CN114301066A - Intelligent power distribution station combined system - Google Patents
Intelligent power distribution station combined system Download PDFInfo
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Abstract
The invention discloses an intelligent distribution area combined system, which is used for carrying out comprehensive control on electric energy quality and providing a low-voltage direct-current distribution interface under the condition of not changing the traditional distribution network system architecture, integrates the electric energy quality control functions of voltage regulation, harmonic control, three-phase load unbalance and the like, and provides a stable and reliable low-voltage direct-current bus to realize plug and play of distributed renewable energy sources, an energy storage system and novel direct-current loads.
Description
Technical Field
The invention belongs to the technical field of power distribution systems of power electronic devices, and particularly relates to an intelligent power distribution station combined system.
Background
With the increasing proportion of renewable energy sources of the power distribution network and the pollution of a large number of nonlinear loads to the power distribution network, the harmonic content and the three-phase imbalance of the power distribution network are further aggravated, and the tasks of reactive compensation, harmonic treatment and three-phase balancing are increasingly severe. Especially, important loads sensitive to the power quality in a power supply area, such as precision instrument manufacturing enterprises, large-scale data centers and the like, have higher requirements on the power quality. Usually, an electric energy management device is adopted to improve the quality of electric energy at the network side, improve the utilization rate of power supply equipment, reduce network loss and reduce power generation cost. The traditional alternating-current distribution network electric energy quality treatment equipment comprises a Static Var Compensator (SVC), a Thyristor Controlled Series Capacitor (TCSC), a static var compensator (STATCOM), an active filter (APF) and the like, wherein the equipment is usually respectively carried out aiming at the problems of reactive compensation, harmonic treatment, voltage compensation and the like, or partial functions in the equipment are integrated together, the solution measures are usually not comprehensive, the single compensation mode is usually repeated in investment, and the integration level and the comprehensive utilization rate of the equipment are lower.
Disclosure of Invention
The invention aims to provide an intelligent distribution station combined system which can provide a stable and reliable low-voltage direct-current bus to realize plug and play of distributed renewable energy sources, an energy storage system and novel direct-current loads.
The technical scheme adopted by the invention is that the intelligent distribution station area combined system comprises three high-voltage side independent windings which are respectively connected with different phases of a three-phase power supply in series, each high-voltage side independent winding is connected with a high-voltage side winding, the three high-voltage side windings are mutually connected, the intelligent distribution station area combined system also comprises three low-voltage side windings, one ends of the three low-voltage side windings are star-connected, the other ends of the three low-voltage side windings are connected with a three-phase nonlinear load, star-connected positions of the three low-voltage side windings are connected with a central line of the three-phase nonlinear load, each high-voltage side winding and one low-voltage side winding are magnetically and reactively coupled through a wound iron core, each high-voltage side independent winding is connected with a bypass switch in parallel, each high-voltage independent side winding is magnetically and reactively coupled with a low-voltage side independent winding through a wound iron core, one ends of the three low-voltage side independent windings are respectively connected with an alternating current side of a preceding-stage voltage source converter through a filter, the other ends of the three low-voltage independent windings are all connected with a central line of the alternating current side of the preceding-stage voltage source converter, the neutral line of the alternating current side of the rear-stage voltage source converter is connected with the neutral line of the three-phase nonlinear load, the three phases of the alternating current side of the rear-stage voltage source converter are respectively connected with the three-phase bus of the load side, and the direct current side of the front-stage voltage source converter and the direct current side of the rear-stage voltage source converter are both connected with the low-voltage direct current power distribution port.
The invention is also characterized in that:
the three high-voltage side windings are connected with each other specifically as follows: the three high-voltage side windings are connected in an angle mode to form a triangle, each angle of the triangle is connected with one high-voltage side independent winding, one high-voltage side winding corresponding to the three-phase power supply A is connected with a low-voltage side winding of the three-phase nonlinear load A phase in a magnetic reaction coupling mode through a wound iron core, the high-voltage side winding corresponding to the three-phase power supply B is connected with a low-voltage side winding of the three-phase nonlinear load B phase in a magnetic reaction coupling mode through the wound iron core, and the high-voltage side winding corresponding to the three-phase power supply C is connected with a low-voltage side winding of the three-phase nonlinear load C phase in a magnetic reaction coupling mode through the wound iron core.
