Bus Frequency Research Articles

Power quality improvement and analysis of interconnected bus system with PMU using VSM-STATCOM

The traditional static synchronous compensator (STATCOM) present in the power grid to compensate instability problem will not be not able to maintain stability of the system due to fluctuations in point of common coupling (PCC) voltage and frequency variation that may result in poor synchronization of the grid. The solution for this is the improvement in conventional STATCOM to virtual synchronous machine–static synchronous compensator (VSM-STATCOM). In this paper an interconnected IEEE-14 bus system is considered for analysis with VSM-STATCOM for improvement in voltage profile on weakest bus of the system. In order to find the weakest bus, load flow analysis is carried out on the bus system using Newton Rapson method. A VSM-STATCOM is connected at that weakest bus in synchronization to the grid injecting reactive power. For the analysis a fault is introduced on any of the line and voltage profile of the weakest bus is observed with and without VSM-STATCOM. The VSM-STATCOM is also compared to a conventional control STATCOM which has no inertia module. A comparative analysis is carrier out with parameters of voltage magnitude and frequency of the weak bus taken into consideration. The magnitude and frequency parameters of conventional STATCOM and VSM-STATCOM are measured using phasor measurement units. The model is designed using MATLAB Simulink power systems library block sets with graphical user interface (GUI) environment.

Complex Frequency

The paper introduces the concept of <i>complex frequency</i>. The imaginary part of the complex frequency is the variation with respect of a synchronous reference of the local bus frequency as commonly defined in power system studies. The real part is defined based on the variation of the voltage magnitude. The latter term is crucial for the correct interpretation and analysis of the variation of the frequency at each bus of the network. The paper also develops a set of differential equations that describe the link between complex powers and complex frequencies at network buses in transient conditions. No simplifications are assumed except for the usual approximations of the models utilized for the transient stability analysis of power systems. A variety of analytical and numerical examples show the applications and potentials of the proposed concept.

Optimal fuzzy logic control of energy storage systems for [formula omitted] support in distribution networks considering battery degradation

High penetration of renewable energy resources into distribution networks induces frequency and voltage fluctuations to the power grids. Unlike high-voltage transmission lines, the x/r ratio of distribution lines is relatively low, thereby frequency support and voltage regulation are closely coupled. Considering their coupling relationship, a rule-based fuzzy logic controller (FLC) is proposed in this paper for battery energy storage systems (BESSs) to coordinately provide bus voltages and frequency support. The membership functions of the FLC are optimized offline to minimize the frequency and voltage deviations using Pareto front criterion. Moreover, with a practical battery aging dataset, a battery degradation model is constructed to design fuzzy rules for prolonging battery lifetime. The proposed method is tested on the IEEE 33-bus distribution network and compared with benchmarking methods. The simulation results verify that the proposed method can simultaneously provide frequency and voltages regulation support to satisfy the operational limits while extending the battery lifetime.

Optimal pricing and investment in a multi-modal city — Introducing a macroscopic network design problem based on the MFD

Improving the performance of an existing transportation system is a challenge for engineers and policy makers as many dimensions and system design variables are interacting. In this paper, we propose the three-dimensional macroscopic fundamental diagram network design problem (3D-MFD-NDP). It is a strategic macroscopic tool to identify the directions of decision making in a multimodal transportation system, where the provision of roads and public transport services are interacting with costs for cars and public transport services in the performance of the entire road surface transportation system. The 3D-MFD-NDP models their effects aggregated at the network level and does not locate all measures to the road network. The objective function of the introduced 3D-MFD-NDP is minimizing the total travel time, while the design variables of the problem are the user costs for cars and bus tickets, the bus headway, the share of dedicated bus lanes and the length of the road network. The advantage of the 3D-MFD-NDP compared to existing approaches is that it is formulated as a mathematical program with equilibrium constraints (MPEC) that allows a fast closed-form solution instead of being simulation-based, usually computing many details not required in strategic decision making. We apply the 3D-MFD-NDP to the greater area of Zurich to study two different problems. First, we investigate how the current network performance can be increased by pricing and investment measures. Despite difficulties in identifying reliable cost information for the provision of roads, we find that substantial travel time savings are possible, especially when limiting car use by restricting its space and increasing its costs. Second, we investigate the response to a 20% population growth in urban and suburban regions with car and public transport prices as well as bus frequency as the free design variables. We find that the system can accommodate the population growth, but as the system costs are shared among more users, the costs per trip are lessened, which attenuates the steering effect of prices.

