Parallel converter cooperative grid-connected control method and device based on fuel cell power generation grid-connected system

Abstract

The invention discloses a parallel converter cooperative grid-connected control method and device based on a fuel cell power generation grid-connected system, and the method comprises the steps: generating a PWM drive signal of a converter through employing a droop control strategy and a sliding mode control strategy when the converter of each power generation unit operates; operating data of each power generation unit and the health state of the fuel cell are collected in real time, information interaction data of adjacent power generation units are combined, and voltage and frequency compensation values of each power generation unit are calculated and used for conducting primary correction on the PWM driving signal; the amplitude deviation between the frequency, the voltage and the phase angle at the common coupling point of the alternating current bus of the power grid and each power generation unit is obtained in real time, a trigger instruction used for controlling switching of a grid-connected mode and an island mode is generated based on the deviation, and a synchronization item is generated based on the deviation in the grid-connected mode and used for conducting secondary correction on the PWM driving signal. The method can improve the stability and operation efficiency of the system, and ensures that the system is stably switched between the grid-connected mode and the island mode.

Description

Technical Field

[0001] The present invention belongs to the field of fuel cell power generation and parallel converter coordinated grid-connected control, and in particular discloses a parallel converter coordinated grid-connected control method and device based on a fuel cell power generation grid-connected system. Background Art

[0002] In the current push for low-carbon emissions and clean energy development, hydrogen, with its high energy density and environmentally friendly characteristics, is becoming a core force in the global energy transition. Hydrogen fuel cells, in particular, are attracting increasing attention as a highly efficient and stable power generation technology. Unlike traditional renewable energy sources, fuel cells can provide continuous and stable power output, effectively alleviating load pressure on the power grid, especially during peak electricity demand. Therefore, the application of fuel cells in power systems, particularly in grid-connected power generation systems, is particularly important.

[0003] A fuel cell grid-connected power generation system primarily consists of multiple distributed fuel cell power generation systems, local loads, grid-connected converters, and the power grid. The core advantage of fuel cell power generation systems lies in their ability to provide stable and continuous power, making them a crucial tool for addressing fluctuations in electricity demand. Unlike traditional generators, the output characteristics of fuel cells are significantly affected by electrochemical polarization, fuel supply conditions, and the health of the power generation units. Existing control strategies fail to fully account for the polarization curve offsets and differences in the health of the power generation units of fuel cells, leading to problems with circulating current and uneven power distribution in multi-parallel systems. As a key component in the system, the grid-connected converter regulates the frequency and voltage of the power output, ensuring a stable connection between the fuel cell power generation system and the power grid. Synchronous converter operation is particularly crucial when switching between system operating modes to ensure synchronization of grid voltage, frequency, and phase angle, thereby ensuring a stable power supply.

[0004] However, a major challenge facing current fuel cell power generation grid-connected systems is that existing synchronization control strategies primarily focus on connecting a single fuel cell power generation system to the grid, lacking unified coordination for multiple parallel fuel cell power generation systems. This limitation impacts the overall performance and flexibility of the system. Furthermore, during the grid connection process, traditional synchronization control methods often rely on phase-locked loops (PLLs) to detect phase angles. However, the nonlinear characteristics of PLLs make tuning difficult and can affect control performance.

[0005] Therefore, it is particularly important to explore more efficient and flexible synchronization control strategies, especially in the application scenarios of multi-parallel fuel cell power generation systems. Summary of the Invention

[0006] In response to the deficiencies in the prior art, the present invention provides a method and device for collaborative grid-connected control of parallel converters based on a fuel cell power generation grid-connected system. The purpose is to ensure that during the operation of the system, multiple grid-connected converters can be collaboratively controlled through a more efficient and flexible synchronization control strategy, so that multiple parallel distributed fuel cell power generation systems can be stably grid-connected, and stable power supply of the fuel cell power generation system and smooth switching of the system operating mode can be achieved.

[0007] In order to achieve the above object, the present invention provides the following technical solutions:

[0008] In a first aspect of the present invention, a method for coordinated grid-connected control of parallel converters based on a fuel cell power generation grid-connected system is provided. The fuel cell power generation grid-connected system includes a plurality of distributed fuel cell power generation units connected in parallel, each power generation unit having a corresponding converter. The method comprises:

[0009] S1. When the converter of each power generation unit is running, a droop control strategy is applied to the external power control loop and a sliding mode control strategy is applied to the internal voltage and current control loop to generate a PWM drive signal for the converter;

[0010] S2. Real-time collection of operating data of each power generation unit and the health status of the fuel cell, combined with information exchange data of adjacent power generation units, to calculate voltage and frequency compensation values ​​of each power generation unit for primary correction of the PWM drive signal;

[0011] S3. Acquire in real time the amplitude deviations between the frequency, voltage, and phase angle at the common coupling point of the AC busbars of the power grid and each power generation unit, generate a trigger instruction for controlling the switching between the grid-connected mode and the island mode based on the deviations, and generate a synchronization item based on the deviations in the grid-connected mode for performing a secondary correction on the PWM drive signal after the primary correction.

[0012] Furthermore, step S1 includes:

[0013] Collect the three-phase voltage and three-phase current output by the converter and the three-phase voltage and three-phase current after filtering by the LCL filter;

[0014] Based on the collected data, d-axis and q-axis reference components of the reference current and reference voltage are generated respectively;

[0015] determining current and voltage scaling factors according to voltage and current limitations during converter operation, and correcting d-axis and q-axis reference components of the reference current and reference voltage based on the current and voltage scalar scaling factors to obtain the corrected d-axis and q-axis reference components of the reference current and reference voltage in the dq coordinate system, respectively, and thereby obtaining the corrected reference current and reference voltage in the dq coordinate system;

[0016] The reference current and reference voltage in the corrected dq coordinate system are transformed to obtain the corresponding three-phase voltage reference value. Adjustments are made based on the obtained three-phase voltage reference value and the three-phase voltage reference value output in the previous period to obtain a PWM signal to control the on and off of the switch tube in the converter.

[0017] Furthermore, the scalar scaling factor α of the current i for:

[0018]

[0019] The d-axis component and q-axis component of the reference current in the corrected dq coordinate system Respectively expressed as:

[0020]

[0021] Scalar scaling factor β for voltage v for:

[0022]

[0023] The d-axis component and q-axis component of the reference voltage in the corrected dq coordinate system Respectively expressed as:

[0024]

[0025] Among them, I max and V max They are the upper limit of current and voltage when the converter is running, i d,ref and i q,ref are the d-axis and q-axis reference components of the current, respectively, v d,ref and v q,ref are the d-axis and q-axis reference components of the voltage respectively.

[0026] Furthermore, step S2 includes:

[0027] Determine the total active power demand and total reactive power demand of the system based on the operating data of each power generation unit;

[0028] Determining a normalized active power distribution weight factor and a reactive power distribution weight factor for each power generation unit based on a health status of the fuel cell in each power generation unit;

[0029] Determining a target active power distribution value and a target reactive power distribution value of each power generation unit based on the total active power demand and the total reactive power demand and the normalized active power distribution weight factor and reactive power distribution weight factor;

[0030] Based on the normalized active power distribution weight factor and reactive power distribution weight factor, combined with the health status of the fuel cell, a corrected active power droop coefficient and a corrected reactive power droop coefficient of each power generation unit are generated;

[0031] Based on the target active power distribution value and target reactive power distribution value of each power generation unit, the corrected active power droop coefficient and the corrected reactive power droop coefficient, and the information interaction data of adjacent power generation units, the voltage and frequency compensation values ​​of each power generation unit are obtained, which are used to perform a correction on the PWM drive signal.

