CN109599860B - Plug-and-play active series type electric energy quality controller with high magnetic conductive material - Google Patents
Plug-and-play active series type electric energy quality controller with high magnetic conductive material Download PDFInfo
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- CN109599860B CN109599860B CN201811457757.8A CN201811457757A CN109599860B CN 109599860 B CN109599860 B CN 109599860B CN 201811457757 A CN201811457757 A CN 201811457757A CN 109599860 B CN109599860 B CN 109599860B
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F27/00—Details of transformers or inductances, in general
- H01F27/24—Magnetic cores
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F38/00—Adaptations of transformers or inductances for specific applications or functions
- H01F38/20—Instruments transformers
- H01F38/38—Instruments transformers for polyphase ac
Abstract
The invention discloses a plug-and-play active series type power quality controller with high magnetic conductive materials, and belongs to the field of power quality controllers. The detection control module in the controller is connected with the PWM driving control module; the PWM driving control module is connected with the inverter module; the inverter module is connected with a secondary side winding of the special transformer module; the primary side of the special mutual inductor is connected in series between the accessed traditional large power grid or microgrid and a load or a grid-connected point, and the primary side of the special mutual inductor is a part of a power grid cable or busbar; the passive filter module is divided into two parts, one part is connected in parallel at one side close to the traditional large power grid or microgrid, and the other part is connected in parallel at one side close to a load or a grid-connected point. The invention can simultaneously realize various power quality control functions; the plug and play can be realized, the installation, the maintenance, the overhaul and the removal are convenient under the condition of not interfering the normal operation of a power grid, and the primary side equivalent impedance can be continuously adjusted in a wide range under the condition of not increasing the size of equipment.
Description
Technical Field
The invention belongs to the field of power quality controllers, and particularly relates to a plug-and-play active series power quality controller with high magnetic permeability materials.
Background
As a main energy source of modern society, electric energy has wide application in various industries. The quality of the electric energy is related to the overall benefit of national economy. With the increase of nonlinear load and impact load in a large power grid, such as the increase of an electric railway, an electric arc furnace and large rectifying equipment, and the wide application of power electronic devices with the characteristics of nonlinearity, diversity and the like, the quality of electric energy in the large power grid is increasingly deteriorated. In recent years, distributed power generation is greatly developed in order to solve the dual pressure of environmental protection and energy shortage, and a microgrid is a key link for seamless access of distributed power generation to a large power grid. The micro-grid operation mode is flexible, the power supply reliability of a user and the utilization rate of distributed energy can be improved, the impact on a large power grid is reduced, and good economic and social benefits are achieved. However, due to the diversity of the micro-grid in the aspects of power supply, load, energy conversion unit, energy storage, operation state and the like, the intermittence and randomness of the distributed power supply, the high permeability between the large power grid and the micro-grid, and the problem of the power quality of the micro-grid is much more serious than that of the traditional large power grid. Therefore, the problem of the power quality of large power grids and micro-grids has become one of the important bottlenecks in the development of modern power systems.
An ideal power system should supply power to users at a specified voltage level with a constant frequency and sinusoidal waveform, and during the power transfer and conversion process, the power voltage waveform should always keep sinusoidal, not interfere with other loads, minimize the loss generated by the power supply line, and provide the maximum power to the users. However, this ideal state does not exist in practice for various reasons, and various problems in grid operation, electrical equipment and electricity usage, that is, quality of electric energy, are caused thereby. At present, the definition of the power quality is not completely the same in all countries of the world, and generally, the power quality mainly includes three aspects of voltage quality, frequency quality and power supply reliability. The power quality problem is summarized to mainly comprise four aspects: voltage fluctuations and flicker, harmonic pollution and voltage three-phase imbalance, voltage reduction and power supply interruption.
As the latest trend and key equipment of consumer power technology, an active series power quality controller capable of realizing multiple power quality adjusting functions becomes a hot point of research in the field. The active series type power quality controller is developed from the theory of a series type active power filter, and has various power quality control functions of harmonic isolation, reactive compensation, power flow control, voltage regulation, fault current limitation, soft start and the like.
However, the existing active series power quality controllers must be connected in series in the power grid, which requires redesigning the structure of a large power grid or a microgrid, requiring power-off installation of a power grid line to which the active series power quality controllers are added, and once the active series power quality controllers fail, the power grid line must be disconnected for maintenance and overhaul, which is undoubtedly not favorable for power supply of the power grid, and does not meet the long-term stable requirement of power grid development. Therefore, the development of an active series power quality controller capable of realizing plug and play has become a key point in the research of governing the power quality of a power grid.
