Table-Based Direct Power Control: A Critical Review for Microgrid Applications

Abstract

Direct power control (DPC) has increasingly gained attention in the last years as a robust and simple control scheme. Yet, the implications of some of the assumptions made by the original table-based DPC are not well explained in the literature. Here, a new formulation of DPC is presented, that allows to analyze the shortcomings of this kind of algorithms, mainly regarding the power limits in which table-based algorithms are valid. This is a key aspect for microgrid applications, as they require a wide range of possible active and reactive power setpoints in order to be able to control the system's voltage and frequency. A new table is then presented that allows to overcome those limitations. The proposed table is valid at any point of the inverter's power limits.Index Terms-Direct power control (DPC), power systems control, switching table, three-phase inverter.

A Review of Power Electronics Based Microgrids

“…Comparative analysis of VOC, VFOC, voltage-based DPC, as well as virtual flux-based DPC methods are provided in [51], [52]. In view of varying switching frequency problem in the DPC method, improved DPC alternatives with constant switching frequency have been developed [53], [54].…”

Investigation on Switching Patterns of Direct Power Control Strategies for Grid-Connected DC–AC Converters Based on Power Variation Rates

“…A few years later, a similar control strategy was presented in [8], which has a more significant impact in the academic community 0885-8993/$26.00 © 2011 IEEE and has become a benchmark to which various new DPC algorithms are compared. It was reported by [11], [12], and [14] that the original switching table for dc-ac converter's hysteresis LUT DPC implementation presented in [8] was confirmed to barely control the active and reactive powers in a smooth way, which as a result produced severe harmonic distortions in the three-phase currents. Several modified switching tables were reported to improve the performance of the hysteresis LUT DPC for grid-connected dc-ac converters [9]- [14].…”

“…It was reported by [11], [12], and [14] that the original switching table for dc-ac converter's hysteresis LUT DPC implementation presented in [8] was confirmed to barely control the active and reactive powers in a smooth way, which as a result produced severe harmonic distortions in the three-phase currents. Several modified switching tables were reported to improve the performance of the hysteresis LUT DPC for grid-connected dc-ac converters [9]- [14]. However, there still exist some drawbacks, including high sampling frequency, e.g., 50 kHz in [9], [10], and [14], and 40 kHz in [22], and obvious steady-state errors in the active power [11]- [13].…”

“…Several modified switching tables were reported to improve the performance of the hysteresis LUT DPC for grid-connected dc-ac converters [9]- [14]. However, there still exist some drawbacks, including high sampling frequency, e.g., 50 kHz in [9], [10], and [14], and 40 kHz in [22], and obvious steady-state errors in the active power [11]- [13]. However, there is no report in the literature on why these steady-state errors are generated and any effective solutions, which is one of main contributions of this paper.…”

An Inductance Voltage Vector Control Strategy and Stability Study Based on Proportional Resonant Regulators under the Stationary αβ Frame for PWM Converters

“…Meanwhile, this voltage oriented control divides alternating current into two parts, active and reactive segments, and then controls them separately with linear PI regulators, which achieves a good dynamic response by the inner current control loop with accurate decoupling calculations and proportional-integral regulating [9]. Some alternative control algorithms have been proposed such as instance predictive control [10], direct power control (DPC) [11], [12], deadbeat control [13]- [15], etc. The main principle of the DPC method is to directly regulate the instantaneous power instead of using the inner current loop, which will produce serious power ripples and a variable switching frequency along with pre-defined on-off forms and hysteresis comparators.…”