Multi-module active power filter control method

Abstract

The application discloses a kind of multi-module active power filter control methods, comprising: detecting load current effective value, according to the size relationship and duration of load current and preset load current threshold, start or stop the operation of active power filter module;According to the output current of the preset capacity allocation strategy of active power filter module is distributed, and the running load rate of the active power filter module being calculated is operated;According to the size relationship and duration of running load rate and preset expected load rate upper limit and preset expected load rate lower limit, start or stop the operation of active power filter module.By the technical scheme of the application, the function that multiple module output currents are automatically distributed according to the size of load is realized, so as to conveniently realize the control of the whole system output and start-stop current, improve the compensation accuracy effect, prolong the service life of the whole system, improve the stability, reduce the failure rate.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of power electronics, in particular to a multi-module active power filter control method. BACKGROUND

[0002] With the development of modern industrial technology, the rapid power electronics of electrical equipment, more and more nonlinear loads are applied in power distribution system. These nonlinear loads provide people with rich, powerful electrical equipment, while generating a large amount of harmonic current, causing a series of power quality problems in transmission and distribution system. Such as system resonance, voltage waveform distortion, occupation of additional system capacity, generation of additional loss, etc. Active power filter is an effective device for harmonic current control of power grid.

[0003] At present, active power filter devices tend to be modular design, standardized production, and parallel connection of unit capacity modules to form larger capacity devices. The current control method of multi-module parallel connection is to allocate the output current of each module as an average allocation, and it is an open-loop control. Due to the inconsistency of each module in the sampling, calculation and output links, the output of each module is not completely equal, and there is an unbalanced output. At this time, it will inevitably lead to the decline of compensation effect. In addition, the existing multi-module parallel operation device is always running at the same time regardless of the size of the load, which will cause waste of device capacity and service life, and a method of automatically putting in the right number of modules according to the size of the load is needed to improve the stability and service life of the whole machine. SUMMARY

[0004] In view of at least one of the above problems, the present application provides a multi-module active power filter control method. Based on the traditional multi-module active power filter control method, based on the effective value of the load current and the effective value of the compensation current, additional capacity distribution and start-stop control algorithm links are added, without increasing the hardware cost of the device, realizing the start and stop of multiple module active power filter and the automatic distribution of the output current of each module according to the size of the load, ensuring that each active power filter module works in a reasonable capacity range as much as possible, thereby conveniently realizing the control of the output and start-stop current of the whole system, improving the compensation precision effect, prolonging the service life of the whole system, improving the stability, reducing the failure rate.

[0005] To achieve the above object, the application provides a multi-module active power filter control method, comprising: detecting a load current effective value, starting or stopping operation of an active power filter module according to a size relationship and a duration of the load current and a preset load current threshold value, distributing output currents of the active power filter modules according to a preset capacity distribution strategy, and calculating an operation load rate of the active power filter modules in operation; and starting or stopping operation of the active power filter module according to a size relationship and a duration of the operation load rate and a preset upper limit and a preset lower limit of an expected load rate.

[0006] In the technical solution, preferably, the multi-module active power filter control method specifically comprises: detecting a load current effective value, stopping all active power filter modules when it is judged that the load current continuously falls below a preset load current threshold value for a preset first duration; starting the active power filter modules when it is judged that the load current continuously exceeds the preset load current threshold value for a preset first duration without the active power filter modules in operation; distributing output currents of the active power filter modules according to a preset capacity distribution strategy and calculating an operation load rate of the active power filter modules in operation when it is judged that the load current continuously exceeds the preset load current threshold value for a preset first duration with the active power filter modules in operation; judging a size relationship of the operation load rate and a preset upper limit and a preset lower limit of an expected load rate; starting a new active power filter module when the operation load rate continuously exceeds the preset upper limit of the expected load rate for a preset second duration; stopping an active power filter module when the operation load rate continuously falls below the preset lower limit of the expected load rate for the preset second duration; and starting an inactive active power filter module to replace an active active power filter module when the operation load rate continuously falls below the preset upper limit of the expected load rate and exceeds the preset lower limit of the expected load rate for a preset third duration.

[0007] In the technical solution, preferably, the calculation of the operation load rate of the active power filter modules in operation specifically comprises: dividing the output current effective value of all the active power filter modules in operation by the sum of the capacities of all the active power filter modules in operation to obtain the operation load rate.

