An electric-hydrogen coupled three-port integrated converter and its control method

Abstract

The present invention proposes an electric-hydrogen coupled three-port integrated converter and its control method, belonging to the technical field of renewable energy hydrogen production. The electric-hydrogen coupled three-port integrated converter, based on a phase-shifted full-bridge converter and a dual-active bridge converter, replaces the busbar of a wind-solar-hydrogen coupled system. By analyzing the converter's operating principle and its inherent power decoupling method, six different operating modes of the converter are designed, and extended phase-shift control is adopted to achieve energy exchange. The electric-hydrogen coupled three-port integrated converter is based on a model of a wind-solar-hydrogen system and adopts an extended phase-shift control strategy to achieve power transmission in the wind-solar-hydrogen coupled system. This overcomes the deficiency of existing wind-solar-hydrogen systems in lacking a magnetic coupling structure. The present invention provides a scientifically sound, highly applicable, highly valuable, and effective electric-hydrogen coupled three-port integrated converter and its control strategy.

Description

Technical Field

[0001] The present invention belongs to the technical field of renewable energy hydrogen production, and in particular relates to an electricity-hydrogen coupled three-port integrated converter and a control method thereof. Background Art

[0002] Electrically coupled hydrogen production systems based on coupled structures such as AC, DC, and AC / DC busbars present challenges such as circulating current, difficulty in coordinated control design, and interactions caused by the parallel operation of multiple two-port DC converters. Multi-port converters using traditional full-bridge structures still experience backflow power at the ports connected to the alkaline electrolyzer, and require more switchgear, resulting in higher costs. Furthermore, to meet the low-voltage, high-current operating characteristics of alkaline electrolyzers and proton exchange membrane fuel cells, additional DC converters are required to mitigate the control difficulties caused by excessive voltage differences. This increases the number of energy conversions and reduces energy utilization. Traditional control strategies for wind-solar-hydrogen coupled systems can be broadly divided into two categories: rule-based and optimization-based approaches. The former offers high reliability and ease of implementation, but relies on engineering experience, which can lead to low efficiency in the coupled system and reduce its ability to respond to sudden disturbances in renewable resources. The latter offers a more flexible solution. However, dynamic programming is computationally inefficient and cannot meet the requirements for fast control, especially for dynamic models with multi-objective problems. Summary of the Invention

[0003] The purpose of the present invention is to provide an electric-hydrogen coupled three-port integrated converter and a control method thereof to solve the technical problem of the lack of a magnetic coupling structure in the existing wind-solar-hydrogen system.

[0004] To achieve the above objectives, the specific technical solutions of the present invention for an electric-hydrogen coupled three-port integrated converter and its control method are as follows:

[0005] The present invention is implemented by the following technical solutions: a model basis for an isolated three-port DC / DC converter-coupled wind-solar-hydrogen system and a power coordination control strategy for the system based on the model predictive control principle, which includes the following contents:

[0006] (1) Application scenarios of the electric-hydrogen coupled three-port integrated converter

[0007] The electric-hydrogen coupling system consists of a power grid, renewable energy (wind power, photovoltaics) and a hydrogen energy storage system. The electricity generated by renewable energy can be connected to the grid or directly supplied to the hydrogen energy storage system. In the hydrogen energy storage system, the electricity can be converted into hydrogen energy and stored in batteries. The DC bus connects the renewable energy, AC power grid and hydrogen energy storage system respectively, thereby realizing energy exchange between the hydrogen energy storage system, renewable energy and the power grid.

[0008] The power electronic device part between the DC bus and the hydrogen energy storage system is the electric-hydrogen coupled three-port integrated converter of the present invention. Figure 1 In the figure, V1, V2, and V3 are the voltages of the three ports of the converter, respectively. Switches S1 to S4 are active switches at the high-voltage side port (port 1), switches S5 to S8 are active switches at the fuel cell port (port 2), D1 to D4 are diodes in the uncontrolled rectifier bridge at the electrolyzer port (port 3), the input (output) capacitors at the primary, secondary, and tertiary ports are C1, C2, and C3, respectively, and L3 is the filter inductor at port 3. k1 With L k2 is the auxiliary inductance of the three-winding transformer (external inductance + transformer leakage inductance), and the square wave outputs of the three full-bridges are expressed as v pri 、v dab and v psfb The winding turns ratio of the low voltage DC bus side, fuel cell side and electrolyzer side is 1:n2:n3, and the current of each winding is i pri 、i dab and i psfb .

[0009] (2) Power decoupling of the electric-hydrogen coupled three-port integrated converter

[0010] The electric-hydrogen coupled three-port integrated converter has inherent cross-coupling of the current between the ports. However, the three-port converter structure can achieve inherent power decoupling from the hardware. The external inductor is connected in series with the high-frequency transformer to ensure that the leakage inductance of the primary side of the converter is low, while the inductance of the other ports (auxiliary inductance + transformer leakage inductance) is relatively high. This feature leads to the approximate decoupling of the individual power flows between the ports, avoiding the need for advanced and complex control methods and the use of excessive power devices, resulting in lower losses and higher efficiency. T1 With L m They are the leakage inductance and magnetizing inductance of the three windings respectively. Since the magnetizing inductance is much larger than the auxiliary inductance, the magnetizing inductance branch can be directly ignored in the circuit.

