| Due to the power fluctuation exist in the front stage AC-DC converter of the single phase AC-DC-DC converter,result in the voltage fluctuating with two times grid frequency of the middle DC-link.Generally,in order to filter out the ripple voltage,the rectifier's output parallel with a LC filter circuit with two times grid frequency.However,the use of the low frequency filter making the volume and weight of the AC-DC-DC converter difficult to be further reduced,together with the cost,herefore,the systerm's application is limited.In this paper,the control strategy of suppressing the affect of the second-order ripple voltage issuing from AC-DC-DC converter without LC filter circuit was studied.Firstly,analyses the suppression research status of second-order ripple voltage exist in dc voltage in the domestic and abroad.Then,discusses the generation mechanism of second-order ripple voltage.Analyze the influence path of second-order ripple voltage in the front stage AC-DC converter and the back stage DC-DC converter respectively,finding that the second-order ripple voltage can affect the converter's output through the control loop and the forward loop in the hardware which will flow into the hardware terminal ports.The emulation in the Matlab verify the correctness of the analysis.Secondly,the controller that suppress the effect of the second-order ripple voltage is designed for the front-end single-phase rectifier and backward stage DC-DC converter respectively.On the basis of the original instantaneous current control in the AC-DC converter,add a notch filter in the control loop to stop the second-order ripple voltage from entering the controller;in the meantime,add an output current disturbance feedforward path to suppress the left harmonic perturbation.For the backward stage DC-DC converter,Design a feedback linearization controller according to the large signal model,making the original multivariable strong coupling nonlinear DC-DC converter to be linearized system and the input decouple from the output.In order to further suppress the DC-DC converter's output voltage ripple,add another output disturbance voltage feed-forward path.Meanwhile,the input voltage feed-forward method is designed for the DC-DC converter.Compared with the traditional proportional integral and input voltage feed-forward method,verify the proposed control is feasibility and effectiveness in the suppression of the second-order ripple voltage.In order to compare the effect,Finally,the program design of the algorithm is performed and a laboratory prototype of single-phase three-level diode-clamped bidirectional isolation AC-DC-DC converter in 220W is built,the steady state and transient experiments is tested.The experiment comparing result among the proposed control,the traditional proportional integral and input voltage feed-forward method,verify the better suppression effectiveness of AC input current and DC output voltage of the system that influenced by the second-order ripple voltage under the proposed control strategy. |
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