SAM
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The DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material.Tue, 11 Aug 2020 18:37:49 GMT2020-08-11T18:37:49ZDirect AC Voltage Control for Grid-Forming Inverters
http://hdl.handle.net/10985/17961
Direct AC Voltage Control for Grid-Forming Inverters
QORAI, Taoufik; LI, Chuanyue; OUE, Ko; GRUSON, François; COLAS, Frédéric; GUILLAUD, Xavier
Grid-forming inverters usually use inner cascaded controllers to regulate output AC voltage and converter output current. However, at the power transmission system level where the power inverter bandwidth is limited, i.e., low switching frequency, it is difcult to tune controller parameters to achieve the desired performances because of control loop interactions. In this paper, a direct AC voltage control-based state-feedback control is applied. Its control gains are tuned using a linear quadratic regulator. In addition, a sensitivity analysis is proposed to choose the right cost factors that allow the system to achieve the imposed specifcations. Conventionally, a system based on direct AC voltage control has no restriction on the inverter current. Hence, in this paper, a threshold virtual impedance has been added to the state-feedback control in order to protect the inverter against overcurrent. The robustness of the proposed control is assessed for diferent short-circuit ratios using smallsignal stability analysis. Then, it is checked in diferent grid topologies using time domain simulations. An experimental test bench is developed in order to validate the proposed control.
Tue, 01 Jan 2019 00:00:00 GMThttp://hdl.handle.net/10985/179612019-01-01T00:00:00ZQORAI, TaoufikLI, ChuanyueOUE, KoGRUSON, FrançoisCOLAS, FrédéricGUILLAUD, XavierGrid-forming inverters usually use inner cascaded controllers to regulate output AC voltage and converter output current. However, at the power transmission system level where the power inverter bandwidth is limited, i.e., low switching frequency, it is difcult to tune controller parameters to achieve the desired performances because of control loop interactions. In this paper, a direct AC voltage control-based state-feedback control is applied. Its control gains are tuned using a linear quadratic regulator. In addition, a sensitivity analysis is proposed to choose the right cost factors that allow the system to achieve the imposed specifcations. Conventionally, a system based on direct AC voltage control has no restriction on the inverter current. Hence, in this paper, a threshold virtual impedance has been added to the state-feedback control in order to protect the inverter against overcurrent. The robustness of the proposed control is assessed for diferent short-circuit ratios using smallsignal stability analysis. Then, it is checked in diferent grid topologies using time domain simulations. An experimental test bench is developed in order to validate the proposed control.Coupling Influence on the dq Impedance Stability Analysis for the Three-Phase Grid-Connected Inverter
http://hdl.handle.net/10985/17101
Coupling Influence on the dq Impedance Stability Analysis for the Three-Phase Grid-Connected Inverter
LI, Chuanyue; QORIA, Taoufik; COLAS, Frédéric; JUN, Liang; WENLONG, Ming; GRUSON, François; GUILLAUD, X.
The dq impedance stability analysis for a grid-connected current-control inverter is based on the impedance ratio matrix. However, the coupled matrix brings difficulties in deriving its eigenvalues for the analysis based on the general Nyquist criterion. If the couplings are ignored for simplification, unacceptable errors will be present in the analysis. In this paper, the influence of the couplings on the dq impedance stability analysis is studied. To take the couplings into account simply, the determinant-based impedance stability analysis is used. The mechanism between the determinant of the impedance-ratio matrix and the inverter stability is unveiled. Compared to the eigenvalues-based analysis, only one determinant rather than two eigenvalue s-function is required for the stability analysis. One Nyquist plot or pole map can be applied to the determinant to check the right-half-plane poles. The accuracy of the determinant-based stability analysis is also checked by comparing with the state-space stability analysis method. For the stability analysis, the coupling influence on the current control, the phase-locked loop, and the grid impedance are studied. The errors can be 10% in the stability analysis if the couplings are ignored.
Tue, 01 Jan 2019 00:00:00 GMThttp://hdl.handle.net/10985/171012019-01-01T00:00:00ZLI, ChuanyueQORIA, TaoufikCOLAS, FrédéricJUN, LiangWENLONG, MingGRUSON, FrançoisGUILLAUD, X.The dq impedance stability analysis for a grid-connected current-control inverter is based on the impedance ratio matrix. However, the coupled matrix brings difficulties in deriving its eigenvalues for the analysis based on the general Nyquist criterion. If the couplings are ignored for simplification, unacceptable errors will be present in the analysis. In this paper, the influence of the couplings on the dq impedance stability analysis is studied. To take the couplings into account simply, the determinant-based impedance stability analysis is used. The mechanism between the determinant of the impedance-ratio matrix and the inverter stability is unveiled. Compared to the eigenvalues-based analysis, only one determinant rather than two eigenvalue s-function is required for the stability analysis. One Nyquist plot or pole map can be applied to the determinant to check the right-half-plane poles. The accuracy of the determinant-based stability analysis is also checked by comparing with the state-space stability analysis method. For the stability analysis, the coupling influence on the current control, the phase-locked loop, and the grid impedance are studied. The errors can be 10% in the stability analysis if the couplings are ignored.Tuning of AC voltage-controlled VSC based Linear Quadratic Regulation
http://hdl.handle.net/10985/15936
Tuning of AC voltage-controlled VSC based Linear Quadratic Regulation
QORIA, Taoufik; LI, Chuanyue; OUE, Ko; GRUSON, François; COLAS, Frédéric; GUILLAUD, Xavier; PREVOST, Thibault
In the near future, power converters will be massively introduced in transmission grids due to renewable energy sources and high voltage direct current (HVDC) increase. Voltage Source Converter (VSC) control laws assume that Synchronous Generators (SGs) build a stiff AC voltage which allows the synchronization of converters. This is one of the major reasons that limit the high integration of currentsource converters in transmission grid. This constraint is no longer relevant when power converters operate as a voltage source based on the grid-forming concept. This concept uses an inner cascaded PI controllers in order to regulate the output AC voltage. However, it is difficult to tune its controller parameters for stable operation in grid-connected mode. This paper proposes an alternative state-feedback control with integral compensator based linear quadratic regulation (LQR) in order to ensure a stable operation and to get a better AC voltage transient and good decoupling between reactive and active power. The proposed control will be fully analyzed and compared to conventional methods.
Tue, 01 Jan 2019 00:00:00 GMThttp://hdl.handle.net/10985/159362019-01-01T00:00:00ZQORIA, TaoufikLI, ChuanyueOUE, KoGRUSON, FrançoisCOLAS, FrédéricGUILLAUD, XavierPREVOST, ThibaultIn the near future, power converters will be massively introduced in transmission grids due to renewable energy sources and high voltage direct current (HVDC) increase. Voltage Source Converter (VSC) control laws assume that Synchronous Generators (SGs) build a stiff AC voltage which allows the synchronization of converters. This is one of the major reasons that limit the high integration of currentsource converters in transmission grid. This constraint is no longer relevant when power converters operate as a voltage source based on the grid-forming concept. This concept uses an inner cascaded PI controllers in order to regulate the output AC voltage. However, it is difficult to tune its controller parameters for stable operation in grid-connected mode. This paper proposes an alternative state-feedback control with integral compensator based linear quadratic regulation (LQR) in order to ensure a stable operation and to get a better AC voltage transient and good decoupling between reactive and active power. The proposed control will be fully analyzed and compared to conventional methods.