# Modélisation et simulation de systèmes électrotechniques pour l'énergie renouvelable, le transport et les applications industrielles: Une brève revue

## Modeling and simulation of Power Electronic based Electrotechnical Systems for Renewable Energy, Transportation and Industrial Applications: A Brief Review

Seyed Masoud Mohseni-Bonab<fnref n="1" />, Innocent Kamwa<fnref n="2" />,*

**RÉSUMÉ.** Dans cet article, une revue complète des recherches récentes sur les systèmes électrotechniques basés sur les convertisseurs de puissance modernes (ETS) est réalisée. En particulier, les ETS basés sur l'électronique de puissance (PE) sont étudiés. La revue de la littérature consiste en une classification standard des ETS basés sur les PE, ainsi qu'une étude sur des forces et les faiblesses de ces dispositifs sur les sources d'énergie renouvelables.

**ABSTRACT.** In this paper, a completed review of recent researches about modern power converter based electrotechnical systems (ETSs) has been carried out. In particular, power electronics (PEs) based ETSs have been investigated. The literature review consists of a standard classification of PEs-based ETSs, along with a survey on strengths and weaknesses of these devices impact on renewable energy sources.

**MOTS-CLÉS:** Systèmes électrotechniques, l'électronique de puissance, sources d'énergie renouvelables, systèmes de stockage d'énergie.

**KEYWORDS:** Electrotechnical systems (ETSs), power electronics (PEs), renewable energy sources (RESs), energy storage systems (ESSs).

<footnote n="1">¹ Department of Electrical Engineering, Laval University, Quebec, G1V0A6, CA.</footnote>

<footnote n="2">² Power System and Mathematics Département, Hydro-Québec/IREQ, Varennes QCJ3X1S1, CA.
s.m.mohsenibonab@ieee.org, * kamwa.innocent@ireq.ca (corresponding author)</footnote>
Acronyms

<table><tr><td>ETSs</td><td>Electrotechnical systems</td></tr><tr><td>PEs</td><td>Power electronics</td></tr><tr><td>RESs</td><td>Renewable energy sources</td></tr><tr><td>ESSs</td><td>Energy storage systems</td></tr><tr><td>DGs</td><td>Distributed generation</td></tr><tr><td>SGs</td><td>Smart Grids</td></tr><tr><td>FACTS</td><td>Flexible AC Transmission System</td></tr><tr><td>HVDC</td><td>High-voltage direct current</td></tr><tr><td>CHP</td><td>Combined heat and power</td></tr><tr><td>WG</td><td>Wind generation</td></tr><tr><td>DFIG</td><td>Doubly fed induction generators</td></tr><tr><td>PMSG</td><td>Permanent magnet synchronous generators</td></tr><tr><td>MPPT</td><td>Maximum power point tracking</td></tr><tr><td>OPF</td><td>Optimal power flow</td></tr><tr><td>SOC</td><td>State of charge</td></tr><tr><td>TNA</td><td>Transient network analyzer</td></tr><tr><td>ATL</td><td>Artificial transmission line</td></tr><tr><td>EMTP</td><td>Electromagnetic transients program</td></tr><tr><td>DTS</td><td>Dispatcher training simulator</td></tr><tr><td>HIL</td><td>Hardware-in-the-loop</td></tr><tr><td>SSSC</td><td>Static synchronous series compensator</td></tr><tr><td>TCSC</td><td>Thyristor controlled series capacitor</td></tr><tr><td>SVC</td><td>Static VAR compensator</td></tr><tr><td>STATCOM</td><td>Static synchronous compensator</td></tr><tr><td>UPFC</td><td>Unified power flow controller</td></tr><tr><td>IPFC</td><td>Interline power flow controller</td></tr></table>
# 1. Introduction

Electrotechnical systems (ETSs) plays an important role in our lives and have a wide range of usage. In this paper, in particular those which are related to modern power electronics (PEs) have been investigated.

This paper is categorized as follows: In section 2 the fundamentals of PE devices are described. Section 3 reviewed the distributed generation and Smart Grid technologies. FACTS devices and HVDC grids are reviewed in section 4 and 5, respectively. Topics related to renewable energies, such as, wind, PV and ESSs are reviewed in section 6. In section 7, SPS and EMTP-RV environments are presented as the best tools for dealing with PEs-based ETSs. Finally, the section 8 concludes the paper. Figure 1 shown the flowchart of this review paper.

