are the inductor resistance and inductance, are the idcg, idcr (3) By using the abc-to-dq transformation matrix, the following equation can be given: (4) Where are the grid voltages in d- and q-axis, are the grid-side converter voltages in d- and ugd, ugq ugcd, ugcq q-axis, are the grid-side converter currents in d- and q-axis, is the electrical angular velocity of the igd, igq ωe grid voltage Neglecting harmonics due to the switching and the losses in the resistance and converter, the following equations can be obtained. (5) Where is the PWM modulation depth of the grid-side converter. m By using the control strategy described, it can be seen that the DC-link voltage can be controlled via The igd. currents and can be regulated by using and respectively. The control scheme thus utilizes igd igq ugcd ugcq current control loops for and with the demand being derived from the DC-link voltage error. The igd igq, igd igq demand determines the reactive power flow between the grid and the grid-side converter. Normally the igq reference value may be set to zero, which ensures zero reactive power exchange between the grid and the side converter. The vector-control scheme for grid-side PWM voltage source converter is shown in Fig.4, where are the reference values of the three phase grid-side converter voltages, u*gcabc u*gcd ,u*gcq are the reference values of the grid-side converter voltages in d- and q-axis, , are the reference ig*d ig*q values of the grid-side converter currents in d- and q-axis. Rotor-side Converter Control Strategy A detailed model of DFIG which includes electro- magnetic transients both in the stator and the rotor circuits is used when performing the transient stability studies. According to a standard per-unit notation, in a reference frame rotating at synchronous speed and taking the motor convention, the transient models of grid-connected DFIG can be represented by the detailed differential equations of the flux linkages:
are the inductor resistance and inductance, idcg, idcr are the (3) By using the abc-to-dq transformation matrix, the following equation can be given: (4) Where ugd, ugq are the grid voltages in d- and q-axis, ugcd, ugcq are the grid-side converter voltages in d- and q-axis, igd, igq are the grid-side converter currents in d- and q-axis, ωe is the electrical angular velocity of the grid voltage Neglecting harmonics due to the switching and the losses in the resistance and converter, the following equations can be obtained. (5) Where m is the PWM modulation depth of the grid-side converter. By using the control strategy described, it can be seen that the DC-link voltage can be controlled via igd. The currents igd and igq can be regulated by using ugcd and ugcq respectively. The control scheme thus utilizes current control loops for igd and igq, with the igd demand being derived from the DC-link voltage error. The igq demand determines the reactive power flow between the grid and the grid-side converter. Normally the igq reference value may be set to zero, which ensures zero reactive power exchange between the grid and the converter. The vector-control scheme for grid-side PWM voltage source converter is shown in Fig.4, where u*gcabc are the reference values of the three phase grid-side converter voltages, u*gcd ,u*gcq are the reference values of the grid-side converter voltages in d- and q-axis, ig*d , ig*q are the reference values of the grid-side converter currents in d- and q-axis. Rotor-side Converter Control Strategy A detailed model of DFIG which includes electro- magnetic transients both in the stator and the rotor circuits is used when performing the transient stability studies. According to a standard per-unit notation, in a reference frame rotating at synchronous speed and taking the motor convention, the transient models of grid-connected DFIG can be represented by the detailed differential equations of the flux linkages: side
EEE6%2004042534.docx