Patent Description:
The present disclosure relates to a fuel cell system and a method for controlling power thereof.

A fuel cell system may generate electrical energy by using a fuel cell stack. For example, when hydrogen is used as fuel of the fuel cell stack, global environment problems may be solved. Accordingly, studies and researches have been consecutively performed on the fuel cell system.

A vehicle employing the fuel cell system may use, as a main power source, a fuel cell to generate electrical energy by using hydrogen fuel, and may include a hybrid power net employing a high voltage battery as a sub-power source, thereby switching an operating mode depending on a traveling situation such that the traveling efficiency is enhanced.

Recently, attempts have been made to apply the fuel cell system to a vehicle, such as an excavator, used in an industrial field.

A fuel cell system applied to the vehicle used in the industrial field includes a battery and a super capacitor in addition to a fuel cell. In this case, the fuel cell, the battery, and the super capacitor may be operated in a hybrid type, so the power efficiency may be enhanced. However, to operate each energy source in the hybrid type, at least three converters have to be provided in the power-net. The converter is a high-price part, so the costs may be increased. <CIT> discloses such kind of fuel cell system with a converter configured to convert power which is input to or output from the battery, a converter configured to convert power which is input to or output from a super capacitor, and a driving converter configured to convert power, which is output from the fuel cell stack or the battery or the super capacitor, into power in a specific level. A power relay system is provided the super capacitor and the converter configured to convert power which is input to or output from a super capacitor. A controller controls the outputs of the converters. <CIT> discloses a further fuel cell system.

This Summary is provided to introduce a selection of concepts in simplified form that are further described below in the Detailed Description.

In one general aspect, a fuel cell system includes a first converter, a fuel cell stack and a battery, the first converter being connected to the fuel cell stack and the battery and being configured to convert power output from a fuel cell stack or a battery into power in a specific level, a second converter to convert power input to or output from the battery, a power relay assembly to control power flow between a super capacitor and the first converter, and a controller to control outputs of the first converter and the second converter depending on a starting state or an operating state of the fuel cell system, and to control the operation of the power relay assembly.

The first converter is disposed on a main bus stage to connect the fuel cell stack to an inverter, and the second converter has one end connected to the main bus stage between the fuel cell stack and the first converter, and has an opposite end connected to the battery, and adjust bi-directional power flow.

The second converter supplies starting power of the fuel cell system and charging power of the super capacitor, by using power discharged from the battery, when the fuel cell system is started.

The first converter supplies the charging power, which is received from the second converter, to the super capacitor through the power relay assembly, when the fuel cell system is started.

The power relay assembly may adjust a voltage between an output stage of the first converter and the super capacitor by using a pre-charge relay before receiving the charging power through the first converter, and may supply the charging power to the super capacitor by using a main relay when the charging power is supplied through the first converter.

The controller may operate the first converter in a constant current mode and may operate the second converter in a constant voltage mode, when the fuel cell system is started.

The controller may set a starting voltage of the fuel cell stack as an output voltage of the second converter, and may set a limit current of the second converter or an allowable discharge current of the battery as a restriction current of the second converter, when the fuel cell system is started.

The controller may set a charging voltage of the super capacitor as the output voltage of the first converter, may set a value, which is obtained by subtracting a required current of an auxiliary device from the allowable discharge current of the battery, as an output current of the first converter, and may set a limit current of the first converter or an allowable charge current of the super capacitor as a restriction current of the first converter, when the fuel cell system is started.

The second converter may adjust and output power discharged from the battery, when the fuel cell system is operated, and the first converter may adjust power output through at least one of the fuel cell stack and the second converter and may output the adjusted power to the inverter, when the fuel cell system is operated.

The controller may operate the first converter in the constant current mode and the second converter in the constant voltage mode, when the fuel cell system is operated.

The controller may set the output voltage of the first converter, based on a measured voltage of the super capacitor, may set an output current of the first converter, based on the ratio between added required power of the fuel cell stack and the battery, and the measured voltage of the super capacitor, and may set the restriction current of the first converter, based on the limit current of the first converter.

The controller may set the output voltage of the second converter, based on a target voltage of the fuel cell stack, when the fuel cell system is operated, may set the output current of the second converter, based on the ratio between the target power of the battery and the measured voltage of the battery, and may set the restriction current of the second converter, based on the allowable discharge current of the battery.

The power relay assembly may supply power, which is discharged from the super capacitor, to the inverter, when the fuel cell system is operated.

In another general aspect, a method for controlling power of a fuel cell system according to the invention includes setting an output of a first converter, which adjusts power output from a fuel cell stack or a battery depending on a starting state or an operating state of the fuel cell system, and an output of a second converter, which adjusts power input to or output from the battery, controlling an operation of a power relay assembly depending on the starting state or the operating state of the fuel cell system, and controlling supplying of power of the fuel cell stack, the battery, and the super capacitor depending on the outputs of the first converter and the second converter and the operation of the power relay assembly.

