Since the harmonic frequency of 400Hz inverter is relatively high, it is difficult to eliminate the low-order harmonics with the traditional dual-loop control. Aiming at achieving zero steady-state error and enhancing the ability to suppress harmonics, the plugged-in repetitive control (RC) with the damping-based notch filter (DNF) is proposed. The DNF not only ensures the high open-loop gain at harmonic frequencies, but also facilitates the stability identification by ‘the two unit circles’. As the magnitude/phase-frequency behavior of the RC control plant is anticipated to be characterized by OdB and 0 degree, the internal current loop is regulated by the elaborated active damping loop with phase compensation. As the minimal-phase behavior is guaranteed, the harmonics around the resonance frequency$\boldsymbol{f}_{\mathbf{r}}$is well suppressed without threatening the stability of the RC-based system. Experimental results finally validate that the total harmonic distortion (THD<1%) is reduced by the elaborated repetitive control strategy.

Digital control is suitable for high-performance 400Hz inverters because of its simple control circuit, strong robustness and good dynamic performance. Considering the efficiency and device characteristics, the frequency modulation ratio of 400Hz inverter is relatively low, which leads to a negative influence on the dynamic performance of the inverter. Meanwhile, the output voltage harmonics of 400Hz SPWM inverter in low frequency band are large because of dead-time effect and digital delay. To cope with these problems, firstly, the influence of dead-time and digital delay is introduced in this paper. Then, the approach which combines reducing switching frequency, adding PR controller with phase compensation and serial harmonic trap is put forward. The dynamic performance and power quality of 400Hz inverter can be improved by the optimization of output filter and control parameters. Theoretical analysis and experimental results verified the proposed control method.

In the inverter-grid interconnected system, the impedance model which breaks the entire system into two independent subsystems is widely adopted to facilitate the stability analysis. This paper shows that the inverter output impedance Zomay be erroneously estimated if the frequency coupling effect of the phase-locked loop (PLL) is overlooked. To fully capture the dynamic interactions between the single-phase inverter and the grid, a multifrequency admittance matrix is proposed based on the linearized small-signal PLL model. Further on, a developed single-frequency output impedance model characterized by clear physical meaning is derived to facilitate the resonance identification and the stability assessment. It is found that Zoalso depends on the grid impedance, which significantly influences the interconnected system stability under the weak grid. Using the impedance-based stability criterion, the stability of the single-phase grid-tied inverter system can be clearly identified. The close match between the theoretical output impedance curve and the measurement result validates the correctness of the proposed impedance model. The experimental waveforms also verify that the dynamic interactions contributed by the frequency-coupling effect of the PLL and the grid impedance.

Swiss-rectifier (SR) is a family of high efficient AC-DC topologies. It's a combination of a three phase unfolder circuit which can convert the three-phase AC voltage into two sets of cyclically varying DC voltages and two symmetric DC-DC converters to achieve power factor correction (PFC). In order to obtain a zero voltage switching (ZVS) isolated single-stage rectifier system, two phase-shifted full-bridge topologies are applied to increase the working frequency of the magnetic elements. However, the current flows through at least four switches during the power conduction or freewheeling period. It is not conducive to improve the efficiency of full-bridge based SR. Thus, an optimized single-stage isolated phase-shifted full-bridge (PSFB) based Swiss-rectifier is proposed. Only one full bridge structure is used to reduce the conduction loss when the power is transmitting. Two voltage clamp branches are used to implement the PFC principle of the SWISS-rectifier. The principle of operation and the analytical equations for the stress in the semiconductor devices are discussed specifically. The performances of the proposed converter are verified by the experiments on a 10-kW 380Vac input/400Vdc output prototype with 90kHz switching frequency.

Motivation: High throughput bisulfite sequencing (BS-seq) is an important technology to generate single-base DNA methylomes in both plants and animals. In order to accelerate the data analysis of BS-seq data, toolkits for visualization are required. Results: ViewBS, an open-source toolkit, can extract and visualize the DNA methylome data easily and with flexibility. By using Tabix, ViewBS can visualize BS-seq for large datasets quickly. ViewBS can generate publication-quality figures, such as meta-plots, heat maps and violin-boxplots, which can help users to answer biological questions. We illustrate its application using BS-seq data from Arabidopsis thaliana. Availability: ViewBS is freely available at: https://github.com/xie186/ViewBS. Contact: [email protected]. Supplementary information: Supplementary data are available at Bioinformatics online.

This paper presents a new middle-stage current-fed high-frequency link inverter (MSCF-HFLI). The proposed inverter only contains one passive buffering energy element comparing with conventional resonant type HFLI, which at least has two passive buffering energy elements. The topology of the proposed inverter is given and the operational principle in a line-frequency cycle is analyzed, which is similar to that of Buck converter in current discontinuous conduction mode (DCM). The constraint relationship, which the proposed inverter must be obeyed, is derived. According to this mathematical relationship, a closed-loop control strategy is proposed for MSCF-HFLI. Experimental verifications are presented to verify the analysis.

A new single-stage and boost-voltage grid-connected inverter with low-frequency current ripple (LFCR) reduction was presented in this paper. It can be applied in fuel cell generation system. The signal modulation method was given within a line cycle. In the proposed inverter, an inverter bridge-leg was shared by Boost converter, which decreased the cost and improved the efficiency of the system. The boost inductor current was operated in discontinuous mode (DCM), which can effectively decrease LFCR in output current of fuel cell. Experimental results were presented to verify the analysis.

The elimination of leakage current is of first importance for transformerless grid-tied photovoltaic (PV) inverters. A unified leakage current analytical model for single phase inverters, which unifies topologies of both transformer and transformerless, is presented in this paper. It is suitable for the analysis of leakage current elimination mechanism for all the bridge topologies, which are systematically analyzed and categorized. After that, the topologies of H5, Heric and a H6-type configuration are optimized. The leakage current of these optimized inverters can be better eliminated by changing the topology configuration and substituting the suppressor way of changing the common impedance with the way of constant common voltage. On the other hand, the inverters can operate in any power factors by means of the optimization of the modulation strategies. A grid-tied photovoltaic inverter experiment is conducted with a 5kW optimized Heric prototype, and the theoretical analysis is verified.

The output voltage range of photovoltaic (PV) cell is widely influenced by the light, temperature and so on. The inverter used in PV system must achieve inversion with a wide range of DC input voltage. A single-stage buck-boost inverter with fewer inductors and capacitors is proposed in this paper based on the topology of full bridge+Boost AC/AC, which is just suitable for PV system, achieving inversion and boosting with a wide range of input. Two modulation methods are compared: constant step-up ratio modulation and dual mode modulation. Along with the relationship of the input DC voltage and the reference AC voltage, the converter complete buck or boost inversion with different equivalent circuits and there are fewer switches working at high frequency in dual mode modulation, which is in favor of the system with high efficiency. Simulation and experimental results are presented to verify the proposed topology can achieve dual mode operation with wide range of input voltage in single-stage power conversion.