The three high-voltage side windings are connected with each other specifically as follows: one end of each of the three high-voltage side windings is star-connected, the other end of each of the three high-voltage side windings is connected with a high-voltage side independent winding, the high-voltage side winding corresponding to the three-phase power supply A is connected with a low-voltage side winding of a three-phase nonlinear load A phase through a wound iron core in a magnetic reaction coupling mode, the high-voltage side winding corresponding to the three-phase power supply B is connected with a low-voltage side winding of a three-phase nonlinear load B phase through a wound iron core in a magnetic reaction coupling mode, and the high-voltage side winding corresponding to the three-phase power supply C is connected with a low-voltage side winding of a three-phase nonlinear load C phase through a wound iron core in a magnetic reaction coupling mode.
The direct current side of the front-stage voltage source converter and the direct current side of the rear-stage voltage source converter are both connected with a separation capacitor in parallel.
Each filter comprises a filter inductor and a filter capacitor, the filter inductors are connected in series between the low-voltage side independent winding and the different phases of the alternating current side of the preceding-stage voltage source converter, and the filter capacitors are connected in parallel between the different phases of the alternating current side of the preceding-stage voltage source converter and the neutral line.
The invention has the beneficial effects that:
the invention provides an intelligent distribution area combined system which carries out comprehensive treatment on the electric energy quality and provides a low-voltage direct-current distribution interface under the condition of not changing the traditional distribution network system framework, integrates the electric energy quality treatment functions of voltage regulation, harmonic treatment, three-phase load unbalance and the like, and provides a stable and reliable low-voltage direct-current bus to realize plug and play of distributed renewable energy sources, an energy storage system and novel direct-current loads.
Drawings
Fig. 1 is a schematic structural diagram of an embodiment of an intelligent distribution substation combined system according to the present invention;
fig. 2 is a schematic structural diagram of a second embodiment of the intelligent distribution substation combined system of the present invention;
FIG. 3 shows a schematic diagram of the voltage regulation control strategy of the present invention;
FIG. 4 shows a schematic diagram of two voltage source converters used in an intelligent distribution substation combined system architecture;
FIG. 5 is a schematic diagram of a three-phase power supply side when a voltage swell and a voltage swell occur;
FIG. 6 shows a schematic diagram of a load side voltage stabilized by regulated modulation;
FIG. 7 shows a block diagram of a control strategy for a harmonic detection element of the harmonic compensation of the later stage voltage source converter;
FIG. 8 shows a block diagram of a harmonic compensation link of harmonic compensation of a rear-stage voltage source converter and a control strategy of voltage stabilization at a direct current side;
FIG. 9 shows an SPWM modulation block diagram for a voltage source converter transistor IGBT;
FIG. 10 shows a schematic diagram of a load side current waveform after harmonic compensation of a later stage voltage source converter;
FIG. 11 is a diagram showing a waveform of a voltage source converter after DC side voltage stabilization;
fig. 12 shows a schematic diagram of the voltage variation of the dc side of the rear-stage voltage source converter.
In the figure, Vga、Vgb、VgcRespectively represent grid-side three-phase voltage A, B, C phase voltage;
Vsa、Vsb、Vscrespectively represent the three-phase voltage A, B, C phase voltage of the user side;
iga、igb、igcrespectively representing the three-phase current A, B, C phase current on the grid side;
isa、isb、iscrespectively representing A, B, C phase currents of a low-voltage side three-phase current;
iLa、iLb、iLca, B, C phase currents respectively representing three-phase currents flowing into the user side;
ifa、ifb、ifcrespectively representing fundamental components of three-phase current A, B, C flowing to the user side;
iha、ihb、ihcrespectively representing harmonic components of the three-phase current A, B, C flowing to the user side;
ia2、ib2、ic2a, B, C phase currents of the output current of the rear-stage voltage source type converter are respectively shown;
idref、iqrefa harmonic current reference value of a user side under a d-q coordinate axis;
id2、iq2actual harmonic compensation current of a later-stage voltage source type converter under the d-q coordinate axes;
Lsea、Lseb、Lsecrespectively representing filter inductors of a preceding-stage voltage source type converter;
Csea、Cseb、Csecrespectively representing filter capacitors of a preceding-stage voltage source type converter;
Lsha、Lshb、Lshcrespectively representing the filter inductors of the post-stage voltage source type converter;
WA1、WB1、WC1respectively representing A, B, C three-phase windings on the high-voltage side of the power frequency transformer;
Wa1、Wb1、Wc1respectively representing A, B, C three-phase windings on the low-voltage side of the power frequency transformer;
WA2、WB2、WC2respectively, representing A, B, C three-phase independent windings on the high-voltage side of the coupling transformer;
Wa2、Wb2、Wc2respectively representing a coupling transformerA, B, C three-phase independent windings on the low voltage side of the transformer;
Cv1、Cv2respectively representing a preceding stage voltage source converter and a succeeding stage voltage source converter;
VTn1、VTn2、VTn3、VTn4four insulated gate bipolar transistors forming an H-bridge in a preceding voltage source converter are shown;
Sn1、Sn2、Sn3、Sn4showing 4 insulated gate bipolar transistors forming an LLC primary inverter bridge;
Dn5、Dn6、Dn7、Dn84 diodes are shown forming an LLC secondary rectifier bridge;
VD1、VD2、VD3、VD4、VD5、VD6、VD7、VD8respectively, 8 insulated gate bipolar transistors in the later stage voltage source converter.
