Control Strategy For Inverter Research Articles

Simplified Predictive Control Strategy for Dual-Input Three-Phase Split-Source Inverter With Minimized Computational Burdens

Simplified Predictive Control Strategy for Dual-Input Three-Phase Split-Source Inverter With Minimized Computational Burdens

Harmonic voltage compensation and harmonic current sharing strategy of grid-forming inverter

In a multi-inverter parallel system, the harmonic governance control strategy may worsen the system's current circulation problem due to the line impedance difference, which could further affect the stable operation of the system. To solve the problem, the strategy considering both power sharing and harmonic control is proposed in this paper. First, the microgrid system with background harmonics is modeled and analyzed. Based on the modeled system, a comprehensive control strategy for the grid inverter with harmonic voltage compensation and harmonic current sharing is established. In this paper, the output signal is controlled by frequency division. This paper adopts grid-forming control in the fundamental wave domain and employs harmonic voltage compensation control in the harmonic domain. The harmonic voltage is synthesized by collecting the specific harmonic current through the band-pass filter, compensating for the harmonic voltage drop on the line to improve the harmonic voltage quality of the point of common coupling(PCC). Aiming at the sharing problem caused by line impedance difference, virtual impedance control is introduced, harmonic impedance is redesigned according to the adjusted output impedance, and the harmonic output impedance before and after adjustment is measured and compared. The simulation results show that the proposed control strategy can not only reduce the harmonic content of the PCC voltage but also achieve the effect of equal harmonic current division.

Switching Frequency Control Strategy of Inverter for Multifrequency Multiload WPT System Based on Hysteresis Current Control

Switching Frequency Control Strategy of Inverter for Multifrequency Multiload WPT System Based on Hysteresis Current Control

Adaptive control strategy for microgrid inverters based on Narendra model

In recent years, microgrid technology has been widely studied and applied. However, with times developing, the installed capacity of distributed power generation devices has been improved, and work is being carried out in increasingly complex situations, resulting in a decline in the control performance of microgrids. In view of this, to effectively improve inverter’s control performance, research is conducted on the fusion of Narendra model and adaptive control strategies for real-time voltage correction and compensation in complex situations. Compared to traditional inverters, inverters under research methods have faster voltage recovery speed when encountering load switching, and can recover in about one cycle, with good control performance. In the comparison between the improved inverter adaptive control system and the inverter adaptive system, the improved inverter voltage recovery speed is faster, can be restored within one cycle, and the control effect of the inverter is better. The harmonic rate of the port voltage has decreased from 10.43 to 1.92%. The applicability of the research method was verified. It indicats that the research method can improve inverter’s control effect and solve problems such as voltage deviation, three-phase asymmetry, harmonic pollution, etc. that are easily generated by the output terminal voltage. Simultaneously, research has provided theoretical basis and data support for the research of microgrids.

Fixed-Time Robust Fractional-Order Sliding Mode Control Strategy for Grid-Connected Inverters Based on Weighted Average Current

Fixed-Time Robust Fractional-Order Sliding Mode Control Strategy for Grid-Connected Inverters Based on Weighted Average Current

Hybrid feedback control of PMSG-based WECS with multilevel flying-capacitor inverter enhanced by fractional order extremum seeking

This paper proposes an original hybrid control strategy for a three-phase multilevel flying capacitor inverter (FCI) used in wind energy conversion system (WECS). A state feedback law, computed using a Lyapunov function and an invariance principle, is designed to manage grid current control and capacitor voltage balancing, guaranteeing the asymptotic stability of the closed-loop system. Additionally, a fractional-order extremum seeking control (FOESC) algorithm for Maximum Power Point Tracking (MPPT) is introduced, which optimizes power capture by adjusting turbine speed from the DC side without requiring a detailed system model (model-free approach). The use of fractional-order calculus leads to improved convergence and more seamless performance while preserving the robust characteristics of the system. The proposed control strategies are validated through simulation, demonstrating improved transient response and stability under varying wind conditions and parameter uncertainties. These results highlight the potential of advanced control algorithms to enhance the efficiency and reliability of wind energy systems, contributing to global efforts to achieve sustainable energy goals.

