Interleaved multi-port non-isolated dc / dc converter and energy distribution dynamic control method thereof

Abstract

This invention proposes an interleaved multi-port non-isolated DC-DC converter and its dynamic energy distribution control method. Addressing the issues of high hardware cost and large size of discrete converter architectures in existing photovoltaic hydrogen production systems, as well as the high voltage stress and limited duty cycle of traditional non-isolated converters under high input voltages, this invention utilizes a multi-port integrated topology to achieve integrated photovoltaic grid connection and hydrogen production functions while reducing the number of switching devices and lowering system hardware costs. Furthermore, by combining a dual control loop strategy based on a PI controller, it achieves photovoltaic maximum power point tracking (MPPT) and hydrogen production distribution of excess power, thereby optimizing the overall system efficiency and dynamic performance.

Description

Technical Field

[0001] This invention belongs to the field of power electronic converter technology, specifically relating to an interleaved multi-port non-isolated DC / DC converter and its dynamic energy distribution control method. Background Technology

[0002] The global energy sector is undergoing a major transformation, moving towards cleaner and more sustainable energy sources driven by efforts to mitigate climate change and enhance energy security. Green hydrogen, as a low-carbon energy carrier, is crucial to this transition. Water electrolysis production powered by renewable energy sources such as solar or wind requires high-power converters to provide the necessary direct current to the electrolyzer. Various electrolyzer technologies exist, including proton exchange membrane (PEM) electrolyzers, alkaline water electrolyzers (AWE), and solid oxide electrolyzers (SOEC). It is projected that by 2030, alkaline electrolyzers will be replaced by PEM electrolyzers, as they are likely to be the greenest hydrogen production technology.

[0003] Currently, the challenge facing PEM lies in the cost of the materials used; however, once operating costs decrease, PEM electrolyzers will expand into industrial applications. PEM offers advantages such as high current density (over 2 A / cm²), low ohmic losses, and reduced operating costs. Furthermore, a crucial characteristic is PEM's rapid proton passage through the membrane, making it suitable for extracting power from intermittent energy sources such as solar and wind power. On the other hand, alkaline systems have a longer lifespan than PEM.

[0004] To produce hydrogen using solar energy (photovoltaics), specialized DC-DC power converters are required. These converters directly connect solar panels to the power system. Unfortunately, only a few companies currently commercially manufacture these converters. In standalone applications, the photovoltaic power source and electrolyzer can be directly interconnected, but introducing a DC-DC power converter is a suitable solution because it allows for optimization of the electrical operating points of both the photovoltaic power source and the electrolyzer. For the electrolyzer, two types of converters can be used: non-isolated and isolated topologies. The choice of topology depends on cost reduction, reliability, and efficiency improvement, as all these parameters directly affect the levelized cost of green hydrogen. Furthermore, the switching frequency or inductance needs to be increased to reduce current ripple. However, this action will affect the converter's switching losses and increase its weight and size.

[0005] The global energy sector is undergoing a profound transformation, accelerating its transition to clean and sustainable energy sources to mitigate climate change and enhance energy security. Green hydrogen, as a low-carbon energy carrier, plays a crucial role in this transformation. Utilizing renewable energy sources such as solar or wind power to drive water electrolysis for hydrogen production has become a current research hotspot. Among various electrolyzer technologies, proton exchange membrane (PEM) electrolyzers are considered the mainstream choice for future industrial applications due to their high current density, low ohmic losses, and rapid response to intermittent power sources.

[0006] However, the power converter is a crucial component for achieving efficient coupling between the photovoltaic system and the PEM electrolyzer. While the photovoltaic power source and electrolyzer can be directly interconnected in a standalone system, this approach makes it difficult to simultaneously optimize the maximum power point tracking (MPPT) of the photovoltaic system and the optimal operating point of the electrolyzer, resulting in overall system inefficiency. Therefore, introducing a DC / DC power converter becomes a necessary solution.

