阅读说明：本技术 用于风力涡轮机中的双馈感应发电机的转子侧变流器的控制系统和方法 (Control system and method for a rotor-side converter of a doubly-fed induction generator in a wind turbine ) 是由 M·利佐莫伦特 I·古德罗德里格斯 M·巴尔尼斯埃斯帕拉德尔 A·阿古多阿拉克 于 2020-05-11 设计创作，主要内容包括：本发明涉及一种针对电网中的扰动用于风力涡轮机中的双馈感应发电机的转子侧变流器的控制方法。本发明还涉及一种用于风力涡轮机中的双馈感应发电机(1)的转子侧变流器(2)的控制系统(11),其特征在于,它包括计算单元(202),计算单元(202)被配置成用于计算至少一个参考电流(i～(*)-(r))。它进一步包括电流控制器(203),电流控制器(203)是被配置成在如下两种不同模式中操作的混合控制器：第一操作模式,优选地在电网中的扰动的瞬变期间来设置,其中电流控制器(203)被配置成以处于线性区域之外的调制指数进行操作；以及第二操作模式,优选地在电网中的扰动的稳态期间来设置,其中电流控制器(203)被配置成以处于线性区域内部的调制指数进行操作,由此即刻提供转子中可用的最大电压(106),以便满足所述至少一个参考电流(i～(*)-(r))。(The invention relates to a control method for a rotor-side converter of a doubly-fed induction generator in a wind turbine for disturbances in the grid. The invention also relates to a control system (11) for a rotor-side converter (2) of a doubly-fed induction generator (1) in a wind turbine, characterized in that it comprises a calculation unit (202), the calculation unit (202) being configured for calculating at least one reference current (i) * r ). It further comprises a current controller (203), a current controller (20)3) Is a hybrid controller configured to operate in two different modes: a first mode of operation, preferably set during a transient of a disturbance in the grid, wherein the current controller (203) is configured to operate with a modulation index outside the linear region; and a second operation mode, preferably set during steady state of disturbances in the grid, wherein the current controller (203) is configured to operate with a modulation index inside the linear region, thereby momentarily providing a maximum voltage (106) available in the rotor in order to meet the at least one reference current (i |) * r ）。)

1. A control system (11) for a rotor-side converter (2) of a doubly-fed induction generator (1) in a wind turbine, characterized in that it comprises:

a calculation unit (202) configured for calculating at least one reference current (i)^* _r) And an

A current controller (203) that is a hybrid controller configured to operate in two different modes:

a first operation mode, preferably set during a transient of a disturbance in the electrical grid, wherein the current controller (203) is configured to operate with a modulation index outside the linear region, an

A second operation mode, preferably set during steady state of disturbances in the electrical grid, wherein the current controller (203) is configured to operate with a modulation index inside the linear region, thereby momentarily providing a maximum voltage (106) available in the rotor in order to meet the at least one reference current (i |)^* _r）。

2. The control system (11) for a rotor-side converter (2) of a doubly-fed induction generator (1) in a wind turbine according to claim 1, characterized in that in the first operation mode the current controller (203) is configured to operate as a direct or hysteretic digital controller providing one of the Pulse Width Modulation (PWM) vectors available in the two or more stages of converter at each of the control sampling times.

3. Control system (11) for a rotor-side converter (2) of a doubly-fed induction generator (1) in a wind turbine according to any of the claims 1 or 2, characterized in that in the second operation mode the current controller (203) is configured to work as a controller commanding a control action in the linear region of the converter, thereby controlling the rotor current to a desired value.

4. The control system (11) for a rotor-side converter (2) of a doubly-fed induction generator (1) in a wind turbine according to any of claims 1 to 3, characterized in that it comprises a modulation block configured to operate at a variable switching frequency in the first operation mode.

5. The control system (11) for a rotor-side converter (2) of a doubly-fed induction generator (1) in a wind turbine according to claim 4, characterized in that the modulation block is configured to operate in the first operation mode with a switching frequency that is variable and inversely proportional to the error in the current.

6. The control system (11) for a rotor-side converter (2) of a doubly-fed induction generator (1) in a wind turbine according to any of the claims 1 to 3, characterized in that the modulation block is configured to operate at a constant switching frequency according to the second operation mode.

7. Control system (11) for a rotor-side converter (2) of a doubly-fed induction generator (1) in a wind turbine according to any of the preceding claims, characterized in that the current controller (203) is further configured for controlling the stator current (104) with a stator reference current.

