State space model enhanced stacked convolutional long short-term memory for blade damage identification

Current vibration-based damage identification methods face difficulties in accurately identify damage features due to the low richness of data feature for wind turbine blade. This article introduces convolutional long short-term memory (ConvLSTM) that can better characterize the spatiotemporal characteristics in deep learning and explores the damage identification method combining stacked ConvLSTM network with structural state space model. A state space model enhanced stacked ConvLSTM for blade damage identification is proposed. First, the vibration signals of the blades at different damage states are converted to time-frequency images through the preprocessing of normalization and wavelet transform. The preprocessing operation improved the damage characteristics of the original vibration signals. Then, the designed stacked ConvLSTM is used to train and test time-frequency images at different damage states and output damage states and corresponding probability values through Softmax component. During the training, the different between the state equation of blades and cell state of stacked ConvLSTM is taken as loss function. Finally, specific parameter of the proposed state space model enhanced stacked ConvLSTM are set using the displacement data of blades in OpenFast software, and the recognition results are compared and validated with the mainstream networks convolutional neural network (CNN), LSTM, and ConvLSTM. The results show that, among these networks, 1D CNN, 2D CNN, LSTM, ConvLSTM, and BConvLSTM, the proposed state space model enhanced stacked ConvLSTM network achieves the best recognition results. Compared with the standard ConvLSTM network, the accuracy and mean intersection over union of the proposed state space model enhanced stacked ConvLSTM network are improved by 1.69% and 4.4%, respectively. Moreover, the proposed state space model enhanced stacked ConvLSTM achieved recognition accuracy of over 97% at different wind turbine blades working conditions. This indicates that the proposed state space model enhanced stacked ConvLSTM for blade damage identification has high accuracy and robustness. The effectiveness of the proposed state space model enhanced stacked ConvLSTM in blade damage identification has been validated again through laboratory scale wind turbine blade damage test.