A method and system for solving PV curve of receiving-end AC system

Abstract

The present invention relates to a PV curve solution method and system for a receiving-end AC system, comprising: setting the receiving-end AC system equivalent to an infinite power source connected in series with an impedance, establishing a mathematical model of a receiving-end inverter station and the receiving-end AC system, and iteratively solving the mathematical model of the receiving-end inverter station and the receiving-end AC system by using the principle that the bus voltages of the receiving-end inverter station and the receiving-end AC system are equal, obtaining the effective value of the commutation bus voltage in the receiving-end AC system at each moment in a control cycle and the active power and reactive power flowing from the receiving-end converter station to the receiving-end AC system at each moment; generating a PV curve of the receiving-end AC system within the control cycle according to the effective value of the commutation bus voltage in the receiving-end AC system at each moment in the control cycle and the active power and reactive power flowing from the receiving-end converter station to the receiving-end AC system at each moment; the technical solution provided by the present invention has fast calculation speed and high calculation accuracy, and can meet the control requirements of a DC system.

Description

Technical Field

[0001] The present invention relates to the technical field of direct current transmission of electric power systems, and in particular to a method and system for solving a PV curve of a receiving-end alternating current system. Background Art

[0002] With the rapid development of high voltage direct current (HVDC) technology, conventional high voltage direct current transmission based on line commutation converter (LCC) has been widely used at home and abroad.

[0003] According to the characteristics of energy and load distribution and grid planning, many power grids will become interconnected power grids containing "multi-infeed DC transmission systems". The commissioning of multiple UHV DC projects can solve the problem of insufficient power supply in the above-mentioned areas, but it also brings some new problems.

[0004] LCC-HVDC is a highly controllable system. The transmission power can change greatly in a short time. It is flexible in operation and has the ability of asynchronous networking. It has a wide range of applications in long-distance large-capacity power transmission and regional power grid interconnection. However, with the commissioning of more and more LCC-HVDC projects, my country's power grid has formed a large-scale AC / DC hybrid power grid, and the mutual influence between the AC system and the DC system is becoming more and more serious.

[0005] For example, when a large disturbance or operation occurs in the AC system, a conventional DC system may experience a commutation failure, which further affects the stability of the AC power grid. Commutation failure is one of the most common faults in conventional DC transmission systems. When the inverter is operating normally, each valve is turned on and off in turn to achieve AC-DC conversion. When a fault occurs in the AC system, the commutation bus voltage decreases. The valve that is scheduled to be turned on receives a trigger pulse and enters the commutation process. Due to the decrease in commutation voltage, the commutation overlap angle becomes larger. The pre-off valve withstands the reverse voltage for too short a time after the current is zero, and the insulation has not yet recovered or the commutation process has not yet been completed. The forward voltage is then subjected to re-conduction, resulting in a commutation failure. Once a commutation failure occurs in the inverter, its output DC voltage drops sharply, resulting in a sharp increase in DC current, which further increases the commutation overlap angle, and easily leads to a commutation failure. If correct control measures are not taken at this time, multiple commutation failures may occur, causing the DC system to be bipolar locked and power transmission interrupted.

[0006] The PV curve is a commonly used system characteristic curve in AC system analysis. It can well reflect the relationship between the node voltage and the transmitted power of the AC system. It is of great significance to the analysis of the AC system. At the same time, the PV curve can also be applied in LCC-HVDC transmission control.

[0007] Since the active power transmitted by LCC-HVDC converters in different control modes is different, the PV curve will change during system operation due to different operating conditions. Therefore, it is necessary to solve the characteristics of the receiving AC system to obtain a bus voltage characteristic curve with a certain degree of accuracy. Since the DC system control speed is relatively fast, a fast solution method for the PV curve is required.

[0008] The existing PV curve is mostly solved by the load growth method using an iterative method. It has high accuracy but slow calculation speed and is difficult to meet the control speed of the DC system. Summary of the invention

[0009] In view of the deficiencies in the prior art, the purpose of the present invention is to provide a PV curve solution method for a receiving-end AC system, which has fast calculation speed and high calculation accuracy and can meet the control requirements of a DC system.

[0010] The purpose of the present invention is achieved by adopting the following technical solutions:

[0011] The present invention provides a method for solving a PV curve of a receiving-end AC system, wherein the method comprises:

[0012] Step 1. Initialize the effective value of the commutation bus voltage in the receiving end AC system at time t and t=t0;

[0013] Step 2. Determine the active power and reactive power flowing into the receiving-end AC system from the receiving-end converter station at time t according to the effective value of the converter bus voltage in the receiving-end AC system at time t;

[0014] Step 3. Determine an estimated value of the effective value of the commutation bus voltage in the receiving-end AC system at time t according to the active power and reactive power flowing into the receiving-end AC system from the receiving-end converter station at time t;

[0015] Step 4. Compare the effective value of the commutation bus voltage in the receiving-end AC system at time t with the estimated value of the effective value of the commutation bus voltage in the receiving-end AC system at time t. If the comparison result satisfies the constraint condition, output the effective value of the commutation bus voltage in the receiving-end AC system at time t and the active power and reactive power flowing into the receiving-end AC system from the receiving-end converter station at time t. Otherwise, update the effective value of the commutation bus voltage in the receiving-end AC system at time t to the estimated value of the effective value of the commutation bus voltage in the receiving-end AC system at time t, and return to step 2.

[0016] Step 5. If t = t end , then use the effective value of the commutation bus voltage in the receiving-end AC system at each moment and the active power and reactive power flowing into the receiving-end AC system from the receiving-end converter station at each moment to generate the PV curve of the receiving-end AC system within the control period, otherwise, let t = t + 1, initialize the effective value of the commutation bus voltage in the receiving-end AC system at time t, and return to step 2;

[0017] Among them, t∈(t0,t end ), t0 is the start time of the control cycle, t end is the end time of the control cycle.

[0018] Preferably, the initialization of the effective value of the commutation bus voltage in the receiving-end AC system at time t includes:

[0019] Let the effective value of the commutation bus voltage in the receiving-end AC system at time t be equal to the rated value of the commutation bus voltage in the receiving-end AC system.

[0020] Preferably, the step 2 comprises: determining the active power P flowing into the receiving-end AC system from the receiving-end converter station at time t according to the following formula: ac (t):

[0021] P ac (t) = P dc (t)-P f (t)

[0022] Where P dc (t) is the active power output of the converter in the receiving-end converter station at time t, P f (t) is the active power absorbed by the reactive power compensation equipment and filter in the receiving-end converter station at time t;

[0023] The reactive power Q flowing into the receiving-end AC system from the receiving-end converter station at time t is determined as follows: ac (t):

[0024] Q dc (t) = Q f (t)-Q dc (t)

[0025] In the formula, Q dc (t) is the reactive power absorbed by the converter in the receiving-end converter station at time t, Q f (t) is the reactive power output by the reactive compensation equipment and filter in the receiving-end converter station at time t.

