Compensation control method and system based on series injection type self-adaptive impedance active power filter

Abstract

The invention discloses a compensation control method and system based on a series injection type self-adaptive impedance active power filter, and aims at overcoming the defects of an active inverter compensation control method in an existing series injection type self-adaptive impedance active power filter structure. And the problems of low compensation precision, poor robustness and the like caused by the influence of grid-side voltage harmonic waves and fundamental wave resonance branch harmonic waves are solved. According to the method, through injection-type adaptive impedance branch element parameter design and control, low capacity of the active inverter and wide reactive compensation capability of the system are realized, and meanwhile, a network side voltage harmonic component extraction module and a fundamental wave resonance branch specified subharmonic current extraction module are added in active inverter compensation control; reference current generated based on grid-side voltage harmonic extraction, a load current harmonic component and a fundamental wave resonance branch specified sub-total harmonic current are added to form an improved active inverter compensation current reference value which participates in control at the same time, and the harmonic suppression capability of the system is further enhanced.

Description

Technical Field

[0001] The present invention relates to the field of current conversion technology in electrical engineering, and in particular to a compensation control method and system for a series-injection type adaptive impedance active power filter. Background Art

[0002] With the grid connection and use of high-power nonlinear devices, the problem of power grid harmonics has become increasingly prominent. As the main device for harmonic governance, power filters can be divided into passive power filters (PPF), active power filters (APF), and hybrid active power filters (HAPF). There are various classification methods for APF, and the common ones are series type, parallel type, and series-parallel type, which are classified based on the system composition and connection method. Among them, the series type and the parallel type can be used alone or in combination with PPF to form HAPF. The series type is commonly used to improve the power supply voltage of the system and the harmonic governance of voltage-type loads. It is connected in series with the transmission line through a transformer, and can achieve voltage harmonic compensation and isolation functions. However, when using the series type alone, there are problems such as high voltage level, strict insulation strength requirements, large losses, and complex protection circuits. Moreover, because the load current flows through the transformer, the capacity requirement of the transformer is very strict, and when the load harmonic content is large, the device capacity will also be very large, and the initial investment is also very large; the parallel type is commonly used for harmonic compensation of current-source type inductive loads. It is connected in parallel with the load to the power grid. Its advantages are simple switching and convenient operation. However, its voltage level is relatively high, the requirements for electronic switching devices are strict, and the compensation current is mainly provided by the inverter, so the capacity of the inverter is required to be very large.

[0003] To solve the problems of high voltage level, large capacity, and high cost of using APF alone, it can be connected in series or parallel with LC to form a resonant injection branch, so that the APF only bears the harmonic voltage and does not bear the fundamental voltage, thereby reducing the voltage level and achieving a reduction in capacity and cost. In addition, in order to further reduce the capacity of the injection type APF and increase the reactive power compensation capacity, PPF can also be connected in parallel on the basis of the single injection type APF. It combines the low-cost advantages of PPF and the compensation performance advantages of APF, so as to achieve good compensation performance with a smaller capacity and lower cost.

[0004] The structure of the series injection type adaptive impedance active power filter can achieve harmonic suppression and wide-range reactive power compensation of a low-capacity active inverter, and can effectively solve the problem that the low capacity of the inverter and wide-range reactive power regulation cannot be taken into account simultaneously. However, the compensation control method of the active inverter in the series injection type adaptive impedance active power filter is the key factor affecting the harmonic compensation accuracy of the system. For a nonlinear load with a capacitor at the output of a rectifier diode, the presence of the capacitor will change the harmonic characteristics of the load. The capacitor has different impedances for harmonics of different frequencies, which may cause some harmonic components to be amplified or attenuated, making the harmonic components more complex. In addition, the charging and discharging process of the capacitor will also generate additional harmonics. These harmonic currents will be transmitted to the grid side and affect the grid side voltage. In the prior art: on the one hand, when there are harmonics in the grid voltage, these harmonics will be injected into the system by the control method of the traditional active inverter part, affecting the compensation accuracy, having limited comprehensive suppression ability for multiple harmonics, poor robustness, and in actual operation, when the harmonic characteristics of the load current change, or there are harmonic interferences in the grid voltage, the compensation effect of the system may be greatly affected, and it is difficult to accurately track and compensate each harmonic; on the other hand, although the fundamental resonance branch presents a high impedance state for harmonics of other frequencies, there will still be a small part of harmonic current generated. The traditional active inverter compensation control method does not consider the influence of this factor, which will also lead to the harmonic compensation accuracy of the system. In view of the deficiencies of the prior art in the harmonic suppression method of the active inverter in the structure of the series injection type adaptive impedance active power filter, it is necessary to solve the influence of the grid side voltage harmonics and the harmonics of the fundamental resonance branch on the system harmonic suppression.

