Extraction method and compensation device of unbalanced load active current

Abstract

The present invention provides an extraction method and compensation device for unbalanced load active current, the method mainly includes a load current acquisition module to acquire the current value of the unbalanced load, an AC voltage acquisition module to acquire the grid voltage, and then respectively sending the sampled current value and the sampled voltage value to the active current extraction module to extract the active current from the unbalanced load current; the method also includes sending the active current to the current command generation module to generate a load current command signal, the load current command signal generates an actual compensation current after passing through a driving module and a main circuit, and is injected into the grid to compensate the load current in real time. The extraction method for unbalanced load active current provided by the present invention can quickly extract the active current component in the unbalanced load current on site, and the extraction method for unbalanced load active current can be used in both single-phase power supply systems and three-phase power supply systems.

Description

Technical Field

[0001] The present invention relates to the technical field of dynamic compensation of power systems, and in particular to a method for extracting active current of an unbalanced load and a compensation device. Background Art

[0002] With the development of my country's economy and the rapid increase in electricity demand, a large number of nonlinear loads have appeared in the power grid. The load current of the nonlinear load (in addition to the positive-sequence fundamental component, it also includes positive-sequence harmonics, negative-sequence fundamentals, and negative-sequence harmonics. In the three-phase four-wire power system, there may also be zero-sequence current) flows into the power grid, forming a power frequency sinusoidal grid voltage drop on the grid impedance, causing distortion and asymmetry of the grid voltage at the grid end, which has a serious impact on the power system and other users of the power system.

[0003] Reactive power and harmonics caused by inductive loads, capacitive loads or thyristor switches in power systems have been a hot topic in academic circles in recent years. Reactive power has certain adverse effects on power supply and consumption, mainly manifested in:

[0004] 1) Reactive power will cause the current to increase and the apparent power to increase, resulting in a decrease in system capacity.

[0005] 2) An increase in reactive power will increase the total current, thereby increasing the losses of equipment and lines.

[0006] 3) It increases the voltage drop of the line, and the impact reactive load will also cause the voltage to fluctuate violently.

[0007] Therefore, it is necessary to extract the active current component from the nonlinear load current. Summary of the invention

[0008] The present invention provides an unbalanced load active current extraction method and compensation device, which can quickly extract the active component in the unbalanced load current for subsequent unbalanced compensation control and maintain the stable operation of the power grid system.

[0009] To achieve the above object, the present invention provides a method for extracting active current of an unbalanced load, the method comprising the following steps:

[0010] Step S11: multiplying the load current sampling value and the AC voltage sampling value to obtain the instantaneous active power of the first load;

[0011] Step S12: filtering out the signal of the frequency not required by the instantaneous active power of the first load to obtain the instantaneous active power of the second load;

[0012] Step S13: filtering out unnecessary high-frequency signals in the instantaneous active power of the second load to obtain the instantaneous active power of the third load;

[0013] Step S14: multiplying the instantaneous active power of the second load and the AC voltage sampling value to obtain intermediate signals A, B, and C;

[0014] Step S15: Calculate the effective value of the AC voltage sampling value and the square of the effective value;

[0015] Step S16: The intermediate signals A, B, and C are divided by the square of the effective value of the AC voltage sampling value to obtain the active current signal of the unbalanced load.

[0016] The above-mentioned method for extracting the active current of the unbalanced load further includes the following steps:

[0017] Step S21: performing Park transformation on the active current signal of the unbalanced load to obtain a d-axis current component, a q-axis current component and a z-axis current component;

[0018] Step S22: filtering the d-axis current component and the q-axis current component respectively;

[0019] Step S23: Perform Park inverse transformation on the filtered d-axis current component, q-axis current component and z-axis current component to obtain a load current command signal.

[0020] The above-mentioned method for extracting active current of unbalanced load further includes the following steps:

[0021] Step 31: Use the load current command signal , as a reference signal to generate an actual compensation current.

[0022] The present invention also provides an unbalanced load compensation device, integrating the unbalanced load active current extraction method as described in claims 1-3, characterized in that it includes:

[0023] A load current acquisition module, wherein the load current acquisition module is used to acquire a load current value;

[0024] An AC voltage acquisition module, wherein the AC voltage acquisition module is used to acquire an AC voltage value;

[0025] An active current extraction module, wherein the active current extraction module is used to extract the active current from the load current;

[0026] A current command generating module, the current command generating module is used to generate a load current command signal from the active current of the load;

[0027] A driving module, the driving module is used to generate a driving signal from the load current command signal;

[0028] The main circuit generates an actual compensation current according to the driving signal.

[0029] The unbalanced load active current extraction method and compensation device provided by the present invention can quickly extract the active current component in the unbalanced load current on site, which is used for the subsequent compensation device to generate compensation current, and the unbalanced load current is compensated in real time, thereby reducing the adverse effects of the reactive component on the power grid and maintaining the stable operation of the power grid system. At the same time, the unbalanced load active current extraction method provided by the present invention can be used in a single-phase system or a three-phase system. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments of the present invention are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can also be obtained based on these drawings.

