Future Energy Solutions demonstrates micro-inverter reference design at InterSolar 2011
Developed in collaboration with Future Electronics’ franchised suppliers Freescale Semiconductor and Fairchild Semiconductor, the design is a two-stage grid-connected micro-inverter providing high efficiency of up to 95% through the implementation of innovative design features including a sophisticated maximum power point tracking (MPPT) technique.
The system is comprised of two boards: a controller board which features the 16-bit MC56F8257 digital signal controller from Freescale, and an inverter board which includes the DC-DC boost and DC-AC inverter stages and an auxiliary power supply. Customers can use the boards as a development platform to which they can easily add peripheral features such as a display screen, user interface and communications. They can also source the original design files from Future Electronics and modify them freely.
The design has adopted a non-isolating topology consisting of a DC-DC boost stage followed by a DC-AC inverter. Its omission of an isolating transformer, normally found in existing micro-inverter designs, helps to reduce losses markedly during power conversion.
The topology allows only a small 50 Hz ripple current to be reflected back from the 240 V AC load to the PV solar panel. The ripple current and ripple voltage are used to implement a fast MPPT technique called ripple correlation control, which is an effective means for capturing the maximum possible power from the PV solar panel throughout the hours of daylight.
Improvements over conventional micro-inverter designs have addressed durability issues as well as efficacy. The micro-inverter was designed from the outset to achieve long-term reliability both through significant derating of components, and through avoiding the use of life-limited aluminium electrolytic capacitors.
Future Electronics provides the developer with two alternative implementations. The demonstration at InterSolar is of an all-analog implementation, which uses active components from Fairchild, including FCB20N60 ultra-fast switch-off MOSFETs and FAN7393 gate drivers.
On its general release, the reference design will also provide a parallel topology in which the boost stage and inverter stage control and MPPT are implemented in software on the MC56F8257 DSC.
The software-based version allows the designer to take advantage of the many peripheral features integrated into the MC56F8257, which include multiple high-resolution PWM channels, two 8-channel 12-bit ADCs, and support for an OLED display. The version also provides the ability to implement quickly new and improved MPPT algorithms – an important consideration given the rapid evolution that the PV inverter market is experiencing.
A standard 160-way Future-Blox interface connects the control board to the inverter stage.
The Future Electronics micro-inverter reference design is being demonstrated at the Shoals Technologies Group stand at InterSolar (8-10 June), booth C2.148.
Visit Future Electronics at www.futureelectronics.com.
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