A new energy hydrogen production system stability improvement method considering harmonic control

Abstract

The present application provides a new energy hydrogen production system stability improvement method considering harmonic control, which is suitable for a grid-connected system composed of synchronous wind turbine generators, hydrogen production devices, energy storage converters, passive filters and grid-connected power grids. First, the frequency domain impedance model of the hydrogen production system is established, and the single-input single-output equivalent method is used to analyze the impedance characteristics of the system and identify the oscillation risk frequency band. In view of the problem that although the energy storage unit can effectively suppress the 5th and 7th characteristic harmonics after the introduction of the active filter, it is easy to introduce negative damping, a phase compensation feedforward link is introduced in the active filter control channel, and the impedance phase characteristics in the target frequency band are reshaped. The present application can maintain good suppression effect of 5th and 7th harmonics, weaken the negative damping characteristics of the system, improve the phase margin of the system, and realize oscillation suppression. The present application considers the demand of harmonic control and stability improvement, and provides an effective technical approach for the safe and stable operation of new energy hydrogen production power system.

Description

Technical Field

[0001] This invention relates to the field of stability analysis and control technology for new energy power systems, specifically to a stability improvement method for new energy hydrogen production systems that also considers harmonic mitigation. Background Technology

[0002] New energy hydrogen production systems, as a crucial technological pathway for achieving efficient renewable energy consumption and large-scale hydrogen utilization, are gradually becoming a research focus in the energy and power sector. Especially with the widespread integration of fluctuating renewable energy sources such as wind power, constructing grid-connected systems that integrate wind power generation, energy storage regulation, and electrolysis hydrogen production not only helps improve renewable energy utilization efficiency but also enables cross-medium conversion and long-term storage of electrical energy into hydrogen, thus possessing significant engineering application value. As system capacity continues to expand and operating scenarios become increasingly complex, how to balance power quality management and dynamic stability improvement while ensuring stable system operation has become a key issue in the research of new energy hydrogen production systems.

[0003] New energy hydrogen production grid-connected systems typically consist of synchronous wind turbine generators, hydrogen production units, energy storage converters, passive filters, and a grid connection. These subsystems are interconnected through a common coupling point, forming a complex dynamic coupling relationship. The front-end of the hydrogen production unit usually employs a thyristor rectifier structure, which generates significant harmonic currents during operation, particularly the 5th and 7th harmonics. These harmonics not only degrade the system's power quality but can also increase line and transformer losses, exacerbate current pulsations and thermal stress within the electrolyzer, and adversely affect hydrogen production efficiency and equipment lifespan. Therefore, effectively suppressing the 5th and 7th harmonics in new energy hydrogen production systems is of significant engineering importance.

[0004] To mitigate the aforementioned harmonic issues, existing research typically employs a combination of passive and active filtering. Passive filters can suppress low-order harmonics at specific harmonic frequencies, but their effectiveness is susceptible to changes in system impedance, operating mode switching, and parameter drift, resulting in relatively limited dynamic adaptability. To further enhance harmonic mitigation accuracy and operational flexibility, introducing active filtering control into energy storage units has become a representative technological approach. While performing power regulation, the energy storage converter, by constructing an active filtering channel based on coordinate transformation, fundamental frequency extraction, and resonance control, can specifically compensate for characteristic harmonics such as the 5th and 7th harmonics, thereby significantly enhancing the system's harmonic suppression capability and improving power quality at the grid connection point.

[0005] However, while the introduction of active power filters into energy storage units can effectively suppress characteristic harmonics such as the 5th and 7th harmonics, their control structure inherently exhibits significant frequency selectivity. This causes the system to exhibit high damping in the target harmonic frequency band, while potentially displaying equivalent negative damping characteristics in non-target frequency bands. Particularly near the filter's design frequency, its amplitude-frequency response typically exhibits a peak, and its phase-frequency characteristics change rapidly. When this frequency band approaches the system's inherent resonant mode, the overall phase margin of the system will significantly decrease, making it more susceptible to oscillation formation conditions. In other words, while active power filters improve harmonic performance, they may also introduce new oscillation risks by altering the equivalent output impedance characteristics of the energy storage unit. Related analyses indicate that while the addition of active power filters significantly suppresses the 5th and 7th harmonics, it may also introduce new oscillation problems, demonstrating a clear coupling and trade-off between harmonic mitigation and oscillation suppression.

