A Predictive Control Scheme for a Single-Phase Grid-Supporting Quasi-Z-Source Inverter and Its Integration With a Frequency Support Strategy

Abstract

Small grid-connected inverters are not friendly to the electrical grid, in the sense they do not take any action to support the grid when contingency events occur. For example, because of their relatively low power capacity, small grid-connected inverters are not designed to provide dynamic frequency support to the grid. On the other hand, it is well known that microgrids and weak grids including distributed generation would benefit significantly if all of the grid-connected converters could support and help against grid frequency disturbances. Within the family of small grid-connected converters, single-phase quasi-Z-source inverters (QZSI) have become an attractive topology, because they represent a reliable and economical alternative, and can be very efficient in applications that demand small or medium powers. However, a major disadvantage is that the control strategy must manage both direct current and alternating current variables through the same group of switches. The latter is a challenging task when implementing predictive control schemes. This paper proposes a finite control set model predictive control (FCS-MPC) strategy for a single-phase grid-supporting QZSI. The proposed predictive scheme can be easily integrated with a complementary control block to provide grid frequency support. Experimental results show evidence of the inverter operating under the proposed control strategy and providing grid frequency support, which demonstrates the feasibility of the proposal.

Variable weight coefficient MPC control strategy for qZSI‐VSG wind power grid‐connected system

“…Due to the difference in voltage amplitude and phase at the time of gridconnected, the voltage at the point of common coupling will be pushed to become consistent and distorted with significant c in Figure 11. Figures 12,13 demonstrate the three-phase current harmonics for different control strategies. It can be seen that using the V-MPC strategy proposed in this article can reduce the disruption of grid current produced by an unbalanced power grid voltage.…”

“…When an ES system is introduced to a qZSI circuit, the complexity of system operation and analysis increases [11,12]. In [13], a control scheme that combines a PWM linear control strategy and a strategy based on FCS-MPC is proposed, increase the complexity of the controller design, requiring PWM generators inevitably. The above mentioned two drawbacks of the FCS-MPC algorithm for qZSI affect the performance of the overall control system strongly.…”

“…FIGURE13 Current waveforms and THD of the VSG side when island to grid with V-MPC (a)Current waveform, (b) Total harmonic distortion.…”

Comparison of FCS-MPC Strategies in a Grid-Connected Single-Phase Quasi-Z Source Inverter

“…Implementing a traditional linear control strategy in a quasi-Z source inverter (qZSI) can be challenging and may not yield the desired results [8,[11][12][13]. To address these challenges, various nonlinear control techniques have been proposed, including fuzzy control [14][15][16], sliding-mode control [17,18], neural networks control [19,20], and finitecontrol-set model predictive control (FCS-MPC) [21][22][23][24][25]. FCS-MPC, also known as direct model predictive control, has gained significant interest in the past 20 years due to its ability to provide fast dynamic responses, handle multiple objectives, and leverage the available computational power.…”

Implementation of New Optimal Control Methodology of Quazi Z-Source Inverter Based on MPC

“…For more information, see https://creativecommons.org/licenses/by-nc-nd/4.0/ operation is based on introducing the nine-state, to be added to the eight cases that existed before by making two switches turn on at the same moment for one leg [11], [12]. ZSI has some advantages, but it also has some problems.…”