SIMOREG 6RA70 Siemens DC Master Variable Speed DC Drive
Design & Mode of Operation
Closed-Loop Functions in Armature Circuit
Design and Mode of Operation
Closed-loop functions in armature circuit
Speed setpoint
The source for the speed setpoint and additional setpoints can be freely
selected through parameter settings, I.e. the setpoint source can be programmed
as:
- Analog values 0 to +10 V, 0 to +20 mA, 4 to 20 mA
- Integrated motorized potentiometer
- Binectors with functions:
Fixed setpoint, inch, crawl
- Serial interfaces on basic unit
- Supplementary boards
The normalization is such that 100 % setpoint (product of main setpoint and additional
setpoints) corresponds to the maximum motor speed.
The speed setpoint can be limited to a minimum or maximum value by means of a
parameter setting or connector. Furthermore, "adding points" are included in the
software to allow, for example, additional setpoints to be injected before or after the
ramp-function generator. The "Setpoint enable" function can be selected with a
binector. After smoothing by a parameterizable filter (PT1 element), the total setpoint
is transferred to the setpoint input of the speed controller. The ramp-function generator is
effective at the same time.
Actual speed value
One of four sources can be selected as the actual speed signal.
- Analog tachometer
The voltage of the tacho-generator at maximum speed can be between 8 and 270 V. The
voltage/maximum speed normalization is set in a parameter.
- Pulse encoder
The type of pulse encoder, the number of marks per revolution and the maximum speed
are set via parameters. The evaluation electronics are capable of processing encoder
signals (symmetrical: With additional inverted track or asymmetrical: Referred to
ground) up to a maximum differential voltage of 27 V.
The rated voltage range (5 V or 15 V) for the encoder is set in a parameter.
With a rated voltage of 15 V, the SIMOREG converter can supply the voltage for
the pulse encoder. 5 V encoders require an external supply. The pulse encoder
is evaluated on the basis of three tracks, i.e. track 1, track 2 and zero marker.
Pulse encoders without a zero marker may also be installed. The zero marker allows an actual position to be acquired. The maximum frequency of the encoder
signals must not exceed 300 kHz. Pulse encoders with at least 1 024 pulses per
revolution are recommended (to ensure smooth running at low speeds).
- Operation without tachometer and with closed-loop EMF control
No actual-value sensor is needed if the closed-loop EMF control function is employed. Instead, the
converter output voltage is measured in the SIMOREG. The measured armature voltage is compensated by
the internal voltage drop in the motor (I*R compensation). The degree of compensation is automatically
determined during the current controller optimization run. The accuracy of this
control method is determined by the temperature-dependent change in resistance in the motor armature circuit and equals
approximately 5 %. In order to achieve greater accuracy, it is advisable to repeat the current controller
optimization run when the motor is warm. Closed-loop EMF control can be employed if the accuracy
requirements are not particularly high, if there is no possibility of installing an encoder and if the motor is
operated in the armature voltage control range.
Caution: The drive cannot be operated in EMF-dependent field- weakening mode
when this control method is employed.
- Freely selectable actual speed signal
Any connector number can be selected as the actual speed signal for this operating mode. This setting is
selected in most cases if the actual speed sensor is implemented on a technological supplementary board.
Before the actual speed value is transferred to the speed controller, it can be smoothed by means of a
parameterizable smoothing (PT1 element) and two adjustable band filters. The
band filters are mostly used in order to filter out resonant frequencies caused by
mechanical resonance. The resonant frequency and filter quality can be selected.
Ramp-function generator
The ramp-function generator converts the specified setpoint after a step change into a
setpoint signal that changes constantly over time. Ramp-up and ramp-down times can
be set independently of one another. The ramp-function generator also features a lower
and upper transition rounding (jerk limitation) which take effect at the beginning and
end of the ramp time respectively.
All time settings for the ramp-function generator are mutually independent.
3 parameter sets are provided for the ramp-function generator times. These can be
selected via binary selectable inputs or a serial interface (via binectors). The generator
parameters can be switched over while the drive is in operation. The value of parameter set 1 can also be
weighted multiplicatively via a connector (in order to change generator data by means of a connector).
When ramp-function generator time settings of zero are entered, the speed setpoint is applied directly to the speed
controller.
