A method, device and transformer for treating three-phase load imbalance

Abstract

The present invention belongs to the technical field of power supply and distribution equipment, and its purpose is to provide a method, device and transformer for managing three-phase load imbalance. The present invention can collect the current signals of each phase, the neutral line current signal and the power factor of the three-phase four-wire power supply in real time, and then obtain the three-phase average current and the current imbalance coefficient of each phase according to the current signal of each phase, and then obtain the three-phase load imbalance according to the three-phase average current signal and the neutral line current signal, and when the three-phase load imbalance exceeds the preset value range, adjust the phase sequence of the three-phase load connected to the three-phase four-wire power supply according to the current imbalance coefficient of each phase, so as to reduce the three-phase load imbalance, and when the three-phase load imbalance does not exceed the preset value range, perform reactive compensation on the three-phase four-wire power supply according to the power factor of each phase, so as to make the three-phase load reach a balanced state, thereby realizing the adjustment of the three-phase load balance connected to the three-phase four-wire power supply, and the automation degree is higher.

Description

Technical Field

[0001] The invention belongs to the technical field of power supply and distribution equipment, and specifically relates to a three-phase load imbalance control method, device and transformer. Background Art

[0002] In the low-voltage power supply and distribution system, the distribution transformers mostly adopt the Y / Yn0 and Dyn11 wiring methods, and a large number of three-phase four-wire wiring methods are adopted. At the same time, many single-phase loads are connected in the three-phase.

[0003] However, in the process of using the prior art, the inventors found that the prior art has at least the following problems:

[0004] In actual work and operation, the way single-phase loads are connected to the low-voltage power supply and distribution system is usually random, which makes the uncertainty of the load properties of the three-phase four-wire power supply access high, and inevitably leads to unbalanced three-phase loads in the low-voltage power supply and distribution system. If the low-voltage power supply and distribution system works for a long time in a state of large three-phase load imbalance, it will have adverse effects on both the low-voltage power grid and electrical equipment, such as: increasing the power loss of the line, increasing the power loss of the distribution transformer, reducing the output of the distribution transformer, generating zero-sequence current in the distribution transformer, affecting the safe operation of electrical equipment, and reducing the efficiency of the transformer.

[0005] In order to control the three-phase load imbalance, the State Grid Corporation of China's enterprise standard Q / GDW 1519-2014 "Distribution Network Operation and Maintenance Regulations" stipulates that the load imbalance of the distribution transformer should meet the following requirements: the load imbalance of the Yyn0 connection transformer shall not exceed 15%, and the neutral current shall not exceed 25% of the rated current of the transformer; the load imbalance of the Dyn11 connection transformer shall not exceed 25%, and the neutral current shall not exceed 40% of the rated current of the transformer. Relevant regulations: The short-term overload operation of the transformer shall not exceed 15% in summer and 1 / 3 in winter. In general, the overload shall not exceed 2 hours, and the maximum shall not exceed 1.3 times the rated capacity of the transformer. It can be seen that being able to effectively control the three-phase load imbalance is of great significance to improving power supply quality and saving energy and reducing losses.

[0006] Among the current methods for managing three-phase load imbalance, the most commonly used methods are online adjustment of the three-phase active load, or reactive compensation to achieve relative balance of the three-phase load, and the method of first adjusting the three-phase active load and then performing reactive compensation to achieve three-phase load balance is rarely used. At the same time, the inventor has not found a method of using the three-phase load imbalance as the first criterion and further detecting the three-phase phase as the second criterion to select whether to use reactive compensation, or first adjusting the three-phase active load and then performing reactive compensation to manage the three-phase load imbalance problem in the three-phase four-wire low-voltage power supply and distribution system. A large number of practices have proved that in the application of the prior art, the three-phase load imbalance device cannot effectively manage the three-phase load imbalance.

[0007] In order to overcome the problem that three-phase load imbalance cannot be effectively managed due to limitations and defects of related technologies, it is necessary to study a three-phase load imbalance management method, device and transformer. Summary of the invention

[0008] The present invention aims to solve the above technical problems at least to a certain extent. The present invention provides a method, device and transformer for controlling three-phase load imbalance.

[0009] In order to achieve the above object, the present invention adopts the following technical solutions:

[0010] In a first aspect, the present invention provides a three-phase load imbalance control method, which is applied to a three-phase four-wire power supply, wherein the three-phase four-wire power supply is connected to a three-phase load; the three-phase load imbalance control method comprises:

[0011] Receiving each phase current signal, a neutral line current signal and each phase power factor in the three-phase four-wire power supply;

[0012] According to the current signals of each phase, the three-phase average current and the current unbalance coefficient of each phase are obtained;

[0013] Obtaining a three-phase load imbalance degree of the three-phase four-wire power supply according to the three-phase average current signal and the neutral line current signal;

[0014] Determine whether the three-phase load imbalance exceeds a preset value range. If so, adjust the phase sequence of the three-phase load connected to the three-phase four-wire power supply according to the current imbalance coefficient of each phase, so as to reduce the three-phase load imbalance, and then re-receive the current signal of each phase, the neutral line current signal and the power factor of each phase of the three-phase four-wire power supply; if not, proceed to the next step;

[0015] Determine whether the power factors of each phase are balanced, if not, proceed to the next step;

[0016] Reactive power compensation is performed on the three-phase four-wire power supply according to the power factor of each phase so as to balance the three-phase load, and then the current signals of each phase, the neutral line current signal and the power factor of each phase of the three-phase four-wire power supply are received again.