[0005] In the prior art and methods, the control method of the active inverter part of the series injection type adaptive impedance active power filter only extracts harmonics from the load current i Lx (x = a, b, c) to obtain the reference value i cxref (x = a, b, c) of the compensation current output by the active inverter. This method only controls the load current harmonics. First, it does not consider the influence of the grid side voltage harmonics on the system. Second, although the fundamental resonance branch presents a high impedance state for harmonics of other frequencies, there will still be a small part of harmonic current generated, affecting the harmonic compensation ability of the system. Therefore, it is also necessary to separately process the specified harmonic currents of the fundamental resonance branch. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a compensation control method and system based on a series injection type adaptive impedance active power filter in view of the deficiencies of the prior art, so as to further enhance the harmonic suppression ability of the system while realizing harmonic suppression and wide-range reactive power compensation of a low-capacity active inverter.

[0007] To solve the above technical problems, the technical solution adopted by the present invention is as follows: A compensation control method for a series-injection type adaptive impedance active power filter. The series-injection type adaptive impedance active power filter includes an active inverter and an injection type adaptive impedance. The injection type adaptive impedance includes an adaptive impedance branch and a fundamental frequency resonance branch. One end of the adaptive impedance branch is connected to the grid side, and the other end is connected to the active inverter and the fundamental wave resonance branch. One end of the fundamental frequency resonance branch is connected in a three-phase star shape, and the other end is connected to the active inverter and the adaptive impedance branch. It includes:

[0008] Extract the harmonic components of the grid-side voltage to generate the reference value of the compensation current of the active inverter based on the grid-side voltage harmonics. Extract the harmonic components in the load current and calculate the total reference value of the compensation current. For the fundamental frequency resonance branch, extract the specified harmonic voltage and convert the specified harmonic voltage into the corresponding reference value of the specified harmonic compensation current.

[0009] Superimpose the reference value of the compensation current of the active inverter, the total reference value of the compensation current, and the reference value of the specified harmonic compensation current to obtain the reference value of the compensation current of the active inverter.

[0010] Compare the reference value of the compensation current of the active inverter with the actual output current of the active inverter to obtain the current difference. Send this current difference into a multi-quasi proportional resonance controller to generate a modulation voltage signal for controlling the active inverter. Perform normalization processing on the modulation voltage signal, and perform PWM modulation on the result of the normalization processing to generate a switching signal to control the conduction and cutoff of the power switching devices in the active inverter.

[0011] In the compensation control of the active inverter of the present invention, a grid-side voltage harmonic component extraction module and a specified harmonic current extraction module for the fundamental frequency resonance branch are added. The reference current generated by extracting the grid-side voltage harmonics, the harmonic components of the load current, and the total specified harmonic current of the fundamental frequency resonance branch are added together to form an improved reference value of the compensation current of the active inverter and participate in the control simultaneously, further enhancing the harmonic suppression ability of the system.

[0012] The present invention also includes an adaptive impedance branch control part, and the adaptive impedance branch control part includes:

[0013] Calculate the instantaneous reactive power of the load and the root mean square value of the grid-side voltage through the collected load current and grid-side voltage.

[0014] According to the calculated instantaneous reactive power q Lx of the load and the root mean square value V sx of the grid-side voltage, calculate the capacitance value and inductance value required for the adaptive impedance branch; x = a, b, c.

[0015] Determine the thyristor trigger angle for reactive power compensation control. Based on the calculated adaptive impedance branch capacitance value and inductance value, determine the trigger angle of the antiparallel thyristors in the adaptive impedance branch.

[0016] In the present invention, by controlling the trigger angle α 1x 、T 1x (x = a, b, c) of the thyristors T x (x = a, b, c) connected in antiparallel in each phase of the adaptive impedance branch to change their on and off times, that is, the equivalent impedance can be changed, and then the compensated reactive power Q cx (x = a, b, c) can be adjusted to achieve harmonic suppression and wide-range reactive power compensation of a low-capacity active inverter.

[0017] The expressions for the instantaneous reactive power q Lx of the load and the root mean square value V sx of the grid-side voltage are:

[0018]

[0019] where, v sx and i Lx respectively represent the three-phase grid-side voltage and the three-phase load current detected in real time, and v sxD and i LxD are the results obtained by lagging v sx and i Lx by π / 2 in phase.

[0020] The calculation formulas for the capacitance value C AI and inductance value L AI required for the adaptive impedance branch are respectively:

[0021]

[0022] where, ω0 is the fundamental angular frequency, Q Lx_max is the maximum value of the load reactive power, and Q Lx_min is the minimum value of the load reactive power.

