KR102216849B1 - Control system for efficient operation of fuel cell - Google Patents

Abstract

The present invention relates to a control system for efficiently operating a fuel cell. A controller according to an embodiment of the present invention, in order to diagnose the state of a stack module, checks a graph of cell voltage characteristic versus current density.

Description

A control system that efficiently operates fuel cells {CONTROL SYSTEM FOR EFFICIENT OPERATION OF FUEL CELL}

The present invention relates to a fuel cell system, and also relates to a control system for efficiently operating a fuel cell.

In addition, the present invention relates to a fuel cell system having a function of controlling a driving mode according to a self-determination based on self-determination based on current cut-off during operation.

A fuel cell is a device that generates electrical energy by electrochemically reacting hydrogen and oxygen. Therefore, as long as fuel is continuously supplied, continuous power generation is possible. Fuel cells are being actively studied as core technologies that utilize hydrogen energy and renewable energy, which are future energy. Among them, SOFC (solid oxide fuel cell) is a fuel cell that can freely use hydrogen and hydrocarbons as fuels and has high energy conversion efficiency, and is one of the most promising future power sources capable of suppressing air pollution.

The present invention is to provide a system that enables effective operation of a fuel cell.

The present invention provides a system for controlling a driving mode by self-determining a state of a fuel cell in real time during operation.

The present invention is to provide a system that maximizes efficiency while ensuring the life of a fuel cell.

According to an embodiment of the present invention, a fuel cell system includes a mechanical balance of plant (MBOP) that supplies fuel and air, a stack module that is an electrochemical generator in which a number of cells are stacked, and a fuel cell system. It includes an electronic balance of plant (EBOP) for controlling the generated electrical energy, the EBOP, diagnoses the state of the stack module in real time, and includes a controller for controlling the operation of the MBOP and the stack module, the The controller determines a variable related to an operation or a state based on information collected from at least one of the MBOP, the stack module, and the EBOP, and controls a driving method according to the determined variable. Here, the driving method is determined based on a voltage value measured when the current is cut off.

The fuel cell system according to the present invention makes it possible to diagnose the state of a fuel cell stack, which was previously only possible in a laboratory, and further, an operation capable of increasing efficiency while ensuring the life of the fuel cell. Makes it possible.

1 shows a fuel cell system according to an embodiment of the present invention.
2 shows the operating principle of a solid oxide fuel cell (SOFC) fuel cell according to an embodiment of the present invention.
3A shows a specific configuration example of a fuel cell system according to an embodiment of the present invention.
3B shows another specific configuration example of a fuel cell system according to an embodiment of the present invention.
4 is a graph showing characteristics of a fuel cell according to an embodiment of the present invention.
5 illustrates a method of controlling a fuel cell according to an embodiment of the present invention.
6 illustrates a method of determining a stack state of a fuel cell according to an embodiment of the present invention.
7 illustrates a method of controlling an operation method of a fuel cell according to an embodiment of the present invention.
8 illustrates a structure for integrated control of a fuel cell system according to an embodiment of the present invention.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Further, in describing the present invention, when it is determined that a detailed description of a related known function or configuration may unnecessarily obscure the subject matter of the present invention, the detailed description thereof will be omitted.

Hereinafter, the present invention relates to a fuel cell system, and relates to a fuel cell system having a function of controlling an operation mode according to a self-determination based on self-determination based on self-diagnosis during operation.

1 shows a fuel cell system according to an embodiment of the present invention.

Referring to FIG. 1, the fuel cell system includes a mechanical balance of plant (MBOP) 110, a stack module 120, and an electronic balance of plant (EBOP) 130.

The MBOP 110 processes and provides materials required for electricity generation of a fuel cell. For example, the MBOP 110 processes and provides fuel, water, and air. The fuel may be liquid natural gas (LNG). That is, the MBOP 110 is a mechanical facility that supplies fuel and air, and includes mechanical devices that supply hydrogen and oxygen to the stack module 120. For example, the MBOP 110 may include at least one of a desulfurizer, a water treatment system (WTS), a blower, a filter, a reformer, a burner, a pump, a valve, and a pipe as a component. I can.