Pilot protection based on mode distance for transmission line connected to renewable energy station

Abstract Affected by the inverter control strategy, fault characteristics of the wind turbine are essentially different from the traditional synchronous power supply, leading to a decrease in sensitivity and even rejection of traditional differential protection. In view of the above problems, this paper studies the fault current waveform distinction between the wind turbine and the synchronous power supply, and uses the mode distance to measure the current waveform difference. The simulation experimental system is built and the results show that the mode distance can reliably identify the faults in and out of the area in various fault scenarios, effectively working out the kinks of the degradation of the differential protection.

Control strategy of PV microgrid grid-connected inverter

Abstract Aiming at the limitation of a three-phase inverter system to access clean energy, a design scheme of a two-stage microgrid grid-connected inverter system is proposed. The traditional double closed-loop control strategy has some disadvantages such as slow response, large fluctuation, and delay of frequency and phase tracking. Therefore, this paper proposes an improved grid-connected control strategy for photovoltaic microgrids with the addition of prediction units, which is established and verified by simulation. The results show that compared with the traditional method, the proposed control method has the advantages of fast dynamic response, small pulsation, and high power quality.

Research on a New Inverter Control Strategy of Induction Heating Power Supply

To achieve “high voltage, low current” in the induction heating power circuit, enhance the flexibility of component selection in the circuit, and improve the quality of the inverter’s output waveform, a new control strategy of a single-phase NPC three-level inverter with unipolar frequency-doubling SPWM method is proposed. With the series connection of IGBTs in a single-phase NPC three-level inverter, the voltage withstand requirement of IGBT is reduced by half. The middle four IGBTs are controlled using unipolar frequency-doubling SPWM, while the outer four IGBTs are turned on later and turned off earlier to address the neutral point voltage imbalance issue in the inverter. Simulation results show that, compared with the traditional bipolar SPWM-controlled single-phase full-bridge inverter, the DC-side input voltage of the inverter can be double, and the current flowing through the entire circuit can be halved under the same output power using the proposed method.

A Flexible Control Strategy for Multi-Functional PV Inverters with Load Compensation Capabilities Considering Current Limitations and Unbalanced Load Conditions

A Flexible Control Strategy for Multi-Functional PV Inverters with Load Compensation Capabilities Considering Current Limitations and Unbalanced Load Conditions

Model predictive control of multilevel inverter used in a wind energy conversion system application

The rapid growth of renewable energy, particularly wind energy, has significantly contributed to global electricity generation, with global renewable energy capacity reaching an all-time high of 3870 gigawatts (GW) in 2023. However, ensuring high power quality for grid integration remains crucial for wind energy's role as a leading source in the energy transition. This necessitates the development of advanced Wind Energy Conversion Systems (WECS) capable of regulating current, voltage, and frequency to ensure power quality. This work proposes a novel predictive control strategy for multilevel inverters in WECS to achieve a total harmonic distortion (THD) below 5% in the generated electrical power. The proposed predictive control algorithm is presented and implemented in a WECS simulation with a multilevel inverter. The performance of the proposed system is evaluated through simulations using MATLAB/SIMULINK. Our results demonstrate that the predictive control approach outperforms traditional controllers for multilevel inverters in terms of output voltage, harmonic reduction, execution time, and overall WECS control.

Expanded virtual vector-based model forecastable control strategy for three-phase two-level inverters

Abstract A three-phase, two-level inverter based on model forecastable control has good transient performance but poor steady-state performance. Considering the limitation of a limited number of discrete voltage vectors in a two-level inverter topology, this paper proposes a virtual vector model prediction method based on the analysis of a time-stepped forecasting model for a three-phase grid-connected inverter. First, three fixed virtual voltage vectors are constructed in each sector, and the action time of the required fundamental vector is found. Then, the cost function is constructed, and the optimum is selected among the virtual and fundamental voltage vectors in each sector. Finally, a hardware-in-the-loop experiment was carried out based on the PE-Expert4 experimental platform developed by Myway Co., LTD. The results show that the proposed virtual vector model forecastable control strategy can effectively improve the transient and steady-state performance of three-phase two-level inverters.