[0006] Research reveals that current research primarily focuses on two areas: impedance modeling and analysis of hydrogen production systems, and phase-compensation impedance shaping for power electronic devices. Existing studies have, on the one hand, conducted impedance modeling and stability analysis of electrolytic hydrogen production systems under weak grid conditions, indicating a significant coupling relationship between the impedance characteristics of the hydrogen production device and control parameters and grid connection conditions. On the other hand, some studies have employed phase compensation or active damping methods to improve the phase-frequency characteristics of key frequency bands in converter system oscillation problems. While these studies provide references for impedance analysis and phase-compensation vibration suppression in hydrogen production systems, a dedicated solution matching the system's operating mechanism is still lacking for the coupling problem in new energy hydrogen production grid-connected systems: "energy storage units participate in active filtering—suppressing the 5th and 7th harmonics—while simultaneously inducing new oscillation risks."

[0007] Research revealed that current studies on power quality and stability in new energy hydrogen production systems are primarily focused on harmonic suppression and stability analysis, lacking a unified solution that simultaneously addresses both harmonic mitigation and resonance suppression. The literature [Zhao W, Nielsen MR, Teodorescu R. Grid integration of a 500 kW alkaline electrolyzer system for harmonic analysis and robust control. e-Prime - Advances in Electrical Engineering, Electronics and Energy, 2023, 5: 100217.] conducted harmonic analysis and robust control research on a 500 kW alkaline electrolyzer grid-connected system, indicating that factors such as short-circuit ratio, control bandwidth, and switching frequency significantly affect the harmonic distortion level of the grid-connected system. This type of research mainly focuses on the harmonic characteristics of hydrogen production systems and their control optimization. The literature [Fang W, Teng Y, Zhang S, et al. Impedancemodeling and stability analysis of electrolysis system for hydrogen production under weak grid. Fuel, 2024, 374:] further illustrates this. [132403.] A comprehensive impedance model, including the electrolyzer, rectifier converter and related control mechanism, was established for the electrolytic hydrogen production system under weak grid conditions. Stability analysis was carried out, revealing the coupling relationship between the impedance characteristics of the hydrogen production device and the control parameters and grid connection conditions. This type of research mainly focuses on system stability and oscillation risk identification.

[0008] In summary, existing technologies have not fully addressed the synergistic optimization problem between power quality management and dynamic stability improvement in renewable hydrogen production grid-connected systems. In particular, they lack an impedance reshaping method for active power filter channels in energy storage systems. This method would mitigate the negative damping characteristics introduced by active power filters in non-target frequency bands while maintaining good suppression of the 5th and 7th harmonics, thereby achieving system oscillation suppression and stability improvement. Therefore, there is an urgent need to propose an impedance reshaping method suitable for renewable hydrogen production grid-connected systems to improve system stability within the target frequency band and enhance its adaptability to complex operating conditions. Summary of the Invention

[0009] In view of the above, the purpose of this invention is to provide a method for improving the stability of a new energy hydrogen production system that takes into account harmonic control. By introducing a phase compensation feedforward link into the active filter control channel of the energy storage converter, targeted phase compensation and impedance reshaping are achieved. While ensuring effective suppression of the 5th and 7th characteristic harmonics, the negative damping characteristics of the energy storage unit in non-target frequency bands are weakened, thereby improving the system impedance phase frequency characteristics, increasing the system stability margin, and providing a reliable technical path for the stable operation of new energy hydrogen production power systems.

[0010] A method for improving the stability of a new energy hydrogen production system that takes into account harmonic mitigation includes the following steps:

[0011] (1) Establish an impedance model for a new energy hydrogen production power system, which includes a synchronous wind turbine generator, a hydrogen production device, an energy storage converter, a passive filter, and a grid-connected power grid; wherein, the hydrogen production device includes an electrolyzer and its upstream thyristor rectifier system, and the energy storage converter has an active filtering function; establish a small-signal frequency domain impedance model for each subsystem at the common coupling point, and perform impedance coupling analysis on the entire system to determine the target frequency band with oscillation risk;

[0012] (2) In the active filter control channel of the energy storage converter, a phase compensation feedforward path is introduced into the current regulation path. By adjusting the dynamic response characteristics of the harmonic compensation current, the equivalent output impedance of the energy storage converter in the target frequency band is reshaped.

