 Inverter Coupled Energy Storage System for Soft-Restarting of Power

System Dynamic Load

VIKRAMSINGH R. PARIHAR1, ROHAN V. THAKUR2, DR. MOHAN B. TASARE3, HARSHADA M.

RAGHUWANSHI4, MOHINI G. FUSE5, DR. SONI A. CHATURVEDI6

1, 2, 3 Department of Electrical Engineering, Prof Ram Meghe College of Engineering and Management,

Badnera-Amravati, INDIA

4 Department of Computer Engineering, Trinity College of Engineering and Research, Pune, INDIA

5Department of Electrical Engineering, Ballarpur Institute of Technology, Ballarpur, Chandrapur, INDIA

6Department of Electronics & Communication Engineering, Priyadarshini College of Engineering, Nagpur,

INDIA

Abstract: - This paper presents the design and implementation of an inverter-coupled energy storage system (ESS)

for the soft-restarting of dynamic loads in power systems, utilizing MATLAB Simulink as the simulation platform.

The proposed system aims to enhance the reliability and stability of power grids by providing a controlled and

efficient method for restarting loads after an interruption. The inverter-coupled ESS integrates a battery storage unit

with a power inverter to supply the necessary energy for a smooth load restart, minimizing the impact on the overall

system. Simulation results demonstrate the effectiveness of the system in maintaining voltage stability, reducing

inrush currents, and ensuring a seamless transition during the load restarting process. The study highlights the

potential of inverter-coupled ESS in modern power systems, offering a robust solution for managing dynamic load

behavior and improving grid resilience.

Key-Words: - Inverter-Coupled Energy Storage System, Soft-Restarting, Power System Stability, Dynamic Load,

MATLAB Simulink, Voltage Stability, Inrush Currents, Battery Storage, Grid Resilience, Power Inverter, Load

Management, Power Grid Reliability

Received: March 28, 2023. Revised: October 15, 2024. Accepted: November 11, 2024. Published: December 9, 2024.

1. Introduction

Industrial processes like producing goods or manufacturing

any product can suffer major loss in financial means due to the

interruption of power cut. These processes get encountered

and get completed with the help of motors which are of ratings

from 0.5 to 500 hp in which 30%-35% are line connected. In

2012, Federation of Indian Chambers of Commerce & Industry

(FICCI) revealed that firms generally do not suffer any

shortfall in production due to the erratic power supply. This is

because the firms have adapted themselves to the current

power scenario so well that all that they suffer is cost

escalation due to the use of power backups to support their

production activity. However, it was considered important to

ask the industrial groups about any shortfall that they might

incur due to the intermittent power supply, in case they do not

use power backups to support their operations, the regarding

results are shown in figure 1 [1]. The main objective of the

study is to understand the impact of power outages on the

Indian industry. An analysis of the shortfall or impact on

production due to power cuts is thus paramount. Generally in

Indian industries, there are several firms which are being

converted to independent power suppliers since they require

continuous power supply to get desired output within

stipulated time to fulfil the customer’s requirement. But it is

not so reliable to consider due to occurrence of certain

mishaps which would not be predictable

International Journal on Applied Physics and Engineering

DOI: 10.37394/232030.2024.3.8

Vikramsingh R. Parihar, Rohan V. Thakur,

Dr. Mohan B. Tasare, Harshada M. Raghuwanshi,

Mohini G. Fuse, Dr. Soni A. Chaturvedi

E-ISSN: 2945-0489

Volume 3, 2024

Figure 1. Distribution of shortfall in production due to outages

by type of enterprises

The graph mentioned in figure 1 shows that due to power

outages, there is significant increase in the shortfall of

production of industrial grades which get noticed over not

using alternate power supply [2]. Also system transients are

also responsible for the highest number of failures of

electronic components [3].

The energy-storage systems (ESSs) can be alternative as an

auxiliary source for industrial plant is reported in studies [4]-

[6]. Some heavy industries such as Pulp and Paper (80-300

MW) commonly generate a fraction (20%) of their own energy

onsite [7]. In this paper, we use ramping power which is

supplied from a local energy-storage system (ESS) inverter.

