Abstract
Acting as an interface between the grid and many energy systems, the active front-end (AFE) has been widely used in a large variety of industrial applications. In this paper, in order to ensure the fast dynamic performance and good disturbance rejection ability of the AFE, a high-gain observer (HGO) plus adaptive super-twisting algorithm (STA) for the three-level neutral-point-clamped (NPC) converter is proposed. Comparing with the conventional PI control strategy, the proposed controller implements the adaptive STA in the voltage regulator to provide a faster transient response. The gains of the adaptive STA keep varying according to the rules being reduced in steady state but increasing in transient conditions. Therefore, the chattering phenomenon is mitigated and the dynamic response is guaranteed. Additionally, to undermine the impact of external disturbances on the dc-link voltage, a high-efficiency HGO is designed in the voltage regulation loop to reject it. Experimental results based on a three-level NPC prototype are given and compared with the conventional PI method to validate the fast dynamic performance and high disturbance rejection ability of the proposed approach.
Highlights
Active front-end (AFE) plays an important role in several industrial applications presenting advantages such as bi-directional power, reliable dc-link voltage regulation, unity power factor, and sinusoidal line currents [1,2]
To enhance the performance of the voltage regulator, a adaptive super-twisting algorithm (STA) control scheme plus high-gain observer (HGO) is proposed for the three-level NPC converter
A HGO-based adaptive STA control strategy is proposed for the dc-link voltage control of NPC converters
Summary
Active front-end (AFE) plays an important role in several industrial applications presenting advantages such as bi-directional power, reliable dc-link voltage regulation, unity power factor, and sinusoidal line currents [1,2]. With the ever-increasing quantity of three-level NPC converters applied in AFE, several concerns of the existing AFE systems are exposed, such as slow dynamical response and sensitivity to external disturbances To mitigate these issues, numerous seminal solutions have been proposed in various literature. Levant proposed the second-order sliding mode theory, including twisting algorithm, super-twisting algorithm (STA), ect [19] The essential of this contribution lies in applying the controller to the derivative of the sliding mode variable, which mitigates the chattering phenomenon and retains the advantages of the conventional SMC [20]. It is highlighted that the gains of the adopted adaptive STA approach are changed in real-time following the designed adaptive law, that is, decreasing in steady state while increasing during the transient Such a feature brings several significant advantages to the controller, including the limited chattering phenomenon and fast response.
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