Local Voltage Research Articles

Fuel starvation in automotive PEMFC stacks: hydrogen stoichiometry and electric cell-to-cell interaction

Fuel gross starvation (FGS) in a polymer electrolyte membrane fuel cell is an error state, during which the supplied amount of fuel is insufficient to sustain the requested electrical current. A novel experimental technique was developed to intentionally provoke well-controlled fuel starvation situations of one single cell in a multi-cell fuel cell stack. This modification was implemented in a 20 cell stack of automotive-sized cell geometry and carbon composite bipolar plates (BP). The intentional fuel starvation situation was analyzed using a printed circuit board to measure the current density distribution (CDD) in addition to a multipoint cell voltage monitoring (CVM) to measure local cell voltages. The provoked detrimental subsidiary reactions of the anode were found to take place spatially separated from the normal hydrogen oxidation reaction. It was therefore possible to determine and intentionally vary the hydrogen stoichiometry of the fuel starved cell. This error state caused intense distortions of the starved cells CDD and local cell voltages. The maximum difference obtained between outlet and inlet voltage of the modified cell was 1.4 V. Compared to the average current density, a more than 4-times higher maximum local current density was measured in the affected cell. Adjacent cells were also affected via electric cell-to-cell interaction. Characteristic patterns therefore became visible in the cell voltage distribution, measured by the inlet and outlet CVM. The use of carbon composite BP is favoring the occurrence of these patterns due to their relatively high electric sheet resistance. Using the new hardware setup, we could investigate the relation between the hydrogen stoichiometry of the affected cell during FGS and the observed irregular redistribution of current density and local cell voltages.

Research on Voltage Coordinated and Stability Control of Condensers Based on Reactive Power Replacement

Abstract In this research, we investigated condenser voltage coordination and stability control systems by analyzing voltage coordinated control mode among excitation, voltage coordination and stability as well as automatic-voltage reactive power control systems. By using dynamic excitation regulation and steady-state regional voltage source control replacement, dynamic reactive power quickly output under fault condition as well as optimized regional reactive power under steady state were realized. The correctness and practicability of the proposed strategy was verified through engineering application. Adopting the reactive power displacement of voltage coordination control system to solve local voltage instability problem after UHV DC blocking. The proposed method realized multi-time scale emergency, recovery and steady-state control of the system under steady and dynamic states.

Scanning Electrochemical Probe Lithography for Ultra-Precision Machining of Micro-Optical Elements with Freeform Curved Surface.

Two challenges should be overcome for the ultra-precision machining of micro-optical element with freeform curved surface: one is the intricate geometry, the other is the hard-to-machining optical materials due to their hardness, brittleness or flexibility. Here scanning electrochemical probe lithography (SECPL) is developed, not only to meet the machining need of intricate geometry by 3D direct writing, but also to overcome the above mentioned mechanical properties by an electrochemical material removal mode. Through the electrochemical probe a localized anodic voltage is applied to drive the localized corrosion of GaAs. The material removal rate is obtained as a function of applied voltage, motion rate, scan segment, etc. Based on the material removal function, an arbitrary geometry can be converted to a spatially distributed voltage. Thus, a series of micro-optical element are fabricated with a machining accuracy in the scale of 100 s of nanometers. Notably, the spiral phase plate shows an excellent performance to transfer parallel light to vortex beam. SECPL demonstrates its excellent controllability and accuracy for the ultra-precision machining of micro-optical devices with freeform curved surface, providing an alternative chemical approach besides the physical and mechanical techniques.

Hierarchical coordination scheme for voltage-aware fast frequency provision with flexible loads

Fast-frequency reserve (FFR) is required to counteract the limited system damping in renewable-rich power systems. Several distributed resources, such as batteries, PVs, and thermal loads, suit this role. However, since the devices are located in distribution grids, local constraints must be considered in the control design. In this work, a coordination scheme is developed to provide FFR without local frequency measurements while using limited communication to the central agent and a neighborhood support system to support local voltages. The proposed scheme is tested through time-domain simulations under diverse grid conditions. The coexistence with other local droop control is evaluated, demonstrating how different types of units with flexible active and reactive power production/consumption can coexist with this scheme. The results highlight that the coordination scheme is a promising alternative to local droop control and can coexist with other schemes.