<figure><img src="image_1.png" /><figcaption>Figure 1. Summary of power electronics based electrotechnical systems components according to paper organization</figcaption></figure>
## 2. An overview of fundamentals of power electronics

Recently with the growth of emerging new technologies in renewable energy systems, the technology of PEs is more important because of many renewable resources are intermittent and without PEs, voltage, frequency, and power output characteristics could not be regulated. The modern distributed structure of a power grid is shown in Figure 2.

<figure><img src="image_2.png" /><figcaption>Figure 2. Modern scenario of the electrical grid</figcaption></figure>

<table><caption>Table 1. Classification of renewable energy sources</caption><thead><tr><th rowspan="2">Renewable energy systems</th><th colspan="2">Housing Applications</th><th colspan="3">Solar Energy</th><th colspan="3">Marine/Fluvial energy</th><th rowspan="2">Wind Energy</th><th rowspan="2">Geothermal Energy</th></tr><tr><th>Proof PV</th><th>Solar thermal roof</th><th>PV Plants</th><th>Solar Thermal</th><th>Wave Energy</th><th>Tidal Energy</th><th>Hydroelectric</th></tr></thead><tbody><tr><td>Maximum nominal power</td><td colspan="2">50 KW</td><td>250 MW</td><td>370 MW</td><td>150 Kw</td><td>256 MW</td><td>14 GW</td><td>6 MW per Tur.</td><td>720 MW</td></tr><tr><td>Usual converter topologies</td><td>DC/AC AC/DC</td><td>*</td><td>DC/DC DC/AC</td><td>*</td><td>AC/DC, DC/DC, DC/AC</td><td></td><td>*</td><td>Back-to-Back</td><td>*</td></tr><tr><td>Typical power semiconductors</td><td>Mosfet</td><td>*</td><td>IGBT IGCT</td><td>*</td><td>IGBT, IGCT</td><td></td><td>*</td><td>IGBT IGCT</td><td>*</td></tr><tr><td>Availability</td><td colspan="3">Solar irradiance dependence</td><td>Random</td><td>Intermittent</td><td>Seasonal</td><td>Random</td><td>Constant</td></tr><tr><td>Technology trend</td><td>Power density efficiency</td><td>Nominal power efficiency</td><td colspan="3">Robustness Under storms</td><td>*</td><td>Gearless, Offshore, Power</td><td>Development cost</td></tr></tbody></table>
Modern distribution systems encounter new challenges due to high penetration of
renewable energy sources (RESs) which are naturally stochastic. Different PEs devices
such as, DC-AC inverters, AC-DC rectifiers, and DC-DC converters are dependent to
the renewable energies. A new classification of RESs is given in Table 1. This
classifcaiton is based on their nominal power, the usual power converters and
corresponding power semiconductors required for the grid integration (if necessary), the
availability of the renewable energy source and the corresponding technology trend.

3. An Overview of Distributed Generation and Smart Grid Concepts and Technologies

Microgrids (MGs) is a promising concept to meet the challenges of integrating
various distributed generators (DGs) and energy storage systems (ESSs) into the
electricity network [1]. Besides, the smart grids (SGs) is conceived as an electric grid
able to deliver electricity in a controlled and smart way to consumers [2].

Based on recent articles in this area [3, 4], the main advantages of smart grids can
be increasing the reliability and efficiency of the power systems.

The supporting idea of the formation of MGs and SGs is that a paradigm consisting
of multiple DG units and aggregated loads are far more reliable, economical and
practical than a single DG unit serving a single load [5]. The implementation of the SGs
and MGs concepts can bring multiple benefits to both of the consumers and distribution
utilities. Examples of such benefits include:

➢ Reliability increase: the capability of the SGs and MGs to operate independently from the main grid allows the MG to feed its loads autonomously when the main grid is not available and thus avoid possible load interruptions [6-8].

➢ Grid support: by clustering loads and DG units and treating each of these clusters as a relatively independent power unit, SGs and MGs can be used to supply electrical services to the main grid especially at the times of grid peak demand [9, 10].

➢ Local community support: with the increasing efficiencies of the DG units, MGs can support local and developing communities' economies by creating jobs within such communities to generate the required electricity instead of importing it from the main grid. The implementation of SGs and MGs can also expedite the development of such communities instead of waiting for the power companies to build centralized power plants that are costly and take much longer to get online [11].
➤ Reducing the carbon footprint: the SGs and MGs can reduce the environmental impacts associated with the construction of large power plants to cope with the electrical load growth by allowing more dependence on small efficient DG units. Moreover, SGs and MGs can largely facilitate the implementation of the combined heat and power (CHP) plants [12].