[0032] Furthermore, the voltage compensation value and the frequency compensation value are calculated by the following formulae respectively:

[0033]

[0034] Where Δf i and ΔV i are the frequency compensation value and voltage compensation value of the i-th power generation unit, c fi 、c pi 、c vi and c Qi are the adjustment factors for frequency, active power, voltage and reactive power respectively, which play a role in adjusting the convergence speed; γ and κ are the dynamic compensation gains corresponding to frequency and voltage respectively; It is estimated online through real-time data, which respectively represents the impact of the dynamic change of the fuel cell output voltage on frequency regulation and voltage control; f ref is the system reference frequency; V ref is the system reference voltage; and They are the corrected active power droop coefficient and the corrected reactive power droop coefficient respectively; and are the target active power allocation values ​​for the i-th and j-th generating units respectively; and are the target reactive power allocation values ​​of the i-th and j-th generating units respectively; f i and f j are the frequencies of the i-th and j-th generating units respectively; V avei and V avej are the estimated average bus voltages of the i-th and j-th generating units respectively; a ij and b i are all weight factors.

[0035] Furthermore, a ij and b i Select by the following formula:

[0036]

[0037] Furthermore, in step S2, performing a correction on the PWM drive signal includes:

[0038] The droop control equation in the droop control strategy is corrected once, which is achieved by the following formula:

[0039]

[0040] Among them, f i ' and V i ' are the corrected output frequency and average bus voltage of the i-th fuel cell power generation unit, θ i ' is the phase angle of the first fuel cell power generation unit after correction, f ni and V ni are the rated output frequency and rated voltage of the i-th fuel cell power generation unit respectively; 1 / s represents the integral link;

[0041] The PWM drive signal is corrected once based on the corrected droop control equation.

[0042] Furthermore, in step S3, the trigger instruction S t Expressed as:

[0043]

[0044] in:

[0045] f dev =|f Grid -f PCC |

[0046] V dev =|V Grid -V PCC |

[0047] θ dev =| Grid -θ PCC |

[0048] When S t When it is 1, it indicates switching to grid-connected mode. t When it is 0, it indicates switching to island mode;

[0049] Among them, V dev 、f dev ,θ dev are the voltage deviation, frequency deviation and phase angle amplitude deviation respectively, f Grid is the grid frequency, f PCC is the common coupling point frequency; V Grid is the grid voltage amplitude, V PCCis the voltage amplitude at the common coupling point; θ Grid is the grid phase angle, θ PCC is the phase angle of the common coupling point; ε f , ε v , ε θ They are the amplitude thresholds of frequency, voltage amplitude, and phase angle respectively.

[0050] Furthermore, the synchronization term includes a frequency synchronization term Δf sysnc , voltage synchronization term ΔV sysnc and the phase angle synchronization term Δθ sysnc ;

[0051] When the trigger instruction S t When Δf changes from 0 to 1, sysnc , ΔV sysnc and Δθ sysnc They are obtained by the following formulas:

[0052] Δf sysnc =f dev ·k f

[0053] ΔV sysnc =V dev ·k v / s

[0054] Δθ sysnc =θ dev ·k θ / s

[0055] When the trigger instruction S t When it remains at 1, Δf sysnc , ΔV sysnc and Δθ sysnc They are obtained by the following formulas:

[0056] Δf sysnc =-f dev ·k f

[0057] ΔV sysnc =-V dev ·k v / s

[0058] Δθ sysnc =θ dev ·k θ / s

[0059] Among them, V dev 、f dev ,θ dev are voltage deviation, frequency deviation and phase angle deviation respectively, k v 、k f and kθ are the integration factors corresponding to voltage, frequency and phase angle respectively, and 1 / s represents the integration link.

[0060] Furthermore, in step S3, performing a second correction on the first-corrected PWM drive signal includes:

[0061] The droop control equation after the primary correction is corrected twice, which is expressed as follows:

[0062]

[0063] Among them, f i ” and V i ” are the output frequency and average bus voltage after secondary correction of the i-th fuel cell power generation unit, θ i " is the phase angle of the second-corrected fuel cell power generation unit of the i-th fuel cell, f ni and V ni is the rated output frequency and rated voltage of the i-th fuel cell power generation unit, and are the corrected active power droop coefficient and the corrected reactive power droop coefficient of the i-th fuel cell power generation unit respectively; and are the target active power distribution value and target reactive power distribution value of the i-th fuel cell power generation unit respectively; Δf i and ΔV i are the frequency compensation value and voltage compensation value of the i-th fuel cell power generation unit respectively; f i is the frequency of the i-th power generation unit; 1 / s represents the integral link; b i is the weight factor; Δf sysnc , ΔV sysnc and Δθ sysnc Represent frequency synchronization term, voltage synchronization term and phase angle synchronization term respectively;

[0064] The PWM drive signal is secondarily corrected based on the secondarily corrected droop control equation.

[0065] In a second aspect of the present invention, a parallel converter coordinated grid-connected control device based on a fuel cell power generation grid-connected system using the method described in the first aspect of the present invention is provided. The device comprises:

[0066] A primary control strategy implementation module is used to apply a droop control strategy to the outer power control loop and a sliding mode control strategy to the inner voltage and current control loops when the converter of each power generation unit is running, and to generate the initial PWM drive signal of the converter;

[0067] A secondary control strategy implementation module is used to collect the operating data of each power generation unit and the health status of the fuel cell in real time, and calculate the voltage and frequency compensation values ​​of each power generation unit in combination with the information exchange data of adjacent power generation units, so as to make a primary correction to the initial PWM drive signal;

[0068] A synchronous control strategy implementation module is used to obtain in real time the deviations between the frequency, voltage and phase angle at the common coupling point of the AC busbars of the power grid and each power generation unit, generate trigger instructions for controlling the switching between the grid-connected mode and the island mode based on the deviations, and generate synchronization items based on the deviations in the grid-connected mode for secondary correction of the initial PWM drive signal.

[0069] In a third aspect of the present invention, a terminal is provided. The terminal includes a processor and a storage medium;

[0070] The storage medium is used to store instructions;

[0071] The processor is configured to operate according to the instructions to execute the steps of the method according to the first aspect of the present invention.

[0072] In a fourth aspect of the present invention, a computer-readable storage medium is provided, on which a computer program is stored, wherein when the program is executed by a processor, the steps of the method according to the first aspect of the present invention are implemented.

[0073] Compared with the existing technology, the above technical solution comprehensively considers the impact that communication, computing and scalability may have on the system, and the beneficial effects produced are:

[0074] 1. The power generation system in this invention is a fuel cell power generation system. Unlike traditional generator sets, fuel cells, as electrochemical energy conversion devices, have output characteristics that are closely related to chemical kinetics, thermodynamics, and mass transfer processes, significantly different from traditional generators and renewable energy sources. By considering the fuel cell's inherent characteristics, a relationship between the fuel cell's state of health (SOH) and power distribution is established. By dynamically adjusting the droop coefficient based on the fuel cell's state of health (SOH), the PWM drive signal is corrected, thereby achieving optimal power distribution of the system's active and reactive power.

[0075] 2. By setting the trigger instruction to change the working state of the fuel cell power generation grid-connected system, the distributed fuel cell power generation unit can be stably connected to the grid when the trigger instruction indicates that the grid-connected conditions are met. When the trigger instruction indicates that the grid-connected conditions are not met, the power generation unit operates in island mode or switching mode, which will not affect the power grid, thereby achieving stable power supply of the fuel cell power generation system and smooth switching of the system between grid-connected operation and island operation mode.

[0076] 3. By applying the first method to determine the synchronization terms of voltage, frequency and phase angle during the switching mode and the grid-connected mode, the droop control equation is corrected twice, thereby correcting the PWM drive signal twice. This can enable each distributed generation unit to meet the grid-connected conditions as soon as possible in the switching mode, and can enable the synchronization terms of voltage and frequency of each distributed generation unit after entering the grid-connected mode to gradually approach 0, thereby ensuring that the reactive power distribution and active power distribution of the system are not changed or affected.

[0077] 4. By considering the current and voltage limitations during converter operation and introducing a scaling factor to dynamically scale the reference current and voltage, the safe operation of the converter in each power generation unit can be ensured.

[0078] 5. To avoid the shortcomings of centralized control, a distributed control mode communication topology interface is adopted. For this purpose, an information interaction model of the fuel cell power generation system is designed to simplify the topology of the communication network.