[0023] The calculation formula for the trigger angle α x of the antiparallel thyristors in the adaptive impedance branch is:

[0024]

[0025] where, X LAI 、X CAI are respectively the fundamental reactances of the inductance L AI 、capacitance C AI in the adaptive impedance branch, Q cx =-q LxDC ,q LxDCis the instantaneous reactive power q of the load Lx The DC component obtained through a second-order low-pass filter where ω c1 is the cut-off angular frequency of the low-pass filter, s is the complex variable in the Laplace transform, used for system transfer function modeling, and ξ c1 is a constant less than 1

[0026] The triggering angle α x and Q cx The relationship between them is as follows

[0027] When Q cx0 ≤Q cx <Q cx1 at this time, α x =α1 = 90°

[0028] When Q cx1 ≤Q cx <Q cx2 at this time, α x =α2

[0029] ……

[0030] When Q cxn-2 ≤Q cx <Q cxn-1 at this time, α x =α n-1 ;

[0031] When Q cxn-1 ≤Q cx <Q cxn at this time, α x =α n = 180°

[0032] where Q cxn is the boundary value for the division of the compensated reactive power Q cx interval, used to define the reactive power range corresponding to different triggering angles. For example, Q cxn-1 ≤Q cx <Q cxn means that when the compensated reactive power falls within this interval, the triggering angle takes α n .

[0033] α n is a specific value of the triggering angle of the inverse-parallel thyristor, corresponding to a specific Q cx interval. As shown in the last row of the table, when Q cx satisfies Q cxn-1 ≤Q cx <Q cxn at this time, the triggering angle α x =α n= 180°, which is used to control the thyristor trigger to achieve the compensation of the reactive power of the load.

[0034] The acquisition process of the grid-side voltage harmonic components includes:

[0035] The three-phase grid-side voltage v detected in real time sx is successively passed through the Clarke and Park transformations to obtain the components v in the two-phase rotating coordinate system sd , v sq ;

[0036] v sd , v sq are passed through a low-pass filter to extract the DC components v sd_DC , v sq_DC ;

[0037] Calculate the AC components: v sd_AC = v sd - v sd_DC , v sq_AC = v sq - v sq_DC ;

[0038] The AC components are successively passed through the inverse Park and Clarke transformations to obtain the grid-side harmonic voltage components;

[0039] Among them, ω c2 is the cut-off angular frequency of the low-pass filter, and ξ c2 is the damping ratio of the low-pass filter.

[0040] The transfer function of the multi-quasi-proportional resonance controller is expressed as: k p is the proportional coefficient, k r is the resonance coefficient, ω c is the cut-off frequency, and ω o is the fundamental angular frequency.

[0041] The fundamental resonance branch includes a series resonance inductor and a resonance capacitor; the adaptive impedance branch includes an inductor and a capacitor. The inductor is connected in series with two antiparallel thyristors to form a series branch, and the series branch is connected in parallel with the capacitor.

[0042] As an inventive concept, the present invention also provides a compensation control system based on a series-injected adaptive impedance active power filter, including a memory, a processor, and a computer program stored on the memory; the processor executes the computer program to implement the steps of the above method.

[0043] Compared with the prior art, the beneficial effects of the present invention are as follows: while achieving harmonic suppression and wide-range reactive power compensation of a low-capacity active inverter, the present invention further strengthens the harmonic suppression ability of the system by improving the compensation control of the active inverter part. Description of the Drawings

[0044] Figure 1 It is a flowchart of the method according to an embodiment of the present invention;

[0045] Figure 2 It is a structural diagram of an injection-type adaptive impedance active power filter system according to an embodiment of the present invention;

[0046] Figure 3 It is a control block diagram of the injection-type adaptive impedance part according to an embodiment of the present invention;

[0047] Figure 4 It is a control structure block diagram of the injection-type adaptive impedance part;

[0048] Figure 5 It is a schematic diagram of the extraction principle of the harmonic component of the load current according to an embodiment of the present invention;

[0049] Figure 6 It is a schematic diagram of the compensation control principle of the active inverter according to an embodiment of the present invention;

[0050] Figure 7 It is a schematic diagram of the extraction principle of the harmonic component of the grid-side voltage according to an embodiment of the present invention;

[0051] Figure 8 It is a schematic diagram of the extraction principle of the harmonic current of a specified order in the fundamental resonance branch according to an embodiment of the present invention;

[0052] Figure 9 It is a simulation result diagram without any compensation;

[0053] Figure 10 It is a simulation result diagram of the traditional compensation method of the active inverter;

[0054] Figure 11 It is a simulation result diagram of the improved compensation method of the active inverter;

[0055] Figure 12 It is a simulation result diagram of the improved compensation method of the active inverter;

[0056] Figure 13 It is a comparison result diagram of the FFT analysis of the grid-side current. Detailed Embodiment

[0057] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Apparently, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0058] Embodiment 1

[0059] As Figure 1 shown, this embodiment provides a compensation control method for a series injection type adaptive impedance active power filter, and its main steps are as follows.

[0060] Use specialized electrical signal detection devices, such as voltage transformers, current transformers, etc., to detect and collect signals such as grid-side voltage, load current, and active inverter output current in real time.

[0061] Calculate relevant electrical parameters. Based on the collected load current and grid-side voltage data, calculate the instantaneous reactive power of the load according to the instantaneous reactive power theory; at the same time, calculate the root mean square value of the grid-side voltage to reflect the effective value of the grid-side voltage.

