Packet-based networking of variable frequency drives

Abstract

One or more Variable Frequency Drives (VFD) are connected to a packet network and the power transistor drive signals normally generated by the VFD to produce a desired Pulse Width Modulated (PWM) motor drive signal are generated by a software controller located in the packet network and transmitted to the VFD. The control of the VFDs can be (1) centralized using some centralized software controller communicating to the VFDs over the packet network, and/or (2) distributed, in which case VFDs can peer with each other over the packet network, to communicate control state.

What is claimed is: 
     
         1 . A method of controlling one or more Variable Frequency Drives (VFD), each VFD configured to generate a Pulse Wdth Modulated (PWM) signal to drive a motor, characterized by:
 for each controlled VFD, calculating a plurality of drive signals to switch a plurality of power transistors in the VFD for a first time interval, to generate a desired PWM signal; and   wirelessly transmitting, in advance of the first time interval, the plurality of drive signals to respective VFDs in at least a main downlink (DL) frame of a transmission packet.   
     
     
         2 . The method of  claim 1  wherein wirelessly transmitting a plurality of drive signals comprises transmitting a plurality of drive signals in a plurality of successive time intervals including the first time interval, wherein the drive signals transmitted in one of the successive time intervals is effective for the next time interval. 
     
     
         3 . The method of  claim 1  wherein the drive signals comprise separate indications to switch each power transistor on or off, and also indicate the timing of the switching. 
     
     
         4 . The method of  claim 3  wherein the drive signals further comprise an indication to switch a braking transistor on or off, and also indicate the timing of the switching. 
     
     
         5 . The method of  claim 3  wherein the timing of each transistor switching signal is an offset from the beginning of the next time interval. 
     
     
         6 . The method of  claim 3  further comprising:
 in one or more of the time intervals, additionally transmitting commands or parameter values to one or more VFDs in an auxiliary DL frame of the transmission packet. 
 
     
     
         7 . The method of  claim 6  further comprising:
 transmitting a command in an auxiliary DL frame for the VFD to run autonomously; and 
 ceasing the transmission of drive signals in a main DL frame to the autonomous VFD. 
 
     
     
         8 . The method of  claim 7  further comprising:
 transmitting a command in an auxiliary DL frame for the VFD to be controlled; and 
 resuming the transmission of drive signals in a main DL frame to the autonomous VFD. 
 
     
     
         9 . The method of  claim 3  further comprising:
 in one or more of the time intervals, receiving from one or more VFDs feedback about the VFD or motor state in a main uplink (UL) frame of a received packet. 
 
     
     
         10 . The method of  claim 1  wherein the same drive signals, commands, or parameter values are broadcast to two or more controlled VFDs. 
     
     
         11 . The method of  claim 1  wherein the drive signals, commands, or parameter values are transmitted individually to each controlled VFD. 
     
     
         12 . A controller configured to control one or more Variable Frequency Drives (VFD), each VFD configured to generate a Pulse Wdth Modulated (PWM) signal to drive a motor, the controller comprising:
 a processor operatively connected to the wireless transceiver, and configured to:
 for each controlled VFD, calculate a plurality of drive signals to switch a plurality of power transistors in the VFD for a time interval, to generate a desired PWM signal; and 
 wirelessly transmit the plurality of drive signals, to each controlled VFD, in advance of the time interval in which they are to be applied, in at least a main downlink (DL) frame of a transmission packet. 
   
     
     
         13 . A method of generating a Pulse Width Modulated (PWM) signal to drive a motor, by a Variable Frequency Drive (VFD) controlled by a remote controller, comprising:
 wirelessly receiving from the controller, in a main downlink (DL) frame of a received packet, a plurality of drive signals for a time interval; and   in a subsequent time interval, switching a plurality of power transistors, according to the received drive signals, to generate the PWM signal.   
     
