Control Method For Inverter Research Articles

High Precision Model Predictive Power Control Method for Battery Energy-Stored Quasi Z-Source Inverter

High Precision Model Predictive Power Control Method for Battery Energy-Stored Quasi Z-Source Inverter

Fuzzy sliding mode control with adaptive exponential reaching law for inverters in the photovoltaic microgrid

Photovoltaic inverters are widely utilized in microgrid systems working as the key equipment for converting solar energy into usable electricity. This paper presents a fuzzy sliding mode control (FSMC) method for the photovoltaic inverter in a microgrid. The inverter module uses voltage control to achieve stable AC output voltage. Moreover, to deal with system uncertainty and non-linearity in the photovoltaic inverter, a fuzzy controller was designed to realize real-time adaptation of the gains of the constant term and the reaching term in the sliding mode control law, which serves as a compensating controller for traditional sliding mode control. The gains of the exponential reaching law can be adjusted according to the system state instead of fixed gains, which can effectively reduce the chattering phenomenon and improve the robustness of the photovoltaic microgrid. Finally, the Lyapunov stability theory was used to ensure the stability of the entire control system, achieving a high-performance independent power supply for loads in a microgrid. Simulation results show that the designed control system is more robust to load disturbances and has superior dynamic performance.

Double-Vector Model-Free Predictive Current Control Method for Voltage Source Inverters With Sampling Noise Suppression

Model-free predictive current control (MFPCC) methods based on look-up tables (LUTs) have been widely applied in voltage source inverters (VSIs) due to their simple implementation and excellent robustness. However, the performance of the VSIs is affected by the voltage vector used, accuracy of current gradients and sampling noise. In order to improve these, a new double-vector MFPCC method is proposed in this paper. First, a synthetic voltage vector composed of double vectors is applied in each control period to reduce current ripples, where the durations of the double vectors are calculated using predicted current gradients. Next, an extended LUT is designed by using the current gradients of the applied synthetic voltage vectors to update all current gradients of eight basic voltage vectors, so as to increase the accuracy of current gradients. Then, the effect of the sampling noise on MFPCC is analyzed in detail and suppressed by a sliding-mode observer (SMO) for the VSIs. Finally, simulation and experimental results have verified the effectiveness of the proposed method.

Reviewing Control Paradigms and Emerging Trends of Grid-Forming Inverters—A Comparative Study

Grid-forming inverters (GFMs) have emerged as crucial components in modern power systems, facilitating the integration of renewable energy sources and enhancing grid stability. The significance of GFMs lies in their ability to autonomously establish grid voltage and frequency, enabling grids to form and improve system flexibility. Discussing control methods for grid-forming inverters is paramount due to their crucial role in shaping grid dynamics and ensuring reliable power delivery. This paper explores the fundamental and advanced control methods employed by GFMs, explaining their operational principles and performance characteristics. Basic control methods typically involve droop control, voltage and frequency regulation, and power-balancing techniques to maintain grid stability under varying operating conditions. Advanced control strategies encompass predictive control, model predictive control (MPC), and adaptive control, which influence advanced algorithms and real-time data for enhanced system responsiveness and efficiency. A detailed analysis and performance comparison of different control methods for GFM is presented, highlighting their strengths, limitations, and suitability for diverse grid environments. Through comprehensive studies, this research interprets the ability of various control strategies to mitigate grid disturbances, optimize power flow, and enhance overall system stability.

A digital hysteresis control method for three-level grid-tie inverter based on online prediction of sampling time without inductance

This article proposed a digital hysteresis control method for three-level grid-tie inverter based on online prediction of sampling time without inductance. The proposed method eliminated the effect on the control accuracy of the inductor changing with the current in the LCL filter of the grid-tie inverter, and reduced the equivalent sampling rate in digital hysteresis control by predicting and correcting the sample time. The simulations and experimental tests confirm the effectiveness of the proposed digital hysteresis control method.