[0062] According to the calculated instantaneous reactive power of the load and the root mean square value of the grid-side voltage, combined with specific calculation formulas and circuit principles, calculate the capacitance value and inductance value required for the adaptive impedance branch.

[0063] Determine the thyristor trigger angle for wide-range reactive power compensation control. According to the calculated capacitance value and inductance value of the adaptive impedance branch, combined with the circuit characteristics and control requirements, determine the trigger angle of the antiparallel thyristor of the adaptive impedance branch.

[0064] Extract the harmonic components of the grid-side voltage to generate the reference value of the active inverter compensation current based on the grid-side voltage harmonics; extract the harmonic components in the load current to calculate the total compensation current reference value together with other harmonic currents; for the fundamental resonance branch, extract the specified harmonic voltage and convert it into the corresponding specified harmonic compensation current reference value based on the impedance model of the fundamental resonance branch.

[0065] Add the above three compensation current values to generate an improved active inverter compensation current reference value for subsequent control.

[0066] Compare the improved active inverter compensation current reference value with the current actually output by the active inverter to obtain a current difference. Send this difference into a multi-quasi-proportional-resonant controller to generate a modulation voltage signal for controlling the active inverter. Further normalize this signal, and use PWM modulation technology to generate a switching signal to precisely control the conduction and cutoff of the power switching devices in the active inverter, thereby achieving precise compensation for system harmonics.

[0067] Figure 2 It is a schematic diagram of the structure of a series-injection type adaptive impedance active power filter system. It mainly consists of four parts: the grid side, an active inverter, an injected type-adaptive impedance (IT-AI), and a load. Among them, the injected type-adaptive impedance part includes an adaptive impedance branch and a fundamental frequency resonant branch, and the load part includes a linear load and a nonlinear load. In the main circuit, the active inverter is connected to the adaptive impedance branch and the fundamental frequency resonant branch; one end of the adaptive impedance branch is connected to the grid side, and the other end is connected to the active inverter and the fundamental wave resonant branch; one end of the fundamental frequency resonant branch is connected in a three-phase star shape, and the other end is connected to the active inverter and the adaptive impedance branch. In the figure, L s represents the equivalent inductance of the grid side. They play a certain filtering role in the circuit, suppressing the high-frequency harmonic current on the grid side from flowing into the main circuit. At the same time, they also participate in the transient process of the circuit, buffering the change of current, and affecting the power factor and stability of the circuit to a certain extent; L load 、R load 、C load respectively represent the equivalent inductance, equivalent resistance, and equivalent capacitance in the load. The nonlinear load will generate harmonic current and reactive power, which will distort the waveform of the grid side current and reduce the power quality, and it is the object that needs to be compensated. C dc represents the DC side capacitor of the active inverter part, L f represents the output filter inductance of the active inverter part. At the same time, the active inverter is connected to the IT-AI through L f , rather than directly connected to the grid side, which can effectively reduce the requirement for the capacity of the inverter. T xu 、T xl (x = a, b, c) represent the power switching devices (such as IGBTs and MOSFETs, etc.) with anti-parallel diodes on the upper and lower bridge arms of each phase of the active inverter part; L1 and C1 respectively represent the resonant inductance and resonant capacitance of the fundamental frequency resonant branch. The fundamental frequency resonant branch enables the active inverter not to bear the fundamental wave voltage, which can effectively reduce the requirement for the capacity of the active inverter; L AI 、C AI respectively represent the inductance and capacitance of the adaptive impedance branch, L AI 、C AIThe parameter coordination can change the equivalent impedance characteristics of the entire IT-IA according to the control strategy, thereby realizing adaptive compensation of reactive power and meeting the needs of different loads; 1x 、T 1x (x=a, b, c) represent the thyristors of each anti-parallel connection in the adaptive impedance branch, T 1x 、T 1x (x=a、b、c) and L AI Series, T 1x 、T 1x (x=a、b、c) and C AI In parallel, by controlling their firing angle α x (x=a, b, c) to change its on and off time, that is, the equivalent impedance of IT-AI can be changed, thereby adjusting the compensated reactive power Q cx (x=a、b、c) size. The series injection adaptive impedance structure can achieve harmonic suppression and wide range reactive power compensation of low capacity active inverter, which can effectively solve the problem that low capacity of inverter and wide range reactive power regulation cannot be taken into account at the same time.

[0068] Figure 3 The figure shows the control structure block diagram of the injection type adaptive impedance part, where v sx (x = a, b, c) and i Lx (x=a, b, c) represent the three-phase grid-side voltage and three-phase load current detected in real time in the system. sx (x = a, b, c) and i Lx (x=a、b、c) After phase lag π / 2, we get v sxD (x = a, b, c) and i LxD (x=a, b, c), through phase shift operation, the three-phase voltage and current signals are delayed by 90 degrees respectively, which are used to calculate the instantaneous reactive power of the load and the RMS value of the grid-side voltage.

