Electric vehicle composite braking system and control method

Abstract

The present invention provides a composite braking system for an electric vehicle, comprising a hydraulic braking module, a regenerative braking module, a vehicle controller VCU, an EBS controller and a motor controller MCU, wherein the regenerative braking module comprises a backup battery, a storage battery, a super capacitor, a flywheel module, a regenerative braking energy management controller MCU, a battery management control unit MCU and an adjustable transformer. The present invention also provides a control method for a composite braking system for an electric vehicle, which can buffer and charge the storage battery and the backup battery through the super capacitor and the flywheel module, and make the storage battery and the backup battery meet the charging conditions by controlling the charging and discharging of the storage battery and the backup battery, so as to recover the regenerative braking energy as much as possible, thereby solving the problem in the prior art that the regenerative braking is affected by the storage battery SOC, the battery temperature and the high-power current cannot be absorbed by the battery, and the proportion of regenerative braking in the total braking is low, thereby improving the energy recovery utilization rate.

Description

Technical Field

[0001] The invention belongs to the field of electric vehicle braking control, and in particular relates to an electric vehicle composite braking system and a control method. Background Art

[0002] In recent years, people have paid more and more attention to the recycling of renewable energy. According to research, cars accelerate and decelerate frequently in urban areas, and the energy dissipated by braking accounts for 40%-50% of the total driving energy. The regenerative braking technology of electric vehicles has the characteristics of large capacity and adjustability. However, since regenerative braking is affected by factors such as battery temperature, SOC status, and regenerative braking power, it will affect the energy recovery of the battery, resulting in low recovery energy. Increasing the energy recovered by automobile regenerative braking is of great significance to improving the vehicle's mileage. In addition, when the braking demand is large and the energy power generated is large and cannot be charged into the battery, accidents may occur, and the frequent charging and discharging of regenerative braking will affect the battery life.

[0003] Therefore, increasing the proportion of regenerative braking in braking, improving the energy recovery rate, reducing battery losses and preventing dangerous accidents caused by batteries are issues that need to be addressed urgently.

[0004] Most of the existing technical solutions fail to provide a specific control strategy and have the problem of low energy recovery efficiency. Therefore, the present invention provides an electric vehicle composite braking system and a control method, which provides a specific control strategy for the regenerative braking system with the goal of recovering as much energy generated by regenerative braking as possible, thereby shortening the regenerative braking energy recovery time and improving the recovery efficiency. Summary of the invention

[0005] In view of the problems existing in the prior art, the present invention provides an electric vehicle composite braking system and a control method, aiming to recover as much braking energy of the vehicle as possible while meeting the braking demand.

[0006] (A) A method for controlling composite braking of an electric vehicle, comprising the following steps:

[0007] S1. The vehicle controller VCU calculates the required total braking force based on the brake pedal displacement sensor and determines whether the required braking force is higher than the regenerative braking force; if so, regenerative-hydraulic hybrid braking is used; if not, only regenerative braking is used;

[0008] S2. After the regenerative braking generates current, the regenerative braking energy management controller MCU determines whether the regenerative braking current power is higher than the maximum charging power of the battery; if so, a super capacitor is used for buffering and the process proceeds to step S3; if not, the process proceeds directly to step S3;

[0009] S3, the battery management control unit MCU determines whether the battery meets the charging conditions; if so, directly charges the battery; if not, proceed to step S4;

[0010] S4, the regenerative braking energy management controller MCU determines whether the regenerative braking current power is higher than the maximum charging power of the backup battery; if so, a super capacitor is used for buffering and the process proceeds to step S5; if not, the process proceeds directly to step S5;

[0011] S5, the battery management control unit MCU determines whether the backup battery meets the charging conditions; if so, the power generated by regenerative braking is charged into the backup battery; if not, the regenerative braking is connected to the flywheel module to convert the kinetic energy of the vehicle into flywheel kinetic energy for storage;

[0012] S6. The battery management control unit MCU determines whether the SOC of the backup battery is higher than the set range. If so, the in-vehicle electrical appliances are powered by the backup battery; if not, the in-vehicle electrical appliances are powered by the storage battery.