[0007] In existing non-isolated DC / DC converters, the classic buck converter is widely used due to its simple structure and low cost. However, as the industry trend moves towards higher DC bus voltages to reduce current transmission losses, traditional Buck converters face significant challenges. First, in applications with high input voltage and low output voltage, the power switches and diodes of traditional Buck converters must withstand the full input voltage stress, placing extremely high demands on the voltage ratings of the devices. Second, to achieve a large voltage conversion ratio, the converter is forced to operate within an extremely narrow duty cycle range, which not only limits control flexibility but also degrades the system's transient response performance. Traditional Buck converters generate significant output current ripple when handling large currents. To suppress ripple, it is usually necessary to increase the filter inductor or increase the switching frequency, which in turn increases the system's size, weight, and switching losses.

[0008] Although existing multiphase interleaving technology has been used to some extent to reduce current ripple and disperse thermal stress in voltage regulators, most current photovoltaic hydrogen production systems still adopt a discrete architecture: that is, a separate converter is required for photovoltaic grid connection, and another separate converter is required for hydrogen production. This discrete architecture not only increases the hardware cost and size of the system, but also makes it difficult to achieve flexible and seamless diversion of photovoltaic surplus energy to the electrolyzer when facing photovoltaic power fluctuations, thus failing to maximize the utilization of renewable energy.

[0009] Therefore, there is an urgent need for a multi-port converter topology and its control method that can integrate grid connection and hydrogen production functions, reduce device stress, and flexibly manage energy flow. Summary of the Invention

[0010] The purpose of this invention is to overcome the technical shortcomings of existing photovoltaic hydrogen production systems, such as high hardware cost and large size of discrete converter architecture, and high voltage stress and limited duty cycle of traditional non-isolated converters under high input voltage. It also addresses the energy distribution problem when photovoltaic power exceeds DC bus demand. This invention proposes an interleaved multi-port non-isolated DC / DC converter and its dynamic energy distribution control method. Through a multi-port integrated topology, the invention integrates photovoltaic grid connection and hydrogen production functions while reducing the number of switching devices and lowering system hardware costs. Combined with a dual control loop strategy based on a PI controller, it achieves photovoltaic maximum power point tracking (MPPT) and hydrogen production distribution of excess power, thereby optimizing the overall system efficiency and dynamic performance.

[0011] To achieve the technical objectives of this invention, the following technical solution is adopted according to the first aspect of this invention:

[0012] An interleaved multi-port non-isolated DC / DC converter, characterized in that it comprises:

[0013] Photovoltaic input port, used to connect to a photovoltaic power generation system;

[0014] DC bus output port, used to connect to DC power grid;

[0015] Hydrogen production port for connecting to a proton exchange membrane (PEM) electrolyzer system;

[0016] A two-phase interleaved boost converter module has its input connected to the photovoltaic input port and its output connected to the DC bus output port via a boost diode; the two-phase interleaved boost converter module includes a boost inductor (L... a L b ), boost switching transistor (S) a1 S b1 ) and boost diode (D a D b );

[0017] Two-phase interleaved buck converter module, including buck switching transistor (S a2 S b2 );

[0018] Among them, the first step-down switching transistor (S) a2 The drain of the circuit is connected to the first boost inductor (L). a ) and the first boost switch (S) a1 The common node of the second step-down switch (S) b2 The input terminal of ) is connected to the second boost inductor (L) b ) and the second boost switch (S) b1 The common node of ); the first buck switch (S a2) and the second step-down switch (S) b2 After the sources of the diodes converge, a blocking diode (D) is connected in series. BD ) and output filter; the blocking diode (D BD The anode of the diode is connected to the source junction of the buck switch, and its anode is connected to the freewheeling diode (D). FW The cathode of the filter inductor and the input terminal of the filter inductor; the freewheeling diode (D) FW The anode of the ) is grounded.

[0019] Furthermore, the converter also includes a control unit configured to execute an excess energy directional allocation mechanism; when the boost inductor (L a L b When the circuit is in the discharge phase, the control unit controls the corresponding buck switch (S) a2 S b2 When the photovoltaic input port is turned on, part of the energy is diverted to the hydrogen production port via the blocking diode and the output LC filter.