[0017] The present invention can effectively control the unbalance of three-phase loads and has a high degree of automation, thus avoiding manual operation by users. Specifically, during the implementation of the present invention, the current signals of each phase, the neutral line current signal and the power factor of the three-phase four-wire power supply can be collected in real time, and then the three-phase average current and the current imbalance coefficient of each phase are calculated according to the current signals of each phase, and then the three-phase load imbalance of the three-phase four-wire power supply is calculated according to the three-phase average current signal and the neutral line current signal. When the three-phase load imbalance exceeds the preset value range, the phase sequence of the three-phase load connected to the three-phase four-wire power supply is adjusted according to the three-phase load imbalance, thereby reducing the three-phase load imbalance. When the three-phase load imbalance does not exceed the preset value range, the power factors of each phase are compared, and the three-phase four-wire power supply is compensated for reactive power according to the power factors of each phase, so that the three-phase load reaches a balanced state, thereby realizing the adjustment of the balance of the three-phase load connected to the three-phase four-wire power supply, and the current signal and power factor collection, phase adjustment and reactive power compensation and other operations can be automatically performed by the machine, with a higher degree of automation, which is suitable for popularization and use.

[0018] In a possible design, adjusting the phase sequence of the three-phase load connected to the three-phase four-wire power supply according to the current unbalance coefficient of each phase includes:

[0019] Select 2n populations with different current unbalance coefficients;

[0020] Taking the three-phase load imbalance as an adaptive function, calculating the population fitness;

[0021] According to the fitness of the population, a chromosome having a better match between the current imbalance coefficient and the three-phase load imbalance is selected through a preset control strategy;

[0022] Perform crossover, inheritance and mutation on chromosomes to obtain a new population with the best combination;

[0023] Determine whether to terminate the calculation according to the preset three-phase load imbalance range. If yes, the optimal three-phase balanced load is obtained, and then proceed to the next step; if no, the population fitness is recalculated using the three-phase load imbalance of the three-phase four-wire power supply as an adaptive function until the optimal three-phase balanced load is obtained;

[0024] According to the optimal three-phase balanced load, the phase sequence of the three-phase load connected to the three-phase four-wire power supply is adjusted.

[0025] In one possible design, the three-phase average current is:

[0026]

[0027] In the formula, I a ,I b and Ic is the three-phase current signal;

[0028] The current unbalance coefficient of any phase is:

[0029]

[0030] In the formula, is the phase current signal.

[0031] In a possible design, the three-phase load imbalance of the three-phase four-wire power supply is:

[0032] or,

[0033]

[0034] In the formula, I 0 is the effective value of the neutral current signal, m is the real part of the vector formula of the neutral current, n is the imaginary part of the vector formula of the neutral current, I av is the three-phase average current; m i is the discrete value of the real part of the vector formula of the neutral current; n i is the discrete value of the imaginary part of the vector formula of the neutral current.

[0035] In the second aspect, the present invention provides a three-phase load imbalance control device, which is applied to a three-phase four-wire power supply, and the three-phase four-wire power supply is connected to a three-phase load; the three-phase load imbalance control device includes a control module, a sampling module, a phase adjustment module and a reactive power compensation module; the input end of the sampling module is connected to the three-phase four-wire power supply, and the output end of the sampling module is connected to the control module; the input end of the phase adjustment module is connected to the three-phase four-wire power supply, the output end of the phase adjustment module is connected to the three-phase load, and the controlled end of the phase adjustment module is connected to the control module; the input end of the reactive power compensation module is connected to the three-phase four-wire power supply, and the controlled end of the reactive power compensation module is connected to the control module; wherein,

[0036] The sampling module is used to collect the current signals of each phase, the neutral line current signal and the power factor in the three-phase four-wire power supply;

[0037] The control module is used to receive the phase current signals, neutral line current signals and power factors output by the sampling module, and obtain the three-phase average current and the phase current imbalance coefficient according to the phase current signals, and then obtain the three-phase load imbalance of the three-phase four-wire power supply according to the three-phase average current signal and the neutral line current signal, and then determine whether the three-phase load imbalance exceeds the preset value range. If so, drive the phase adjustment module to adjust the phase sequence of the three-phase load connected to the three-phase four-wire power supply according to the phase current imbalance coefficient, so as to reduce the three-phase load imbalance, and then re-receive the phase current signals, neutral line current signals and power factors of the three-phase four-wire power supply; if not, compare the power factors of the phases, and drive the reactive compensation module to perform reactive compensation on the three-phase four-wire power supply according to the power factors of the phases, so as to make the three-phase load reach a balanced state, and then re-receive the phase current signals, neutral line current signals and power factors of the three-phase four-wire power supply.