     
         14 . The method of  claim 13  wherein wirelessly receiving a plurality of drive signals comprises receiving the plurality of drive signals in each successive time interval, and wherein a subsequent time interval comprises the next time interval. 
     
     
         15 . The method of  claim 13  wherein the drive signals comprise separate indications to switch each power transistor on or off, and also indicate the timing of the switching. 
     
     
         16 . The method of  claim 15  wherein the drive signals further comprise an indication to switch a braking transistor on or off, and also indicate the timing of the switching. 
     
     
         17 . The method of  claim 15  wherein the timing of each transistor switching signal is an offset from the beginning of the next time interval. 
     
     
         18 . The method of  claim 13  further comprising:
 in one or more of the time intervals, additionally receiving commands or parameter values in an auxiliary DL frame of the received packet. 
 
     
     
         19 . The method of  claim 18  further comprising:
 receiving a command in an auxiliary DL frame to run autonomously; and 
 generating drive signals to switch the transistors. 
 
     
     
         20 . The method of  claim 19  further comprising:
 receiving a command in an auxiliary DL frame to again be controlled; and 
 resuming switching the transistors according to drive signals received in each time interval from the controller. 
 
     
     
         21 . The method of  claim 13  further comprising:
 in one or more of the time intervals, wirelessly transmitting to the controller feedback about the VFD or motor state in a main uplink (UL) frame of a transmitted packet. 
 
     
     
         22 . The method of  claim 21  wherein the feedback includes one or more of instantaneous motor speed, instantaneous motor current, power transistor temperature, motor rotor temperature, DC bus voltage, and an indication for the controller to calculate motor speed from current and voltage. 
     
     
         23 . The method of  claim 21  further comprising:
 in one or more of the time intervals, wirelessly transmitting to the controller the value of one or more parameters in an auxiliary uplink (UL) frame of a transmitted packet. 
 
     
     
         24 . A Variable Frequency Drive (VFD) configured to generate a Pulse Width Modulated (PWM) signal to drive a motor, controlled by a remote controller, said VFD comprising:
 a transceiver; and   a processor operatively connected to the wireless transceiver, and configured to:
 wirelessly receive from the controller, in a main downlink (DL) frame of a received packet, a plurality of drive signals for a time interval; and 
 in a subsequent time interval, switch a plurality of power transistors, according to the received drive signals, to generate the PWM signal. 
   
     
     
       25. A method of controlling two or more Variable Frequency Drives (VFD), each VFD configured to generate a Pulse Width Modulated (PWM) signal to drive a motor, comprising, in each of a plurality of successive time intervals and for each controlled VFD:
 calculating a plurality of drive signals to switch a plurality of power transistors in a power section of the VFD for a subsequent time interval, to generate a desired PWM signal;   wirelessly transmitting, the plurality of drive signals to the VFD in a single main downlink (DL) frame of a DL transmission packet, the DL frame instructing the VFD as to which of the plurality of power transistors are switched on and off in the subsequent time interval; and   wherein the DL transmission packet for each VFD includes an individual identifier for the VFD and is transmitted over a packet-switched network.    
     
     
       26. The method of  claim 25  wherein the drive signals comprise separate indications to switch each power transistor on or off, and also indicate the timing of the switching.  
     
     
       27. The method of  claim 25  further comprising:
 in one or more of the time intervals, additionally transmitting commands or parameter values to one or more VFDs in an auxiliary DL frame of the transmission packet.  
 
     
     
       28. The method of  claim 25  wherein a header of the main DL frame includes an indicator field to indicate presence of an auxiliary DL frame in the transmission packet.  
     
     
       29. The method of  claim 28  further comprising:
 transmitting a first command in an auxiliary DL frame for the VFD to run autonomously and ceasing, responsive to the first command, the transmission of drive signals in a main DL frame to the autonomous VFD; and 
 transmitting a second command in an auxiliary DL frame for the VFD to be controlled and resuming, responsive to the second command, the transmission of drive signals in a main DL frame to the autonomous VFD.  
 