The stack module 120 generates electricity using the processed materials supplied from the MBOP 110. The stack module 120 includes a plurality of cells. In other words, the stack module 120 is an electrochemical generator in which a plurality of cells are stacked. The stack module 120 has a structure in which cells composed of an electrode, an electrolyte, and a separator are stacked and generates electricity through an electrochemical reaction of hydrogen and oxygen, and can be said to be the most essential element of a fuel cell system. A cell is a structure comprising an anode, a cathode, and an electrolyte. For example, the stack module 120 may have a structure in which 54 or 100 cells are stacked. The operating principle of the cells included in the stack module 120 will be described below with reference to FIG. 2. The stack module 120 may be referred to as an SOFC stack module.

The EBOP 130 manages control and electrical signals for the fuel cell system. That is, the EBOP 130 controls electric energy generated in the fuel cell system. The EBOP 130 may be an electrical installation including a power conversion device that converts a direct current (DC) into an alternative current (AC). The EBOP 130 converts electric energy in the form of direct current generated from the fuel cell stack into an alternating current form, transmits the energy generated to the system, and controls the fuel cell system. The EBOP 130 may operate in a current type in which a current is fixed or a voltage type in which a voltage is fixed according to a load.

Hydrogen and oxygen are produced when water is electrolyzed. The fuel cell reverses this process and performs electrochemical power generation by obtaining electricity from hydrogen and oxygen. In other words, fuel cells produce water, electricity, and heat from hydrogen and oxygen. Thus, electricity and heat are generated simultaneously, and a desired voltage and current are obtained according to the structure.

In general, in order to generate electricity in the basic cell of a fuel cell, when hydrogen is supplied to the anode and oxygen is supplied to the cathode, water is generated by combining with ions that have moved through the electrolyte, and electrons are transferred to the cathode through an external conductor. Will move. During this process, an external flow of electrons forms a current, and accordingly, electricity is generated.

2 shows the operating principle of a fuel cell according to an embodiment of the present invention. 2 is an example of a structure of a solid oxide fuel cell. Referring to FIG. 2, the cell is composed of a permeable anode 201, an impermeable electrolyte 202, and a permeable cathode 203. When hydrogen (H ₂ ) and carbon monoxide (CO), which are fuels, are supplied to the side of the permeable anode 201, hydrogen (H ₂ ) is provided toward the impermeable electrolyte 202 through the permeable anode 201, and oxygen ions (O ^2- ) It is combined with water (H ₂ O) and carbon dioxide (CO ₂ ) are produced as by-products. When air is supplied to the side of the permeable cathode 203, oxygen (O ₂ ) is provided toward the impermeable electrolyte 202 through the permeable cathode 203, and oxygen ions (O ^{2 -} ) are combined with electrons carried through the conducting wire. Is made and supplied to the anode through an electrolyte. Accordingly, oxygen ions (O ^2- ) and hydrogen (H ₂ ) passing through the impermeable electrolyte 202 in the anode 201 react to generate water (H ₂ O), and in this process, electrons (e) Occurs.

The detailed configuration of the MBOP 110, the stack module 120, and the EBOP 130 shown in FIG. 1 may vary according to various embodiments. For example, the detailed configuration of the MBOP 110, the stack module 120, and the EBOP 130 may be the same as those of FIG. 3A or 3B below.

3A shows a specific configuration example of a fuel cell system according to an embodiment of the present invention. Referring to FIG. 3A, the MBOP 110 includes a desulfurizer, a water treatment system, and a low-temperature mechanical device such as a blower. The desulfurizer is a device that removes sulfur mixed in LNG used as fuel. The stack module 120 includes a stack and a high temperature mechanical device such as a heat exchanger and a burner. The EBOP 130 includes a controller, a thermometer, a pressure gauge, a flow, a DC/DC converter, and a DC/AC converter.

3B shows another specific configuration example of a fuel cell system according to an embodiment of the present invention. Referring to FIG. 3B, MBOP 110 includes a desulfurizer, a water treatment system, a blower, a humidifier, a pre-reformer, a CO-polisher, and a gas burner. The stack module 120 includes an internal reformer and cells. The EBOP 130 includes a power control unit (PCU).

Depending on the design of the fuel cell, the area and structure of the electrode varies. Therefore, the efficiency is different for each fuel cell. To compare the performance of the fuel cell, the amount of current generated per electrode unit area (cm ² ) is used as a measure, which may be referred to as current density (A/cm ² , mA/cm ² ). A graph showing the characteristics of a fuel cell current and voltage is referred to as a current-voltage curve or a polarization curve, and an example is shown in FIG. 4.

4 is a graph showing characteristics of a fuel cell according to an embodiment of the present invention. 4 is a graph showing a change in cell potential according to a current density.

