A fuel cell network construction control method and device based on multi-mode switching

Abstract

The application discloses a kind of fuel cell network construction control method and device based on multi-mode switching, method includes: according to fuel utilization and hydrogen inflow rate, the maximum output current of fuel cell is obtained;According to upstream hydrogen production rate, hydrogen storage tank minimum and maximum capacity value and fuel utilization, the long-time current constraint of fuel cell is constructed;According to the range relationship between the integral of the output current of fuel cell to time and long-time current constraint, the DC / DC side reference current of fuel cell is obtained;According to DC / DC side reference current, the first current is obtained based on droop control;The first current is compared with output current maximum, and the smaller value is obtained to obtain the current loop reference current;According to current loop reference current, DC / DC control is carried out;DC / AC control is carried out using matching control based on direct current side voltage dynamics.

Description

Technical Field

[0001] This invention relates to the field of novel power distribution systems, and in particular to a fuel cell grid control method and apparatus based on multi-mode switching. Background Technology

[0002] With a high proportion of new energy sources and power electronic equipment being connected to the grid, the power system exhibits characteristics of low inertia, strong randomness, and weak disturbance immunity, which seriously affects the system's stable operation capability. Hydrogen energy, as a low-carbon, high-efficiency, long-term energy storage medium, can achieve electricity-hydrogen-electricity conversion through technologies such as wind and solar hydrogen production and fuel cell power generation, thereby improving the system's operational flexibility and long-term stability.

[0003] Fuel cells, as the core equipment for hydrogen-to-electricity conversion, have broad application prospects in the power, transportation, and aviation sectors. Fuel cells are mostly connected to the low-voltage AC power grid through a two-stage DC / DC and DC / AC conversion, and their operating modes are mainly divided into constant fuel flow and constant fuel utilization modes. Existing fuel cells connected to the grid in a grid-connected manner lack independent operation and inertia support capabilities. In recent years, grid-connected control technology has attracted much attention due to its ability to simulate the inertia support and independent operation capabilities of synchronous generators. For fuel cell systems, achieving grid-connected control first requires solving the problem of primary-side energy source. However, existing fuel cell grid control technologies typically maintain a constant power output for fuel cells, with frequency regulation and inertia support primarily provided by parallel energy storage units. This leads to parallel power distribution issues, failing to fully leverage the power support and grid operation capabilities of the fuel cell stack itself. Furthermore, they often fail to consider the maximum output capacity of the fuel cell, making it susceptible to DC voltage instability under disturbances. Additionally, the strong nonlinearity of fuel cell output voltage and current limits its short-term power output, and factors such as hydrogen storage status, fuel production rate, and DC capacitor status all constrain the grid operation capability of the fuel cell. Current technologies fail to comprehensively characterize the safe operating boundaries of grid-connected fuel cells and lack suitable grid support strategies.

[0004] Therefore, a new technical solution is urgently needed to address the technical challenges of constructing a grid control strategy for fuel cells. Summary of the Invention

[0005] This invention provides a fuel cell network control method and apparatus based on multi-mode switching, which solves the technical problem of how to construct a fuel cell network control strategy.

[0006] To achieve the above objectives, the present invention provides a fuel cell grid control method based on multi-mode switching, comprising:

[0007] The maximum output current of the fuel cell is obtained based on the fuel utilization rate and hydrogen inflow rate; the long-term current constraint of the fuel cell is constructed based on the upstream hydrogen production rate, the minimum and maximum capacity of the hydrogen storage tank, and the fuel utilization rate.

[0008] The DC / DC side reference current of the fuel cell is obtained based on the range relationship between the integral of the fuel cell output current over time and the long-term current constraint; a first current is obtained based on the DC / DC side reference current using droop control; the first current is compared with the maximum value of the output current, and the smaller value is taken to obtain the current loop reference current; DC / DC control is performed based on the current loop reference current; DC / AC control is performed using matching control based on the dynamic DC side voltage.

[0009] Preferably, the maximum output current of the fuel cell is obtained based on fuel utilization rate and hydrogen inflow rate, including:

[0010] When a fuel cell operates at a constant fuel utilization rate, the fuel utilization rate is... Represented as:

[0011] ;

[0012] in, and These represent the inflow and outflow rates of hydrogen gas, respectively. It is the reaction constant; The output current of the fuel cell, This refers to the fuel injection rate; It is a time constant; For the Laplace operator;

[0013] The upper and lower limits of the fuel injection rate, affected by the valve, are expressed as follows:

[0014] ;

[0015] in, and These are the minimum and maximum fuel injection rates, respectively;

[0016] Based on the output power characteristics of fuel cells, the short-term output current of a fuel cell should be less than the maximum current corresponding to the maximum power output point, while also considering fuel utilization efficiency. It can be seen that, When the value is 1, the power output capability is maximized. Therefore, the short-time current constraints of the fuel cell include:

[0017] ;

[0018] Therefore, the maximum output current of the fuel cell is obtained. .