[0013] (3) Plot the impedance characteristic curves of the energy storage converter and the system as a whole before and after impedance reshaping, analyze the phase compensation effect, and verify the oscillation suppression effect of the system after impedance reshaping and its ability to adapt to complex operating conditions by combining the time-domain simulation model.

[0014] Furthermore, in the aforementioned new energy hydrogen production power system, the thyristor rectification process in the front stage of the hydrogen production device injects low-order characteristic harmonics such as the 5th and 7th orders into the system. Passive filters are used to suppress the corresponding low-order harmonics, while the energy storage converter further compensates for the characteristic harmonics such as the 5th and 7th orders by constructing an active filter control channel, thereby improving the power quality of the system.

[0015] In new energy hydrogen production and power systems, system oscillations originate from impedance interactions between the hydrogen production unit, the power grid, and the energy storage unit. While active power filtering in the energy storage unit can effectively suppress the 5th and 7th characteristic harmonics, its control structure exhibits frequency selectivity. This can introduce rapid phase drops and negative damping effects in non-target frequency bands, increasing the risk of system oscillations. Therefore, impedance reshaping is necessary to improve the damping characteristics of the energy storage unit in the corresponding frequency bands to mitigate oscillation risks.

[0016] Furthermore, in step (2), impedance reshaping is achieved by introducing a phase compensation feedforward path in the current regulation path of the active filter control channel. The purpose is to achieve directional adjustment of the phase characteristics of the target frequency band while keeping the original active filter control structure of the energy storage converter as unchanged as possible, so as to avoid significant adverse effects on the original harmonic control performance and basic dynamic response of the system.

[0017] Furthermore, the phase compensation feedforward path in step (2) is composed of a phase compensator. The phase compensator improves the phase margin of the system by raising the impedance phase of the energy storage converter in the target frequency band, weakening its negative damping characteristics, and improving the impedance characteristics of the energy storage unit and the system as a whole, thereby achieving oscillation suppression and enhancing the stable operation capability of the new energy hydrogen production power system under power fluctuation and operating mode changes.

[0018] Furthermore, in step (2), the expression for the phase compensator can be defined as:

[0019]

[0020] Where T is the time constant and α is the proportionality coefficient, and 0 < α < 1 is satisfied to provide positive phase compensation in the target frequency band, thereby improving the phase frequency characteristics of the system impedance.

[0021] Further, in step (3), the parameters within the feasible domain are selected to set the phase compensator, and the active filter control channel of the energy storage converter is impedance reshaping through the phase compensation feedforward path. The impedance characteristic curves of the energy storage converter and the system as a whole before and after impedance reshaping are plotted, and the phase compensation effect is analyzed. At the same time, combined with the time-domain simulation model, the oscillation suppression effect of the system after impedance reshaping is verified on the basis of maintaining the suppression capability of the 5th and 7th characteristic harmonics, as well as the improvement effect of the adaptability of the new energy hydrogen production power system to changes in operating conditions and power fluctuations.

[0022] This invention proposes an oscillation suppression method for new energy hydrogen production power systems. It introduces a phase compensation feedforward stage into the active filter control channel of the energy storage converter. Based on the impedance-phase characteristics of the target frequency band, the feasible domain of the compensator parameters is determined. The tuned phase compensator is then used to achieve targeted phase compensation and impedance reshaping. This effectively suppresses the 5th and 7th characteristic harmonics while weakening the negative damping characteristics of the energy storage unit in non-target frequency bands, improving the impedance characteristics of the system in the target frequency band, and enhancing the system stability margin. This method addresses the dual needs of harmonic control and oscillation suppression in new energy hydrogen production systems, providing a reliable technical path for the stable operation of new energy hydrogen production power systems. Attached Figure Description

[0023] Figure 1 This is the topology of a hydrogen production equipment system according to an embodiment of the present invention.

[0024] Figure 2 The energy storage unit system topology and control structure are shown in this embodiment of the invention.

