Balancing safety and cost-effectiveness in solar-power inverter installations

In response to rising fossil fuel costs and environmental concerns, installation rates of solar photovoltaic panels, are rising rapidly. A further factor encouraging PV deployment has been incentives in the form of favorable feed-in tariffs to national grids; almost 99% of the energy produced by solar installations is “grid-connected” via an inverter.  All PV installations demand accurate measurement of generated current, both for efficient control of the inverter, and protection purposes.

Grid-connected inverters may include a transformer to provide galvanic isolation: transformer-less configurations incur a higher risk of leakage to earth. Four main inverter designs are commonly encountered. Two designs use a transformer (at low or high frequency) and two designs are transformer-less; with or without a DC chopper or step-up converter. For cost but also size, efficiency, weight reasons, transformers are less favored for new designs.

This article looks at issues including:

• Maximum power point control, inverter control and protection
• DC current injection measurement
• Leakage current measurement
• Earth fault current measurement
• Closed-loop fluxgate technology
• Standards compliance

To read the article in its entirety, which originally appeared in EE Times Europe (Power Management), click here.

About the authors
Bernard Richard is Business Development Manager, Renewable Energy and Power Supply; Claude Gudel is Research & Development Senior Engineer; and Stéphane Rollier is Product and MarCom Manager, all at LEM (Geneva, Switzerland), a vendor of current and voltage transducers  (http://www.lem.com).