Output current limiting method and apparatus for power quality manager

Abstract

The application discloses an output current limiting method and device of a power quality manager, and belongs to the technical field of power quality management, which comprises the following steps: sampling three-phase load currents, and extracting three-phase active current amplitudes, three-phase reactive current amplitudes and harmonic current amplitudes based on the three-phase load currents; calculating the average value of the three-phase active current amplitudes, and determining three-phase active compensation current amplitudes based on the average value, the three-phase active current amplitudes and a compensation current upper limit; calculating the residual capacity of three-phase output currents according to the compensation current upper limit and the three-phase active compensation current amplitudes; determining three-phase reactive compensation current amplitudes based on the three-phase reactive current amplitudes and the residual capacity of the three-phase output currents; calculating three-phase total output currents, and outputting the three-phase total output currents after limiting. The application improves the adaptability of the power quality manager to different loads.

Description

Technical Field

[0001] This invention relates to the field of power quality management technology, and specifically to a method and apparatus for limiting the output current of a power quality manager. Background Technology

[0002] Power electronic equipment and nonlinear loads inject large amounts of harmonics and reactive currents into the power grid, causing problems such as grid voltage distortion, grid losses, and power equipment failures. Existing solutions to these problems involve using active power filters (APFs) and static var generators (SVGs) to compensate for reactive power and harmonic currents. However, three-phase four-wire power systems frequently experience three-phase active current imbalances, leading to neutral point shifts and changes in phase voltages that affect the safe operation of electrical equipment. Unbalanced voltages have positive-sequence, negative-sequence, and zero-sequence components. When a motor is driven, the braking effect of the negative-sequence magnetic field inevitably reduces the motor's output power, resulting in decreased motor efficiency. Simultaneously, the motor's temperature rise and reactive power losses increase with the degree of three-phase voltage imbalance.

[0003] To simultaneously address the imbalances in reactive power, harmonic currents, and three-phase active current in a three-phase four-wire power grid system, a three-phase four-wire power quality manager was developed. A key function of the three-phase four-wire power quality manager is to regulate the unbalanced active current across the three phases, ensuring equal amplitudes. This significantly reduces line losses during power distribution and transmission, and also achieves near-perfect voltage balance across the three phases. During operation, the three-phase four-wire power quality manager needs to simultaneously regulate the unbalanced active current and compensate for reactive and harmonic currents. However, due to constantly changing grid load conditions, the theoretical output current amplitude of the power quality manager often exceeds its rated value, necessitating current limiting.

[0004] Because the power quality manager needs to simultaneously regulate the unbalanced active current of the three phases and compensate for the reactive current and harmonic current, and because the DC-side voltage regulation method of the three-phase four-wire power quality manager is self-regulating, the sum of the three-phase active currents must be zero during steady-state operation. Common limiting methods include truncation, direct proportional, and modulated wave limiting. However, using common limiting methods has the following disadvantages:

[0005] (1) Truncation method

[0006] The cutoff method sets the upper limit of the power quality manager's output current to M, and any current amplitude exceeding this limit is restricted to M. While simple, this method results in the sum of the three-phase active currents no longer being zero, failing to meet the normal operation requirements of the power quality manager, and also generating new harmonic currents.

[0007] (2) Direct Proportion Method

[0008] The direct proportional method refers to comparing the output current amplitudes of each phase of the power quality manager and finding the current amplitude I with the largest amplitude. om The maximum allowable output current amplitude I using the power quality manager. max Divide by I om The proportional limiting factor K is obtained, and then the output current amplitude of each phase of the power quality manager is multiplied by the proportional limiting factor K, thereby limiting the output current of each phase of the power quality manager to the allowable range.

[0009] The direct proportional method can ensure that the sum of the three-phase active currents is zero, allowing the power quality manager to operate normally. However, it also proportionally limits the reactive and harmonic currents, sacrificing some of the equipment's compensation capacity.

[0010] (3) Modulation wave limiting method

[0011] Modulation wave limiting limits the modulation wave, thereby restricting the output current of the equipment. Currently, this method is mainly used in APF harmonic compensation, where suitable compensation coefficients are found by considering different combinations of harmonics. The process is complex and may fail to compensate for the main harmonic components. Power quality managers, however, must compensate for reactive and harmonic currents while also regulating unbalanced active currents, ensuring the sum of the three-phase active currents is zero. Therefore, modulation wave limiting is not suitable for power quality managers.

