Search Results (8)

In response to the high energy consumption and carbon emission issues in the electrolytic aluminum industry, this paper proposes a multi-time-scale optimization and control method for electrolytic aluminum plants with high photovoltaic penetration. First, a plant architecture is established, which includes traditional power systems, renewable energy systems, and electrolytic aluminum loads. A mathematical model for flexible resources such as thermal power units, on-load tap-changing transformers, thyristor-controlled voltage regulators, saturable reactors, and electrolytic cells is developed. Based on this, a two-level optimization control strategy is designed, consisting of a day-ahead and real-time control layer: the day-ahead layer targets economic and low-carbon operation, while the real-time layer aims to stabilize the DC bus voltage. Using actual data from an electrolytic aluminum plant in Southwest China, simulations are conducted on the MATLAB 2021a platform, and the effectiveness of the strategy is verified through hardware-in-the-loop experiments. The results demonstrate that the proposed method can effectively increase the photovoltaic utilization rate, reduce thermal power output and operational costs, and decrease carbon emissions, providing a feasible solution for the green and low-carbon transformation of the electrolytic aluminum industry. Full article

DC circuit breakers (DCCBs) are the key equipment to rapidly interrupt the fault current in high-voltage DC power grids and ensure the safe operation of the system. However, most DCCBs do not take current-limiting measures and rely solely on current-limiting reactors in the system to limit the rate of current rise during the interruption process. The extensive use of fully controlled power electronic devices in circuit breakers (CBs) results in high costs. To address the issues above, this paper proposes a DCCB topology with a current-limiting function based on thyristors and diodes, which can reduce the cost of CB while ensuring reliable interruption. The impact of various parameters on CB performance is analyzed using numerical calculations to optimize the parameters. Then, a simulation model of a 500 kV/16 kA DCCB is built in PSCAD/EMTDC, and the performance of the proposed CB topology is compared with the other CB topologies. By comparison, the proposed DCCB topology can reliably isolate fault currents and reduce the amplitude of fault currents and the cost of CBs. Significantly, the energy absorbed by the metal oxide varistor (MOV) during the interruption process decreases by 64.2%, reducing the cost and volume of the MOV. Finally, the feasibility of the CB is further verified in the ±500 kV 4-terminal high-voltage DC power grid simulation model. The results show that the proposed DCCB topology can limit the fault current rise rate, interrupt and isolate the fault reliably, and reduce the cost. Full article

This paper presents a case study in which the influence of the 6-pulse thyristor-bridge input reactor size on the shunt active power filter (SAPF)’s work performance is investigated. The purpose of using an SAPF in the power system is in most cases for fundamental harmonic reactive power compensation, harmonics and asymmetry mitigation. The work efficiency of such a filter depends not only on the designed control system, interface filter and dc-link capacitor parameters, but also on the parameters of the electrical system in which it is connected. Therefore, it is necessary to study and know the power system (supplier and consumer sides) before its installation. For instance, in the electrical system with diode or thyristor-bridge as loads, the SAPF performance efficiency may not be satisfied due to the high rate of current change (di/dt) at the points of commutation notches. In this paper, the performed simulation and laboratory experiments show that for a better operating efficiency of the SAPF, the input reactor parameters should be selected based not only on the effective reduction in the inverter switching ripple or the control system demand, but also on the parameters of the load, such as the parameters of the diode or thyristor-bridge input reactor. Apart from the experimental demonstrations on how the input reactor size influences the SAPF work efficiency, the novelties in this paper are: the formulated recommendations on how to choose the SAPF input reactor parameters (the SAPF is more efficient in terms of harmonics, asymmetry and reactive power mitigation when the inductance of its input reactor (L-filter) is smaller than the one of the diode or thyristor-bridge input reactor); the proposed SAPF control system; the proposed expressions to compute the SAPF input reactor inductance, DC voltage and capacitor. Full article

One of the most common power problems today is communication and control delays. This can adversely affect decision interaction in grid security management. This paper focuses on communication signal delays and how to identify and address communication system failure issues in the context of grid monitoring and control, with emphasis on communication signal delay. An application to solve this problem uses a thyristor switch capacitor (TSC) and a thyristor-controlled reactor (TCR) to improve the power quality of the Rwandan National Grid (RNG) with synchronous and PV generators. It is to counteract the negative effects of time delays. To this end, the TSC and TCR architectures use two methods: the fuzzy logic controller (FLC) method and the modified predictor method (MPM). The experiment was performed using the Simulink MATLAB tool. The power quality of the system was assessed using two indicators: the voltage index and total harmonic distortion. The FLC-based performance was shown to outperform the MPM for temporary or permanent failures if the correct outcome was found. As a result, we are still unsure if TSC and TCR can continue to provide favorable results in the event of a network cyber-attack. Full article

Different types of fault current limiters (FCLs) have been developed and designed based on non-superconducting DC reactors (NSDRs). This paper proposes a controllable dual-bridge FCL (CDBFCL) based on the NSDR for use in an AC-type micro-grid. It includes a NSDR and two series and shunt bridge circuits. The series bridge is based on diode semiconductor switches and is coupled in series with the line via a transformer. The shunt bridge is based on thyristor semiconductor switches and is coupled in parallel with the line. The shunt bridge provides a variable voltage source. It compensates for the DC side voltage drop due to NSDR resistance and semiconductor switches during normal operating condition. In addition, by controlling the shunt bridge firing angle, it produces a controllable DC voltage, which can control the fault current amplitude during a fault. The structure, principle operating work, and control system of the proposed CDBFCL are presented. The CDBFCL performance is studied analytically and through simulation by the PSCAD/EMTDC software. In addition, the simulation results are compared with those obtained experimentally from a prototype CDBFCL and show a close correlation. Full article

The thyristor-controlled reactor (TCR) compensator for smooth asymmetric compensation of reactive power in a low-voltage utility grid is proposed in this work. Two different topologies of compensator were investigated: topology based on a single-cored three-phase reactor and topology with separate reactors for every phase. The investigation of the proposed TCR compensator was performed experimentally using a developed experimental test bench for 12 kVAr total reactive power. The obtained results show that employment of separate reactors for every phase allows us to control the reactive power in every phase independently, and that the TCR compensator with three single-phase reactors is suitable for smooth and asymmetric compensation of reactive power in a low-voltage utility grid. Full article

This paper proposes a new hybrid static VAR compensator (SVC) with a series active filter (AF). The proposed hybrid SVC consists of a series AF and SVC. The series AF, which is connected in series to phase-leading capacitors in the SVC, performs for a resistor for source-side harmonic currents. A sinusoidal source current with a unity power factor is obtained with the series AF, although the thyristor-controlled reactor generates harmonic currents. A digital computer simulation was implemented to confirm the validity and high practicability of the proposed hybrid SVC using PSIM software. The simulation results demonstrate that sinusoidal source currents with a unity power factor are achieved with the proposed hybrid SVC. Full article

The static VAR compensators having fixed capacitor thyristor controlled reactor (FC-TCR) used to improve voltage stability in power systems are nonlinear elements. The fixed capacitor group will produce reactive power while the thyristor controlled reactor will consume reactive power in compensators having FC-TCR. Changing the firing angles of TCR provides the reactive power variation of the system since the reactive power production of capacitors is fixed at a determined voltage level. In some cases, the variation of these firing angles will cause the harmonics in the system. In this study, TCR's are discussed to be harmonic sources and the resonance case caused by harmonics has been investigated with Fourier Matrix Model and MATLAB Software. Full article