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Z. Lu and G. Zhu
distribution networks in terms of distributed new energy access, diversification of
load and power demand, stability and economic efficiency of power supply, etc.
As urban planning has been detached from power system planning in China, the
distribution network structure is not fully aligned with load development, so the
planning and development of distribution networks and power quality increasingly
fall short of the demand of urban development (Liu et al. 2015).
DC power grids have been mainly built on the flexible DC transmission technology. Compared with conventional DC transmission, flexible transmission requires
no commutation voltage from the AC grid, and thus is highly suitable for such
scenarios as isolated power supply, access to renewable power, capacity expansion
and renovation in cities. In the technical report of the CIGRE working group B4.52,
DC power grid is defined as a direct current network composed of a radial network
of converters. DC grid is characterized by higher redundancy and more flexible and
diversified operation than traditional flexible DC transmission (Boroyevich et al.
2010).
Different from AC distribution grid, power load of DC distribution grid is supplied
by DC bus, which requires no extra rectifier equipment for power supply when applied
to settings with large DC load, demonstrating greater advantages of application. DC
distribution network features minor line loss, high reliability and strong access to
distributed power supply with no need for phase-frequency control (Sun et al. 2016).
The basic topological structure of DC distribution network includes ring, radial and
two-terminal distribution, etc. Power supply of radial network is less reliable, but
is much easier for control and protection; while that of ring network enjoys high
reliability, but lacks control and protection.
Existing DC power distribution systems, such as the SBN (Sustainable Building
and NanoGrids) (Marquardt 2011) proposed by Virginia Tech University of United
States, adopt two voltage classes of 380 and 48 V to form a radial topology. The
FREEDM (Future Renewable Electric Energy Delivery and Management) system
brought up by North Carolina State University is a plug-and-play radial network
(Marquardt 2011). At present, DC power distribution networks have been applied
in communication power distribution, vessel power distribution and subway electric
traction, etc., but the application of ring network has been a rarity, and no standards have been formulated for the selection of voltage class for corresponding DC
distribution network.
On the whole, technologies for the planning and application, scheduling and
control, safe operation and protection of DC distribution network are not yet mature.
But with the cost reduction of power electronic devices, development and application
of DC circuit breakers, flexible access of distributed energy, and fault current limits
of the network, DC distribution network will promise a brighter prospect for adoption
(Yan et al. 2019).
Z. Lu and G. Zhu
distribution networks in terms of distributed new energy access, diversification of
load and power demand, stability and economic efficiency of power supply, etc.
As urban planning has been detached from power system planning in China, the
distribution network structure is not fully aligned with load development, so the
planning and development of distribution networks and power quality increasingly
fall short of the demand of urban development (Liu et al. 2015).
DC power grids have been mainly built on the flexible DC transmission technology. Compared with conventional DC transmission, flexible transmission requires
no commutation voltage from the AC grid, and thus is highly suitable for such
scenarios as isolated power supply, access to renewable power, capacity expansion
and renovation in cities. In the technical report of the CIGRE working group B4.52,
DC power grid is defined as a direct current network composed of a radial network
of converters. DC grid is characterized by higher redundancy and more flexible and
diversified operation than traditional flexible DC transmission (Boroyevich et al.
2010).
Different from AC distribution grid, power load of DC distribution grid is supplied
by DC bus, which requires no extra rectifier equipment for power supply when applied
to settings with large DC load, demonstrating greater advantages of application. DC
distribution network features minor line loss, high reliability and strong access to
distributed power supply with no need for phase-frequency control (Sun et al. 2016).
The basic topological structure of DC distribution network includes ring, radial and
two-terminal distribution, etc. Power supply of radial network is less reliable, but
is much easier for control and protection; while that of ring network enjoys high
reliability, but lacks control and protection.
Existing DC power distribution systems, such as the SBN (Sustainable Building
and NanoGrids) (Marquardt 2011) proposed by Virginia Tech University of United
States, adopt two voltage classes of 380 and 48 V to form a radial topology. The
FREEDM (Future Renewable Electric Energy Delivery and Management) system
brought up by North Carolina State University is a plug-and-play radial network
(Marquardt 2011). At present, DC power distribution networks have been applied
in communication power distribution, vessel power distribution and subway electric
traction, etc., but the application of ring network has been a rarity, and no standards have been formulated for the selection of voltage class for corresponding DC
distribution network.
On the whole, technologies for the planning and application, scheduling and
control, safe operation and protection of DC distribution network are not yet mature.
But with the cost reduction of power electronic devices, development and application
of DC circuit breakers, flexible access of distributed energy, and fault current limits
of the network, DC distribution network will promise a brighter prospect for adoption
(Yan et al. 2019).