KR20100005767A - Method for controlling fuel cell output of fuel cell hybrid vehicle - Google Patents

Abstract

PURPOSE: A method for controlling a fuel cell output of a fuel cell hybrid vehicle is provided to improve system efficiency and fuel efficiency by controlling the fuel cell output according the energy level stored in the charging unit. CONSTITUTION: A power system of a fuel cell hybrid vehicle includes a fuel cell(110) as a main power source and a storage unit(131) as an auxiliary unit. A power converter(121) and a direct connection switch(125) are arranged between the fuel cell and the storage unit. A converter controller(122) controls the driving of the power converter by sensing the output voltage of the power converter. The output of the fuel cell is controlled to a fuel cell generation stop mode, a fuel cell constant current operation mode, or fuel cell-storage direct connection operation mode.

Description

Method for controlling fuel cell output of fuel cell hybrid vehicle

The present invention relates to a fuel cell output control method for increasing regenerative braking of a fuel cell hybrid vehicle, and more particularly, to a fuel cell including a fuel cell as a main power source and a power storage means (supercap or battery) as an auxiliary power source- Power storage means relates to a fuel cell output control method that can improve the fuel efficiency and system efficiency by controlling the output of the fuel cell according to the energy level stored in the power storage means in a hybrid vehicle.

A fuel cell is a kind of power generation device that converts chemical energy of fuel into electric energy by electrochemical reaction in the fuel cell stack without converting it into heat by combustion. It can also be applied to the power supply of electrical / electronic products, especially portable devices.

As an example of such a fuel cell, a polymer electrolyte membrane fuel cell (PEMFC), which is most frequently researched as a power supply for driving a vehicle, has a membrane centered around an electrolyte membrane through which hydrogen ions move. Membrane Electrode Assembly (MEA) with a catalytic electrode layer on both sides, a gas diffusion layer (GDL) that distributes the reactants evenly and delivers the generated electrical energy. And a gasket and fastening mechanism for maintaining the airtightness and proper fastening pressure of the reactor bodies and cooling water, and a bipolar plate for moving the reactor bodies and cooling water.

In the fuel cell, hydrogen as the fuel and oxygen (air) as the oxidant are respectively supplied to the anode and the cathode of the membrane electrode assembly through the flow path of the separator, and the hydrogen is the anode ('fuel electrode' or 'water'). And the oxygen (air) are supplied to the cathode ('air' or 'oxygen', also known as 'reduction electrode'). Supplied to the anode hydrogen is a hydrogen ion (proton, H ⁺⁾ and electrons by the electrode catalyst constructed on both sides of the electrolyte membrane (electron, e ^-) are decomposed into, passed through only the hydrogen ion in the optional electrolyte membrane cation exchange membrane The electrons are transferred to the cathode through the gas diffusion layer and the separation plate which is a conductor. In the cathode, the hydrogen ions supplied through the electrolyte membrane and the electrons transferred through the separator meet with oxygen in the air supplied to the cathode by the air supply device to generate a reaction. At this time, due to the movement of hydrogen ions, a flow of electrons occurs through an external conductor, and the flow of electrons generates current.

On the other hand, when only the fuel cell is used as a power source of the vehicle, the fuel cell is in charge of all the loads constituting the vehicle, and thus there is a disadvantage in that performance is deteriorated in a low operating area of the fuel cell. In addition, there is a problem in that the acceleration performance of the vehicle is deteriorated due to a failure to supply sufficient voltage required by the driving motor due to an output characteristic in which the output voltage is drastically reduced in a high speed driving region requiring a high voltage. In addition, when a sudden load is applied to the vehicle, the fuel cell output voltage suddenly drops and the vehicle performance is deteriorated due to a failure to supply sufficient power to the driving motor. Overloading the battery). In addition, since the fuel cell has a unidirectional output characteristic, energy input from the driving motor may not be recovered when the vehicle is braked, thereby reducing the efficiency of the vehicle system.

A fuel cell hybrid vehicle has been developed as a solution to compensate for the above disadvantages. Such a fuel cell hybrid vehicle is a system equipped with a high voltage battery or a supercapacitor (supercap) as a separate power source for providing power required for driving a motor in addition to a fuel cell as a main power source in a large vehicle such as a bus as well as a small vehicle. to be. Currently, fuel cell-powered means direct hybrid vehicles that do not use power converters are being studied. Fuel cell-powered means direct hybrid vehicles have excellent fuel economy (large regenerative braking, high efficiency of supercap power storage means, power converters). ), Fuel cell durability is increased, and control reliability is excellent (automatic power assist, auto regenerative braking function).