[0011] By converting the inductance parameters of port 2 and port 3 to port 1, we can obtain formula (1).

[0012]

[0013] n2 is the transformation ratio between the secondary side and the primary side,

[0014] n3 is the transformation ratio between the tertiary side and the primary side,

[0015] L k1 , L k2 is the auxiliary inductance of the three-winding transformer (external inductance + transformer leakage inductance),

[0016] LT1 is the leakage inductance of the three-winding transformer,

[0017] L r1 is the primary side inductance of the transformer,

[0018] L r2 , L r3 is the converted secondary and tertiary inductance;

[0019] The voltage at point p in the star equivalent circuit is shown in formula (2):

[0020]

[0021] v p is the voltage at point p in the star equivalent circuit,

[0022] v pri 、v dab and v psfb For the square wave output of three full bridges,

[0023] n2 is the transformation ratio between the secondary side and the primary side,

[0024] n3 is the transformation ratio between the tertiary side and the primary side,

[0025] L r1 is the primary side inductance of the transformer,

[0026] L r2 , L r3 is the converted secondary and tertiary inductance;

[0027] Assume that the inductance of the transformer secondary and tertiary sides referred to the primary side is equal, that is,

[0028] L r2 =L r3 =L s (3)

[0029] L r2 , L r3 is the converted transformer secondary and tertiary inductance,

[0030] L s The equal inductance of the secondary and tertiary sides referred to the primary side;

[0031] Substituting formula (3) into formula (2), we can get v p Simplified to:

[0032]

[0033] v p is the voltage at point p in the star equivalent circuit,

[0034] vpri 、v dab and v psfb For the square wave output of three full bridges,

[0035] n2 is the transformation ratio between the secondary side and the primary side,

[0036] n3 is the transformation ratio between the tertiary side and the primary side,

[0037] L r1 is the primary side inductance of the transformer,

[0038] L s The equal inductance of the secondary and tertiary sides referred to the primary side;

[0039] The current of the fuel cell port and the electrolyzer port after being converted to the primary side is:

[0040]

[0041] i2 and i3 are the values ​​of the fuel cell port current converted to the primary side and the electrolyzer port current converted to the primary side,

[0042] v pri 、v dab and v psfb For the square wave output of three full bridges,

[0043] n2 is the transformation ratio between the secondary side and the primary side,

[0044] n3 is the transformation ratio between the tertiary side and the primary side,

[0045] L r1 is the primary side inductance of the transformer,

[0046] L r2 , L r3 is the converted secondary and tertiary inductance,

[0047] L s The equal inductance of the secondary and tertiary sides referred to the primary side;

[0048] Omit the external leakage inductance of one of the ports, which is called the "master" port, and all other ports are called "slave ports." Depending on the application, a voltage source such as the grid should be connected to the master port. Let the primary leakage inductance L be r1 ≈0, v pri =v p .

[0049] At this point, we can know that the equivalent inductance L of the three-port converter is s >>L r1 ,available:

[0050]

[0051] L r1 is the primary side inductance of the transformer,

[0052] L s The equal inductance of the secondary and tertiary sides referred to the primary side;

[0053] Substituting formula (6) into formula (5), the inductor currents i2 and i3 in the fuel cell and electrolyzer ports can be simplified to:

[0054]

[0055] i2 and i3 are the values ​​of the fuel cell port current converted to the primary side and the electrolyzer port current converted to the primary side,

[0056] v pri 、v dab and v psfb For the square wave output of three full bridges,

[0057] n2 is the transformation ratio between the secondary side and the primary side,

[0058] n3 is the transformation ratio between the tertiary side and the primary side,

[0059] L r2 , L r3 is the converted secondary and tertiary inductance of the transformer;

[0060] From formula (7), we can see that when assuming L r1 ≈0, it can be seen that the inductor currents i2 and i3 in the fuel cell and electrolyzer ports are only related to the primary side midpoint voltage v p , the secondary side midpoint voltage itself, and has nothing to do with the other port midpoint voltage.

[0061] Therefore, this three-port converter structure achieves inherent power decoupling from a hardware perspective. The external inductor, connected in series with the high-frequency transformer, ensures low leakage inductance on the converter's primary side, while the inductance of the other ports (auxiliary inductance + transformer leakage inductance) is relatively high. This characteristic results in a near-decoupling of the individual power flows between the ports, avoiding the need for advanced and complex control methods and the use of excessive power devices, resulting in lower losses and higher efficiency.

[0062] (3) Control method and operating mode of the electric-hydrogen coupled three-port integrated converter

[0063] The control method of the electric-hydrogen coupled three-port integrated converter is as follows:

[0064] Step 1: Combined with an isolated three-port converter, a three-port integrated converter based on a phase-shifted full-bridge converter and a dual active bridge converter is used to couple the converter to hydrogen.

