Peak current limiting method for static var generator

Abstract

The invention relates to a peak current limiting method for a static var generator, which comprises the following steps of: performing amplitude limiting on the maximum output current value of a fundamental wave and a harmonic wave by adopting a working mode of a reactive compensation priority, calculating a reactive current component, an unbalanced current component and a zero sequence current component of a power grid current, and calculating the peak current of the static var generator. Obtaining a reactive current compensation output value, an unbalanced current compensation output value and a zero sequence current compensation output value; and calculating a three-phase sine instruction value of the fundamental current, carrying out amplitude limiting on each harmonic component, and carrying out compensation output on each current after amplitude limiting output. The method has the advantages that the static var generator adopts a compensation priority, reactive power, unbalance and harmonic current compensation functions of the compensation device are flexibly set according to different working condition requirements of users, and a single or comprehensive compensation function is realized; the static var generator carries out independent amplitude limiting on each harmonic output current instruction value, and harmonic compensation times and amplitudes can be reasonably configured according to harmonics of different times generated under different working conditions.

Description

Technical Field

[0001] The present invention relates to the technical field of power system power quality monitoring and control, and in particular to a peak current limiting method for a static VAR generator. Background Art

[0002] With the development of industry, a large number of rectifiers have been put into operation in the equipment used by users. Various impact loads, unbalanced loads, large loads, and a large number of inductive loads have seriously reduced the power supply quality of the power grid. With the development of high-tech and the application of a large number of precision electronic equipment, higher requirements have been put forward for the power quality of the power grid. The power quality problem in the power system has become more and more the focus of academic research and product development.

[0003] The quality of voltage and current has a significant impact on the stability of the power grid, the safe operation of power equipment, and industrial and agricultural production. Reactive power and harmonics are two important factors that affect the current and voltage of the power grid, especially for the terminal system of the power grid of a certain scale. Static VAR generators (SVG) are widely used in the distribution networks of industry, commerce, and institutions, such as power systems, electrolytic and electroplating enterprises, water treatment equipment, petrochemical enterprises, large shopping malls and office system buildings, precision electronics enterprises, power supply systems of airports and ports, medical institutions, etc. Depending on the application object, low-voltage static VAR generators are used to compensate for load reactive power, imbalance, harmonics, etc. In some cases where the on-site working conditions are relatively complex, it often happens that SVG does not make a reasonable allocation in the compensation function. When the output is saturated, some power quality indicators of the compensated power grid may not meet user needs, affecting the safety and stability of production. Summary of the invention

[0004] The purpose of the present invention is to provide a peak current limiting method for a static VAR generator, which allocates compensation functions according to user needs, effectively allocates the compensation amplitude range of reactive, unbalanced and harmonic currents, and enables the SVG device to meet the optimal overall compensation effect for the power grid.

[0005] To achieve the above object, the present invention is implemented through the following technical solutions:

[0006] A peak current limiting method for a static VAR generator comprises the following steps:

[0007] S1, SVG adopts reactive power compensation priority working mode;

[0008] S2 and SVG limit the maximum output current values ​​of fundamental wave and harmonics;

[0009] S3, calculating the reactive current component, unbalanced current component and zero-sequence current component of the grid current, for compensating the reactive current, unbalanced current and zero-sequence current;

[0010] S4, respectively limiting the reactive current component, the unbalanced current component and the zero-sequence current component to obtain the SVG reactive current compensation output value, the unbalanced current compensation output value and the zero-sequence current compensation output value;

[0011] S5, calculating the three-phase sinusoidal command value of the SVG fundamental current, which is used to determine whether the three-phase current exceeds the maximum value of the SVG fundamental output current;

[0012] S6, limiting the output of the three-phase sinusoidal command value of the SVG fundamental current, so as to be used by the SVG to perform PI control on the fundamental compensation current;

[0013] S7, calculating each harmonic component of the grid current to compensate for the harmonic current in the grid;

[0014] S8. Limiting each harmonic component, and outputting each current compensation output after limiting, which is used for SVG to perform PI control on the harmonic compensation current.

[0015] In step S1, the reactive power compensation priority is set: if the reactive current priority compensation value I q_Level <Unbalanced current priority compensation value I nz_Level <Harmonic current priority compensation value I harm_Level , then the priority level during limiting is: reactive current limiting value I q_Lim >Unbalanced current limit value I nz_Lim >Harmonic current limit value I harm_Lim_n .