[0026] Furthermore, the active power P output by the converter in the receiving-end converter station at time t is determined by the following formula: dc (t):

[0027] P dc (t) = I dc (t)·U dc (t)

[0028] In the formula, I dc (t) is the DC current of the converter in the receiving-end converter station at time t, U dc(t) is the DC voltage of the converter in the receiving-end converter station at time t;

[0029] The reactive power Q absorbed by the converter in the receiving-end converter station at time t is determined as follows: dc (t):

[0030]

[0031] In the formula, is the power factor of the converter in the receiving-end converter station at time t;

[0032] The active power P absorbed by the reactive compensation equipment and filter in the receiving-end converter station at time t is determined by the following formula: f (t):

[0033] P f (t) = U1(t) 2 ·G

[0034] Where G is the conductance value of the reactive compensation equipment and filter in the receiving-end converter station, and U1(t) is the effective value of the converter bus voltage in the receiving-end AC system at time t;

[0035] The reactive power Q output by the reactive compensation equipment and filter in the receiving-end converter station at time t is determined as follows: f (t):

[0036] Q f (t) = U1(t) 2 ·B+Q RC

[0037] In the formula, Q RC is the reactive power value output by the dynamic reactive power compensation device in the receiving-end converter station, and B is the susceptance value of the reactive power compensation equipment and filter in the receiving-end converter station.

[0038] Furthermore, if the working mode of the converter in the receiving-end converter station at time t is that the rectifier-side current is constant and the inverter-side voltage is constant, then the DC current I of the converter in the receiving-end converter station at time t is dc (t) = I dcr , the DC voltage U of the converter in the receiving converter station at time t dc (t) = U dcr , and determine the power factor of the converter in the receiving end converter station at time t according to the following formula:

[0039]

[0040] In the formula, π is the pi, K is the transformation ratio of the grid side to the valve side of the converter in the receiving end converter station;

[0041] If the working mode of the converter in the receiving-end converter station at time t is that the current on the rectifier side is constant and the arc extinction angle on the inverter side is constant, then the DC current I of the converter in the receiving-end converter station at time t is dc (t) = I dcr , the arc extinction angle of the converter in the receiving end converter station at time t is γ(t) = γ ref , and determine the power factor of the converter in the receiving end converter station at time t according to the following formula:

[0042]

[0043] Determine the DC voltage U of the converter in the receiving-end converter station at time t as follows: dc (t):

[0044]

[0045] Where N is the number of 6-pulse converters per pole in the receiving converter station, X r2 is the equivalent commutation reactance of the converter in the receiving-end converter station;

[0046] If the working mode of the converter in the receiving-end converter station at time t is that the rectifier side power is constant and the inverter side voltage is constant, then the active power P output by the converter in the receiving-end converter station at time t is dc (t) = P dcr , the DC voltage U of the converter in the receiving converter station at time t dc (t) = U dcr , and determine the power factor of the converter in the receiving end converter station at time t according to the following formula:

[0047]

[0048] Where U dcr Set the voltage control reference value for the converter in the receiving-end converter station;

[0049] If the working mode of the converter in the receiving-end converter station at time t is that the rectifier side power is constant and the inverter side arc extinction angle is constant, then the active power P output by the converter in the receiving-end converter station at time t is dc (t) = P dcr , the arc extinction angle of the converter in the receiving end converter station at time t is γ(t) = γ ref , and determine the power factor of the converter in the receiving end converter station at time t according to the following formula:

[0050]

[0051] Among them, I dcr is the constant current control reference value of the converter in the receiving converter station, U dcris the reference value for the constant voltage control of the converter in the receiving converter station, γ ref P is the reference value for the arc extinction angle control of the converter in the receiving converter station. dcr Set the active power control reference value for the converter in the receiving converter station.

[0052] Preferably, the step 3 comprises: determining the estimated value U of the effective value of the commutation bus voltage in the receiving end AC system at the time t according to the following formula: s (t):

[0053]

[0054] Where P ac (t) is the active power flowing into the receiving-end AC system from the receiving-end converter station at time t, Q ac (t) is the reactive power flowing into the receiving-end AC system from the receiving-end converter station at time t, U1(t) is the effective value of the converter bus voltage in the receiving-end AC system at time t, δ(t) is the phase difference between the converter bus voltage in the receiving-end AC system and the voltage of the AC unit in the receiving-end AC system at time t, U2(t) is the effective value of the voltage of the AC unit in the receiving-end AC system at time t, R is the resistance value in the receiving-end AC system, and X is the reactance value in the receiving-end AC system.

[0055] Preferably, the constraint condition is:

[0056] |U s (t)-U1(t)|<10 -5

[0057] Where U1(t) is the effective value of the commutation bus voltage in the receiving end AC system at time t, and U s (t) is the estimated value of the effective value of the commutation bus voltage in the receiving-end AC system at time t.

[0058] The present invention provides a PV curve solution system for a receiving-end AC system, wherein the improvement is that the system comprises:

[0059] An initialization module is used to initialize the effective value of the commutation bus voltage in the receiving end AC system at time t and t=t0;

[0060] The first determination module is used to determine the active power and reactive power flowing into the receiving-end AC system from the receiving-end converter station at time t according to the effective value of the converter bus voltage in the receiving-end AC system at time t;

[0061] The second determination module is used to determine the estimated value of the effective value of the commutation bus voltage in the receiving-end AC system at time t according to the active power and reactive power flowing into the receiving-end AC system from the receiving-end converter station at time t;

[0062] A comparison module is used to compare the effective value of the commutation bus voltage in the receiving-end AC system at time t with the estimated value of the effective value of the commutation bus voltage in the receiving-end AC system at time t. If the comparison result satisfies the constraint condition, the effective value of the commutation bus voltage in the receiving-end AC system at time t and the active power and reactive power flowing into the receiving-end AC system from the receiving-end converter station at time t are output; otherwise, the effective value of the commutation bus voltage in the receiving-end AC system at time t is updated to the estimated value of the effective value of the commutation bus voltage in the receiving-end AC system at time t, and the process returns to step 2;

[0063] Generate module for if t=t end , then use the effective value of the commutation bus voltage in the receiving-end AC system at each moment and the active power and reactive power flowing into the receiving-end AC system from the receiving-end converter station at each moment to generate the PV curve of the receiving-end AC system within the control period, otherwise, let t = t + 1, initialize the effective value of the commutation bus voltage in the receiving-end AC system at time t, and return to step 2;

[0064] Among them, t∈(t0,t end ), t0 is the start time of the control cycle, t end is the end time of the control cycle.

[0065] Preferably, the initialization of the effective value of the commutation bus voltage in the receiving-end AC system at time t includes:

[0066] Let the effective value of the commutation bus voltage in the receiving-end AC system at time t be equal to the rated value of the commutation bus voltage in the receiving-end AC system.

[0067] Preferably, the first determining module is used to: determine the active power P flowing into the receiving-end AC system from the receiving-end converter station at time t according to the following formula: ac (t):

[0068] P ac (t) = P dc (t)-P f (t)

[0069] Where P dc (t) is the active power output of the converter in the receiving-end converter station at time t, P f (t) is the active power absorbed by the reactive power compensation equipment and filter in the receiving-end converter station at time t;

[0070] The reactive power Q flowing into the receiving-end AC system from the receiving-end converter station at time t is determined as follows: ac (t):

[0071] Q dc (t) = Q f (t)-Q dc (t)

[0072] In the formula, Q dc (t) is the reactive power absorbed by the converter in the receiving-end converter station at time t, Q f (t) is the reactive power output by the reactive compensation equipment and filter in the receiving-end converter station at time t.

