CN102832638A - Wind farm low voltage ride-through control system based on battery energy storage - Google Patents

Abstract

The invention discloses a wind farm low-voltage ride-through control system based on battery energy storage, including a data collector, a data analyzer, a control module, a smoothing control module, a battery energy storage system, an AC/DC converter, a wind farm and For the power grid, the data analyzer is used to compare the PCC point voltage Vpcc with the PCC point voltage set value Vref: when Vpcc<Vref, the control module plays a role, and the control module controls the battery energy storage system to enter the low voltage ride-through control strategy; when Vpcc When =Vref, the smoothing control module plays a role, and the smoothing control module controls the battery energy storage system to put into smoothing control strategy. The low-voltage ride-through control system for wind farms based on battery energy storage of the present invention starts from the battery energy storage system, analyzes the voltage of the common connection point (PCC) of the wind/energy storage system, and controls the operating status of the battery to meet the requirements of wind power. System low voltage ride through control capability.

Description

A low-voltage ride-through control system for wind farms based on battery energy storage

technical field

The invention belongs to the technical field of wind power generation, and in particular relates to a control method for solving low-voltage ride-through of a wind farm.

Background technique

Because wind power has the advantages of saving power system operating costs and no pollution, it has developed rapidly in many countries in recent years. With the large-scale grid-connection of wind power, it is particularly important to improve the operation capability of the wind power system in the case of grid faults. Therefore, the wind power grid-connected operation guidelines require that wind turbines should have low-voltage ride-through (LVRT) capabilities during grid voltage drops. Due to the weak low-voltage ride-through capability of wind turbines, the LVRT problem of wind farms has become a research hotspot at home and abroad. There are two main ways to realize LVRT, one is to improve the control strategy of the converter, this method is generally applicable to the case of a small voltage drop. When a serious fault occurs in the power grid, it is difficult to realize LVRT only by improving the control strategy of the converter, and the hardware control circuit must be added, so another method is to increase the hardware control circuit, such as adding a crowbar circuit on the rotor side. . As a flexible and adjustable battery energy storage system, it can not only smooth the wind power output, but also effectively improve the LVRT capability of the wind farm.

Therefore, a new low-voltage ride-through control system for wind farms based on battery energy storage systems is needed to solve the above problems.

Contents of the invention

Purpose of the invention: The present invention aims at the deficiencies of the low-voltage ride-through control method of the wind farm in the prior art, and provides a low-voltage ride-through control method of the wind farm based on a battery energy storage system.

Technical solution: In order to solve the above technical problems, the low-voltage ride-through control method for wind farms based on the battery energy storage system of the present invention adopts the following technical solutions:

A low-voltage ride-through control system for wind farms based on battery energy storage, characterized in that it includes a data collector, a data analyzer, a control module, a smooth control module, a battery energy storage system, an AC/DC converter, a wind farm and power grid, the data collector is connected to the data analyzer, the data analyzer is connected to the control module and the smoothing control module, and both the control module and the smoothing control module are connected to the AC/DC converter, The battery energy storage system is connected to the AC/DC converter, the wind farm is connected to the grid and connected to the AC/DC converter; the data collector is used to collect PCC points of the wind farm and the battery energy storage system voltage Vpcc, and input the PCC point voltage Vpcc into the data analyzer; the data analyzer is used to compare the PCC point voltage Vpcc with the voltage setting value Vref of the PCC point: when Vpcc<Vref, the The control module plays a role, and the control module controls the battery energy storage system to enter the low voltage ride-through control strategy; when Vpcc=Vref, the smoothing control module plays a role, and the smoothing control module controls the battery energy storage system Throw in a smooth control strategy. The PCC point voltage is the common connection point voltage.

Beneficial effects: The low-voltage ride-through control system for wind farms based on battery energy storage in the present invention starts from the battery energy storage system, analyzes the voltage of the common connection point (PCC) of the wind/energy storage system, controls the operating status of the battery, and To meet the low voltage ride through control capability of wind power system.

