Siemens MASTERDRIVE

Siemens MASTERDRIVES provide an excellent solution for industrial applications worldwide. In addition to standard air cooled units, water cooled versions can be used in areas with high ambient temperature or where external air cooling is unavailable. MASTERDRIVES can be used for variable-speed control on motors rated from 1 to 5,000 HP. MASTERDRIVES are available for all major worldwide 3-phase supply voltages: 380-460, 500-575, and 660-690 volts. The Siemens
MASTERDRIVES can also be referred to by a model series number, 6SE70.




Versions
There are two versions of the MASTERDRIVES product: vector control (VC) and motion control (MC).



Vector Control (VC)
One mode of operation in the MASTERDRIVES is vector control (VC), which is the focus of this part of the course. In the past, the dynamic response of a DC motor was generally considered significantly better than an AC motor. An AC motor, however, is less expensive and requires less maintenance than a DC motor. Using a complex mathematical motor model and proprietary internal computer algorithms vector control is able to exert the necessary control over an AC motor so that its performance is equal to that of a DC motor. Vector control, flux vector, and field orientation are terms that describe this specialized control technique of AC drives.

Vector control drives have 4-quadrant operation and control torque and speed continuously through zero speed, and can hold a motor stationary against an applied torque. Speed control is exact, even with varying loads. Speed control reaction time is ≤ 45 ms without tacho feedback, and ≤ 20 ms with tacho feedback. Maximum torque is available up to base speed. Torque control reaction time is ≤ 10 ms in torque control with feedback.


Motion Control (MC)
A second mode of operation available on the MASTERDRIVES is motion control (MC). Servo drives are designed to operate with a specific motor and are designed to achieve speed precision and fast response to a speed change. Servo applications typically have rapid start-stop cycles, require zero speed holding torque and high accelerating torque from zero speed, and are used positioning applications. In a packaging machine, for example, material may have to start and stop at various positions along a conveyor system.


AC - AC (Converter)
The terms AC - AC and DC - AC refers to hardware methods of configuring MASTERDRIVES. AC - AC in the MASTERDRIVE
VC family refers to a single drive, connected to an AC source, controlling an AC motor, an AC motor with a tacho, or Multimotor applications




DC - AC (Inverter)
The MASTERDRIVE VC can also be configured so that a common DC bus supplies power to several AC inverters.
Common DC bus systems also allow single and Multimotor combinations. This is referred to as DC-AC. An advantage to this system is that energy regenerated by one inverter can be consumed by another inverter on the same bus.




Braking Choices
The dynamics of certain loads require four-quadrant operation. Torque will always act to cause the rotor to run towards synchronous speed. If the synchronous speed is suddenly reduced, negative torque is developed in the motor. This could occur, for example when a stop command is initiated and the drive tries to slow down to bring the motor to a stop. The motor acts like a generator by converting mechanical power from the shaft into electrical power which is returned to the AC Drive. This is known as regeneration, and helps slow the motor. Braking occurs in quadrants II and IV. When equipped with an optional braking unit, Siemens MASTERDRIVEs are capable of four-quadrant operation.



One method of dealing with negative torque and the current it produces is controlled deceleration. Voltage and frequency is reduced gradually until the motor is at stop. This would be similar to slowly removing your foot from the accelerator of a car. Many applications, however, require the motor to stop quicker, and the drive must be capable of handling the excess energy produced by motor when this is done.


Rectifier Regenerative
Front End Another method of dealing with excessive regeneration is with a rectifier regenerative front end. Diodes in the converter section are replaced with SCRs and a second regenerative bridge is added. An SCR functions similarly to a diode rectifier, except that it has a gate lead, which is used to turn the SCR on. This allows the control logic to control when the converter bridge and regen bridge are turned on.





A simplified block diagram provides a clearer view of the regen process. When the motor needs motoring energy to accelerate or maintain speed against the inertia of a load, the converter bridge is turned on. When the motor is in the regenerative mode, it acts like a generator, supplying electrical energy back to the DC link. When the DC link voltage reaches a predetermined level the motoring SCRs are switched off and the regen (generating) SCRs are switched on.





This allows the excess energy to be returned to the AC line in the form of AC current.





ACTIVE FRONT END
An ACTIVE FRONT END (AFE) is another option available to control regenerative voltage. With this option the diodes in the converter bridge are replaced with IGBT modules and a Clean Power Filter. The IGBT, controlled by control logic, operates in both motoring and regenerating modes






Harmonics are created by electronic circuits, such as the nonlinear loads of adjustable speed drives. Harmonics can cause problems to connected loads. The base frequency is said to be the fundamental frequency or first harmonic. Additional harmonics that are superimposed on the fundamental frequency are usually whole number multiples of the first harmonic. The fifth harmonic of a 60 Hz power supply, for example, is 300 Hz (60 x 5).
A distinct advantage of Siemens MASTERDRIVES equipped with AFE and a Clean Power Filter is they are optimally harmonized with each other to eliminate harmonics and provide a clean power supply. In addition, the Siemens AFE allows for capacitive KVAR production which effectively compensates for other inductive loads in an industrial plant. This helps reduce the overall utility bill.

Programming and Operating Sources
Access is gained to the MASTERDRIVE VC for programming operating parameters and motion profiles from the following sources:

Operator Control Panel (OP1S)

Parameterization Unit (PMU)

Various Serial Interfaces
PC Based Software (Simovis)

PMU, OP1S, and HMI Panels
The MASTERDRIVE can be programmed and operated by the PMU, OP1S, or other SIMATIC HMI device such as the TP170A (shown), TP170B, OP27, or MP370.

Parameters, such as ramp times, minimum and maximum frequencies, 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. The TP170A uses a touch-sensitive screen for control and monitoring.
Serial communication is available through RS232 or RS485 connections. The OP1S can be mounted directly on the PMU or up to 200 meters away. An additional 5 volt power supply is required for remote operation over 5 meters. The TP170A is powered from the drive and standard PROFIBUS connections