[0069] The calculation of the instantaneous reactive power of the load is shown in formula (1), and the calculation of the root mean square value of the grid-side voltage is shown in formula (2).

[0070]

[0071]

[0072] The calculation of injection type adaptive impedance parameters includes the adaptive impedance branch capacitance value C AI and inductance value L AI The calculation formula is as follows:

[0073]

[0074] Where ω0 is the fundamental angular frequency, QLx_max (x = a, b, c) is the maximum value of the load reactive power, Q Lx_min (x = a, b, c) is the minimum value of the load reactive power. The capacitance value and inductance value of the adaptive impedance branch calculated by formulas (3) and (4) can achieve the compensation of reactive power in the range of [[Q Lx_min , Q Lx_max .

[0075] The trigger angle α of the antiparallel thyristors in the adaptive impedance branch x (x = a, b, c) and the reactive power Q compensated by the adaptive impedance branch cx (x = a, b, c) satisfy the following relationship:

[0076]

[0077] Where, V sx (x = a, b, c) is the root mean square value of the grid-side phase voltage, X LAI , X CAI are the fundamental reactances of L AI and C AI respectively. At the same time, the reactive power Q compensated by the adaptive impedance branch cx (x = a, b, c) and the load reactive power q LxDC (x = a, b, c) have the following relationship:

[0078] Q cx = -q LxDC (6)

[0079] Where, q LxDC (x = a, b, c) is the DC component of the load instantaneous reactive power q Lx (x = a, b, c) obtained through the second-order low-pass filter shown in formula (7), ω c1 is the cut-off angular frequency of the low-pass filter, taking ω c1 = 10π, ξ c1 is the damping ratio of the low-pass filter, taking ξ c1 = 0.707.

[0080]

[0081] According to the relationship between the trigger angle α of the antiparallel thyristors x (x = a, b, c) and the reactive power Q compensated by the adaptive impedance branch cx (x = a, b, c) shown in formula (5), a corresponding look-up table can be established, as shown in Table 1. Based on the look-up table, according to the calculated load reactive power q LxDC (x = a, b, c), by controlling the trigger angle α of the antiparallel thyristors x(x = a, b, c) compensates for the reactive power q of the load LxDC (x = a, b, c) further compares the phase angle θ of the grid-side phase voltage PLLx (x = a, b, c) and α x (x = a, b, c), when θ PLLx > α x the triggering signal of thyristor T 1x is output; when θ PLLx > 180° + α x the triggering signal of thyristor T 2x is output. The triggering angle interval α x (x = a, b, c) and the corresponding reactive power range are set according to the actual situation.

[0082] Table 1 Triggering angle α x Lookup table

[0083] <![CDATA[Q cx > <![CDATA[α x > <![CDATA[Q cx0 ≤Q cx <Q cx1 > <![CDATA[α x = α1 = 90°]]> <![CDATA[Q cx1 ≤Q cx <Q cx2 > <![CDATA[α x = α2]]> …… …… <![CDATA[Q cxn-2 ≤Q cx <Q cxn-1 > <![CDATA[α x = α n-1 > <![CDATA[Q cxn-1 ≤Q cx <Q cxn > <![CDATA[α x = α n = 180°]]>

[0084] In the IT-AI part, the fundamental resonance inductor L1 and the fundamental resonance capacitor C1 of the fundamental resonance branch satisfy the relationship shown in Equation (8). By means of the fundamental frequency resonance branch, the active inverter does not bear the fundamental voltage, thus effectively reducing the capacity requirement of the active inverter.

[0085]

[0086] The control structure block diagram of the traditional active inverter part in the series injection type adaptive impedance active power filter is as Figure 4 shown.

[0087] First, extract the harmonic components i Lxh (x = a, b, c) of the load current. The load current i Lx (x = a, b, c) is transformed into the components i Ld , i Lq in the two-phase rotating coordinate system through Clarke and Park transformations, where the coordinate transformation angle θ PLL is obtained based on the grid-side voltage through a phase-locked loop. The DC components i Ld , i Lq are extracted from i Ld_DC , i Lq_DC through a digital moving average filter as shown in Equation (9). Further, the AC components i Ld_AC = i Ld - i Ld_DC , i Lq_AC = i Lq - i Lq_DC are obtained. After Park and Clarke inverse transformations, the load harmonic current i Lxh(x = a, b, c).

[0088]

[0089] Take the load harmonic current i Lxh (x = a, b, c) as the reference value of the active inverter output compensation current, and compare it with the actually detected output current i lx (x = a, b, c) of the active inverter bridge arm. Then, send the difference into the multi-band proportional-resonant controller to obtain the modulation voltage signal v xref (x = a, b, c) of the active inverter. Further perform normalization processing and adopt the SPWM modulation method to obtain the switching signal for controlling the conduction of some switching devices T xu 、T xl (x = a, b, c). Usually, the harmonic frequency of the grid-side current caused by the nonlinear load is the k = 6n ± 1 (n = 1, 2, 3...) times of the fundamental frequency of 50 Hz, and the higher the frequency, the less the harmonic content. Among them, the resonant frequencies of the multi-band proportional-resonant controller are set to the 5th, 7th, 11th, and 13th times of the fundamental frequency of 50 Hz to effectively suppress the harmonics.

