For$LCL$type grid-connected inverters, inverter-side current control (ICC) mode is more promising for industrial applications for the convenience in the protection of power switches, e.g., IGBTs. However, the time delay in digital control causes the limited stable region of single-loop ICC. To enhance the stability of the system, capacitor-current-feedback active damping (CCF-AD) has been widely used to achieve the dual-loop current control. However, most of the existing designs of CCF-AD are under grid-side current control, while the passivity-based design of CCF-AD for the ICC has yet to receive much attention. For achieving passive output admittance of the inverter, this paper reveals a small delay needs to be introduced into the CCF-AD loop for the ICC. The parameter design of CCF-AD is detailed in this paper. Finally, the experimental results verify the theoretical analysis.

The LCL-type grid-connected inverter (GCI) with inverter-side current control (ICC) has been extensively implemented for the advantages of its over-current protection ability and low cost. However, in the scenario of distorted grid voltage, due to indirect control of the grid-side current, ICC lacks relevant information about the grid current harmonics, thus, the harmonics can freely flow into the filter capacitor and distort the grid current. In this paper, a capacitor current compensation scheme with active damping and repetitive controller (RC) is proposed to enhance the grid current quality. Besides, the output admittance of the inverter is tuned to be passive below Nyquist frequency to ensure a sufficient stability condition. Finally, the effectiveness of the proposed method for the grid current quality enhancement is verified by experimental results.

In high-power applications, output filters are essential components of grid-connected inverters (GCIs) for filtering switching ripples. These filters are closely related to the electrical indexes and control performance of the GCI, including power density, efficiency, stability, etc. Therefore, they are often co-designed with constraints on electrical indexes and damping coefficients. However, damping coefficients can not provide sufficient stability conditions. To overcome it, this paper proposes a passivity-based multi-objective LTCL-RC filter design method. The proposed method can achieve passive output admittance at the full-frequency range to maintain a sufficient stability condition. To be specific, the Pareto optimization with respect to power density, efficiency and passivity is introduced to select parameters. Furthermore, a 4MW-GCI filter design example is provided to highlight its superiority over other state-of-the-art design methods, and the effectiveness of the proposed filter design approach in ensuring system stability is also verified on a scaled-down 1.4kW-VSI experimental prototype.

This paper proposes a passivity-based design method of 6k±1-order harmonic repetitive control (6k±1 RC) for LCL-type grid-connected inverters (GCIs). According to the proposed design method, the output admittance of the 6k±1 RC-RC-controlled inverters is tuned to be passive at all frequencies so that it can be plug-and-play connected to the grid regardless of the grid impedance variations. Meanwhile, compared with the traditional repetitive control (CRC), 6k±1 RC has a faster error convergence rate and can produce low THD and high tracking accuracy even in distorted grid conditions. Experimental results verify the effectiveness of the proposed method.

The study focuses on the reliability and lifespan of Insulated Gate Bipolar Transistors (IGBTs), which play a vital role in renewable energy power generation systems. To assess the performance of IGBT-based power devices, a power cycle test platform is developed. This platform incorporates a single-phase inverter bridge circuit with Sinusoidal Pulse Width Modulation (SPWM) control technology. By simulating real-world operating conditions across various application scenarios, the platform provides evaluation parameters of IGBTs' thermal characteristics and lifespan, offering data models to analyze their service life. The research covers multiple aspects, including the design of main circuit parameters, current closed-loop control design and hardware circuit test. Additionally, a semi-physical simulation platform is designed to validate the research findings by reproducing working conditions and measuring the junction temperature.

Model predictive control (MPC) has been widely considered as a design strategy for grid-interactive applications due to its simplicity and ease of implementation. However, the control performance of the inverter depends heavily on the accuracy of the system model when using the MPC-based method. To design cost-effective and high-efficiency inverters, the magnetic powder core-based filter inductor is a potential candidate since it involves the advantages of moderate cost and low losses. In the inverter operation, inductor current can vary from 0 to rated value in one line cycle of the grid. This will result in wide inductance variation, which may inevitably increase the current ripple and even deteriorate system stability. In this paper, an inductance estimation algorithm was introduced to the MPC method for a single-phase three-level inverter. By replacing the nominal value of the inductor with the predicted value obtained by the estimation algorithm, better performances can be achieved for the grid current tracking and neutral point potentials (NPPs) balance control in both steady and dynamic state. Finally, all-digital simulation results are presented to verify the theoretical expectations and the effectiveness of the proposed scheme.