Fault detection and synchronization control in hybrid DC/AC microgrids using grid-forming inverter DC-link controller

This paper introduces a DC-link fault detection and synchronization control strategy for grid-forming inverters in hybrid DC/AC microgrids, aiming to bolster system stability and reliability. The proposed control scheme seamlessly integrates DC-link fault detection with virtual synchronous generator (VSG) control, facilitating inertia emulation and synchronization without the need for a phase-locked loop (PLL). The DC bus controller is designed to swiftly identify faults triggered by power imbalances, such as load fluctuations or generator integration, and dynamically adjust the power reference for the VSG controller to ensure inertia emulation. The Ziegler-Nichols method is utilized for meticulous tuning of the DC-link controller gains, while the modified swing equation governs VSG inertia and synchronization. MATLAB/Simulink demonstrate the superior performance of the proposed method compared to traditional GFM control strategies. Specifically, the proposed controller improved the frequency nadir to 59.98 Hz compared to 59.75 Hz and showed an enhanced power step response of 7.9×10^5 W compared to 6.9×10^5 W for conventional control method. The proposed GFM control also eliminated the 10×10^6 W switching spike observed with conventional controllers. These findings highlight the potential of this fault-controller approach to advance the reliability and efficiency of hybrid DC/AC microgrids.

Design of voltage and frequency stabilization system for fishing vessel shaft generator based on UPS backup power supply

Abstract A fishing boat shaft generator is a kind of power supply device driven by the main diesel engine, which has the advantage of saving energy compared with a diesel generator and eliminating the need to be equipped with an additional diesel engine, witnessing wide applications in the use of power supply equipment for fishing boats. However, because the shaft generator is mounted on the main diesel engine, the fishing boat encounters bad sea conditions at sea, and the speed of the diesel engine fluctuates, resulting in the instability of the power frequency and voltage sent by the shaft generator, which will endanger the electrical equipment of the fishing vessel in serious cases. In this paper, a design of a voltage and frequency stabilization system for a fishing vessel shaft generator based on a UPS backup power supply was proposed. The system consists of a three-phase shaft generator, inverter, battery, and electrical equipment. The inverter control strategy is introduced, and the battery charge/discharge and DC boost are designed.

A Simplified Model Predictive Current Control Strategy for Six-phase H-bridge Inverters

Background: The double-end H-bridge inverters can realize independent control of the stator voltage in each phase and have flexible advantages of modulation and fault tolerance; thus, they are more suitable for multi-phase fault-tolerant motor drives. However, due to the increase of voltage vectors and the coupling between the electromagnetic and non-electromagnetic quantities, the normal control strategies for traditional three-phase motor drives do not work anymore. Objective: This paper aimed to propose a simplified model predictive current control strategy based on the vector space decomposition (VSD) and the vectors’ gradual simplification for the three-level six-phase H-bridge inverters. Methods: Firstly, the 729 physical variables were decomposed and mapped onto the fundamental αβ subspace, harmonic xy subspace, and the zero-sequence o1o2 subspace based on the VSD. Then, to eliminate the influence of the harmonic and zero-sequence components on the control performance and make an easy digital implementation, vectors’ simplification has been proposed based on the in-depth analysis of the relationship between the voltage vectors mapped onto different subspaces and vectors’ stratification. With the simplification method, the number of voltage vectors was simplified from 729 to 12, and then the selected voltage vectors were used in the rolling optimization of the model predictive current control (MPCC) to choose the optimal one. Finally, sufficient experiments were carried out including static and dynamic conditions, different modulation index and power factor, etc., to verify the feasibility of the proposed strategy. Results: The simulation and experimental results show that with the simplified MPCC strategy, both the static and dynamic performances are relatively good, and the THDs of the phase current under different modulations and power factors are relatively low. Conclusion: The proposed MPCC algorithm for the three-level six-phase H-bridge inverters has shown obvious improvement in solving the control problems of multi-vectors and complex redundancy issues.

Research on Inverter Control Strategy Based on FPGA

Abstract This study adopts a composite repetitive controller strategy in a three-phase four-wire circuit, combining proportional resonance and repetitive control, which effectively suppresses harmonics and improves system performance. At higher switching frequencies, FPGA is used to achieve efficient control to ensure system stability and performance. This research provides new ideas for improving the performance of on-board inverters, especially in terms of high-speed control, nonlinear load and harmonic processing. SiC devices and composite control strategies provide more sustainable solutions for future rail transit systems.