The plug-and-play active series power quality controller can be well connected between a traditional large power grid and a micro grid, and can be conveniently installed, maintained and overhauled on the basis of not changing the structure of the existing power grid. Once a fault occurs, the plug-and-play active series type power quality controller can be immediately removed, and the normal operation of a power grid is not influenced. However, most plug-and-play active series power quality controllers use a special transformer as a basis of equipment, in order to realize plug-and-play, the primary side of the special transformer only has one circuit of a power grid cable, the obtainable magnetic flux density is very low, the magnetic flux leakage is very large, and the magnetic flux transmission efficiency is very low, so that the equivalent impedance adjustment range of the plug-and-play active series power quality controllers is very small. In order to enlarge the equivalent impedance adjusting range of the plug-and-play active series power quality controller, the method of increasing the length of the special mutual inductor is adopted, so that the length of the equipment is lengthened, the volume is enlarged, the cost is increased, and the operation of the equipment in a net hanging mode is difficult.
Disclosure of Invention
In view of the above-identified deficiencies in the art or needs for improvement, the present invention provides a plug-and-play active series power quality controller having a high permeability material, the purpose is that the hollow column iron core is used as the iron core of the specially-made mutual inductor, the access structure can be simplified, the controller can be accessed to the power grid by directly penetrating the power grid cable or bus bar through the iron core, the difficulties of the conventional active series type power quality controller in the aspects of installation, maintenance, overhaul, removal and the like are solved, the active series type power quality controller can be plugged and used, the iron core is manufactured by utilizing the characteristic of the magnetic conductive material with high magnetic conductivity to improve the magnetic flux transmission efficiency, the primary side equivalent impedance of the plug-and-play active series power quality controller can be continuously adjusted in a wide range under the condition of not increasing the volume of equipment, and various power quality control functions can be completed in a power grid.
To achieve the above object, according to one aspect of the present invention, there is provided a plug-and-play active series type power quality controller having a high permeability material, comprising: the system comprises a detection control module, a PWM driving control module, an inverter module, a specially-made mutual inductor module and a passive filter module;
the output end of the detection control module is connected with the input end of the PWM driving control module; the output end of the PWM driving control module is connected with the input end of the inverter module; the output end of the inverter module is connected with a secondary side winding of the specially-made mutual inductor module;
the special transformer module comprises three special transformers, and primary sides of the special transformers are respectively connected in series in each phase line between an accessed traditional large power grid or microgrid and a load or a grid-connected point; the iron core of each special mutual inductor is of a hollow columnar structure, and a part of each phase cable or bus bar of a large power grid or a micro grid directly penetrates through the iron core to serve as a primary side winding; the material of the iron core is a magnetic conductive material with relative magnetic conductivity exceeding 100 at fundamental frequency, and Z is set1For leakage reactance, Z, of the primary side of a specially-made transformermFor excitation impedance of specially-made transformers, Z2The secondary side leakage reactance of the specially-made mutual inductor is equivalent to the leakage reactance of the primary side when Z ismIs far greater than Z1And Z2Time, primary side equivalent impedance ZAXContinuously adjustable over a wide range, approximately:
ZAX≈α(5)
wherein alpha is a plurality of control parameters, and various governing functions of the power quality are realized by adjusting the plurality of control parameters alpha.
The passive filter module comprises two passive filters, one passive filter is connected in parallel at one side close to a traditional large power grid or microgrid, and the other passive filter is connected in parallel at one side close to a load or a grid-connected point; the primary side of each special transformer is connected between the parallel connection points of the two passive filters in series;
the detection control module is used for detecting the current of the power grid, and generating a control signal according to the current and sending the control signal to the PWM driving control module; the PWM driving control module is used for generating a driving signal to drive the inverter module to work; and the inverter module is used for generating voltage proportional to the detected power grid current according to the driving signal, filtering the voltage and applying the filtered voltage to two ends of a secondary side winding of each special transformer.
Further, the iron core material is silicon steel sheet, high permeability ferronickel alloy, amorphous soft magnetic alloy or film alloy.
Further, ZmAnd Z1Or Z2' is greater than 100.
Further, the electric energy quality management realized by adjusting the complex control parameter alpha comprises harmonic isolation, reactive compensation, power flow control, voltage regulation, fault current limiting and/or soft start.