[0019] Preferably, the long-term current constraints for fuel cells, constructed based on upstream hydrogen production rate, minimum and maximum capacity of hydrogen storage tanks, and fuel utilization rate, include:

[0020] Fuel capacity in hydrogen storage tank The range constraints must satisfy:

[0021] ;

[0022] in, and These are the minimum and maximum capacity values ​​for the hydrogen storage tank, respectively. for Fuel capacity at any given time;

[0023] Assumption At any given time, the fuel capacity is ,but for:

[0024] ;

[0025] in, for The fuel injection rate at any given time; The hydrogen production rate of the upstream hydrogen production equipment;

[0026] Combined with fuel capacity Scope constraints and ,get:

[0027] ;

[0028] fuel utilization rate Substituting these values, the long-term current constraints for the fuel cell are obtained as follows:

[0029] ;

[0030] Preferably, the DC / DC side reference current of the fuel cell is obtained based on the range relationship between the integral of the fuel cell's output current over time and the long-term current constraint, including:

[0031] Mode 1: When the output current is integrated over time Real-time monitoring of the fuel cell output current within the long-term current constraint range. The reference current on the DC / DC side of the fuel cell is calculated according to the first update method. Initial value; when Reaching the maximum output current At that time, the DC / DC side reference current of the fuel cell is updated according to the first update method. ;when The maximum output current was not reached. At the same time, maintain the reference current on the DC / DC side of the fuel cell. constant;

[0032] The first update method includes performing PI errorless adjustment of fuel utilization rate based on the deviation between real-time fuel utilization rate and rated fuel utilization rate to obtain the real-time fuel injection rate. Based on the real-time fuel injection rate Obtain the DC / DC side reference current of the fuel cell ;

[0033] Mode 2: When the output current is integrated over time When the current exceeds the upper limit of the long-term current constraint, the minimum fuel injection rate is used. Obtain the DC / DC side reference current of the fuel cell ;

[0034] Mode 3: When the output current is integrated over time When the current is less than the upper limit of the long-term current constraint, the maximum fuel injection rate is used. Obtain the DC / DC side reference current of the fuel cell .

[0035] Preferred, Mode 1 includes:

[0036] In Mode 1, the DC / DC side reference current of the fuel cell is obtained according to the first update method. Represented as:

[0037] ;

[0038] in, and These represent the proportional and integral coefficients of the Pi controller, respectively. This indicates the rated fuel utilization rate.

[0039] Preferably, Mode 2 includes:

[0040] In Mode 2, the reference current on the DC / DC side of the fuel cell... Represented as:

[0041] ;

[0042] Preferred, Mode 3 includes:

[0043] In Mode 3, the reference current on the DC / DC side of the fuel cell... Represented as:

[0044] ;

[0045] Preferably, DC / DC control based on the current loop reference current includes:

[0046] Reference current of the current loop Subtract the output current of the fuel cell Then, PI control and PWM modulation are performed sequentially to obtain the modulated voltage. , is represented as:

[0047] ;

[0048] in, and These are the proportional and integral coefficients of the PI controller before PWM modulation in DC / DC control;

[0049] According to the modulation voltage PWM modulation is applied to the DC / DC converter to achieve DC / DC control.

[0050] Preferably, DC / AC control using dynamic matching control based on DC-side voltage includes:

[0051] Matching control based on DC-side voltage dynamics includes:

[0052] The active-frequency control loop is represented as:

[0053] ;

[0054] The reactive power-voltage loop uses droop control, as shown below:

[0055] ;

[0056] in, The rated angular frequency; and These are the DC side voltage and the reference voltage, respectively. This is the active power droop coefficient; The phase angle is output by the converter; and These are the rated voltage and the modulation voltage, respectively. and These are the output reactive power and the reference reactive power, respectively. The reactive power-voltage droop factor;

[0057] modulating voltage AC side output voltage Input voltage control stage, in Error-free tracking is performed using PI control in the coordinate system to obtain the reference current for the current loop. and ; set the current loop reference current and Input current control loop, in Error-free tracking is performed using PI control in a coordinate system to obtain the reference voltage of the DC / AC converter. Components; based on the reference voltage of the DC / AC converter Component and converter output phase angle go through After conversion, PWM modulation is performed to generate a PWM signal to drive the DC / AC converter.

[0058] The present invention also provides a fuel cell network control device based on multi-mode switching, used in the method of the present invention, the device comprising a first module, a second module and a third module;

[0059] The first module is used to obtain the maximum output current of the fuel cell based on the fuel utilization rate and hydrogen inflow rate; and to construct the long-term current constraint of the fuel cell based on the upstream hydrogen production rate, the minimum and maximum capacity of the hydrogen storage tank and the fuel utilization rate.

[0060] The second module is used to obtain the DC / DC side reference current of the fuel cell based on the range relationship between the integral of the fuel cell's output current over time and the long-term current constraint; and to obtain the first current based on the DC / DC side reference current using droop control.

[0061] The third module is used to compare the first current with the maximum value of the output current, take the smaller value to obtain the current loop reference current; perform DC / DC control based on the current loop reference current; and perform DC / AC control using matching control based on the dynamic DC-side voltage.