In FIG. 4, activation loss 410 is a loss that occurs when a chemical reaction occurs by transferring electric charge from the electrode surface. Voltage loss occurs during the hydrogen oxidation reaction at the fuel cell electrode and the oxygen reduction reaction at the air electrode, which is referred to as activation loss. As shown in Fig. 4, the activation loss is prominent when the current density is small.

Ohmic Resistance Loss (420) is the loss of resistance components that appear as resistance and charge pass through the electrolyte. In order to determine the performance of the fuel cell, an area specific resistance (ASR) of an electrode defined as a product of an electrode area (cm ² ) and a total resistance (Ω) may be used. According to ohm's law (V=IХ, voltage (V) = current density (A/cm ² ) Х ² Ω) loss occurs. That is, as the current density increases, the cell voltage decreases in the form of a linear function having a constant slope. This is called ohmic resistance loss.

The concentration loss 430 is a loss that occurs due to a lack of ability to maintain an initial concentration as a reactant material is consumed in an electrode by an electrochemical reaction. When the current density is increased gradually, the voltage drops sharply at some point to reach a current density value of 0V, which is understood as a situation in which the supply rate of hydrogen to the fuel electrode layer has reached its limit. In other words, the supply rate of hydrogen as fuel is slower than the rate of consumption of hydrogen by the reaction, so that the hydrogen oxidation reaction cannot proceed any more. This state is called concentration loss, and in other words, it is also called mass transfer loss.

The I-V characteristic graph as shown in FIG. 4 may change according to the use of the fuel cell. For example, as the period of use increases, the tendency of the graph as shown in FIG. 4 to move to the left is observed. Therefore, if the relationship between the output voltage and the current can be confirmed, a characteristic graph of the current fuel cell can be confirmed. With this in mind, the fuel cell system according to the present invention determines the state of the fuel cell based on the characteristic graph, determines the driving conditions necessary to meet the given conditions in the current state, and then adaptively controls the driving mode. have.

To this end, the EBOP 130 includes a controller for diagnosing a state of a stack of fuel cells and controlling an operation mode based on the state of the stack. The controller may monitor the performance and condition of the fuel cell system, and control the operation of components of the fuel cell system. According to an embodiment of the present invention, in order to monitor and analyze a state during operation or when stopped, the controller may determine characteristics such as a cell voltage and current density relationship graph, and determine a state based thereon. That is, the controller can collect and analyze the current density measurement value according to the cell voltage. To this end, the controller may include at least one processor or microprocessor for a required operation, and may include a memory for at least temporarily storing generated data. Hereinafter, operations of the controller of the EBOP 130 will be described with reference to FIGS. 5 to 8.

5 illustrates a method of controlling a fuel cell according to an embodiment of the present invention.

5, the controller diagnoses the stack state (S501). For example, the controller may diagnose the stack state by applying a signal for checking the state of the stack of the fuel cell and checking the output. As another example, the controller may diagnose the stack state by controlling the fuel cell system to be in a constant state for inspection and then checking a change in output. Through this, the controller can grasp the characteristic graph (eg, I-V curve) of the stack, or grasp electrical resistance, reaction rate resistance, and mass transfer resistance.

Subsequently, the controller determines a driving method according to the stack state (S502). By analyzing the state of the stack, the controller can estimate the usage period of the stack, future performance changes according to the operation method, and the availability period. Based on various information such as the estimated period of use and the period of availability, the controller selects an operation method that meets the given conditions. For example, a given condition may include a life expectancy of the fuel cell system, an environment of use of the fuel cell system, a history of use of the fuel cell system, and the like. The operation method may be determined in a manner of prioritizing an operation period or an output priority.

Thereafter, the controller applies the determined driving method (S503). The controller may adjust and apply at least one control variable related to the fuel cell system according to the determined operation mode. For example, the control variables may include temperature, flow rate, pressure, output, and the like. The control variable is adjusted according to the operation method, and the correlation between control variables such as operation period, efficiency, etc. defined in the operation method is determined in advance, and can be stored in a database (DB). Alternatively, correlations between control variables such as operation period, efficiency, and the like may be defined and learned based on artificial intelligent (AI) technology.

As one of the methods for diagnosing the state of the stack of the fuel cell, a current interruption (CI) method will be described below. The CI technique is a method of measuring key performance characteristics of a cell by analyzing the pattern in which the voltage changes to an open circuit state when power generation is stopped, that is, when the current is cut off. In order to perform the CI technique, at least 10 µs of sampling data may be required. A method for diagnosing a stack state using the CI technique is shown in FIG. 6 below.