Detailed Description
The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.
The invention relates to an intelligent distribution area combined system, which comprises three high-voltage side independent windings respectively connected with different phases of a three-phase power supply in series, wherein each high-voltage side independent winding is connected with a high-voltage side winding, the three high-voltage side windings are mutually connected, the three low-voltage side windings are connected with a three-phase nonlinear load at one end, the star joint of the three low-voltage side windings is connected with the central line of the three-phase nonlinear load, each high-voltage side winding and one low-voltage side winding are magnetically and reactively coupled through a wound iron core, each high-voltage side independent winding is connected with a bypass switch in parallel, each high-voltage side independent winding is magnetically and reactively coupled with a low-voltage side independent winding through a wound iron core, one end of each low-voltage side independent winding is respectively connected with the alternating current side of a preceding-stage voltage source converter through a filter, the other end of each low-voltage side independent winding is connected with the alternating current side central line of the preceding-stage voltage source converter, each filter comprises a filter inductor and a filter capacitor, wherein the filter inductor is connected in series between the low-voltage side independent winding and the different phase of the alternating current side of the preceding-stage voltage source converter, and the filter capacitor is connected in parallel between the different phase of the alternating current side of the preceding-stage voltage source converter and the neutral line; the direct current side of the front-stage voltage source converter and the direct current side of the rear-stage voltage source converter are both connected with a low-voltage direct current distribution port, and the direct current side of the front-stage voltage source converter and the direct current side of the rear-stage voltage source converter are both connected with a separation capacitor in parallel.
The first embodiment is as follows:
as shown in fig. 1, the three high-voltage side windings are connected to each other specifically as follows: the three high-voltage side windings are connected in an angle mode to form a triangle, each angle of the triangle is connected with one high-voltage side independent winding, one high-voltage side winding corresponding to the three-phase power supply A is connected with a low-voltage side winding of the three-phase nonlinear load A phase in a magnetic reaction coupling mode through a wound iron core, the high-voltage side winding corresponding to the three-phase power supply B is connected with a low-voltage side winding of the three-phase nonlinear load B phase in a magnetic reaction coupling mode through the wound iron core, and the high-voltage side winding corresponding to the three-phase power supply C is connected with a low-voltage side winding of the three-phase nonlinear load C phase in a magnetic reaction coupling mode through the wound iron core.
Example two:
as shown in fig. 2, the three high-voltage side windings are connected to each other specifically as follows: one end of each of the three high-voltage side windings is star-connected, the other end of each of the three high-voltage side windings is connected with one high-voltage side independent winding, the high-voltage side winding corresponding to the three-phase power supply A is connected with the low-voltage side winding of the three-phase nonlinear load A phase in a magnetic reaction coupling mode through a wound iron core, the high-voltage side winding corresponding to the three-phase power supply B is connected with the low-voltage side winding of the three-phase nonlinear load B phase in a magnetic reaction coupling mode through a wound iron core, and the high-voltage side winding corresponding to the three-phase power supply C is connected with the low-voltage side winding of the three-phase nonlinear load C phase in a magnetic reaction coupling mode through a wound iron core.
