The Study of Transition to the Isolated Operation of Power Supply

Systems with Distributed Generation Plants and High Power Energy

Storage Units

Yuri N. Bulatov

, Andrey V. Kryukov

2,3 b

and Konstantin V. Suslov

Department of Electric Power and Electrical Engineering, Bratsk State University, Bratsk, Russia

Department of Transport Electric Power, Irkutsk State Transport University, Irkutsk, Russia

Department of Power Supply and Electrical Engineering, Irkutsk National Research Technical University, Irkutsk, Russia

Keywords: Distributed Generation Plants, Power Supply Systems, Energy Storage, Isolated Mode, Asynchronous Load,

Automatic Excitation Controller, Automatic Speed Controller, Simulation.

Abstract: The development of power engineering, under current conditions, is aimed at the use of distributed

generation plants in power supply systems located in immediate proximity from power consumers. The

article deals with power supply system with turbo generator plant and high power energy storage unit.

Description of a power supply system model with turbo generator plant, energy storage unit and

asynchronous load is provided, and modeling results of power supply system transition to the isolated

operating mode. The model of the power supply system under study was carried out in the MATLAB

environment using the Simulink and SimPowerSystems simulation packages. In work is a description of the

PSS model used with DG plant and ESU, as well as the simulation results. Based on the computer

simulation results the conclusion, that use of prognostic controllers turbo generator plant allows improving

the damping properties of the system when switching to an isolated mode of operation.

https://orcid.org/0000-0002-3716-5357

https://orcid.org/0000-0001-6543-1790

https://orcid.org/0000-0003-0484-2857

1 INTRODUCTION

Currently, it is expedient to use distributed

generation (DG) plants located in immediate vicinity

from power consumers (Ackermann et al., 2001), for

power supply systems (PSS) development and

modernization. This approach enhances the

consumers power supply reliability and reduce

losses associated with power transfer

(Rugthaicharoencheep and Auchariyamet, 2012).

The use of DG plants affects the PSS power quality

in a positively (Sikorski and Rezmer, 2015), (Hariri

and Faruque, 2014).

The PSS parallel operation with DG plants and

high-capacity electrical energy system (EES) allows

to stabilize voltage and frequency at various

disturbances. At the same time, such parallel

operation mode results in short circuit currents

increase, sophistication of relay protection devices

and modes control. In emergency situations it is

expedient to use the island (isolated) mode when DG

plants are separated in clusters to supply the part of

essential consumers (Martinez-Cid and O'Neill-

Carrillo, 2010), (Saleh et al., 2015). To enhance the

PSS functional reliability, a number of tasks shall be

solved, which includes DG plants optimal control at

the transition to the isolated mode (Arai et al., 2009).

In this case, it is necessary to consider the types of

DG plants and their generators used, restrictions on

the consumers maximum load, the nature of the

load, as well as the effect of a sharp increase or

decrease in load on generating plants.

DG plants, operating on the basis of synchronous

turbo- and hydrogenerators, provide a sufficiently

large power to supply industrial consumers.

Automatic excitation controllers (AEC) and

automatic speed controllers (ASC) of rotor rotation

allow to increase the stability of synchronous

generators operation in PSS.

142

Bulatov, Y., Kryukov, A. and Suslov, K.

The Study of Transition to the Isolated Operation of Power Supply Systems with Distributed Generation Plants and High Power Energy Storage Units.

DOI: 10.5220/0010435801420147

In Proceedings of the 10th International Conference on Smart Cities and Green ICT Systems (SMARTGREENS 2021), pages 142-147

ISBN: 978-989-758-512-8

The tasks of constructing and adjusting

regulators of DG plants operating in PSS under

various operating modes, can be solved using energy

storage units (Lombardi et al., 2014) and intelligent

control technologies (Magdi and Fouad, 2015),

(Wang et al., 2018).

The studies carried out indicate that the use of

fuzzy controllers (Voropai and Etingov, 2001),

(Kryukov et al., 2017) and predictive algorithms

(Camacho and Bordons, 2007), (Bulatov et al.,

2018) is an effective way to control synchronous

generators. This approach makes it possible to create

adaptive systems. However, the practical application

of such systems requires laborious research on

complex models, while taking into account a large

number of possible operating modes in order to

determine their influence on the control parameters

and quality indicators of the control process.

The purpose of this work is to study the

behaviour of the proposed prognostic AEC and ASC

of synchronous generators during the transition of a

PSS with a powerful asynchronous load to the island

(isolated) mode. The studies were carried out for

PSS of an industrial enterprise with a turbogenerator

plant (TGP) and a high-power electric energy

storage unit (ESU). The simulation was performed

in MATLAB using Simulink and SimPowerSystems

packages. Below is a description of the PSS model

used with DG plant and ESU, as well as the

simulation results.