Considerations about an outbound bus lane in an urban area

This paper examines the feasibility of inserting a new exclusive bus lane in the public transport network of an urban area. It gives data and a case study example that demonstrate how a bus lane can be evaluated especially how a bus lane of a relatively limited length and of a relatively low bus frequency is worth being implemented – normally - in the case of a one-way street connecting the city center with the suburbs. The approach followed, analyses the findings from a case study in the eastern part of Thessaloniki, the second largest city in Greece with a population of approximately one million inhabitants. The bus lane used as the case study is focused on an outbound direction along a one-way street that connects the city center with the eastern suburbs of the city. This bus lane operates during part of the day according to the traffic conditions and the demand needs along the road corridor where it is located. The analysis includes field measurements of traffic data along the bus lane as well as a questionnaire-based survey that was mainly focused to investigate the quality of the service as perceived by the passengers. The paper shows that such bus lane can be fully justified (though with a reduced number of buses per hour), in terms of the travel time savings that it provides, the uninterrupted bus flow operation that it provides (that minimises the time they spend on the bus) and other characteristics. Parking restrictions and other traffic regulations enforcement is, however, necessary to prevent violations by drivers of private cars and minimise any adverse effects on the bus lane’s operation.

Power coordination control strategy of microgrid based on photovoltaic generation

In order to solve the large-scale grid-connected photovoltaic cells caused by power fluctuations, power quality decline and other issues. This paper proposes and researches a power coordination control strategy for microgrid based on photovoltaic power generation. The principle of photovoltaic cells and the switching of maximum power point tracking and limited power mode are studied. The stability control methods of DC bus voltage, AC bus wire and frequency are studied. The model of microgrid is established and moreover, based on the power of microgrid and the charging state of storage battery, the operation of microgrid is divided into different working modes. The stable operation of microgrid is realized by adjusting the output power of each unit in different working modes. The calculation shows that the control strategy can effectively reduce the power fluctuation in the microgrid and improve the output power of renewable energy. Finally, the feasibility and effectiveness of the proposed methods are verified by experiments.

Effects of the COVID-19 pandemic on public bus occupancy and real-world tailpipe emissions of gaseous pollutants per passenger kilometer traveled

Public buses typically have less emission per passenger kilometer traveled (PKT) than private cars and motorcycles, and the emission benefit of public buses increases with ridership. However, the drop in public bus usage during the novel coronavirus (COVID-19) pandemic could lead to an increase in air pollutant emissions per PKT, making the emission benefits of public buses questionable. This study investigated the effects of the COVID-19 pandemic on public bus occupancy rates in Taichung City, Taiwan, and also compared real-world emissions per PKT of carbon monoxide (CO), total hydrocarbons (THC), nitric oxide (NO), and carbon dioxide (CO2) of a public bus before and during the pandemic. Mean bus occupancy rates were 11–25% on different bus routes before the pandemic, indicating that only a fourth or less of the bus passenger capacity was utilized. During the pandemic, mean bus occupancy rates dropped to 4–15%. Moreover, the public bus was less polluting based on CO and THC emissions than the car and motorcycle, even at the low passenger occupancy rates observed during the pandemic. However, NO and CO2 emissions per PKT of the bus were remarkably higher during the pandemic than those of the car and motorcycle. Furthermore, we estimated the break-even passenger occupancy rate for buses as 15%, which was the minimum threshold occupancy rate below which the buses would be more polluting than cars and motorcycles in terms of CO, THC, and CO2 emissions per PKT. Our findings will help transport management authorities and policymakers to optimize bus route designs and frequencies and implement anti-pandemic measures to maximize the environmental benefits of the public bus transit systems.