[0065] Step 2: Analyze the working principle of the converter and perform power decoupling;

[0066] Step 3: Design six different operating modes of the electricity-hydrogen coupled three-port integrated converter and use extended phase-shift control to achieve energy exchange;

[0067] The active bridges of port 1 and port 2 are respectively the leading bridge and the lagging bridge, so that the phase shift duty ratio The phase shift duty ratio between S1 and S3 in the leading bridge is called D1, which is called the inner phase shift ratio; the phase shift duty ratio between S1 and S5 between the leading bridge and the lagging bridge is called D2, which is called the outer phase shift ratio. In the extended phase shift control, the switching frequency of all active tubes is fixed at f s , T s The duty cycle of all active transistor drive signals is fixed at 50% for half of the switching cycle. The drive signals of a pair of active transistors in the same bridge arm of the leading bridge are complementary. Unlike the leading bridge, the drive signals of the diagonal active transistors in the lagging bridge are the same, that is, the drive signals of S5 and S8, and S6 and S7 are the same.

[0068] Let the internal phase shift ratio D1 = 1, D2 = D, and the converter becomes a single phase shift control. The modulation strategy of the electric-hydrogen coupled three-port integrated converter only has extended phase shift modulation control and single phase shift modulation control. The per-unit transmission power of the converter is shown in formula (8):

[0069]

[0070] P * EPS To normalize the transmission power of the converter under extended phase shift modulation control,

[0071] P1 is the actual outflow power of port 1 under extended phase shift modulation control,

[0072] P is the actual outflow power of port 1 under single phase shift modulation control,

[0073] P N is the maximum transmission power of the converter under single phase shift modulation control,

[0074] P * SPS To normalize the transmission power of the converter under single phase shift modulation control,

[0075] D is the phase shift duty cycle, is the phase shift angle,

[0076] D1 is the phase shift duty ratio between S1 and S3 in the leading bridge.

[0077] D2 is the phase shift duty ratio of S1 and S5 between the leading bridge and the lagging bridge, compared with the external shift,

[0078] n2 is the transformation ratio between the secondary side and the primary side,

[0079] V1 and V2 are the voltages of converter port 1 and port 2,

[0080] f s The switching frequency of all active tubes is fixed.

[0081] L k1 is the auxiliary inductance of the three-winding transformer;

[0082] P2 is the transmission power of port 2, which is defined as the average power flowing from the transformer into port 2 of the three-port converter. The relationship between its output size and the shift ratios D1 and D2 is determined by formula (8), as follows: Figure 2 shown.

[0083] After the three-port converter is naturally decoupled, the fuel cell port and the electrolyzer port can be controlled independently. Therefore, when the output power of these two ports is adjusted at the same time, the control strategy is as follows: Figure 3 As shown, the fuel cell port uses a fast current control loop; the electrolyzer port uses a relatively slow voltage control loop. That is, through D1 and D2, the fuel cell port and the electrolyzer port can operate independently or simultaneously to handle the power mismatch between renewable energy and electrolyzer load through the combination of proton exchange membrane fuel cells and batteries. When the electrolyzer port is in an open circuit state, the converter is controlled by single-phase shift modulation due to its simplicity and effectiveness. At this time, D1 = 0, and the relationship between the power transmitted by port 2, P2, and the shift ratio is as follows: Figure 2 When the two ports are operating simultaneously, the converter adopts hybrid phase shift control, which is equivalent to extended phase shift modulation control. D1≠0, the transmission power P2 of port 2 and the phase shift ratio are related as follows: Figure 2 Right).

[0084] When P2 = 0, it can be seen from formula (8) that different transformer leakage inductance and the actual value of the voltage V2 at the fuel cell port will affect the value of D2. The value of D2 when P2 = 0 is defined as zero crossing point 1 (D2 < 0) and zero crossing point 2 (D2 > 0), as follows: Figure 2 Left).

[0085] Combined with the actual operating conditions of the new energy coupled hydrogen energy storage system, 6 different working modes can be achieved by adjusting the different shift ratios D1 and D2, such as Figure 4 shown.

[0086] (1) Renewable energy battery charging mode (Mode 1)

[0087] In this working mode, if the electrolyzer is shut down due to failure, maintenance, full hydrogen storage tank, etc., the battery will absorb the remaining power of renewable energy connected to the grid, including fluctuating power and abandoned wind / solar power.

[0088] (2) Fuel cell / battery grid connection mode (Mode 2)

[0089] In this operating mode, the power delivered by renewable energy is unable to support the grid demand, the electrolyzer is shut down, and the fuel cell / battery generates electricity.

[0090] (3) Parallel mode of hydrogen production and charging using renewable energy (Mode 3)

[0091] In this operating mode, batteries and electrolyzers are used to absorb excess renewable resources, or when the power fluctuation of renewable energy is greater than the allowable power fluctuation width of hydrogen production, batteries are used to store energy to balance the excess power of renewable energy and prevent damage to the electrolyzer.

[0092] (4) Direct hydrogen production from renewable energy (Mode 4)

[0093] In this working mode, the fuel cell port is disconnected, the battery does not participate in energy exchange, and the electrolyzer either absorbs renewable energy within the allowable power fluctuation range or meets the peak and frequency regulation requirements of the power grid.

