Everything under control

Increase efficiency, save costs, and avoid wear and tear - frequency converters optimize the operation of electric motors in industrial applications, building technology, and even electric vehicles. But how exactly does a converter work? How can harmonic contamination in the power grid be avoided? And is it even worth purchasing?

Frequency converters are a type of power converter and are capable of converting one electrical characteristic into another. In Germany, alternating current flows through the lines into households at a frequency of 50 hertz and a voltage of 230 volts per phase. In industrial environments, voltages of 400, 500, and 690 volts are used for three-phase consumers. A frequency converter in its widely used form consists of the following components:

• a rectifier, which converts the alternating voltage from the mains connection into direct voltage,
• an intermediate circuit, which smooths and buffers the direct voltage,
• an inverter, which converts the direct voltage back into alternating voltage with the desired properties.

A frequency converter is used to convert an alternating current (AC) voltage via a DC link into another form of AC voltage with a variable frequency or voltage.

Only as fast as necessary

An electric motor runs at a fixed speed when directly connected to the power grid. If, for example, you want to regulate the flow of water in a pipe system pumped by a fixed-speed pump, you can use mechanical throttling via valves. Such systems with electric motors without a frequency converter are therefore comparable to a car that always drives at full throttle, regardless of traffic conditions, and only regulates its speed with the brakes. This type of operation wastes energy and contributes to wear on the motor and other components. By using frequency converters, the power can be adapted to the actual requirements of an application and saves a lot of energy. The motor runs only as fast as necessary.

This allows operators to increase, decrease, or maintain a constant speed at which a motor operates. Frequency converters are thus able to start motors smoothly and avoid sudden stops. In elevators, this function contributes to comfort, while in industrial environments, such as conveyor belts, it is necessary to ensure smooth process flow.

A frequency converter does not need to know the motor's power output, as it primarily regulates the motor's torque and speed. The machine operator or the process control system determines the speed or torque required by a specific application. In a pump, this depends, among other things, on the amount of fluid to be pumped, the pressure, viscosity, or temperature.

Durable, economical, efficient

Frequency converters significantly reduce the energy consumption of the entire application, in some cases by up to 70 percent, which is not only very climate-friendly but also has a positive impact on operating costs. ABB frequency converters are even capable of feeding motor braking energy back into the power grid. In electric cars, this is called recuperation. These devices have recently been certified, allowing them to be used as part of a power generation system, such as a small hydropower plant connected to the public grid. They thus contribute to renewable power generation.

In addition, the smooth start-up of the motor protects the components, prevents wear and unnecessary mechanical stress, and thus ensures a longer service life. A motor that always runs at its limit wears out faster than one that adapts to the respective requirements.

Frequency converters also improve the control of industrial applications. They act like cruise control for industrial plants and automate control. Modern frequency converters not only offer standard setting options but also internal programming options that can be intelligently used for flexible adaptation to changing requirements.

The problem with harmonics

Although the use of frequency converters enables significant energy and cost savings, they can also lead to harmonics in the power grid. Harmonics distort the pure sine wave of the current and thus also the grid voltage. This distortion carries the risk of several negative effects: It can disrupt measuring equipment, cause interference with communications equipment, or even damage sensitive electronic devices. Furthermore, harmonics can, in some cases, cause overheating of cables and transformers.

Over-dimensioning system components to reliably tolerate harmonics is expensive. Instead, the goal should be to achieve low harmonic content to keep the power grid clean and stable. The solution is the use of Ultra-Low Harmonic Drives (ULHD). This type of frequency converter uses a special, modern technology to rectify the voltage instead of a simple diode rectifier. This allows ULHD drives to achieve an exceptionally low harmonic content, up to 97 percent lower than that of conventional frequency converters. ULHD drives thus achieve a total current distortion of typically three percent, which is almost an ideal sinusoidal current that protects the power grid.

Wide range of applications

With harmonics under control, there are virtually no limits to the use of frequency converters. That's why they are installed wherever electric motors are used. And that's more common than you might think. Industrial manufacturing uses frequency converters to better adapt motors to requirements and thus increase system efficiency. Electric motors are used to control conveyor belts, cranes, pumps, and fans, as well as most production machines such as extruders, metal rolling mills, and paper machines.

In building technology, heating, ventilation, and air conditioning systems, as well as fans, pumps, and compressors, are powered by electric motors. Elevators are also electrically powered. The energy sector relies on frequency converters to optimize power generation. In the water industry, they are used in sewage treatment plants, irrigation systems, and water treatment plants.

The transportation sector is also increasingly relying on electric motors. They are installed in vehicles, powering trains, and even ships. With the rise of electromobility, the number of electric motors and thus frequency converters on the roads is also increasing.

Conclusion: Is a frequency converter worthwhile?

Although frequency converters involve an initial investment, they quickly pay for themselves. Especially with high electricity prices, the initial investment pays for itself in a short time. Frequency converters also demonstrate their advantages in applications where motors run at a single speed for extended periods. They ensure smooth start-up, thus protecting the system and extending the service life of components. Frequency converters thus help get the most out of every motor – for as long and as efficiently as possible.