[0038] In a possible design, when the reactive power compensation module performs reactive power compensation on the three-phase four-wire power supply, a combined compensation method consisting of Y-type split-phase compensation and Δ-type joint compensation is adopted.

[0039] In a possible design, the three-phase load imbalance control device also includes a PWM generation module, and the control end of the reactive power compensation module is connected to the control module through the PWM generation module.

[0040] In a possible design, the three-phase load imbalance control device also includes a liquid crystal display module, which is connected to the control module and is used to display the power factor, the current signal and the three-phase load imbalance.

[0041] In a possible design, the three-phase load imbalance control device also includes an indication module, which is connected to the control module and is used to give a reminder when a prompt signal is received.

[0042] In a third aspect, the present invention provides a transformer, comprising a three-phase load imbalance control device as described in any one of the above items.

[0043] In a fourth aspect, the present invention provides a low voltage distribution network system, comprising the transformer as described above.

[0044] In a fifth aspect, the present invention provides an electronic device, comprising:

[0045] a memory for storing computer program instructions; and,

[0046] A processor is used to execute the computer program instructions to complete the operation of the three-phase load imbalance control method as described in any one of the above items.

[0047] In a sixth aspect, the present invention provides a computer-readable storage medium for storing computer program instructions readable by a computer, wherein the computer program instructions are configured to execute the operations of the three-phase load imbalance control method as described in any one of the above items when running. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 is a flow chart of the method for controlling the three-phase load imbalance in Example 1;

[0049] Figure 2 is a flow chart of phase adjustment according to the three-phase load imbalance in Example 1;

[0050] Figure 3 is a structural block diagram of the three-phase load imbalance control device in Example 2;

[0051] Figure 4 It is an application block diagram of the three-phase load imbalance control device in Example 2;

[0052] Figure 5 is a pin diagram of the sampling module in Example 2;

[0053] Figure 6 is a pin diagram of the phase modulation module in Example 2;

[0054] Figure 7 is a pin diagram of the reactive power compensation module in Example 2;

[0055] Figure 8 It is a circuit schematic diagram of the phase modulation module, the three-phase four-wire power supply and the three-phase load in Example 2;

[0056] Fig. 9 It is a circuit schematic diagram of the reactive power compensation module and the three-phase four-wire power supply in Example 2. DETAILED DESCRIPTION

[0057] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the present invention will be briefly introduced below in combination with the drawings and the description of the embodiments or the prior art. Obviously, the following description of the structure of the drawings is only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work. It should be noted that the description of these embodiments is used to help understand the present invention, but does not constitute a limitation of the present invention.

[0058] Embodiment 1:

[0059] This embodiment discloses a method for managing three-phase load imbalance, which is applied to a three-phase four-wire power supply, wherein the three-phase four-wire power supply is connected to a three-phase load; Figure 1 As shown, a method for managing three-phase load imbalance may include but is not limited to the following steps:

[0060] S101. Receive the current signal of each phase, the neutral line current signal and the power factor of each phase in the three-phase four-wire power supply;

[0061] S102. Obtain the three-phase average current and the current imbalance coefficient of each phase according to the current signal of each phase;

[0062] Specifically, in this embodiment, the three-phase average current is:

[0063]

[0064] In the formula, I a ,I b and I c is the three-phase current signal;

[0065] The current unbalance coefficient of any phase is:

[0066]

[0067] In the formula, is the phase current signal.

[0068] S103. Obtain the three-phase load imbalance of the three-phase four-wire power supply according to the three-phase average current signal and the neutral line current signal;

[0069] In this embodiment, the three-phase load imbalance of the three-phase four-wire power supply is:

[0070] or,

[0071]

[0072] In the formula, I 0 is the effective value of the neutral current signal, m is the real part of the vector formula of the neutral current, n is the imaginary part of the vector formula of the neutral current, I av is the three-phase average current; m i is the discrete value of the real part of the vector formula of the neutral current; n i is the discrete value of the imaginary part of the vector formula of the neutral current.

