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The energy storage inverter system has the characteristics of nonlinearity, strong coupling,variable parameters, and flexible mode switching between parallel and off grid. In order to improvethe control performance of the grid‐side inverter of the energy storage system, an improved LinearActive Disturbance Rejection Control (LADRC) based on proport...
Citations
... The reference value of current can be assumed as constant, namely i (k + l) = i (k ). However, due to the digital time delay in the control process, calculation, sampling and gate driver cannot be avoided in the real system [25][26][27]. In (8), the predictive current signal i (k + l) is calculated by using the measured grid current i (k ) and voltage u sx (k ), and the selected switching states should be applied at instant k . ...
... The inner current loop with DPC-MPC strategy aims at controlling the input current to follow its reference and correct the power factor. The DPC control is mainly composed of sector selection, power of the conventional hysteresis comparison, switch table and outer regulation, by vector look-up table control device on and off, with the traditional current model also has the defects of frequency is not fixed, detrimental to the system filtering and loss [27,28]. In this paper, we introduce the SVPWM modulation DPC -MPC control to avoid the shortcomings of traditional algorithm. ...
Model predictive control has been wildly used in the modern power electronic converter with the advantages of the multi‐objective optimization, no additional modulator is required and small grid current harmonic. However, the switching operation is not constant and higher sampling frequency must be required. A novel direct power control using model predictive control (DPC‐MPC) strategy is presented in this paper, which achieve the optimal vector prediction scheme with constant switching frequency operation. The calculation process is greatly simplified due to the optimal voltage vector generated directly, then, it applied to the control of a three‐phase three‐level T‐type grid converter. A cost function is first built to balance the neutral‐point‐potential voltage. After then, the cost function is updated by considering the delay caused by the calculation, sampling and gate driver. Finally, a comprehensive comparative study with the conventional DPC‐MPC strategy is introduced to verify the superiority of the presented DPC‐MPC. The simulation and experimental results show that the steady and the transient performance of the grid current with the proposed DPC‐MPC control strategy are effectively improved. © 2021 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.
... Without loss of generality, the circuit topology of a three-phase T-type grid-connected rectifier [12,13] adopted is shown in the Fig. 1. The utilized symbols are listed below: u sx (x = a, b, c) represents the electromotive force of the power grid; i sx denotes the grid current; L x defines the inductance; R x denote the parasitic resistance; C 1 and C 2 are the dc-link capacitors; R L1 and R L2 are the positive and negative bus loads , respectively; u p and u n defines the positive and negative dc voltage, respectively; u 0 represents the output voltage of the dc-link. ...
... Aiming to solve the above defects effectively, various control strategies concerning the neutral point voltage balance have been presented, such as Refs. [12,15] In this work, the neutral point potential balance control with presented modulation scheme is discussed below. ...
T‐type pulse width modulation controlled three‐level circuit is the mainstream topology in current medium power distributed PV inverters, charging station and active power filter system with the advantages of high equivalent switching frequency, high efficiency, small filter inductance and small grid current harmonic. Aiming at the inherent problems of midpoint voltage fluctuation and complex of the traditional three‐level space vector pulse width modulation (SVPWM) scheme of a three‐level T‐type rectifier, a new equivalent method of SVPWM strategy used in three‐level converter based on acting time equivalence was proposed, which needs no trigonometric function, irrational operation, and complex coordinate transformation. By the means of rotating the target vector in other sectors to the first sector, the dwell time of vectors can be calculated by the unified formula, and the formula for calculating the dwell time is deduced based on two levels SVM. Then, the control problems of the neutral‐point voltage balance in T‐type three‐level converter topology are analyzed and studied. Through the PI control of electric charge of one capacitor, the neutral‐point voltage can be kept to be half of the DC supply voltage stably. To verify the correctness and effectiveness of the proposed control strategy, a complete simulation model and experimental prototype platform under the digital control is established. The results show that the implementation of this method is very simple and it could decrease calculation error and keep the neutral point potential balance, which makes the results more accurate. © 2020 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.
... To avoid transient instability, the authors of [19] calculated critical clearing time but it is not feasible since the transient events types are unknown to the PV plant operator. The authors of [20,21] turned to the method of increasing the capacity of DC-link capacitance. In [20], the minimum value of a DC-link capacitance was designed to remove the right-half-plane pole for a more stable operation. ...
... In [20], the minimum value of a DC-link capacitance was designed to remove the right-half-plane pole for a more stable operation. The authors of [21] added DC-link capacitance to provide inertia and to reduce impacts from transient events. These methods are more feasible than using critical clear time but installing capacitors with additional capacity increases costs which lower the economy of PV plants. ...
The world‐wide application of photovoltaic (PV) plants is a promising solution to the energy crisis. However, PV plants usually suffer from transient instability due to weakness in dynamical adaptability. This study, based on the transient stability mechanism, devises an adaptive control scheme to achieve transient stability enhancement for PV plants. The transient stability mechanism shows that the active droop factor is negatively associated with the transient stability whereas the reactive droop factor is positively associated. The transient stability enhancement is implemented by increasing the reactive droop factor and reducing the active droop factor to raise the power angle curve. The proposed control scheme adjusts the droop factors dynamically during the transient events by detecting the real‐time electrical quantities. The control scheme advances in a designed activation module which is able to judge if there exist transient events. A series of simulation cases demonstrate the effectiveness of the control scheme in different transient events. Simulation results show that the control scheme adjusts droop factors adaptively and possesses better transient stability than the normal droop control.
