Side Bus Research Articles

Application of optimized photovoltaic grid-connected control system based on modular multilevel converters

Photovoltaic power generation is a promising method for generating electricity with a wide range of applications and development potential. It primarily utilizes solar energy and offers sustainable development, green environmental benefits, and abundant solar energy resources. However, there are many external factors that can affect the output characteristics of Photovoltaic cells and the effectiveness of the grid-connected control system. This study describes the introduction of Modular Multilevel Converter (MMC) technology into photovoltaic power generation systems to improve power generation efficiency. It proposes optimizing and improving the technology by adjusting the temperature and magnitude of lighting and combining traditional algorithms to propose a composite control algorithm. The photovoltaic power generation system employs the modular multi-level converter technology to enhance power generation efficiency alongside optimization and improvement. The temperature and size of light are regulated alongside the traditional algorithm to introduce the composite control algorithm. The improved composite algorithm surpasses the traditional one after experimental comparison of the results. The testing of a model photovoltaic power grid-connected system shows that the combination of modular multi-level converter technology and a photovoltaic grid-connected system, incorporating composite proportional integral control and quasi-proportional resonant control algorithms, yields improved results and feasibility. With rationality and effective control. The simulation results show that at 0.5 s, the light intensity suddenly increases from 750 to 1000 W/m2, and the direct-current voltage suddenly increases for a short time, but then decreases rapidly and finally returns to a stable level close to the rated voltage. From this, it can be seen that when the light intensity continues to change, the voltage value on the direct-current bus side of this MMC grid-tied photovoltaic system can still be maintained close to the rated value, ensuring the operational stability of the entire system. Sensibly and effectively controlled. The implementation of MMC technology in photovoltaic power generation systems enhances power generation efficiency, whilst simultaneously supporting the advancement of photovoltaic power generation and contributing towards environmental protection in the long term.

Harmonic current suppression method of virtual DC motor based on fuzzy sliding mode

Abstract In the operation of power grid, the low frequency subharmonics in power lines are easy to cause harmonic current problems. A harmonic current suppression method is constructed based on fuzzy sliding mode and virtual DC motor (VDC). First, the adaptive linear network is introduced to compare and analyze the output value and the actual value in the power line, and the possible harmonic current is obtained, which is detected and discretized. After that, this study adopts Fuzzy sliding mode control (FSMC) strategy for VDC, uses FSMC to participate in on-off control of VDC, and then realizes the suppression of harmonic current in VDC ports. In addition, the model also uses the circuit superposition theorem and the amount of harmonic data to be compensated by FSMC. The whole method uses VDC control technology to ensure the voltage stability of DC bus and load side when the load changes. In this physical experiment, harmonic current generated by load disturbance is eliminated by reducing DC harmonic voltage, so as to achieve the suppression of DC port harmonic current. Experimental results show that the third and fifth harmonics in power lines can be eliminated by this method to a large extent. Therefore, the proposed method can accurately detect and eliminate the harmonic current caused by sudden load change, and then realize the suppression of VDC harmonic current.

Design and Implementation of DSP-based Three-level Simplified SPWM Modulation Method

The traditional three-level sinusoidal pulse width modulation (SPWM) requires two carriers to be compared with the modulating waveform to get the duty cycle, which can not be realized in a single-core DSP chip with high requirements. This paper proposes a three-level single-carrier SPWM waveform implementation method that does not increase the hardware cost. The scheme is based on the DSP28335 chip, using the DSP chip’s increment/decrement counting method, the comparison counter, and the DSP interrupts to compare the carrier waveform with the modulating waveform and get the PWM drive signals with different duty cycles. Simulation results show that compared with the traditional three-level SPWM algorithm, the proposed three-level simplified SPWM modulation not only controls the hardware cost, but also optimizes the bias of the intermediate capacitor voltage on the DC bus side, which reduces the harmonic distortion of the grid, shortens the time for the DC output voltage to reach the steady state, and verifies the effectiveness of the proposed modulation method.