Generalized control for distributed energy inverter in community microgrid system: Off-grid and grid-connected operation

With the increasing penetration of distributed energy resources (DER) in microgrids, DER power inverters have become a critical asset for providing power support to these microgrids. Meanwhile, the grid-forming (GFM) inverters, among these DER inverters, have gained significant attention in microgrid applications for their capability to enable the DERs to operate in different microgrid conditions and various operation modes. Moreover, with the implementation of these GFM inverters, smooth operation mode transition, GFM functions as well as black start functions can be obtained to improve the operation of the microgrid systems. In this article, a generalized control method for a single-phase GFM inverter is developed for community microgrid applications, facilitating smooth operation behavior in both operation modes with grid support functions and stable transition for different microgrid conditions. The control design procedure and function analysis of the proposed control method are explained in detail based on the community microgrid system. The effectiveness of the method in this paper is demonstrated on a 10 kW single-phase GFM inverter prototype with comparison to a model predictive method in recent literature.

Improved Carrier-Based Modulation for the Single-Phase T-Type qZ Source Inverter

The Quasi-Impedance-Source Inverter (Quasi-Z inverter) is an interesting DC-AC converter topology that can be used in applications such as fuel cells and photovoltaic generators. This topology allows for both boost capability and DC-side continuous input current. Another very interesting feature is its reliability, as it limits the current when two switches on one leg are conducting simultaneously. This is due to an extra conduction state, specifically the shoot-through state. However, the shoot-through state also causes a loss of performance, increasing electromagnetic interference and harmonic distortion. To address these issues, this work proposes a modified carrier-based control method for the T-Type single-phase quasi-Z inverter. The modified carrier-based method introduces the use of two additional states to replace the standard shoot-through state. The additional states are called the upper shoot-through and the lower shoot-through. An approach to minimize the number of switches that change state during transitions will also be considered to reduce switching losses, improving the converter efficiency. The proposed modified carrier-based control strategy will be tested using computer simulations and laboratory experiments. From the obtained results, the theoretical considerations are confirmed. In fact, through the presented results, it is possible to understand important improvements that can be obtained in the THD of the output voltage and load current. In addition, it is also possible to verify that the modified carrier method also reduces the input current ripple.

A Communication-Less Secondary Control Method for Parallel Grid-Forming Inverters in Islanded Microgrids Based on Mode Switching

A Communication-Less Secondary Control Method for Parallel Grid-Forming Inverters in Islanded Microgrids Based on Mode Switching

A Control Architecture for Regulating Voltage and Power Flows in a Networked Microgrid System

This paper presents a unique control system to regulate power exchanges and load bus voltage in a networked microgrid (NMG) system comprising AC and DC microgrids. During the islanding of a microgrid in this NMG system, load voltage and power balance can get disturbed. A control system and associated converter and inverter control methods are presented to rectify these issues. An efficient model predictive control (MPC) method, which gives a tracking error of 50% lower than a conventional proportional-integral (PI) controller, is used to control multiple inverters in the NMG system. Simulation studies are conducted to test the NMG in islanding and load change scenarios. With the help of these studies, it is verified that the MPC-controlled inverters can provide better tracking accuracy in achieving desired power flows in the NMG system.

A control method of parallel inverter for smart islanding of a local power system

Various types of distributed generators based on renewable energy become available today. The trends can make some small-scale power networks stand alone with an individual style and benefits, which is referred to as a concept of microgrid. To achieve its stable operation, a parallel inverter which is installed at the coupling point of the microgrid and utility can provide good performance. This paper deals with a control system of the inverter to keep high power quality by supporting the operation of islanding microgrid. The proposed system is tested under some situations including the condition of distributed generator with simulation studies.

