Browsing by Author "Rahman, F M Mahafugur"
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- Equivalence of the integrator-based and disturbance-observer-based state-space current controllers for grid converters
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2021-06) Rahman, F M Mahafugur; Pirsto, Ville; Kukkola, Jarno; Hinkkanen, Marko; Pérez-Estévez, Diego; Doval-Gandoy, JesúsThis article deals with discrete-time state-space current controllers for three-phase grid converters equipped with an LCL filter. The integral action in the controller can be implemented either using an integrator or a disturbance observer. The results show that the disturbance-observer-based and integrator-based controllers become mathematically equal if the feedforward gains are selected to be equal, the feedforward zero is placed to cancel the pole originating from the integral action, and the closed-loop poles are placed identically. The equivalent performance in both designs is verified by means of analyses and experiments. The equivalence is also shown for double-frequency current controllers. - Observers for discrete-time current control of converters equipped with an LCL filter
A4 Artikkeli konferenssijulkaisussa(2020-10-11) Rahman, F M Mahafugur; Kukkola, Jarno; Pirsto, Ville; Routimo, Mikko; Hinkkanen, MarkoThis paper studies the current-type observer, the prediction-type observer, and the reduced-order observer for discrete-time state-space current control of grid converters with an LCL filter. The robustness against parameter errors and the dynamic performance obtained with these three observers are compared by means of analysis and experiments. A unified control algorithm framework is developed to compare the structures of these observers. It is found that the reduced-order observer is merely a special case of the current-type observer. With the presented design examples, where the resonant poles are damped by means of radial projection, the use of either the current-type or the reduced-order observer leads to better disturbance rejection against the grid-voltage dip and harmonics as compared to the prediction-type observer. All the observers provide equal reference-tracking performance under nominal conditions. For a large parameter error in the grid-side inductance, the prediction-type observer leads to unstable operation of converter. - Real-time identification method for LCL filters used with grid converters
A4 Artikkeli konferenssijulkaisussa(2019-09-29) Pirsto, Ville; Kukkola, Jarno; Rahman, F M Mahafugur; Hinkkanen, MarkoThis paper presents a real-time algorithm for identifying the inductance and capacitance values of LCL filters used with grid converters. As a side product, the grid inductance seen from the point of common coupling is also estimated. A wideband excitation signal is added to the converter voltage reference. During the excitation, the converter currents and the converter voltage reference are sampled. The samples are preprocessed in real time by removing DC biases and significant grid-frequency harmonics. Parameters of a discrete-time model are estimated at each sampling instant with a recursive estimation algorithm. The model parameter estimates are translated into inductance and capacitance values. The method can be embedded to a control system of PWM-based converters in a plug-in manner. Only the DC-link voltage and converter currents need to be measured. Simulation and experimental results are presented for a 12.5-kVA grid converter system to evaluate the proposed method. - Real-time identification of LCL filters employed with grid converters
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2020-09-01) Pirsto, Ville; Kukkola, Jarno; Rahman, F M Mahafugur; Hinkkanen, MarkoThis article presents a real-time identification method for LCL filters used with three-phase grid converters. The method can be applied to identify both the inductance and capacitance values of the filter and the series resistance seen by the converter. As a side-product, an estimate of the grid inductance seen from the point of connection is also obtained. A wideband excitation signal is added to the converter voltage reference. During the excitation, converter current and converter voltage reference samples are used for identification. The samples are preprocessed in real time by removing dc biases and significant grid-frequency harmonics. Parameters of two discrete-Time models are estimated at each sampling instant with a recursive estimation algorithm. Depending on the estimated model, the model parameter estimates are translated to either the resistance or the inductance and capacitance values of the system. The method can be embedded to a control system of pulsewidth-modulation-based converters in a plug-in manner. Only the dc-link voltage and converter currents need to be measured. Simulation and experimental results are presented for a 12.5-kVA grid converter system to evaluate the proposed method. - State-space control for LCL filters: Converter versus grid current measurement
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2020-11-01) Rahman, F M Mahafugur; Pirsto, Ville; Kukkola, Jarno; Routimo, Mikko; Hinkkanen, MarkoThis article deals with discrete-time state-space current control of three-phase converters equipped with an LCL filter. Either the converter or grid current is measured, and the unknown states are estimated using a reduced-order observer. The stability and dynamic performance of the control designs based on these two current measurement options are compared by means of analysis and experiments at different sampling frequencies and under varying grid conditions, ranging from strong to very weak. Equal reference-tracking performance under nominal conditions is used as a basis for comparison between these two options. If a strong grid is assumed in the control tuning, the controller based on the grid current measurement (GCM) is found to be more robust against varying grid conditions in a wide range of sampling frequencies than the controller based on the converter current measurement (CCM). The CCM leads to better dynamic performance as compared to the GCM if the resonance frequency of the system falls below the critical resonance frequency. - Weak-grid tolerant positive- and negative-sequence current control of voltage-source converters
A4 Artikkeli konferenssijulkaisussa(2021) Pirsto, Ville; Kukkola, Jarno; Rahman, F M Mahafugur; Hinkkanen, MarkoThis paper deals with positive- and negative-sequence current control of voltage-source converters. An enhanced weak-grid tolerant state-feedback controller design based on direct pole placement approach is proposed. The controller is synthesized from a body of literature on multi-frequency current control of grid converters. The resulting design yields consistent dynamic performance for varying grid strengths, and remains stable even under very weak grids. Due to the explicit parameterization of the pole locations, complex optimization methods often associated with robust control designs are avoided, which simplifies the controller design process.