CN106911143A - A kind of Inverter Station modeling power method after the locking suitable for extra-high voltage direct-current - Google Patents

Abstract

The invention discloses a kind of Inverter Station modeling power method after locking suitable for extra-high voltage direct-current, belong to power system modeling field.Demand of the present invention for receiving end grid side, according to the mechanism of the transfer of pole power and idle control after extra-high voltage direct-current locking, the active model modelling approach of Inverter Station and the idle model modelling approach under extra-high voltage direct-current latch status are proposed respectively, and furthermore present the parameter acquiring method in model.The modeling method has correctness and accuracy, can be applied to simulation study and the engineering of actual AC network electromechanical process.

Description

Inversion station power modeling method suitable for extra-high voltage direct current locked

Technical Field

The invention relates to the technical field of power system modeling, in particular to an inversion station power modeling method suitable for extra-high voltage direct current blocking.

Background

The ultra-high voltage direct current transmission (UHVDC) has the advantages of large transmission capacity, small transmission loss, long transmission distance and the like, is beneficial to realizing the optimized configuration of energy resources in China, is developed rapidly, and plays an important role in the strategy of 'West-east transmission' in China.

In daily operation, a direct current transmission system converter fault or a direct current line fault can cause a direct current system commutation failure or direct current blocking, in an alternating current and direct current series-parallel power grid, direct current and alternating current are mutually influenced, and a short-circuit fault on the side of an alternating current system can cause a direct current system commutation failure or even a direct current blocking fault. But after the locking occurs, the influence on the receiving end alternating current power grid is serious. After the extra-high voltage inverter station is locked, the influence on a receiving-end power grid is mainly caused by the great change of active power and reactive power output by the station.

At present, few researches are carried out on the output active power and reactive power of the inversion station after the ultrahigh voltage direct current blocking, and a model for describing the power change characteristic of the inversion station is lacked. Therefore, the output power model of the inverter station after locking is established, and the model is applied to simulation research and engineering of the electromechanical process of the actual alternating current power grid, so that necessary foundation can be provided for further researching the dynamic influence of the receiving-end power grid under the locking condition.

Disclosure of Invention

The invention aims to overcome the defects in the prior art, provides an inverter station power modeling method suitable for extra-high voltage direct current blocking, provides an inverter station active model modeling method and an inverter station reactive model modeling method under the extra-high voltage direct current blocking condition respectively, and can be applied to simulation research and engineering of the electromechanical process of an actual alternating current power grid.

In order to solve the technical problem, the invention provides a power modeling method of an inverter station suitable for extra-high voltage direct current blocking, which is characterized in that power comprises active power and reactive power, wherein the active power modeling process comprises the following steps:

step S11, completing inter-electrode power transfer after single-electrode locking, and calculating current reference value I required by healthy electrode_{ref sound pole}；

Step S12, the active power is the product of DC current and DC voltage when I_{ref sound pole}Not exceeding the maximum allowable rated current I_maxThe active output model is:

wherein, P₀Active power output by the inverter station during normal operation; t is t₀Time of day unipolar latching, P_minMinimum value of DC power after locking, tau is pole power transfer time, I_{ref sound pole}The corresponding pole voltage is voltage U_d1；

When I is_{ref sound pole}Exceeds the maximum allowable rated current I_maxThe active output model is:

wherein k is the overload operation multiple,t_kfor overload operation time, k.I_maxThe corresponding pole voltage is voltage U_d2；I_maxThe corresponding pole voltage is voltage U_d3；

The reactive power modeling process comprises the following steps:

step S21, in the pole power transfer process, the reactive power consumption value Q of the stage is determined according to the active power of different stages_c；

Step S22, calculating the compensation reactive power Q of the reactive equipment of the inverter station according to the number of the reactive compensation equipment groups in current operation_f；

Step S23, according to formula Q_i＝Q_f-Q_cCalculating output reactive Q of inverter station_i；

And step S24, judging whether the reactive power is in an allowable range according to a reactive power control strategy of the direct current system, switching the reactive power compensation equipment, repeating the process, and obtaining an output reactive model of the inverter station after the reactive power is not changed any more.

Further, the calculation formula of the current required by the healthy pole after the locking of the single pole is as follows:

wherein, P_refIs a reference value of polar power, P_{Loss of power}For transmission power of the faulty pole, U_{Bipolar junction}、U_{Health care pole}Respectively bipolar voltage and healthy voltage in operation.

Further, the inverter side reactive power consumption calculation formula is as follows:

wherein,for power factor of the inverting side, P_dIs active in DC, Q_cReactive power is consumed for the inverter side.

