A universal charge controller for integrating distributed energy resources

Centralized electric grids provide power to much of the world's population, yet cost and technical constraints prevent grid extension to 1.2 billion people living without power today. Off-grid and micro-grid power systems are solutions to electrifying remote areas of developing countries. Generally, these systems include a mix of renewables, storage, conventional generation, and demand response or metering, with a wide variety of controllers needed to address the many possible power system configurations and component specifications. Existing low-cost technologies have limited interoperability and flexibility to span the problem space. This paper seeks to address this need and describes the motivation, requirements, specifications, prototyping, and early testing of a Universal Charge Controller (UCC) that integrates with various sources, loads, and storage. The UCC meets load requirements for a household or other small building up to 500W peak load capacity. Power source connections include solar photovoltaics (18-24VDC), battery storage (12-24VDC), an AC micro-grid (110/220VAC), or a DC micro-grid (50-70VDC). This flexibility, combined with intelligent controls, permits the UCC to serve as the keystone in connecting various energy architectures as a community develops over time. The UCC can charge a 12V or 24V Lead Acid or Lithium-Ion battery from one or more sources (current controlled or voltage controlled). Storage charging efficiency is improved with Maximum Power Point Tracking (MPPT) during the conversion of solar power. The accuracy of the design parameters was analyzed by testing different use cases on a commercial development board with results used to refine specifications and schematics of the UCC prototype. Technical specifications and design documentation are in development through an open source partnership with IEEE Smart Village to promote widespread adoption.