Abstract
The smart transformer has been widely applied for the integration of renewables and loads. For the smart transformer application, the voltage control of low-voltage inverter is important for feeding the load. In this paper, a multi-objective optimization control design approach which comprehensively considers all aspects of indexes, such as linear quadratic (LQ) index, H∞ norm, and closed-loop poles placement, is proposed based on the linear matrix inequality (LMI) solution. The proposed approach is able to alleviate the weight of the designer from the tedious design process of the multiple resonant controllers and the selection of the weighting matrix for the LQ control. Besides that, some excellent performances such as fast recovering time, low total harmonic distortion (THD) and high robustness are achieved by the proposed approach. The THD are 0.5% and 1.7% for linear and non-linear loads, respectively. The voltage drop for linear load step is reduced to 10 V. The proposed approach is applied to a 5 kVA three-phase inverter to yield an optimal control law. Results from the simulation and experiment presented herein will illustrate and validate the proposed approach.
Highlights
The smart transformers (STs) have good application prospects in smart grids and microgrids for the integration of renewables and different AC and direct current (DC) loads [1,2]
On the other hand, where the additional state is avoided, the load current feedforward control is used to reduce the steady error in [35]. It is virtually a full state feedback control, which is designed by the linear quadratic regulator (LQR) method under the rotating reference frame (RRF)
This paper tries to achieve two fundamental purposes: (1) to supply a convenient, systematic and effective design approach for the multiple resonant controllers, and (2) to liberate the designer from the subjective and time-consuming selection of the high-dimension weighting matrix Q for the linear quadratic regulation (LQR). Based on these two objectives, this paper converts minimizing of the LQ index into an linear matrix inequality (LMI) feasible problem whereby relying on the LMI optimization solver searches out the optimal weight matrix with the additional restraints of H∞ norm and regional poles placement
Summary
The smart transformers (STs) have good application prospects in smart grids and microgrids for the integration of renewables and different AC and DC loads [1,2]. On the other hand, where the additional state is avoided, the load current feedforward control is used to reduce the steady error in [35] It is virtually a full state feedback control, which is designed by the linear quadratic regulator (LQR) method under the rotating reference frame (RRF). This paper tries to achieve two fundamental purposes: (1) to supply a convenient, systematic and effective design approach for the multiple resonant controllers, and (2) to liberate the designer from the subjective and time-consuming selection of the high-dimension weighting matrix Q for the LQR Based on these two objectives, this paper converts minimizing of the LQ index into an LMI feasible problem whereby relying on the LMI optimization solver searches out the optimal weight matrix with the additional restraints of H∞ norm and regional poles placement. The outstanding performance of the proposed approach is verified by simulation and experiment
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