Showing papers on "Ripple published in 2014"

Ultraflat Interleaved Triangular Current Mode (TCM) Single-Phase PFC Rectifier

Abstract: This paper presents the analysis and realization of a topology suitable to realize a power factor correction (PFC) rectifier with a thickness of only a few millimeters. The low height of the converter requires all components to be integrated into the printed circuit board (PCB). Still reasonable dimensions of the converter PCB are feasible (221 mm × 157 mm for a 200 W PFC rectifier), since PCB-integrated inductors and capacitors allow for high energy densities due to their large surface area which facilitates a low thermal resistance to ambient. A multicell totem-pole PFC rectifier employing a soft-switching modulation scheme over the complete mains period is identified as an adequate topology. The mode of operation is entitled triangular current mode (TCM) due to the triangular-shaped inductor currents. The modulation technique requires a reliable description of the switching transition of a half-bridge in order to provide accurate timing parameters. For this purpose, a simplified model of the nonlinear MOSFETs' output capacitances facilitates closed-form analytical expressions for duty cycle and switching frequency. Furthermore, this paper details the control of three interleaved converter cells which yields a reduction of the input current ripple. A 200 W TCM PFC rectifier with a low height of 5 mm has been realized and measurement results are provided in order to validate the theoretical considerations. The presented TCM PFC rectifier achieves an efficiency of 94.6% and a power factor of 99.3% at nominal power.

Systematic Design of the Lead-Lag Network Method for Active Damping in LCL-Filter Based Three Phase Converters

Abstract: Three-phase active rectifiers guarantee sinusoidal input currents and unity power factor at the price of a high switching frequency ripple. To adopt an LCL-filter, instead of an L-filter, allows using reduced values for the inductances and so preserving dynamics. However, stability problems can arise in the current control loop if the present resonance is not properly damped. Passive damping simply adds resistors in series with the LCL-filter capacitors. This simplicity is at the expense of increased losses and encumbrances. Active damping modifies the control algorithm to attain stability without using dissipative elements but, sometimes, needing additional sensors. This solution has been addressed in many publications. The lead-lag network method is one of the first reported procedures and continues being in use. However, neither there is a direct tuning procedure (without trial and error) nor its rationale has been explained. Thus, in this paper a straightforward procedure is developed to tune the lead-lag network with the help of software tools. The rationale of this procedure, based on the capacitor current feedback, is elucidated. Stability is studied by means of the root locus analysis in z-plane. Selecting the lead-lag network for the maximum damping in the closed-loop poles uses a simple optimization algorithm. The robustness against the grid inductance variation is also analyzed. Simulations and experiments confirm the validity of the proposed design flow.

A Switched-Capacitor-Based Active-Network Converter With High Voltage Gain

Abstract: The voltage gain of traditional boost converter is limited due to the high current ripple, high voltage stress across active switch and diode, and low efficiency associated with large duty ratio operation. High voltage gain is required in applications, such as the renewable energy power systems with low input voltage. A high step-up voltage gain active-network converter with switched-capacitor technique is proposed in this paper. The proposed converter can achieve high voltage gain without extremely high duty ratio. In addition, the voltage stress of the active switches and output diodes is low. Therefore, low voltage components can be adopted to reduce the conduction loss and cost. The operating principle and steady-state analysis are discussed in detail. A prototype with 20-40-V input voltage, 200-V output voltage, and 200-W output power has been established in the laboratory. Experimental results are given to verify the analysis and advantages of the proposed converter.

Pulsewidth Modulation of Z-Source Inverters With Minimum Inductor Current Ripple

Abstract: This paper proposes the pulsewidth modulation (PWM) strategy of Z-source inverters (ZSIs) with minimum inductor current ripple. In existing PWM strategy with single-phase shoot-through, the shoot-through time interval is divided into six equal parts, therefore the three phase legs bear the equal shoot-through time interval. In this manner, the allotment and arrangement of the shoot-through state is easy to realize, but the inductor current ripple is not optimized. This causes to use relatively large inductors. In the proposed PWM strategy, the shoot-through time intervals of three phase legs are calculated and rearranged according to the active state and zero state time intervals to achieve the minimum current ripple across the Z-source inductor, while maintaining the same total shoot-through time interval. The principle of the proposed PWM strategy is analyzed in detail, and the comparison of current ripple under the traditional and proposed PWM strategy is given. Simulation and experimental results on the series ZSI are shown to verify the analysis.