[0016] In step S2, SVG limits the maximum output current values ​​of the fundamental wave and harmonics as follows:

[0017] If the reactive current priority compensation value I q_Level =1, and the reactive current priority compensation value I q_Level <= SVG total compensation value Compensation_Numbers, SVG fundamental compensation current output maximum value I max_mag =SVG output current limit value I svg_limit ;

[0018] If the unbalanced current is compensated first, I nz_Level =1, and the unbalanced current priority compensation value I nz_Level <= SVG total compensation value Compensation_Numbers, maximum fundamental wave output I max_mag =SVG output current limit value I svg_limit ;

[0019] If the harmonic current priority compensation value I harm_Level =1, and the harmonic current priority compensation value Iq_Level <= SVG total compensation value Compensation_Numbers, then the maximum value of SVG fundamental compensation current output I max_mag =0.5;

[0020] The power quality analyzer analyzes the current at the maximum load on site to obtain the reactive power, unbalance and harmonic values, and then designs the reactive current limit value I according to the user's actual compensation capacity requirements. q_Lim , unbalanced current limit value I nz_Lim , harmonic current limit value I harm_Lim_n Limiting is performed.

[0021] In step S3, the reactive current component, unbalanced current component and zero-sequence current component of the grid current are calculated as follows:

[0022] The reactive current component I is calculated by rotating the coordinate axis through Clark transformation and Park transformation. pq_Load , the active component of unbalanced current I nd_Load , reactive component I nq_Load , and the active component of zero-sequence current I zd_Load , zero sequence reactive component I zq_Load , the formula is as follows:

[0023]

[0024] In formula ①, I a ,I b ,I c They are the three-phase currents on the load side, I Z is the zero-sequence current, and θ is the grid voltage phase-locking angle.

[0025] In step S4, the reactive current component I pq_Load , unbalanced current active component I nd_Load , reactive component I nq_Load , zero sequence current active component I zd_Load , zero sequence reactive component I zq_Load The SVG reactive current compensation output value I is obtained by limiting the amplitude of the SVG reactive current. pq , the active component of the unbalanced current compensation output value I nd , reactive component I nq , zero-sequence current compensation output value active component I zd , reactive component I zq , the content is as follows:

[0026] SVG reactive current compensation output value I pq , the formula is as follows:

[0027] if(I pq_Load >Iq_Lim )

[0028] I pq =I q_Lim

[0029] else

[0030] I pq =I pq_Load ②

[0031] SVG unbalanced current compensation output value, the formula is as follows:

[0032] if(I nd_Load >I nz_Lim )

[0033] I nd =I nz_Lim

[0034] else

[0035] I nd =I nd_Load

[0036] if(I nq_Load >I nz_Lim )

[0037] I nq =I nz_Lim

[0038] else

[0039] I nq =I nq_Load ③

[0040] The calculation formula of SVG zero-sequence current compensation output value is as follows:

[0041] if(I zd_Load >I nz_Lim )

[0042] I zd =I nz_Lim

[0043] else

[0044] I zd =I zd_Load

[0045] if(I zq_Load >I nz_Lim )

[0046] I zq =I nz_Lim

[0047] else

[0048] I zq =I zq_Load ④.

[0049] In step S5, the active component I is outputted by the three-phase unbalanced negative sequence compensation. nd , reactive component I nq , zero-sequence current compensation output value active component I zd , reactive component I zq , the three-phase fundamental compensation current command value I is calculated by Clark inverse transformation and Park inverse transformation a_mag ,I b_mag ,I c_mag , the formula is as follows:

[0050]

[0051] In step S6, the three-phase current command values ​​are respectively compared with the SVG output current maximum value I max_mag After comparison, the limited output is performed, and the three-phase current value after the limited output is rotated for the PI control of the SVG output current. The formula is as follows:

[0052] if(I a_mag >I max_mag )

[0053] I a_mag =I max_mag

[0054] else

[0055] I a_mag =I a_mag

[0056] if(I b_mag >I max_mag )

[0057] I b_mag =I max_mag

[0058] else

[0059] I b_mag =I b_mag

[0060] if(I c_mag >I max_mag )

[0061] I c_mag =I max_mag

[0062] else

[0063] I c_mag =Ic_mag ⑥.

[0064] In step S7, the harmonic components of the grid current are calculated as follows:

[0065] The coordinate axis is rotated by Clark transformation and Park transformation to calculate the positive sequence active component of harmonic current I harm_n_pd_Load , positive sequence reactive component I harm_n_pq_Load , negative sequence active component I harm_n_nd_Load , negative sequence reactive component I harm_n_nq_Load , zero sequence active component I harm_n_zd_Load , zero sequence reactive component I harm_n_zq_Load , the formula is as follows:

[0066]

[0067] In formula ⑦, I a ,I b ,I c is the three-phase current on the load side, I z is the zero-sequence current, n is the harmonic order, and θ is the grid voltage phase-locking angle.