Repetitive controller (RC) has the merits of simple structure, small computational burden, and providing zero steady-state control error for the closed-loop at the zero frequency, fundamental frequency, and its multiples. However, for a distributed generation (DG) interfacing converter with the auxiliary harmonic compensation capability, its harmonic control loop often does not need to control the direct current (DC) and fundamental frequency components, thereof RC is inapplicable. To address this issue, this paper proposes a new harmonic RC (HRC) for DG interfacing converters. To construct the HRC, a digital second-order high pass filter and a notch filter are respectively used to cancel poles of the internal model of conventional RC at zero and fundamental frequencies. When implemented in the harmonic control loop of the DG converter, the proposed HRC only deals with harmonics, avoiding the extra harmonic extraction. Both the mathematic model derivation and the controller parameters design are given in detail in the paper. Finally, experiments are performed to validate the effectiveness of the proposed scheme.

The time delay of digital control would make the equivalent output admittance of voltage source converter(VSC) non-passive, which may lead to the resonant instable problem. In this paper, the Luenberger observer-based active damping method is researched to make the admittance passive. The method contains two part: firstly, the observer predicts the capacitor current of the LCL filter; secondly, carrying out the active damping by using the predicted current. It turns out that the passivity of VSC's equivalent admittance is affected by both the observer and active damping, and the passive equivalent admittance can be obtained by properly designing the observer and active damping parameters. In practical application, the observer-based active damping method can not only avoid using additional current sensors but also make the equivalent admittance passive below the Nyquist frequency. The simulation results verified the effectiveness of the proposed method for improving stability.

The triangle carrier based pulse width modulation (TCB-PWM) can be functionally equivalent to space vector base PWM (SVB-PWM). For multi-level inverter, it is very difficult to realize the SVB-PWM because its vector space is very complex. In this paper, a unified TCB-PWM strategy for three-phase N-level diode clamped inverter, including continuous PWM (CPWM) and discontinuous PWM (DPWM), is proposed. With the proposed strategy, the final modulation signals can be easily obtained by twice common mode voltage (CMV) injections. The PWM driver signals are generated by comparing the final modulation signals and phase deposition triangle carriers. Especially, the procedures to realize different types of PWM method are demonstrated in this paper. The proposed method can be directly implemented in digital processers.

Shunt active power filters (S-APF) are highly popular ways for harmonic compensation due to the high performance and simplicity of installation. S-APF is commonly controlled in current control mode with load harmonic current detection, which is not quite suitable for the distributed power generation system (DPGS) where the nonlinear loads are highly dispersed. Local harmonic voltage detection based Resistive-APF (R-APF) seems more suitable to be applied in the DPGS, however, R-APF suffers from poor compensation performance and difficulty of parameter tuning. In this paper, a direct harmonic voltage control strategy for the S-APF is proposed with local point of common coupling (PCC) voltage detection only. The control strategy design procedure is given in detail. Simulation is conducted in Matlab/Simulink to compare the performance between the R-APF and the proposed method. The results validate superiority of the proposed method.

Because of the low power losses and moderate cost, the magnetic powder cores are popular in producing the filtering inductors for the high efficient and cost-effective power converters. However, the soft magnetic property of the powder cores leads to the wide variation of inductance along with the changing of the inductor current in one cycle of the grid, which challenges the system stability and power quality. In this paper, the current-dependent small-signal model of a three-phase LCL-filtered inverter is derived for designing the corresponding controller. Based on the developed small-signal model, a capacitor current feedback based active damping loop and a fractional order repetitive control based compound current control loop are designed to stabilize the system and enhance the control accuracy in steady-state, respectively. The controller design procedure is given in detail. Finally, all-digital simulation has been conducted on a 3.7 kVA inverter system to verify the theoretical expectations.

This paper presents a linear active disturbance rejection control (LADRC) for grid-connected converter with LCL filter. The high rejection performance for external disturbance, internal decoupling, parameter variation is achieved by adopting extended state observer(ESO) and designing controller with direct pole placement. Robustness of parameter uncertainty and sensitivity of input disturbance are analyzed in frequency domain to demonstrate the superior characteristic in disturbance rejection. The theoretical analysis is verified in Matlab/Simulink. The simulation results show the excellent capability of rejection in grid voltage disturbance.