Xiaoqing Zhang

In order to ensure continuous DC link current, the overlap time introduced in the switching process of the current source rectifier (CSR) can lead to undesirable harmonics and reduce grid-side current quality. To address this issue, a hybrid space vector modulation (HSVM) method is proposed. This method designs two current vector sequence modes by reconstructing the sequence of the dwell current vectors. Then, an adaptive threshold decision (ATD) method is introduced, which can dynamically select two sequence modes during the modulation process to solve the current sharing phenomenon. The proposed method no longer need to add overlap time in modulation and fundamentally eliminates the overlap time effect (OTE). Moreover, it can minimize the switching times by using reverse voltage to block the on-state switches. By comparing with the ideal five-segment space vector modulation, theoretical analysis, simulation and experimental results prove the effectiveness of HSVM in improving system performance and minimizing the number of switching operations.

In order to effectively reduce the current distortion caused by introducing overlap time, an overlap-time optimization space vector modulation (SVM) method based on vector sequential reconstruction (VSR-SVM) for current source converters (CSCs) is proposed. First, the rules that are not affected by the overlap-time effect (OTE) are identified, and the sequence of the current vectors is adjusted on this basis to eliminate the OTE within the carrier. Next, a modulation increment is added to the adjusted modulation signal to obtain a new modulation signal to remove the OTE between carriers. Then, the driving signals are obtained by comparing the new modulation signals with the carrier. Finally, the overlap time is added after the turn-off signals to correct the dwell time. This method intentionally modifies the modulation signals so that the effective dwell time of the current vector is the same as the ideal dwell time. Simulation and experimental results show that this method can effectively improve the current quality under different power factors, loads, overlap time, and modulation indices.

In this article, an insulated gate bipolar transistor (IGBT) open-circuit (OC) fault diagnosis method based on horizonadaptive period correction (HaPC) is proposed for voltage source inverter (VSI). It can achieve the diagnosis and location of any IGBT OC fault under frequency variation conditions. First, a horizon-adaptive period extraction (HaPE) method is proposed, which is used to accurately obtain the period of the current signal as the frequency changes. HaPE converts the signal from the time domain to the phase domain to indirectly obtain the period of the current signal, while making the number of sampling points in each period the same. Second, a multidimensional characteristic extraction based on virtual time domain period correction (VTDPC) method is proposed. It can achieve the identity of different period characteristics, thereby greatly reducing the amount of training data. Finally, support vector machine (SVM) algorithm is used for classification to locate faults. Compared with other fault diagnosis algorithms, the proposed method is not affected by the amplitude and period changes caused by frequency changes, and can accurately locate faults. Simulation and experiments verify the accuracy and effectiveness of the proposed fault diagnosis method in VSI OC fault diagnosis.