[0068] In step S8, the harmonic current positive sequence active component I harm_n_pd_Load , positive sequence reactive component I harm_n_pq_Load , negative sequence active component I harm_n_nd_Load , negative sequence reactive component I harm_n_nq_Load , zero sequence active component I harm_n_zd_Load , zero sequence reactive component I harm_n_zq_Load The amplitude is limited respectively to obtain the positive sequence active component output value I of SVG harmonic compensation current harm_n_pd , positive sequence reactive component output value I harm_n_pq , negative sequence active component output value I harm_n_nd , negative sequence reactive component output value I harm_n_nq , zero sequence active component output value I harm_n_zd , zero sequence reactive component output value I harm_n_zq , the content is as follows:

[0069] SVG harmonic compensation current positive sequence active component output value I harm_n_pd , the formula is as follows:

[0070] if(I harm_n_pd_Load >I harm_lim_n )

[0071] I harm_n_pd =I harm_lim_n

[0072] else

[0073] I harm_n_pd =Iharm_n_pd_Load ⑧

[0074] SVG harmonic compensation current positive sequence reactive component output value I harm_n_pq , the formula is as follows:

[0075] if(I harm_n_pq_Load >I harm_lim_n )

[0076] I harm_n_pq =I harm_lim_n

[0077] else

[0078] I harm_n_pq =I harm_n_pq_Load ⑨

[0079] SVG harmonic compensation current negative sequence active component output value I harm_n_nd , the formula is as follows:

[0080] if(I harm_n_nd_Load >I harm_lim_n )

[0081] I harm_n_nd =I harm_lim_n

[0082] else

[0083] I harm_n_nd =I harm_n_nd_Load ⑩

[0084] SVG harmonic compensation current negative sequence reactive component output value I harm_n_nq , the formula is as follows:

[0085] if(I harm_n_nq_Load >I harm_lim_n )

[0086] I harm_n_nq =I harm_lim_n

[0087] else

[0088]

[0089] SVG harmonic compensation current zero-sequence active component output value I harm_n_zd , the formula is as follows:

[0090] if(I harm_n_zd_Load >I harm_lim_n )

[0091] I harm_n_zd =I harm_lim_n

[0092] else

[0093]

[0094] SVG harmonic compensation current zero-sequence reactive component output value I harm_n_zq , the formula is as follows:

[0095] if(I harm_n_zq_Load >I harm_lim_n )

[0096] I harm_n_zq =I harm_lim_n

[0097] else

[0098]

[0099] The current compensation outputs after the limiting output are used in SVG to perform PI control on the harmonic compensation current.

[0100] A computer device includes: at least one processor, and a memory communicatively connected to the at least one processor, wherein the memory stores instructions executable by the at least one processor, and the instructions are executed by the at least one processor so that the at least one processor executes a peak current limiting method for a static VAR generator.

[0101] A computer-readable storage medium stores computer instructions, wherein the computer instructions are used to enable a computer to execute a peak current limiting method for a static VAR generator.

[0102] Compared with the prior art, the present invention has the following beneficial effects:

[0103] 1. The static VAR generator adopts the compensation priority working mode. According to the different working conditions of the user, the compensation function of the reactive power, unbalance and harmonic current of the compensation device can be flexibly set to realize single or comprehensive compensation function;

[0104] 2. The static VAR generator independently limits the output current command value of each harmonic, and can reasonably configure the harmonic compensation order and amplitude according to the harmonics of different orders generated under different working conditions;

[0105] 3. Amplitude limitation on the dq coordinate axis and amplitude limitation on the abc coordinate axis, the process includes multiple rotations of the coordinate axis. BRIEF DESCRIPTION OF THE DRAWINGS

[0106] Figure 1 It is a flow chart of peak current limiting of static VAR generator.

[0107] Figure 2 It is the control logic diagram of the peak current limiting of the static VAR generator.

[0108] Figure 3 It is the peak current limit of the harmonic current of the static VAR generator. DETAILED DESCRIPTION

[0109] The present invention is described in detail below in conjunction with the accompanying drawings, but it should be noted that the implementation of the present invention is not limited to the following embodiments.

[0110] See Figure 1-Figure 3 , a peak current limiting method for a static reactive generator, which is composed of reactive current limiting, unbalanced current limiting and harmonic current limiting; the peak current limiting method includes compensation priorities of reactive, unbalanced and harmonic currents; the peak current limiting method includes amplitude limiting on the dq coordinate axis and amplitude limiting on the abc coordinate axis, and the process includes multiple rotations of the coordinate axis, and flexibly configures reactive, unbalanced and harmonic compensation functions to realize single or comprehensive compensation functions, and can arbitrarily configure the priority of the compensation function to realize targeted compensation for different sites, and ensure the optimal compensation for the power grid, specifically including:

[0111] A peak current limiting method for a static VAR generator, specifically comprising:

[0112] S1, SVG adopts reactive power compensation priority mode; set reactive power compensation priority: if reactive current priority compensation value I q_Level <Unbalanced current priority compensation value I nz_Level <Harmonic current priority compensation value I harm_Level , then the priority level during limiting is: reactive current limiting value I q_Lim >Unbalanced current limit value I nz_Lim >Harmonic current limit value I harm_Lim_n .

