Modular multilevel cascaded converter-based STATCOMs are scalable to higher voltages without requiring a step-up transformer with multiple windings and can be realized using a low switching frequency, giving lower harmonic content and hence a reduced filtering requirement. The paper presents a new injection technique to extend the operating ranges of MMCC STATCOMs when used for negative sequence and reactive current compensation. A non-sinusoidal voltage or current containing a fundamental and its third harmonic component is injected to achieve phase cluster voltage balance. This technique reduces the maximum dc-link voltage for the star configuration, and the maximum converter phase circulating current for the Delta case, compared to applying only sinusoidal zero sequence components for mitigating the same degree of load unbalance. The analysis is confirmed experimentally, showing that the third harmonic injection can allow a significant improvement of STATCOM capability for simultaneous compensation of unbalanced load and reactive curre

This paper presents a novel configuration of a unified power flow controller (UPFC) comprising a modular multilevel cascaded converter (MMCC) with a full-bridge inverter. The MMCC has one end of phase-legs shunt-connected to the transmission line. The other end connects in parallel to the primary terminals of a series line transformer, and the ac output terminals of a full-bridge dc-ac inverter. The submodules in the MMCC are full-bridge flying capacitor converters. This UPFC is compared to another type of MMCC-UPFC which uses double-star configuration, and submodules are of half-bridge chopper circuits; this is referred to as the Double Star Chopper Cells UPFC (DSCC-UPFC). The comparison is in terms of footprint, cost and performance. The new topology is lighter, more efficient and cheaper than the DSCC. Its operation principle and control scheme, which combines the regulations of voltage and of power flow along the transmission line are presented. Simulation studies for this new MMCC-UPFC realizing power flow control in a dual voltage sourced power network are presented and show good performance under varying operation conditions. The paper also evaluates the power control margins of this device.

Voltage source inverters are extensively used in the grid connection of renewable energy-sourced generators, and multilevel converters, in particular, have attracted a great deal of attention in recent years. This paper investigates the application of a novel passivity-based sliding mode (PSM) control scheme on three-level grid-tie active Neutral-Point-Clamped (ANPC) inverters that yield fast and stable responses to grid impedance variations. Simulation studies confirm that this control scheme can produce high tracking performance and is also robust against grid load variations. Furthermore, to enhance ANPC efficiency, the loss distribution of switching devices controlled by the proposed strategy is evaluated. An optimal scheme is finally proposed for allocating silicon and Wide-Band-Gap switching devices, resulting in a hybrid ANPC inverter capable of achieving a desirable trade-off between the power losses and the device cost.

In most of current studies on SSVEP based BCIs, low-frequency and medium-frequency visual stimuli are used, and subjects are prone to fatigue. The BCI based on high-frequency SSVEP can improve the comfort level of subjects in experiment and reduce the possibility of inducing diseases such as epilepsy. This paper proposed a method combining empirical modal decomposition (EMD) and canonical correlation analysis (CCA) to improve the classification accuracy of high-frequency SSVEP. The experiment results show that the EMD-CCA based method is more suitable for high-frequency SSVEP based BCI, which can achieve a maximum accuracy of 93.68% and an information transmission rate of 15.0236 bit/min ^-1 .

Study on retaining good classification performance when reducing training effort is valuable for the development of brain-computer interface (BCI). In this paper, an improved self-training algorithm using only a small number of labeled samples is adapted for motor imagery EEG classification. Unlike the traditional self-training algorithm that uses only one classifier, an additional classifier is introduced in the improved version for sample selection, which helps to reduce the error reinforcement, increases the classification accuracy, and improves the convergence in the iteration process. Experiment results show that the improved self-training algorithm outperforms its prototype in the two-class classifications. Even for the subjects who have performance degradation when using the traditional self-training algorithm, the improved algorithm still increases the classification performance iteration by iteration. We also compare the improved method with a supervised method which uses all the training data, and there are no significant differences in classification accuracy. It can achieve a little higher performance comparing with an existing semi-supervised method on the same data.

The paper proposes a parallel transformerless (TL) static synchronous series compensator (SSSC) for the control of power flow along the power distribution lines under balanced or unbalanced voltages. This new SSSC configuration offers the advantages of a fast dynamic response, light weight, and high efficiency. By connecting multiple SSSCs in parallel, the current rating is increased, which improves the grid power transfer capabilities and flexibility. However, there may be circulating current flowing between the parallel-connected inverters, hence causing losses. A modified model predictive control scheme is thus developed, which ensures that the proposed SSSC accurately tracks the reference currents while effectively mitigating the circulating current. The model and cost function of the controller are derived and analyzed in the paper. A real-time simulation of a power line with the parallel TL SSSC controlled by a hardware-in-loop (HIL) DSP is developed to validate the performance of this device under both balanced and unbalanced line voltages.