In the new energy grid connected system, the grid-forming inverter can improve the stability of weak grid or island operation mode, VSG control can enhance system stability and improve dynamic response. but it is difficult to adjust the control parameters in the dynamic process. Due to the self-learning ability of deep reinforcement learning (DRL), especially the advantage of deep deterministic strategy gradient (DDPG) in high-dimensional continuous control of power converter, this paper proposed an adaptive VSG controller based on DDPG, which can realize real-time optimization for the virtual inertia J and virtual damping D. In addition, it can also optimize the PI parameters of PCC voltage loop according to the change of system load, which can reduce the fluctuation of PCC voltage when the system load fluctuates, and improve the response speed and steady-state performance of PCC voltage recovery. The verification results confirm the effectiveness of PCC voltage stability.

With the increasingly severe global energy crisis, photovoltaic(PV) power generation has become a crucial link to alleviate the energy crisis. Energy storage system is commonly used in PV power generation system, and its control and monitoring affect the normal operation of PV system. Based on the Thevenin equivalent circuit model, this paper designed a linear sliding mode observer (LSMO) and a SMO based on the super-twisting algorithm to estimate the State-of-Charge(SoC) and the State-of-Energy(SoE) of the lithium-ion battery. The accuracy and robustness of the proposed SoC and SoE observers are verified by dynamic stress test (DST) experimental data.

Neutral-point clamped (NPC) three-level inverter is widely used in medium and high power circuits because of its low harmonic content and good voltage withstand capability of switching tubes, but it is necessary to carry out the mid-point voltage balancing control of NPC three-level inverter in the practical application; in this paper, on the basis of NPC three-level inverter with increased bridge arms, the paper proposed a fully-actuated control method, the mathematical model is established and the control rate is deduced. The simulation results verify the neutral point voltage balance effect of NPC three-level inverter.

This paper presents a study on the control of the neutral point of DC/AC converters connected to an unbalanced 3-phase 4-wire grid. The mathematical models of the converters, including an LCL filter, and the neutral line circuit in both balanced and unbalanced 3-phase 4-wire grids are developed. An active balancing method is employed to maintain the DC bus voltage's zero DC offset voltage. A virtual control technique is implemented in the controller design. Furthermore, a sliding mode control strategy is proposed to regulate the neutral point of DC/AC converters. The efficacy of the proposed approach is demonstrated through simulation results.

With the power grid gradually to a high proportion of new energy, high proportion of power electronic device direction forward. Grid-connected inverter is widely used as an important power electronic device in new energy power generation, and the power grid also presents the characteristics of weak power grid. The interaction between the two makes the wide-frequency oscillation problem of grid-connected systems and the frequency coupling phenomenon become more and more prominent. The previous analysis methods usually assume that the three-phase interconnection system can be decoupled into the single in single out positive sequence subsystem and the negative sequence subsystem in the frequency domain. However, due to the high proportion of new energy connected to the grid, the frequency coupling in the grid is relatively obvious, leading to instability. In this paper, the frequency coupling characteristics of grid-connected inverters based on LCL are studied, and the analysis models considering various frequency coupling reasons are established and verified. On this basis, the influence factors of frequency coupling are analyzed.

In this paper, the research object of the three-phase LCL inverter under the AC microgrid is studied. Transforming the LCL inverter model to the Euler Lagrange (EL) equation and judging the passive characters of the EL model. Based on the theory of passive based control (PBC), a double closed-loop control with PBC control as the inner current loop and PI control as the outer voltage loop is proposed. The superiority of the PBC- PI controller in stabilizing the DC bus voltage and grid-connected current is verified under the conditions of sudden changes in DC side input and sudden changes in grid voltage. The comparative simulation results verified the the proposed strategy has better stability and rapidity.

The high penetration of grid-connected photovoltaic (PV) inverter into power grid results in difficulties to guaranty the generator-load power balancing. That is due to the intermittence of solar energy and non-dispatchability nature of PV generators. Therefore, to enhance generator-load power balancing, this paper proposes a control method allowing the single-stage PV inverters to autonomously dispatch the generated power for the frequency change compensation. To achieve that, a single inverter in the system estimates the available power by generating the reference DC-link voltage corresponding to the maximum power; whereas other inverters in the system dispatch the available power by drooping DC-link voltage with respect to the change in system frequency. The simulations are performed by means of PLECS simulation software. The results confirm the effectiveness of the proposed power dispatching control method, where the power dispatching by single-stage PV inverter is achieved under several operating conditions of grid frequency change.

