UK solar firm discloses novel inverter topology

Cambridge-based solar inverter firm Enecsys has revealed details of its novel power architecture, which eliminates electrolytic capacitors to increase reliability.

The firm's designs are intended to be fixed to the back of solar panels, producing 240V 50Hz directly - called micro-inverters by the solar industry to distinguish then from larger remote-mounted inverters that take power from a string of solar panels.

Direct mounting means micro-inverters have to operate at high ambient temperature, and if they contain electrolytic capacitors, said Enecsys, these will cause the inverter to fail well before the panel's predicted 25 year life.

With a patented topology, the firm has eliminated electrolytics and has instead moved to film capacitors, custom made by for the inverter, with a service life of 200,000 hours at 85°C and rated voltage, Enecsys founder and chief architect Dr Lesley Chisenga told Electronics Weekly, adding: "The various bits of the topology are known. It is the configuration of the three stages that no one has done before."

The first stage is a boost converter that produces a DC link voltage of up to 600V.

This is followed by second stage: a current output buck converter which is tolerant of up to 120V of ripple on its input. "Another aspect of our intellectual property covers the significant ripple capability of the second stage," added Chisenga.

The main energy reservoir capacitor is connected to the 600V DC link, where the high voltage plus the ripple tolerance of the second stage mean that only 30µF is needed to deliver 240W at the output - a value that can be made from film capacitors without resorting to electrolytics.