KR20170013671A - A control apparatus for precharging of high voltage battery for electric vehicle - Google Patents

Abstract

The present invention relates to a pre-charging control apparatus for a high-voltage battery for an electric vehicle. The pre-charging control apparatus for a high-voltage battery for an electric vehicle comprises: a charging unit which stores DC power in a high-voltage battery; a voltage divider unit which divides an input voltage of the high-voltage battery; a main relay unit which connects and disconnects a connection between the high-voltage battery and the charging unit; a pre-charging switching unit which is connected between the voltage divider unit and the charging unit, and which is switched on and off based on a switching control signal so that a part of a charging voltage divided by the voltage divider unit is introduced into the charging unit or blocked; a resonance inductor unit which is connected to the pre-charging switching unit in series, and which causes a part of a charging voltage divided by the voltage divider unit to resonate and to be supplied to the charging unit; and a control unit which, in the state in which the main relay unit is turned off, outputs the switching control signal so that the pre-charging switching unit is turned on upon pre-charging of the charging unit and then outputs the switching control signal so that the main relay unit is turned on and the pre-charging switching unit is turned off at the same time after a preset pre-charging time. Accordingly, provided are effects in which a surge current generated at a high-voltage terminal input capacitor, i.e., the charging unit, due to a sudden change in a voltage during initial establishment of a connection to the high-voltage battery can be effectively suppressed, and in which energy efficiency can be further improved.

Description

TECHNICAL FIELD [0001] The present invention relates to an initial charge control apparatus for a high voltage battery for an electric vehicle,

The present invention relates to an initial charge of a high voltage battery for an electric vehicle, and more particularly, to a charge / discharge circuit for a high voltage battery using a plurality of auxiliary capacitors and a resonant energy, The present invention relates to an initial charge control device for a high voltage battery for an electric vehicle, which can effectively suppress current and increase energy efficiency.

Recently, there has been a growing interest in environmental issues, especially global warming and climate change. Many countries have been discussing the implementation of the Convention on Climate Change to reduce CO2 emissions. In this discussion, the cause of global warming is the increase of carbon dioxide generation, The increase is attributed to carbon emissions from automobiles.

According to the carbon emission control policy, automobiles based on petroleum have been required to increase fuel efficiency and reduce carbon emissions. There are various types of electric cars or hybrid cars that do not generate exhaust gas And the demand is also rapidly increasing.

The electric vehicle or the hybrid vehicle uses a high voltage power source as a main battery to drive the motor to provide driving power to the vehicle. A high voltage battery, which is an energy storage device used in an electric vehicle or a fuel cell vehicle including the hybrid vehicle, generates a high voltage by connecting a plurality of unit cells (modules) in series and generates high electric power using the high voltage battery.

The power unit of the electric vehicle or the hybrid vehicle is composed of a high voltage battery, an inverter, an engine, a motor, and a mission. The energy stored in the high voltage battery is supplied to the motor Accelerating, high-efficiency point operation of the engine, etc. When surplus energy is generated in the engine, the motor is used as a generator and the surplus energy is stored in the high-voltage battery.

A high voltage relay is used for ON / OFF control between the high voltage battery and the inverter. Since this high-voltage relay may fail due to the peak current, it is necessary to limit the peak current flowing in the high-voltage relay. Since such a peak current can be generated at the time of initial charging, the peak current of the high-voltage relay must be designed to be limited in designing the initial charging circuit of the high-voltage battery.

In order to prevent the surge phenomenon, an initial charge relay (precharge relay) and an initial charge resistance (precharge resistor) are connected to the high voltage relay in parallel.

That is, when the high voltage battery and the inverter are connected, the initial charge relay is connected to delay the rise of the power supply voltage to the inverter to prevent a rapid current flow to prevent relay sticking and damage to the vehicle system.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a surge arising in a high-voltage short-circuit input capacitor due to a sudden change in voltage at the time of initial connection with a high-voltage battery using a plurality of auxiliary capacitors and a resonant energy, The present invention provides an initial charge control device for a high voltage battery for an electric vehicle, which can effectively suppress current and increase energy efficiency.