[0062] The present invention has the following beneficial effects:

[0063] The fuel cell network control method based on multi-mode switching of the present invention establishes a safe operating boundary for the fuel cell across multiple time scales, switches the operating mode according to the hydrogen storage state, and dynamically adjusts the reference current on the DC / DC side of the fuel cell according to the maximum output current corresponding to the current fuel injection rate. This enables rapid inertia support within hundreds of milliseconds and second-level frequency modulation control, while also possessing independent operating capability. It effectively solves the problems of nonlinear electrochemical output characteristics, hydrogen storage state constraints, and the lack of safe operating boundaries in existing control methods for fuel cells.

[0064] The fuel cell grid control device based on multi-mode switching of the present invention, used in the method of the present invention, has the same beneficial effects as the method of the present invention.

[0065] In addition to the objectives, features, and advantages described above, the present invention has other objectives, features, and advantages. The invention will now be described in further detail with reference to the accompanying drawings. Attached Figure Description

[0066] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0067] Figure 1 This is a schematic diagram of the fuel cell network topology and control according to a preferred embodiment of the present invention.

[0068] Figure 2 This is a schematic diagram of the output voltage-current curve of a fuel cell according to a preferred embodiment of the present invention.

[0069] Figure 3 This is a schematic diagram of the output power-current curve of a fuel cell according to a preferred embodiment of the present invention.

[0070] Figure 4 This is a schematic diagram of the method flow of a preferred embodiment of the present invention.

[0071] Figure 5 This is a schematic diagram of the DC / DC conversion working mode of a preferred embodiment of the present invention.

[0072] Figure 6 This is a schematic diagram of the operating characteristics of a fuel cell under multiple constraints according to a preferred embodiment of the present invention.

[0073] Figure 7 This is a simulation diagram of a preferred embodiment of the present invention (1).

[0074] Figure 8 This is a simulation diagram of case (2) of a preferred embodiment of the present invention. Detailed Implementation

[0075] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings, but the present invention can be implemented in many different ways as defined and covered by the claims.

[0076] The fuel cell network topology involved in the preferred embodiment of the present invention is described in [reference needed]. Figure 1 The electrochemical reaction process of a fuel cell is related to its real-time operating state, causing the equivalent internal resistance of the fuel cell to change with the output current. Its output voltage-current curve is shown below. Figure 2 As shown. When the fuel cell output current is near its rated value, the system operates in the ohmic region, and the output voltage... With current The relationship between the output voltage and current is approximately linear. However, when the fuel cell output current is too small or too large, the output voltage and current exhibit a strongly nonlinear relationship, and the system operates in the activation or concentration region. Under constant fuel flow conditions, the nonlinear characteristic of the output voltage-current leads to the existence of a maximum power point (MPP) in the fuel cell, the corresponding current value of which can be denoted as... ,like Figure 3 As shown. During transient processes such as load disturbances, the nonlinear electrochemical characteristics of fuel cells cause variations in their output current. Greater than Output power The decrease limits the short-term power output capability of fuel cells.

[0077] Based on the above analysis, see Figure 4 In a preferred embodiment of the present invention, a fuel cell grid control method based on multi-mode switching is provided, comprising:

[0078] S1. Obtain the maximum output current of the fuel cell based on the fuel utilization rate and hydrogen inflow rate; construct the long-term current constraint of the fuel cell based on the upstream hydrogen production rate, the minimum and maximum capacity of the hydrogen storage tank, and the fuel utilization rate.

[0079] In a preferred embodiment of the present invention, obtaining the maximum output current of the fuel cell based on fuel utilization rate and hydrogen inflow rate includes:

[0080] Under normal operating conditions, fuel cells typically operate in a constant fuel utilization rate mode. When a fuel cell operates in a constant fuel utilization rate state, the fuel utilization rate... Represented as:

[0081] ;

[0082] in, and These represent the inflow and outflow rates of hydrogen gas, respectively. It is the reaction constant; The output current of the fuel cell, This refers to the fuel injection rate; It is a time constant; For the Laplace operator.

[0083] The upper and lower limits of the fuel injection rate, affected by the valve, are expressed as follows:

[0084] ;

[0085] in, and These represent the minimum and maximum fuel injection rates, respectively.

[0086] Under normal operating conditions The value is typically between 0.5 and 0.9. Below 0.5, fuel utilization is low and economical; while excessively high utilization shortens battery life and reduces stable operation. In this embodiment, a value of 0.7 is preferred. If constant fuel utilization is maintained, the fuel cell can maintain its operation within a suitable range during load disturbances by injecting or reducing fuel supply. However, hydrogen injection in the fuel cell involves generating hydrogen through a fuel preparation stage after fuel injection. This fuel preparation stage can be considered as having a first-order delay, meaning that the fuel preparation stage requires a certain amount of time to switch from fuel injection to hydrogen injection. Therefore, under load disturbances, the system cannot quickly inject hydrogen to improve the power output of the fuel cell, resulting in limited short-term power output.

