Novosibirsk State Technical University (NSTU) has proposed a method for multifactorial assessment of locations for the installation of electric charging stations (ECS). It allows you to take into account the urban environment, scenarios for the use of electric vehicles and the limitations of electrical distribution networks. The developed approach is universal and can be applied when planning charging infrastructure in different cities.
As Pavel Kazak, an assistant at the Department of Power Supply at NSTU-NETI, notes, it is important to approach the design of the charging infrastructure, taking into account the fact that an electric car is not just a means of transportation - it is a high-tech device that consumes a significant amount of energy and needs to be charged. Using an electric car based on the model of a digital device forces us to look at this type of transport in a new way.
"How do we use the phone? We put it on slow charge at night and hope that we have enough for the whole day. But if it's not enough, then we're looking for charging where we are, so that we can charge up as quickly as possible and get on with our business. We have one smartphone usage scenario at work, another at home, and so on. If we take into account the functional areas of the city, then we can build the infrastructure in such a way that it is really user-friendly and at the same time predictable and understandable to power engineers," said Pavel Kazak.
Charging stations are an additional distributed stochastic load and have a significant impact on the urban power supply system. For example, mass use of chargers during peak hours can lead to exceeding the permissible load and, as a result, to emergency shutdowns, damage to equipment, etc. In Russia, according to forecasts, the electric vehicle market will move to a mass level by 2030, the share of sales will reach 12-25% by 2035, which makes the task of reasonable selection of sites for the placement of electric vehicles urgent.
As part of his dissertation, Pavel Kazak conducted a large-scale study of the influence of the topology of the charging station network on the operating modes of power supply systems in megacities. Data on the load of electrical networks in the business zone of Novosibirsk were taken (an electrical network diagram with measurements for the current year and retrospective data) and an analysis of changes in the load schedule was carried out, taking into account charging stations. The simulation results showed that with the spontaneous placement of the EHS and the absence of regulation of the charging load, the risk of local overloads, shortage of the network reserve, increased power losses and deterioration of voltage levels increases. To reduce these risks, it is necessary to take into account not only the locations of the ECS, but also their operating modes during the day.
"We decided to develop a methodology that would explain what electric vehicles are, electric charging stations, how they should work, and provide effective tools for making informed decisions about where and which charges to install in order to ensure user convenience and not overload the city's power grid. The approach to charging infrastructure planning is based on the allocation of typical zones into which any megacity can be divided, and on behavioral scenarios based on data on the time spent by people in different zones. People stay in the residential area in the evening and at night, they come to work in the business area and spend the day there. There are also transit zones - entry or exit from the city. Each of them requires your own types of charging. In a residential area where an electric vehicle can charge throughout the night, slow, low-power charging is needed. The car stays in the business area for a limited time, so the charging infrastructure performs the function of pick-up stations, that is, it is focused on short-term recharging without prolonged parking, rather than fully replenishing the charge. Fast DC stations with a limited charging session time are advisable here. In the transit zone, fast charging is possible with a time limit of no more than an hour," Pavel Kazak said.
Scientists at NSTU-NETI have predicted the operating mode of the electric grid, taking into account the developed proposals for the distribution of charging station capacity by type of zones and time constraints. For example, limiting charging during periods when it does not correspond to the usage scenario of a particular zone, and transferring part of the load from the evening maximum to less busy intervals of the day. The forecast showed that the proposed measures can reduce the depth of voltage drawdowns, reduce the load on transformers and reduce power losses.
The developed methodology is based on an integral assessment of the site based on six factors: traffic intensity, availability of free space and parking, the possibility of connecting to the electric grid, the cost of the land, distance from existing agricultural facilities and the prospects for the development of the area. A discrete rating scale is set for each factor, and the weighting coefficients are determined by Saati's analyzing hierarchies. Based on a comprehensive analysis of the proposed addresses, an estimated integral indicator of suitability for each site is derived, which makes it possible to rank sites according to the degree of suitability for hosting ECS.
"For example, a contractor who plans to install a certain number of charging stations gives a list of addresses and asks to analyze whether the installation is appropriate. We evaluate each address according to an integral indicator of suitability and give an expert opinion: out of 10 proposed addresses, three are categorically not recommended due to low demand./lack of power, five - with reservations, two - fully suitable for installation. Resources should be directed where there is behavioral demand and technical opportunity," explains Pavel Kazak.
Since it is difficult to analyze a large number of locations manually, a software package has been developed to evaluate the location of the ECS. The software consists of two parts. The first module is the preprocessing of the source data and the evaluation of the location. The program analyzes the factors affecting the effectiveness of the ECS installation and issues an expert opinion on each location based on the suitability indicator. The second module is engaged in preprocessing the initial network data for further calculation of the steady-state mode. It is calculated to assess the likelihood of abnormal situations when adding load to the ECS. The software has received a certificate of state registration of a computer program.
The scientists tested the methodology on real ECSes in Novosibirsk and Moscow. In the course of the study, implementation certificates were received from major industry companies in Novosibirsk. The proposed methodology can be used by city authorities and investors to make an informed choice of ECS installation sites and can be scaled to any city.
Earlier, NSTU-NETI developed an innovative battery heating system for electric vehicles and released the first batch of electric charging stations capable of operating at extremely low temperatures.