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Optimal power flow (OPF) is an important tool in an electricity market. Despite traditional optimisation techniques being implemented successfully in the existing power systems, there are still difficulties. One of these difficulties is that it is easy to be caught by a local minimum solution because OPF is a mathematically nonconvex problem with multimodal characteristics. The paper proposes a hybrid optimisation algorithm for solving OPF problems with multimodal characteristics. The hybrid algorithm is structured in two stages. The first stage uses the chaos optimisation algorithm (COA), while successive linear programming (SLP) is employed in the second stage. A linear predictor-corrector primal-dual interior point (PCPDIP) method is applied to solving a sequence of linearised sub-problems. The hybrid algorithm involves two levels of optimisation, namely global search by the COA and local search by the linear interior point method, which co-operates in a global process of optimisation. It can provide more robust convergence on OPF problems than either algorithm alone. IEEE-14, -30 and -57 bus test systems with complex objective functions are run. Numerical results illustrate the feasibility and potential of the proposed hybrid algorithm.