Documentation Help Center. Implement phasor model of variable speed doubly-fed induction generator driven by wind turbine. Power flow, as illustrated in the figure, describes the operating principle of the Wind Turbine Doubly-Fed Induction Generator. The Power Flow. Rotational speed of the magnetic flux in the air-gap of the generator, this speed is named synchronous speed. It is proportional to the frequency of the grid voltage and to the number of generator poles.
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Documentation Help Center. Implement phasor model of variable speed doubly-fed induction generator driven by wind turbine. Power flow, as illustrated in the figure, describes the operating principle of the Wind Turbine Doubly-Fed Induction Generator. The Power Flow.
Rotational speed of the magnetic flux in the air-gap of the generator, this speed is named synchronous speed. It is proportional to the frequency of the grid voltage and to the number of generator poles. Generally the absolute value of slip is much lower than 1 and, consequently, P r is only a fraction of P s.
P r is positive for negative slip speed greater than synchronous speed and it is negative for positive slip speed lower than synchronous speed. For super-synchronous speed operation, P r is transmitted to DC bus capacitor and tends to rise the DC voltage. For subsynchronous speed operation, P r is taken out of DC bus capacitor and tends to decrease the DC voltage. C grid is used to generate or absorb the power P gc in order to keep the DC voltage constant.
The power control is explained below. The phase-sequence of the AC voltage generated by C rotor is positive for subsynchronous speed and negative for super-synchronous speed. The frequency of this voltage is equal to the product of the grid frequency and the absolute value of the slip. C rotor and C grid have the capability of generating or absorbing reactive power and could be used to control the reactive power or the voltage at the grid terminals. The rotor-side converter is used to control the wind turbine output power and the voltage or reactive power measured at the grid terminals.
The power is controlled in order to follow a pre-defined power-speed characteristic, named tracking characteristic. An example of such a characteristic is illustrated by the ABCD curve superimposed to the mechanical power characteristics of the turbine obtained at different wind speeds.
Turbine Characteristics and Tracking Characteristic. The tracking characteristic is defined by four points: A, B, C, and D. From zero speed to speed of point A, the reference power is zero.
Between point A and point B the tracking characteristic is a straight line, the speed of point B must be greater than the speed of point A. Between point B and point C the tracking characteristic is the locus of the maximum power of the turbine maxima of the turbine power versus turbine speed curves. The tracking characteristic is a straight line from point C and point D. The power at point D is one per unit 1 pu and the speed of the point D must be greater than the speed of point C.
Beyond point D the reference power is a constant equal to one per unit 1 pu. The generic power control loop is illustrated in the figure. Rotor-Side Converter Control System. The actual electrical output power, measured at the grid terminals of the wind turbine, is added to the total power losses mechanical and electrical and is compared with the reference power obtained from the tracking characteristic. A Proportional-Integral PI regulator is used to reduce the power error to zero.
This is the current component that produces the electromagnetic torque T em. The output of this current controller is the voltage Vqr generated by C rotor. The current regulator is assisted by feed forward terms which predict Vqr. The voltage or the reactive power at grid terminals is controlled by the reactive current flowing in the converter C rotor. The generic control loop is illustrated in the figure.
Wind Turbine V-I Characteristic. When the wind turbine is operated in voltage regulation mode, it implements the following V-I characteristic. As long as the reactive current stays within the maximum current values -Imax, Imax imposed by the converter rating, the voltage is regulated at the reference voltage Vref. In the voltage regulation mode, the V-I characteristic is described by the following equation:.
When the wind turbine is operated in var regulation mode, the reactive power at grid terminals is kept constant by a var regulator. The same current regulator as for the power control is used to regulate the actual Idr component of positive-sequence current to its reference value. The output of this regulator is the d-axis voltage Vdr generated by C rotor. The current regulator is assisted by feed forward terms which predict Vdr.
The maximum value of this current is limited to 1 pu. The converter C grid is used to regulate the voltage of the DC bus capacitor. In addition, this model allows using C grid converter to generate or absorb reactive power. The control system is illustrated in the figure.
Grid-Side Converter Control System. Measurement systems measuring the d and q components of AC positive-sequence currents to be controlled as well as the DC voltage Vdc. An outer regulation loop consisting of a DC voltage regulator. An inner current regulation loop consisting of a current regulator.
The current regulator is assisted by feed forward terms which predict the C grid output voltage. The maximum value of this current is limited to a value defined by the converter maximum power at nominal voltage. The pitch angle is kept constant at zero degrees until the speed reaches point D speed of the tracking characteristic. Beyond point D the pitch angle is proportional to the speed deviation from point D speed.
The control system is illustrated in the following figure. Pitch Control System. See documentation of this model for more details.
The doubly-fed induction generator phasor model is the same as the wound rotor asynchronous machine see the Machines library with the following two points of difference:. Only the positive-sequence is taken into account, the negative-sequence has been eliminated. A trip input has been added. When this input is high, the induction generator is disconnected from the grid and from C rotor.
Use the Display listbox to select which group of parameters you want to visualize. This external torque must be in pu based on the nominal electric power and synchronous speed. For example, the external torque may come from a user defined turbine model. Following the convention used in the induction machine, the torque must be negative for power generation. Default is cleared. The nominal power in VA, the nominal line-to-line voltage in Vrms and the nominal system frequency in hertz.
Default is [1. The stator resistance Rs and leakage inductance Lls in pu based on the generator rating. Default is [ 0. The rotor resistance Rr' and leakage inductance Llr', both referred to the stator, in pu based on the generator rating. The magnetizing inductance Lm in pu based on the generator rating.
Default is 2. Combined generator and turbine inertia constant H in seconds, combined viscous friction factor F in pu based on the generator rating and number of pole pairs p. Default is [5. You may need to use your own turbine model, in order for example, to implement different power characteristics or to implement the shaft stiffness.
Your model must then output the mechanical torque applied to the generator shaft. If the inertia and the friction factor of the turbine are implemented inside the turbine model you specify only the generator inertia constant H and the generator friction factor F. Default is [0.
This parameter is not visible when the External turbine Tm mechanical torque input parameter is selected. The nominal turbine mechanical output power in watts. Default is 1. Specify the speeds of point A to point D of the tracking characteristic in pu of the synchronous speed. Specify the power of point C of the tracking characteristic in pu of the Nominal wind turbine mechanical output power.
Default is 0. The power at point C is the maximum turbine output power for the specified wind speed. Default is Proportional gain Kp of the pitch controller.
The speed deviation is the difference between actual speed and speed of point D in pu of synchronous speed.
Click to plot the turbine power characteristics at zero degree of pitch angle for different wind speeds. The tracking characteristic is also displayed on the same figure. The maximum power of both C grid and C rotor in pu of the nominal power. This parameter is used to compute the maximum current at 1 pu of voltage for C grid.
The maximum current for C rotor is 1 pu. The coupling inductance L and its resistance R in pu based on the generator rating. The coupling inductor initial phasor current in positive-sequence. If you know the initial value of the current corresponding to the WTDFIG operating point you may specify it in order to start simulation in steady state. If you don't know this value, you can leave [0 90].
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