To prevent short-circuits between the upper and lower switches of power converters from over-current protection, the dead time is mandatory in the switching gating signal for voltage source converters. However, this results in many negative effects on system operations, such as output voltage and current distortions (e.g., increased level of fifth and seventh harmonics), zero-current-clamping phenomenon, and output fundamental-frequency voltage reduction. Many solutions have been presented to cope with this problem. First, the dead-time effect is analyzed by taking into account factors such as the zero-clamping phenomenon, voltage drops on diodes and transistors, and the parameters of inverter loads, as well as the parasitic nature of semiconductor switches. Second, the state-of-the-art dead-time compensation algorithms are presented in this paper. Third, the advantages and disadvantages of existing algorithms are discussed, together with the future trends of dead-time compensation algorithms. This article provides a complete scenario of dead-time compensation with control strategies for voltage source converters for researchers to identify suitable solutions based on demand and application.

It is challenging for current source rectifier (CSR) to assure the satisfactory tracking performance, robustness and immunity ability simultaneously in face with various uncertainties and disturbances. Aiming at this problem, this paper proposes a composite control strategy that combines the fixed-time sliding mode disturbance observer (SMDO) with continuous finite-time backstepping control (FTBC) based on the recursive design concept. In contrast to the conventional infinite time asymptotic convergence, the FTBC ensures the close-loop system to reach a steady state in a finite time. To guarantee the rapidity and robustness of the proposed strategy, the fixed-time SMDO with the convergence time independent of the initial state of the system is designed to accurately estimates the matched and mismatched disturbances at a fixed time, and thus correct them in the control law for accurate current tracking. Meanwhile, the finite-time differentiator (FTD) is designed to obtain the desired differential signal, avoiding repeated derivative issue of the traditional backstepping control. Then, the stability of three-phase CSR closed-loop system is proved based on the finite-time Lyapunov stability theoretically. Finally, the comprehensive test results verify that the proposed strategy outperforms the comparative baseline controllers with a better static-dynamic performance and superior immunity and robustness which covering load disturbances, tracking reference step change and parameter uncertainties.

For single-phase current source converters, there is an inherent limitation in DC-side low-frequency power oscillation, which is twice the grid fundamental frequency. In practice, it transfers to the DC side and results in the low-frequency DC-link ripple. One possible solution is to install excessively large DC-link inductance for attenuating the ripple. However, it is of bulky size and not cost-effective. Another method is to use the passive LC branch for bypassing the power decoupling, but this is still not cost-effective due to the low-frequency LC circuit. Recently, active power decoupling techniques for the current source converters have been sparsely reported in literature. However, there has been no attempt to classify and understand them in a systematic way so far. In order to fill this gap, an overview of the active power decoupling for single-phase current source converters is presented in this paper. Systematic classification and comparison are provided for researchers and engineers to select the appropriate solutions for their specific applications.

DC-link dynamic is one of the most important issues for current source converters (CSC). In practice, the dc-link voltage suffers from the slow dynamic due to grid disturbances, which will affect the quality of output waveform and damage the converter. Many solutions have been presented to cope with it, but none of them achieve the zero dynamic dc-link voltage control. In order to fill the technical gap, a novel solution is proposed in this article. First, the impact of grid disturbances on the CSC is discussed with instantaneous power theory and small-signal model analysis. Second, a new solution is presented to eliminate the adverse impacts of grid disturbances, so as to achieve the zero dynamic dc-link control concept. Meanwhile, the power quality of grid current is improved. Finally, the experiments for the proposed solution under grid disturbances are carried out with TMS320F28335 DSP + XC3400 FPGA digital control hardware platform. The experimental results verify the effectiveness of the proposed solution.

It is a big challenge for current source converter (CSC) to ensure the desired tracking performance, robustness, and immunity simultaneously in the presence of resonance caused by the grid-side LC filter and slowly time-varying filter parameters or load disturbances. Aiming at this problem, combining the advantages of passivity-based control (PBC) and nonsingular terminal sliding mode control (NTSMC), a hybrid PBC-NTSMC method is proposed. Based on virtual damping injection and energy dissipation theory, the PBC is first designed for the inner loop followed by the construction of the Euler–Lagrange model. In this way, the resonance suppression is realized and the CSC system is proved to be passive. Furthermore, the NTSMC is combined with PBC to improve the dynamic response, reduce the chattering problem of traditional sliding mode control, and enhance the robustness of the system while maintaining passivity. In addition, the power references are modified to enable system to flexibly configure the control target depending on actual application requirements under nonideal grid. To further enhance the immunity, an ultralocal model predictive controller based on extended state observer disturbance estimation is designed for the outer loop. Finally, the simulation and experimental results verify the effectiveness of the proposed method.

As one of the most important performance indices of a current-source converter, dc-link current ripple is closely related to the modulation strategy. Excessive dc-link current ripple not only reduces the system efficiency but also increases the total harmonic distortion of grid current and leads to more electromagnetic interference. To get around this problem, optimizing the modulation strategy is more attractive compared with increasing the inductor or switching frequency. To this end, based on the detailed analysis of the mechanism to reduce the dc-link current ripple and the inherent deficiency of the current ripple continuous increase phenomenon between two adjacent sequences, in this article, a novel modulation strategy by employing an optimized switching sequence according to the modulation index is proposed. By applying the proposed modulation strategy, the current ripple is effectively reduced in the full range of the modulation index. Furthermore, the proposed scheme is easy to implement in practice without increasing the switching frequency or inductor. Finally, the selected experimental results confirm the validity of the theoretical analysis.