[0094] (5) Battery-assisted renewable energy hydrogen production mode (Mode 5)

[0095] In this working mode, battery discharge and renewable energy together power the electrolyzer, ensuring that when the power of renewable energy generation drops sharply, the electrolyzer always operates reliably and stably above the safe operating power of hydrogen, thereby ensuring the quality of hydrogen in the electrolyzer, system safety, and extending the life of the electrolyzer; at the same time, the participation of the battery can ensure that when the power of renewable energy fluctuates, the adjustment characteristics of the electrolyzer can be used to quickly compensate for short-term power shortages.

[0096] (6) Mode 6 to ensure the minimum technical output of the electrolyzer

[0097] In this operating mode, the battery at the electrolyzer port needs to independently power the electrolyzer to ensure hot standby. During this period, the grid's power load is high, and all renewable energy output is supplied to the grid, leaving less power available for the electrolyzer to absorb. Given the long startup time of the electrolyzer and the impact of frequent starts and stops on its lifespan, the battery is used to independently power the electrolyzer. This ensures safe operation of the electrolyzer while also taking advantage of its adjustable characteristics.

[0098] The invention provides an electric-hydrogen coupled three-port integrated converter and a control method thereof, which has the following advantages: providing a scientific and reasonable, highly applicable, high application value and good effect electric-hydrogen coupled three-port integrated converter control method.

[0099] This strategy allows the system to operate in different modes by simply adjusting the phase shift, ensuring the safety and operational characteristics of the alkaline electrolyzer, while also providing electrical isolation for the power-hydrogen coupling system. This invention boasts scientific rationality, strong applicability, high application value, and excellent results, and is of great significance for the in-depth study and commercial application of power-hydrogen coupling systems with magnetic coupling structures. BRIEF DESCRIPTION OF THE DRAWINGS

[0100] Figure 1 It is the structural diagram of the electric-hydrogen coupling system;

[0101] Figure 2 It is the power transfer characteristics of the electric-hydrogen coupled three-port integrated converter;

[0102] Figure 3 It is a control method for an electric-hydrogen coupled three-port integrated converter;

[0103] Figure 4 It is the working mode of the electric-hydrogen coupled three-port integrated converter;

[0104] Figure 5 It is the power transmitted by port 2 of the electric-hydrogen coupled three-port integrated converter;

[0105] Figure 6 The port 2 of the electric-hydrogen coupled three-port integrated converter is moved outward compared to D2;

[0106] Figure 7 It is the power transmitted by port 3 of the electric-hydrogen coupled three-port integrated converter;

[0107] Figure 8 The port 3 of the electric-hydrogen coupled three-port integrated converter is shifted inward compared to D2;

[0108] Figure 9 This is a specific application example of the electric-hydrogen coupled three-port integrated converter. DETAILED DESCRIPTION

[0109] In order to better understand the purpose, structure and function of the present invention, the following is a further detailed description of an electric-hydrogen coupled three-port integrated converter and a control method thereof in conjunction with the accompanying drawings.

[0110] The conceptual basis of the present invention is that, in a wind-solar-hydrogen coupling system including wind power, photovoltaics, power grids, loads, electrolyzers, fuel cells, batteries, and hydrogen storage tanks, in view of the uncertainty of renewable energy and the operating characteristics of electrolyzers and fuel cells, such as low-voltage and high-current operating conditions and regulation characteristics, the unidirectional power flow of the electrolyzer and the bidirectional power flow characteristics of the battery are considered, and combined with the rapidly developing isolated three-port converter, an isolated three-port DC / DC converter based on a phase-shifted full-bridge converter and a dual-active bridge converter is used to replace the busbar of the coupling system. By power decoupling and analyzing the working principle of the converter, six different operating modes of the converter are designed, and extended phase-shift control is used to realize energy exchange.

[0111] (1) Application scenarios of the electric-hydrogen coupled three-port integrated converter

[0112] The electric-hydrogen coupling system consists of a power grid, renewable energy (wind power, photovoltaics) and a hydrogen energy storage system. The electricity generated by renewable energy can be connected to the grid or directly supplied to the hydrogen energy storage system. In the hydrogen energy storage system, the electricity can be converted into hydrogen energy and stored in batteries. The DC bus connects the renewable energy, AC power grid and hydrogen energy storage system respectively, thereby realizing energy exchange between the hydrogen energy storage system, renewable energy and the power grid.

[0113] The power electronic device part between the DC bus and the hydrogen energy storage system is the electric-hydrogen coupled three-port integrated converter of the present invention. Figure 1 In the figure, V1, V2, and V3 are the voltages of the three ports of the converter, respectively. Switches S1 to S4 are active switches at the high-voltage side port (port 1), switches S5 to S8 are active switches at the fuel cell port (port 2), D1 to D4 are diodes in the uncontrolled rectifier bridge at the electrolyzer port (port 3), the input (output) capacitors at the primary, secondary, and tertiary ports are C1, C2, and C3, respectively, and L3 is the filter inductor at port 3. k1 With L k2 is the auxiliary inductance of the three-winding transformer (external inductance + transformer leakage inductance), and the square wave outputs of the three full-bridges are expressed as v pri 、v dab and v psfb The winding turns ratio of the low voltage DC bus side, fuel cell side and electrolyzer side is 1:n2:n3, and the current of each winding is i pri 、i dab and i psfb .