➤ As mentioned above, SGs and MGs can operate in both grid-connected and islanded modes. In the islanded mode, the key questions are how to ensure the supply-demand balance within the microgrid and how to achieve this in the most cost-effective way. Wind and solar power are among the most promising renewable power supply alternatives due to their abundance, cleanness, and free primary energy source. However, the intermittency of wind and solar power supply poses new challenges to the operation and control of autonomous MGs, especially under high penetration levels [1]. The popular maximum power point tracking (MPPT) algorithms emphasize high energy usage efficiency but may cause a supply-demand imbalance when the available renewable generation is not equal to the total load demands, especially for autonomous MGs [13]. Furthermore, it should be noted that in modern grids, power management and stability assurance are critical tasks because of the variables involved in generation and on the demand side. There are many different methods to approach these problems. However, the absorption and injection of energy by energy storage systems (ESSs) may be the best solution for managing this issue well [14].

## 4. FACTS Devices

There are a variety types of the FACTS devices implements as shown in Figure 3. These tools are either series or parallel, or a combination of two in the circuit, which has the capabilities of: increasing the transmission capacity, improving the dynamic and permanent stability, improving the oscillation and improving the stability of the voltage [15].

With the rapid development of power electronic technologies, utilizing Flexible AC Transmission System (FACTS) for performance improvement of existing transmission systems has been made economic and practical. FACTS devices enhance the controllability of the transmission lines and increase their power transfer capability [16, 17].

In recent years, there has been an increasing trend in the development and use of FACTS controllers in power transmission systems. The power electronics-based FACTS
devices provide more flexibility to AC power systems. Flexibility is interpreted as the capability of a system to respond quickly to the control input and to change in its operating point [18].

<figure><img src="image_3.png" /><figcaption>Figure 3. Overview of FACTS devices</figcaption></figure>

# 5. HVDC Transmission Systems

AC transmission lines are the most popular and most commonly used lines in power grids, but nowadays, due to several following reasons, HVDC transmission systems have become very popular in certain applications [19]:

* In HVAC lines, when the length of the lines are increased, the power transmission capability is reduced, but with utilizing HVDC systems, the amount of transferred power would be the constant value.

* Directly connecting two AC systems with different fundamental frequencies.

* From economic costs point of view, there is a critical distance beyond which the investment cost for building new HVDC transmission lines is less than that for its AC counterpart.

* From environmental aspects point of view, such as lower visual impact and space requirements [20], HVDC transmission lines are better.
HVDC installations include several devices. Among them, one of the most important is the power electronic converter. As for FACTS devices, the power semiconductor technology used for building the power converter can be thyristor-controlled or gate-controlled power switches [21].

Depending on the rated power range of the transmission line, different HVDC technologies can be chosen. In addition, the application and location of the transmission system define the most suitable configuration of the HVDC system. Different valid configurations can be described for systems built with CSC-HVDC (Figure 4 (a)) or VSC-HVDC (Figure 4 (b)) technologies [20, 21]. These two types and also a simplest configuration (back-to-back system), is presented in Figure 4 (c).

<figure><img src="image_4.png" /><figcaption>Figure 4. HVDC technologies: (a) CSC-HVDC, (b) VSC-HVDC and (c) back-to-back configurations</figcaption></figure>
# 6. Renewable Energy Technologies

## 6.1. Wind Energy

The existing wind farms are usually employing variable speed turbine technology. In this context, doubly fed induction generators (DFIGs) and permanent magnet synchronous generators (PMSG) are attractive choices [22]. These machines are able to exchange reactive power with the AC network they connected. In [23], a detailed model of capability curve for DFIG is developed. This model is utilized in [24] and [25] to incorporate wind farms in the OPF problem. Also, PMSG is basically synchronous generators and the corresponding capability curve is well known.

## 6.2. PV

The continuously decreasing price of PV modules and the strong support of governments in pushing this technology have led to the consideration of PV and solar thermal energy as important factors in the present and future renewable energy market. One important part of these installations is based on housing applications (<5 kW), but as part of the great evolution of the PV sector in recent years, larger PV power plants are steadily being constructed, which currently achieve a nominal power up to 250MW (Agua Caliente Solar Project in the United States). Today, the main installed PV capacity is grid-connected with the off-grid sector accounting for an estimated 2% of global capacity [19].

