Active power filter grid side single CT control method and control system

Abstract

The present invention provides a single-group CT control method and control system for an active power filter grid side, belonging to the field of power electronics technology. The method described in the present application dynamically collects the grid side current and the output current of the APF module in real time; obtains the number of parallel APF modules; and calculates the load current; extracts the sine component and cosine component of each harmonic of the load current at the current time, calculates the sine component and cosine component of each harmonic to be compensated at the current time and their corresponding average values; calculates the difference between the average value and the sine component and cosine component of each harmonic at the previous time, adjusts the difference and synthesizes a given current, and adjusts the output current of the APF module to offset the load current. In this way, current sharing compensation of multiple APF modules can be achieved through a single group of CTs on the grid side, which can effectively save system costs, improve system stability, and avoid the problem of detection deviations of different CTs affecting the compensation effect.

Description

Technical Field

[0001] The present invention relates to the field of power electronics technology, and in particular to a control method and control system for a single CT group on the grid side of an active power filter. Background Art

[0002] The shunt active power filter (APF) is connected in parallel to the power grid system. It detects the load current in the power grid in real time through an external current transformer (CT), and obtains the harmonic current contained in the load current through the harmonic extraction algorithm on the control unit. It further generates PWM pulses to drive the converter to generate a current in the opposite direction of the extracted load harmonic current. By offsetting the harmonic current of the load, the harmonics in the power grid are eliminated. Since the detection unit (current transformer (CT)) and the control unit detect and extract the harmonic current of the load in real time, the shunt active power filter APF also needs to dynamically compensate for the harmonic current in real time, ultimately reducing the total harmonic distortion (THDI) of the power grid current.

[0003] Depending on the installation locations of APF and CT, there are two compensation forms based on the load side and the grid side. When multiple APFs are compensated in parallel, a group of CTs are shared between modules through the CT lines in series. When the CT is on the load side, each APF compensates for each harmonic current by extracting the harmonic current divided by N (the number of parallel modules). However, when the CT is on the grid side, the CT current includes both the load current and the APF output current. If only one group of CTs on the grid side is used and the above-mentioned load-side method is adopted, during the load change process, the CT current detected by any APF also includes the dynamic current output by other APF modules in the parallel system. During the dynamic adjustment process, the harmonic current output by this APF module will be compensated by other APF modules, which will cause circulation between multiple APF modules, resulting in instability of the compensation system and even cause resonance problems in the system. To solve the above-mentioned existing problems, the current existing technology generally adds another set of identical CTs to collect the total APF output current, and physically connects the two sets of CTs together. In this way, the load current can be obtained by subtracting the total APF output current from the grid-side CT current. The above-mentioned load-side algorithm is then used to achieve the purpose of APF current sharing and harmonic compensation. However, the existing solution also increases costs by adding a set of CTs. At the same time, different CTs also have the problem of detection deviation, and the detection deviation will also affect the compensation effect. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a single-group CT control method and control system for an active power filter on the grid side, aiming to solve the problem that an additional group of CT detection is needed on the grid side, which increases costs, and different CT detections also have detection deviations, and the detection deviations will also affect the compensation effect.

[0005] The technical solutions adopted by the present invention to solve the above technical problems are as follows:

[0006] A first aspect of the present invention provides a method for controlling a single CT group on the grid side of an active power filter, the method comprising the following steps:

[0007] Real-time dynamic collection of grid-side current and APF module output current;

[0008] Get the number of parallel APF modules;

[0009] Calculate the load current according to the grid-side current, the APF module output current, and the number of APF modules;

[0010] Extract the sine and cosine components of each harmonic of the load current at the current time;

[0011] Calculate the sine component and cosine component of each harmonic to be compensated at the current time and the average value of the sine component and cosine component corresponding to each harmonic;

[0012] Calculate the difference between the average value of the sine component and cosine component of each harmonic at the current time and the sine component and cosine component of each harmonic at the previous time;

[0013] The difference between the sine component and the cosine component of each harmonic is adjusted and synthesized into a given current;

[0014] The output current of the APF module is adjusted according to the given current to follow the given current.

[0015] In one embodiment, the capacities of the APF modules may be the same or different. When the capacities of the APF modules are different, after the real-time dynamic acquisition of the grid-side current and the APF module output current and before the calculation of the load current, the steps further include:

[0016] The APF module sends out the capacity of the module and receives the capacity of other APF modules;

[0017] Calculate the total capacity of parallel APF modules to compensate for harmonics;

[0018] Calculate the capacity share of this module based on the capacity of this module and the total capacity of the parallel APF modules.

[0019] In one embodiment, after the step of extracting the sine component and cosine component of each harmonic of the load current at the current time, the method further includes:

[0020] Receive the sine and cosine components of each harmonic calculated by other APF modules;

[0021] Send out the sine and cosine components of each harmonic calculated by the current APF module.

[0022] In one embodiment, the formula for calculating the load current based on the collected grid-side current, the APF module output current, and the number of APF modules is:

[0023] i Load =i CT -Ni APF

[0024] Among them, i Load is the calculated load current, i CT is the collected grid-side current, i APF is the output current of any APF module, N represents the number of parallel APF modules, and N is greater than or equal to 1.

[0025] In one embodiment, extracting the sine component and cosine component of each harmonic of the load current at the current time, and calculating the sine component and cosine component of each harmonic to be compensated at the current time and the average value of the sine component and cosine component of each harmonic includes:

[0026] The sine and cosine components of each harmonic of the load current extracted by the harmonic extraction algorithm are expressed by the following formula:

[0027]

[0028] Among them, i L o ad is the load current, Q k Indicates the extraction of the sinusoidal component of the kth harmonic; P k Indicates the extraction of the cosine component of the kth harmonic;

[0029] Number the N APF modules in sequence and calculate the sinusoidal component Q of the kth harmonic extracted by the APF module numbered m. km and cosine component P km ;

[0030] The sine component and cosine component of the kth harmonic to be compensated are calculated by the APF module numbered m.

