Section Il. OVERALL CIRCUIT ANALYSIS
2-4. Electronic Section
2 - 3 . Electromechanical Section
(1) Control of the voltage and frequency of the in-
The electromechanical section of the inverter consists
verter output is accomplished in the voltage and fre-
of motor B1 and generator G1. Both units share the
quency regulator by establishing the exact moment to
same housing, with separate stationary windings. The
turn on conduction through motor B1 and generator G1
armature of the motor and the exciter of the generator
share a common shaft. .
(2) The ac sample from the generator field coils is
a. Motor B1. Motor B1 is a, four-pole, series-shunt
applied to circuit board Al, where it is converted into
motor with windings wound in magnetic opposition to
voltage and frequency error signals.
each other. It operates on 28 vdc input power drawn
(3) Circuit board A2 contains shunt field power
from the aircraft electrical system.
transistor Q3 which pulses 28 vdc power to the shunt
(1) Power for operation of the motor is applied
field of motor B1 for frequency control.
through a set of series coils (Ll through L4) and a
(4) Circuit board A3 is identical with board A2
shunt coil (L5). The series coils and the shunt coil are
and functions in the same manner, except that it pulses
connected so that they are always magnetically op-
posed to each other. Four dc brushes are located at the
neutral point between the four coils (poles); therefore,
(5) Circuit board Al contains the circuit compo-
adjacent commutator bars on the armature reach a dc
nents for sensing and controlling the operation of the
brush when no voltage is between brushes.
power transistors on circuit boards A2 and A3,
(2) When 28 vdc is impressed upon series coils L1
b. CSV2215-2 and CSV2215-3 Regulator (fig. 2-3).
through L4, current will flow from the negative ter-
(1) The regulator senses one phase of the motor-
minal of TB1 through the armature and brushes of
generator's ac output; separate parts of the regulator
motor Bl, the series coils, and choke L10 to the positive
compare magnitudes of the sensed ac voltage and fre-
terminal of TB1. Current also flows from ground
quency to their respective preset values. If an error ex-
through shunt coil L5, and choke L10 to the positive
ists between either of the motor-generator's controlled
terminal of TB1. The magnetic field resulting from the
entities and it preset comparator, the regulator will
current flow through coils L1 through L5 reacts with
function to minimize that error, maintaining ac output
the magnetic field set up by current flow through the
voltage and frequency within the desired tolerance.
armature of motor B1, causing the armature to rotate.
(2) The regulator controls the field currents bv
(3) By rotating through a magnetic field, the ar-
alternately switching the field transistor into satu-
mature causes a counter electromotive force (cemf) to
rated on and off states. This switching rate is propor-
be induced in the armature winding. The speed of ar-
tional to the ac frequency, due to the method of sensing
mature rotation continues to increase until the cemf is
used. The proportionality of on-time and off-time,
almost equal to the dc input. The small difference be-
which determines the average field voltage (and so
tween the cemf and the dc input permits the flow of
field current) is a function of the respxtive error sig-
enough current to keep the armature rotating.
b. Generator G1. The ac generator is a rotating-
(3) To provide continuous field current, essential
field type generator. Direct current from the external
for satisfactory motor-generator performance, each
source is fed to the rotor through the sliprings and the
field is connected across a diode in the regulator, com-
four ac contact brushes.
monly called a free-wheeling or commutating diode.
(1) When motor B1 starts, it turns the exciter of
During the time that the controlling transistor is in the
generator G1. As the exciter rotates, magnetic fields
off state, the field current flows through this diode,
set up by the current through the exciter windings pass
decaying only slightly until the next on state occurs.
conductors in the ac field coils (IA, L?, and L8) and in-
c. 4B93-1-A Regulator (FO-1). All components of
duce an alternating current.
the 4B93-1-A regulator are located on a single circuit
(2) Alternating current is then passed through
board assembly. This regulator functions as described
filter FL1 and made available at ac power connector
Section Ill. CIRCUIT ANALYSIS, CSV1186-1
netted to positive dc and the other side is connected to
the collector of power transistor Q6. When the power
transistor is on, total dc voltage appears across the
a. One side of the generator exciter field is con-