8. The control system (11) for a rotor-side converter (2) of a doubly-fed induction generator (1) in a wind turbine as claimed in any of the preceding claims, characterized in that the current controller (203) is further configured for controlling the line current (105) of the wind turbine with a line current reference.

9. The control system (11) for a rotor-side converter (2) of a doubly-fed induction generator (1) in a wind turbine according to any of the preceding claims, characterized in that it further comprises a sequence sensor (201), the sequence sensor (201) being configured for separately evaluating the voltage and current positive and negative sequences.

10. The control system (11) for a rotor-side converter (2) of a doubly-fed induction generator (1) in a wind turbine according to claim 9, characterized in that it further comprises a calculation unit (202), the calculation unit (202) being configured for calculating at least one reference current (i) from the positive and negative sequences of voltages and currents evaluated by the sequence sensor (201)^* _r) Preferably a rotor reference current, which can be performed by the rotor-side converter (2) in a steady state.

11. The control system (11) for a rotor-side converter (2) of a doubly-fed induction generator (1) in a wind turbine according to claim 10, characterized in that the calculation unit (202) is further configured for calculating at least one stator reference current from the positive and negative sequences of voltages and currents evaluated by the sequence sensor (201).

12. The control system (11) for a rotor-side converter (2) of a doubly-fed induction generator (1) in a wind turbine according to claim 10 or 11, characterized in that the calculation unit (202) is further configured to calculate at least one total reference line current from the positive and negative sequences of voltages and currents evaluated by the sequence sensor (201).

13. Control system (11) for a rotor-side converter (2) of a doubly-fed induction generator (1) in a wind turbine according to any of the preceding claims, characterized in that the current controller (203) is further configured for adjusting the positive and negative sequences of the rotor current simultaneously.

14. Control system (11) for a rotor-side converter (2) of a doubly-fed induction generator (1) in a wind turbine according to any of the preceding claims, characterized in that the current controller (203) is further configured for adjusting the positive sequence and the negative sequence of the stator current simultaneously.

15. Control system (11) for a rotor-side converter (2) of a doubly-fed induction generator (1) in a wind turbine according to any of the preceding claims, characterized in that the instantaneous current controller (203) is further configured for simultaneously regulating the positive sequence and the negative sequence of the line current.

16. A control method for a rotor-side converter (2) of a doubly-fed induction generator (1) in a wind turbine, the control method being performed with the system of any of the preceding claims, characterized in that the method comprises:

a step for calculating at least one reference current, and

a step for current regulation, preferably a step for regulating the rotor current, wherein the maximum voltage available in the rotor is instantaneously provided in order to meet the at least one reference current (i)^* _r) It is further characterized in that the step for current regulation comprises:

a first operating mode, preferably set during a transient of a disturbance in the grid, corresponding to a modulation index outside the linear region, and

a second operating mode, preferably set during steady state of disturbances in the grid, which corresponds to a modulation index that is inside the linear region.

Technical Field

The object of the present invention is a control system and method for a rotor-side converter (converter) of a doubly-fed induction generator in a wind turbine for disturbances in the grid.

Background

For the rotor-side converter of a doubly-fed induction generator (DFIG) in a wind generator, there are a wide variety of controllers, which can be grouped into classical vector control, dual-vector control and direct control controllers.

Vector Control (VC) is the most common technique and it requires a Pulse Width Modulator (PWM). The combination with the modulator provides a constant switching frequency and low current harmonic content. This is known from the publications "R.Pena, J.C. Clare and G.M. Asher", "double fed induction generator using back-to-back PWM converters and its application to variable-speed wind-energy generation", "in IEE Proceedings-Electric Power Applications, vol.143, No. 3, pp. 231, 241, May 1996". Under normal operating conditions, vector control operation is acceptable, but under fault or accident conditions, such as, for example, voltage dip (dip) and overvoltage (overvoltage), vector control operation provides poor performance.

Dual Vector Control (DVC) adds a second controller to the original Vector Control (VC) to adjust negative sequences, such as described in the publications "M. Chomat, J. Bendl and L. Schreier," Extended vector control of double fed machine under underlying Power network conditions, "2002 International reference Power Electronics, Machines and Drives (Conf. Publ. number 487), 2002, pp. 329-" 334 ". Some recent work has improved Dual Vector Control (DVC) with alternative structural or reference generation for minimizing oscillations in DC bus and torque (torque). However, none of the known vector control or dual vector control techniques fully utilize converter performance or optimize its operation under thermal constraints, and none of them provide full regulation capability of the negative sequence in the most severe imbalance dips.