[0020] To achieve the technical objectives of this invention, the following technical solution is adopted according to a second aspect of this invention:

[0021] The energy distribution dynamic control method based on the above converter includes the following steps:

[0022] Step S1: Obtain the status of the photovoltaic system and generate the total reference current using the maximum power point tracking (MPPT) algorithm, while monitoring the target power demand of the DC bus. ) and actual power ( When generating the reference current, the total photovoltaic output reference current calculated by the MPPT algorithm is multiplied by a coefficient of 1 / 2, and used as the reference current of the first boost inductor and the second boost inductor, respectively. Closed-loop tracking is performed using two independent proportional-integral (PI) controllers.

[0023] Step S2: Calculate the power difference between the available photovoltaic power and the DC bus power demand. ,definition .

[0024] Step S3: Based on The converter is controlled to switch modes. When ΔP≤0, it is determined that the photovoltaic power is insufficient or just meets the DC bus demand, and the converter is controlled to enter the pure grid-connected power supply mode. When ΔP>0, it is determined that the photovoltaic power is excessive, and the converter is controlled to enter the grid-connected and hydrogen production hybrid mode.

[0025] Step S4: In hybrid mode, perform gate timing synchronization control to... The corresponding energy is allocated to the PEM electrolyzer. The specific gate control strategy is: only when the boost inductor (L...)... a The transistor is in the discharge phase, i.e., the boost switch (S) is in the discharge phase. a1 During the shutdown period, the control step-down switch (S) is activated. a2 ) conducts; only when the boost inductor (L b The transistor is in the discharge phase, i.e., the boost switch (S) is in the discharge phase. b1 During the shutdown period, the control step-down switch (S) is activated. b2 ) is turned on; the step-down switch (S) is turned on. a2 S b2 The switching action maintains a 180-degree phase difference to achieve staggered step-down operation.

[0026] Further, the process of generating the reference current in step S3 includes: multiplying the total photovoltaic output reference current calculated by the MPPT algorithm by a coefficient of 1 / 2, and using this as the reference current of the boost inductor (I1). La_ref I Lb_ref ); using two independent proportional-integral (PI) controllers to control the current (Ii) of the two boost inductors respectively. la I Lb ) performs closed-loop tracking control to generate a boost switching transistor (S) a1 S b1 The driving signal of ).

[0027] Furthermore, the specific strategy for gate timing synchronization control in step S4 is as follows: detect the driving timing of the boost switch; only when the first boost inductor (L... a The first boost switch (S) is in the discharge phase. a1 During the shutdown period, the first step-down switch (S) is controlled. a2 ) conducts only when the second boost inductor (L b The second boost switch (S) is in the discharge phase. b1 During the shutdown period, the second step-down switch (S) is controlled. b2 ) is turned on; the first step-down switch (S) is turned on. a2 ) and the second step-down switching transistor (S) b2 The switching action maintains a 180-degree phase difference to achieve staggered step-down operation.

[0028] Furthermore, in step S4, the excess power... The adjustment is achieved through dual closed-loop control: the outer loop is the power control loop, which calculates the power difference. As a reference input, the reference current (Io) of the electrolyzer is generated by the outer loop PI controller. elec_ref The inner loop is a current control loop: it controls the reference current of the electrolytic cell (I). elec_ref ) and actual electrolytic cell current (Iele The deviation input to the PI controller generates a step-down switching transistor (S) a2 S b2 The duty cycle signal is used to achieve accurate tracking and allocation of excess power.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] 1. High Integration and Low Cost in Multi-Port Topologies: Addressing the technical challenges of strong coupling interference and easily disrupted interleaved ripple cancellation characteristics in multi-phase interleaved multi-port topologies, this invention constructs a compact non-isolated multi-port topology by reusing a boost inductor as the input source of a buck converter, and employs a timing control strategy for discharge-stage conduction to achieve waveform decoupling. Compared to the traditional architecture using separate converters for grid connection and hydrogen production, this solution significantly reduces the number of magnetic components, lowering system size and hardware costs.