Accurate Capacitor Voltage Ripple Estimation and Current Control Considerations for Grid-Connected Modular Multilevel Converters

Abstract: In this paper, the analytical solution for the submodule voltage ripple equations of a modular multilevel converter (MMC) is derived, based on the knowledge of the external voltage/current magnitudes, and enhancing a concept previously presented in the literature. In order to achieve high accuracy, all passive elements of the converter, common-mode voltage injection as well as intentionally imposed circulating current harmonics are taken into consideration. The natural charge level mechanism of the capacitor voltages is also explained. As application examples, the three- as well as the two-phase grid-connected MMC cases are chosen. The control of line and circulating currents is also discussed and two respective independent feedback loops are formed. The concept of fictive-axis emulation is tailored for the two-phase MMC case, in order to achieve vector control of the line current and therefore straightforward desired injection of active and reactive power. Finally, the development of a reduced-scale laboratory prototype is presented and a full set of experimental results are provided, verifying the aforementioned concepts.

An Active Power-Decoupling Method for Single-Phase AC–DC Converters

Abstract: This paper presents an active topology for power decoupling in single-phase ac-dc converters, featuring the effective suppression of low-frequency power ripple which is an inherent problem in single-phase energy conversion systems. This topology is composed of an H-bridge circuit and a ripple power-decoupling circuit. The ripple power-decoupling circuit shares one bridge arm with the H-bridge circuit so it has less additional components: just one IGBT, one diode, and an energy-storage inductor. Its modulation strategy is properly devised to coordinate the operation of decoupling circuit and H-bridge circuit. To enhance the power-decoupling performance, a direct ripple power-cancellation method based on energy-storage inductor is proposed. A multiresonant controller with feed-forward control is introduced for fast and precise current tracking. The effectiveness of this topology has been verified by detailed simulation studies as well as the laboratory prototype experiment results.

Minimization of Grid Current Distortion in Parallel-Connected Converters Through Carrier Interleaving

Abstract: Identical parallel-connected converters with unequal load sharing have unequal terminal voltages. The difference in terminal voltages is more pronounced in case of back-to-back connected converters, operated in power circulation mode for the purpose of endurance tests. In this paper, a synchronous reference-frame-based analysis is presented to estimate the grid current distortion in interleaved grid-connected converters with unequal terminal voltages. Influence of carrier interleaving angle on rms grid current ripple is studied theoretically as well as experimentally. Optimum interleaving angle to minimize the rms grid current ripple is investigated for different applications of parallel converters. The applications include unity power factor rectifiers, inverters for renewable energy sources, reactive power compensators, and circulating-power test setup used for thermal testing of high-power converters. Optimum interleaving angle is shown to be a strong function of the average of the modulation indices of the two converters, irrespective of the application. The findings are verified experimentally on two parallel-connected converters, with a circulating reactive power of up to 150 kVA between them.

Open-Circuit Fault Diagnosis in Interleaved DC–DC Converters

Abstract: Interleaved dc-dc converters have been widely applied, because of their benefits related to efficiency, size, thermal management, modularity, and output current ripple cancellation. These converters present an enhanced fault tolerance capability, but an open-circuit fault can leads to ripple beyond load requirements. This paper presents a fault-diagnostic method for interleaved dc-dc converters using only the dc-link current derivative sign features. The dc-link current derivative is thoroughly studied for both healthy and faulty modes. Its sign variation during different time intervals defined by the number of switches in conduction mode contains important information for open-circuit fault detection. The presented method is robust to transients and current imbalance between phases and no additional sensors are required. A photovoltaic system application is presented to validate this method.

An Active Low-Frequency Ripple Control Method Based on the Virtual Capacitor Concept for BIPV Systems

Abstract: This paper proposes an active low-frequency ripple control device (ALFRCD) based on virtual capacitor concept for building-integrated photovoltaic (BIPV) systems. With this method, the power quality of the BIPV system can be enhanced, and the lifetime and reliability are superior by reducing electrolytic capacitors. The low-frequency ripple current caused by the single-phase inverter can be compensated promptly by introducing a current integrator instead of unit feedback in the control strategy of the ALFRCD. With this current integrator, the device is unable to output dc current, which is similar to the function of a capacitor. Compared with the conventional method with high-pass filter, the presented method can achieve better compensation efficiency at most of the low frequencies and the response speed is superior as well. In addition, only one more integrator is needed in the control loop, which indicates the conciseness of the method. The performance is analyzed and the design algorithm is introduced in detail. Simulations and experimental results verified the proposed method's reliability and superiority in comparison with the method with high-pass filter and a proportional-integral controller.

