Low-frequency Current Ripple Research Articles

Comprehensive influences measurement and analysis of power converter low frequency current ripple on PEM fuel cell

To deeply understand the influences of power converter's low frequency current ripple (LFCR) and harmonics on a proton exchange membrane fuel cell (PEMFC) in its power conditioning system (PCS), a comprehensive measurement and analysis of the influences of LFCR and harmonics on PEMFC's performance and durability is investigated in this paper. Based on an equivalent circuit model of PEMFC stack and a mechanism model for evaluating the LFCR effects on the PEMFC, this paper studies primarily and systematically the comprehensive influences of LFCR and harmonics on PEMFC performances and durability, such as (1) degrading the PEMFC performance, (2) shortening the lifetime of PEMFC, (3) reducing the stack output power, (4) lowing its availability efficiency, (5) producing more heat and raising the PEMFC temperature, (6) consuming more fuel, and (7) decreasing the fuel utilization. Finally, a Horizon 300 W PEMFC stack is implemented and tested.

Three-Phase Three-Level Flying Capacitor PV Generation System with an Embedded Ripple Correlation Control MPPT Algorithm

This paper presents the implementation of a maximum power point tracking (MPPT) algorithm in a multilevel three-phase photovoltaic (PV) system using the ripple correlation control (RCC) method. Basically, RCC adopts the inherent oscillations of PV current and voltage as perturbation, and it has been predominantly used for single-phase configurations, where the oscillations correspond to the 2nd order harmonics. The implementation of an RCC-MPPT algorithm in a three-phase system has not been presented yet in the literature. In this paper, the considered three-phase three-level converter is a three-level flying capacitor (FC) inverter. The proffered RCC method uses the 3rd harmonic components of PV current and voltage for the estimation of the voltage derivative of the power dPpv/dVpv (or current, dIpv/dVpv), compelling the PV array to operate at or very close to the maximum power point. The analysis and calculation of the low-frequency PV current and voltage ripple harmonic components in the three-phase flying capacitor inverter is presented first, with reference to centered carrier-based three-level PWM. The whole grid-connected PV generation scheme has been implemented by MATLAB/Simulink, and detailed numerical simulations verified the effectiveness of the control method in both steady-state and dynamic conditions, emulating different sun irradiance transients.

LED Series Current Regulator Based on a Modified Class-E Resonant Inverter

This paper presents a new topology based on a modified class-E resonant inverter used as an LED series current regulator. The proposed topology behaves as a controllable nondissipative impedance that adjusts the current flowing through the lamp. In this circuit, the LED is placed at the dc side of the class-E inverter, in series with the input filter inductance. The power handled by the ac side is sent back to the input by means of two diodes. Despite the addition of these two diodes, the converter maintains all the advantages of the class-E inverter: low component count, simple control, and extremely low switching losses. The LED current can be controlled with a small variation of the operating frequency. This way, the low-frequency current ripple of the lamp can be strongly reduced even when there is a considerably high input voltage excursion, such as the one expected in electrolyticless high-power-factor LED ballast. This paper proposes a simplified methodology based on the fundamental approach aiming to design and build a laboratory prototype. The prototype is designed in order to minimize the effect of LED voltage in the output current. This way, the input voltage ripple can be canceled using a simple feedforward control.

Repetitive Controller of Capacitor-Less Current-Fed Dual-Half-Bridge Converter for Grid-Connected Fuel Cell System