[0008] In the technical scheme, preferably, the preset upper limit of the expected load rate and the preset lower limit of the expected load rate are preset according to the power device capacity of the active power filter module, and the preset upper limit of the expected load rate and the preset lower limit of the expected load rate represent the optimal output capacity proportion of the active power filter module.

[0009] In the technical scheme, preferably, the preset capacity distribution strategy is that, according to the total load harmonic current of the load, the active power filter module outputs compensation current according to the weighted average coefficient of the power device capacity of each active power filter module, and the power device capacity of each active power filter module can be different.

[0010] In the technical scheme, preferably, according to the size relationship and the duration of the running load rate, the preset upper limit of the expected load rate and the preset lower limit of the expected load rate, the starting and stopping of the active power filter module during the running process of the active power filter module are performed according to the operation of a first-in-first-out stack.

[0011] In the technical scheme, preferably, the preset first duration and the preset second duration are set according to the switching life of the switching contactor of the active power filter module and the time period of load fluctuation.

[0012] Compared with the prior art, the active power filter of the application has the following advantages: based on the effective value of the load current and the effective value of the compensation current, additional capacity distribution and start-stop control algorithm links are added, in the case of not increasing the hardware cost of the equipment, the functions of starting and stopping of multiple module active power filters and automatic distribution of the output current of each module according to the size of the load are realized, each active power filter module is ensured to work in a reasonable capacity range as much as possible, the output and start-stop current control of the whole system is conveniently realized, the compensation precision effect is improved, the service life of the whole system is prolonged, the stability is improved, and the failure rate is reduced. BRIEF DESCRIPTION OF DRAWINGS

[0013] Figure 1 It is a schematic diagram of the working principle of the existing multi-module active power filter;

[0014] Figure 2.1 It is a schematic diagram of the grid voltage and current signal without active power filter compensation;

[0015] Figure 2.2 It is a schematic diagram of the grid voltage and current signal with active power filter compensation;

[0016] Figure 3 It is a logic diagram of the compensation current distribution strategy of the multi-module active power filter disclosed in an embodiment of the application;

[0017] Figure 4 Flow chart of the multi-module active power filter control method according to the first embodiment of the present application;

[0018] Figure 5 Flow chart of the multi-module active power filter control method according to the second embodiment of the present application;

[0019] Figure 6 Flow chart of the multi-module active power filter control method according to the third embodiment of the present application;

[0020] Figure 7.1 and 7.2 Trend waveform diagram of the start-stop of the whole device according to the load current change of the present application;

[0021] Figure 7.3 and 7.4 Trend waveform diagram of the start-stop of different modules according to the load harmonic current change of the present application. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical scheme and advantages of the embodiments of the present application clearer, the technical scheme of the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0023] The present application will be described in further detail below with reference to the drawings:

[0024] As Figure 1 shown is the working schematic diagram of the existing multi-module active power filter. N active power filter modules are connected in parallel between the power grid and the load. In the figure, I g represents the power grid current, I L represents the load current, I F represents the fundamental component of the load current, I H represents the harmonic component, I1 to I n represents the compensation output current of each module. Under ideal conditions, I1+I2+…I n =I H , so that there is only the fundamental current I F at the power grid side. When the load is a nonlinear load, the load current I L contains a large amount of harmonic current component, which affects the power supply quality and power supply safety.

[0025] As Figure 2.1As shown, when the active power filter is not turned on, the grid current and the load current are exactly the same. Figure 2.2 As shown, when the active power filter is turned on, it injects a harmonic current into the power grid that is equal in magnitude but opposite in phase to the harmonic current in the load, thus canceling out the original harmonic current in the load. When the active power filter is turned on, the harmonic current in the load is filtered out, and the distortion of the current waveform is improved.

[0026] like Figure 3 As shown, multiple active power filter modules share the load's total harmonic current components. Each module compensates according to a weighted average coefficient of its own capacity. First, the sum of the rated capacities of all normally operational modules is calculated as C. A The compensation coefficient for each module is Thus, the compensation current for each module is the total load harmonic current multiplied by its respective compensation coefficient.