Since, the output of PV panels is a DC voltage, and the existence of a power converter is required to generate an output AC voltage, ETSs impacts on PV panels is really important.

## 6.3. Energy Storage Systems

Energy storage is the capture of energy produced at one time for use at a later time. Energy comes in multiple forms including radiation, chemical, gravitational potential, electrical potential, electricity, elevated temperature, latent heat and kinetic. ESSs involve converting energy from forms that are difficult to store to more conveniently or economically storable forms. Some technologies provide short-term energy storage, while others can endure for much longer. In the following the energy storage technologies are included. Investigations of the challenges and barriers to power systems indicate that ESSs should aim at the following three targets [26, 27]:
* Enhancing the reliability of renewable energy sources (RESs);

* Improving the resilience of the grid and resolving its issues;

* Realizing the benefits of smart grids and optimizing generation to suit demand;

* By storing energy when it is easily available and dispatching it during shortages, the combination of energy storage technology and RESs can help to stabilize power output while also enhancing the reliability of RESs. Moreover, ESSs can increase the resilience of systems during weather variations, natural disasters, and so on.

Indeed, in implementing an optimum storage project, three different steps are needed to be considered [28]:

* Investigating the type and size of the storage system and selecting the one that is best for the system.

* Defining the best control strategy for the application considering the selected storage system.

* Investigating the net present value of the storage system.

Besides, to store the generated power, it is necessary to convert it into other forms of energy, such as chemical or mechanical energy. Energy storage consists of three different steps [29]:

* Charge: absorbing electrical energy from sources

* Storage: converting electrical energy to other types of energy and storing it

* Discharge: injecting the stored electrical energy back into the system

### 6.3.1. Batteries

The battery stores energy in an electrochemical form and is the most widely used device for energy storage in a variety of applications. There are different kinds of batteries with different chemicals. The idea behind them is that the two different chemicals within a battery cell have different loads and are connected with a negative (cathode) and the other with a positive electrode (anode). When connected to an appliance the negative electrode supplies a current of electrons that flow through the appliance and are accepted by the positive electrode. There are two basic types of electrochemical batteries [30]:

1) **Primary Battery:** converts chemical energy into electric energy. The electrochemical reaction in a primary battery is nonreversible, and the battery is
discarded after a full discharge. For this reason, it finds applications where a high energy density for one-time use is required.

2) **Secondary Battery:** also known as the rechargeable battery. The electrochemical reaction in the secondary battery is reversible. After a discharge, it can be recharged by injecting a direct current from an external source. This type of battery converts chemical energy into electric energy in the discharge mode. In the charge mode, it converts the electric energy into chemical energy. In both modes, a small fraction of energy is converted into heat, which is dissipated to the surrounding medium. The round-trip conversion efficiency is between 70 and 80%.

For the use of storing energy produced by renewable energy sources only rechargeable batteries are relevant and will be considered.

There are at least six major rechargeable batteries available today. They are as follows:

* Lead-acid (Pb-acid)

* Nickel-cadmium (NiCd)

* Nickel-metal hydride (NiMH)

* Lithium-ion (Li-ion)

* Lithium-polymer (Li-poly)

* Zinc-air

The battery's latest maximum capacity, denoted by $Q_m$, is measured in ampere-hours (Ah), meaning it can deliver $Q_m$ A for one hour or $Q_m/n$ A for n hours. The product of the voltage and ampere-hour forms the watt-hour (Wh) which is the energy rating that the battery can deliver to a load from the fully charged condition.

The battery charge and discharge rates are stated in units of its capacity in Ah. For instance, charging a 100-Ah battery at $Q_m/10$ rate means charging at $100/10 = 10$ A. Discharging that battery at $Q_m/2$ rate means drawing $100/2 = 50$ A, at which rate the battery will be fully discharged in 2 h. The state of charge (SOC) of the battery at any time is defined as the following: [30]

$$SOC = \frac{Ah \text{ capacity remaining in the battery}}{\text{battery's latest maximum capacity}} \quad (1)$$

The SOC is the ratio between remaining capacity and the full charge, equal to 100% for full charge and 0% for full discharge. The SOC and its relation to capacity ($Q_m$) is outlined in the following equation [31]:

$$SoC(\%) = \left( \frac{Q_m - \int idt}{Q_m} \right) \times 100 \quad (2)$$
According to the degradation of $Q_m$, state of health (SOH) is defined as [31]:

$$SOH(\%) = \left( \frac{Q_m}{Q_{nom}} \right) \times 100 \qquad (3)$$

Where the $Q_{nom}$ is the battery's nominal capacity. A battery's SOH normally ranges within 0-100%, but when it is new, the SOH can be slightly larger than 100% due to product variations. The end of life of a Li-ion battery is commonly defined by the maximum cycles when the SOH drops to 80%. SOH is a key indicator of safe operation because it provides a timely warning that replacement is required.

