Unit5 smart power grid systems

SMART-GRIDS: BASIC PRINCIPLES, DESIGN AND
AUTOMATION
UNIT5: SMART POWER GRID SYSTEMS

Course content:
• Unit 1: Introduction to course
• Unit 2: Energy and Civilization
• Unit 3: Basics of Power-Grids
• Unit 4: Modeling converters in Micro-Grid power systems
• Unit 5: Smart Power-Grid Systems
• Unit 6: Micro-Grid Solar Energy systems
• Unit 7: Micro-Grid Wind Energy Systems
• Unit 8: Load flow analysis of Power-Grids and Micro-Grids
• Unit 9: Power Grid and Micro-Grid fault study analysis
SMART-GRIDS: BASIC PRINCIPLES, DESIGN AND
AUTOMATION

5.1 Introduction
5.2 Power Grid Operation
5.3 The vertically and market-structured utility
5.4 Power Grid operations control
5.5 Load-Frequency control
5.6 Automatic generation control
5.7 Basic concepts of a smart power grid
5.8 Load factor and real-time pricing
5.9 A Cyber-controlled Smart Grid
5.10 Smart-Grid development
Unit 5: Smart Power Grid Systems
Unit 3 Contents

• In a smart power grid system, a large number of microgrids
operate as part of an interconnected power grid.
• For example, a photovoltaic - (PV - ) based residential
system with its local storage system and load would be one
of the smallest microgrids in the smart power grid system.
• To understand the new paradigm of tomorrow’ s smart
power grid design and operation, we need to understand
today’ s electric power grid operation and costs of design
5.1 Introduction

5
• In this Chapter, we introduce the basic system concepts of
sensing, measurement, integrated communications, smart
meters, and high green energy penetration of intermittent
generation sources.
• We also introduce the basic concepts of generator
operation, power ﬂow, the limit of power ﬂow on
transmission lines, and load factor calculation and its impact
on the operation of a smart grid and microgrids.
5.1 Introduction
Understanding functioning of Power Grid=Able to design a micro-
Grid!

6
• …provide continuous quality service at an acceptable
voltage and frequency with adequate security, reliability, and
an acceptable impact upon the environment— without
damage to the power grid equipment
• Minimum cost!
Inter-related objectives of a
power-delivery system

7
5.2 Power Grid Operation IF in the power grid the line
connecting bus 2 and bus 4
is out of service, the power
grid is secure if it still can
serve all loads.

8
• The energy resources of a large power system consist
of hydro and nuclear energy, fossil fuel, renewable
energy sources such as wind and solar energy, as well
as green energy sources such as fuel cells, combined
heat and power (CHP; also known as cogeneration),
and microturbines.
• These resources must be managed and
synchronized to satisfy the load demand of the
power grid!
• Peak demands must be satisfied: daily peak demand
over a week, a weekly peak demand over a month, and
a monthly peak demand over a year
Cost of
distribution and
generation
minimised!

9
peak demand
is twice the
minimum
power demand

10
the peak power
demand occurs on
Monday and the
minimum power
demand occurs on
Sunday
Weekly basis!

11
Unit 5: Basics of Power Grids
Decision time
involved in
operations planning
and control of the
power grid
The vertical axis:
decision time for
implementing a
function. The
horizontal axis
indicates where the
control of a function
takes place

12
Supervisory Control and Data Acquisition (SCADA) system (belongs to EMS):
consists of data acquisition and control hardware and software, man –
machine and interface software systems, and dual computer systems
with real-time operating systems.
The primary functions of SCADA are
(1) to collect information throughout the power grid,
(2) to send the collected data through the power grid communication system
to the control center, and
(3) to display the data in the control center for power grid operators to use for
decision making and in the determination of the application function for grid
operation..

13
• As part of the smart power grid design, additional data concerning the
energy resources such as wind, solar, PV energy sources, and real - time
pricing from the power market must be incorporated into the SCADA
system.
• Distributed over a wide area, the smart power grid must be optimized for its
efﬁcient and stable operation — yet another task for the SCADA system!

