Motor reactors

High-speed switching of the power transistors causes capacitive charge/discharge currents in the motor cable and motor, as well as steep voltage rises and peak voltages in the motor windings. These currents can be reduced through the installation of a motor reactor.

The voltage drop across the motor reactor is normally negligible at output frequencies of 60 Hz and below. The per unit voltage drop u_k across the reactor is between 1 % and 4 % at rated current and 50 Hz. With a cos ? of 0.86 and an output frequency of 50 Hz, the motor voltage across the motor reactor is about 2 % lower than in systems without a motor reactor.

Phasor diagram of motor with motor reactor

Motor reactors are compatible with all modulation types (space vector modulation, edge modulation).

Sine-wave filters

Sine-wave filters are low-pass LC filters which allow easy passage to only the fundamental component of the square-wave, pulse-width-modulation output voltage of a Power Module or Motor Module. The resonant frequency of the sine-wave filter must be significantly lower than the pulse frequency of the Power Module or Motor Module and be dimensioned with a sufficient margin to the maximum permissible output frequency. Sine-wave filters therefore define the choice of pulse frequency and place a limit on the maximum possible output frequency. This type of filter is compatible only with space vector modulation. The output voltage of a Power Module or Motor Module is thus limited to an output voltage (rms value) of approximately 0.67 x DC link voltage. With the voltage drop across the sinusoidal filter, the maximum possible output voltage (rms value) is approximately 0.63 x DC link voltage. Parameters are used to register a sine-wave filter with the Control Unit. This ensures that all those values that are dependent on it, such as permissible modulation modes and maximum output frequency, are correctly predefined.

Sine-wave filters can be used only in conjunction with Vector and V/f Control modes.

Sensor Modules

Signal conditioning for various encoders (incremental encoder sin/cos 1 V_pp, absolute encoder, resolver) takes place remotely, i.e. in the vicinity of the encoder with customized Sensor Modules. Depending on the measuring system, SMC10, SMC20 or SMC30 Sensor Modules will be used. The Sensor Modules are designed to be mounted on DIN rails. They are also used for the signal conditioning of external (machine) encoders.

Expansion modules

The CU320 2 Control Unit features interfaces and terminals for communication as standard. SINAMICS S120 offers the following expansion modules:

• TB30 Terminal Board (terminal expansion for plugging into the option slot on the CU320?2 Control Unit)
• TM31 Terminal Module (terminal expansion for connection via DRIVE?CLiQ)

The following criteria regarding the use of expansion modules must be taken into account:

• Only one option board can be plugged into the option slot on the CU320?2 Control Unit.
• A maximum of 8 Terminal Modules may be operated in a drive line-up.

Braking Modules and braking resistors

Braking units comprise of a Braking Module and a braking resistor, which must be attached externally.

Braking units are used when

• regenerative energy occurs occasionally and briefly, for example when the brake is applied to the drive (EMERGENCY STOP) and the drive has no regenerative feedback capability
• the drive features regenerative feedback units but cannot return the energy fast enough to the supply on an "EMERGENCY STOP"
• the drive needs to be shut down after a power failure

The braking units for Power Modules in blocksize format consist of braking resistors only, as they feature a Braking Module as standard.

A number of Braking Modules can be connected in parallel to the DC link in order to increase the braking power. Each Braking Module requires its own braking resistor. It is not permissible to operate a mix of braking units in booksize and chassis format on the same DC link.

The braking power required is calculated from the DC link power P_d of the drive line-up or Power Module in generator operation.

Braking Modules and braking resistors for booksize format

To operate booksize format Braking Modules, a minimum capacitance is required in the DC link. This capacitance is determined by the braking resistor used.

Braking resistor 0.3 kW/25 kW > DC link capacitance 220 ?F

Braking resistor 1.5 kW/100 kW > DC link capacitance 330 ?F

The capacitance of the booksize format Braking Module of 110 ?F is included in the total capacitance value. If the DC link capacitance is not sufficient for the use of one or more Braking Modules, a Capacitor Module can be added to increase the effective DC link capacitance of the drive line-up.

When booksize format Braking Modules are connected in parallel, the minimum capacitance specified above must be available for each Braking Module.

Note: Only booksize format modules that are directly connected to each other via the DC link busbar can be included in the total capacitance.

If the DC link capacitance is not sufficient for the operation of a number of Braking Modules, Capacitor Modules can be used to increase the DC link capacitance. The max. permissible DC link capacitance of a drive line-up on a Line Module must be taken into account. The max. DC link capacitances to be taken into account for precharging current limiting on the Line Modules are listed in the technical specifications for the Line Modules.

The braking resistor discharges the excess energy from the DC link:

Duty cycle for braking resistors

Braking Modules and braking resistors for chassis format

Braking Modules with a braking power of 25 kW (for type FX) and 50 kW (for types GX, HX and JX) are available with matching braking resistors for chassis format units. Braking units can be connected in parallel to obtain higher braking powers. In this case, the units can be installed at the Line Module end or Motor Module end.

