Grid-tied Converters Research Articles

A Non-Linear Control Technique for Single Phase qZSI

Quasi-Z-source inverters, or qZSIs, are a common type of inverter used in transformer-less systems because they can boost or buck input voltage without a requirement for a DC- DC converter. A transformer is not necessary for the qZSI's single-stage conversion to operate as a grid-tie converter. In transformer-less designs common mode current is the major problem, though, because there is no galvanic isolation. To reduce the common mode current, this article offers controlling the qZSI using a modified pulse width modulation (PWM) approach two additional semiconductor switches. The developed methodology provides a practical means of integrating solar photovoltaic systems into the grid. what the recommended topology's attributes should be: 1)It uses the phase-leg shoot through to boost the direct current and voltage to required level by eliminating the need for a second dc-dc converter. 2) Freewheeling is achieved while removing PWM deadtime by employing extra linked switches.

Enhanced DC Building Distribution Performance Using a Modular Grid-Tied Converter Design

This work quantifies the techno-economic performance of AC and DC residential building distribution. Two methods, utilising software and hardware configurations, are showcased to improve DC distribution: (i) a novel rule-based battery dual-objective operation (DOO) and (ii) a modular Master/Slave design of the grid-tied converter (GC). Both methods use the GC’s load-dependent efficiency characteristic, eliminating partial-load operation and enhancing energy efficiency. The work uses measured annual PV and load data to evaluate the performance of the methods compared to AC and DC references. The techno-economic analysis includes the annual net electricity bill and monetised battery degradation. The results show that the DOO eliminates GC partial-load operation at the cost of increased battery usage, resulting in marginal net savings. In contrast, the modular converter design significantly reduces losses: −157 kWh/a (−31%) and −121 kWh/a (−26%), respectively, relative to the DC and AC references. For a parametric sweep of electricity price and discount rate, the Lifetime Operating Cost (LOC) comparison shows savings from DC of up to USD 575 compared to AC.

Real-time Assessment of Ride-through Capability of Grid-tied Converter in Renewable Power Applications

This paper presents a comprehensive strategy for controlling grid-tied converters, with the primary goal of seamlessly integrating renewable power sources into the grid while ensuring stability and reliability. The control strategy is designed to achieve unity power factor operation under normal grid conditions, while also adhering to ride-through requirements to withstand voltage dips. Using the Typhoon HIL604 real-time simulation platform, extensive testing of the grid-tied converter is conducted to validate its performance. The results of the performance assessment are thoroughly analyzed and presented to exemplify the efficacy of the proposed control strategy. Notably, the paper emphasizes the converter's operation at unity power factor during normal grid conditions, indicating maximized active power delivery to the grid. Furthermore, the grid-tied converter demonstrates impressive ride-through capability during symmetrical voltage dip, achieved through the dynamic adjustment of grid current references to maintain grid stability. This research contributes to the advancement of grid-tied converter control strategies, offering insights into enhancing the integration of renewable power sources into the power grid while upholding system reliability and stability. Overall, this research offers valuable insights into the practical implementation of grid-tied converters for renewable power integration. It presents a comprehensive control strategy that not only enhances the integration of renewable power sources into the power grid but also prioritizes system reliability and stability.

Thiran filter-based fractional delay compensation for grid-tied converters

Thiran filter-based fractional delay compensation for grid-tied converters

Dc-Link Ripple Suppression of Cascaded H-Bridge Based MV Grid Emulator Apparatus for Analysis and Testing of Grid-Tied Converters in Distribution System

Dc-Link Ripple Suppression of Cascaded H-Bridge Based MV Grid Emulator Apparatus for Analysis and Testing of Grid-Tied Converters in Distribution System

Model predictive control of NPC three-level grid-tied converter based on reconstructed current

Model predictive control of NPC three-level grid-tied converter based on reconstructed current

Multi-Frequency Small-Signal Modeling for Three-Phase Grid-Tied Converter Considering Digital Control and PWM Effect

Multi-Frequency Small-Signal Modeling for Three-Phase Grid-Tied Converter Considering Digital Control and PWM Effect

A Fixed Switching Frequency Direct Model Predictive Control for Grid-Tied Converters with LCL Filters under Adverse Grid Conditions

A Fixed Switching Frequency Direct Model Predictive Control for Grid-Tied Converters with <i>LCL</i> Filters under Adverse Grid Conditions

Electromagnetic Integration of Decoupled LCL-Filter for Grid-Tied Converters With FMLF Technique