[0113] S2 and SVG limit the maximum output current values ​​of the fundamental wave and harmonics as follows:

[0114] If the reactive current priority compensation value I q_Level =1, and the reactive current priority compensation value I q_Level <= SVG total compensation value Compensation_Numbers, SVG fundamental compensation current output maximum value I max_mag =SVG output current limit value I svg_limit ;

[0115] If the unbalanced current is compensated first, I nz_Level =1, and the unbalanced current priority compensation value I nz_Level <= SVG total compensation value Compensation_Numbers, maximum fundamental wave output I max_mag =SVG output current limit value Isvg_limit ;

[0116] If the harmonic current priority compensation value I harm_Level =1, and the harmonic current priority compensation value I q_Level <= SVG total compensation value Compensation_Numbers, then the maximum value of SVG fundamental compensation current output I max_mag =0.5;

[0117] The power quality analyzer analyzes the current at the maximum load on site to obtain the reactive power, unbalance and harmonic values, and then designs the reactive current limit value I according to the user's actual compensation capacity requirements. q_Lim , unbalanced current limit value I nz_Lim , harmonic current limit value I harm_Lim_n Limiting is performed.

[0118] S3. Calculate the reactive current component, unbalanced current component and zero-sequence current component of the grid current to compensate for the reactive current, unbalanced current and zero-sequence current. The contents are as follows:

[0119] The reactive current component I is calculated by rotating the coordinate axis through Clark transformation and Park transformation. pq_Load , the active component of unbalanced current I nd_Load , reactive component I nq_Load , and the active component of zero-sequence current I zd_Load , zero sequence reactive component I zq_Load , the formula is as follows:

[0120]

[0121] In formula ①, I a ,I b ,I c They are the three-phase currents on the load side, I Z is the zero-sequence current, and θ is the grid voltage phase-locking angle.

[0122] S4, respectively, the reactive current component I pq_Load , unbalanced current active component I nd_Load , reactive component I nq_Load , zero sequence current active component I zd_Load , zero sequence reactive component I zq_Load The SVG reactive current compensation output value I is obtained by limiting the amplitude of the SVG reactive current. pq , the active component of the unbalanced current compensation output value I nd , reactive component I nq , zero-sequence current compensation output value active component I zd , reactive component I zq , the content is as follows:

[0123] SVG reactive current compensation output value I pq , the formula is as follows:

[0124] if(I pq_Load >I q_Lim )

[0125] I pq =I q_Lim

[0126] else

[0127] I pq =I pq_Load ②

[0128] SVG unbalanced current compensation output value, the formula is as follows:

[0129] If(I nd_Load >I nz_Lim )

[0130] I nd =I nz_Lim

[0131] else

[0132] I nd =I nd_Load

[0133] if(I nq_Load >I nz_Lim )

[0134] I nq =I nz_Lim

[0135] else

[0136] I nq =I nq_Load ③

[0137] The calculation formula of SVG zero-sequence current compensation output value is as follows:

[0138] if(I zd_Load >I nz_Lim )

[0139] I zd =I nz_Lim

[0140] else

[0141] I zd =I zd_Load

[0142] if(I zq_Load >Inz_Lim )

[0143] I zq =I nz_Lim

[0144] else

[0145] I zq =I zq_Load ④.

[0146] S5, calculating the three-phase sinusoidal command value of the SVG fundamental current, which is used to determine whether the three-phase current exceeds the maximum value of the SVG fundamental output current;

[0147] Through the three-phase unbalanced negative sequence compensation output value active component I nd , reactive component I nq , zero-sequence current compensation output value active component I zd , reactive component I zq , the three-phase fundamental compensation current command value I is calculated by Clark inverse transformation and Park inverse transformation a_mag ,I b_mag ,I c_mag , the formula is as follows:

[0148]

[0149] S6, compare the three-phase current command values ​​with the SVG output current maximum value I max_mag After comparison, the limited output is performed, and the three-phase current value after the limited output is rotated for the PI control of the SVG output current. The formula is as follows:

[0150] if(I a_mag >I max_mag )

[0151] I a_mag =I max_mag

[0152] else

[0153] I a_mag =I a_mag

[0154] if(I b_mag >I mag_mag )

[0155] I b_mag =I max_mag

[0156] else

[0157] I b_mag =I b_mag

[0158] if(I c_mag >I max_mag )

[0159] I c_mag =I max_mag

[0160] else

[0161] I c_mag =I c_mag ⑥.

