Voltage-Modulated Direct Power Control for a Weak Grid-Connected Voltage Source Inverters

Abstract

In this paper, we design a voltage modulated direct power control (VM-DPC) for a three-phase voltage source inverter (VSI) connected to a weak grid, where the PLL system may make the system unstable if the conventional vector current control (VCC) method is applied. Compared with the conventional VCC method, the main advantage of the proposed VM-DPC method is that the PLL system is eliminated. Moreover, in order to inject the rated real power to the weak grid, the VSI system should generate some certain amount of reactive power as well. An eigenvalues based analysis shows the system with the proposed method tracks its desired dynamics in the certain operating range. Both simulation and experimental results match the theoretical expectations closely. Index Terms-Voltage source inverter, voltage modulated direct power control (VM-DPC), vector current controller, weak grid, stable system.

Passivity-Based Analysis and Performance Enhancement of a Vector Controlled VSC Connected to a Weak AC Grid

“…and due to the squares involved, C * C ≥ 0. Following the expressions in (17) and the above conditions, it can be established that it is desired to have CC * ≈ 0. Any C * C 0 puts a higher minimum bound on AB; hence, this imposes difficulty on efforts to reduce the negativity or improve the positivity of the system.…”

“…Although this seems to provide relief under fairly low SCR, the active power capability is still limited. In a bid to eliminate the impacts of the PLL, the authors in [14]- [17] tackled the problem by eliminating the VCC and necessity for PLL. However, the PLL and inner current controller were suggested as backups.…”

Sliding Mode Control With Grid Voltage Modulated DPC for Voltage Source Inverters Under Distorted Grid Voltage

“…Substituting (2) and (7) into (5), the state-space models of the fundamental component of real and reactive powers are given as follows [48]:…”

“…In [48], the stability analysis for a weak grid-connected inverter was given. In this study, only a stiff grid is considered, i.e., the line impedance is zero, Consequently, the error dynamics could be obtained based on [48] as (18) where…”

Coordinated Derived Current Control of DFIG’s RSC and GSC Without PLL Under Unbalanced Grid Voltage Conditions

“…Direct power control (DPC) serves as a PLL-less method and has been widely studied. In [16], [17], a grid voltage modulated-DPC is proposed with the feed-forward and feedback controllers. In [18], a virtual phase angle is used for coordinate transformations in the place of the voltage phase angle from PLL and then based on this, an improved DPC is developed.…”