بهبود پایداری سیستم بهساز توان پیل سوختی متصل به شبکه با فیلتر lcl با جبرانسازی فاز کنترل ‌کننده جریان

اینورترهای متصل به شبکه در اتصال منابع تولید پراکنده و منابع انرژی تجدیدپذیر به شبکه نقش اساسی ایفا می‌کنند. جهت افزایش کیفیت توان تزریقی به شبکه از فیلترهای مختلف از جمله فیلتر lcl استفاده می‌شود. در کنار تشدید ذاتی فیلتر lcl، شبکه ضعیف با امپدانس شبکه متغیر منجر به ناپایداری سیستم انتقال توان می‌شود. هدف این مقاله، بهبود کیفیت توان تزریقی پیل سوختی متصل به شبکه مبتنی بر فیلتر lcl با کنترل مبتنی بر فیدبک جریان شبکه و میرایی فعال جریان خازن است. اگرچه از نظر تئوری میرایی فعال می‌تواند رفتار پسیو اینورتر متصل به شبکه را تضمین کند، اما عملکرد سیستم هم به تاخیر فاز کنترل‌کننده جریان و هم به نوسانات پارامترهای فیلتر حساس است. برای کنترل این دو عامل، جبران‌ساز فاز مناسب برای افزایش رفتار انفعالی پیشنهاد شده است. در این مقاله سیستم بهساز توان پیل سوختی متصل به شبکه با فیلتر lcl با کنترل مبتنی بر جریان شبکه و میرایی فعال جریان خازن مورد مطالعه قرار گرفته و عملکرد انفعالی و پایدار این سیستم با در نظر گرفتن تاثیر تاخیر فاز تنظیم کننده جریان مورد ارزیابی قرار گرفته است. روند طراحی سیستماتیک پارامترهای سیستم کنترل با جزئیات لازم بیان شده و عملکرد انفعالی سیستم متصل به شبکه مورد ارزیابی قرار گرفته است. نتایج شبیه‌سازی سیستم بهساز توان پیل سوختی متصل به شبکه نشانگر تزریق جریان با کیفیت بسیار مناسب و رفتار انفعالی سیستم تحت تغییرات امپدانس شبکه ضعیف است.

stability improvement of lcl-based fuel cell power quality enhancement system utilizing phase compensation of current regulator

grid-connected inverters are key devices for transferring power from distributed generation systems and renewable energy sources to the grid. to suppress current harmonics and enhance the quality of the injected power, various filters are employed, among which the lcl filter is widely used. however, due to the inherent resonance of the lcl filter, the variable impedance of weak grids can introduce disturbances at the inverter output, ultimately leading to system instability. the objective of this paper is to improve the power quality of a fuel-cell-based grid-connected system employing an lcl filter, using a control strategy based on grid-current feedback and active damping of the capacitor current. in this study, a grid-connected fuel cell power-conditioning system with an lcl filter is analyzed. the stable and passive behavior of the system is evaluated while considering the influence of current regulator phase delay. furthermore, the design procedure and simulation results of the system under study are presented in detail.the system under study is composed of an inverter is employed to connect the fuel cell to the grid. to eliminate the dominant harmonics at the inverter output, an lcl filter is implemented. the inverter control strategy incorporates grid-current feedback and active damping of the capacitor current. the filter parameters l1, c, and l2​ correspond to the inverter-side inductor, filter capacitor, and grid-side inductor of the lcl filter, respectively. the grid impedance, which includes the transmission lines, transformer, and power factor correction capacitor, is modeled by an equivalent parallel lg-cg ​circuit.  since the output voltage of the fuel cell is insufficient for direct grid connection, a dc–dc converter is employed to step up the voltage level. considering the characteristics of the fuel cell, this converter must operate with a continuous input current with very low ripple.in the current control loop, the grid current il2 is regulated to be sinusoidal and synchronized with the point of common coupling (pcc) voltage. the pcc voltage (vpcc​) is measured through a phase-locked loop (pll) to ensure synchronization, where θ represents the detected grid voltage angle. this angle θ, combined with the reference current amplitude i∗, is used to generate the current reference (iref​). the error signal between il2​ and iref​ is processed by the current regulator gi​. to damp the resonance of the lcl filter, the capacitor current feedback (ic​) is fed back with a damping factor kd​. finally, the outputs of the current regulator gi​ and the active damping term are combined to generate the modulation signal vm​. using digital pulse-width modulation (pwm), the corresponding gate signals for the power switches are produced. the proportional–resonant current regulator is denoted by gi​.to validate the accuracy of the theoretical analysis and the feasibility of the proposed control strategy, the required simulations have been carried out. the output power of the grid-connected fuel cell power-conditioning system is considered to be approximately 8.5 kw. in the first stage, the fuel cell voltage is boosted by means of a dc–dc boost converter. subsequently, the dc-link voltage is injected into the grid through a grid-connected inverter equipped with an lcl filter. the inverter control strategy is based on grid-current regulation combined with active damping of the capacitor current. moreover, to compensate for the phase delay in the control system, a phase-delay compensator is employed to enhance the quality of the injected power. to demonstrate the dynamic behavior of the studied system, the fuel cell input fuel flow is varied dynamically, so that the accuracy and effectiveness of the control strategy in injecting power proportional to the fuel cell’s generated power can be evaluated. under full fuel flow, the system produces approximately 5.8 kw. when the fuel flow is reduced by 20%, the output power decreases to about 4.65 kw. once the fuel flow is increased again, the generated power returns to its nominal value with appropriate dynamic performance.