Further, the harmonic isolation method is as follows:
when the conventional large power grid or microgrid and the load (or grid-connected point) contain harmonics, the formula (5) is expressed as follows by the superposition theorem:
wherein the primary side equivalent impedance ZAXIs decomposed into primary side fundamental wave equivalent impedance
And primary side nth harmonic equivalent impedance
The complex control parameter alpha is decomposed into a fundamental complex control parameter alpha(1)And n-th harmonic complex control parameter alpha(n)；
The detection control module respectively detects and controls the fundamental wave and the harmonic wave: for the fundamental wave, a fundamental wave complex control parameter alpha is set(1)About 0, the equivalent impedance of the fundamental wave at the primary side of the transformer
The voltage is about 0, and the special mutual inductor has no influence on the normal work of the power grid; for the nth harmonic, setting the complex control parameter alpha of the nth harmonic(n)The value of (c) is such that the primary side of the transformer is aligned n timesHarmonics present as large impedances
The harmonic current is forced to flow into the passive filter module, so that harmonic isolation is realized;
further, the reactive compensation method comprises the following steps:
according to the formula (5), let α ═ r + jx, r and x are real numbers, and j is an imaginary unit, then α ═ r + jx can be equivalent to a positive resistance, a negative resistance, an inductance or a capacitance, and let r ═ 0 according to the requirement of the reactive power of the power grid, and by adjusting the value of x, it is equivalent to connecting a reactive power device in series in the power grid line, and plays a role of reactive power compensation;
further, the method for power flow control comprises the following steps:
the equivalent impedance Z of the primary side of the specially-made mutual inductor can be adjusted by adjusting the amplitude of the complex control parameter alphaAXThe equivalent impedance of the access line is further changed, so that the distribution of the active power and the reactive power of the power grid is changed, and the effect of controlling the power flow distribution of the power grid is achieved;
further, the method of voltage regulation is as follows:
the low voltage problems and voltage fluctuations occurring in the grid are mostly caused by insufficient reactive power of the grid or uneven distribution of the power flow, so that adjusting the voltage of the grid can be classified as reactive compensation and power flow control problems. From the above analysis, it has been demonstrated that the present invention can function as a voltage regulator.
Further, the method of fault current limiting and soft start is as follows:
when the power grid normally works, alpha is made to be 0, the active series type power quality controller cannot influence the normal work of the power grid, and when the power grid fails or needs soft start, the value of alpha is increased, so that the fault current or the starting current is limited to the level which can be borne by the power grid, and the effects of fault current limiting and soft start are achieved.
In general, compared with the prior art, the above technical solution contemplated by the present invention can obtain the following beneficial effects:
(1) the hollow columnar specially-made iron core is adopted, the power grid cable or the busbar can be used normally by directly penetrating the iron core, plug and play can be realized, and the power grid cable or the busbar is convenient to mount, maintain, overhaul and dismount under the condition of not interfering the normal operation of the power grid.
(2) The characteristics of the high-permeability magnetic conduction material are utilized to improve the magnetic flux transmission efficiency, and the primary side equivalent impedance of the plug-and-play active series power quality controller can be continuously adjusted in a wide range under the condition that the volume of equipment is not increased.
(3) According to the topological structure of the series active power filter, the internal control strategy is changed, and the power quality control functions of harmonic isolation, reactive compensation, power flow control, voltage regulation, fault current limitation, soft start and the like can be realized at the same time.
