Home Energy Storage – Bidirectional Control to Balance Power Transfer

August 21, 2017

The variability of renewable power sources such as solar and wind for home energy means that batteries are needed to balance the system: either storing excess power from the grid or supplying power back to the grid as necessary. As this is an immature market and standards are yet to be set, different grid and battery voltages and AC or DC solutions are being used. However, they all need bidirectional converters to transfer power between the grid and the batteries.

One home energy system manufacturer was looking for a flexible system that could be adapted to provide an optimized solution for different requirements. High efficiency, small size, low cost, and bi-directional power transmission (for both regulation and transformation) were all critical requirements.

Providing bidirectional conversion has traditionally required complex systems that switch between two back-to-back converters. This approach, however, requires one power chain for each direction of energy flow, making the systems less efficient, larger and more expensive.

Home Energy Power System Using BiDirectional Components

Home Energy Power System Using BiDirectional Components (click to enlarge)

The solution chosen by the manufacturer uses Vicor’s bi-directional BCM Bus Converter Module to act as a bridge between the different grid and battery voltages. A BCM provides isolation, and automatically switches between stepping up or down the voltage in a fixed ratio, depending on the direction of energy flow. BCMs therefore act as if they were “DC transformers”. To learn more about the unique reverse mode capability of the BCM, view our on-demand webinar, Enabling Bi-Directional Energy Flow Using DC Power Transformers.

In this specific application, the BCM offers bi-directional transformation and isolation functionality to create a high voltage from a 48V battery. As BCMs are fixed-ratio converters, regulation is needed on the low-voltage side to guarantee that the input voltage of the AC inverter stays within the specified limits. This is achieved by using three PRM regulators in parallel. PRMs can be paralleled easily, without the need for complex additional circuitry, providing flexible and easily scalable regulation.

Combining the bidirectional capability of the BCMs with either a switching matrix around the PRMs or another set of PRMs in the opposite direction enables the system to work in reverse mode and charge the battery from the high-voltage grid.

The small size and the high efficiency of the devices involved enables the integration of the complete solution into a very thin housing, which can be either mounted on or hidden behind walls.

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