Voltage regulation during short-circuit faults in low voltage distributed generation systems

As the penetration of inverter-based distributed generations into microgrids continues to rise, the significance of power electronic inverters in modern power systems becomes increasingly pronounced. They are designed to have fault ride-through capabilities, enabling them to sustain operation even during and after fault conditions. This paper presents a novel voltage compensation strategy based on the line impedances addressing both positive and negative-sequence aspects, for a three-phase three-wire inverter deployed to regulate the low-voltage network during unsymmetrical faults, thereby preserving voltage stability. The control strategy is carried out in a synchronous reference frame (dq) to govern the positive and negative-sequence voltages and currents of the inverter. By synthesizing AC currents, the inverter restores the positive-sequence voltage to its rated value while mitigating negative-sequence voltage at the point of common coupling arising from unsymmetrical faults. Through MATLAB/Simulink, are investigated three unsymmetrical fault scenarios (single line-to-ground, line-to-line, and double line-to-ground faults) within the low-voltage distribution network of the 18-bus European Cigré, incorporating three inverters equipped with the proposed voltage support capability. The results confirm that inverter-interfaced distributed generators with local voltage support can improve the system’s fault ride-through capability by reducing voltage drops and unbalances.

Research on optimization and improvement method of new energy access grid stability based on transient stability margin index

Abstract This paper focuses on the potential local voltage stability risks and transient stability margin decline in the power grid after the large-scale integration of new energy. Based on the transient stability margin index of the power grid, a method for evaluating and optimizing the transient stability margin after the integration of wind power into the power grid is proposed. This paper provides guidance for the grid connection points and voltage level determination of the wind power access system during the planning phase, as well as the configuration of reactive power compensation devices such as SVGs.

Quantitative and qualitative assessment of left atrial cardiomyopathy as well as prediction of atrial fibrillation recurrences upon PVI using machine learning

Abstract Introduction Atrial fibrillation (AF) is one of the most common heart pathologies in daily clinical practice and confers significant mortality and morbidity. However, AF ablation often proves ineffective - even after successful pulmonary vein isolation (PVI). The prediction of PVI failure for the long-term treatment of AF as well as the improved assessment of the underlying substrate appears pivotal. We hypothesize, that ML can be applied to better characterize the substrate and recurrence in AF patients upon PVI. Methods & Results We retrospectively evaluated data from 205 patients that underwent AF ablation between 2019 and 2023, including high-density 3D electroanatomic maps (sinus rhythm), LA rotational angiography, invasive LA hemodynamic measurements (after transseptal passage), echocardiography, 12-lead ECG and laboratory testing. A neuronal net was trained on selected features extracted from those datasets using supervised learning and employed to predict measures of atrial cardiomyopathy and AF recurrence. Patients were 66±1 years old and received first or second pulmonary vein isolation (PVI) for paroxysmal atrial fibrillation with 18% documented recurrences upon a mean follow-up of 23±1months. First, we extensively refined or developed tools for automated P-wave analysis from 12-lead ECGs as well as local LA voltage and volume quantification. Next, LA hemodynamics and volumes were assessed: Mean LA volume as derived from rotational angiography significantly correlated with LA volume index as obtained using echocardiography. Interestingly, LA size showed no correlation with NT-proBNP, LA low voltage or LA hemodynamics. In addition, global (25±2% of total LA area) and local (i.e. anterior, posterior, roof) LA voltage was determined and shown to be an independent predictor of AF recurrence. In our first unselected subset of 136 patients with 2nd PVI for atrial fibrillation, our ML models predicted LA fibrosis (i.e. low voltage regions; Utah stage) from 12-lead ECGs with an accuracy of 90%. Accuracy was 87% for the prediction of AF recurrences from LA pressure and low-voltage regions. In addition, the algorithm predicted AF recurrences from 12-lead SR ECGs obtained before PVI with an accuracy of 91%. Conclusion Artificial neural networks allow to quantitatively and qualitatively predict measures of atrial cardiomyopathy and atrial fibrillation recurrence probability upon complete PVI with high accuracy.Figures

Spatial relationship between left peri-atrial fat with underlying arrhythmogenic substrate in patients with atrial fibrillation - innocent bystander or culprit?

