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<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Nat,<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>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.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>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.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>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.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>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.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Richard<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
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<p class=MsoNormal><b><font size=2 face=Tahoma><span style='font-size:10.0pt;
font-family:Tahoma;font-weight:bold'>From:</span></font></b><font size=2
face=Tahoma><span style='font-size:10.0pt;font-family:Tahoma'>
nsrca-discussion-bounces@lists.nsrca.org
[mailto:nsrca-discussion-bounces@lists.nsrca.org] <b><span style='font-weight:
bold'>On Behalf Of </span></b>Nat Penton<br>
<b><span style='font-weight:bold'>Sent:</span></b> Tuesday, July 24, 2007 3:26
PM<br>
<b><span style='font-weight:bold'>To:</span></b> <st1:PersonName w:st="on">NSRCA
Mailing List</st1:PersonName><br>
<b><span style='font-weight:bold'>Subject:</span></b> [NSRCA-discussion] ESC</span></font><o:p></o:p></p>
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<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'><o:p> </o:p></span></font></p>
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<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>OK, I need educating.</span></font><o:p></o:p></p>
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<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>I realize the ESC converts single phase to three phase. Does
it alter the speed of the motor by changing amplitude or frequency ?</span></font><o:p></o:p></p>
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<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'> <o:p></o:p></span></font></p>
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<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>Why did it burn up the ESC (fast, like in quick) when I
accidently single phased
? TIA
Nat</span></font><o:p></o:p></p>
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