Project Subjects
Trunk Power System Planning and Operation Under
Large Penetration of Intermittent Generations
Background and Objective
The expected large penetration of renewable generations, especially photovoltaic generations in the future
may cause deterioration in quality of voltage and frequency. Therefore, a more sophisticated operation and control scheme, which harmonizes the operations of trunk transmission system and distribution systems, is necessary
to maintain power quality, while utilizing the large number of intermittent generations. As one of steps to develop
such a new scheme, demonstration projects are in progress, where renewable generations are installed in powersystems on small islands to assess their impact on power quality and to develop suitable control schemes for such
power systems.
In this project, we focused on the operation of trunk power system to efﬁciently maintain power quality
under the large penetration of renewable generations by a harmonization with operation of autonomous demandarea power systems. Currently we develop assessment tools for trunk power system planning and operation,
which explicitly consider renewable generations, to identify the impact of large penetration of intermittent generations on power quality.

Main results
1. Development of assessment tools of power balancing in trunk power systems(1) Development of a generation adequacy assessment tool
A reliability assessment tool has been developed, which explicitly considers the probabilistic characteristics of intermittent generations output to assess generation adequacy under a large penetration of renewable generations (Fig. 1). The developed tool can assess generation adequacy under heavy load condition and generation
surplus under light load condition, taking hourly probabilistic distributions of PV generation output into account.
(2) Development of a power balancing assessment tool
An assessment tool for generation operation has been developed, which considers day-ahead generation planning and hourly PV generation output scenarios (Fig. 2). The output of renewable generations may
considerably differ from its day-ahead forecast and this difference may have a large impact on generation reserve
requirement and operation of generations supplying reserve power. The developed tool can assess such an impact
quantitatively (Fig. 3).
2. Development of a simulation tool of supply-demand control of small island power systems
A simulation tool of supply-demand control of small island power systems has been developed. The
developed tool can simulate the behavior of PV generations, wind power generations and battery storage systems
as well as diesel and gas turbine generation systems, which are usually installed in small island power systems(Fig. 4(a)). The tool can analyze how ﬂuctuation of demand and PV systems output inﬂuence frequency deviations, taking both long-term (e.g. hourly) ﬂuctuation and short-term ﬂuctuation into account. One of the useful
applications of the developed tool is the study of control schemes of battery storage systems to suppress frequency
ﬂuctuations (Fig. 4(b)).

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Environmental and Energy Utilization TechnologyStart
Iteration forhourlyperiods ofinterest

Day-ahead generation planning

DemandGeneration adequacy andgeneration surplus evaluationof hourly period of interest

24

Generation operation to obtainhourly power balancing
・Various PV generations output scenarios areconsidered.
・Generation units are redispatched in each hourly
periods to keep power balance.

Obtain results for allperiods?

Next hourly period
Results obtained：-Expected generation
inadequacy and surplus undera given generation reserve forboth all periods and eachperiods of interest

Results obtained:- Power unbalance (insufficiencyof reserve capacity) andutilization of generation units
under given generation reserve
requirement and PV
generations output scenarios

End

Fig.1 Flowchart of the developed generation
adequacy assessment tool

電源の利用率Utilizationof generating units（PVなしの場合を1.0として正規化）(1.0for utilization in case of no PV)0.96

16%

Utilization of gen. units
調整電源の稼働中利用率
Day-ahead reserve requirement
前日に確保が必要となる予備率

0.95

EndFig. 2 Flowchart of the developed power balancing assessment tool
＜Assumptions＞
・50GW PV capacity
・Off-peak day (Sunday in May)・3% generation reserve should be kept
In operation.
・Power balancing is obtained byregulating output of thermal units.

14%

0.94

12%

0.93

10%

0.92

8%

0.91

6%

0.90

4%

0.89

2%

予備率[%]
Generation
reserve [%]12- Generation scheduling based on expecteddemand curve and hourly PV generations output.
- Expected PV output is assumed to be a standard
curve based on weather.
- The obtained schedule satisfies the given
generation reserve requirement.

・Probabilistic characteristics
considered:
Output of PV generations
Output of hydro generations
DemandUnplanned outage

N hours
1StartImprovement of PV output forecast
error leads to:(1) reduction of day-ahead reserve
requirement(2) higher utilization of generating
units

0.88

0%
29%
14%
8%
Maximum errorof day-ahead PV output forecast
PV出力の前日想定誤差の最大Fig. 3 Impact of day-ahead PV output forecast error on generation reserve requirement and operationof generations supplying reserve power

総需要
Demandディーゼル1
Diesel 1

協調分

ガスタービン1GasTurbine 1GasTurbine n
ガスタービンnBattery
Storage
蓄電池
PV

LFC機能
LFC

LFC
LFC
指令値
signals-3

10Power
output
発電機出力

ディーゼルnDiesel n

EDC
EDC機能(not（未実装）
implemented)

PVなし
PVあり
PVあり＋出力変動抑制
PVあり＋ガバナフリー)

EDC
EDC
signals
指令値2

LFC: LFC：負荷周波数制御
Load Frequency Control
EDC:EDC：経済負荷配分制御
Economic Dispatch Control-210Simulationof generating units
発電機・系統模擬
and whole power system

Supply-demandcontrol
需給制御システム
system models

Δf－Σ＋1Ms

M:M:
inertia
系統のconstantof the慣性定数
whole system：周波数偏差Δ ｆfrequency
Δf:deviation-4

10-510Windpower
風力発電-610010110210
変動周期 (秒)103104(a) Main components of the developed simulation tool(b) Effect of battery storage systems control
The tool can simulate behaviors of PV generations, wind power
on frequency ﬂuctuation
generations and battery storage systems as well as diesel and
The tool can evaluate the effects of various control
gas turbine generation systems.
schemes to suppress frequency ﬂuctuations.
Fig. 4 Developed simulation tool of supply-demand control of small island power systems

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