Rockwell Automation MinPak Plus DC Drive User Manual - Manual (Page 70)

C:2
The relative timing of the gate pulse with respect to the AĆC plant supply will determine the conduction angle - that
is, relative conduction time - of the thyristor and of the bridge. Thus the average DĆC output voltage from the bridge
to the motor armature is controlled.
Firing the thyristor gates early in the positive halfĆcycle of the incoming sinusoid allows it to conduct for a relatively
long time until commutated off by the line. This produces low values of average DĆC output voltage to the motor
armature.
The power modules rated at
1 /
4
thru 3 HP use a single discrete Power Cube which contains 4 SCRs. Power modules
rated at 5 HP use 2 Power Cubes each containing 2 SCRs.
The mechanical design of the MinPak Plus Power Cube provides excellent heatĆtransfer characteristics. Because of
its modular design, the small unit is easily replaced.
Gating Sequence, Current Flow - The basic fullĆwave, fullĆcontrol rectifier bridge is shown in Figure CĆ1. When L1
(181) is positive with respect to L2 (182), current flows through thyristor No. 3, on through the motor armature, and,
when the gates to thyristors No. 3 and 2 are gated ON, through thyristor No. 2.
Conversely, when L2 (182) is positive with respect to L1 (181), current flows through thyristor No. 4, on through the
motor armature, and to thyristor No. 1 when the gates to thyristors No. 4 and 1 are gated ON.
A unique Reliance circuit prevents both sets of thyristors - No. 3 and 2 and No. 4 and 1 - from being gated ON at
the same time. This guards against a short circuit.
Peak operating overloads such as those experienced on acceleration, shock loading, etc., are guarded against by a
fastĆacting, currentĆlimiting circuit in the regulator.
Transient Protection - The controller's internal Power Cube thyristors are protected from AĆC line voltage surges by
a metal oxide varistor (MOV) surge suppressor connected directly across the AĆC line. (Refer to Figure CĆ1). The
MOV is available as a replaceable module in case its energy absorption rating is exceeded. An RĆC network is
connected across the DĆC output of the Power Cube. (Refer to Figure CĆ1) This network prevents ringing" in the
armature circuit caused by various motors and DĆC line voltage spikes.
Field Supply - The optional Field Supply Kit is available for use with MinPak Plus controllers used with motors rated
at 1 /
4
thru 5 HP. The Kit is standard on controllers for 3 - 5 HP applications.
The Field Supply is a constantĆpotential rectifier consisting of 4 diodes. This supply provides 50 or 100 VDC from a
115 VAC power source. It also provides 100 or 200 VDC from a 230 VAC power source.
The Field Supply is protected by the MOV surge suppressor.
Regulator Module - The Regulator Module, a standard component of each MinPak Plus controller, is discussed
with respect to functions and descriptions.
The Regulator Module provides major and minor loop regulation, thyristor gate firing and sequencing. It also
provides protective functions for the 4 thyristor power modules.
The Regulator Module provides the following basic functions:
D Major loop armature voltage regulation, or speed (tachometer) regulation, or counter EMF regulation
D Linear reference timing for controlled acceleration and deceleration
D Current minor loop regulator
D Thyristor gate driver circuits
D Isolated armature voltage feedback
D Rectifier and scaling resistors for isolated current transformer inputs to provide current feedback
D Start, stop, jog sequencing
D PowerĆup and powerĆdown sequencing
Description - The Regulator Module is a printed circuit board which occupies approximately half of the MinPak Plus
controller's Chassis. Directly behind it there is an isolation transformer which supplies isolated, lowĆvoltage AĆC
power to the Regulator Module power supplies.