Abstract Introduction Peri-atrial fat may have pro-inflammatory and pro-fibrotic effects on atrial myocardium and increase the risk of developing atrial fibrillation. Consistent with prior evidence, we have previously shown that peri-atrial fat volume, but not fat attenuation (an imaging biomarker of inflammation), was associated with prevalent atrial fibrillation. Whether this association is secondary to "outside-to-inside" tissue cross talk with local adverse electrical remodelling of adjacent atrial cardiomyocytes is not known. Purpose In this novel proof of concept study, we aimed to identify a spatial relationship between left peri-atrial fat and potentially arrhythmogenic substrate (low voltage areas and slow conduction pathways) in the left atrial myocardium. Methods Contrast-enhanced cardiac computed tomography (CT) imaging and electroanatomic mapping, during coronary sinus pacing, were performed pre-ablation in atrial fibrillation patients (n=27). The left atrium and surrounding peri-atrial fat were segmented and quantified using seg3D2 and CEMRGapp. We performed registration of the electroanatomic map onto the CT-derived left atrial mesh using OpenEP and EP Workbench. Mean fat volume and attenuation around each electroanatomic point (within a 3mm radial region of interest) were correlated with local voltage and conduction velocity. Results A total of 24,839 electroanatomic points were registered onto the 3D CT-derived left atrial mesh, with a median of 935 points (range 673 to 1150) per patient. The average bipolar voltage and conduction velocity in the left atrium was 1.92±1.91 mV and 0.66±0.47 ms-1 respectively. In comparison to areas with little/no surrounding periatrial fat (Quartile 1, ≤0.93 mm3 fat per electroanatomic point), areas with the highest burden of fat (Quartile 4, ≥17.6 mm3) had significantly lower bipolar voltage (1.69±1.7 vs 2.09±2.0 mV, p<0.001) and conduction velocity (0.627±0.43 vs 0.700±0.47 ms-1, p<0.001). However, the overall correlation between periatrial fat volume with bipolar voltage (r=-0.06, p<0.001) and conduction velocity (r=-0.07, p<0.001) was weak. High, not low, fat attenuation (Quartile 4; >-46.5HU vs Quartile 1; ≤-75.5HU) was associated with increased bipolar voltage (2.23±2.1 vs 1.63±1.6 mV) and conduction velocity (0.703±0.42 vs 0.623±0.39 ms-1 respectively). Conclusion There is a weak correlation between periatrial fat and localized adverse electrical remodelling. The relationship between fat attenuation and electrophysiological properties was inverted. These findings confirm an association between peri-atrial fat burden but call question as to whether peri-atrial fat inflammation is implicated in atrial fibrillation pathogenesis.

Real-time characterization of radiofrequency lesions by local multifrequency impedance with thermal correction

Abstract Background/Introduction Recent studies have shown that measuring local impedance (LI) at a single frequency can be useful for real-time characterization of radiofrequency (RF) lesion size during arrhythmia ablation procedures. (1) However, these systems do not take into account the effect of the increase in tissue temperature on the impedance measurement itself, which could be avoided by comparing the impedance at different frequencies. Purpose The aim of this study was to evaluate the ability of local multifrequency impedance (LMI) to characterize the size of RF lesions in real-time, while correcting for the thermal effect on the measurement. Methods Lesions were performed on the epicardium in 5 anesthetized pigs while measuring IML (from 1 to 209 kHz) before, during, and after ablations (20W/30W/40W, 60s, >10g) through a conventional irrigated electrocatheter connected to a cardiac navigation system and a RF generator. In these measurements, the thermal effect on the tissue was corrected by assuming that the changes in impedance at high frequency were only due to the temperature variation and not to the injury itself. Local voltage (Vuni) was also measured before and after ablations, and catheter-measured temperature and contact force were monitored. At the end of the procedure, the animals were sacrificed, and a histological study of the lesions was performed. Results A total of 43 effective lesions (11±2 per animal) were performed. The 40W lesions were deeper and wider than the 20W lesions (6,6 ± 3,3 mm vs. 5,4 ± 2,0 mm vs. 4,0 ± 1,9 mm; ANOVA p<0.05) and presented a significant decrease in unipolar voltage that was similar among the different lesions (40W vs. 20W: 56% vs. 40%; ANOVA p=ns; Figure). Four seconds after the start of the ablation the 40W lesions had a greater decrease in IML than the 30W and 20W lesions (73±14Ω vs. 85±4Ω vs. 100±12Ω; ANOVA p<0.05). After thermal adjustment, IML recorded 30 and 55 seconds after the start of the ablation correlated better with the final depth of the lesion than IL or Vuni (Table). Conclusions The measure of IML during ablation allows a better quantification of the changes in the structural characteristics of myocardial tissue than local impedance at a single frequency. The increase in tissue temperature during ablation influences the values of local impedance and should be considered when creating new impedance-based metrics to predict the chronic size of the RF lesion.Figure.Lesion quantification by LMITable.Correlation analysis