[0079] In summary, the present invention generates a PWM drive signal by applying a droop control strategy to the external power control loop and a sliding mode control strategy to the internal voltage and current control loop. The PWM drive signal is corrected once in combination with the health status of the fuel cell and the information interaction data of the adjacent power generation units. The PWM drive signal is then corrected twice in combination with the frequency, voltage and phase angle deviations. This not only ensures the stable power supply of the fuel cell power generation system, but also achieves smooth switching between the grid-connected mode and the island mode through a precise control mechanism, greatly improving the flexibility of the distributed fuel cell power generation system and enabling it to operate reliably in various power grid environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0080] In order to make the system structure and method flow of the present invention clearer, the system and method of the present invention are described in detail with reference to the following drawings, wherein:

[0081] Figure 1 A flow chart of a method for controlling the coordinated grid connection of parallel converters based on a fuel cell power generation grid connection system according to an embodiment of the present invention;

[0082] Figure 2 A schematic structural diagram of a fuel cell power generation grid-connected system provided by an embodiment of the present invention;

[0083] Figure 3 A schematic diagram of a voltage and frequency primary control strategy for a fuel cell power generation grid-connected system provided by an embodiment of the present invention;

[0084] Figure 4 A schematic diagram of a distributed voltage and frequency secondary control strategy for a fuel cell power generation grid-connected system provided by an embodiment of the present invention;

[0085] Figure 5Schematic diagram of the grid-side synchronization control strategy of the fuel cell power generation grid-connected system provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0086] The following embodiments of the present invention are described in further detail with reference to the accompanying drawings and examples. The following embodiments are used to illustrate the present invention but are not intended to limit the scope of the present invention.

[0087] Example 1

[0088] This embodiment relates to a method for coordinated grid-connected control of parallel converters based on a fuel cell power generation grid-connected system.

[0089] To ensure stable AC grid connection of the power output of the converter and power dispatch between multiple parallel-connected converters, the present invention requires synchronization of each converter before grid connection. To achieve this, it is necessary to collect the voltage, frequency, and phase angle parameters at the point of common coupling (PCC) between the AC condenser and the main grid.

[0090] Furthermore, due to the heavy burden of communication, computation, and scalability, a centralized control model could potentially degrade the stable operation of the entire system. Therefore, in this example, a distributed control model is adopted to avoid the drawbacks of centralized control. Distributed control, due to its simplicity, sparseness, and robustness of the communication network, is a suitable choice for parallel grid-connected converters in fuel cell power generation systems.

[0091] The control strategy proposed in this example is to drive multiple parallel-operating grid-connected converters to synchronize with the power grid in a point-to-point mode. Since the system usually contains multiple fuel cell power generation systems operating in parallel for power generation, it is very important to study the coordinated control strategy of parallel-connected grid-connected converters.

[0092] The proposed control strategy uses a distributed controller to interact between adjacent fuel cell power generation systems. It only needs to transmit synchronization information to the voltage and frequency control strategy link of the converter connected to the leader power generation unit LeaderFuelCell once, which can make the entire system more flexible and simple.

[0093] As an electrochemical energy conversion device, the output characteristics of fuel cells are closely related to chemical kinetics, thermodynamics, and mass transfer processes, which are significantly different from traditional generators and renewable energy sources. The formula for calculating the output voltage of a fuel cell can be expressed as:

[0094] V fc =E therom -V cat -V ohm -V conc

[0095] Among them, Etherom represents the thermodynamic equilibrium potential, which is related to the Gibbs free energy of fuel and oxidant; V cat It represents the activation polarization loss, reflects the electrochemical reaction kinetic resistance, and has a nonlinear relationship with temperature T and catalyst activity; V ohm represents the ohmic polarization loss, which is caused by the conduction impedance of the electrolyte and electrode materials; V conc represents concentration polarization losses, which are caused by reactant diffusion limitations.

[0096] Different fuel cell units have different polarization curves due to manufacturing differences, aging or operating conditions, which results in a shift in the output voltage V under the same load. fci There are differences. If current-sharing control is directly adopted, it will cause circulating current problems and reduce system efficiency. Therefore, it is necessary to introduce online identification of polarization model parameters in distributed control and dynamically adjust the droop coefficient.

[0097] Furthermore, considering the fuel cell's own characteristics, the relationship between the fuel cell health state (SOH) and power distribution is established. The health state of the fuel cell represents the degree of its performance degradation and can be quantified by the change in the slope of the polarization curve. The calculation process is:

[0098]

[0099] Among them, η act,new Represents the activation polarization loss of the fuel cell in the initial calibration state; η act,i represents the activation efficiency of the i-th fuel cell power generation unit; R ohm,new Represents the ohmic impedance of the fuel cell in the initial calibration state; R ohm,i represents the ohmic impedance of the i-th fuel cell power generation unit.

[0100] In the formula, η act,new As a benchmark value, it is used to compare the activation efficiency of the current unit. If the current activation loss increases, η act,i Decreases, indicating that the catalyst is aging, which will reduce its ratio and reduce the health of the reaction cell; R ohm,new Indicates the ohmic impedance of the fuel cell in the initial calibration state. If the current power generation unit ohmic impedance R ohm,i If it increases, it means that aging has caused material degradation, then the ratio decreases and the health of the reaction cell decreases.

[0101] Furthermore, a hydrogen supply rate v is established for the fuel cell power generation unit. H2,i and the current density i of the power generation unit fc,i The relationship between:

[0102]

[0103] Among them, the current density of the power generation unit Obtained through measurement, F represents the Faraday constant, η fuel Indicates fuel utilization.

[0104] like Figure 2 The schematic diagram of the structure of the fuel cell power generation grid-connected system involved in the method described in this embodiment is shown. The fuel cell power generation grid-connected system includes multiple distributed fuel cell power generation units connected in parallel, each power generation unit has a corresponding converter, and the output of each converter is connected to an LCL filter, where R1+jX1, R2+jX2, R3+jX3...R n +jX n is the line impedance on the grid-connected converter side, R Grid +jX Grid is the line impedance on the grid side. fc1 、V fc2 、V fc3 ...V fcn Indicates the output voltage of the fuel cell power generation system.

[0105] based on Figure 2 The structural diagram of the fuel cell power generation grid-connected system shown in FIG. 1 is a schematic diagram of the structure of the fuel cell power generation grid-connected system. The method of this embodiment involves a voltage-frequency primary control strategy, a distributed voltage-frequency secondary control strategy, and a grid-side synchronization control strategy.

[0106] The overall control objectives expected to be achieved in this example are as follows:

[0107] (1) Realize voltage synchronization: adjust the estimated average voltage of each grid-connected converter bus to V ref , adjust the voltage at the common coupling point to the main grid voltage.

[0108]

[0109] Where V ref is the reference voltage of multiple parallel grid-connected converters, V avei and V avej Estimate the average busbar voltage for two parallel grid-connected converters, V PCC is the voltage at the common coupling point, V Grid The main grid voltage.

[0110] (2) Achieve frequency and phase angle synchronization: Adjust the frequency of each grid-connected converter to f ref , adjust the phase angle of the common coupling point to the main grid phase angle.

[0111]

[0112] where f ref is the reference frequency of the parallel grid-connected converter, f i and f jare the frequencies of the i-th converter and the j-th converter, θ PCC is the common coupling point phase angle, θ Grid The main network phase angle.

[0113] Specifically, if Figure 1 The parallel converter coordinated grid-connected control method based on the fuel cell power generation grid-connected system of this embodiment includes the following steps:

[0114] S1. When the converter of each power generation unit is running, a droop control strategy is applied to the external power control loop and a sliding mode control strategy is applied to the internal voltage and current control loop to generate a PWM drive signal for the converter.

[0115] This step corresponds to the frequency and voltage primary control strategy.

[0116] The external power control loop is a key control link in the coordinated grid-connected control system for parallel converters. It coordinates power distribution among the parallel converters to maintain global system frequency and voltage stability. The internal voltage and current control loops are responsible for rapidly tracking the voltage and current reference values ​​given by the external power control loop to ensure high-quality power output.