Improved model predictive control method for a five-level inverter with coupled inductors

Improved model predictive control method for a five-level inverter with coupled inductors

Research on the Control Method of the PV Grid-Connected Inverter under an Asymmetrical Power Grid Fault

The negative-sequence current component and harmonic components generated when an asymmetrical fault occurs in the power grid seriously affect the normal operation of the photovoltaic (PV) grid-connected inverter. In order to suppress the negative-sequence current component and the harmonic component of the grid-connected current, and to meet the normal grid-connected operation requirements of the PV grid-connected inverter when asymmetrical faults occur in the grid, this paper proposes the proportional integral double-resonant (PI-DR) current controller, which consists of the PI controller and double-resonant controllers. The PI-DR current controller can directly control the negative-sequence current component and the grid-connected current harmonic component in the output current in the forward synchronous rotating coordinate system, without decomposing the positive and negative sequence currents. The PI-DR current controller ensures that the PV grid-connected inverter can realize normal grid-connected operation and improves the quality of the power when an asymmetrical fault occurs in the power grid. MATLAB/Simulink experiments show that the PI-DR current controller can improve the dynamic characteristics of the PV grid-connected inverter and improve the operating capability of the system when an asymmetrical fault occurs in the power grid.

A Decentralized Control Strategy for Series-Connected Single-Phase Two-Stage Photovoltaic Grid-Connected Inverters

Currently, most of the series inverter control methods rely on communication, which greatly reduces the reliability of the system and increases the cost. To address the above problems, this paper proposes a decentralized control strategy for series-connected single-phase two-stage grid-connected photovoltaic (PV) inverters. By improving the traditional droop control, the frequency and phase of the output voltage of each inverter unit are consistent and self-synchronized with the power grid while relying only on local independent control, and each unit realizes maximum power point tracking (MPPT). At different light intensities, each series-connected unit can quickly track the new maximum power point while still maintaining self-synchronization between the units. The system stability is analyzed via the small signal method, and sufficient conditions for system stability are obtained. Finally, the simulation results verify the correctness and effectiveness of the proposed control strategy.

A Current Control Method for Grid-Connected Inverters

It is simple to implement conventional current control with a proportional integral (PI) controller. However, system stability and dynamic performance are not perfect, particularly when operating under unfavorable conditions. In this paper, an improved control method is proposed by introducing a compensation unit. The compensation unit can effectively compensate the system’s phase around the crossover frequency, greatly enhancing the system’s phase margin and stability. It is also capable of handling weak-grid conditions. In this paper, the concept of the proposed compensation unit is explained first. Then, the corresponding mathematical model for the current control loop is built, and system bode diagrams for the conventional and proposed methods are compared. Furthermore, the effect of the parameters for the compensation unit is investigated, and an optimization method is proposed to determine optimal parameters. In addition, to handle weak-grid conditions, the proposed scheme is expanded by including the compensation unit in the grid’s feed-forward loop. Finally, an experimental platform is constructed, and the experimental results are presented to validate the proposed method.

Passivity-Based Control Method for Three-Level Photovoltaic Inverter to Mitigate Common-Mode Resonant Current

In transformerless three-level photovoltaic inverter systems, the modified LC filter, which directly connects the dc-side neutral point to the common point of filter capacitors, is considered to be an ideal scheme to suppress the troublesome leakage current. However, a new common-mode (CM) resonant current is emerged, which leads to inverter-side current distortion and even system instability. Therefore, a second-order passivity-based controller in time domain featuring with excellent system stability is proposed for the CM resonant current mitigation. First, the reason of CM resonant current generation with the modified LC filter is analysed in detail. Then, the CM current model is derived, which reveals that it is a second-order system. The passivity of this second-order model is strictly proved. Moreover, based on the passive control theory, zero state detectable theory and Lyapunov stability theorem, a second-order passivity-based controller is designed step by step to suppress the CM resonant current, and the system global asymptotic stability is also proved. The proposed controller is based on time domain, which is more intuitive and avoids the error amplification in the conversion from frequency domain to time domain. Finally, the effectiveness and the correctness of theoretical derivation of the passivity-based control method are validated by experiments. Compared with passive damping resistor method, the proposed method not only has better performance, but also avoids the use of real resistor and reduces the cost by using software instead of hardware.

A safe power controlling method for a phase-shift migration inverter to drive a high-power ultrasonic transducer.