The setting of the output may include setting a starting voltage of the fuel cell stack as an output voltage of the second converter, when the fuel cell system is started, and setting a limit current of the second converter or an allowable discharge current of the battery as a restriction current of the second converter.

The setting of the output may include setting a charging voltage of the super capacitor as the output voltage of the first converter, setting a value, which is obtained by subtracting a required current of an auxiliary device from an allowable discharge current of the battery, as an output current of the first converter, and setting a limit current of the first converter or an allowable charge current of the super capacitor as the restriction current of the first converter, when the fuel cell system is started.

The controlling of the supplying of the power may include supplying, by the second converter, starting power of the fuel cell system by using power discharged from the battery, when the fuel cell system is started.

The controlling of the supplying of the power may include supplying, by the second converter, charging power of the super capacitor by using power discharged from the battery, when the fuel cell system is started.

The method may further include adjusting, by the first converter, the charging power, which is received from the second converter, and supplying adjusted charging power to the super capacitor through the power relay assembly, when the fuel cell system is started.

The controlling of the supplying of the power may include adjusting, by a power relay assembly connected to the super capacitor, a voltage between an output stage of the first converter and the super capacitor by using a pre-charge relay before supplying the charging power to the super capacitor, and supplying, by the power relay assembly, the charging power to the super capacitor by using a main relay when the charging power is supplied through the first converter.

The setting of the output may include setting the output voltage of the first converter, based on a measured voltage of the super capacitor, when the fuel cell system is operated, setting an output current of the first converter, based on the ratio between added required power of the fuel cell stack and the battery, and the measured voltage of the super capacitor, and setting the restriction current of the first converter, based on the limit current of the first converter.

The setting of the output may include setting the output voltage of the second converter, based on a target voltage of the fuel cell stack, when the fuel cell system is operated, setting the output current of the second converter, based on the ratio between the target power of the battery and the measured voltage, and setting the restriction current of the second converter, based on the allowable discharge current of the battery.

The controlling of the supplying of the power may include adjusting and outputting, by the second converter, power discharged from the battery, when the fuel cell system is operated, and adjusting, by the first converter, power output through at least one of the fuel cell stack and the second converter and supplying the adjusted power to the inverter.

The controlling of the supplying of the power may include supplying, by the power relay assembly, the power discharged from the super capacitor to the inverter, when the fuel cell system is operated.

The above and other objects, features and advantages of the present disclosure will be more apparent from the following detailed description taken in conjunction with the accompanying drawings:.

Hereinafter, some embodiments and examples of the present disclosure will be described in detail with reference to the exemplary drawings. In adding the reference numerals to the components of each drawing, it should be noted that the identical or equivalent component is designated by the identical numeral even when they are displayed on other drawings. Further, in describing the embodiment of the present disclosure, a detailed description of well-known features or functions will be ruled out in order not to unnecessarily obscure the gist of the present disclosure.

In addition, in the following description of components according to an embodiment of the present disclosure, the terms 'first', 'second', 'A', 'B', '(a)', and '(b)' may be used. These terms are merely intended to distinguish one component from another component, and the terms do not limit the nature, sequence or order of the constituent components. In addition, unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meanings as those generally understood by those skilled in the art to which the present disclosure pertains. Such terms as those defined in a generally used dictionary are to be interpreted as having meanings equal to the contextual meanings in the relevant field of art, and are not to be interpreted as having ideal or excessively formal meanings unless clearly defined as having such in the present application.

<FIG> is a view illustrating a fuel cell system, according to an embodiment of the present disclosure.

Referring to <FIG>, according to an embodiment of the present disclosure, a fuel cell system may include a fuel cell stack <NUM>, an inverter <NUM>, a motor <NUM>, auxiliary device <NUM>, a battery <NUM>, and a super capacitor <NUM>, a first converter <NUM>, a second converter <NUM>, and a power relay assembly (PRA) <NUM>. In addition, the fuel cell system further includes a controller <NUM> to control the power flow of the fuel cell system.

The fuel cell stack <NUM> (or which may be referred to as a 'fuel cell') has a structure capable of producing electricity through a redox reaction between a fuel (e.g., hydrogen) and an oxidizing agent (e.g., air). For example, the fuel cell stack <NUM> may include a membrane electrode assembly (MEA) in which catalyst electrode layers making electrochemical reactions are attached to opposite sides of an electrolyte membrane for moving hydrogen ions, a gas diffusion layer (GDL), which uniformly distributes reaction gases and transfers generated electrical energy, a gasket and fastening mechanism to maintain airtightness and proper fastening pressure of the reaction gases and a first coolant, and a bipolar plate to move the reaction gases and the first coolant.