[0013] Furthermore, in step S1, when the vehicle only uses regenerative braking, if the long-range radar detects that the distance between the vehicle and the obstacle in front is less than the safe distance, the hydraulic brake will participate in emergency braking.

[0014] Furthermore, in step S3, when charging the battery, the charging voltage is adjusted by an adjustable transformer so that the charging voltage is equal to the optimal charging voltage of the battery.

[0015] Furthermore, in step S5, when charging the backup battery, the charging voltage is adjusted by an adjustable transformer so that the charging voltage is equal to the optimal charging voltage of the backup battery.

[0016] Furthermore, when the regenerative braking current power exceeds the acceptable range of the supercapacitor, the battery and the backup battery, and the backup battery or the storage battery meets the charging conditions, the regenerative braking hub motor is connected to the flywheel module to convert the vehicle's kinetic energy into the kinetic energy of the flywheel module, and then charges the battery or the backup battery; when the regenerative braking current power exceeds the acceptable range of the supercapacitor, the battery and the backup battery, and the backup battery and the storage battery do not meet the charging conditions, the regenerative braking hub motor is connected to the flywheel module to convert the vehicle's kinetic energy into the kinetic energy of the flywheel module. When the car is driven again, the flywheel module is connected to the wheel to provide power together with the hub motor, thereby absorbing the regenerative braking energy as much as possible while increasing the acceleration of the car.

[0017] Furthermore, in step S6, when the backup battery SOC>50% and the battery state meets the charging conditions, the backup battery charges the battery; when the backup battery SOC>50% and the battery state does not meet the charging conditions, the in-vehicle electrical appliances are preferentially powered by the backup battery.

[0018] Furthermore, when the electric vehicle is charged externally, the storage battery is charged first, and the backup battery is charged after the storage battery is fully charged. When the backup battery SOC ≥ 50%, the charging of the backup battery is stopped to allow it to absorb as much electricity as possible generated by regenerative braking.

[0019] Furthermore, the backup battery is only used to charge the storage battery and supply power to the electrical appliances in the vehicle, but does not drive the vehicle.

[0020] Furthermore, when the states of the storage battery / backup battery satisfy the following equations at the same time, the regenerative charging condition is met:

[0021]

[0022] Where T is the current temperature of the battery / backup battery, T min and T max is the minimum and maximum temperature of the battery / backup battery; SOC is the state of charge of the battery / backup battery, SOC min and SOC max is the minimum and maximum remaining capacity of the battery / backup battery; P is the electric power generated by regenerative braking, P max is the maximum power that the battery / backup battery can accept; S is the air pressure inside the battery / backup battery, S max It is the maximum safe air pressure in the battery / backup battery.

[0023] Furthermore, the backup battery SOC is calculated as follows:

[0024]

[0025] The approximate calculation formula of the regenerative braking current power is (due to the small size of L, it is ignored in the power calculation):

[0026]

[0027] The calculation method of regenerative braking force is:

[0028] T c =t·i2 3)

[0029] In formula 1), E use is the energy used by the battery, E total is the total energy of the battery;

[0030] In formula 2), K is the back electromotive force coefficient, ω is the motor speed, R is the equivalent capacitance, L is the inductance, U is the charging voltage, and i1 is the regenerative braking current;

[0031] In formula 3), Tc is the motor regenerative braking torque, t is the torque coefficient of the hub motor, and i2 is the current charged into the hub motor.

[0032] Furthermore, since the vehicle is subject to air resistance, rolling resistance, etc. when braking, regenerative braking is activated when the vehicle speed is greater than the minimum speed that can generate regenerative braking.

[0033] Furthermore, when the electric vehicle only uses regenerative braking, the vehicle controller VCU controls the braking torque of the four wheel hub motors to be equal to the braking force required by the vehicle, and adjusts the regenerative braking power of each wheel hub motor according to the road information on which the vehicle is currently traveling, thereby realizing the vehicle stability control function to meet the vehicle's stable driving under different road conditions or sharp turns, and improve the vehicle's driving stability.

[0034] Furthermore, the vehicle controller VCU adjusts the regenerative braking of each wheel hub motor through the EBS controller to adjust the side slip angle, so that the vehicle has understeer and the car can drive stably in cornering conditions.