     
     
       30. The method of  claim 25  further comprising:
 in one or more of the time intervals, receiving from one or more VFDs feedback about the VFD or motor state in a main uplink (UL) frame of a received packet.  
 
     
     
       31. A method of generating a Pulse Width Modulated (PWM) signal to drive a motor, by a Variable Frequency Drive (VFD) controlled by a remote controller, comprising:
 wirelessly receiving from the controller, in a first time interval, a single main downlink (DL) frame of a DL transmission packet containing a plurality of drive signals for switching a plurality of power transistors in a power section of the VFD in a subsequent time interval; and   in the subsequent time interval, switching the plurality of power transistors, according to the received drive signals, to generate the PWM signal; and   wherein the DL transmission packet for each VFD includes an individual identifier for the VFD and is transmitted over a packet-switched network.    
     
     
       32. The method of  claim 31 , further comprising:
 in one or more of the time intervals, additionally receiving commands or parameter values in an auxiliary DL frame of the DL transmission packet.    
     
     
       33. The method of  claim 32 , further comprising:
 receiving a first command in an auxiliary DL frame to run autonomously and, in response, generating drive signals to switch the transistors; and   receiving a second command in an auxiliary DL frame to again be controlled, and, in response, resuming switching the transistors according to drive signals received in each time interval from the controller.    
     
     
       34. The method of  claim 31 , further comprising:
 in one or more of the time intervals, wirelessly transmitting to the controller feedback about a state of the VFD or a state of the motor in a main uplink (UL) frame of an UL transmission packet.    
     
     
       35. The method of  claim 34  wherein the feedback includes one or more of instantaneous motor speed, instantaneous motor current, power transistor temperature, motor rotor temperature, DC bus voltage, and an indication for the controller to calculate motor speed from current and voltage.  
     
     
       36. The method of  claim 34 , wherein the UL transmission packet comprises an auxiliary UL frame including one or more operating parameters of the VFD.  
     
     
       37. The method of  claim 36 , wherein a header of the main UL frame includes an indicator field to indicate presence of an auxiliary UL frame in the UL transmission packet. 
     
     
       38. The method of  claim 36 , wherein a header of the main UL frame includes a group identifier field to indicate a parameter group to which the operating parameters belong.  
     
     
       39. A Variable Frequency Drive (VFD) configured to generate a Pulse Width Modulated (PWM) signal to drive a motor, wherein the VFD is controlled by a remote controller, the VFD comprising:
 a wireless transceiver;
 a processing circuit operatively connected to the wireless transceiver, and configured to: 
 wirelessly receive from the controller, in a first time interval, a single main downlink (DL) frame of a DL transmission packet containing a plurality of drive signals for switching a plurality of power transistors in a power section of the VFD in a subsequent time interval; and 
 in the subsequent time interval, switch the plurality of power transistors, according to the received drive signals, to generate the PWM signal; and 
 wherein the DL transmission packet for each VFD includes an individual identifier for the VFD and is transmitted over a packet-switched network.  
   
     
     
       40. A controller configured to control two or more Variable Frequency Drives (VFD), each VFD configured to generate a Pulse Width Modulated (PWM) signal to drive a motor, the controller comprising:
 a wireless transceiver;   a processing circuit operatively connected to the wireless transceiver, configured to, in
 each of a plurality of successive time intervals and for each controlled VFD: 
 calculate a plurality of drive signals to switch a plurality of power transistors in a power section of the VFD for a subsequent time interval, to generate a desired PWM signal; 
 wirelessly transmit, the plurality of drive signals to respective VFDs in a single main downlink (DL) frame of a DL transmission packet for the VFD, the DL frame instructs the VFD as to which of the plurality of power transistors are switched on and off in the subsequent time interval; and 
 wherein the DL transmission packet for each VFD includes an individual identifier for the VFD and is transmitted over a packet-switched network.