In order to further explain the circuit connection relationship and the using method of the present invention, the following description is made with reference to the accompanying drawings:
as in FIG. 1 or FIG. 2, the three high side windings are denoted as WA1、WB1、WC1The three low-voltage side windings are denoted as Wa1、Wb1、Wc1The three high-voltage side windings and the three low-voltage side windings form a power frequency transformer, the high-voltage side windings of the power frequency transformer are connected in a delta-type (or Y-type) mode, and the low-voltage side windings of the power frequency transformer are connected in a Y modenType connection with simultaneous extraction of A2'、B2'、C2' three-phase port, connecting the low voltage AC bus. Three high side independent windings are denoted WA2、WB2、WC2The three low-voltage side independent windings are denoted as Wa2、Wb2、Wc2The three high-voltage side independent windings and the three low-voltage side independent windings form a coupling transformer, wherein the high-voltage side independent winding W of the coupling transformerA2、WB2、 WC2In series with the high side A, B, C three phase ac bus, namely: wA2In series with A.C. bus, WB2In series with B AC bus-bar, WC2Is connected with a C alternating current bus in series and is provided with a high-voltage side independent winding WA2、WB2、WC2Two ends are provided with a high-voltage side bypass switch Sa、Sb、ScAnd the on-off of the independent winding on the high-voltage side of the coupling transformer is controlled. The connection mode of the low-voltage side independent winding is YnA phase connection, the A phase winding comprising a2、a2' two-port, B-phase winding comprising B2、b2' two-port, C-phase winding comprising C2、c2' two ports, wherein a2'、b2'、c2' three ports are connected to form the middle point of the low-voltage side independent winding. The back-to-back converter comprises a front-stage voltage source converter CV1 and a rear-stage voltage source converter CV2, the two voltage source converters are in a three-phase four-wire system, and the AC side of the front-stage voltage source converter CV1 comprises A1、B1、C1、 O1Four ports, wherein A1Independent winding W on low-voltage side of port and coupling transformera2End of same name a2Are connected to each other, B1Independent winding W on low-voltage side of port and coupling transformerb2End with the same name b2Are connected to each other, C1Port and coupling transformerIndependent winding W at low-voltage side of transformerc2End of same name c2To each other, O1The port is connected with the middle point of the independent winding on the low-voltage side of the coupling transformer. The AC side of the voltage source converter CV2 of the rear stage comprises A2、B2、C2、O2Four ports, wherein A2Port A is drawn forth with industrial frequency transformer low pressure side A looks generating line2' connected to, B2Port B is drawn forth with industrial frequency transformer low pressure side B looks generating line2' connected to, C2Port and power frequency transformer low voltage side C phase bus leading-out port C2' connected to, O2Port and power frequency transformer low-voltage side neutral line leading-out port O2' connected while withdrawing A3、B3、C3、O3And the four ports are used for connecting a three-phase load. The DC sides of the two voltage source converters can adopt a separation capacitor (or a single capacitor) to stabilize the voltage of the DC sides. DC side port V of preceding stage voltage source converter CV1dc1+And a DC side port V of a rear-stage voltage source converter CV2dc2+Connected as the positive port V of the low-voltage direct current of the intelligent distribution transformerdc+Front stage voltage source converter CV1 DC side port Vdc1-And a DC side port V of a rear-stage voltage source converter CV2dc2-Connected as a low-voltage DC negative electrode port V of an intelligent distribution transformerdc-And novel source/charge friendly access of photovoltaic, energy storage, automobile charging pile, fan and the like is realized.
The high-voltage side winding of the industrial frequency transformer adopts a delta-shaped connection mode, namely A, B, C three-phase end-to-end connection, and the low-voltage side winding of the industrial frequency transformer adopts YnType connection, i.e. end a1'、b1'、c1' connected to, first section a1、b1、c1And leading out a three-phase alternating current bus.
The high-voltage side winding of the industrial frequency transformer adopts a Y-shaped connection mode, namely A, B, C three-phase ends are connected with n, and the low-voltage side winding of the industrial frequency transformer adopts YnType connections, i.e. three-phase terminals a1'、b1'、c1' connected to, first section a1、b1、c1And leading out a three-phase alternating current bus.