[0035] (ii) The present invention also provides an electric vehicle composite braking system, including a hydraulic braking module, a regenerative braking module, a vehicle controller VCU, an EBS controller and a motor controller MCU, wherein the vehicle controller VCU is connected to the EBS controller and the motor controller MCU, the motor controller MCU is connected to the wheel hub motor, and the EBS controller is connected to the hydraulic braking module and the regenerative braking module. The regenerative braking module includes a backup battery, a storage battery, a super capacitor, a flywheel module, a regenerative braking energy management controller MCU and a battery management control unit MCU; the regenerative braking energy source is connected to the super capacitor, the backup battery and the storage battery, and the super capacitor is connected to the backup battery and the storage battery respectively; the battery management control unit MCU is connected to the backup battery and the storage battery; the regenerative braking energy management controller MCU is connected to the battery management control unit MCU, the super capacitor and the flywheel module, for controlling the charging and discharging of the super capacitor, the backup battery and the storage battery and controlling the operation of the flywheel module; the flywheel module is connected to the wheel.

[0036] Furthermore, the present invention is also provided with an adjustable transformer, which is connected to the regenerative braking energy source on the one hand and to the backup battery and the storage battery on the other hand; when charging the storage battery / backup battery, the charging voltage is adjusted by the adjustable transformer so that the charging voltage is equal to the optimal charging voltage of the storage battery / backup battery.

[0037] The beneficial effects of the present invention are:

[0038] The present invention proposes a composite braking system and control method for electric vehicles, and provides a detailed control strategy. The system can buffer and charge the storage battery and the backup battery through the supercapacitor and the flywheel module, and make the storage battery and the backup battery meet the charging conditions by controlling the charging and discharging of the storage battery and the backup battery, and recover as much braking energy of the vehicle as possible under the premise of meeting the braking requirements, thereby solving the problem of low proportion of regenerative braking in total braking and low energy recovery rate caused by the battery SOC, battery temperature, and the inability of high-power current to charge the battery in the prior art. The present invention proposes a specific control strategy for regenerative braking to increase the proportion of regenerative braking in braking, and can control the charging voltage at the optimal charging voltage of the battery, reduce the loss of battery life, and increase the vehicle's mileage. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 This is a schematic diagram of the principle structure of the electric vehicle composite braking system of the present invention;

[0040] Figure 2 This is a flow chart of the electric vehicle composite braking system of the present invention. DETAILED DESCRIPTION

[0041] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in combination with the embodiments of the present invention and the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0042] Example 1

[0043] Reference Figure 1 An embodiment of the present invention provides an electric vehicle composite braking system, including a hydraulic braking module, a regenerative braking module, a vehicle controller VCU, an EBS controller and a motor controller MCU.

[0044] Among them, the vehicle controller VCU is connected to the EBS controller and the motor controller MCU, and the motor controller MCU is connected to the hub motor.

[0045] The EBS controller connects the hydraulic brake module and the regenerative brake module.

[0046] The regenerative braking module includes a backup battery, a storage battery, a super capacitor, a flywheel module, a regenerative braking energy management controller MCU, a battery management control unit MCU and an adjustable transformer.

[0047] The regenerative braking energy source is connected to a supercapacitor, a backup battery and a storage battery, and the supercapacitor is connected to the backup battery and the storage battery respectively; the battery management control unit MCU is connected to the backup battery and the storage battery; the regenerative braking energy management controller MCU is connected to the battery management control unit MCU, the supercapacitor and the flywheel module, and is used to control the charging and discharging of the supercapacitor, the backup battery and the storage battery, and control the operation of the flywheel module, and the flywheel module is connected to the wheel.

[0048] The adjustable transformer is connected to the regenerative braking energy source on the one hand, and is connected to the backup battery and the storage battery on the other hand. When charging the storage battery / backup battery, the charging voltage is adjusted by the adjustable transformer so that the charging voltage is equal to the optimal charging voltage of the storage battery / backup battery (approximately 1.2-1.3 times the electromotive force), so that the charging time is minimized and the recovery efficiency of braking energy is improved.