Current-Ripple Prediction for Three-Phase PWM Converters

Abstract: The three-phase pulsewidth-modulation (PWM) converter is one of the most widely used topologies for power conversion In order to design PWM methods, the influence of PWM methods on the current ripple is needed This paper studies the current ripple of a three-phase PWM converter with general PWM methods for the design and control of this kind of converter The current ripple is analyzed with eight different Thevenin equivalent circuits for the eight different voltage vectors Then, the current-ripple slope and effective time could be achieved for every period The current ripple could be predicted with both peak and rms values Analytical predicted results show that discontinuous PWM could generate obviously bigger current ripples than space vector PMW for both peak and rms values with the same conditions Simulation and experiments are built to verify the analytical results, proving that the theoretical prediction is valid This analysis provides the basis for the design and control of the PWM method for converters

Combined Unipolar and Bipolar PWM for Current Distortion Improvement During Power Compensation

Abstract: To eliminate leakage ground current while achieve high efficiency, many transformerless photovoltaic inverters with unipolar pulse width modulation (UP-PWM) have been proposed and verified with real power injection only. However, in 2011, German standard VDE-AR-N 4105 updated the requirement that the inverters should satisfy the power factor from 0.9 leading to 0.9 lagging at power level higher than 4.6 kVA. When compensating the reactive power under a leading power factor, the inverter with UP-PWM might not have sufficient voltage to magnetize the inductor, which results in current distortion at zero crossing. It is hard to comply with the requirement of 1% displacement-factor accuracy. The reactive power can be well compensated with a bipolar PWM (BP-PWM) scheme; however, this will result in high current ripple and high switching loss. In this study, for reducing the current distortion under leading power factors and increasing the inductor current in the negative power region, UP-PWM is changed to BP-PWM. While in the positive power region, the inverter operation is still kept with UP-PWM to yield higher efficiency and lower current ripple. The proposed combination of UP-PWM and BP-PWM can improve the current distortion and reduce THD, while still can sustain high efficiency even with the power factors other than unity. Experimental results measured from a 5 kVA PV inverter have verified the analysis and discussion of the proposed approach.

Design of a Low-Torque-Ripple Fractional-Slot Interior Permanent-Magnet Motor

Abstract: Despite a strong nonlinear behavior and a complex design, the interior permanent-magnet (IPM) machine is proposed as a good candidate among the PM machines owing to its interesting peculiarities, i.e., higher torque in flux-weakening operation, higher fault tolerance, and ability to adopt low-cost PMs. A second trend in designing PM machines concerns the adoption of fractional-slot (FS) nonoverlapped coil windings, which reduce the end winding length and consequently the Joule losses and the cost. Therefore, the adoption of an IPM machine with an FS winding aims to combine both advantages: high torque and efficiency in a wide operating region. However, the combination of an anisotropic rotor and an FS winding stator causes some problems. The interaction between the magnetomotive force harmonics due to the stator current and the rotor anisotropy causes a very high torque ripple. This paper illustrates a procedure in designing an IPM motor with the FS winding exhibiting a low torque ripple. The design strategy is based on two consecutive steps: at first, the winding is optimized by taking a multilayer structure, and then, the rotor geometry is optimized by adopting a nonsymmetric structure. As an example, a 12-slot 10-pole IPM machine is considered, achieving a torque ripple lower than 1.5% at full load.

Calculation of Output Voltage Ripple and Design Considerations of SEPIC Converter

Abstract: In this paper, a design method is proposed for finding the equivalent inductance and capacitance of the single-ended primary-inductor converter (SEPIC). The relations of the output voltage ripple (OVR) of the SEPIC converter are obtained in complete inductor supply mode-continuous conduction mode (CISM-CCM), incomplete inductor supply mode-CCM (IISM-CCM), and IISM-discontinuous conduction mode (IISM-DCM). The maximum of OVR (MOVR) is investigated for a specified range of the input voltage and load resistance. This value of the MOVR is obtained for the minimum values of input voltage and load resistance. In this paper, the minimum values of the equivalent inductance and capacitance are calculated in obtaining the minimum value of the MOVR. One of the other performed studies in this paper is calculation of the switch peak current in CCM and DCM. In addition, the converter is designed based on the minimum values of the MOVR and stress of the switching current. Experimental and simulation results are used to prove the validity of the presented theoretical subjects.