Simultaneous compensation of distorted DC bus and AC side voltage using enhanced virtual synchronous generator in Islanded DC microgrid

ABSTRACT There are many effective techniques for virtual inertia emulation in DC microgrids that can help DC bus voltage stability through power exchange with virtual inertia injection. But one of the vexingly complicated challenges in virtual inertia emulation is the connection of unbalanced loads on the AC side of a DC microgrid. Unbalanced AC loads connected to a DC microgrid may cause severe fluctuations in DC bus voltage and battery power, as well as distorting AC side voltage. The need to solve this issue is very important because it can be a threat to the microgrid DC bus voltage stability and feed sensitive loads. One effective method to mimic the real inertia feature and dampen the unfavourable unbalanced conditions is to employ a virtual synchronous generator (VSG) equipped with a decoupled double synchronous reference frame (DDSRF) approach. The DDSRF can extract positive and negative components with high precision and create pure DC signals for the control system to improve accuracy and controllability. Hence, this paper investigates a combination of a VSG structure enhanced with a DDSRF technique to attenuate the fluctuations of DC bus voltage, battery power, and AC-side voltage caused by an unbalanced AC load in an islanded DC microgrid. The simulation results confirm that the unbalanced loads connected to the AC side of the microgrid are destructive for DC bus voltage, battery power, and also create voltage imbalances for AC loads. Furthermore, the proposed DDSRF-based VSG control system that has been implemented on the AC side of the microgrid can strongly dampen the fluctuations on the DC bus, battery, and AC loads.

Analysis of Electric Bus Utilization for Urban Transport using Bus Route, Passenger Demand and Fuel Consumptuion (Blok M-Kota Corridor Case)

Buses as a means of public transportation can greatly reduce traffic problems in urban areas through the use of, among other things, innovative techniques and technologies. The development of innovative technologies increasingly oriented towards the electrification of vehicle propulsion systems is expected to lead to the reduction of harmful emissions, increased vehicle efficiency, improved performance, reduced fuel consumption, and reduced noise. This study aims to determine the comparison of Transjakarta electric buses with conventional buses owned by Transjakarta, identify and evaluate the condition of the electric bus side. This study uses quantitative methods. The results of the study show a comparison of the operational cost calculation as indicated by the calculation of direct costs and indirect costs. The unit price for a bus/km for a diesel bus is Rp. 51,796, on the electric bus Rp. 224,991, and BBG buses for Rp. 82,227. where in the comparison of BOK diesel buses are cheaper than electric buses and CNG. The most expensive cost is the replacement of spare parts, especially the price of the battery which needs to be replaced every 10 years. 3,876, while bbg buses require much cheaper, which is Rp. 630. The calculation results of the electric bus battery consumption on the use of 1 route with a distance of 30.8 on weekdays on average 11.5% while on weekends it is 9.5%. At the kWh consumption, the electric bus requires the consumption of kWh per trip with a distance of 31.4 km is 23.57 kWh. From this value, it is known that the efficiency is 1.3 km/1 kWh. In charging the battery, the average battery charging time on the electric bus is 134 minutes or about 2.23 hours.

Error Analysis Due to the Transient Reactance of the Generator in Simulation Verification of Power System Inertia Evaluation

In the simulation validation process of the inertia evaluation model, it is necessary to collect the power and frequency data of a node accurately after the disturbance and use a reasonable data processing algorithm to reduce the error. Given that the power and frequency characteristics of the generator outlet side bus are similar to those of the generator, some research work selects the generator outlet side bus as the test object of the power and frequency data acquisition device. However, the generator outlet side bus inertia and the theoretical generator inertia are not equivalent because of the generator transient reactance. In this paper, we first establish a 3-machine 6-node inertia simulation model using a constant power load connected via a circuit breaker to provide system unbalanced power and then simulate the generator outlet side bus inertia under two conditions of the transient reactance set to zero and non-zero. Through comparison with the theoretical generator inertia, it is concluded that the generator outlet side bus inertia represents the theoretical generator inertia only when the transient reactance is set to zero. This conclusion applies to complex power systems as well.