Bus Frequency Optimization in a Large-Scale Multi-Modal Transportation System: Integrating 3d-Mfd and Dynamic Traffic Assignment

Bus Frequency Optimization in a Large-Scale Multi-Modal Transportation System: Integrating 3d-Mfd and Dynamic Traffic Assignment

Online Estimation of POI-level Aggregated Inertia Considering Frequency Spatial Correlation

Online estimation of power system inertia provides the essential basis for frequency stability analysis and control. This paper proposes an approach to estimate the aggregated inertia at the point of interconnection (POI), which can be further used to calculate the power system total inertia and to monitor the inertia spatial distribution. Based on the spatial correlation of the power system frequency, the general correlation between the rotor speed and network bus frequency is derived. Furthermore, the phasor measurement unit placement principle for inertia estimation is given, and the impacts of redundant and lacking frequency measurement are analyzed. The proposed method is designed for the field implementation scenario, where ambient measurement data are used and the requirement for mechanical power measurement is relaxed. Simulation results carried out on the modified IEEE 39-bus System show that the proposed approach can accurately estimate POI-level inertia under different conditions, including poor data quality, lacking POI frequency, parameter and topology error, and renewable power generation penetration.

Analysis of Bus Fare Structure to Observe Modal Shift, Operator Profit, and Land-Use Choices through Combined Unified Transport Model

In order to design sustainable urban transport systems, the inclusion of the behaviors of different stakeholders is imperative. In this study, we formulated the interactions of behaviors between transport operator, landowner, workplace, residence, route and mode choices, and location of firms and businesses through a combined unified model of land-use and transport system. The commuters have two mode choices for traveling: private car and public bus. They are inclined to choose a transit mode with minimum traveling costs. We combined two models, maximization of operator profit constrained by bus frequency, while maintaining the formulation of other stakeholders through an assignment sub-model. The resulting formulation is bi-level, which is optimally solved for a small-sized instance containing two zones. The findings suggest that if the bus fare is reduced, the demand of public bus is increased. However, the operators’ profit is optimized within a certain range of fares and is lowered when the fare is too low or too high. It is determined that maximum bus frequency does not guarantee maximum profit to the service operator. The impacts of traveling costs on residence choice behavior suggest that if link fares are more, many of people opt not to travel between different zones. The analysis results presented in this paper are calculated for two types of link fares: a fixed fare (30 currency), and a range of link fare (5 to 100 currency). Different variants of the same formulation can be applied for real settings to better comprehend the nature of the model and its applications.

Kerbside NOx and CO concentrations and emission factors of vehicles on a busy road

Vehicular emissions contribute to roadside pollutants in cities, yet on-road emission estimates remain relatively uncommon. Nevertheless, they make an important contribution to exposure along Hong Kong's congested roads and street canyons. This study used kerbside microsensor-based monitors on Hennessy Road, one of the busiest roads in the north part of Hong Kong Island, to determine both concentrations and emission factors (EFs) of NOx and CO. Kerbside NOx and CO concentrations are skewed, with high concentrations representing plume segments from larger vehicles. The average EFs for each minute of traffic was determined from the pollutant concentration ratio with ΔCO2. These related to bus frequency for NOx, and EURO 4 or lower-emission standard vehicles for CO. The 1-min mean EFNOx 7.55 g kg−1 and EFCO 12.6 g kg−1 are typical for flows for the fleet dominated by buses, but highly skewed (Weibull shape parameter ∼0.44). Individual vehicle EFs were determined from peaks in NOx, CO and CO2, and number plates. Leading and trailing parts of the plume segments gave similar EFs (R2 > 0.95), suggesting this method was reasonably robust across the vehicle passage. Nevertheless, these EFs were also skewed, but the shape parameter was again ∼0.44. EFNOX for vehicle classes was: buses > goods vehicles > private cars > vans > taxis and diesel > petrol > LPG, with larger engine sizes also dominant. Differences were more difficult to assess with CO, but LPG vehicles had the highest EFs. Our EF estimates lay in the range found in previous studies but differ from fleet emissions calculated for regulatory purposes in Hong Kong (EMFAC). However, some high EMFAC emitters were also high in our estimates for individual vehicles. Vehicles may not perform on-road as inventory calculations suggest. The high EF variability found in our study implies that a large sample is required to assess the likely emissions from a vehicle fleet.

Decentralized data-driven estimation of generator rotor speed and inertia constant based on adaptive unscented Kalman filter

This paper proposes an online decentralized and data-driven method for synchronous generator rotor speed and inertia estimation. First, an analytical relationship between the generator terminal voltage/current phasors and its internal rotor speed is derived using the Thevenin equivalent. The parameters of the latter are obtained via a recursive estimator, which allows us to estimate the generator’s internal rotor speed from voltage/current phasors without the need for any generator information. Second, we reformulate the equivalent swing equation into the Kalman filter form, which enables us to use a priori-estimated internal rotor speed along with measured real and reactive power injections to obtain an estimate of the inertia for each online synchronous generator. This is achieved through an adaptive unscented Kalman filter. We demonstrate that the use of terminal bus frequency to approximate the rotor speed for inertia estimation by existing methods leads to large estimation biases/errors. Numerical simulations carried out on the IEEE 39-bus and Texas 2000-bus systems reveal that our proposed method is consistently more accurate than existing methods. Moreover, our proposed method is insensitive to both the type and location of system disturbances, and it is robust to different levels of measurement noise.