Drawings
FIG. 1 is a schematic diagram of the structure of the access grid system of the present invention in the preferred embodiment of the present invention;
FIG. 2 is an equivalent circuit diagram of a T-shape of a specialized transformer in accordance with a preferred embodiment of the present invention;
fig. 3(a) and 3(b) are schematic diagrams of the primary side and the secondary side of the closed-end columnar iron core purpose-made transformer provided by the invention respectively; wherein, 3(a) is a schematic diagram of the primary side structure of the closed hollow columnar iron core special transformer, and 3(b) is a schematic diagram of the secondary side structure of the closed hollow columnar iron core special transformer;
fig. 4(a) and 4(b) are schematic diagrams of a primary side and a secondary side of the open-ended cylindrical iron core purpose-made transformer according to the present invention, respectively; wherein, 4(a) is a primary side structure schematic diagram of the special transformer with the open hollow columnar iron core, and 4(b) is a secondary side structure schematic diagram of the special transformer with the open hollow columnar iron core;
fig. 5(a) and 5(b) are schematic diagrams of a primary side and a secondary side of a closed-end special transformer suitable for a busbar according to the present invention; wherein, 5(a) is a schematic diagram of a primary side structure of a closed-end special transformer suitable for a busbar; 5(b) is a schematic structural diagram of a secondary side of a closed special transformer suitable for a busbar;
fig. 6(a) and 6(b) are schematic diagrams of a primary side and a secondary side of the open-ended special transformer for the busbar according to the present invention, respectively; wherein 6(a) is a schematic diagram of a primary side structure of an open-ended special transformer suitable for a busbar; 6(b) a schematic diagram of a secondary side structure of an open-ended special transformer suitable for a busbar;
FIG. 7 is a B-I graph of a specially made transformer core in accordance with a preferred embodiment of the present invention;
fig. 8(a) -8(c) are schematic diagrams of the closed-end cylindrical iron core specially-made transformer according to the present invention, respectively; wherein, 8(a) is a 3D model schematic diagram of the closed hollow columnar iron core special transformer; and 8(b) is the front view of the closed hollow columnar iron core special transformer, and 8(c) is the side view of the closed hollow columnar iron core special transformer.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
The plug-and-play active series power quality controller with the high magnetic permeability material is improved and designed aiming at the defects that the conventional active series power quality controller is difficult to install, maintain, overhaul, disassemble and the like, and the primary side equivalent impedance of the plug-and-play equipment cannot be continuously adjusted in a wide range under the condition of not increasing the volume of the equipment.
First, the basic operation principle of the plug-and-play active series power quality controller with high permeability material proposed by the present invention will be explained. Fig. 1 is a schematic diagram of a plug-and-play active series power quality controller accessing a power grid system. The plug-and-play active series type power quality controller is connected in series between a traditional large power grid (or microgrid) and a load (or a grid-connected point). The invention provides a plug-and-play multifunctional power quality controller with high magnetic conductive material, comprising: the system comprises a detection control module, a PWM driving control module, an inverter module, a specially-made mutual inductor module and a passive filter module; the detection control module detects the current I of the power gridgGenerating a control signal through a control algorithm and sending the control signal to a PWM driving control module; the PWM driving control module generates a driving signal for driving the inverter module to work; the inverter module comprises an LC filter circuit and a voltage source inverter, wherein the LC filter circuit consists of a capacitor and an inductor and is connected with the voltage source inverter and used for filtering harmonic waves around the switching frequency of the voltage source inverter; the inverter module is connected with the secondary side ax of the special mutual inductor module, generates voltage which is proportional to the detected power grid current after receiving the driving signal of the PWM driving control module, and applies the voltage to two ends of the secondary side of the special mutual inductor module after filtering; the primary side AX of the specially-made mutual inductor module is connected in series between an accessed traditional large power grid (or microgrid) and a load (or a grid-connected point), and the primary side AX is a part of a power grid cable or busbar and can be equivalent to four-quadrant continuously adjustable impedance with an impedance value; the passive filter module is divided into two parts, one part is connected in parallel to one side close to a traditional large power grid (or microgrid) and used for preventing harmonic waves of the power grid from flowing into a load (or a grid-connected point), and the other part is connected in parallel to one side close to the load (or the grid-connected point) and used for preventing harmonic waves generated by the load (or the grid-connected point) from flowing into the traditional large power grid (or microgrid).
Fig. 2 is a T-shaped equivalent circuit diagram of the special transformer. From fig. 2, a phasor expression of the voltage equation of the tailored transformer can be obtained:
U1＝I1Z1+(I1+I′2)Zm (1)
-U′2＝I′2Z′2+(I1+I′2)Zm (2)
U1voltage of two ends of a primary side of the special transformer is provided; u'2The voltage at two ends of a secondary side winding of the special transformer is equivalent to the voltage at a primary side of the special transformer; i is1The primary side current of the specially-made mutual inductor is the current I of the power grid in the present examplegThe same applies below; i is2The current of the secondary side winding of the specially-made mutual inductor is equivalent to the current of the primary side of the specially-made mutual inductor, Z1For primary side leakage reactance, Z, of specially-made transformersmExcitation impedance for specially-made mutual inductor；Z′2The secondary side leakage reactance of the specially-made mutual inductor is equivalent to the leakage reactance of the primary side.
