Accurate and fast transient stability assessment is helpful for grid operators to take effective emergency control actions after faults. The gradual deployment of the wide-area measurement system provides a basis for ...Accurate and fast transient stability assessment is helpful for grid operators to take effective emergency control actions after faults. The gradual deployment of the wide-area measurement system provides a basis for introducing machine learning into transient stability assessment (TSA). However, the application of the machine learning model is restricted by the imbalance of samples in actual systems. In this paper, a time-adaptive assessment model with imbalance correction based on the ratio of loss function values is built to realize accurate and fast TSA. First, a long short-term memory (LSTM)-based model whose optimization goal is to reduce the prediction loss at a fixed time step is established. Several LSTM-based models with different decision time values are integrated as a multiple LSTM (MLSTM) TSA model. It is found that the effect of imbalanced samples on model parameters can be quantified by the loss function values. Then, the ratio of loss function values of two classes is obtained by pre-training, by which the imbalance degree of data can be quantified. The correction coefficient is determined and used to retrain LSTMs to solve the evaluation tendency problem. Simulation results in an IEEE 39-bus system and an actual power system show the excellent performance of the proposed imbalance correction scheme and evaluation scheme. Compared with traditional methods, imbalance correction can be achieved with better results.展开更多
In terahertz communication,the direct frequency conversion structure in which orthogonal mixer is the main frequency conversion unit,makes engineers get into trouble of in-phase(I)branch and quadrature(Q)branch imbala...In terahertz communication,the direct frequency conversion structure in which orthogonal mixer is the main frequency conversion unit,makes engineers get into trouble of in-phase(I)branch and quadrature(Q)branch imbalance,carrier wave leakage,etc.These damages result in system performance tremendous degrades.We proposed a semiblind method to estimate the I/Q imbalance of THz orthogonal modulator,based on predefined preamble and pilot symbols for quadrature amplitude modulation(QAM).In this paper,a transmitter with Y band quadrature mixer and 20Gbps base-band signal has been tested.The bandwidth of the baseband signal was 7GHz,and the modulation type was 16QAM.By this method,7dB improvement of the system’s symbol Mean Square Error(MSE)has been got.That means the proposed method can be used to eliminate the I/Q imbalance effectively.展开更多
This paper presents a VHF（30-300 MHz） RF programmable gain amplifier（PGA） with an adaptive phase correction technique.The proposed technique effectively mitigates phase errors over the VHF band,and the RFPGA as a ...This paper presents a VHF（30-300 MHz） RF programmable gain amplifier（PGA） with an adaptive phase correction technique.The proposed technique effectively mitigates phase errors over the VHF band,and the RFPGA as a whole satisfies all the specifications of the China mobile multimedia broadcasting VHF band applications.The RFPGA is implemented with a TSMC 0.25μm CMOS process.Measurement results reveal a gain range of around 61 dB,an ⅡP3 of-7 dBm at maximum gain,a power consumption of 10.2 mA at maximum gain,and a phase imbalance of less than 0.3 degrees.展开更多
文摘Accurate and fast transient stability assessment is helpful for grid operators to take effective emergency control actions after faults. The gradual deployment of the wide-area measurement system provides a basis for introducing machine learning into transient stability assessment (TSA). However, the application of the machine learning model is restricted by the imbalance of samples in actual systems. In this paper, a time-adaptive assessment model with imbalance correction based on the ratio of loss function values is built to realize accurate and fast TSA. First, a long short-term memory (LSTM)-based model whose optimization goal is to reduce the prediction loss at a fixed time step is established. Several LSTM-based models with different decision time values are integrated as a multiple LSTM (MLSTM) TSA model. It is found that the effect of imbalanced samples on model parameters can be quantified by the loss function values. Then, the ratio of loss function values of two classes is obtained by pre-training, by which the imbalance degree of data can be quantified. The correction coefficient is determined and used to retrain LSTMs to solve the evaluation tendency problem. Simulation results in an IEEE 39-bus system and an actual power system show the excellent performance of the proposed imbalance correction scheme and evaluation scheme. Compared with traditional methods, imbalance correction can be achieved with better results.
基金National Key RD Program of China Grant(2018YFB1801504)the President Funding of China Academy of Engineering Physics with No.YZJJLX2018009.
文摘In terahertz communication,the direct frequency conversion structure in which orthogonal mixer is the main frequency conversion unit,makes engineers get into trouble of in-phase(I)branch and quadrature(Q)branch imbalance,carrier wave leakage,etc.These damages result in system performance tremendous degrades.We proposed a semiblind method to estimate the I/Q imbalance of THz orthogonal modulator,based on predefined preamble and pilot symbols for quadrature amplitude modulation(QAM).In this paper,a transmitter with Y band quadrature mixer and 20Gbps base-band signal has been tested.The bandwidth of the baseband signal was 7GHz,and the modulation type was 16QAM.By this method,7dB improvement of the system’s symbol Mean Square Error(MSE)has been got.That means the proposed method can be used to eliminate the I/Q imbalance effectively.
文摘This paper presents a VHF（30-300 MHz） RF programmable gain amplifier（PGA） with an adaptive phase correction technique.The proposed technique effectively mitigates phase errors over the VHF band,and the RFPGA as a whole satisfies all the specifications of the China mobile multimedia broadcasting VHF band applications.The RFPGA is implemented with a TSMC 0.25μm CMOS process.Measurement results reveal a gain range of around 61 dB,an ⅡP3 of-7 dBm at maximum gain,a power consumption of 10.2 mA at maximum gain,and a phase imbalance of less than 0.3 degrees.
