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Passive trap filters are widely used in high power Voltage Source Inverters (VSI) for the switching harmonic attenuation. The usage of the passive trap filters requires clustered and fixed switching harmonic spectrum, which is not the case for low pulse-ratio or Variable Switching Frequency (VSF) Pulse Width Modulation (PWM). Switching harmonic compensating using auxiliary power converters has been...
This paper proposes a unified impedance model for analyzing the effect of Phase-Locked Loop (PLL) on the stability of grid-connected voltage-source converters. In the approach, the dq-frame impedance model is transformed into the stationary αβ-frame by means of complex transfer functions and complex space vectors, which not only predicts the stability impact of the PLL, but reveals also its frequency...
Constant power load converter will introduce unstable factor to the cascaded system. Exchanging the position of constant power load converter as the source converter can improve system stability. Active solutions to modify the negative impedance of constant power load converter can also make the system more stable. The concept of coordinative front-to-end impedance control is proposed in this paper,...
PI controllers are frequently implemented in cascaded converter system to control the DC-link voltage, because they can achieve zero steady state error. However the PI controller adds a pole at the origin point and a zero on the left half plane, and it increases the control system type number, and then the system is more difficult to control. This paper proposed a DC-link control method for the two...
Active damping of LCL-filter resonance based on single-state feedback control is widely used with voltage source converters. Its robustness against grid impedance variation has always been a major concern with its controller design. To deal with this issue, this paper begins by developing a generalized impedance-based model of grid current control with feedback-type active damping. Then, a controller...
This paper discusses the dynamic interaction of multi-paralleled inverters within a weak grid. Interactive current and common current models are proposed to explain the interaction among these inverters, which are studied with both open loop and closed loop analysis. An aggregated model is proposed to describe the totality of multi-inverters. Additionally, system stability is explicitly studied and...
This paper introduces a new inverter topology called a “quasi-Y-source inverter”. The proposed inverter inherits all the advantages of the original Y-source inverter. In addition, the new topology draws continuous current from the source which is required for many renewable sources. It also has dc-current-blocking capacitors, which avoids saturation in the transformer core. Simulations and experimental...
This paper proposes a unified grid current control for grid-interactive distributed generation inverters. In the approach, the grid-side current, instead of inverter-side current, is controlled as an inner loop, while the filter capacitor voltage is indirectly regulated through a virtual admittance in the outer loop. It, therefore, provides several superior features over traditional control schemes:...
Paralleled grid-connected inverters with LCL-filters are coupled through the non-negligible grid impedance. However, the coupling effects among inverters and grid are usually ignored during the design, which may lead to unexpected system resonance and even instability. This paper thus investigates the resonance characteristic and stability analysis in multi-paralleled grid-connected inverters with...
DC microgrids are gaining interest due to higher efficiencies of DC distribution compared with AC. The benefits of DC systems have been widely researched for data centers, IT facilities and residential applications. The research focus, however, has been more on system architecture and optimal voltage level, less on optimized operation and control of generation sources. The latter theme is perused...
Coupled inductors have lately been used with impedance-source networks for keeping their shoot-through times short, while providing higher voltage boosts. The parameter that is critical to the operation of such impedance network based converter with coupled inductors is the leakage inductances. However, the role of leakage inductances and its effect on the converter performance is often overlooked...
This paper presents an autonomous power sharing scheme for economic operation of grid-connected DC microgrid. Autonomous economic operation approach has already been tested for standalone AC microgrids to reduce the overall generation cost and proven a simple and easier to realize compared with the centralized management approach. In this paper, the same concept has been extended to grid-connected...
This paper introduces a new 3-phase Y-source inverter whose gain is presently not matched by classical impedance-network-based inverters operating at the same duty ratio. The proposed network uses a tightly coupled transformer with three windings. By squeezing the shoot-through range while keeping higher boost, the inverter can operate at a higher modulation index, thereby minimizing switching device...
This paper introduces a Y-shaped impedance network for realizing converters that demand a high voltage gain while using a small duty ratio. To achieve that, the proposed network uses a tightly coupled transformer with three windings, whose obtained gain is presently not matched by existing networks operated at the same duty ratio. This capability has been demonstrated by mathematical derivation for...
Z-source inverters are a new class of inverters proposed with output voltage or current buck-boost ability. Despite their general attractiveness, there are some present limitations faced by existing Z-source inverters. Most of which are linked to their requirement for low modulation ratio at high input-to-output gain, and the presence of an impedance network. The former means a high dc-link voltage,...
A new family of voltage-type Г-source inverters is proposed in this paper. It uses a unique Г-shaped impedance network for boosting its output voltage in addition to its usual voltage buck mode inherited from a traditional voltage-source inverter. Comparing with other techniques, the proposed inverters use lesser components, while yet producing flexible enhanced gains. Gain tuning is effected here...
Z-source inverter is a recently proposed single-stage inverter with added voltage-boost capability for complementing the usual voltage-buck operation of a traditional voltage-source inverter. In spite of that added feature, the overall voltage gain might still be relatively low for certain applications like the grid connection of low-voltage renewable sources that might not favor multiple series connection...
This paper presents the concept of using a new tapped-inductor (TL) Z-source impedance network for implementing Z-source inverters. By replacing the original two inductors found in the classical impedance network with two modified 2-terminal TL cells, output voltage range of the new inverter can widely be expanded. This means a larger gain, which in principle, can be adjusted freely by varying the...
High performance voltage and current-source inverters (VSI and CSI) are widely required in various industrial applications such as servo-motor drives, special power supplies, distributed power systems and hybrid electric vehicles. However, the traditional VSI and CSI have been seriously restricted due to their narrow obtainable output voltage range, short-through problems caused by misgating and some...
Multilevel inverters are getting more and more attracted because they have better output waveform quality and lower semiconductor voltage stress. The Z-source NPC is a kind of single stage multilevel inverter which has the ability of voltage boost. But the boost capability is relatively low when they are subject to the renewable sources. To date, three distinct types of impedance networks can be summarized...
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