Electromagnetic Integration of Decoupled <i>LCL</i>-Filter for Grid-Tied Converters With FMLF Technique

An Iterative Equal Area Criterion for Transient Stability Analysis of Grid-Tied Converter Systems With Varying Damping

With the increasing penetration of renewable energy generators, the stability issues of grid-tied converter systems become much more important. However, due to the high nonlinearity and varying damping of converter systems, conventional transient stability analysis methods are not applicable, which may bring to conservativeness or misjudgment on stability assessment. In this paper, the transient stability of grid-tied converter systems with varying damping is investigated to provide stability boundary estimation. Firstly, considering the frequency mutation of the phase-locked loop (PLL) caused by various perturbations, a modified swing equation model of grid-tied converter systems is built, which greatly improves the mathematical model accuracy under transient disturbances. To evaluate the impacts of varying damping and frequency mutation, an iterative equal area criterion (ITEAC) method is proposed with the iterative calculation of the accelerating and decelerating area, which renders stability boundaries with high accuracy. Moreover, the impacts of controller and system parameters on stability boundaries are quantitatively analyzed. Eventually, simulation and hardware-in-loop experiments are performed to verify the effectiveness and superiority of the proposed ITEAC.

Two-Stage Coordination Scheme for Multiple EV Charging Stations Connected to an Exclusive DC Feeder Considering Grid-Tie Converter Limitation

Two-Stage Coordination Scheme for Multiple EV Charging Stations Connected to an Exclusive DC Feeder Considering Grid-Tie Converter Limitation

Self-induced and Mutual-induced Emissions of Grid-Tied Converters

Self-induced and Mutual-induced Emissions of Grid-Tied Converters

A Decoupling Control Method for Converting DIDO Sequence Admittance Model of Grid-Tied Converter System Into SISO

This paper proposes a decoupling control method to eliminate frequency coupling in three-phase grid-tied system. Firstly, the admittance model of three-phase <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LCL</i> -type three-phase grid-tied converter (GTC) considering DC-bus voltage control (DVC) loop and phase-locked loop (PLL) is established in <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dq</i> -domain frame, and the influence of asymmetrical DVC and PLL control structure on frequency coupling oscillation is analyzed. Then decoupling factors are added to the DVC loop and current control (CC) loop to achieve that the off-diagonal elements of the sequence admittance matrix of the GTC are 0, which means the frequency coupling in the GTC is eliminated. Therefore, the GTC system can be regarded as a single input single output (SISO) system, and the stability can be analyzed by the classic Nyquist criterion in the sequence-domain frame. Compared with the double input double output (DIDO) system, the resulted SISO system convenient for calculating the stability margin of the system and guiding parameter design. In addition, the SISO system is easier to be analyzed on the oscillation and resonance mechanism, and the analysis results can be used to optimize the design of the converter controller, grid planning and operation. Finally, simulation and experiment verify the feasibility and effectiveness of the proposed decoupling control method.

Dominant mode identification for grey-box grid-tied converters

The dominant modes of the system can be described by the critical eigenvalues, which reflect the stability and stability margin. This paper proposes a dominant mode identification (DMI) method to assess the stability of the grey-box grid-tied converter. First, the analytical relationship between the eigenvalues and the transfer function is clarified based on the small-signal model. Furthermore, the critical eigenvalues are estimated by the system’s transfer function. On this basis, the discrete transfer function of the grey-box grid-tied converter is constructed utilizing the frequency sweeping technique. Finally, the critical eigenvalues are determined using the measured data based on the customized particle swarm optimization algorithm. The method can apply to different grid connection scenarios of converter-based components and is easy to implement. The DMI method can not only assess the stability margin of grey-box grid-tied converters in operation, but also predict the stability of black-box converters after being connected to the grid in the planning stage.

Cyber resilience of power electronics-enabled power systems: A review

The demand for carbon neutrality leads to the transition from traditional synchronous generator-based power systems to power electronics-enabled power systems. The controllability and observability of power electronics devices are achieved by underlying metering and communication infrastructures, which are vulnerable to cyber-attacks. This review comprehensively investigates the cyber resilience of power electronics-enabled power systems from three aspects, i.e., before, during, and after cyber-attack events. Specifically, the cyber resilience of multiple power electronics devices in power generation (photovoltaic and wind), power transmission (high-voltage direct-current), power prosumption (electric vehicle, smart building, microgrid), power storage, and grid-tied converters, are addressed, respectively. In addition, this review thoroughly investigates the representative cyber-attack events, cyber-defense threats, cybersecurity regulations, and graphical cyber–physical architectures of the power electronics-enabled power system. As a result, this review proposes a general cybersecurity paradigm of power electronics closed-loop controllers. Therein, the cyber timescale, stealthiness, and threat between power electronics closed-loop controllers and power grid open-loop applications are investigated, respectively.