As described above, the hybrid vehicle directly connected to the fuel cell and the power storage means continuously outputs a constant power from the fuel cell, and the driving is performed. When the power remains, the power storage means is charged with surplus power, and the power is insufficient when the power is insufficient. An operation mode in which power is supplemented by power storage means has been applied.

For example, a description of the power net configuration of a fuel cell-supercap hybrid vehicle using a super cap as a power storage means includes a fuel cell used as a main power source, a super cap used as an auxiliary power source, and a main bus stage and a super output side of a fuel cell. Supercap Precharge Unit interposed between the caps, a power module for rotating the drive motor, which is connected to the output of the fuel cell and the supercap, receives DC current from it, and receives 3-phase PWM (Pulse Width Modulation). It includes a motor controller (including an inverter) that generates and controls motor drive and regenerative braking. The supercap initial charging unit is used for charging the discharged supercap voltage only at initial startup.

In this configuration, a fuel cell that supplies hydrogen from a hydrogen tank and air from an air blower (not shown) to generate electricity by an electrochemical reaction between hydrogen and oxygen in the air is used as the main power source. The drive motor and MCU are connected directly to the fuel cell via the main bus stage, and the supercap is connected through the initial charging unit for power assistance (power assist) and regenerative braking.

Next, a brief description of the configuration of the fuel cell system in order to help the understanding of the present invention, Figure 1 attached shows an air supply and a hydrogen supply. As shown, the dry air supplied through the air blower 28 is humidified through the humidifier 29 and then supplied to the cathode of the fuel cell stack 2, and the exhaust gas of the cathode is generated in the water. It is used to humidify dry air to be delivered to the humidifier 29 in a humidified state by the components and to be supplied to the cathode by the air blower 28.

The hydrogen supply unit consists of two lines, the first line supplying hydrogen to the anode of the fuel cell stack 2 through a low pressure regulator (LPR) 23, and through a hydrogen recycle blower 24. Some of the hydrogen at the anode outlet stage is recycled. The second line supplies high pressure hydrogen directly to the anode via valve 25 and ejector 26, where some of the hydrogen at the anode outlet is recycled and supplied through the ejector.

In addition, the phenomenon that the remaining hydrogen remaining in the anode passes directly through the electrolyte membrane and reacts with the oxygen of the cathode without generating electricity is called hydrogen crossover.In order to reduce the amount of hydrogen crossover, the anode pressure is lowered and the stack output is reduced in the low power section. The pressure should be increased in the high power section. This is solved by using the low pressure regulator 23 alone when low pressure is required, and by supplying high pressure hydrogen through the control of the valve 25 when high pressure is required or when hydrogen is purged. As the anode pressure (hydrogen pressure) increases, the amount of hydrogen crossover increases, and since hydrogen crossover adversely affects fuel economy and fuel cell durability, it is necessary to maintain an appropriate anode pressure. The hydrogen purge valve 27 is used to secure the stack performance by discharging impurities and condensed water of the anode stage, and the anode outlet stage is connected to the water trap 31 to store the condensed water and then to a certain level. Upon reaching it exits through the valve 32.

On the other hand, the driving mode of a hybrid vehicle including a fuel cell as a main power source and a supercap (or a high voltage battery as a secondary battery) as a secondary power source includes a fuel cell driving mode (EV mode) for driving a motor using only the fuel cell as a power source; It is divided into a hybrid mode (HEV mode) for driving a motor using a fuel cell and a supercap as a power source, and a regenerative braking mode in which the supercap is charged.

However, the fuel cell-supercap direct hybrid vehicle has a problem in that the supercap is automatically charged by the fuel cell, thereby limiting regenerative braking. Therefore, this problem can be solved by controlling the operation of the fuel cell in the low power section and the regenerative braking time point, and the fuel efficiency can be increased by refraining from using the fuel cell in the low power section.