In the fuel cell stack <NUM>, hydrogen serving as fuel and air (oxygen) serving as an oxidizing agent are respectively supplied to an anode and cathode of the membrane electrode assembly through a fluid passage of a separator. In this case, the hydrogen may be supplied to the anode, and the air may be supplied to the cathode. The hydrogen supplied to the anode is decomposed into hydrogen ions (protons) and electrons (protons) by the catalyst of the electrode layers formed on opposite sides of the electrolyte membrane. Among them, only the hydrogen ion may be transmitted to the cathode through the electrolyte membrane which is a cation exchange membrane. In addition, the electron may be transmitted to the cathode through the gas diffusion layer and the separator which are conductors. In the cathode, hydrogen ions supplied through the electrolyte membrane and electrons transferred through the separator may meet with oxygen in the air supplied to the cathode by an air supply device to generate water. As electrons flow through an external conductive line due to the movement of the hydrogen ions, the electrical energy may be generated.

The fuel cell stack <NUM>, which serves as a main power source of a vehicle, that is, a fuel cell vehicle, having the fuel cell system supplies power necessary for the driving of the motor <NUM> by using the produced electrical energy. In this case, the fuel cell vehicle may include an industrial vehicle, such as an excavator, at a construction site.

Meanwhile, the fuel cell stack <NUM> may supply power to charge the battery <NUM> and/or the super capacitor <NUM>.

The output of the fuel cell stack <NUM> is controlled by the controller <NUM>.

The inverter <NUM>, the motor <NUM>, the auxiliary device <NUM>, the battery <NUM>, the super capacitor <NUM>, the first converter <NUM>, the second converter <NUM>, and the power relay assembly (PRA) <NUM> are connected to a main bus stage connected to an output stage of the fuel cell stack <NUM>.

The inverter <NUM> converts high-voltage direct current (DC) power, which is received from the fuel cell stack <NUM>, into alternating current (AC) power to drive the motor <NUM> and transmits the AC power to the motor <NUM>.

The inverter <NUM> may receive the high-voltage DC power from the battery <NUM> and/or the super capacitor <NUM> connected to the main bus stage. In this case, the inverter <NUM> may convert the high-voltage DC power, which is received from the battery <NUM> or the super capacitor <NUM>, into the AC power for driving the motor <NUM> and may provide the converted AC power to the motor <NUM>.

When the fuel cell vehicle operates in a fuel cell mode, the inverter <NUM> may receive power for driving the motor <NUM> from the fuel cell stack <NUM>. When the fuel cell vehicle operates in an electrical vehicle (EV) mode, the inverter <NUM> may receive the power for driving the motor <NUM> from the battery <NUM> and/or the super capacitor <NUM>. Meanwhile, when the fuel cell vehicle operates in a hybrid mode, the inverter <NUM> may receive the power for driving the motor <NUM> from the fuel cell stack <NUM>, the battery <NUM>, and the super capacitor <NUM>.

In this case, the inverter <NUM> may include a plurality of switching devices (not illustrated). A plurality of switching devices may be controlled through a pulse width modulation (PWM) scheme to generate the AC power. In this case, a scheme of controlling the plurality of switching devices is not limited to any one, and it is obvious that the plurality of switching devices may be controlled through different schemes according to embodiments.

The AC power generated from the inverter <NUM> is supplied to the motor <NUM>. Accordingly, the motor <NUM> is driven using the AC power supplied from the inverter <NUM>. The motor <NUM> may generate rotational force using the AC power supplied from the inverter <NUM>, and may apply the generated rotational force to a driving wheel of the fuel cell vehicle.

Meanwhile, the motor <NUM> generates electrical energy by using braking force generated during regenerative braking. In this case, the inverter <NUM> may convert power of the electrical energy generated from the motor <NUM> during the regenerative braking and may provide the converted power as charging power of the super capacitor <NUM>.

The auxiliary device <NUM> may include auxiliary devices necessary for driving the fuel cell stack <NUM>. For example, the auxiliary device <NUM> may include a blower, an air compressor, an injector, a cooling water circulation pump, and various control valves.

The auxiliary device <NUM> may operate by receiving driving power from the fuel cell stack <NUM>. In addition, the auxiliary device <NUM> may operate by receiving the driving power from the battery <NUM>, when the fuel cell system is started at an initial stage.

The battery <NUM> is an auxiliary power source of the fuel cell vehicle and is charged using electrical energy generated from the fuel cell stack <NUM>.

The battery <NUM> may discharge the charged electrical energy to supply power necessary for driving the motor <NUM>.

In addition, the battery <NUM> may discharge electrical energy at the initial start of the fuel cell system to supply power required to drive the auxiliary device <NUM>. In addition, the battery <NUM> may discharge the electrical energy charged at the initial start of the fuel cell system to supply power necessary for charging the super capacitor <NUM>.

In this case, a discharge amount of the battery <NUM> may be controlled by the controller <NUM>.

The super capacitor <NUM> is an auxiliary power source of the fuel cell vehicle like the battery <NUM>, and is charged using electrical energy generated from the fuel cell stack <NUM>. The super capacitor <NUM> may be charged using power supplied from the battery <NUM> at the initial start of the fuel cell system. In addition, the super capacitor <NUM> may be charged using power generated from the motor <NUM> during regenerative braking.