Preferably, the smoothing control module includes a battery charge and discharge selector, which compares the output power P of the wind farm with the set maximum value Pmax and minimum value Pmin of the wind farm output power, and when P>Pmax, the battery charge and discharge selector Control the charging of the battery energy storage system; when P<Pmin, the battery charge and discharge selector controls the discharge of the battery energy storage system, thereby realizing a smooth control strategy.

Preferably, the control module adjusts the modulated wave amplitude and phase of the modulated wave controlled by PWM according to the dynamic change of the PCC point voltage Vpcc, and dynamically tracks the set value Vref, obtains the modulated wave signal controlled by PWM and performs a process with the triangular carrier signal. PWM control, so as to realize the low voltage ride through control strategy. PWM control (that is, Pulse WidthModulation-pulse width modulation or pulse width modulation) pulse width modulation (PWM) is a very effective technology that uses the digital output of a microprocessor to control analog circuits, and is widely used in measurement, communication into many areas of power control and conversion.

Preferably, the control module includes a PI regulator and a fuzzy PI controller, the active reference current _idref passes through the PI regulator and increases the coupling voltage _id ωL to obtain the modulation wave amplitude A controlled by PWM, and the active reference current _idref =P _ref /V, wherein, V is the effective value of the battery output voltage, and P _ref is the active power reference value; the PCC point voltage Vpcc dynamically tracks the set value Vref, and generates the reactive current reference value i _qref through the fuzzy PI controller , and then pass through the PI regulator and increase the coupling voltage i _q ωL to obtain the PWM-controlled modulation wave phase α, and the PWM-controlled modulation wave signal Acos(ωt+α) can be obtained through the above control. The present invention dynamically tracks and controls its setting value by observing the voltage of the PCC point, adopts active and reactive power decoupling PI control algorithm, and considers the deficiency of traditional PI control dynamic difference, etc., and applies fuzzy control strategy to it. By tracking and controlling the voltage reference value of the grid-connected point, and adjusting the amplitude and phase of the modulation wave signal in the PWM control through the fuzzy PI controller, the modulation wave signal of the PWM control is obtained to achieve the purpose of low voltage ride-through control of the wind farm.

Preferably, the AC/DC converter adopts an IGBT switch, compares the modulated wave signal controlled by PWM with the triangular carrier signal with an amplitude of ±1 to obtain a pulse signal, and the pulse signal is the PWM control signal, and the The PWM control signal is used to control the state of the IGBT switch of the AC/DC converter. The invention adopts the PWM control technology of the three-phase bridge circuit composed of the fully-controlled power switching device IGBT, which effectively reduces the reactive power loss of the converter, and is beneficial for the battery to participate in the low-voltage ride-through control of the system. The IGBT switch is a fully controlled power switching device, which has the advantages of low driving power, low saturation voltage, and fast switching speed, and is widely used in 600V and above converter systems.

Preferably, the control module also includes a fuzzy logic reasoner, and the fuzzy PI control method includes the following steps:

1) When the PCC point voltage is disturbed, an error e is generated;

2) Generate PI parameter adjustment increments ΔK _p and Δk _i through the fuzzy logic reasoner;

3), according to the formula $\left\{\begin{array}{c}{K}_p^{\&prime;}=K_p+{\mathrm{\&Delta;K}}_p\\ k_i^{\&prime;}=k_i+{\mathrm{\&Delta;k}}_i\end{array}\right.$ Adjust the PI parameter values K _p and _ki to obtain the parameters of the fuzzy PI controller

The _parameter setting values K' _p , k' _i are used as the new parameter values _of the fuzzy PI regulator.

Preferably, the input and output of the fuzzy logic reasoner both use triangular membership functions to establish fuzzy rules.