According to an aspect of the present invention, there is provided an electric vehicle comprising: a charging unit for storing a DC power of a high voltage battery for an electric vehicle; A voltage divider for dividing an input voltage of the high voltage battery; A main relay unit for interrupting connection between the high voltage battery and the charging unit; An initial charging switch unit connected between the voltage division unit and the charging unit and switching on / off according to a switching control signal so that a part of the charging voltage divided from the voltage division unit is input or blocked to the charging unit; A resonance inductor unit connected in series with the initial charge switch unit and resonating a part of the charge voltage divided from the voltage divider unit to supply the resonance inductor to the charger unit; And the main relay unit is turned off to output a switching control signal so that the initial charge switch unit is turned on at the time of initial charging of the charger unit and then the main relay unit is turned on after a predetermined initial charge time And outputting a switching control signal so that the initial charging switch unit is turned off at the same time when the initial charging switch unit is turned on.

Here, the voltage division unit may include first and second auxiliary capacitors connected in parallel to the positive and negative output terminals of the high voltage battery, and the first and second auxiliary capacitors connected in series, It is preferable to be connected between the capacitors.

The first and second auxiliary capacitors may have the same capacity so as to be respectively applied to half of the input voltage of the high voltage battery.

Preferably, the resonance time can be determined by the LC time constant of the resonance inductor unit and the charging unit.

Preferably, the resonance current can be determined by the impedance of the resonance inductor unit and the charging unit.

Preferably, the initial charge time and current limit may be set by adjusting the resonant inductor value of the resonant inductor.

Preferably, the initial charge time may be set to 1/2 of the entire resonance period.

The controller may further include a voltage detector for detecting an output voltage of the charging unit, wherein the controller outputs a switching control signal to turn on the initial charging switch unit at the initial charging of the charging unit, When the detected output voltage value is greater than a preset reference voltage value, the main relay unit may be turned on and a switching control signal may be output so that the initial charge switch unit is turned off.

Preferably, the reference voltage value may be set to a voltage value at which the charging voltage of the charging unit and the voltage level of the high-voltage battery become equal to each other.

According to the apparatus for controlling the initial charge of a high voltage battery for an electric vehicle of the present invention as described above, when a plurality of auxiliary capacitors and a resonant energy are used to cause an abrupt voltage change during an initial connection with a high voltage battery, The surge current can be effectively suppressed and the energy efficiency can be further increased.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a configuration diagram for explaining an initial charging circuit of a conventional high voltage battery for an electric vehicle; FIG.
2 is a graph showing the waveforms of voltage and current according to the operation of the conventional main relay and the initial charge relay.
3 is an overall block diagram illustrating an initial charge control apparatus for a high voltage battery for an electric vehicle according to an embodiment of the present invention.
4 is a graph showing voltage and current waveforms according to operations of a main relay unit and an initial charge switch unit applied to an embodiment of the present invention.

The above and other objects, features, and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings, which are not intended to limit the scope of the present invention. In the following description, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the following embodiments of the present invention may be modified into various other forms, and the scope of the present invention is not limited to the embodiments described below. The embodiments of the present invention are provided to enable those skilled in the art to more fully understand the present invention. In the drawings, the same reference numerals are used to denote the same or similar elements.

FIG. 1 is a diagram illustrating an initial charging circuit of a conventional high-voltage battery for an electric vehicle, and FIG. 2 is a graph showing voltage and current waveforms according to the operation of a conventional main relay and an initial charging relay.

Referring to FIGS. 1 and 2, an initial charging circuit of a conventional high-voltage battery for an electric vehicle includes a high voltage battery (HVB), which is a power source of a vehicle, and a relay for connecting a battery line A high voltage relay (HVR), and the like.

The high voltage battery unit HVB is a secondary battery capable of charging and discharging at a high voltage and supplies power required by an electric load such as a motor of a vehicle such as an inverter or an LDC, And the electric power of the external charger of the vehicle is supplied.

The high voltage battery unit HVB has a structure in which a plurality of cells are connected in series for a required high voltage output and is a physical safety device for an overcurrent. When an overcurrent flows, a fuse ).

The purpose of using the high voltage relay unit (HVR) is to ensure complete electrical insulation between the energy storage medium and other systems. When the vehicle is in operation, the relays are short-circuited to supply power, but the key off In maintenance, emergency, and emergency situations, the relay is opened to ensure electrical stability.