Bandwidth-tunable narrowband rectangular optical filter based on stimulated Brillouin scattering in optical fiber.

Abstract: We propose a rectangular optical filter based on stimulated Brillouin scattering (SBS) in optical fiber with bandwidth tuning from 50 MHz to 4 GHz at less than 15-MHz resolution. The rectangular shape of the filter is precisely achieved utilizing digital feedback control of the comb-like pump spectral lines. The passband ripple is suppressed to ~1 dB by mitigating the nonlinearity influences of the comb-like pump lines generated in electrical and optical components and fibers. Moreover a fiber with a single Brillouin peak is employed to further reduce the in-band ripple and the out-of-band SBS gain at the same time. Finally, we analyze the noise performance of the filter at different bandwidth cases and demonstrate the system performance of the proposed filter with 2.1-GHz bandwidth and 19-dB gain by amplifying a 2-GHz orthogonal frequency-division-multiplexing (OFDM) signal with quadrature-phase-shift-keying (QPSK) and 16-quadrature-amplitude-modulation (16-QAM) on each subscriber.

On the Voltage Ripple Reduction Control of the Linear Switched Reluctance Generator for Wave Energy Utilization

Abstract: This paper discusses about the voltage output ripple reduction and error minimization for the direct-drive, linear switched reluctance generator (LSRG)-based wave power generation system. First, the concept of the LSRG-based wave power generation system is studied. According to the characteristics of the LSRG, the suitable drive circuit dedicated to proper current excitation and generation is established. Second, the reasons that cause voltage output ripples are investigated. To reduce the remarkable ripples from phase current commutations, a current distribution function (CDF) is proposed based on the minimized copper loss principle. Third, the dual-loop control strategy with current and voltage as the inner and outer loop is constructed, implemented with the proposed CDF. Theoretical bases of the control strategy are derived. The simulation results prove that the proposed control algorithm is capable of voltage ripple suppression and error reduction within the range of ±0.5 V over the entire operation speed for wave energy extraction, validated by experimental verification.

A dual voltage control strategy for single-phase PWM converters with power decoupling function

Abstract: The inherent double line ripple power in single-phase systems is adverse to the performance of power electronics converters, e.g., limited lifetime due to the requirement of large electrolytic capacitors and low voltage control bandwidth due to harmonic disturbance. In this paper, an active converter topology based on a symmetrical half-bridge circuit is proposed to decouple the ripple power so that balanced instantaneous power flow is assured between source and load, and the required dc-link capacitance can be dramatically reduced. For proper closed-loop regulation, the small signal modeling of the proposed system is presented, and a dual voltage control strategy is then proposed, which comprises one voltage loop implemented in the synchronous reference frame for active power balancing, and another one implemented in the stationary reference frame for ripple power compensation. Special attention is given to the bandwidth of voltage control loops because the variation of dc-link voltage should be kept within an acceptable range during load transients. This is particularly important for systems with reduced dc-link capacitance because they are of lower energy capacity, and the dc-link voltage is therefore very sensitive to step load changes. Comprehensive simulation and experimental results are presented to show the effectiveness of the proposed circuit and control algorithm.

Small-Signal Analysis and Optimal Design of External Ramp for Constant On-Time V $^{\bf 2}$ Control With Multilayer Ceramic Caps

Abstract: Recently, constant on-time V2 control, and its variety named constant on-time control, or constant on-time ripple-based control is more and more popular in industry products due to features of high light-load efficiency, simple implementation, and fast transient response. However, subharmonic oscillation occurs when using multilayer ceramic caps due to the lagging phase of the capacitor voltage relative to the inductor current. External ramp compensation is one simple solution to solve the instability issue. However, the characteristics of constant on-time V2 control with external ramp are not fully understood and no explicit design guidelines for the external ramp are provided. This paper investigates the small-signal characteristics of constant on-time V2 control with external ramp compensation by providing a factorized, easy-to-use small-signal model. The external ramp is a critical parameter because it directly affects the position and damping of two pairs of double poles. Based on this fact, design guidelines of the external ramp for optimal dynamic performance are provided. Moreover, the effect of duty cycle is investigated. Finally, the small-signal experimental results and load transient performance are presented to verify the small-signal analysis and proposed design guideline.