Most microgrid (MG) inverters are based on the voltage and current double loop control structure of PI to achieve control objectives, but the controller parameter setting is complex and the dynamic response speed is slow. In this paper, the predictive model control (MPC) is used to replace the traditional voltage and current double loop modulation for T-type three-level inverter to improve the dynamic response speed and parameter setting. At the same time, aiming at the complexity of online calculation of MPC algorithm of T-type three-level inverter, an optimized algorithm is proposed and the redundant vectors are eliminated in advance, the speed of MPC is increased and improve the total harmonic distortion (THD) of MG inverter output waveform.

This paper presents a feed-forward decoupling control method to enhance the stability of a photovoltaic (PV) inverter connected to a weak grid. As the grid weakens, the point of common coupling (PCC) voltage becomes sensitive to the active power. This increases the coupling effects between control loops, Phase-Locked Loop (PLL) and grid dynamics, which deteriorate system stability. Therefore, in this paper, a decoupling control method is proposed in which the reference active current obtained by regulating the DC-link voltage to its reference value is feed-forwarded to modulate the reactive current reference generated by regulating the PCC voltage to its predefined value. As result, the robust performance of the PV inverter connected to a weak grid has been yielded, where the inverter stability is maintained for both wider PLL bandwidth and high grid impedance. Based on open-loop bode plot and closed-loop eigenvalues of the DC-link voltage control (DVC) loop, a stability analysis of the proposed control method and the conventional vector control method has been performed. Then, the proposed method is verified through simulation results obtained by PLECS.

Most of the microgrid inverters are based on PI-based voltage and current double-loop control structure to achieve control target, but the controller parameter setting is complicated and the dynamic response speed is slow. The paper adopt Predictive Models Control (MPC) replace traditional voltage and current double-loop and modulation to improve the dynamic response speed and parameters tuning. In order to maintain the damping character of microgrid and overcome droop control frequency change rate, this paper adopts the strategy of Virtual Synchronous Generator (VSG) in the power loop to make the system have inertia and enhance stability. The simulation comparison verifies the proposed control strategy is effective and the faster response speed.

In order to ensure good power quality, the grid-connected inverter mostly uses phase-locked loop (PLL) to maintain synchronization with large power grid. But the PLL will cause a negative-impact on the stability of grid-connected inverter under weak grids. The paper analyzes the equivalent impedance of the PLL under the weak grid firstly. Then the paper proposed a self-synchronization strategy using DC bus voltage and reactive power control to synchronize the frequency and amplitude with the grid-connected inverter instead of the applying PLL. Applying the proposed method to the on/off grid switching condition, a pre-synchronization control strategy based on virtual power is proposed to achieve seamless switching of the grid-connected inverter. At last, the designed self-synchronization control strategy and pre-synchronization strategy are verified on the Plecs simulation platform.

This paper mainly solves the problem of on/off-grid switching for Energy Router grid-connected inverters on the AC side. A control strategy based on sliding mode disturbance observer is proposed to suppress the disturbance of the output current to the output voltage. At the same time, the improved pre-synchronization method is used to achieve fast synchronization of voltage amplitude and phase. An improved frequency shift method is proposed for islanding detection for droop control grid-connected inverters. Finally, the proposed methods are verified by simulation in MATLAB/Simulink.

New studies on grid-connected voltage-source inverters (VSIs) show that sequence-admittance-based stability analysis model cannot be simply simplified as decoupled positive-sequence and negative-sequence impedance ratio because of sequence-couplings resulting from the outer asymmetric power control loops, such as the phase locked loop (PLL) and direct voltage control. Additionally, compared with single grid-connected VSI system, parallel-connected VSIs have stronger circuit-couplings via grid impedance. To get accurate stability conclusions in wider frequency range, both couplings are considered in this paper, and this paper firstly derives a sequence-admittance-based stability analysis model to capture resonances in parallel-connected VSIs. The proposed model is described as open-loop model and closed-loop model, to which Nyquist stability criterion is effectively applied instead of the complicated generalized Nyquist stability criterion. Take the PLL-induced low-frequency resonance for example, stability analysis of the studied cases is successfully conducted. Finally, time-domain simulations verify the accuracy and simplicity of the proposed model.