Also, in case of a primary accident, it prevents the occurrence of a serious secondary accident such as electric shock or fire due to high voltage, and also functions to shut off the dark current of the battery. 1 is a diagram showing a high voltage battery and a relay in a hybrid or electric vehicle. The hybrid battery or the electric vehicle includes a high voltage battery 10, a main relay 20, A precharge resistor 32, a high voltage stage input capacitor 40 and an electrical load (e.g., inverter, LDC, etc.) 50 are shown.

The initial charging relay 31 and the initial charging resistor 32 are connected in series to constitute an initial charging unit 30 and the initial charging unit 30 is connected to the high voltage battery 10 and the capacitor DC (DC) link ends in parallel with the main relay 20. [

At this time, the high-voltage short-circuit input capacitor 40 is a component that functions as a buffer by properly charging / discharging between the high-voltage battery 10 and the electric load 50 to cope with sudden power fluctuation of the electric load 50.

In the hybrid or electric vehicle, a direct current (DC) -link voltage is conducted to the motor by using the initial charging unit 30 as described above in order to prevent damage to the inverter due to a surge current. The surge current generated when the main relay 20 is turned on is cut off, thereby preventing component damage and relay fusion caused by the surge current.

2, when the initial charge relay 31 is first turned on, the peak voltage due to the resistance is limited so that the high-voltage short-circuit capacitor 40 is charged and then the main relay 20 is charged. And the initial charge relay 31 is turned off to start charging / discharging.

That is, the initial charging relay 31 is first turned on in the initial charging operation, and the high-voltage short-circuit input capacitor 40 is charged by the capacitor capacity and the time and current value formed by the initial charging resistor 32.

The main relay 20 is made conductive after the high voltage short input capacitor 40 is charged with the voltage level of the high voltage battery 10 and the initial charge relay 31 is opened to form a current conduction path in the main operation. The voltage and current shape of the high-voltage short-circuit input capacitor 40 at this time is shown in FIG.

That is, in the conventional hybrid or electric vehicle constructed as described above, when the main relay 20 is connected in a state where the high-voltage short-circuit input capacitor 40 is not charged at the time of starting, the initial rush current flows considerably, do.

1, the initial charging relay 31 and the initial charging resistor 32 are connected in parallel with the main relay 20 at the front end of the high voltage terminal input capacitor 40 to control the initial inrush current, The inrush current was limited.

The process of limiting the initial inrush current is as follows. First, when the initial charging relay 31 is turned on to charge the high-voltage short-circuit input capacitor 40 below a predetermined current value through the initial charging resistor 32 and reaches a predetermined voltage or higher, the main relay 20 ) To 'ON'. Then, while the initial inrush current is limited, the input voltage and the voltage of the high-voltage short-circuit input capacitor 40 coincide with each other.

In the prior art, since the initial charging relay 31, which is a mechanical relay, and the initial charging resistor 32, that is, the wattage resistance, are used to constitute the initial charging section 30 of the hybrid or electric vehicle, there was. In addition, since the relays are mechanical, they do not have a long life and have a disadvantage that a large amount of watt resistance is used and the total volume becomes very large.

In addition, in the case of the prior art, since the charging is performed using the initial charging resistor 32 at the time of initial charging, the energy efficiency is lowered due to the resistance loss. In particular, in the case of a charger that starts up each time the vehicle is started, such as a DC / DC converter, a resistance loss occurs every time the vehicle is started.

Accordingly, there is a need for a solution to the problem of noise and lifetime of the mechanical relay, the volume problem of the Watt resistor, the energy efficiency resistance, and the like in the initial charging section 30 of the hybrid or electric vehicle.

In order to solve such a problem, the present invention can effectively suppress a surge current generated in a high-voltage short-circuit input capacitor due to a sudden change in voltage at the time of initial connection with a high-voltage battery using resonance energy with a plurality of auxiliary capacitors It is a characteristic technology that can further increase energy efficiency.

FIG. 3 is a block diagram illustrating an initial charge control apparatus for a high-voltage battery for an electric vehicle according to an embodiment of the present invention. FIG. 4 is a block diagram illustrating an operation of a main relay and an initial charge switch unit according to an embodiment of the present invention. And FIG.

