Academic literature on the topic 'Pulsating power decoupling'

Abstract Traditional three-phase four-leg inverters are widely used in microgrid systems because of their ability to carry unbalanced loads, but unbalanced load currents will cause instantaneous power to contain double-frequency fluctuations, which will affect the normal operation of the microgrid system. In order to solve the above problems, this paper proposes an improved three-phase four-leg topology and its control strategy, so that the secondary pulsating power on the load side can be provided by the decoupling capacitor. Then the working principle of the proposed topology and its control strategy is analyzed, and the relationship between the current stress of the power device and various influencing factors is deduced. Finally, An experimental prototype was built to verify the effectiveness of the proposed solution.

Due to fewer conduction devices in operating condition, the bridgeless power factor correction (PFC) converter is more efficient than the traditional PFC circuit. However, to achieve a low output voltage ripple on the DC side, a large electrolytic capacitor must be connected in parallel to the output end. To reduce the value of capacitance, this paper proposes a dual-boost bridgeless PFC converter with a bidirectional buck/boost power decoupling converter in the latter stage. The bidirectional converter absorbs double-line-frequency ripple, lowering the power pulsation at the output end while realizing power decoupling. The one-cycle control is adopted in bridgeless PFC converter, so that the input current can follow the input voltage to achieve power factor correction and decrease harmonic pollution. The power decoupling circuit is designed with a voltage outer loop using PI control and a current inner loop using model predictive current control, which alleviates the output voltage fluctuation caused by the reduction of the capacitance value of the filter capacitor, for the purpose of realizing non-electrolytic capacitor. Finally, the topology and control strategy involved in this paper are simulated and experimented to verify the validity and superiority of the theory.

This paper presents an improved topology for three-phase to single-phase matrix converter (3-1 MC), and discusses the power decoupling method, closed-loop control strategy, etc. These studies make the single-output MC have good features, such as sinusoidal input current, low total harmonic distortion (THD), compensating the shortcomings of traditional 3-1 MC caused by the output power pulsation. According to the improved scheme, a novel closed-loop control strategy based on virtual dc voltage feedback is proposed. The strategy completes the closed-loop control of 3-1 MC by taking the virtual dc voltage as outer-loop controlled variable and the input current as inner-loop controlled variable. Consequently, the power factor correction (PFC) of 3-1 MC is achieved, and the control stability is improved. Finally, a series of stimulation and experiments for a prototype with 115V/400Hz output are conducted, the results show that the power decoupling method and control strategy are practically correct and feasible.

Due to the inherent frequency ripple in single-phase photovoltaic (PV) grid-connected solar inverters, the Maximum Power Point Tracking (MPPT) will inevitably be affected. To improve the MPPT performances, a passive LC power decoupling circuit with a Robust Sliding-Mode Control (RSMC) is proposed in this article. The frequency pulsation on the DC link is effectively canceled with the passive LC decoupling path. Thus, the MPPT accuracy is significantly enhanced, and the utilization of a small DC-link capacitor becomes possible. The resonance between the LC circuit and the main DC-link capacitor appears, which can be damped through an active damping method. The proposed RSMC offers good steady-state, dynamic performance (voltage fluctuation and settling time), and the robustness of the DC-link voltage, which is also beneficial to MPPT control in terms of high accuracy and fast dynamics. The systematic design of RSMC is presented, and a detailed parameter optimization design of the LC decoupling circuit is discussed. Experimental tests are performed on a 2.5-kW single-phase grid-connected solar inverter, and the results validate the effectiveness of the proposed strategy.

