e components is accomplished with
electronic hardware and technology software.
Speed Control with
Speed control is one mode of MASTER-Electronics/' >operation. The drive will attempt
CEMF Feedback
to maintain a constant speed regardless of the loads torque. A
speed reference is input into a ramp function generator which
applies reference voltage to the speed controller over a
specified period of time. This allows a smoother acceleration of
the motor and connected load. The output of the speed
controller is routed to the firing circuit, which controls the
amount of voltage applied to the armature.
You will recall that V
a
(applied voltage) = I
a
R
a
+ CEMF. I
a
R
a
is
proportional to load and is generally 10% of nameplate
armature voltage at 100% load. Therefore, as load torque/
current varies between 0 and 100%, I
a
R
a
varies from 0 to 50
VDC for a 500 VDC armature.
V
a
and I
a
are constantly monitored. R
a
is measured during the
comissioning and tuning of the drive. Because V
a
, I
a
, and R
a
are
known values, CEMF (E
a
) can be precisely calculated. CEMF is
proportional to speed and the speed controller uses this value
to calculate actual speed. Speed control with CEMF feedback
can only be used on applications where the motor operates
between zero and base speed. CEMF feedback provides
approximately 2-5% speed regulation. 55
Speed Control with
A tachometer can be used when a more accurate
Tach Feedback
measurement of speed is needed, or when the motor will be
operated above base speed. A measurement of actual speed is
returned to the speed controller. The speed controller will make
armature voltage adjustments to maintain constant speed with
variations in load. If, for example, load is suddenly increased the
motor will slow, reducing speed feedback. The speed controller
will output a higher signal to the current controller, which will
increase the firing angle of the firing circuit. The resulting
increased armature voltage applies more torque to the motor to
offset the increased load. Motor speed will increase until it is
equal with the speed reference setpoint.
When the motor is rotating faster than desired speed armature
voltage is reduced. In a four-quad drive DC armature voltage
could momentarily be reversed to slow the motor at a faster
rate to the desired speed. Several tachs can be used with the
SIMOREG 6RA70. DC tachs can provide approximately 0.10 to
2% regulation. Digital (pulse) tachs can provide approximately
0.10 to 0.25% regulation. These values vary depending on the
tach and the operating conditions. 56
Current Measurement
The drive monitors current, which is summed with the speed
control signal at the current controller. The drive acts to
maintain current at or below rated current by reducing armature
voltage if necessary. This results in a corresponding reduction in
speed until the cause of the overcurrent is removed.
Torque Control
Some applications require the motor to operate with a specific
torque regardless of speed. The outer loop (speed feedback) is
removed and a torque reference is input. The current controller
is effectively a torque controller because torque is directly
proportional to current. 57
Tuning the Drive
A feature of the SIMOREG 6RA70 DC MASTER is the ability to
self tune for a given motor and associated load. An improperly
tuned control may result in an excessive speed overshoot
when changing from one speed to another. Oscillations can
occur which contribute to system instability.
A properly tuned drive will have an initial overshoot of
approximately 43% and settle into a new speed quickly. This
provides a stable system with quick response.
The SIMOREG 6RA70 DC MASTER has three self-tuning
routines to match the performance of the drive to the
controlled motor and associated load. Armature Tuning tunes the drive to the motor
characteristics Speed Tuning tunes the drive to the connected load CEMF Tuning tunes the drive for field weakening 58
CUD1 Board
The CUD1 board is the main control board for the SIMOREG
6RA70. This board contains the necessary software and
hardware interfaces for operating the drive in speed or torque
control. It has input and output connections for wiring the
control devices of various functions such as start/stop
pushbuttons and speed potentiometer. The CUD1 board has
comprehensive diagnostics for troubleshooting. CUD1 also
contains the necessary software for self-tuning.
Programmable binary outputs, used to indicate the condition of
the drive, are available on X171. Binary inputs are also available
to start and stop the drive on X171. In addition, there are two
programmable binary inputs for such functions as reverse and
jog. The 6RA70 accepts analog inputs for speed control on
X174. Programmable analog outputs on X175 provide meter
indication of various drive parameters such as current and
voltage. A motor temperature switch can be connected to X174
and is used to stop the drive if the motor becomes overheated.