Further, the reactive power that can be provided by a single set of reactive power compensation devices is calculated by the following formula:

in the formula of U_i、U_NThe voltage of the alternating current system and the voltage of the rated alternating current system are respectively in normal operation; q_f0,Q_fNRespectively corresponding reactive power under the voltage of an alternating current system in normal operation and the reactive power under the voltage of a rated alternating current system;

then the reactive power calculation formula provided by the reactive power compensation equipment is as follows:

Q_f＝nQ_f0

in the formula, n is the number of reactive equipment groups which are currently put into operation.

Further, the reactive power control method comprises the following steps:

1) when Q is satisfied_f-Q_c≤Q_minWhen the reactive power provided by the reactive power equipment is not enough to compensate the reactive power consumed by the converter station, the converter station absorbs the reactive power from the alternating current system, the reactive power control sends a reactive power compensation device input command at the moment, and the time t passes₁Putting into reactive equipment;

2) when Q is satisfied_f-Q_c≥Q_maxWhen the reactive power provided by the reactive power equipment is not consumed by the reactive power surplus converter station, the converter station injects the surplus reactive power into the alternating current system, at the moment, the reactive power control sends out a reactive power compensation device cutting-off command, and the time t passes₂And then cutting off the reactive equipment.

Further, U_d1、U_d2、U_d3The values are determined from a direct current system control characteristic map.

Compared with the prior art, the invention has the following beneficial effects: the invention provides an output model of an inverter station after extra-high voltage direct current blocking on the basis of combining the pole power transfer and reactive power control principle after extra-high voltage direct current blocking. A specific time domain mathematical model is provided for the output active power of the inverter station, and a detailed reactive model modeling process is provided for the output reactive power of the inverter station. The model has certain correctness and validity, can be applied to simulation research and engineering of the electromechanical process of an actual alternating current power grid, and is beneficial to more effectively researching the influence of the extra-high voltage direct current blocking on a receiving-end power grid.

Drawings

FIG. 1 is a pole power transfer process after extra-high voltage DC single pole latching;

FIG. 2 is a basic control characteristic of an extra-high voltage DC transmission system;

FIG. 3 is a graph of change in current reference value for a healthy pole during pole power transfer;

FIG. 4 is a comparison of the active model and measured data established by the present invention;

FIG. 5 is a modeling flow of an inverter station reactive model;

fig. 6 is an inverter power characteristic diagram.

Detailed Description

The invention is further described below with reference to the accompanying drawings. The following examples are only for illustrating the technical solutions of the present invention more clearly, and the protection scope of the present invention is not limited thereby.

The invention discloses a power modeling method of an inverter station after extra-high voltage direct current blocking, wherein the power comprises active power and reactive power, and the active power modeling process comprises the following steps:

step S11, completing inter-electrode power transfer after single-electrode locking, and calculating current reference value I required by healthy electrode_{ref sound pole}；

The extra-high voltage direct current transmission system adopts a bipolar two-end neutral point grounding mode, and each pole adopts a wiring mode of connecting 2 12 pulse current converters in series. The bipolar (positive and negative) electrodes operate simultaneously, when a problem occurs in a device or system of one electrode, the electrode is called a fault electrode, and the corresponding other electrode is called a health electrode.

When the ultra-high voltage direct current system has monopolar locking, the function of interelectrode power transfer (PPT) is completed, namely the power of a fault electrode is transferred to a healthy electrode. The flow of transferring the power of the failed pole to the healthy pole is roughly as shown in fig. 1: receiving pole power reference value P of bipolar control layer_refThen, when one pole is locked, the fault pole is in a locked state, while the healthy pole is still in a bipolar power control mode, and in order to maintain the transmission power unchanged, the interpolar power transfer function loses the power P of the fault pole_{Loss of power}Sending to the health pole, which converts it into a current command I_{ref compensation}Current command I applied after the pole_{Original ref}To compensate for the lost transmission power. Finally, the bipolar control layer outputs the current command value I_{ref sound pole}To the converter control layer of the healthy pole.

Therefore, the calculation formula of the current required by the healthy pole after the monopolar locking is as follows:

wherein, P_refIs a reference value of polar power, P_{Loss of power}For transmission power of the faulty pole, U_{Bipolar junction}、U_{Health care pole}The parameters are bipolar voltage and healthy voltage in operation respectively, and can be directly obtained according to the current operation state of the direct current system.

And step S12, determining active power models of different stages in the pole power transfer process.

