Power Flow in a Multi-Frequency HVac and HVdc System: Formulation, Solution, and Validation

Abstract

This paper proposes a novel power flow formulation and solution algorithm for a generalized large-scale intercon nected transmission system encompassing multi-frequency HVac and HV dc grids having arbitrary numbers of buses, topologies, and operating frequencies. Back-to-back and ac/dc voltage-source converters are employed to interconnect and control the voltage and power interchange between two power grids operating at different frequencies. The power flow formulation is based on a steady-state model of back-to-back and ac/dc converters operated in centralized and distributed droop control strategies. Each power grid is represented by a set of nonlinear power balance equations. These equations are solved simultaneously using a unified power flow algorithm, taking into account generator and converter limits. It is shown that the solution convergence is achieved rapidly despite the system size, topology, and converter control strategies. The efficacy and accuracy of the proposed steady-state solution algorithm are demonstrated by comparing the numerical solution to the one obtained by time-domain electromagnetic models of multi-frequency HVac and HV de transmission systems with fully controllable back to-back and ac/dc converters. The results obtained by using the proposed algorithm and the time-domain simulation are practically identical.

Loss Minimization With Optimal Power Dispatch in Multi-Frequency HVac Power Systems

“…VIII. APPENDIX This section shows the exact symmetric Hessian matrices corresponding to constraints (16) - (22), while the corresponding Jacobian matrices can be found from the PF study in [10]. Since the formulations are similar for both VSC 1 and VSC 2 sides, the grid notations s and l associated with 60-Hz HVac and LF-HVac grids, respectively, are dropped.…”

“…The design of a grid-forming control for back-to-back (BTB) voltage-source converters (VSC) to maintain a stable offshore voltage for a long LF-HVac system is discussed in [9]. In [10], the control and coordination of BTB converters to form an LF-HVac grid and connect to a standard 50/60-Hz HVac and HVdc grids are presented. A generalized unified power flow (PF) formulation in polar coordinates and solution for such a multi-frequency HVac -HVdc power system are also included.…”

The Performance of the BTB-VSC for Active Power Balancing, Reactive Power Compensation and Current Harmonic Filtering in the Interconnected Systems

“…In fact, this type of configuration is the most used for WECS and MAECS [6,12,[18][19][20][21][22]. To achieve the objectives described above, control of the BTB-VSC is developed considering synchronous coordinates such as the rotating (dq0) [6,7,12,14,15,18,22,25,27,31] and stationary (αβ0) [17,23,29,31], as well as the time-domain or conventional (abc) [9,26,30], reference frame. Typically, depending on the used reference frame, the adopted control structure is chosen.…”

A Novel Control Scheme for Multi-Terminal Low-Frequency AC Electrical Energy Transmission Systems Using Modular Multilevel Matrix Converters and Virtual Synchronous Generator Concept

“…First, it supports the stability of the system by improving the voltage profile due to lower voltage drop. Second, it reduces the reactive power, to provide lower active power losses in a longer maximal transmission distance [9].The ac-ac converter acts as an interface between the low frequency side and the 50 Hz or 60 Hz grid. Many existing applications act as frequency converters choices for the LFAC system.…”

“…First, it supports the stability of the system by improving the voltage profile due to lower voltage drop. Second, it reduces the reactive power, to provide lower active power losses in a longer maximal transmission distance [9].…”