3 and 4, an initial charge control apparatus for a high voltage battery for an electric vehicle according to an embodiment of the present invention includes a high voltage battery (HVB) 100 for an electric vehicle, a charger 150, A voltage divider 200, a main relay unit 250, an initial charge switch unit 300, a resonant inductor unit 350, a controller 400, and the like.

Here, the high-voltage battery 100 for an electric vehicle is an energy storing means for supplying driving power to the motor 500. The high-voltage battery 100 is charged according to a charging power outputted from a power converter (not shown) do.

The power converter performs a function of converting and transforming power supplied from an external power supply unit (not shown) to charge the high-voltage battery 100. The AC / DC (AC / DC) (DC) power so as to be charged in the battery 100 and outputs the converted power.

In this case, the power supply unit may include a grid such as a power construction that generally produces and supplies electricity, and means capable of supplying electricity to the power converter, including means capable of producing and / or supplying electricity, It is used to include all power sources.

For example, the power converter may include a system, a company that supplies electricity to the railway or an urban railway by receiving electricity generated from the system, a small hydropower, a photovoltaic (PV), a solar thermal, Renewable energy processing system that supplies electricity from renewable energy such as wind power, waste energy, bio energy, geothermal, and ocean energy. And a power supply unit including at least one of the power supply units.

The power converter may be, for example, an AC / DC converter or a DC / DC converter. The AC / DC converter converts an input AC voltage into a DC voltage. The AC / DC converter includes a rectifier for rectifying an input AC voltage, at least one inductor, a switch, a diode, and a capacitor Capacitors, and the like.

The DC / DC converter adjusts the phases of the plurality of switches to generate a charging voltage for charging the high voltage battery 100, which is the main battery of the electric vehicle, or the low voltage battery (LVB), which is the auxiliary battery. The charge voltage generated by the DC / DC converter is transferred to the high voltage battery 100 or the low voltage battery LVB.

The DC / DC converter is charged to a bi-directional high voltage DC / DC converter (BHDC) or a low voltage battery (LVB) for converting a voltage input to / output from the high voltage battery 100 And a low voltage DC / DC converter for transmitting electric power to various electric loads (e.g., a head lamp, a wiper, a blower, etc.) of the vehicle.

The electric motor 500 is a motor that provides power to the electric vehicle and is driven by an alternating current (AC) power source output through the inverter unit 450. This electric motor 500 includes a stator and a rotor, and the phase alternating current power of a predetermined frequency is applied to the coils of the stator of each phase (U phase, V phase, W phase) so that the rotor rotates. Meanwhile, the electric motor 500 is preferably implemented as a three-phase electric motor such as a BLDC electric motor and a synRM electric motor, but the present invention is not limited thereto, and various forms are possible.

The inverter unit 450 is a power converter that converts the DC power stored in the charger 150 into the AC power. The inverter 450 converts the DC power supplied from the high voltage battery 100 to AC power and outputs the AC power.

The inverter unit 450 converts the direct-current power to a three-phase alternating-current power and supplies the drive current to the motor 500. The inverter 450 converts the pulse supplied from the controller 400 or a separate inverter controller (not shown) Pulse width modulation (PWM) control of the motor 500 according to a pulse width modulation (PWM) signal.

That is, the inverter unit 450 switches a plurality of semiconductor switching devices provided in the inverter unit 450 according to a pulse width modulation (PWM) signal received from the control unit 400 or the inverter control unit, And supplies an alternating current to the electric motor 500 to control the driving of the electric motor 500 by pulse width modulation (PWM).

When the switching control signal from the control unit 400 or the inverter control unit, that is, a pulse width modulation (PWM) signal, is input to the gate terminal of each semiconductor switching element, each semiconductor switching element performs a switching operation. As a result, three-phase AC power having a predetermined frequency is output. The three-phase alternating current power output from the inverter unit 450 is applied to each phase (U phase, V phase, W phase) of the electric motor 500.

Here, the pulse width modulation (PWM) control means that the inverter unit 450 controls the motor current supplied to the motor 500 in accordance with the pulse width modulation (PWM) signal, and the motor current is supplied to the motor 500). ≪ / RTI >

The semiconductor switching element may be a semiconductor switch that is turned on or off by a gate control. For example, the metal oxide semiconductor field effect transistor Metal Oxide Semiconductor Field Effect Transistor (MOSFET), Silicon Coupled Rectifier (SCR), and IGBT (Insulated Gate Bipolar Transistor).

