Fuel cell networking control method and device based on multi-mode switching

Abstract

The invention discloses a fuel cell networking control method and device based on multi-mode switching. The method comprises the following steps: obtaining the maximum value of the output current of a fuel cell according to the fuel utilization rate and the hydrogen inflow rate; constructing a long-time current constraint of the fuel cell according to the upstream hydrogen production rate, the minimum and maximum capacity values of the hydrogen storage tank and the fuel utilization rate; obtaining a DC / DC side reference current of the fuel cell according to the range relation between the integral of the output current of the fuel cell to time and the long-time current constraint; obtaining a first current based on droop control according to the DC / DC side reference current; comparing the first current with the maximum value of the output current, and taking a smaller value to obtain a current loop reference current; performing DC / DC control according to the current loop reference current; and DC / AC control is carried out by adopting matching control based on DC side voltage dynamics.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of new power distribution systems, in particular to a fuel cell network construction control method and device based on multi-mode switching. BACKGROUND

[0002] With high proportion of new energy and high proportion of power electronic equipment accessing the power grid, the power system presents low inertia, strong randomness and weak anti-disturbance characteristics, which seriously affects the stable operation ability of the system. Hydrogen energy, as a low-carbon and efficient long-time energy storage medium, can realize electric-hydrogen-electric conversion through wind-solar hydrogen production and fuel cell power generation, etc., and improve the system operation flexibility and long-time stability.

[0003] Fuel cells, as the core equipment of hydrogen-electric conversion, have broad application prospects in the fields of power, transportation and aviation. Fuel cells are usually connected to low-voltage AC power grid through two-stage DC / DC and DC / AC conversion, and their operation modes are mainly divided into two modes: constant fuel flow and constant fuel utilization. The existing fuel cells connected to the grid in the form of grid-following do not have independent operation and inertia support capability. In recent years, network construction control technology has attracted much attention due to its ability to simulate the inertia support and independent operation of synchronous generators. For fuel cell systems, the first step to achieve network construction control is to solve the problem of energy source at the primary side. However, in the existing fuel cell network construction control technology, on the one hand, fuel cells are usually kept in a constant power output state, and the frequency regulation and inertia support capability are mainly provided by parallel energy storage units, which face the problem of parallel power distribution, and none of them can tap the power support and network operation capability of fuel cell stacks; on the other hand, the maximum output capacity of fuel cells is usually not considered, so the DC voltage is prone to instability under disturbance; in addition, due to the strong nonlinearity of fuel cell output voltage and current, the short-time output power capability is limited, and the hydrogen storage state, fuel preparation rate and DC capacitor state will also restrict the network operation capability of fuel cells. The existing technology cannot fully characterize the safe operation boundary of network construction fuel cells, and lacks applicable network construction support strategies.

[0004] Therefore, there is an urgent need for a new technical solution to solve the technical problem of how to construct the network control strategy of fuel cells. SUMMARY

[0005] The present application provides a fuel cell network construction control method and device based on multi-mode switching to solve the technical problem of how to construct the network control strategy of fuel cells.

[0006] To achieve the above-mentioned purpose, the present application provides a fuel cell network construction control method based on multi-mode switching, comprising: The maximum output current of the fuel cell is obtained according to the fuel utilization and the hydrogen inflow rate; the long-time current constraint of the fuel cell is constructed according to the upstream hydrogen production rate, the minimum and maximum capacity values of the hydrogen storage tank and the fuel utilization; The DC / DC side reference current of the fuel cell is obtained according to the range relation between the integral of the output current of the fuel cell with respect to time and the long-time current constraint; the first current is obtained based on droop control according to the DC / DC side reference current; the current loop reference current is obtained by comparing the first current with the maximum output current and taking the smaller one; the DC / DC control is performed according to the current loop reference current; the DC / AC control is performed by using matching control based on the dynamic of the direct current side voltage.

[0007] Preferably, the maximum output current of the fuel cell obtained according to the fuel utilization and the hydrogen inflow rate comprises: The fuel utilization is constant when the fuel cell works in the constant fuel utilization state. ; Wherein, and are the hydrogen inflow and outflow rates respectively; is the reaction constant; is the output current of the fuel cell, is the fuel injection rate; is the time constant; is the Laplace operator; The upper and lower limits of the fuel injection rate are represented as: ; Wherein, and are the minimum and maximum values of the fuel injection rate respectively; Based on the output power characteristics of the fuel cell, the short-time output current of the fuel cell should be less than the maximum current corresponding to the maximum power output point, and based on the fuel utilization It can be known that, when the fuel utilization is 1, the power output capability is maximum, and therefore the short-time current constraint of the fuel cell comprises: ; Therefore, the maximum output current of the fuel cell is obtained as .