Description of drawings

Fig. 1 is a schematic structural diagram of a low-voltage ride-through control system for a wind farm based on battery energy storage in the present invention;

Fig. 2 is a schematic structural diagram of the control module in the low-voltage ride-through control system of the wind farm based on battery energy storage in the present invention;

Fig. 3 is a schematic structural diagram of the smoothing control module in the low-voltage ride-through control system of the wind farm based on battery energy storage in the present invention;

Fig. 4 is the dynamic response of the PCC point voltage without adding the battery energy storage system of the control system of the present invention constructed by the application software PSCAD;

Fig. 5 is the dynamic response of the A-phase current of the stator and rotor of the doubly-fed induction wind power generator without adding the battery energy storage system of the control system of the present invention constructed by the application software PSCAD;

Fig. 6 is the dynamic response of the PCC point voltage under the increase of the battery energy storage system of the control system of the present invention constructed by the application software PSCAD;

Fig. 7 is the dynamic response of the A-phase current of the stator and rotor of the doubly-fed induction wind power generator under the addition of the battery energy storage system of the control system of the present invention constructed by the application software PSCAD;

Fig. 8 is the reactive power response of the battery energy storage system under the addition of the battery energy storage system of the control system of the present invention constructed by the application software PSCAD;

Detailed ways

Below in conjunction with accompanying drawing and specific embodiment, further illustrate the present invention, should be understood that these embodiments are only for illustrating the present invention and are not intended to limit the scope of the present invention, after having read the present invention, those skilled in the art will understand various aspects of the present invention Modifications in equivalent forms all fall within the scope defined by the appended claims of this application.

Please refer to Fig. 1, the overall structural block diagram of the wind farm low voltage ride through control system based on battery energy storage in the present invention, the control system includes a data collector 1, a data analyzer 2, a control module 3, a smoothing control module 4, a battery Energy storage system 5 , AC/DC converter 6 , wind farm 7 and power grid 8 . The PCC point voltage Vpcc (that is, the grid connection point voltage) of the wind farm 7 and the battery energy storage system 5 (wind/storage system) is obtained through the data collector 1, and is input into the data analyzer 2 for comparison with the PCC point voltage setting value Vref analyze. Determine the switching operation status of the battery. When the system fails, that is, when Vpcc<Vref, the battery energy storage system 5 enters the low voltage ride-through control strategy, and the control module 3 works at this time; when the system operates normally, that is, when Vpcc=Vref, the battery energy storage system 5 The energy storage system 5 is put into the smoothing control strategy, and the smoothing control module 4 works at this moment. The control strategy is based on comparing the output power P of the wind farm with the set maximum value Pmax and minimum value Pmin of the wind farm output power. When P>Pmax, the wind power is too much and the battery is charged; when P<Pmin, the wind power is insufficient. , the battery discharges. The smoothing control module 4 includes a battery charge and discharge selector 12, which compares the output power P of the wind farm with the set maximum value Pmax and minimum value Pmin of the output power of the wind farm. When P>Pmax, the wind power is too much, and the battery charge The discharge selector 12 controls the charging of the battery energy storage system 5; when P<Pmin, the wind power is insufficient, and the battery charge and discharge selector 12 controls the battery energy storage system 5 to discharge.

As shown in FIG. 2 , the structural diagram of the control module in the low-voltage ride-through control method for wind farms based on battery energy storage includes a PI regulator 9 and a fuzzy PI controller 10 . The control module is a strategy for the battery energy storage system 5 to be put into low-voltage ride-through control. The active current reference _idref =P _ref /V is used as the control tracking battery output active reference, through the PI regulator 9 and the coupled voltage _id ωL is added to obtain the modulated wave amplitude A of PWM control. Among them, _idref =P _ref /V (V is the effective value of the battery output voltage) is used as the reference quantity for controlling and tracking the battery output active current, that is, the D-axis control reference quantity of the battery output AC side, reflecting the demand for active power of the system. The PCC point voltage Vpcc dynamically tracks the set value Vref, generates a reactive current reference value i _qref through the fuzzy PI controller 10, and serves as a reference value for the Q-axis control of the battery output AC side, and then passes through the PI regulator 9 to increase the coupling voltage i _q ωL The phase α of the modulated wave controlled by PWM is obtained, and thus the modulated wave signal Acos(ωt+α) controlled by PWM is obtained. Wherein, the AC/DC converter 6 adopts IGBT switches. Comparing the modulated wave signal Acos(ωt+α) with the triangular carrier signal with an amplitude of ±1, the pulse signal, that is, the PWM switching signal is obtained, and the PWM switching signal is used to control the switching state of the AC/DC converter 6 IGBT. The method of using the PWM switch signal to control the IGBT switch state is as follows: compare the modulated wave signal controlled by PWM with the triangular carrier signal with an amplitude of ±1 to obtain the signal that triggers the IGBT switch of the AC/DC converter.