Modified Extended Complex Kalman Filter for DC Offset and Distortion Rejection in Grid-Tie Transformerless Converters

Proper operation of the grid-tie transformerless converters under unbalanced and distorted conditions entails a precise detection of the frequency and fundamental component of the grid voltage. One of the main problems that could arise during the estimation of grid parameters is the existence of a DC offset generated from measurement and A/D conversion. This undesirable induced DC offset could appear as a part of the reference sinusoidal current of grid-tie converters. Although literature has proposed the use of an extended complex Kalman filter (ECKF) for the estimation of positive and negative sequence voltage components as a promising competitor to phase locked loops, mitigating the effect of possible DC offsets when a Kalman filter is employed remains scarce. This paper proposes a new extended complex Kalman filter to improve the filter stability for estimating the frequency and the fundamental positive and negative symmetrical components of the grid voltages, where DC offset, scaling error, and noise can successfully be rejected. The theoretical findings are experimentally validated.

Asymmetrical Fault Ride-Through and Power Oscillation Characterization for Grid-Tied Voltage Source Converters

As the number of converter-interfaced distributed energy resources connected to the power system continues to increase rapidly, recent grid codes require these grid-tied converters to maintain grid connection during fault to ensure power supply security and reliability. In this work, we analyze the oscillation in the injected real and reactive power that a grid-tied voltage source converter (VSC) introduces as it attempts to contribute to the power quality and improve the voltage at the point of common coupling (PCC) during an asymmetrical fault. We propose a new double sequence current reference generation method that can be utilized to derive a closed-form quantification of the peak value of both the real and reactive power oscillation during asymmetrical fault ride-through (AFRT) analytically. Effect of the resulting bus voltage oscillation and ripple current requirement at twice the grid frequency, corresponding to the real power oscillation, on the input DC bus capacitor and upstream converter is analyzed for facilitating system component sizing. Furthermore, the proposed current reference generation formulation helps control the negative-sequence current injection during fault to assist with fault identification. The theoretical analysis is validated through simulation in <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">PLECS</i> for both asymmetrical and symmetrical fault scenarios. Experimental results for a three-phase, grid-tied VSC operating under both asymmetrical and symmetrical faults are provided to evaluate the performance of the proposed current reference generation method and validate the analysis presented.

Stability analysis of hybrid synchronization controller based grid forming control

Synchronization units are vital for the stable operation of grid-tied converters in generation and transmission. There are two main synchronization units, i.e., phase-locked loop (PLL) and power synchronization controller (PSC), with the corresponding drawbacks in weak and strong grid respectively. Recently, the hybrid synchronization controller (HSC) is proposed in order to make up the deficiencies of PLL and PSC in weak and strong grid respectively. This paper deduces the detailed impedance characteristics of PSC and HSC and compares their cons and pros to show the stability mechanism of HSC. Moreover, two types of HSCs are also presented and compared in this article with slight difference in structure. It is found that the impedance of Type II based HSC has smaller amplitude and better phase margin than PSC around fundamental frequency, while Type I based HSC has larger amplitude and less phase margin than PSC. Type II based HSC can improve the stability and Type I based HSC can worsen the stability compared with PSC. Realtime experiments are carried out to verify this.

Research on the Mechanism of Simultaneous Instability of dq Frame Sub- and Super-Synchronous Oscillations in Grid-Tied Converter

Research on the Mechanism of Simultaneous Instability of <i>dq</i> Frame Sub- and Super-Synchronous Oscillations in Grid-Tied Converter

Cooperative Fault Ride Through Strategy for Paralleled Grid-Tied Converters

Parallel systems are the trend of the grid-tied converters, which can improve the transmission power. Under fault conditions, the operation of the converter needs to be switched safely to ensure no disconnection. The cooperation between multiple converters can better cope with fault conditions and support the grid voltage. This paper proposes a coordinated fault ride through strategy. This strategy can ensure that the converters transfer the required reactive power into the grid according to their ability, and calculates the current feasible region. The residual capacity is used to transmit photovoltaic power within the current feasible region. Thus, the converters can operate within the safety region and help to restore the grid voltage. Simulation results verify the correctness of the proposed strategy.