A Novel Quasi-Resonant Bridge Modular Switched-Capacitor Converter With Enhanced Efficiency and Reduced Output Voltage Ripple

Abstract: A novel quasi-resonant bridge modular switched-capacitor converter (BMSCC) is proposed in the paper. The main merit is that its resonant circuit has high stability and simplicity, resulting from the employment of the stray inductance distributed in the circuit as a collective resonant inductor. Accordingly, the current spike during switching operation is removed due to zero-current-switching (ZCS) realization. Another distinct merit is that the proposed converter features symmetric construction. With this kind of construction, the voltage ripple of charge/pump capacitors can be cancelled out with each other and then output voltage ripple will be largely reduced. Thus, it is unnecessary to use a bulky capacitor to reduce output voltage ripple. Compared with conventional SCCs, at the same conversion ratio, the BMSCC with symmetric construction requires fewer switches and capacitors with lower voltage stress, so as to cut the size and cost and promote the power destiny further. It is also noteworthy that the symmetric construction character assures that the two symmetric parts can work independently under a simplified control strategy. In addition, the modular configuration contributes to convenient voltage extension conveniently. The simulation and experimental results of a 100 W prototype with a voltage conversion ratio of eight validate the principle and features of this topology.

A General Current Ripple Prediction Method for the Multiphase Voltage Source Converter

Abstract: Current ripple is generated by pulse width modulation (PWM) switching in multiphase voltage source converters (VSCs). This letter introduces a general and fast current ripple prediction method for multiphase VSCs with arbitrary phase numbers. An equivalent converter-load model is derived for the n -phase converter system. By combining the common-mode voltage of both converter terminal and load, the equivalent circuit for each phase can be modeled. The voltage dropping on the ac inductor can be calculated for the 2 n + 2 zones in each switching cycle based on the equivalent circuit for each phase. Then the current ripple can be reconstructed based on the linear di/dt model in each zone. Simulation examples of five- and six-phase converters prove that the current prediction method is accurate. With this real-time prediction method, the current ripple can be controlled in application. An application example of five-phase variable switching frequency PWM is introduced to control the peak current ripple and reduce the switching losses.

A Family of Dual-Phase-Combined Zero-Current Switching Switched-Capacitor Converters

Abstract: A family of dual-phase-combined resonant switched-capacitor (SC) converters with a similar structure is presented in this paper. Comparing with their conventional single-phase version, each of the proposed dual-phase converters is more than just a switched capacitor but also provides the service of two phases operated in the fully complementary manner. This design provides a more stable output voltage with low ripple and significantly reduces the quantity of switches. These converters therefore have the common features of smaller size, lower cost, and higher power density than the conventional multiphase SC converters. With the zero-current switching technique, the proposed converters also possess high-power conversion efficiency. The detailed analysis of the circuit operation and voltage ripples is presented. Experimental results are also provided to confirm the performance of the new family of converters.

Validation of a clinical assessment of spectral-ripple resolution for cochlear implant users.

Abstract: Objectives Nonspeech psychophysical tests of spectral resolution, such as the spectral-ripple discrimination task, have been shown to correlate with speech-recognition performance in cochlear implant (CI) users. However, these tests are best suited for use in the research laboratory setting and are impractical for clinical use. A test of spectral resolution that is quicker and could more easily be implemented in the clinical setting has been developed. The objectives of this study were (1) To determine whether this new clinical ripple test would yield individual results equivalent to the longer, adaptive version of the ripple-discrimination test; (2) To evaluate test-retest reliability for the clinical ripple measure; and (3) To examine the relationship between clinical ripple performance and monosyllabic word recognition in quiet for a group of CI listeners. Design Twenty-eight CI recipients participated in the study. Each subject was tested on both the adaptive and the clinical versions of spectral ripple discrimination, as well as consonant-nucleus-consonant word recognition in quiet. The adaptive version of spectral ripple used a two-up, one-down procedure for determining spectral ripple discrimination threshold. The clinical ripple test used a method of constant stimuli, with trials for each of 12 fixed ripple densities occurring six times in random order. Results from the clinical ripple test (proportion correct) were then compared with ripple-discrimination thresholds (in ripples per octave) from the adaptive test. Results The clinical ripple test showed strong concurrent validity, evidenced by a good correlation between clinical ripple and adaptive ripple results (r = 0.79), as well as a correlation with word recognition (r = 0.7). Excellent test-retest reliability was also demonstrated with a high test-retest correlation (r = 0.9). Conclusions The clinical ripple test is a reliable nonlinguistic measure of spectral resolution, optimized for use with CI users in a clinical setting. The test might be useful as a diagnostic tool or as a possible surrogate outcome measure for evaluating treatment effects in hearing.