[0090] The transfer function of the multi-band proportional-resonant controller is shown in Equation (10). Among them, the proportional coefficient k p adjusts the overall gain, which can quickly respond to the error of the system and accelerate the dynamic response speed of the system; the resonant coefficient k r adjusts the gain at each resonant point. At the specific resonant frequency kω o , the resonant link can provide a higher gain, so as to selectively amplify or adjust the signal near this frequency; the cut-off frequency ω c is the bandwidth parameter of the resonant link, which determines the frequency selection characteristic of the resonant link. ω o is the fundamental angular frequency, and take ω o = 100π.

[0091]

[0092] Since the control method of the traditional active inverter part only extracts harmonics from the load current i Lx (x = a, b, c) to obtain the reference value i cxref (x = a, b, c) of the active inverter output compensation current, and only controls the load current harmonics. First, the influence of the grid-side voltage harmonics on the system is not considered. Second, although the fundamental resonant branch presents a high impedance state to the harmonics of other frequencies, there will still be a small part of harmonic current generated. Therefore, it is also necessary to separately process the specified sub-harmonic current of the fundamental resonant branch.

[0093] For the harmonic variation on the grid side caused by the non-linear load with a capacitor at the rectifier output, when there are harmonics in the grid voltage in the traditional control method of the active inverter part, these harmonics will be injected into the system, affecting the compensation accuracy, having limited comprehensive suppression ability for multiple harmonics, and poor robustness. Moreover, in actual operation, when the harmonic characteristics of the load current change, or there are harmonic interferences in the grid voltage, the compensation effect of the system may be greatly affected, and it is difficult to accurately track and compensate each harmonic.

[0094] Therefore, based on the previous research, this embodiment proposes an improved compensation control method based on a series-injection type adaptive impedance active power filter. Figure 6 It is the improved active inverter compensation control structure block diagram considering the grid side voltage harmonics and the fundamental harmonic resonance branch harmonics.

[0095] Considering the influence of the grid side voltage harmonics, a grid side voltage harmonic component extraction module is added to the control of the active inverter part, extracting the harmonic components v sx (x = a, b, c) from the grid side voltage v sxh (x = a, b, c); and comparing them with the corresponding grid side voltage harmonic reference values v sxhref (x = a, b, c), usually taking v sxhref = 0; taking the difference between the two values and generating the corresponding reference current i cxref2 (x = a, b, c) through the multi-quasi proportional resonance control link, where the multi-quasi proportional resonance control transfer function is shown in Equation (10). This can effectively suppress the influence of the grid side voltage harmonics on the system and improve the compensation accuracy of the system under the condition of grid voltage distortion.

[0096] Among them, the extraction of the grid side voltage harmonic components is as Figure 7 shown. The three-phase grid side voltage v sx (x = a, b, c) detected by the system is transformed through the Clarke and Park transformations to obtain the components v sd , v sq in the two-phase rotating coordinate system, where the coordinate transformation angle θ PLL is obtained based on the grid side voltage through the phase-locked loop; v sd , v sq are used to extract the DC components v sd_DC , v sq_DC through the low-pass filter, as shown in Equation (11), ω c2 is the cut-off angular frequency of the low-pass filter, taking ω c2 = 20π, ξ c2 is the damping ratio of the low-pass filter, taking ξ c2 = 0.707; taking the difference of the results to further obtain the AC component v sd_AC = v sd - v sd_DC, v sq_AC = v sq -v sq_DC , after park and clarke inverse transformation, the grid-side harmonic voltage v sxh (x = a, b, c) is obtained.

[0097]

[0098] Considering the harmonic influence existing in the fundamental resonance branch, it is processed separately, and a designated sub-harmonic current extraction module for the fundamental resonance branch is added. Take the inverse of v rx (x = a, b, c), and through a plurality of band-pass filters centered on the designated sub-harmonic frequency and connected in parallel, the designated sub-total harmonic voltage v rxkh (x = a, b, c) of the fundamental resonance branch is obtained. The center frequency of the band-pass filter is the k = 6n ± 1 (n = 1, 2, 3...) times of the fundamental frequency 50Hz. The transfer function of the nth band-pass filter is shown in the following formula (12), where ω o is the fundamental angular frequency. Take ω o = 100π, and ξ n is the damping ratio coefficient of the nth parallel band-pass filter, and this value participates in adjusting the bandwidth of the band-pass filter. Then divide the designated sub-total harmonic voltage v rxkh (x = a, b, c) of the fundamental resonance branch by the equivalent transfer function G1(s) of the fundamental resonance branch impedance to obtain the designated sub-total harmonic current i rxkh (x = a, b, c) to be compensated, where K r1 is the compensation coefficient, and it is taken as -1.