[0012] In related technologies, the paper "A Novel Algorithm for Active Compensation Current Exceeding Equipment Capacity in Three-Phase Four-Wire Unbalanced Regulators" published in the Engineering Science and Technology of Electrical Appliances and Energy Efficiency Management II on February 28, 2022, proposes a method for proportionally reducing the active compensation current. This method can avoid the drawbacks of the limiting method, even if the active compensation current waveform is distorted and the sum of the three-phase active currents flowing into the equipment is not zero, causing fluctuations in the DC side voltage of the equipment.

[0013] However, this new algorithm only limits the active current, but does not separate the reactive current and harmonic current. When the reactive current and harmonic current are too large, such as exceeding the upper limit of the power quality manager's compensation current, the part exceeding the upper limit of the power quality manager's compensation current will be cut off when the total current is output, and the sinusoidal nature of the output current cannot be guaranteed. Summary of the Invention

[0014] The technical problem to be solved by this invention is how to avoid introducing new harmonics and improve the adaptability of power quality managers to different loads.

[0015] The present invention solves the above-mentioned technical problems through the following technical means:

[0016] On one hand, the present invention proposes an output current limiting method for a power quality manager, the method comprising:

[0017] The three-phase load current is sampled, and the amplitudes of the three-phase active current, the three-phase reactive current, and the harmonic current are extracted based on the three-phase load current.

[0018] Calculate the average value of the three-phase active current amplitude, and determine the three-phase active compensation current amplitude based on the average value, the three-phase active current amplitude, and the upper limit of the compensation current.

[0019] Calculate the remaining capacity of the three-phase output current based on the upper limit of the compensation current and the amplitude of the three-phase active power compensation current.

[0020] Based on the amplitude of the three-phase reactive current and the remaining capacity of the three-phase output current, the amplitude of the three-phase reactive compensation current is determined.

[0021] Based on the amplitudes of the three-phase active power compensation current, the three-phase reactive power compensation current, and the harmonic current, the total three-phase output current is calculated, and the total three-phase output current is output after being limited.

[0022] This invention separates reactive current and harmonic current, and performs direct or proportional balancing regulation on unbalanced three-phase active current. At the same time, it compensates reactive and harmonic current separately within the maximum capacity range of the equipment, so that the sinusoidal nature of the grid current is guaranteed. Moreover, no new harmonics will be generated due to the final amplitude limiting cutoff, regardless of the load current waveform, thus improving the adaptability of the power quality manager to different loads.

[0023] Further, the sampling of the three-phase load current, and the extraction of the three-phase active current amplitude, three-phase reactive current amplitude, and harmonic current amplitude based on the three-phase load current, includes:

[0024] The amplitude of the three-phase active current is obtained by multiplying the three-phase load current by the sinusoidal signal and then passing the result through a low-pass filter.

[0025] The three-phase load current is multiplied by a cosine signal and then passed through a low-pass filter to obtain the amplitude of the three-phase reactive current.

[0026] The harmonic current amplitude is obtained by subtracting the amplitudes of the three-phase active current and the three-phase reactive current from the three-phase load current.

[0027] Further, the step of calculating the average value of the three-phase active current amplitude, and determining the three-phase active compensation current amplitude based on the average value, the three-phase active current amplitude, and the upper limit of the compensation current, includes:

[0028] Calculate the average value of the three-phase active current amplitude, and subtract the average value from the three-phase active current amplitude to obtain three difference values;

[0029] Determine whether the maximum value among the three differences is less than the upper limit of the compensation current;

[0030] If so, the three differences are taken as the amplitude of the three-phase active power compensation current;

[0031] If not, the amplitude of the three differences is limited using the proportional method and then used as the amplitude of the three-phase active power compensation current.

[0032] Further, determining the amplitude of the three-phase reactive current compensation based on the amplitude of the three-phase reactive current and the remaining capacity of the three-phase output current includes:

[0033] The reactive current amplitude of each phase in the three-phase reactive current amplitude is compared with the remaining output current capacity of the corresponding phase:

[0034] If the reactive current amplitude of a certain phase is less than or equal to the remaining output current capacity of the corresponding phase, then the reactive current amplitude of that phase shall be used as the reactive compensation current amplitude of that phase.

[0035] If the reactive current amplitude of a certain phase is greater than the remaining capacity of the output current of the corresponding phase, then the remaining capacity of the output current of that phase shall be used as the reactive compensation current amplitude of that phase.

