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APPLICATION OF RESONANT METHODS OF ELECTRIC POWER TRANSMISSION IN POWER SUPPLY OF LARGE AIRPLANES
02.04.2025 18:43
[ 3. Nauki techniczne]
Автор: Oleksandr Sieliukov, Dr. tech. sci, Professor, School of Aerospace Engineering, Xi'an Jiaotong University, Xi'an, China, State Key Laboratory for Strength and Vibration of Mechanical Structures; Cai Licong, master student, School of Aerospace Engineering, Xi'an Jiaotong University, Xi'an, China, State Key Laboratory for Strength and Vibration of Mechanical Structures
ORCID: 0000-0001-7979-3434 Oleksandr Sieliukov
ORCID: 0009-0003-9423-7075 Cai Licong
Currently, aviation technology is evolving in the direction of intelligence and electrification. Intelligent electric aircraft with powerful energy is a trend in the future development of aviation technology. Now the world has great hopes for new layouts and aerodynamics in airplanes with electric propulsion.
In prospective air transport products, such as airplanes, it is not essential for the battery pack to be located next to the electric motor it powers. Instead, the battery is likely to be positioned closer to the aircraft's center of gravity due to its weight and size. The engines may be situated on the wings or in the tail section. In this scenario, an electrical cable must be installed as a power line between the battery and the engine, which requires thicker and heavier wires as the power of the electric motor increases. The electric current flowing through this cable generates heat, leading to technological losses during the transmission of electrical power from the battery to the electric motor.
The problem of reducing these technological costs should be addressed by utilizing new-generation electrical systems that employ high-frequency alternating current, enabling the creation of electrical equipment with significantly smaller dimensions compared to equipment operating on direct current from a battery. Such systems must utilize the phenomenon of resonance, be capable of transmitting electricity through a thin wire cable line, and consist of a voltage and frequency conversion device for transmitting power through the cable, the power cable line itself, and a device for converting the voltage back to the form required to power the motors. The motors in this case may be either DC or AC. For the first time, the transmission of electricity through a single-wire cable line at an increased frequency was proposed and realized by N. Tesla more than 100 years ago [1].
It is known that the set of equipment developed at the Research Institute of Railway Transport [2, p.295] operated at a frequency of up to 10 kHz and a voltage of up to 1000 V in the power line allowed to transmit electricity through a single-wire power line with a capacity of up to 3 kW at a distance of up to 2 km. According to the results of their tests, it was determined that the overall efficiency was 83 %.
Another experiment investigated how the quality of grounding affects the maximum power transmitted by the receiving converter [3, p. 14]. The results indicate that even with minimal grounding of the receiving converter, the difference in transmitted power is not significant. However, when grounding is established using a wire, electricity can be transmitted at approximately 1 kW.
As in all static electrical energy converters, the efficiency of a resonant single-wire electrical energy transmission system increases with increasing load power. The efficiency of the converter equipment itself at its maximum load can reach 88-91%.
In the resonant system, the transmission line capacitance is a component of the resonant loop. Using this cable as a transmission line only slightly reduces the resonant frequency, and the transmitted power during the same experiment was 2.5 kW. However, in a non-resonant power transmission system operating at a higher frequency, this capacitance acts as a reactive load, leading to a maximum transmitted power of only 750 W. The transmission system is designed to operate at voltages up to 1000 V, and the electromagnetic radiation level was measured for comparison with sanitary standards and regulations. Measurements of the maximum values of alternating electric and magnetic field intensity at personnel workplaces in the frequency band of 2 kHz to 400 kHz were conducted at three points (0.7 m, 1.5 m, and 2 m above the floor) along the transmission line suspended in the air at a height of 3 meters. The results indicated that the maximum values of the alternating electric field in the frequency range of 2 - 400 kHz were 100-150 V/m, significantly lower than the maximum permissible level for personnel, set at 500 V/m. Similarly, the maximum values of the alternating magnetic field in the same frequency range were found to be between 0.6 and 1.7 μT, also well below the maximum permissible level for personnel, which is 62.5 μT [5].
Figure 1: Resonant wire system of electric power transmission [4, p.36]: 1 - frequency converter; 2 - capacitance of the resonant circuit of the step-up transformer; 3 - resonant circuit of the step-up transformer; 4 - single-wire line; 5 - resonant circuit of the step-down transformer; 6 - capacitance of the resonant circuit of the step-down transformer; 7 - rectifier-inverter; 8 - load; 9 - isolated capacitance
The principle of operation of a resonant power transmission system is based on the use of two transformers operating at a frequency of several kHz and a single-wire line between them, with line voltage up to 10 kV when operating in resonant mode (Fig.1). The transmitting transformer acts as a resonant transformer, setting the operational frequency of the power transmission system. The receiving transformer serves as a broadband step-down transformer. In this case, the elements of the airplane body are used as the second wire.