The inverter unit 450 converts the direct current bus voltage into a three-phase alternating current by connecting the six semiconductor switching elements to a three-phase full bridge, and supplies the three-phase alternating current to the electric motor 900, Circuit.

That is, the inverter unit 450 includes a plurality of inverter semiconductor switching elements. The inverter unit 450 converts the smoothed DC power into a three-phase AC power having a predetermined frequency by an ON / OFF operation of the semiconductor switching element, do.

Specifically, a pair of Sangam semiconductor switching elements and a Sangam semiconductor switching element, which are connected in series to each other, are paired, and three pairs of Sangam and Haam semiconductor switching elements are connected in parallel to each other. Diodes are connected in anti-parallel to each semiconductor switching element.

That is, the U phase arm is composed of series connected NPN transistors, the V phase arm is composed of series connected NPN transistors, and the W phase arm is composed of series connected NPN transistors. Between each of the collectors and emitters of the NPN transistor are connected diodes for flowing current from the emitter to the collector.

The charging unit 150 performs a function of storing the energy of the direct current power outputted from the high voltage battery 100. The direct current power of the high voltage battery 100 is smoothed, It is possible to perform a function of keeping it close. At this time, the charging unit 150 may include at least one capacitor for smoothing the input DC power.

The charging unit 150 may include a DC link capacitor having one end connected to the positive output terminal of the high voltage battery 100 and the other end connected to the negative output terminal of the high voltage battery 100.

The DC link capacitor is preferably an electrolytic capacitor connected to the high voltage battery 100 for accumulating energy, but the present invention is not limited thereto, and may be realized by other types of capacitors, capacitors, and the like.

The voltage divider 200 divides the input voltage of the high voltage battery 100 and is connected in parallel to the positive and negative output terminals of the high voltage battery 100. In addition, Capacitors C1 and C2, and one end of the initial charge switch unit 300 is connected between the first and second auxiliary capacitors C1 and C2.

It is preferable that the first and second auxiliary capacitors C1 and C2 have the same capacity so as to be applied to each half of the input voltage of the high voltage battery 100, respectively.

The main relay unit 250 is a switch for interrupting the connection between the high voltage battery 100 and the charging unit 150 and is provided between the high voltage battery 100 and the charging unit 150 or between the high voltage battery 100 and the inverter unit 450 And performs a function of interrupting the DC power supplied from the high voltage battery 100 to the inverter unit 450.

That is, the main relay unit 250 is turned on / off so that the driving power output from the high-voltage battery 100 is input to or blocked from the charging unit 150 according to the control signal of the controller 400. [ .

The initial charging switch unit 300 is connected between the voltage divider 200 and the charging unit 150. The initial charging switch unit 300 switches the switching control signal to the charging unit 150 so that some charging voltage divided from the voltage divider 200 is input / And performs ON / OFF switching according to the ON / OFF state.

The initial charge switch unit 300 may include a semiconductor switch that is turned on or turned off by a gate control. For example, the initial charge switch unit 300 may include a metal oxide semiconductor field effect A metal oxide semiconductor field effect transistor (MOSFET), a silicon coupled rectifier (SCR), and an insulated gate bipolar transistor (IGBT).

Meanwhile, the initial charge switch unit 300 can be replaced with a switch configuration using an FET and an IGBT using a relay in addition to the semiconductor switch described above.

The resonance inductor unit 350 is connected in series between the initial charge switch unit 300 and the charging unit 150 and has a function of resonating a part of the charge voltage divided from the voltage division unit 200 and supplying the resonance inductor unit 350 with the charging unit 150 .

At this time, the resonance time can be determined by LC time constants of the resonance inductor unit 350 and the charging unit 150, and the resonance current can be determined by the impedance of the resonance inductor unit 350 and the charging unit 150.

Also, the initial charging time and current limit value can be set by adjusting the resonance inductor value of the resonance inductor unit 350.

That is, since the present invention utilizes resonance, the charging time is determined by the energy source used for the resonance, the charging capacity of the resonating inductor unit 350, and the charging unit 150. The charging current is determined by the impedance between the resonant inductor section 350 and the charging capacity of the charging section 150. Therefore, since the resonance is used as compared with the conventional resistance method, the resistance loss value is reduced.