High-voltage side winding string of coupling transformerIn the three-phase alternating current bus of network side is joined in, and coupling transformer high pressure side both ends and have bypass switch, promptly: a-phase bypass switch SaAnd at the high-voltage side winding W of the coupling transformerA2Both ends of (a); b-phase bypass switch SbAnd at the high-voltage side winding W of the coupling transformerB2Both ends of (a); c-phase bypass switch ScAnd at the high-voltage side winding W of the coupling transformerC2At both ends of the same. The on-off time of the coupling transformer can be controlled, and the bypass switch is switched off when the voltage regulation operation is needed; when the three-phase power supply voltage is stable, the bypass switch is closed.
The control mode of voltage regulation of the intelligent power distribution station combined system adopts independent control of each phase, when voltage fluctuation occurs to any phase of A, B, C, the control of each phase independently acts to collect voltage fluctuation values higher or lower than the normal voltage level, the voltage fluctuation values are eliminated through the control of the coupling transformer, and the voltage is always controlled within the normal level.
In the invention, the control strategies of the first embodiment and the second embodiment are consistent, taking the first embodiment as an example:
as shown in FIG. 1, a power frequency transformer T1Comprising a ferromagnetic core, a high-voltage side winding WA1、WB1、WC1By angular connection, low-voltage side winding Wa1、Wb1、Wc1The star connection is adopted, wherein the magnetic core material is silicon steel sheets, and the transformation ratio of the high-voltage side winding to the low-voltage side winding of the industrial frequency transformer is 14140: 311. The high-voltage side winding of the coupling transformer is connected in series in the distribution line to provide compensation voltage when the network side fluctuates, and the low-voltage side winding is connected with the preceding-stage voltage source converter CV1Filter device Lse、CseWherein the preceding-stage voltage source converter CV is increased1And in the compensation range, the transformation ratio of the high-voltage side winding to the low-voltage side winding is selected to be 3: 1. In order to improve the working efficiency and the operation reliability of the whole device, the coupling transformer T is arranged2The high side winding incorporates a bypass switching device. When the bypass switch is switched on when the three-phase power supply voltage stably operates, the preceding-stage voltage source converter CV1Do not work to reduce power conversion loss; current stage voltage source converter CV1When a fault occurs, the operation is rapidThereby bypass switch combined floodgate realizes protecting the distribution lines. Coupling transformer T2And the low-voltage side winding is connected to an alternating-current side output port of the preceding-stage voltage source converter through a filter device. v. ofca、vcb、vccShowing the compensation voltage, v, supplied by a preceding voltage source converterca、vcb、vccVia a coupling transformer T2Obtaining the high-voltage side compensation voltage v after boostingsea、vseb、vsec. In the first embodiment, the voltage compensation range is designed to be ± 10%, and the amplitude of the grid-side phase voltage is assumed to be 8164V. In a certain time period, the three-phase voltage on the grid side suddenly fluctuates (suddenly rises or drops) within +/-10%, and the CV of the preceding-stage voltage source converter is adjusted1V of AC side outputca、vcb、vccThe voltage stabilizes the effective value of the user side voltage at 220V.
FIG. 4 illustrates a back-to-back voltage source converter topology for an intelligent distribution grid integrated system architecture, including a pre-stage voltage source converter CV1And a subsequent voltage source converter CV2. The output port of the AC side of the preceding stage voltage source converter is filtered by a filter Lse、CseAnd the low-voltage side winding of the coupling transformer is connected. Preceding stage voltage source converter CV1DC side port and back-stage voltage source converter CV2DC side port common low voltage DC bus VdcThe voltage source converter CV of the later stage2The output port of the AC side is connected with the filter inductor LshAnd then is connected with the user side alternating current bus in parallel.
According to the formula (1), A, B, C after the three-phase voltage acquisition signal is processed by delaying for a quarter cycle, the amplitude V of each phase voltage can be calculatedgkm. In the embodiment, the voltage amplitude of each phase voltage is 8164V under steady-state operation (if three-phase power supply voltage fluctuates in a certain period of time, the amplitude can suddenly rise or drop), and the phase of each phase voltage can be obtained through the phase-locked loop. Because the power frequency transformer adopts delta/YnIn the connection mode, the phase angle between the three-phase power voltage and the voltage difference of 30 ° at the user side needs to be compensated to the modulation duty ratio of the preceding-stage voltage source converter CV1 as shown in formula (2) when performing voltage compensation control.