Open-Circuit Fault Diagnosis and Tolerant Method of Multiport Triple Active-Bridge DC-DC Converter

The triple active-bridge (TAB) DC-DC converter, as a representative multiport converter, is widely used in DC distribution system. The open-circuit fault (OCF) of TAB seriously threatens the system safety operation. In this article, an OCF diagnosis and tolerant method is proposed for TAB converter to reduce the impact of OCF. The fault mode of TAB converter is first analyzed. Based on the analysis, an fault diagnosis method using the average value of bridge arm midpoint voltage and inductance current is proposed. To eliminate the DC bias and over-current caused by OCF, the symmetrical topology is constructed by modulation reconfiguration, and corresponding fault-tolerant operation strategies are proposed for OCF at different locations. When the OCF occurs on the bipolar DC bus side, the fault bus is cut off, while ensuring the power transmission between the monopolar bus and the critical load. When the OCF occurs on the critical load side, the bipolar DC bus could still supply its power. Based on the above strategy, the power transmission capability under OCF is guaranteed and the reliability of TAB converter is improved. Finally, the OCF diagnosis and fault-tolerant operation methods are verified through comparative numerical simulation and experimental results.

Research on Distributed Photovoltaic Grid-connected Mode Based on PSASP

With the continuous implementation of the carbon peak and carbon neutrality, a large number of distributed solar power stations have been integrated into the grid, which has caused a strong impact on the safe and stable operation of the traditional power system. Based on this, the grid-connected mode of distributed solar power stations is studied, and three types of grid connection are proposed. Mode A is merged into the 66 kV bus side of the 220 kV substation through the 66 kV dedicated line; Mode B is merged into the 66 kV bus side of the 66 kV substation through the 66 kV dedicated line; Mode C is T-connected to the 66 kV transmission line through 66 kV dedicated line. By using a power system analysis software package (PSASP), we can build a model of a certain regional power grid and study the effects of the above three grid-connected modes on system voltage stability, short-circuit current, and network loss. The study shows that the three modes are all feasible. Mode A has the smallest change in voltage quality and short-circuit current of the grid-connected substation and has the smallest network loss of the three modes.

Fractional-Order-Based Low-Order Harmonic Current Suppression Method Considering Asymmetrical Capacitor Parameters

The problem of the second harmonic current (SHC) on the dc bus side of the single-phase inverter system has attracted widespread attention. The active power decoupling method based on dual capacitors can suppress SHC effectively. However, the asymmetrical capacitor parameters will deteriorate the SHC suppression performance and lead to the first-order harmonic current. To eliminate these low-order harmonic currents, this article proposes a SHC suppression method based on the fractional-order capacitor (FOC), where no power supply is employed and little loss is incurred. The capacitance and the order of the proposed FOC can, both, be adjusted. The principle and operating mode of the FOC are analyzed, and the control strategy of adjustment is given. The method can realize the SHC suppression with the advantages of a simple control strategy, hot-swappable, and high flexibility. Most importantly, the method can effectively suppress the first-order harmonic current caused by the asymmetrical parameters of the capacitors. Finally, an 800 W prototype based on the proposed method is built, and the simulation and experimental results both verify the effectiveness of the proposed method.

Availability Capacity Evaluation and Reliability Assessment of Integrated Systems Using Metaheuristic Algorithm