This power is fed to the industrial power system bus and then

ensures a transient-free load transfer to the grid source. This

method is termed as ‘Soft-Restarting’ which is initiated after

an occurrence of three-phase-to-ground fault which is external

to the load zone supplied by ESS. There are certain benefits of

soft-restarting (SR) method which are as follows:

1. Automatic and continuous process.

2. No process downtime so no any external handling (labour

operation) requires to restore the system hence labour cost get

reduced.

3. Method ensures predefined inrush currents.

4. Line equipment like distribution transformer can be

downsized or their maintenance can be delayed.

5. Unsuccessful reclosing attempts get avoided after the

occurrence of faults or momentary interruptions.

6. Synchronization is achieved by the inverter to perform a

transient-free load transfer to the grid source.

2. Proposed System

In this section, the generalized view of the system and circuit

breakers operating sequence is discussed for better

understanding of the system.

2.1 Generalized View of the System

The system which is proposed in this paper is as shown in

figure 2, which includes an industrial load connected to the

industrial bus i.e. load-bus as named in the figure 1. As stated

earlier, industrial loads varies from o.5 hp to 500 hp motors, so

here the use of an asynchronous motor of rated power 400 hp

has been done which is considered as an industrial load. To

drive the load bus, bus is getting supply from grid source and

at fault condition bus gets disconnected due to the operation of

circuit breakers: circuit breaker 1 (CB_1), circuit breaker 2

(CB_2) and main circuit breaker (CB_main). The sequence of

operation of circuit breakers plays vital role in maintaining

proper condition of the network [8]. Mainly we are dealt with

the circuit breaker and relay operation to carry out the

effectiveness of the soft-restarting method. Simpler way to

carry out this process is to understand the circuit breakers

operation thoroughly and to use it in simulation. Which is

described preceding to this as below.

Figure 2. A small representative of an industrial power

network with line connected asynchronous motor

2.2 Circuit Breaker’s Operating Sequence

In this system, we are considering a fault occurrence which is a

three-phase-to-ground fault in somewhere between circuit

breaker-1 and circuit breaker-2. This fault is considered as

much severe as compared to other types of fault. Such fault

can harm or damage a system permanently [9]. Several circuit

breakers are used for the purpose of protection of system or

any equipment depending on their requirement and parameters

[10]. Following operations takes place during s oft-restarting

process.

International Journal on Applied Physics and Engineering

DOI: 10.37394/232030.2024.3.8

Vikramsingh R. Parihar, Rohan V. Thakur,

Dr. Mohan B. Tasare, Harshada M. Raghuwanshi,

Mohini G. Fuse, Dr. Soni A. Chaturvedi

E-ISSN: 2945-0489

Volume 3, 2024

1. A three-phase-to-ground fault takes place in between

CB_1 and CB_2.

2. Following this fault, CB_1-CB_2 and CB_main get

tripped in response to overcurrent and undervoltage relay

respectively.

3. While the system gets isolated from the load bus, then

inverter-coupled ESS starts supplying the power by closing its

circuit breaker which is normally open. ESS then supply the

ramp power to the load bus until the voltage and frequency

ratio (V/Hz) get matched to the grid source supply. This

situation is called as ramp-up process in which inverter supply

ramping power to the load bus.

4. As soon as voltage and frequency get matched, inverter

stops supplying the power and load get transferred to the grid

source by reclosing the CB_main and tripping off circuit

breaker of energy storage system (CB_ESS).

There are certain conventional practices which are used for the

reclosing of the motors after fault conditions. These

conventional practices are harmful since there is certain

amount of residual voltage present in the motors which would

be dangerous for system restoration [11]-[12]. To avoid a

possible cascaded voltage collapse that may result from this

effect, the system must quickly be restored to normal condition

[13]. Hence by using soft-restarting method, one can avoid

such hazards since in soft-restarting, the loads get transferred

to the utility without any transients.