WALK MODELLING WHEN DESIGNING SMALL BUS TRANSIT NETWORKS

Models for the design of public bus transit networks are usually based on the historically observed origin-demand travel patterns of potential passengers. The option of a passenger choosing to walk is, however, not usually incorporated into the design models for such networks. We argue that the absence of this model feature might lead to significant sub-optimality, especially in the design of small public bus transit networks. A novel approach to including this feature in the bus frequency setting aspect of public bus transit network design models is demonstrated in this paper, in which passenger transit modal choices are modelled on the basis of an existing optimal strategy transit assignment model. The newly proposed bi-objective route design and frequency setting models are applied to a realistic case study involving the establishment of a public bus transit system for students on a university campus; and this model implementation is used to gain insight into passenger route choice behaviour, based on individual preferences between walking or using buses. It is shown in the context of this case study that including the option of a passenger walking in the design models for public bus transit networks can affect the efficacy of the final network, especially if the network is small.

Event-Triggered Mechanism Based Control Method of SMES to Improve Microgrids Stability Under Extreme Conditions

Microgrids with multiple converters suffer from excessive pressure on the communication network during traditional voltage and frequency regulation control. This paper proposed an event-triggered control strategy based superconducting magnetic energy storage (SMES) scheme to improve AC microgrids stability under successive disconnection of sources or step change of loads. By designing an event-triggered mechanism, each converter in the microgrid sends its own information to SMES in a non-periodic way. Then the control method of bus voltage and frequency regulation using SMES is constructed, which enables SMES to update its control mode. The microgrid model is established in PSCAD/EMTDC, and two cases of extreme conditions are conducted to demonstrate the effectiveness of the proposed method.

Improving the stability of hybrid microgrids by nonlinear centralized control in island performance

In this paper, based on the nonlinear controller, a new structure is presented for centralized control of hybrid microgrids. In the proposed model, AC and DC buses are used to connect AC and DC sources and loads respectively. A bidirectional interface converter (BIC) is provided for the electrical and control connection of these two buses. Here, based on the generalized backstepping method (GBM), a new method is presented for integrated and simultaneous controlling of AC bus frequency and DC bus voltage. The advantages of this method are the centralized control of the hybrid microgrid, taking into account the dynamics of the whole system and the interaction of its state variables with each other. Harmonized and optimal exchange of power and precise regulation of control signals in this structure has led to improved stability and thus improved system performance. The comparative results of centralized and decentralized control show the efficiency of the proposed model to reduce fluctuations and improve the stability of the system.

Covid-19 need not spell the death of public transport: Learning from Hanoi's safety measures

ObjectivesIn contrast to other cities worldwide, the pandemic has not decimated bus ridership in Hanoi. Notably, the Vietnamese capital has mostly relied on the use of face masks and hand sanitizer during travel, instead of requiring physical distancing on buses. This study examines public bus passengers’ levels of compliance with Covid-19 safety measures, and the factors that affect compliance. MethodsFace-to-face surveys were administered between 7 September and 3 October 2020, right after the end of the third wave of Covid-19 in Hanoi on 51 bus routes. Exploratory Factor Analysis was carried out to extract factors from attitudinal statements. The extracted factors, passengers’ socio-demographic traits, and their bus use patterns were modelled to determine which variables lead to more compliance with Covid-19 safety measures. ResultsWe found that 100% of passengers wore face masks (which were mandated), albeit 11% did so incorrectly, while only 28% of passengers used the hand sanitizer provided by bus operators (which was recommended but not required). In addition, 38% of passengers carried their own bottles of hand sanitizer while travelling, despite a relatively low risk of contracting the virus. Women, older passengers, and urbanites were less likely to sanitise their hands. Frequent bus travellers behaved like the population at large with regard to protective measures against Covid-19. ConclusionsHanoi's overall measures - full use of face masks and partial use of hand sanitizer - were sufficient to contain three relatively minor Covid-19 waves while still maintaining regular bus operations most of the time. If other cities were able to reach these levels of compliance, most would be in much better position vis-à-vis public transport use during the pandemic (or an epidemic). Our findings suggest that mandates work much better than awareness raising campaigns, although the latter have a role to play.

