Bo Yang

Bio: Bo Yang is an academic researcher from Chinese Academy of Sciences. The author has contributed to research in topics: Power semiconductor device & Power module. The author has an hindex of 4, co-authored 13 publications receiving 40 citations.

A closed-loop voltage balance method for five-level diode-clamped inverters

Abstract: Voltage deviations of dc-link capacitors are the main problem of multilevel diode-clamped converters (DCC). In this paper, a novel carrier-based voltage balance method is proposed to balance the dc-link capacitors of five-level DCCs. The proposed method is characterized by injecting proper zero-sequence voltages in the modulation signals of carrier-based modulators. The effects of the injected zero-sequence voltages on the dc-link floating nodes are mathematically analyzed. Hereby, a closed-loop algorithm is proposed to determine the optimal zero-sequence voltages. Compared with the existing space vector based voltage balance methods, the proposed methods are easier to be implemented. Simulation and experimental results prove the effectiveness of the proposed voltage balance method.

Study on reducing switching current in dual bridge series resonant DC/DC converter

Abstract: Dual bridge series resonant DC/DC converter (DBSRC) usually works at continuous current mode (CCM), whose switching frequency is set higher than resonant frequency. Thus, soft switch-on and soft switch-off of power switch cannot be realized simultaneously with no extra snubber circuit connected. And the primary measure to reduce switching losses is to reduce the switching current of power devices. The commutations of DBSRC in different conditions are analyzed in this paper and the values of switch-on and switch-off current are derived from this model. From the view of reducing switching current, this paper gives a guideline to select the parameters of DBSRC correctly, including the voltage conversion ratio (M), the ratio between switching frequency and resonant frequency (F) and the characteristic impedance (Zr). The simulation obtains the switching currents at different F, M and Zr, whose results verify the effectiveness of theoretical analysis. And the experiment results prove a better system efficiency with a better selection of switching frequency.

Influence of parasitic elements of busbar on the turn-off voltage oscillation of SiC MOSFET half-bridge module

Abstract: In high-power converters based on SiC-MOSFET half-bridge modules, laminated busbar plays a critical role in linking the DC capacitor bank to power modules. The busbar stray capacitance has the same order of magnitude with drain-source capacitance of SiC-MOSFET and has a great impact on the turn-off voltage oscillation of SiC-MOSFET. In this paper, parasitic elements of a three-layer laminated busbar are extracted and a busbar model with consideration of stray capacitance is obtained. A spectrum analysis is performed on a small-signal model of equivalent circuit of double pulse test (DPT), and the model with busbar stray capacitance has lower oscillation frequency of turn-off voltage. The results of simulation and experiment of DPT indicate that the simulation waveforms of model with busbar stray capacitance are more consistent with the experimental waveforms over the entire voltage levels, which proves a greater accuracy of the proposed busbar model.

A modified general model for sic power MOSFET in rail transportation application

Abstract: A compact behavioral model for SiC power MOSFET is proposed. By applying more degrees of freedom in the channel current expression, removing the drift resistance and rectifying junction capacitance mathematical model, the proposed model can accurately reproduces those static and dynamic characteristics in datasheet. The convergence problem of original model is solved and less simulation time is needed. Moreover, the model was promoted to simulate 1200V/300A power module, which is suitable for rail transportation application.

Analysis and Comparison of High Power Bidirectional Isolated DC/DC Converters for Power Electronic Transformer

Abstract: Bidirectional isolated DC/DC converter is the core component of power electronic transformer (PET). And bidirectional series resonant DC/DC converter (SRC), dual active bridge DC/DC converter (DAB) and dual bridge series resonant DC/DC converter (DBSRC) are three great candidates for PET application. The operation principles and control methods of these converters are briefly analyzed in this paper. Then, the performance in current stress, output voltage characteristic, hard-switching current and system efficiency are compared from the perspective of simulation and experiments, whose results help to select a suitable DC/DC topology for PET.

A Novel Active Gate Driver for Improving Switching Performance of High-Power SiC MOSFET Modules

Abstract: Featuring higher switching speed and lower losses, the silicon carbide mosfet s (SiC mosfet s) are widely used in higher power density and higher efficiency power electronic applications as a new solution. However, the increase of the switching speed induces oscillations, overshoots, electromagnetic interference (EMI), and even additional losses. In this paper, a novel active gate driver (AGD) for high-power SiC mosfet s is presented to fully utilize its potential of high-speed characteristic under different operation temperatures and load currents. The principle of the AGD is based on drive voltage decrement during the voltage and current slopes since high dV/dt and dI/dt are the source of the overshoots, oscillations, and EMI problems. In addition, the optimal drive voltage switching delay time has been analyzed and calculated considering a tradeoff between switching losses and switching stresses. Compared to conventional gate driver with fixed drive voltage, the proposed AGD has the capability of suppressing the overshoots, oscillations, and reducing losses without compromising the EMI. Finally, the switching performance of the AGD was experimentally verified on 1.2 kV/300 A and 1.7 kV/300 A SiC mosfet s in double pulse test under different operation temperatures and load currents. In addition, an EMI discussion and cost analysis were realized for AGD.

