CN111628507A - A Novel Coordinated Control Method of Camera and SVG for Suppressing Transient Overvoltage - Google Patents

Abstract

The invention discloses a novel coordinated control method of a camera and an SVG for suppressing transient overvoltage. Aiming at the situation of transient overvoltage at the sending end caused by DC commutation failure and blocking fault, the following methods are proposed: During steady-state operation, optimize the dynamic reactive power reserve of the new type of camera and SVG, and when the fault occurs, it is based on the difference of commutation failure and blocking. In different situations, switch the working mode of the camera and SVG, supplemented by the switching control of the filter, especially using the SVG control link that introduces the voltage-current slope control, by controlling the two operating parameters of the SVG, on the basis of the voltage regulation of the new camera Improve the transient overvoltage suppression capability to achieve the ideal coordinated control effect. The invention effectively suppresses the transient overvoltage of the DC transmission end under the condition of DC transmission commutation failure/blocking, achieves a good coordinated control voltage capability, and reduces the off-grid phenomenon of the wind farm fans at the DC transmission end due to transient overvoltage .

Description

A Novel Coordinated Control Method of Camera and SVG for Suppressing Transient Overvoltage

technical field

The invention relates to the technical field of power systems, in particular to a novel coordinated control method for a camera and SVG for suppressing transient overvoltage

Background technique

Most of the UHVDC transmission ends in my country are weak transmission end systems developed by large-scale new energy sources such as wind power. In this case, new energy sources will be disconnected from the grid in a large area.

As a rotating device, the new camera can provide short-circuit capacity for the system, and the adjustment capacity is not affected by the system, and has unique advantages in providing large-capacity dynamic reactive power support. The new generation of new camera has been optimized in terms of transient response and overload capability, and currently has the fastest instantaneous reactive power support speed. However, the new type of camera has a single model, a large number of supporting equipment, a huge area, and the phase-advance capability is relatively poor compared with the late-phase capability and the response speed of its own excitation control system is slow, so the adjustment effect of voltage fluctuations in the face of continuous commutation failure is not ideal. , the new type of camera alone cannot completely solve the problem of new energy off-grid under the aforementioned fault conditions. And most of the current research is to install a new type of camera on the DC receiving end, and there is a lack of research and practical application on the DC sending end.

As the fastest reactive power compensation equipment in power electronics, SVG overcomes the shortcomings of traditional passive compensation devices such as slow response, large volume, large harmonics and loss. However, the reactive power regulation ability is still affected by the system, and the power electronic components have poor high voltage resistance. However, compared with the new camera, it has the advantages of flexible configuration capacity and small footprint. And it can quickly reach full power to absorb reactive power after the transient voltage rises, especially for the overvoltage suppression effect after DC blocking.

Due to the variety of power electronic equipment in the rectifier station, the installation of SVG has potential disturbance risks, and the new type of rectifier is currently only 300Mvar, which is suitable for high voltage levels, and its volume is not suitable for wind farms. Therefore, the new type of condenser can only be installed on the side of the rectifier station, and SVG is put into each wind farm for on-site compensation. However, how to coordinate the overall reactive power regulation mode of the new type of camera and SVG on the DC transmission side to achieve a good transient overvoltage suppression effect is an urgent problem to be solved at this stage.

SUMMARY OF THE INVENTION

Aiming at the defects or improvement needs of the prior art, the present invention provides a new type of camera and SVG coordinated control method for suppressing the transient overvoltage of the DC transmission terminal, which mainly includes proposing a new type of camera and SVG for suppressing the DC transmission terminal. The coordinated control method of transient pressure rise effect, and the specific parameters of the method are optimized and adjusted. The results show that the coordinated control method improves the reactive power support effect of the new type of condenser and SVG, reduces the transient overvoltage of the wind farm busbar near the DC transmission end, and reduces the low-voltage off-grid and high-voltage off-grid probability of fans, namely Improve the safety and stability of UHVDC transmission. For achieving the above object, the technical method adopted by the present invention is:

Step 1: On the side of the rectifier station, under the steady-state operating condition, the new type of condenser adopts the constant reactive power operation mode. Let the new type of rectifier take on a part of the reactive power required for the normal operation of the rectifier station. In order to ensure that the voltage fluctuation of the filter switching busbar is not more than 1%, the new type of camera needs to reserve a certain static reactive power reserve.