Aujourd'hui, les systèmes photovoltaïques connectés au réseau sont de plus en plus utilisés parmi les systèmes à énergies renouvelables. L’élément clé du système de conversion de puissance est le convertisseur statique connecté au réseau. Pour les applications de faible puissance, le convertisseur monophasé est le meilleur compromis. Les structures de conversion mono-étage permettent d’avoir un rendement plus élevé ainsi qu'un coût et une taille réduits. Cependant, dans des conditions de faible irradiation la tension PV chute, ce qui entraîne l'arrêt de l'onduleur et la perte totale de puissance injectée. Par conséquent, les systèmes à un étage de conversion souffrent d'une plage de fonctionnement réduite. Dans ce travail, nous proposons des solutions pour améliorer le rendement et la fiabilité des systèmes mono-étage connectés au réseau. Pour cela, dans la première partie, un contrôleur basé sur le mode glissant terminal rapide est combiné à un contrôle direct de la puissance. Il est associé à un algorithme de suivi du point de puissance maximale. Les simulations et les résultats expérimentaux sur un banc d'essai de 1kW montrent l'efficacité de la proposition en termes de performance dynamique, de faible distorsion harmonique totale et de robustesse aux variations d'irradiance. Les systèmes mono-étage sont également confrontés à une ondulation de puissance sur le bus continu à la fréquence double de celle du réseau. Ces ondulations de puissance sont néfastes à la durée de vie des panneaux solaires. Ainsi, la deuxième partie de ce travail propose de développer un dispositif qui simultanément réduit les ondulations de puissance et compense la chute de tension. Le dispositif est constitué de deux convertisseurs statiques : un flyback à faible puissance et un pont complet (H-bridge). Le compensateur hybride augmente la plage de fonctionnement de l'onduleur, empêchant son arrêt. Il contribue aussi à augmenter la fiabilité du système. Un banc expérimental de 1kW a été dimensionné et réalisé. Il a permis d’évaluer le dispositif sur plusieurs points de fonctionnement. Les résultats en régime permanent montrent que le compensateur hybride peut simultanément réaliser une atténuation de 85% des ondulations de puissance et une compensation de 20% de la chute de tension. Le dispositif a également de bonnes performances en régime transitoire. Dans la troisième partie de ce travail, la surveillance des modules PV est abordée afin d'augmenter la fiabilité. La méthode proposée est basée sur la spectroscopie d'impédance. Elle ne nécessite pas d’équipement supplémentaire car elle utilise le circuit qui permet d’atténuer les ondulations de puissance. De plus elle ne nécessite pas d'interrompre la production d'électricité. Les résultats de simulation, à l'aide de MATLAB-Simulink®, montrent une réduction de plus de 80% de l'amplitude des ondulations de la tension aux bornes des modules PV. Les résultats montrent que la spectroscopie d'impédance permet d’estimer les paramètres de l'impédance du module PV avec une erreur relative inférieure à 5%. L’évolution de ces paramètres en cours de fonctionnement devrait permettre de surveiller l’état de santé du panneau
Today, grid-connected photovoltaic systems are becoming an increasingly important part of renewable energy. The power conversion system's heart is the grid-connected interface converter based on power electronics. The single-phase inverter is the best compromise for low power applications as an interface for power conversion. Single-stage systems offer higher efficiency and lower cost and size. However, the PV voltage drops under low irradiance conditions, leading to inverter shut down and the total injected power loss.As a consequence, single-stage systems suffer from a low operating range. This work addresses the critical issues of the single-stage single-phase grid-connected PV system, including reliability and efficiency. A fast terminal sliding mode combined with direct power control is proposed in the first part. It is associated with a maximum power point tracking algorithm with power output. Simulations and experimental results on a 1kW test bench show the proposal's effectiveness in terms of dynamic performance, low total harmonic distortion and robustness to irradiance variations. Single-phase power systems also face pulsating power at twice the mains frequency on the DC bus. This pulsating power should not be transferred to the PV side as it reduces the efficiency of the solar panel. Thus, the second part of this work proposes a dual-function decoupling circuit: it mitigates pulsating power and compensates for the voltage drop. Thanks to the following additional power converters, these objectives are fulfilled: a low power flyback and an H-bridge. The hybrid compensator increases the inverter's operating range, prevents its shutdown, and increases the system reliability. A 1kW experimental bench has been designed to evaluate the proposal for several operating points. The steady-state results show that the hybrid compensator can simultaneously achieve 85% compensation of the pulsating power and 20% compensation of the voltage drop. The circuit also shows good transient responses. In the third part of this work, monitoring and fault diagnosis of PV modules are addressed to increase system reliability, efficiency, and safety. The proposed fault diagnosis method is based on online PV impedance spectroscopy without additional equipment. It does not require interrupting the power production and uses the pulsating power decoupling circuit as an impedance spectroscopy tool. The simulation results, using MATLAB-Simulink®, show a reduction of more than 80% ripples amplitude of the PV modules terminal voltage. The results also show that impedance spectroscopy can estimate the PV module impedance parameters with a lower than 5% relative error. The evolution of these parameters during operation should make it possible to monitor the health of the panel

碩士
明志科技大學
電機工程系碩士班
102
This thesis developed a power control with a power pulsation compensation method for a single-phase grid-connected PV system. Use TI TMS320F28335 digital signal processor as the control center to build a digital phase-lock-loop (DPLL), power control, and power pulsation compensation. Based on the DPLL, the frequency, phase angle, and amplitude of the grid voltage are obtained by the second-order generalized integrator quadrature-signal generator (SOGI-QSG), synchronous frame conversion, and phase angle control loop. The DPLL can reduce the interference of the harmonics. Through the improved single-phase power control method proposed in this paper to control active power and reactive power ingredients which are injected into the grid system, the power factor and efficiency are improved, the current harmonics are reduced dramatically, and the power quality of the overall system is also enhanced. The output power of a single-phase voltage-source inverter has inherently twice frequency power pulsation that causes the output current distortion and reduces the utility of renew power module. The power pulsation is double the line frequency and no manipulation of switching frequency or inverter topology can reduce the energy requirements. In this work a power pulsation decoupling method is proposed by integrated with digital phase lock-loop, power control and a bi-direction buck-boost converter at dc side. Experimental results have demonstrated that the current produced by power pulsation is reduced dramatically and the output current of a renew energy module is almost constant.

Abstract In this work, a hydraulic state of the art injection molding machine is retrofitted with a dual pump drive. The dual pump drive is an electro-hydraulic speed-variable drive, with focus on high bandwidth control through secondary control principles. Secondary control is based on providing the torque references for the electric machines directly, instead of a speed reference. The pressure control loop is based on decoupling of the piston load pressure and sum pressure enabling the possibility to utilize two SISO controllers. The application is the injection cylinder of an industrial injection molding machine, retrofitted with the designed dual pump drive. Experimental results for the proposed secondary control structure are presented and difficulties of implementation are documented, and a large gap between the theoretical achievable bandwidth and the experimental achievable bandwidth is shown. Three possible reasons for this gap are identified, namely amplification of high frequency components from e.g. signal noise on sensors, the use of axial piston pumps which induce pressure pulsations and the influence of the discrete sample time of the digital controller hardware. Lastly future work within the field is considered, including possible methods to minimize the influence of the identified issues.