As such, the process of stopping and resuming the generation of fuel cells (Fuel Cell Stop / Fuel Cell Restart process), i.e., fuel cell-battery, fuel cell, if necessary during vehicle operation to improve fuel efficiency. In the supercap hybrid vehicle, the idle stop / release control process (fuel cell on / off control process) that temporarily stops the generation of fuel cells should be considered. The idle stop of the fuel cell during vehicle operation is clearly different from the complete shutdown of the fuel cell system after the vehicle has been driven, so the control process for the idle stop of the fuel cell is different from the system shutdown control process. Clearly, you need to differentiate.

As a prior art for improving fuel efficiency of a hybrid vehicle having a fuel cell and a power storage means, US Patent Publication No. 2003/118876 discloses a relay connected between a fuel cell and a supercap when a low output section or a supercap voltage is higher than a predetermined level. A technology is disclosed in which a fuel cell output is made by switching off a fuel cell output by shutting off a switch and increasing the required vehicle output or when a supercap voltage is higher than a predetermined level. In this case, in order to implement idle stop / release, the relay switch of the main bus stage for turning off the output of the fuel cell is turned on / off, and a separate relay cutoff control is required. The patent does not perform any control other than to shut off and connect the output of the fuel cell (to control the on / off relay switch for this). In addition, when regenerative braking, the relay switch is immediately turned off and the relay switch is directly connected when the fuel cell is generated when the voltage exceeds a predetermined voltage. That is, part of the regenerative braking amount is consumed in the fuel cell accessory and used for power generation of the fuel cell. This is to prevent the voltage increase of the main bus stage.

In addition, U.S. Pat.No.6484075 determines the idle state through the number of wheel revolutions, brake operation, SOC (State of Charge), electrical load, etc. to cut off the power supply by the fuel cell, and the power storage device is below the set SOC value. A technique is disclosed for resuming power supply when dropped. The conditions for entering the idle stop are very limited here (when the vehicle is stopped, the load is below a certain value, the brake is in operation and the SOC value is above a certain value), and a DC / DC chopper and The same separate device is required, using a DC / DC chopper to limit the current when the idle stop is released and connected directly to the supercap. The DC / DC chopper is a buck type converter and is used for current limiting purposes when directly connected after cutting off the fuel cell current.

However, there is a need for a method of improving fuel efficiency and system efficiency while controlling fuel cells more efficiently by using a simpler control technique, which is different from the above-described prior art.

Accordingly, the present invention has been made in view of the above, and the energy level stored in the power storage means in a fuel cell-power storage means hybrid vehicle having a fuel cell as a main power source and a power storage means (supercap or battery) as a secondary power source. Accordingly, an object of the present invention is to provide a fuel cell output control method capable of efficiently controlling the output of a fuel cell to improve fuel efficiency and system efficiency.

In order to achieve the above object, the present invention, in the fuel cell hybrid vehicle having a fuel cell as the main power source and the power storage means as a secondary power source, a power conversion device for the constant current operation of the fuel cell between the fuel cell and the power storage means; Direct connection switch for directly connecting / blocking between the fuel cell and the power storage means,

A fuel cell power generation stop mode for stopping power generation of the fuel cell according to the amount of electrical energy of the power storage means, a fuel cell constant current operation mode for operating the power conversion device for constant output operation of the fuel cell at the highest efficiency point, and And a direct connection between the fuel cell and the power storage means by a direct switch and controlling the output of the fuel cell in any one mode selected from a fuel cell-power storage means direct operation mode that controls the fuel cell output according to the vehicle demand load. A fuel cell output control method of a fuel cell hybrid vehicle is provided.

In a preferred embodiment, if the amount of electric energy of the power storage means in the fuel cell power generation stop mode is less than the reference value for resuming fuel cell power generation and the elapsed time after the fuel cell power generation stops satisfies a predetermined minimum holding time or more, a direct switch In the off state of the fuel cell is characterized in that the conversion to the constant current operating mode.

Further, in the fuel cell constant current operating mode, the fuel cell accessory is subjected to constant output control while the power converter operates to apply a voltage of a load amount corresponding to the highest efficiency point to the output side of the fuel cell so that the output current of the fuel cell is constant. Constant power operation is maintained.

Here, the power converter is a step-up converter, the converter controller senses the output terminal voltage of the step-up converter through a voltage sensor to control the driving of the step-up converter to apply a voltage of the load amount corresponding to the highest efficiency point Can be.

And when the amount of electric energy of the power storage means is less than a reference value for fuel cell-supercap direct connection in the fuel cell constant current operating mode, the direct switch connects directly between the fuel cell and power storage means and operates the power converter. It is characterized by being switched to the fuel cell-power storage means direct operation mode by stopping the.

