IEEE Power Electronics Magazine - June 2015 - 41

power switching function effectively
and efficiently.
Today, PE has outgrown its classic
definition. It has evolved to include just
about all aspects of electrical and electronic engineering, as shown in Figure 1(b). It includes analog and digital
circuits, converter circuits, magnetic
and electric machines, linear and nonlinear control, energy generation and
storage, system engineering and integration, radio-frequency (RF) circuits,
antennas, ICs and monolithic passives,
and power semiconductors and ICs.
Today, PE encompasses the typical
coursework of any electrical and computer engineering program.

Microgrids
A microgrid is an autonomous electric
power subsystem. It can be dc, ac, or
a hybrid of dc and ac. A structured
microgrid is integrated with loads,
energy sources, storage devices, sensors, and data buses, and is an autonomous subsystem that includes the following features:
■■balance of energy over the intended operation and capacity
■■reconfigurability for stand-alone
or grid-connected operation
■■resiliency with fault tolerance and
fault isolation
■■bidirectional power flow
■■modularity and scalability.
There are many benefits that a microgrid can bring to a
user locally. The local benefits of microgrids are as follows:
■■enhanced energy efficiency
■■reduced electricity cost
■■improved power quality
■■greater availability of power (particularly when grid tied)
■■enhanced energy independence
■■combined utility generation (gas, heat, water, and
communication)
■■environmental conservation using renewables locally
■■creation of a natural platform for local generation and
integration
■■resiliency with redundancy and recovery
■■building structure for the next higher-level grid(s).
Microgrids are beneficial to grid operators globally. Microgrids bring benefits globally to the grid by
■■enhancing distributed generation with a high percentage
of renewables
■■enhancing distributed storage
■■accommodating new demand from electric vehicles
■■allowing smart metering to do transactive (dynamic)
pricing
■■enabling local energy management without burdening the
grid bandwidth for communication
■■preprocessing data locally to reduce the required grid
capacity
■■providing predictive local control to enhance grid stability
■■using bidirectional flow to enhance energy availability
to grid
■■providing a balance between the distribution grid and
microgrids
■■using their ability to island.
dC microgrids are particularly advantageous for practice due to their many benefits, which include higher efficiency, more robust system operation, no impedance
matching issues, no synchronization, simple waveforms,
and a large body of knowledge in PE and systems being
directly leveraged. Figure 3 shows an example of a resilient
dc microgrid for mission-critical space applications [2].

Wireless energy
harvesting is a
quintessential example
of the ever-diversifying
technical landscape of
PE as a technology
that crosscuts many
fields of electrical
engineering.

Green Energy System Integration
One of the most significant system applications of PE is
the integration of green energy systems. Figure 2 illustrates the concept of green energy system integration.
Solar and wind energy systems are maturing fast to penetrate deeply into the energy market to provide electricity
for average consumers. The technologies for individual
systems are mature, and recent trends are toward the
integration of solar farms with wind farms, particularly
with offshore wind farms. To transmit the power from offshore to onshore, new high-voltage dc (HVdC) transmission technology has been developed and deployed around
the world. The new technology leverages the recent progress in PE, such as HV IGBTs and multilevel voltagesource converter (VSC) circuit topology. (More details on
multilevel power are given in the "High Power Goes Multilevel" section.)
Relative to wind and solar energy systems, wave and
tidal energy systems are less mature. Except for a few cases of deployments for tidal barrages, they are still in the
demonstration and testing stage. The idea is to leverage
wave and tidal energies to supplement the intermittency
of wind and solar energies. The challenges are in the initial
cost, transmission to shore, and environmental footprint.
PE can help with underwater power converters and subsea
cable for power control and distribution.
A more recent trend in system integration is the development and deployment of energy-storage devices and
resources to enhance system performance, hardware reliability, and power availability. There are many forms
of energy storage being used, such as batteries, pumped
hydro, compressed air, flywheels, hydrogen, fuel cells, and
thermal energy. Once all these technologies are successfully developed, deployed, and integrated, we will have
truly sustainable energy systems for years to come. PE engineers will be the best system integration engineers since
intimate knowledge about the system hardware is essential for the successful integration of any system.

June 2015

z IEEE PowEr ElEctronIcs MagazInE

Table of Contents for the Digital Edition of IEEE Power Electronics Magazine - June 2015