Model Predictive Current Control Of PWM Rectifier And The Research Of LCL Filter

An increasing attention has been paid on the three-phase rectifier with pulse width modulation (PWM) due to its well-known advantages of bidirectional power flow, low harmonic distortion of power source current, high power factor (near unity) and adjustable dc-bus voltage, etc. As a real green power converter, PWM rectifier has been widely used in active power filter (APF), unified power flow control (UPFC), superconducting magnetic energy storage (SMES), high-voltage direct current transmission (HVDC), electric drive and renewable energy generation like solar and wind, etc. In addition, it is also the main connection device of the smart grid technology, such as grid storage, flexible power transmission and transformation, renewable energy generation, controllable load and so on. Model predictive control (MPC) is a novel control strategy. The application study of MPC in PWM rectifier has made significant progress. In this paper, the thorough research has been made on model predictive current control (MPCC), and comparison study has made between MPCC and the traditional control method. In order to further improve the filtering performance of PWM rectifier, LCL filter technology and its control strategy was analyzed in this paper, and the correctness of the theory is verified by simulation and experimental research.This paper introduces the traditional current control method (grid voltage oriented control, VOC), and model predicted current control is another current control method, also called as single vector MPCC. Their theoretical background is described, and the advantages and disadvantages of each scheme are studied through analysis and a series of experiments. A comprehensive comparison and evaluation are implemented for VOC and MPCC from several aspects such as algorithm complexity, steady state and dynamic performances, current THD. Compared to the conventional control strategy VOC, MPCC is intuitive in principle and easy to understand. Furthermore, it does not require any regulators such as PI in VOCIn order to further simplify the single vector MPCC (also named FCSMPCC), two kinds of quick voltage vector selection methods are introduced in the paper, which is DCC and simplified FCSMPCC. The reason of quick voltage vector selection is explained in detail using strict mathematical proof. The relationship between these methods are analyzed in theory and confirmed by both simulation and experimental results. DCC and S-FCSMPCC are more efficient in voltage vector selection as only one prediction is required, and DCC and S-FCSMPCC can be considered as a special case of FCSMPCC. Based on the steady-state performance study of MPCC. this paper proposes a double vector model predictive current control (DV-MPCC). so as to effectively improve the steady-state performance of the system, significantly reduce the current ripple and current total harmonic distortion (THD). The so-called double vector means that two voltage vectors, a non-zero voltage vector and a zero voltage vector, are applied during one control cycle. In the paper, three kinds of vector duration calculation methods (FCSMPCC, DCC and S-FCSMPCC) are introduced. Compared with FCSMPCC, the vector duration calculation methods of DCC and S-FCSMPCC are simpler. Based on the DV-MPCC, a more powerful double vector MPCC is proposed to further improve the steady-state performance. Its name is generalized double vector MPCC (GV-MPCC). In GV-MPCC, there are also two voltage vector selected. However, it is more precise in the vector selection for GV-MPCC. So the GV-MPCC could achieve the best control performance during single vector MPCC and DV-MPCC.In this paper, the mathematical model of LCL filter under different coordinate is established and the LCL parameters design method is proposed. Active damping simulation research, based on capacitive current and grid current feedback, has been made. The effectiveness of LCL filter is verified by simulation.By using the fast algorithm implementation method based on the Matlab model, the code generation of various methods is obtained very quickly. The effectiveness of the proposed MPCC and the fast algorithm implementation method are verified by experiment. The upper machine based on keys and digital tube is developed. So, the PWM rectifier could be controlled without emulator. The upper machine contains the main control performance, such as parameters given, stop control system operation and the system status display. Finally, over-current protection is realized by using CPLD.