[0073] It should be noted that since the three-phase four-wire power supply in the low-voltage power supply and distribution system generally exhibits a three-phase load imbalance state with unbalanced three-phase power factor and unbalanced amplitude, a targeted three-phase load imbalance algorithm is required to play an effective reference role. The three-phase load imbalance of the three-phase four-wire power supply mentioned in this embodiment is obtained based on the discrete analysis of the neutral line current of the three-phase four-wire power supply in the low-voltage power supply and distribution system. Specifically, in this embodiment, the derivation process of the three-phase load imbalance of the three-phase four-wire power supply is as follows:

[0074] By transforming the above formula (1), we can get:

[0075]

[0076] Assume that the current unbalance coefficients of each phase are β a , β b , β c , the three-phase power factor angles are The three-phase current amplitudes are I am , I bm , I cm , then the instantaneous signal of the three-phase current amplitude can be expressed as:

[0077]

[0078] Substituting (2) into (3) we get:

[0079]

[0080] According to the vector formula of neutral line current: i 0 =i at +i bt +i ct ; (5)

[0081] Substituting (4) into (5) we can get the vector formula of the neutral line current at this time:

[0082]

[0083] Let the real part of equation (6) be m and the imaginary part be n, then the effective value of the neutral line current is:

[0084]

[0085] Considering the actual situation of the low-voltage power supply and distribution system, the real and imaginary parts of equation (6) are discretized to obtain:

[0086]

[0087] Where: β ai , β bi , βci are the current unbalance coefficients of phases A, B and C at the i-th moment respectively. They are the power factor angles of the three-phase loads A, B and C at the i-th moment respectively.

[0088] Based on the above analysis, if we want to balance the three-phase load through governance and make the current flowing through the neutral line zero, then we only have:

[0089] m i 2 +n i 2 =0; (9)

[0090] Substituting the relevant parameters and expanding them according to the trigonometric function relationship, we can get:

[0091]

[0092] Solving (10) yields It can be seen that for a three-phase power factor unbalanced system, if the three-phase load is to be balanced, the three-phase power factor angle must be achieved through compensation. Otherwise, even if the three-phase current amplitudes are equal, the impedance angles are asymmetric and current will still flow through the neutral line, causing invisible three-phase load imbalance. It can be seen that it is not enough to use the three-phase load imbalance as the criterion. It is also necessary to judge whether the three-phase power factor is balanced as the second criterion to effectively control the three-phase load imbalance.

[0093] Combining equations (6) to (8), we can obtain:

[0094]

[0095] The symbol ε is proposed for the three-phase load unbalance ui Description:

[0096] Can be ordered:

[0097] or

[0098] Note: Equations (12) and (13) can be used as two forms of the first criterion.

[0099] S104. Determine whether the three-phase load imbalance exceeds the preset value range, if yes, proceed to step S105; if no, proceed to step S106;

[0100] S105. According to the current imbalance coefficient of each phase, the phase adjustment module is driven to operate to adjust the phase sequence of the three-phase load connected to the three-phase four-wire power supply so as to reduce the three-phase load imbalance, and then the current signals of each phase, the neutral line current signal and the power factor of each phase of the three-phase four-wire power supply are received again, that is, returning to step S101;

[0101] In this embodiment, Figure 2 As shown, adjusting the phase sequence of the three-phase load connected to the three-phase four-wire power supply according to the unbalance coefficient of each phase current includes:

[0102] a1. Select 2n populations with different current unbalance coefficients; where n is a positive integer;

[0103] a2. The three-phase load imbalance is used as an adaptive function to calculate the population fitness;

[0104] a3. According to the fitness of the population, a chromosome with a better match between the current imbalance coefficient and the three-phase load imbalance is selected through a preset control strategy;

[0105] a4. Carry out crossover, inheritance and mutation processing on chromosomes to obtain a new population with the optimal combination;

[0106] a5. Determine whether to terminate the calculation according to the preset three-phase load imbalance range. If so, the optimal three-phase balanced load is obtained, and then proceed to the next step; if not, the three-phase load imbalance of the three-phase four-wire power supply is recalculated as an adaptive function to calculate the population fitness until the optimal three-phase balanced load is obtained;

[0107] a6. According to the optimal three-phase balanced load, adjust the phase sequence of the three-phase load connected to the three-phase four-wire power supply.

[0108] In this embodiment, based on the above process, the best three-phase balanced load can be easily obtained. According to the best three-phase balanced load, the phase sequence of the three-phase load connected to the three-phase four-wire power supply is adjusted, that is, a phase-adjusting switch of a reasonable load is selected from the phase-adjusting module, and then the phase sequence of the three-phase load connected to the three-phase four-wire power supply is adjusted through the phase-adjusting switch, so as to make the three-phase load relatively balanced, so as to reduce the imbalance of the three-phase load.

[0109] S106. Determine whether the power factors of each phase are balanced. If so, re-receive the current signals of each phase, the neutral line current signal and the power factors of each phase of the three-phase four-wire power supply, and return to step S101; if not, proceed to step S107;

[0110] Specifically, in this embodiment, the process of detecting whether the three-phase phases are symmetrical is as follows:

[0111] The three-phase phase can be obtained by solving the inverse cosine function of the sampled three-phase power factor. If the collected power factors of the three phases A, B, and C are respectively:

[0112] The control module solves the inverse cosine function based on the three-phase power factor detected by sampling, and the phases of the three phases A, B, and C are: If the difference between the two is 120°, then When , the three-phase power factor is considered balanced.