[0031] The sine component calculated by the APF module numbered m Cosine component Transmit to other APF modules in parallel in the system and receive the sinusoidal components sent by other APF modules Cosine component

[0032] According to the sine component Cosine component The average values ​​of the sine and cosine components of the kth harmonic are:

[0033]

[0034]

[0035] Where m is a natural number less than or equal to N, P avgk represents the average value of the cosine component of the kth harmonic, Q avgk Represents the average value of the sinusoidal component of the kth harmonic.

[0036] In one embodiment, when the capacities of the APF modules are different, the formula for the average value of the sine component and the cosine component of the kth harmonic is: equal

[0037] in, C k is the current APF module capacity, C Total It is the total capacity of all parallel APF modules. After adjustment, APF modules of different capacities will output in proportion to their capacity.

[0038] In one embodiment, the subtraction of the average value of the sine component and the cosine component of each harmonic at the current time from the sine component and the cosine component of each harmonic at the previous time comprises using the following formula:

[0039] E Qk =Q avgk -Q ref (a-1) k

[0040] E Pk =P avgk -P ref (a-1) k

[0041] Adjusting the difference between the sine component and the cosine component of each harmonic includes adjusting the sine component and the cosine component of the kth harmonic of the APF module using the formula:

[0042] Q ref (a) k =Q ref (a-1) k +E Qk *k pk

[0043] P ref (a) k =P ref (a-1) k +EPk *k pk

[0044] Among them, E Qk is the difference between the average value of the sinusoidal component of the kth harmonic and the given sinusoidal component of the previous time,

[0045] E Pk is the difference between the average value of the cosine component of the kth harmonic and the given cosine component of the previous time,

[0046] k pk is the kth harmonic proportional adjustment coefficient,

[0047] Q ref (a) k is the adjusted kth harmonic sinusoidal component,

[0048] P ref (a) k is the adjusted kth harmonic cosine component,

[0049] Q ref (a-1) k is the kth harmonic sinusoidal component of the previous time,

[0050] P ref (a-1) k is the kth harmonic cosine component of the previous time.

[0051] In one embodiment, the formula for adjusting the difference between the sine component and the cosine component of each harmonic to synthesize the given current is:

[0052]

[0053] Among them, i ref is the given current, ω is the fundamental angular frequency, k is the harmonic order, Q ref (a) k is the kth harmonic sinusoidal component at the current time, P ref (a) k is the kth harmonic cosine component at the current time.

[0054] A second aspect of the present invention further provides an active power filter grid-side single-group CT control system, the system adopts the above-mentioned active power filter grid-side single-group CT control method, the system includes a plurality of APF modules connected in parallel on the grid side and a current transformer connected in series with the plurality of APF modules, the APF modules are connected by a communication line, the current transformer is used to collect grid-side current, the APF module includes a sampling unit, an algorithm unit, and a communication unit connected to each other, and the algorithm unit is also connected to a converter; wherein

[0055] The sampling unit is used to receive the grid-side current collected by the current transformer and collect the output current of the APF module;

[0056] The algorithm unit is used to calculate the sine component and cosine component of each harmonic to be compensated at the current time and the average value of the sine component and cosine component corresponding to each harmonic, and to find the difference between the calculated average value and the sine component and cosine component of each harmonic at the previous time, adjust the difference between the sine component and cosine component of each harmonic to be calculated and synthesize a given current, and at the same time control and adjust the deviation between the given current and the output current of the APF module;

[0057] The converter is configured to generate an output current that varies with the given current;

[0058] The communication unit is used for communication and interaction between parallel APF modules.

[0059] In one embodiment, the algorithm unit is configured to execute the following algorithm:

[0060] The sine and cosine components of each harmonic of the load current extracted by the harmonic extraction algorithm are expressed by the following formula:

[0061] Among them, i L o ad is the load current, Q k Indicates the extraction of the sinusoidal component of the kth harmonic; P k Indicates the extraction of the cosine component of the kth harmonic;

[0062] Number the N APF modules in sequence and calculate the sinusoidal component Q of the kth harmonic extracted by the APF module numbered m. km and cosine component P km ;

[0063] The sine component and cosine component of the kth harmonic to be compensated are calculated by the APF module numbered m.

[0064] According to the sine component and cosine components The average value of the sine and cosine components of the kth harmonic is:

[0065]

[0066]

[0067] Where m is a natural number less than or equal to N, P avgk represents the average value of the cosine component of the kth harmonic, Q avgk represents the average value of the sinusoidal component of the kth harmonic;

[0068] When the capacities of the APF modules are different, the formula for the average value of the sine component and cosine component of the kth harmonic is equal

[0069] in, C k is the current APF module capacity, C Total It is the total capacity of all parallel APF modules. After adjustment, APF modules of different capacities will output in proportion to their capacity.

[0070] In one embodiment, the algorithm unit is further configured to execute the following algorithm:

[0071] Calculate the difference between the sine and cosine components of each harmonic; the formula is as follows:

[0072] E Qk =Q avgk -Q ref (a-1) k

[0073] E Pk =P avgk -P ref (a-1) k

[0074] The sine and cosine components of the kth harmonic of the APF module are adjusted according to the following formula:

[0075] Q ref (a) k =Q ref (a-1) k +E Qk *k pk

[0076] P ref (a) k =P ref (a-1) k +E Pk *k pk

[0077] Among them, E Qk It is the difference between the average value of the sinusoidal component of the kth harmonic and the given sinusoidal component of the previous time;

[0078] E Pk It is the difference between the average value of the cosine component of the kth harmonic and the given cosine component of the previous time;

[0079] k pk is the kth harmonic proportional adjustment coefficient;

[0080] Q ref (a) k is the adjusted kth harmonic sinusoidal component;

[0081] P ref (a) k is the adjusted kth harmonic cosine component;

[0082] P avgk represents the average value of the cosine component of the kth harmonic,

[0083] Q avgk represents the average value of the sinusoidal component of the kth harmonic;

[0084] Q ref (a-1) k is the kth harmonic sinusoidal component of the previous time;

[0085] P ref (a-1) k is the kth harmonic cosine component of the previous time;

[0086] The formula for synthesizing the given current by adjusting the difference between the sine component and cosine component of each harmonic is:

[0087]

[0088] Among them, i ref is the given current, ω is the fundamental angular frequency, k is the harmonic order, Q ref (a) k is the kth harmonic sinusoidal component at the current time, P ref (a) k is the kth harmonic cosine component at the current time.

