Intelligent motor regulation
A large proportion of all industrial motors and the methods for controlling them are known to waste energy. Frequency converters for electronic speed regulation are a viable option for activating a considerable level of potential energy savings.
Frequency converters save energy by regulating the motor speed and torque to match the application requirements. This means that the motor consumes only the electrical energy that is required at a given moment.
Soft starterFrequency converter
Cost-effective selection of regulation
Energy-saving and technical optimisation measures are expected to amortise within a reasonable timeframe. It is advisable to limit the measures taken only to those that are essential. That is why we distinguish between three broad scenarios:
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Soft starter
For applications that are always operated with the same load, the motor speed and torque can be selected to match the load, so that the system operates at a very high level of efficiency.
A soft starter increases the service life for the motor and the entire system by protecting against overloads. The soft starter optimises the starting currents, which place a heavy load on the motor in conventional starting methods. The driven units are also protected because there are no peak loads or vibrations due to abrupt starting.
  Schneider Electric, Altistart |   Carlo Gavazzi, RSE4002-B / |   Siemens, Sirius 3RW30, |
Frequency converter
A frequency converter is always absolutely necessary if speed regulation is required, i.e. for conveyor belts, fans, mixers etc.
It is also sensible to use a converter whenever speed regulation can be used to adjust the operating point to the system requirements. A typical example of this is night-time reduction for heaters or for pumps that are dimensioned too large: instead of "pushing the pipe closed" the pump speed is regulated using the frequency converter. This is the better solution in terms of both the energy consumption and the pump lifetime.
Not least importantly, frequency converters also offer the possibility of adjusting a system to the optimal operating point. Example: The energy consumption for pumps or fans increases as the cube of the delivery rate. If the delivery rate is reduced by just a little, the energy consumption decreases at a much higher rate. Since frequency converters have an efficiency considerably greater than 95%, this method amortises itself in a short time.
Recovery of braking energy by DC/DC coupling (Siemens)
  Hitachi NE-S1, 4.0 kWConverter with very fast digital inputs and precise motor regulation. 24 VDC power supply unit for feeding external components. |  Siemens SINAMICS V20Cost-efficient 1-/3-phase converter with analogue and digital inputs/outputs and integrated EMC filter. |   Mitsubishi FR-D740, 5,5 kWConverter with integrated RS485 and USB interfaces, emergency stop function. Parameterisation via PC. |
Side effects
The mode of operation of the converters is usually based on a frequency-modulated square-wave voltage Uout (PWM) in the kilohertz range. A nearly sinusoidal current Iout flows due to induction in the motor. See figure.
In the most unfavourable case, the frequency converter causes undesired interference due to the PWM if not properly installed. These include:
- Circuit feedback due to harmonic waves
- High-frequency interference due to the pulsating switching of the IGBT
- Parasitic earth currents
This interference can propagate by galvanic, inductive or capacitive coupling. Therefore the following principles apply to the operation of frequency converters:
- Ensure generous earthing/equipotential bonding for all components
- Shield the engine supply cable (pay attention to EMC fittings!)
- Filter