[0036] Further, the step of calculating the total three-phase output current based on the amplitudes of the three-phase active power compensation current, the three-phase reactive power compensation current, and the harmonic current, and then limiting the total three-phase output current before outputting it, includes:

[0037] The sum of the amplitudes of the three-phase active power compensation current, the three-phase reactive power compensation current, and the harmonic current is taken as the total three-phase output current.

[0038] Determine whether the total three-phase output current is less than or equal to the upper limit of the compensation current;

[0039] If so, the total three-phase output current will be output directly;

[0040] If not, the portion of the total three-phase output current that exceeds the upper limit of the compensation current will be truncated before being output.

[0041] Furthermore, the present invention also proposes an output current limiting device for a power quality manager, the device comprising:

[0042] The extraction module is used to sample the three-phase load current and extract the amplitude of the three-phase active current, the amplitude of the three-phase reactive current, and the amplitude of the harmonic current based on the three-phase load current.

[0043] The first determining module is used to calculate the average value of the three-phase active current amplitude, and determine the three-phase active compensation current amplitude based on the average value, the three-phase active current amplitude and the compensation current upper limit.

[0044] The remaining capacity calculation module is used to calculate the remaining capacity of the three-phase output current based on the upper limit of the compensation current and the amplitude of the three-phase active power compensation current.

[0045] The second determining module is used to determine the amplitude of the three-phase reactive current based on the amplitude of the three-phase reactive current and the remaining capacity of the three-phase output current.

[0046] The output module is used to calculate the total three-phase output current based on the amplitude of the three-phase active power compensation current, the amplitude of the three-phase reactive power compensation current and the amplitude of the harmonic current, and to output the total three-phase output current after limiting the amplitude.

[0047] Furthermore, the extraction module includes:

[0048] The first extraction unit is used to multiply the three-phase load current with a sinusoidal signal and then pass it through a low-pass filter to obtain the amplitude of the three-phase active current.

[0049] The second extraction unit is used to extract the amplitude of the three-phase reactive current by multiplying the three-phase load current by the cosine signal and passing it through a low-pass filter.

[0050] The third extraction unit is used to obtain the harmonic current amplitude by subtracting the amplitude of the three-phase active current and the amplitude of the three-phase reactive current from the three-phase load current.

[0051] Further, the first determining module includes:

[0052] The difference calculation unit is used to calculate the average value of the three-phase active current amplitude, and to subtract the average value from the three-phase active current amplitude to obtain three difference values;

[0053] The first judgment unit is used to determine whether the maximum value among the three differences is less than the upper limit of the compensation current.

[0054] The first determining unit is configured to, when the output result of the first determining unit is yes, use the three differences as the amplitude of the three-phase active power compensation current; and to, when the output result of the first determining unit is no, use the proportional method to limit the amplitude of the three differences and use it as the amplitude of the three-phase active power compensation current.

[0055] Further, the second determining module includes:

[0056] The comparison unit is used to compare the reactive current amplitude of each phase of the three-phase reactive current amplitude with the remaining output current capacity of the corresponding phase:

[0057] The second determining unit is used to determine the reactive current amplitude of a certain phase as the reactive compensation current amplitude of that phase when the reactive current amplitude of a certain phase is less than or equal to the output current remaining capacity of the corresponding phase.

[0058] The second determining unit is used to determine the reactive current amplitude of a phase as the reactive compensation current amplitude of that phase if the reactive current amplitude of a certain phase is greater than the remaining capacity of the output current of the corresponding phase.

[0059] Furthermore, the output module includes:

[0060] The summation unit is used to sum the amplitudes of the three-phase active power compensation current, the three-phase reactive power compensation current, and the harmonic current to obtain the total three-phase output current.

[0061] The second judgment unit is used to determine whether the total output current of the three phases is less than or equal to the upper limit of the compensation current.

[0062] The output unit is configured to directly output the total three-phase output current when the output result of the second judgment unit is yes; and to truncate the portion of the total three-phase output current that exceeds the upper limit of the compensation current before outputting it when the output result of the second judgment unit is no.

[0063] The advantages of this invention are:

[0064] (1) This invention separates reactive current and harmonic current, and performs direct or proportional balance adjustment on unbalanced three-phase active current. At the same time, it compensates reactive current and harmonics separately within the maximum capacity range of the equipment, so that the sinusoidal nature of the grid current is guaranteed. Moreover, no matter what the load current waveform is, no new harmonics will be generated due to the final amplitude limiting cutoff, thus improving the adaptability of the power quality manager to different loads.