Here, it is preferable to directly charge the air supply of the fuel cell stack for a preset time before directly connecting the fuel cell and the power storage means with the direct connection switch.

The power storage means voltage measured by the voltage sensor of the main bus terminal may be used as the amount of electrical energy of the power storage means.

Accordingly, in the fuel cell output control method according to the present invention, the fuel cell is basically operated at the highest efficiency point, and when the output of the power storage means and energy are insufficient, the fuel cell and the power storage means are operated directly. When the energy level of the power storage means rises, such as a stop or a low output section, the fuel cell is controlled to stop power generation so that the fuel cell can be intensively operated at the highest efficiency point, thereby improving fuel economy and system efficiency. .

In particular, if necessary, by directly connecting the fuel cell and the power storage means to perform a load following operation in which the output of the fuel cell is matched to the required load of the vehicle, and a constant current operation in which the fuel cell is operated at the highest efficiency point in the selected section. By increasing fuel cell high efficiency section operation, it is possible to achieve fuel efficiency and system efficiency.

In addition, it is possible to maximize the fuel efficiency improvement by completely stopping the power generation of the fuel cell in the section where the output of the fuel cell is unnecessary. In addition, it is possible to increase the durability of the fuel cell by reducing the OCV interval, it is advantageous in terms of fuel cell protection, such as easy control of the fuel cell current limit in the emergency.

Hereinafter, preferred embodiments of the present invention will be described in detail.

The present invention relates to an efficient control method of fuel cell output for improving fuel efficiency of a fuel cell hybrid vehicle, comprising a fuel cell-storage means hybrid having a fuel cell as a main power source and a power storage stage (supercap or battery) as an auxiliary power source. The present invention relates to a fuel cell output control method capable of efficiently controlling fuel output according to energy levels stored in power storage means in a vehicle, thereby improving fuel efficiency and system efficiency.

As described above, the fuel cell-storage means (e.g., supercap) direct hybrid system that does not use a power converter has excellent fuel economy (large regenerative braking, high efficiency of the supercap itself), increased fuel cell durability, and excellent control reliability. Automatic power assist, automatic regenerative braking function), but there is a problem of automatic charging of the power storage means from the fuel cell, thereby limiting the regenerative braking due to the voltage increase of the power storage means. For example, when the automatic charging of the supercap, which is the power storage means, is performed by the fuel cell, the amount of electrical energy charged in the supercap increases, and the amount of electrical energy charged by the rotational braking decreases. This can be solved by controlling to stop the operation of the fuel cell in the low power section and the regenerative braking section. In particular, if the generation of the fuel cell is stopped during the regenerative braking as described above, the regenerative braking amount and fuel economy can be increased.

Therefore, in the present invention, the output of the fuel cell is efficiently controlled according to the energy level of the power storage means as the auxiliary power source (in the following description, the main bus terminal voltage / supercap voltage corresponding to the amount of electric energy of the power storage means). The fuel cell operates at constant efficiency at the highest efficiency point, and when the output of the power storage means and energy are insufficient, the fuel cell is directly connected to the power storage means. The main feature is that the fuel cell can be intensively operated at the highest efficiency point by controlling to stop, thereby making it possible to improve fuel economy and system efficiency of the fuel cell.

To this end, the present invention includes a power converter designed with a minimum capacity that satisfies the current output of the fuel cell's highest efficiency point, and a direct switch selectively connecting / stopping the fuel cell and the supercap, thereby stopping power generation of the fuel cell. 3-step control in stop) mode, constant current operation mode of fuel cell, and fuel cell-supercap direct operation mode.

In order to increase fuel efficiency in fuel cell hybrid vehicles, it is also necessary to increase the efficiency of individual components, but it is also important to develop optimal vehicle driving technology. Factors that can increase fuel economy include the reduction of fuel cell accessory and vehicle accessory drive, the increase of regenerative braking rate and the increase of hydrogen utilization rate. This can be solved through a ban. In the low power section, the fuel cell system has a higher efficiency than the output required for driving the system, which is inferior in efficiency due to the large output of the fuel cell accessory (air blower, hydrogen recirculation blower, water pump, etc.). Therefore, the present invention uses a method of directly controlling the output of the fuel cell in order to avoid the use of a low-power section of low efficiency and to improve the efficiency of the fuel cell system. This not only improves the efficiency of the fuel cell system in the low power section, but also prevents the automatic charging of the power storage means during regenerative braking, which is a disadvantage of the fuel cell-power storage means hybrid system, thereby preventing the reduction of the regenerative braking amount due to the increase in the power storage means voltage.

