With the increase of switching frequency and power density of power converters, the cost and difficulty for reducing electromagnetic interference (EMI) are increased. Since the passive EMI filters (PEFs) are bulky and heavy, they are difficult to meet the high-power density requirements of power converters. In recent years, the active EMI filters (AEFs) have attracted more and more attention due to their advantages on small size and high integration. However, AEFs have the disadvantages on poor high-frequency suppression effect and high cost in real applications. The limited filtering effect means that AEFs often cannot operate independently and exist in the form of compensating PEFs. To solve the above problem, a variable Y-capacitor based AEF (VYC-AEF) topology is firstly proposed in this paper by using a voltage and current dual-sampling structure, to realize the low cost and high insertion loss. Further, the design method of the proposed VYC-AEF is provided in detail. Following, the simulation and experimental results prove that VYC-AEF can greatly improve the filtering effect of Y-capacitor, and has high insertion loss compared with the existing AEF. Finally, the cost comparison with the existing AEF and PEF is given. Therefore, this paper provides a new choice for EMI suppressing of the power converters with the requirements of low cost and high-power density.

Virtual synchronous generator (VSG) could provide larger inertia and damping support for distributed generation system. However, VSG also suffers the stability problems under the disturbances, which makes the controller design of VSG face challenges. In this paper, a novel eigenvalue sensitivity-based stability improvement control method of VSG is proposed, which can improve the stable region of the control parameters, thereby, improve the robustness of the VSG. Firstly, the stability improvement mechanism is introduced based on the time-domain model of a VSG, then the stable region of the control parameters is analyzed and the effect of stability improvement is verified by circuit simulation. Finally, the conclusions are drawn. This paper provides a new way for VSGs with the high stability requirement to generate the control strategies.

Overshoot is a key dynamic index of DC-DC converters. Excessive overshoot is harmful to DC converters, which could break down switch devices, threaten the safe operation of the system. In this paper, a voltage overshoot design method for DC-DC converters based on state overshoot concept is firstly proposed to obtain the accurate voltage overshoot in the theoretical design stage by reasonably designing the PI parameters. Next, taking buck converter, boost converter and two-stage cascaded buck converter as examples, the ranges of PI parameters by considering the set voltage overshoot are designed theoretically. Finally, the time-domain waveforms from the simulation and experiment of the above three DC-DC converters are provided to show the correctness and the applicability of the proposed method in real engineering. This method provides an accurate and practical design method of voltage overshoot for DC-DC converters.

Due to the fluctuation of the power grid and the use of filters, the grid-connected inverter is prone to oscillation, so it is very important to develop an universal stability-improving method for the grid-connected inverters. The traditional stability improvement methods are mostly based on the frequency-domain transfer functions, and the proposed method has great randomness. In this paper, a stability improvement method based on parameter sensitivity combining time-domain Floquet theory is proposed firstly, which can develop a series stability-improving methods for the grid-connected inverter according to the practical requirements, without deriving the complex input impedance and output impedance of the inverter system. Further, taking a single-phase gird-inverter as an example, the proposed stability-improving method is introduced and verified in simulation. Finally, the correctness and the effectiveness of the proposed method is proved by the simulation results.

LLC resonant converter is widely used in DC-DC conversion of switching power supply with its inherent soft switching and low loss performance, and its stability is particularly important. Recently, some scholars applied the stability method based on Floquet theory in the time-domain to the stability analysis of LLC resonant converter. The stability margin of the original control maybe insufficient when LLC resonant converter work under different operating conditions. Therefore, it is necessary to improve the stability margin of LLC resonant converter system. In this paper, on the basis of the time-domain Jacobian matrix model of LLC system according to the Floquet theory, combining with eigenvalue sensitivity analysis and matrix elementary transformation, the stability improvement method of additional resonant current peak proportion control is proposed. Secondly, the stable range of the newly added control parameter is analyzed based on Floquet stability criterion. Finally, theoretical analysis and PSIM simulation verify the effectiveness of the proposed additional control method and improve the stability margin of the control parameter of original system.

The contribution of SiC power devices to the whole power conversion system still lacks comparative analysis verification. This paper experimentally investigates a high-performance All-SiC power module to provide solid evidence for the excellent performance of SiC semiconductor in the high power electrical energy conversion. The All-SiC power module in this paper, featured with high-efficiency and high-power-density, is intended for the power supply rectifier of electrolysis inactivation in the Ballast Water Management System (BWMS). Conventional All-Si power module for BWMS rectifier used low switching frequency Si IGBTs as their power devices, resulting in low power density and limited efficiency. This paper schemes the technical approach based on fast switching SiC MOSFETs, and then experimentally investigates the performance of it. Finally, the comparison between the traditional All-SiC and All-SiC power modules verifies the technical advantages by using SiC MOSFETs as the power devices.