Step 2: Wind farm side: Under steady-state operating conditions, SVG adopts constant reactive power operation mode. Real-time monitoring of the wind farm bus voltage Us, compared to the wind farm bus voltage U _N required by the system, when Us < 0.95 _UN or Us > 1.01 _UN , the wind farm side SVG switches to constant voltage control with 1.0 _UN as the constant value, Otherwise, the voltage fluctuation that is considered acceptable is still controlled by constant reactive power. The SVG constant voltage control mode adopts the voltage regulation mode that introduces the slope characteristic. Set the SVG voltage-current control slope parameter adjuster to adjust the slope parameter K _D .

Step 3: When the commutation failure occurs in the DC transmission, the new type of inverter on the rectifier station side switches to the constant voltage control mode, and the new type of inverter uses its fast transient response capability to adjust the bus voltage of the rectifier station. If continuous commutation failure occurs, the filter on the rectifier station side starts to cut off at the second commutation failure, otherwise the rectifier station filter does not act.

Step 4: When the commutation failure occurs in the DC transmission, the SVG on the wind farm side enters the constant voltage control mode, and at the same time adjusts the SVG voltage-current control slope parameter to increase the SVG voltage-current control slope parameter K _D . When the voltage is lower than the reference value, the grid voltage reference value parameter U _ref of the SVG control system is appropriately increased; when the voltage is higher than the reference value, the grid voltage reference value parameter U _ref of the SVG control system is appropriately decreased.

Step 5: When DC blocking occurs, or commutation failure eventually leads to DC blocking, the voltage in the vicinity of the DC sending end presents a characteristic of "dramatic increase". The new type of condenser on the rectifier station side maintains the constant voltage control mode, absorbs excess reactive power, and at the same time the rectifier station cuts off the filter command.

Step 6: When DC blocking occurs, or the commutation failure eventually leads to DC blocking, the bus voltage of the wind farm also exhibits the characteristics of "dramatic increase". The SVG is maintained in the constant reactive power mode, and the SVG is controlled to work in a full perceptual saturation working state to absorb excess reactive power.

Control effect: The novel camera and SVG coordinated control method for suppressing transient overvoltage provided by the present invention has significant advantages:

(1) For the overall DC transmission end, a new type of condenser is installed in the rectifier station, and SVG is installed on the bus side of the wind farm to realize the optimal solution for spatial coordination of the overall reactive power compensation device at the DC transmission end. And the parameters of the new type of camera and SVG during steady-state operation are adjusted to effectively improve the standby dynamic reactive power capacity, so as to achieve the best effect of dealing with the transient voltage rise of the DC sending end.

(2) In view of the relatively weak phasing capability of the new type of camera, SVG is used to control the voltage of the wind farm’s generator-side busbar, and the new type of camera is used to further alleviate the transient state of the wind farm’s generator-side busbar under the condition of DC transmission commutation failure/DC blocking. The voltage mutation amplitude, through SVG, makes up for the adverse effect of the excitation control delay of the new type of camera. And the detailed adjustment of control parameters is carried out according to the actual operation of the wind farm, which can effectively reduce the off-grid rate of the DC sending end fans under the condition of commutation failure.

(3) While achieving on-site compensation for the rectifier station and SVG for the wind farm, respectively, the new type of condenser and SVG should be used to deal with the transient voltage rise of the DC transmission terminal. The operation mode under fault conditions achieves a good coordinated step-down effect, and takes into account the coordinated control of the new type of condenser and rectifier station filter, SVG and other reactive power sources in the wind farm.

Description of drawings

The technical solutions of the present invention will be further described in detail below with reference to the accompanying drawings.

