WO2016119585A1

WO2016119585A1 - Power oscillation suppression method for double-fed wind turbine using super capacitor energy storage system

Info

Publication number: WO2016119585A1
Application number: PCT/CN2016/070532
Authority: WO
Inventors: 汪宁渤; 丁坤; 周识远; 张琛; 李征; 蔡旭; 蔡游明; 何世恩; 李津; 路亮; 摆念宗
Original assignee: 国家电网公司; 国网甘肃省电力公司; 甘肃省电力公司风电技术中心; 上海交通大学
Priority date: 2015-01-27
Filing date: 2016-01-09
Publication date: 2016-08-04
Also published as: CN104638661A

Abstract

A power oscillation suppression method for a double-fed wind turbine using a super capacitor energy storage system, specifically comprising: connecting a super capacitor to a rotor side current transformer via a DC/DC interface circuit, the super capacitor and the rotor side current transformer of a double-fed wind turbine sharing a DC bus; and building an equivalent circuit. The equivalent circuit is a loop formed by connecting a capacitor Csc, a resistor Rres, an inductor L, a DC/DC interface circuit first switch and a capacitor Cdc in series sequentially, two ends of the capacitor Cdc being connected in parallel to a resistor R, a node between the inductor L and the DC/DC interface circuit first switch being a node A, a node between the capacitor Csc and the capacitor Cdc being a node B, and a DC/DC interface circuit second switch being connected between the node A and the node B. The method achieves the aims of not only effectively damping shaft system oscillation but also preventing the output power of the double-fed wind turbine from being influenced by damping power.

Description

Power oscillation suppression method for doubly-fed wind turbines using super capacitor energy storage system

Technical field

The invention relates to the field of wind power generation and its grid-connected control, and in particular to a power oscillation suppression method for a doubly-fed wind turbine using a supercapacitor energy storage system.

Background technique

At present, the large-scale wind power integration and grid connection has an important impact on the stability of the power system. Although the commercial variable-speed wind turbines use a large number of converter technologies to achieve synchronous grid connection, the generator and grid frequency can be asynchronously operated, which enhances the flexible control of the wind turbine. This asynchronous operation of frequency does not mean that the electromechanical is completely decoupled. Different unit control strategies (such as maximum power tracking control, constant power control, etc.) reflect different degrees of electromechanical coupling. In addition, under grid faults, this The electromechanical coupling effect is more obvious.

The MW-class doubly-fed wind turbine drive train is highly flexible, and there is an oscillation frequency (about 1 Hz) close to the low-frequency oscillation of the system. There is a risk of inducing oscillation instability of the system. Therefore, it is necessary to add a shaft system similar to the synchronous machine PSS to the wind turbine. Stabilizer.

The prior art solution adopts an auxiliary auxiliary damping control loop directly in the power control loop of the wind turbine to realize electrical damping and suppress shafting oscillation, but this scheme will inject power for suppressing shafting oscillation into the power grid, so it is not good. of.

Summary of the invention

In summary, it is necessary to propose a power oscillation suppression method for a doubly-fed wind turbine using a supercapacitor energy storage system, which not only can effectively dampen the shafting oscillation, but also ensure that the output power of the unit is not affected by the damping power.

A power oscillation suppression method for a doubly-fed wind turbine using a supercapacitor energy storage system, comprising:

The supercapacitor is connected to the rotor-side converter through a DC/DC interface circuit, and the supercapacitor shares a DC bus with the doubly-fed wind turbine converter, and an equivalent circuit is established. The equivalent circuit is a capacitor C _sc and a resistor. R _res , inductor L, rotor-side converter U ₁ and capacitor C _{dc are} sequentially connected in series to form a loop, and both ends of the capacitor C _dc are connected in parallel with a resistor R, a node between the inductor L and the rotor-side converter U ₁ For the A node, the node between the capacitor C _sc and the capacitor C _dc is a B node, and the rotor-side converter U ₂ is connected between the A node and the B node, and the capacitance C _dc and the capacitance C _sc represent DC bus capacitor and super capacitor, resistor R _res is super capacitor equivalent series resistance, resistor R is equivalent load, signal S ₁ on rotor side converter U ₁ and signal S ₂ on rotor side converter U ₂ For the DC/DC converter control signal, the current I _sc and the current I _dc are the inductor current and the DC bus capacitor current, respectively, and the voltage E _sc and the voltage E _dc are the super capacitor and the DC bus voltage, respectively;

The specific method is: controlling the functions in the formula (1) and the formula (2) by using a double closed loop cascade control structure of the inductor current inner loop and the DC bus voltage outer loop,

(1)

(2)

Where D is the duty cycle steady state value, s is the Laplacian operator, L is the inductance value of the DC/DC interface circuit, that is, the inductance value of the inductance L in the equivalent circuit, and d is the duty cycle disturbance value.