14
• Problems of operations planning can be divided in four Tasks:
(1) to schedule all resources and facilities yearly,
(2) on a monthly basis for satisfying the forecasted monthly peak load,
(3) then utilizing the weekly results to produce a daily schedule,
(4) ﬁnally using the daily schedule to prepare a feasible and secure
hourly schedule.

15
• The scheduling of resources and facilities on a weekly basis is
accomplished through medium- term operation planning.
• This task consists of two functions: a weekly load forecasting program and
a hydrothermal coordination program.
The hydrothermal coordination program determines the best schedule of
operation of the hydro and thermal units such that the amount of fuel
consumed in the thermal units is minimized, and the weekly load
demand of the system is satisﬁed.
As renewable energy sources are increasingly used in the power grid, the
operation planning will become highly complex due to the intermittent nature
of renewable energy sources.

16
• The weekly scheduling of facilities and resources on a daily basis
is performed by short - term operation planning, which consists of a
short - term load forecasting program, a security analysis
simulations program, and a unit commitment program.
• The short - term load forecasting estimates the hourly load
demands of the next 168 hours.

17
5.3 The vertically and market-structured Utility
Vertically-integrated Power
Utility
The power delivered first to large
cities, and then through a radial
distribution, to rural areas

18
Market-operated Power Grid
• In this structure, the independent system operator (ISO) is in charge of
power grid operation.
• ISO energy - management computer systems compute the operating
reserve that is necessary to maintain reliable interconnected power grid
operation.
“ Each control area shall operate its power resources to provide for a level of
operating reserve sufﬁcient to account for such factors as errors in
forecasting, generation and transmission equipment unavailability, number
and size of generating units, system equipment forced outage rates,
maintenance schedules, regulating requirements, and regional and system
load diversity. ”

19
Market-operated Power Grid
• ISO energy - management
computer systems compute the
operating reserve that is necessary
to maintain reliable interconnected
power grid operation – Stabilize
the grid!
A Market - Structured Power
Grid

20
5.4 Power Grid Operations control
• The primary functions of operations control are satisfying the
instantaneous load on a second - to - second and minute - to - minute
basis.
Some of these functions are
1. Load frequency control (LFC)
2. Automatic - generation control (AGC)
3. Network topology determination (NTD)
4. State estimation (SE)
5. On - line load ﬂow and contingency studies
6. Schedule of transactions (ST)
7. Economic dispatch calculation (EDC)
8. Operating reserve calculation (ORC)
9. Load management system (LMS)

21
5.4 Power Grid Operations control
The decision time of operations control is from dynamic response in a fraction
of a cycle in LFC,
• to 1 – 10 seconds for automatic - generation control,
• to 5 – 10 minutes for economic - dispatch calculations,
• and from a second up to 30 minutes for a load management system.
However, with the implementation of a smart grid system with a
high penetration of renewable green energy sources and a smart
metering system, we will have a more - complex power system.

22
• LFC is also referred to as the governor response control loop as shown in
Figure below
• As the load demand of the power system increases/decreases, the speed
of the generators decreases/increases and this reduces/increases the
system frequency.
The power system - frequency
control must be maintained for the
power grid to remain stable.!

23
• In the AC power grids, all generating sources are operating in
parallel and all (inject) supply power to the power grid. This means
that all power sources are operating at the same system frequency.
• The generators are operating at the system frequency; they are all
synchronized and operating at the same synchronized speed: all are
supplying (injecting) power to the power grid. The synchronized speed can
be computed as
𝜔 𝑠𝑦𝑛 =
2
𝑃
𝜔𝑠
where 𝜔𝑠 is the system frequency and P is the number of magnetic Poles.

24
• In AC systems, the energy cannot be stored; it can only be exchanged
between inductors and capacitors of the system and is consumed by
loads.
• Therefore, for an AC system to operate at a stable frequency,
the power generated by AC sources must be equal to the
system loads.
What about the losses??

25
• However, the loads on the system are controlled by the energy users, i.e.,
when we turn off a light, we reduce the system load; when we turn on a
light on, we increase the system load.
• In response to load changes, the energy is supplied from the inertia
energy stored in the massive mass of a rotor. However, at every instant,
the balance between energy supplied to the grid and the energy
consumed by loads plus losses are maintained. This concept can be
expressed as
Generated
power
Power consumed
by load
N: number of
generators/loads

26
Governing system control:
• At time t load increases spontaneously-- frequency drops!
the system has a feedback loop that is called the load - speed control and as
the system frequency drops, the feedback loop increases the input power to
match the system generation with the system load.
the governor opens the turbine valves to increase the input power that
in turn speeds up the shaft of the generator!