This paper proposes a repetitive controller (RC) for a capacitor-less current-fed dual-half-bridge (CF-DHB) converter for a grid-connected fuel cell system. The pulsating power caused by the ac grid makes the dc-link voltage and input current fluctuate with twice the grid frequency. To achieve zero-voltage-switching (ZVS) for the capacitor-less CF-DHB converter and to increase the lifetime of the fuel cell, we need to suppress the low-frequency dc-link voltage ripple and the low-frequency input current ripple. We first make use of the duty cycle to regulate the dc-link voltage, and of the phase-shift angle to regulate the input current. Because the transfer function from the duty cycle to the dc-link voltage has a right-half plane (RHP) zero, the conventional proportional-integral controller cannot achieve satisfactory performance at the dc-link voltage. To compensate for the phase lag due to the existence of the RHP zero, we propose to use an RC with phase-lead compensation for dc-link voltage control. Because the transfer function from the phase-shift angle to the input current has one left-half plane zero, the conventional RC is used to control the input current. In developing the proposed controller, we first derive the dynamic model of the CF-DHB converter in the grid-connected environment, and then use the model to design an RC. We also provide a detailed and practical design guideline to select the control parameters of the capacitor-less CF-DHB converter that can meet the desired performance. The proposed RC can reduce the input current ripple significantly and suppress the dc-link voltage ripple within the predetermined range and thereby achieves ZVS. Experimental results demonstrate that the proposed control scheme achieves desirable performance.

Modelling, control and performance analysis of a single‐stage single‐phase inverter with reduced low‐frequency input current ripple

A large amount of ripple at twice the output frequency will emerge in the input current due to the pulsating output power in a single-phase inverter. A current-fed-type single-stage single-phase inverter is investigated. Based on the switch multiplexing technique, it can realise not only dc-ac power conversion but also low-frequency input current ripple reduction with a lower number of power switches. A control strategy is proposed, which is capable of controlling both the input and output port performance. The operation performance is analysed, including circuit parameters, efficiency and dynamic behaviour. Besides, the equivalence of control strategy and the similarity of circuit component rating are revealed between this single-stage inverter and a conventional two-stage inverter. The single-stage inverter is preferred in the applications which are sensitive to the power switch number and low-frequency input current ripple. Finally, some experimental results are performed to verify the theoretical analysis.

Low-Frequency Impedance Monitoring and Corresponding Failure Criteria for Aluminum Electrolytic Capacitors

Condition monitoring of aluminum electrolytic capacitors (AECs) is essential for predictive maintenance of power electronic converters. The AEC is considered at the end of its life when its capacitance or equivalent series resistance (ESR) reaches corresponding critical values. In the literature, it is found that either of these parameters may reach its critical limit depending on the operating conditions and applications. However, most of the existing health monitoring techniques of the AEC in dc–dc converters are based on the estimation of ESR. To address the aforementioned issue, this paper proposes to estimate the low-frequency impedance of the AEC, which is dominated by its capacitance value, thereby allowing health monitoring based on the capacitance value. The technique is based on injection of a low-frequency current ripple into the AEC using duty ratio control of the dc–dc converter. The parameters of new and aged capacitors are experimentally obtained at various temperatures and are used to establish the failure criteria. Furthermore, the proposed method is applicable for both the continuous conduction mode and the discontinuous conduction mode (DCM) of operation. For DCM operation, a sampling instant to recover a low-frequency waveform is suggested based on mathematical analysis. Detailed simulation studies are performed and results are included in this paper. Experimentation is carried out on a dc–dc boost converter integrating solar photovoltaic with the dc system. Experimental results are found to be in agreement with simulation results.

Optimized Constant Current and Ripple Control of Non-electrolytic Capacitor LED AC/DC Power

For the traditional power supply of the non-continuous load Boost-Buck LED, when it has a high power factor, it will produce a significant low frequency ripple current. In this paper, a new type of LED driver power supply technology based on buck boost topology is proposed. The advantage of this technique is that the low frequency ripple current is greatly reduced without affecting the performance of the power factor and the advantages of high efficiency and low cost of the traditional boost buck LED driver are also preserved. We validate the performance of this new technology through a 30W and 50V-2A experimental prototype.