[0065] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0066] Figure 1 This is a flowchart illustrating the output current limiting method of a power quality manager in one embodiment of the present invention;

[0067] Figure 2 This is a schematic diagram of the three-phase compensation current waveform of the power quality manager using the traditional compensation current limiting method in one embodiment of the present invention;

[0068] Figure 3 This is a schematic diagram of the three-phase compensation current waveform using a novel algorithm for reactive power extraction and amplitude limiting in one embodiment of the present invention.

[0069] Figure 4 This is a schematic diagram of the output current limiting device of the power quality manager in another embodiment of the present invention. Detailed Implementation

[0070] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0071] like Figure 1 As shown, the first embodiment of the present invention proposes an output current limiting method for a power quality manager, the method comprising the following steps:

[0072] S10. Sample the three-phase load current, and extract the amplitude of the three-phase active current, the amplitude of the three-phase reactive current, and the amplitude of the harmonic current based on the three-phase load current.

[0073] S20. Calculate the average value of the three-phase active current amplitude, and determine the three-phase active compensation current amplitude based on the average value, the three-phase active current amplitude, and the upper limit of the compensation current.

[0074] S30. Calculate the remaining capacity of the three-phase output current based on the upper limit of the compensation current and the amplitude of the three-phase active power compensation current.

[0075] S40. Based on the amplitude of the three-phase reactive current and the remaining capacity of the three-phase output current, determine the amplitude of the three-phase reactive compensation current.

[0076] S50. Based on the amplitude of the three-phase active power compensation current, the amplitude of the three-phase reactive power compensation current and the amplitude of the harmonic current, calculate the total three-phase output current, and output the total three-phase output current after limiting its amplitude.

[0077] It should be noted that the existing compensation current calculation algorithm does not take into account the sinusoidal nature of the output current. It either truncates or proportionally limits the reactive current and harmonic current after separating the active current without processing. However, neither of these two situations can guarantee the sinusoidal nature of the output current and will generate new grid-connected harmonic currents, which to some extent endangers the stability of the power grid.

[0078] This embodiment separates reactive current and harmonic current, and performs direct or proportional balancing adjustment on unbalanced three-phase active current. At the same time, it compensates reactive current and harmonics separately within the maximum capacity range of the equipment, so that the sinusoidal nature of the grid current is guaranteed. Moreover, no new harmonics will be generated due to the final amplitude limiting cutoff, regardless of the load current waveform, thus improving the adaptability of the power quality manager to different loads.

[0079] In one embodiment, step S10 specifically includes the following steps:

[0080] S11. Multiply the three-phase load current by the sinusoidal signal and pass it through a low-pass filter to obtain the amplitude of the three-phase active current.

[0081] Specifically, in this embodiment, the three-phase load current i La i Lb i Lc Multiplying it by a sinusoidal signal with the same frequency and phase and an amplitude of 2, and then passing it through a low-pass filter, yields the active power amplitude I of the load current. Lpa I Lpb I Lpc .

[0082] Among them, i La Indicates the load current of phase A, i Lb Indicates the load current of phase B, i Lc I represents the load current of phase C. Lpa I represents the amplitude of the active current in phase A. Lpb I represents the amplitude of the active current in phase B. Lpc This represents the amplitude of the active current in phase C.

[0083] S12. Multiply the three-phase load current by the cosine signal and pass it through a low-pass filter to obtain the amplitude of the three-phase reactive current.

[0084] Specifically, in this embodiment, the three-phase load current i La i Lb i Lc Multiplying it by a cosine signal with the same frequency and phase and an amplitude of 2, and then passing it through a low-pass filter, yields the reactive power amplitude I of the load current. Lqa I Lqb I Lqc .

[0085] Among them, I Lqa I represents the amplitude of the reactive current in phase A. Lqb I represents the amplitude of the reactive current in phase B. Lqc This represents the amplitude of the reactive current in phase C.

[0086] S13. The harmonic current amplitude is obtained by subtracting the amplitude of the three-phase active current and the amplitude of the three-phase reactive current from the three-phase load current.

[0087] In one embodiment, step S20 includes the following steps:

[0088] S21. Calculate the average value of the three-phase active current amplitude, and subtract the average value from the three-phase active current amplitude to obtain three difference values.