[0073] Furthermore, the active power P output by the converter in the receiving-end converter station at time t is determined by the following formula: dc (t):

[0074] P dc (t) = I dc (t)·U dc (t)

[0075] In the formula, I dc (t) is the DC current of the converter in the receiving-end converter station at time t, U dc (t) is the DC voltage of the converter in the receiving-end converter station at time t;

[0076] The reactive power Q absorbed by the converter in the receiving-end converter station at time t is determined as follows: dc (t):

[0077]

[0078] In the formula, is the power factor of the converter in the receiving-end converter station at time t;

[0079] The active power P absorbed by the reactive compensation equipment and filter in the receiving-end converter station at time t is determined by the following formula: f (t):

[0080] P f (t) = U1(t) 2 ·G

[0081] Where G is the conductance value of the reactive compensation equipment and filter in the receiving-end converter station, and U1(t) is the effective value of the converter bus voltage in the receiving-end AC system at time t;

[0082] The reactive power Q output by the reactive compensation equipment and filter in the receiving-end converter station at time t is determined as follows: f (t):

[0083] Q f (t) = U1(t) 2 ·B+Q RC

[0084] In the formula, Q RC is the reactive power value output by the dynamic reactive power compensation device in the receiving-end converter station, and B is the susceptance value of the reactive power compensation equipment and filter in the receiving-end converter station.

[0085] Furthermore, if the working mode of the converter in the receiving-end converter station at time t is that the rectifier-side current is constant and the inverter-side voltage is constant, then the DC current I of the converter in the receiving-end converter station at time t is dc (t) = I dcr , the DC voltage U of the converter in the receiving converter station at time t dc (t) = U dcr , and determine the power factor of the converter in the receiving end converter station at time t according to the following formula:

[0086]

[0087] In the formula, π is the pi, K is the transformation ratio of the grid side to the valve side of the converter in the receiving end converter station;

[0088] If the working mode of the converter in the receiving-end converter station at time t is that the current on the rectifier side is constant and the arc extinction angle on the inverter side is constant, then the DC current I of the converter in the receiving-end converter station at time t is dc (t) = I dcr , the arc extinction angle of the converter in the receiving end converter station at time t is γ(t) = γ ref , and determine the power factor of the converter in the receiving end converter station at time t according to the following formula:

[0089]

[0090] Determine the DC voltage U of the converter in the receiving-end converter station at time t as follows: dc (t):

[0091]

[0092] Where N is the number of 6-pulse converters per pole in the receiving converter station, X r2 is the equivalent commutation reactance of the converter in the receiving-end converter station;

[0093] If the working mode of the converter in the receiving-end converter station at time t is that the rectifier side power is constant and the inverter side voltage is constant, then the active power P output by the converter in the receiving-end converter station at time t is dc (t) = P dcr , the DC voltage U of the converter in the receiving converter station at time t dc (t) = U dcr , and determine the power factor of the converter in the receiving end converter station at time t according to the following formula:

[0094]

[0095] Where U dcr Set the voltage control reference value for the converter in the receiving-end converter station;

[0096] If the working mode of the converter in the receiving-end converter station at time t is that the rectifier side power is constant and the inverter side arc extinction angle is constant, then the active power P output by the converter in the receiving-end converter station at time t is dc (t) = P dcr , the arc extinction angle of the converter in the receiving end converter station at time t is γ(t) = γ ref , and determine the power factor of the converter in the receiving end converter station at time t according to the following formula:

[0097]

[0098] Among them, I dcr is the constant current control reference value of the converter in the receiving converter station, U dcr is the reference value for the constant voltage control of the converter in the receiving converter station, γ ref P is the reference value for the arc extinction angle control of the converter in the receiving converter station. dcr Set the active power control reference value for the converter in the receiving converter station.

[0099] Preferably, the second determination module is used to: determine the estimated value U of the effective value of the commutation bus voltage in the receiving-end AC system at time t according to the following formula: s (t):

[0100]

[0101] Where P ac (t) is the active power flowing into the receiving-end AC system from the receiving-end converter station at time t, Q ac (t) is the reactive power flowing into the receiving-end AC system from the receiving-end converter station at time t, U1(t) is the effective value of the converter bus voltage in the receiving-end AC system at time t, δ(t) is the phase difference between the converter bus voltage in the receiving-end AC system and the voltage of the AC unit in the receiving-end AC system at time t, U2(t) is the effective value of the voltage of the AC unit in the receiving-end AC system at time t, R is the resistance value in the receiving-end AC system, and X is the reactance value in the receiving-end AC system.

[0102] Preferably, the constraint condition is:

[0103] |U s (t)-U1(t)|<10 -5

[0104] Where U1(t) is the effective value of the commutation bus voltage in the receiving end AC system at time t, and U s (t) is the estimated value of the effective value of the commutation bus voltage in the receiving-end AC system at time t.

[0105] Compared with the closest prior art, the present invention has the following beneficial effects:

[0106] The technical solution provided by the present invention comprises the following steps: step 1. initializing the effective value of the commutation bus voltage in the receiving-end AC system at time t and t=t0; step 2. determining the active power and reactive power flowing into the receiving-end AC system from the receiving-end converter station at time t according to the effective value of the commutation bus voltage in the receiving-end AC system at time t; step 3. determining the estimated value of the effective value of the commutation bus voltage in the receiving-end AC system at time t according to the active power and reactive power flowing into the receiving-end AC system from the receiving-end converter station at time t; step 4. comparing the effective value of the commutation bus voltage in the receiving-end AC system at time t with the estimated value of the effective value of the commutation bus voltage in the receiving-end AC system at time t, and if the comparison result satisfies the constraint condition, outputting the effective value of the commutation bus voltage in the receiving-end AC system at time t and the active power and reactive power flowing into the receiving-end AC system from the receiving-end converter station at time t, otherwise, updating the effective value of the commutation bus voltage in the receiving-end AC system at time t to the estimated value of the effective value of the commutation bus voltage in the receiving-end AC system at time t, and returning to step 2; step 5. if t=t end , the PV curve of the receiving-end AC system within the control period is generated by using the effective value of the commutation bus voltage in the receiving-end AC system at each moment and the active power and reactive power flowing into the receiving-end AC system from the receiving-end converter station at each moment. Otherwise, let t = t + 1, initialize the effective value of the commutation bus voltage in the receiving-end AC system at time t, and return to step 2; the above scheme introduces the commutation bus voltage into the DC control system, which can quickly adjust the DC power generation active power reference value, reduce the probability of LCC-HVDC commutation failure, and facilitate LCC-HVDC power transmission after the AC system fails. At the same time, the strength of the receiving-end AC system is introduced into the PV curve, which can be used to analyze the impact of the strength of the AC system on the commutation failure. BRIEF DESCRIPTION OF THE DRAWINGS

[0107] Figure 1 It is a flow chart of the method for solving the PV curve of the receiving-end AC system;

[0108] Figure 2 is a connection structure diagram of a receiving-end converter and a receiving-end AC system in an embodiment of the present invention;

[0109] Figure 3 It is a schematic diagram of the structure of reactive power compensation equipment and filter in a receiving-end converter station in an embodiment of the present invention;

[0110] Figure 4 is a structural diagram of a receiving-end AC system in an embodiment of the present invention;

[0111] Figure 5a -5d is a schematic diagram of the PV curve of the receiving-end AC system of control mode 1-4 in the embodiment of the present invention;

[0112] Figure 6It is a structural diagram of the PV curve solution system of the receiving-end AC system. DETAILED DESCRIPTION

[0113] The specific implementation modes of the present invention will be further described in detail below in conjunction with the accompanying drawings.