Capacitance Minimization in Offline LED Drivers Using an Active-Ripple-Compensation Technique

This study proposes a novel approach for low-frequency output current ripple minimization in offline light-emitting diode (LED) drivers. This strategy is based on the large-signal modulation of the LED converter duty-cycle so that the output ripple can be reduced and, consequently, the required filtering capacitances of the converter can be somehow decreased. This technique is devised to be used on converters in which a single control loop is employed, such as offline integrated converters, where a single control loop is responsible to control the output current while maintaining the high power factor at the input (mains). The duty-cycle modulation is used to change the shape of the main waveforms of the converter, especially input and output currents. This allows for a reduction of the output current peak-to-peak ripple while the harmonic content of the input current is increased but kept within the limits imposed by the IEC standard. An application example for an integrated two-stage converter based on the cascade connection of two buck-boost converters is shown. Experimental results from a 70-W laboratory prototype supplied from a 115-V grid were carried out and compared with conventional approaches in order to verify the feasibility of the proposed technique.

Low Frequency Current Ripple Mitigation of Two Stage Three-Phase PEMFC Generation Systems

This paper presents a two stage three-phase proton exchange membrane fuel cell (PEMFC) generation system. When the system is connected to a three-phase load, it is very sensitive to the characteristics and type of the load. Especially unbalanced three-phase loads, which result in a pulsating power that is twice the output frequency at the inverter output, and cause the dc-link to generate low frequency ripples. This penetrates to the fuel cell side through the front-end dc-dc converter, which makes the fuel cell work in an unsafe condition and degrades its lifespan. In this paper, the generation and propagation mechanism of low frequency ripple is analyzed and its impact on fuel cells is presented based on the PEMFC output characteristics model. Then a novel method to evaluate low frequency current ripple control capability is investigated. Moreover, a control scheme with bandpass filter inserted into the current feed-forward path, and ripple duty ratio compensation based on current mode control with notch filter is also proposed to achieve low frequency ripple suppression and dynamic characteristics improvement during load transients. Finally, different control methods are verified and compared by simulation and experimental results.

Low-Frequency Input Current Ripple Reduction Based on Load Current Feedforward in a Two-Stage Single-Phase Inverter

A large amount of ripple at twice the output frequency will emerge in the input current due to the pulsating output power in a two-stage single-phase inverter. To reduce the low-frequency input current ripple, a control strategy is presented in this paper based on the front-end dc-dc converter load current feedforward. It intends to control the dc bus voltage to swing properly at twice the output frequency, making the dc bus capacitor supply nearly all the pulsating power. The implementation method is illustrated, and the operation performance analysis as well as the key parameter design principle is provided. Introducing the proposed feedforward path is able to significantly suppress the input current ripple with little impacts on the original system stability, steady-state tracking accuracy, and dynamic response. Finally, experimental results performed on a buck-type stand-alone two-stage single-phase inverter prototype verify the validity of proposed method and the correctness of analysis.

Current Ripple Damping Control to Minimize Impedance Network for Single-Phase Quasi-Z Source Inverter System

The single-phase quasi-Z source inverter (qZSI) topology has recently attracted attention for single-phase grid-tie photovoltaic (PV) applications. However, due to the inherent second-harmonic power flow in single-phase systems, a large qZS network is required to reduce the second-harmonic component of currents and voltages on the dc side. Minimization of the qZS network remains an open issue. This paper proposes a technique that minimizes the qZS capacitance and inductance of the single-phase qZSI topology by employing dc-side low-frequency current ripple damping control. Through analysis of power flow, a second-harmonic power model is derived and the ripple power is analyzed for minimization of the qZS network. A current ripple damping control is proposed to ensure suppression of second-harmonic power flow through the inductors. Simulation and experimental results verify the theoretical analysis, damping control, and the proposed design minimization of the qZS network for the single-phase topology.