During battery charging, the energy management software monitors the SOC, the overall health, and safe termination criteria. The continuously monitored operating parameters are the battery voltage, current, and temperature. The charging timer is started after all initial checks are successfully completed. Charging may be suspended (but not reset) if it detects any violation of critical safety criteria. The timer stops charging if the defect persists beyond a certain time limit. Normal charging has the following three phases:

* Bulk (fast) charge, which deposits 80 to 90% of the drained capacity

* Taper charge, in which the charge rate is gradually cut back to top off the remaining capacity

* Trickle (float) charge after the battery is fully charged to counter the self-discharge rate

The bulk-charge and the taper-charge termination criteria are preloaded in the battery management software to match the battery electrochemistry and system design parameters. For example, the NiCd and NiMH batteries are generally charged at a constant current (shown in Figure 5), terminating the charging when the continuously monitored ΔV is detected negative. On the other hand, the Li-ion battery, being sensitive to overcharging, is charged at a constant voltage, tapering off the charge current as needed (Figure 6).

<figure><img src="image_5.png" /><figcaption>Figure 5: Constant current charging of NiCd and NiMH batteries.</figcaption></figure>
<figure><img src="image_6.png" /><figcaption>Figure 6: Constant voltage charging of Li-ion battery.</figcaption></figure>

# 7. EMT simulation tools

Since the development of investigation methods of ETSs is a very important task in power systems operations, scientists and engineers paid more attention to ETSs in their research because of their applications in PEs. It is also a challenge that a lot of elements and devices that form an electrotechnical system have a complex intrinsic structure, and employment of specialized environment for their simulation. Analyzing ETSs generally is categorized in the two following forms:

- Dynamic analysis

- Steady-state analysis

In the area of dynamic analysis, the set of blocks contains the models of the complex systems. PEs-based ETSs can be simulated with different graphical programming languages, according to several publications in this area. Two powerful softwares, which are highly recommended by researchers and scientists are: 1) SimPowerSystems (SPS) [32] and 2) EMTP-RV [33]. SimPowerSystems operates in the Simulink environment.

Real-time power system simulation is becoming a standard technology in designing new devices and analyzing power system dynamics [34, 35]. Simulation of power system dynamics is an old technology in power system engineering. There are different forms for dynamics analysis: transient network analyzer (TNA), artificial transmission line (ATL), analogue simulator, electromagnetic transients program (EMTP), transient stability analysis and long-term dynamic simulation program, dispatcher training simulator (DTS), etc. In addition for real time simulation different environments have been introduced in the papers: RTDS [36], eMEGAsim [37] and HYPERSIM [38] are some of real-time simulators that are reported in the literature.

Hydro-Quebec (HQ), as a pioneer in this field, has extensively used its real-time simulation facilities for testing protection systems, new controllers and various FACTS systems and for optimization of existing controls. The outputs of HQ researches in real-time simulations are really extensive. For instance, in [39, 40] IREQ's power system
simulator features have been introduced. The application of this simulator on hardware-
in-the-loop (HIL) testing of HVDC, FACTS controllers and protection systems as well
as for the integration of wind generation on Hydro Québec's network are studied in this
paper in detail. In addition, in [41], a validation test of IREQ's power system simulator
with a relatively large AC-DC interconnected network including generators (turbine,
AVR), dynamic loads and a full bipole HVDC transmission system, are performed and
different characteristics of this simulator such as simulation time step are discussed. The
studied network is simulated on both Hypersim real-time simulator and on the hybrid
simulator that is connected with the real external HVDC controls.

8. Conclusion

From the technical comparison it can be concluded that modern power converter
based electrotechnical systems (ETSs) applications have grown rapidly in recent years
due to their undeniable roles in power systems schematics. In this review paper, the
literature review consists of a standard classification of power electronics (PEs)-based
ETSs, along with a survey on strengths and weaknesses of these devices impact on
renewable energy sources.

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