102 . Node  102  is connected to motor transmit circuit  92  at node  104 . Nodes  98  and  102  are connected to an optocoupler  106 . Optocoupler  106  is connected to a node  108 , which is connected to a resistor  110  and microcontroller  22 . Resistor  110  is connected to a power supply  111 . 
     Motor transmit circuit  92  includes a power terminal VCC  112 , a transmit terminal TxIN  114 , and a ground terminal COM  116 . A zener diode  118  is connected between TxIN terminal  114  and COM terminal  116 . Terminal VCC  112  is connected to a node  120 , which is connected to a zener diode  122  and resistors  124  and  126 . Zener diode  122  is connected to a node  104 , which is connected to terminal COM  116 . Resistor  124  is connected to a node  128  which is connected to a base  130  of transistor  132  and a collector  134  of transistor  136 . A collector  138  of transistor  132  is connected to terminal TxIN  114  and an emitter  140  of transistor  132  is connected to node  104 . Collector  134  of transistor  136  is connected to base  130  of transistor  132  via node  128 , and an emitter  142  of transistor  136  is connected to node  104 . A base  144  of transistor  136  is connected to a node  146 . Node  146  is connected to resistor  126  and to an optocoupler  148  that is connected to node  104 . Optocoupler  148  is also connected to power supply  111  and to a resistor  150 , which is connected to microcontroller  22 . 
     Controller interface circuit  24  is electrically connected by a serial cable  28  to motor control circuit  26 . In one embodiment, the connection of controller interface circuit  24  to motor control circuit  26  enables controller  16  to communicate with ECM  20 . Serial cable  28  in one embodiment is a four-wire serial interface. In one embodiment, serial cable  28  has a length of ten feet. In an alternative embodiment, serial cable  28  has a length of one-hundred feet. Referring specifically to  FIG. 2  and  FIG. 3 , in one embodiment, controller receiver circuit  32  is electrically connected to motor transmitter circuit  92 , and controller transmitter circuit  30  is electrically connected to motor receiver circuit  90 . In order for controller interface circuit  24  to send and receive messages to/from motor control circuit  26 , TxOut terminal  50  is connected to RxIN terminal  94 , ground terminal  80  is connected to COM terminal  116 , RxIN terminal  54  is connected to TxIN terminal  114 , and VCC terminal  52  is connected to VCC terminal  112 . 
     Controller interface circuit  24  accepts signals from controller  16  (shown in  FIG. 1 ). Once a signal is received from controller  16 , the signal is converted to a voltage level that can be accepted by ECM  20 . In one embodiment, the signal is converted by controller interface circuit  24  to at least an infrared signal, an RF signal, and digitally encoded over a power line prior to output to motor control interface  26 . In one embodiment, controller interface circuit  24  and motor control interface  26  are configured for bi-directional communication with one another. In one embodiment, motor control interface  26  is configured to accept at least one of a voltage signal, an infrared signal, an RF signal, and a digitally encoded power line signal. Motor receiver circuit  90  accepts the signal from controller transmitter circuit  30  and transmits the signal through optocoupler  106  to ECM  20 . ECM  20  then responds by transmitting a voltage signal to motor transmitter circuit  92 . In one embodiment, ECM  20  transmits at least one of an infrared signal and a RF signal to motor transmit circuit  92 . The transmitted signal is converted by motor transmit circuit  92  and transmitted to controller receiver circuit  32  where the signal is adjusted to a voltage level to communicate with controller  16 . 
     In addition, motor control interface circuit  26  provides isolation between controller  16  and ECM  20 . Microcontroller  22  in one embodiment, is not isolated from an AC powerline (not shown). Optocouplers  106  and  148  are, therefore, utilized to isolate motor control interface circuit  26  from microcontroller  22 . The interface between control interface circuit  24  and motor control circuit  26  is a four-wire serial interface. The four-wire serial interface is utilized for noise immunity. 
     Electrical interface  12  commands ECM  20  (shown in  FIG. 1 ) to be configured in various embodiments, e.g., as a constant torque machine, a constant airflow machine, or a constant speed machine. As a constant torque machine, motor torque is regulated by controlling motor current, regardless of operating speed. When operating as a constant torque machine, torque production is linearized and speeds are compensated over the motor&#39;s operating speed/torque plane. When operating as a constant airflow machine, a set of constants that describe HVAC system  14  for constant airflow are downloaded to motor  20 . The constants optimize ECM  20  operation to provide more accurate airflow regulation in a given operating region. Therefore, as a constant airflow machine, ECM  20  acts as an airflow sensor delivering constant airflow for a given system. As a constant speed machine, ECM  20  will regulate speed regardless of torque requirements provided that a maximum torque value is not exceeded. 
     In alternative embodiments, interface circuit  12  controls operating profiles, delay profiles, slew rates, speed limit, dynamic braking and control of inrush current of ECM  20 . In an alternative embodiment, interface circuit  12  interrogates ECM  20  to determine operating status, operating speed, operating torque, input power consumption, under speed condition, and a time of operation at a given power level. In yet another embodiment, interface circuit  12  can access read/write data and program data to control memory of ECM  20 . 
     In another embodiment, interface circuit  12  is connected to residential HVAC furnaces, fan coils, heat pumps, and heat recovery ventilators. In still another embodiment, interface circuit  12  is connected to residential HVAC air conditioners (not shown) where a blower motor (not shown) is connected to a HVAC system controller (not shown). 
     In an additional embodiment, interface circuit  12  is used in a clean room environment (not shown). In a further embodiment, interface circuit  12  is used in a commercial variable air volume system (not shown). When used in a clean room environment or in a commercial variable air volume system, a dedicated controller (not shown) is electrically connected to interface circuit  12 , or a centralized controller (not shown) is connected to interface circuit  12  to provide individual control via a common communications bus (not shown). 
     As a result, a cost-effective and reliable electrical interface circuit, including a motor control interface circuit and a controller interface circuit, that couples a controller to an ECM is provided. 
     While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.