The super capacitor <NUM> may discharge the charged electrical energy to supply power necessary for driving the motor <NUM>. The discharge amount of the super capacitor <NUM> may be controlled by the controller <NUM>.

The first converter <NUM> is disposed on the main bus stage between the fuel cell stack <NUM> and the inverter <NUM>. The first converter <NUM>, which is a power converter to adjust power output from the fuel cell stack <NUM> or the battery <NUM> and to output the adjusted power to the main bus stage, may include a uni-directional high voltage DC-DC converter (HDC).

For example, the first converter <NUM> may adjust power output from the fuel cell stack <NUM> or the battery <NUM> and may supply the adjusted power to the inverter <NUM> connected to the main bus stage.

In addition, the first converter <NUM> may adjust power output from the fuel cell stack <NUM> or the battery <NUM> and may supply the adjusted power to the super capacitor <NUM> connected to the main bus stage, such that the super capacitor <NUM> is charged with power.

In this case, the controller <NUM> may determine an output voltage, an output current, and a restriction current of the first converter <NUM>. Accordingly, the first converter <NUM> may adjust power output to the main bus stage, depending on the output voltage, the output current, and the restriction current determined by the controller <NUM>.

One end of the second converter <NUM> is connected to the main bus stage between the fuel cell stack <NUM> and the first converter <NUM>, and an opposite end of the second converter <NUM> may be connected to the battery <NUM>.

The second converter <NUM>, which is a power converter that adjusts power input to or output from the battery <NUM>, may include a bi-directional high voltage DC-DC converter (BHDC) that controls bi-directional movement of a current.

For example, the second converter <NUM> may adjust the power supplied from the fuel cell stack <NUM> to supply the adjusted power as the charging power of the battery <NUM>. In addition, the second converter <NUM> may adjust power generated from the motor <NUM> during the regenerative braking to supply the power as the charging power of the battery <NUM>.

Meanwhile, the second converter <NUM> adjusts the power discharged from the battery <NUM> when the fuel cell system is started and outputs the power to the main bus stage. In this case, the power output to the main bus stage may be supplied as driving power of the auxiliary device <NUM>, and may be supplied as charging power of the super capacitor <NUM>.

In this case, the controller <NUM> may determine an output voltage, an output current, and a restriction current of the second converter <NUM>. Accordingly, the first converter <NUM> may adjust power output to the main bus stage or the battery <NUM> depending on the output voltage, the output current, and the restriction current determined by the controller <NUM>.

The power relay assembly <NUM> may include a main relay disposed on a line connecting the super capacitor <NUM> to the main bus stage, a pre-charge relay connected in parallel to the main relay, and a pre-charge resistor connected in series to one end of the pre-charge relay.

The power relay assembly <NUM> may apply or block power flowing between the super capacitor <NUM> and the main bus stage by opening and closing the main relay and the pre-charge relay. In this case, the opening and closing operations of the main relay and the pre-charge relay may be controlled by the controller <NUM>.

In this case, the power relay assembly <NUM> may prevent the first converter <NUM> and the inverter <NUM> from being damaged by the remaining voltage of the super capacitor <NUM> when the fuel cell system is initially started.

The power relay assembly <NUM> may further include a current sensor (not illustrated). The current sensor may detect a direction of a current flowing between the super capacitor <NUM> and the main bus stage.

The controller <NUM> may perform power control for each unit of the fuel cell system. In this case, the controller <NUM> may be an upper controller.

The controller <NUM> according may be a hardware device such as a processor or a central processing unit (CPU), or a program implemented by a processor. The controller <NUM> may be connected to each component of the fuel cell system to perform an overall function of the fuel cell system.

When the fuel cell system is started, the controller <NUM> may control a power flow for starting the fuel cell stack <NUM> and charging the super capacitor <NUM>.

In this case, the controller <NUM> may determine the outputs of the first converter <NUM> and the second converter <NUM> and may control the operation of the power relay assembly <NUM>.

For example, the controller <NUM> drives the second converter <NUM> in a constant voltage mode to start the fuel cell stack <NUM>. In this case, the controller <NUM> determines the output voltage of the second converter <NUM> to the starting voltage. In addition, the controller <NUM> sets a limit current of the second converter <NUM> or an allowable discharge current of the battery <NUM> to a restriction current of the second converter <NUM>. In this case, the controller <NUM> may determine a less value of the limit current of the second converter <NUM> and the allowable discharge current of the battery <NUM>, as the restriction current of the second converter <NUM>.

Accordingly, when the battery <NUM> discharges power, the second converter <NUM> may supply power discharged from the battery <NUM> to the auxiliary device <NUM> to start the fuel cell stack <NUM>.

