Owner`s manual

Owner’s Manual
Theory of Operation page 4 — 1
Theory of Operation
This chapter describes the theory of operation of the S4 inverter system.
4.0 SCOPE
The following is a brief description of the mechanical configuration and how the S4 inverter system functions. It is not
intended to provide complete details of all of the circuits within the unit, but gives some details as to the function of each
block. The system is a modular 48VDC to 120/240VAC inverter, which consists of 3.5 kVA/3KW modules housed in a
“Receiver” cabinet. Inverter systems can be ordered with one to six power modules (3.5 kVA to 21 kVA). Inverter
systems are available in the following power levels: 3.5 kVA/3KW, 7 kVA/6KW, 10.5 kVA/9KW, 14 kVA/12KW, 17.5
kVA/15KW, and 21 kVA/18KW. The inverter is designed to be a N+1 redundant system. Redundancy, or increased
power capability can be added at a later date by adding more power modules. Figure 4.1 is a block diagram of a 21 kVA
inverter. Figure 4.2 is an electrical block diagram of the “Inverter” system.
“Receiver” Cabinet Configuration
See Figure 2-2 for System Component Descriptions of the 7 kVA. On the top left-hand side of the “Receiver” cabinet,
two “Controllers” printed circuit boards are installed, one on top of the other. On top left-hand side of the “receiver” is
an alarm relay printed circuit board. The top part of the “Receiver” cabinet is common to all power level configurations.
In a 21 kVA system, immediately below the “Controller” are three 5.25” high “Power Module” chassis. Below the three
power modules is a 5.25” high “Static Switch”. The “Static Switch” in an integral part of the “Receiver” as are the inverter
output EMI filters, AC input/output terminal block, AC output and back-feed current sensing transformers, and DC input
termination bus bars. Three more “Power Modules” are installed immediately below the “Static Switch”. In the “Static
Switch” area, provisions are made for the user to select either 120VAC or 240VAC output. This is accomplished via bus
bar strap selection on the output terminals of the EMI filter and positioning a jumper plug on the Static Switch gate driver
PCB, which is located on the side of the receiver.
4.1 “Receiver” Cabinet “Controller”
In the “Receiver” cabinet is a printed circuit board called a “Controller” which has a microprocessor (Intel 80C198KC),
Read Only Memory (Waferr Scale “PDS301), and other associated electronics. This “Controller” is the “brain” of the
system and operates the power modules and “Static Switch”. As an option, two “Controller” boards can be installed
which will provide redundancy. The “Controller” circuit boards are located in the top right hand side of the “Receiver”
cabinet. If the redundant option is selected, only one processor operates at a given time. If the operating micro should
“get lost”, that is, not go through the code string properly in the allotted 250 micro-seconds, its hardware “watch dog”
timer will expire, issue a reset signal, at which time the faulty micro will be disconnected from the system. The redundant
micro will become activated. The microprocessors has eight analogue inputs, thus it inspects the AC input voltage, AC
load voltage, AC output current, AC back-feed current, DC input voltage, DC input current, number of power modules
installed, and number of power modules operating.
4.2 LCD “Display” Panel
The processor front panel, called a “Display” panel has a two line, twenty character “Liquid Crystal Display” (LCD) and
a scroll switch. This will allow the operator to “scroll” through the display for reading the AC input voltage, frequency, AC
load voltage, DC input voltage, DC input current, output watts, percent load (higher of VA or Watts), number of power
modules installed, and number of power modules operating. Each processor has “STATUS” LEDs associated with it,
each LED being tri-colored. One STATUS LED is for Utility power, the other for inverter. Two red “blown fuse” indica-
tors are located on the top right-hand side of the “Display” panel, which give the status of the output filter capacitor fuses.
These LEDs will be illuminated if a fuse is blown. There is a DB-9 connector for the RS-232 communication, and a
master inverter ON/Standby switch. This switch is a rocker switch and is recessed in the front panel so as to require
deliberate action by the operator to turn the system “ON” or to “Standby.