[0162] S7. Calculate the harmonic components of the grid current to compensate for the harmonic current in the grid. The contents are as follows:

[0163] The coordinate axis is rotated by Clark transformation and Park transformation to calculate the positive sequence active component of harmonic current I harm_n_pd_Load , positive sequence reactive component I harm_n_pq_Load , negative sequence active component I harm_n_nd_Load , negative sequence reactive component I harm_n_nq_Load , zero sequence active component I harm_n_zd_Load , zero sequence reactive component I harm_n_zq_Load , the formula is as follows:

[0164]

[0165]

[0166] In formula ⑦, I a ,I b ,I c is the three-phase current on the load side, I z is the zero-sequence current, n is the harmonic order, and θ is the grid voltage phase-locking angle.

[0167] S8, the harmonic current positive sequence active component I harm_n_pd_Load , positive sequence reactive component I harm_n_pq_Load , negative sequence active component I harm_n_nd_Load , negative sequence reactive component I harm_n_nq_Load , zero sequence active component I harm_n_zd_Load , zero sequence reactive component I harm_n_zq_Load The amplitude is limited respectively to obtain the positive sequence active component output value I of SVG harmonic compensation current harm_n_pd , positive sequence reactive component output value I harm_n_pq , negative sequence active component output value I harm_n_nd , negative sequence reactive component output value I harm_n_nq , zero sequence active component output value I harm_n_zd , zero sequence reactive component output value I harm_n_zq , the content is as follows:

[0168] SVG harmonic compensation current positive sequence active component output value I harm_n_pd , the formula is as follows:

[0169] if(I harm_n_pd_Load >I harm_lim_n )

[0170] I harm_n_pd =I harm_lim_n

[0171] else

[0172] I harm_n_pd =I harm_n_pd_Load ⑧

[0173] SVG harmonic compensation current positive sequence reactive component output value I harm_n_pq , the formula is as follows:

[0174] if(I harm_n_pq_Load >I harm_lim_n )

[0175] I harm_n_pq =I harm_lim_n

[0176] else

[0177] I harm_n_pq =I harm_n_pq_Load ⑨

[0178] SVG harmonic compensation current negative sequence active component output value I harm_n_nd , the formula is as follows:

[0179] if(I harm_n_nd_Load >I harm_lim_n )

[0180] I harm_n_nd =I harm_lim_n

[0181] else

[0182] I harm_n_nd =I harm_n_nd_Load ⑩

[0183] SVG harmonic compensation current negative sequence reactive component output value I harm_n_nq , the formula is as follows:

[0184] if(I harm_n_nq_Load >I harm_lim_n )

[0185] I harm_n_nq =I harm_lim_n

[0186] else

[0187]

[0188] SVG harmonic compensation current zero-sequence active component output value I harm_n_zd , the formula is as follows:

[0189] if(I harm_n_zd_Load >I harm_lim_n )

[0190] I harm_n_zd =I harm_lim_n

[0191] else

[0192]

[0193] SVG harmonic compensation current zero-sequence reactive component output value I harm_n_zq , the formula is as follows:

[0194] if(I harm_n_zq_Load >I harm_lim_n )

[0195] I harm_n_zq =I harm_lim_n

[0196] else

[0197]

[0198] The current compensation outputs after the limiting output are used in SVG to perform PI control on the harmonic compensation current.

[0199] The following examples are implemented on the premise of the technical solution of the present invention, and provide detailed implementation methods and specific operation processes, but the protection scope of the present invention is not limited to the following examples. The methods used in the following examples are conventional methods unless otherwise specified.

[0200] Example 1

[0201] Taking the power quality management plan of an old chemical plant in a workshop of an industrial park as an example, the content is as follows:

[0202] 1. Project Background

[0203] There is a large amount of reactive power and harmonic current in the power distribution system of the string inverter aging workshop. According to the operating experience of the headquarters' No. 1 workshop, the thermal protection of the main switch of the aging workshop distribution system often trips before on-site compensation, causing product aging interruptions. If not managed, the current status cannot meet the power consumption of the string aging, and the transformer may even be overloaded, affecting production.

[0204] 1. Data Analysis

[0205] 1) The on-site aging workshop is an inverter feedback test workshop, where low power factor and three-phase imbalance are common.

[0206] 2) There are still certain current harmonics in the on-site power distribution system, mainly the 5th, 7th, 11th and 13th harmonics;

[0207] 3) By reducing the reactive power and harmonic current of the system, the load capacity of the aging workshop can be effectively improved;

[0208] 4) The thermal effect generated by harmonic current is greater than that of fundamental reactive current, that is, harmonic current has a greater negative impact on circuit breakers. It is recommended to give priority to the control of harmonic current.

