Title: | LCL-suodattimella varustetun verkkosuuntaajan virtasäätö tilasäädintä ja –havaitsijaa käyttäen Current control of a grid converter equipped with an LCL filter using state-space controller and observer |
Author(s): | Haanpää, Kimmo |
Date: | 2016-04-04 |
Language: | fi |
Pages: | 80+13 |
Major/Subject: | Sähkökäytöt |
Degree programme: | EST - Elektroniikka ja sähkötekniikka (TS2005) |
Supervising professor(s): | Hinkkanen, Marko |
Thesis advisor(s): | Kukkola, Jarno |
Keywords: | LCL-suodatin, tilahavaitsija, tilasäädin, verkkosuuntaaja, verkkovirta, virtasäätö |
Location: | P1 | Archive |
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Abstract:In this thesis, the control of a three-phase, voltage source converter, equipped with an LCL filter, is implemented using a state-space controller and observer. The grid currents are measured for the state-space controller. Capacitator voltages and converter currents are estimated using a state observer. A continuous-time switching-cycle-averaged model is presented for the converter. A continuous-time model is created. The controller is analyzed in stiff and weak grids. State space representations are created for the LCL filter and current controller. Equations are derived for tuning the controller. The controller is compared to a reference controller, that uses the same state-space controller and measures converter currents. The controller is tuned using the tuning parameters of the reference controller. The current controller and the reference controller sensitivity to parameter errors is analyzed using the root locus. The controller dynamics are compared to each other by simulating the reference step response and grid voltage sag using the correct parameter values. A stability margin of 0,7. . . 1,3 times the nominal value of the given parameters is chosen. The root loci indicate that with the feedback of the grid current, the current controller is more sensitive to parameter errors compared to the reference controller. The root loci also show that the system is unstable, when the parameters of the LCL filter are 1,2 times higher than the nominal values. The controller presented in this thesis is unable to fulfill the required robustness using the reference controller tuning parameters. This thesis proposes a higher value for the damping ratio of the resonating poles. The proposed damping ratio is used to stabilize the controller within the required stability area. Simulations show the proposed controller dynamics and the reference controller to be identical when using the reference controller tuning parameters. The proposed damping ratio was found not to significantly increase the need for control effort. |
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