Functions of the closed-loop control in the armature circuit

Speed setpoint

The source of the speed setpoint and additional setpoints can be freely selected by making the appropriate parameter settings:

• Entered using analog values 0 to ± 10 V, 0 to ± 20 mA, 4 to 20 mA
• Entered via the fieldbus interface PROFIBUS, Ethernet interface for PROFINET (optional)
• Via the integrated motorized potentiometer
• Via binectors with the functions: Fixed setpoint, jogging, crawl
• Entered via serial interfaces of the SINAMICS DC MASTER
• Entered via supplementary modules
• The scaling is realized so that 100 % setpoint (formed from the main setpoint and supplementary setpoints) corresponds to the max. motor speed.
• The setpoint can be limited to a min. and max. value via a parameter or connector. Further, additional points are provided in the firmware e.g. in order to be able to enter supplementary setpoints before or after the ramp-function generator. The "setpoint enable function" can be selected using a binector. After a parameterizable filter function (PT1 element), the summed setpoint is transferred to the setpoint input of the speed controller. In this case, the ramp-function generator is also active.

Actual speed

One of four sources can be selected as signal for the speed actual value.

• Analog tachometer
  The voltage of the tachogenerator at the maximum speed can be between 8 and 270 V. Adaptation to the voltage is realized using parameters.
• Pulse encoder
  The pulse encoder type, the number of pulses per revolution and the maximum speed are set using parameters. From the evaluation electronics, the encoder signals (symmetrical: with additional, inverted track, non-symmetrical: referred to ground) can be processed up to a maximum differential voltage of 27 V.
  The rated voltage range (5 or 15 V) for the encoder can be selected using parameters. For a rated voltage of 15 V, the power supply for the pulse encoder can be taken from the DC converter.
  5 V encoders require an external power supply. The pulse encoder is evaluated across the three tracks: Track 1, track 2 and zero mark. However, pulse encoders without zero mark can can also be used. A position actual value can be sensed using the zero mark. The max. frequency of the encoder pulses can be 300 kHz. Pulse encoders with a minimum of 1 024 pulses per revolution are recommended (due to the smooth running property at low speeds).
• Operation without tachometer with closed-loop EMF control
  A speed actual value encoder is not required for the closed-loop EMF control. In this case, the output voltage of the device is measured in the DC converter. The measured armature voltage is compensated by the internal voltage drop across the motor (IR compensation). The level of compensation is automatically determined during the current controller optimization run. The accuracy of this control method, which is defined by the temperature-dependent change in the motor armature circuit resistance, is approximately 5 %. We recommend that the current controller optimization run is repeated when the motor is in the warm operating condition to achieve a higher degree of precision. The closed loop EMF control can be used if the requirements on the precision are not so high, if it is not possible to mount an encoder and the motor is operated in the armature voltage control range.
  Notice: In this mode, EMF-dependent field weakening is not possible.
• Freely selectable speed actual value signal
  For this mode, any connector number can be selected as speed actual value signal. This setting is especially selected if the speed actual value sensing is implemented on a supplementary technology module.
  Before the speed actual value is transferred to the speed controller, it can be smoothed using a parameterizable smoothing element (PT1 element) and two adjustable bandstop filters. Bandstop filters are used primarily for the purpose of filtering out resonant frequencies caused by mechanical resonance. The resonant frequency and the filter quality factor can be set.

Ramp-function generator

When there is a step change in the setpoint applied at its input, the ramp-function generator converts the setpoint into a signal with a steady rate of rise. Ramp-up time and ramp-down time can be selected independently of one another. In addition, the ramp-function generator has initial and final rounding-off (jerk limiting) that are effective at the beginning and end of the ramp-up time.

All of the times for the ramp-function generator can be set independently of one another.

Three parameter sets are available for the ramp-function generator times; these can be selected via binary select inputs or a serial interface (via binectors). The ramp-up function generator parameters can be switched over in operation. In addition, a multiplication factor can be applied to the value of parameter set 1 via a connector (to change the ramp-function generator data via a connector). When entering ramp-function generator times with the value zero, the speed setpoint is directly input into the speed controller.