Setting the current I of the primary side of a special transformer1The voltage across the secondary side winding is equivalent to the voltage U ' across the primary side by detecting the voltage U ' across the secondary side winding generated by the control module, the PWM drive control module and the inverter module '2Is composed of
U′2＝αI1 (3)
Where α is a complex control parameter, α can be expressed as α ═ r + jx, r and x are real numbers, and j is an imaginary symbol. The voltage source type inverter in the inverter module is used for converting UdThe provided DC signal is converted into AND1Same frequency AC voltage signal U2And loading the current to two ends of a secondary side winding of the specially-made mutual inductor. DC side voltage U of inverterdThere are three sources: 1) a capacitor is connected to the direct current side, and the voltage of the direct current side is stabilized by controlling an inverter; 2) a storage battery is connected to the direct current side, and stable direct current side voltage is obtained by controlling an inverter; 3) the power is obtained through induction of a power system, and stable direct-current side voltage is obtained through rectification.
Obtaining the equivalent impedance Z of the primary side of the special transformer by the simultaneous formulas (1) - (3)AXComprises the following steps:
Z1leakage reactance of the primary side of a special mutual inductor; zmExcitation impedance of a specially-made mutual inductor; u shape1For the voltage across the primary side of a specially-made transformer, I1Is the current on the primary side of a specially-made mutual inductor, namely the power grid current, Z'2The secondary side leakage reactance of the specially-made mutual inductor is equivalent to the leakage reactance of the primary side. When Z ismIs far greater than Z1And Z'2(ZmAnd Z1Or Z'2Is greater than 100), the primary side equivalent impedance can be approximated to
ZAX≈α (5)
Where α is a complex control parameter, α can be set to α ═ r + jx, and r and x are both real numbersAt this time, the primary side equivalent impedance ZAXCan be represented as a four-quadrant continuously adjustable impedance with one impedance value. By utilizing the property of the active series type power quality controller, after the active series type power quality controller is connected in series into a power grid, the comprehensive treatment of the power quality can be realized by adjusting a plurality of control parameters alpha.
The method for realizing various power quality control functions by the active series power quality controller is described as follows:
(1) harmonic isolation
When the traditional large power grid (or microgrid) and the load (or grid-connected point) contain harmonics, the fundamental waves and the harmonics can be respectively analyzed and designed through the superposition principle. By the superposition theorem, equation (5) can be expressed as:
wherein the primary side equivalent impedance ZAXIs decomposed into primary side fundamental wave equivalent impedance
And primary side nth harmonic equivalent impedance
The complex control parameter alpha is decomposed into a fundamental complex control parameter alpha(1)And n-th harmonic complex control parameter alpha(n). The whole detection control module respectively detects and controls fundamental waves and harmonic waves through an algorithm according to a superposition principle: for the fundamental wave, a fundamental wave complex control parameter alpha is set(1)About 0, the equivalent impedance of the fundamental wave at the primary side of the transformer
About 0, the mutual inductor has no influence on the normal operation of the system; for n-th harmonic wave, reasonably setting n-th harmonic wave complex control parameter alpha(n)The value of (a) makes the primary side of the transformer present a large impedance to the nth harmonic
Harmonic currents will be forced to flow into the passive filter module, serving as harmonic isolation.
(2) Reactive compensation
During operation of the grid, situations sometimes arise where the reactive power required by the load exceeds the ability of the generator to output reactive power. Reactive compensation, called reactive power compensation, is a technology for improving the power factor of a power grid, reducing the loss of a power supply transformer and a transmission line, improving the power supply efficiency and the electric energy quality, and improving the power supply environment in an electric power supply system. As can be seen from equation (5), the active series power quality controller may exhibit a four-quadrant continuously adjustable impedance, i.e., α ═ r + jx may be equivalent to a positive resistor, a negative resistor, an inductor, and a capacitor. According to the requirement of the reactive power of the power grid, r is made to be 0, the value of x is reasonably set, namely, a reactive power device is connected in series in a power grid line, and the reactive power compensation function is achieved.
(3) Power flow control
The distribution of the power flow in the grid, i.e. the distribution of the active power and the reactive power, is closely related to the impedance of the grid lines. The primary side of the transformer is connected into a power grid in series, and the primary side of the transformer presents an adjustable impedance. Therefore, the equivalent impedance Z of the primary side of the transformer can be adjusted by adjusting the magnitude of the complex control parameter alphaAXAnd further, the equivalent impedance of the line is changed, so that the distribution of the active power and the reactive power of the power grid is changed, and the effect of controlling the power flow distribution of the power grid is achieved.