[0089] The embodiment of the present invention provides a single-group CT control method and control system for the grid side of an active power filter. The method described in the embodiment of the present application dynamically collects the grid side current and the output current of the APF module in real time; obtains the number of parallel APF modules; calculates the load current according to the collected grid side current and the output current of the APF module and the number of APF modules; extracts the sine component and cosine component of each harmonic of the load current at the current time; calculates the sine component and cosine component of each harmonic to be compensated at the current time and the average value of the sine component and cosine component of each harmonic; and adds the sine component and cosine component of each harmonic at the current time. The average value of the component is given by the sine component and the cosine component of each harmonic at the previous time, the difference between the sine component and the cosine component of each harmonic is adjusted and synthesized into a given current, and the output current of the APF module is adjusted to follow the given current and offset with the load current; the present application implements the algorithm through software control, which can achieve current sharing compensation for multiple APF modules through a single group of CTs on the grid side. Compared with the prior art, the method described in the embodiment of the present application can effectively save system costs, improve system stability, and avoid the problem that different CT detections have detection deviations that affect the compensation effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0090] Figure 1 This is a method flow chart of an embodiment of a method for controlling a single group of CTs on the grid side of an active power filter according to the present invention;

[0091] Figure 2 A method flow chart of another embodiment of the method for controlling a single CT group on the grid side of an active power filter provided by an embodiment of the present invention;

[0092] Figure 3 This is a structural block diagram of a single-group CT control system on the grid side of an active power filter according to an embodiment of the present invention;

[0093] Figure 4 The figure is a schematic structural diagram of a single-group CT control system on the grid side of an active power filter according to an embodiment of the present invention. DETAILED DESCRIPTION

[0094] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention clearer and more understandable, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0095] The parallel active power filter (APF) is connected in parallel in the power grid system. For any APF, the harmonic current i APF Can be expressed by the following formula:

[0096]

[0097] Among them, ω is the fundamental angular frequency, k is the harmonic order, A k is the kth harmonic sinusoidal component, B k is the kth harmonic cosine component.

[0098] According to the above formula, if the sine and cosine components of each harmonic output by each APF module in the parallel system are the same, then the amplitude and phase of the harmonic current output by each APF module in the parallel system are also the same. However, due to the circulating current generated between multiple APF modules, there will inevitably be a large deviation in the sine and cosine components of the harmonic output. According to the control principle, the output of the APF will follow the changes in the reference (given) current. Therefore, as long as the sine and cosine components of the given current of each APF are adjusted in real time so that the sine and cosine components of the harmonic output by the APF module maintain a dynamic balance, multiple APF modules can be compensated by using a single group of CTs on the grid side.

[0099] The specific implementation of the multi-module parallel control method of the active power filter of the present application is described in detail below.

[0100] Example 1:

[0101] This invention provides a method for controlling a single CT group on the grid side of an active power filter. Figure 1 and Figure 2 , the method comprises the following steps:

[0102] S101, real-time dynamic collection of grid side current and APF module output current;

[0103] Specifically, a current transformer is used to dynamically collect the grid-side current in real time, the collected grid-side current is received by a sampling unit of the APF module, and the output current of the APF module is dynamically collected at the same time.

[0104] S102, obtaining the number of parallel APF modules;

[0105] Specifically, obtaining the number of parallel APF modules includes the following steps:

[0106] The APF module sends out the working status of the module and receives the working status sent by other APF modules;

[0107] The number of working parallel APF modules is obtained based on the working status of all APF modules.

[0108] S103, calculating the load current according to the collected grid-side current, the APF module output current, and the number of APF modules;

[0109] Specifically, we first assume that the parallel system composed of N APF modules has a steady-state output. At this time, the output current of each APF module is the same. Assuming that the output current collected by any APF module is i APF , then the total output current can be considered as Ni APF , for any APF module connected in parallel in the system, the calculated load current is:

[0110] i Load =i CT -Ni APF (2)

[0111] Among them, i Load is the calculated load current, i CT is the collected grid-side current.

[0112] S104, extracting the sine component and cosine component of each harmonic of the load current at the current time;

[0113] Specifically, through the harmonic extraction algorithm (Fourier or other harmonic extraction algorithm), the sine component and cosine component of each harmonic of the load current extracted by any APF module can be expressed as:

[0114]

[0115] Among them, Q k 、P k Extract the sine component and cosine component of the kth harmonic respectively, number the N APF modules in sequence, and let Q km , P km They represent the sine component and cosine component of the kth harmonic extracted by the APF module numbered m;

[0116] S105, calculating the sine component and cosine component of each harmonic to be compensated at the current time and the average value of the sine component and cosine component of each harmonic;

[0117] Specifically, receive the sine and cosine components of each harmonic calculated by other APF modules; send out the sine and cosine components of each harmonic calculated by the current APF module. For N APF modules, number the APF modules in sequence and calculate the sine component Q of the kth harmonic extracted by the APF module numbered m. km and cosine component P km ;

[0118] For the APF module numbered m, the sine component and cosine component of the kth harmonic to be compensated are calculated as follows: The sinusoidal component calculated by the current APF module is transmitted through the communication unit of the APF module numbered m. Cosine component Transmit to other APF modules in parallel in the system, and receive the sinusoidal components sent by other APF modules at the same time Cosine component The average values ​​of the sine and cosine components of the kth harmonic can be obtained as follows:

[0119]

[0120]

[0121] Where m is a natural number less than or equal to N, P avgk represents the average value of the cosine component of the kth harmonic, Q avgk Represents the average value of the sinusoidal component of the kth harmonic.