Rhythm matters: sinus and pace rhythm map significantly differ in endo/epicardial 3D electroanatomic mapping

Abstract Introduction Left ventricular substrate assessment utilizing ultra-high density multipolar catheters is frequently used to guide ablation procedures in patients with scar related ventricular tachycardia. However, 3D electroanatomic mapping is often performed during either sinus or paced rhythm. The effect of the modality (sinus vs. paced) used during mapping on substrate assessment remains elusive. Methods and Results We compared biventricular endo- and epicardial 3D high-density voltage and activation maps in sinus- and right ventricular-paced rhythm in domestic pigs. Data was acquired using a 20-polar mapping catheter with a cardiac tissue proximity filter based on catheter location and impedance measurements. Ventricular pacing (120 bmp) was performed with a permanent pacemaker electrode in right ventricular septal position, and high-density maps were acquired from the endo- and epicardium in sinus and paced rhythm (criterion for low voltage: <0.5 mV). Electroanatomical voltage and activation high-density (>6500 points per heart) mapping were performed with sufficient coverage in the right and left ventricles and the epicardium. The size of the low voltage area varied significantly between sinus and right ventricular-paced rhythm, particularly in epicardial mapping. In SR, the total low voltage was 7.2 ± 5.8%, while 11.1 ± 0.03% in paced rhythm. SR and paced maps revealed e.g. low voltage areas in the basal to apical anterior wall corresponding to the LAD regions, however, this was especially pronounced in sinus maps (e.g. pig 1: 64.2 cm²) compared to the paced rhythm map (e.g. pig 1: 32.8 cm²). Conclusion The extent of low voltage regions differed significantly in RV/LV, endo- and epicardially. Sinus maps showed the most accurate electrical representation of local voltage and corresponded correctly to local anatomical landmarks like e.g. the LAD with its surrounding epicardial fat tissue.3D biventricular epicardial voltage map

An Enhanced Power Allocation Strategy for Microgrids Considering Frequency and Voltage Restoration

In a microgrid, load power should be properly shared among multiple distributed generation (DG) units, not only for fundamental power but also for negative sequence and harmonic power. In this paper, the operation of a microgrid under imbalance and nonlinear load conditions is studied, and a consensus algorithm-based distributed control strategy is proposed for the microgrid power allocation, frequency, and voltage restoration. First of all, the output current of DG unit is decomposed by second-order generalized integrator (SOGI) modules to obtain the fundamental power and harmonic power through the power calculation formula. Then, state values of DG units, such as local power, frequency, and voltage, are transmitted on a sparse communication network. Under the action of a consensus algorithm, the real power of DG units is allocated following the equal increment principle; the reactive power, imbalance, and harmonic power are allocated according to the capacities of DG units; and the frequency of the microgrid and the voltage at the point of common coupling (PCC) are rated. In the consensus-based strategy, DG units only communicate with their neighbor units; thus, the “plug and play” function is reserved. Compared with the centralized control strategy, the proposed strategy with a distributed consensus protocol can simplify the maintenance and possible expansions of the system, making the microgrid more flexible. Moreover, as the structure of the detailed network is not required, it is easy to apply in practice. Simulation and experiment results are presented to verify the proposed method.

A coordinated voltage control scheme based on linearized power flow functions for non-optimal and optimal problems

This paper proposes a coordinated voltage control scheme for transmission systems based on linearized power flow functions to determine the set points of local control voltage devices. The scheme considers models and interactions between different devices to attain the appropriate performance (non-optimal or optimal) of the whole power system. The sensitivity analysis is used to formulate a partly linearized model that relates the voltage variations of buses to the reactive power variation of synchronous machines, settings of static VAr compensators (SVCs), shunt capacitors susceptance, and tap position of load tap changers (LTCs) to determine the set of the settings of the voltage control devices. Two formulations are proposed by considering the susceptance of SVCs or the slope and reference voltage of characteristics of SVCs as control variables. The developed formulation based on the linearized power flow functions provides the possibility of the practical implementation of the coordinated voltage control scheme, especially the optimal one, by reducing the model complexity and solving time. The performance of the proposed formulations is investigated by some studies of voltage control and an optimally coordinated problem on the IEEE 30-bus and IEEE 118-bus test systems.

