A digital adaptive voltage positioning (Digital AVP) technique with fast transient response for voltage regulators (VRs) is proposed in this paper. In this proposed digital control architecture, two digital-to-analog converters (DACs) are used instead of analog-to-digital converters (ADCs), thus significantly reducing system complexity. Both the voltage and current references are changed dynamically at DAC clock frequency resulting in fast transient response. Different from other control methods (the output voltage tracks the voltage reference), the generated voltage reference is always trying to track the output voltage. A straightforward control law is used, which does not require compensator. Moreover, the proposed control technique automatically avoids the limit cycle by automatic dithering method. Further, it allows the use of non-linear control methods which significantly improve transient response speed. Finally, a two-phase 12V-to-1V, 40 A, 250 kHz synchronous buck converter with the proposed digital controller was designed to verify the theoretical analysis by simulation and experimental results.
Defects such as insulator, pins, and counterweight in highvoltage transmission lines affect the stability of the power system. The small targets such as pins in the unmanned aerial vehicle (UAV) inspection images of transmission lines occupy a small proportion in the images and the characteristic representations are poor which results a low defect detection rate and a high false positive rate. This paper proposed a transmission line pin defect detection algorithm based on improved Faster R-CNN. First, the pre-training weights with higher matching degree are obtained based on transfer learning. And it is applied to construct defect detection model. Then, the regional proposal network is used to extract features in the model. The results of defect detection are obtained by regression calculation and classification of regional characteristics. The experimental results show that the accuracy of the pin defect detection of the transmission line reaches 81.25%
Cascaded module topology is widely used in large scale photovoltaic system because of its easy expansion and small output harmonic. For traditional photovoltaic three-phase inverter topology, the power generation of each phase bridge can be unequal because of nonuniform solar illumination, partial shading, or unequal module temperatures, resulting in the interphase power imbalance. The DC-link capacitance is usually very large to decouple the fluctuating power, resulting in a large volume of the converter. In this paper, a novel modular three-phase converter topology applied to large scale photovoltaic systems is proposed, which can realize the automatic interphase power balance, and make the fluctuating power offset in a four-winding transformer, greatly reduce the size and cost of the converter and improve the power density of the PV system. The feasibility of the proposed topology is verified by simulation.
This paper proposed an MMC topology integrated with a three-port coupling transformer and its modulation strategy. The coupling of the three-phase sub-module capacitor greatly reduces the voltage ripple of the sub-module capacitor, thereby greatly reducing the volume and cost of the system. In addition, by integrating an arm of the additional circuit with the half-bridge of the MMC, the structure of the additional circuit can be further simplified. This paper also studies the parameter design scheme of the system. The research shows that by configuring the system parameters, partial soft switching of the decoupling circuit can be realized, thereby reducing the power loss of the system. Simulation results validate the effectiveness of the proposed topology and modulation strategy.
The wide band-gap (WBG) devices have received widespread attention due to their excellent characteristics like low on-resistance, fast switching speed and better thermal conductivity. However, the crosstalk problem restricts the performance of high-speed WBG transistors in bridge-leg converters. What's more, in high current converters, the crosstalk problem will become more severe. To overcome the crosstalk problem in high current converters and fulfill the WBG devices' high-speed potentials, a simple positive and negative crosstalk mitigation method is presented in this article. This method does not require extra auxiliary controlled switches and extra control strategies, and can mitigate the positive and negative crosstalk spikes. What's more, it is simple implementation, and can be easily integrated with the conventional voltage source gate drivers. The effectiveness of the presented crosstalk suppression method is proved by the simulated and experimental outcomes.
Single-phase single-stage nonisolated photovoltaic (PV) grid-tied inverters mainly suffer from issues of the common-mode leakage current and double-line-frequency power oscillation. Aiming to address these issues, this article designs a new single-phase PV grid-tied inverter with only two switches. The structure of the proposed inverter allows the neutral line of the alternating current (ac) grid to be directly connected to the negative pole of the PV panel so that the common-mode leakage current can be completely eliminated. Additionally, a power decoupling method is proposed to suppress the double-line-frequency power oscillation. Then an improved control strategy is presented in this article to solve the stability problem of the proposed inverter when it is connected to a weak grid. It should be noted that the designed inverter can also output reactive power, achieve zero-voltage switching, track the maximum power point, and step up the input voltage. The validity of the proposed inverter and improved control strategy is verified by simulation and experimental results.
A novel digital adaptive voltage positioning (digital AVP) technique was proposed in. Good transient performance had been achieved without using complicated control. In this paper, a small signal model is proposed for this mixed-signal digital controller. It is revealed by this small signal model that the inner current loop is in analog and the voltage loop is in digital, thus the controller can benefit from both: having valuable features of digital control but without limitations such as limit cycle. On the other hand, dynamic behavior of the voltage regulator with this digital AVP controller under large load transient is analyzed. With optimized bandwidth designed for switching stability, the VR with the digital AVP controller exhibits very excellent dynamic performance because of non-linear multi-mode control.
Demanding the accuracy and reliability of the thermal design of high-power density inverter, aluminum substrate has been widely used due to its high thermal conductivity and well insulation performance. This paper provides a complete set of thermal design optimization method: The main power module losses are analyzed. Considering the accurate thermal resistance models for heatsink of variable structural types is hard to modelling, the method of combining finite element simulation and Minitab response surface optimization is mainly used to carry out the multi-objective optimization design with the substrate thickness, fin radius and fin length as the optimization objectives. Finally, it is verified that the heatsink model and optimization method are highly convenient and effective, and can provide a reliable method for structural optimization of heatsink for inverters.
Although compact fluorescent lamps (CFLs) have been on the market for a long time, many of them do not achieve the same power factor as the incandescent lamps do, which presents a significant problem for the utility with the current widespread use of CFLs for household lightings. A simple single-switch electronic ballast with passive valley-fill power factor correction is proposed in this paper for CFL application. The proposed single-switch ballast circuit is able to achieve zero current switching to maximize the circuit efficiency. A simple feedback circuit with duty ratio control is also proposed to improve the high lamp current crest factor caused by the valley-fill circuit. Detailed descriptions and analysis of the circuit operating principles are provided in this paper. Simulation and experimental results are given on a 13-W CFL tube from Osram Sylvania to highlight the merits of the proposed work.
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