Contemporarily, the development of distributed generations (DGs) technologies is fetching more, and their deployment in power systems is becoming broad and diverse. Consequently, several glitches are found in the recent studies due to the inappropriate/inadequate penetrations. This work aims to improve the reliable operation of the power system employing reliability indices using a metaheuristic-based algorithm before and after DGs penetration with feeder system. The assessment procedure is carried out using MATLAB software and Modified Salp Swarm Algorithm (MSSA) that helps assess the Reliability indices of the proposed integrated IEEE RTS79 system for seven different configurations. This algorithm modifies two control parameters of the actual SSA algorithm and offers a perfect balance between the exploration and exploitation. Further, the effectiveness of the proposed schemes is assessed using various reliability indices. Also, the available capacity of the extended system is computed for the best configuration of the considered system. The results confirm the level of reliable operation of the extended DGs along with the standard RTS system. Specifically, the overall reliability of the system displays superior performance when the tie lines 1 and 2 of the DG connected with buses 9 and 10, respectively. The reliability indices of this case namely SAIFI, SAIDI, CAIDI, ASAI, AUSI, EUE, and AEUE shows enhancement about 12.5%, 4.32%, 7.28%, 1.09%, 4.53%, 12.00%, and 0.19%, respectively. Also, a probability of available capacity at the low voltage bus side is accomplished a good scale about 212.07 times/year.

Uses of Superconducting Magnetic Energy Storage Systems in Microgrids under Unbalanced Inductive Loads and Partial Shading Conditions

Superconducting magnetic energy storage (SMES) systems are characterized by their high-power density; they are integrated into high-energy density storage systems, such as batteries, to produce hybrid energy storage systems (HESSs), resulting in the increased performance of renewable energy sources (RESs). Incorporating RESs and HESS into a DC bus to obtain a DC microgrid concept is considered a more attractive option for solving system reliability and stability issues. In this paper, we focus on employing SMES systems based on their characteristics of a fast response and high efficiency, which contribute to increased battery lifespan, and reducing the mismatch between the energy supplied by the renewable energy source and the load demand by compensating for the effects of partial shading on the PV system on the DC bus side and the imbalance in loads on the other side of the AC bus. The incremental conductance algorithm (INC) is used for maximum power point tracking (MPPT) in the PV system. Fuzzy logic control (FLC) is proposed for the generation of control signals for the DC–DC chopper used to charge/discharge the SMES coil. Simulations using MATLAB/Simulink were then carried out to assess the proposed models of the (standalone and grid) connection systems.

A Model Predictive Controlled Bidirectional Four Quadrant Flying Capacitor DC/DC Converter Applied in Energy Storage System

Energy storage system (ESS) has been widely used in photovoltaic system to ensure stable power generation. This article proposes a flying capacitor bidirectional buck–boost converter (FCBBC), aiming at making the ESS work with bidirectional four quadrant in the wide dc+bus voltage variation condition. With the symmetrical modulation strategy, the proposed FCBBC can achieve seamless switching between buck and boost mode to match the voltage changes at energy storage and dc bus side. Meanwhile, considering the ESS application requirements, a fixed frequency model predictive control (MPC) strategy based on binary search algorithm is proposed to achieve the control purpose. The decoupling relationship between flying capacitor (FC) and output voltage is derived so that the proposed MPC strategy can control the voltage of two FCs simultaneously. In addition, the adoption of binary search algorithm effectively reduces the computation load of the proposed MPC strategy. Finally, the effectiveness of the proposed converter and MPC strategy are verified with a downscaled ESS experimental platform.

A simulation based large bus side slip and rollover threshold study in slope-curve section under adverse weathers.

To study the side slip and rollover threshold of large bus in slope–curve section under adverse weather, factors that affect the safety of large buses that run in slope–curve section, such as rain, snow, cross-wind environmental factors, and road geometry, were analyzed to obtain the friction coefficient of the road surface under different rainfall and snowfall intensities through field measurements and to determine the six-component force coefficient of wind that acts on large buses through wind tunnel tests. The force analysis of large bus in slope-curve section was carried out, and the mechanical equations of large bus under the limit conditions of sideslip and rollover in slope-curve section were established. TruckSim simulation test platform was used to establish a three-dimensional road model and large bus mechanical model at a design speed of 100 km/h. Input parameters, such as cross-wind speed and road friction coefficient, simulate the impact of wind-rain/snow coupling. Under the combined action of wind-rain/snow, the operation test of large bus in slope-curve section was carried out, and the key parameters and indicators of the sideslip and rollover of large bus in slope-curve section were outputted and analyzed. The sudden change point of lateral acceleration is the judging condition for sideslip of large bus in slope-curve section under different road friction coefficient (0.2–0.7), changing from 0.15m/s2 and stabilizing to 0.52 m/s2, and a 0N vertical reaction force of the inner tire is the critical judging condition for rollover under road friction coefficient0.8, and the operating speed thresholds were proposed under different road friction coefficient. This study is expected to provide theoretical support for the speed limit of large bus in slope-curve section under adverse weather.