[0031] Figure 1 A system block diagram of unbalanced load current compensation provided by the present invention;

[0032] Figure 2 for Figure 1 A specific embodiment of a module for extracting load active current;

[0033] Figure 3 It is a block diagram of an embodiment of Park transformation;

[0034] Figure 4 The present invention is a flow chart of the method for extracting active current of unbalanced load.

[0035] Figure 5 This is a flow chart of the method for generating current instructions according to the present invention.

[0036] Legend: 1 is a three-phase power supply, 2 is an unbalanced load, 3 is a compensation device, 31 is a control module, 32 is a main circuit, 311 is an AC voltage acquisition module, 312 is a load current acquisition module, 313 is an active current extraction module, 314 is a current command generation module, and 315 is a drive circuit. DETAILED DESCRIPTION

[0037] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the described embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0038] Figure 1The figure shows a system block diagram of the unbalanced load current compensation provided by the present invention, wherein 1 is a three-phase power supply, 2 is an unbalanced load, and 3 is a compensation device, and the compensation device 3 can be an active filter. In the compensation device 3, we designed a control module 31 and a main circuit 32, and the control module 31 can realize the functions of extracting the active current in the unbalanced load current, generating a load current command signal, and generating a drive signal; the main circuit 32 generates compensation currents ica / icb / icc / icn according to the drive signal, and injects them into the three-phase power grid to compensate the unbalanced load current in real time. The control module 31 includes an AC voltage acquisition module 311, a load current acquisition module 312, an active current extraction module 313, a current instruction generation module 314 and a drive circuit 315. The load current acquisition module 312 acquires the current iLa / iLb / iLc of the unbalanced load 2, and the AC voltage acquisition module 311 acquires the grid voltage va / vb / vc, and respectively sends the current sampling value iLa' / iLb' / iLc' and the voltage sampling value va' / vb' / vc' to the active current extraction module 313 to provide The active current iPa / iPb / iPc in the current iLa / iLb / iLc of the unbalanced load 2 is taken out, and the active current iPa / iPb / iPc is sent to the current command generation module 314 to generate a load current command signal Ia* / Ib* / Ic*. After the load current command signal Ia* / Ib* / Ic* generates a drive signal of the main circuit 32 through the drive module 315, the compensation current ica / icb / icc / icn generated by the main circuit 32 is injected into the power grid to compensate the load current in real time.

[0039] Figure 2 for Figure 1 In a specific embodiment of the active current extraction module 313, the load current sampling value iLa' / iLb' / iLc' and the AC voltage sampling value va' / vb' / vc' are calculated by the first multiplier 3131 to obtain the first load instantaneous active power P a / P b / P c , and then processed by the notch filter 3132 to obtain the second load instantaneous active power P' a / P' b / P' c , the low-pass filter 3133 is used to filter and obtain the instantaneous active power P" of the third load a / P” b / P” c The second multiplier 3134 multiplies the AC voltage sampling value va' / vb' / vc' by the instantaneous active power P" of the third load. a / P” b / P” cThe intermediate signal A / B / C is obtained by multiplication, and the divider 3135 divides the intermediate signal A / B / C by the square value U of the AC voltage sampling value. 2 a_rms / U 2 b_rms / U 2 c_rms, and the active current iPa / iPb / iPc in the current iLa / iLb / iLc of the unbalanced load 2 is obtained. The above-mentioned various types of operators can be operators built with analog circuits, and more preferably, they are operation modules in operation chips, such as TMS320F28335 of TI. The low-pass filter 3133 can select a filter with a higher cut-off frequency, and the delay can be controlled at the us level to achieve real rapid extraction of active components. After the unbalanced load active current iPa / iPb / iPc is extracted by the above method, the load current command signal Ia* / Ib* / Ic* can be generated by the current command generation module 314.

[0040] The active current extraction module 313 includes a method for extracting the active current of the unbalanced load, such as Figure 3 As shown, it mainly includes the following steps:

[0041] Step S11: Multiply the load current sampling value iLa' / iLb' / iLc' and the AC voltage sampling value va' / vb' / vc' to obtain the load instantaneous active power P a , P b , P c ;

[0042] Step S12: After filtering out the instantaneous active power P of the first load a , P b , P c Unnecessary frequency signal, get the second load instantaneous active power P' a , P′ b , P′ c ;

[0043] Step S13: Filter out the instantaneous active power P' of the second load a , P′ b , P′ c The signal is sent to a low-pass filter to filter out the unnecessary high-frequency signal and obtain the instantaneous active power P″ of the third load. a , P″ b , P″ c ;

[0044] Step S14: The instantaneous active power P″ of the third load a , P″ b , P″ cThe signal is multiplied with the AC voltage sampling value va' / vb' / vc' to obtain the intermediate signal A / B / C;

[0045] Step S15: The effective value U of the AC voltage sampling value of the AC voltage sampling value va' / vb' / vc' a_rms , U b_rms , U c_rms , and the square value of the AC voltage sampling value

[0046] Step S16: Divide the intermediate signals A, B, and C by the square value of the AC voltage sampling value It is sent to the divider to obtain the active current signal iPa / iPb / iPc of the unbalanced load.

