Matching the output voltage level of the energy recovery device and the voltage of the on-board network

. This article deals with the possibilities of applying magnetic dampers for damping of mechanical vibrations, both of car body and of radio-electronic equipment. An electronic device is proposed to adapt the output voltage of the energy recovery device to the voltage of the car's on-board network or to the power supply voltage of the radio-electronic equipment. In addition, the developed device can be used in conjunction with an energy recovery system for vehicle braking


Introduction
Various energy recovery facilities (ERF) (suspension vibration energy, vehicle braking energy, etc.) are now widely used nowadays. Recuperation in the case of electric vehicles is particularly important because of their inherent lack of electricity. Regenerative power supply units are designed to convert source energy into electrical energy. In this case, the output voltage depends on the driving conditions and the quality of the road surface. However, in operation, there are very often differences between the voltage of the battery that needs to be recharged and the voltage of the energy storage device within the ERF. These differences are due to various factors, such as driving conditions, including the different temperature coefficients of voltage (TCV) of ERFs incorporating lithium-ion batteries and lead-acid vehicle batteries being charged. The task of matching the voltage levels of the ERF and the rechargeable battery is particularly important for the implementation and use of ERFs in various vehicles. This article provides a theoretical justification for the practical solutions for matching the ERF output voltage to the battery voltage presented in the patent of the authors [10]. Figure 1 shows the functional diagram for stabilising the ERF voltage level to the level required to charge the accumulator battery (ACB).

Lead-acid battery (LAB)
These types of batteries are currently the most studied. Let's look at the basic methods of charging the LAB: the first case is when the charging current is constant, with a LAB battery voltage of 2.7V. The second case charging voltage should be 2.3-2.4V per LAB battery. This method is used when charging the LAB under operating conditions. 100% charging of LAB occurs when the electrode mass is converted to spongy lead from lead sulphate. The lifetime of an automotive LAB depends on the voltage level of the alternator which provides the necessary charging voltage [2]. Figure 2 shows the lifetime of the LAB 6ST-60 in relation to the voltage level of the vehicle alternator [2]. The main disadvantage of the above methods of charging car batteries is that these methods do not provide maximum LAB durability. For example, for a 6ST-60 battery with an operating voltage of 12 V, with a charging voltage of 2.3-2.4 V, the battery voltage is often 13.8-14.4 V.
In addition to the above methods, many accelerated charging methods have been developed, but a detailed review of these methods is beyond the scope of this study.
The voltage regulator has an error of tenths of a volt [1,4]. Such voltage level fluctuations have a negative effect on the lifetime of the LAB. Therefore, the task of improving the accuracy of voltage regulators is relevant [3].
When designing a regulator, it is also necessary to consider the dependence of EMF on temperature.

Lithium-ion batteries
They are mainly used to power electronic equipment as well as traction batteries for vehicles. [5,6,7] The main advantages of lithium-ion batteries are: -Very high energy density (ratio of battery capacity to battery volume); -High current that the battery can handle; -No maintenance costs; -Self-discharge of the battery; -Finished; -No memory effect; -Build batteries in all sizes and shapes; -Wide range of operating temperatures. Each advantage predetermines the use of lithium-ion ACBs in a specific field. For example, their high energy density makes them an indispensable source for small devices.

Obvious disadvantages of lithium-ion ACB
-high price; -battery performance deteriorates markedly at high temperatures, and battery capacity decreases at low temperatures; -ACB life depends on the time of use; -There is a risk of battery explosion or fire; -Fewer charge and discharge cycles compared to lead-acid ACB -Batteries require stricter adherence to charging and other operating rules than lead-acid batteries.

Characteristics of lithium-ion batteries
First, we will look at those that have a noticeable impact on performance and battery life.
Danger of battery combustion.

Deterioration
Most ACBs cannot last more than five years, nor can lead-acid ACBs. Optimal storage conditions are as follows: 40% charge, temperature 0-10 degrees Celsius. And a shelf life of up to five years means a capacity reduction of up to 80% of rated capacity.

Operating temperature
The operating temperature range of lithium-ion ACBs is between -20 ... 50 oC. Charging of ACBs at low temperatures should be avoided. The capacity of the ACB decreases as the temperature decreases. At temperatures below zero °C, the battery can be discharged twice as quickly, i.e., up to 50% capacity loss. ACB characteristics depend on battery technology and can vary considerably.
Typical discharge characteristics over the operating temperature range are shown in Figure 3.
Let us estimate the TKN of a lithium-ion ACB. The output voltage changes by 0.25V when the temperature changes between 10°C and 600°C, so the TKN of a fully charged battery is ~3 10 5 −  + V/K. Thus lead-acid and lithium-ion ACBs differ both in their voltage levels but also in their temperature dependencies, and these two facts must be taken into account when designing a charge-to-voltage (VV) converter for energy recovery.
Problem solving. In the circuit shown in Figure 1, the PWM driver (2) and the pulsed supply voltage converter (4) scale the voltage of the RVS (3) to the required voltage. In order to be able to work with any battery, the operation of the converter (4) must be adapted depending on the type and type of ACB used (lead-acid or lithium-ion). Typical schemes of RVS are considered by the authors in [8]. Principle electric diagram of RVS is presented in Fig. 4.
Therefore, let us take a closer look at this source. Voltage between the emitters of transistors is defined by the formula: Here T is temperature, K; k is Boltzmann constant, J/K; n1 -Collector current ratio of the transistors, e -electron charge, 1. 6 10 -19 Cl; The following can be deduced from Ohm's law: From formulas (1) and (2) it follows that: (3) Fig. 4. Schematic diagram of the RVS [8].
The current in resistor R4 can be found from the equation: And the voltage of R4 will be equal to: Then the potential at the bases of the transistors is obtained from the expression: • (n 1 + 1)lnn 1 ] = 0.
Then there will be full compensation for the effect of temperature. However, in some cases, full compensation does not meet the requirements of the battery-side source because the EMI varies with the motor compartment temperature. Therefore, the stabiliser output voltage equal to the reference voltage source (RVS) must depend on temperature in the same way as the EMI of a fully charged battery [8,9,10]. Adjustment of the VTC, as can be seen from equation (7), is possible by changing two variables: 3 4 R R or n. The collector current ratio of the transistors is often chosen to be on the order of 10 and is held by operational amplifier feedback. Therefore, it is recommended to adjust the TCN by changing R3 or R4. We do this with resistor R3. So, when replacing the LAB with a lithium-RVS battery to get a different VTC, the resistance of R3 must be changed. To change the RVS voltage level, the resistor R5 must be changed. As can be seen from equation (6), the voltage across resistance R4 is directly proportional to temperature and can be applied as a temperature sensor when designing an electronic thermometer circuit.

Results and Discussion
The paper presents theoretical substantiation of a device developed by the authors that stabilises the voltage level when charging different types of accumulators over a wide temperature range. Charging of different types of accumulators can be done by switching two resistors in RVS simultaneously. Note that the proposed device can be used to charge the well-studied lead-acid and lithium-ion batteries during braking [11,12] and damping of suspension oscillations [13,14]. The approach proposed by the authors can be used in any converter circuits [15,16,17]. Note that if the battery is fully charged, the output voltage of the inverter can be used, for example, to drive an electric pump sucking air into a pressure vessel. The excess pressure in the vessel is a kind of accumulator and can be used to start the engine, e.g., in a start-stop system.