27
We must also control the
terminal voltages of
generators and power
factors.!
Voltage Regulator and Turbine
- Governor Controls for a
Steam Turbine - Generator

28
Important analysis studies in power system planning, design,
and operation:
1. Power Flow Studies:
2. Short-Circuit Studies
Given the system model, the bus voltages, and load, we compute balanced
and unbalanced fault currents that can ﬂow on the system if a fault happens.
Based on this study, we calculate the short- circuit currents that the breakers
may experience upon occurrence of a fault.

29
We can identify different dynamic problems that can affect a power grid:
1. Electrical dynamics and excitation controls may have a duration of
several cycles to a few seconds.
2. Governing and LFC may have a dynamic duration of several seconds
to a few minutes.
3. A prime - mover and an energy supply control system may have a
dynamic duration of several minutes. A prime- mover is a steam-
generating power system.

30
• The system load has a general pattern of increasing slowly
during the day and then decreasing at night.
• The cost of generated power is not the same for all generating units.
• Therefore, more power generation is assigned to the least costly
units.
• In addition, a few lines connect one power grid to another neighboring
power grid (Tie lines).
.
• Tie lines are controlled to import or export power according to set agreed
contracts.

31
• To control both the power ﬂow through transmission tie lines and the
system frequency, the concept of area control error (ACE) is deﬁned as

32
The AGC software control is designed to accomplish the following objectives:
1. Match area generation to area load, i.e., match the tie-line interchanges
with the schedules and control the system frequency.
2. Distribute the changing loads among generators to minimize the operating
costs.
To obtain a meaningful regulation (i.e., reducing the ACE to
zero), the load demands of the system are sampled every
few seconds.

33
When a large number of energy users turn their lights off, they create
high - and low - frequency load ﬂuctuations. The low - frequency load
ﬂuctuation has a clear load rise or a load drop trend. This change of load
is controlled by AGC as shown below:

34
• The microgrid concept assumes a cluster of loads and its microsources,
such as photovoltaic, wind, and combined heat and power (CHP) are
operating as a single controllable power grid.
• To the local power grid, this cluster becomes a single dispatchable load.
• When a microgrid power grid is connected to a power grid, the microgrid
bus voltage is controlled by the local power grid.
The microgrid cannot change the power grid bus voltage and the power
grid frequency!
• The AGC also controls the connected microgrids in a large
interconnected power grid

35
• When the balance between generation and load is disturbed, the dynamics
of the generators and loads can cause the system frequency and/or
voltages to vary, and if this oscillation persists, it will lead to system
collapse of the local power grid and connected microgrids.
• If the load increases rapidly and the power grid frequency drops, then
steam units open the steam valves and hydro unit control loops will open
the hydro gates, to supply energy to stabilize the system frequency.
This action takes place regardless of the cost of energy
from generating units. All units that are under LFC
participate in the regulation of the power system
frequency. This is called the governor speed control

36
5.7 Operating reserve calculation
• The spinning reserve is the amount of additional power that is distributed
in the form of a few megawatts among many generators operating in the
power grid.
• The real - time pricing and smart meters will empower many energy end
users to participate in proving the spinning reserves in the future operation
of power systems, increasing overall efﬁciency, and reducing the cost of
operation of power grids.
• These units are under AGC control and can dispatch
power to ensure the balance of system loads and
system generation

37
5.8 Basic concepts of a Smart Power Grid
.
• The classical power system operation has no control over the loads except
in an emergency situation when a portion of the loads can be dropped as
needed to balance the power grid generation with its loads.
• Therefore, much equipment is used for a short time during the peak power
demand but it remains idle during daily operations.
In a classical power grid, a ﬁxed price is charged to energy users.
However, the cost of energy is highest during the daily peak load
operation

38
• For an efﬁcient smart power grid system design and operation:
• communication system,
• cyber network,
• sensors,
• and smart meters
must be installed to curtail (περικοπή) the system peak loads when the cost
of electric energy is highest!.
• The smart power grid introduces a sensing, monitoring, and control
system that provides end users with the cost of energy at any
moment through real- time pricing..