[0025] Figure 3 This is the control structure of the reshaped active filter according to an embodiment of the present invention.

[0026] Figure 4 The diagram shows the impedance Bode plots of the active filter before and after compensation in an embodiment of the present invention.

[0027] Figure 5 The impedance Bode plots of the energy storage unit before and after compensation are shown in the embodiment of the present invention.

[0028] Figure 6 The impedance Bode plots of the hydrogen production system before and after compensation are shown in an embodiment of the present invention.

[0029] Figure 7 FFT analysis of the grid-connected point current before adding the active filter.

[0030] Figure 8 This is an FFT analysis diagram of the grid connection point current after adding an active filter but without phase compensation, according to an embodiment of the present invention.

[0031] Figure 9 This is an FFT analysis diagram of the grid connection point current after phase compensation in an embodiment of the present invention. Detailed Implementation

[0032] To describe the present invention in more detail, the technical solution of the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0033] This invention proposes a method for improving the stability of a new energy hydrogen production system while taking into account harmonic control. It is applicable to grid-connected systems consisting of synchronous wind turbine generators, hydrogen production devices, energy storage converters, passive filters, and a grid-connected power grid. The method introduces a phase compensation feedforward stage into the active filter control channel of the energy storage converter to reshape the impedance phase characteristics within the target frequency band. This maintains good suppression of the 5th and 7th harmonics while weakening the negative damping effect in non-target frequency bands, thereby improving the system's stability margin.

[0034] (1) Establishing a small-signal frequency domain impedance description of the hydrogen production system

[0035] like Figure 1 As shown, the hydrogen production section of a new energy hydrogen production power system mainly consists of a three-phase AC power grid, a transformer, a thyristor rectifier bridge, a DC-side filter, and an electrolyzer. The three-phase AC power grid outputs a three-phase voltage v. a v b v cAfter passing through a transformer, the current is connected to a three-phase fully controlled rectifier bridge composed of thyristors S1 to S6; the AC side of the rectifier bridge is connected to the power grid, and the DC side is connected to a smoothing inductor L. d With filter capacitor C d After forming a DC filter stage, it is connected to the electrolyzer load. Since the electrolyzer itself has significant electrochemical dynamic characteristics, and the thyristor rectification process introduces frequency coupling between the AC and DC sides, it is necessary to establish the electrolyzer impedance model and the rectifier bridge switching function separately, and then obtain the AC side impedance model of the hydrogen production port. In this invention, this is used to describe the small-signal frequency domain impedance of the hydrogen production system formed on this basis.

[0036] The impedance characteristics of an electrolytic cell can be expressed as:

[0037]

[0038] In the formula R ohm R represents the equivalent ohmic resistance of the electrolytic cell stack. act,a R represents the small-signal equivalent resistance of the anodic activation branch. act,c N represents the small-signal equivalent resistance of the cathode activation branch. s Indicates the number of cells in the electrolytic cell, A represents the electrode area, and C represents the number of cells in the electrolytic cell. dl,a C represents the anodic double-layer capacitance. dl,c This represents the cathode double-layer capacitance.

[0039] After the double Fourier transform, the rectifier bridge switching function can be expressed as:

[0040]

[0041] In the formula, f1 is the fundamental frequency of the power grid, f p A is the frequency of the injected disturbance voltage. p Φ is the disturbance amplitude obtained by combining the phase angle disturbance Δθ and the firing angle disturbance Δα. Ap This is the phase angle of the merged disturbance term.

[0042] Using the voltage-current equations, the AC impedance model of the hydrogen production port of the hydrogen production system can be obtained as follows:

[0043]

[0044] in:

[0045]

[0046]

[0047]

[0048]

[0049] (2) Establish an energy storage impedance model containing active filter equipment

