IEEE Electrification Magazine - June 2017 - 29

is critical to the economic benefits analysis and reliable operation of these systems. This article introduces
microgrid development in China and proposes a rule
for renewable energy and energy storage capacity
configuration in isolated microgrids.

Microgrids in China
Microgrid technology is quickly developing in China. By
the end of 2016, there were more than 100 put into operation there, including on-grid and isolated microgrids.
The capacities of these microgrid projects range from several kilowatts to dozens of megawatts. The microgrids'
voltage levels include 220 V, 380 V, 10 kV, and 35 kV. The
typical application scenarios cover areas such as residential housing, commercial buildings, schools and other
public buildings, islands, commercial and industrial
parks, towns, industrial factories, and laboratories of universities and institutes. All of these microgrids contain
energy storage batteries and renewable energy generation, such as PV and wind units. Some microgrids also
include gas or diesel units. Table 1 shows some large or
typical microgrids in China.

Project 1: Hybrid PV Energy
Storage Isolated Microgrid
A hybrid PV energy storage isolated microgrid, which
includes 3.087-MW peak PVs, 1.2-MWh lithium iron phosphate batteries, and 4-MWh lead-acid batteries (Figures 1
and 2), is located in Yanglong Town, Qilian County, Qinghai Province, China. This area is far away from an existing
power system, so this is an isolated microgrid. PVs and
energy storage are installed centrally and supply the electrical power to the residential and mining industrial loads
through 10-kV transmission lines.

Project 2: Hybrid PV Wind Energy
Storage On-Grid Microgrid

IMAGE COURTESY OF HU XIE, SHU ZHENG, AND MING NI

and the microgrid control system is complicated, so economic and stability control issues have restricted the development of a large-scale isolated microgrid.
The energy storage system can improve the inertia
of the system and stabilize the system after disturbance, but its cost is high. Renewable energy has the
same economic issue, together with the operation
issue (intermittent and uncertain). Therefore, optimal
configuration of the capacities of the renewable energy
resources and energy storage in the isolated microgrid

This microgrid, which includes 1.5-MW wind power,
300-kW peak PVs, 2-MWh lead-acid batteries, and 500-kW
supercapacitors, is located in Dongtou Town, Zhejiang
Province, China (Figures 3 and 4). PVs and energy storage
are centrally installed, and wind units are connected to
the 10-kV buses in the microgrid. These resources supply
electrical power to the island load through 10-kV transmission lines. The microgrid connects to the mainland
power system through two 10-kV submarine cables. When
the mainland power system runs normally, the microgrid
is in on-grid mode. If the mainland power system cannot
supply power to the island due to maintenance or failure,
the microgrid is switched to off-grid mode. This system
can seamlessly switch between on-grid and off-grid
modes under all working conditions.
All microgrids contain renewable energy and energy
storage. How the capacity of renewable energy and energy
storage is configured will have great influence on the
reliable and economic operation of the microgrid.
IEEE Electrific ation Magazine / j une 2 0 1 7

Table of Contents for the Digital Edition of IEEE Electrification Magazine - June 2017