Stability Analysis of AC/DC Microgrids in Island Mode

This study aims to introduce a new structure based on a nonlinear controller for controlling and analyzing the stability of the microgrids. In the proposed model, AC and DC resources and loads are located on two different sides. In addition, an AC/DC bidirectional interface converter is applied to supply loads by AC/DC sources. There are AC/DC products on both sides of the converter and each side can supply the load of the other side via a bidirectional interface converter and its load. Alternatively, an energy storage system is used for the system stability on the DC side. The nonlinear microgrid controller is designed to adjust the AC bus side frequency and the DC bus side voltage properly. In this structure, the coordinated optimal power exchange and precise regulation of control signals lead to constant improvement. Thus, system performance is improved. The results show that the proposed model is efficient for both reduction of the fluctuations and improvement of the system stability

Supercapacitor hybrid energy storage system applied to photovoltaic power generation

In order to solve the problem of power pulsation at the DC bus side caused by uneven illumination or load fluctuation, a hybrid energy storage system for supercapacitors is proposed. In the hybrid energy storage circuit, inductors are added to form a high-frequency filter with the supercapacitor, and the supercapacitor absorbs the high-frequency current component of the DC side. The traditional droop control strategy is adopted to effectively filter the high-frequency current component of the battery side, and the battery is responsible for processing the low-frequency current component. The simulation results show that the proposed hybrid energy storage system can reduce the voltage pulsation of the DC bus, and the response and recovery speed is faster, which can effectively suppress the power pulsation on the side of the photovoltaic DC bus.

Analysis of Single-phase Grounding Fault with Distributed Generation in Distribution Network

Different distributed generation (DG) types and neutral grounding methods affect single-phase ground fault current characteristics of distribution network. To analyse the single-phase ground fault current characteristics, this paper establishes a single-phase ground fault model with rotating and inverter-type DG accessed using symmetrical component method. By considering different grounding methods of distribution bus side and DG side, distribution characteristics and change laws of fault current as well as sequence currents on both sides of fault point when single-phase short circuits occur in different positions of system are discussed. To verify correctness of analysis, simulation experiments of models is carried out by Simulink. The results of this paper can provide reference for system relay protection configuration and neutral grounding method selection.

Influencing factors and countermeasure analysis of a 800kV coupling capacitor dielectric loss test

The coupling capacitor is installed on the AC bus side of the converter station for AC filtering to filter out a large amount of harmonics generated by the converter during the AC/DC conversion process. Therefore, the reliability assessment test of its insulation status is of great importance to the safety and stability of the UHV power grid Meaning. In the UHV field test, the dielectric loss factor of the coupling capacitor is tested at a voltage of 10 kV and below, but the device itself has the Garton effect, and the abnormal data measured at some times cannot truly reflect the insulation state of the device. The thesis analyzes the abnormality of the dielectric loss factor test data of 800kV coupling capacitors in UHV converter stations from the structure, use conditions and test methods of the equipment, and gives a detailed analysis of the causes of the abnormality. Recommendations for operation.