[0031] 2. Flexible Energy Allocation and Multi-Port Decoupling Control: Addressing the technical challenges of complex multi-source power flow and susceptibility to coupling interference in control loops within integrated multi-port topologies, this invention proposes a dynamic dual-control loop strategy based on a PI controller. This strategy enables seamless switching between "pure grid-connected" and "hybrid hydrogen production" modes, ensuring that excess photovoltaic energy is fully absorbed by the PEM electrolyzer, maximizing renewable energy utilization. This hierarchical control architecture achieves decoupling at the energy management level, ensuring stable DC bus voltage and non-interfering MPPT tracking during dynamic adjustment of hydrogen production power. Attached Figure Description

[0032] The following is a description of some aspects and specific embodiments, which are illustrated by way of example and in conjunction with the accompanying drawings:

[0033] Figure 1 This invention illustrates a multi-port non-isolated DC / DC converter topology according to an embodiment of the present invention.

[0034] Figure 2 A logic control block diagram of one embodiment of the control loop 1 of the present invention is shown.

[0035] Figure 3 A logic control block diagram of one embodiment of the control loop 2 of the present invention is shown.

[0036] Figure 4 A schematic diagram of the gate drive timing of the converter switching transistor of the present invention is shown.

[0037] Figure 5 The simulation response waveforms of the system provided in the embodiment, including photovoltaic power, DC bus power, and PEM electrolyzer power, are shown. Detailed Implementation

[0038] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. The following embodiments can help developers in related fields to further understand the technical solutions of the present invention. It should be noted that the embodiments are intended to explain the present invention, but not to limit the present invention.

[0039] Example 1: Circuit Construction of an Interleaved Multiport Non-isolated DC / DC Converter

[0040] like Figure 1 As shown, this embodiment constructs an interleaved multi-port non-isolated DC / DC converter for photovoltaic hydrogen production systems. In terms of hardware connections, this embodiment employs a two-phase interleaved structure to reduce current ripple. Specifically, the boost inductor L... a L b It serves not only as an energy storage element in the boost converter but also as an input source for the downstream buck converter.

[0041] Boost side: Positive terminal connection L of the photovoltaic array a and L b One end. L a The other end is connected to the boost switch S a1 The drain and boost diode D a anode; L b The other end is connected to the boost switch S b1 The drain and boost diode D b The anode. D a With D b The cathodes converge and are then connected to the DC bus capacitor C. out .

[0042] Buck converter on hydrogen side: Buck switch S a2 The drain is directly derived from L a With S a1 The common node (i.e., the output terminal of the boost inductor); the buck switch S b2 The drain is derived from L b With S b1 The public node. S a2 With S b2 After the sources converge, a blocking diode D is first connected in series. BD It is then connected to the PEM electrolytic cell via an LC filter.

[0043] Protection design: In the blocking diode D BD A freewheeling diode D is connected in reverse parallel between the front end (i.e., the switch junction point) and ground. FW It is used to provide a current loop during the turn-off period of the buck switch.

[0044] Example 2: Specific Implementation of Dynamic Energy Distribution Control Strategy

[0045] like Figure 2 and Figure 3 As shown, this embodiment employs a dynamic energy management strategy based on a dual-closed-loop PI controller.

[0046] 1. Boost MPPT Control (Main Circuit): The control system first acquires the voltage and current of the photovoltaic array, and calculates the total photovoltaic maximum power point current reference value using the perturbation and observation method. To ensure current balance in the two-phase interleaved boost inductors, this total reference value is processed by a gain module with a coefficient of 1 / 2, and then used as L... a and L b Current loop reference input (I La_ref I Lb_ref Two independent PI controllers adjust S respectively. a1 and S b1 The duty cycle ensures that the photovoltaic system always operates at its maximum power point.

[0047] 2. Step-down energy distribution control (auxiliary circuit): The core of this circuit lies in handling power difference. .

