This paper presents a current control scheme for a voltage-source converter connected to the grid through an LCL filter. The proposed current control is based on the linear quadratic (LQ) Gaussian (LQG) servo controller technique, which combines the LQ regulator and the Kalman filter (KF). The use of the KF instead of a Luenberger estimator improves the quality of the estimation of state variables in noisy environments, increasing the noise immunity of the control loop. This paper focuses on giving some criteria and practical hints to choose both the KF and LQ design parameters to achieve null steady-state tracking error, channel decoupling, and noise immunity. Furthermore, this paper analyzes the steady-state KF approximation that allows a significant decrement in the computational complexity of the algorithm at nearly no cost in accuracy. Simulation and experimental results prove the correct operation of the proposed LQG current control and the possible advantages of using KF to estimate the state vector.

New energy concepts such as distributed power generation systems (DPGSs) are changing the face of electric distribution and transmission. Power electronics researchers try to apply new electronic controller solutions with the capacity of implementing new and more complex control algorithms combined with internal high-speed communication interfaces. Thus, it is possible to monitor, store, and transfer a large number of internal variables that can be sent online to local or remote hosts in order to take new set points of different generation units. With this objective, this paper presents the design, implementation, and test of an industrial multiprocessor controller based on a floating-point digital signal processor (DSP) and a field-programmable gate array, which operate cooperatively. The communication architecture, which has been added to the proposed electronic solution, consists of a universal serial bus (USB), implemented with a minimum use of the DSP core, and a controller area network (CAN) bus that permits distributed control. Although the proposed system can be readily applied to any DPGS, in this paper, it is focused on a 150-kVA back-to-back three-level neutral-point-clamped voltage source converter for wind turbine applications.

As the number of wind power applications with power electronic interfaces in the grid increases, it is becoming unacceptable to disconnect the generating units every time disturbances occur, especially under voltage dips, as was a common practice in the past. Keeping the converter online during unbalanced voltage, and guaranteeing the actual standards of the converter connected to the grid, is becoming a very critical issue. From these goals, the design of a robust back-to-back neutral point clamped (three levels) voltage source converter of 150 kVA is developed in this paper. The converter is divided into two main parts: the power electronic system and the control electronic system. Concerning the first part, on the one hand, the paper presents the designs of active and passive components as insulated gate bipolar transistor, free-wheeling diodes, clamping diodes, grid filter, DC-bus capacitors, etc.; and on the other hand, the converter requirements are analyzed to ride through real grid conditions, i.e., unbalanced voltage dips. Concerning the control electronic system, the chosen electronic structure and the task distribution between the two processors used are shown.

Predictive control is generating considerable interest when it comes to implementing current control strategies in power converters. Remarkable accuracy and fast dynamic response are its main characteristics. However, this technique is computationally demanding compared to classic control schemes. This is particularly true in multilevel converters, where several variables of the system such as currents, switching frequency and neutral-point voltage balancing, to name a few, are controlled simultaneously. An important issue is to reduce the delay between the variable sampling and the instant at which the switching state is applied to the converter. Although DSP-based implementations have been proven to be an effective solution, the parallel nature of predictive controllers better fits with the architecture of field-programmable gate array (FPGA) devices. This paper presents a new approach to the FPGA-based implementation of a predictive current controller for a multilevel converter. This approach also aims to reduce the average switching frequency and obtain neutral-point voltage balancing. The switching state is applied in the same sampling period in which the controlled variables are measured thereby enhancing the dynamic response of the system.