[0122] S106, calculating the difference between the average value of the sine component and cosine component of each harmonic at the current time and the given sine component and cosine component of each harmonic at the previous time;

[0123] Specifically, according to the above-mentioned average value of the sine component and cosine component of the kth harmonic, the average value of the sine component and cosine component of the current harmonic and the given difference between the sine component and cosine component of the previous harmonic are calculated; the formula is as follows:

[0124] E Qk =Q avgk -Q ref (a-1) k (6)

[0125] E Pk =P avgk -P ref (a-1) k (7)

[0126] Among them, E Qk is the difference between the average value of the sinusoidal component of the kth harmonic and the given sinusoidal component of the previous time,

[0127] E Pk It is the difference between the average value of the cosine component of the kth harmonic and the given sine component of the previous time.

[0128] S107, adjusting the difference between the sine component and the cosine component of each harmonic to be obtained and synthesizing a given current;

[0129] Specifically, according to the above-mentioned average values ​​of the sine component and cosine component of the kth harmonic, after calculating the difference between the sine component and cosine component of each harmonic, it is further possible to add a loop adjustment to the sine component and cosine component of each harmonic to synthesize a given current, so that the output current of each APF module is dynamically balanced.

[0130] The harmonic sinusoidal component adjustment adopts the following formula:

[0131] Q ref (a) k =Q ref (a-1) k +E Qk *k pk

[0132] Combined with the harmonic sinusoidal component given difference formula (6), the comprehensive expression is:

[0133] Q ref (a) k =Q ref (a-1) k +(Q avgk -Q ref (a-1) k )k pk (6-1)

[0134] The harmonic cosine component adjustment adopts the following formula:

[0135] P ref (a) k =P ref (a-1) k +E Pk *k pk

[0136] Combined with the harmonic cosine component given difference formula (7), the comprehensive expression is:

[0137] P ref (a) k =P ref (a-1) k +(P avgk -P ref (a-1) k )k pk (7-1)

[0138] Among them, k pk is the kth harmonic proportional adjustment coefficient,

[0139] Q ref (a) k is the adjusted kth harmonic sinusoidal component,

[0140] P ref (a) k is the adjusted kth harmonic cosine component,

[0141] Q ref (a-1) k is the kth harmonic sinusoidal component of the previous time,

[0142] P ref (a-1) k is the kth harmonic cosine component of the previous time.

[0143] According to the sine and cosine components of the kth harmonic obtained above, the formula for adjusting and synthesizing the given current is:

[0144]

[0145] Among them, i ref is the given current, ω is the fundamental angular frequency, k is the harmonic order, Q ref (a) k The kth harmonic sinusoidal component of the current time is given, P ref (a) k The kth harmonic cosine component is given at the current time.

[0146] Since each APF module is phase-locked to track the grid voltage, it can be ensured that the sin(kωt) and cos(kωt) of each APF module are the same. When the system is in steady state, The deviation is zero, and the i of each APF module ref The same can maintain the dynamic equalization of the harmonics output by each APF module.

[0147] S108 , adjusting the output current of the APF module according to the given current to follow the given current.

[0148] Specifically, the deviation between the synthesized given current and the output current of the APF module is adjusted by the algorithm unit, and a PWM pulse regulation converter is further generated by adopting control algorithms such as PR control and repetitive control, so that its output follows the same current as the given current, and the output current and the load harmonic current offset each other.

[0149] The capacities of the APF modules may be the same or different. In this embodiment, the capacities of the APF modules are the same. In one embodiment, when the capacities of the APF modules are different, after the real-time dynamic collection of the grid-side current and the harmonic current output by the APF module and before the calculation of the load current, the following steps are further included:

[0150] S201, the APF module sends the capacity of the module and receives the capacity of other APF modules;

[0151] S202, calculating the total capacity of the parallel APF modules for compensating harmonics;

[0152] S203. Calculate the capacity proportion of the APF module according to the capacity of the APF module and the total capacity of the parallel APF modules.

[0153] When the capacities of the APF modules are different, the average values ​​of the sine and cosine components of the kth harmonic in formulas (4) and (5) are: equal

[0154] in, C k is the current APF module capacity, C Total It is the total capacity of all parallel APF modules. After adjustment, APF modules of different capacities will output in proportion to their capacity.

[0155] After obtaining the average value of the sine component and cosine component of the kth harmonic, the output current of each APF module can be dynamically balanced by further adding loop adjustments of the sine component and cosine component of each harmonic.

[0156] The following example illustrates the method of the embodiment of the present application, where two APF modules of equal capacity are connected in parallel in a system and the load contains the fifth harmonic. Assume that the APF modules are numbered 1# and 2#, respectively, and the expression of the load current is:

[0157] i Load =100sin(ωt+ψ1)+100sin(5ωt)+50cos(5ωt),

[0158] When the APF module is not compensated, the grid-side CT currents detected by the 1# and 2# APF modules are:

[0159] i CT =100sin(ωt+ψ1)+100sin(5ωt)+50cos(5ωt),

[0160] Since the output harmonics of 1# and 2#APF modules are both 0 at this time, the 5th harmonic sine component extracted by the harmonic extraction algorithm is 100A and the cosine component is 50A. The 5th harmonic sine component to be compensated calculated by 1#APF module is Cosine component The 5th harmonic sinusoidal component to be compensated calculated by 2#APF module Cosine component

[0161] Furthermore, the average values ​​of the sine component and the cosine component are obtained as Q avg5 =50,P avg5 =25, for the 5th harmonic sinusoidal component of 1#APF module:

[0162] P ref (a) 51 =Pref (a-1) 51 +(25-P ref (a-1) 51 )*k p5 ,

[0163] It can be seen that after the compensation reaches steady state, P ref (a) 51 =25, for the 5th harmonic cosine component of 1#APF module: Q ref (a) 51 =Q ref (a-1) 51 +(50-Q ref (a-1) 51 )*k p5 ,

[0164] It can be seen that after the compensation reaches steady state, Q ref (a) 51 =50,

[0165] The same result is obtained for 2#APF module. ref (a) 52 =25,Q ref (a) 52 =50, if the 2#APF module exits due to a fault, the harmonics compensated by the 2#APF module will be released to the grid. CT =100sin(ωt+ψ1)+50sin(5ωt)+25cos(5ωt), since the harmonics compensated by the 1#APF module are i APF =50sin(5ωt)+25cos(5ωt), and the 1#APF module detects through the communication unit that only this APF module is performing online compensation, so the extracted 5th harmonic sine component is 100A and the cosine component is 50A. Cosine component

[0166] The average values ​​of the sine component and cosine component are further obtained as: Q avg5 =100,P avg5 =50, because when the 2#APF module exits, the initial state of the 5th cosine harmonic of the 1#APF module is P ref (a) 51 =25,Q ref (a) 51 =50, then

[0167] P ref (a) 51 =25+(50-25)*k p5 , Q ref(a) 51 =50+(100-50)*k p5 , we can know that:

[0168] Steady-state P ref (a) 51 =50,Q ref (a) 51 =100. It can be seen from the embodiments of the present application that the method of the present invention can realize current sharing compensation for multiple APF modules using a single group of CTs on the grid side.

[0169] The control method for a single CT group on the grid side of the active power filter described in the embodiment of the present application dynamically collects the grid side current and the output current of the APF module in real time; obtains the number of parallel APF modules; calculates the load current based on the collected grid side current and the output current of the APF module and the number of APF modules; extracts the sine component and cosine component of each harmonic of the load current at the current time; calculates the sine component and cosine component of each harmonic to be compensated at the current time and the average value of the sine component and cosine component of each harmonic; compares the average value of the sine component and cosine component of each harmonic at the current time with the average value of the sine component and cosine component of the previous time; The difference between the sine component and the cosine component of each harmonic is given, the difference between the sine component and the cosine component of each harmonic is adjusted and synthesized into a given current, and the output current of the APF module is adjusted to follow the given current and offset with the load current; the present application implements the algorithm through software control, so that current sharing compensation of multiple APF modules can be achieved through a single group of CTs on the grid side. Compared with the prior art, the method described in the embodiment of the present application can effectively save system cost, improve system stability, and avoid the problem that detection deviation of different CTs affects the compensation effect.

[0170] Example 2:

[0171] See also Figure 3 and Figure 4 , the embodiment of the present application also provides an active power filter grid-side single-group CT control system, the active power filter grid-side single-group CT control system is applied in the above-mentioned active power filter grid-side single-group CT control method, the system includes a plurality of APF modules 10 connected in parallel on the grid side and a current transformer 20 connected in series with the plurality of APF modules, the APF modules 10 are connected to each other via a communication line, the current transformer 20 is used to collect grid-side current, the APF module 10 includes a sampling unit 101, an algorithm unit 102, and a communication unit 103 connected to each other, the algorithm unit 101 is also connected to a converter 104; wherein

[0172] The sampling unit 101 is used to receive the grid-side current collected by the current transformer 20 and collect the output current of the APF module 10;

[0173] The algorithm unit 102 is used to calculate the sine component and cosine component of each harmonic to be compensated at the current time and the average value of the sine component and cosine component of each harmonic, and calculate the difference between the average value and the sine component and cosine component of each harmonic at the previous time, adjust the difference between the sine component and cosine component of each harmonic to synthesize a given current, and control and adjust the deviation between the given current and the output current of the APF module;

[0174] The converter 104 is configured to generate an output current that varies with the given current.

[0175] The communication unit 103 is used for communication and interaction between parallel APF modules.

[0176] Specifically, the algorithm unit 102 is configured to execute the following algorithm:

[0177] The sine and cosine components of each harmonic of the load current extracted using the harmonic extraction algorithm can be expressed by the following formula:

[0178]

[0179] Among them, i L o ad is the load current, Q k Indicates the extraction of the sinusoidal component of the kth harmonic; P k Indicates the extraction of the cosine component of the kth harmonic;

[0180] Number the N APF modules in sequence and calculate the sinusoidal component Q of the kth harmonic extracted by the APF module numbered m. km and cosine component P km ;

[0181] The sine component and cosine component of the kth harmonic to be compensated are calculated by the APF module numbered m.

[0182] The sinusoidal component calculated by the APF module numbered m is transmitted through the communication unit 103 Cosine component Transmit to other APF modules in the parallel APF module system, and receive the sinusoidal components emitted by other APF modules at the same time Cosine component

[0183] According to the sine component and cosine components The average value of the sine and cosine components of the kth harmonic is:

[0184]

[0185]

[0186] Where m is less than or equal to N; P avgk represents the average value of the cosine component of the kth harmonic, Q avgk represents the average value of the sinusoidal component of the kth harmonic;

[0187] When the capacities of the APF modules are different, the formula for the average value of the sine component and cosine component of the kth harmonic is equal

[0188] in, C k is the current APF module capacity, C Total It is the total capacity of all parallel APF modules. After adjustment, APF modules of different capacities will output in proportion to their capacity.

[0189] The difference between the average value of the sine and cosine components of the current harmonics and the sine and cosine components of the previous harmonics is calculated using the following formula:

[0190] E Qk =Q avgk -Q ref (a-1) k (6)

[0191] E Pk =P avgk -P ref (a-1) k (7)

[0192] Among them, E Qk is the difference between the average value of the sinusoidal component of the kth harmonic and the given sinusoidal component of the previous time,

[0193] E Pk is the difference between the average value of the cosine component of the kth harmonic and the given cosine component of the previous time,

[0194] Q ref (a-1) k is the kth harmonic sinusoidal component of the previous time,

[0195] P ref (a-1) k is the kth harmonic cosine component of the previous time.