(4) Voltage regulation
The low voltage problem and voltage fluctuation in the power grid are mostly caused by insufficient reactive power of the system or uneven power flow distribution, so that the voltage regulation of the power grid can be classified into the problems of reactive power compensation and power flow control. From the above analysis, it has been demonstrated that the present invention can function as a voltage regulator.
(5) Fault current limiting and soft start
When the power grid normally works, the equivalent impedance of the active series type power quality controller needs to be ensured to be 0, and the normal work of the system is not influenced. When a fault state occurs or the system is in soft start, the value of the equivalent impedance needs to be increased rapidly, and the large current is limited. According to the requirement, when the power grid normally works, alpha is set to be 0, and the active series type power quality controller cannot influence the normal work of the system. When a fault state is detected or the system needs soft start, the value of alpha is increased, so that the fault current or the starting current can be limited to the level which can be borne by the system, and the functions of fault current limitation and soft start are achieved.
Next, the structure and shape of the plug-and-play active series power quality controller with high permeability material according to the present invention will be explained.
The invention provides a special mutual inductor module of a plug-and-play active series power quality controller with high magnetic permeability materials, which comprises a primary side winding and a secondary side winding, wherein the primary side winding is a part of a power grid cable or a busbar, and the secondary side winding is wound along the axial direction and is connected with the output end of an inverter module. The iron core of the special transformer can be designed into a cylindrical shape or a rectangular shape according to the condition of a bus at the installation position, and can be designed into an open shape or a closed shape according to the installation requirement, as shown in figures 3 to 6 respectively. Therefore, the primary side of the special transformer is the power grid cable or the busbar, the number of turns of the secondary side winding is designed according to the use requirement without designing 1 turn.
The plug-and-play of different modes is realized by adopting a closed current transformer type or open transformer type access mode and matching with different module integration modes, and the plug-and-play system can be suitable for different scenes. For example, for a scene allowing a compensation circuit to be accessed for a long time or frequently, a closed design is adopted, and the hollow cylindrical iron core is directly penetrated on the busbar during routine maintenance or initial installation of a power grid, and can be used at any time later; for scenes that the compensation circuit is inconvenient to access for a long time or does not need to be frequently accessed, the specially-made mutual inductor can be made into a closed independent module which is preset on a power grid busbar, and other modules of the voltage compensator are directly plugged for use when voltage compensation is needed; or an open design is directly used, the iron core is directly opened when needed, the busbar is arranged in, and then the voltage compensator is closed to be connected in series with the power grid for normal use; for users who need to frequently compensate different power grids, the special mutual inductor with the open design can also be used as an independent module, so that the users can conveniently replace different special mutual inductors at any time according to different power grids.
Next, the materials used in the plug-and-play active series power quality controller with high permeability material according to the present invention will be described.
According to the above analysis, in order to realize various power quality management functions of the plug-and-play active series power quality controller, such as harmonic isolation, reactive compensation, power flow control, voltage regulation, fault current limitation, soft start, etc., the primary side equivalent impedance of the plug-and-play active series power quality controller must be adjustable within a wide range. The formula (4) is a complete expression of the equivalent impedance of the primary side of the specially-made transformer, and the following proves that the equivalent impedance of the formula (4) can meet the condition of being adjustable in a wide range: zmIs far greater than Z1And Z'2That is, the formula (4) can be simplified to the formula (5).
Is provided with Zm＝kZ1＝kZ′2And k is a real multiple, equation (4) can be simplified as follows:
as can be seen from the formula (6): with constant parameter α, ZAXIs a monotonically increasing function of k, when k is 0, ZAX0 is approximately distributed; when k → ∞ is reached, ZAXα is approximately distributed; so in order to guarantee that the maximum regulation range can be obtained at the same plant capacity, the condition k → ∞, i.e. Z, must be satisfiedmIs far greater than Z1And Z'2(general Z)mAnd Z1Or Z'2Is greater than 100), in which case equation (4) can be simplified to equation (5).
In order to realize plug and play of the active series type power quality controller, the primary side of the special mutual inductor module can only be a power grid cable or a busbar connected to a power grid, and the number of winding turns is only 1 turn. FIG. 7 is a B-I curve diagram of a specially made transformer core, wherein the curve is obliqueRatio and excitation impedance ZmIs in direct proportion. As can be seen from fig. 7: the smaller the number of winding turns N is, the smaller the excitation impedance ZmThe smaller. When the number of turns of the primary side winding of the special transformer module is only 1 turn, the obtainable magnetic flux density is very low and the magnetic leakage is very large, namely the excitation impedance ZmVery small and leaky reactance Z1And Z'2Increase, extremely low magnetic flux transmission efficiency, and failure to satisfy ZmIs far greater than Z1And Z'2The conditions of (1). This results in that the equivalent impedance adjustment range of the plug-and-play active series type power quality controller becomes small.