[0049] Example 2

[0050] This embodiment provides a method for controlling a composite brake of an electric vehicle driven by four wheel hub motors, which is implemented based on the composite brake system of the electric vehicle described in Embodiment 1 and includes the following steps:

[0051] Step S1: When the car needs to brake, the driver steps on the brake pedal, and the vehicle controller VCU calculates the total braking force required by the driver based on the brake pedal displacement sensor, and determines whether the required braking force is higher than the regenerative braking force.

[0052] The calculation method of regenerative braking force is: T c =t·i2, where T c is the regenerative braking torque, t is the torque coefficient of the hub motor, i2 is the current charged into the hub motor, and the charging current of the motor is set according to the nonlinear saturation characteristics of the motor and charging safety.

[0053] When the maximum regenerative braking can meet the braking force required by the car, the hydraulic brake will not intervene and only the regenerative brake will be used. When the car is only using regenerative braking, if the long-range radar detects that the car is not safe enough to avoid the obstacle in front, the hydraulic brake will be involved in emergency braking to ensure driving safety.

[0054] When the maximum regenerative braking cannot meet the braking force required by the vehicle, hydraulic braking and regenerative braking are used together to meet the braking force requirements. After the vehicle controller VCU allocates the proportion of hydraulic braking and regenerative braking, the EBS controller adjusts the braking force of each wheel according to the current driving state of the vehicle to prevent wheel locking and ensure that the vehicle slip rate is near the peak adhesion coefficient to ensure driving safety.

[0055] Step S2: After regenerative braking generates current, the regenerative braking energy management controller MCU determines whether the regenerative braking current power is higher than the maximum charging power of the battery; if so, a supercapacitor is used for buffering to reduce the power to an acceptable range for the battery, and then the process proceeds to step S3; if not, the process proceeds directly to step S3.

[0056] The approximate calculation formula for the regenerative braking current power is (due to the small size of L, it is ignored in the power calculation):

[0057]

[0058] Where K is the back electromotive force coefficient, ω is the motor speed, R is the equivalent capacitance, L is the inductance, U is the charging voltage, i1 is the regenerative braking current, and the value of P changes according to the change of U value.

[0059] Step S3: The battery management control unit MCU determines whether the battery meets the charging conditions; if so, the power generated by regenerative braking is directly charged into the battery. When charging the battery, the regenerative current voltage is adjusted through the adjustable transformer so that the charging voltage is equal to the optimal charging voltage of the battery. Make the charging time as short as possible and improve the recycling efficiency; if not, go to step S4.

[0060] When the battery status satisfies the following equations at the same time, it meets the regenerative charging conditions:

[0061]

[0062] The calculation method of battery SOC is:

[0063]

[0064] Where T is the current temperature of the battery, T min and T max The minimum and maximum temperatures of the battery are defined;

[0065] SOC is the state of charge of the battery. min and SOC max The minimum remaining capacity and maximum remaining capacity of the specified battery;

[0066] P is the electric power generated by regenerative braking, P max is the maximum power that the battery can accept;

[0067] S is the gas pressure inside the battery, S max It is the maximum safe pressure in the battery;

[0068] E use is the energy used by the battery, E total is the total energy of the battery.

[0069] Step S4, the regenerative braking energy management controller MCU determines whether the regenerative braking current power is higher than the maximum charging power of the backup battery (the calculation method is the same as step S2); if so, use supercapacitors for buffering to reduce the power to an acceptable range for the backup battery, and enter step S5; if not, directly enter step S5.

[0070] Step S5, the battery management control unit MCU determines whether the backup battery meets the charging conditions (the charging conditions of the backup battery are the same as those of the storage battery); if so, the power generated by regenerative braking is charged into the backup battery. When charging the backup battery, the charging voltage is adjusted through the adjustable transformer so that the charging voltage is equal to the optimal charging voltage of the backup battery; if not, the regenerative braking is connected to the flywheel module to convert the kinetic energy of the vehicle into flywheel kinetic energy for storage;

[0071] Step S6, the battery management control unit MCU determines whether the SOC of the backup battery is higher than the set range. If so, the in-vehicle electrical appliances are powered by the backup battery; if not, the in-vehicle electrical appliances are powered by the storage battery.