An ISOP Hybrid DC Transformer Combining Multiple SRCs and DAB Converters to Interconnect MVDC and LVDC Distribution Networks

Abstract: A hybrid dc transformer (DCT) combining multiple series resonant converters (SRCs) and dual-active bridge (DAB) converters with input-series-output-parallel (ISOP) configuration is proposed in this article. The proposed DCT is suitable for connecting medium-voltage dc and low-voltage dc distribution networks, which combines SRCs as the majority modules for power transmission and DAB converters as the minority modules for terminal voltage regulation or power regulation. Benefiting from the hybrid circuit topology, the proposed DCT can achieve a higher efficiency than the ISOP DAB converters with a reduced complexity in the communication and control, while maintaining the controllability of the dc voltage/power. The operation principles of the proposed DCT are analyzed and key parameters design are presented. Then, a 1 MW, 10 kV/750 V hybrid DCT is simulated and a DCT prototype of 2 kW, 400/100 V is built to verify the theoretical analysis.

A Generalized Carrier-Overlapped PWM Method for Neutral-Point-Clamped Multilevel Converters

Abstract: The neutral-point voltage unbalance problem holds back the extensive application of neutral-point-clamped (NPC) multilevel converters with more than three voltage levels in industry. Traditional phase-disposition pulsewidth modulation (PDPWM) or nearest-three-vector (NTV) modulation cannot achieve the voltage balance over the full modulation indexes and load power factors when the voltage level is higher than three. To solve this problem, a novel generalized carrier-based PWM method, named carrier-overlapped PWM (COPWM), for NPC multilevel converters is proposed in this article, which is proven to satisfy the volt–second balance principle. With this modulation method, the average values of all the neutral-point currents are equal to zero in a fundamental period, and therefore, all the dc-link capacitor voltages can be naturally balanced in the ideal and steady-state conditions. In order to simplify its implementation, an equivalent multireference modulation method with only one triangular carrier is also derived. Simulation and experimental results on a five-level diode-clamped inverter are presented to verify the proposed modulation method.

Analysis and Assessment of Modular Multilevel Converter Internal Control Schemes

Abstract: Adoption of distributed submodule (SM) capacitors in a modular multilevel converter (MMC) necessitates complex controllers to ensure the stability of its internal dynamics. This paper presents comprehensive analysis and assessment of different proportional resonant (PR)-based control schemes proposed to stabilize the internal dynamics and ensure ac and dc sides power quality of the MMC within a dc transmission system. With the consideration of passive component tolerances, different energy- and voltage-based control schemes under various conditions are analyzed. It has been established that without vertical voltage balance control, unequal passive component values in the upper and lower arms of the same phase leg may cause: unbalanced fundamental currents in the arms, unequal dc voltage across the arms, and fundamental oscillations in the common-mode currents that lead to fundamental frequency ripple in the dc-link current. The theoretical analysis that explains this mechanism is presented, and is used to show that vertical voltage balancing is necessary for the nullification of arm voltage difference and suppression of odd oscillations caused by capacitive/inductive asymmetry between arms of the same phase leg. Simulations support the theoretical analysis and the effectiveness of voltage balancing in ensuring correct operation, independent of tolerances of the MMC passive elements, and operating conditions. A new direct method for elimination of fundamental oscillations in the common-mode and dc-link current is proposed. Experimental results from a single-phase MMC prototype validate the presented theoretical discussions and simulations.

Model Predictive Power Control for Bidirectional Series-Resonant Isolated DC–DC Converters With Fast Dynamic Response in Locomotive Traction System

Abstract: High-frequency bidirectional dual-bridge series-resonant dc–dc converters have been attracted more attention in power electronic transformer (PET) due to high power density and efficiency. In this article, a model predictive power control method with phase shift modulation is proposed, to improve the dynamic response and robustness of the converter without load current sensor. In addition, the proposed method is insensitive to the resonant parameters in the adopted converter and can keep excellent dynamic characteristics even if the resonant parameter deviates from the desired operating point, which indicates good robustness. Effectiveness of the proposed control is verified on a 400-W scale-down experimental prototype with resistance load and inverter load, respectively. Compared with traditional voltage loop control and model predictive voltage control schemes, the proposed scheme can achieve a faster dynamic response of the output voltage in load and input voltage step change.