The aim of this work is to investigate and analyze the operation mechanism and power control principle of a bolted Langevin type (BLT)-loaded phase-shifted control inverter and to find a safe power control method for a phase-shifted control inverter used to drive a high-power BLT by preventing the differential current (shock current) from occurring in the right branches of a phase-shifted full-bridge circuit. In this paper, by allowing the inverter operating frequency to operate under inductive loads that coincide with the zero points of voltage and current rather than the resonant frequency of the BLT, which results in the generation of a shock current in the right branch of the full-bridge circuit, the switches of the right-branch also enabled zero-voltage, zero-current switching on (ZVZCS turn-on). The proposed method can fundamentally eliminate the generation of shock current by realizing ZVZCS turn-on on the right-branch switch elements of the inverter. The phase-shift angle control limit for power control by this scheme is 90° and the power control range is 20%-100%.

Continuous Time Least Square PI Control Method for Quasi-Z Source Inverter

Continuous Time Least Square PI Control Method for Quasi-Z Source Inverter

Pole Placement-Based Current Control Method for CSI-Fed PMSM Drive With Eliminating Capacitor Voltage Sampling

This article proposes a pole placement based current control method for the current source inverter (CSI) fed permanent magnet synchronous machine (PMSM) drive with eliminating capacitor voltage sampling. Firstly, a generalized <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$N$</tex-math></inline-formula> -order feedback form of motor current and CSI output current is proposed in the stationary <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\alpha \beta$</tex-math></inline-formula> frame, for the arbitrary pole placement of the control plant. With the proposed pole placement method, the resonance frequency is moved closer to the Nyquist frequency and the resonance peak is damped. On this basis, a linear controller is proposed in the synchronous <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$dq$</tex-math></inline-formula> frame for the high-performance current control of PMSM. Moreover, the control parameter selection method is presented based on the consideration of open-loop crossover frequency and phase margin (PM). In this way, the desired PM and enough gain margin (GM) can be achieved, thus guaranteeing the stability and robustness of the system. Finally, the effectiveness of the proposed method is verified by lab-scaled experiments.

Research into a Method of Forming Neutral Point Voltage in a Three-Phase Four-Wire Voltage Inverter

Three-phase four-wire voltage inverters are commonly used in energy complexes based on distributed generation sources (solar panels, wind power plants, hydrogen fuel cells) and accumulator batteries. They allow to power loads, including single-phase ones, which require neutral point connection. In these cases, phase voltage formed by spatial pulse-width modulation (PWM) methods considerably differs from sinusoidal waves and has high total harmonic distortions of voltage and current curves. This article is devoted to research into the authors’ control method of a three-phase four-wire inverter, allowing for the rectification of the form of phase voltage supplying the load when applying the most common PWM (SVPWM, DPWMMIN, DPWMMAX, GDPWM) methods. The description of the method and its research results by simulation modeling and test bench are presented in the article. The simulation modeling was carried out by the developed Simulink-model of the three-phase four-wire inverter and its control system. The modeling results showed that the method application ensures sinusoidal voltage form when applying any PWM method. At this, THDU was reduced from 21.56% to 4.39%, while THDI was reduced from 21.16% to 1.69%. Experimental tests were carried out by a test bench featuring an uninterruptible power supply source. The authors researched the inverter operation as a component of the test bench under the control of the proposed method to form neutral point voltage. The experimental test results coincided with the simulation modeling results.

An improved maximum boost control technique for CDBC-based three-level ZSI

ABSTRACT This study presents an improved maximum boost control (MBC) method for three-level impedance source inverter. This technique offers removal of sixth frequency component from the inductor current present in the existing MBC technique of ZSI (Impedance Source Inverter). In addition, the proposed technique reduces the common mode voltage to 1/6th of dc bus voltage. The conventional zero vectors of three-level switching diagram are suitably modified and implemented for the case of 3L-CDBCZSI (three level controlled diode bridge clamped based impedance source inverter). It offers increased switching frequency of impedance network and reduces the size of passive components. On the basis of the proposed technique, the merits offered by 3L-CDBCZSI are highlighted and compared with T-type and diode clamped based ZSI. Simulation and experimental results are presented to verify the correctness of the proposed method.