Hereinafter, the description of the present invention will be described with an example of a fuel cell-supercap hybrid vehicle, and it can be easily understood by those skilled in the art that the supercap can be replaced by a high voltage battery which is another auxiliary power source (fuel cell-battery hybrid vehicle). Could be. It is well known that supercaps and batteries are both power storage means capable of charging and discharging, and that they are used as auxiliary power sources of fuel cell hybrid vehicles.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

2 is a block diagram illustrating a power system of a fuel cell-supercap hybrid vehicle to which the present invention is applied. As shown in FIG. 2, a fuel cell including a fuel cell (stack) and a fuel cell accessory as a main power source is shown. The system 110, a fuel cell system controller 111 for controlling system driving such as fuel cell accessories, a power converter 120, a supercap 131 as an auxiliary power source, and an inverter 141 for driving a motor are provided. It is provided. In addition, a voltage sensor 132 and a current sensor 133 are provided at a main bus terminal to which the super cap 131 is connected.

The power converter 120 is installed between the fuel cell (which is the fuel cell system 110 in FIG. 2) and the super cap 131 so that a constant current can be output from the fuel cell 110 so as to output a constant current. Power conversion device 121 that serves as a kind of load for the direct connection switch 125 is installed between the fuel cell 110 and the super cap 131 selectively connected / cut off between the fuel cell and the super cap 131. Selects an operation mode of the converter controller 122 and the fuel cell 110 to control the driving of the power converter 121 by sensing the output terminal voltage of the power converter 121 through the voltage sensor 124. An upper controller for controlling includes a power distribution controller 123 for controlling the driving of the converter controller 122 and the direct connection switch 125. In the present invention, the operation mode selection and control of the fuel cell is performed through cooperative control between controllers such as a power distribution controller 123, a fuel cell system controller 111, a converter controller 122, and the like.

The power converter 121 is a device that acts as a load to output a constant current from the fuel cell 110 in operation, and is connected to the main bus terminal so as to be located between the fuel cell 110 and the super cap 131. do.

In the present invention, the power converter 121 may be a step-up converter capable of step-up operation under the control of the converter controller 122. The step-up converter 121 is operated to maintain a constant output stage voltage under the control of the converter controller 122, which constants the load applied to the output side of the fuel cell system, that is, the output side voltage applied to the fuel cell system. In order to maintain the fuel cell system, the output voltage applied to the fuel cell system is kept constant so that the fuel cell output current can be fixed at a selected value (constant current operation of the fuel cell).

As is well known, the fuel cell system 110 is driven and controlled by system components such as fuel cell accessories such that a current corresponding to the load on the stack output side can be output. That is, as much as the current is extracted from the output side by the load, the fuel cell system 110 performs the system control in which the corresponding current output is made.

Accordingly, when the load on the output side of the fuel cell system is specifically set and maintained by the operation of the step-up converter 121, the component of the fuel cell system 110, that is, the fuel cell view, can be made so that a corresponding constant current output can be made. If the current flows in a constant output operation, and eventually controls the driving of the step-up converter 121 to fix the load amount, the output current value of the fuel cell is fixed to a desired operating point and the constant output operation is possible.

In particular, the constant current mode operation of the fuel cell in the present invention using the step-up converter 121, one-point operation at the highest efficiency point of the fuel cell, that is, a constant current of the highest efficiency point from the fuel cell regardless of the supercap voltage change Constant current operation is performed to output the value.

That is, as the constant current operation of the fuel cell at the highest efficiency, the step-up converter 121 is driven and controlled to apply the voltage of the load amount corresponding to the highest efficiency point to the output side of the fuel cell to maintain the output current of the fuel cell constant. Done. For example, as shown in FIG. 3, if the value corresponding to the fuel cell load having the highest efficiency is 10 A (ampere), the step-down converter (operating under load) 121 is driven to output the 10 A from the fuel cell. The fuel cell output is fixed at 10A. For constant current operation of the fuel cell, the fuel cell accessory is regulated by the fuel cell system controller 111 so that the constant output state of the fuel cell is maintained at the same time as the operation of the step-down converter 121 which fixes the load amount.