Connections are also available on X173 for a digital tach. 59
Typical Connections
The following diagram shows a typical connection used to
operate the drive. A normally open (NO) contact is used to start
and stop the drive.
Alternately, pushbuttons can be used to start and stop the
drive. 60
Programming and
SIMOREG 6RA70 drives can be programmed and operated
Operating Sources
from various sources, such as the PMU, OP1S, or other
SIMATIC® HMI device such as the TP170A, TP170B, OP27, or
MP370. In addition to these, various methods of serial
communication is available through RS232 or RS485
connections. These will be discussed later in this section with
the option boards.
The PMU can be used alone or with the OP1S. The OP1S can
be mounted directly on the PMU or up to 200 meters away
with an external power supply. Parameters, such as ramp
times, minimum and maximum speed, and modes of operation
are easily set. The changeover key (P) toggles the display
between a parameter number and the value of the parameter.
The up and down pushbuttons scroll through parameters and
are used to select a parameter value, once the P key sets the
parameter. The OP1S has a numbered key pad for direct entry.
SIMATIC HMI Devices
Another, more robust option, is a SIMATIC HMI device such as
the TP170A. The TP170A uses a touch-sensitive screen for
control and monitoring. It is powered from the drive and
standard PROFIBUS connections. 61
CUD2 Expansion Board
The CUD2 is typically selected when additional inputs and
outputs (I/O) are required. CUD2 I/O is selectable. An
advantage to the CUD2 expansion board is that it mounts
directly on the CUD1 and requires no additional hardware. The
CUD2 provides four optically isolated binary inputs, four
selectable binary inputs to ground, two analog inputs, one
analog input for motor temperature evaluation, two binary
outputs, and one serial interface. In addition to the expanded
I/O, the CUD2 provides a parallel interface for paralleling up to
six power modules. 62
EB1 and EB2
EB1 and EB2 are half-sized expansion boards that provide a
Expansion Boards
number of additional I/O possibilities. EB1 has three binary
inputs and four bidirectional binary I/O. Bidirectional I/O can be
configured as a binary input or output. One of the analog inputs
is used as a voltage or current reference input. Two of the
analog inputs can also be configured as binary inputs.
EB2 has two binary inputs, one analog input, one analog
output, and four relay contacts. Three of the contacts are
normally open (NO) and one of the contacts can be configured
as normally open (NO) or normally closed (NC).
T400 Technology Board
The T400 is an option board that is used to provide specialized
features for applications, such as winders, tension control,
position control, and hoisting gear. In addition to applying
built-in technology functions, users familiar with the Siemens
PLC software SIMATIC STEP-7 can also implement their own
process functions.
To implement the various control functions required by specific
applications the T400 has two analog outputs, five analog
inputs, two binary outputs, eight binary inputs, four bidirectional
binary inputs/outputs, two incremental encoder inputs, and two
serial interfaces.
I/O
CUD2
EB1
EB2
Isolated Binary Inputs
4
0
0
Binary Inputs
4
3
2
Bidirectional Binary I/O
0
4
0
Analog Inputs
2
3
1
Analog Outputs
2
2
1
Relay (Binary) Outputs
2
0
4
Serial Interface
1
0
0
Parallel Converter Interface
1
0
0 63
Communications
One of the strong points of the SIMOREG 6RA70 is its serial
interface capabilities, which makes it easy to integrate the
drive with other automation components. Communication
options are available for PROFIBUS-DP, SIMOLINK®, CAN, and
DeviceNet communications.
SLB
The SLB communication board is used for peer-to-peer
communication with other Siemens drives via SIMOLINK.
SIMOLINK is a high speed fiber optic ring bus that allows
various data to be passed from one drive to the next.
Communication is not limited to the SIMOREG 6RA70.
SIMOLINK can also communicate between Siemens AC drives
such as the MASTERDRIVE MC and MASTERDRIVE VC.
CBP2
PROFIBUS-DP is an open bus standard for a wide range of
applications in various manufacturing and automation
applications. Siemens DC drives can easily communicate with
other control devices such as p