power+: history and evolution

In recent decades, research in the HVAC/R market has focused on the design of units with increasingly high performance, a low environmental impact and optimised energy efficiency. One of the most effective solutions currently available for achieving energy savings in refrigeration systems involves modulating compressor cooling capacity.

This continuous research has led to the adoption of the latest-generation variable-speed compressors, which are no longer equipped with traditional asynchronous AC motors, but rather with more efficient permanent magnet brushless DC motors. Unlike traditional AC motors, DC motors cannot work by simply connecting them to the mains power supply, rather they need a power control device to vary their speed.

Power+ is the CAREL product range designed for driving variable-speed compressors equipped with the latest-generation permanent magnet motors. For almost 10 years, CAREL has been offering its customers one of the best solutions for reducing energy consumption in compressor racks.



Towards the end of 2009, CAREL launched one of the first inverters to be manufactured in Europe for DC compressors, Power+, currently identified as the PSD0 series. At the time, there were four power ranges available: 1ph 230V 12-16 A; 3ph 400V 14-22 A.



Increasing demand and market opportunities, plus the expanding range of DC compressors available, led to the development of a new Power+ inverter platform. CAREL decided to continue investing in variable-speed technology, and the PSD1 series was officially launched in 2014.

PSD1 was designed with special attention to improving the features and extending the power range, thus optimising costs. The PSD1 platform was launched with four main power ranges: 1ph 230V 10 A; 1ph 230V 12-16 A; 3ph 400V 18-24 A; 3ph 400V 35-40.

Complete control of a wide range of DC compressors
Thermodynamic and electrical control of more than 350 compressors. All approved by CAREL and available for immediate selection.

Crankcase heater function
This function keeps the compressor crankcase warm enough to prevent the oil from cooling, eliminating the need for an external heater.



Thanks to the experience acquired with the Power+ PSD0 and PSD1 series products, as well as analysis of market evolutions, in 2018 the new Power+ PSD2 series was launched, boasting innovative features that are unique on the market. The PSD2 series meets the highest energy efficiency standards required by the Ecodesign directive, and the entire series can be configured in terms of mechanical characteristics and refrigerant type, with numerous compressors officially tested in CAREL’s laboratories.

The firmware is certified class B in accordance with EN/UL60730-1, meaning PSD2 offers certified compressor protection, eliminating the need for the external protection devices that are mandatory for units equipped with DC compressors and require 60335-1 certification. PSD2 was developed to meet the most stringent standards for residential applications. Thanks to its innovative features, it quickly became a success across the world, especially on heat pump units.

The PSD2 series is now officially on the market with even more versatile configurability (more than 48 possible versions available for each power range) and in various power ranges: 1ph 230V 12 A; 1ph 230V 15-18 A; 1ph 230V 25-30 A; 3ph 400V 18-24 A; 3ph 400V 35-40 A; 3ph 400V 60 A.

Safety software to protect the compressor
Class B certified software protects the compressor against overload or locked rotor, without requiring additional components.

STO - Safety Torque Off
The STO input can be used to protect the compressor (thermal overload) and the unit (high pressure). “Certification in accordance with EN60335-1 and EN60730-1"

Certification for residential applications
Power+ products are classified as electronic variable-frequency drives, and are therefore certified in accordance with the relevant product standards (EN61800). The units where the drive is installed often need to comply with different regulations relating to the specific application. For this reason, it has been decided to obtain higher-level certification, in accordance with the strictest standards for residential applications, such as EN/UL60730-1.

Residential electromagnetic (EMC) compatibility
The new series has been designed to guarantee the highest electromagnetic compatibility (residential environments) without the use of additional filters. The products have been tested in a sample installation representing a typical refrigeration unit, so as to provide customers detailed installation instructions.