[0089] Specifically, the formula for calculating the average value of the three-phase active current amplitude is as follows:

[0090]

[0091] The difference between the average value of the three-phase active current amplitude and the three-phase active current amplitude is calculated as follows:

[0092]

[0093] In the formula: I avg I represents the average value of the three-phase active current amplitude. adv I represents the difference between the amplitude and the average value of the active current in phase A. bdv I represents the difference between the amplitude and the average value of the active current in phase B. cdv This represents the difference between the amplitude and the average value of the active current in phase C.

[0094] S22. Determine whether the maximum value among the three differences is less than or equal to the upper limit of the compensation current. If yes, proceed to step S23; otherwise, proceed to step S24.

[0095] S23. The three differences are used as the amplitude of the three-phase active power compensation current.

[0096] Specifically, from I adv I bdv and I cdv The maximum value is taken as the maximum amplitude I of the active current compensated by the power quality manager. dvmax And in |I dvmax |≤I max At that time, there were:

[0097]

[0098] In the formula: I max To compensate for the upper limit of current, Iao1 I is the active power amplitude of phase A of the power quality manager compensation current. bo1 I is the active power amplitude of phase B for the power quality manager compensation current. co1 The active power amplitude of phase C for power quality manager compensation current.

[0099] S24. After limiting the three differences using the proportional method, the amplitude is taken as the amplitude of the three-phase active power compensation current.

[0100] Specifically, in |I dvmax |≤I max At that time, there were:

[0101]

[0102] In one embodiment, in step S30, the formula for calculating the remaining capacity of the three-phase output current is:

[0103]

[0104] In the formula, I are For the residual compensation current capacity of phase A of the power quality manager, I bre For the residual compensation current capacity of phase B of the power quality manager, I cre This refers to the residual compensation current capacity of phase C of the power quality manager.

[0105] In one embodiment, step S40 includes the following steps:

[0106] S41. Compare the reactive current amplitude of each phase in the three-phase reactive current amplitude with the remaining output current capacity of the corresponding phase.

[0107] S42. If the reactive current amplitude of a certain phase is less than or equal to the remaining output current capacity of the corresponding phase, then the reactive current amplitude of that phase shall be used as the reactive compensation current amplitude of that phase.

[0108] S43. If the reactive current amplitude of a certain phase is greater than the remaining capacity of the output current of the corresponding phase, then the remaining capacity of the output current of that phase shall be used as the reactive compensation current amplitude of that phase.

[0109] It should be noted that in this embodiment, if the three-phase reactive current amplitude of the power quality manager is within the allowable output range, no processing is performed on the three-phase reactive current amplitude; if the three-phase reactive current amplitude exceeds the remaining capacity of that phase, the remaining capacity is used as the reactive current compensation current amplitude for that phase, specifically:

[0110] If |I Lqx |≤I xre , then I xo2 =I Lqx ;

[0111] If |I Lqx |>I xre ,but

[0112] Among them, I xo2 The reactive power amplitude of the compensation current for the power quality manager can be x, which can be a, b, or c.

[0113] In one embodiment, step S50 includes the following steps:

[0114] S51. Sum the amplitudes of the three-phase active power compensation current, the three-phase reactive power compensation current, and the harmonic current to obtain the total three-phase output current.

[0115] S52. Determine whether the total output current of the three phases is less than or equal to the upper limit of the compensation current. If yes, proceed to step S53; otherwise, proceed to step S54.

[0116] S53. Directly output the total three-phase output current.

[0117] S54. The portion of the total three-phase output current that exceeds the upper limit of the compensation current is cut off and then output.

[0118] It should be noted that if the total three-phase output current of the power quality manager is less than or equal to I... max No processing is required. If the total three-phase output current of the power quality manager exceeds the power quality manager's compensation current limit I... max Then, the portion of the total three-phase output current exceeding the upper limit will be cut off, and the upper limit value I will be output. max .

[0119] This embodiment separates reactive current from harmonic current through a reactive current extraction algorithm and applies a novel limiting algorithm to ensure the sinusoidal nature of the grid-connected current. Furthermore, regardless of the load current waveform, no new harmonics will be generated due to the final limiting truncation process, thus improving the power quality manager's adaptability to different loads.