Probabilistic photovoltaic generation and load demand uncertainties modelling for active distribution networks hosting capacity calculations

With the increasing integration of photovoltaic (PV) systems in active distribution networks (ADNs), accurate modelling of PV power generation and the network demand has become essential, especially for system operators (SO). However, existing studies have focused on deterministic representations of hourly profiles for PV generation and load consumption, which cannot thoroughly evaluate the existing uncertainties of PV power output and load demands. In this study, uncertain parameters load demand and PV power output profile will be modelled with forecasted values, and their profile will be obtained over probability density functions (PDFs). Firstly, a vast quantity of realistic load and PV generation profiles are produced over a day with 15-minute resolution, with a scenario generation method using the Monte Carlo methodology. Afterward, the generated scenarios are reduced to a set of scenarios to represent the span of all generated scenarios. A fully local reactive power regulation strategy is used in this study to evaluate the hosting capacity of the ADN. This proposed method is tested on modified 33-bus and 69-bus distribution test systems by using practical solar generation and load data. The proposed methodology results in the hosting capacity improvement by 20% besides the existing Q-Voltage and PF-Power local voltage control methods, where it has the flexibility to be implemented to any distribution feeder.

A Decentralized Voltage Regulation Scheme Using Improved Volt‐Var Function of PV Smart Inverter

With the growing distributed PV installation rate in distribution systems, voltage regulation difficulties such as local voltage violations and fluctuations have become common. To solve the voltage regulation problems, the local voltage regulation method using volt‐var (VV) function is effective for its high regulation speed, high accuracy, and flexibility. However, there are still hurdles on real application, such as parameter setting difficulties, insufficient voltage fluctuation mitigation effect, and unfairness of reactive power generation between PV customers. To further improve the VV function, this paper proposes a PID closed‐loop based VV function and mode‐switching function of PV smart inverter (SI). To validate the proposed methods, numerical simulations were conducted using a 6‐feeder distribution system model based on the JST‐CREST 126 distribution feeder model. According to the simulation result, the proposed method can better mitigate the local voltage violation compared to basic VV function based on the VV curve, also improve the fairness between PV customers, while the total reactive power generation and tap operations increases for the aim of more adequate voltage regulation. © 2024 The Authors. IEEJ Transactions on Electrical and Electronic Engineering published by Institute of Electrical Engineers of Japan and Wiley Periodicals LLC.

Real-time data acquisition inside high-pressure PEM water electrolyzer

This study used the micro-electro-mechanical systems (MEMS) technology to develop a high-pressure resistant flexible 7-in-1 microsensor (voltage, current, humidity, temperature, pressure, flow, and hydrogen). The microsensor is integrated with a flexible printed circuit (FPC) for real-time data acquisition of local voltage, current, humidity, temperature, pressure, flow, and hydrogen variations in different positions inside a high-pressure proton exchange membrane water electrolyzer (PEMWE). The goal of developing such microsensor is to observe the influence of temperature and pressure on the PEMWE. The operational safety of hydrogen is ensured by using a micro hydrogen sensor.

Non-Invasive Measurement of Impedance Spectra Distribution in Polymer Electrolyte Fuel Cells

Localized measurement of the impedance distribution in an operating polymer electrolyte fuel cell stack is of great importance in providing information on its state of health and performance. However, the current methods’ invasiveness is a brake to a more widespread utilization. This work presents a non-invasive way to measure and interpret local impedance spectra. It is based on local AC current supply and local voltage measurements performed all around the cell via conductive pins contacting the outer surface of the flow fields. The different local spectra are measured on a single cell within a 200 cm2 six-cell stack under different operation conditions and compared to a reference case with homogeneous current density. A simple equivalent electrical circuit is used to fit the impedance spectra and to extract membrane and charge transfer resistance. The variations of these two values are analyzed at five different positions along the channel for different cathode stoichiometries and gas flow configurations.

