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Load Flow
Published in Antonio Gómez-Expósito, Antonio J. Conejo, Claudio A. Cañizares, Electric Energy Systems, 2018
Antonio Gómez-Expósito, Fernando L. Alvarado
It may be correctly argued that the slack bus concept is a mathematical artifact, without any direct link to the real world, as no bus in the system is explicitly in charge of providing all ohmic losses. Indeed, for very large systems, power losses may exceed by far the capacity of certain generators. However, if an estimation of power losses is available, which is usually the case, then all generators can share a fraction of those losses. This way, in addition to its own power, the slack bus will be responsible only for the power system imbalance, that is, the difference between the total load plus actual losses and the total specified generation, leading to a power flow profile closely resembling actual operation. Unlike ohmic losses, the resulting system imbalance may be positive or negative. In Reference 1, instead of determining a priori which bus plays the role of slack bus, it is selected on the fly during the load flow computation process in such a way that the system power imbalance is minimized.
Newton Power Flow Modeling of Voltage-Sourced Converter Based HVDC Systems
Published in Suman Bhowmick, Flexible AC Transmission Systems (FACTS), 2018
Now, similar to AC power flow, a slack bus is chosen for the DC power flow and its voltage is pre specified. It serves the dual role of providing the DC voltage control and balancing the active power exchange among the converters. From Figure 8.2, in the p terminal DC system, the first terminal is chosen as the DC slack bus, by convention. This is represented as () VDC1SP−VDC1cal=0
Power Flow on Transmission Networks
Published in George Kusic, Computer-Aided Power Systems Analysis, 2018
where the slack bus voltage is a known, fixed reference. In Equation 5.36, δt is the phase angle of the ith bus with respect to the slack bus and Vl the magnitude of the ith bus voltage. The 2n − 2 nonlinear equations f(X) are the calculated real and reactive power injections, while b is the specified power at the bus. The power flow problem is to find the power system state vector Xk that satisfies the desired or constrained power at the buses.
A Novel Modified Decoupled Newton-Raphson Load Flow Method with Distributed Slack Bus for Islanded Microgrids Considering Frequency Variations
Published in Electric Power Components and Systems, 2023
Ashiq Hussain Lone, Neeraj Gupta
A comparison of the conventional NR load flow and the modified decoupled NR load flow methods has been briefly given in Figure 3. As this is clearly shown in figure that we can not have a slack bus in case of an islanded MG. In a power system, a slack bus is a bus whose voltage and frequency stays constant regardless of the number of tappings taken from it; also, a slack bus is anticipated to meet all the system losses. Because the sources in an islanded MG have low ratings, no bus may be picked to serve as a slack bus. The following are the key advantages of distributed slack bus:
Optimal energy management in a microgrid with known power from the grid based on a particle swarm optimisation embedded fuzzy multi-objective approach
Published in International Journal of Ambient Energy, 2022
Hemanth Chaduvula, Debapriya Das
In this work, a 33-bus grid-connected microgrid system and a 33-bus microgrid system with zero bus DER are shown in Figure 1 and Figure 2, respectively. A 69-bus microgrid system with unknown power from grid and with zero bus DER are presented in Figure 3 and Figure 4, respectively. In both the systems, CHP units of type biomass (BIO), natural gas fuel cell (NGFC) and natural gas turbine (NGT), and heat boiler are integrated. The NGT unit has a lower fuel cost coefficient and the BIO produces least emission in the system. The fuel cost-coefficient of NGFC unit is lower than that of BIO but higher than that of NGT. The emission from NGFC is huge. The grid’s electricity price varies according to the off-peak and peak periods. The emission by the grid is lower than that of NGT and NGFC units. In the case of GMG, active and reactive powers are undefined at the slack bus. So the slack bus is responsible for maintaining the power balance in the system. In the case of ZBMG, the power taken from the grid is known and so one of the dispatchable DER units (zero bus DER) in the system is responsible for satisfying the power balance. The NGT-type zero bus DER is chosen for its fuel and emission characteristics. The location of NGT is obtained at bus 6 in the case of a 33-bus distribution system, as shown in Figure 2, and at bus 9 in the case of a 69-bus distribution system, as shown in Figure 4, based on minimum power loss condition (Das, Mukherjee, and Das 2019). The boiler produces heat when there is insufficient heat generation from CHP units to meet the heat demand in the system. The 33-bus system has a peak electrical demand of 3.715 MW, 2.3 MVAR, and the 69-bus system has a peak electrical demand of 3.8022 MW, 2.6946 MVAR. Both systems have a peak heat demand of 6 MW. A 24 h (= 24) load pattern for electrical and heat demand is shown in Figure 5, and it is derived from (Grigg et al. 1999). From Figure 5, the peak value of the electrical and heat load occurs at the12th and 18th hours, and the minimum value of the electrical and heat load occurs at the 4th and 5th hours, respectively.