[0114] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0115] The present invention provides a method for solving the PV curve of a receiving-end AC system, such as Figure 1 As shown, the method includes:

[0116] Step 101. Initialize the effective value of the commutation bus voltage in the receiving end AC system at time t and t=t0;

[0117] Step 102: Determine the active power and reactive power flowing into the receiving-end AC system from the receiving-end converter station at time t according to the effective value of the converter bus voltage in the receiving-end AC system at time t;

[0118] Step 103: Determine an estimated value of the effective value of the converter bus voltage in the receiving-end AC system at time t according to the active power and reactive power flowing into the receiving-end AC system from the receiving-end converter station at time t;

[0119] Step 104. Compare the effective value of the commutation bus voltage in the receiving-end AC system at time t with the estimated value of the effective value of the commutation bus voltage in the receiving-end AC system at time t. If the comparison result satisfies the constraint condition, output the effective value of the commutation bus voltage in the receiving-end AC system at time t and the active power and reactive power flowing into the receiving-end AC system from the receiving-end converter station at time t. Otherwise, update the effective value of the commutation bus voltage in the receiving-end AC system at time t to the estimated value of the effective value of the commutation bus voltage in the receiving-end AC system at time t, and return to step 2.

[0120] Step 105. If t = t end , then use the effective value of the commutation bus voltage in the receiving-end AC system at each moment and the active power and reactive power flowing into the receiving-end AC system from the receiving-end converter station at each moment to generate the PV curve of the receiving-end AC system within the control period, otherwise, let t = t + 1, initialize the effective value of the commutation bus voltage in the receiving-end AC system at time t, and return to step 2;

[0121] Among them, t∈(t0,t end ), t0 is the start time of the control cycle, tend is the end time of the control cycle.

[0122] Specifically, the initialization of the effective value of the commutation bus voltage in the receiving-end AC system at time t includes:

[0123] Let the effective value of the commutation bus voltage in the receiving-end AC system at time t be equal to the rated value of the commutation bus voltage in the receiving-end AC system.

[0124] Specifically, the step 2 includes: determining the active power P flowing into the receiving-end AC system from the receiving-end converter station at time t according to the following formula: ac (t):

[0125] P ac (t) = P dc (t)-P f (t)

[0126] Where P dc (t) is the active power output of the converter in the receiving-end converter station at time t, P f (t) is the active power absorbed by the reactive power compensation equipment and filter in the receiving-end converter station at time t;

[0127] The reactive power Q flowing into the receiving-end AC system from the receiving-end converter station at time t is determined as follows: ac (t):

[0128] Q dc (t) = Q f (t)-Q dc (t)

[0129] In the formula, Q dc (t) is the reactive power absorbed by the converter in the receiving-end converter station at time t, Q f (t) is the reactive power output by the reactive compensation equipment and filter in the receiving-end converter station at time t.

[0130] Furthermore, the active power P output by the converter in the receiving-end converter station at time t is determined by the following formula: dc (t):

[0131] P dc (t) = I dc (t)·U dc (t)

[0132] In the formula, I dc (t) is the DC current of the converter in the receiving-end converter station at time t, U dc (t) is the DC voltage of the converter in the receiving-end converter station at time t;

[0133] The reactive power Q absorbed by the converter in the receiving-end converter station at time t is determined as follows: dc(t):

[0134]

[0135] In the formula, is the power factor of the converter in the receiving-end converter station at time t;

[0136] In the preferred embodiment of the present invention, Figure 2 As shown in the figure, the receiving-end converter station is directly connected to the receiving-end AC system; the voltage amplitude of the converter bus in the receiving-end converter station is not only related to the parameters of the receiving-end AC system, but also to the power flowing into the AC system through the converter bus. Therefore, it is necessary to derive the reactive power absorbed when the converter transmits different active powers, and then solve the active and reactive powers transmitted by the converter station to the AC system, so as to solve the converter bus voltage.

[0137] The active power P absorbed by the reactive compensation equipment and filter in the receiving-end converter station at time t is determined by the following formula: f (t):

[0138] P f (t) = U1(t) 2 ·G

[0139] Where G is the conductance value of the reactive compensation equipment and filter in the receiving-end converter station, and U1(t) is the effective value of the converter bus voltage in the receiving-end AC system at time t;

[0140] The reactive power Q output by the reactive compensation equipment and filter in the receiving-end converter station at time t is determined as follows: f (t):

[0141] Q f (t) = U1(t) 2 ·B+Q RC

[0142] In the formula, Q RC is the reactive power value output by the dynamic reactive power compensation device in the receiving-end converter station, and B is the susceptance value of the reactive power compensation equipment and filter in the receiving-end converter station.

[0143] In a specific embodiment of the present invention, in the Cigre benchmark HVDC direct current transmission model, the filter and reactive power compensation device are composed of resistors, inductors and capacitors. The specific topology is as follows: Figure 3 As shown;

[0144] The filters in the converter station are all passive filters, which are composed of capacitors, reactances and resistors in series and parallel. Most DC system reactive compensation devices use fixed capacitor compensation. Therefore, the reactive compensation and filter in the converter station can be equivalent to a constant impedance or constant admittance. The active power absorbed and the reactive power emitted are related to the AC voltage amplitude at its access point. If the equivalent admittance of the reactive compensation and filter connected in the DC converter station is Y=G+jB, G is the conductance value and B is the susceptance value. F and Q F The expressions are:

[0145]

[0146] In the above formula, all reference directions are positive when outflowing from the system and negative when inflowing into the system. Figure 2 If the converter station includes a dynamic reactive power compensation device such as SVC, and the reactive power it generates is Q RC , then the above formula can be rewritten as:

[0147]

[0148] When the DC power is reduced in transient state, the reactive power demand of the converter is reduced. The excess reactive power of the reactive compensation device and the filter enters the AC system, which increases the voltage of the commutation bus. There is no need to switch the filter and reactive compensation device when the DC power is reduced. Therefore, in the calculation process, the equivalent admittance Y is a constant.