[0120] Figure 2 and Figure 3 The figures show a comparison of the three-phase compensation current waveforms obtained by the power quality manager using the traditional compensation current limiting method and the method described in this embodiment. Figure 2 Each curve in the diagram represents the current waveform of one phase out of the three phases. Figure 3 Each curve represents the current waveform of one of the three phases. Figure 2 In the above scenario, the active current compensation value of phase C exceeded the limit and was directly clipped. The active current compensation value of phase A did not exceed the limit, but the remaining capacity was insufficient to compensate for the reactive current, resulting in clipping. The sum of the active and reactive currents of phase B exceeded the limit, and the waveform compensation was good. Figure 3 In this process, the three-phase compensation current is limited to the upper limit of the compensation current, and no clipping phenomenon occurs.

[0121] Furthermore, a second embodiment of the present invention also proposes an output current limiting device for a power quality manager, the device comprising:

[0122] Extraction module 10 is used to sample the three-phase load current and extract the amplitude of the three-phase active current, the amplitude of the three-phase reactive current, and the amplitude of the harmonic current based on the three-phase load current.

[0123] The first determining module 20 is used to calculate the average value of the three-phase active current amplitude, and determine the three-phase active compensation current amplitude based on the average value, the three-phase active current amplitude and the compensation current upper limit.

[0124] The remaining capacity calculation module 30 is used to calculate the remaining capacity of the three-phase output current based on the upper limit of the compensation current and the amplitude of the three-phase active power compensation current.

[0125] The second determining module 40 is used to determine the amplitude of the three-phase reactive current compensation based on the amplitude of the three-phase reactive current and the remaining capacity of the three-phase output current.

[0126] The output module 50 is used to calculate the total three-phase output current based on the amplitude of the three-phase active power compensation current, the amplitude of the three-phase reactive power compensation current and the amplitude of the harmonic current, and to output the total three-phase output current after limiting the amplitude.

[0127] In one embodiment, the extraction module 10 includes:

[0128] The first extraction unit is used to multiply the three-phase load current with a sinusoidal signal and then pass it through a low-pass filter to obtain the amplitude of the three-phase active current.

[0129] The second extraction unit is used to extract the amplitude of the three-phase reactive current by multiplying the three-phase load current by the cosine signal and passing it through a low-pass filter.

[0130] The third extraction unit is used to obtain the harmonic current amplitude by subtracting the amplitude of the three-phase active current and the amplitude of the three-phase reactive current from the three-phase load current.

[0131] In one embodiment, the first determining module 20 includes:

[0132] The difference calculation unit is used to calculate the average value of the three-phase active current amplitude, and to subtract the average value from the three-phase active current amplitude to obtain three difference values;

[0133] The first judgment unit is used to determine whether the maximum value among the three differences is less than the upper limit of the compensation current.

[0134] The first determining unit is configured to, when the output result of the first determining unit is yes, use the three differences as the amplitude of the three-phase active power compensation current; and to, when the output result of the first determining unit is no, use the proportional method to limit the amplitude of the three differences and use it as the amplitude of the three-phase active power compensation current.

[0135] In one embodiment, the second determining module 40 includes:

[0136] The comparison unit is used to compare the reactive current amplitude of each phase of the three-phase reactive current amplitude with the remaining output current capacity of the corresponding phase:

[0137] The second determining unit is used to determine the reactive current amplitude of a certain phase as the reactive compensation current amplitude of that phase when the reactive current amplitude of a certain phase is less than or equal to the output current remaining capacity of the corresponding phase.

[0138] The second determining unit is used to determine the reactive current amplitude of a phase as the reactive compensation current amplitude of that phase if the reactive current amplitude of a certain phase is greater than the remaining capacity of the output current of the corresponding phase.

[0139] In one embodiment, the output module 50 includes:

[0140] The summation unit is used to sum the amplitudes of the three-phase active power compensation current, the three-phase reactive power compensation current, and the harmonic current to obtain the total three-phase output current.

[0141] The second judgment unit is used to determine whether the total output current of the three phases is less than or equal to the upper limit of the compensation current.

[0142] The output unit is configured to directly output the total three-phase output current when the output result of the second judgment unit is yes; and to truncate the portion of the total three-phase output current that exceeds the upper limit of the compensation current before outputting it when the output result of the second judgment unit is no.

[0143] It should be noted that the existing compensation current calculation algorithm does not take into account the sinusoidal nature of the output current. It either truncates or proportionally limits the reactive current and harmonic current after separating the active current without processing. However, neither of these two situations can guarantee the sinusoidal nature of the output current and will generate new grid-connected harmonic currents, which to some extent endangers the stability of the power grid.