After the single pole is locked, the direct current voltage of the sound pole can generate certain change due to the change of the direct current under the control mode of the inverter station. As shown in the control characteristic diagram of fig. 2, the abscissa I_dRepresenting direct current, ordinate U_dRepresenting the DC voltage, α representing the firing angle of the rectifying side, gamma representing the arc-quenching angle of the inverting side, the basic control characteristic of the rectifying side consists of constant current characteristic (a straight line IC section in the figure) and constant antenna α₀Characteristic (JI segment) composition; the basic control characteristic of the inversion side consists of a constant voltage characteristic (BK section) and a constant current characteristic (BE section); in the normal state, the operating current is determined by the rectifier constant current characteristic, and the operating voltage is determined by the inverter constant voltage characteristic (i.e., point a in fig. 2).

At different stages of the pole power transfer process, the current reference of the healthy pole will change, as shown in FIG. 3, i.e., the IC representing the constant current control will move (to the dashed lines); the operating point a is therefore also moved to a ', a ", a'", the ordinate of the respective operating point representing the respective dc voltage. Therefore, the operating point a also changes, resulting in a change in the dc voltage. The active power of the dc is known as the product of the dc current and the dc voltage, and the variation of the dc voltage needs to be taken into account for the accuracy of the model.

The establishment criterion of the active model of the inverter station is the product of the direct current system current and the inverter station voltage. When I is_{ref sound pole}When the current is within the allowable range, I_{ref sound pole}Not exceeding the maximum allowable rated current I_maxThe active power output model of the inverter station after the monopole locking is obtained by the observation and summary of the existing engineering and is as follows:

the method comprises three stages: at t₀Before the moment, the direct current system is not locked, and the output active power of the inverter station is an initial value P₀(active power in normal operation); t is t₀The monopole locking happens at any moment, the power of the fault pole is reduced to 0 almost instantly, and the power of the healthy pole is reduced to the minimum power value P under the influence of the fault pole_minAt the same time, the pole power transfer function is acted, the active power begins to recover, the pole power transfer time is tau, and the pole power transfer time is from the lowest power value P_minThe process between the power values after the extreme power is finished is simulated by adopting a straight-line climbing process, and the slope isAfter a short time τ, i.e., after the pole power transfer is complete, the current reference value of the sound pole becomes I_{ref sound pole}At this time I_{ref sound pole}The corresponding pole voltage is voltage U_d1The active power at this stage is the product of these two values.

P_minFor the lowest power value to which the DC power is reduced after blocking, obtained from a large number of data analyses, P_minAnd P_{Health care}There is a certain fold relation, i.e. P_min＝λP_{Health care}，P_{Health care}This power value is the dc real power of the sound pole during normal operation (i.e., before latching), and is known during normal operation. When the healthy electrode is operated at full pressure, lambda is 0.6; when the sound stage is operating at half pressure, λ is 0.3. Voltage U_d1The values need to be determined from the dc system control map. τ represents the time for the pole power transfer to complete, which is short in practical engineering, typically several hundred milliseconds, and this parameter has little effect on the model and can be given as 0.15 s.

When I is_{ref sound pole}Exceeds the maximum allowable rated current I_maxAnd the active output model of the inverter station after the monopole locking is obtained by the observation and summary of the existing engineering and is as follows:

the method comprises four stages: at t₀Before time, DC systemIf the system is not locked, the output active power of the inverter station is an initial value P₀；t₀The monopole locking happens at any moment, the power of the fault pole is reduced to 0 almost instantly, and the power of the healthy pole is reduced to P under the influence of the fault pole_minAt the same time, the pole power transfer function is acted, the active power begins to recover, the pole power transfer time is tau, and the pole power transfer time is from the lowest power value P_minThe process between the active power values in the overload running state is simulated by adopting a straight-line climbing process, and the slope isAfter a short time τ, i.e. after the pole power transfer, in the overload operating state, the maximum permissible rated current I is k times as high as the sound pole_maxOperation t_kSecond, at this time k.I_maxThe corresponding pole voltage is voltage U_d2Active power is equal to direct current k.I_maxMultiplied by the direct voltage U_d2(ii) a Then the current is reduced back to the maximum rated current I_maxFinal stable phase of operation, at this time I_maxThe corresponding pole voltage is voltage U_d3Active equal to DC current I_maxMultiplied by the direct voltage U_d3。

Wherein, U_d2、U_d3Respectively, the DC reference value is k.I_max、I_maxVoltage of the corresponding direct current, U_d2、U_d3The values need to be determined from the dc system control map. Maximum allowable operating rated current I_maxOverload operation times k and overload operation times t_kThe parameters are set in the direct current engineering and can be directly obtained.

