Synchronous Inverter Research Articles

Analysis of adaptive parameter tuning control strategy of VSG

Abstract The traditional virtual synchronous inverter employs constant inertia and damping control, resulting in poor reliability when the system faces disturbances. Consequently, this paper proposes a synchronous virtual machine network control strategy based on adaptive technology. Firstly, the traditional principle is analyzed, followed by an examination of the effects of varying inertia and damping levels on the power grid. Leveraging the power angle characteristic and frequency oscillation characteristic of synchronous generators, an inertia and damping adaptive control strategy is devised. Subsequently, the effectiveness of the strategy is validated through simulation curves generated by a Simlink model.

Single-phase synchronous inverter control for fault management using emulation signal generators

Grid-forming (GFM) inverters are promising solutions for future power systems with high penetration of renewables. The successful design of GFM inverters is crucial for achieving current limiting, enabling them to withstand disturbances such as voltage sags and phase jumps in grid voltages. However, when the parameters are not properly tuned, a cascaded voltage and current controller can compromise grid stabilization performance due to issues like controller windup, post-fault recovery failure, and harmonic instability. To address this challenge, this paper proposes a dual control scheme consisting of GFM and current control that work in parallel. The dual control scheme incorporates emulation signal generators integrated with the dual controllers. This integration allows for adjusting their internal states during standby mode to track to references, enabling a seamless transition between the running and standby modes. Numerical simulations and experiments demonstrate that the proposed controller exhibits promising performance under both normal and faulted conditions.

Extended Application of Improved D-D-Σ Current Control in Synchronous Inverter Cluster Considering N Times Equivalent Impedance

Extended Application of Improved D-D-Σ Current Control in Synchronous Inverter Cluster Considering <i>N</i> Times Equivalent Impedance

Development of Single-Phase Synchronous Inverter for Single-Phase Microgrid

The work is based on a collaboration between Hiroshima University and Kure KOSEN College. This paper presents the design concept, hardware, and applications of a single-phase synchronous inverter (SSI), a specially designed grid-forming inverter (GFM) for single-phase micro-grid (SMGs). The SSI is designed for the conventional 100/200 V distribution network and is based on the concept of “Non-Interference Core (NIC) dynamic model”. Novel contributions of this paper are: (1) A root mean square (RMS) model of NIC-SSI was developed, combined with the conventional power system model, and verified through the comparison with the hardware-in-the-loop (HIL) simulation and SSI hardware experiments; (2) using the developed RMS simulation tool, the stabilization effect of the SSIs was investigated in condition under which the SSIs are massively installed in a distribution system; (3) off-grid SMG operations using SSIs under various ill-conditioned loads were demonstrated. The results show that the SSI has the considerable ability of grid stability enhancements for frequency, transient, and small-signal stabilities. The proposed SMG using SSIs is promising.

Linearized Minimum Current Stress Modulation Scheme of Single-Phase Bidirectional DAB AC–DC Converters

In this paper, the detailed steps for the derivation of linearized minimum current stress (LMCS) modulation scheme for single-phase bidirectional and isolated dual active bridge (DAB) ac-dc converters is presented. In order to reduce the current stress of the converter, a Lagrange multiplier method (LMM) scheme is designed to obtain the control coordinates constraint on the minimum value of the current stress. Compared with the conventional minimum current stress (MCS) control scheme, the proposed scheme realizes the linearization of power control, which significantly reduces the complexity of the controller algorithm. Moreover, the synchronous inverter control applied to the back-stage full-bridge is designed. Thus, the single stage power conversion is realized and the converter topology is electrolytic capacitorless, which promote the improvement of system reliability and power density. The impact of the ZVS scheme is analyzed in detail, and the adaptive-ZVS scheme for less system loss is selected. Finally, experimental results confirm the validity and feasibility of the proposed control scheme.