Speed controller
The speed controller compares the speed setpoint and actual value and, if these two
quantities deviate, applies a corresponding current set point to the current controller
(operating principle: Closed-loop speed control with subordinate current controller). The
speed controller is a PI controller with additional selectable 0 component. A switchable
speed droop can also be parameterized. All controller characteristics can be set
independently of one another. The value of Kp (gain) can be adapted as the function of
a connector signal (external or internal).
The P gain of the speed controller can be adapted as a function of actual speed,
actual current, setpoint/actual value deviation or winding diameter.
To achieve a better dynamic
response in the speed control
loop, a feedforward control
function can be applied by, for
example, adding a torque setpoint quantity after the
controller as a function of friction or drive moment of inertia. The friction and moment of
inertia compensation values can
be calculated in an automatic
optimization run.
The output quantity of the
speed controller directly after
enabling can be set via a parameter.
Depending on how parameters
are set, the speed controller
can be bypassed and the converter operated under torque
or current control. Furthermore,
it is possible to switch between
closed-loop speed control/closed-loop torque control in
operation by means of selection function "Master/slave
switch-over". The function can be selected as a binary assignable-function terminal or a
serial interface. The torque setpoint is applied by
means of a selectable connector and can thus be supplied by an analog assignable-function terminal or a serial interface.
In "slave drive" operation (under torque or current control), a limiting controller is
active. Here, the limiting controller can intervene on the basis of an adjustable,
parameterized speed limit in order to prevent the drive from accelerating too far. In
this case, the drive is limited to an adjustable speed deviation.
Torque limitation
Dependlng on parameterization, the speed controller output acts as either the torque setpoint or current setpoint. In
closed-loop torque control mode, the speed controller output is weighted with machine
flux F and then transferred as a current setpolnt to the current limitation. Torque-control mode
is mostly used in conjunction field weakening so that the maximum motor torque can be
limited Independently of speed.
The following functions are available:
- Independent setting of positlve and negative torque limits via parameters.
- Switchover of torque limit via binector as a function of a parameterizable
changeover speed.
- Free input of torque limit by means of a connector, e.g. via analog input or serial interface.
The lowest input quantity is always applied as the current torque limit. Additional torque
setpoints can be added after the torque limit.
Current limitation
The purpose of the current limitation set after the torque limit is to protect the
converter and motor. The lowest input quantity is always applied as the current limit.
The following current limit values can be set:
- Independent setting of positive and negative current limits via parameters (setting of maximum motor current).
- Free input of current limit via a connector, e.g. from an analog input or serial interface.
- Separate setting of current limit via parameters for shutdown and fast stop.
- Speed-dependent current limitation: Parameters can be set to implement an automatically triggered, speed-dependent reduction in the current limitation at high speeds (commutation limit curve of motor).
- I2t monitoring of power section: The temperature of the thyristors is calculated for all current values. When the thyristor limit temperature is reached, the
converter current is either reduced to rated DC current or the converter shut
down with fault message, depending on how the appropriate response parameter is set. This function is provided to protect the
thyristors.
Current controller
The current controller is a PI controller with mutually independent P gain and reset time
settings. The P or I component can also be deactivated (to obtain pure P controller or
pure I controller). The actual current is acquired on the three-phase AC side by means
of current transformers and applied to the current controller after A/D conversion via a
burden and rectifying circuit. The resolution is 10 bits for converter rated current. The
current limiting output is applied as the current setpoint.
The current controller output transfers the firing angle to the gating unit, the
feedforward control function acts in parallel.
Feedforward control
The feedforward control function in the current control loop improves the dynamic
response of the control, allowing rise times of between 6 and 9 ms to be achieved in
the current controlloop. The feedforward control operates as a function of the current
setpoint and motor EMF and ensures that the necessary firing angle is transferred
speedily to the gating unit, in both intermittent and continuous DC operation or when
the torque direction is reversed.
Auto-reversing module
The auto-reversing module (only on converters for fourquadrant drives) acts in
conjunction with the current control loop to define the logical sequence of all processes
required to reverse the torque direction. One torque direction can be disabled by a
parameter setting if necessary.
Gating unit
The gating unit generates the gate pulses for the power section thyristors in
synchronism with the line voltage. Synchronization is implemented independently of the
rotating field and electronics supply and is measured on the power section. The gating
pulse position timing is determined by the output values of the current controller and
feedforward control. The firing angle setting limit can be set in a parameter.
The gating unit is automatically adjusted to the connected line frequency within a frequency range
of 45 to 65 Hz.
Siemens Energy & Automation
SIMOREG DC Master Base Drive Operating Instructions
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