[0099]

[0100] The reference current i cxref2 (x = a, b, c) generated based on the extraction of grid-side voltage harmonics, the extracted harmonic components of the load current i Lxh (x = a, b, c), and the designated sub-total harmonic current i rxkh (x = a, b, c) of the fundamental resonance branch are added together to form the improved active inverter compensation current reference value i cxref (x = a, b, c) and participate in the control simultaneously. This method can more accurately control the specific sub-harmonic currents of each part of the system, enhance the adaptability and compensation ability of the system to different sub-harmonics, and improve the robustness of the system. Similarly, make a difference comparison between i cxref (x = a, b, c) and the actually detected output current i lx (x = a, b, c) of the active inverter bridge arm, and then send the difference into the multi-quasi proportional resonance controller to obtain the modulation voltage signal v xref(x = a, b, c). Further perform normalization processing and adopt the SPWM modulation method to obtain the switching signals for the conduction of some switching devices T xu 、T xl (x = a, b, c).

[0101] The following Table 2 shows the simulation parameters of the improved compensation control method based on the series injection type adaptive impedance active power filter, which are used to verify that the present invention can effectively realize the improvement effect on system harmonic suppression.

[0102] Table 2 System simulation parameters

[0103]

[0104] Perform simulation based on the system parameters shown in Table 2. The total simulation time is set to 1 s, and compensation control is performed at 0.3 s. Figure 9 is the simulation result diagram without any compensation, Figure 10 is the simulation result diagram of the traditional compensation method of the active inverter, Figure 11 is the simulation result diagram of the improved active inverter compensation method when only considering the influence of grid-side voltage harmonics, Figure 12 is the simulation result diagram of the improved active inverter compensation method when simultaneously considering the influence of grid-side voltage harmonics and the harmonics of the fundamental resonance branch. Figures 9 to 12 The waveform diagrams shown include the grid-side voltage v sx (x = a, b, c), the grid-side current i sx (x = a, b, c), the load current i Lx (x = a, b, c), and the output current i of the active inverter lx (x = a, b, c) simulation results.

[0105] Further perform FFT analysis on the grid-side current i sx (x = a, b, c). Taking phase a as an example, as Figure 13 shown, perform FFT analysis at the same moment. Without adding suppression, due to the existence of non-linear loads, the harmonic distortion rate (THD) of the grid-side current is 64.34%; when using the traditional active inverter method, the grid-side current THD can be reduced to 9.96%; when using the improved active inverter compensation method that only considers the influence of grid-side voltage harmonics, the grid-side current THD is reduced to 3.81%, and the improvement effect is obvious; when using the improved active inverter compensation method that simultaneously considers the influence of grid-side voltage harmonics and the harmonics of the fundamental resonance branch, the grid-side current THD is further reduced to 3.06%.

[0106] Compare and observe the grid-side current waveform i sx(x = a, b, c), it can be intuitively seen that the embodiments of the present invention have an obvious improvement and optimization effect on the harmonic suppression effect; from the FFT comparison analysis results, it can be quantitatively seen that the improved active inverter control method proposed in the embodiments of the present invention has an obvious improvement and optimization effect on the harmonic suppression effect. In summary of the simulation results, the improved compensation control method based on the series injection type adaptive impedance active power filter proposed in the embodiments of the present invention is effective in both theoretical research and method implementation.

[0107] Embodiment 2

[0108] Embodiment 2 of the present invention provides a control system corresponding to the above Embodiment 1, including a memory, a processor, and a computer program stored on the memory; the processor executes the computer program on the memory to implement the steps of the method in the above Embodiment 1.

[0109] In some implementations, the memory may be a high-speed random access memory (RAM: Random Access Memory), and may also include a non-volatile memory, such as at least one disk memory.

[0110] In other implementations, the processor may be a general-purpose processor of various types such as a central processing unit (CPU) and a digital signal processor (DSP), which are not limited herein.

[0111] Although the preferred embodiments of the present application have been described, those skilled in the art can make additional changes and modifications to these embodiments once they know the basic creative concepts. Therefore, the appended claims are intended to be interpreted to include the preferred embodiments and all changes and modifications falling within the scope of the present application.

[0112] Obviously, those skilled in the art can make various changes and modifications to the present application without departing from the spirit and scope of the present application. Thus, if these modifications and variations of the present application fall within the scope of the claims of the present application and their equivalent technologies, the present application also intends to include these changes and modifications.