[0027] Therefore, the current coefficient of each module compensation is related to the sum of the module capacities under normal operation and its own rated capacity, and satisfies ∑K n =1, and when the load changes, each module compensates based on the product of its coefficient and the load harmonic current. However, when the load harmonic content is much smaller than the sum of the module capacities, each module will output a very small compensation current. Since the accuracy and efficiency of each module in the entire device, including sampling, calculation, and output control, are poor when compensating for small currents, each module operates in a non-ideal state, and the overall machine performance is also poor.

[0028] Example 1:

[0029] like Figure 4 As shown, a multi-module active power filter control method according to the present invention includes: detecting the effective value of the load current; starting or stopping the operation of the active power filter module according to the relationship between the load current and a preset load current threshold and the duration; allocating the output current of the active power filter module according to a preset capacity allocation strategy, and calculating the operating load rate of the operating active power filter module; starting or stopping the operation of the active power filter module according to the relationship between the operating load rate and a preset upper limit of the expected load rate and a preset lower limit of the expected load rate and the duration.

[0030] In the above embodiments, preferably, the multi-module active power filter control method specifically includes:

[0031] 1) Define the number N of active power filter modules in the multi-module active power system;

[0032] 2) set the preset expected load rate upper limit N2_U and the preset expected load rate lower limit N2_D of the expected multi-module active filter system average load rate;

[0033] 3) set the preset second duration T2 of the expected module switching time interval;

[0034] 4) set the preset load current threshold N1 of the expected multi-module active filter system required to start running;

[0035] 5) set the preset first duration T1 of the expected detection time interval of the whole machine shutdown or start;

[0036] 6) detect the load current effective value, and when it is judged that the load current continuously falls below the preset load current threshold N1 for the preset first duration T1, shut down all active power filter modules;

[0037] 7) when it is judged that the load current continuously exceeds the preset load current threshold N1 for the preset first duration T1 without active power filter module running, start the active power filter module;

[0038] 8) when it is judged that the load current continuously exceeds the preset load current threshold for the preset first duration T1 with active power filter module running, distribute the output current of each active power filter module according to the preset capacity distribution strategy;

[0039] 9) calculate the running load rate η of the running active power filter module, and judge the size relationship between the running load rate η and the preset expected load rate upper limit N2_U and the preset expected load rate lower limit N2_D;

[0040] 10) when the running load rate η continuously exceeds the preset expected load rate upper limit N2_U for the preset second duration T2, judge whether there is an active power filter module not running, and if so, start a new active power filter module;

[0041] 11) when the running load rate η continuously falls below the preset expected load rate lower limit N2_D for the preset second duration T2, judge whether there is more than one active power filter module not stopped running, and if so, stop one active power filter module;

[0042] 12) when the running load rate η continuously falls below the preset expected load rate upper limit N2_U and exceeds the preset expected load rate lower limit N2_D for the preset third duration T3, start an inactive active power filter module to replace one running active power filter module;

[0043] 13) return to step 1) and loop detection.

[0044] In the above embodiment, preferably, the operation load rate η of the running active power filter module is specifically calculated by dividing the effective value of the output current of all running active power filter modules by the sum of the capacities of all running active power filter modules.

[0045] In the above embodiment, preferably, the preset upper limit N2_U and lower limit N2_D of the expected load rate are preset according to the power device capacity of the active power filter module, and the preset upper limit N2_U and lower limit N2_D of the expected load rate represent the optimal output capacity ratio of the active power filter module. Generally, when the output current operation load rate η of the active power filter module satisfies N2_D < η < N2_U, it is the ideal output load rate of the active power filter module.

[0046] In the above embodiment, preferably, the preset capacity allocation strategy is to output compensation current according to the weighted average coefficient of the power device capacity of each active power filter module according to the total load harmonic current of the load, and the power device capacity of each active power filter module can be different or equal.

[0047] In the above embodiment, preferably, according to the size relationship and duration of the operation load rate η and the preset upper limit N2_U and lower limit N2_D of the expected load rate, the starting and stopping of the active power filter module during the operation process of the active power filter module are performed according to the operation of the first-in-first-out stack.

[0048] In the above embodiment, preferably, the preset first duration T1 and the preset second duration T2 are set according to the switching life of the switching contactor of the active power filter module and the time period of the load fluctuation. Generally, the preset first duration T1 is the time condition for judging the load current, and when the duration exceeds the preset first duration T1, it can be judged that the load operation enters the small load state or the normal load state, and the time interval of the module switching, i.e. the preset second duration T2, is the switching time interval that the switching contactor of the active power filter module can withstand.