Actual measurement data of certain locking of a direct current project in the south of the river is used for corresponding to the model of the formula (3) to establish an active power model of the inverter station, the model is compared with the actual measurement data, and the result is shown in figure 4, so that the correctness and the effectiveness of the model are illustrated, and the change of the active power after locking can be accurately represented.

The process of modeling reactive power, as shown in fig. 5, includes the following steps:

step S21, in the pole power transfer process, the reactive power consumption value Q of the stage is determined according to the active power of different stages_c。

In the pole power transfer process, due to the large change of the direct current active power, the reactive power consumed by the converter station can also change along with the direct current active power. In the prior art, under the existing steady state condition, the inverter side reactive power consumption calculation formula is as follows:

wherein, U_dTo invert the side voltage, I_dIs direct current; u shape_iIs the alternating voltage of the current conversion bus; x_iIn order to change the current into the leakage reactance,for power factor of the inverting side, P_dIs active in DC, Q_cReactive power is consumed for the inverter side. That is, in the case where both the operation mode and the operation parameters are determined, the operation curve in which the consumed reactive power varies with the active power can be determined, and the curve of fig. 6 is a graph of the relationship between the active power and the reactive power on the inverter side under the constant γ -angle control according to this formula. I.e. there must be a certain reactive power consumption value for each active value. Thus, the reactive power consumption value for the different phases can be determined from the active power of this phase.

Step S22, calculating the compensation reactive power Q of the reactive equipment of the inverter station according to the number of the reactive compensation equipment groups in current operation_f。

The reactive power which can be provided by the single group of reactive power compensation devices is calculated by the following formula:

in the formula of U_i、U_NRespectively, the voltage of the AC system during normal operationAnd rated ac system voltage; q_f0,Q_fNRespectively corresponding reactive power under the voltage of the alternating current system in normal operation and the reactive power under the voltage of the rated alternating current system. Wherein Q_fN、U_NThe reactive power (or called rated compensation power) and the rated voltage of a single group of reactive compensation equipment under the rated voltage can be directly given by a user.

Further, the reactive power provided by the reactive power compensation equipment needs to be calculated according to the number of groups of reactive power compensation equipment currently put into operation, i.e. the reactive power provided by the reactive power compensation equipment is calculated according to the number of groups of reactive power compensation equipment currently put into operation

Q_f＝nQ_f0(6)

In the formula, n is the number of reactive equipment groups which are put into operation at present, and Q_f0And the reactive power is provided for the single group of reactive compensation devices under the current voltage.

Step S23, according to formula Q_i＝Q_f-Q_cCalculating output reactive Q of inverter station_i。

Calculating the reactive power output to the alternating current system by the inverter station according to the current reactive compensation capacity and the reactive power consumption of the inverter station, wherein the calculation formula is as follows:

Q_i＝Q_f-Q_c(7)

step S24, according to the reactive power control strategy of the DC system, judging whether the reactive power is in the allowable range (limit value [ Q ]_min,Q_max]) And switching reactive compensation equipment, repeating the processes, and obtaining the output reactive model of the inverter station after the reactive power is not changed any more.

As known, the reactive power control strategy in the prior art is:

1) when Q is satisfied_f-Q_c≤Q_minWhen the reactive power provided by the reactive power equipment is not enough to compensate the reactive power consumed by the converter station, the converter station absorbs the reactive power from the alternating current system, the reactive power control sends a reactive power compensation device input command at the moment, and the specified time t passes₁And then putting into reactive equipment.

2) When Q is satisfied_f-Q_c≥Q_maxWhen the reactive power provided by the reactive power equipment is not consumed by the reactive power surplus converter station, the converter station injects the surplus reactive power into the alternating current system, and at the moment, the reactive power control sends out a reactive power compensation device cutting-off command, and the specified time t passes₂And then cutting off the reactive equipment.

And then judging whether the reactive power is in an allowable range (limit value [ Q ]) according to a reactive power control strategy of the direct current system_min,Q_max]) And switching the reactive compensation equipment. Minimum switching group number and limit value Q in reactive switching strategy_min、Q_maxAnd switching time t₁、t₂All are set in the station control and can be directly obtained by the user.

Calculating the output reactive Q of the inverter station at each time point after the unipolar locking according to the time passage_i＝Q_f-Q_cAnd repeating the reactive power control strategy, and obtaining the output reactive power model of the inverter station after the reactive power is not changed any more.

The above description is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, several modifications and variations can be made without departing from the technical principle of the present invention, and these modifications and variations should also be regarded as the protection scope of the present invention.