Among them, the fuzzy PI control mechanism is:

1) When the PCC point voltage is disturbed, an error e is generated;

2) Generate PI parameter adjustment increments ΔK _p and Δk _i through the fuzzy logic reasoner;

3), according to the formula $\left\{\begin{array}{c}{K}_p^{\&prime;}=K_p+{\mathrm{\&Delta;K}}_p\\ k_i^{\&prime;}=k_i+{\mathrm{\&Delta;k}}_i\end{array}\right.$ The PI parameter values K _p and _ki are adjusted to obtain the parameter setting values K' _p and k' _i of the fuzzy PI controller, and the parameter setting values are used as the new parameter values of the fuzzy PI regulator.

The low voltage ride through control principle of the present invention: firstly, starting from the battery energy storage system, the voltage of the common connection point (PCC) of the wind/energy storage system is analyzed, and an instruction to control the operating status of the battery is proposed to meet the requirements of the low voltage of the wind power system. Voltage ride-through control capability; secondly, due to the poor response of traditional PI control, fuzzy control is applied to it to improve the LVRT effect; finally, increase the coupling voltage, properly adjust the amplitude and phase of the modulation wave signal in PWM control, and The PWM technology is used to control the three-phase bridge circuit composed of the fully-controlled power switching device IGBT, thereby realizing the battery energy storage system to improve the low-voltage ride-through function of the system.

Comparing with attached drawings 1 and 2, the above control system is built on the simulation software PSCAD platform.

It is assumed that a battery energy storage system 5 is added at the exit 7 of a wind farm. The battery uses a lithium battery energy storage system. A three-phase short-circuit fault occurs at the grid connection point. The fault drop depth is 30% and the fault lasts for 0.5s.

As shown in Fig. 4 and Fig. 5, the control system of the present invention constructed by applying the simulation software PSCAD is without adding the lithium battery energy storage system 5 and the dynamics of the PCC point voltage and the stator and rotor A-phase current of the double-fed induction wind generator (DFIG). response. When the power grid fails, when the wind farm is not controlled by the battery energy storage system 5, the voltage at the PCC point drops rapidly to 0.7pu, which causes the current of the DFIG stator and rotor to increase, which brings a great impact on the converter.

As shown in Fig. 6, Fig. 7 and Fig. 8, the control system of the present invention constructed by using the simulation software PSCAD dynamically responds to the PCC point voltage and the A-phase current of the DFIG stator and rotor under the battery energy storage system 5. The battery energy storage system 5 immediately responds to compensate reactive power to support the voltage stability of the common connection point, as shown in Fig. 8 . Due to the recovery of the system voltage, the stator and rotor currents of DFIG also responded and were controlled within the expected range. The rise of the stator current was lower than twice the rated value, and the rotor current was basically controlled at the initial value, as shown in Figure 7. The addition of BESS control system enables the system to return to the initial value in time, the wind farm realizes low voltage ride through, and the system returns to stability.

The present invention dynamically tracks and controls its setting value by observing the voltage of the PCC point, adopts active and reactive power decoupling PI control algorithm, and considers the deficiency of traditional PI control dynamic difference, etc., and applies fuzzy control strategy to it. By tracking and controlling the voltage reference value of the grid-connected point, and adjusting the amplitude and phase of the modulation wave signal in the PWM control through the fuzzy PI controller, the modulation wave signal of the PWM control is obtained to achieve the purpose of low voltage ride-through control of the wind farm. The PWM control technology of the three-phase bridge circuit composed of fully-controlled power switching devices IGBT is adopted, which effectively reduces the reactive power loss of the converter, and is beneficial for the battery to participate in the low-voltage ride-through control of the system.