This paper proposes an energy router topology based on virtual generator theory. The AC and DC interfaces in this paper are controlled by a virtual synchronous generator (VSG)and virtual DC generator (VDG)to achieve coordinated control of AC and DC interface energy, respectively. The mathematical models of virtual DC generator and virtual AC generator control are also established separately, and AC and DC-side coordinated control was realized. Three kinds of working conditions were analyzed to verify the proposed energy router topology. The MATLAB simulation results verify the correctness and effectiveness of the proposed circuit topology and control strategy.

Virtual synchronous generator (VSG) is a grid-connected inverter control algorithm developed rapidly in recent years, which can provide inertia and dynamic frequency support for the grid. This article mainly studies the VSG control of grid-connected inverter based on microgrid, the VSG algorithm is adopted in the power outer loop, and designs the voltage and full-order sliding mode control current double loop to improve the stability of the system. With this method, the robustness of the system is enhanced, and the stable operation of the system is achieved while dynamic performance ensured. The feasibility and effectiveness of the above control algorithms are verified by building a simulation model in MATLAB software.

Grid-connected converters have been widely used in distributed generations. However, the resonance brought by converters in weak grid has been a great threat to system stability. Impedance-based method provides a powerful tool for stability analysis. Active damping is also widely applied to improve system stability. This paper derives the impedance model of grid-connected converter system and analyzes the harmonic resonance mechanism. The effects of passive damping and active damping are also compared, especially their influence on non-passive region. Impact of capacitor current feedback gain on the output admittance is also analyzed. High-pass filter is used to compensate the digital control delay and reduce the non-passive region of output admittance. An improved active damping is proposed to eliminate second harmonic introduced by active damping. The performance of proposed method is verified in Matlab/Simulink simulations. The simulation result shows the effectiveness of proposed method.

The paper firstly establishes a passivity-based control (PBC) of a double-fed inductor generator (DFIG). A new control method of the DFIG is proposed with the outer speed loop controlled by a full-order terminal sliding mode (TSM) controller to undertake maximum wind power point tracking (MPPT), while the inner current control loop is a PBC designed to manage the three-phase PWM rectifier. Simulation results show that the controller design is effective and that the system exhibits satisfactory performance.

For the actuator uncertain nonlinear system, the paper proposed a nonsingular terminal sliding-mode (NTSM) control. The proposed strategy not only can eliminate the singularity problem but also can converge to the equilibrium point in finite time. The paper designed the controller for the two-order system and the higher-order uncertain actuator systems, respectively. The simulation results validate the proposed method.

This paper proposes an adaptive full-order Sliding Mode Observer (SMO) for the rotor speed and position estimation in the Permanent Magnet Synchronous Generator (PMSG). A full-order terminal SMO is designed to make the estimated stator current track the actual stator current, and eliminate the chattering. Furthermore, A back Electro Motive Force (EMF) observer adopts adaptive control to estimate the back EMF. Thus the rotor speed can be estimated from the adaptive law, and the rotor position can be calculated by the back EMF. The design of the adaptive back EMF observer further reduced the chattering. Compared simulation results are presented to validate the proposed method.

The paper firstly establishes a port-controlled Hamiltonian dissipation (PCHD) based model of a direct-drive permanent magnet synchronous generator (D-PMSG). A new double loop control of the D-PMSG is proposed with the outer speed loop controlled by a non-singular higher-order terminal sliding mode (NHTSM) controller to undertake maximum wind power point tracking (MPPT). In the inner current control loop is a passivity-based controller (PBC) designed to manage the three-phase PWM rectifier. Simulation results show that the controller design is effective and that the system exhibits satisfactory performance.

The robotic system of a two-link flexible manipulator is decomposed into an input-output subsystem and a zero dynamics subsystem using the input-output linearization technique. A novel inverse dynamics nonsingular terminal sliding mode controller is designed to make the input-output subsystem converge to its equilibrium point in finite time. The parameters of the zero dynamic subsystem are optimized by a genetic algorithm so that the zero dynamics subsystem is asymptotically stable at equilibrium point and finally the whole original flexible manipulator system is guaranteed to be asymptotically stable. Additionally, in order to overcome the chattering, this paper adapts a fuzzy logic controller to realize the nonlinear switching function. Simulation results are presented to validate the design.