2 DESCRIPTION OF PSS MODEL

USED WITH DG PLANT AND

ENERGY STORAGE UNIT

The diagram of the PSS under study, provided in

Figure 1, had links with EES via two 110/10 kV

transformers (T-1 and T-2) each having power of

6300 kVA. The main power consumers of the PSS

under study are asynchronous motors (AM): two

high-voltage AMs with a power of 670 kW each, as

well as a large number of low-voltage AMs which

are taken into account in the model in the form of

equivalent units with transformers and cable lines

with a power of 930 kW and 1485 kW, respectively,

powered from different bus sections (Figure 1). The

PSS includes a TGP with a power of 3125 kVA and

a high power ESU.

The model of the PSS under study was carried

out in the MATLAB environment using the

Simulink and SimPowerSystems simulation

packages.

Figure 1: The diagram of the PSS under study of an

industrial facility: CL – cable line.

The model of the used TGP steam turbine was

described by the following differential equation:

μ=+⋅

, (1)

where

P – turbine power; μ – opening of a

controlling element;

T – turbine time constant (was

taken for practical reasons equal to 0.2 s).

The TGP generator excitation system was

modeled using the first-order aperiodic link with

transfer function

10250

+s.

(Anderson and Fouad,

2003), and a series-connected amplifier with transfer

function

10010

+s.

, where s – Laplasian operator.

To stabilize the voltage on the TGP generator

terminals and the rotor speed, as well as to increase

stability, the model uses AEC and ASC, which are

proportional-integral-differential (PID) controllers

with or without prognostic links.

It is proposed to use a prognostic AEC as an

excitation regulator for TGP synchronous generator,

whose Simulink-model block diagram is shown in

Figure 2. The diagram of the used Simulink-model of

prognostic ASC is shown in Figure 3 (Bulatov et al.,

2018). The proposed AEC and ASC models differ

from the known ones in that a linear prognostic link

with a transfer function

1s +

with a series-

connected electronic amplifier having transfer

function is used at the controller output

1s +

. The

following numerical values of the parameters were

accepted in modelling: K

=1; T

=0.001 s.

The Study of Transition to the Isolated Operation of Power Supply Systems with Distributed Generation Plants and High Power Energy

Storage Units

143

−

ω0

ω1

1060

020

+s.

1150

020

+s.

1050

050

+s.

Setω

SetU

1020

+s.

150 +

+⋅

KsTK

apa

Figure 2: A structural model diagram of the prognostic AEC: U

– an instantaneous value of generator voltage; SetU

– a set

value of generator voltage; I

– generator excitation current;ω

– a generator rotor speed instantaneous value; Setω

– a

generator rotor speed set value; k

, k

1If

, k

0ω

, k

1ω

– tuning coefficients of AEC; T

– the prognostic link time constant.

Setω

180/pi

)))(cos(sqrt*7004.0/1 u

1+s

1+sT

Figure 3: A structural model diagram of the prognostic ASC: K

, K

– tuning coefficients of ASC.

AEC and ASC tuning coefficients were

determined based on practical considerations and

were assumed to be the same for classical PID

controllers and devices with a prognostic link. The

prognostic time constant for ASC was determined

automatically (Bulatov et al., 2018) and changed

subject to the generator load angle δ according to the

following function:

δ cos

4281,

ASC

The time constant of the prognostic link was

determined for AEC

AEC

in accordance with the

method described in (Bulatov et al., 2018), and was

assumed to be equal to 0.125 s. It should be noted,

that the method used for determining the time

constants of AEC and ASC prognostic links is

universal and can be used in schemes with any

number of generators and power consumers.

The use of ESU based on large capacity

accumulator batteries is a promising development

line for use in smart EES. The work uses lithium-ion

storage batteries due to their advantage over other

ESU types (Nishi, 2001). The Battery unit of the

SimPowerSystems package of the MATLAB system

was used as a model of lithium-ion accumulator

batteries. The ESU, the power of which was 3 MW

in the course of simulation, can be charged from the

EES or from the TGP during the minimum loads

periods.

3 SIMULATION RESULTS

The studies were carried out during the PSS

transition to an isolated operation mode with the

following technical equipment of the DG plants:

 the use of TGP with prognostic AEC and ASC

or with classical controllers;

 the use of high power ESU, in which case, the

ESU is permanently connected or automatically

connected when the voltage drops.

The initial load of the TGP was 80%, and when

switching to the island operation mode, the

generator was found to overloaded. Such a mode

cannot exist continuously, therefore, to compensate

for the generating capacity shortage in the PSS, a

ESU was used, the power and capacity of which

were sufficient for a continuous consumer supply.