[0048] Judgment logic: The system monitors the target power demand of the DC bus in real time. ) and actual power ( ).

[0049] Dual-loop regulation: When photovoltaic power is excessive (ΔP>0), the outer loop PI controller generates the electrolytic cell reference current I based on the bus power deviation. elec_ref The inner-loop PI controller is based on the actual electrolytic cell current I. ele Tracking this reference value, a step-down switch S is generated. a2 S b2 The control signal.

[0050] Gate timing synchronization (e.g.) Figure 4 ): The controller locks the phase of the boost switch, forcing S a2 Only in S a1 Turning on during shutdown, S b2 Only in S b1 It is switched on during shutdown. This "off-peak power extraction" method avoids energy conflicts.

[0051] Example 3: Simulation Verification Based on a 100kW Photovoltaic Hydrogen Production System

[0052] To verify the effectiveness of the present invention, the above system was built in the PSCAD / EMTDC simulation environment.

[0053] 1. System parameter settings: photovoltaic array rated power 100kW; DC bus target voltage 1.2kV; converter switching frequency 50kHz; both boost inductor and buck inductor are 3mH; DC bus target power is set to a constant value of 70kW.

[0054] 2. Dynamic Operation Process and Test Results: The simulation simulated the entire process of the stepwise change in photovoltaic irradiance, with the time axis set as follows:

[0055] Phase 1 (0~0.5s): Photovoltaic irradiance set at 500W / m 2 At this point, the photovoltaic output power is low, not exceeding the 70kW requirement of the DC bus. Simulation results show that ΔP < 0, the step-down circuit is closed, the PEM electrolyzer power is 0, and all photovoltaic energy is delivered to the DC bus.

[0056] Phase Two (0.5s~1.0s): Photovoltaic irradiance jumps to 800W / m 2 At this moment, the photovoltaic output power surged and exceeded 70kW. The control system detected ΔP>0 and immediately activated the step-down circuit. The waveform showed that the PEM electrolyzer current rose rapidly and stabilized to track the reference value, absorbing about 10-15kW of excess power, while the DC bus power remained stable at 70kW, unaffected by the photovoltaic fluctuations.

[0057] Phase 3 (1.0s~1.5s): Photovoltaic irradiance further increases to 1000W / m 2 The photovoltaic output reached its peak, and ΔP further increased. Simulation showed that the power of the PEM electrolyzer increased by a step, completely absorbing the newly added excess energy and achieving the control objective of "fluctuating photovoltaic output, constant bus power, and full hydrogen production from surplus energy".

[0058] 3. Effect Analysis: such as Figure 5 The power response curves shown verify the dynamic stability of this invention under multiple operating conditions. When the photovoltaic input power undergoes a step change, the control system achieves a millisecond-level response speed. Precise capture of photovoltaic surplus energy is achieved. The actual absorbed power of the PEM electrolyzer (red curve) can quickly and accurately track changes in photovoltaic surplus power, proving the effectiveness of the surplus energy directional allocation mechanism. Strong decoupling control of the DC bus is achieved. Regardless of how drastic the photovoltaic power fluctuations, the DC bus power (green curve) remains stable at the set value (70kW), without significant voltage drops or power surges, ensuring the power supply quality on the grid side.

[0059] Specific embodiments of the present invention have been described above. It should be noted that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various changes and modifications within the scope of the claims, which do not affect the essence of the present invention. Unless otherwise specified, the embodiments and features described in this application can be arbitrarily combined with each other.