Meanwhile, since the voltage of the super capacitor <NUM> naturally decreases due to self-discharge when left unattended, charging of the super capacitor <NUM> is required when the fuel cell system is started at the initial stage. Accordingly, when the fuel cell stack <NUM> is started, the controller <NUM> operates the power relay assembly <NUM> for charging the super capacitor <NUM> and drives the first converter <NUM> in a constant current mode.

In this case, the controller <NUM> determines the output voltage of the first converter <NUM> to the charging voltage of the super capacitor <NUM>. In addition, the controller <NUM> determine, as the output current of the first converter <NUM>, a value obtained by subtracting a required current of the auxiliary device <NUM> from the allowable discharge current of the battery <NUM>. In addition, the controller <NUM> determines, as the restriction current of the first converter <NUM>, the limit current of the first converter <NUM> or an allowable charge current of the super capacitor <NUM>. In this case, the controller <NUM> may determine a less value of the limit current of the first converter <NUM> and an allowable charge current of the super capacitor <NUM> as the restriction current of the first converter <NUM>.

Accordingly, when the fuel cell system is initially started, the first converter <NUM> and the second converter <NUM> may supply some of the power discharged from the battery <NUM> as power for charging the super capacitor <NUM>. For example, the first converter <NUM> and the second converter <NUM> may supply the remaining power of the power, which discharged from the battery <NUM> to the super capacitor <NUM>, except for the required power of the auxiliary device <NUM>.

In this case, the power relay assembly <NUM> induces a voltage of the super capacitor <NUM>, an output voltage of the first converter <NUM>, and an input voltage of the inverter <NUM> to be equal to each other, by using the pre-charge relay before driving the first converter <NUM>. Thereafter, when the first converter <NUM> is operated in a constant current mode, the power relay assembly <NUM> supplies charging power to the super capacitor <NUM> through the main relay.

Hereinafter, the operation of controlling power when the fuel cell system is started will be described in more detail with reference to <FIG> and <FIG>.

<FIG> is a view illustrating energy flow when a fuel cell system is started, according to an embodiment of the present disclosure. <FIG> is a view illustrating the operating state of a converter when a fuel cell system is started, according to an embodiment of the present disclosure.

Referring to <FIG> and <FIG>, the controller <NUM> may determine the driving mode, the output voltage, and the restriction current of the second converter <NUM>, to provide power to the auxiliary device <NUM> along a first route R11, when the fuel cell system is started.

In this case, as illustrated in <FIG>, the controller <NUM> may set the driving mode of the second converter <NUM> to a constant voltage mode, set the output voltage of the second converter <NUM> by the starting voltage, and set the restriction current of the second converter <NUM> by the limit current of the second converter <NUM>, or the allowable discharge current of the battery <NUM>, for starting the fuel cell.

In addition, the controller <NUM> may set the driving mode, the output voltage, the output current, and the restriction current of the first converter <NUM> to provide charging power to the super capacitor <NUM> along a second route R12, when the fuel cell system is initially started.

In this case, as illustrated in <FIG>, the controller <NUM> may set the driving mode of the first converter <NUM> to a constant current mode, may set the output voltage of the first converter <NUM> to the voltage of the super capacitor <NUM>, set the output current of the first converter <NUM> to a value, which is obtained by subtracting the required current of the auxiliary device <NUM> from a dischargeable current of the battery <NUM>, and set a restriction current to the limit current of the first converter <NUM> or an allowable charge current of the super capacitor <NUM>, for charging of the super capacitor <NUM>.

As illustrated in <FIG>, when the outputs of the first converter <NUM> and the second converter <NUM> are determined, the battery <NUM> discharges electrical energy, and the second converter <NUM> adjusts power discharged from the battery <NUM> to supply starting power to the auxiliary device <NUM> along the first route R11.

Accordingly, the auxiliary device <NUM> completes starting by driving the fuel cell stack <NUM> by using power supplied from the second converter <NUM>.

In addition, the second converter <NUM> may adjust the power discharged from the battery <NUM> to output the adjusted power to the first converter <NUM> along a second route R12. In this case, the first converter <NUM> adjusts the power output from the second converter <NUM> to supply charging power to the super capacitor <NUM> along the second route R12.

In this case, the controller <NUM> may control the power relay assembly <NUM>, which is connected to the super capacitor <NUM> on the second route R12, to be turned on, before the charging power is supplied from the first converter <NUM>.

Accordingly, the power relay assembly <NUM> transmits the charging power supplied from the first converter <NUM> to the super capacitor <NUM> to charge the super capacitor <NUM>.

The controller <NUM> may control the operation of the power relay assembly <NUM> to be turned off, when the charging of the super capacitor <NUM> is completed.

Meanwhile, the controller <NUM> may control the power flow of the fuel cell stack <NUM>, the battery <NUM>, and the super capacitor <NUM> during operation after the starting of the fuel cell stack <NUM> is completed.

For example, the controller <NUM> may control the output of the first converter <NUM> to supply the output power of the fuel cell stack <NUM> to the inverter <NUM>, when the fuel cell system is operated.