The step-up converter 121 may be designed with a minimum capacity that satisfies the current output of the fuel cell highest efficiency point, and above that, the fuel cell 110 and the supercap 131 are connected using the direct switch 125. As it is used directly, the step-up converter can be designed and provided with a smaller capacity than the existing converter.

In the power system configuration of FIG. 2, the direct connection switch 125 may be a relay or an IGBT element, and the fuel cell 110 and the supercap 131 may be selectively connected or disconnected by the direct connection switch 125. Therefore, compared with the conventional fuel cell-supercap direct connection system, the freedom of control of fuel cell output is increased, which is advantageous in terms of fuel efficiency and fuel cell protection.

4 is a flowchart illustrating a method for controlling a fuel cell output according to the present invention, which illustrates a process of converting an operation mode of a fuel cell during vehicle acceleration. 5 is a diagram illustrating an operation region of a fuel cell during a mode conversion process during vehicle acceleration according to the present invention, and FIG. 6 is a diagram for describing an operation region determination algorithm of a fuel cell.

For reference, in FIGS. 4 to 6, V _SC represents a supercap voltage (= main bus terminal voltage, and represents the amount of electric energy charged in the super cap), and I _{FC _ CMD} represents a fuel cell constant current in a constant current operating mode. Value, and V _{FC _STOP} represents a reference voltage for stopping fuel cell generation. Also OCV is the no-load output voltage (Open Circuit Voltage) of the fuel cell, V _{FC_START} is a reference voltage to restart the fuel cell power generation, V _{FC _STOP_ regen} is a reference voltage for stopping the time of regenerative braking fuel cell power generation, V _{DC _OFF Denotes} a reference voltage for releasing the fuel cell-supercap direct connection, and V _{DC _START} denotes a reference voltage for performing the fuel cell-supercap direct connection, respectively. Also _{Regen _min_off} T denotes a fuel cell power generation stop minimum holding time, T _{DC _Delay} the fuel cell shows a super cap directly up time.

In the present invention, depending on the vehicle load and the amount of electric energy charged in the supercap (here, the main bus terminal voltage), the power generation stop mode of the fuel cell, the constant current operating mode of the fuel cell, the fuel cell-supercap direct operation mode As an example of a process in which the conversion control is performed, a feature of the fuel cell output control according to the present invention will be described.

First, in the fuel cell stop mode (Fuel Cell Stop Mode), the power distribution controller 123 turns off the direct connection switch (125) to cut off the connection between the fuel cell 110 and the super cap 131, The operation of the step-up converter (power converter) 121 is stopped through the converter controller 122, and the fuel cell accessory is stopped through the fuel cell system controller 111 to completely stop the power generation of the fuel cell. (S11).

In the state in which power generation of the fuel cell is stopped as described above, the power distribution controller 123 is the amount of electrical energy charged in the super cap 131, that is, the super cap sensed by the voltage sensor 132 of the main bus terminal. By comparing the voltage V _sc (which becomes the main bus terminal voltage with reference to the example of FIG. 2) with a preset reference voltage V _{FC _START} for restarting fuel cell power generation (S12), the supercap voltage is the reference voltage. If lower than (V _sc <V _{FC _START} ) and the elapsed time after stopping the fuel cell generation (stop mode holding time) meets the preset generation stop minimum holding time (T _{Regen _min_off} ) or more, the fuel cell constant current operation ( Prepare Constant Current Mode. Here, the reason why the stop mode holding time is provided is to prevent frequent fuel cell on / off (power generation resume) / off (power generation stop).

For constant current operation of the fuel cell, the fuel cell system controller 111 starts to drive fuel cell accessories such as an air blower, a hydrogen recirculation blower, a water pump, and performs constant power control necessary for controlling the constant current operation of the fuel cell (S13). In operation S14 and S15, the power distribution controller 123 operates the step-up converter 121 through the converter controller 122 while maintaining the off state of the direct connection switch 125 (S14 and S15). .

Subsequently, the power distribution controller 123 determines that the supercap voltage V _sc drops below a predetermined reference voltage V _{DC _ START} for performing the fuel cell-supercap direct connection during the constant current operation of the fuel cell. Preparations for entering the battery-supercap direct connection mode are made.