The method for increasing the adjustment range of equivalent impedance is analyzed by taking the closed-end column-shaped iron core special transformer shown in fig. 8(a) -8(c) as an example, wherein r1Is the inner diameter of the iron core, r2Is the outer diameter of the iron core, x1Is the axial length of the core. According to a calculation formula of the inductance with the iron core, the equivalent excitation inductance of the closed columnar iron core specially-made transformer is obtained as follows:
wherein, N is the number of winding turns, and N is 1; mu.s0Is a vacuum permeability, mu0＝4π×10-7；μrIs the relative permeability of the core material; and pi is the circumferential ratio. And the relation between the excitation inductance and the excitation impedance is Zm＝ωLm＝2πfLmWhere f is the fundamental frequency.
In general r1And r2The diameter of the power grid cable and the equipment design standard of the power grid are constant and can not be changed. Therefore, by increasing the equivalent field impedance ZmTo satisfy ZmIs far greater than Z1And Z'2Only by increasing the axial length x of the core of the specially made transformer1Or by selecting a magnetic conductive material with higher magnetic permeability. But under the condition of high load of the traditional large power grid, the axial length x of the iron core of the special mutual inductor is increased1X required for the process of1The value is too large, the volume and the weight of the equipment are too large, the net hanging and the maintenance are difficult, and the actual net hanging operation is difficult. Therefore, the present inventionThe iron core material of the special mutual inductor in the plug-and-play active series type power quality controller is made of magnetic conductive material with high magnetic conductivity.
The magnetic conductive material with high magnetic conductivity is used as the iron core, so that the magnetic flux transmission efficiency is greatly improved, and on one hand, the equivalent excitation impedance Z can be increasedmOn the other hand, leakage reactance Z can be reduced1And Z'2So that Z ismIs far greater than Z1And Z'2The conditions can be more fully satisfied, and the equivalent impedance of the plug-and-play active series power quality controller can be continuously adjusted in a wide range.
The relative permeability μ of each material is as followsrTypical values of (a):
1) casting iron: 200-400;
2) nickel-iron alloy: 2000-6000;
3) silicon steel sheet: 6000- > 12000;
4) manganese zinc ferrite: 10000-;
5) permalloy (permalloy): 18000-;
6) amorphous soft magnetic alloy: 30000 400000;
the commonly used iron core material of the specially-made mutual inductor is a silicon steel sheet, and the typical value of the relative permeability of the iron core material is about 8000; if a magnetic conductive material with high magnetic conductivity is adopted, such as permalloy (permalloy), amorphous soft magnetic alloy and the like, Z can be mademIncreases the value of (a) by about 20 times, and can greatly reduce Z1And Z'2A value of (a) sufficient to satisfy ZmIs far greater than Z1And Z'2The requirements of (a). Therefore, the plug-and-play active series power quality controller with the high magnetic conductive material can realize the continuous adjustment of the primary side equivalent impedance in a wide range under the condition of not increasing the volume of equipment.
