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This paper presents a method to shed off the least important loads in a microgrid operated at constant frequency under the contingency of inadequate power generation. Different from conventional frequency deviation based load shedding, this paper discusses in detail how to shed off load based on the voltage deviation. The key issue is to differentiate whether the voltage deviation is due to sudden...
Single-phase two-stage inverters generally use an intermediate capacitor to buffer the power imbalance between DC input and AC output. However, the resultant low-frequency voltage ripple on this intermediate capacitor may produce low-frequency ripple at the source side, especially when the front-end dc/dc converter operates in continuous conduction mode (CCM). Some common solutions to reducing this...
According to the traditional control of three-phase inverter, basing on the transient mathematical model of second order of virtual synchronous generator, the three loops control of power-voltage-current with virtual synchronous generator (VSG) by using the feedback of capacitance's voltage and current was built. And the proportional and integral control was applied in the loop of voltage to ensure...
In virtual flux droop method, power sharing is achieved by adjusting flux amplitude and angle which has some advantages of simplicity of control and lower voltage and frequency deviation. In this paper, a switch module of power calculation was firstly designed to balance system dynamic response and power fluctuation in flux droop controller. Then an improved direct flux controller was proposed to...
The topology of neutral-point clamped (NPC) is widely used for multilevel inverters, and the balance of the neutral-point voltage is one of the key technologies which determines the performance of Permanent Magnet Synchronous Motor(PMSM). Repetitive control can ensure control precisions by keeping the appropriateness of the control signal when the system is stable. In this paper, neutral-point balancing...
In the distributed generation systems, three-phase inverters are the basement because they are used as power electronics interface between the generators and the grid. Cascaded multi-level H-bridge inverters are widely used for industrial application due to the simple topology and good power quality. However, unbalanced power source problem will easily happen in such an application. In this paper,...
This paper proposes a novel control strategy for the smooth transition between grid-attached and islanded mode of microgrid. The proposed control strategy is based on a proportional resonant current controller to regulate inverter current, without requiring any islanding detection algorithm or switching between different controllers. Equal power sharing is achieved as well by droop control using reference...
Inverters in back to back (B2B) connection are utilized to convert the voltage and frequency of the power source to another format. Typical application of inverters is the wind power system. This study presents a B2B inverter for equal voltage and frequency format conversion in which one inverter works to get power from the grid to charge the DC capacitor and another inverter returns most of the active...
In this paper, control and operation of a microgrid having inverter based solar photovoltaic (PV) and diesel engine is presented. The microgrid is designed to meet rural applications. In the proposed microgrid, a water pumping system is considered as a dump load for ensuring economic operation of microgrid. Three scenarios i.e fully loaded, partially loaded and lightly loaded are considered to evaluate...
Due to the inherently distributed and heterogeneous nature of the microgrids, distributed control can be a promising approach to improving the stability, reliability and scalability of the microgrids compared with centralized control strategies. This work studies the distributed reactive power sharing problem for a microgrid with connected AC inverters. Under the lossless assumption of the microgrid,...
The traditional DG (distributed generation) wireless droop control base on “power-voltage-current” close loop is widely used. The power sharing performance of this method is significantly affected by the feeder impedance, mismatch inverter parameters, and unbalanced local load. Due to the affection of mismatched line impedance, the traditional droop method cannot make the reactive power shared accurately...
In this paper, we propose a secondary voltage control approach of islanded microgrid based on distributed model predictive control (DMPC). Each submodule of a distributed generation (DG) is modeled in a rotation reference frame and combine them to achieve the nonlinear complete model. Considering the nonlinear DG dynamics, an input-output feedback linearization is developed. Besides, all DGs only...
For an inverter drive induction motor control system, a typical problem encountered is the nonlinear voltage gain caused by the non ideal characteristics of the power inverter. The switch dead time will introduce waveform distortion and fundamental voltage drop to the system. If not compensated, such distortions will introduce harmonic components which will cause additional loss in the induction machine...
Secondary frequency control, i.e., the task of restoring the network frequency to its nominal value following a disturbance, is an important control objective in microgrids. In the present paper, we compare distributed secondary control strategies with regard to their behaviour under the explicit consideration of clock drifts. In particular we show that, if not considered in the tuning procedure,...
Induction motor (IM) is the workhorse of the industries. Amongst various speed control schemes for IM, variable-voltage variable-frequency (VVVF) is popularly used. Inverters are broadly used to produce variable/controlled frequency and variable/controlled output voltage for various applications like ac machine drives, switched mode power supply (SMPS), uninterruptible power supplies (UPS), etc. This...
As the penetration level of grid-connected PV systems increases, more advanced control functionality is demanded. In order to ensure smooth and friendly grid integration as well as enable more PV installations, the power generated by PV systems needs to be flexible and capable of: 1) limiting the maximum feed-in power, 2) ensuring a smooth change rate, and 3) providing a power reserve. Besides, such...
In microgrids, photovoltaic (PV) and storage are integrated as a droop-controlled ideal source, which is not practical and challenges the system efficiency. Instead, PV-storage can be allocated separately. This PV-storage independent system is more flexible and easier to optimize. But, the conventional PQ-controlled PVs rely on master voltage-controlled storage sources. In this paper, a novel operation...
The virtual synchronous generator (VSG) is a control scheme applied to the grid-tied inverter to increase system inertia by imitating the rotor inertia of synchronous generator (SG). However, due to the imitation on rotor inertia VSG control may lead to the power and frequency oscillation after a change or disturbance, which decreases the reliability of inverters. In this paper, the process of active...
This paper presents a control solution designed to improve the dynamic response capability of autonomous microgrids (MGs). For this purpose, an MG-forming inverter (MGFI) controlled to take over the load only in transitory regimes by using a virtual synchronous generator operation mode is proposed. The MGFI, based on a supercapacitor energy storage system, is relived of the permanent load by distributing...
The application of consensus theory in the control of islanded microgrids (MG) is gaining increased attention because it facilitates the development of distributed control solutions. In particular, its application to active power sharing and frequency regulation has lead to satisfactory results. This paper analyses the effect that local clock drifts have in the parallel operation of voltage source...
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