Patent application US 2010/117605 a1 discloses a method and a device for operating an asynchronous motor with double feed, having a stator connected to the grid and a rotor connected to an inverter. The inverter is designed such that it imposes (impress) a target value for the electrical variable in the rotor. The method allows for an active reduction in torque that occurs during transient grid voltage changes.

Patent application US 2019/140569 a1 describes a system and a method for operating a power system with a doubly fed induction generator, the power system comprising a power converter with a line-side converter, a DC link, and a rotor-side converter. The rotor-side converter is configured to convert DC power on the DC link to an AC signal for the rotor bus. The one or more control devices are configured to operate the rotor-side converter in an overmodulation scheme (overmodulation region) to provide an AC signal for the rotor bus.

The use of direct control, which may include hysteresis control in its group, is very widespread in DFIG converters. In contrast to linear control, such as vector and bi-vector control, direct control does not necessarily use Pulse Width Modulators (PWM), whereby the switching frequency is variable, and these are usually much faster. Known systems use power direct control for minimizing active and reactive power ripple (ripple) in the stator, as well as for normal operating conditions. However, the system requires a high computational load, since the power quality would otherwise be severely affected, something that would be punished by Grid Codes (GC).

Direct control applications are more meaningful in transient conditions of grid faults. Stator active and reactive power direct control systems are also known in order to obtain sinusoidal currents in the stator, minimization of torque ripple or constant active power during imbalance faults, and variable hysteresis control systems aimed at having fast dynamics in the rotor currents.

The interconnection of distributed generation power systems is dictated by the Grid Code (GC). Grid codes involve, among other requirements, Low Voltage (LVRT) and High Voltage (HVRT) ride through (edge through), where the generating unit (generating unit) not only has to remain connected, but it also injects reactive current into the positive sequence in order to counteract the disturbance. Among this type of requirements, Grid Codes (GCs) are increasingly demanding with respect to dynamic response (number of sequences injected and response time), fault profile, and number of consecutive faults.

Wind generators based on Doubly Fed Induction Generators (DFIGs) are particularly sensitive to disturbances in the grid voltage due to the direct connection between the stator windings and the grid (see fig. 1). Thus, during voltage dips and overvoltages, where the grid voltage changes suddenly, high transient currents in the stator and rotor are generated due to the new magnetized operating point of the generator. As the nominal power of the power generating unit increases, the magnitude of these currents becomes dangerously close to the ultimate tensile strength of the existing low voltage power electronic semiconductor, the Insulated Gate Bipolar Transistor (IGBT), forcing the equipment to open during a disturbance and thus not complying with major Grid Code (GC) requirements. Furthermore, the presence of these transient currents limits the converter control in order to comply with dynamic requirements, since it requires a large amount of voltage from the rotor.

In the case of an asymmetric fault (e.g., a two-phase voltage drop), the power system must also face the presence of negative sequence voltages and currents. Negative sequence regulation in DFIG-based systems is not easy because it requires higher rotor voltages, as set forth in the above-cited publications "r. Pena, j.c. class and g.m. ash," double fed induction generator using back-to-back PWM converters and its application to variable-speed with-energy generation, "in ie processes-Electric Power Applications, vol.143, No. 3, pp. 231, 241, May 1996". If the control algorithm of the converter cannot properly regulate the negative sequence, the electrical system (converter, generator, transformer and divider) must withstand unnecessarily high rotor and stator steady state currents and excessive use of the chopper. Thus, the ability of the system to face severe faults in magnitude and/or duration, as well as continuous faults, is severely limited. Furthermore, in the particular case of the german grid code (standard [2] VDE) for a wind farm connected to a high voltage grid, the power generating unit must also inject reactive current into the negative sequence, similar to the above-mentioned injection of reactive current in the positive sequence.

In summary, compliance with existing and future grid regulations (and power system integrity) in DFIG-based wind turbines is at serious risk when faced with LVRT and HVRT requirements, because:

the transient currents of the stator and rotor may be high enough to force the power generating unit to switch off;

the steady current of the rotor, and the energy to be dissipated in the brake chopper, may be high enough to force the power generating unit to switch off in large, deep and repetitive asymmetric voltage dips;

in some Grid Codes (GC), negative sequence regulation is already mandatory.