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (8)
1. A plug and play active series type power quality controller having high permeability magnetic material, comprising: the system comprises a detection control module, a PWM driving control module, an inverter module, a specially-made mutual inductor module and a passive filter module;
the output end of the detection control module is connected with the input end of the PWM driving control module; the output end of the PWM driving control module is connected with the input end of the inverter module; the output end of the inverter module is connected with a secondary side winding of the specially-made mutual inductor module;
the special mutual inductor module comprises three special mutual inductors, and primary sides of the special mutual inductors are respectively connected in series in phase lines between an accessed large power grid or microgrid and a load or a grid-connected point; the iron core of each special mutual inductor is of a hollow columnar structure, and a part of each phase cable or bus bar of a large power grid or a micro grid directly penetrates through the iron core to serve as a primary side winding; the material of the iron core is a magnetic conductive material with relative magnetic conductivity exceeding 100 at fundamental frequency, and Z is set1For leakage reactance, Z, of the primary side of a specially-made transformermIs the excitation impedance of a specially-made mutual inductor Z'2In order to make the secondary side leakage reactance of the special mutual inductor equivalent to the leakage reactance of the primary side, when ZmIs far greater than Z1And Z'2Time, primary side equivalent impedance ZAXContinuously adjustable over a wide range, approximately:
ZAX≈α (5)
wherein alpha is a plurality of control parameters, and various governing functions of the power quality are realized by adjusting the plurality of control parameters alpha;
the reactive compensation method comprises the following steps:
according to the formula (5), let α ═ r + jx, r and x are real numbers, and j is an imaginary unit, then α ═ r + jx can be equivalent to a positive resistance, a negative resistance, an inductance or a capacitance, and let r ═ 0 according to the requirement of the reactive power of the power grid, and by adjusting the value of x, it is equivalent to connecting a reactive power device in series in the power grid line, and plays a role of reactive power compensation;
the passive filter module comprises two passive filters, one passive filter is connected in parallel at one side close to a large power grid or a microgrid, and the other passive filter is connected in parallel at one side close to a load or a grid-connected point; the primary side of each special transformer is connected between the parallel connection points of the two passive filters in series;
the detection control module is used for detecting the current of the power grid, and generating a control signal according to the current and sending the control signal to the PWM driving control module; the PWM driving control module is used for generating a driving signal to drive the inverter module to work; and the inverter module is used for generating voltage proportional to the detected power grid current according to the driving signal, filtering the voltage and applying the filtered voltage to two ends of a secondary side winding of each special transformer.
2. The plug-and-play active series type power quality controller with mu-metal material of claim 1, wherein the core material is silicon steel sheet, mu-metal, amorphous soft magnetic alloy or thin film alloy.
3. A plug-and-play active series type power quality controller with high permeability material as claimed in claim 1 or 2, characterized in that ZmAnd Z1Or Z'2Is greater than 100.
4. A plug-and-play active series type power quality controller with high permeability material according to claim 1 or 2, characterized in that the power quality governance by adjusting the complex control parameter α comprises harmonic isolation, reactive compensation, power flow control, voltage regulation, fault current limitation and/or soft start.
5. The plug-and-play active series type power quality controller with high permeability material of claim 4, wherein the harmonic isolation method is as follows:
when the large power grid or the microgrid and the load or the grid-connected point contain harmonics, the formula (5) is expressed by the superposition theorem as follows:
wherein the primary side equivalent impedance ZAXIs decomposed into primary side fundamental wave equivalent impedance
And primary side nth harmonic equivalent impedance
The complex control parameter alpha is decomposed into a fundamental complex control parameter alpha(1)And n-th harmonic complex control parameter alpha(n)；
The detection control module respectively detects and controls the fundamental wave and the harmonic wave: for the fundamental wave, a fundamental wave complex control parameter alpha is set(1)About 0, the equivalent impedance of the fundamental wave at the primary side of the transformer
The voltage is about 0, and the special mutual inductor has no influence on the normal work of the power grid; for the nth harmonic, setting the complex control parameter alpha of the nth harmonic(n)The value of (a) makes the primary side of the transformer present a large impedance to the nth harmonic
And the harmonic current is forced to flow into the passive filter module, so that harmonic isolation is realized.
6. The plug-and-play active series power quality controller with high permeability material of claim 4, wherein the power flow control method comprises the following steps:
the equivalent impedance Z of the primary side of the specially-made mutual inductor can be adjusted by adjusting the amplitude of the complex control parameter alphaAXAnd further, the equivalent impedance of the access line is changed, so that the distribution of the active power and the reactive power of the power grid is changed, and the effect of controlling the power flow distribution of the power grid is achieved.
7. The plug-and-play active series power quality controller with high permeability material of claim 4, wherein the voltage regulation method is as follows:
the low-voltage problem and voltage fluctuation in the power grid are mostly caused by insufficient reactive power of the power grid or uneven power flow distribution, so that the voltage of the power grid is regulated and classified into the problems of reactive compensation and power flow control, and the reactive compensation and the power flow control are realized by regulating a plurality of control parameters alpha to play a role in voltage regulation.
8. The plug-and-play active series type power quality controller with high permeability material of claim 4, wherein the method of fault current limiting and soft start is as follows:
when the power grid normally works, alpha is made to be 0, the active series type power quality controller cannot influence the normal work of the power grid, and when the power grid fails or needs soft start, the value of alpha is increased, so that the fault current or the starting current is limited to the level which can be borne by the power grid, and the effects of fault current limiting and soft start are achieved.
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