Figure 1 SVG control model diagram with slope control introduced

Figure 2 is the SVG voltage-current characteristic curve

Figure 3 shows the variation of the fan bus voltage in the case of continuous commutation failure in the simulation results

Figure 4 is the simulation result of the change of the fan bus voltage in the case of DC blocking

Figure 5 shows the simulation results of the reactive power output of SVG and the new type of camera under the condition of DC blocking.

Detailed ways

In order to better understand the present invention, the content of the invention is described in detail below, and is explained in conjunction with the accompanying drawings, and a simulation example is given to verify the effect of the present invention.

Specifically include the following steps:

Step 1: On the side of the rectifier station, under the steady-state operating condition, the new type of condenser adopts the constant reactive power operation mode. Let the new type of rectifier take on a part of the reactive power required for the normal operation of the rectifier station. In order to ensure that the voltage fluctuation of the filter switching busbar is not more than 1%, the new type of camera needs to reserve a certain static reactive power reserve.

ΔQ=Q _f -(U _n ×1%)/k

In the formula: Q _f is the capacity of a single filter; k is the ratio of the voltage to the reactive power injected into the system, that is, the reactive voltage sensitivity coefficient; U _n is the AC bus voltage rating of the converter station. Therefore, the maximum and minimum values of the reactive power output of the new type of condenser are Q _max =S _n -ΔQ respectively

Q _min =S _j -ΔQ

In the formula, _Sn is the maximum retardation reactive power of the new-type camera; _Sj is the maximum phase-advancing reactive power of the new-type camera.

According to the reactive power compensation amount of the new type of rectifier, the input amount of the filter of the rectifier station is adjusted as follows:

Q _f =Q _R -S _n

In the formula: Q _f is the reactive power required by the filter; Q _R is the reactive power absorbed by the converter valve. The input amount of the filter is the reactive power absorbed by the converter valve minus the setting output of the new type of condenser. The converter station and the new type of condenser as a whole exchange reactive power close to 0 to the system. In this way, the input amount of the DC filter is reduced, so that the reactive power of the DC commutation failure/blocking excess is reduced, the instantaneous reactive power absorption of the new camera is guaranteed, and the transient overvoltage value in the case of DC commutation failure/blocking is further suppressed. . It avoids the problem of insufficient dynamic fallback reserve caused by the independent control filter and the new camera.

Step 2: Wind farm side: Under the steady-state operating condition, SVG adopts the constant reactive power operation mode to reduce the probability of abnormal oscillation of the voltage of the wind power collection system. It should be noted that when the wind farm system adjusts the SVG and the wind turbine in a steady state, due to the fast response of the SVG, the SVG is generally adjusted first, and the wind turbine is adjusted after the SVG adjustment capability is insufficient; however, considering the risk of DC commutation failure and blocking , SVG is required to provide reactive power to support the voltage of the grid-connected point, so SVG should leave a certain reactive power margin during the adjustment process, which is set to 50% of the total reactive power capacity, which is set as the optimal dynamic reactive power reserve point of SVG . Real-time monitoring of SVG grid-connected point voltage U _s , compared with the wind farm bus voltage U _N required by the system, when U _s < _0.95UN or U _s > _1.01UN , no matter whether commutation failure/blocking failure occurs on the DC side, the wind farm side SVGs are always converted to constant voltage control mode with 1.0U _N as constant value, otherwise the voltage fluctuation deemed acceptable will still be controlled by constant reactive power. The SVG constant voltage control mode adopts the voltage regulation mode that introduces the slope characteristic. Set the SVG voltage-current control slope parameter regulator. If there is no DC commutation failure/blocking failure, it is only voltage fluctuation, and the SVG voltage-current control slope parameter K _D takes 2%. Its control model is shown in Figure 1.

Step 3: When the commutation failure occurs in the DC transmission, the voltage in the vicinity of the DC transmission end exhibits the characteristic of "first decrease and then increase". The new rectifier station side switch is switched to the constant voltage control mode. The new rectifier rectifier uses its fast transient response capability to adjust the bus voltage of the rectifier station. The specific performance is: when the voltage drops, the new rectifier quickly emits a large amount of reactive power according to its strong excitation characteristics. Support the bus voltage of the rectifier station; when the voltage rises, the new type of condenser absorbs a large amount of reactive power in the system according to the instantaneous, reducing the busbar voltage of the rectifier station. If continuous commutation failure occurs, the filter on the rectifier station side starts to cut off at the second commutation failure, otherwise the rectifier station filter does not act.