Claims (7)

1. A low-voltage ride-through control system for wind farms based on battery energy storage, characterized in that it includes a data collector (1), a data analyzer (2), a control module (3), a smooth control module (4), a battery Energy storage system (5), AC/DC converter (6), wind farm (7) and power grid (8), the data collector is connected to the data analyzer, and the data analyzer is connected to the control module (3) and a smoothing control module (4), the control module (3) and the smoothing control module (4) are both connected to the AC/DC converter (6), and the battery energy storage system (5) The AC/DC converter is connected, the wind farm (7) is connected to the power grid (8) and the AC/DC converter (6); the data collector (1) is used to collect (7) and the battery energy storage system (5) PCC point voltage Vpcc, and input the PCC point voltage Vpcc into the data analyzer (2); the data analyzer (2) is used to convert the PCC point voltage Vpcc is compared with the voltage setting value Vref of the PCC point: when Vpcc<Vref, the control module (3) plays a role, and the control module (3) controls the battery energy storage system (5) to put into low-voltage ride-through Control strategy; when Vpcc=Vref, the smoothing control module (4) plays a role, and the smoothing control module (4) controls the battery energy storage system (5) to put into a smoothing control strategy. 2. The low-voltage ride-through control system for wind farms based on battery energy storage according to claim 1, characterized in that the smoothing control module (4) includes a battery charge and discharge selector (12), and the wind farm (7) The output power P is compared with the maximum value Pmax and the minimum value Pmin of the set wind farm output power. When P>Pmax, the battery charge and discharge selector (12) controls the battery energy storage system (5) to charge; when P<Pmin , the battery charge and discharge selector (12) controls the discharge of the battery energy storage system (5), thereby realizing a smooth control strategy. 3. The low-voltage ride-through control system for wind farms based on battery energy storage according to claim 1, characterized in that the control module (3) includes a fuzzy PI controller (10), according to the dynamic change of the PCC point voltage Vpcc , use the fuzzy PI controller (10) to dynamically track the voltage set value Vref of the PCC point, adjust the amplitude and phase of the modulated wave controlled by PWM, obtain the modulated wave signal controlled by PWM and perform PWM control with the triangular carrier signal , so as to realize the low voltage ride through control strategy. 4. The low-voltage ride-through control system for wind farms based on battery energy storage according to claim 3, wherein the control module (3) further includes a PI regulator (9), and the active reference current _idref passes through the PI regulator (9) and increase the coupling voltage _id ωL to obtain the modulation wave amplitude A controlled by PWM, the active reference current _idref = P _ref /V, where V is the effective value of the battery output voltage, and P _ref is the active power reference value; the PCC point voltage Vpcc dynamically tracks the set value Vref, generates the reactive current reference value i _qref through the fuzzy PI controller (10), and then passes through the PI regulator (9) and increases the coupling voltage i _q ωL to obtain The modulated wave phase α controlled by PWM can be obtained through the above control to obtain the modulated wave signal Acos(ωt+α) controlled by PWM. 5. The low-voltage ride-through control system for wind farms based on battery energy storage according to claim 3, characterized in that the AC/DC converter (6) uses IGBT switches to combine the modulation wave signal controlled by PWM with the amplitude The triangular carrier signal with a value of ±1 is compared to obtain a pulse signal, and the pulse signal is a PWM control signal, and the PWM control signal is used to control the state of the IGBT switch of the AC/DC converter. 6. The low-voltage ride-through control system for wind farms based on battery energy storage according to claim 4, wherein the control module (3) further includes a fuzzy logic reasoner, and the fuzzy PI control method includes the following steps: 1) When the PCC point voltage is disturbed, an error e is generated; 2) Generate PI parameter adjustment increments ΔK _p and Δk _i through the fuzzy logic reasoner (11); 3), according to the formula $\left\{\begin{array}{c}{K}_p^{\&prime;}=K_p+{\mathrm{\&Delta;K}}_p\\ k_i^{\&prime;}=k_i+{\mathrm{\&Delta;k}}_i\end{array}\right.$ Adjust the PI parameter values K _p and k _i to obtain the parameter setting values K′ _p and k′ i of the fuzzy PI controller (10), and use the setting values K′ _p and k _{′ i as} the fuzzy PI regulator ( 10) New parameter values. 7. The low-voltage ride-through control system for wind farms based on battery energy storage according to claim 6, wherein the input and output of the fuzzy logic reasoner (11) both use triangular membership functions to establish fuzzy rules.

Images