Low Frequency Current Ripple Reduction Technique With Active Control In A Power System With Inverter Load

During the next few years there will be a profound change in the generation and usage of energy, influenced factors such as environment, capital and production costs as well as geopolitical factors, old power stations in the world will be phased out. Newer power stations, having large output capacity will be difficult to permit in many existing political climates. With global warming now apparent, environment and efficient fuel utilization have become significant factors in the adaptation of newer and emerging energy conversion technologies. High installation cost is the major obstacle of the commercialization of fuel cell for distributed power generation. A fuel cell power system that contains a dc-ac inverter tends to draw an ac ripple current at twice the output frequency. Such a ripple current may shorten input cell lifespan and worsen the efficiency and output capacity. In this paper, an advanced active control technique is proposed to incorporate a current control loop in the dc-dc converter for ripple reduction. This will reduce both size and cost of the system. The proposed active ripple reduction method has been verified with MATLAB simulation.

Analysis of Input Current Ripple and Optimum Filter Capacitor for Fuel-Cell-Based Single-Phase Inverter

Most single-phase inverters, being sourced by fuel cell stacks (FCSs), subject the stacks to reflected low-frequency (120 Hz) current ripples that ride on average dc currents. The ripple current impacts the sizing and efficiency of the FCS. As such and typically, a passive or active filter is required at the input of the inverter (or output of the FCS) to mitigate the ripple current. Toward that end, this paper outlines a guideline to choose the optimum size of a passive input-filter capacitor for a fuel-cell-based power system from the standpoints of the overall system energy density and cost. Detailed case-specific simulation results, based on an analytical approach, are provided to illustrate key issues for both unity power factor as well as harmonic loads.

Single-Stage and Boost-Voltage Grid-Connected Inverter for Fuel-Cell Generation System

According to the requirement of fuel cell generation system, this paper presents a new single-stage and boost-voltage grid-connected inverter, as well as the signal modulation diagram in a line cycle. In the proposed inverter, one of the bridge legs is shared with a boost converter. The boost inductor current is designed in discontinuous conduction mode, which can effectively decrease low-frequency current ripple (LFCR) in the output current of the fuel cell. The switching modes of the proposed inverter are analyzed in positive and negative half line cycles, respectively. The LFCR in the output current of the fuel cell is analyzed, from which the design principle of the boost voltage inductor is obtained. The per-unit current values of the shared switches and the loss of the whole system are derived and compared with those of the conventional inverter. Experimental verifications are presented to verify the theoretical analysis.

An Average Current Modulation Method for Single-Stage LED Drivers With High Power Factor and Zero Low-Frequency Current Ripple

Conventional single-stage light-emitting diode (LED) drivers with a high power factor (PF) contain a significant LED current ripple at twice the ac line frequency, and would require large energy storage capacitors to limit the effect on LED light. Conventional designs and novel control techniques aim to power LED loads with a dc voltage to ensure a limited low-frequency LED current ripple. This paper proposes an average current modulation method that is designed to operate in conjunction with single-stage PF correction (PFC) circuits that contain significant ac voltage ripple, while maintaining zero low-frequency current ripple. This allows the energy storage capacitance of the PFC stage to be reduced, avoiding the need for electrolytic-type capacitors and prolonging the life of the LED driver. The average current modulation circuit requires a single low-voltage MOSFET, a current sense resistor, and a simple control circuit. By requiring no additional magnetic components, the cost of the current modulation circuit is very low and has minimal impact on the efficiency of the overall LED driver. Two experimental prototypes, an 8.75-W system with a buck–boost PFC converter and a 25-W system with a flyback PFC converter, have been built to verify the capability and excellent performance of the proposed driving technique.

Static and Dynamic Photoelectrothermal Modeling of LED Lamps Including Low-Frequency Current Ripple Effects

In this paper, a static and dynamic photoelectrothermal model including the impact of low-frequency current ripple on light-emitting diodes (LEDs) performance is proposed. The objective of this study is to evaluate the dynamical interaction among thermal, photometrical, and electrical properties of the LEDs when they are supplied by a dc constant current with a superposed low frequency sinusoidal ripple, which is the common case in offline LED drivers. Therefore, this paper presents both a model and experimental data for analyzing the LED photometrical behavior in terms of luminous flux, efficacy, flicker, and chromaticity. Three laboratory prototypes with different heat sinks and LED models have been tested. Experimental results are presented to evaluate the LED photometrical behavior under the aforementioned operating conditions and to validate the proposed modeling methodology.