The inventive control method for a rotor-side converter of a DFIG converter of a wind turbine improves the performance of the system with respect to the above mentioned disadvantages.

Disclosure of Invention

The invention describes a control system for a rotor-side converter of a doubly-fed induction generator in a wind turbine, comprising:

a calculation unit configured for calculating at least one reference current, preferably a reference current of the rotor, an

A current controller, which is a hybrid controller configured to operate in two different modes, wherein a first mode of operation is preferably set during transients of disturbances in the electrical grid, wherein the current controller is configured to operate with a modulation index outside the linear region, and a second mode of operation is preferably set during steady state of disturbances in the electrical grid, wherein the current controller is configured to operate with a modulation index inside the linear region, thereby instantly (instantly) providing the maximum voltage available in the rotor in order to meet the at least one reference current. Preferably, the rotor current is regulated and it is a transient controller configured for momentarily providing a maximum voltage available in the rotor in order to meet the at least one reference current, preferably the rotor reference current.

The term "instantaneously providing" or "instantaneous" refers to providing the maximum voltage available in the rotor in one single control step by means of a current controller. In this way, the response time of the current controller is defined only by the hardware capabilities and the imposed control limits. This results in a fast response of the current controller.

The characteristics defining the controller are:

transient, mixed and non-linear. In one aspect, the basic principle of controller operation is based on instantaneously minimizing the difference between the measured rotor current and the desired current depending on the modulation index. In another aspect, to achieve this transient nature, the control action is non-linear.

Finally, it is a hybrid controller, since the controller operates in two different modes depending on the ability to meet the desired current command. The transition between modes may be automatic and it does not require any modification or state machine. Preferably, the operating modes are:

a first mode of operation wherein the controller is configured to operate as a direct or hysteretic digital controller providing one of the Pulse Width Modulation (PWM) vectors available in the two or more stage converter in each control sample time. Preferably, the first mode of operation corresponds to a modulation index that is outside the linear region, i.e., above the linear boundary limit or within the overmodulation region. This mode of operation is characterized by: a finite variable switching frequency between a maximum frequency and a minimum frequency provided by the rotor frequency. Therefore, the controller not only limits the conduction loss (conduction loss) using its transient response, but also reduces the switching loss when the conduction loss inevitably increases due to an increase in fault current, that is, it reduces the rotor current during a transient and satisfies the rotor reference current;

a second operating mode, wherein the controller is configured to operate with a modulation index in the linear region and is configured to operate as a controller commanding a control action in the linear region of the current transformer, thereby controlling the rotor current to a desired value. The controller in this second mode may be implemented using a proportional Plus Integral (PI), resonant, dead beat (dead beat) controller, or the like.

The modulation index, as known in the art, may be defined as the ratio of the magnitude of the rotor voltage reference to half of the available DC bus voltage.

Optionally, the control system further comprises a sequence sensor configured for separately evaluating the voltage and current positive and negative sequences.

Optionally, the controller is prepared for adjusting the current positive and negative sequences, wherein it is preferably configured for adjusting the measured rotor currents following the at least one rotor reference current.

The at least one reference current of the rotor is calculated in order to comply with grid regulation reactive current requirements.

Optionally, the system comprises a modulation block configured to operate in the first mode of operation at a variable switching frequency, preferably inversely proportional to the error in the current.

Optionally, the modulation block is configured to operate at a constant switching frequency in a second mode of operation.

Optionally, the system further comprises a sequence sensor configured for separately evaluating the voltage and current positive and negative sequences.

Optionally, the system further comprises a calculation unit configured for calculating at least one reference current, preferably a reference current of the rotor, from the positive and negative sequences of voltages and currents evaluated by the sequence sensor, which may be achieved by the rotor converter in a steady state.

Optionally, the calculation unit is further configured for calculating at least one reference current of the stator from the positive and negative sequences of voltages and currents evaluated by the sequence sensor.

Optionally, the calculation unit is further configured for calculating at least one bus reference current from the positive and negative sequences of voltages and currents evaluated by the sequence sensor.

Optionally, the instantaneous current controller is further configured to simultaneously regulate the positive and negative sequences of the rotor current and/or the stator current and/or the line current.

A second aspect of the invention describes a control method for a rotor-side converter of a doubly-fed induction generator in a wind turbine, the control method being performed with the system described above, the method comprising:

a step for calculating at least one reference current, preferably a reference current of the rotor, an

A step for current regulation, preferably for regulating the rotor current, wherein the maximum voltage available in the rotor is instantaneously provided in order to meet the at least one reference current, preferably the reference current of the rotor.

