Development of a capacitive-inductive power supply system for an electric vehicle

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Introduction              

The analysis of energy storage devices of modern electric transport has revealed the main disadvantages of batteries. These include low specific parameters in terms of energy and power, as well as deterioration of characteristics with an increase in current and a decrease in ambient temperature [12]. This leads to the fact that the power reserve of an electric car is several times less than that of a similar wheeled vehicle with an internal combustion engine. In addition, the charge time of the traction battery is several hours, while refueling the fuel tank of a passenger car takes about a minute. In this regard, the problem of developing an alternative system of traction electrical equipment is very relevant. Transferring energy to an electric vehicle in a contactless way may prove to be a promising solution. Table 1 summarizes data on research and development in the field of contactless power supply of electric vehicles [2-11].

Table. 1

Some developments in the field of contactless power supply of electric vehicles

Project name	Country	Year	Vehicle type	Power, kW	Efficiency, %	Frequency, kHz
Bombardier PRIMOVE	Canada	2018	Tram, electric bus	200	85	20
KAIST OLEV 4G	Korean Republic	2015	Electric bus	100	80	20
Qualcomm FABRIC	USA	2017	Electric car	20	85	85
ORNL	USA	2022	Truck, electric bus, electric car	200	85	85
Electreon	Israel	2023	Truck, electric bus, electric car	70	85	85
Toyota	Japan	2020	Electric bus, electric car	10	85	85

Resonant contactless power supply system with one primary winding Figure 1 shows the electrical diagram of the contactless power supply system of an electric vehicle with one primary winding [1]. Fig. 1 Electrical diagram of the contactless power supply system of an electric vehicle with one primary winding             A controlled inverter containing transistor switches Q1...Q4 generates an input voltage u1(t). Capacitors Cp and Cs, as well as inductors Ls, are used to compensate for reactive power. The primary winding L1 is located under the surface of the roadway and has a transformer connection with the secondary winding L2 installed on board the electric vehicle. The output voltage u2(t) is converted by a single-phase two-half-period rectifier to charge the traction battery.             The highest efficiency of the system is achieved when transmitting energy at a resonant frequency:                                     (1) The inductance of the compensating coils is determined based on the inductance of the primary and secondary windings:   ,                                             (2)             where: α is the calculated coefficient. It is selected arbitrarily in the range The capacities of serial capacitors are determined by the expression (3):                                      (3) The characteristic of the output voltage of the inverter is described by equation (4): ,                                   (4)             where:             D is the duty cycle of the inverter. The effective value of the input voltage of the rectifier is determined by the formula (5):                                   (5) Primary and secondary currents:                                              (6) Inverter output current:                                            (7) Input current of the rectifier:                                          (8) Thus, the transmitted power can be calculated according to (9):                                         (9)             The main advantages of single primary winding systems are ease of operation and high specific primary power. The disadvantages include low specific secondary power. Resonant power supply system with multiple primary windings   Fig. 2 Electrical diagram of the resonant power supply system of an electric vehicle with several primary windings             Figure 1.2 shows the electrical diagram of the resonant power supply system of an electric vehicle with several primary windings [1]. In this system, inverters and compensating devices are connected in parallel, which makes it possible to implement a system with several primary windings. The voltage is applied to each of them individually. Otherwise, the device and the principle of operation are similar to the system discussed above.                         The output power is determined according to the expression (10):                                 (10) Analyzing (10), it can be concluded that the transmitted power is defined as the modulus of the sum of the capacities of the primary windings. Thus, the inclusion of any primary winding does not always lead to an increase in power in the secondary, since the magnetic induction vector can be directed against the main flow. In this case, the inverter controlling the negatively coupled winding must be switched off. Fig. 3 Curves of changes in the efficiency of the system over time Figure 3 shows the curves of changes in the efficiency of the system over time [1]. As can be seen from the characteristics, the efficiency of the device is very high and is about 92%. The main advantage of the system is high efficiency. Disadvantages include a complex control system and low specific primary power. Electrostatic power supply system   The methods of transferring electricity to the vehicle discussed above involve the organization of an air transformer. Thus, their work is based on Faraday's law of electromagnetic induction: ε=w                                                  (11)             where:             w is the number of turns of the winding;             F is the magnetic flux, Wb. This section provides a method for transmitting electricity through an air condenser.             The device of the vehicle's power supply system by the method of electrostatic induction [13] is shown in Figure 4. Fig. 4 Device of the vehicle power supply system by electrostatic induction: 1 – electric vehicle; 2 – power source; 3 – secondary transformer winding; 4 – primary transformer circuit; 5, 8, 9 – network cables; 6 – neutral plate; 7 – converter and switching equipment; 10 – support surface; 11 – on–board energy storage; 12 – air gap; 13 - wheel.   The power source is powered by a transformer connected to the mains cables. An electrostatic field arises between them and the neutral plate of the capacitor. Converter-switching equipment is used to coordinate the input voltage and the charge voltage of the on-board storage device.             The power transmitted through the air condenser to the vehicle is determined by the formula (12): ;                                         (12) where: ƒ0 – resonant frequency, Hz; C is the capacity of the air condenser, F; V is the voltage in the line, in; K0 is the coupling coefficient.             Advantages: High efficiency; High handling properties of an electric vehicle; The possibility of power supply to other vehicles, including those with propellers made of dielectric material. Disadvantages: Large dimensions of the equipment; Low specific energy; High demands on the source of electricity. Development of a block diagram of traction electrical equipment of an electric vehicle with a capacitive-inductive power supply system               The conducted review and analysis of various methods of contactless energy transmission, as well as R&D on the research topic, showed broad prospects for using an inductive transmission method with a single primary winding due to the following advantages: small dimensions of equipment, high specific energy, the possibility of using energy sources with low parameters, ease of operation, as well as high efficiency. The use of electric traction in transport has a number of advantages [18-19]. However, the specific energy of chemical storage does not exceed 576 J/g, which is about 100 times lower than that of gasoline or diesel fuel [20]. In this regard, electric vehicles are equipped with rechargeable batteries, the mass of which reaches 30% of the total mass of the vehicle with an equal power reserve with a similar car [12]. On the other hand, electric vehicles are currently operated mainly in cities where there is a cyclical mode of movement with a constant alternation of phases of acceleration, uniform movement, braking and stopping.             The cycle specified in UNECE Regulation No. 83 has been adopted as a cycle for testing vehicles for fuel efficiency and exhaust gas toxicity [14]. According to the rules, the cycle consists of two parts – urban and mainline. Since research and calculations will be carried out for an urban electric vehicle, it is advisable to use only the first part of the cycle. The total duration of the urban cycle is 195 s. Fig. 5 Calculated urban traffic cycle according to UNECE Regulation No. 83 Let's analyze the urban cycle. The distance between stops is small (about 300...500 m), since there is a large amount of traffic interference in the city, such as traffic lights, pedestrian crossings, artificial bumps, etc. In this regard, an electric car requires a relatively small amount of energy to overcome the distance from stop to stop. However, frequent accelerations imply high power costs. Up to 80% of the storage capacity is required to overcome the inertia of the vehicle [20]. Therefore, the energy storage device must have a high specific power in order to have acceptable weight and size parameters.             As is known, capacitive energy storage devices have high specific power, but relatively low specific energy, and chemical NE have exactly the opposite properties [12]. In addition, capacitors with a double electric layer are characterized by simplicity of design, ease of use, safety, environmental friendliness, and most importantly, the ability to quickly accumulate and release stored energy. ENE are operable at low negative temperatures and are able to withstand deep discharges, overcharges and short circuits. The service life, in particular, of molecular storage devices (MCE) provides more than 500,000 charge-discharge cycles, which is three orders of magnitude longer than that of batteries [15-16].             Figure 6 shows a diagram of the traction electrical equipment system of an electric vehicle with capacitive-inductive power supply. Fig. 6 Diagram of the electric vehicle traction system: TEM is an electric traction machine. Under the support surface is the primary winding of the air transformer, to which an alternating mains voltage is applied. As a result of the flow of the primary current, an alternating magnetic field arises, penetrating the coils of the secondary winding, which can be placed both inside the tires (according to Figure 6) and in the lower part of the electric vehicle. An EMF of self-induction occurs in the secondary winding, which is applied to the input of the rectifier. In the case of placing the secondary winding inside the tires, brushes and contact rings are used to supply the EMF. A thyristor rectifier is provided to convert alternating current into direct current and regulate the charge voltage of the capacitor bank. During acceleration or uniform movement of the electric vehicle, the voltage of the capacitor bank is applied to the input of a three-phase inverter to which the synchronous machine is connected. The torque of the synchronous machine is transmitted to the driving wheels by means of the main gear, differential and drive shafts. Figure 6 shows a variant using a gimbal transmission. During regenerative braking, the torque from the driving wheels is supplied to the synchronous machine using the above mechanisms, which is switched to generator mode. To charge the capacitor bank, the alternating current of the synchronous machine is converted to direct current by a three-phase two-half-period rectifier. Figure 7 shows the algorithm of operation of the traction electrical equipment system (STEE) in the urban traffic cycle. Fig. 7 Algorithm of STEE operation in the urban traffic cycle: CB – use of capacitor bank energy for movement; RB – regenerative braking Thus, as a result of the study, a scheme for the traction electrical equipment of an electric vehicle with capacitive-inductive power supply was developed, and an algorithm for its operation in the urban traffic cycle was determined in accordance with UNECE Regulation No. 83.