[0087] With constant fuel flow, the system's nonlinear power output characteristics are as follows: Figure 3 As shown. If the system operating point is A, when the load increases, the system operating point moves to point A', and the fuel cell output power increases, which can meet the load power demand. If the system operating point is B, when the load increases, the system operating point moves to point B', and the fuel cell output power decreases, further aggravating the power imbalance and easily causing DC side voltage collapse. Therefore, the short-term output current of the fuel cell cannot exceed the value corresponding to MPP. .

[0088] Therefore, based on the output power characteristics of a fuel cell, the short-term output current of the fuel cell should be less than the maximum current corresponding to the maximum power output point, while also considering fuel utilization efficiency. From the expression, we can see that When the value is 1, the power output capability is maximized. Therefore, the short-time current constraints of the fuel cell include:

[0089] ;

[0090] Therefore, the maximum output current of the fuel cell is obtained. In a preferred embodiment of the present invention Figure 1 In this context, the short-time current constraint of the fuel cell is denoted as Equation 1.

[0091] In a preferred embodiment of the present invention, the long-term current constraint of the fuel cell, based on the upstream hydrogen production rate, the minimum and maximum capacity values ​​of the hydrogen storage tank, and the fuel utilization rate, includes:

[0092] Fuel capacity in hydrogen storage tank The range constraints must satisfy:

[0093] ;

[0094] in, and These are the minimum and maximum capacity values ​​for the hydrogen storage tank, respectively. for Fuel capacity at any given time;

[0095] Assumption At any given time, the fuel capacity is ,but for:

[0096] ;

[0097] in, for The fuel injection rate at any given time; The hydrogen production rate of the upstream hydrogen production equipment;

[0098] Combined with fuel capacity Scope constraints and ,get:

[0099] ;

[0100] fuel utilization rate Substituting these values, the long-term current constraints for the fuel cell are obtained as follows:

[0101] ;

[0102] In the preferred embodiment of the present invention Figure 5 In the equation, the long-term current constraint of the fuel cell is denoted as Equation 3.

[0103] Fuel capacity The range constraint gives the operating boundary of the fuel cell for long-term operation. If there is no hydrogen production stage upstream, the hydrogen production rate is... The value is 0. The lower operating limit in the long-term current constraint of a fuel cell indicates that when operating in parallel with hydrogen production units such as electrolyzers, the start-up and shutdown of the fuel cell are constrained by this lower limit, while the upper operating limit indicates that the power output capacity of the fuel cell will be limited when the hydrogen storage tank capacity is insufficient. The long-term current constraint of a fuel cell can serve as the controllable operating boundary for a system with bidirectional hydrogen-to-electricity conversion capability.

[0104] S2. Obtain the DC / DC side reference current of the fuel cell based on the range relationship between the integral of the fuel cell output current over time and the long-term current constraint; obtain the first current based on the DC / DC side reference current and droop control.

[0105] Depending on the hydrogen storage state, the DC / DC converter can operate in three different modes. See [link / reference] Figure 5 In a preferred embodiment of the present invention, obtaining the DC / DC side reference current of the fuel cell based on the range relationship between the integral of the fuel cell's output current over time and the long-term current constraint includes:

[0106] Mode 1: When the output current is integrated over time Real-time monitoring of the fuel cell output current within the long-term current constraint range. The reference current on the DC / DC side of the fuel cell is calculated according to the first update method. Initial value; when Reaching the maximum output current At that time, the DC / DC side reference current of the fuel cell is updated according to the first update method. ;when The maximum output current was not reached. At the same time, maintain the reference current on the DC / DC side of the fuel cell. constant;

[0107] The first update method includes performing PI errorless adjustment of fuel utilization rate based on the deviation between real-time fuel utilization rate and rated fuel utilization rate, to obtain a real-time fuel injection rate for restoring fuel utilization rate to the rated value. Based on the real-time fuel injection rate Obtain the DC / DC side reference current of the fuel cell .

[0108] In Mode 1, the DC / DC side reference current of the fuel cell is obtained according to the first update method. Represented as:

[0109] ;

[0110] in, and These represent the proportional and integral coefficients of the Pi controller, respectively. This represents the rated fuel utilization rate, which ranges from 0.5 to 0.9, and is preferably 0.7 in this embodiment.

[0111] In the first mode, the fuel cell operates in grid-connected control mode, which can flexibly participate in grid frequency regulation.

[0112] Mode 2: When the output current is integrated over time When the current exceeds the upper limit of the long-term current constraint, the minimum fuel injection rate is used. Obtain the DC / DC side reference current of the fuel cell .

[0113] In Mode 2, the reference current on the DC / DC side of the fuel cell... Represented as:

[0114] ;

[0115] In Mode 2, if the hydrogen storage tank's fuel capacity is insufficient, the fuel cell will be gradually phased out. Considering the system's power balance requirements, the gas valve will maintain a minimum fuel flow rate. Once fuel is injected, the fuel cell will supply power to the grid at the maximum output current available under constant flow conditions. Mode 2 has almost no frequency regulation capability.

[0116] Mode 3: When the output current is integrated over time When the current is less than the upper limit of the long-term current constraint, the maximum fuel injection rate is used. Obtain the DC / DC side reference current of the fuel cell .