[0113] S107. Drive the reactive power compensation module to perform reactive power compensation on the three-phase four-wire power supply according to the power factor of each phase so that the three-phase load reaches a balanced state. In this embodiment, the result of reactive power compensation is to reduce the imbalance of the three-phase load to 0, and then re-receive the current signals of each phase, the neutral line current signal and the power factor of each phase of the three-phase four-wire power supply, that is, return to step S101.

[0114] In this embodiment, after receiving the current signals of each phase, the neutral line current signal and the power factor of each phase in the three-phase four-wire power supply in step S101, the method further includes:

[0115] S108. Compare the sampling values ​​of each phase current signal, neutral line current signal and each phase power factor with the preset values ​​as a protection judgment for the low-voltage power supply and distribution system, so as to perform over- and under-voltage protection operations, over- and under-current protection operations, leakage protection operations, arc protection operations and / or harmonic protection operations on the low-voltage power supply and distribution system.

[0116] It should be noted that, in this embodiment, reactive power compensation is performed on the three-phase four-wire power supply according to the power factor of each phase, including: connecting the load with a higher power factor in the phase with a higher load rate of the three-phase four-wire power supply to the phase with a lower load rate and a lower power factor. Specifically, when the reactive power compensation module performs reactive power compensation on the three-phase four-wire power supply, a combined compensation method consisting of Y-type phase compensation and Δ-type joint compensation is adopted, and the compensation method is as follows: which phase of the three phases of the three-phase four-wire power supply needs to be compensated, the corresponding switching fast switch corresponding to the Y-type phase compensation in the reactive power compensation module is turned on and switched in, and then Δ-type joint compensation is performed to reduce the three-phase load imbalance to the minimum range.

[0117] It should be understood that, in this embodiment, the three-phase load imbalance control method can be but is not limited to being executed based on the control module in the three-phase load imbalance control device, wherein the three-phase load imbalance control device includes a control module, a sampling module, a phase adjustment module and a reactive power compensation module; the input end of the sampling module is connected to the three-phase four-wire power supply, and the output end of the sampling module is connected to the control module; the input end of the phase adjustment module is connected to the three-phase four-wire power supply, and the output end of the phase adjustment module is connected to the three-phase load; The controlled end of the block is connected to the control module; the input end of the reactive compensation module is connected to the three-phase four-wire power supply, and the controlled end of the reactive compensation module is connected to the control module; wherein, the current signals of each phase and the neutral line current signal in the three-phase four-wire power supply are collected by the sampling module, and the control module can drive the phase adjustment module to adjust the phase sequence of the three-phase load connected to the three-phase four-wire power supply according to the current imbalance coefficient of each phase; the control module can also drive the reactive compensation module to perform reactive compensation on the three-phase four-wire power supply according to the power factor of each phase.

[0118] This embodiment can effectively control the imbalance of three-phase loads and has a high degree of automation, thus avoiding manual operation by users. Specifically, during the implementation of this embodiment, the current signals of each phase, the neutral line current signal and the power factor of the three-phase four-wire power supply can be collected in real time, and then the three-phase average current and the current imbalance coefficient of each phase are calculated according to the current signals of each phase, and then the three-phase load imbalance of the three-phase four-wire power supply is calculated according to the three-phase average current signal and the neutral line current signal. When the three-phase load imbalance exceeds the preset value range, the phase sequence of the three-phase load connected to the three-phase four-wire power supply is adjusted according to the current imbalance coefficient of each phase, so as to reduce the three-phase load imbalance. When the three-phase load imbalance does not exceed the preset value range, the power factors of each phase are compared, and the three-phase four-wire power supply is compensated for reactive power according to the power factors of each phase, so that the three-phase load reaches a balanced state, thereby realizing the adjustment of the balance of the three-phase load connected to the three-phase four-wire power supply, and the current signal and power factor collection, phase adjustment and reactive power compensation and other operations can be automatically performed by the machine, with a higher degree of automation, which is suitable for popularization and use.

[0119] Embodiment 2:

[0120] This embodiment discloses a three-phase load imbalance control device, which is applied to a three-phase four-wire power supply 200, and the three-phase four-wire power supply 200 is connected to a three-phase load 300; in this embodiment, the three-phase load imbalance control device is used to implement the three-phase load imbalance control method in Example 1, such as Figures 3 to 7As shown, it includes a control module 100, a sampling module 160, a phase adjustment module 150 and a reactive power compensation module 110; the input end of the sampling module 160 is connected to the three-phase four-wire power supply 200, and the output end of the sampling module 160 is connected to the control module 100; the input end of the phase adjustment module 150 is connected to the three-phase four-wire power supply 200, the output end of the phase adjustment module 150 is connected to the three-phase load 300, and the controlled end of the phase adjustment module 150 is connected to the control module 100; the input end of the reactive power compensation module 110 is connected to the three-phase four-wire power supply 200, and the controlled end of the reactive power compensation module 110 is connected to the control module 100; wherein,