Claims (6)

1. A power modeling method of an inverter station suitable for extra-high voltage direct current blocking is characterized in that power comprises active power and reactive power, wherein the active power modeling process comprises the following steps:

step S11, completing inter-electrode power transfer after single-electrode locking, and calculating current reference value I required by healthy electrode_{ref sound pole}；

Step S12, the active power is the product of DC current and DC voltage when I_{ref sound pole}Not exceeding the maximum allowable rated current I_maxThe active output model is:

wherein, P₀Active power output by the inverter station during normal operation; t is t₀Time of day unipolar latching, P_minMinimum value of DC power after locking, tau is pole power transfer time, I_{ref sound pole}The corresponding pole voltage is voltage U_d1；

When I is_{ref sound pole}Exceeds the maximum allowable rated current I_maxThe active output model is:

$P=\left\{\begin{array}{cc}{P}_0& t\∈\[0,t_0)\\ P_{\min }+(k\·I_{\max }\·U_{d2}-P_{\min })\·\frac{t-t_0}{\mathrm{\τ}}& t\∈\[t_0,t_0+\mathrm{\τ})\\ k\·I_{\max }\·U_{d2}& t\∈\[t_0+\mathrm{\τ},t_0+\mathrm{\τ}+t_k)\\ I_{\max }\·U_{d2}& t\∈\[t_0+\mathrm{\τ}+t_k,\mathrm{\∞})\end{array}\right.$

wherein k is the overload operation multiple, t_kFor overload operation time, k.I_maxThe corresponding pole voltage is voltage U_d2；I_maxThe corresponding pole voltage is voltage U_d3；

The reactive power modeling process comprises the following steps:

step S21, in the pole power transfer process, the reactive power consumption value Q of the stage is determined according to the active power of different stages_c；

Step S22, calculating the compensation reactive power Q of the reactive equipment of the inverter station according to the number of the reactive compensation equipment groups in current operation_f；

Step S23, according to formula Q_i＝Q_f-Q_cCalculating output reactive Q of inverter station_i；

And step S24, judging whether the reactive power is in an allowable range according to a reactive power control strategy of the direct current system, switching the reactive power compensation equipment, repeating the process, and obtaining an output reactive model of the inverter station after the reactive power is not changed any more.

2. The method for modeling the power of the inverter station after the ultra-high voltage direct current blocking according to claim 1, wherein a calculation formula of the current required by a healthy pole after the single-pole blocking is as follows:

wherein, P_refIs a reference value of polar power, P_{Loss of power}For transmission power of the faulty pole, U_{Bipolar junction}、U_{Health care pole}Respectively bipolar voltage and healthy voltage in operation.

3. The method for modeling the power of the inverter station after the extra-high voltage direct current blocking according to claim 1, wherein a reactive power consumption calculation formula at an inverter side is as follows:

wherein,for power factor of the inverting side, P_dIs active in DC, Q_cReactive power is consumed for the inverter side.

4. The modeling method for the power of the inverter station after the extra-high voltage direct current blocking according to claim 1, wherein the reactive power which can be provided by a single group of reactive power compensation devices is calculated by the following formula:

$Q_{f0}={\left(\frac{U_i}{U_N}\right)}^2{Q}_{fN}$

in the formula of U_i、U_NThe voltage of the alternating current system and the voltage of the rated alternating current system are respectively in normal operation; q_f0,Q_fNRespectively corresponding reactive power under the voltage of an alternating current system in normal operation and the reactive power under the voltage of a rated alternating current system;

then the reactive power calculation formula provided by the reactive power compensation equipment is as follows:

Q_f＝nQ_f0

in the formula, n is the number of reactive equipment groups which are currently put into operation.

5. The method for modeling the power of the inverter station after the extra-high voltage direct current blocking according to claim 1, wherein the reactive power control method comprises the following steps:

1) when Q is satisfied_f-Q_c≤Q_minWhen the reactive power provided by the reactive power equipment is not enough to compensate the reactive power consumed by the converter station, the converter station absorbs the reactive power from the alternating current system, the reactive power control sends a reactive power compensation device input command at the moment, and the time t passes₁Putting into reactive equipment;

2) when Q is satisfied_f-Q_c≥Q_maxWhen the reactive power provided by the reactive power equipment is not consumed by the reactive power surplus converter station, the converter station injects the surplus reactive power into the alternating current system, at the moment, the reactive power control sends out a reactive power compensation device cutting-off command, and the time t passes₂And then cutting off the reactive equipment.

6. The method for modeling the power of the inverter station after the ultra-high voltage direct current blocking according to claim 1, wherein U is used_d1、U_d2、U_d3The values are determined from a direct current system control characteristic map.