A resonant transmission transformer consists of a power resonant circuit and a step-up/step-down winding. The receiving transformer does not affect the resonant frequency of the transmission system, allowing multiple transformers to be connected to the transmission line, provided the total power does not exceed the transmission voltage converter's capacity.
The maximum output power of the converter depends on the voltage applied to the circuit, the voltage across the circuit, the circuit capacitance, the frequency and other parameters. Calculation of the maximum output power of a resonant circuit is based on the formula for the quality factor of a loaded circuit. The primary factor that determines the power of the resonant converter at a given frequency is the capacitance of the circuit capacitor. To reduce the mass dimensions of transformers, it is necessary to use cores. A receiving transformer based on a magnetically soft core is calculated using standard techniques. By changing the frequency, the transmitted power can be adjusted, for example, for control systems or airplane lights.
Resonant systems provide high power transmission efficiency when the entire system is tuned to specific parameters such as voltage, frequency, and load. However, a modern airplane experiences a time-varying load during flight, and the output voltage at the receiving end fluctuates several times, which is unacceptable for operating electrical equipment.
In flight, the load resistance in the aircraft power system changes significantly: the load is at its maximum at takeoff and at its minimum at cruising speed, which causes the output voltage to decrease as the load increases. To address the issue of significant changes in load resistance, it is necessary to employ a resonant power transmission system with output voltage stabilization.
Figure 2. Block diagram of the frequency conversion unit of a resonant power transmission system with output voltage stabilization
In this device (Fig. 2), power element 2 is regulated by set generator 1, which adjusts its frequency and voltage to align with the transmission line voltage via control unit 3. This unit stabilizes the voltage in the transmission line, irrespective of the load.
Since resonant systems operate at higher frequencies with higher voltages, electromagnetic radiation is present in a single-wire unshielded transmission line.
Thus, modern electrical power transmission systems use two- and three-wire lines to transfer electrical energy from the generator to the receiver via current and voltage waves. The primary losses stem from Joule heating resulting from the resistance of the wires, caused by the flow of active conduction current along the closed loop from the generator to the receiver and back.
The following advantages of the resonant single-wire system of electric power transmission at increased frequency have been revealed in the course of our own research:
- increased safety of operation: Compared to the transmission of electric energy at the same effective voltage level in the wire relative to ground for both direct and alternating current at a frequency of 50 Hz, no step voltage is generated. When the effective voltage of the wire is up to 1 kV, an electric shock to a person at high frequency does not occur.
- small mass dimensions of voltage converters compared to a similar system at 50 Hz frequency;
- it is possible to transmit electrical power over a single wire by using the airplane hull as the ground to transfer power between the transmitting and receiving units. At low loads, the receiving units can sometimes operate without a ground connection.
- both single-core wires and shielded cables can function as transmission lines, with the cross-sectional areas of the cable conductors being 20 to 50 times smaller than those utilized in DC power supply systems.
- there is no effect on wire communication channels within the frequency range of 1000-3400 Hz due to the mismatch of operating frequency ranges for other aircraft equipment.
- more than one power consumer can be connected to one resonant transmission system with output voltage stabilization function;
- a resonant power transmission system is not vulnerable to short circuits in the load because the system operates out of resonance, and the voltage converter remains idle.
- short circuits are impossible in a single-conductor cable, and a single-conductor cable cannot cause a fire;
- single-wire power transmission systems operating at higher frequencies, even without superconductivity technology, are more efficient than single-wire-to-ground lines using direct current or alternating current at industrial frequency. The efficiency of the equipment in a resonant power transmission system can exceed 80 %.
- in a resonant transmission line, the levels of electromagnetic fields comply with sanitary norms and regulations. Additional cable shielding will reduce electric and magnetic fields around the cable line.
References
1. Method of transmitting power over a single wire. URL: https://molotokrus.ua/sposob-peredachi-energii-po-odnomu-provodu (date of circulation 28.03.2025).
2. D. V. Ermolenko, l. Yu. Yuferev, O. A. Roshchin. Test results of the resonant single-wire system of electric power transmission to the infrastructure objects of JSC “Russian Railways”. Bulletin of the Railway Transport Research Institute. 2018. ISSN 2223 – 9731.
3.Yu. Yuferev. Features of the operation of single-wire power grids of increased frequency. Agricultural machinery and technologies. 2017. N4. С. 14-19. URL: https://www.journal-vniizht.ua/jour/article/view/211(date of circulation 28.03.2025).
4. Strebkov D.S., Nekrasov A.I. Resonance methods of electric energy transfer. 2006. 304 рр. URL: https://rusneb.ua/catalog/000199_000009_009579769 (date of circulation 28.03.2025).
5. State sanitary norms and rules for the protection of the population from the effects of electromagnetic radiation. URL: https://zakon.rada.gov.ua/laws/show/z0488-96#n13 (date of circulation 28.03.2025).
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