[0117] In Mode 3, the reference current on the DC / DC side of the fuel cell... Represented as:

[0118] ;

[0119] In Mode 3, the hydrogen storage tank has sufficient fuel reserves. To ensure the normal operation of the upstream hydrogen production equipment, the gas valve will operate at maximum fuel flow. Fuel is injected into the fuel cell. To ensure the safe and stable operation of the system, the fuel utilization rate of the fuel cell will be maintained at a low level, and a certain frequency regulation capability will be maintained while injecting power into the system.

[0120] In a preferred embodiment of the present invention, based on the DC / DC side reference current The first current is obtained based on droop control. include:

[0121] On the DC / DC side, since the fuel utilization rate of the fuel cell is controlled at around the rated fuel utilization rate during normal operation, and the fuel cell stack itself has a certain power reserve, the output current can be adjusted according to changes in the grid frequency. The droop relationship between the fuel cell stack output current and frequency is expressed as:

[0122] ;

[0123] in, This refers to the droop coefficient in droop control. Angular frequency; This is the rated angular frequency.

[0124] S3. Compare the first current with the maximum value of the output current and take the smaller value to obtain the current loop reference current; perform DC / DC control based on the current loop reference current; and perform DC / AC control using matching control based on the dynamic DC-side voltage.

[0125] In a preferred embodiment of the present invention, the first current is... With the maximum output current Compare the values ​​and take the smaller value to obtain the current loop reference current. Comparative expressions include:

[0126] ;

[0127] In the preferred embodiment of the present invention Figure 1 In this context, the above comparison formula is denoted as Formula Two.

[0128] In a preferred embodiment of the present invention, DC / DC control based on the current loop reference current includes:

[0129] Reference current of the current loop Subtract the output current of the fuel cell Then, PI control and PWM modulation are performed sequentially to obtain the modulated voltage. , is represented as:

[0130] ;

[0131] in, and These are the proportional and integral coefficients of the PI controller before PWM modulation in DC / DC control;

[0132] According to the modulation voltage PWM modulation is applied to the DC / DC converter to achieve DC / DC control.

[0133] In a preferred embodiment of the present invention, DC / AC control using dynamic matching control based on DC-side voltage includes:

[0134] Matching control based on DC-side voltage dynamics includes:

[0135] The active-frequency control loop is represented as:

[0136] ;

[0137] The reactive power-voltage loop uses droop control, as shown below:

[0138] ;

[0139] in, Angular frequency; The rated angular frequency; and These are the DC side voltage and the reference voltage, respectively. This is the active power droop coefficient; The phase angle is output by the converter; and These are the rated voltage and the modulation voltage, respectively. and These are the output reactive power and the reference reactive power, respectively. The reactive power-voltage droop factor;

[0140] modulating voltage AC side output voltage Input voltage control stage, in Error-free tracking is performed using PI control in the coordinate system to obtain the reference current for the current loop. and ; set the current loop reference current and Input current control loop, in Error-free tracking is performed using PI control in a coordinate system to obtain the reference voltage of the DC / AC converter. Components; based on the reference voltage of the DC / AC converter Component and converter output phase angle go through After conversion, PWM modulation is performed to generate a PWM signal to drive the DC / AC converter.

[0141] In a preferred embodiment of the present invention, a design method for key parameters is also provided, including:

[0142] In DC / AC conversion:

[0143] Salient of reactive voltage loop It can be obtained from the following formula:

[0144] ;

[0145] When the AC side voltage deviates by ±10%, the reactive power fluctuation is 100%.

[0146] DC-side voltage and frequency droop factor It can be obtained from the following formula:

[0147] ;

[0148] in, Indicates the AC side voltage offset; Indicates the reactive power offset; Indicates the angular frequency offset; This represents the offset of the square of the DC side voltage.

[0149] According to the requirements of the national standard GB / T 33592—2017 for distributed power generation grid connection, when the frequency fluctuation range is within -0.5Hz to 0.5Hz, the distributed power generation needs to maintain grid connection operation. Therefore, this embodiment sets the DC side voltage fluctuation to ±10% when the grid frequency deviates by ±1%. In this embodiment, and The values ​​are 4 and 10 respectively. The voltage and current inner loop control is set to... It is implemented in the coordinate axis, and fast tracking is achieved by the PI control loop.

[0150] In DC / DC conversion:

[0151] Current-frequency droop factor in DC / DC conversion satisfy:

[0152] ;

[0153] in, This indicates the change in the output current of the fuel cell.

[0154] When the grid frequency deviates by 0.1Hz, the fuel cell output current increases from the rated value to the maximum output current. Therefore, in this embodiment... The value is 500.

[0155] See Figure 5 When operating in mode one, the fuel cell dynamically adjusts the injected fuel via a PI controller based on fuel utilization deviations to accelerate fuel preparation. Figure 5 The parameters of the PI controller in the design are based on the fuel preparation delay stage:

[0156] ;

[0157] At this point, the time constant of the fuel cell fuel utilization control stage is 1 / To improve the response speed of fuel injection in fuel cells, its time constant... The setting is around 0.5 seconds, therefore in this article... The value is 2. The value is 10.