Comprehensive Modeling of Single-Phase Quasi-Z-Source Photovoltaic Inverter to Investigate Low-Frequency Voltage and Current Ripple

The second harmonic (2ω) power ripple of single-phase quasi-Z-source (qZS) photovoltaic (PV) inverter highly affects the whole system's design and performance. The topology's 2ω ripple model is very important to analyze qZS PV inverter's 2ω voltage and current ripple. The existing models did not consider the PV-panel dynamic and terminal capacitors, which causes the theoretical results apart from the truth. In this paper, a comprehensive modeling for single-phase qZS-PV inverter is proposed, where the 2ω ripple model of the qZS-PV inverter system with a real PV source is established and discussed without and with a PV terminal capacitor. The influences from qZS inductance and capacitance, and PV-panel terminal capacitance to the 2ω voltage and current ripple are investigated using the built model. The system parameter design method is proposed to mitigate this ripple. Simulation and experimental results validate the proposed 2ω ripple model and parameter design method.

Low‐frequency dc bus ripple cancellation in single phase pulse‐width modulation inverters

This study presents a topology for a single-phase pulse-width modulation (PWM) converter which achieves low-frequency ripple reduction in the dc bus even when there are grid frequency variations. A hybrid filter is introduced to absorb the low-frequency current ripple in the dc bus. The control strategy for the proposed filter does not require the measurement of the dc bus ripple current. The design criteria for selecting the filter components are also presented in this study. The effectiveness of the proposed circuit has been tested and validated experimentally. A smaller dc-link capacitor is sufficient to keep the low-frequency bus ripple to an acceptable range in the proposed topology.

Steady-State and Dynamic Input Current Low-Frequency Ripple Evaluation and Reduction in Two-Stage Single-Phase Inverters With Back Current Gain Model

Due to nonlinear time-varying characteristic of a single-phase dc/ac inverter, its front-end dc/dc converter tends to draw an alternate current ripple current at twice the output frequency, which may cause interaction issues, e.g., stability problem and input ripple current limit in distributed generation systems. A novel method is proposed to evaluate the behavior of low-frequency input current ripple. This approach is based on back current gain Ai (s) (input current to output current) model of the dc/dc converter. The theoretic model with different control schemes is verified in Saber environment. It is indicated and proved that the average current mode control strategy is more effective as compared with linear voltage mode control and open-loop control schemes. Design principles are presented based on Ai (s) as guidelines. Dynamic response with bandwidth limitation is also discussed and improved with proposed proportional-resonant (PR) filter placed based on Ai (s) model. Detail simulation and experiment results for different linear control and nonlinear control strategies, 50 and 400 Hz, buck-type stand-alone two-stage single-phase systems are provided to verify the proposed back current gain model and PR-filter solutions.

Equivalent Circuit Modeling of PEM Fuel Cell Degradation Combined With a LFRC

This approach investigates with an equivalent circuit modeling a polymer electrolyte membrane (PEM) fuel cell degradation combined with a low-frequency ripple current (LFRC) that may shorten the fuel cell life and worsen the fuel efficiency. Through the immediate measurement of the impedance curves on single cells obtained after cycling for hours and operating in cathode flooding and membrane dehydration modes at variable frequencies, it has been shown that the impedance magnitude of a fuel cell injecting a LFRC increased when compared with that of a high-frequency ripple current. This study develops these investigations one step further by designing equivalent circuit elements like resistance and capacitance by electrochemical impedance spectroscopy. Impedance-based model is able to describe the dynamic behavior of the PEM fuel cell. For validation of the proposed fuel cell model, an experimental study has been carried out for a 1.2-kW Nexa module.