The simulation results of the PSS transition to the

isolated operation mode in the form of time

dependences of the power on the TGP turbine shaft,

the rotor speed and the generator voltage are

provided in Figure 4. Figure 5 shows the time

dependences of the PSS frequency in the specified

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144

operation mode. The time dependences presented in

Figures 4 and 5, indicate that the use of a high-

power ESU in PSS allows the generator load

shedding and more efficient stabilization of

frequency at PSS transition to the isolated mode.

However, at the same time, there is an increase in

overshoot, oscillation, and transient time for the

rotor speed and voltage of the TGP generator.

It can also be noted that the use of prognostic

AEC and ASC of the TGP generator makes it

possible to improve the system damper properties

without employing the optimization procedures for

controller settings: the value of overshoot,

oscillation, and transient time for the speed of the

generator rotor speed, the turbine shaft power, and

the frequency of the mains voltage, are reduced. At

the same time, in the mode under study, the

prognostic link in the AEC has virtually no effect on

the voltage at the terminals of the TGP generator.

(a) (b)

Figure 4: Parameters of the TGP during the transition to the island (isolated) operation mode of the PSS: (a) – classic AEC

and ASC were used; (b) – prognostic AEC and ASC were used; 1 – ESU is disabled; 2 – ESU is always on.

The Study of Transition to the Isolated Operation of Power Supply Systems with Distributed Generation Plants and High Power Energy

Storage Units

145

(a) (b)

Figure 5: The frequency in the mains during the PSS transition to the island (isolated) operation mode: (a) – classic AEC

and ASC were used; (b) – prognostic AEC and ASC were used; 1 – ESU is disabled; 2 – ESU is always on.

(a) (b)

Figure 6: TGP parameters with auto prognostic ASC and prognostic AEC (a, b, c) and frequency in the mains (d) when the

PSS transition to an isolated operation mode: ESU is connected automatically when the voltage drops.

Also, a simulation was carried out for the transition of

the PSS to an isolated operation mode when the ESU

is disconnected, and which was connected

automatically when the voltage on the 10 kV buses

dropped. Figure 6 shows the simulation results in the

form of TGP parameters and frequency in the PSS.

A comparative analysis of the simulation results

for the PSS transition to the isolated operation mode

allows us to make a conclusion that it is effective to

use high power ESU to increase the reliability of

consumers power supply and to prevent the overload

mode of the used distributed generation plant.

At the same time, in comparison with the PSS

operation mode, when the ESU is disabled, slightly

larger deviations and fluctuations in the voltage and

rotor speed of the generator of the DG plant are

observed, which can be minimized due to the use of

the prognostic AEC and ASC.

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4 CONCLUSIONS

Based on the computer simulation results of the PSS

operation modes with the DG plants and ESU when

the links with the high-power EES are disabled, the

following conclusions can be drawn:

1. The use of high power ESU in PSS allows to

deload the TGP generator without disconnecting

important consumers, which is especially important

for the PSS with a shortage of generating plants.

2. The use of ESU in all considered modes

allows to better stabilize the mains frequency,

however, in this case, there is an increase in

overshoot, oscillation and transient process time for

the rotor speed and TGP generator voltage. The

overvoltage arising on the generator terminals

during the transition to the island operation mode is

accounted for an abrupt drop in the TGP load during

the redistribution of consumer supply from the ESU.

3. The use of the TGP generator auto prognostic

ASC allows to improve the damping properties of

the system without using the controllers settings

optimization procedures: the amount of overshoot,

oscillation and transition process time for the

generator rotor speed, power on the turbine shaft and

the mains voltage frequency are reduced. The

prognostic AEC has virtually no effect on the

voltage on the TGP generator terminals in the mode

under consideration.

4. The use of the ESU, which is automatically

connected to the 10 kV PSS buses when the voltage

drops, makes it possible to somewhat reduce the

overvoltage on the generator terminals during its

load shedding, as well as to further reduce the

required mechanical power on the TGP turbine shaft

in comparison with the permanently connected ESU.

5. The proposed prognostic controllers of

synchronous generators can be recommended to

increase the DG plants stability in PSS during the

transition to an isolated mode. It is expedient to

conduct further research based on more complex

computer models, as well as on PSS physical models

with DG plants. It is advisable to conduct further

research with respect to coordinated operation of DG

plant controllers and the energy storage unit.

ACKNOWLEDGEMENTS

The research was carried out within the state

assignment of Ministry of Science and Higher

Education of the Russian Federation (project code:

0667-2020-0039).

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