[0158] See Figure 6 Based on the above, the operating characteristics of the fuel cell in the preferred embodiment of the present invention under multiple constraints are analyzed. When the system operates in mode one, the frequency regulation capability exhibits piecewise continuous characteristics. The system starts from the rated point... At startup, the fuel cell output current is When an increase in load causes a decrease in frequency, the system rapidly increases the output current through current-frequency droop. The operating point moves along the droop line towards... The point at which the maximum output current is reached under the current fuel flow rate. Subsequently, the system triggered zero-error fuel utilization rate regulation, and the fuel injection rate was adjusted from... Increase to Increase the current limit to The running point was moved to Point, continue along the perpendicular line towards Point frequency regulation. Point E represents the system operating in mode two, where the fuel injection rate is maintained at its minimum. The fuel cell output current is the maximum value under this condition. It has almost no frequency regulation capability. Point F represents the system operating in mode three, where the fuel cell maintains maximum fuel flow. It is operational and can provide frequency adjustment capabilities. Figure 6 middle , and This represents the frequency at the corresponding point.

[0159] The fuel cell network control method based on multi-mode switching of the present invention establishes a safe operating boundary for the fuel cell across multiple time scales, switches the operating mode according to the hydrogen storage state, and dynamically adjusts the reference current on the DC / DC side of the fuel cell according to the maximum output current corresponding to the current fuel injection rate. This enables rapid inertia support within hundreds of milliseconds and second-level frequency modulation control, while also possessing independent operating capability. It effectively solves the problems of nonlinear electrochemical output characteristics, hydrogen storage state constraints, and the lack of safe operating boundaries in existing control methods for fuel cells.

[0160] In a preferred embodiment of the present invention, a fuel cell network control device based on multi-mode switching is also provided for use with the method of the present invention. The device includes a first module, a second module, and a third module.

[0161] The first module is used to obtain the maximum output current of the fuel cell based on the fuel utilization rate and hydrogen inflow rate; and to construct the long-term current constraint of the fuel cell based on the upstream hydrogen production rate, the minimum and maximum capacity of the hydrogen storage tank and the fuel utilization rate.

[0162] The second module is used to obtain the DC / DC side reference current of the fuel cell based on the range relationship between the integral of the fuel cell's output current over time and the long-term current constraint; and to obtain the first current based on the DC / DC side reference current using droop control.

[0163] The third module is used to compare the first current with the maximum value of the output current, take the smaller value to obtain the current loop reference current; perform DC / DC control based on the current loop reference current; and perform DC / AC control using matching control based on the dynamic DC-side voltage.

[0164] The fuel cell grid control device based on multi-mode switching of the present invention, used in the method of the present invention, has the same beneficial effects as the method of the present invention.

[0165] Verification section:

[0166] In a preferred embodiment of the present invention, the effectiveness of the proposed control strategy is verified through two case studies. This embodiment uses PSCAD / EMTDC to build a simulation model of a single fuel cell connected to an infinite power grid. The topology of the model is as follows: Figure 1 As shown in Table 1, the fuel cell stack and its main parameters are presented. The specific simulation conditions and results will be described below.

[0167] Table 1 Fuel Cell Parameters

[0168] ;

[0169] In Table 1, Denotes Faraday's constant; Molar entropy represents the thermodynamic parameter. This indicates the rated voltage value of a single fuel cell stack; Indicates the number of fuel cell stacks connected in series; Indicates the hydrogen time constant; and Indicates parameters related to activation loss; This represents the time constant of the fuel preparation process; Indicates the exchange current density; This represents the water vapor time constant; Indicates the operating temperature; Indicates the hydrogen reaction constant; This represents the water vapor reaction constant; Indicates the oxygen reaction constant; This represents the oxygen time constant.

[0170] Case (1): Operating characteristics and multi-mode switching characteristics under different modes

[0171] See Figure 7 The simulation conditions are as follows: at 0s, the hydrogen storage tank is at full capacity and the fuel cell operates in mode three; at 2s, the grid frequency drops to 49.95Hz; at 4s, the hydrogen storage tank capacity decreases and the fuel cell switches to mode one; at 6s, the grid frequency recovers to 50Hz; at 8s, the hydrogen storage tank capacity is low and the fuel cell switches to mode two; at 10s, the grid frequency changes again to 49.9Hz.