[0049] In the above embodiment, preferably, the setting of the load current threshold N1 refers to the value when the load current is small enough to be ignored, at which time the active filter can stop compensating harmonics. Generally, when the load current is less than the load current threshold, it is considered that the load on site belongs to the small load state, the harmonic current generated is small enough, and the key equipment has been shut down, at which time the active power filter can be shut down and hibernate, and does not need to compensate.

[0050] Embodiment two:

[0051] As Figure 5 shown, the multi-module active power filter control method disclosed in Example Two, compared with Example One, uses different preset load current threshold values when performing comparison calculation of load current and preset load current threshold, and the running and stopping values are different, and the preset first duration of comparison is different.

[0052] Example Three:

[0053] As Figure 6 shown, the multi-module active power filter control method disclosed in Example Three, compared with Example One, uses different values of determination time of different comparison threshold (such as T2A and T2B shown in the figure) when performing comparison of load rate η and preset expected load rate threshold upper limit and preset expected load rate threshold lower limit.

[0054] Taking the control method of the above Example One as an example, as Figure 7.1 shown, specifically, assuming that the initial load has no current, all active power filter modules are in a shutdown state, when the load changes, the effective value of the load current I L >N1, at this time timer 1 starts, and the state of the load current is timed, if the load current always satisfies I L >N1 within the timing time T1, a start instruction is issued to all active power filter modules, if I L <N1 occurs within the timing time T1, the timer is reset and timing is restarted. In Figure 7.1 , N1 is set to 10 and T1 is set to 30, and only when I L >10 and lasts for 30s, the start instruction start is 1.

[0055] As Figure 7.2 shown, when the load current changes, the effective value of the load current I L ≤N1, at this time timer 2 starts, and the state of the load current is timed, if the load current always satisfies I L ≤N1 within the timing time T1, a shutdown instruction is issued to all active power filter modules running, if I L >N1 occurs within the timing time T1, timer 2 is reset and timing is restarted. In Figure 7.2 , N1 is set to 10 and T1 is set to 30, and only when I L ≤10 and lasts for 30s, the shutdown instruction is 1.

[0056] When the active power filter modules are in operation, each active power filter module calculates its operation load rate as the effective value of its output compensation current divided by its rated capacity. Since the compensation current coefficient of each active power filter module is its rated capacity, the operation load rates of all active power filter modules are equal when the compensation current deviation of each active power filter module is ignored. Generally, the overall operation load rate η can be obtained by averaging the load rates of all active power filter modules in operation.

[0057] Then, the operation load rate η is compared with the preset expected load rate threshold N2_U and N2_D to control the start and stop of different active power filter modules. Specifically, assuming that the active power filter modules are in normal compensation operation, when the load current decreases at a certain moment, the compensation currents of all active power filter modules in operation also decrease accordingly. At this time, the operation load rate η decreases. When the load decreases to make the operation load rate η less than the preset expected load rate lower limit N2_D, the timer 3 starts timing, and the state of the operation load rate η is timed. If the condition η < N2_D is always met within the timing time T2 and more than two active power filter modules are in operation, the system removes one active power filter module according to the principle of first-in first-out. After removing one active power filter module, the compensation current of the load is shared by the remaining active power filter modules in operation. At this time, the operation load rate η increases. If the operation load rate η is still less than the preset expected load rate lower limit N2_D, the above steps are repeated until only one active power filter module is in standby operation. As shown in FIG. 4, IL_H is the harmonic current component contained in the load, and n is the number of active power filter modules in operation. In the figure, the capacity of each module is 100 A, and the setting time T2 is 10 s. It can be seen that when the load decreases, the load rate η also decreases. When the triggering condition is met, the load rate increases after removing one active power filter module. When the load continues to decrease, the system control module removes one active power filter module until only one active power filter module is in compensation operation. Figure 7.3