Decentralized Control for Multiple Network-Forming Inverters in a Solar PV-BESS Based Standalone Microgrid System

—This research paper focuses on decentralized control of an AC microgrid in standalone mode. The microgrid includes three solar PV arrays accompanied by three battery energy storage systems (BESS), utilizing renewable distributed energy resources (DERs). The connection between each DER system and the microgrid is established through a network-forming three-phase voltage source inverter (VSI). The microgrid’s operation is regulated using modified droop control, incorporating virtual impedance and feed-forward derivative in primary control, along with a phase-locked loop (PLL) system for inverter synchronization. A master-slave control configuration is employed between the VSIs to mitigate voltage amplitude and frequency deviations induced by primary control. These enhancements ensure smooth power distribution and maintain voltage amplitude and frequency within specified limits across different operational scenarios. Control operations are performed in a stationary frame ( frame) using Clarke’s transformation, and PR controllers regulate VSI’s output voltage and current. The research paper shows the effectiveness of controlled microgrid operations using MATLAB/Simulink software in various conditions including intermittent PV system behavior, load dynamics, and DER connection/disconnection challenges. Simulation results show that the proposed approach enhances stability and performance of the microgrid system, especially in managing power fluctuations and maintaining a constant frequency response.

An improved transient stability control method for virtual synchronous inverters considering virtual impedance

An improved transient stability control method for virtual synchronous inverters considering virtual impedance

Single‐phase Synchronous Inverter with Overcurrent Protection using Current Controller with Latched Limit Strategy

This paper proposes a controller for single‐phase synchronous inverters (SSIs) that was designed to stabilize the performance of a grid while providing overcurrent protection during the occurrence of a fault. The proposed controller for an SSI eliminates the multiple feedback control loops consisting of voltage and current controllers under normal conditions to avoid the instability attributed to them. To output the designed voltage precisely calculated using the core circuit, including a swing equation and speed governor, we employ the latched limit strategy for the overcurrent protection, which is combined with a proportional resonance current controller. Numerical simulations and experiments demonstrated that the proposed controller provides the designed performance while ensuring overcurrent protection during normal operation. © 2023 The Authors. IEEJ Transactions on Electrical and Electronic Engineering published by Institute of Electrical Engineer of Japan and Wiley Periodicals LLC.

分散型蓄電システム管理のためのマイクログリッド周波数制御

This paper proposes a novel frequency control method for the management of distributed energy storage resources in AC microgrid. Distributed autonomous controls by the individual prosumers perform an efficient coordination of SOCs which are automatically controlled to a same value that indicates the total SOC in the microgrid. The coordination is realized by the proposed control law that allows frequency deviation in a specified bandwidth. The proposed method has been developed in order for the microgrid operation by SSI, the single-phase synchronous inverters developed by the authors, while useful for general AC microgrid to increase the resilience of power supply.

The Dynamic Response of SPWM vs. SVPWM Synchronverter

This paper explores the use of Space Vector Pulse Width Modulation (SVPWM) instead of Sinusoidal Pulse Width Modulation (SPWM) to evaluate dynamic response of the synchronous inverter (synchronverter). The paper presents a comprehensive comparison between the SVPWM and SPWM for the dynamic response of synchronverter. This comparison aspects contain: the grid frequency, the active and reactive power, line current and its THD and rate of change of frequency (RoCoF) in case of using both modulation techniques. Despite the complexity of using SVPWM, it has several advantages over SPWM. With the increased penetration of renewable energy sources in power systems, the system inertia is reduced, and the frequency deviations becomes greater and faster. The results of this paper show that SVPWM contributes to reducing the rate of change of frequency (RoCoF) which enhances the system inertia. The results show a more stable behavior of SVPWM than the SPWM. Moreover, SVPWM reduces the total harmonics distortion (THD) of the current by 7% as compared to SPWM. Furthermore, the use of SVPWM reduces the complexity and the cost of the used filter. Matlab/Simulink is used for results validation.

A novel design of single‐phase microgrid based on non‐interference core synchronous inverters for power system stabilization

AbstractThis paper summarizes our recent work on Grid‐Forming Inverter (GFM) application to power systems. We have developed a novel design of GFM, a single‐phase synchronous inverter (SSI) for the conventional 100/200V distribution network based on the concept of “non‐interference core (NIC) dynamic model.” This paper first explains the design concept of NIC‐SSI and a simulation model of SSI for power system analysis. Then the stabilization effect is investigated, where the installation of SSI on the single‐phase consumer side is assumed as a new concept. The improvement of frequency and transient stability are evaluated. The SSI model is verified by comparing the developed root mean square (RMS) simulation, hardware‐in‐the‐loop (HIL) simulation, and the experiment using SSI hardware. The simulation results show that the SSI has the considerable ability of grid stabilization. Singlephase micro‐grid (SMG) operations using SSIs are also presented. The effectiveness of SMG operations is shown based on laboratory experiments.

