Ask ten industrial engineers what a frequency converter is and nine will think of a variable frequency drive (VFD). They are not wrong: VFDs are ubiquitous in industry for controlling the speed of electric motors. But there is a category of frequency converter that goes unnoticed and solves a completely different problem: fixed-frequency AC/AC converters.

An AC/AC converter takes alternating current at one frequency and voltage and converts it into alternating current at another frequency and voltage. No moving parts, no mechanical wear, with efficiencies of 92–96%. And it solves problems that cost companies tens of thousands of euros every year.

The problem: a world divided between 50 Hz and 60 Hz

The world operates on two main grid frequencies. Europe, most of Asia, Africa and South America use 50 Hz. North America, part of South America, South Korea, Saudi Arabia and several other countries use 60 Hz. This division is not an academic detail: it is a real operational problem.

A three-phase induction motor designed for 50 Hz / 400 Vac will run 20% faster if connected directly to a 60 Hz grid. Torque curves change. Cooling capacity is reduced. In compressors, pumps and machine tools, this can mean anything from reduced performance to mechanical failure.

Applications where AC/AC is essential

Export manufacturing

A Spanish company builds industrial equipment for 50 Hz. It wins a contract in the United States, Saudi Arabia or Mexico. Instead of redesigning the machine (cost: EUR 15,000–75,000 per model), it installs a frequency converter between the local grid and the machine. The machine receives 50 Hz / 400 Vac as if it were in Spain.

Railway

Train HVAC compressors are designed for a specific frequency. When the train runs under different catenary systems or crosses borders, the available frequency may change. An AC/AC converter ensures that the compressor always operates at its design frequency. Premium supplies AC/AC converters that perform exactly this function on high-speed trains.

Marine

A ship built in Europe (50 Hz) docks at a port in the United States (60 Hz). Without frequency conversion, motors, galley equipment and air conditioning run out of specification or simply fail. An on-board AC/AC converter eliminates the problem.

Industry

Machinery imported from countries with a different frequency, test laboratories that need to simulate the conditions of another frequency, frequency-sensitive process equipment.

Why a VFD is not the solution

If a VFD can vary the frequency, it seems logical to use it as a fixed converter. But a VFD produces a PWM waveform, not a clean sine wave. For motors (inductive loads) this is acceptable, because the motor filters the waveform. For transformers, resistors, electronics and mixed loads, harmonic distortion causes problems: overheating, interference and erratic operation.

A dedicated AC/AC converter includes an output filter that produces a true sine wave with THD below 3%. It is compatible with any type of load: motors, transformers, resistive heaters, electronics and lighting.

From Barcelona, from 1 kW to 72 kW

We manufacture AC/AC frequency converters at our plant in Barcelona, with power ratings from 1 kW to 72 kW. Our platforms are EN 50155 certified for railway applications and designed for demanding industrial environments. From AC/AC converters in service on regional trains in northern Europe to those powering HVAC compressors on high-speed trains, we have real production experience in the most demanding applications.

If you have an application that requires frequency conversion, we can probably solve it with an existing platform configuration, without the cost or lead time of a fully custom design.

About Premium SA — Founded in Barcelona in 1981, Premium SA designs and manufactures custom power converters for railway, industrial, energy and defence applications, with over 40 years of experience.