Product Overview 1-17
1560D-UM051D-EN-P – February 2005
Hardware Description The following sections contain descriptions of system components and
system operation. Each section will be described to give the user an
understanding of the MV Dialog Plus
TM
to facilitate operation and main-
tenance of the system. Refer to Figure 1.17, Typical MV Dialog Plus
Power System Diagram.
Power Module
The controller consists of three power modules, one for each phase. Each
power module consists of incoming and outgoing terminals for cables, SCRs,
heatsink and clamp assembly. The SCRs are connected in inverse parallel
(and in series for 12- or 18-SCR assemblies) to form a three-phase, AC
line controller configuration.
Each power module includes a snubber circuit to limit the rate of rise in
voltage across each SCR pair. The module also includes patented gate
driver circuits which derive their power from the snubber circuit.
Voltage sharing resistors are connected across each SCR pair to provide
static voltage balance for series-connected SCRs. These resistors are
tapped to provide a reference for overvoltage protection circuitry on the
gate driver board.
A resistive voltage divider is used to reduce the line- and load-side voltages
to lower levels that can be measured by the SMC Dialog Plus™ control
module. The resistors for the top portion of the divider are located on the
Voltage Divider Resistor circuit board, and the bottom portion of the
divider is on the Voltage Feedback circuit board. The latter board provides
the resistor connection to ground, and power Zener diodes (with their own
ground connection) as a protection circuit to prevent high voltages from
entering the control module if a resistor or resistor ground were to open
circuit. The voltage feedback board provides the voltage reference signals
to the interface board for connection to the control module.
Self-Powered Silicon-Controlled Rectifier Gate Driver Board
This board provides the turn-on capability for SCR devices. The board
also provides optical fibre isolation between itself and the gating source
logic. It is powered by recovering energy from the snubber circuit, so it is
fully isolated from the control and logic circuits; it is self-economizing
when the unit is not running, or is in bypass mode.
Note: If pump control or soft stop options are used, the gate driver boards
are powered continuously using separate power supply boards.
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