That is, excessive current may flow when directly connected in a state where there is a voltage difference between the fuel cell 110 and the super cap 131, so that the current flow is prepared by supercharging the air supply of the fuel cell stack in advance for a predetermined time ( S16, S17). Subsequently, when the supercharge maintenance time passes the set time T _{DC_Delay} , the direct connection switch 125 is turned on to directly connect the fuel cell 110 and the super cap 131 to stop the operation of the step-up converter 121. (S18, S19). During the air charging, the driving of the air blower is controlled to supercharge the air by a predetermined amount through the fuel cell system controller 111.

In addition, fuel cell accessory (air blower, hydrogen recirculation blower, water) according to the vehicle demand load by the fuel cell system controller 111 in the operation stop of the step-up converter 121 and the on-line switch 125 is turned on. The driving of the pump) is controlled (Load Following) (S20), thereby completing the entry into the fuel cell-supercap direct operation mode (S21).

In this way, in the present invention, according to the energy level stored in the power storage means (supercap), the control of the fuel cell power generation, the constant current operation of the fuel cell, the fuel cell-supercap direct operation is controlled in three stages of operation mode, such a fuel cell The three-stage control of the output enables efficient operation of the fuel cell hybrid system.

In summary, basically, the power converter (step-up converter) 121 is used to operate the fuel cell 110 at a constant current at the highest efficiency point, but the power storage means voltage is below a certain level or the required output of the vehicle is a certain level. When the output and energy of the power storage means 131 is insufficient, the power converter 121 is turned off and the direct connection switch 125 is turned on to directly connect the fuel cell 110 and the power storage means 131. When operating, and when the power storage means voltage rises above a certain level, such as during a stop or a low output section, the fuel cell is controlled to stop the power generation. Enhancements and system efficiencies are possible.

Particularly, in the present invention, if necessary, a constant current operation is performed by directly connecting the fuel cell and the power storage means to perform a load following operation in which the output of the fuel cell is matched to the vehicle demand load, and also driving the fuel cell at the highest efficiency point in the selected section. By doing so, it is possible to increase fuel cell high efficiency section operation to achieve fuel efficiency and system efficiency. In addition, it is possible to maximize the fuel efficiency improvement by completely stopping the power generation of the fuel cell in the section where the output of the fuel cell is unnecessary. In addition, it is possible to increase the durability of the fuel cell by reducing the OCV section, it is advantageous in terms of fuel cell protection, such as ease of control of fuel cell current limit in an emergency.

On the other hand, the present inventors applied the present invention directly to the vehicle and carried out a driving test in the urban mode (UDDS), the results are as shown in Figure 7 attached. As shown, the fuel cell was operated in three modes of power generation stop, constant current operation, and load follow operation after direct connection. That is, when the supercap voltage rises above the set level (V _SC > V _{DC _OFF} ) in the direct operation section (FC _ON = 1, FC _DC = 1) where the load following operation is performed, the fuel cell is turned off. When the fuel cell enters (FC _ON = 0, FC _DC = 0, I _FC = 0), and the supercap voltage falls below the set level in the power generation stop section (V _SC <V _{FC _START} ), the fuel cell is turned on again and the constant current Run (FC _ON = 1, FC _DC = 0).

In addition, when the constant current operation and the generation stop are repeated, and the super cap voltage drops below the set level in the constant current operation state (V _SC <V _{DC _ START} ), the direct connection switch is turned on and the fuel cell is loaded following operation. FC _ON = 1, FC _DC = 1).

The fuel cell voltage (V _FC ) could be maintained at OCV through the stop of the power generation in the stoppage of the fuel cell generation [fuel cell current (I _FC ) = 0]. Constant current output could be achieved.

In FIG. 7, FC _ON = 1 represents a power generation state (on state) of the fuel cell, FC _ON = 0 represents a power generation stop state (off state) of the fuel cell, and FC _DC = 1 represents a fuel cell-supercap direct connection state. , FC _DC = 0 indicates the fuel cell-supercap direct disconnection state. In addition, I _INV , I _FC and I _SC represent the inverter, fuel cell and supercap current, respectively.

8 and 9 are analysis results showing that fuel cell system efficiency and energy use distribution are improved when the present invention is applied, (a) is a state before improvement and (b) is improved according to the present invention. It shows the state after. UDDS shows the distribution of energy use in urban cycles. Referring to FIG. 8, it can be seen that the fuel cell operating point is concentrated at the highest efficiency point (see dotted line in FIG. 8). Furthermore, the fuel cell accessory can be operated accordingly during constant current operation, thereby greatly improving the efficiency of the fuel cell system. Can be. This effect of the present invention is more pronounced when the average required output of the vehicle in the driving mode is near the fuel cell maximum efficiency point, and in the urban mode.