[0114] (2) Power decoupling of the electric-hydrogen coupled three-port integrated converter

[0115] The electric-hydrogen coupled three-port integrated converter has inherent cross-coupling of currents between ports. T1 With L mThey are the leakage inductance and magnetizing inductance of the three windings respectively. Since the magnetizing inductance is much larger than the auxiliary inductance, the magnetizing inductance branch can be directly ignored in the circuit.

[0116] By converting the inductance parameters of port 2 and port 3 to port 1, we can obtain formula (1).

[0117]

[0118] n2 is the transformation ratio between the secondary side and the primary side,

[0119] n3 is the transformation ratio between the tertiary side and the primary side,

[0120] L k1 , L k2 is the auxiliary inductance of the three-winding transformer (external inductance + transformer leakage inductance),

[0121] L T1 is the leakage inductance of the three-winding transformer,

[0122] L r1 is the primary side inductance of the transformer,

[0123] L r2 , L r3 is the converted secondary and tertiary inductance;

[0124] The voltage at point p in the star equivalent circuit is shown in formula (2):

[0125]

[0126] v p is the voltage at point p in the star equivalent circuit,

[0127] v pri 、v dab and v psfb For the square wave output of three full bridges,

[0128] n2 is the transformation ratio between the secondary side and the primary side,

[0129] n3 is the transformation ratio between the tertiary side and the primary side,

[0130] L r1 is the primary side inductance of the transformer,

[0131] L r2 , L r3 is the converted secondary and tertiary inductance;

[0132] Assume that the inductance of the transformer secondary and tertiary sides referred to the primary side is equal, that is,

[0133] L r2 =L r3 =Ls (3)

[0134] L r2 , L r3 is the converted transformer secondary and tertiary inductance,

[0135] L s The equal inductance of the secondary and tertiary sides referred to the primary side;

[0136] Substituting formula (3) into formula (2), we can get v p Simplified to:

[0137]

[0138] v p is the voltage at point p in the star equivalent circuit,

[0139] v pri 、v dab and v psfb For the square wave output of three full bridges,

[0140] n2 is the transformation ratio between the secondary side and the primary side,

[0141] n3 is the transformation ratio between the tertiary side and the primary side,

[0142] L r1 is the primary side inductance of the transformer,

[0143] L s The equal inductance of the secondary and tertiary sides referred to the primary side;

[0144] The current of the fuel cell port and the electrolyzer port after being converted to the primary side is:

[0145]

[0146] i2 and i3 are the values ​​of the fuel cell port current converted to the primary side and the electrolyzer port current converted to the primary side,

[0147] v pri 、v dab and v psfb For the square wave output of three full bridges,

[0148] n2 is the transformation ratio between the secondary side and the primary side,

[0149] n3 is the transformation ratio between the tertiary side and the primary side,

[0150] L r1 is the primary side inductance of the transformer,

[0151] L r2 , L r3is the converted secondary and tertiary inductance,

[0152] L s The equal inductance of the secondary and tertiary sides referred to the primary side;

[0153] Omit the external leakage inductance of one of the ports, which is called the "master" port, and all other ports are called "slave ports." Depending on the application, a voltage source such as the grid should be connected to the master port. Let the primary leakage inductance L be r1 ≈0, v pri =v p .

[0154] At this point, we can know that the equivalent inductance L of the three-port converter is s >>L r1 ,available:

[0155]

[0156] L r1 is the primary side inductance of the transformer,

[0157] L s The equal inductance of the secondary and tertiary sides referred to the primary side;

[0158] Substituting formula (6) into formula (5), the inductor currents i2 and i3 in the fuel cell and electrolyzer ports can be simplified to:

[0159]

[0160] i2 and i3 are the values ​​of the fuel cell port current converted to the primary side and the electrolyzer port current converted to the primary side,

[0161] v pri 、v dab and v psfb For the square wave output of three full bridges,

[0162] n2 is the transformation ratio between the secondary side and the primary side,

[0163] n3 is the transformation ratio between the tertiary side and the primary side,

[0164] L r2 , L r3 is the converted secondary and tertiary inductance of the transformer;

[0165] From formula (7), we can see that when assuming L r1 ≈0, it can be seen that the inductor currents i2 and i3 in the fuel cell and electrolyzer ports are only related to the primary side midpoint voltage v p , the secondary side midpoint voltage itself, and has nothing to do with the other port midpoint voltage.

[0166] Therefore, this three-port converter structure achieves inherent power decoupling from a hardware perspective. The external inductor, connected in series with the high-frequency transformer, ensures low leakage inductance on the converter's primary side, while the inductance of the other ports (auxiliary inductance + transformer leakage inductance) is relatively high. This characteristic results in a near-decoupling of the individual power flows between the ports, avoiding the need for advanced and complex control methods and the use of excessive power devices, resulting in lower losses and higher efficiency.