[0008] Preferably, the long-time current constraint of the fuel cell constructed according to the upstream hydrogen production rate, the minimum and maximum capacity values of the hydrogen storage tank and the fuel utilization comprises: The range constraint of the fuel capacity in the hydrogen storage tank needs to satisfy: ; Wherein, 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: ; 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: 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; 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 ; 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 ; Mode three: when the integral of the output current over time is less than the upper limit of the long-time current constraint, the DC / DC side reference current of the fuel cell is obtained according to the fuel injection rate maximum .

[0009] Preferably, mode one comprises: In mode one, the DC / DC side reference current of the fuel cell is obtained according to the first updating method is expressed as: ; wherein, and respectively represent the proportional coefficient and the integral coefficient of the PI controller; represents the rated fuel utilization rate.

[0010] Preferably, mode two comprises: In mode two, the DC / DC side reference current of the fuel cell is obtained according to the second updating method is expressed as: ; Preferably, mode three comprises: In mode three, the DC / DC side reference current of the fuel cell is obtained according to the third updating method is expressed as: ; Preferably, the DC / DC control according to the current loop reference current comprises: Subtracting the output current of the fuel cell from the current loop reference current , the PI control and the PWM modulation are sequentially performed to obtain the modulation voltage , which is expressed as: ; wherein, and respectively represent the proportional coefficient and the integral coefficient of the PI controller before the PWM modulation in the DC / DC control; The DC / DC converter is PWM modulated according to the modulation voltage to realize the DC / DC control.

[0011] Preferably, the DC / AC control by using the matching control based on the dynamic DC side voltage comprises: The matching control based on the dynamic DC side voltage comprises: the active-power-frequency control loop, which is expressed 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; 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.

[0012] 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; 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. 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. 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.

[0013] The present invention has the following beneficial effects: The multi-mode switching based fuel cell network construction control method of the application can realize rapid inertia support within hundreds of milliseconds and frequency modulation control within seconds, has independent operation ability, and effectively solves the problems of fuel cell due to non-linear electrochemical output characteristics, hydrogen storage state constraints, and lack of safe operation boundary in existing control.

[0014] The multi-mode switching based fuel cell network construction control device of the application is used for the method of the application, and has the same beneficial effects as the method of the application.

[0015] In addition to the purposes, features and advantages described above, the application has other purposes, features and advantages. The application will be further described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF DRAWINGS

[0016] The accompanying drawings, which form a part of the application, are intended to provide further understanding of the application, and the illustrative embodiments of the application and their description serve to explain the application. The accompanying drawings do not constitute an inappropriate limitation on the application. In the drawings: Figure 1 The fuel cell network topology and control schematic diagram of the preferred embodiment of the application.

[0017] Figure 2 The fuel cell output voltage-current curve schematic diagram of the preferred embodiment of the application.

[0018] Figure 3 The fuel cell output power-current curve schematic diagram of the preferred embodiment of the application.

[0019] Figure 4 The method flow schematic diagram of the preferred embodiment of the application.

[0020] Figure 5 The DC / DC conversion working mode schematic diagram of the preferred embodiment of the application.

[0021] Figure 6 The operation characteristic schematic diagram of the fuel cell under multiple constraints of the preferred embodiment of the application.

[0022] Figure 7 The case (1) simulation schematic diagram of the preferred embodiment of the application.

[0023] Figure 8 The case (2) simulation schematic diagram of the preferred embodiment of the application. DETAILED DESCRIPTION

[0024] The embodiments of the present application will be described in detail below with reference to the accompanying drawings, but the present application can be implemented in various ways as defined and covered by the claims.

[0025] The fuel cell network topology involved in the preferred embodiments of the present application is shown in Figure 1 . The fuel cell electrochemical reaction process is related to the real-time operating state, resulting in the fuel cell equivalent internal resistance changing with the output current, and its output voltage-current curve is shown in Figure 2 . When the fuel cell output current is near the rated value, the system works in the ohmic region, and the output voltage shows an approximately linear relationship with the current . However, when the fuel cell output current is too small or too large, its output voltage and current show strong nonlinear relationship, and the system works in the activation region or the concentration region. Under the condition of constant fuel flow, the output voltage-current nonlinear characteristics result in the existence of a maximum power output point (MPP) of the fuel cell, and the corresponding current value can be denoted as , as shown in Figure 3 . In the transient process such as load disturbance, the nonlinear electrochemical characteristics of the fuel cell make its output power decrease when the output current is greater than , limiting the short-time power output capability of the fuel cell.