In order to estimate the short-circuit capability of SiC MOSFET-based power converter, this paper proposes a behavioral model of SiC MOSFET that can be used for short-circuit simulation in PSpice, and the leakage current generated during short circuit is considered, which is an early warning of device failure. The short-circuit characteristic of SiC MOSFET is discussed and analyzed, and a thermal model of case-to-junction is built to describe the junction temperature of SiC MOSFET during short-circuit condition. Based on the junction temperature information, the channel current model and leakage current model are established respectively. The simulation results show that the short-circuit model can correctly reflect the static characteristic and short-circuit characteristic of SiC MOSFET. This circuit model can provide guidance for the design of short circuit protection circuit.

Chaotic pulse width modulation (PWM) is introduced to Boost converters to suppress its electromagnetic interference. However, the conventional stability criterion with linear modeling method is not accurate and unpractical for chaotic PWM Boost converters because of the chaotic dynamic characteristics and the switching frequency variation. In this paper, the describing function method is applied to model the switching process under chaotic PWM in Boost converters with considering the chaotic switching frequency. Further, based on the derived describing function, the accurate stability analysis criterion of chaotic PWM Boost converters can be obtained, the stable region is a little smaller compared with the conventional PWM with fixed switching frequency. Finally, the simulation and experiment results demonstrate the accuracy and effectiveness of the proposed describing function method based on a Boost converter. Therefore, this paper provides a stability analysis method for Boost converters under chaotic PWM.

To solve the simulation convergence problem of Silicon Carbide metal-oxide semiconductor field effect transistor (SiC MOSFET) models, this paper proposes a non-segmented model for SiC MOSFETs, which uses non-segmented, smooth continuous equations to describe the static and dynamic characteristics of SiC MOSFET. Further, the static characteristic of SiC MOSFET obtained by the non-segmented model is verified by comparing the simulation curves with the static curves provided in datasheet, and the dynamic characteristic is verified by comparing the simulation rise time and fall time of voltage with the datasheet based on the double pulse simulation circuit. The accuracy and good convergence of non-segmented model provide a good way to research the power converters with SiC MOSFETs by simulation way.

This paper proposes a parameter design method to optimize the single-phase synchronverter (SPSV) dynamic stability considering the influence of low-pass filter, which in the torque measurement loop and reactive power measurement loop is essential for SPSV to filter out twice the line-frequency power oscillation. The oscillation is inherent from the character of single-phase power calculation. However, the low-pass filter will influence SPSV dynamic stability by introducing a delay element into the SPSV control loop. This paper reveals how the low-pass filter impacts the SPSV dynamic stability by using small signal model. Furthermore, a parameter design method is proposed to maintain SPSV dynamic stability and avoid large overshoot during the dynamic process when grid voltage or frequency changes. Finally, the analysis and parameter design method are verified by simulation and experiment.

Ferrite chokes are often applied to suppress electromagnetic interference (EMI) in power converters. In this paper, an improved ferrite choke RLC model and its parameters determination method are proposed. The improved ferrite choke RLC model can overcome the limitation of the existing RLC model in the low frequency band, and the proposed parameters determination method can calculate the values of RLC parameters more accurate according to curve fitting of the ferrite choke datasheet. The effectiveness of the improved ferrite choke RLC model is verified by simulation based on a PWM rectifier, and the accuracy of the parameters determination method is verified by the impedance fitting results. The proposed ferrite choke RLC model and parameters determination method in this paper can provide ferrite choke choosing guidance for power converters in engineering application.

In the operation of a photovoltaic system, one of the most important issues is absorbing maximum power from the PV array under continuous and rapid changing irradiance condition. The sampling points obtained at different moments are not on the PV characteristic curve with the same irradiance, so the MPPT strategy may misjudge. In this paper, a novel method to track the MPP is presented, which is based on three-point disturbance observation. The proposed algorithm utilizes three operating points that work in different duty cycle, using two points to restore a virtual operating point which is the same PV characteristic curve as the rest of the point. The proposed algorithm suppress the oscillation and misjudgment problem of traditional P&O method. And simulation and experimental results validate the performance of the proposed algorithm under continuous and rapidly changing irradiation conditions.