A 63% Efficiency 1.29-W Single-Link Multiple-Output (SLiMO) Isolated DC–DC Converter Using FPC Micro-Transformer With Local Voltage and Global Power Regulations

A 63% Efficiency 1.29-W Single-Link Multiple-Output (SLiMO) Isolated DC–DC Converter Using FPC Micro-Transformer With Local Voltage and Global Power Regulations

Coordinated frequency support strategy for VSC-HVDC integrated offshore wind farm system

The large-scale offshore wind power integrated into the onshore power grid through voltage source converter-based high voltage direct current (VSC-HVDC) system is unable to provide inertia response and frequency support to the onshore power grid. To improve the frequency characteristics of the receiving-end power grid, a coordinated frequency control strategy combining VSC-HVDC and offshore wind power is proposed. The onshore converter adopts virtual inertia control, which uses DC capacitors to absorb or release energy for inertia support after the receiving-end grid is disturbed. Wind-farm-side VSC (WFVSC) obtains the frequency signal of the receiving-end power grid by detecting the local DC voltage. The offshore wind farm (OWF) transfers the frequency deviation into an additional power signal and sends it to the power controller to adjust the output, thereby performing inertia and primary frequency response. In addition, a secondary frequency regulation strategy for wind farms has been designed to achieve non-difference frequency regulation of the receiving-end power grid. Finally, a simulation model of VSC-HVDC integrated OWF system is constructed to demonstrate the proposed coordinated frequency control strategy for VSC-HVDC and OWF. The results indicate that the proposed control strategy can effectively enhance the frequency support capability of the receiving-end power grid.

Area-weighted unipolar voltage to predict heart failure outcomes in patients with ischaemic cardiomyopathy and ventricular tachycardia.

Patients with ischaemic cardiomyopathy (ICM) referred for catheter ablation of ventricular tachycardia (VT) are at risk for end-stage heart failure (HF) due to adverse remodelling. Local unipolar voltages (UV) decrease with loss of viable myocardium. A UV parameter reflecting global viable myocardium may predict prognosis. We evaluate if a newly proposed parameter, area-weighted unipolar voltage (awUV), can predict HF-related outcomes [HFO; HF death/left ventricular (LV) assist device/heart transplant] in ICM. From endocardial voltage maps of consecutive patients with ICM referred for VT ablation, awUV was calculated by weighted interpolation of local UV. Associations between clinical and mapping parameters and HFO were evaluated and validated in a second cohort. The derivation cohort consisted of 90 patients [age 68 ±8 years; LV ejection fraction (LVEF) 35% interquartile range (IQR) (24-40)] and validation cohort of 60 patients [age 67 ± 9, LVEF 39% IQR (29-45)]. In the derivation cohort, during a median follow-up of 45 months [IQR (34-83)], 36 (43%) patients died and 23 (26%) had HFO. Patients with HFO had lower awUV [4.51 IQR (3.69-5.31) vs. 7.03 IQR (6.08-9.2), P < 0.001]. A reduction in awUV [optimal awUV (5.58) cut-off determined by receiver operating characteristics analysis] was a strong predictor of HFO (3-year HFO survival 97% vs. 57%). The cut-off value was confirmed in the validation cohort (2-year HFO-free survival 96% vs. 60%). The newly proposed parameter awUV, easily available from routine voltage mapping, may be useful at identifying ICM patients at high risk for HFO.

Measurement and simulation of voltage differences under ribs and channels and temperature variations within channels in PEMEC

The internal voltage inhomogeneity in a proton exchange membrane electrolyzer cell (PEMEC) is experimentally investigated by using customized gaskets. Three miniature thermocouples are strategically placed inside the channels, specifically in the inlet region, middle region, and outlet region, to monitor temperature variations along the channels. Local voltage measurements are conducted in 13 regions corresponding to the flow channels and 12 regions corresponding to the ribs, under various operating conditions. Additionally, a three-dimensional simulation is performed to analyze the underlying causes of non-uniform voltage distribution and temperature variation. The results reveal contrasting trends in temperature changes along the flow direction, attributable to the varying magnitudes of heat loss and electrochemical heat at different current densities. At low current densities, temperatures increase from the inlet to the outlet along the channels, while at high current densities, temperatures decrease in the same direction. Furthermore, the local voltages of the flow channels (Vchan) and the ribs (Vrib) exhibit different increases along the flow direction at various current densities with the Vchan consistently smaller than Vrib. The inhomogeneity of Vchan is found to be greater than that of Vrib due to bubble disturbances in the channels. The proposed measurement principle for local voltage distribution in PEMECs provides insights into the performance discrepancies between the channel and rib scales in the flow field, thereby enhancing our understanding of electrical property inhomogeneity within the cell.