[0117] like Figure 3 The figure shows a schematic diagram of the primary control strategy of a fuel cell power generation grid-connected system. It includes a power control loop, a voltage control loop, and a current control loop. Step S1 specifically includes:

[0118] S11, collecting the three-phase voltage and three-phase current output by the converter and the three-phase voltage and three-phase current after being filtered by the LCL filter.

[0119] In this step, the three-phase voltage and three-phase current output by the converter correspond to Figure 2 The three-phase voltage and three-phase current output by the middle converter 1~n can be expressed as v abc and i abc Indicates that the three-phase voltage and three-phase current after LCL filter filtering correspond to Figure 2 The three-phase voltage and three-phase current after filtering by LCL filters 1 to n can be expressed as v oabc and i oabc Indicates that.

[0120] S12. Based on the collected data, generate d-axis and q-axis reference components of the reference current and reference voltage respectively.

[0121] In this step, for the outer power control loop, droop control consists of Pf (active power and frequency) and QV (reactive power and voltage) control, which can be expressed as:

[0122]

[0123] Where f is the actual frequency of the system; f n is the rated frequency; P is the actual active power of the system; m p is the basic active power-frequency droop control coefficient, which indicates the frequency deviation caused by active power changes; V is the actual voltage amplitude of the system; V n is the rated voltage amplitude; Q is the actual reactive power of the system; n q It is the basic reactive power and voltage droop control coefficient, which indicates the voltage deviation caused by reactive power changes.

[0124] Thus, the corresponding three-phase reference voltage value components are obtained, and the calculation process is as follows:

[0125]

[0126] Thus, the corresponding d-axis and q-axis components of the current and voltage are obtained. Then, based on the characteristic formulas of the inductor and capacitor, and the corresponding coordinate components of the current and voltage, the mathematical relationship between the current and voltage of the LCL filter system in this example system is analyzed, and the following calculation formula can be obtained:

[0127]

[0128]

[0129] According to the above calculation formula and the corresponding d and q axis components of the voltage and current, the reference current i is obtained by calculation ref The expressions for the d-axis and q-axis reference components are:

[0130]

[0131] Among them, C f is the equivalent capacitance value of the LLC part, ζ v is the weight factor, μ v ,λ v is a positive weight factor, S vd and S vq is the parameter obtained in the sliding mode control process, e vd The calculation process is: vd =V odref -V od , e vq The calculation process is: vq =V oqref -V oq ,i od and i oq are the corresponding components of the d-axis and q-axis of the voltage control loop.

[0132] The same analysis process as above can be used to obtain the reference voltage Vref The calculation expressions of the d-axis and q-axis reference components are:

[0133]

[0134] Among them, L f is the equivalent inductance value of the LLC part, ζ i is the weight factor, μ i ,λ i is a positive weight factor, S id and S iq is the parameter obtained in the sliding mode control process, e id The calculation process is: id =i d,ref -i d , e id The calculation process is: iq =i q,ref -i q ,i d and i q are the corresponding components of the d-axis and q-axis of the current control loop.

[0135] S13. Determine the scaling factors of the current and voltage according to the voltage and current limitations during converter operation, and correct the dq-axis reference components of the reference current and reference voltage based on the scaling factors of the current and voltage to obtain the d-axis and q-axis reference components of the corrected reference current and reference voltage in the dq coordinate system, respectively, and further obtain the corrected reference current and reference voltage in the dq coordinate system.

[0136] Considering the current reference value i d,ref and i q,ref Should meet the following requirements:

[0137]

[0138] Among them I max is the maximum allowable current of the converter.

[0139]

[0140] Therefore, a scalar scaling factor α is introduced for the current i Dynamically scale the reference current:

[0141]

[0142] The d-axis component and q-axis component of the reference current in the corrected dq coordinate system Respectively expressed as:

[0143]

[0144] Then we can get the reference current in the corrected dq coordinate system, and its amplitude is Expressed as

[0145]

[0146] Considering the voltage reference value v d,ref and v q,ref Should meet the following requirements:

[0147]

[0148] Where V max is the maximum allowable voltage of the converter.

[0149]

[0150] Therefore, a scalar scaling factor β of the voltage is introduced v Limit the output voltage reference value:

[0151]

[0152] The d-axis component and q-axis component of the reference voltage in the corrected dq coordinate system Represents the reference current for:

[0153]

[0154] Then we can get the reference voltage in the corrected dq coordinate system, and its amplitude is Expressed as

[0155]

[0156] above and It reflects the overall magnitude of the corrected reference current and reference voltage, and reflects the comprehensive reference level in the dq coordinate system after considering the constraints. It is used in subsequent control and analysis links to ensure that the current and voltage are effectively controlled within the system's tolerable range.

[0157] S14. The reference current and reference voltage in the corrected dq coordinate system are subjected to coordinate transformation to obtain corresponding three-phase voltage reference values. Adjustments are made based on the obtained three-phase voltage reference values ​​and the three-phase voltage reference values ​​output in the previous period to obtain PWM signals to control the on and off of the switching tubes in the converter.

[0158] This step can change the operating state of the converter and adjust the system operating state to ensure stable operation. The specific coordinate transformation method from the dq coordinate system to the three-phase coordinate system, as well as the content of obtaining the PWM signal based on the three-phase voltage reference value, are prior art and will not be repeated here.

[0159] S2. Real-time collection of operating data of each power generation unit and health status of the fuel cell, combined with information exchange data of adjacent power generation units, to calculate voltage and frequency compensation values ​​of each power generation unit for a correction of the PWM drive signal.

[0160] This step corresponds to the distributed voltage-frequency secondary control strategy.

[0161] In this example, the communication topology is connected in the form of Figure 2 As shown, in a multi-parallel fuel cell power generation system, each parallel fuel cell power generation unit can be considered a unit that exchanges information with adjacent fuel cell power generation units. A communication link is established between the grid-side information and the leader power generation unit, LeaderFuelCell, to determine whether the grid-connected switch is operating and to obtain additional synchronization conditions for the grid-side synchronization controller. Because the connection paths in the communication topology affect the convergence speed of the distributed algorithm, comprehensive consideration is required to find a topology that can quickly respond and stabilize the system, simplifying the connection paths. Furthermore, increasing the number of connection paths in the communication topology will correspondingly increase communication complexity, thereby increasing the burden on the communication structure. Considering various factors, the design of the communication topology requires a balance between convergence speed and communication complexity. Therefore, this embodiment adopts a sparse connection method for data exchange between the fuel cell power generation system and adjacent fuel cell power generation systems. Compared to connection methods that rely on central control or a single path for signal transmission, this sparse connection method enables the system to respond quickly and converge to a stable state. In particular, in the face of external interference or failures, the system can quickly adjust to ensure stable operation. At the same time, this topology also avoids the impact of increased bus load and communication complexity on the stable operation of the system as the system scale expands.

[0162] The information exchange data between adjacent power generation units may include information such as voltage, frequency, active power and reactive power output by converters in adjacent power generation units.

[0163] For the parallel converter system based on distributed fuel cell power generation, this example proposes a distributed secondary voltage frequency control strategy to compensate for the output frequency and voltage deviation, while dynamically adjusting the droop coefficient according to the health status of the fuel cell to achieve optimal power distribution. Figure 4 Shown is a diagram of distributed secondary voltage and frequency control strategy information interaction according to an embodiment of the present invention.

[0164] The objectives of the distributed secondary voltage-frequency control method proposed in this example can be summarized as follows:

[0165] (1) Restore the average bus voltage and output frequency of each fuel cell power generation system to the reference value.

[0166] (2) Realize the proportional distribution of active and reactive power among various fuel cell power generation systems.

[0167] Specifically, step S2 includes the following sub-steps:

[0168] S21. Determine the total active power demand and total reactive power demand of the system based on the operating data of each power generation unit.