[0144] This embodiment separates reactive current and harmonic current, and performs direct or proportional balancing adjustment on unbalanced three-phase active current. At the same time, it compensates reactive current and harmonics separately within the maximum capacity range of the equipment, so that the sinusoidal nature of the grid current is guaranteed. Moreover, no new harmonics will be generated due to the final amplitude limiting cutoff, regardless of the load current waveform, thus improving the adaptability of the power quality manager to different loads.

[0145] It should be noted that other embodiments or implementation methods of the power quality manager output current limiting device described in this invention can refer to the above-described method embodiments, and will not be repeated here.

[0146] It should be noted that the logic and / or steps represented in the flowchart or otherwise described herein, for example, can be considered as a sequenced list of executable instructions for implementing logical functions, and can be embodied in any computer-readable medium for use by, or in conjunction with, an instruction execution system, apparatus, or device (such as a computer-based system, a processor-included system, or other system that can fetch and execute instructions from, an instruction execution system, apparatus, or device). For the purposes of this specification, "computer-readable medium" can be any means that can contain, store, communicate, propagate, or transmit programs for use by, or in conjunction with, an instruction execution system, apparatus, or device. More specific examples (a non-exhaustive list) of computer-readable media include: an electrical connection having one or more wires (electronic device), a portable computer disk drive (magnetic device), random access memory (RAM), read-only memory (ROM), erasable and editable read-only memory (EPROM or flash memory), fiber optic devices, and portable optical disc read-only memory (CDROM). Alternatively, the computer-readable medium may be paper or other suitable media on which the program can be printed, since the program can be obtained electronically, for example, by optically scanning the paper or other medium, followed by editing, interpreting, or otherwise processing as necessary, and then stored in a computer memory.

[0147] It should be understood that various parts of the present invention can be implemented in hardware, software, firmware, or a combination thereof. In the above embodiments, multiple steps or methods can be implemented in software or firmware stored in memory and executed by a suitable instruction execution system. For example, if implemented in hardware, as in another embodiment, it can be implemented using any one or a combination of the following techniques known in the art: discrete logic circuits having logic gates for implementing logical functions on data signals, application-specific integrated circuits (ASICs) having suitable combinational logic gates, programmable gate arrays (PGAs), field-programmable gate arrays (FPGAs), etc.

[0148] In the description of this specification, references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0149] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0150] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for limiting the output current of a power quality manager, characterized in that, The method includes: The three-phase load current is sampled, and the amplitudes of the three-phase active current, three-phase reactive current, and harmonic current are extracted based on the three-phase load current. This includes multiplying the three-phase load current by a sine signal and passing the result through a low-pass filter to obtain the amplitude of the three-phase active current; multiplying the three-phase load current by a cosine signal and passing the result through a low-pass filter to obtain the amplitude of the three-phase reactive current; and subtracting the amplitudes of the three-phase active current and the three-phase reactive current from the three-phase load current to obtain the amplitude of the harmonic current. Calculate the average value of the three-phase active current amplitude, and determine the three-phase active compensation current amplitude based on the average value, the three-phase active current amplitude, and the upper limit of the compensation current. Calculate the remaining capacity of the three-phase output current based on the upper limit of the compensation current and the amplitude of the three-phase active power compensation current. Based on the three-phase reactive current amplitude and the remaining capacity of the three-phase output current, the amplitude of the three-phase reactive current compensation current is determined, including: comparing the reactive current amplitude of each phase of the three-phase reactive current amplitude with the remaining capacity of the output current of the corresponding phase; if the reactive current amplitude of a certain phase is less than or equal to the remaining capacity of the output current of the corresponding phase, then the reactive current amplitude of that phase is taken as the reactive current compensation current amplitude of that phase; if the reactive current amplitude of a certain phase is greater than the remaining capacity of the output current of the corresponding phase, then the remaining capacity of the output current of that phase is taken as the reactive current compensation current amplitude of that phase. Based on the amplitudes of the three-phase active power compensation current, the three-phase reactive power compensation current, and the harmonic current, the total three-phase output current is calculated, and the total three-phase output current is output after being limited.

