IEEE Power & Energy Magazine - November/December 2019 - 85

Market design and system requirements should promote
performance so that any provider using any technology can support
the grid on an even, cost-sensitive playing field.
4 Hz/s frequency variations. A temporary 900-MW limit
on installed wind capacity was imposed in 2006 in Alberta
so that the province's grid code could be updated to include
forecasting and wind-power management (power limiting and
ramp rate control). Currently, Canada has nearly 13,000 MW
of wind supplying between 2 and 12% of the provincial
demand. While the provincial grid codes have ensured overall
grid reliability so far, there are some notable trends.
✔ The grid codes are being expanded to include specific
requirements for new technologies, such as utility-scale
solar and battery energy storage.
✔ The provision of frequency control is becoming mandatory for all generators.
✔ Validated electromagnetic transient models are being requested in addition to traditional stability models.
✔ New wind facilities are being asked to be capable of
providing a fast frequency or synthetic inertial response.

Grid Code Trends in China
At the beginning of 2017, China started to upgrade its grid
code for wind power interconnection. The main purpose of
this upgrade is to enable wind power to better support the grid
and ensure system reliability, considering that the penetration
of wind power will increase significantly in the next 10 years.
The new requirements refer only to the newly built wind plants
and not to retrofitting existing wind plants.
With the increasing penetration of renewable energy and displacement of conventional synchronous generators, grid operational behavior is dramatically changing. As a result, several
issues need to be addressed.
✔ The absence of voltage- and frequency-regulation
capability of renewable energy generators may cause
the disturbance-recovery capability of the BPS
to deteriorate.
✔ Because of the lower voltage and frequency tolerance
of wind and PV generation than conventional synchronous generators, large renewable generation outages
may occur during ultrahigh-voltage (UHV) dc system
blocking faults.
✔ System stability modes are changing in a more complicated way because of the interactions between power electronics fed by renewable generation with UHV
dc systems.
Several new technical requirements are still under consideration. These include HV ride-through capability with a 500ms duration of 1.3-p.u. system overvoltage at the point of connection; inertial response; and primary frequency regulation
november/december 2019

capability with 6% headroom of rated power with a response
time of 12 s, which is faster than for conventional generation.
These new wind turbines (and wind plants) requirements normally do not require additional hardware but may be achieved
by readjusting the controls or software settings, which adds
slightly to cost.

The Australia National Electricity Market
In Australia, new technical standards for generators came
into effect in 2018. These included several new and modified
requirements for large generating systems. The changes introduced additional requirements to ride through successive disturbances, modified requirements for reactive current injection
(with distinct ones for synchronous and asynchronous generating systems), and made other key changes relating to active
power and frequency-control capability. This was the Australia National Electricity Market's (NEM's) most detailed review
of generator technical requirements since 2006-2007, when
changes were first made to accommodate grid-scale asynchronous generating systems.
In 2017-2018, system strength impact assessment rules and
guidelines were introduced in the NEM to ensure adequate
assessment of asynchronous generator performance in weak
networks, including associated provisions for connecting generators to remediate any resulting reduction of system strength
(Figure 4). Based on detailed wide-network modeling through
EMT analysis techniques using PSCAD, the assessment of
system strength and the weak-grid phenomena has been undertaken to identify whether there is a restriction on the ability of
the power system to maintain stability.
Wind and solar resources, for the most part, are connecting
to weakly interconnected fringe areas of the grid, remote from
synchronous machines, resulting in these key challenges.
✔ In areas where synchronous generators have traditionally been located, there is an increasing need to manage HVs on the extra HV transmission system network
through line switching and out-of-merit generator dispatch during light-load conditions.
✔ In areas where proposals are made to connect asynchronous generators, single contingency risks as well
as planned or unplanned outages are resulting in significant constraints on asynchronous plants due to
potential control system instability in these circumstances as well as an emerging need to limit generation to mitigate spinning reserve requirements.
Recent events have demonstrated the significant effects of withdrawal of primary frequency response capabilities in the NEM
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IEEE Power & Energy Magazine - November/December 2019

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