[0169] Among them, the total active power demand P total and the total reactive power demand Q total The calculation formula is:

[0170]

[0171] Among them, P i is the total active power demand of the i-th generating unit, V fc,i and I fc,i are the output voltage and output current of the i-th power generation unit, n is the number of power generation units, Q load,i is the reactive power demand of the i-th generating unit.

[0172] S22 . Determine a normalized active power distribution weight factor and a reactive power distribution weight factor of each power generation unit based on the health status of the fuel cell in each power generation unit.

[0173] Differences in fuel cell health status will lead to different maximum power output capabilities between units. Traditional average power distribution will accelerate the aging of fuel cell power generation units in low health status. For this reason, a health status weight factor is added to the power distribution to achieve optimized power distribution according to health status. In this way, power distribution according to health status and capacity is achieved, avoiding overload of fuel cell power generation units in low health status.

[0174] The health status of a fuel cell characterizes the degree of its performance degradation, which can be quantified by the change in the slope of the polarization curve. The calculation process is:

[0175]

[0176] Among them, η act,new Indicates the electrocatalytic activity of the fuel cell at the initial calibration state; η act,i represents the electrocatalytic activity of the i-th fuel cell power generation unit; R ohm,newRepresents the ohmic impedance of the fuel cell in the initial calibration state; R ohm,i represents the ohmic impedance of the i-th fuel cell power generation unit.

[0177] In the formula, η act,new As a benchmark value, it is used to compare the electrocatalytic activity of the current unit. If the current fuel cell catalyst ages, resulting in increased activation loss and reduced electrocatalytic activity, η act,i If it increases, the ratio will decrease, and the health of the reaction battery will decrease; R ohm,new Indicates the ohmic impedance of the fuel cell in the initial calibration state. If the current power generation unit ohmic impedance R ohm,i If it increases, it means that aging has caused material degradation, then the ratio decreases and the health of the reaction cell decreases.

[0178] It represents the normalized active power distribution weight factor, and its calculation formula is:

[0179]

[0180] in, is the sum of the active power distribution weight factors of all adjacent power generation units of power generation unit i, N i is the set of all adjacent power generation units of power generation i, k is any adjacent power generation unit of power generation unit i; ω P,ij It represents the weight factor of power allocation, and its calculation formula is:

[0181]

[0182] Among them, ω P,max 、ω P,min Respectively represent the upper and lower limits of the active power allocation weight factor; SOH j represents the health status of the jth fuel cell power generation unit; P max,j It represents the maximum available active power of the j-th power generation unit. The other parameters are the same as those in the above active power allocation weight factor.

[0183] It represents the reactive power distribution weight factor after normalization, and its calculation formula is:

[0184]

[0185] in, is the sum of the reactive power allocation weight factors of all adjacent power generation units of power generation unit i, N i is the set of all adjacent power generation units of power generation i, k is any adjacent power generation unit of power generation unit i; ω Q,ijRepresents the weight factor of reactive power distribution, and its calculation formula is:

[0186]

[0187] Among them, ω Q,max 、ω Q,min Respectively represent the upper and lower limits of the reactive power distribution weight factor; SOH j Indicates the health status of the jth fuel cell power generation unit; Q max,j represents the maximum available reactive power of the jth generating unit; ‖‖x i -x j ‖‖ represents the state distance between the i-th unit and the j-th unit; ξ is a quantity set to prevent the denominator from being zero.

[0188] S23. Determine a target active power distribution value and a target reactive power distribution value of each power generation unit based on the total active power demand and the total reactive power demand and the normalized active power distribution weight factor and reactive power distribution weight factor.

[0189] First, the active power distribution is analyzed. The target active power distribution value of the i-th fuel cell power generation unit is calculated as follows:

[0190]

[0191] The first term represents the static allocation based on health status and maximum active capacity; the second term represents the dynamic compensation based on the active power deviation of adjacent generating units.

[0192] Among them, SOH i Indicates the health status of the i-th power generation unit; P max,i P represents the maximum available power of the i-th power generation unit, which is determined by the polarization curve and operating conditions of the fuel cell. total Represents the total power demand of the system, shared by all parallel units. Represents the weighted maximum power sum of all units in the system.

[0193] in, Represents the power deviation compensation between the i-th power generation unit and the adjacent units.

[0194] First, the reactive power distribution is analyzed. The target reactive power distribution value of the i-th fuel cell power generation unit is calculated as follows:

[0195]

[0196] The first term represents the static allocation based on the health status and maximum reactive power; the second term represents the dynamic compensation based on the reactive power deviation of adjacent generating units.

[0197] Among them, Q max,i Represents the maximum available reactive power of the i-th generating unit. total Represents the total reactive power demand of the system, which is shared by all parallel units. Represents the weighted reactive power sum of all units in the system. The remaining parameters are the same as those introduced in the above active power allocation weight factor.

[0198] in, Represents the power deviation compensation between the i-th power generation unit and the adjacent units.

[0199] S24 . Based on the normalized active power distribution weight factor and reactive power distribution weight factor and the health status of the fuel cell, generate a modified active power droop coefficient and a modified reactive power droop coefficient of each power generation unit.

[0200] Traditional active power-frequency droop coefficient m Pi and reactive-voltage droop coefficient n Qi The calculation formulas are:

[0201]

[0202] Where ΔP max,i , ΔQ max,i is the current maximum power margin of the i-th power generation unit, Δf max is the maximum allowable frequency deviation, ΔV max is the maximum allowable voltage deviation.

[0203] By introducing the health status of the fuel cell power generation unit and the dynamic weight factor control, the calculation formulas for the corrected active power droop coefficient and the corrected reactive power droop coefficient can be obtained:

[0204]

[0205] S25. Based on the target active power distribution value and target reactive power distribution value of each power generation unit, the corrected active power droop coefficient and the corrected reactive power droop coefficient, and the information interaction data of adjacent power generation units, the voltage and frequency compensation values ​​of each power generation unit are obtained for performing a correction on the PWM drive signal.

[0206] Frequency compensation value Δf of each power generation unit i and voltage compensation value ΔV i The calculation formulas are:

[0207]

[0208] Where Δf i and ΔVi are the frequency compensation value and voltage compensation value of the i-th power generation unit, c fi 、c Pi 、c vi and c Qi are the adjustment factors for frequency, active power, voltage and reactive power respectively, which play a role in adjusting the convergence speed; γ and κ are the corresponding dynamic compensation gains respectively, which are used to suppress the response lag of the fuel cell; It is estimated online through real-time data, which respectively represents the impact of the dynamic change of the fuel cell output voltage on frequency regulation and voltage control; f ref is the system reference frequency; V ref is the system reference voltage; and They are the corrected active power droop coefficient and the corrected reactive power droop coefficient respectively; and are the target active power allocation values ​​for the i-th and j-th generating units respectively; and are the target reactive power allocation values ​​of the i-th and j-th generating units respectively; f i and f j are the frequencies of the i-th and j-th generating units respectively; V avei and V avej are the estimated average bus voltages of the i-th and j-th generating units respectively; for the weight factor a involved ij and b i The selection of reference is as follows:

[0209]

[0210] Furthermore, it is explained that as long as the primary voltage and frequency control link of the converter connected to the leader power generation unit LeaderFuelCell in the system obtains the input reference value, the average bus voltage recovery and proportional reactive power sharing as well as the frequency recovery and proportional active power sharing can be achieved.

[0211] Furthermore, in this step, performing a correction on the PWM drive signal includes:

[0212] The droop control equation in the droop control strategy is corrected once, which is achieved by the following formula:

[0213]

[0214] Among them, f i ' and V i ' are the corrected output frequency and average bus voltage of the i-th fuel cell power generation unit, θ i' is the phase angle of the first fuel cell power generation unit after correction, f ni and V ni are the rated output frequency and rated voltage of the i-th fuel cell power generation unit respectively; 1 / s represents the integral link;

[0215] Then, the PWM drive signal is corrected based on the corrected droop control equation. The specific process of obtaining the PWM drive signal based on the known droop control equation belongs to the prior art and will not be described in detail here.