[0072] Specifically, when the backup battery SOC>50% and the battery state meets the charging conditions, the backup battery will charge the battery to increase the mileage of the electric vehicle; when the backup battery SOC>50% and the battery state does not meet the charging conditions, the in-vehicle electrical appliances will be powered by the backup battery first. The backup battery only charges the battery and supplies power to the in-vehicle electrical appliances, and does not drive the vehicle to ensure that the temperature and pressure of the backup battery are as close to the normal range as possible.

[0073] When an electric vehicle is charged externally, the battery is charged first, and the backup battery is charged after the battery is full. When the backup battery SOC ≥ 50%, the backup battery is stopped from being charged to ensure that it can absorb more electricity generated by regenerative braking during regenerative braking. When driving the vehicle, only the battery is used to drive it, so that the backup battery can meet the rechargeable state as much as possible.

[0074] In addition, in the present invention, when the regenerative braking current power exceeds the maximum acceptable charging power of the supercapacitor, the storage battery and the backup battery, and the backup battery or the storage battery meets the charging conditions, the regenerative braking hub motor is connected to the flywheel module to convert the kinetic energy of the vehicle into the kinetic energy of the flywheel module, and then charges the storage battery or the backup battery. When the regenerative braking current power exceeds the maximum acceptable charging power of the supercapacitor, the storage battery and the backup battery, and the backup battery and the storage battery do not meet the charging conditions, the regenerative braking hub motor is connected to the flywheel module when braking is required, and the kinetic energy of the vehicle is converted into the kinetic energy of the flywheel module for preservation. When the car is driven again, the flywheel module is connected to the wheel and provides power together with the hub motor, while absorbing the regenerative braking energy as much as possible and increasing the acceleration of the car. When the storage battery and the backup battery cannot store energy, the regenerative braking system only uses the flywheel module for braking. When the flywheel speed of the flywheel module reaches its maximum value and cannot absorb all the kinetic energy of the vehicle, the hydraulic brake intervenes to ensure driving safety.

[0075] The vehicle controller VCU adjusts the intensity of the wheel hub motor regenerative braking through the ESC module according to the current driving state of the vehicle. When passing through complex road conditions, the tire adhesion coefficient can be improved. When turning, the side slip angle can be adjusted to make the vehicle understeer, thereby improving the vehicle's stable driving.

[0076] The above are only preferred embodiments of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, some improvements and modifications without departing from the principle of the present invention should be regarded as the protection scope of the present invention.

Claims

1. A composite braking control method for an electric vehicle, characterized in that: The following steps are involved: S1. The vehicle controller VCU calculates the required total braking force based on the brake pedal displacement sensor and determines whether the required braking force is higher than the regenerative braking force; if so, regenerative-hydraulic hybrid braking is used; if not, only regenerative braking is used; S2. After regenerative braking generates electrical energy, the regenerative braking energy management controller MCU determines whether the power of the regenerative braking electrical energy is higher than the maximum charging power of the battery; if so, a super capacitor is used for buffering and the process proceeds to step S3; if not, the process proceeds directly to step S3; S3, the battery management control unit MCU determines whether the battery meets the charging conditions; if so, directly charges the battery; if not, proceed to step S4; S4, the regenerative braking energy management controller MCU determines whether the regenerative braking current power is higher than the maximum charging power of the backup battery; if so, a super capacitor is used for buffering and the process proceeds to step S5; if not, the process proceeds directly to step S5; S5, the battery management control unit MCU determines whether the backup battery meets the charging conditions; if so, the power generated by regenerative braking is charged into the backup battery; if not, the regenerative braking is connected to the flywheel module to convert the kinetic energy of the vehicle into flywheel kinetic energy; S6. The battery management control unit MCU determines whether the SOC of the backup battery is higher than the set range. If so, the in-vehicle electrical appliances are powered by the backup battery; if not, the in-vehicle electrical appliances are powered by the storage battery; When the regenerative braking current power exceeds the maximum acceptable power of the supercapacitor, storage battery and backup battery, and the backup battery or storage battery meets the charging conditions, the regenerative braking hub motor is connected to the flywheel module to convert the vehicle's kinetic energy into the kinetic energy of the flywheel module, and then charges the storage battery or backup battery; when the regenerative braking current power exceeds the maximum acceptable power of the supercapacitor, storage battery and backup battery, and the backup battery and storage battery do not meet the charging conditions, the regenerative braking hub motor is connected to the flywheel module to convert the vehicle's kinetic energy into the kinetic energy of the flywheel module. When the car is driven again, the flywheel module is connected to the wheel to provide power together with the hub motor, thereby absorbing the regenerative braking energy while increasing the acceleration of the car; When the status of the storage battery / backup battery satisfies the following equations at the same time, the regenerative charging conditions are met: Where T is the current temperature of the battery / backup battery, T min and T max is the minimum and maximum temperature of the battery / backup battery; SOC is the state of charge of the battery / backup battery, SOC min and SOC max is the minimum and maximum remaining capacity of the battery / backup battery; P is the electric power generated by regenerative braking, P max is the maximum power that the battery / backup battery can accept; S is the air pressure inside the battery / backup battery, S max It is the maximum safe air pressure in the battery / backup battery.