A novel RMPC strategy for three-phase inverters operating in grid-connected and standalone modes

One of the main features of microgrids is the capability of operating in both grid-connected (GC) and standalone (SA) modes. This paper presents a novel dual mode robust model predictive control (RMPC) strategy for a three-phase inverter with an LCL filter in both GC and SA operating modes under the filter’s parameter uncertainty. At first, a disturbance observer gain is obtained by solving a linear matrix inequality (LMI), which is determined to preserve the stability of the algorithm. The designed disturbance observer takes into account the polytopic uncertainty of system parameters. A performance index with two weighting matrices is then defined and solved in an infinite horizon by turning it into an optimization problem under LMI constraints. The performance of the control strategy highly depends on the weighting matrices. Hence, an optimization algorithm is formulated to ascertain the best matrices values for both GC and SA operation modes. Given the nonlinearity issue, particle swarm optimization (PSO) is employed to derive the optimal weighting matrices offline. To evaluate the proposed control strategy’s effectiveness, simulations and experiments are performed under several scenarios in both GC and SA operating modes. The results reveal the proposed control strategy’s powerfulness compared to other techniques in the presence of grid voltage and load current disturbances for both inverter operating modes.

Adaptive low voltage crossing strategy for symmetrical faults of networked inverters

Abstract Due to the inability of grid-following control methods to compensate for the comprehensive reduction in system inertia, strength, and short-circuit capacity caused by the decreased proportion of synchronous machines, the grid exhibits insufficient resilience to disturbances, leading to severe stability risks in terms of rotor angle, frequency, and voltage. Grid-forming inverters have emerged to address this issue. During symmetrical faults, the low-voltage ride-through of grid-forming inverters often involves freezing the reactive power loop, resulting in a direct output of higher voltage and reactive current. However, an increase in reactive power command leads to a sharp rise in the internal potential magnitude of grid-forming inverters. Upon clearance of the grid fault, the excessively high internal potential may cause a rapid, short-term increase in terminal voltage, potentially resulting in overvoltage, which is detrimental to the operation of grid-connected equipment. In response to this issue, this paper proposes an adaptive low-voltage ride-through control strategy for grid-forming inverters under symmetrical faults controlled by a virtual synchronous machine control method. Initially, a virtual synchronous machine control model is established. Limiting current is achieved through the construction of a fixed virtual impedance loop. The issues associated with fixed virtual impedance current limiting are analyzed, leading to the proposal of an adaptive virtual impedance control strategy. Finally, the feasibility of the proposed method is verified through simulation experiments.

Multi-DG qZSI based grid tied inverters

The increasing adoption of distributed generation (DG) systems, driven by their numerous advantages, has led to a growing utilization of hybrid systems. Multilevel converters have emerged as essential components in power electronics applications, offering benefits such as harmonic reduction. However, designing effective control strategies for multilevel inverters presents challenges. This paper proposes a multi-DG quasi-Z-Source Inverter (qZSI) designed with a cascaded H-bridge controller. The incorporation of qZSI in the system enhances reliability and component safety while enabling the implementation of additional shoot-through control. This feature facilitates the balancing of inequalities arising from the two DG sources, thereby improving disturbance rejection. Furthermore, a current control scheme is implemented on the AC side to seamlessly feed active power into the grid without introducing distortions in current injection. Overall, the proposed system addresses key challenges in multilevel inverter design and offers a promising solution for efficient and reliable grid integration of DG systems. This work is thus useful in variety of applications, including electric vehicles and environment sustainability.

Adaptive reactive power control strategy for grid-forming inverter under symmetrical fault

Abstract Due to the inability of the grid-type control method to compensate for the comprehensive reduction in system inertia, strength, and short-circuit capacity caused by the proportional decrease of synchronous machines, the power grid exhibits insufficient resistance to disturbances, leading to severe stability risks in terms of rotor angle, frequency, and voltage. In response to these challenges, grid-forming inverters have emerged. Under symmetrical faults, the low-voltage ride-through of grid-forming inverters is often accompanied by a frozen reactive power environment, resulting in a direct output of increased voltage and reactive current. However, an elevated reactive power command can cause a sharp increase in the potential amplitude within grid-forming inverters. After the grid fault is cleared, the excessively high internal potential can cause a short-term and rapid increase in terminal voltage, potentially leading to overvoltage, which is detrimental to the operation of grid-connected devices. To address this issue, this paper first employs a grid-forming inverter controlled by a virtual synchronous machine control method. Using the grid positive-sequence voltage as a reference value, it identifies whether a voltage drop fault has occurred. Based on this, an adaptive reactive power control strategy is proposed, which can promptly achieve the same effect as the frozen reactive power environment during faults, while also promptly restoring the reactive power environment after fault clearance, thereby avoiding overvoltage issues. The feasibility of the proposed method is verified through the establishment of a simulation system.