Demonstration Experiment of Parallel Operation of Synchronous Generator and Voltage Controlled Virtual Synchronous Inverter

Demonstration Experiment of Parallel Operation of Synchronous Generator and Voltage Controlled Virtual Synchronous Inverter

Synchronization of Inverters in Grid Forming Mode

This article compares two strategies for seamless (re)connection of grid-forming inverters to a microgrid powered by droop-controlled inverters. While an incoming inverter must be synced to the microgrid, seamless syncing and power-sharing are technical challenges for grid-forming inverters. In the first strategy, called the output-sync method, an incoming inverter is synced to the microgrid, and then the circuit breaker is closed for power-sharing. In the second strategy, called the controller-sync method, the inverter initially contributes at zero power following the microgrid frequency, and then the controller is transferred to the mode of power-sharing. Remarkably, the circuit breaker can be kept closed during the syncing process using the controller-sync method as the inverter starts from zero power contribution. In this novel strategy, two controller sets run in parallel, i.e., two parallel control paths are in place for obtaining the magnitude and the phase angle of the PWM reference signal. These parallel paths are synced for seamless transitions when only one of them is engaged to generate the PWM reference signal. The efficacy of these control strategies has been tested in a hardware setup of a microgrid fed by two 5kVA 208V droop-controlled inverters, and the results are presented in this article. This article is also accompanied by a video clip demonstrating the performance of the output-sync and controller-sync methods in the laboratory.

Latched Limit Strategy for Single-phase Synchronous Inverter for Realization of Designed Grid Forming Performance

Single-phase synchronous inverters (SSIs) with synthetic inertia connect to single-phase circuits and stabilize the grid. They also improve grid resilience by forming and operating an islanded single-phase microgrid when disasters disconnect the single-phase circuits from the bulk power system. Generally, voltage and current feedback controllers are implemented in grid-connected converters to track the output voltage to the voltage reference and protect themselves from overcurrent when the fault occurs. However, controllers with multiple feedback control loops in SSIs impair the grid stabilization performance depending on grid frequency variations. Without optimal parameter tuning according to grid conditions, they also cause instability of the controller during the islanding operation of a single-phase microgrid. This paper proposes a controller to realize the designed grid forming performance and avoid the above problems inherent in SSIs. The SSI with the proposed controller works as a grid forming inverter in a normal condition without the multiple feedback loops, stabilizing the grid and operating a single-phase microgrid stably. When an overcurrent is detected, the SSI shifts from a grid forming mode to a current control mode using a latched limit strategy to protect semiconductor devices from the overcurrent. Since the appropriate switching between the two modes is essential for realizing the designed performance of the SSI, the proposed controller employs a modified current-trip voltage-reset limit. Numerical simulations and experiments demonstrate that the proposed controller provides the designed performance in both normal and faulted conditions.

Low Frequency Damping Control for Power Electronics-Based AC Grid Using Inverters with Built-In PSS

Low frequency oscillations are the most easily occurring dynamic stability problem in the power system. With the increasing capacity of power electronic equipment, the coupling coordination of a synchronous generator and inverter in a low frequency range is worth to be studied further. This paper analyzes the mechanism of the interaction between a normal active/reactive power control grid-connected inverters and power regulation of a synchronous generator. Based on the mechanism, the power system stabilizer built in the inverter is used to increase damping in low frequency range. The small-signal model for electromagnetic torque interaction between the grid-connected inverters and the generator is analyzed first. The small-signal model is the basis for the inverters to provide damping with specific amplitude and phase. The additional damping torque control of the inverters is realized through a built-in power system stabilizer. The fundamentals and the structure of a built-in power system stabilizer are illustrated. The built-in power system stabilizer can be realized through the active or reactive power control loop. The parameter design method is also proposed. With the proposed model and suppression method, the inverters can provide a certain damping torque to improve system stability. Finally, detailed system damping simulation results of the universal step test verify that the analysis is valid and effective.

Review on virtual synchronous generator technologies

With the increased penetration of renewable generation such as photovoltaics and wind turbines, the equivalent inertia and equivalent damping of the power system gradually decrease, which will result in stability problems becoming more and more serious. Virtual synchronous generator (VSG) technologies can enable power electronic interface inverters to simulate the external characteristics of synchronous generators (SG), thereby controlling grid-connected inverters as synchronous inverters and greatly improving the grid's ability to accept distributed power supplies. Additionally, it also effectively reduces the impact of the traditional grid-connected inverter on the stable operation of the power system during the grid-connected and off-grid process, which shows natural friendliness to the power grid. Therefore, VSG technologies have great research value and wide application prospects. This paper first expounds the basic idea of VSG, then further analyses and studies it from mathematical modelling, control strategies, stability analysis and application prospects, and finally puts forward several possible future research directions based on the project of my task group.