On the other hand, when the resonance energy is Vin, the resonance voltage is generated up to 0 to 2 Vin, and the object is to make the charging voltage of the high-voltage short-circuit input capacitor equal to the voltage Vs of the high-voltage battery 100 , The resonance energy source (Vin) should be 1 / 2Vs. Therefore, the resonance energy is made to be 1/2 of the high-voltage battery 100 by using the first and second auxiliary capacitors C1 and C2.

The control unit 400 performs overall control in connection with the charging of the high voltage battery 100. In particular, when the main relay unit 250 is turned off, The main relay unit 250 is turned on after a preset initial charge time and the initial charge switch unit 300 is turned off after the switch unit 300 is turned on OFF ").

At this time, it is preferable that the initial charging time is set to 1/2 of the entire resonance period.

In addition, the controller 400 may further include a voltage detector 550 for detecting the output voltage of the charger 150. In this case, when the initial charge switch unit 300 is turned on The main relay unit 250 is turned on and the initial charge switch unit 250 is turned on when the output voltage value detected by the voltage detection unit 550 is greater than a preset reference voltage value 300 may be turned off.

In this case, the reference voltage value is preferably set to a voltage value at which the charging voltage of the charging unit 150 and the voltage level of the high-voltage battery 100 are equal to each other.

Although the preferred embodiment of the initial charge control apparatus for a high voltage battery for an electric vehicle according to the present invention has been described above, the present invention is not limited thereto. It is possible to carry out the modification by branching, and this also belongs to the present invention.

100: high voltage battery, 150: charger unit,
200: voltage division unit, 250: main relay unit,
300: initial charge switch unit, 350: resonant inductor unit,
400: control unit, 450: inverter unit,
500: electric motor, 550: voltage detector

Claims (9)

A charging unit for storing a DC power of a high voltage battery for an electric vehicle;
A voltage divider for dividing an input voltage of the high voltage battery;
A main relay unit for interrupting connection between the high voltage battery and the charging unit;
An initial charging switch unit connected between the voltage division unit and the charging unit and switching on / off according to a switching control signal so that a part of the charging voltage divided from the voltage division unit is input or blocked to the charging unit;
A resonance inductor unit connected in series with the initial charge switch unit and resonating a part of the charge voltage divided from the voltage divider unit to supply the resonance inductor to the charger unit; And
The control unit outputs a switching control signal so that the initial charging switch unit is turned ON at the time of initial charging of the charger unit in a state where the main relay unit is turned OFF and then the main relay unit is turned ON And outputting a switching control signal such that the initial charge switch unit is turned off at the same time as the initial charge switch unit is turned off.
The method according to claim 1,
Wherein the voltage division unit comprises first and second auxiliary capacitors connected in parallel to the positive and negative output terminals of the high voltage battery and connected in series with each other and one end of the initial charging switch unit is connected to the first and second auxiliary capacitors Wherein the battery is connected between the first battery and the second battery.
3. The method of claim 2,
Wherein the first and second auxiliary capacitors have the same capacity so as to be respectively applied to 1/2 of the input voltage of the high voltage battery.
The method according to claim 1,
Wherein the resonance time is determined by the LC time constant of the resonance inductor unit and the charging unit.
The method according to claim 1,
Wherein the resonance current is determined by the impedance of the resonance inductor unit and the charging unit.
The method according to claim 1,
Wherein an initial charge time and a current limit value are set by adjusting a resonance inductor value of the resonance inductor unit.
The method according to claim 1,
Wherein the initial charging time is set to 1/2 of the entire resonance period.
The method according to claim 1,
And a voltage detector for detecting an output voltage of the charging unit,
Wherein when the output voltage value detected by the voltage detection unit is greater than a predetermined reference voltage value after the initial charge switch unit is turned on at the initial charging of the charger unit, And a switching control signal is outputted so that the initial charging switch unit is turned off when the first charging switch unit is turned on.
9. The method of claim 8,
Wherein the reference voltage value is set to a voltage value at which the charging voltage of the charging unit and the voltage level of the high-voltage battery become equal to each other.

Images