Coordination and Optimization of Grid-Tied Power Converters

It is universally accepted that power systems around the world are experiencing a paradigm shift with the involvement of power electronics. In particular, renewable generation systems, battery energy storage systems, and electric vehicle chargers necessitate grid-tied power converters, which gradually become enabling devices in more-electronics power systems, to provide efficient and flexible bidirectional power regulation. This chapter briefly overviews the configurations of renewable generation systems, battery energy storage systems, and DC charging piles, which lay a solid foundation to further explore the coordination and optimization of grid-tied power converters from the perspective of pulse width modulation.

This chapter introduces the topologies, modulation schemes, ac filters and basic control scheme of grid-tied power converters so that the readers can know how grid-tied power converters work.

This chapter begins with the analysis of random phase shift angles of multiple PWM carriers and derives how the random phase shift angles affect the differential mode and common mode switching harmonics. Next, it is clearly pointed out that the coordination of PWM is effective in reducing switching harmonics. On top of that, the coordination principles are presented.

In this chapter, three kinds of PWM carrier synchronization techniques are presented, which can be classified as centralized mode, master-slave mode and distributed mode. For each mode, the details of commonly used methods are presented and analyzed. After the introduction of specific techniques, these modes are compared and summarized.

To set the optimized phase shift angles of multiple PWM carriers, many operating parameters should be taken into account. Some parameters, e.g. output filter parameters and rated switching frequency, seldom change during operation, while others, e.g. dc-link voltage, grid impedance, and output power, may change within the limited range. In addition, some parameters, e.g. the number of parallel-connected converters, change randomly. Therefore, building the optimization model according to the control objective and then solving the optimization model to obtain the proper phase shift angles of PWM carriers in the open-loop mode are important. This chapter begins with the basic principles of open-loop operation. Then, the optimization models for single-objective and multi-objectives are built. Finally, the methods for solving these models are presented following with the improved online fast calculation. The selected experimental results verified the performances of open-loop optimization schemes.

In order to further improve the adaptivity of PWM coordination, the closed-loop correction strategies are presented in this chapter. It begins with the basic concept and presents the closed-loop correction strategy for multi-input single-output (MISO) systems. Then, the “Min–Max” closed-loop correction strategy for multi-input multi-output (MIMO) systems is elaborated.

When using the PWM coordination, grid-tied power converters can be redesigned by considering multiple converters as one single system. This chapter will first analyze the principles of the optimized design method. Secondly, all operating considerations, including the specific GSPWM characteristics, are represented by the constructed general models. Thirdly, to easily evaluate the operational performance, the general models are simplified by analyzing the worst operating conditions so that the operating boundaries can be derived. Finally, taking the minimization of power losses as an exemplified objective, we demonstrate how the key parameters are selected.

After introducing the basic principles and details of PWM coordination and corresponding optimization methods from Chaps. 3 to 7, this chapter presents a practical demonstration of the proposed methodology in battery energy storage systems. The chapter reveals important implementation problems and relevant viable solutions, thereby laying the ground for better operations of multiple parallel-connected grid-tied power converters.