[0121] The sampling module 160 is used to collect the current signal of each phase, the neutral line current signal and the power factor of each phase in the three-phase four-wire power supply 200;

[0122] The control module 100 is used to receive the current signals of each phase, the neutral line current signal and the power factor of each phase output by the sampling module 160, and obtain the three-phase average current and the current imbalance coefficient of each phase according to the current signal of each phase, and then obtain the three-phase load imbalance of the three-phase four-wire power supply 200 according to the three-phase average current signal and the neutral line current signal, and then determine whether the three-phase load imbalance exceeds the preset value range, and if so, drive the phase adjustment module 150 to adjust the three-phase load 300 to be connected according to the current imbalance coefficient of each phase. The phase sequence of the three-phase four-wire power supply 200 is determined so as to reduce the imbalance of the three-phase load, and then the current signals of each phase, the neutral line current signal and the power factor of each phase of the three-phase four-wire power supply 200 are received again; if not, the power factors of each phase are compared, and according to the power factors of each phase, the reactive power compensation module 110 is driven to perform reactive power compensation on the three-phase four-wire power supply 200 so as to make the three-phase load 300 reach a balanced state, and then the current signals of each phase, the neutral line current signal and the power factor of each phase of the three-phase four-wire power supply 200 are received again.

[0123] Specifically, in this embodiment, the control module 100 can be a general-purpose processor, including a central processing unit (CPU), a network processor (NP), etc., and can also be a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA) or other programmable logic devices, discrete gates or transistor logic devices, discrete hardware components. Among them, the general-purpose processor can be a microprocessor, or any conventional processor, etc. Specifically, in this embodiment, the control module 100 uses a single-chip microcomputer of an industrial-grade chip STM32.

[0124] In this embodiment, the sampling module 160 has four signal input terminals, and the four signal input terminals of the sampling module 160 are respectively connected to the A phase, B phase, C phase and neutral line N of the three-phase four-wire power supply 200, and the sampling module 160 has four signal output terminals, which are all connected to the control module 100.

[0125] In this embodiment, the phase-adjusting module 150 has four signal input terminals, which are connected to the three-phase four-wire power supply 200. Specifically, the four signal input terminals of the phase-adjusting module 150 are respectively connected to the A phase, B phase, C phase and neutral line N of the three-phase four-wire power supply 200; the phase-adjusting module 150 has four signal output terminals, which are respectively connected to the three-phase load 300, and are used to phase-adjust the three-phase load 300 when the imbalance degree of the three-phase load exceeds the preset value range; the phase-adjusting module 150 has multiple control terminals, which are all connected to the control module 100. In addition, in this embodiment, if Figure 8 As shown, the phase-adjusting module 150 includes a phase-adjusting switch, and the phase-adjusting switch is used to phase-adjust the three-phase load 300; wherein, the phase-adjusting switch is in multiple groups, and the multiple groups of phase-adjusting switches all adopt solid-state relays based on high-power IGBTs.

[0126] In this embodiment, the reactive power compensation module 110 has four signal input terminals, which are connected to the three-phase four-wire power supply 200. Specifically, the four signal input terminals of the reactive power compensation module 110 are respectively connected to the A phase, B phase, C phase and neutral line N of the three-phase four-wire power supply 200; the reactive power compensation module 110 has multiple control terminals, which are all connected to the control module 100, and are used to perform reactive power compensation on the three-phase four-wire power supply 200 when the three-phase load imbalance does not exceed the preset value range. In addition, in this embodiment, if Fig. 9 As shown, the reactive power compensation module 110 includes a compensation switching switch, which is used to perform reactive power compensation on the three-phase four-wire power supply 200; wherein, the compensation switching switches are multiple groups, and the multiple groups of compensation switching switches all adopt a mobile compensator based on high-power IGBT and capacitor composition.

[0127] In this embodiment, when the reactive power compensation module 110 performs reactive power compensation on the three-phase four-wire power supply 200, a combined compensation method consisting of Y-type phase-splitting compensation and Δ-type joint compensation is adopted.

[0128] Specifically, when the reactive power compensation module 110 performs reactive power compensation on the three-phase four-wire power supply 200, the compensation method is as follows: which phase of the three phases of the three-phase four-wire power supply 200 needs to be compensated, the corresponding switching fast switch corresponding to the Y-type phase compensation in the reactive power compensation module 110 is turned on and switched in, and then Δ-type joint compensation is performed to reduce the imbalance of the three-phase load to the minimum range.

