Grid connecting system of permanent magnet synchronous wind driven generator

[0024] Example

[0025] like figure 1 As shown, a permanent magnet synchronous wind turbine grid-connected system includes a wind turbine 1, a permanent magnet synchronous generator 2, a generator-side converter 3, a DC boost module 4, a grid-side converter 5, and a control module. 6 and energy storage module 7. Wind turbine 1, permanent magnet synchronous motor 2, generator-side converter 3, DC boost module 4 and grid-side converter 5 are connected in sequence and then connected to grid 8, generator-side converter 3 and DC boost module A first capacitor C1 is connected in parallel between 4, a second capacitor C2 is connected in parallel between the DC boost module 4 and the grid-side converter 5, and the energy storage module 7 is connected in parallel between the second capacitor C2 and the grid-side converter 5 , the control module 6 is respectively connected with the generator-side converter 3, the DC boosting module 4, the grid-side converter 5 and the energy storage module 7 to control them. Among them, the DC boost module 4 is as follows figure 2 As shown, including a single-phase full-bridge inverter circuit 41, a high-frequency transformer 42 and a single-phase full-bridge rectifier circuit 43 connected in sequence, the energy storage module 7 adopts a crowbar energy storage circuit, and the crowbar energy storage circuit includes a first power device. A bidirectional half-bridge buck-boost circuit composed of T1 and the second power device T2 in series in the same direction, an inductor L, and a resistor R sc and supercapacitor C sc , the two ends of the bidirectional half-bridge buck-boost circuit are respectively connected to the two ends of the second capacitor C2, the inductance L, the resistance R sc and supercapacitor C sc After being connected in series, the two ends of the second power device T2 are connected in parallel. The first power device T1 and the second power device T2 may adopt IGBT, IGCT or power MOSFET.

[0026] The working process of the whole system is as follows: the wind turbine 1 converts wind energy into mechanical energy, drives the permanent magnet synchronous generator 2 to output electric energy, and the generator-side converter 3 rectifies the alternating current output from the permanent magnet synchronous generator 2 into 1200V direct current, and passes The DC boosting module 4 boosts the voltage to 18kV, and then inverts it into 10kV AC with constant frequency and constant voltage through the grid-side converter 5 and then sends it to the grid.

[0027] When the system is working, the control process of the control module is as follows:

[0028] Under the changing wind speed, the speed reference value ω of the permanent magnet synchronous generator is calculated from the wind speed and the blade tip speed ratio curve * , control the speed of the permanent magnet synchronous generator, so that the speed ω meets the optimal tip speed ratio λ=λ oct , the maximum power corresponding to the current wind speed can be obtained to achieve maximum wind energy tracking.

[0029] The control of the generator-side converter adopts the double closed-loop control mode of speed outer loop and current inner loop to control the electromagnetic torque and electromagnetic power of the generator. The permanent magnet adopts radial surface distribution, the stator d and q axis inductances are equal, L d =L q. The rotational speed value ω calculated according to the maximum wind energy tracking algorithm * As the given value of the speed loop, the difference compared with the generator speed feedback value ω is sent to the PI controller with integral and output limiting, and the given value i of the stator q-axis current is output sq *. The given value i of the stator d-axis current sd * Set to 0. According to the voltage and electromagnetic torque equations of the permanent magnet synchronous generator, the double-loop decoupling control block diagram of the generator-side converter, such as Figure 4 shown.

[0030] The control of the grid-side converter adopts the voltage outer loop and the current inner loop double closed-loop control mode, the function is to keep the DC bus voltage constant and realize the decoupling control of active power and reactive power. Let the d-axis be oriented to the grid voltage vector, u gd =u g , u gq =0, set the DC voltage reference value U dc * and DC voltage feedback value U dc The difference after comparison is sent to the PI controller, and the output I d * As a reference value, the output active power is controlled, and the reactive power is set to 0, so that the system runs in the state of unity power factor. The double-loop decoupling control block diagram of the grid-side converter is attached Figure 5 shown.

[0031] The single-phase inverter and rectifier in the DC boost link are all controlled by PWM, and the drive signal is a complementary trigger pulse with a duty cycle of 50%. The working mode of the bidirectional half-bridge buck-boost circuit in the DC side energy storage circuit is determined by the power imbalance. At steady state, P s =P g , the circuit does not work; when P sP g , it works in buck mode, and the supercapacitor absorbs energy; when P s gWhen working in boost mode, the supercapacitor releases energy. To fully utilize the capacity of the converter, limit the current to 1.5p.u. The smoother the DC voltage, the better the generator's operation, so limit the capacitor voltage to as close to 1p.u. as possible.

[0032] The simulation process using MATLAB in the present invention is divided into two parts: (1) maximum power tracking and grid-connected performance when the wind speed suddenly changes; (2) the stability of the wind power system when the grid voltage drops.

[0033] (1) Suppose the system runs at the rated wind speed v=12m/s, the wind speed drops to 10m/s at t=0.7s, and the wind speed returns to the rated value at t=1.2s, and the simulation time is 2s. Image 6 (a), 6(b), and 6(c) are the grid-connected voltage and current waveforms, respectively, where the dotted line is the voltage and the solid line is the current. Figure 7 (a) and 7(b) are graphs of grid-connected power and power factor, respectively. It can be seen from the simulation results that the amplitude of the grid-connected current is greatly reduced by using the high-voltage grid-connected method. When the wind speed changes, the current changes very smoothly, thereby reducing the impact on the grid.

[0034] (2) Assuming that the wind power system operates at the rated wind speed, the grid voltage drops to 20% of the rated value at 0.5s, the voltage begins to recover gradually at 1.125s, and the voltage recovers to 90% of the rated value at 2.5s, and the simulation time is 3s. Figure 8 (a) is the voltage waveform diagram of the grid-connected point, Figure 8 (b) is the waveform of the DC side voltage when no energy storage device is added, Figure 8 (c) is the generator speed waveform diagram when no energy storage device is added. When the grid voltage drops, both the DC side voltage and the generator speed increase significantly. After adding the supercapacitor, its DC side voltage waveform, generator speed waveform, grid-connected current waveform and grid-connected power waveform are respectively as follows Figure 9 (a), 9(b), 9(c) and 9(d). It can be seen from the above simulation results that during the grid voltage drop, the grid-connected current is limited to within 1.5p.u., the energy storage circuit absorbs the excess energy on the DC side, so that the DC voltage remains stable, and the speed and electromagnetic torque of the generator maintain stable values. , the wind power system has a strong low voltage ride-through capability, which not only protects the wind power system, but also provides continuous power support to the power grid.