[0047] The active current of the unbalanced load extracted by the above method filters out other signals except the fundamental active current, thereby ensuring the extraction accuracy of the active current.

[0048] The method for generating the load current command signal by the current command generating module 314 is as follows: Figure 5 As shown, the following steps are included:

[0049] Step S21: Perform Park transformation on the active current signal iPa / iPb / iPc of the unbalanced load to obtain the d-axis current component i d , q-axis current component i q and the z-axis current component i z ;

[0050] Step S22: Filter out the d-axis current component i d and the q-axis current component i q The component of the frequency that is not needed is obtained, and the d-axis current component of the required frequency is obtained' d and q-axis current component' q ;

[0051] Step S23: The filtered d-axis current component ' d , q-axis current component' q and z-axis current component' z Perform Park inverse transformation to obtain the load current command signal

[0052] The load current command signal generated by the above method A compensation current is generated after passing through the driving module 315 and the main circuit 32 to compensate the load current in real time.

[0053] The Park transformation in step S21 is mainly performed in two steps: Figure 3 As shown:

[0054] First, the three-phase stationary coordinate system and the two-phase stationary coordinate system are transformed, that is, the abc coordinates are transformed to the α and β coordinates. After the coordinate transformation, the unbalanced load active current signal iPa / iPb / iPc and the current signal i α 、i β The relationship between them is:

[0055]

[0056] Then, the two-phase stationary α, β coordinate system is transformed into the two-phase rotating d, q coordinate system, and the d, q coordinate axes are rotated at an angular velocity ω. Since the α, β coordinate system is stationary, an angle θ=t will be generated between the α axis and the d axis, and the angle θ changes with time. From this, the relationship between the rotating d, q coordinate axes and the stationary α, β coordinate axes is derived as follows:

[0057]

[0058] In the abc coordinate system, the unbalanced load active current i a 、i b 、i c is an AC signal. After the above Park transformation, the DC signal i in the d and q coordinate systems is obtained. d 、i q .

[0059] The Park inverse transformation process in step S23 is the inverse process of the Park transformation in step S21, and its transformation process will not be discussed here.

[0060] The method for extracting the active current of the unbalanced load provided by the present invention can quickly extract the active current from the unbalanced load current on site. At the same time, the unbalanced load current compensation device provided by the present invention can generate the compensation current in real time and inject it into the power grid to realize the active current compensation of the unbalanced load and maintain the stable operation of the power grid system.

[0061] It can be understood that the above specific description of the present invention is only used to illustrate the present invention and is not limited to the technical solutions described in the embodiments of the present invention. Those skilled in the art should understand that the present invention can still be modified or replaced by equivalents to achieve the same technical effects; as long as the use requirements are met, they are within the protection scope of the present invention.

Claims

1. A method for extracting active current of an unbalanced load, characterized in that: The method comprises the following steps: Step S11: multiplying the load current sampling value and the AC voltage sampling value to obtain the instantaneous active power of the first load; Step S12: filtering out the signal of a specific frequency point that is not required by the instantaneous active power of the first load to obtain the instantaneous active power of the second load; Step S13: filtering out unnecessary high-frequency signals in the instantaneous active power of the second load to obtain the instantaneous active power of the third load; Step S14: multiplying the instantaneous active power of the third load and the AC voltage sampling value to obtain intermediate signals A, B, and C; Step S15: Calculate the effective value of the AC voltage sampling value and the square of the effective value; Step S16: The intermediate signals A, B, and C are divided by the square of the effective value of the AC voltage sampling value to obtain the active current signal of the unbalanced load.

2. The method for extracting active current of unbalanced load according to claim 1, characterized in that: The following steps are also included: Step S21: performing Park transformation on the active current signal of the unbalanced load to obtain a d-axis current component, a q-axis current component and a z-axis current component; Step S22: filtering the d-axis current component and the q-axis current component respectively; Step S23: Perform Park inverse transformation on the filtered d-axis current component, q-axis current component and z-axis current component to obtain a load current command signal.

3. The method for extracting active current of unbalanced load as claimed in claim 2, characterized in that: It also includes the following steps, Step 31: Using the load current command signal as a reference signal to generate an actual compensation current.

4. An unbalanced load compensation device, based on the unbalanced load active current extraction method according to any one of claims 1 to 3, characterized in that include, A load current acquisition module, wherein the load current acquisition module is used to acquire a load current value; An AC voltage acquisition module, wherein the AC voltage acquisition module is used to acquire an AC voltage value; An active current extraction module, wherein the active current extraction module is used to extract the active current from the load current; A current command generating module, the current command generating module is used to generate a load current command signal from the active current of the load; A driving module, the driving module is used to generate a driving signal from the load current command signal; The main circuit generates an actual compensation current according to the driving signal.

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