Preferably, the DC/DC interface circuit employs a bidirectional buck-boost circuit.

Compared with the prior art, the technical solution of the present invention, by adding a super capacitor, when power oscillation suppression is required, the grid-side converter controls the DC component of the rotor power, and performs feedforward control on the stator oscillation power. The DC bus will oscillate. Due to the supercapacitor control of the DC bus, the oscillating power is injected into the supercapacitor via the DC bus. Achieving not only can effectively dampen the shafting oscillation, but also ensure that the output power of the unit is not affected by the damping power. And since only the oscillation power is absorbed, the required supercapacitance capacity is small.

DRAWINGS

FIG. 1 is a schematic diagram of a super capacitor installation principle in a power oscillation suppression method for a doubly-fed wind turbine using a super capacitor energy storage system according to an embodiment of the present invention.

2 is an electronic circuit diagram of an equivalent circuit in a power oscillation suppression method for a doubly-fed wind turbine using a supercapacitor energy storage system according to an embodiment of the present invention.

Figure 3 is a block diagram of the principle of electrical resistance control.

Figure 4 is a block diagram of the supercapacitor control principle.

Fig. 5 is a block diagram showing the principle of switching control of the grid side converter.

Figure 6 is a simulation diagram of the grid voltage.

Figure 7 is a graph of DC bus and super capacitor voltage response.

Fig. 8 is a graph showing the comparison of the presence or absence of power oscillation suppression.

Figure 9 is a graph comparing the speed of the generator.

Main component symbol description

双馈发电机 Double feed generator	11
转子侧变流器 Rotor side converter	22

The invention will be further illustrated by the following detailed description in conjunction with the accompanying drawings.

detailed description

The preferred embodiments of the present invention are described with reference to the accompanying drawings, which are intended to illustrate and illustrate the invention.

A power oscillation suppression method for a doubly-fed wind turbine using a supercapacitor energy storage system, specifically comprising:

The supercapacitor is connected to the rotor-side converter through a DC/DC interface circuit, and the supercapacitor shares a DC bus with the doubly-fed wind turbine converter, and an equivalent circuit is established. The equivalent circuit is shown in FIG. 2, and the capacitor C _Sc , the resistor R _res , the inductor L, the rotor-side converter U ₁ and the capacitor C _{dc are} sequentially connected in series to form a loop, the capacitor C _dc , the parallel resistance R at both ends, the node between the inductor L and the rotor-side converter U ₁ For node A, the node between capacitor C _sc and capacitor C _dc is node B, and rotor-side converter U ₂ is connected between node A and node B. Capacitor C _dc and capacitor C _sc represent DC bus capacitor and super capacitor. _RES is the resistance R ESR super-capacitor, the equivalent load resistance R, the rotor side converter on the U signal S _₁₁ and the rotor side converter on the signal S ₂ U ₂ DC / DC converter control The signal, current I _sc and current I _dc are the inductor current and the DC bus capacitor current, respectively, and the voltage E _sc and the voltage E _dc are the supercapacitor and the DC bus voltage, respectively.

(1)

(2)

Where D is the duty cycle steady state value, s is the Laplacian operator, and L is the DC/DC interface circuit.

The inductance value is the inductance value of the inductance L in the equivalent circuit, and d is the duty cycle disturbance value.

Among them, the DC/DC interface circuit uses a bidirectional buck-boost circuit.

The supercapacitor control strategy is shown in Figure 4. The dual closed-loop cascade control structure of the inductor current (IL) inner loop and the DC bus voltage (Edc) outer loop is used. The control objects are equation (1) and equation (2).

As shown in Figure 1, the supercapacitor shares a DC bus with the doubly-fed wind turbine converter. The interface circuit uses a bidirectional buck-boost circuit, as shown in Figure 2. In the figure, C _dc and C _sc represent the DC bus capacitance and Super capacitor, R _res is the super capacitor equivalent series resistance, R is the equivalent load, S ₁ , S ₂ is the DC/DC converter control signal, I _sc , I _dc are the inductor current and DC bus capacitor current respectively, E _sc , E _dc is the super capacitor and DC bus voltage respectively.