[0209] 2. Solution

[0210] When the equipment capacity is 10 136K inverters, the on-site working conditions are analyzed by the power quality analyzer as follows:

[0211] 1) Reactive power demand: reactive current is 200A;

[0212] 2) Unbalanced current demand: 80A;

[0213] 3) Harmonic demand (preliminary measurement of 16 online aging products below 110K, 5th harmonic demand: 180A; 7th harmonic demand: 160A; 11th harmonic demand: 150A; 13th harmonic demand: 120A)

[0214] SVG rated current is 500A.

[0215] After standardizing each current with the rated current, we can find:

[0216] Reactive current I q_ref =0.5;

[0217] Unbalanced current I n_ref =0.16;

[0218] 5th harmonic current I ham_5 =0.36;

[0219] 7th harmonic current I ham_7 =0.32;

[0220] 11th harmonic current I ham_11 =0.3;

[0221] 13th harmonic current I ham_13 =0.24;

[0222] It can be concluded that:

[0223] I ham_5 +I ham_7+I ham_11 +I ham_13 >I q >I n；

[0224] The harmonic current value at the user site is the largest. It is recommended to give priority to the control of harmonic current. Therefore, the priority of each compensation current is set as follows:

[0225] I harm_Level =1;

[0226] I q_Level =2;

[0227] I nz_Level =3;

[0228] Set the SVG output current limit value to:

[0229] I SVG_Limit =0.9;

[0230] I max_mag =0.5;

[0231] Set the SVG reactive current limit value I q_Lim , unbalanced current limit value I nz_Lim , harmonic current limit value I harm_Lim_n Set to:

[0232] I q_Lim =0.5;

[0233] I nz_Lim =0.2;

[0234] I harm_Lim_5 =0.4;

[0235] I harm_Lim_7 =0.4;

[0236] I harm_Lim_5 =0.35;

[0237] I harm_Lim_7 =0.3.

[0238] Example 2

[0239] Taking the power quality management plan of a steel rolling plant as an example, the content is as follows:

[0240] 1. Project Background

[0241] The test plants are the steel rolling plant and the vertical kiln plant. The bus loads are aerial vehicles, DC motors, and roller motors. The on-site bus power factor is low and contains low-order harmonics.

[0242] 2. Solution

[0243] After testing, it was found that the 5th and 7th harmonic currents of the busbar of the II# rolling mill of the steel mill substation exceeded the standard, the power factor was low, and the long-term and short-term flicker exceeded the standard. All other electrical energy indicators were in line with national standards.

[0244] 1) Reactive power demand: reactive current is 1300A;

[0245] 2) Unbalanced current demand: 30A;

[0246] 3) Harmonic demand (preliminary measurement of 16 online aging products below 110K, 5th harmonic demand: 120A; 11th harmonic demand: 50A);

[0247] SVG rated current is 1500A.

[0248] After standardizing each current with the rated current, we can find:

[0249] Reactive current I q_ref =0.867;

[0250] Unbalanced current I n_ref =0.02;

[0251] 5th harmonic current I ham_5 =0.08;

[0252] 11th harmonic current I ham_11 =0.033;

[0253] It can be concluded that:

[0254] I q >I ham_5 >I ham_11 >I n；

[0255] Therefore, the priority of each compensation current is set as:

[0256] I q_Level =1;

[0257] I harm_Level =2;

[0258] I nz_Level =3;

[0259] Set the SVG output current limit value to:

[0260] I SVG_Limit =0.9;

[0261] I max_mag =0.9;

[0262] Set the SVG reactive current limit value Iq_Lim , unbalanced current limit value I nz_Lim , harmonic current limit value I harm_Lim_n Set to:

[0263] I q_Lim =0.9;

[0264] I nz_Lim =0.05;

[0265] I harm_Lim_5 =0.1;

[0266] I harm_Lim_7 =0.05.

[0267] The static VAR generator of the present invention adopts a compensation priority working mode, and can flexibly set the compensation functions of reactive power, unbalance and harmonic currents of the compensation device according to different working conditions of users, so as to realize a single or comprehensive compensation function; the static VAR generator independently limits the output current command value of each harmonic, and can reasonably configure the harmonic compensation order and amplitude according to the harmonics of different orders generated under different working conditions; the amplitude limit on the dq coordinate axis and the amplitude limit on the abc coordinate axis include multiple rotations of the coordinate axis in the process.