[0129] In this embodiment, the control module 100 can be directly connected to the reactive power compensation module 110. In this case, the control module 100 adopts a control module 100 that can output PWM waves, such as a single-chip microcomputer of the STM32 series. Of course, the control module 100 can also adopt a control module 100 that cannot output PWM waves. In this case, the three-phase load imbalance control device also includes a PWM generation module 120, and the control end of the reactive power compensation module 110 is connected to the control module 100 through the PWM generation module 120. Specifically, in this embodiment, the PWM generation module 120 has multiple input ends, and the multiple input ends of the PWM generation module 120 are all connected to the control module 100. The PWM generation module 120 also has multiple output ends, and the multiple output ends of the PWM generation module 120 are respectively connected to the control end of the reactive power compensation module 110, so as to realize the control of the compensation switching switch in the reactive power compensation module 110 through the control module 100.

[0130] In this embodiment, the three-phase load imbalance control device further includes a liquid crystal display module 170, which is connected to the control module 100 and is used to display the power factor, the current signal and the three-phase load imbalance. It should be noted that, through the liquid crystal display module 170, it is convenient for the staff to intuitively understand the power factor, current signal and three-phase load imbalance of the three-phase four-wire power supply 200, so that the staff can intuitively see the control status of the three-phase load imbalance.

[0131] In this embodiment, the three-phase load imbalance control device further includes an indication module 130, which is connected to the control module 100 and is used to give a reminder when a prompt signal is received. Specifically, in this embodiment, the indication module 130 includes a working indication module 130 composed of a resistor and a light-emitting diode, and an alarm indication module 130 composed of a resistor, a triode and a buzzer.

[0132] In this embodiment, the three-phase load imbalance control device further includes a local power module 140, which is used to provide power supply to the control module 100, the sampling module 160, the phase adjustment module 150, the reactive power compensation module 110, the PWM generation module 120, the indication module 130 and the liquid crystal display module 170. Specifically, the local power supply has two input terminals, which are respectively connected to any phase of the three-phase four-wire power supply 200, and multiple output terminals, which are respectively connected to the control module 100, the reactive power compensation module 110, the PWM generation module 120, the indication module 130, the phase adjustment module 150, the sampling module 160 and the liquid crystal display module 170, so as to provide power support to each module.

[0133] Embodiment 3:

[0134] Based on Example 2, this example discloses a transformer, which includes the three-phase load imbalance control device in Example 2.

[0135] Embodiment 4:

[0136] Based on Example 2, this example discloses a low-voltage distribution network system, which includes the transformer in Example 3.

[0137] Embodiment 5:

[0138] Based on Embodiment 1, this embodiment discloses an electronic device, which may be a smart phone, a tablet computer, a laptop computer, or a desktop computer, etc. The electronic device may be referred to as a terminal, a portable terminal, a desktop terminal, etc. Specifically, the electronic device includes:

[0139] a memory for storing computer program instructions; and,

[0140] A processor is used to execute the computer program instructions to complete the operation of the three-phase load imbalance control method as described in any one of Example 1.

[0141] Embodiment 6:

[0142] Based on any one of Embodiments 1 or 5, this embodiment discloses a computer-readable storage medium for storing computer-readable computer program instructions, wherein the computer program instructions are configured to execute the operations of the three-phase load imbalance control method as described in Embodiment 1 during runtime.

[0143] Obviously, those skilled in the art should understand that the above modules or steps of the present invention can be implemented by a general computing device, they can be concentrated on a single computing device, or distributed on a network composed of multiple computing devices, and optionally, they can be implemented by a program code executable by a computing device, so that they can be stored in a storage device and executed by the computing device, or they can be made into individual integrated circuit modules, or multiple modules or steps therein can be made into a single integrated circuit module for implementation. Thus, the present invention is not limited to any specific combination of hardware and software.

[0144] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the above embodiments, a person skilled in the art should understand that the technical solutions described in the above embodiments can still be modified, or some of the technical features can be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

[0145] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the protection scope of the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A three-phase load imbalance control method, applied to a three-phase four-wire power supply, wherein the three-phase four-wire power supply is connected to a three-phase load; characterized in that: The three-phase load imbalance control method comprises: Receiving each phase current signal, a neutral line current signal and each phase power factor in the three-phase four-wire power supply; According to the current signals of each phase, the three-phase average current and the current unbalance coefficient of each phase are obtained; Obtaining a three-phase load imbalance degree of the three-phase four-wire power supply according to the three-phase average current signal and the neutral line current signal; Determine whether the three-phase load imbalance exceeds a preset value range. If so, adjust the phase sequence of the three-phase load connected to the three-phase four-wire power supply according to the current imbalance coefficient of each phase, so as to reduce the three-phase load imbalance, and then re-receive the current signal of each phase, the neutral line current signal and the power factor of each phase of the three-phase four-wire power supply; if not, proceed to the next step; Determine whether the power factors of each phase are balanced, if not, proceed to the next step; Performing reactive power compensation on the three-phase four-wire power supply according to the power factor of each phase so as to make the three-phase load reach a balanced state, and then re-receiving the current signal of each phase, the neutral line current signal and the power factor of each phase of the three-phase four-wire power supply; The three-phase average current is: In the formula, I a ,I b and I c is the three-phase current signal; The current unbalance coefficient of any phase is: In the formula, is the phase current signal; The three-phase load imbalance of the three-phase four-wire power supply is: or, Where I0 is the effective value of the neutral line current signal, m is the real part of the vector formula of the neutral current, n is the imaginary part of the vector formula of the neutral current, I av is the three-phase average current; m i is the discrete value of the real part of the vector formula of the neutral current; n i is the discrete value of the imaginary part of the vector formula of the neutral current.