[0216] S3. Acquire in real time the amplitude deviations between the frequency, voltage, and phase angle at the common coupling point of the AC busbars of the power grid and each power generation unit, generate a trigger instruction for controlling the switching between the grid-connected mode and the island mode based on the deviations, and generate a synchronization item based on the deviations in the grid-connected mode for performing a secondary correction on the PWM drive signal after the primary correction.

[0217] like Figure 5 The figure shows a schematic diagram of the grid-side synchronous control strategy of an embodiment of the present invention. As can be seen from the system diagram, in order to achieve the successful switching of the grid-connected converter based on the fuel cell power generation system between the island mode and the grid-connected mode, a trigger instruction S is designed to achieve the stable switching of the system between the grid-connected mode and the island mode. t , and gives the definition of the trigger signal action judgment formula. After the system receives the grid-connected operation signal, the leader power generation unit LeaderFuelCell power generation system adjusts according to the additional synchronization items obtained by the grid-side synchronization controller and transmits the relevant information to the adjacent fuel cell power generation system. Each power generation system adjusts the power generation frequency, voltage and phase angle. When the frequency, voltage and phase angle of the actual output of the system meet the grid-connected switch action conditions, the switch is activated and the Δf in the grid-side synchronization controller is changed. sysnc and ΔV sysnc When the system receives the off-grid operation signal, it operates in island mode.

[0218] When the grid connection standard requirements are met, the trigger instruction S t When the condition is 1, the distributed fuel cell power generation system operates stably in the grid-connected working mode; when the grid-connected conditions are not met, the instruction S is triggered. t When the power supply is 0, the system operates in island mode, supplying power to the loads within the system without impacting the grid. By establishing relevant mathematical models and deriving corresponding control parameters, the fuel cell power generation system achieves stable power supply and smooth switching between grid-connected and island operation modes.

[0219] When the system receives the grid-connected operation signal, the grid-connected converter connected to the leader generating unit LeaderFuelCell receives the additional synchronization term Δf from the grid-side synchronization controller.sysnc , ΔV sysnc and Δθ sysnc , passing the relevant information to the adjacent grid-connected converter, and then acting on all parallel converters. This method adjusts the voltage, frequency and phase angle of the fuel cell power generation system through a distributed secondary voltage and frequency controller.

[0220] The voltage amplitude and phase angle between the point of common coupling PCC and the grid can be calculated using the following formula:

[0221]

[0222] Among them, v dPCC 、v qPCC 、v dGrid and v qGrid They represent the d-axis and q-axis voltage values ​​of the common coupling point PCC and the d-axis and q-axis voltage values ​​of the power grid respectively.

[0223] The calculation process of voltage and phase angle deviation is as follows:

[0224]

[0225] Among them, V Grid and V PCC are the grid voltage amplitude and the common coupling point voltage amplitude, θ Grid and θ PCC are the grid phase angle and the common coupling point phase angle respectively. The voltage deviation V is obtained by the voltage and phase angle deviation calculation formula. dev and phase angle deviation θ dev .

[0226] Secondly, in order to achieve frequency synchronization, that is, to eliminate the frequency deviation, the frequency deviation f dev Defined as:

[0227] f dev =f Grid -f PCC

[0228] Among them, f Grid and f PCC are the grid frequency and the frequency at the point of common coupling, respectively.

[0229] Therefore, when the system receives the grid-connected operation signal (ie S t When ΔV changes from 0 to 1), in order to achieve voltage and phase angle synchronization, that is, to eliminate voltage and phase angle deviation, the voltage and phase angle synchronization term ΔV is calculated. sysnc and Δθ sysnc include:

[0230] ΔV sysnc =V dev ·kv / s

[0231] Δθ sysnc =θ dev ·k θ / s

[0232] Calculate the frequency synchronization term Δf sysnc include:

[0233] Δf sysnc =f dev ·k f

[0234] Among them, k v 、k θ and k f is the integration factor, and both are greater than 0; 1 / s represents the integration link.

[0235] In addition, in order to enable the fuel cell power generation system to be connected to the main grid, ΔV sysnc The purpose of tending to zero is to ensure that the reactive power distribution will not change. t When the trigger signal remains at 1, the change of ΔV sysnc The calculation formula is used to obtain a ΔV that can make the converter run stably. sysnc At the same time, in order to make Δf sysnc When S approaches zero, it ensures that the system active power distribution is not affected. t When the trigger signal remains at 1, Δf will change sysnc The calculation formula is used to obtain a Δf that makes the system run stably. sysnc .

[0236] Therefore, when S t =1, additional voltage synchronization term ΔV sysnc The calculation formula is:

[0237] ΔV sysnc =-V dev ·k v / s

[0238] Additional frequency control term Δf sysnc The calculation formula is:

[0239] Δf sysnc =-f dev ·k f

[0240] Among them, k v and k f is the integration factor, and both are greater than 0; 1 / s represents the integration link.

[0241] The phase angle synchronization term Δθ sysncIt does not affect the active load sharing. After the system is connected to the main grid, the frequency of the fuel cell power generation system will be consistent with the main grid. Therefore, there is no need to change Δθ sysnc In other words, when S t = 1, additional phase angle synchronization term Δθ sysnc The calculation formula is still:

[0242] Δθ sysnc =θ dev ·k θ / s

[0243] About trigger instruction S t According to the standard requirements, during the synchronization of the generator set, the synchronization parameters should meet the following requirements:

[0244] f dev =|f Grid -f PCC |≤ε f

[0245] V dev =|V Grid -V PCC |≤ε v

[0246] θ dev =|θ G rid-θ PCC |≤ε θ

[0247] Among them, f Grid is the grid frequency, f PCC is the common coupling point frequency; V Grid is the grid voltage amplitude, V PCC is the voltage amplitude at the common coupling point; θ Grid is the grid phase angle, θ PCC is the phase angle of the common coupling point; ε f , ε v , ε θ are the synchronization parameters of frequency, voltage amplitude and phase angle respectively.

[0248] Therefore, the output formula for the trigger instruction is:

[0249]

[0250] That is, when all three conditions are met, the instruction S is triggered. t =1, otherwise it is 0. If it is 1, it means the system is in grid-connected operation, otherwise it is in island operation. f , ε v , ε θFor example, they may be 0.5 Hz, 0.03 pu and 20° respectively.

[0251] Furthermore, performing a secondary correction on the PWM drive signal after the primary correction includes:

[0252] The droop control equation after the primary correction is corrected twice, including setting the droop control function of the converter connected to the leader unit LeaderFuelCell to:

[0253]

[0254] Where, ΔV sysnc , Δθ sysnc , Δf sysnc are additional synchronization terms for frequency, voltage, and phase angle, respectively, and b i is the weight factor.

[0255] Then, the PWM drive signal is subjected to a secondary correction based on the quadratically corrected droop control equation. The specific process of obtaining the PWM drive signal based on the known droop control equation belongs to the prior art and will not be described in detail here.

[0256] This embodiment proposes a parallel converter collaborative grid-connected control method based on a fuel cell power generation grid-connected system, which aims to optimize the power output and grid-connected efficiency in new energy applications. With the rapid development of new energy technologies, especially the widespread application of distributed fuel cell power generation, achieving stable and efficient grid connection has become key. To this end, this embodiment effectively improves the stability and coordination of the distributed power generation system during the grid-connected process by establishing a parallel grid-connected converter system analysis model, a converter primary control analysis model, a distributed fuel cell secondary voltage and frequency control analysis model, and a grid-side synchronous control strategy analysis model, thereby ensuring that new energy power is efficiently, safely, and stably integrated into the grid.

[0257] Example 2

[0258] This embodiment provides a parallel converter coordinated grid-connected control device based on a fuel cell power generation grid-connected system using the method described in Example 1. The device includes:

[0259] A primary control strategy implementation module is used to apply a droop control strategy to the outer power control loop and a sliding mode control strategy to the inner voltage and current control loops when the converter of each power generation unit is running, and to generate the initial PWM drive signal of the converter;

[0260] A secondary control strategy implementation module is used to collect the operating data of each power generation unit and the health status of the fuel cell in real time, and calculate the voltage and frequency compensation values ​​of each power generation unit in combination with the information exchange data of adjacent power generation units, so as to make a primary correction to the initial PWM drive signal;

[0261] A synchronous control strategy implementation module is used to obtain in real time the deviations between the frequency, voltage and phase angle at the common coupling point of the AC busbars of the power grid and each power generation unit, generate trigger instructions for controlling the switching between the grid-connected mode and the island mode based on the deviations, and generate synchronization items based on the deviations in the grid-connected mode for secondary correction of the initial PWM drive signal.