Claims

1. A peak current limiting method for a static VAR generator, characterized in that: Specifically include: S1, SVG adopts reactive power compensation priority working mode; S2 and SVG limit the maximum output current values ​​of fundamental wave and harmonics; S3, calculating the reactive current component, unbalanced current component and zero-sequence current component of the grid current, for compensating the reactive current, unbalanced current and zero-sequence current; S4, respectively limiting the reactive current component, the unbalanced current component and the zero-sequence current component to obtain the SVG reactive current compensation output value, the unbalanced current compensation output value and the zero-sequence current compensation output value; S5, calculating the three-phase sinusoidal command value of the SVG fundamental current, which is used to determine whether the three-phase current exceeds the maximum value of the SVG fundamental output current; S6, limiting the output of the three-phase sinusoidal command value of the SVG fundamental current, so as to be used by the SVG to perform PI control on the fundamental compensation current; S7, calculating each harmonic component of the grid current to compensate for the harmonic current in the grid; S8. Limiting each harmonic component, and outputting each current compensation output after limiting, which is used for SVG to perform PI control on the harmonic compensation current.

2. A peak current limiting method for a static VAR generator according to claim 1, characterized in that: In step S1, the reactive power compensation priority is set: if the reactive current priority compensation value I q_Level <Unbalanced current priority compensation value I nz_Level <Harmonic current priority compensation value I harm_Level , then the priority level during limiting is: reactive current limiting value I q_Lim >Unbalanced current limit value I nz_Lim >Harmonic current limit value I harm_Lim_n .

3. A peak current limiting method for a static VAR generator according to claim 1, characterized in that: In step S2, the SVG limits the maximum output current values ​​of the fundamental wave and harmonics, as follows: If the reactive current priority compensation value I q_Level =1, and the reactive current priority compensation value I q_Level <= SVG total compensation value Compensation_Numbers, SVG fundamental compensation current output maximum value I max_mag =SVG output current limit value I svg_limit ; If the unbalanced current is compensated first, I nz_Level =1, and the unbalanced current priority compensation value I nz_Level <= SVG total compensation value Compensation_Numbers, maximum fundamental wave output I max_mag =SVG output current limit value I svg_limit ; If the harmonic current priority compensation value I harm_Level =1, and the harmonic current priority compensation value I q_Level <= SVG total compensation value Compensation_Numbers, then the maximum value of SVG fundamental compensation current output I max_mag =0.5; The power quality analyzer analyzes the current at the maximum load on site to obtain the reactive power, unbalance and harmonic values, and then designs the reactive current limit value I according to the user's actual compensation capacity requirements. q_Lim , unbalanced current limit value I nz_Lim , harmonic current limit value I harm_Lim_n Limiting is performed.

4. A peak current limiting method for a static VAR generator according to claim 1, characterized in that: In step S3, the reactive current component, unbalanced current component and zero-sequence current component of the grid current are calculated as follows: The reactive current component I is calculated by rotating the coordinate axis through Clark transformation and Park transformation. pq_Load , the active component of unbalanced current I nd_Load , reactive component I nq_Load , and the active component of zero-sequence current I zd_Load , zero sequence reactive component I zq_Load , the formula is as follows: I pd_Load =iα*cosθ+iβ*sinθ I pq_Load =iα*sinθ-iβ*cosθ I nd_Load =iα*cosθ-iβ*sinθ I nq_Load =-iα*sinθ-iβ*cosθ AND zd_Load =2*iz*cosθ I zq_Load =2*iz*sinθ ① In formula ①, I a ,I b ,I c They are the three-phase currents on the load side, I Z is the zero-sequence current, and θ is the grid voltage phase-locking angle.