Design Optimization of a Double-Sided Hybrid Excited Linear Flux Switching PM Motor With Low Force Ripple

Abstract: This paper describes design techniques for a doublesided hybrid excited linear flux switching permanent magnet motor to achieve low force ripple while satisfying the required average thrust force. In this paper, we employ auxiliary poles fixed to both sides of the mover and determine the switching signal turn-on angle to reduce the force ripple in the initial design. Then, the sensitivity analysis of two split ratios is conducted to provide a feasible search direction for the optimization process. Finally, a finite-element-based optimization is utilized to minimize the force ripple and to satisfy the required average thrust force. Simulation results are validated by experimental measurement.

A Soft Switching Full Bridge Converter With Reduced Parasitic Oscillation in a Wide Load Range

Abstract: A phase-shift zero voltage switching (ZVS) pulse width modulation full-bridge converter with reduced parasitic oscillation across the rectifier is proposed. The introduced auxiliary transformer used as a voltage source forces the primary current commutating in advance. Parasitic voltage oscillation at secondary is well reduced and there is no duty cycle loss. ZVS of primary switches can be achieved in much wide load range with the help of an auxiliary coupled inductor, and the main transformer continuously transfers energy to load in a whole switching cycle, resulting in no circulating time, and ripple current flowing through the output filter inductor decreases significantly. In this paper, operation principle of the circuit is analyzed in detail. Besides, discussion of key characteristics and design considerations are also included. Finally, experimental results from a 480-W/48-V, 100-kHz prototype are presented to confirm the superior features of the proposed converter.

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

Abstract: 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.

Suppression of injection voltage disturbance for High Frequency square-wave injection sensorless drive with regulation of induced High Frequency current ripple

Abstract: In square wave voltage signal injection sensorless drive, the injection voltage can be distorted by the inverter nonlinearity effects especially when the injection voltage is low. If that happens, High Frequency (HF) current signal which contains the rotor position information could be also distorted, which directly leads to an error in the position estimation. This paper analyzes the effects of the inverter nonlinearity to injection voltage, to induced current ripple, and to the position estimation performance in sequence and proposes a voltage injection method to minimize the impact of the inverter nonlinearity by the regulation of HF current ripple. By simulations and experiments, performance of the proposed method has been verified. The experimental results show 34.9% reduction of noise input in the position estimation and 19.7% improvement of the position estimation performance under 15% of rated voltage signal injection.

Diagnosis of PEM Fuel Cell Drying and Flooding Based on Power Converter Ripple

Abstract: This paper discusses the possibility to use the current ripple introduced by switch mode power converters for low-cost monitoring of polymer electrolyte membrane (PEM) fuel cell (FC) state-of-health, suitable for commercial applications that cannot afford dedicated instrumentation. In more details, an estimate of the ohmic resistance, which is a good indicator of the membrane water content, can be obtained from the high-frequency ripple response by data processing in the frequency domain, while lower frequency ripple at 100/120 Hz (when present) is in the typical frequency range of activation processes. All the available impedance estimates, together with the dc voltage measurement, can be used to promptly detect FC drying and flooding, that are the two opposite failure modes as far as water balance is concerned. The proposed diagnostic approach is tested on a single PEM FC in drying and flooding conditions, by emulating three-phase and single-phase inverter ripples by means of an electronic load.

A Continuous-Time Ripple Reduction Technique for Spinning-Current Hall Sensors

Abstract: This paper presents a new ripple-reduction technique for spinning-current Hall sensors, which obviates the need for low-pass filtering to suppress the ripple caused by up-modulated sensor offset. A continuous-time ripple-free output is achieved by the use of three ripple reduction loops (RRLs), which continuously sense the offset ripple and then use this information to drive a feedback loop that cancels sensor offset before amplification. Since no low-pass filter is involved, the bandwidth of the resulting system can be much higher than the spinning frequency. Moreover, since the front-end no longer has to process sensor offset, the requirements on its dynamic range can be significantly relaxed. A prototype system consisting of a Hall sensor readout system realized in a 0.18 μm CMOS process was combined with three off-chip RRLs realized with off-chip electronics. At a spinning frequency of 1 kHz, the RRLs reduce the offset ripple by more than 40 dB to about 10 μT, while also achieving low offset (25 μT) and wide bandwidth (over 100 kHz).