[0050] like Figure 2 As shown, the energy storage unit adopts a voltage source grid-connected converter structure. Its main circuit includes a battery energy storage unit, a three-phase bridge converter, an AC side filter inductor, and a grid connection interface. The three-phase bridge converter outputs a three-phase modulated voltage v. ea v eb v ec After passing through the AC side filter inductor, three-phase current i is injected into the grid connection point PCC. ea i eb i ec In grid-connected control, the system collects the three-phase voltage v on the grid side. a v b v c v is obtained through abc / dq coordinate transformation d v q And through phase-locked loop H PLL (s) Obtain the synchronization angle θ PLL Simultaneously, the grid-connected current is collected and transformed using an abc / dq converter to obtain i. ed i eq This is to achieve closed-loop regulation of the converter in a synchronous rotating coordinate system. M in the diagram... d M q These represent the control quantities of the modulation signal on the d-axis and q-axis, respectively. After inverse dq / abc transformation, a three-phase modulation wave is generated, driving the energy storage converter to complete energy exchange and grid connection control. An active filtering function is introduced into its control channel. This active filtering control channel consists of current detection, coordinate transformation, fundamental frequency extraction, harmonic component extraction, and current regulation. Its purpose is to utilize the redundant capacity of the energy storage unit to specifically compensate for the 5th and 7th harmonics generated by the hydrogen production system, thereby improving the power quality at the grid connection point.

[0051] Based on the above control structure, an equivalent impedance model of the energy storage unit after the introduction of active filtering function can be established:

[0052]

[0053] In the formula, Z 11 (s) and Z 22 (s) represent the intrinsic impedance terms of the positive-sequence and negative-sequence channels of the energy storage unit, respectively. 11 (s), S 12 (s), S 21 (s), S 22 (s) represents the additional coupling term introduced by the phase-locked loop coupling, H 11 (s), H 12 (s), H21 (s), H 22 (s) represents the influence of the active filter control channel on each element of the admittance matrix of the energy storage unit.

[0054] (3) Further analysis of the frequency response of the active filter reveals that its amplitude-frequency characteristic typically exhibits a peak near the characteristic filtering frequency, while the phase curve drops significantly after passing the corresponding frequency. This phase drop reduces the equivalent damping level of the energy storage converter in the corresponding frequency band and significantly decreases the overall phase margin of the system, thus becoming an important cause of oscillation. Therefore, a phase compensation feedforward circuit is introduced into the active filter control channel of the energy storage converter to specifically adjust the phase characteristics within the target frequency band.

[0055] The reshaped active filter stage is as follows: Figure 3 As shown, based on the original adjustment mechanism, phase compensation feedforward links G are introduced into the d-axis and q-axis harmonic current adjustment paths respectively. lead (s). This link is connected in series with G. R (s) is located in the branch, and is connected to the original H. ei (s), K de The control unit and other components work together to shape the frequency response of the harmonic compensation current channel. Its function is to proactively correct the phase response of the compensation current within the target frequency band, mitigating the negative damping effect caused by the rapid phase lag of the original active filter in a specific frequency band. This improves the equivalent output impedance characteristics of the energy storage unit at the grid connection point, achieving impedance reshaping and enhancing system stability margin. While maintaining the compensation capability for the 5th and 7th harmonics, it reduces the risk of high-frequency oscillations introduced by active filter control. The phase compensation device adopts a proactive phase compensation structure, and its transfer function can be written as:

[0056]

[0057] Where T is the time constant and α is the proportionality coefficient, satisfying 0 < α < 1, to provide positive phase compensation within the target frequency band, thereby improving the phase-frequency characteristics of the system impedance. The compensated active filter transfer function can be written as:

[0058]

[0059] Where, k r,h For the resonant gain, ω c,h ω is the shear angular frequency. s,h It is the resonant angular frequency, used to selectively enhance and compensate for specific harmonic frequency components.

[0060] (4) After completing the phase compensation design, compare the impedance characteristics of the active filter, energy storage unit, and overall system before and after impedance reshaping. The impedance Bode plots of the active filter before and after compensation are shown below. Figure 4 As shown, the impedance Bode plot of the energy storage unit is as follows: Figure 5 As shown, the impedance Bode plot of the hydrogen production system is as follows: Figure 6 As shown in the figure. The results show that the phase of the active filter is significantly raised after compensation, the negative resistance region of the energy storage unit disappears in the sixth harmonic band, and the negative resistance region of the hydrogen production system disappears in the 425Hz band.

