[NSRCA-discussion] ESC

[Richard Lewis]

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

 

  _____  

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

-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.nsrca.org/pipermail/nsrca-discussion/attachments/20070724/177d0a40/attachment.html