[0058] ​Similarly, when the load current increases at a certain moment, the compensation current of all active power filter modules in operation also increases accordingly, the operation load rate η rises, when the load current increases to make the operation load rate η greater than the preset expected load rate upper limit N2_U, the timer 4 starts timing, and the operation load rate η is timed, if the condition η>N2_U is always met within the timing time T2 and there is still an idle active power filter module not put into operation, the system puts into an active power filter module according to the principle of first cutting and first putting. After putting in an active power filter module, the compensation current of the load is shared by more active power filter modules, at this time, the operation load rate η decreases, if the operation load rate η is still greater than the preset expected load rate upper limit N2_U, the above steps are repeated until all modules are put into operation. As shown in the figure, Figure 7.4 IL_H is the harmonic current component contained in the load, n is the number of modules in operation, in the figure, the capacity of each module is 100A, and there are three modules in total, it can be seen that when the load current rises, the operation load rate η rises, when the trigger condition η>N2_U is met and the duration is 10s, one module is put into operation, the load rate decreases, when the load continues to increase, the system control module is put into operation until three modules are put into operation.

[0059] When the load current is stable and meets N2_D<η<N2_U, the operation state of the module is also stable, considering that the condition of some active power filter modules always operate and some active power filter modules always stop occurs, which is not conducive to the service life of the whole system, at this time, the system rotates according to the set operation time T3, that is, the active power filter module that has been operated for a long time is replaced, which can improve the service life of the whole machine.

[0060] The above is only a preferred embodiment of the present application and is not used to limit the present application, for those skilled in the art, the present application can have various changes and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A multi-module active power filter control method for controlling start-stop operation and output distribution of a plurality of active power filter modules, characterized by, The method comprises: detecting the effective value of the load current, and starting or stopping the operation of the active power filter module according to the magnitude relationship and duration of the load current and a preset load current threshold; allocating the output current of the active power filter module according to a preset capacity allocation strategy, and calculating the operation load rate of the active power filter module in operation, wherein the preset capacity allocation strategy is that the compensation current is output according to the weighted average coefficient of the power device capacity of each active power filter module according to the total load harmonic current of the load, and the power device capacity of each active power filter module allows to exist difference; starting or stopping the operation of the active power filter module according to the magnitude relationship and duration of the operation load rate and a preset upper limit of the expected load rate and a preset lower limit of the expected load rate.

2. The multi-module active power filter control method of claim 1, wherein, Specifically, the method comprises: detecting the effective value of the load current, and stopping all active power filter modules when it is judged that the load current continuously falls below the preset load current threshold for a preset first duration; starting the active power filter module when it is judged that the load current continuously exceeds the preset load current threshold for a preset first duration without the active power filter module in operation; allocating the output current of each active power filter module according to a preset capacity allocation strategy, and calculating the operation load rate of the active power filter module in operation when it is judged that the load current continuously exceeds the preset load current threshold for a preset first duration with the active power filter module in operation; judging the magnitude relationship of the operation load rate and a preset upper limit of the expected load rate and a preset lower limit of the expected load rate; judging whether there is the active power filter module without starting operation when the operation load rate continuously exceeds the preset upper limit of the expected load rate for a preset second duration, and starting a new active power filter module if there is; judging whether there is more than two active power filter modules without stopping operation when the operation load rate continuously falls below the preset lower limit of the expected load rate for the preset second duration, and stopping the active power filter module if there is; starting the active power filter module without operation to replace the active power filter module in operation when the operation load rate continuously falls below the preset upper limit of the expected load rate and exceeds the preset lower limit of the expected load rate for a preset third duration.

3. The multi-module active power filter control method of claim 1 or 2, wherein, The calculation of the operation load rate of the active power filter module in operation specifically comprises: dividing the effective value of the output current of all active power filter modules in operation by the sum of the capacities of all active power filter modules in operation to obtain the operation load rate.

4. The multi-module active power filter control method of claim 1 or 2, wherein, The preset upper limit of the expected load rate and the preset lower limit of the expected load rate are preset according to the power device capacity of the active power filter module, and the preset upper limit of the expected load rate and the preset lower limit of the expected load rate represent the optimal output capacity ratio of the active power filter module.

5. The multi-module active power filter control method of claim 1 or 2, wherein, According to the magnitude relationship and duration of the operation load rate with the preset upper limit and lower limit of the expected load rate, the starting and stopping of the active power filter module is performed according to the operation of the first-in-first-out stack.

6. The multi-module active power filter control method of claim 1 or 2, wherein, The preset first duration and the preset second duration are set according to the switching life of the switching contactor of the active power filter module and the time period of load fluctuation.

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