[0149] Furthermore, if the working mode of the converter in the receiving-end converter station at time t is that the rectifier-side current is constant and the inverter-side voltage is constant, then the DC current I of the converter in the receiving-end converter station at time t is dc (t) = I dcr , the DC voltage U of the converter in the receiving converter station at time t dc (t) = U dcr , and determine the power factor of the converter in the receiving end converter station at time t according to the following formula:

[0150]

[0151] In the formula, π is the pi, K is the transformation ratio of the grid side to the valve side of the converter in the receiving end converter station;

[0152] If the working mode of the converter in the receiving-end converter station at time t is that the current on the rectifier side is constant and the arc extinction angle on the inverter side is constant, then the DC current I of the converter in the receiving-end converter station at time t is dc (t) = I dcr , the arc extinction angle of the converter in the receiving end converter station at time t is γ(t) = γ ref , and determine the power factor of the converter in the receiving end converter station at time t according to the following formula:

[0153]

[0154] Determine the DC voltage U of the converter in the receiving-end converter station at time t as follows: dc (t):

[0155]

[0156] Where N is the number of 6-pulse converters per pole in the receiving converter station, X r2 is the equivalent commutation reactance of the converter in the receiving-end converter station;

[0157] If the working mode of the converter in the receiving-end converter station at time t is that the rectifier side power is constant and the inverter side voltage is constant, then the active power P output by the converter in the receiving-end converter station at time t is dc (t) = P dcr , the DC voltage U of the converter in the receiving converter station at time t dc (t) = U dcr , and determine the power factor of the converter in the receiving end converter station at time t according to the following formula:

[0158]

[0159] Where U dcr Set the voltage control reference value for the converter in the receiving-end converter station;

[0160] If the working mode of the converter in the receiving-end converter station at time t is that the rectifier side power is constant and the inverter side arc extinction angle is constant, then the active power P output by the converter in the receiving-end converter station at time t is dc (t) = P dcr , the arc extinction angle of the converter in the receiving end converter station at time t is γ(t) = γ ref , and determine the power factor of the converter in the receiving end converter station at time t according to the following formula:

[0161]

[0162] Among them, I dcr is the constant current control reference value of the converter in the receiving converter station, U dcr is the reference value for the constant voltage control of the converter in the receiving converter station, γ ref P is the reference value for the arc extinction angle control of the converter in the receiving converter station. dcr Set the active power control reference value for the converter in the receiving converter station.

[0163] In a specific embodiment of the present invention, the converter in the receiving-end converter station has four working modes, as shown in Table 1:

[0164] Table 1

[0165] Control method 1 2 3 4 Rectification side Constant current Constant current Constant power Constant power Inverter side Constant voltage Fixed arc extinction angle Constant voltage Fixed arc extinction angle

[0166] Under the same receiving-end AC system bus voltage, the working modes of the converters in the receiving-end converter station are different, and the active power and reactive power input from the receiving-end converter station to the receiving-end AC system are different.

[0167] Specifically, the step 3 includes: determining the estimated value U of the effective value of the commutation bus voltage in the receiving-end AC system at time t according to the following formula: s (t):

[0168]

[0169] Where P ac (t) is the active power flowing into the receiving-end AC system from the receiving-end converter station at time t, Q ac (t) is the reactive power flowing into the receiving-end AC system from the receiving-end converter station at time t, U1(t) is the effective value of the converter bus voltage in the receiving-end AC system at time t, δ(t) is the phase difference between the converter bus voltage in the receiving-end AC system and the voltage of the AC unit in the receiving-end AC system at time t, U2(t) is the effective value of the voltage of the AC unit in the receiving-end AC system at time t, R is the resistance value in the receiving-end AC system, and X is the reactance value in the receiving-end AC system.

[0170] In a specific embodiment of the present invention, the receiving end communication system is as follows: Figure 4 As shown in the figure, it can be seen that it is necessary to derive the infinite AC system voltage Active power P ac and reactive power Q ac Under known conditions, calculate the voltage at the commutation bus The calculation expression of the estimated value of the effective value of the commutation bus voltage in the receiving end AC system at the time t is determined as follows: s The specific process of (t) can be:

[0171] At time t, the active power P flowing into the receiving-end AC system from the receiving-end converter station ac (t); the reactive power Q flowing into the receiving-end AC system from the receiving-end converter station at time t ac (t), so the power S flowing into the receiving-end AC system from the receiving-end converter station at time t satisfies S=P ac (t)+jQ ac (t);

[0172] And because the power S flowing into the receiving-end AC system from the receiving-end converter station at time t satisfies:

[0173]

[0174] Therefore, the following equation relationship is established according to the above formula:

[0175]

[0176] By transforming the above formula, we can get:

[0177]

[0178] Rearranging the above formula, we can get:

[0179] Eliminating δ(t) in the above formula, we can get:

[0180] Simplifying, we get:

[0181]

[0182] Specifically, the constraints are:

[0183] |U s (t)-U1(t)|<10 -5

[0184] Where U1(t) is the effective value of the commutation bus voltage in the receiving end AC system at time t, and U s (t) is the estimated value of the effective value of the commutation bus voltage in the receiving-end AC system at time t.

[0185] In a specific embodiment of the present invention, in the Cigre Benchmark HVDC model in PSCAD / EMTDC, the AC system parameters are shown in Table 2:

[0186] Table 2

[0187]

[0188] By adjusting the constant current control reference value of the converter in the receiving-end converter station, the constant voltage control reference value of the converter in the receiving-end converter station, the constant arc extinction angle control reference value of the converter in the receiving-end converter station, and the constant active power control reference value of the converter in the receiving-end converter station, the active power flowing into the AC system through the converter bus is adjusted. The reactive power is not controlled, and the reactive power flowing into the AC system from the converter station is automatically calculated by the reactive balance in the converter station. Therefore, R, X, U2, and Q are known, and can be calculated by the formula:

[0189]

[0190] Output the PV curve of the commutation bus.

[0191] The accuracy of the technical solution of the present invention is verified, and the verification model is the Cigre_benchmark DC transmission system model, which is an earth return line monopole DC transmission system.

[0192] In the HVDC model of PSCAD / EMTDC, the relationship between the converter bus voltage in the receiving converter station and the DC system transmission power under different control modes is measured according to the control mode combinations listed in Table 1, and compared with the simulation measurement results to verify the calculation accuracy.

[0193] The comparison between simulation and calculation results is shown in Figure 5:

[0194] Figure 5(a)-Figure 5(d) They are respectively a PV curve at the commutation bus of the PSCAD model corresponding to when the working mode of the converter of the receiving-end converter station is control mode 1 to control mode 4 and a schematic diagram of the PV curve at the commutation bus using the technical solution of the present invention;

[0195] It is easy to see from the figure that when the fixed DC voltage control method is adopted at the receiving end, the calculation method provided by the technical solution of the present invention has a high accuracy, and the difference is basically between -2% and 0. However, when the fixed arc extinction angle control is adopted at the receiving end, the accuracy is lower, but it still remains between -4% and 0. And the above four control methods have good accuracy when close to the rated operating conditions. Therefore, it can be concluded from the above figure that no matter what control method is used, within the DC power transmission range, the AC voltage obtained by calculation is basically consistent with the PSCAD simulation, and can be applied to PV curve control.