[0196] Specifically, after obtaining the average value of the sine component and cosine component of the kth harmonic according to the above, the difference between the sine component and cosine component of each harmonic can be further calculated, and the loop adjustment of the sine component and cosine component of each harmonic can be added to synthesize a given current, so that the output current of each APF module is dynamically balanced.

[0197] The harmonic sinusoidal component adjustment adopts the following formula:

[0198] Q ref (a) k =Q ref (a-1) k +E Qk *k pk

[0199] Combined with the harmonic sinusoidal component given difference formula (6), the comprehensive expression is:

[0200] Q ref (a) k =Q ref (a-1) k +(Q avgk -Q ref (a-1) k )k pk (6-1)

[0201] The harmonic cosine component adjustment adopts the following formula:

[0202] P ref (a) k =P ref (a-1) k +E Pk *k pk

[0203] The harmonic cosine component is given by the difference formula (7), which is comprehensively expressed as:

[0204] P ref (a) k =P ref (a-1) k +(P avgk -P ref (a-1) k )k pk (7-1)

[0205] Among them, E Qk is the difference between the average value of the sinusoidal component of the kth harmonic and the given sinusoidal component of the previous time,

[0206] E Pk is the difference between the average value of the cosine component of the kth harmonic and the given cosine component of the previous time,

[0207] k pk is the kth harmonic proportional adjustment coefficient,

[0208] Q ref (a) k is the adjusted kth harmonic sinusoidal component,

[0209] P ref (a) k is the adjusted kth harmonic cosine component,

[0210] Q ref (a-1) k is the kth harmonic sinusoidal component of the previous time,

[0211] P ref (a-1) k is the kth harmonic cosine component of the previous time.

[0212] According to the sine and cosine components of the kth harmonic obtained above, the formula for adjusting and synthesizing the given current is:

[0213]

[0214] Among them, i ref is the given current, ω is the fundamental angular frequency, k is the harmonic order, Q ref (a) k is the kth harmonic sinusoidal component, P ref (a) k is the kth harmonic cosine component.

[0215] Specifically, the communication unit 103 is configured to: calculate the sinusoidal component obtained by the APF module numbered m Cosine component Transmit to other APF modules in the parallel APF module system, and receive the sinusoidal components emitted by other APF modules at the same time Cosine component

[0216] The following example illustrates the working principle of the single-group CT control system on the grid side of the active power filter described in the embodiment of the present application, taking two APF modules of equal capacity connected in parallel in the system and the load containing the fifth harmonic as an example. Assume that the APF modules are numbered 1# and 2#, respectively, and the expression of the load current is:

[0217] i Load =100sin(ωt+ψ1)+100sin(5ωt)+50cos(5ωt),

[0218] When the APF module is not compensated, the CT currents detected by the 1# and 2# APF modules are:

[0219] i CT =100sin(ωt+ψ1)+100sin(5ωt)+50cos(5ωt),

[0220] Since the output harmonics of 1# and 2#APF modules are both 0 at this time, the 5th harmonic sine component extracted by the harmonic extraction algorithm is 100A and the cosine component is 50A. The 5th harmonic sine component to be compensated calculated by 1#APF module is Cosine component The 5th harmonic sinusoidal component to be compensated calculated by 2#APF module Cosine component

[0221] Furthermore, the average values ​​of the sine component and the cosine component are obtained by the algorithm unit 102 and are Q avg5 =50,P avg5 =25, for the 5th harmonic sinusoidal component of 1#APF module:

[0222] P ref (a) 51 =P ref (a-1) 51 +(25-P ref (a-1) 51 )*k p5 ,

[0223] It can be seen that after the compensation reaches steady state, P ref (a) 51 =25, for the 5th harmonic cosine component of 1#APF module: Q ref (a) 51 =Q ref (a-1) 51 +(50-Q ref (a-1) 51 )*k p5 ,

[0224] It can be seen that after the compensation reaches steady state, Q ref (a) 51 =50,

[0225] The same result is obtained for 2#APF module. ref (a) 52 =25,Q ref (a) 52 =50, if the 2#APF module exits due to a fault, the harmonics compensated by the 2#APF module will be released into the power grid. For the 1#APF module, the current transformer detected by the current transformer is CT=100sin(ωt+ψ1)+50sin(5ωt)+25cos(5ωt), so the harmonic compensated by 1#APF module is i APF =50sin(5ωt)+25cos(5ωt). Since the 1#APF module detects through the communication unit that only this APF module is online for compensation, the extracted 5th harmonic sine component is 100A and the cosine component is 50A, that is, Cosine component

[0226] The average values ​​of the sine component and cosine component are further obtained as: Q avg5 =100,P avg5 =50, because when the 2#APF module exits, the initial state of the 5th harmonic of the 1#APF module is P ref (a) 51 =25,Q ref (a) 51 =50, then

[0227] P ref (a) 51 =25+(50-25)*k p5 , Q ref (a) 51 =50+(100-50)*k p5 , we can know that:

[0228] Steady-state P ref (a) 51 =50,Q ref (a) 51 =100. It can be seen from the embodiment that the active power filter grid-side single-group CT control system of the present invention can realize current sharing compensation for multiple parallel APF modules through a single group of CTs on the grid side.