[0172] During the 0-4s period, the fuel cell operates in mode three, and the hydrogen storage tank... Fuel is injected into the system at a rate of [missing value]. During the 0-2s period, the fuel cell maintains a fuel utilization rate of 0.7, a system frequency of 50Hz, and a DC-side voltage of 800V. At 2s, when the grid frequency is disturbed, the fuel cell DC-side voltage drops proportionally to 780V, and the output current increases to approximately 180A according to the frequency-current droop relationship. Since the fuel injection rate remains constant, the fuel utilization rate of the fuel cell rises to 0.85. At 4s, the fuel cell switches to Mode 1 operation, and the hydrogen storage tank begins to adjust the fuel injection according to the fuel utilization rate, gradually decreasing the fuel injection rate to 0.3mol / s, and the fuel utilization rate gradually recovers to 0.7. Simultaneously, the fuel cell output power decreases synchronously. When the grid frequency recovers to the rated frequency at 6s, according to the frequency-current droop relationship, the fuel cell output power further decreases to approximately 90A, the fuel injection rate decreases to approximately 0.25mol / s, and the fuel utilization rate remains at 0.7. The fuel cell DC-side voltage recovers to 800V. At 8s, the hydrogen storage tank pressure further decreases, and the fuel cell switches to Mode 2 operation, at which point the fuel cell maintains the minimum fuel injection rate. Due to delays in the fuel preparation process, the amount of hydrogen injected... The flow rate gradually decreases to 0.1 mol / s. At this point, the fuel cell maintains its maximum output capacity, with a fuel utilization rate of 1, and its output current gradually decreases as the injected fuel decreases. When the grid frequency drops to 49 Hz in 10 seconds, the fuel cell does not follow the grid frequency fluctuations to change its output, maintaining its maximum output capacity to support the grid.

[0173] Case (2): Independent operation and load disturbance characteristics during unplanned islanding

[0174] The simulation conditions are as follows: the hydrogen storage tank is fully fueled, and the fuel cell is operating in Mode 1. At 2 seconds, a grid disturbance occurs, and the fuel cell enters unplanned islanding operation with load. At 4 seconds and 6 seconds, the load increases by 10kW and 12kW, respectively. See the simulation results for Case 2. Figure 8 As shown. Figure 8 middle and These represent the output of active power and reactive power, respectively.

[0175] During the first 0-2 seconds, the fuel cell operates in grid-connected mode with a DC voltage of 800V, a fuel utilization rate of 0.7, and a fuel injection rate of 0.25 mol / s. When switching from grid-connected to islanded operation at 2 seconds, due to the relatively small local load (20kW), the AC output current... The sudden decrease in power caused a surge in the DC-side voltage to 820V. Based on the matching control characteristics, the islanded system frequency synchronization increased to 50.1Hz. At this point, the fuel cell will rapidly reduce its output power to suppress system frequency and DC-side voltage changes according to the frequency-current droop relationship. Furthermore, the reduction in fuel cell output power leads to a decrease in fuel efficiency to approximately 0.5. Figure 4 Under mode one control, the fuel cell will reduce fuel injection. And the amount of hydrogen injected is reduced simultaneously during the fuel preparation process. This allows the fuel utilization rate to gradually recover to 0.7. At this point, the system frequency and DC-side voltage both recover to 50Hz and 800V, respectively. After adding a 10kW load in 4 seconds, the DC-side capacitor releases energy due to AC-side power imbalance, causing the voltage to drop to 0.76kV and the system frequency to drop to 49.9Hz. At this moment, the fuel cell output power increases instantaneously. Then, the fuel utilization rate control loop gradually restores the fuel utilization rate to its rated value by adjusting the fuel injection amount. The DC-side voltage and system frequency also recover to their rated values ​​after being controlled by the gas valve. When a 12kW load is added in 6 seconds, the fuel cell instantly increases its output power to 35kW. Then, under the action of the fuel utilization rate control loop, the above process is repeated to maintain the safe and stable operation of the islanded system.

[0176] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A fuel cell grid control method based on multi-mode switching, characterized in that, include: The maximum output current of the fuel cell is obtained based on the fuel utilization rate and the hydrogen inflow rate. The long-term current constraint of the fuel cell is constructed based on the upstream hydrogen production rate, the minimum and maximum capacity of the hydrogen storage tank, and the fuel utilization rate. The DC / DC side reference current of the fuel cell is obtained based on the range relationship between the integral of the fuel cell output current over time and the long-term current constraint; a first current is obtained based on the DC / DC side reference current using droop control; the first current is compared with the maximum value of the output current, and the smaller value is taken to obtain the current loop reference current; DC / DC control is performed based on the current loop reference current; DC / AC control is performed using matching control based on dynamic DC-side voltage. The DC / DC side reference current of the fuel cell is obtained based on the range relationship between the integral of the fuel cell's output current over time and the long-term current constraint, including: Mode 1: When the integral of the output current with respect to time Within the long-term current constraint range, the output current of the fuel cell is monitored in real time. The reference current on the DC / DC side of the fuel cell is calculated according to the first update method. Initial value; when Reaching the maximum output current At that time, the DC / DC side reference current of the fuel cell is updated according to the first update method. ;when The maximum output current was not reached. At the same time, maintain the reference current on the DC / DC side of the fuel cell. constant; The first update method includes performing PI errorless adjustment of fuel utilization rate based on the deviation between real-time fuel utilization rate and rated fuel utilization rate to obtain the real-time fuel injection rate. According to the real-time fuel injection rate Obtain the DC / DC side reference current of the fuel cell ; Mode 2: When the integral of the output current with respect to time When the current exceeds the upper limit of the long-term current constraint, the minimum fuel injection rate is used. Obtain the DC / DC side reference current of the fuel cell ; Mode 3: When the output current is integrated over time When the current is less than the upper limit of the long-term current constraint, the maximum fuel injection rate is used. Obtain the DC / DC side reference current of the fuel cell .

