[NSRCA-discussion] ESC

[Lance Van Nostrand]

Thanks Richard.  I thought the motors were multiphase DC motors and the ESC sequentially energized the windings at the desired rpm and increased the voltage when the stator fell too far behind.
--Lance

  ----- Original Message ----- 
  From: Richard Lewis 
  To: 'NSRCA Mailing List' 
  Sent: Tuesday, July 24, 2007 4:57 PM
  Subject: Re: [NSRCA-discussion] ESC


  Nat,

   

  The ESC has a set of transistors arranged in a three phase bridge arrangement.  The 3-phase bridge is supplied by the DC from the batteries and through a complex switching algorithm it synthesizes a three phase AC voltage that is applied to the motor windings.  The motor is a permanent magnet synchronous AC motor.  The speed of a synchronous machine is directly proportional to the speed of the rotating magnetic field applied.  The voltage applied to the motor is in short pulses at a fixed frequency know as the carrier frequency.  The width of these pulses is modulated (pulse width modulation or PWM) to produce an average voltage waveform that approximates the sinusoidal shape required to operate the motor efficiently.  The amplitude of the synthesized sinusoidal voltage waveform is varied proportionally with the frequency to produce the proper flux within the motor for a given frequency.

   

  To answer the question, the speed controller varies the frequency to control the speed of the motor.  The ESC varies the voltage to control the flux in the motor.

   

  The single phase case would cause the connected windings to draw excessive current without the third phase to balance the effective impedance in the motor winding and take out the transistors easily.

   

  In modern industrial Variable Frequency Drives (VFD) the transistors have many protection mechanisms from fuses which are relatively slow to an internal gate cutoff that can stop excessive current within a single pulse to protect the transistor from damage due to excessive current.  In comparison, the ESC's we use have little or no protection from excessive current.

   

  Richard

   


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  From: nsrca-discussion-bounces at lists.nsrca.org [mailto:nsrca-discussion-bounces at lists.nsrca.org] On Behalf Of Nat Penton
  Sent: Tuesday, July 24, 2007 3:26 PM
  To: NSRCA Mailing List
  Subject: [NSRCA-discussion] ESC

   

  OK, I need educating.

  I realize the ESC converts single phase to three phase. Does it alter the speed of the motor by changing  amplitude or frequency ?

   

  Why did it burn up the ESC (fast, like in quick) when I accidently single phased ?           TIA   Nat



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