3. Inverter-Coupled Energy Storge

System Contol

In this proposed system, we are using an three -phase three-

level diode clamped inverter to supply ramp power to the load

bus for achieving synchronization with the system. Actually,

the generation of ramp-power is not so easy. It requires certain

control variables for the operation of synchronous reference-

frame phase locked loop (SRF-PLL) and for maintaining the

V/Hz ramp control. SRF-PLL related with ramp control is

shown in figure 3.

As shown in figure 3, the current feedback is only used to

adjust the V/Hz ramp. An open loop V/Hz supply is generated

by the ESS inverter to power up Bus-2 (Load Bus). The

control variables are obtained by abc-to-dq transformation. Vq

and Ѡline are derived from SRF-PLL [14] and are used as

inputs to the Vq-Controller and frequency-controller

respectively. But before these we have to derive the positive

sequence componet of the voltage which is used to fed at the

abc -to-dq transformation. This positive sequence of the

voltage can be derived with the help of sequence analyzer

[15]-[16].

Here we are not using Vd to adjust the magnitude and

frequency of the V/Hz ramp, so it is set to zero. As Vd_inv =

0, hence the inverter output voltage magnitude is:

abc-to-dq transformation also known as Park’s Transformation

[17], which gives line voltages which have been detected as

positive sequence voltages into dq variables as:

Where,

Vabc_line = (rms) magnitude of line-to-neutral voltage at

load bus;

Ѡline = detected line frequency

Ѡinv = detected inverter output frequency

Ɵline and Ɵinv0 = phase angle constant. We select time zero

such that Ɵline = 0 and Ɵinv0 = 0

δ is the voltage angle between Vabc_line and Vinv with phase

angle of 0 degree referred to the ESS bus or load bus. We are

not using d-axis voltage as a control variable for inverter,

hence we will use only equation for further analysis. The phase

angle δ is derived from the transformer coupling impedance

+ jXT. The frequency controller block is used to control the

detected line frequency is as shown in figure 5. In which

output Vq from abc-to-dq transformation is fed to the

controller block, from which we are getting theta (Ɵ). Ɵ is

being used as a control variable for the inverter and is given to

the inverter as an input.

Figure 3. Control schematic of inverter-coupled ESS

International Journal on Applied Physics and Engineering

DOI: 10.37394/232030.2024.3.8

Vikramsingh R. Parihar, Rohan V. Thakur,

Dr. Mohan B. Tasare, Harshada M. Raghuwanshi,

Mohini G. Fuse, Dr. Soni A. Chaturvedi

E-ISSN: 2945-0489

Volume 3, 2024

Figure 4. Positive sequence analyzer

Figure 5. Frequency controller

4. Operation During Ramp (V/Hz)

Control

The decaying voltage and frequency at time of fault condition,

given by Vq0 and f0 respectively, have a non-linear

relationship that will highly depend on the inertia of the motor

load connected to the load bus. The operation during ramp

control in which Vq at time t i.e Vq(t) is simply get controlled

by PI controller as shown in figure 6.

Figure 6. Vq controller

Therefore Vq(t) is defined as:

for t = any time in between the operation of ramp control when

inverter supplying ramp power. mvq is slope of the voltage

ramp and it is controlled by PI controller.

Where, t = any time in between the operation of ramp control

and finv = rated inverter output frequency

Equation (5) is used to determine frequency of the inverter

which is then used to determine the angle input (Ɵinv) to the

inverter from:

5. Simulation Parameters and Results

An industrial optimized asynchronous motor is considered as a

load which is driven by load torque given to the shaft and it is

expressed [18] as:

where,

Tinit = initial load torque during startup

= final load torque



= motor speed in rad/sec

TB = base torque in N-m

Table 1: Parameters For Asynchronous Motor

Prated (hp)

400

VLrated

480

f (Hz)

N (rpm)

1470

J (kg-m²)

0.089

F(N.m.s.)