39
Furthermore, the smart power grid:
1. Supplies the platform for the use of renewable green energy sources and
adequate emergency power for major metropolitan load centers.
2. It safeguards against a complete blackout of the interconnected
power grids due to man-made events or environmental calamity. It also
allows for the break - up of the interconnected power grid into smaller,
regional clusters.
• enables every energy user to become an energy producer!

40
A Cyber - Controlled
Smart Grid
The cyber- fusion point (CFP)
represents a node of the smart grid
system where the renewable green
energy system is connected to large -
scale interconnected systems.

41
• The CFP is the node in the system that receives data from upstream, i.e.,
from the interconnected network, and downstream, i.e., from the microgrid
renewable green energy (MRG) system and its associated smart metering
systems.
• The CFP node is the smart node of the system where the status of the
network is evaluated and controlled, and where economic decisions are
made as to how to operate the local MRG system.
• A CFP also evaluates whether its MRG system should be operated as an
independent grid system or as a grid system separate from the large
interconnected system.

42
It enables end users to adjust the time of their energy usage for nonessential
activities based on the expected real - time price of energy.
The knowledge gained from smart meters permits the power grid operators to
spot power outages more quickly and smooth demand in response to real -
time pricing as the cost of power varies during the day
Two - way communication is a key characteristic of the smart power grid
energy system.

43
5.9 The load factor
• Ratio of a customer ’ s average power demand to its peak demand
• * Deﬁnes the cost to the supplier per unit of energy delivered in that
period
Daily, monthly or
Yearly basis!
A desirable load factor is close to one, so that
peak demand and average demand are close to
each other

44
5.9 The load factor
Example: An industrial site has a constant power demand of 100 kW
over a year of energy consumption. Compute the customer load factor
over one year of providing energy to this site
Therefore, the load factor of this customer is 100%

45
5.9 The load factor
• A commercial site has peak demand of 200 k W during 12 hours a
day and an average demand of 50 k W demand the rest of a day.
• Compute the customer load factor over one year of providing
energy to this site. Explain the associated cost of providing energy
to the industrial site (previous example) and the commercial site.

46
5.9 The load factor
When the load factor is close to
unity (100%), the generating
plant is efﬁciently used. The cost
of supplying power to the load is
more when the load factor is
low.

47
5.9.1 The Load Factor and Real - Time Pricing
Suppose a PV plant of 1000 kW capacity is constructed for $500 per kW.
Compute the cost of energy per kWh to the end users for one year of
operation at full capacity if the total cost on investment is to be recovered in 2
years when the PV plant operates 6 hours a day on the average for 2 years
and the cost of production is negligible.

48
5.9.1 The Load Factor and Real - Time Pricing
Cost in Cents per kWh as a
Function of Load Factor

49
• A cyber - controlled smart grid consists of many distributed generation
stations in the form of microgrids. The microgrids incorporate intelligent
load control equipment in its design, operation, and communication.
• Smart appliances such as refrigerators, washing machines, dishwashers,
and microwaves can be turned off if the energy end user elects to reduce
energy use.
• Furthermore, the emergency load reduction can be achieved by turning off
millions of air conditioners on a rotation basis for a few minutes.
better control
energy usage!
End users
control their
energy costs!
Energy end-users become
energy producers

50
• Cyber - controlled smart grid technology has three important elements:
• sensing and measurement tools,
• a smart transducer,
• an integrated communication system
• Transducers are sensors and actuators play a central role in automatic
computerized data acquisition and monitoring of smart grid power systems.
• The smart transducer/controller is also able to locally implement the
control action based on feedback at the transducer interface.
Advanced
technology: micro-
controllers, digital
signal processors
a digital sensor,
a processing
unit, and a
communication
interface

Unit5 smart power grid systems

More Related Content

What's hot (18)

Similar to Unit5 smart power grid systems (20)

Recently uploaded (20)

Unit5 smart power grid systems