Ke Zou

A Universal Selective Harmonic Elimination Method for High-Power Inverters

In medium-/high-power inverters, optimal pulse-width modulation (OPWM) is often used to reduce the switching frequency and at the same time, realize selective harmonic elimination (SHE). For both two-level and multilevel inverters, most selective harmonic elimination (SHE) studies are based on solving multiple variable high-order nonlinear equations. Furthermore, for multilevel inverters, SHE has been often studied based on the assumption of balanced dc levels and single switching per level. In this paper, the authors further developed harmonics injection and equal area criteria-based four-equation method to realize OPWM for two-level inverters and multilevel inverters with unbalanced dc sources. For the cases, where only small number of voltage levels are available, weight oriented junction point distribution is utilized to enhance the performance of the four-equation method. A case study of multilevel inverter at low-modulation index is used as an example. Compared with existing methods, the proposed method does not involve complex equation groups and is much easier to be utilized in the case of large number of switching angles, or multiple switching angles per voltage level in multilevel inverters.

Characteristic Study and Time-Domain Discrete- Wavelet-Transform Based Hybrid Detection of Series DC Arc Faults

DC arc fault introduces major safety concerns in a wide variety of components in dc networks. However, the randomness and instability of dc arc makes it difficult to be detected. In this paper, an experimental system was designed and tested at different load current, dc source voltage, and gap length to evaluate the impact of each parameter to the dc arc. Based on the experimental results, characteristics in the electrical behavior were studied and fault detection oriented analysis was conducted. A detection algorithm utilizing both time and time-frequency domain characteristics was proposed to differentiate between dc arc fault and normal condition. The detection algorithm was then realized on a digital signal processing board and tested to verify the effectiveness. Experimental results show that the proposed algorithm can detect arc fault in a timely manner and is free of nuisance trip from normal circuit operations such as load change condition.

A Switched-Capacitor Voltage Tripler With Automatic Interleaving Capability

This paper presents a high-efficiency switched-capacitor voltage tripler topology aimed at high-power applications. A soft-switching scheme without the addition of extra components is adopted to minimize the switching loss and the electromagnetic interference noises. A two-step current charging method is used to enable the input current and output voltage interleaving functionality without adding an excessive number of components. The large loss on the input capacitor that exists in the traditional switched-capacitor topologies is eliminated by employing this interleaving scheme. The soft switching and interleaving results are analyzed in detail. The experimental results for a 2-kW prototype are demonstrated to verify the functionality of the proposed topology.

Switched-Capacitor-Cell-Based Voltage Multipliers and DC–AC Inverters

In this paper, several modular converter topologies based on a switched-capacitor-cell concept are introduced for high-power applications. Two types of switched-capacitor cells, including the full cell and the half-cell, are discussed. The full cell can be used for dc-ac inversion, and the half-cell is utilized in both dc-dc and dc-ac applications. A rotational charging scheme is adopted for the half-cell-based dc-dc voltage multiplier to eliminate the large output capacitor that exists in many traditional switched-capacitor topologies. A soft-switching scheme, which does not require extra components, is adopted to reduce the switching loss and electromagnetic interference. A variable switching frequency control scheme is proposed to realize soft switching for dc-ac inverters. The experimental results on a 2-kW prototype are presented to verify the proposed topologies.

A gallium-nitride switched-capacitor circuit using synchronous rectification

The promise of wide band-gap materials has the potential to usher in a new era of power electronics not seen since the introduction of the Silicon (Si) Metal Oxide Semiconductor Field Effect Transistor (MOSFET) and Bipolar Junction Transistor (BJT). The physical characteristics of Gallium Nitride (GaN) make it theoretically superior to Si in such aspects as temperature of operation, switching speed, and efficiency. While much research has been conducted on the High Electron Mobility Transistor (HEMT) made of GaN and Aluminum Gallium Nitride (AlGaN), the discussion of third quadrant operation is sparse. Furthermore, the merits of the AlGaN/GaN HEMT, in particular its switching speed, make it suitable for switched-capacitor circuits. Thus, this paper focuses on the AlGaN/GaN HEMTs third quadrant operation and demonstrates this functionality in a switched capacitor circuit.

A high frequency battery model for current ripple analysis

In applications where batteries work together with power electronic circuits, the current ripple generated by the power electronics will be shared by both the battery and passive components in the circuit. The amount of ripple absorbed by the battery depends on its impedance at the switching frequency of power electronics. This paper presents an impedance based high frequency battery model derived from test results of a NiMH battery using a novel battery impedance tester. The possible reasons for the battery impedance characteristics in high frequency region, including skin effect and proximity effect, are also discussed. This battery model can be directly used in current ripple analysis, passive components design and control strategy optimization of power electronic circuits. The effect of the passive component values on the battery current ripple is analyzed using the ac equivalent circuit of the test setup.

A Gallium Nitride switched-capacitor power inverter for photovoltaic applications

A Gallium Nitride (GaN) based switched-capacitor module integrated inverter (MII) is presented in this paper. This two stage solution first employs a dc/dc quadrupler that utilizes an interleaving charging scheme. This strategy not only reduces the high frequency current ripple subjected to the photovoltaic panel, but also decreases the voltage ripple on the DC link between the two stages. The second stage is a five-level boost inverter that is responsible for both maximum power point tracking (MPPT) and minimizing reactive power flow. Both stages utilize a resonant soft-switching scheme in the capacitor charging current loops to increase the MIIs efficiency. Basic theoretical analysis and experimental results for the individual stages are included.

A Gallium Nitride Switched-Capacitor Circuit Using Synchronous Rectification

The physical characteristics of gallium nitride (GaN) make it theoretically superior to silicon (Si) in such aspects as the temperature of operation, switching speed, breakdown voltage, and efficiency. While much research has been conducted on GaN devices, the discussion of third-quadrant operation is limited. Furthermore, the merits of GaN transistors, particularly their fast switching speed and low on-resistance, make them suitable for switched-capacitor circuits. This paper demonstrates the ability of a GaN transistor to function as a synchronous rectifier in a switched-capacitor circuit. A 500 W GaN-based voltage doubler capable of achieving zero-current switching is presented with supporting experimental results. This circuit achieves peak efficiencies of 97.6% and 96.6% while switching at frequencies of 382 and 893 kHz, respectively.

Switched capacitor cell based Dc-dc and Dc-ac converters

This paper introduces a modular converter topology based on switched capacitor cells. Two types of cells are discussed in this paper. The full cell switched capacitor structure, which can be used in dc/ac inversion and the half cell structure that has applications in both dc/dc and dc/ac conversion. There are several merits to this converter topology; it has a modular structure, the capacitor count is minimized, and with dc/ac converter there is good redundancy. When utilized as a dc/dc converter, the required output capacitance is minimized and soft switching can be achieved. The basic analysis, simulation results and experimental results on a 1 kW cell prototype are presented.

Minimum power loss control — thermoelectric technology in power electronics cooling

This paper investigates the possibility of using thermoelectric cooling (TEC) modules to improve the power density of power electronics systems. A simple test setup served for comparison purposes is built. The result shows that, through the use of TEC modules to actively cool power electronics devices, the power handling capability is improved versus that of an identical passively cooled system. Then a minimum power loss control strategy for TEC is proposed. Experimental results are shown to demonstrate the effectiveness of the proposed control strategy.