[0167] (3) Control method and operating mode of the electric-hydrogen coupled three-port integrated converter

[0168] The active bridges of port 1 and port 2 are respectively the leading bridge and the lagging bridge, so that the phase shift duty ratio The phase shift duty ratio between S1 and S3 in the leading bridge is called D1, which is called the inner phase shift ratio; the phase shift duty ratio between S1 and S5 between the leading bridge and the lagging bridge is called D2, which is called the outer phase shift ratio. In the extended phase shift control, the switching frequency of all active tubes is fixed at f s , T s The duty cycle of all active transistor drive signals is fixed at 50% for half of the switching cycle. The drive signals of a pair of active transistors in the same bridge arm of the leading bridge are complementary. Unlike the leading bridge, the drive signals of the diagonal active transistors in the lagging bridge are the same, that is, the drive signals of S5 and S8, and S6 and S7 are the same.

[0169] Let the internal phase shift ratio D1 = 1, D2 = D, and the converter becomes a single phase shift control. The modulation strategy of the electric-hydrogen coupled three-port integrated converter only has extended phase shift modulation control and single phase shift modulation control. The per-unit transmission power of the converter is shown in formula (8):

[0170]

[0171] P * EPS To normalize the transmission power of the converter under extended phase shift modulation control,

[0172] P1 is the actual outflow power of port 1 under extended phase shift modulation control,

[0173] P is the actual outflow power of port 1 under single phase shift modulation control,

[0174] P N is the maximum transmission power of the converter under single phase shift modulation control,

[0175] P * SPS To normalize the transmission power of the converter under single phase shift modulation control,

[0176] D is the phase shift duty cycle, is the phase shift angle,

[0177] D1 is the phase shift duty ratio between S1 and S3 in the leading bridge.

[0178] D2 is the phase shift duty ratio of S1 and S5 between the leading bridge and the lagging bridge, compared with the external shift,

[0179] n2 is the transformation ratio between the secondary side and the primary side,

[0180] V1 and V2 are the voltages of converter port 1 and port 2,

[0181] f s The switching frequency of all active tubes is fixed.

[0182] L k1 is the auxiliary inductance of the three-winding transformer;

[0183] P2 is the transmission power of port 2, which is defined as the average power flowing from the transformer into port 2 of the three-port converter. The relationship between its output size and the shift ratios D1 and D2 is determined by formula (8), as follows: Figure 2 shown.

[0184] After the three-port converter is naturally decoupled, the fuel cell port and the electrolyzer port can be controlled independently. Therefore, when the output power of these two ports is adjusted at the same time, the control strategy is as follows: Figure 3 As shown, the fuel cell port uses a fast current control loop; the electrolyzer port uses a relatively slow voltage control loop. That is, through D1 and D2, the fuel cell port and the electrolyzer port can operate independently or simultaneously to handle the power mismatch between renewable energy and electrolyzer load through the combination of proton exchange membrane fuel cells and batteries. When the electrolyzer port is in an open circuit state, the converter is controlled by single-phase shift modulation due to its simplicity and effectiveness. At this time, D1 = 0, and the relationship between the power transmitted by port 2, P2, and the shift ratio is as follows: Figure 2 When the two ports are operating simultaneously, the converter adopts hybrid phase shift control, which is equivalent to extended phase shift modulation control. D1≠0, the transmission power P2 of port 2 and the phase shift ratio are related as follows: Figure 2 Right).

[0185] When P2 = 0, it can be seen from formula (8) that different transformer leakage inductance and the actual value of the voltage V2 at the fuel cell port will affect the value of D2. The value of D2 when P2 = 0 is defined as zero crossing point 1 (D2 < 0) and zero crossing point 2 (D2 > 0), as follows: Figure 2 Left).

[0186] Combined with the actual operating conditions of the new energy coupled hydrogen energy storage system, 6 different working modes can be achieved by adjusting the different shift ratios D1 and D2, such as Figure 4shown.

[0187] (1) Renewable energy battery charging mode (Mode 1)

[0188] In this working mode, if the electrolyzer is shut down due to failure, maintenance, full hydrogen storage tank, etc., the battery will absorb the remaining power of renewable energy connected to the grid, including fluctuating power and abandoned wind / solar power.

[0189] (2) Fuel cell / battery grid connection mode (Mode 2)

[0190] In this operating mode, the power delivered by renewable energy is unable to support the grid demand, the electrolyzer is shut down, and the fuel cell / battery generates electricity.

[0191] (3) Parallel mode of hydrogen production and charging using renewable energy (Mode 3)

[0192] In this operating mode, batteries and electrolyzers are used to absorb excess renewable resources, or when the power fluctuation of renewable energy is greater than the allowable power fluctuation width of hydrogen production, batteries are used to store energy to balance the excess power of renewable energy and prevent damage to the electrolyzer.

[0193] (4) Direct hydrogen production from renewable energy (Mode 4)

[0194] In this working mode, the fuel cell port is disconnected, the battery does not participate in energy exchange, and the electrolyzer either absorbs renewable energy within the allowable power fluctuation range or meets the peak and frequency regulation requirements of the power grid.