When the fuel cell vehicle operates in the hybrid mode, the controller <NUM> may supply power from the battery <NUM> and/or the super capacitor <NUM> to the inverter <NUM> for a load variation, which exceeds the reference range, of the fuel cell stack <NUM>.

In this case, the controller <NUM> may control the output of the first converter <NUM>, based on the added required power of the fuel cell stack <NUM> and the battery <NUM>. In addition, the controller <NUM> may control the output of the second converter <NUM>, based on the target power of the battery <NUM> and the target voltage of the fuel cell stack <NUM> to supply power from the battery <NUM> to the inverter <NUM>.

In addition, the controller <NUM> may control the relay operation of the power relay assembly <NUM> to supply the power, which is charged in the super capacitor <NUM>, to the inverter <NUM>.

Hereinafter, the operation of controlling power when a fuel cell system is operated will be described with reference to <FIG> and <FIG>.

<FIG> is a view illustrating energy flow when a fuel cell system is operated, according to an embodiment of the present disclosure, and <FIG> is a view illustrating the operating state of a converter when a fuel cell system is operated, according to an embodiment of the present disclosure.

Referring to <FIG> and <FIG>, when the fuel cell system is operated, the fuel cell stack <NUM> supplies power to the inverter <NUM> along a third route R21. In this case, the fuel cell stack <NUM> supplies, to the inverter <NUM>, power corresponding to the variation of the load of the inverter <NUM>, which is measured when the inverter <NUM> and the motor <NUM> are driven, and present in a first range of a static load consecutively measured.

In this case, the first converter <NUM> disposed on the third route R21 may adjust the power supplied from the fuel cell stack <NUM> and may output the power to the inverter <NUM>.

The fuel cell stack <NUM> may supply driving power to the auxiliary device <NUM> along a fourth route R22 connected to the third route R21. In addition, the fuel cell stack <NUM> may supply charging power to the battery <NUM> and/or the super capacitor <NUM> along a fifth route R23 and/or a sixth route R24 connected to the third route <NUM>.

When power is requested to be supplied to the inverter <NUM> during operation of the fuel cell system, the battery <NUM> may supply power to the inverter <NUM> along the fifth route R23 and the third route R21.

In this case, the battery <NUM> may supply, to the inverter <NUM>, power, which corresponds to the variation of a load of the inverter <NUM> measured when the inverter <NUM> and the motor <NUM> are driven and present within a second range set for a band pass filter (BPF). The second range may correspond to an intermediate frequency range between the first range of a static load supplied by the fuel cell and a third range set for a high pass filter. The detailed range may be modified according to embodiments.

In this case, the second converter <NUM> disposed on the fifth route R23 and the first converter <NUM> disposed on the third route R21 may adjust power supplied from the battery <NUM> and output the adjusted power to the inverter <NUM>.

In this case, the first converter <NUM> may adjust power, based on the sum of the power of the fuel cell stack <NUM> and the power supplied from the battery <NUM>, and may output the adjusted power to the inverter <NUM>, when the power is supplied from the fuel cell stack <NUM> and the battery <NUM>.

In addition, when power is requested to be supplied to the inverter <NUM> during operation of the fuel cell system, the super capacitor <NUM> may supply power to the inverter <NUM> along a sixth route R24 and the fourth route R22.

In this case, the super capacitor <NUM> may supply, to the inverter <NUM>, power corresponding to the variation of a load of the inverter <NUM>, which is measured when the inverter <NUM> and the motor <NUM> are driven and present within a third range set to the HPF (High Pass Filter) of the load of the inverter <NUM>. In this case, the third range may be a load range that is rapidly fluctuated, and may correspond to a frequency range higher than the second range. The detailed range may be modified according to embodiments.

In this case, the power relay assembly <NUM> disposed on the sixth route R24 may provide power supplied from the super capacitor <NUM> to the inverter <NUM>.

Accordingly, the controller <NUM> may control operations of the first converter <NUM>, the second converter <NUM>, and the power relay assembly <NUM> to supply power of the fuel cell stack <NUM>, the battery <NUM>, and the super capacitor <NUM> to the inverter <NUM>, when the fuel cell system is operated.

In this case, as illustrated in <FIG>, the controller <NUM> sets the driving mode of the first converter <NUM> to the constant current mode. In addition, the controller <NUM> may set the output voltage of the first converter <NUM> to the measured voltage of the super capacitor <NUM>, set the output current based on the ratio of the added required power of the fuel cell stack <NUM> and the battery <NUM> to the measured voltage of the super capacitor <NUM>, and set the restriction current to the limit current of the first converter <NUM>.

In addition, the controller <NUM> sets the driving mode of the second converter <NUM> to the constant voltage mode. In addition, the controller <NUM> may set the output voltage of the second converter <NUM> to the target voltage of the fuel cell stack <NUM>, set the output current, based on the ratio of the target power of the battery <NUM> to the measured voltage of the battery <NUM>, and set the restriction current to the allowable discharge current of the battery <NUM>.