6 illustrates a method of determining a stack state of a fuel cell according to an embodiment of the present invention. The method described later is related to the CI technique.

Referring to FIG. 6, the controller forcibly cuts off the current, or a natural stop occurs due to a failure or line disturbance (S601). Accordingly, the operation of the fuel cell is stopped. The forced current cutoff is performed at the time when it is determined that diagnosis of the fuel cell stack status is necessary, for example, by a command from the system administrator, or is performed periodically, or automatically according to the satisfaction of certain conditions. I can. If a trip occurs at a similar time point to be measured, the periodic automatic stop is omitted.

Then, the controller calculates the impedance (S602). That is, the controller may check a change in voltage over time in a state in which the current is blocked, and calculate the impedance based on this. For example, the controller may measure and store voltage data at 100 to 1 MHz sample intervals during tripping. For example, in the case of forcibly blocking the current, the controller may block the current at 100 to 1 MHz sample intervals, check the corresponding voltage, and calculate the impedance.

Then, the controller determines the stack state (S603). The controller can determine the stack state based on the calculated impedance. For example, the controller can determine the electrical resistance, reaction rate resistance, and mass transfer resistance of the stack. Furthermore, the controller can check the characteristic graph of the stack (eg, I-V curve). Here, the stack state is determined for each cell or for each cell group.

As described with reference to FIG. 6, a stack state may be diagnosed using a CI technique. Through the CI technique, electrical resistance, reaction rate resistance, mass transfer resistance, etc. can be determined. Here, the mass transfer resistance may be determined by subtracting β from the open circuit voltage (OCV), and β may be defined as the sum of electrical resistance and reaction rate resistance.

7 illustrates a method of controlling an operation method of a fuel cell according to an embodiment of the present invention.

Referring to FIG. 7, the controller checks the warranty period (S701). The warranty period is determined at the manufacturing stage according to the characteristics and design of the fuel cell, and the manufacturing date and the warranty period may be stored in the memory during the manufacturing stage.

Subsequently, the controller determines whether the warranty period has elapsed (S702). That is, the controller can check the current date and determine whether the current warranty period has elapsed by referring to the manufacturing date and the warranty period.

If the warranty period has not elapsed, the controller determines a driving method to enable operation during the warranty period (S703). The controller may check the remaining time until expiration of the warranty period and determine the operation method in a manner prioritizing the operation period in consideration of the current state of the stack. For example, even if the efficiency is lowered to a certain level or less, the controller may adjust the operation method so that electricity is continuously produced during the warranty period.

If the warranty period has not elapsed, the controller determines an operation method to enable operation with the maximum output (S704). Since the warranty period of the fuel cell system has elapsed, the controller can determine the driving mode with an output priority method that maximizes output.

In the embodiment of FIG. 7, depending on whether the warranty period has elapsed, the operation period priority or the output priority branching. At this time, when the operation method is decided prior to the operation period because the warranty period has not elapsed, a certain level of efficiency is lowered. At this time, the degree of efficiency lowered compared to the maximum efficiency may vary depending on the remaining period of the warranty period. Furthermore, the degree of the lowered efficiency may be determined based on the electricity consumption pattern of the fuel cell system to date. That is, since it is not necessary to generate electricity with an efficiency greater than the amount consumed, the controller may determine the required level of efficiency by further considering the amount of electricity consumption.

The above-described embodiments have been described in consideration of the situation of controlling one stack module. However, similar control as described above may be performed on a plurality of stack modules. Hereinafter, FIG. 8 illustrates a structure capable of controlling a plurality of stack modules.

8 illustrates a structure for integrated control of a fuel cell system according to an embodiment of the present invention.

Referring to FIG. 8, the fuel cell system includes an MBOP 110, a stack module 120, and an EBOP 130, and includes a controller 132, which is a component for controlling them. The controller 132 corresponds to the controller described in the above-described embodiments. In FIG. 8, the controller 132 is shown to be separated from the EBOP 130, but may be implemented in an embedded form included in the EBOP 130, and only the operation mode determination is separated by taking over the impedance and resistance values diagnosed by the EBOP. Thus, it may be placed in the controller 132.

The controller 132 is a sequence control (eg, heat-up, operation mode, cool-down control, etc.), feedback control (eg, flow control, temperature control, pressure control, etc.), EBOP control (eg, power control, stack It is in charge of status information (material transfer resistance, etc.) control), can change operating variables through real-time monitoring during operation, and can perform status control and predictive diagnosis.