[0196] The present invention provides a PV curve solution system for a receiving-end AC system, such as Figure 6 As shown, the system comprises:

[0197] An initialization module is used to initialize the effective value of the commutation bus voltage in the receiving end AC system at time t and t=t0;

[0198] The first determination module is used to determine the active power and reactive power flowing into the receiving-end AC system from the receiving-end converter station at time t according to the effective value of the converter bus voltage in the receiving-end AC system at time t;

[0199] The second determination module is used to determine the estimated value of the effective value of the commutation bus voltage in the receiving-end AC system at time t according to the active power and reactive power flowing into the receiving-end AC system from the receiving-end converter station at time t;

[0200] A comparison module is used to compare the effective value of the commutation bus voltage in the receiving-end AC system at time t with the estimated value of the effective value of the commutation bus voltage in the receiving-end AC system at time t. If the comparison result satisfies the constraint condition, the effective value of the commutation bus voltage in the receiving-end AC system at time t and the active power and reactive power flowing into the receiving-end AC system from the receiving-end converter station at time t are output; otherwise, the effective value of the commutation bus voltage in the receiving-end AC system at time t is updated to the estimated value of the effective value of the commutation bus voltage in the receiving-end AC system at time t, and the process returns to step 2;

[0201] Generate module for if t=t end , then use the effective value of the commutation bus voltage in the receiving-end AC system at each moment and the active power and reactive power flowing into the receiving-end AC system from the receiving-end converter station at each moment to generate the PV curve of the receiving-end AC system within the control period, otherwise, let t = t + 1, initialize the effective value of the commutation bus voltage in the receiving-end AC system at time t, and return to step 2;

[0202] Among them, t∈(t0,t end ), t0 is the start time of the control cycle, t end is the end time of the control cycle.

[0203] Specifically, the initialization of the effective value of the commutation bus voltage in the receiving-end AC system at time t includes:

[0204] Let the effective value of the commutation bus voltage in the receiving-end AC system at time t be equal to the rated value of the commutation bus voltage in the receiving-end AC system.

[0205] Specifically, the first determination module is used to determine the active power P flowing into the receiving-end AC system from the receiving-end converter station at time t according to the following formula: ac (t):

[0206] P ac (t) = P dc (t)-P f (t)

[0207] Where P dc (t) is the active power output of the converter in the receiving-end converter station at time t, P f (t) is the active power absorbed by the reactive power compensation equipment and filter in the receiving-end converter station at time t;

[0208] The reactive power Q flowing into the receiving-end AC system from the receiving-end converter station at time t is determined as follows: ac (t):

[0209] Q dc (t) = Q f (t)-Q dc (t)

[0210] In the formula, Q dc (t) is the reactive power absorbed by the converter in the receiving-end converter station at time t, Q f (t) is the reactive power output by the reactive compensation equipment and filter in the receiving-end converter station at time t.

[0211] Specifically, the active power P output by the converter in the receiving-end converter station at time t is determined as follows: dc (t):

[0212] P dc (t) = I dc (t)·U dc (t)

[0213] In the formula, I dc (t) is the DC current of the converter in the receiving-end converter station at time t, U dc (t) is the DC voltage of the converter in the receiving-end converter station at time t;

[0214] The reactive power Q absorbed by the converter in the receiving-end converter station at time t is determined as follows: dc (t):

[0215]

[0216] In the formula, is the power factor of the converter in the receiving-end converter station at time t;

[0217] The active power P absorbed by the reactive compensation equipment and filter in the receiving-end converter station at time t is determined by the following formula: f (t):

[0218] P f (t) = U1(t) 2 ·G

[0219] Where G is the conductance value of the reactive compensation equipment and filter in the receiving-end converter station, and U1(t) is the effective value of the converter bus voltage in the receiving-end AC system at time t;

[0220] The reactive power Q output by the reactive compensation equipment and filter in the receiving-end converter station at time t is determined as follows: f (t):

[0221] Q f (t) = U1(t) 2 ·B+Q RC

[0222] In the formula, Q RC is the reactive power value output by the dynamic reactive power compensation device in the receiving-end converter station, and B is the susceptance value of the reactive power compensation equipment and filter in the receiving-end converter station.

[0223] Specifically, if the working mode of the converter in the receiving-end converter station at time t is that the rectifier-side current is constant and the inverter-side voltage is constant, then the DC current I of the converter in the receiving-end converter station at time t is dc (t) = I dcr , the DC voltage U of the converter in the receiving converter station at time t dc (t) = U dcr , and determine the power factor of the converter in the receiving end converter station at time t according to the following formula:

[0224]

[0225] In the formula, π is the pi, K is the transformation ratio of the grid side to the valve side of the converter in the receiving end converter station;

[0226] If the working mode of the converter in the receiving-end converter station at time t is that the current on the rectifier side is constant and the arc extinction angle on the inverter side is constant, then the DC current I of the converter in the receiving-end converter station at time t is dc (t) = I dcr , the arc extinction angle of the converter in the receiving end converter station at time t is γ(t) = γ ref , and determine the power factor of the converter in the receiving end converter station at time t according to the following formula:

[0227]

[0228] Determine the DC voltage U of the converter in the receiving-end converter station at time t as follows: dc (t):

[0229]

[0230] Where N is the number of 6-pulse converters per pole in the receiving converter station, X r2 is the equivalent commutation reactance of the converter in the receiving-end converter station;

[0231] If the working mode of the converter in the receiving-end converter station at time t is that the rectifier side power is constant and the inverter side voltage is constant, then the active power P output by the converter in the receiving-end converter station at time t is dc (t) = P dcr , the DC voltage U of the converter in the receiving converter station at time t dc (t) = U dcr , and determine the power factor of the converter in the receiving end converter station at time t according to the following formula:

[0232]

[0233] Where U dcr Set the voltage control reference value for the converter in the receiving-end converter station;

[0234] If the working mode of the converter in the receiving-end converter station at time t is that the rectifier side power is constant and the inverter side arc extinction angle is constant, then the active power P output by the converter in the receiving-end converter station at time t is dc (t) = P dcr , the arc extinction angle of the converter in the receiving end converter station at time t is γ(t) = γ ref , and determine the power factor of the converter in the receiving end converter station at time t according to the following formula:

[0235]

[0236] Among them, I dcr is the constant current control reference value of the converter in the receiving converter station, U dcr is the reference value for the constant voltage control of the converter in the receiving converter station, γ ref P is the reference value for the arc extinction angle control of the converter in the receiving converter station. dcr Set the active power control reference value for the converter in the receiving converter station.

[0237] Specifically, the second determination module is used to determine the estimated value U of the effective value of the commutation bus voltage in the receiving-end AC system at time t according to the following formula: s (t):

[0238]

[0239] Where P ac (t) is the active power flowing into the receiving-end AC system from the receiving-end converter station at time t, Q ac (t) is the reactive power flowing into the receiving-end AC system from the receiving-end converter station at time t, U1(t) is the effective value of the converter bus voltage in the receiving-end AC system at time t, δ(t) is the phase difference between the converter bus voltage in the receiving-end AC system and the voltage of the AC unit in the receiving-end AC system at time t, U2(t) is the effective value of the voltage of the AC unit in the receiving-end AC system at time t, R is the resistance value in the receiving-end AC system, and X is the reactance value in the receiving-end AC system.

[0240] Specifically, the constraints are:

[0241] |U s (t)-U1(t)|<10 -5

[0242] Where U1(t) is the effective value of the commutation bus voltage in the receiving end AC system at time t, and U s (t) is the estimated value of the effective value of the commutation bus voltage in the receiving-end AC system at time t.

[0243] Those skilled in the art will appreciate that the embodiments of the present application may be provided as methods, systems, or computer program products. Therefore, the present application may adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment in combination with software and hardware. Moreover, the present application may adopt the form of a computer program product implemented in one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) that include computer-usable program code.