[0026] Based on the above analysis, referring to Figure 4 , in the preferred embodiments of the present application, a fuel cell network control method based on multi-mode switching is provided, comprising: S1, obtaining the maximum output current of the fuel cell according to the fuel utilization rate and the hydrogen inflow rate; constructing the long-time current constraint of the fuel cell according to the upstream hydrogen production rate, the minimum and maximum capacity values of the hydrogen storage tank and the fuel utilization rate.

[0027] In the preferred embodiments of the present application, obtaining the maximum output current of the fuel cell according to the fuel utilization rate and the hydrogen inflow rate comprises: Under normal operating conditions, the fuel cell usually works in the constant fuel utilization mode. When the fuel cell works in the constant fuel utilization state, the fuel utilization rate is expressed as: ; wherein, and are the hydrogen inflow and outflow rates, respectively; is the reaction constant; is the output current of the fuel cell, is the fuel injection rate; is the time constant; for the Laplace operator.

[0028] The upper and lower limits of the fuel injection rate are expressed as: ; wherein, and are the minimum and maximum values of the fuel injection rate, respectively.

[0029] In the normal operating state, The value is usually between 0.5 and 0.9, and below 0.5, the fuel utilization is low and the economy is poor; and too high fuel utilization will shorten the battery life and reduce the stable operation capacity. The value of the preferred embodiment is preferably 0.7. If the constant fuel utilization mode is maintained, when a load disturbance occurs, the fuel cell can inject or reduce the fuel supply to ensure that the fuel cell operates in a suitable operating range. However, the hydrogen injection of the fuel cell is generated by the hydrogen generated after the fuel injection through the fuel preparation link, which can be equivalent to a first-order delay, which means that the fuel preparation link needs a certain time to change the fuel injection to hydrogen injection. Therefore, under the load disturbance, the system cannot quickly inject hydrogen to improve the power output capacity of the fuel cell, resulting in limited short-time power output capacity.

[0030] Under the condition that the fuel flow is constant, the nonlinear power output characteristics of the system are as shown in Figure 3 If the system operating point is A, when the load is increased, the system operating point moves to the A' point, the fuel cell output power increases, and the power demand of the load can be met. If the system operating point is B, when the load is increased, the system operating point moves to the B' point, the fuel cell output power decreases, further aggravating the power imbalance, and is easy to cause the collapse of the direct current side voltage. Therefore, the short-time output current of the fuel cell cannot exceed the maximum current corresponding to the MPP. .

[0031] Therefore, based on the output power characteristics of the fuel cell, the short-time output current of the fuel cell should be less than the maximum current corresponding to the maximum power output point, and based on the expression of the fuel utilization , when is 1, the power output capacity is maximum, and the short-time current constraint of the fuel cell includes: ; Therefore, the maximum output current of the fuel cell is obtained. In the Figure 1 preferred embodiment of the present application, the short-time current constraint of the fuel cell is recorded as Equation One.

[0032] In the preferred embodiment of the present application, the long-time current constraint of the fuel cell includes: Fuel capacity in hydrogen storage tank 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: ; In the preferred embodiment of the present invention Figure 5 In this context, the long-term current constraint of the fuel cell is denoted as Equation 3.

[0033] 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.

[0034] 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.

[0035] 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: 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; 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 .

[0036] 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 represents the rated fuel utilization rate, which ranges from 0.5 to 0.9, and is preferably 0.7 in this embodiment.

[0037] In the first mode, the fuel cell operates in grid-connected control mode, which can flexibly participate in grid frequency regulation.

[0038] 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 .

[0039] In Mode 2, the reference current on the DC / DC side of the fuel cell... Represented as: ; 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. The fuel cell injects power into the grid with the maximum output current that can be provided under the constant flow condition. Mode two has little frequency regulation capability.

[0040] Mode three: when the integral of the output current over time is less than the upper limit of the long-term current constraint, the maximum fuel injection rate is obtained according to the fuel injection rate .

[0041] In mode three, the DC / DC side reference current of the fuel cell is expressed as: ; In mode three, the hydrogen storage tank has sufficient fuel storage, and in order to meet the normal operation of the upstream hydrogen production equipment, the gas valve will inject fuel into the fuel cell with the maximum fuel flow . In order 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 the frequency regulation capability will be maintained while injecting power into the system.

