Abstract
Inductive-capacitive-inductive (LCL)-type filters are currently preferred as a replacement for L-type filters in distributed generation (DG) power systems, due to their superior harmonic attenuation capability. However, the third-order dynamics introduced by LCL filters pose a challenge to design a satisfactory controller for such a system. Conventionally, an LCL-filtered grid-connected inverter can be effectively controlled by using a full-state feedback control. However, this control approach requires the measurement of all system state variables, which brings about more complexity for the inverter system. To address this issue, this paper presents a systematic procedure to design an observer-based integral state feedback control for a LCL-filtered grid-connected inverter in the discrete-time domain. The proposed control scheme consists of an integral state feedback controller and a full-state observer which uses the control input, grid-side currents, and grid voltages to predict all the system state variables. Therefore, only the grid-side current sensors and grid voltage sensors are required to implement the proposed control scheme. Due to the discrete-time integrator incorporated in the state feedback controller, the proposed control scheme ensures both the reference tracking and disturbance rejection performance of the inverter system in a practical and simple way. As a result, superior control performance can be achieved by using the reduced number of sensors, which significantly reduces the cost and complexity of the LCL-filtered grid-connected inverter system in DG applications. To verify the practical usefulness of the proposed control scheme, a 2 kW three-phase prototype grid-connected inverter has been constructed, and the proposed control system has been implemented based on 32-bit floating-point digital signal processor (DSP) TMS320F28335. The effectiveness of the proposed scheme is demonstrated through the comprehensive simulation and experimental results.
Highlights
Renewable energy sources, such as wind and solar, are becoming reliable alternatives to fossil fuel.In order to integrate these renewable energies into the utility grid, distributed generation (DG) power systems have drawn much attention from academia, because of their effectiveness and reliability [1,2].Due to the strong requirement of the high energy efficiency and the flexibility to operate in both the grid-connected and island modes, power electronic converters are typically used in DG application systems
For the experimental validation of the proposed control scheme, the experimental setup has been constructed, which consists of a digital signal processor (DSP)-based controller, a three-phase inverter connected to the grid through an LCL filter, a magnetic contactor for grid connecting operation, and an AC power source to imitate three-phase grid voltages
The control algorithm is performed by a 32-bit floating-point DSP TMS320F28335 [23], to control a 2 kW laboratory prototype inverter
Summary
Renewable energy sources, such as wind and solar, are becoming reliable alternatives to fossil fuel. To implement the integral state feedback controller, the measurement of all system states should be required, which increases the cost and complexity of system, due to the necessity of additional sensors To overcome such a limitation, this paper presents a systematic design procedure for a LCL-filtered. The proposed control scheme ensures both the reference tracking and disturbance rejection performance of the inverter system by using only the measurement of the grid-side currents and grid voltages. This significantly reduces the cost and complexity of the LCL-filtered grid-connected inverter system in DG applications. In addition to providing a systematic design methodology, the proposed control scheme can be a very practical approach of designing a grid-connected inverter in DG applications by virtue of its simplicity and low cost
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