Claims

1. A compensation control method based on a series injection type adaptive impedance active power filter, wherein the series injection type adaptive impedance active power filter comprises an active inverter and an injection type adaptive impedance, wherein the injection type adaptive impedance comprises an adaptive impedance branch and a fundamental frequency resonance branch, wherein one end of the adaptive impedance branch is connected to a grid side, and the other end is connected to the active inverter and the fundamental frequency resonance branch; One end of the fundamental frequency resonant branch is connected in a three-phase star shape, and the other end is connected to an active inverter and an adaptive impedance branch; it is characterized by comprising: Extract the grid-side voltage harmonic components and generate the active inverter compensation current reference value based on the grid-side voltage harmonics; extract the harmonic components in the load current and calculate the total compensation current reference value; for the fundamental resonant branch, extract the specified harmonic voltage and convert the specified harmonic voltage into the corresponding specified harmonic compensation current reference value; Superimposing the active inverter compensation current reference value, the total compensation current reference value, and the specified subharmonic compensation current reference value to obtain the active inverter compensation current reference value; The active inverter compensation current reference value is compared with the current actually output by the active inverter to obtain a current difference, which is sent to a multi-quasi-proportional resonant controller to generate a modulation voltage signal for controlling the active inverter, which is normalized, and a PWM modulation is performed on the result of the normalization to generate a switching signal to control the on and off of a power switching device in the active inverter.

2. The compensation control method based on series injection adaptive impedance active power filter according to claim 1 is characterized in that: The method further comprises an adaptive impedance branch control part, wherein the adaptive impedance branch control part comprises: The instantaneous reactive power of the load and the RMS value of the grid-side voltage are calculated by the collected load current and grid-side voltage; According to the calculated load instantaneous reactive power q Lx and the grid-side voltage RMS value V sx , calculate the capacitance and inductance required for the adaptive impedance branch; x = a, b, c; The trigger angle of the thyristor is determined to perform reactive power compensation control, and the trigger angle of the anti-parallel thyristor of the adaptive impedance branch is determined according to the calculated capacitance value and inductance value of the adaptive impedance branch.

3. The compensation control method based on series injection adaptive impedance active power filter according to claim 2 is characterized in that: Load instantaneous reactive power q Lx and the grid-side voltage RMS value V sx The expression is: Among them, v sx and i Lx They represent the three-phase grid voltage and three-phase load current detected in real time, v sxD and i LxD They are v sx and i Lx The result is obtained after a phase lag of π / 2.

4. The compensation control method based on series injection adaptive impedance active power filter according to claim 2 is characterized in that: The capacitance value C required for the adaptive impedance branch AI and inductance value L AI The calculation formulas are: Where ω0 is the fundamental angular frequency, Q Lx_max is the maximum reactive power of the load, Q Lx_min is the minimum value of load reactive power.

5. The compensation control method based on series injection adaptive impedance active power filter according to claim 2 is characterized in that: Triggering angle α of the anti-parallel thyristor in the adaptive impedance branch x The calculation formula is: Among them, X LAI , X CAI They are the adaptive impedance branch inductance L AI , capacitor C AI Fundamental reactance, Q cx =-q LxDC ,q LxDC is the instantaneous reactive power of the load q Lx The DC component is obtained by passing it through a second-order low-pass filter.

6. The compensation control method based on series injection adaptive impedance active power filter according to claim 5 is characterized in that: Among them, ω c1 is the cutoff frequency of the low-pass filter, s is the complex variable in the Laplace transform, ξ c1 is a constant less than 1.

7. The compensation control method based on series injection adaptive impedance active power filter according to claim 5 or 6, characterized in that: Trigger angle α x With Q cx The relationship between them is: When Q cx0 ≤Q cx cx1 When α x =α1=90°;​ When Q cx1 ≤Q cx cx2 When α x =α2;​ …… When Q cxn-2 ≤Q cx cxn-1 When α x =α n-1 ;​ When Q cxn-1 ≤Q cx cxn When α x =α n =180°;​ Q cxn is the compensation reactive power Q cx The boundary value of the interval division; α n It is the specific value of the trigger angle of the anti-parallel thyristor.

8. The compensation control method based on series injection adaptive impedance active power filter according to claim 1, characterized in that: The process of obtaining the grid-side voltage harmonic components includes: The real-time detected three-phase grid-side voltage v sx Through Clarke and Park transformations, we can get the component v in the two-phase rotating coordinate system. sd 、v sq ; v sd 、v sq The DC component v is extracted by a low-pass filter sd_DC 、v sq_DC ; Calculate the AC component: v sd_AC =v sd -v sd_DC 、v sq_AC =v sq -v sq_DC ; The AC components are subjected to Park and Clarke inverse transformations in sequence to obtain grid-side harmonic voltage components; in, ω c2 is the low-pass filter cutoff frequency, ξ c2 is the damping ratio of the low-pass filter.

9. The compensation control method based on series injection adaptive impedance active power filter according to claim 1, characterized in that: The transfer function of the multi-quasi-proportional resonant controller is expressed as: k p is the proportionality coefficient, k r is the resonance coefficient, ω c is the cut-off frequency, ω o is the fundamental angular frequency.

10. A compensation control system based on a series injection adaptive impedance active power filter, comprising a memory, a processor and a computer program stored in the memory; characterized in that: The processor executes the computer program to implement the steps of the method according to any one of claims 1 to 9.

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