[0262] Example 3

[0263] This embodiment provides a terminal including a processor and a storage medium. The storage medium is configured to store instructions; the processor is configured to operate according to the instructions to execute the steps of the method according to Embodiment 1. The specific steps are not described in detail here.

[0264] Example 4

[0265] This embodiment provides a computer-readable storage medium on which a computer program is stored. When the program is executed by a processor, the steps of the method described in Example 1 are implemented. The specific steps are not repeated here.

[0266] Compared with the existing collaborative control method of parallel grid-connected converters, the present invention comprehensively considers the possible impact of communication, computing power and system scalability on system performance during the design process. Unlike traditional generator sets, the present invention adopts a fuel cell power generation system as the power generation system, giving full play to its high efficiency and environmental protection characteristics. At the same time, in order to overcome the limitations of the centralized control mode, the present invention introduces a distributed control mode and designs a communication topology interface to ensure that each converter can work effectively together. In addition, based on the characteristics of the fuel cell power generation system, the present invention specially designs its information interaction model to simplify the topology of the communication network. Through this model, the system can transmit information more efficiently, reduce communication delays, and improve the stability and response speed of the system. This design not only enhances the scalability of the system, but also provides strong support for the application of fuel cell technology in smart grids.

[0267] Furthermore, the grid-side synchronization control strategy proposed in this invention ensures stable grid-connected operation of the distributed fuel cell power generation system by intelligently adjusting the operating state of the parallel converters. In grid-connected mode, the system automatically synchronizes with the grid to ensure stable output of voltage, frequency, and power. If the system fails to meet grid-connected conditions, the control strategy automatically switches to island mode, operating independently while avoiding any impact on the grid. In island mode, the fuel cell power generation system independently supplies power to local loads, ensuring that the power supply is not affected by grid fluctuations.

[0268] In addition, the parallel converter collaborative control method proposed in the present invention not only ensures the stable power supply of the fuel cell power generation system, but also realizes the smooth switching between the grid-connected mode and the island mode through a precise control mechanism. The system will not experience drastic fluctuations in voltage or frequency during the mode switching process, thereby avoiding the transient instability that may be caused by traditional control methods. Such a smooth transition greatly improves the reliability of the system and reduces the risk of grid shock or equipment damage caused by switching. Through this intelligent switching and adjustment, the grid-side synchronous control strategy enhances the flexibility of the distributed fuel cell power generation system, enabling it to operate reliably in various power grid environments. Whether in grid-connected or island mode, the system can respond quickly according to the actual situation, effectively ensuring the stability of the power supply.

[0269] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or make equivalent replacements for some or all of the technical features therein. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope defined by the claims of the present invention.

[0270] The present disclosure may be a system, method and / or computer program product. The computer program product may include a computer-readable storage medium carrying computer-readable program instructions for causing a processor to implement various aspects of the present disclosure.

[0271] Computer-readable storage medium can be a tangible device that can keep and store the instruction used by the instruction execution device.Computer-readable storage medium can be, for example, but not limited to, an electrical storage device, a magnetic storage device, an optical storage device, an electromagnetic storage device, a semiconductor storage device or any suitable combination thereof.The more specific example (non-exhaustive list) of computer-readable storage medium includes: a portable computer disk, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), a static random access memory (SRAM), a portable compact disc read-only memory (CD-ROM), a digital versatile disk (DVD), a memory stick, a floppy disk, a mechanical encoding device, for example, a punch card or a convex structure in a groove having instructions stored thereon and any suitable combination thereof.Computer-readable storage medium used herein is not interpreted as a transient signal itself, such as radio waves or other freely propagating electromagnetic waves, electromagnetic waves propagated by waveguides or other transmission media (for example, light pulses by fiber optic cables) or electrical signals transmitted by wires.

[0272] The computer-readable program instructions described herein can be downloaded from a computer-readable storage medium to each computing / processing device, or downloaded to an external computer or external storage device via a network, such as the Internet, a local area network, a wide area network, and / or a wireless network. The network can include copper transmission cables, fiber optic transmission, wireless transmission, routers, firewalls, switches, gateway computers, and / or edge servers. The network adapter card or network interface in each computing / processing device receives the computer-readable program instructions from the network and forwards the computer-readable program instructions to be stored in the computer-readable storage medium in each computing / processing device.

[0273] The computer program instructions for performing the operations of the present disclosure may be assembly instructions, instruction set architecture (ISA) instructions, machine instructions, machine-dependent instructions, microcode, firmware instructions, state setting data, or source code or object code written in any combination of one or more programming languages, including object-oriented programming languages ​​such as Smalltalk, C++, and conventional procedural programming languages ​​such as "C" language or similar programming languages. Computer-readable program instructions may be executed entirely on a user's computer, partially on a user's computer, as an independent software package, partially on a user's computer, partially on a remote computer, or entirely on a remote computer or server. In the case of a remote computer, the remote computer may be connected to the user's computer via any type of network, including a local area network (LAN) or a wide area network (WAN), or may be connected to an external computer (e.g., utilizing an Internet service provider to connect via the Internet). In some embodiments, an electronic circuit, such as a programmable logic circuit, a field programmable gate array (FPGA), or a programmable logic array (PLA), may be personalized by utilizing the state information of the computer-readable program instructions. The electronic circuit may execute the computer-readable program instructions, thereby realizing various aspects of the present disclosure.

[0274] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered by the scope of protection of the claims of the present invention.

Claims

1. A method for coordinated grid-connected control of parallel converters based on a fuel cell power generation grid-connected system, characterized in that: The fuel cell power generation grid-connected system includes a plurality of distributed fuel cell power generation units connected in parallel, each power generation unit having a corresponding converter; the method includes: S1. When the converter of each power generation unit is running, a droop control strategy is applied to the external power control loop and a sliding mode control strategy is applied to the internal voltage and current control loop to generate a PWM drive signal for the converter; S2. Real-time collection of operating data of each power generation unit and the health status of the fuel cell, combined with information exchange data of adjacent power generation units, to calculate voltage and frequency compensation values ​​of each power generation unit for primary correction of the PWM drive signal; S3. Acquire in real time the amplitude deviations between the frequency, voltage, and phase angle at the common coupling point of the AC busbars of the power grid and each power generation unit, generate a trigger instruction for controlling the switching between the grid-connected mode and the island mode based on the deviations, and generate a synchronization item based on the deviations in the grid-connected mode for performing a secondary correction on the PWM drive signal after the primary correction.

2. The method for controlling the coordinated grid connection of parallel converters based on a fuel cell power generation grid connection system according to claim 1, characterized in that: Step S1 includes: Collect the three-phase voltage and three-phase current output by the converter and the three-phase voltage and three-phase current after filtering by the LCL filter; Based on the collected data, d-axis and q-axis reference components of the reference current and reference voltage are generated respectively; determining current and voltage scaling factors according to voltage and current limitations during converter operation, and correcting d-axis and q-axis reference components of the reference current and reference voltage based on the current and voltage scalar scaling factors to obtain the corrected d-axis and q-axis reference components of the reference current and reference voltage in the dq coordinate system, respectively, and thereby obtaining the corrected reference current and reference voltage in the dq coordinate system; The reference current and reference voltage in the corrected dq coordinate system are transformed to obtain the corresponding three-phase voltage reference value. Adjustments are made based on the obtained three-phase voltage reference value and the three-phase voltage reference value output in the previous period to obtain a PWM signal to control the on and off of the switch tube in the converter.