The steps for current regulation include:

a first operating mode, preferably set during transients of disturbances in the grid, corresponding to modulation indexes outside the linear region; and

a second operating mode, preferably set during steady state of disturbances in the grid, which corresponds to a modulation index that is inside the linear region.

The control system and method thus constituted for the rotor-side converter of a doubly-fed induction generator in a wind turbine have the following advantages:

it brings about optimization of converter operation during transients generated by faults in the grid: that is, it minimizes fault current and reduces switching losses with subsequent reduction in thermal stress;

it adds dynamics to comply with the goals established by GC, an

It provides a total adjustment of the positive and negative sequences to be controlled in a severe imbalance fault.

Drawings

In order to achieve the description made and to provide a better understanding of the nature of the invention, according to a preferred practical embodiment thereof, for illustrative but not limiting purposes, a set of drawings is attached as part of the description, these drawings representing the following:

fig. 1. It shows an electrical scheme of a wind turbine with a DFIG generator;

fig. 2. It shows a solution of the inventive control system for a rotor-side converter of a DFIG converter of a wind turbine.

Detailed Description

The following is a detailed description of the electrical system of the doubly fed induction generator (1) of a wind turbine of the present invention and the associated control method for the rotor side converter (2). The windings of the doubly fed induction generator (1) are connected to a rotor three-phase bridge (2). The rotor-side converter shares its DC connection (4) with a three-phase electrical network bridge (3). The three-phase AC connection of the electrical bridge (3) may comprise a three-phase power filter (5). Likewise, the AC three-phase connection of the rotor-side converter (2) may comprise a three-phase power filter (6). The AC three-phase connection of the electrical network bridge and the stator windings are connected to the low-voltage windings of a three-phase step-up transformer (7). Both the AC three-phase connection of the electrical network bridge and the stator winding may have contactors (8) and switches (9) in order to make the electrical operation easier and to ensure protection. Both the rotor-side converter (2) and the grid bridge (3) are commanded by trigger signals (101, 102) of their semiconductor devices. The computation and control (10) logic unit is responsible for providing the trigger signals (101, 102).

The calculation and control logic unit (10) is where the control method of the invention is implemented. According to this embodiment, a control system (11) for a rotor-side converter of a doubly-fed induction generator in a wind turbine comprises:

a sequence sensor (201) configured for separately evaluating a voltage and a current positive sequence and a negative sequence;

a calculation unit (202) for calculating at least a reference current (i) from the positive and negative sequences of voltages and currents evaluated by the sequence sensor (201) in a steady state^* _r) Preferably the reference current of the rotor;

a current controller (203), preferably for the rotor current (103) or alternatively for the stator current (104) or for the line current (105), wherein the current controller (203) is a transient controller for instantaneously providing a maximum voltage (106) available in the rotor in order to meet at least one reference current (i |)^* _r) And it is also configured to useA non-linear hybrid controller for providing a rotor voltage within a usable voltage range. The current controller (203) includes pulse width modulation logic (PWM). The current controller (203) provides a trigger signal (101) for the rotor three-phase bridge (2).

The current controller (203) may operate in two different modes. The transition between modes is automatic and it does not require any modifications or state machines. These modes are:

a first mode of operation in which the current controller (203) operates as a direct, hysteretic digital controller or the like providing one of the pulse width modulator vectors available in the two or more stage converter at each control sample time, wherein the first mode of operation corresponds to a modulation index that is outside of the converter linear region (i.e., within the overmodulation region). Overmodulation operation means the possibility of operating with a high modulation index (including the maximum theoretical limit). Thus, an operation characterized by a variable switching frequency is obtained;

a second operation mode, wherein the current controller (203) is configured to operate as a deadbeat controller or the like, which commands a control action that momentarily takes the current under control to a desired value, wherein the second operation mode is performed with a modulation index that is within the linear region of the converter. In this second mode of operation, the switching frequency is constant. The method is configured for setting the current controller (203) in the second operation mode, preferably during steady state of the fault, i.e. when the current command can arrive instantaneously.

The current controller (203) is also a transient controller configured for regulating the current positive and negative sequences and preferably for regulating the measured current of the rotor following at least one rotor current reference supplied by an external block providing a reference current that the rotor converter can achieve in steady state.