Specifications

14
JOHNSON CONTROLS
Form 201.28-NM1.EN.PED/CE (0211)
PRODUCT DESCRIPTION
An integral liquid cooled, transistorized, PWM,
Variable Speed Drive (VSD) is controlled by the
chiller microprocessor control panel to start/stop, select
compressors to run, and select compressor speed. Power
Factor is 95% at part or full load.
The chiller microprocessor communicates with the VSD
Logic Board via a 3-wire RS-485 opto coupled data link.
The VSD Logic Board runs the number of compressors
required to meet the load and the compressors to the
speed requested by the chiller microprocessor.
The basic system control and VSD system architecture is
shown in Figure 2.
FIGURE 2 - CHILLER CONTROL SYSTEM
LD15028
INPUTS
Pressure Transducers
Temperature Sensors
Switches
Liquid Flow
High Pressure
Start/Stop
Level
Customer Supplied
Contacts
CONTROL
PANEL
Chiller Control
Board)
Microprocessor
User Interface
Display and
Keypad
DISPLAY
KEYPAD
MOTOR
OUTPUTS
Relay Output Board)
Solenoids
Contactors
Alarm
Pump
Compressor Heater
Run Status
Evaporator Heater
VSD
VSD Logic Board
SCR Trigger Board
Power Components
PWM (Speed Control)
COMMUNICATIONS
Building Automation
Printer Modem
LD15158
3 Phase Power Line
AC/DC Rectifi er
Power Driver
IGBT Gate Driver
VSD Logic Board
Inverter
PWM Signal
Signal From Main Control Panel
Rectifi er
Compressor 1
Compressor 2
Rectifi er Controller
SCR Trigger Board
(IGBT)