Step 4: When the commutation failure occurs in the DC transmission, the bus voltage of the wind farm also exhibits the characteristic of “first decrease and then increase”. The SVG enters the constant voltage control mode, and adjusts the SVG voltage-current control slope parameter regulator at the same time, and increases the SVG voltage-current control slope parameter K _D to 5%. When the voltage is lower than the reference value, appropriately increase the grid voltage reference value parameter U _ref of the SVG control system to improve the SVG voltage-current characteristics, so that the SVG can quickly provide the maximum capacitive reactive current; when the voltage is higher than the reference value, Appropriately reduce the grid voltage reference parameter U _ref of the SVG control system to reduce the SVG voltage-current characteristics, so that the SVG can quickly provide the maximum inductive reactive current. The SVG voltage-current characteristic curve is shown in Figure 2 of the description. Combined with Figure 2 of the description, the advantages of the SVG introduced in this patent with slope control are explained:

(1) Adjust the same target to greatly reduce the constant reactive power capacity of the required SVG

(2) Prevent SVG from reaching the maximum limit of its output reactive power too frequently

(3) In the case of multiple SVGs running in parallel, it is beneficial to the reasonable distribution of their respective output reactive powers

Step 5: When DC blocking occurs, or commutation failure eventually leads to DC blocking, the voltage in the vicinity of the DC sending end presents a characteristic of "dramatic increase". The new type of condenser on the rectifier station side maintains the constant voltage control mode, absorbs excess reactive power, and at the same time the rectifier station cuts off the filter command.

Step 6: When DC blocking occurs, or the commutation failure eventually leads to DC blocking, the bus voltage of the wind farm also exhibits the characteristics of "dramatic increase". Check whether the filter branch in the wind farm is in operation. If the filter branch is in the enabled state, exit the filter branch first. The SVG is maintained in the constant reactive power mode, and the SVG is controlled to work in a full perceptual saturation working state to absorb excess reactive power.

According to the above-mentioned specific embodiment, the present invention provides the following simulation verification:

Simulation Verification 1:

According to the invention, a new type of condenser is installed on the AC side busbar of the rectifier station, and SVG is installed in some wind farms in the near area for coordinated control. Comparative analysis of the busbar voltages without adding a new type of condenser, adding a new type of condenser to the rectifier station, and adding a new type of condenser to the rectifier station and adding SVG to the near-area wind farm at the same time. 3. The simulation system takes the Jiuhu DC system and the wind farm near the Qilian converter station for simulation experiments.

Taking the Qilian converter station and its nearby Gan'an wind farm as an example, two new-type condensers were installed in the Qilian converter station, each with a capacity of 300MVA. SVG is installed on Gan'an 62S3, the exit bus of one of the wind farms, with a capacity of 60MVA. Simulate three consecutive commutation failures in Qishao DC, and compare and observe the voltage fluctuations of the bus Gan'an 62S3 in the original condition, only installing a new type of condenser at the Qishao converter station, and adding a new type of condenser at the rectifier station while adding SVG to the wind farm.

As shown in Figure 3 of the manual, it can be seen from the simulation results that when the first commutation failure occurs in 0.2 seconds, when a new type of camera is installed in the rectifier station, the minimum voltage of the first voltage fluctuation rises by 0.0108p.u., and the maximum voltage decreases. 0.0024p.u., but due to a certain delay in the excitation control system of the new camera and the existence of low excitation protection, when the second commutation failure in 0.6 seconds and the third commutation failure in 1.0 seconds come consecutively, the new camera can still be compared. It is good to lift the transient low voltage, but in the transient overvoltage condition it increases the bus voltage peak value by 0.0026p.u.