Fault characteristics of Inverter-Interfaced Distributed Generation

Distributed generations can be divided into traditional synchronous generators and inverter interfaced distributed generations (IIDG) according to their different operation mode. While the fault characteristics of IIDG is different from traditional Distributed Generators, the in-depth analysis on output characteristics and fault characteristics of IIDG are the foundation of micro grid protection. The mathematical models under P/Q and V/F control strategy are discussed. After simplifying its model, the fault characteristics of IIDG under P/Q and V/F control strategy are studied using the simulation of PSCAD/EMTDC. The analysis on the fault characteristics of IIDG that lays the theoretical foundation for the micro-grid relay protection.

Model predictive control method with common-mode voltage suppression for dual three-phase permanent magnet synchronous motor

Recently, the interest in model predictive control (MPC) and dual three-phase drives has been growing rapidly. Due to the high redundancy of voltage vector in the system composed of dual three-phase permanent magnetic synchronous motor (PMSM) and six-phase inverter, the computational complexity and current harmonics of MPC are high. In addition, the zero vector has been used by traditional MPC, which will cause higher common-mode voltage. In this paper, a novel MPC method with twice predictions and synthetic vectors is proposed which can not only suppress common-mode voltage, but also reduce computational complexity and current harmonics. The mathematical model of a dual three-phase PMSM are verified by the experimental results under the common-mode voltage suppression.

Frequency Adaptive Current Control Scheme for Grid-connected Inverter without Grid Voltage Sensors Based on Gradient Steepest Descent Method

This paper presents a frequency adaptive grid voltage sensorless control scheme of a grid-connected inductive–capacitive–inductive (LCL)-filtered inverter, which is based on an adaptive current controller and a grid voltage observer. The frequency adaptive current controller is constructed by a full-state feedback regulator with the augmentation of multiple control terms to restrain not only the inherent resonance phenomenon that is caused by LCL filter, but also current harmonic distortions from an adverse grid environment. The number of required sensing devices is minimized in the proposed scheme by means of a discrete-time current-type observer, which estimates the system state variables, and gradient-method-based observers, which estimate the grid voltages and frequency simultaneously at different grid conditions. The estimated grid frequency is utilized in the current control loop to provide high-quality grid-injected currents, even under harmonic distortions and the frequency variation of grid voltages. As a result, the grid frequency adaptive control performance as well as the robustness against distorted grid voltages can be realized. Finally, an inverter synchronization task without using grid voltage sensors is accomplished by a fundamental grid voltage filter and a phase-locked loop to detect the actual grid phase angle. The stability and convergence performance of the proposed observers have been studied by means of the Lyapunov theory to ensure a high accuracy tracking performance of estimated variables. Simulation and experimental results are presented to validate the feasibility and the effectiveness of the proposed control approach.

Design and implementation of a series switching SPSI for PV cell to use in carrier based grid synchronous system

A carrier-based grid synchronous method is proposed to develop the system efficiency, phase and power quality of the inverter output waves. The operating principle of a single-phase phase synchronous inverter (SPSI) is introduced, with proper synchronous paid to the switching-frequency synchronizing voltage made by the interleaved process, as well as actual mitigation approaches. In the construction of the SPSI, input and output filters are electrically coupled with the two sides of an inverter. The inverter power electronic switches and other electrical components are operated by carrier-based grid synchronous controller (CBGSC) with PWM regulator. The SPSI is designed and implemented with the Toshiba 40WR21 IGBT, Digital Microcontroller pulse controller (DMPC) and 4N35 Optocoupler with a fundamental frequency of 50Hz. The other parameters are considered as load resistance, =11Ω, duty cycle, 85%, carrier frequency, 2.5kHz and input DC voltage, ± 340V. In addition, LCL lowpass grid filters are used to convert squire wave to sine wave with required phase and frequency. Finally, the simulated and experimental results obtained with a carrier-based grid synchronous SPSI experimental prototype are exposed for justification, showing the phase error of 55% improvement, reduced 11% of THD and the conversion efficiency of 97.02% highly predicted by the proposed design technique to improve the microgrid system.