... Among the various multilevel topologies, some popular selections include the neutralpoint-clamped (NPC), flying capacitors (FC), and cascaded H-bridge (CHB) [4], [5]. The three-level T-type inverter (3LTI), a relatively recent three-level inverter topology, is implemented by connecting active bidirectional switches between the dc-link midpoint and three-phase outputs of the conventional two-level inverter [6]- [15]. Compared to the three-phase three-level NPC inverter, 3LTI can provide lower conduction losses and fewer diodes while retaining the benefit of the three-level inverter such as the stepped output voltage waveform. ...
... The fault-tolerant control strategies for a 3LTI under an open-circuit fault condition are proposed by measuring the bridge voltage or neutral-point voltage [8]- [11]. The 3LTI can be applied in various industrial applications such as photovoltaic (PV) generation [12], permanent-magnet synchronous motor (PMSM) drives [13], [14], and energy storage systems [15]. ...
... By substituting (15) into (6), the boost factor is given by ...
Two topologies are designed by combining a modified-Z-source (MZS) network consisting of three diodes, two inductors and four capacitors to a traditional three-level T-type inverter (3LTI), and embedding either one or two dc sources in the impedance network, which are named as asymmetrical embedded MZS-3LTI (AEMZS-3LTI) and symmetrical embedded MZS-3LTI (SEMZS-3LTI). The proposed topologies provide a highly boosted ac output voltage with five voltage levels and ensure a continuous dc source current by adopting the embedded concept. Operating analysis is performed and a comparison of the two proposed topologies with five different topologies combining the impedance network and 3LTI or neutral-point-clamped (NPC) inverter is provided. A novel modulation technique is proposed for effectively controlling the upper and lower shoot-through states with a simple logic circuit and balancing a neutral-point voltage. The validity of the proposed topologies and the modulation technique is demonstrated through simulation and experimental results.
... The power angle vector of VSG is shown in Fig. 3 [27]. ...
... The simple model of VSG while in grid-connected operation state is shown in Fig. 4 [27]. The active power and reactive power are calculated as follows: ...
... where Q * is the reference value of reactive power, k Q the adjustment coefficient of reactive power, R′ the armature resistance of VSG, L the synchronous reactance, u s the effective value of grid voltage, and u vsg the effective value of VSG voltage. The VSG control schematic diagram is shown in Fig. 5 [27]. J is the moment of inertia, T e is the electromagnetic torque created by electromagnetic power, and D is the damping coefficient. ...
Modular multilevel converter-battery energy storage system (MMC-BESS) has a good engineering
application. When MMC-BESS is connected to the grid, the real-time phase angle
of grid is an important parameter. When MMC-BESS is connected to the grid, a
simulation model based on virtual synchronous generator (VSG) is built in
MATLAB. The results show the control algorithm based on VSG can improve the
dynamic response of the system and stably detect the phase angle of the
grid.
Microgrids can operate stably in both islanded and grid-connected modes, and the transition between these modes enhances system reliability and flexibility, enabling microgrids to adapt to diverse operational requirements and environmental conditions. The switching process, however, may introduce transient voltage and frequency fluctuations, causing voltage and current shocks to the grid and potentially damaging devices and systems connected to the microgrid. To address this issue, this study introduces a novel approach based on the Extended State Observer (ESO) and the Super-Twisting Algorithm (STA). Power conversion systems use Virtual Synchronous Generator (VSG) control and Power-Quality (PQ) control when they are connected to the grid or when the microgrid is not connected to the grid. VSG and PQ share a current loop. Transitioning the reference current generated by the outer loop achieves the switching of control strategies. A real-time observer is designed to estimate and compensate for current fluctuations, disturbances, and variations in id, iq, and system parameters during the switching process to facilitate a smooth transition of control strategies. Furthermore, to enhance the dynamic response and robustness of the system, the Proportional–Integral (PI) controller in the ESO is replaced with a novel super-twisting sliding mode controller based on a boundary layer. The Lyapunov stability principle is applied to ensure asymptotic stability under disturbances. The proposed control strategy is validated through simulation using a seamless switching model of the power conversion system developed on the Matlab/Simulink (R2021b) platform. Simulation results demonstrate that the optimized control strategy enables smooth microgrid transitions, thereby improving the overall reliability of grid operations.
The Distributed Generators (DGs) based on Renewable Energy System (RES) lack the inertia (rotating mass) and damping features of conventional power system, where fossil fuel based synchronous generators are dominant. The consequence of insignificant inertia and damping on grid stability and dynamic performance is further compounded with growing intermittent RES introduction into the grid. The use of RES based converters with appropriate Virtual Synchronous Generator (VSG) control strategy offers the necessary inertia support which culminates exceptional grid stability enhancement. However, the existing VSG studies focused on inverters in steady-state and under balanced grid voltage without emphasis on VSG dynamic performance during fault and other transients. Conversely, under fault conditions, it’s imperative to investigate the dynamic performance of the VSG control strategies while ensuring the protection of inverters owing to their low overvoltage and overcurrent tolerance capacities. Consequently, this study investigated the two methods of Virtual Synchronous Machine (VISMA) and carried out a comparative analysis to observe how the two methods ensure the VSG-inverter’s sustained grid connection under grid fault. Fault-Ride-Through (FRT) is the ability of electrical generating units to remain grid connected in the brief periods of fault and after fault clearance. Conclusions are drawn as to which VISMA strategies provide a better performance in terms of fault ride-through capability, current-limiting and recovery from faults.
