Chapter 2. FUNCTIONING OF EQUIPMENT - TM-11-6125-259-300010

TM 11-6125-259-30

CHAPTER 2

FUNCTIONING OF EQUIPMENT

2-1. Static Inverter Block Diagram Functional

ground (referred to as a short to ground in the text)

Description

for the center tap of the two input chokes, which

The inverter, consists of the following subassem-

with this high current flow stores energy. During

the next cycle of operation the choke energy is

blies and sections (see block diagram, fig. 2-1): In-

discharged into the power capacitors.

put and Output EMI Filters. Start Up Regulator,

e. Power Capacitors. The power capacitors are

Boost Regulation Control, Input Chokes, Power

charged by the energy stored in the input chokes.

Capacitors, Logic, Overvoltage Sense, Overcurrent

The 37 vdc output of the power capacitors is used by

Sense, Major and Minor Drive, Major and Minor

the major and minor drive circuits, the major and

Bridge Converters, Output Voltage Sense, and Out-

minor bridge converter circuits and initially for

put Filter.

power for the start up regulator.

a. Input EMI (Electromagnetic Interference)

f. Logic. The logic circuit functions as follows:

Filter. The EMI filter reduces conducted and

logic to prduce major and minor drive waveforms,

radiated energy.

turn-on time delay logic, input overvoltage logic and

b. Start Up Regulator. The start up regulator

output overcurrent sense logic. The drive logic

p r o v i d e s regulated +5 vdc and +15 vdc bias

develops waveforms from a 9.6 KHz oscillator that

v o l t a g e s to the logic circuits and the boost

are fed to the major and minor drive circuits to

r e g u l a t i o n control. At turn-on, the start up

f i n a l l y produce major and minor quasi sine

regulator receives its input power from the power

waveforms that are fed to output voltage trans-

capacitors. After turn-on the start up regulator

formers T1 and T2. At inverter turn-on, the +15 V

receives its input from rectified voltages from the

comes on at once and the turn-on time delay logic

minor bridge converter transformer T2.

generates a signal which allows the other circuits to

c. Boost Regulation Control. This overall

stabilize before the drive waveforms and the +5 vdc

regulation circuit consists of part of the A2 assem-

and 37 vdc supplies are energized. The input

bly (high level boost) and A3 assembly (low level

overvoltage logic generates inverter shutdown

boost) and the entire A7 assembly (boost regulator).

signals for the major and minor bridges (cuts off the

The A2 and A3 assemblies function in an identical

drive waveforms) and turns off the 37 vdc supply.

way in this circuit; each one servicing an input

The output overcurrent sense logic maintains a 7.5

choke (L201, L301). The overall circuit regulates the

amp inverter output current for five seconds after

37 vdc supply. The regulation is accomplished by

an overload current of 200% or greater (output short

changing the duty cycle ratio (choke charge time to

circuit) is detected. The inverter output is then

choke discharge-into-power-capacitors time) of the

cycled off and on until overcurrent condition is

t w o input chokes which feed into the power

removed.

capacitors to form the 7 vdc supply. The duty cycle

g. Overvoltage Sense. The overvoltage sense

ratio is proportional to the input voltage and the in-

circuit detects an excessive (44 vdc) level of inverter

verter output load. The A7 boost regulator alter-

input voltage or 37 vdc supply voltage in the form of

nately acts to charge and discharge the two input

transient or static potentials. The overvoltage sense

chokes into the power capacitors in order to create a

circuit will shut down the inverter output and the 37

push-pull effect. The circuit also makes use of a

vdc supply for the duration of the overvoltage.

power ratio transfer (low voltage_high current ver-

h. Overcurrent Sense. The overcurrent sense

sus high voltage_low current) and, in addition, the

circuit provides inverter protection from overloads

circuit receives an error signal from the output

greater than 200% and support output short circuit

voltage sense circuit and this back-loop regulation

current at 2.5 times the rated current for a duration

enables fine control of the 37 vdc and the output ac

of five seconds following the application of a short.

voltage.

The current sense circuit monitors the output of

d. Input Chokes. The two input chokes are con-

each phase through current transformers. Each

nected to the inverter input voltage on one end and

transformer output is rectified by diodes to produce

to the power capacitors on the other end. The boost

an equivalent dc voltage that is fed into the output

regulator alternately provides a low impedance to

2-1