Speed controller

The speed controller compares the setpoint and actual value of the speed and if there is a deviation, enters an appropriate current setpoint into the current controller (principle: Speed control with lower-level current controller). The speed controller is implemented as PI controller with additional D component that can be selected. Further, a switchable droop function can be parameterized. All of the controller parameters can be adjusted independently of one another. The value for K_p (gain) can be adapted depending on a connector signal (external or internal).

In this case, the P gain of the speed controller can be adapted depending on the speed actual value, current actual value, setpoint-actual value distance or the wound roll diameter. This can be precontrolled in order to achieve a high dynamic performance in the speed control loop. For this purpose, e.g. depending on the friction and the moment of inertia of the drive, a torque setpoint signal can be added after the speed controller. The friction and moment of inertia compensation are determined using an automatic optimization run.

The output quantity of the speed controller can be directly adjusted via parameter after the controller has been enabled.

Depending on the parameterization, the speed controller can be bypassed and the converter controlled either with closed-loop torque or current control. In addition, it is also possible to switch between speed control/torque control in operation using the "leading/following switchover" selection function. The function can be selected as binector using a binary user-assignable terminal or a serial interface. The torque setpoint is input via a selectable connector and can therefore come from an analog user-assignable terminal or via a serial interface.

A limiting controller is active when in the following drive state (torque or current controlled operation). In this case, depending on a speed limit that can be selected using parameters, the limiting controller can intervene in order to prevent the drive accelerating in an uncontrolled fashion. In this case, the drive is limited to an adjustable speed deviation.

Torque limitation

The speed controller output represents the torque setpoint or current setpoint depending on what has been parameterized. In torque-controlled operation, the speed controller output is weighted with the machine flux П† and transferred to a current limiting stage as a current setpoint. Torque control is primarily used in field weakening operation in order to limit the maximum motor torque independent of the speed.

The following functions are available:

• Independent setting of positive and negative torque limits using parameters.
• Switchover of the torque limit using a binector as a function of a parameterizable switchover speed.
• Free input of a torque limit by means of a connector signal, e.g. via an analog input or via serial interface.
• The lowest specified quantity should always be effective as the actual torque limit. Additional torque setpoints can be added after the torque limit.

Current limiting

The current limit that can be adjusted after the torque limit is used to protect the converter and the motor. The lowest specified quantity is always effective as the actual current limit.

The following current limit values can be set:

• Independent setting of positive and negative current limits using parameters (max. motor current setting).
• Free input of a current limit using a connector, e.g. from an analog input or via a serial interface.
• Separate setting of current limit using parameters for stopping and quick stop.
• Speed-dependent current limiting: An automatically initiated, speed-dependent reduction of the current limit at high speeds can be parameterized (commutation limit curve of the motor).
• I²t monitoring of the power section: The thermal state of the thyristors is calculated for all current values. When the thyristor limit temperature is reached, the unit responds as a function of parameter settings, i.e. the converter current is reduced to the rated DC current or the unit is shut down with a fault message. This function is used to protect the thyristors.

Current controller

The current controller is implemented as PI controller with P gain and integral time that can be set independently from one another. The P and I components can also be deactivated (pure P controller or pure I controller). The current actual value is sensed using a current transformer on the three-phase side and is fed to the current controller via a load resistor and rectification after analog-digital conversion. The resolution is 10 bits for the rated current. The current limit output is used as current setpoint.

The current controller output transfers the firing angle to the gating unit - the precontrol function is effective in parallel.

Precontrol

The precontrol in the current control loop improves the dynamic performance of the closed-loop control. This allows rise times of between 6 and 9 ms in the current control loop. The precontrol is effective dependent on the current setpoint and EMF of the motor and ensures - for intermittent and continuous current or when the torque direction is reversed - that the required firing angle is quickly transferred as setpoint to the gating unit.