When a Braking Module is installed in a Basic Line Module of size GB, the cables supplied for the DC link connection are too short. In this case, the cable harness set 6SL3366?2NG00?0AA0 must be ordered to make the Braking Module connection.

The Braking Module features an electronics interface (X21) with monitoring function. The braking resistor housing contains a monitoring thermal contact. Both these monitors can be integrated into the warning or shutdown circuits of the drive system.

Calculation of Braking Module and braking resistor requirements

• For periodic duty cycles with a cycle duration of ? 90 s, the average value of the braking power within this duty cycle must be defined. The relevant cycle duration must be applied as the time base.
• For periodic duty cycles with a cycle duration of ? 90 s or for sporadic braking operations, a time interval of 90 s in which the highest average value occurs must be selected. The 90 s period must be applied as the time base.

Apart from the average braking power, the required peak braking power must also be taken into account when braking units are selected (Braking Module and braking resistor).

Basic data

Load diagram

Braking resistors for Power Modules in blocksize format

The braking resistors for the FSA and FSB frame sizes are designed as substructure components. Braking resistors for frame sizes FSC to FSF should be mounted outside the control cabinet due to their high heat losses.

The Control Unit monitors the pulse/pause ratio (ON time/OFF time) of the braking resistor and shuts it down on faults if it calculates that the resistor is at risk of overheating.

Braking resistors feature a temperature switch with NC contacts that open when the permissible temperature is exceeded. The temperature switch must be evaluated to prevent consequential damage if the braking resistor overheats.

The braking power P_mech on the motor shaft is higher than the power loss of the braking resistor, as this only needs to convert the DC link energy into heat.

The DC link power P_d of the Power Module in generator mode is calculated from the shaft power P_mech of the motor and the power loss in the motor P_{v motor} and in the Power Module P_{v Power Module} as:

P_d = P_mech – P_{v motor} – P_{v Power Module} = P_{braking resistor}

The power losses can be estimated from the efficiency values of the motor ?_m and Power Module ?_wr:

P_{braking resistor} = P_d = P_mech ? ?_m ? ?_wr

Booksize format Capacitor Module

The Capacitor Module functions as a short-term energy buffer, e.g. for bridging brief power failures or for storing braking energy. The buffered energy W can be calculated with the following formula:

W = ? ? C ? (V_d1² – V_d2²)

C = effective capacity of Capacitor Module 4 mF

V_d1 = DC link voltage when buffering starts

V_d2 = DC link voltage when buffering ends

Example:

V_d1 = 600 V; V_d2 = 430 V

The resultant energy calculation is W = 350 Ws

With this energy, for example, it is possible to buffer a 3 kW Motor Module for about 100 ms.

Control Supply Module in booksize format

The Control Supply Module provides a 24 V DC power supply via the line or DC link in order to maintain the electronics power supply for the components in the event of a line failure. This makes it possible, for example, to make emergency retraction movements in the event of the failure of the line supply.

External 24 V DC supply of components

Power units (Line Modules and Motor Modules) and other system components must be provided with a 24 V DC voltage via an electronics power supply made available externally.

SITOP devices, which are available as a modular solution, are provided as the external 24 V DC electronics power supply.

Connecting the external electronics power supply

The current requirement I_{DC ext} is calculated with the following formula:

? [Control Unit + built-in options (e.g. TB30 + CBC10) + system components + Line Module + ? (Motor Modules + SMCxx + motor brake control)]

The other system components (e.g. line contactor) must also be taken into account.

The current requirement of individual components can be found in the relevant technical specifications.

Limit values for the configuration:

• The current-carrying capacity of the integrated 24 V DC busbar (featured only in booksize format) is max. 20 A.
• In the event of higher current requirements, a number of 24 V DC power supplies must be provided in one drive line-up. The other infeeds are implemented by means of 24 V terminal adapters (booksize format only).
• Cable cross sections of up to 2.5 mm? may be connected to the Control Units, Terminal Boards, Terminal Modules and Sensor Modules.
• Cable cross sections of up to 6 mm? may be connected to the 24 V terminal adapters (booksize format only) for the Line Modules and Motor Modules.
• The external 24 V DC power supply should only be used for the SINAMICS components and the direct loads.

Capacitors in the electronics supply of most components must be charged when the 24 V DC supply is first switched on. To charge these capacitors, the power supply must first supply a current peak which can be a multiple of the current requirement I_{DC ext} calculated above. Allowance must be made for this current peak when selecting protective elements, e.g. miniature circuit breakers, for incorporation in the 24 V DC supply system (types with let-through I²t values according to characteristic D). The current peak flows for an interval t_e of a few 100 ms. The peak value is determined by the impedance of the 24 V DC supply and its electronically limited maximum current.

Typical waveform of the switch-on current of the external 24 V DC supply