2. A three-phase load imbalance control method according to claim 1, characterized in that: Adjusting the phase sequence of the three-phase load connected to the three-phase four-wire power supply according to the current unbalance coefficient of each phase includes: Select 2n populations with different current unbalance coefficients; Taking the three-phase load imbalance as an adaptive function, calculating the population fitness; According to the fitness of the population, a chromosome having a better match between the current imbalance coefficient and the three-phase load imbalance is selected through a preset control strategy; Perform crossover, inheritance and mutation on chromosomes to obtain a new population with the best combination; Determine whether to terminate the calculation according to the preset three-phase load imbalance range. If yes, the optimal three-phase balanced load is obtained, and then proceed to the next step; if no, the population fitness is recalculated using the three-phase load imbalance of the three-phase four-wire power supply as an adaptive function until the optimal three-phase balanced load is obtained; According to the optimal three-phase balanced load, the phase sequence of the three-phase load connected to the three-phase four-wire power supply is adjusted.

3. A three-phase load imbalance control device, applied to a three-phase four-wire power supply, wherein the three-phase four-wire power supply is connected to a three-phase load; characterized in that: The three-phase load imbalance control device includes a control module, a sampling module, a phase adjustment module and a reactive power compensation module; the input end of the sampling module is connected to the three-phase four-wire power supply, and the output end of the sampling module is connected to the control module; the input end of the phase adjustment module is connected to the three-phase four-wire power supply, the output end of the phase adjustment module is connected to the three-phase load, and the controlled end of the phase adjustment module is connected to the control module; the input end of the reactive power compensation module is connected to the three-phase four-wire power supply, and the controlled end of the reactive power compensation module is connected to the control module; wherein, The sampling module is used to collect the current signals of each phase, the neutral line current signal and the power factor in the three-phase four-wire power supply; The control module is used to receive the phase current signals, neutral line current signals and power factors output by the sampling module, and obtain the three-phase average current and the current imbalance coefficient of each phase according to the current signals of each phase, and then obtain the three-phase load imbalance of the three-phase four-wire power supply according to the three-phase average current signal and the neutral line current signal, and then determine whether the three-phase load imbalance exceeds the preset value range. If so, according to the current imbalance coefficient of each phase, drive the phase adjustment module to adjust the phase sequence of the three-phase load connected to the three-phase four-wire power supply, so as to reduce the three-phase load imbalance, and then re-receive the phase current signals, neutral line current signals and power factors of the three-phase four-wire power supply; if not, compare the power factors of each phase, and according to the power factors of each phase, drive the reactive compensation module to perform reactive compensation on the three-phase four-wire power supply, so as to make the three-phase load reach a balanced state, and then re-receive the phase current signals, neutral line current signals and power factors of the three-phase four-wire power supply; The three-phase average current is: In the formula, I a ,I b and I c is the three-phase current signal; The current unbalance coefficient of any phase is: In the formula, is the phase current signal; The three-phase load imbalance of the three-phase four-wire power supply is: or, Where I0 is the effective value of the neutral line current signal, m is the real part of the vector formula of the neutral current, n is the imaginary part of the vector formula of the neutral current, I av is the three-phase average current; m i is the discrete value of the real part of the vector formula of the neutral current; n i is the discrete value of the imaginary part of the vector formula of the neutral current.

4. A three-phase load imbalance control device according to claim 3, characterized in that: When the reactive power compensation module performs reactive power compensation on the three-phase four-wire power supply, a combined compensation method consisting of Y-type split-phase compensation and Δ-type joint compensation is adopted.

5. The three-phase load imbalance control device according to claim 3 is characterized in that: The three-phase load imbalance control device also includes a PWM generation module, and the control end of the reactive power compensation module is connected to the control module through the PWM generation module.

6. A three-phase load imbalance control device according to claim 3, characterized in that: The three-phase load imbalance control device also includes a liquid crystal display module, which is connected to the control module and is used to display the power factor, the current signal and the three-phase load imbalance.

7. The three-phase load imbalance control device according to claim 3 is characterized in that: The three-phase load imbalance control device also includes an indication module, which is connected to the control module and is used to give a reminder when a prompt signal is received.

8. A transformer, characterized in that: It comprises a three-phase load imbalance control device as described in any one of claims 3 to 7.

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