Investigation of an IEC 61850 standard-based process bus implementation of a protection and control scheme for parallelly connected transformers

PurposeThis paper aims to focus on the implementation of the International Electrotechnical Commission (IEC) 61850–9-2 standard based process bus with merging units (MUs) and sampled values (SV) to improve the protection and control systems. The digital process interface is important to be included on the process bus level.Design/methodology/approachThe IEC 61850–9-2 process bus standard is not extensively used in regard to SV when the IEC 61850 standard is implemented by power utilities. Many protection and control intelligent electronic devices (IEDs) are connected to a substation communication network, routers and switches using fibre-optic linked Ethernet. However, inductive current transformers (CTs) and voltage transformers (VTs) secondary circuits are still hardwired to the IEDs. The paper highlight issues with the copper wires for currents signals and how these issues can be eliminated by using the MUs and the SV protocol. The voltage regulator control IED of each transformer is required to regulate the voltage level of the secondary side bus bar it is connected to. All the regulating IEDs of parallel-connected transformers are required to communicate with each other to share information. They collectively control the bus bar voltage depending on the switching configuration of the parallel transformers.FindingsIt is shown that process bus information such as the high voltage switchgear status information of primary plant in the yard, can be used to improve the substation protection and control systems. The power transformer protection and voltage regulator control are focused on.Research limitations/implicationsThe deliverables of the research work can be applied in: The Centre for Substation Automation and Energy Management systems of the Department of Electrical Engineering, power utilities and other establishments using power systems and digital substations in the electrical supply industry. The research work on the thesis led to the development of a laboratory test-bench where students can learn and understand the basics of the IEC 61850–9-2 SVs principles. The test-bench components such as the IEDs, real-time digital simulator, standalone MUs and Ethernet equipment can be used for future research applications. The test-bench can be used to demonstrate during course work for students at the University, the basics of digital substations using a process bus network with IEDs, MUs and Ethernet equipment.Practical implicationsThe research work showed where lab equipment is getting outdated and future equipment will be required for research work in IEC 61850–9-2 process bus.Originality/valuePower utilities can benefit from implementing the IEC 61850 part 9–2 of the standard and by using MUs and other process interface information in substations. A cost reduction in high voltage equipment, substation installation and commissioning costs and better performance of protection and control system can be achieved.

An Evaluation Method for Commutation Failure Caused by Waveform Distortion

Commutation failure is a key issue that affects the safe operation of HVDC transmission systems. Scholars at home and abroad have conducted research on the mechanism, evaluation indicators, and control strategies of commutation failure. However, most of the researches are aimed at the working conditions of commutation failure caused by a short-circuit fault on the AC side. There are few studies on the commutation failure caused by the harmonic injection on the AC side and the distortion of the AC bus voltage waveform. This paper clarifies the mechanism of commutation failure caused by waveform distortion, and proposes an index of harmonic commutation margin. On this basis, an evaluation method for commutation failure caused by waveform distortion is proposed. By predicting the commutation voltage-time area and optimization methods to assess whether the current voltage conditions have the risk of commutation failure. Finally, an electromagnetic transient simulation model is established on PSCAD/EMTDC, and the evaluation method in this chapter is verified by simulating the working conditions of the inverter side bus voltage waveform distortion. The results show its effectiveness in evaluating the commutation failure. The research provides a theoretical basis to the implementation of the control function and has broad engineering application prospects.

Weighted Islanding Detection for DC Microgrid Based on Random Forest Classification

At present, the main form of microgrid is AC grid. DC microgrids have received extensive attention and research with the rapid development of various DC power. The operation mode of the DC microgrid is divided into grid-connected operation and islanding operation. Islanding is formed after the circuit breaker tripped, which connects microgrid to large grid. Islanding operation can be divided into planned islanding and unplanned islanding. Unplanned islanding will cause certain harm to users and systems, so it is necessary to detect islanding accurately in the DC microgrid. This paper proposes an islanding detection method for DC microgrid based on random forest classification. Firstly, raw data is cleaned, extracted features and generated feature vector set. The extracted features include six islanding characteristic indexes, which consist of voltage, current, output active power and their first order backward difference on the DC bus side. Then, based on random forest classification, building the islanding detection model. Islanding detection model for DC microgrid can distinguish islanding event successfully and accurately. Based on weighted random forest classification, it can detect islanding event more accurately compared with decision tree classification when processing large amounts of data.