Converter　fault　diagnosis　is　an　important　research　content　for　reliable　operation　of　power　electronic　system.　Taking　Dual　Active　Bridge　(DAB)　converter　as　the　object,　this　paper　proposes　a　Wavelet　Packet-RBF　Neural　Network　based　open　circuit　fault　diagnosis　method　for　DAB　converter.　Firstly,　the　fault　signal　is　decomposed　and　reconstructed　by　multi-scale　wavelet　packet,　and　the　wavelet　packet　energy　is　extracted　as　the　fault　feature　vector.　Then,　Principal　Component　Analysis　(PCA)　was　used　to　reduce　the　dimension.　Finally,　the　fault　is　diagnosed　by　RBF　neural　network.　The　Hardware-in-the-Loop　simulation　results　show　that　the　fault　diagnosis　method　has　the　advantages　of　high　accuracy　and　short　diagnosis　time,　and　the　feasibility　and　the　advanced　nature　of　the　proposed　method　are　verified.　©　2021　IEEE