3. The method for controlling the coordinated grid connection of parallel converters based on a fuel cell power generation grid connection system according to claim 2, characterized in that: Scalar scaling factor α of the current i for: The d-axis component and q-axis component of the reference current in the corrected dq coordinate system Respectively expressed as: Scalar scaling factor β for voltage v for: The d-axis component and q-axis component of the reference voltage in the corrected dq coordinate system Respectively expressed as: Among them, I max and V max are the upper limit of current and voltage when the converter is running; i d,ref and i q,ref are the d-axis and q-axis reference components of the current respectively; v d,ref and v q,ref are the d-axis and q-axis reference components of the voltage respectively.

4. The method for controlling the coordinated grid connection of parallel converters based on a fuel cell power generation grid connection system according to claim 1, characterized in that: Step S2 includes: Determine the total active power demand and total reactive power demand of the system based on the operating data of each power generation unit; Determining a normalized active power distribution weight factor and a reactive power distribution weight factor for each power generation unit based on a health status of the fuel cell in each power generation unit; Determining a target active power distribution value and a target reactive power distribution value of each power generation unit based on the total active power demand and the total reactive power demand and the normalized active power distribution weight factor and reactive power distribution weight factor; Based on the normalized active power distribution weight factor and reactive power distribution weight factor, combined with the health status of the fuel cell, a corrected active power droop coefficient and a corrected reactive power droop coefficient of each power generation unit are generated; Based on the target active power distribution value and target reactive power distribution value of each power generation unit, the corrected active power droop coefficient and the corrected reactive power droop coefficient, and the information interaction data of adjacent power generation units, the voltage compensation value and frequency compensation value of each power generation unit are obtained, which are used to perform a correction on the PWM drive signal.

5. The method for controlling the coordinated grid connection of parallel converters based on a fuel cell power generation grid connection system according to claim 4, characterized in that: The voltage compensation value and the frequency compensation value are calculated by the following formulas: Where Δf i and ΔV i are the frequency compensation value and voltage compensation value of the i-th power generation unit, c fi 、c Pi 、c vi and c Qi are the adjustment factors for frequency, active power, voltage and reactive power respectively, which play a role in adjusting the convergence speed; γ and κ are the dynamic compensation gains corresponding to frequency and voltage respectively; It is estimated online through real-time data, which respectively represents the impact of the dynamic change of the fuel cell output voltage on frequency regulation and voltage control; f ref is the system reference frequency; V ref is the system reference voltage; and are the corrected active power droop coefficient and the corrected reactive power droop coefficient respectively; P i * and are the target active power allocation values ​​for the i-th and j-th generating units respectively; and are the target reactive power allocation values ​​of the i-th and j-th generating units respectively; f i and f j are the frequencies of the i-th and j-th generating units respectively; V avei and V avej are the estimated average bus voltages of the i-th and j-th generating units respectively; a ij and b i are all weight factors.

6. The method for coordinated grid-connected control of parallel converters based on a fuel cell power generation grid-connected system according to claim 5, characterized in that: a ij and b i Select by the following formula:

7. The method for controlling the coordinated grid connection of parallel converters based on a fuel cell power generation grid connection system according to claim 5, characterized in that: In step S2, performing a correction on the PWM drive signal includes: The droop control equation in the droop control strategy is corrected once, which is achieved by the following formula: Among them, f i ' and V i ' are the corrected output frequency and average bus voltage of the i-th fuel cell power generation unit, θ i ' is the phase angle of the first fuel cell power generation unit after correction, f ni and V ni are the rated output frequency and rated voltage of the i-th fuel cell power generation unit respectively; 1 / s represents the integral link; The PWM drive signal is corrected once based on the corrected droop control equation.

8. The method for controlling the coordinated grid connection of parallel converters based on a fuel cell power generation grid connection system according to claim 1, characterized in that: In step S3, the trigger instruction S t Expressed as: in: f dev =|f Grid -f PCC | V dev =|V Grid -V PCC | i dev =|θ Grid -θ PCC | When S t When it is 1, it indicates switching to grid-connected mode. t When it is 0, it indicates switching to island mode; Among them, V dev 、f dev ,θ dev are the voltage deviation, frequency deviation and phase angle amplitude deviation respectively, f Grid is the grid frequency, f PCC is the common coupling point frequency; V Grid is the grid voltage amplitude, V PCC is the voltage amplitude at the common coupling point; θ Grid is the grid phase angle, θ PCC is the phase angle of the common coupling point; ε f , ε v , ε θ They are the amplitude thresholds of frequency, voltage amplitude, and phase angle respectively.

9. The method for controlling the coordinated grid connection of parallel converters based on a fuel cell power generation grid connection system according to claim 8, characterized in that: The synchronization term includes a frequency synchronization term Δf sysnc , voltage synchronization term ΔV sysnc and the phase angle synchronization term Δθ sysnc ; When the trigger instruction S t When Δf changes from 0 to 1, sysnc , ΔV sysnc and Δθ sysnc They are obtained by the following formulas: Δf sysnc =f dev ·k f ΔV sysnc =V dev ·k v / s Dth sysnc =θ dev ·k θ / s When the trigger instruction S t When it remains at 1, Δf sysnc , ΔV sysnc and Δθ sysnc They are obtained by the following formulas: Δf sysnc =-f dev ·k f ΔV sysnc =-V dev ·k v / s Dth sysnc =θ dev ·k θ / s Among them, V dev 、f dev ,θ dev are voltage deviation, frequency deviation and phase angle deviation respectively, k v 、k f and k θ are the integration factors corresponding to voltage, frequency and phase angle respectively, and 1 / s represents the integration link.

10. The method for coordinated grid-connected control of parallel converters based on a fuel cell power generation grid-connected system according to claim 9, characterized in that: In step S3, performing a second correction on the PWM drive signal after the first correction includes: The droop control equation after the primary correction is corrected twice, which is expressed as follows: Among them, f i ” and V i ” are the output frequency and average bus voltage after secondary correction of the i-th fuel cell power generation unit, θ i " is the phase angle of the ith fuel cell power generation unit after secondary correction, f ni and V ni is the rated output frequency and rated voltage of the i-th fuel cell power generation unit, and are the corrected active power droop coefficient and the corrected reactive power droop coefficient of the i-th fuel cell power generation unit respectively; P i * and are the target active power distribution value and target reactive power distribution value of the i-th fuel cell power generation unit respectively; Δf i and ΔV i are the frequency compensation value and voltage compensation value of the i-th fuel cell power generation unit respectively; f i is the frequency of the i-th power generation unit; 1 / s represents the integral link; b i is the weight factor; Δf sysnc , ΔV sysnc and Δθ sysnc Represent frequency synchronization term, voltage synchronization term and phase angle synchronization term respectively; The PWM drive signal is secondarily corrected based on the secondarily corrected droop control equation.

11. A parallel converter coordinated grid-connected control device based on a fuel cell power generation grid-connected system using the method according to any one of claims 1 to 10, characterized in that: include: A primary control strategy implementation module is used to apply a droop control strategy to the outer power control loop and a sliding mode control strategy to the inner voltage and current control loops when the converter of each power generation unit is running, and to generate the initial PWM drive signal of the converter; A secondary control strategy implementation module is used to collect the operating data of each power generation unit and the health status of the fuel cell in real time, and calculate the voltage and frequency compensation values ​​of each power generation unit in combination with the information exchange data of adjacent power generation units, so as to make a primary correction to the initial PWM drive signal; A synchronous control strategy implementation module is used to obtain in real time the deviations between the frequency, voltage and phase angle at the common coupling point of the AC busbars of the power grid and each power generation unit, generate trigger instructions for controlling the switching between the grid-connected mode and the island mode based on the deviations, and generate synchronization items based on the deviations in the grid-connected mode for secondary correction of the initial PWM drive signal.

12. A terminal comprising a processor and a storage medium; characterized in that: The storage medium is used to store instructions; The processor is configured to operate according to the instructions to execute the steps of the method according to any one of claims 1 to 10.

13. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the program is executed by a processor, the steps of the method according to any one of claims 1 to 10 are implemented.

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