[0229] The active power filter grid-side single-group CT control system described in the embodiment of the present application collects the grid-side current through the current transformer 20, and the communication unit 103 realizes communication interaction between the parallel APF modules, and the sampling unit 101 collects the output current of the APF module; the algorithm unit 102 calculates the sine component and cosine component of each harmonic to be compensated at the current time and the average value of the sine component and cosine component of each harmonic, and calculates the difference between the average value of the sine component and cosine component of each harmonic and the sine component and cosine component of each harmonic at the previous time, adjusts the difference between the sine component and cosine component of each harmonic to be calculated and synthesizes a given current, and adjusts the output current of the APF module to follow the given current so that it and the harmonic current contained in the load offset each other, so that current sharing compensation of multiple APF modules can be achieved through a single group of CTs on the grid side. Compared with the prior art, the system described in the embodiment of the present application can effectively save system cost, improve system stability, and avoid the problem of detection deviation of different CTs affecting the compensation effect.

[0230] Example 3:

[0231] According to one embodiment of the present invention, a computer-readable storage medium is provided, on which a computer program is stored. When the computer program is executed by a processor, the steps of the above-mentioned active power filter grid-side single CT control method are implemented. The specific steps are as described in Example 1 and are not repeated here.

[0232] The memory in this embodiment can be used to store software programs and various data. The memory may primarily include a program storage area and a data storage area. The program storage area may store an operating system, at least one application required for a function, and the data storage area may store data generated based on the use of the mobile phone. Furthermore, the memory may include high-speed random access memory and non-volatile memory, such as at least one disk storage device, flash memory device, or other volatile solid-state storage device.

[0233] According to an example of this embodiment, all or part of the processes in the above-mentioned method can be completed by a computer program instructing related hardware. The program can be stored in a computer-readable storage medium. For example, in the embodiment of the present invention, the program can be stored in a storage medium of a computer system and executed by at least one processor in the computer system to implement the processes including the embodiments of the above-mentioned methods. The storage medium includes but is not limited to a magnetic disk, a USB flash drive, an optical disk, a read-only memory (ROM), etc.

[0234] It should be noted that, in this document, the terms "comprises," "includes," or any other variations thereof are intended to encompass non-exclusive inclusion, such that a process, method, article, or apparatus comprising a series of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of other identical elements in the process, method, article, or apparatus comprising the element.

[0235] The serial numbers of the above embodiments of the present invention are for description only and do not represent the advantages or disadvantages of the embodiments.

[0236] Through the description of the above embodiments, those skilled in the art can clearly understand that the above-mentioned embodiment methods can be implemented by means of software plus the necessary general hardware platform, and of course can also be implemented by hardware, but in many cases the former is a better embodiment. Based on this understanding, the technical solution of the present invention, or the part that contributes to the prior art, can be embodied in the form of a software product, which is stored in a storage medium (such as ROM / RAM, magnetic disk, optical disk), and includes a number of instructions for enabling a terminal (which can be a mobile phone, computer, server, air conditioner, or network device, etc.) to execute the methods described in each embodiment of the present invention.

[0237] The embodiments of the present invention are described above in conjunction with the accompanying drawings, but the present invention is not limited to the above-mentioned specific implementation methods. The above-mentioned specific implementation methods are merely illustrative and not restrictive. Under the guidance of the present invention, ordinary technicians in this field can also make many forms without departing from the scope of protection of the present invention and the claims, all of which are protected by the present invention.

Claims

1. A method for controlling a single CT group on the grid side of an active power filter, characterized in that: The method comprises the following steps: Real-time dynamic collection of grid-side current and APF module output current; Get the number of parallel APF modules; Calculate the load current according to the grid-side current, the APF module output current, and the number of APF modules; Extract the sine and cosine components of each harmonic of the load current at the current time; Calculate the sine component and cosine component of each harmonic to be compensated at the current time and the average value of the sine component and cosine component corresponding to each harmonic; Calculate the difference between the average value of the sine component and cosine component of each harmonic at the current time and the sine component and cosine component of each harmonic at the previous time; The difference between the sine component and the cosine component of each harmonic is adjusted and synthesized into a given current; The output current of the APF module is adjusted according to the given current to follow the given current.

2. The active power filter grid side single CT control method according to claim 1, characterized in that: The capacities of the APF modules may be the same or different. When the capacities of the APF modules are different, after the real-time dynamic acquisition of the grid-side current and the APF module output current and before the calculation of the load current, the method further includes the following steps: The APF module sends out the capacity of the module and receives the capacity of other APF modules; Calculate the total capacity of parallel APF modules to compensate for harmonics; Calculate the capacity share of this module based on the capacity of this module and the total capacity of the parallel APF modules.

3. The active power filter grid-side single CT control method according to claim 1 or 2, characterized in that: After the step of extracting the sine component and cosine component of each harmonic of the load current at the current time, the method further includes: Receive the sine and cosine components of each harmonic calculated by other APF modules; Send out the sine and cosine components of each harmonic calculated by the current APF module.

4. The active power filter grid-side single CT control method according to claim 3, characterized in that: The formula for calculating the load current based on the collected grid-side current, the APF module output current, and the number of APF modules is: it Load =i CT -In APF Among them, i Load is the calculated load current, i CT is the collected grid-side current, i APF is the output current of any APF module, N represents the number of parallel APF modules, and N is greater than or equal to 1.

5. The active power filter grid side single CT control method according to claim 4, characterized in that: The extracting of the sine component and cosine component of each harmonic of the load current at the current time, and calculating the sine component and cosine component of each harmonic to be compensated at the current time and the average value of the sine component and cosine component of each harmonic includes: The sine and cosine components of each harmonic of the load current extracted by the harmonic extraction algorithm are expressed by the following formula: Among them, i Load is the load current, Q k Indicates the extraction of the sinusoidal component of the kth harmonic; P k Indicates the extraction of the cosine component of the kth harmonic; Number the N APF modules in sequence and calculate the sinusoidal component Q of the kth harmonic extracted by the APF module numbered m. km and cosine component P km ; The sine component and cosine component of the kth harmonic to be compensated are calculated by the APF module numbered m. The sine component calculated by the APF module numbered m Cosine component Transmit to other APF modules in parallel in the system and receive the sinusoidal components sent by other APF modules Cosine component According to the sine component Cosine component The average values ​​of the sine and cosine components of the kth harmonic are: Where m is a natural number less than or equal to N, P avgk represents the average value of the cosine component of the kth harmonic, Q avgk Represents the average value of the sinusoidal component of the kth harmonic.