 

About the authors

Egor M. Klimov

Moscow Polytechnic University

Author for correspondence.
Email: egormixalich71@mail.ru
ORCID iD: 0009-0004-9739-0267
SPIN-code: 2759-7425

Assistant of the Electrical Equipment and Industrial Electronics Department

Russian Federation, 38 Bolshaya Semyonovskaya street, 107023 Moscow

Anatoly M. Fironov

Moscow Polytechnic University

Email: a.m.fironov@mospolytech.ru
ORCID iD: 0000-0003-2683-9958
SPIN-code: 8824-5702
Scopus Author ID: 462035

Associate Professor, Cand. Sci. (Tech.), Associate Professor of the Land Vehicles Department

Russian Federation, 38 Bolshaya Semyonovskaya street, 107023 Moscow

Ruslan A. Maleev

Moscow Polytechnic University

Email: 19rusmal@gmail.com
ORCID iD: 0000-0003-3430-6406
SPIN-code: 7801-3294

Associate Professor, Cand. Sci. (Tech.), Professor of the Electrical Equipment and Industrial Electronics Department

Russian Federation, 38 Bolshaya Semyonovskaya street, 107023 Moscow

Sergey M. Zuev

MIREA-Russian Technological University

Email: sergei_zuev@mail.ru
ORCID iD: 0000-0001-7033-1882
SPIN-code: 6602-6618

Associate Professor, Cand. Sci. (Physics and Mathematics), Associate Professor of the department of Optoelectronic devices and systems

Russian Federation, 78, Vernadsky Avenue., 119454 Moscow

References

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