Mixed Scheduling Model for Limited-Stop and Normal Bus Service with Fleet Size Constraint

Limited-stop service is useful to increase operation efficiency where the demand is unbalanced at different stops and unidirectional. A mixed scheduling model for limited-stop buses and normal buses is proposed considering the fleet size constraint. This model can optimize the total cost in terms of waiting time, in-vehicle time and operation cost by simultaneously adjusting the frequencies of limited-stop buses and normal buses. The feasibility and validity of the proposed model is shown by applying it to one bus route in the city of Zhenjiang, China. The results indicate that the mixed scheduling service can reduce the total cost and travel time compared with the single scheduling service in the case of unbalanced passenger flow distribution and fleet constraints. With a larger fleet, the mixed scheduling service is superior. There is an optimal fleet allocation that minimizes the cost for the system, and a significant saving could be attained by the mixed scheduling service. This study contributed to the depth analysis of the relationship among the influencing factors of mixed scheduling, such as fleet size constraint, departure interval and cost.

Adaptive synergistic control strategy for a hybrid AC/DC microgrid during normal operation and contingencies

This paper proposes an adaptive synergistic control strategy for a hybrid AC/DC microgrid to overcome its vulnerability to notable grid impedance variation provoked by load changes. Microgrid employs an internal DC link incorporating hybrid renewable resources represented by wind turbine generator, photovoltaic arrays and hybrid energy storage system. The latter comprises supercapacitor stacks for fast compensation and a hydrogen management scheme for long-term energy storage to counteract renewable resources indeterminacy. The internal DC link is attached to the AC side via a grid-side converter to constantly realize bus voltage and frequency constancy. The central premise of the proposed strategy during normal conditions is to meet load obligation via proper sharing of demanded power among hybrid resources and storage systems, optimize operation schedule of hydrogen management scheme to guarantee longer lifetime, enhance microgrid stability against abrupt loads disconnections when load shedding is activated during extremely low microgrid production. Accordingly, grid-side converter control structure is adaptively modulated based grid impedance estimation at the AC side in response to load manipulations to alleviate its impact on AC bus voltage stability. Furthermore, two series-connected resistive-type super fault current limiters are attached at the AC bus to mitigate large transient currents caused by different faults. The simulation results, so extensively obtained, reveal seamless exchange of desired load power during entire operational modes and decrease of bus voltage perturbations caused by extensive load variations thus enhancing microgrid robustness against parameters uncertainty. In addition, microgrid is maintained connected and protected during severe symmetrical and asymmetrical faults.

Hybrid Dual-Loop Control for Current Regulation and Low-Frequency Ripple Rejection in Led Drivers

This paper presents a new hybrid dual-loop control system for the DC/DC LLC resonant converter, operating as a downstream DC/DC converter in a two independent stage offline LED driver. The outer loop employs a PI controller to maintain the average LED current regulated at the reference value and reject parametric variation. The inner loop implements an adaptive periodic disturbance rejection (APDR) subsystem, thus conceiving the hybrid PI\&amp;APDR controller. The APDR subsystem is designed to strictly reject the bus voltage ripple and limit its transmission to the LED current. Experimental results show the proposed controller feasibility in achieving good tracking behavior, reduced output current ripple under different bus voltage ripple amplitude and frequency, robustness against parametric variations, and simple implementation and design. For the sake of completeness, the proposed PI&amp;APDR is compared with the conventional proportional resonant controller employing experimental results and extra analysis based on simulations.

Type-2 fuzzy logic based transit priority strategy

We proposed in this paper Type-2 Fuzzy Logic-based transit priority strategy. The developed strategy belongs to the class of active priority strategies. At the same time, it is a conditional priority strategy. We tried to find out the finest trade-off between transit and traffic delay. The suggested approach used the data collected from the VISSIM analysis. The simulation tests were performed on the section of an arterial with two intersections in downtown Belgrade, Serbia. The obtained results are promising. It looks that the developed strategy could improve traffic operations in cities, or areas, with high bus frequencies and/or low or medium traffic volume.