2. The electric vehicle compound braking control method according to claim 1, characterized in that: In step S1, when the vehicle only uses regenerative braking, if the long-range radar detects that the distance between the vehicle and the obstacle in front is less than the safe distance, hydraulic braking participates in braking.

3. The electric vehicle compound braking control method according to claim 1, characterized in that: In step S3, when charging the battery, the charging voltage is adjusted by the adjustable transformer so that the charging voltage is equal to the optimal charging voltage of the battery; In step S5, when charging the backup battery, the charging voltage is adjusted by the adjustable transformer so that the charging voltage is equal to the optimal charging voltage of the backup battery.

4. The electric vehicle compound braking control method according to claim 1, characterized in that: In step S6, when the backup battery SOC>50% and the battery state meets the charging conditions, the backup battery charges the battery; when the backup battery SOC>50% and the battery state does not meet the charging conditions, the in-vehicle electrical appliances are preferentially powered by the backup battery.

5. The electric vehicle compound braking control method according to claim 1, characterized in that: When the electric vehicle is charged externally, the storage battery is charged first, and the backup battery is charged after the storage battery is full. When the backup battery SOC ≥ 50%, the charging of the backup battery is stopped; The backup battery is only used to charge the storage battery and supply power to the electrical appliances in the vehicle, but does not drive the vehicle.

6. The electric vehicle compound braking control method according to claim 1, characterized in that: The calculation method of the backup battery SOC is: The approximate calculation formula of the regenerative braking current power is: The calculation method of regenerative braking force is: T c =t·i2 3) In formula 1), E use is the energy used by the battery, E total is the total energy of the battery; In formula 2), K is the back electromotive force coefficient, ω is the motor speed, R is the equivalent capacitance, L is the inductance, U is the charging voltage, and i1 is the regenerative braking current; In formula 3), T c is the motor regenerative braking torque, t is the torque coefficient of the hub motor, and i2 is the current charged into the hub motor.

7. An electric vehicle composite braking system for implementing the electric vehicle composite braking control method of claim 1, comprising a hydraulic braking module, a regenerative braking module, a vehicle controller VCU, an EBS controller and a motor controller MCU, wherein the vehicle controller VCU is connected to the EBS controller and the motor controller MCU, the motor controller MCU is connected to the wheel hub motor, and the EBS controller is connected to the hydraulic braking module and the regenerative braking module, characterized in that: The regenerative braking module includes a backup battery, a storage battery, a super capacitor, a flywheel module, a regenerative braking energy management controller MCU and a battery management control unit MCU; The regenerative braking energy source is connected to a supercapacitor, a backup battery and a storage battery, wherein the supercapacitor is connected to the backup battery and the storage battery respectively; and the battery management control unit MCU is connected to the backup battery and the storage battery; The regenerative braking energy management controller MCU is connected to the battery management control unit MCU, the supercapacitor and the flywheel module, and is used to control the charging and discharging of the supercapacitor, the backup battery and the storage battery, and to control the operation of the flywheel module; the flywheel module is connected to the wheel.

8. The electric vehicle composite brake system according to claim 7, characterized in that: An adjustable transformer is also provided, which is connected to the regenerative braking energy source on the one hand and to the backup battery and the storage battery on the other hand; When charging the storage battery / backup battery, the charging voltage is adjusted by the adjustable transformer so that the charging voltage is equal to the optimal charging voltage of the storage battery / backup battery.

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