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Harmonic power can be shared by controlling the equivalent harmonic impedance of distributed generation (DG) units in islanded microgrids. This paper firstly reviews several methods for controlling the equivalent harmonic impedance of DGs and adopts the method based on resistive active power filter (R-APF). Then, a droop relationship between the equivalent harmonic impedance of DGs and their remaining...
For a grid-connected Voltage-Source Converter (VSC), dynamics of the grid synchronization plays an important role in affecting the converter performances and stability. Due to its significance, this paper gives a comparative analysis about some basic grid synchronization schemes, through viewpoint of dynamic performances, which appeared as the impacts of voltage perturbation on the estimated angle...
In this paper, a single inductor-single sensor based photovoltaic optimizer with an optimal current point tracking strategy is proposed. With only one inductor, one sensor and one MPPT unit, this optimizer can not only make all submodules output their individual maximum powers, but also utilize the least components compared with current solutions, greatly reducing the size and cost of photovoltaic...
This paper proposes a new control scheme for harmonic power sharing and PCC voltage harmonics compensation in islanded microgrids by adopting virtual harmonic impedance method. Firstly, a droop relationship between the equivalent harmonic impedance of distributed generation (DG) units and their remaining power capacities (ZDG_h_eq-SDG_remaining droop relationship) is put forward. Then, a virtual harmonic...
This paper proposes an impedance-based active-filter additional control method for grid connected PWM-converters, by which a PWM-converter can help improve the voltage quality at a sensitive load bus (SLB) of a complex network with many distributed unbalanced loads and nonlinear loads. To realize the method, the information of the voltage to be compensated needs to be acquired and transferred to the...
The interaction of power electronic converters in a microgrid can introduce system instability and power quality issues. Existing investigations focus on interactions either in low frequency regions, such as the constant power load, or in very high frequency regions like electro-magnetic interference. However, interactions of power converters around their switching frequency range are not included...
Recent development renewable energy increases the requirement in constructing multi-terminal HVDC systems or HVDC grids. To increase the system reliability, an HVDC circuit breaker will be required. However the existing HVDC breakers developed in recent years use large amount of IGBTs. Considering the cost reduction in real HVDC grids, this paper presents a novel hybrid HVDC circuit breaker. The proposed...
This paper proposes a novel passive hybrid high-voltage DC circuit breaker based on thyristors. A current commutation circuit to turn off the thyristors is designed with elements of relatively low current and voltage ratings. Moreover, voltage balancing strategy is applied to protect the series-connected device.
An improved modulation algorithm is proposed for three-phase face-to-face topology. The algorithm could make the face-to-face dc transformer use 1: 1 ac transformer or omit ac transformer in a wide variable ratio range to reducing the volume of the system. The simulation in MATLAB/Simulink validates the proposed algorithm.
PV systems are influenced by disproportionate impacts on energy production due to mismatch cases frequently. The occurrence of multiple maximum power points (MPPs) adds complexity to the tracking process in different PV systems. However, current Maximum Power Point Tracking (MPPT) techniques exhibit limited performance. This paper introduces an Enhanced simulated annealing (ESA) based GMPPT technique...
Since the photovoltaic power generation, wind power and other distributed power supply are volatile and random, they will affect the stability of the grid frequency. In order to improve the voltage and frequency in micro-grid, the virtual synchronous generator control strategy is proposed for inverter control, which can emulate the behavior of synchronous generator, decrease rate of change of frequency...
Shunt active power filters (SAPF) generally compensate harmonic current of centralized non-linear loads, which may cause undesired economical burden for networks with distributed harmonic sources. This paper proposed an SAPF predictive control method based on online impedance measurement which can suppress the network-wide harmonics systematically in an optimized way.
Control of power electronic generations is important in microgrids and power systems. Droop control is proposed for reasonable power allocation among different inverters. Moreover, virtual synchronous generator is proposed to improve frequency dynamics in transient state. Therefore, inertia design in VSG is necessary for integrating power electronic generations into grids. Frequency dynamic and stability...
Harmonic power sharing and PCC voltage quality are both important issues for the power quality of islanded microgrids. This paper proposes a new control scheme to deal with those two issues based on controlling the equivalent harmonic impedance of DGs. With the proposed control scheme, harmonic power is shared according to remaining power capacities of DGs and PCC voltage harmonics are effectively...
The converter valve is the critical link of AC and DC system and the most commonly used switching devices for converter valve are thyristors. The performance of thyristors could significantly affect the performance of converter valve while the transient characteristics and second order effects of thyristor are critical to determine the reliability of converter valve in HVDC (High Voltage Direct Current)...
Recent research on high voltage and power DC/DC converter mainly focus on the face-to-face topology based on modular multilevel converters (MMC). The topology consists of two MMC which are coupled by a transformer. It is easy to extend the module number according to the voltage level. However, the present modulation method in this topology cannot regulate the voltage transformation ratio on two dc...
Due to rapid deployments of power electronics in renewable energy sources and new loads, high levels of harmonics causes problems in current distribution systems. This paper presents an advanced harmonic extraction technique for detecting and extracting selected harmonics in a medium-voltage high-power system. A time-transformation technique is developed which can accurately extract the desired harmonics...
In recent years, photovoltaic power generation has been more and more popular, because it has many advantages, clean energy and widely distributed. However, in the development process photovoltaic power generation also encountered a lot of obstacles, such as tracking the global maximum power point (GMPPT). Due to the photovoltaic system will be blocked by the photovoltaic panels appear multiple peaks,...
In high power applications, the insulated-gate bipolar transistors (IGBTs) are often required to be connected in parallel in order to withstand the large load current. However, the current of paralleled IGBTs may not be shared equally due to spread of parameters. The current unbalance in transient and steady state can result in overheat and overcurrent destruction of the devices. In this paper a novel...
With increasing penetration of the intermittent and fluctuating renewable energy resources, control strategy of inverters in microgrid is important. Therefore, due to lack of inertia in power electronic converters, virtual synchronous generator control is proposed to introduce backup inertia and improve dynamic performance of frequency. Researches recently have proposed different methods on control...
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