2. The output current limiting method for a power quality manager as described in claim 1, characterized in that, The calculation of the average value of the three-phase active current amplitude, and the determination of the three-phase active compensation current amplitude based on the average value, the three-phase active current amplitude, and the upper limit of the compensation current, includes: Calculate the average value of the three-phase active current amplitude, and subtract the average value from the three-phase active current amplitude to obtain three difference values; Determine whether the maximum value among the three differences is less than or equal to the upper limit of the compensation current; If so, the three differences are taken as the amplitude of the three-phase active power compensation current; If not, the amplitude of the three differences is limited using the proportional method and then used as the amplitude of the three-phase active power compensation current.

3. The output current limiting method for a power quality manager as described in claim 1, characterized in that, The step of calculating the total three-phase output current based on the amplitudes of the three-phase active power compensation current, the three-phase reactive power compensation current, and the harmonic current, and then limiting the total three-phase output current before outputting it, includes: The sum of the amplitudes of the three-phase active power compensation current, the three-phase reactive power compensation current, and the harmonic current is taken as the total three-phase output current. Determine whether the total three-phase output current is less than or equal to the upper limit of the compensation current; If so, the total three-phase output current will be output directly; If not, the portion of the total three-phase output current that exceeds the upper limit of the compensation current will be truncated before being output.

4. An output current limiting device for a power quality manager, characterized in that, The device includes: The extraction module is used to sample the three-phase load current and extract the amplitude of the three-phase active current, the amplitude of the three-phase reactive current, and the amplitude of the harmonic current based on the three-phase load current. The first determining module is used to calculate the average value of the three-phase active current amplitude, and determine the three-phase active compensation current amplitude based on the average value, the three-phase active current amplitude and the compensation current upper limit. The remaining capacity calculation module is used to calculate the remaining capacity of the three-phase output current based on the upper limit of the compensation current and the amplitude of the three-phase active power compensation current. The second determining module is used to determine the amplitude of the three-phase reactive current compensation based on the amplitude of the three-phase reactive current and the remaining capacity of the three-phase output current. The second determining module includes: The comparison unit is used to compare the reactive current amplitude of each phase of the three-phase reactive current amplitude with the remaining capacity of the output current of the corresponding phase. The second determination unit is used to determine the reactive current amplitude of a phase as the reactive compensation current amplitude of that phase if the reactive current amplitude of a phase is less than or equal to the remaining capacity of the output current of the corresponding phase. The second determination unit is used to determine the remaining capacity of the output current of a phase as the reactive compensation current amplitude of that phase if the reactive current amplitude of a phase is greater than the remaining capacity of the output current of the corresponding phase. The output module is used to calculate the total three-phase output current based on the amplitude of the three-phase active power compensation current, the amplitude of the three-phase reactive power compensation current, and the amplitude of the harmonic current, and to output the total three-phase output current after limiting its amplitude. The extraction module includes: The first extraction unit is used to multiply the three-phase load current with a sinusoidal signal and then pass it through a low-pass filter to obtain the amplitude of the three-phase active current. The second extraction unit is used to extract the amplitude of the three-phase reactive current by multiplying the three-phase load current by the cosine signal and passing it through a low-pass filter. The third extraction unit is used to obtain the harmonic current amplitude by subtracting the amplitude of the three-phase active current and the amplitude of the three-phase reactive current from the three-phase load current.

5. The output current limiting device for the power quality manager as described in claim 4, characterized in that, The first determining module includes: The difference calculation unit is used to calculate the average value of the three-phase active current amplitude, and to subtract the average value from the three-phase active current amplitude to obtain three difference values; The first judgment unit is used to determine whether the maximum value among the three differences is less than the upper limit of the compensation current. The first determining unit is configured to, when the output result of the first determining unit is yes, use the three differences as the amplitude of the three-phase active power compensation current; and to, when the output result of the first determining unit is no, use the proportional method to limit the amplitude of the three differences and use it as the amplitude of the three-phase active power compensation current.

6. The output current limiting device for a power quality manager as described in claim 4, characterized in that, The output module includes: The summation unit is used to sum the amplitudes of the three-phase active power compensation current, the three-phase reactive power compensation current, and the harmonic current to obtain the total three-phase output current. The second judgment unit is used to determine whether the total output current of the three phases is less than or equal to the upper limit of the compensation current. The output unit is configured to directly output the total three-phase output current when the output result of the second judgment unit is yes; and to truncate the portion of the total three-phase output current that exceeds the upper limit of the compensation current before outputting it when the output result of the second judgment unit is no.

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