[0195] (5) Battery-assisted renewable energy hydrogen production mode (Mode 5)

[0196] In this working mode, battery discharge and renewable energy together power the electrolyzer, ensuring that when the power of renewable energy generation drops sharply, the electrolyzer always operates reliably and stably above the safe operating power of hydrogen, thereby ensuring the quality of hydrogen in the electrolyzer, system safety, and extending the life of the electrolyzer; at the same time, the participation of the battery can ensure that when the power of renewable energy fluctuates, the adjustment characteristics of the electrolyzer can be used to quickly compensate for short-term power shortages.

[0197] (6) Mode 6 to ensure the minimum technical output of the electrolyzer

[0198] In this operating mode, the battery at the electrolyzer port needs to independently power the electrolyzer to ensure hot standby. During this period, the grid's power load is high, and all renewable energy output is supplied to the grid, leaving less power available for the electrolyzer to absorb. Given the long startup time of the electrolyzer and the impact of frequent starts and stops on its lifespan, the battery is used to independently power the electrolyzer. This ensures safe operation of the electrolyzer while also taking advantage of its adjustable characteristics.

[0199] Specific examples:

[0200] Taking the wind power, photovoltaic and load curves of a certain place as an example, the power generated in 0-1 second and 2.1-2.3 seconds is relatively small, and the maximum power generated at 1.7 seconds is about 15kW. The photovoltaic array mainly generates power in 0.5-2.8 seconds. The photovoltaic power gradually increases in 1-1.2 seconds, and then drops to 1000W in 2.8 seconds. At 1.5 seconds, the maximum power provided by photovoltaics is about 7kW. 1.2-2.1 seconds and 2.2-2.8 seconds are two peak power consumption periods. After 2.8 seconds, the total load power gradually decreases. The electric-hydrogen coupled three-port integrated converter can quickly change the direction or average size of the power flow transmitted to port 2 through the transformer by changing the outward displacement D2, so as to meet the rapid adjustment needs of fuel cells and batteries, such as Figure 5 、 Figure 6 The extended phase shift control of the electric-hydrogen coupled three-port integrated converter can achieve unidirectional power transmission to the alkaline electrolyzer at the electrolyzer port and the stable low ripple current required for electrolysis by changing the internal phase shift phase D1 without considering the power exchange and voltage values ​​of other ports, as shown in FIG. Figure 7 、 Figure 8 Energy exchange is achieved through the electric-hydrogen coupled three-port integrated converter of the present invention, as shown in FIG. Figure 9 As shown, the converter operates in Mode 5 and Mode 6 at 1.02-1.11 seconds, 1.3-1.4 seconds, and 2.82-2.86 seconds, and in Mode 3 at 1.54-1.88 seconds and 2.9-3 seconds, effectively utilizing net power and improving its ability to absorb renewable energy. The converter operates in Mode 2 when wind power, photovoltaic power generation, and load power are supplemented by batteries and proton exchange membrane fuel cells.

[0201] It will be understood that the present invention is described by way of some embodiments, and it will be appreciated by those skilled in the art that various changes or equivalent substitutions may be made to these features and embodiments without departing from the spirit and scope of the present invention. In addition, under the teachings of the present invention, these features and embodiments may be modified to adapt to specific circumstances and materials without departing from the spirit and scope of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are intended to be protected by the present invention.