As illustrated in <FIG>, when the outputs of the first converter <NUM> and the second converter <NUM> are determined, the fuel cell stack <NUM> may output power by the target power. In this case, the output power may be output to the first converter <NUM> and the auxiliary device <NUM>. The first converter <NUM> adjusts the power output from the fuel cell stack <NUM> and supplies the adjusted power to the inverter <NUM> along the third route R21.

In this case, the target power of the fuel cell stack <NUM> may be obtained by adding the required power of the auxiliary device <NUM> and the required power of the fuel cell stack <NUM>. The required power of the fuel cell stack <NUM> may be obtained by subtracting the target power of the battery <NUM> from the added required power of the fuel cell stack <NUM> and the battery <NUM>.

The added required power of the fuel cell stack <NUM> and the battery <NUM> may be obtained by subtracting the target power of the super capacitor <NUM> from the load measured when the inverter <NUM> is driven. The target power of the super capacitor <NUM> may be obtained by subtracting power, which is calculated corresponding to a voltage obtained by subtracting the measured voltage of the super capacitor <NUM> from the target voltage calculated based on the target SOC of the super capacitor <NUM>, from the required power of the super capacitor <NUM>, which is calculated through the HPF, of the load of the inverter <NUM>.

The target power of the battery <NUM> may be obtained by subtracting power, which is calculated corresponding to a voltage obtained by subtracting the measured voltage of the battery <NUM> from the target voltage calculated based on the target SOC of the battery <NUM>, from the required power of the battery <NUM> calculated through BPF, of the added required power of the fuel cell stack <NUM> and the battery <NUM>.

In addition, the battery <NUM> may discharge energy by the target power, and the second converter <NUM> may adjust the power discharged from the battery <NUM> to output the adjusted power to the first converter <NUM> along the fifth route R23 and third route R21. In this case, the first converter <NUM> adjusts the power output from the second converter <NUM> to supply power to the inverter <NUM> along the second route R21.

In addition, the super capacitor <NUM> discharges energy by the target power, and the power relay assembly <NUM> supplies power, which is discharged from the super capacitor <NUM>, to the inverter <NUM>.

Accordingly, the inverter <NUM> operates while consecutively receiving power, which is within the first range, from the fuel cell stack <NUM>. In addition, the inverter <NUM> may receive power through the battery <NUM> with respect to a load variation within the second range, and power through the super capacitor <NUM> with respect to the rapid load variation within the third range, during the operation of the inverter <NUM>.

Hereinafter, the operating flow of the fuel cell system having the above structure according to the present disclosure will be described in more detail.

<FIG> is a view illustrating the operating flow for a method for controlling power when a fuel cell system is started, according to an embodiment of the present disclosure.

Referring to <FIG>, when a power pack is started (S110), the fuel cell system controls the second converter <NUM> to be turned on (S120), and controls the power relay assembly (PRA) <NUM> to be turned on (S150).

The fuel cell system starts the fuel cell stack <NUM>, as the power of the battery <NUM> is supplied to the auxiliary device <NUM> through the second converter <NUM> in S120 (S130).

Meanwhile, when the output voltage of the first converter <NUM> is equal to the voltage of the super capacitor <NUM> by the pre-charge relay of the power relay assembly PRA <NUM> in S150 (S160), the fuel cell system controls the first converter <NUM> to be turned on (S170).

Thereafter, the fuel cell system starts charging the super capacitor <NUM> by supplying power of the battery <NUM> to the super capacitor <NUM> through the second converter <NUM> and the first converter <NUM> (S180).

The fuel cell system determines whether the starting of the fuel cell stack <NUM> is completed (S140). In addition, the fuel cell system determines whether charging of the super capacitor <NUM> is completed (S190).

The fuel cell system terminates the starting of the power pack (S210), when the start state of the fuel cell stack <NUM> is confirmed and the charge completion state of the super capacitor <NUM> is confirmed (S200).

Thereafter, the fuel cell system may start the operation of the fuel cell system.

<FIG> is a view illustrating an operating flow of a method for controlling power during operation of a fuel cell system according to an embodiment of the present disclosure.

Referring to <FIG>, when the inverter <NUM> is operated (S310), the fuel cell system measures a load (S320).

The fuel cell system calculates the variation of the load measured in S320 based on the HPF (S330), and supplies power corresponding to the load variation calculated in the S330 from the super capacitor <NUM> to the inverter <NUM> (S340).

In addition, the fuel cell system calculates the remaining part of load measured in S320 except for the power supplied by the super capacitor <NUM> in S340, as the added required power of the fuel cell stack <NUM> and the battery <NUM>, and sets the output of the first converter <NUM> based on the added required power of the fuel cell stack <NUM> and the battery <NUM> (S350).

A detailed operation of setting the output of the first converter <NUM> in step S350 will be described with reference to <FIG>.