Claims

1. An interleaved multi-port non-isolated DC / DC converter, characterized in that, include: Photovoltaic input port, used to connect to a photovoltaic power generation system; DC bus output port, used to connect to DC power grid; Hydrogen production port for connecting to a proton exchange membrane (PEM) electrolyzer system; A two-phase interleaved boost converter module has its input connected to the photovoltaic input port and its output connected to the DC bus output port via a boost diode; the two-phase interleaved boost converter module includes a boost inductor (L... a L b ), boost switching transistor (S) a1 S b1 ) and boost diode (D a D b ); Two-phase interleaved buck converter module, including buck switching transistor (S a2 S b2 ); Among them, the first step-down switching transistor (S) a2 The drain of the circuit is connected to the first boost inductor (L). a ) and the first boost switch (S) a1 The common node of the second step-down switch (S) b2 The input terminal of ) is connected to the second boost inductor (L) b ) and the second boost switch (S) b1 The common node of ); the first buck switch (S a2 ) and the second step-down switch (S) b2 After the sources of the diodes converge, a blocking diode (D) is connected in series. BD ) and output filter; the blocking diode (D BD The anode of the diode is connected to the source junction of the buck switch, and its anode is connected to the freewheeling diode (D). FW The cathode of the filter inductor and the input terminal of the filter inductor; the freewheeling diode (D) FW The anode of the ) is grounded.

2. The interleaved multi-port non-isolated DC / DC converter as described in claim 1, characterized in that, The converter also includes a control unit configured to execute an excess energy directional allocation mechanism; when the boost inductor (L a L b When the circuit is in the discharge phase, the control unit controls the corresponding buck switch (S) a2 S b2 When the photovoltaic input port is turned on, part of the energy is diverted to the hydrogen production port via the blocking diode and the output LC filter.

3. A dynamic energy distribution control method based on the converter of claim 2, characterized in that, Includes the following steps: Step S1: Obtain the maximum power point tracking (MPPT) current reference value of the photovoltaic system and monitor the target power demand of the DC bus. ) and actual power ( ); Step S2: Calculate the power difference between the available photovoltaic power and the DC bus power demand. ,definition （1） in, This is the actual power. For the target power requirement; Step S3: Based on the power difference The converter is controlled to switch modes: when ΔP≤0, it is determined that the photovoltaic power is insufficient or just meets the DC bus demand, and the converter is controlled to enter the pure grid-connected power supply mode; when ΔP>0, it is determined that the photovoltaic power is excessive, and the converter is controlled to enter the grid-connected and hydrogen production hybrid mode. Step S4: In the grid-connected and hydrogen production hybrid mode, gate timing synchronization control is executed to transfer power to the DC bus while simultaneously controlling excess power. Directly guided to the PEM electrolyzer.

4. The dynamic energy distribution control method as described in claim 3, characterized in that, The process of generating the reference current in step S3 includes: multiplying the total photovoltaic output reference current calculated by the MPPT algorithm by a coefficient of 1 / 2, and using this as the reference current of the boost inductor (I1). La_ref I Lb_ref ); using two independent proportional-integral (PI) controllers to control the current (Ii) of the two boost inductors respectively. la I Lb ) performs closed-loop tracking control to generate a boost switching transistor (S) a1 S b1 The driving signal of ).

5. The dynamic energy distribution control method as described in claim 3, characterized in that, The specific strategy for gate timing synchronization control in step S4 is as follows: detect the drive timing of the boost switch; only when the first boost inductor (L... a The first boost switch (S) is in the discharge phase. a1 During the shutdown period, the first step-down switch (S) is controlled. a2 ) conducts only when the second boost inductor (L b The second boost switch (S) is in the discharge phase. b1 During the shutdown period, the second step-down switch (S) is controlled. b2 ) is turned on; the first step-down switch (S) is turned on. a2 ) and the second step-down switching transistor (S) b2 The switching action maintains a 180-degree phase difference to achieve staggered step-down operation.

6. The dynamic energy distribution control method as described in claim 3, characterized in that, In step S4, excess power is... The adjustment is achieved through dual closed-loop control: the outer loop is the power control loop, which calculates the power difference. As a reference input, the reference current (Io) of the electrolyzer is generated by the outer loop PI controller. elec_ref The inner loop is a current control loop: it controls the reference current of the electrolytic cell (I). elec_ref ) and actual electrolytic cell current (I ele The deviation input to the PI controller generates a step-down switching transistor (S) a2 S b2 The duty cycle signal is used to achieve accurate tracking and allocation of excess power.

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