0.0065

Rs (Ω)

0.435

Rr (Ω)

0.816

Lls (H)

0.00016

Llr (H)

0.00019

Lm (H)

0.6931

Table II. Transformer Parameters

Rated Power

1.2 MVA

Voltage Rating

2000V/480V, Y-Y

Impedance

4+j3.4%

Table III. Parameters For Ess

Battery Voltage

1.2 MVA

Inverter Switching

500

International Journal on Applied Physics and Engineering

DOI: 10.37394/232030.2024.3.8

Vikramsingh R. Parihar, Rohan V. Thakur,

Dr. Mohan B. Tasare, Harshada M. Raghuwanshi,

Mohini G. Fuse, Dr. Soni A. Chaturvedi

E-ISSN: 2945-0489

Volume 3, 2024

Frequency

5.1. During Normal Restarting

At fault condition, CB1, CB2 and CB_main get tripped.

According to the characteristics of their respective fault

clearance timing, each of them clear the fault with respect to

overcurrent and undervoltage of the system condition. So at

normal restarting of the system, it requires much timing for

system restoration and for transferring the load to the utility.

Hence during normal restarting of the system, corresponding

voltage and current results are as shown for the proposed

system which is simulated using MATLAB/SIMULINK.

Figure 7. Rated voltage

Figure 8. Output voltage at load bus during normal restarting

Figure 9. Output current at load bus during normal restarting

5.2. During Soft-Restarting

The output results for soft-restarting method is as shown

below, in which the time required for the system to close and

to transfer the load to the utility get reduced, hence better and

fast service restoration is achieved. Also for the current output,

the transients which were noticed even after the normal

restarting of the system get overcome and time required is also

less as compared to normal restarting method.

Figure 10. Output voltage at load bus during soft-restarting

Figure 11. Output current at load bus during soft -restarting

Figure 12. Output Positive sequence voltage

Figure 13. Output voltage from abc to dq transformation

International Journal on Applied Physics and Engineering

DOI: 10.37394/232030.2024.3.8

Vikramsingh R. Parihar, Rohan V. Thakur,

Dr. Mohan B. Tasare, Harshada M. Raghuwanshi,

Mohini G. Fuse, Dr. Soni A. Chaturvedi

E-ISSN: 2945-0489

Volume 3, 2024

Figure 14. Inverter output voltage

Figure 15. Output rotor current

Figure 16. Output stator current

Figure 17. Motor speed

Figure 18. Electromagnetic torque output

6. Conclusion

For transient-free load transfer in industrial power network, a

system is proposed in this paper. The res ults are simulation

based which are obtained for the proposed system parameters.

The current transient during normal restarting and during soft

restarting has been compared, by which we come across the

fine results of soft-restarting in which current trans ients are

get reduced and the time required for the system restoration is

also get reduced. Hence this method is reliable in case of

industrial loads for acquiring service restoration after fault as

quick as possible.

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International Journal on Applied Physics and Engineering

DOI: 10.37394/232030.2024.3.8

Vikramsingh R. Parihar, Rohan V. Thakur,

Dr. Mohan B. Tasare, Harshada M. Raghuwanshi,

Mohini G. Fuse, Dr. Soni A. Chaturvedi

E-ISSN: 2945-0489

Volume 3, 2024

Contribution of Individual Authors to the

Creation of a Scientific Article (Ghostwriting

Policy)

The authors equally contributed in the present

research, at all stages from the formulation of the

problem to the final findings and solution.

Sources of Funding for Research Presented in a

Scientific Article or Scientific Article Itself

No funding was received for conducting this study.

Conflict of Interest

The authors have no conflicts of interest to declare

that are relevant to the content of this article.

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(Attribution 4.0 International, CC BY 4.0)

This article is published under the terms of the

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International Journal on Applied Physics and Engineering

DOI: 10.37394/232030.2024.3.8

Vikramsingh R. Parihar, Rohan V. Thakur,

Dr. Mohan B. Tasare, Harshada M. Raghuwanshi,

Mohini G. Fuse, Dr. Soni A. Chaturvedi

E-ISSN: 2945-0489

Volume 3, 2024