Referring to <FIG>, the fuel cell system may supply, through the first converter (HDC) <NUM>, the added required power (FC + BAT required power) of the fuel cell stack <NUM> and the battery <NUM>, which is obtained by subtracting the target power (Scap target power) of the super capacitor <NUM> from the load of the inverter.

In this case, the Scap target power may be obtained by subtracting specific Scap power from the Scap required power. The Scap required power may be calculated based on a high pass filter (HPF) among the loads of the inverter <NUM>. The specific Scap power may be obtained by applying a voltage value, which is obtained by subtracting the measured Scap voltage from the Scap target voltage calculated based on the target SOC of the Scap to the lookup table (LUT).

In addition, the fuel cell system may set the output current of the first converter HDC <NUM> based on the ratio of the FC + BAT required power to the Scap measured voltage.

In addition, the fuel cell system may set the output voltage of the first converter HDC <NUM> based on the measured Scap voltage.

In addition, the fuel cell system calculates a load variation, based on a band pass filter (BPF) of the added required power of the fuel cell stack <NUM> and the battery <NUM> (S360). In this case, the fuel cell system may calculate the target power of the battery <NUM> based on the load variation calculated in S360.

The fuel cell system sets the output of the second converter <NUM> based on the target power of the battery <NUM> and the target power of the fuel cell stack <NUM> (S370).

A detailed operation of setting the output of the second converter <NUM> in S370 will be described with reference to <FIG>.

Referring to <FIG>, the fuel cell system may set an output current of the second converter BHDC <NUM> from a ratio of the target power (BAT target power) of the battery <NUM> to the measured voltage (BAT measurement voltage) of the battery <NUM>.

In this case, the BAT target power may be obtained by subtracting specific BAT power from the BAT required power. The BAT required power may be calculated from the added required power of FC+BAT, based on based on the BPF. The specific BAT power may be obtained by applying a voltage value, which is obtained by subtracting the BAT measured voltage from the BAT target voltage calculated based on the BAT target SOC, to the lookup table LUT.

In addition, the fuel cell system may set the output voltage of the second converter BHDC <NUM> based on the target voltage of the fuel cell stack <NUM>.

In this case, the FC target voltage may be obtained by applying the FC target power to the lookup table LUT. The FC target power may be obtained by adding the required power of the auxiliary device <NUM> to the FC required power. In addition, the FC required power may be obtained by subtracting the BAT target power from the BAT+FC required power.

When the outputs of the first converter <NUM> and the second converter <NUM> are determined through the above processes, the fuel cell stack <NUM> and the battery <NUM> supply power to the inverter <NUM> (S380). In step S380, the fuel cell stack <NUM> may supply power to the inverter <NUM> through the first converter <NUM>, and the battery <NUM> may supply power to the inverter <NUM> through the second converter <NUM> and the first converter <NUM>.

Hereinabove, although the present disclosure has been described with reference to exemplary embodiments and the accompanying drawings, the present disclosure is not limited thereto, but may be variously modified and altered by those skilled in the art to which the present disclosure pertains.

According to the present disclosure, the converter applied to the power net may be substituted with the power relay assembly (PRA), thereby minimizing the number of the converters to reduce costs and efficiently operating several energy sources.

Claim 1:
A fuel cell system comprising:
a first converter (<NUM>), a fuel cell stack (<NUM>) and a battery (<NUM>), the first converter (<NUM>) being connected to the fuel cell stack (<NUM>) and the battery (<NUM>) and being configured to convert power, which is output from the fuel cell stack (<NUM>) or the battery (<NUM>), into power in a specific level;
a second converter (<NUM>) configured to convert power which is input to or output from the battery (<NUM>);
a super capacitor (<NUM>);
a power relay assembly (<NUM>) configured to control power flow between the super capacitor (<NUM>) and the first converter (<NUM>); and
a controller (<NUM>) configured to control outputs of the first converter (<NUM>) and the second converter (<NUM>), depending on a starting state or an operating state of the fuel cell system, and to control an operation of the power relay assembly (<NUM>), wherein the first converter (<NUM>) is disposed on a main bus stage to connect the fuel cell stack (<NUM>) to an inverter (<NUM>), and
wherein the second converter (<NUM>) has one end connected to the main bus stage between the fuel cell stack (<NUM>) and the first converter (<NUM>), and an opposite end connected to the battery (<NUM>), and is configured to adjust bi-directional power flow; wherein the power relay assembly (<NUM>) has one end connected to the main bus stage between the first converter (<NUM>) and the inverter (<NUM>), and an opposite end connected to the super capacitor (<NUM>), and is configured to adjust bi-directional power flow; wherein the second converter (<NUM>) is configured to supply starting power of the fuel cell system and charging power of the super capacitor (<NUM>), by using power discharged from the battery (<NUM>), when the fuel cell system is started, and wherein the first converter (<NUM>) is configured to supply the charging power, which is received from the second converter (<NUM>), to the super capacitor (<NUM>) through the power relay assembly (<NUM>), when the fuel cell system is started.