[0244] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0245] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture including an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0246] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0247] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A method for solving the PV curve of a receiving-end AC system, characterized in that: The method comprises: Step 1. Initialize the effective value of the commutation bus voltage in the receiving end AC system at time t and t=t0; Step 2. Determine the active power and reactive power flowing into the receiving-end AC system from the receiving-end converter station at time t according to the effective value of the converter bus voltage in the receiving-end AC system at time t; Step 3. Determine an estimated value of the effective value of the commutation bus voltage in the receiving-end AC system at time t according to the active power and reactive power flowing into the receiving-end AC system from the receiving-end converter station at time t; Step 4. Compare the effective value of the commutation bus voltage in the receiving-end AC system at time t with the estimated value of the effective value of the commutation bus voltage in the receiving-end AC system at time t. If the comparison result satisfies the constraint condition, output the effective value of the commutation bus voltage in the receiving-end AC system at time t and the active power and reactive power flowing into the receiving-end AC system from the receiving-end converter station at time t. Otherwise, update the effective value of the commutation bus voltage in the receiving-end AC system at time t to the estimated value of the effective value of the commutation bus voltage in the receiving-end AC system at time t, and return to step 2. Step 5. If t = t end , then use the effective value of the commutation bus voltage in the receiving-end AC system at each moment and the active power and reactive power flowing into the receiving-end AC system from the receiving-end converter station at each moment to generate the PV curve of the receiving-end AC system within the control period, otherwise, let t = t + 1, initialize the effective value of the commutation bus voltage in the receiving-end AC system at time t, and return to step 2; Among them, t∈(t0,t end ), t0 is the start time of the control cycle, t end is the end time of the control cycle.

2. The method according to claim 1, characterized in that The initialization of the effective value of the commutation bus voltage in the receiving-end AC system at time t includes: Let the effective value of the commutation bus voltage in the receiving-end AC system at time t be equal to the rated value of the commutation bus voltage in the receiving-end AC system.

3. The method according to claim 1, characterized in that The step 2 comprises: determining the active power P flowing into the receiving-end AC system from the receiving-end converter station at time t according to the following formula: ac (t): P ac (t)=P dc (t)-P f (t) Where P dc (t) is the active power output of the converter in the receiving-end converter station at time t, P f (t) is the active power absorbed by the reactive power compensation equipment and filter in the receiving-end converter station at time t; The reactive power Q flowing into the receiving-end AC system from the receiving-end converter station at time t is determined as follows: ac (t): Q dc (t)=Q f (t)-Q dc (t) In the formula, Q dc (t) is the reactive power absorbed by the converter in the receiving-end converter station at time t, Q f (t) is the reactive power output by the reactive compensation equipment and filter in the receiving-end converter station at time t.

4. The method according to claim 3, characterized in that The active power P output by the converter in the receiving-end converter station at time t is determined by the following formula: dc (t): P dc (t)=I dc (t)·U dc (t) In the formula, I dc (t) is the DC current of the converter in the receiving-end converter station at time t, U dc (t) is the DC voltage of the converter in the receiving-end converter station at time t; The reactive power Q absorbed by the converter in the receiving-end converter station at time t is determined as follows: dc (t): In the formula, is the power factor of the converter in the receiving-end converter station at time t; The active power P absorbed by the reactive compensation equipment and filter in the receiving-end converter station at time t is determined by the following formula: f (t): P f (t)=U1(t) 2 ·G Where G is the conductance value of the reactive compensation equipment and filter in the receiving-end converter station, and U1(t) is the effective value of the converter bus voltage in the receiving-end AC system at time t; The reactive power Q output by the reactive compensation equipment and filter in the receiving-end converter station at time t is determined as follows: f (t): Q f (t)=U1(t) 2 ·B+Q RC In the formula, Q RC is the reactive power value output by the dynamic reactive power compensation device in the receiving-end converter station, and B is the susceptance value of the reactive power compensation equipment and filter in the receiving-end converter station.

5. The method according to claim 4, characterized in that If the working mode of the converter in the receiving-end converter station at time t is that the rectifier-side current is constant and the inverter-side voltage is constant, then the DC current I of the converter in the receiving-end converter station at time t is dc (t) = I dcr , the DC voltage U of the converter in the receiving converter station at time t dc (t) = U dcr , and determine the power factor of the converter in the receiving-end converter station at time t according to the following formula: In the formula, π is the pi, K is the transformation ratio of the grid side to the valve side of the converter in the receiving end converter station; If the working mode of the converter in the receiving-end converter station at time t is that the current on the rectifier side is constant and the arc extinction angle on the inverter side is constant, then the DC current I of the converter in the receiving-end converter station at time t is dc (t) = I dcr , the arc extinction angle of the converter in the receiving end converter station at time t is γ(t) = γ ref , and determine the power factor of the converter in the receiving-end converter station at time t according to the following formula: Determine the DC voltage U of the converter in the receiving-end converter station at time t as follows: dc (t): Where N is the number of 6-pulse converters per pole in the receiving converter station, X r2 is the equivalent commutation reactance of the converter in the receiving-end converter station; If the working mode of the converter in the receiving-end converter station at time t is that the rectifier side power is constant and the inverter side voltage is constant, then the active power P output by the converter in the receiving-end converter station at time t is dc (t) = P dcr , the DC voltage U of the converter in the receiving converter station at time t dc (t) = U dcr , and determine the power factor of the converter in the receiving-end converter station at time t according to the following formula: Where U dcr Set the voltage control reference value for the converter in the receiving-end converter station; If the working mode of the converter in the receiving-end converter station at time t is that the rectifier side power is constant and the inverter side arc extinction angle is constant, then the active power P output by the converter in the receiving-end converter station at time t is dc (t) = P dcr , the arc extinction angle of the converter in the receiving end converter station at time t is γ(t) = γ ref , and determine the power factor of the converter in the receiving-end converter station at time t according to the following formula: Among them, I dcr is the constant current control reference value of the converter in the receiving converter station, U dcr is the reference value for the constant voltage control of the converter in the receiving converter station, γ ref P is the reference value for the arc extinction angle control of the converter in the receiving converter station. dcr Set the active power control reference value for the converter in the receiving converter station.

6. The method according to claim 1, characterized in that The step 3 comprises: determining the estimated value U of the effective value of the commutation bus voltage in the receiving-end AC system at time t according to the formula: s (t): Where P ac (t) is the active power flowing into the receiving-end AC system from the receiving-end converter station at time t, Q ac (t) is the reactive power flowing into the receiving-end AC system from the receiving-end converter station at time t, U1(t) is the effective value of the converter bus voltage in the receiving-end AC system at time t, δ(t) is the phase difference between the converter bus voltage in the receiving-end AC system and the voltage of the AC unit in the receiving-end AC system at time t, U2(t) is the effective value of the voltage of the AC unit in the receiving-end AC system at time t, R is the resistance value in the receiving-end AC system, and X is the reactance value in the receiving-end AC system.

7. The method according to claim 1, characterized in that The constraints are: |U s (t)-U1(t)|<10 -5 Where U1(t) is the effective value of the commutation bus voltage in the receiving end AC system at time t, and U s (t) is the estimated value of the effective value of the commutation bus voltage in the receiving-end AC system at time t.