[0061] Furthermore, the phase compensation circuit was enabled in the electromagnetic transient simulation model, and the system operation was verified in the time domain. Simulation results show that while maintaining good suppression of the 5th and 7th characteristic harmonics, the phase drop phenomenon at approximately 425Hz was significantly suppressed, and the corresponding oscillation component was significantly weakened or even disappeared, indicating that the system recovered stability after impedance reshaping. The FFT analysis of the grid-connected point current before adding the active filter is as follows: Figure 7 As shown, the FFT analysis after adding an active filter but without phase compensation is as follows: Figure 8 As shown, the FFT analysis after adding phase compensation is as follows: Figure 9 As shown.

[0062] In summary, this invention constructs an impedance model of the hydrogen production system, identifies the negative damping problem introduced by the active filter in non-target frequency bands, and introduces a phase compensation feedforward stage in the active filter control channel to achieve impedance reshaping in the target frequency band. This method effectively suppresses the 5th and 7th characteristic harmonics while improving the system's phase characteristics and damping level, thus addressing both harmonic mitigation and oscillation suppression requirements. This provides a reliable technical path for the stable operation of new energy hydrogen production power systems.

[0063] The above embodiments are only used to illustrate the technical concept of the present invention. Any equivalent substitutions or modifications made to the control structure, parameter form, model expression, or verification method within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for improving the stability of a new energy hydrogen production system while taking into account harmonic control, characterized in that, Includes the following steps: (1) Establish an impedance model for a new energy hydrogen production power system, which includes a synchronous wind turbine generator, a hydrogen production device, an energy storage converter, a passive filter, and a grid-connected power grid; wherein, the hydrogen production device includes an electrolyzer and its upstream thyristor rectifier system, and the energy storage converter has an active filtering function; establish a small-signal frequency domain impedance model for each subsystem at the common coupling point, and perform impedance coupling analysis on the entire system to determine the target frequency band with oscillation risk; (2) In the active filter control channel of the energy storage converter, a phase compensation feedforward path is introduced into the current regulation path. By adjusting the dynamic response characteristics of the harmonic compensation current, the equivalent output impedance of the energy storage converter in the target frequency band is reshaped. (3) Plot the impedance characteristic curves of the energy storage converter and the system as a whole before and after impedance reshaping, analyze the phase compensation effect, and verify the oscillation suppression effect of the system after impedance reshaping and its ability to adapt to complex operating conditions by combining the time-domain simulation model.

2. The method for improving the stability of a new energy hydrogen production system while taking into account harmonic control, as described in claim 1, is characterized in that... In the aforementioned new energy hydrogen production and power system, the thyristor rectification process in the front stage of the hydrogen production device injects low-order characteristic harmonics such as the 5th and 7th orders into the system. Passive filters are used to suppress the corresponding low-order harmonics, while energy storage converters further compensate for the characteristic harmonics such as the 5th and 7th orders by constructing an active filter control channel, thereby improving the power quality of the system.

3. The method for improving the stability of a new energy hydrogen production system while taking into account harmonic control, as described in claim 1, is characterized in that... In step (2), impedance reshaping is achieved by introducing a phase compensation feedforward path into the current regulation path of the active filter control channel.

4. The method for improving the stability of a new energy hydrogen production system while taking into account harmonic control, as described in claim 3, is characterized in that... The phase compensation feedforward path in step (2) is composed of a phase compensator. The phase compensator improves the phase margin of the system by raising the impedance phase of the energy storage converter in the target frequency band, weakening its negative damping characteristics, improving the impedance characteristics of the energy storage unit and the system as a whole, thereby achieving oscillation suppression and enhancing the stable operation capability of the new energy hydrogen production power system under power fluctuation and operation mode change conditions.

5. The method for improving the stability of a new energy hydrogen production system while taking into account harmonic control, as described in claim 3, is characterized in that... In step (2), the expression for the phase compensator can be defined as: Where T is the time constant and α is the proportionality coefficient, and 0 < α < 1 is satisfied to provide positive phase compensation in the target frequency band, thereby improving the phase frequency characteristics of the system impedance.

6. The method for improving the stability of a new energy hydrogen production system while taking into account harmonic control, as described in claim 3, is characterized in that... In step (4), the parameters within the feasible domain are selected to set the phase compensator, and the impedance of the active filter control channel of the energy storage converter is reshaped through the phase compensation feedforward path.

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