2. The fuel cell grid control method based on multi-mode switching according to claim 1, characterized in that, The method for obtaining the maximum output current of the fuel cell based on fuel utilization rate and hydrogen inflow rate includes: When a fuel cell operates at a constant fuel utilization rate, the fuel utilization rate is... Represented as: ； in, and These represent the inflow and outflow rates of hydrogen gas, respectively. It is the reaction constant; The output current of the fuel cell, This refers to the fuel injection rate; It is a time constant; For the Laplace operator; The upper and lower limits of the fuel injection rate, affected by the valve, are expressed as follows: ； in, and These are the minimum and maximum fuel injection rates, respectively; Based on the output power characteristics of fuel cells, the short-term output current of a fuel cell should be less than the maximum current corresponding to the maximum power output point, while also considering fuel utilization efficiency. It can be seen that, When the value is 1, the power output capability is maximized. Therefore, the short-time current constraints of the fuel cell include: ； Therefore, the maximum output current of the fuel cell is obtained. .

3. The fuel cell grid control method based on multi-mode switching according to claim 2, characterized in that, The long-term current constraint for the fuel cell, constructed based on the upstream hydrogen production rate, the minimum and maximum capacity of the hydrogen storage tank, and the fuel utilization rate, includes: Fuel capacity S in hydrogen storage tank SOH The range constraints must satisfy: ； in, and These are the minimum and maximum capacity values ​​for the hydrogen storage tank, respectively. for Fuel capacity at any given time; Assumption At any given time, the fuel capacity is ,but for: ； in, for The fuel injection rate at any given time; The hydrogen production rate of the upstream hydrogen production equipment; Combined with fuel capacity Scope constraints and ,get: ； fuel utilization rate Substituting these values, the long-term current constraints for the fuel cell are obtained as follows: 。 4. The fuel cell grid control method based on multi-mode switching according to claim 3, characterized in that, The first mode includes: In Mode 1, the DC / DC side reference current of the fuel cell is obtained according to the first update method. Represented as: ； in, and These represent the proportional and integral coefficients of the Pi controller, respectively. This indicates the rated fuel utilization rate.

5. The fuel cell grid control method based on multi-mode switching according to claim 4, characterized in that, The second mode includes: In Mode 2, the reference current on the DC / DC side of the fuel cell... Represented as: 。 6. The fuel cell grid control method based on multi-mode switching according to claim 5, characterized in that, The third mode includes: In Mode 3, the reference current on the DC / DC side of the fuel cell... Represented as: 。 7. The fuel cell grid control method based on multi-mode switching according to claim 6, characterized in that, DC / DC control based on the current loop reference current includes: The current loop reference current Subtract the output current of the fuel cell Then, PI control and PWM modulation are performed sequentially to obtain the modulated voltage. , represented as: ； in, and These are the proportional and integral coefficients of the PI controller before PWM modulation in DC / DC control; According to the modulation voltage PWM modulation is applied to the DC / DC converter to achieve DC / DC control.

8. The fuel cell grid control method based on multi-mode switching according to claim 7, characterized in that, The DC / AC control using dynamic matching control based on DC-side voltage includes: The matching control based on DC-side voltage dynamics includes: The active-frequency control loop is represented as: ； The reactive power-voltage loop uses droop control, as shown below: ； in, The rated angular frequency; and These are the DC side voltage and the reference voltage, respectively. This is the active power droop coefficient; The phase angle is output by the converter; and These are the rated voltage and the modulation voltage, respectively. and These are the output reactive power and the reference reactive power, respectively. The reactive power-voltage droop factor; The modulation voltage AC side output voltage Input voltage control stage, in Error-free tracking is performed using PI control in the coordinate system to obtain the reference current for the current loop. and ; the reference current of the current loop and Input current control loop, in Error-free tracking is performed using PI control in a coordinate system to obtain the reference voltage of the DC / AC converter. Components; based on the reference voltage of the DC / AC converter Components and the output phase angle of the converter go through After conversion, PWM modulation is performed to generate a PWM signal to drive the DC / AC converter.

9. A fuel cell grid control device based on multi-mode switching, used in the method described in any one of claims 1 to 8, characterized in that, The device includes a first module, a second module, and a third module; The first module is used to obtain the maximum output current of the fuel cell based on the fuel utilization rate and the hydrogen inflow rate; and to construct the long-term current constraint of the fuel cell based on the upstream hydrogen production rate, the minimum and maximum capacity of the hydrogen storage tank and the fuel utilization rate. The second module is used to obtain the DC / DC side reference current of the fuel cell based on the range relationship between the integral of the fuel cell output current over time and the long-term current constraint; and to obtain the first current based on the DC / DC side reference current using droop control. The third module is used to compare the first current with the maximum value of the output current and take the smaller value to obtain the current loop reference current. DC / DC control is performed based on the current loop reference current; DC / AC control is performed using matching control based on dynamic DC-side voltage.

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