FTM Board Club
Future Electronics
MICRO-INV-FBLOX
PV Micro-inverter board

In present PV Solar installations one large central inverter sources AC mains from a range of PV solar panels and tracks Maximum Power Point (MPPT) across the array of PV Solar panels.

Using the centralised inverter methodology one mismatched or degraded panel can dictate the overall system performance. Microinverters, which convert DC to AC mains for individual or small numbers of PV solar panels, can circumvent this potential problem by performing MPPT locally.

The Future designed 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. Designers 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.

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 50Hz ripple current to be reflected back from the 240V 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.

The design provides the developer with two alternative implementations:
1) an all-analogue implementation, which uses active components from Fairchild, including FCB20N60 ultra-fast switch-off MOSFETs and FAN7393 gate drivers.

2) A parallel topology in which the boost stage and inverter stage control and MPPT are implemented in software on the MC56F8257 DSC.

This 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. It 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.

Features
  • Solar PV panel output to AC mains conversion efficiency of 94%
  • Maximum Power: 200W
  • Solar PV panel voltage range: 31V to 65V (typically 60 to 72 cell size panels)
  • MPPT tracking
    Wireless and power line modem plug-in
  • Non-isolated configuration
  • 220V-240Vac mains output, 200W maximum