[0042] In the preferred embodiment of the present application, the DC / DC side reference current is obtained based on droop control , which includes: On the DC / DC side, since the fuel utilization rate of the fuel cell is controlled around the rated fuel utilization rate during normal operation, the stack body has a certain power reserve, so the output current can be adjusted according to the change of the grid frequency. The droop relationship between the stack output current and the frequency is expressed as: ; wherein, is the droop coefficient in the droop control; is the angular frequency; is the rated angular frequency.

[0043] S3, compare the first current with the maximum output current to obtain the current loop reference current; perform DC / DC control according to the current loop reference current; and perform DC / AC control using matching control based on the dynamic voltage on the DC side.

[0044] In the preferred embodiment of the present application, the first current is compared with the maximum output current to obtain the current loop reference current , and the comparison formula includes: ; In the preferred embodiment of the present application, Figure 1 the above comparison formula is denoted as formula two.

[0045] In the preferred embodiment of the present application, the DC / DC control according to the current loop reference current comprises: Subtracting the output current of the fuel cell from the current loop reference current Subtracting the output current of the fuel cell from the current loop reference current Subtracting the output current of the fuel cell from the current loop reference current , which is expressed as: ; wherein, and are the proportional coefficient and the integral coefficient of the PI controller before PWM modulation in the DC / DC control, respectively; According to the modulation voltage PWM modulation is performed on the DC / DC converter to realize the DC / DC control.

[0046] In the preferred embodiment of the present application, the DC / AC control by the matching control based on the dynamic DC side voltage comprises: The matching control based on the dynamic DC side voltage comprises: The active-frequency control loop is expressed as: ; The reactive-voltage loop adopts droop control, which is expressed as: ; wherein, is the angular frequency; is the rated angular frequency; and are the DC side voltage and the reference voltage, respectively; is the active droop coefficient; is the phase angle of the converter output; and are the rated voltage and the modulation voltage, respectively; and are the output reactive and the reference reactive, respectively; is the reactive-voltage droop coefficient; The modulation voltage is input into the voltage control loop, and the current loop reference current is obtained by PI control in the coordinate system without error tracking; and ; the current loop reference current and are input into the current control loop, and the DC / AC converter reference voltage is obtained by PI control in the component; the component of the reference voltage of the DC / AC converter component and the phase angle of the converter output after transformation PWM modulation is performed after transformation, and a PWM signal is generated to drive the DC / AC converter.

[0047] In the preferred embodiment of the present application, a design method of key parameters is also provided, including: In the DC / AC conversion: the droop coefficient of the reactive voltage loop which can be obtained by the following formula: ; When the AC side voltage deviates by ±10%, the reactive power fluctuation is 100%.

[0048] And the DC side voltage and frequency droop coefficient which can be obtained by the following formula: ; wherein, represents the deviation of the AC side voltage; represents the deviation of the reactive power; represents the deviation of the angular frequency; represents the deviation of the square of the DC side voltage.

[0049] According to the requirements of the national standard “GB / T 33592—2017” for the grid connection specification of distributed power supply, when the frequency fluctuation range is in the interval of -0.5Hz~0.5Hz, the distributed power supply needs to remain grid-connected operation. Therefore, in the present embodiment, when the grid frequency deviates by ±1%, the DC side voltage fluctuates by ±10%. In the present embodiment, and are respectively 4 and 10. The voltage and current inner loop control is realized in the coordinate axis, and is realized by a PI control link to achieve fast tracking.

[0050] In the DC / DC conversion: current-frequency droop coefficient in DC / DC conversion satisfies: ; wherein, represents the change amount of the fuel cell output current.

[0051] 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 the present embodiment, is 500.

[0052] Referring to Figure 5When 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: ; 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.

[0053] 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 Raise 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.

[0054] The multi-mode switching based fuel cell network construction control method of the application can realize rapid inertia support within hundreds of milliseconds and frequency modulation control within seconds, has independent operation capability, and effectively solves the problems of fuel cell due to non-linear electrochemical output characteristics, hydrogen storage state constraints, and lack of safe operation boundary of existing control.

[0055] In the preferred embodiment of the application, a multi-mode switching based fuel cell network construction control device is also provided, which is used for the method of the application, and the device comprises a first module, a second module and a third module. The first module is used for obtaining the maximum output current of the fuel cell according to the fuel utilization rate and the hydrogen inflow rate, and constructing the long-time current constraint of the fuel cell according to the upstream hydrogen production rate, the minimum and maximum capacity values of the hydrogen storage tank and the fuel utilization rate. The second module is used for obtaining the DC / DC side reference current of the fuel cell according to the range relationship between the integral of the output current of the fuel cell with respect to time and the long-time current constraint, and obtaining the first current based on the droop control according to the DC / DC side reference current. The third module is used for comparing the first current with the maximum output current to obtain the current loop reference current, performing DC / DC control according to the current loop reference current, and performing DC / AC control by using the matching control based on the dynamic DC side voltage.