6. The active power filter grid-side single CT control method according to claim 5, characterized in that: When the capacities of the APF modules are different, the formula for the average value of the sine component and cosine component of the kth harmonic is equal in, C k is the current APF module capacity, C Total It is the total capacity of all parallel APF modules. After adjustment, APF modules of different capacities will output in proportion to their capacity.

7. The control method for a single CT group on the grid side of an active power filter according to claim 5 or 6, characterized in that: The difference between the average value of the sine component and the cosine component of each harmonic at the current time and the sine component and the cosine component of each harmonic at the previous time includes using the following formula: E Qk =Q avgk -Q ref (a-1) k E Pk =P avgk -P ref (a-1) k Adjusting the difference between the sine component and the cosine component of each harmonic includes adjusting the sine component and the cosine component of the kth harmonic of the APF module using the formula: Q ref (a) k =Q ref (a-1) k +E Qk *k pk P ref (a) k =P ref (a-1) k +E Pk *k pk Among them, E Qk is the difference between the average value of the sinusoidal component of the kth harmonic and the given sinusoidal component of the previous time, E Pk is the difference between the average value of the cosine component of the kth harmonic and the given cosine component of the previous time, k pk is the kth harmonic proportional adjustment coefficient, Q ref (a) k is the adjusted kth harmonic sinusoidal component, P ref (a) k is the adjusted kth harmonic cosine component, Q ref (a-1) k is the kth harmonic sinusoidal component of the previous time, P ref (a-1) k is the kth harmonic cosine component of the previous time.

8. The control method for a single CT group on the grid side of an active power filter according to claim 7, characterized in that: The formula for adjusting the difference between the sine component and the cosine component of each harmonic to synthesize the given current is: Among them, i ref is the given current, ω is the fundamental angular frequency, k is the harmonic order, Q ref (a) k is the kth harmonic sinusoidal component at the current time, P ref (a) k is the kth harmonic cosine component at the current time.

9. A single-group CT control system for a grid-side active power filter, wherein the control method for a single-group CT for a grid-side active power filter described in any one of items 1 to 8 above is applied, and wherein: The system includes a plurality of APF modules connected in parallel on the grid side and a current transformer connected in series with the plurality of APF modules. The APF modules are connected via a communication line. The current transformer is used to collect grid-side current. The APF module includes a sampling unit, an algorithm unit, and a communication unit connected to each other. The algorithm unit is also connected to a converter. The sampling unit is used to receive the grid-side current collected by the current transformer and collect the output current of the APF module; The algorithm unit is used to calculate the sine component and cosine component of each harmonic to be compensated at the current time and the average value of the sine component and cosine component corresponding to each harmonic, and to find the difference between the calculated average value and the sine component and cosine component of each harmonic at the previous time, adjust the difference between the sine component and cosine component of each harmonic to be calculated and synthesize a given current, and at the same time control and adjust the deviation between the given current and the output current of the APF module; The converter is configured to generate an output current that varies with the given current; The communication unit is used for communication and interaction between parallel APF modules.

10. The active power filter grid-side single CT control system according to claim 9, characterized in that: The algorithm unit is configured to execute the following algorithm: The sine and cosine components of each harmonic of the load current extracted by the harmonic extraction algorithm are expressed by the following formula: Among them, i Load is the load current, Q k Indicates the extraction of the sinusoidal component of the kth harmonic; P k Indicates the extraction of the cosine component of the kth harmonic; Number the N APF modules in sequence and calculate the sinusoidal component Q of the kth harmonic extracted by the APF module numbered m. km and cosine component P km ; The sine component and cosine component of the kth harmonic to be compensated are calculated by the APF module numbered m. According to the sine component and cosine components The average values ​​of the sine and cosine components of the kth harmonic are: Where m is a natural number less than or equal to N, P avgk represents the average value of the cosine component of the kth harmonic, Q avgk represents the average value of the sinusoidal component of the kth harmonic; When the capacities of the APF modules are different, the formula for the average value of the sine component and cosine component of the kth harmonic is equal in, C k is the current APF module capacity, C Total It is the total capacity of all parallel APF modules. After adjustment, APF modules of different capacities will output in proportion to their capacity.

11. The active power filter grid-side single CT control system according to claim 10, characterized in that: The algorithm unit is further configured to execute the following algorithm: Calculate the difference between the sine and cosine components of each harmonic; the formula is as follows: E Qk =Q avgk -Q ref (a-1) k E Pk =P avgk -P ref (a-1) k The sine and cosine components of the kth harmonic of the APF module are adjusted according to the following formula: Q ref (a) k =Q ref (a-1) k +E Qk *k pk P ref (a) k =P ref (a-1) k +E Pk *k pk Among them, E Qk It is the difference between the average value of the sinusoidal component of the kth harmonic and the given sinusoidal component of the previous time; E Pk It is the difference between the average value of the cosine component of the kth harmonic and the given cosine component of the previous time; k pk is the kth harmonic proportional adjustment coefficient; Q ref (a) k is the adjusted kth harmonic sinusoidal component; P ref (a) k is the adjusted kth harmonic cosine component; P avgk represents the average value of the cosine component of the kth harmonic, Q avgk represents the average value of the sinusoidal component of the kth harmonic; Q ref (a-1) k is the kth harmonic sinusoidal component of the previous time; P ref (a-1) k is the kth harmonic cosine component of the previous time; The formula for synthesizing the given current by adjusting the difference between the sine component and cosine component of each harmonic is: Among them, i ref is the given current, ω is the fundamental angular frequency, k is the harmonic order, Q ref (a) k is the kth harmonic sinusoidal component at the current time, P ref (a) k is the kth harmonic cosine component at the current time.

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