Claims

1. An electric-hydrogen coupled three-port integrated converter, characterized in that: The electric-hydrogen coupled three-port integrated converter has three ports, namely a renewable energy port, a fuel cell port, and an electrolyzer port. Switch tubes S1 to S4 are active switch tubes for the high-voltage side port, switch tubes S5 to S8 are active switch tubes for the fuel cell port, D1 to D4 are diodes in the uncontrolled rectifier bridge of the electrolyzer port, the input / output capacitors of the primary, secondary and tertiary side ports are C1, C2 and C3 respectively, L3 is the filter inductor in port 3, and L k1 With L k2 is the auxiliary inductance of the three-winding transformer, and the square wave outputs of the three full-bridges are expressed as v pri 、v dab and v psfb The turns ratio of the low voltage DC bus side, fuel cell side and electrolyzer side is 1:n2:n3, and the current of each winding is i pri 、i dab and i psfb ; The control method of the electric-hydrogen coupled three-port integrated converter is as follows: Step 1: Combined with an isolated three-port converter, a three-port integrated converter based on a phase-shifted full-bridge converter and a dual active bridge converter is used to couple the converter to hydrogen. Step 2: Analyze the working principle of the converter and perform power decoupling; Step 3: Design six different operating modes of the electricity-hydrogen coupled three-port integrated converter and use extended phase-shift control to achieve energy exchange; Specifically include the following: The active bridges of port 1 and port 2 are respectively the leading bridge and the lagging bridge, so that the phase shift duty ratio is the phase shift angle, the phase shift duty ratio between S1 and S3 in the leading bridge is called D1, which is called the inner phase shift ratio; the phase shift duty ratio between S1 and S5 between the leading bridge and the lagging bridge is called D2, which is called the outer phase shift ratio; in the extended phase shift control, the switching frequency of all active tubes is fixed at f s , T s The duty cycle of all active transistor drive signals is fixed at 50% for half of the switching cycle. The drive signals of a pair of active transistors on the same bridge arm of the leading bridge are complementary. Unlike the leading bridge, the drive signals of the diagonal active transistors of the lagging bridge are the same, that is, the drive signals of S5 and S8; S6 and S7 are the same. Let the internal phase shift ratio D1 = 1, D2 = D, and the converter becomes a single phase shift control. The modulation strategy of the electric-hydrogen coupled three-port integrated converter only has extended phase shift modulation control and single phase shift modulation control. The per-unit transmission power of the converter is shown in formula (8): P * EPS To normalize the transmission power of the converter under extended phase shift modulation control; P1 is the actual outflow power of port 1 under extended phase shift modulation control; P is the actual outflow power of port 1 under single phase shift modulation control; P N is the maximum transmission power of the converter under single phase shift modulation control; P * SPS To normalize the transmission power of the converter under single phase shift modulation control; D is the phase shift duty cycle, is the phase shift angle; D1 is the duty ratio of the phase shift between S1 and S3 in the leading bridge, compared to the internal phase shift ratio; D2 is the phase shift duty ratio of S1 and S5 between the leading bridge and the lagging bridge, compared with the external shift ratio; n2 is the transformation ratio between the secondary side and the primary side; V1 and V2 are the voltages at ports 1 and 2 of the converter; f s The switching frequency of all active tubes is fixed; L k1 is the auxiliary inductance of the three-winding transformer; P2 is the transmission power of port 2, which is defined as the average power flowing from the transformer into port 2 of the three-port converter. The relationship between its output size and the shift ratios D1 and D2 is determined by formula (8).

2. The control method of the electric-hydrogen coupled three-port integrated converter according to claim 1, characterized in that: In step 2, the active bridges of the renewable energy port and the fuel cell port are respectively the leading bridge and the lagging bridge, so that the phase shift duty ratio is the phase shift angle, the phase shift duty ratio between S1 and S3 in the leading bridge is called D1, which is called the inner phase shift ratio; the phase shift duty ratio between S1 and S5 between the leading bridge and the lagging bridge is called D2, which is called the outer phase shift ratio; in the extended phase shift control, the switching frequency of all active tubes is fixed at f s , T s The duty cycle of all active transistor drive signals is fixed at 50% for half of the switching period. The drive signals of a pair of active transistors on the same bridge arm of the leading bridge are complementary. Unlike the leading bridge, the drive signals of the diagonal active transistors of the lagging bridge are the same, that is, the drive signals of S5 and S8; S6 and S7 are the same.

3. The control method of the electric-hydrogen coupled three-port integrated converter according to claim 1, characterized in that: In step 2, the fuel cell port and the electrolyzer port can be operated independently or simultaneously through D1 and D2, so as to handle the power mismatch between renewable energy and electrolyzer load through the combination of proton exchange membrane fuel cell and battery; When the electrolyzer port is in an open circuit state, the converter is controlled by single phase shift modulation, and D1 = 0; When the two ports are operating simultaneously, the converter adopts hybrid phase-shift control, which is equivalent to extended phase-shift modulation control, and D1≠0.

4. The control method of the electric-hydrogen coupled three-port integrated converter according to claim 1, characterized in that: In step 3, the six operating modes of the electricity-hydrogen coupled three-port integrated converter are as follows: Mode 1: Renewable energy battery charging mode. When the electrolyzer is shut down due to failure, maintenance, full hydrogen storage tank, etc., the battery absorbs the surplus power of renewable energy grid connection, including fluctuating power and abandoned wind / solar power. Mode 2: Fuel cell / battery grid access mode, where renewable energy transmission power is insufficient to support grid demand, the electrolyzer is shut down, and the fuel cell / battery generates electricity; Mode 3: Renewable energy hydrogen production and charging in parallel, using batteries and electrolyzers to absorb excess renewable resources. Or, when renewable energy power fluctuations exceed the allowable power fluctuation width for hydrogen production, batteries are used to store energy to balance the excess renewable energy power and prevent damage to the electrolyzer. Mode 4: Direct hydrogen production from renewable energy. The fuel cell port is disconnected, the battery does not participate in energy exchange, and the electrolyzer absorbs renewable energy within the allowable power fluctuation range or meets the peak and frequency regulation requirements of the power grid. Mode 5: Battery-assisted renewable energy hydrogen production mode, in which battery discharge and renewable energy together power the electrolyzer, ensuring that when the renewable energy power generation power drops sharply, the electrolyzer always operates reliably and stably above the safe operating power of hydrogen; Mode 6: To ensure the minimum technical output of the electrolyzer, the battery at the electrolyzer port needs to power the electrolyzer independently to ensure hot standby of the electrolyzer. At this time, the power load of the grid is high, and all the output power of renewable energy is supplied to the grid, while the power available for the electrolyzer to absorb is relatively small. The battery is used to power the electrolyzer independently.

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