[0056] The multi-mode switching based fuel cell network construction control device of the application is used for the method of the application, and has the same beneficial effects as the method of the application.

[0057] Verification part: In the preferred embodiment of the application, the effectiveness of the control strategy is verified by two cases. In this embodiment, a single fuel cell access to an infinite grid simulation model is built based on PSCAD / EMTDC, and the topology structure of the built model is as shown in Figure 1 The stack and body parameters of the fuel cell are as shown in Table 1. The specific simulation conditions and simulation results will be introduced below.

[0058] Table 1 Fuel cell parameters ; In Table 1, Faraday constant is represented by F; Thermodynamic parameter molar entropy is represented by S; Single stack rated voltage value is represented by U; Fuel cell stack series number is represented by N; Hydrogen time constant is represented by T; and represents the activation loss related parameter; represents the time constant of the fuel preparation section; represents the exchange current density; represents the water vapor time constant; represents the operating temperature; represents the hydrogen reaction constant; represents the water vapor reaction constant; represents the oxygen reaction constant; represents the oxygen time constant.

[0059] Case (1): operating characteristics in different modes and multi-mode switching characteristics Referring to Figure 7 , the simulation conditions are as follows: at 0 s, the hydrogen storage tank is full, and the fuel cell operates in mode three; at 2 s, the grid frequency drops to 49.95 Hz; at 4 s, the hydrogen storage tank capacity decreases, and the fuel cell switches to mode one state operation; at 6 s, the grid frequency returns to 50 Hz; at 8 s, the hydrogen storage tank hydrogen capacity is low, and the fuel cell switches to mode two state operation; at 10 s, the grid frequency changes to 49.9 Hz again.

[0060] During 0~4s, the fuel cell operates in mode three state, and the hydrogen storage tank injects fuel into the system at a rate of During 0~2s, the fuel cell maintains a fuel utilization rate of 0.7, the system frequency remains 50 Hz, and the DC side voltage is 800 V. When the grid frequency is disturbed at 2 s, the fuel cell DC side voltage is proportionally reduced to 780 V, and the output current is increased to about 180 A according to the frequency-current droop relationship. Since the fuel injection amount remains unchanged, the fuel utilization rate of the fuel cell rises to 0.85. At 4 s, the fuel cell switches to mode one state operation, and the hydrogen storage tank adjusts the fuel injection according to the fuel utilization rate, and the fuel injection amount gradually decreases to 0.3 mol / s, and the fuel utilization rate gradually recovers to 0.7. At the same time, the output power of the fuel cell is synchronously reduced. When the grid frequency returns to the rated frequency at 6 s, the output power of the fuel cell is further reduced to about 90 A according to the frequency-current droop relationship, the fuel injection amount is reduced to about 0.25 mol / s, and the fuel utilization rate is maintained at 0.7. The DC side voltage of the fuel cell returns to 800 V. At 8 s, the pressure of the hydrogen storage tank is further reduced, and the fuel cell switches to mode two state operation. At this time, the fuel cell maintains the minimum fuel injection amount Due to the delay of the fuel preparation section, the hydrogen injection amount 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 change its output power according to the grid frequency fluctuations, maintaining its maximum output capacity to support the grid.

[0061] Case (2): Independent operation and load disturbance characteristics during unplanned islanding 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.

[0062] 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.

[0063] The above merely provides the preferred embodiments of the present application, and is not used to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modifications, equivalent replacements, improvements, etc. made within the principles and technical scope of the present application shall fall into the scope of the present application.

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.

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 process of 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: 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 .

5. The fuel cell grid control method based on multi-mode switching according to claim 4, 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.

6. The fuel cell grid control method based on multi-mode switching according to claim 5, characterized in that, The second mode includes: In Mode 2, 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, Mode 3 includes: In Mode 3, the reference current on the DC / DC side of the fuel cell... Represented as: 。 8. The fuel cell grid control method based on multi-mode switching according to claim 7, 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.

9. The fuel cell grid control method based on multi-mode switching according to claim 8, 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.

10. A fuel cell grid control device based on multi-mode switching, used in the method described in any one of claims 1 to 9, 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'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. 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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