Auto-reversing module

In conjunction with the current control loop, the auto-reversing module (only for units with four-quadrant drives) ensures the logical sequence of all of the operations and processes required to change the torque direction. The torque direction can also be disabled when required via parameter.

Gating unit

The gating unit generates the firing pulses for the power section thyristors in synchronism with the line supply voltage. The synchronization is independent of the speed and the electronics supply and is sensed at the power section. The timing of the firing pulses is defined by the output values of the current controller and the precontrol. The firing angle limit can be set using parameters.

In a frequency range from 45 to 65 Hz, the gating unit automatically adapts itself to the actual line frequency.

Functions of the closed-loop control in the field circuit

EMF controller

The EMF controller compares the setpoint and actual value of the EMF (induced motor voltage) and enters the setpoint for the field current controller. This therefore permits field weakening control that is dependent on the EMF.
The EMF controller operates as PI controller; P and I components can be adjusted independently of one another and/or the controller can be operated as pure P controller or pure I controller. A precontrol function operates in parallel to the EMF controller. Depending on the speed, it precontrols the field current setpoint using an automatically recorded field characteristic (refer to the optimization runs). There is an adding point after the EMF controller, where the supplementary field current setpoints can be entered either via a connector, via an analog input or a serial interface. The limit is then effective for the field current setpoint. In this case, the field current setpoint can be limited to a minimum and a maximum value that can be set independently from one another. The limit is realized using a parameter or a connector. The minimum for the upper limit or the maximum for the lower limit is effective.

Field current controller

The field current controller is a PI controller - where K_p and T_n can be independently set. It can also be operated as pure P and I controller. A precontrol function operates in parallel to the field current controller. This calculates and sets the firing angle for the field circuit as a function of current setpoint and line supply voltage. The precontrol supports the current controller and ensures that the field circuit has the appropriate dynamic performance.

Gating unit

The gating unit generates the firing pulses for the power section thyristors in synchronism with the line supply voltage in the field circuit. The synchronization is detected in the power section and is therefore independent of the electronics power supply. The timing of the firing pulses is defined by the output values of the current controller and the precontrol. The firing angle limit can be set using parameters. In a frequency range from 45 to 65 Hz, the gating unit automatically adapts itself to the actual line supply voltage.

Communication between drive components

DRIVE-CLiQ

Communication between SINAMICS components is realized using the standard internal SINAMICS interface DRIVE-CLiQ (this is an abbreviation for Drive Component Link with IQ). This couples the Control Unit with the connected drive components (e.g. DC converter, Terminal Modules).

DRIVE-CLiQ provides standard digital interfaces for all SINAMICS drives. This permits modularization of the drive functions and thus increased flexibility for customized solutions (allows power and intelligence to be separated).

The DRIVE-CLiQ hardware is based on the Industrial Ethernet standard and uses twisted-pair cables. The DRIVE-CLiQ line provides the transmit and receive signals and also the 24 V power supply.

Setpoints and actual values, control commands, status feedback signals and electronic rating plate data of the drive components are transferred via DRIVE-CLiQ. Only original Siemens cables must be used for DRIVE-CLiQ cables. As a result of the special transfer and damping properties, only these cables can guarantee that the system functions perfectly.

SINAMICS Link

SINAMICS Link allows data to be directly exchanged between several (2 to 64) Control Units. A higher-level master is not required. The following Control Units support SINAMICS Link:

• CU320-2
• Advanced CUD

In order to use SINAMICS Link, all of the Control Units must be equipped with the CBE20 Communication Board (option G20). For the Advanced CUD, a memory card is also required (options S01, S02). Communication can either be synchronous (only CU320-2) or non-synchronous or a combination of both. Each participant can send and receive up to 16 process data words. For instance, SINAMICS Link can be used for the following applications:

• Torque distribution for n drives
• Setpoint cascade for n drives
• Load distribution of drives coupled through a material web
• Master-slave function for infeed units
• Couplings between SINAMICS units