After the SVG is installed on the wind farm bus, under the coordinated control of the new camera and SVG, the minimum voltage rises by 0.0224p.u. and the maximum voltage decreases by 0.0124p.u. during the first commutation failure. It can quickly reach full capacity regulation, and the voltage regulation effect is much better than that of only the new type of camera.

Simulation verification 2:

Still taking the Qilian converter station and the busbar of the nearby Gan'an wind farm as examples, the Qishao DC blocking simulation is carried out. DC blocking occurs at the time of setting 2s. The simulation results are shown in Figure 4 of the manual. When the rectifier station is equipped with a new type of camera, the instantaneous voltage peak of Gan'an 62S3 busbar blocking is reduced by 0.0052p.u., and the peak value is further reduced by 0.0020p.u. after the wind farm busbar is installed with SVG, and the subsequent steady state The voltage is reduced by 0.0164p.u., which reflects the powerful control ability of the new camera combined with SVG to deal with transient voltage rise.

After the lockout, the reactive power output of the new type of camera and SVG is shown in Figure 5 of the manual. It can be seen that because the 300MVA new type of camera is under low excitation control, the reactive power is further controlled at 165Mvar, while the reactive power of the SVG during overvoltage exceeds more than 60Mvar, although the response speed is slightly slower than the new type of camera, it can quickly reach full power and absorb reactive power. The combination of the two has a good suppression effect on steady-state overvoltage after DC blocking.

The above are only examples of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention are included in the application for pending approval of the present invention. within the scope of the claims.

Claims (4)

1. A novel phase modulator and SVG coordinated control method for suppressing transient overvoltage is characterized in that: the method comprises a novel coordination control method for improving and suppressing the transient voltage rise effect of a direct current transmission end by using a phase modulator and an SVG (static var generator), and a parameter regulation scheme of the coordination control method.

2. The novel phase modulator and SVG coordinated operation control method of claim 1 for improving and suppressing transient voltage rise effect of DC transmitting end, comprising the steps of:

(1) on the side of the rectifier station, under the steady state operation condition, the novel phase modulator adopts a constant reactive power operation mode. Meanwhile, the novel phase modulator needs to keep certain static reactive power reserve.

(2) Wind farm side: under the steady-state operation condition, the SVG adopts a constant reactive power operation mode. Monitoring wind farm bus voltage Us in real time, comparing the system requirement wind farm bus voltage U_NWhen Us<0.95U_NOr Us>1.01U_NMeanwhile, the SVG at the wind power plant side is switched to 1.0U_NConstant voltage control for constant values, otherwise voltage fluctuations deemed acceptable are still subject to constant reactive power control. The SVG constant voltage control mode adopts a voltage regulation mode introducing slope characteristics.

(3) When the direct current transmission has phase commutation failure, the novel phase modulator at the rectifier station side is switched to a constant voltage control mode. And if continuous commutation fails, the filter on the side of the rectifier station starts to cut off when the commutation fails for the second time, otherwise, the filter of the rectifier station does not act.

(4) When the phase change failure occurs in the direct current power transmission, the SVG at the wind power plant side enters a constant voltage control mode, and simultaneously adjusts the SVG voltage-current control slope parameter adjuster to increase the SVG voltage-current control slope parameter K_D. And adjusting the power grid voltage reference value parameter U of the SVG control system according to the voltage_ref。

(5) When direct current blocking occurs, the novel phase modulator on the rectifier station side maintains a constant voltage control mode, and meanwhile, the rectifier station cuts off a filter instruction.

(6) When direct current blocking occurs, the SVG at the wind power plant side is maintained in a constant reactive power mode, and the SVG is controlled to work in a full-sensitivity saturated working state.

3. The parametric modulation scheme of claim 1: the method is characterized in that: the method comprises the following steps:

in the step (2), the SVG voltage-current control slope parameter regulator is set to regulate the slope parameter K_DThe content was 2%.

4. The parametric modulation scheme of claim 1: the method is characterized in that: the method comprises the following steps: in the step (4), the SVG voltage-current control slope parameter K is increased_DThe content was 5%.

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