The controller 132 may be connected to the upper control system 810 through an external communication network (eg, Ethernet). The upper control system 810 is connected to controllers of a plurality of fuel cell systems, and is in charge of integrated control for parallel operation for each unit module (6/24/120kW) and for adjusting load sharing when a unit module fails.

Stability and reliability of the entire system may be improved based on state monitoring of the controller 132 and the upper control system 810. It is also possible to prioritize the desired item among the lifespan and power generation output of the stack module. By replacing the unit module, the continuity of operation of the system is ensured. For example, various methods such as individual independent operation, integrated parallel operation, and load variable operation may be supported.

The controller 132 monitors and analyzes the state of the fuel cell during operation, and may adjust operation parameters according to the analysis result. Through this, the controller 132 prevents a trip and improves reliability. In addition, the controller 132 may perform rapid cause analysis and action when a trip or a system is stopped, and accordingly, the operation rate will increase. For example, principal component analysis may include monitoring/diagnosing conditions by dualizing operation and control variables.

In addition, AI (artificial intelligent)-RNN (recurrent neural network)-based diagnosis may be performed, and accordingly, a reference value reset according to a normal state change until the end of life and precise diagnosis during trip are possible. RNN-based diagnosis can be performed based on real-time data. The intelligent controller can use the RNN to determine the normal state during operation and for precise diagnosis when stopped. The RNN can be trained or learned with data obtained from other external fuel cell systems.

Due to the functions as described above, the efficiency of the fuel cell system can be greatly increased. The controller 132 may control the operation mode of the fuel cell according to a given policy. Here, controlling the driving mode means adjusting variables related to driving or variables related to the state of the fuel cell. For example, variables include temperature, flow, pressure, power, etc.

The policy for control may include life priority, output quantity priority, or output priority. For example, if the operation period required by the fuel cell system has not yet been met, the driving mode may be controlled according to a life-priority policy. Thereafter, when the operation period elapses, the driving mode may be controlled according to the output amount or the output priority policy for the remaining period.

As a state monitoring during operation, the controller 132 may perform operations such as changing an abnormal setting value (changing a normal state), changing an operation variable according to an abnormality, and predicting a failure. As a precise diagnosis of faults when stopped, the intelligent controller can perform operations such as analyzing the root cause of a fault, analyzing a countermeasure, and converting a case search DB (database).

Although specific embodiments have been described in the detailed description of the present invention, various modifications are possible without departing from the scope of the present invention. Therefore, the scope of the present invention is limited to the described embodiments and should not be determined, and should be determined by the scope of the claims and equivalents as well as the scope of the claims to be described later.

Claims (1)

In a control system for efficiently operating a fuel cell,
MBOP (mechanical balance of plant), a mechanical facility that supplies fuel and air;
A stack module that is an electrochemical generator in which a plurality of cells are stacked;
It includes an electronic balance of plant (EBOP) that controls thermal energy and electrical energy generated in a fuel cell system,
The EBOP includes a controller for diagnosing the state of the stack module, and controlling the MBOP and the operation of the stack module,
The controller blocks the current by stopping power generation at regular sample intervals, and analyzes a pattern in which the voltage changes to an open circuit state when the current is cut off, through a current interruption (CI) technique, After determining a state for each cell group, determining a driving method according to the determined state, controlling the MBOP, the stack module, and the EBOP according to the determined driving method,
The state of the stack module includes electrical resistance, reaction rate resistance, and mass transfer resistance,
The operation method includes adjustment of control variables including temperature, flow rate, pressure, and output,
The operation method is determined in consideration of a required life of the fuel cell system, a use environment of the fuel cell system, and a usage history of the fuel cell system,
The driving method belongs to one of a first driving method that prioritizes life maintenance or a second driving method that prioritizes an output amount,
The first operation mode is selected when the warranty period determined at the time of manufacturing the fuel cell system has not elapsed,
The second driving method is selected when the warranty period has elapsed,
The first driving method provides lower efficiency compared to the second driving method,
The level of efficiency of the first operation mode is determined so that the fuel cell system can produce electricity during the remaining warranty period and can produce electricity at a level below the electricity consumption amount determined by a past electricity consumption pattern. and,
In order to diagnose the state of the stack module, the controller checks a graph of cell voltage characteristics versus current density,
Control system.

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