8. A PV curve solution system for a receiving-end AC system, characterized in that: The system comprises: An initialization module is used to initialize the effective value of the commutation bus voltage in the receiving end AC system at time t and t=t0; The first determination module is used to determine the active power and reactive power flowing into the receiving-end AC system from the receiving-end converter station at time t according to the effective value of the converter bus voltage in the receiving-end AC system at time t; The second determination module is used to determine the estimated value of the effective value of the commutation bus voltage in the receiving-end AC system at time t according to the active power and reactive power flowing into the receiving-end AC system from the receiving-end converter station at time t; A comparison module is used to compare the effective value of the commutation bus voltage in the receiving-end AC system at time t with the estimated value of the effective value of the commutation bus voltage in the receiving-end AC system at time t. If the comparison result satisfies the constraint condition, the effective value of the commutation bus voltage in the receiving-end AC system at time t and the active power and reactive power flowing into the receiving-end AC system from the receiving-end converter station at time t are output; otherwise, the effective value of the commutation bus voltage in the receiving-end AC system at time t is updated to the estimated value of the effective value of the commutation bus voltage in the receiving-end AC system at time t, and the process returns to step 2; Generate module for if t=t end , then use the effective value of the commutation bus voltage in the receiving-end AC system at each moment and the active power and reactive power flowing into the receiving-end AC system from the receiving-end converter station at each moment to generate the PV curve of the receiving-end AC system within the control period, otherwise, let t = t + 1, initialize the effective value of the commutation bus voltage in the receiving-end AC system at time t, and return to step 2; Among them, t∈(t0,t end ), t0 is the start time of the control cycle, t end is the end time of the control cycle.

9. The system according to claim 8, characterized in that The initialization of the effective value of the commutation bus voltage in the receiving-end AC system at time t includes: Let the effective value of the commutation bus voltage in the receiving-end AC system at time t be equal to the rated value of the commutation bus voltage in the receiving-end AC system.

10. The system according to claim 8, characterized in that The first determination module is used to determine the active power P flowing into the receiving-end AC system from the receiving-end converter station at time t according to the following formula: ac (t): P ac (t)=P dc (t)-P f (t) Where P dc (t) is the active power output of the converter in the receiving-end converter station at time t, P f (t) is the active power absorbed by the reactive power compensation equipment and filter in the receiving-end converter station at time t; The reactive power Q flowing into the receiving-end AC system from the receiving-end converter station at time t is determined as follows: ac (t): Q dc (t)=Q f (t)-Q dc (t) In the formula, Q dc (t) is the reactive power absorbed by the converter in the receiving-end converter station at time t, Q f (t) is the reactive power output by the reactive compensation equipment and filter in the receiving-end converter station at time t.

11. The system according to claim 10, characterized in that The active power P output by the converter in the receiving-end converter station at time t is determined by the following formula: dc (t): P dc (t)=I dc (t)·U dc (t) In the formula, I dc (t) is the DC current of the converter in the receiving-end converter station at time t, U dc (t) is the DC voltage of the converter in the receiving-end converter station at time t; The reactive power Q absorbed by the converter in the receiving-end converter station at time t is determined as follows: dc (t): In the formula, is the power factor of the converter in the receiving-end converter station at time t; The active power P absorbed by the reactive compensation equipment and filter in the receiving-end converter station at time t is determined by the following formula: f (t): P f (t)=U1(t) 2 ·G Where G is the conductance value of the reactive compensation equipment and filter in the receiving-end converter station, and U1(t) is the effective value of the converter bus voltage in the receiving-end AC system at time t; The reactive power Q output by the reactive compensation equipment and filter in the receiving-end converter station at time t is determined as follows: f (t): Q f (t)=U1(t) 2 ·B+Q RC In the formula, Q RC is the reactive power value output by the dynamic reactive power compensation device in the receiving-end converter station, and B is the susceptance value of the reactive power compensation equipment and filter in the receiving-end converter station.

12. The system according to claim 11, characterized in that If the working mode of the converter in the receiving-end converter station at time t is that the rectifier-side current is constant and the inverter-side voltage is constant, then the DC current I of the converter in the receiving-end converter station at time t is dc (t) = I dcr , the DC voltage U of the converter in the receiving converter station at time t dc (t) = U dcr , and determine the power factor of the converter in the receiving-end converter station at time t according to the following formula: In the formula, π is the pi, K is the transformation ratio of the grid side to the valve side of the converter in the receiving end converter station; If the working mode of the converter in the receiving-end converter station at time t is that the current on the rectifier side is constant and the arc extinction angle on the inverter side is constant, then the DC current I of the converter in the receiving-end converter station at time t is dc (t) = I dcr , the arc extinction angle of the converter in the receiving end converter station at time t is γ(t) = γ ref , and determine the power factor of the converter in the receiving-end converter station at time t according to the following formula: Determine the DC voltage U of the converter in the receiving-end converter station at time t as follows: dc (t): Where N is the number of 6-pulse converters per pole in the receiving converter station, X r2 is the equivalent commutation reactance of the converter in the receiving-end converter station; If the working mode of the converter in the receiving-end converter station at time t is that the rectifier side power is constant and the inverter side voltage is constant, then the active power P output by the converter in the receiving-end converter station at time t is dc (t) = P dcr , the DC voltage U of the converter in the receiving converter station at time t dc (t) = U dcr , and determine the power factor of the converter in the receiving-end converter station at time t according to the following formula: Where U dcr Set the voltage control reference value for the converter in the receiving-end converter station; If the working mode of the converter in the receiving-end converter station at time t is that the rectifier side power is constant and the inverter side arc extinction angle is constant, then the active power P output by the converter in the receiving-end converter station at time t is dc (t) = P dcr , the arc extinction angle of the converter in the receiving end converter station at time t is γ(t) = γ ref , and determine the power factor of the converter in the receiving-end converter station at time t according to the following formula: Among them, I dcr is the constant current control reference value of the converter in the receiving converter station, U dcr is the reference value for the constant voltage control of the converter in the receiving converter station, γ ref P is the reference value for the arc extinction angle control of the converter in the receiving converter station. dcr Set the active power control reference value for the converter in the receiving converter station.

13. The system of claim 8, wherein: The second determination module is used to determine the estimated value U of the effective value of the commutation bus voltage in the receiving-end AC system at time t according to the following formula: s (t): Where P ac (t) is the active power flowing into the receiving-end AC system from the receiving-end converter station at time t, Q ac (t) is the reactive power flowing into the receiving-end AC system from the receiving-end converter station at time t, U1(t) is the effective value of the converter bus voltage in the receiving-end AC system at time t, δ(t) is the phase difference between the converter bus voltage in the receiving-end AC system and the voltage of the AC unit in the receiving-end AC system at time t, U2(t) is the effective value of the voltage of the AC unit in the receiving-end AC system at time t, R is the resistance value in the receiving-end AC system, and X is the reactance value in the receiving-end AC system.

14. The system of claim 8, wherein: The constraints are: |U s (t)-U1(t)|<10 -5 Where U1(t) is the effective value of the commutation bus voltage in the receiving end AC system at time t, and U s (t) is the estimated value of the effective value of the commutation bus voltage in the receiving-end AC system at time t.

Images