In the application of the present invention, a fuel efficiency improvement of about 7% was predicted even when considering the DCDClossEnergy caused by the power converter, and this fuel efficiency improvement is due to the reduction of fuel cell accessory consumption energy (HVBopEnergy) ( See dashed line in FIG. 9). In FIG. 9, 'Fuel Cell Net Power' is an output obtained by subtracting the power required for the fuel cell accessory from the fuel cell output, and means an output from the fuel cell to the vehicle load.

1 is a view showing the configuration of a fuel cell system;

2 is a block diagram showing a power system of a fuel cell-supercap hybrid vehicle to which the present invention is applied;

3 is a view showing the highest efficiency point of the fuel cell system,

4 is a flowchart showing a fuel cell output control method according to the present invention;

5 is a view showing an operating region of a fuel cell in a mode conversion process during vehicle acceleration according to the present invention;

6 is a view for explaining an example of a fuel cell operating area determination algorithm according to the present invention;

7 is a view showing the result of applying the present invention to the actual vehicle,

8 and 9 are analysis results showing that the fuel cell system efficiency and energy use distribution is improved when the present invention is applied.

<Explanation of symbols for the main parts of the drawings>

110: fuel cell system 111: fuel cell system controller

120: power converter 121: step-up converter (power converter)

122: converter controller 123: power distribution controller

125: direct connection switch 131: super cap (power storage means)

141: inverter 142: drive motor

Claims (7)

In a fuel cell hybrid vehicle having a fuel cell as a main power source and a power storage means as a secondary power source, a power converter for constant current operation of the fuel cell between the fuel cell and the power storage means, and directly connecting / blocking the fuel cell and the power storage means. Has a direct switch for the A fuel cell power generation stop mode for stopping power generation of the fuel cell according to the amount of electrical energy of the power storage means, a fuel cell constant current operation mode for operating the power conversion device for constant output operation of the fuel cell at the highest efficiency point, and And a direct connection between the fuel cell and the power storage means by a direct switch and controlling the output of the fuel cell in any one mode selected from a fuel cell-power storage means direct operation mode that controls the fuel cell output according to the vehicle demand load. Fuel cell output control method of a fuel cell hybrid vehicle. The method according to claim 1, In the fuel cell power generation stop mode, if the amount of electrical energy of the power storage means is less than a reference value for resuming fuel cell power generation and the elapsed time after stopping the fuel cell power generation satisfies the predetermined minimum holding time or more, the fuel is directly turned off. A fuel cell output control method for a fuel cell hybrid vehicle, characterized by being converted to a battery constant current operating mode. The method according to claim 1, In the fuel cell constant current operating mode, the fuel cell accessory is subjected to constant power control while the power converter operates to apply a voltage of a load amount corresponding to the highest efficiency point to the output side of the fuel cell so that the output current of the fuel cell is constant. A fuel cell output control method for a fuel cell hybrid vehicle, characterized in that the constant power operation is maintained. The method according to claim 3, The power converter is a step-up converter, the converter controller senses the output terminal voltage of the step-up converter through a voltage sensor to control the driving of the step-up converter to apply a voltage of the load amount corresponding to the highest efficiency point A fuel cell output control method for a fuel cell hybrid vehicle. The method according to claim 1, In the fuel cell constant current operating mode, when the amount of electrical energy of the power storage means is less than the reference value for the fuel cell-supercap direct connection, the direct switch connects directly between the fuel cell and the power storage means and operates the power converter. The fuel cell output control method of a fuel cell hybrid vehicle, characterized in that the fuel cell hybrid vehicle is converted to a direct connection mode of the fuel cell-storage means. The method according to claim 5, And directly charging the air supply of the fuel cell stack for a preset time before directly connecting the fuel cell and the power storage means by the direct switch, and then directly connecting the fuel cell to the fuel cell hybrid vehicle. The method according to claim 1, A method for controlling fuel cell output of a fuel cell hybrid vehicle, wherein the amount of electrical energy of the power storage means is a power storage means voltage measured by a voltage sensor at a main bus terminal.

Images