The power oscillation suppression control strategy consists of two main components: a rotor converter for electrical resistance; a supercapacitor and a grid-side converter for power oscillation suppression.

The rotor current transformer electrical resistance increase strategy is as follows:

(3)

As shown in Fig. 3, the electric damping is realized by the active additional control. By measuring the generator speed signal ω _r , the dominant oscillating frequency component is extracted according to equation (3) (ξ is the damping ratio, ω _osc is the characteristic angular frequency), Additional electrical damping torque ΔT _e , superimposed on the original electromagnetic torque of the converter

(calculated by maximum power tracking), through the torque closed loop to obtain the required rotor rotor current straight axis given component

.

As shown in FIG. 5, when power oscillation suppression is not required (mode 1), the grid-side converter controls the DC bus. When power oscillation suppression is required (mode 2), the grid-side converter controls the DC component of the rotor power. The feedforward control power of the stator is fed forward. At this time, the DC bus will oscillate. Due to the supercapacitor control of the DC bus, the oscillation power is injected into the super capacitor through the DC bus. Since only the oscillation power is absorbed, the required supercapacitance value is required. Smaller.

Feasibility verification (simulation):

Simulation condition: The shafting of the doubly-fed wind turbine is excited by the three-phase short-circuit fault of the grid. The fault causes the grid-connected voltage to drop to 0.3 pu for 625 ms. The initial state of the unit is 85% rated. Compare the influence of power oscillation suppression strategy on the dynamic characteristics of the grid-connected wind turbine.

It can be seen from Fig. 7 that during the transient fault of the power grid, the supercapacitor has greatly improved the transient characteristics of the DC bus, ensuring that the DC bus is not under voltage. Since the super capacitor only absorbs the transient power, its voltage hardly rises. After the fault is recovered, the network recovers. The side converter control strategy is switched to suppress power oscillation. At this time, the super capacitor only absorbs a certain oscillation power, and the voltage rise is small. It can be seen from Fig. 8 that during the fault, the grid-side converter control strategy is switched to the DC bus voltage control (mode 1), and the delay is 0.2s after the fault recovery to the power oscillation suppression control (mode 2). The reason for the delay is to avoid The influence of the open stator power jump on the signal extraction of the trap is switched to the power oscillation suppression strategy. It can be clearly seen that the grid-connected power of the doubly-fed wind turbine does not contain the oscillation component, which is relatively stable, and at the same time, due to the additional electrical damping. The action, the speed oscillation also gets faster damping as shown in Figure 9.

In addition, those skilled in the art can make other changes within the spirit of the invention, and it is to be understood that these changes are intended to be included within the scope of the invention.

Claims

A power oscillation suppression method for a doubly-fed wind turbine using a supercapacitor energy storage system, comprising:

The supercapacitor is connected to the rotor-side converter through a DC/DC interface circuit, and the supercapacitor shares a DC bus with the doubly-fed wind turbine converter, and an equivalent circuit is established. The equivalent circuit is a capacitor C sc and a resistor. R res , inductor L, rotor-side converter U 1 and capacitor C dc are sequentially connected in series to form a loop, and both ends of the capacitor C dc are connected in parallel with a resistor R, a node between the inductor L and the rotor-side converter U 1 For the node A, the node between the capacitor C sc and the capacitor C dc is a node B, and the rotor-side converter U 2 is connected between the node A and the node B, and the capacitor C dc and the capacitor C sc represent a direct current. Bus capacitance and super capacitor, the resistance R res is the super capacitor equivalent series resistance, the resistance R is the equivalent load, the signal S 1 on the rotor side converter U 1 and the signal S 2 on the rotor side converter U 2 are The DC/DC converter control signal, the current I sc and the current I dc are the inductor current and the DC bus capacitor current, respectively, and the voltage E sc and the voltage E dc are the super capacitor and the DC bus voltage, respectively;

The specific method is: controlling the functions in the formula (1) and the formula (2) by using a double closed loop cascade control structure of the inductor current inner loop and the DC bus voltage outer loop,

(1)

(2)

Where D is the duty cycle steady state value, s is the Laplacian operator, and L is the DC/DC interface circuit.

The inductance value is the inductance value of the inductance L in the equivalent circuit, and d is the duty cycle disturbance value.
The doubly-fed wind turbine power oscillation suppression method using a super capacitor energy storage system according to claim 1, wherein the DC/DC interface circuit adopts a bidirectional buck-boost circuit.