5. A peak current limiting method for a static VAR generator according to claim 1, characterized in that: In step S4, the reactive current component I pq_Load , unbalanced current active component I nd_Load , reactive component I nq_Load , zero sequence current active component I zd_Load , zero sequence reactive component I zq_Load The SVG reactive current compensation output value I is obtained by limiting the amplitude of the SVG reactive current. pq , the active component of the unbalanced current compensation output value I nd , reactive component I nq , zero-sequence current compensation output value active component I zd , reactive component I zq , the content is as follows: SVG reactive current compensation output value I pq , the formula is as follows: if(I pq_Load >I q_Lim ) I pq =I q_Lim else I pq =I pq_Load ② SVG unbalanced current compensation output value, the formula is as follows: if(I nd_Load >I nz_Lim ) I nd =I nz_Lim else I nd =I nd_Load if(I nq_Load >I nz_Lim ) I nq =I nz_Lim else I nq =I nq_Load ③ The calculation formula of SVG zero-sequence current compensation output value is as follows: if(I zd_Load >I nz_Lim ) I zd =I nz_Lim else I zd =I zd_Load if(I zq_Load >I nz_Lim ) I zq =I nz_Lim else I zq =I zq_Load ④。 6. A peak current limiting method for a static VAR generator according to claim 1, characterized in that: In step S5, the active component I is outputted by the three-phase unbalanced negative sequence compensation. nd , reactive component I nq , zero-sequence current compensation output value active component I zd , reactive component I zq , the three-phase fundamental compensation current command value i is calculated by Clark inverse transformation and Park inverse transformation a_mag 、i b_mag 、i c_mag , the formula is as follows: I pd =I pd_ref iα inv =I pd *cosθ+I pq *sinθ+I nd *cosθ-I nq *sinθ iβ inv =I pd *sinθ-I pd *cosθ-I nd *sinθ-I nq *cosθ from inv =I zd *cosθ+I zq *sinθ I a_mag =iα inv +iz inv 7. A peak current limiting method for a static VAR generator according to claim 1, characterized in that: In step S6, the three-phase current command values ​​are respectively compared with the SVG output current maximum value I max_mag After comparison, the limited output is performed, and the three-phase current value after the limited output is rotated for the PI control of the SVG output current. The formula is as follows: if(I a_mag >I max_mag ) I a_mag =I max_mag else I a_mag =I a_mag if(I b_mag >I max_mag ) I b_mag =I max_mag else I b_mag =I b_mag if(I c_mag >I max_mag ) I c_mag =I max_mag else I c_mag =I c_mag ⑥。 8. A peak current limiting method for a static VAR generator according to claim 1, characterized in that: In step S7, the calculation of each harmonic component of the grid current is as follows: The coordinate axis is rotated by Clark transformation and Park transformation to calculate the positive sequence active component of harmonic current I harm_n_pd_Load , positive sequence reactive component I harm_n_pq_Load , negative sequence active component I harm_n_nd_Load , negative sequence reactive component I harm_n_nq_Load , zero sequence active component I harm_n_zd_Load , zero sequence reactive component I harm_n_zq_Load , the formula is as follows: I harm_b_pd_Load =iα*cos nθ+iβ*sin nθ I harm_n_pq_Load =iα*sin nθ-iβ*cos nθ I harm_n_nd_Load =iα*cos nθ-iβ*sin nθ I harm_n_nq_Load =-iα*sin nθ-iβ*cos nθ I harm_n_zd_ref =2*iz*cos nθ I harm_n_xq_ref =2*iz*sinnθ ⑦ In formula ⑦, I a ,I b ,I c is the three-phase current on the load side, I z is the zero-sequence current, n is the harmonic order, and θ is the grid voltage phase-locking angle.

9. A peak current limiting method for a static VAR generator according to claim 1, characterized in that: In step S8, the harmonic current positive sequence active component I harm_n_pd_Load , positive sequence reactive component I harm_n_pq_Load , negative sequence active component I harm_n_nd_Load , negative sequence reactive component I harm_n_nq_Load , zero sequence active component I harm_n_zd_Load , zero sequence reactive component I harm_n_zq_Load The amplitude is limited respectively to obtain the positive sequence active component output value I of SVG harmonic compensation current harm_n_pd , positive sequence reactive component output value I harm_n_pq , negative sequence active component output value I harm_n_nd , negative sequence reactive component output value I harm_n_nq , zero sequence active component output value I harm_n_zd , zero sequence reactive component output value I harm_n_zq , the content is as follows: SVG harmonic compensation current positive sequence active component output value I harm_n_pd , the formula is as follows: if(I harm_n_pd_Load >I harm_lim_n ) I harm_n_pd =I harm_lim_n else I harm_n_pd =I harm_n_pd_Load ⑧ SVG harmonic compensation current positive sequence reactive component output value I harm_n_pq , the formula is as follows: if(I harm_n_pq_Load >I harm_lim_n ) I harm_n_pq =I harm_lim_n else I harm_n_pq =I harm_n_pq_Load ⑨SVG harmonic compensation current negative sequence active component output value I harm_n_nd , the formula is as follows: if(I harm_n_nd_Load >I harm_lim_n ) I harm_n_nd =I harm_lim_n else I harm_n_nd =I harm_n_nd_Load ⑩SVG harmonic compensation current negative sequence reactive component output value I harm_n_nq , the formula is as follows: if(I harm_n_nq_Load >I harm_lim_n ) I harm_n_nq =I harm_lim_n else SVG harmonic compensation current zero-sequence active component output value I harm_n_zd , the formula is as follows: if(I harm_n_zd_Load >I harm_lim_n ) I harm_n_zd =I harm_lim_n else SVG harmonic compensation current zero-sequence reactive component output value I harm_n_zq , the formula is as follows: if(I harm_n_zq_Load >I harm_lim_n ) I harm_n_zq =I harm_lim_n else The current compensation outputs after the limiting output are used in SVG to perform PI control on the harmonic compensation current.

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