Wherein, VgkmIs the amplitude of the voltage on the high-voltage side, VrefIs a reference value when the high pressure side is stable, and θ represents the angle of the high pressure side.
When the three-phase power supply voltage fluctuates, the control system monitors the amplitude of the three-phase power supply voltage in real time, obtains the fluctuation quantity of the three-phase power supply voltage after making a difference with the amplitude of the grid-side reference voltage, and uses the fluctuation quantity as the reference voltage v of the output port of the preceding-stage voltage source converter CV1ca、vcb、vcc。
The dynamic voltage compensation control strategy adopts double-loop control of a voltage outer loop current inner loop, a PR (Proportional resonant Controller) Controller is adopted by an outer loop to control voltage error, a P Controller (Proportional Controller) Controller is adopted by an inner loop to control current error, and feed-forward compensation is added to realize a wide voltage regulation range and improve the dynamic response characteristic of a closed-loop system. The error signal is input to a controller of a preceding stage voltage source converter CV1 to regulate the voltage v at the output port of the preceding stage voltage source converterca、vcb、vccTo realize the user side voltage vsa、vsb、vscStabilize at the reference voltage value.
Preceding stage voltage source converter CV1And a subsequent voltage source converter CV2May be a voltage source converter having the VSC structure shown in figure 4. In the first embodiment, the forward stage voltage source converter CV1 includes A, B, C and three legs, including VT1、VT2、VT3、VT4、VT5、VT6Six Insulated Gate Bipolar Transistors (IGBTs) and anti-parallel diodes, where VT1、VT4Constituting a preceding-stage voltage source converterArm of phase A, VT2、VT5B-phase bridge arm, VT, constituting a preceding-stage voltage source converter3、VT6And a C-phase bridge arm of the preceding-stage voltage source converter is formed. The preceding stage voltage source converter passes through the filter inductor Lsea、Lseb、 LsecFilter capacitor Csea、Cseb、CsecAnd connecting the transformer to a low-voltage side winding of the coupling transformer, wherein filter parameters are respectively 500uH and 20 uF. Preceding stage voltage source converter CV1And a subsequent voltage source converter CV2DC bus V with 800V common voltage gradedcDC bus capacitor CdcThe direct current bus of the converter has a separated capacitor lead-out structure, and the capacitor lead-out structure is connected with a neutral point of a preceding voltage source converter to form a zero sequence path of the converter. The topology of the preceding-stage voltage source converter is not limited to a three-phase PWM converter, and a three-level, three-phase, four-bridge arm and other voltage source type converter topology structure can be adopted as long as the voltage value of the output port can be adjusted.
When the three-phase power supply voltage fluctuates (suddenly rises or falls), the voltage waveform of the combined system structure of the intelligent distribution area, which is used for compensating the dynamic voltage on the user side, is shown in fig. 5 and 6, wherein the dotted line represents the winding voltage on the high-voltage side of the power frequency transformer, and the solid line represents the winding voltage on the low-voltage side of the power frequency transformer. In the stage of 0.05s-0.1s, the three-phase power supply voltage does not fluctuate, and the peak voltage of the user side voltage is stabilized at 311V; the 10% voltage peak value of the three-phase power supply voltage suddenly rises to 8980V in the stage of 0.1s-0.2s, and the preceding-stage voltage source converter CV1Detecting a sudden rise in three-phase supply voltage and regulating the output port voltage vca、 vcb、vccPeak voltage of 272V, which is equal to three-phase power supply voltage Vga、vgb、vgcIn phase. The transformation ratio of the coupling transformer adopted in the example is 3:1, the peak voltage value of the high-voltage side winding is 816V, and the peak voltage value of the low-voltage side winding is 272V. The peak voltage of the user side is rapidly stabilized from 342V to 311V after 0.01 s; the three-phase power supply voltage is recovered to the rated voltage in the stage of 0.2s-0.3s, and the preceding-stage voltage source converter CV1Detecting three-phase mains voltage variations and regulating auxiliary winding voltage vca、vcb、vccAbout 0V; the voltage peak value of the three-phase power supply voltage falling by 10% is reduced to 7348V in the 0.3s-0.4s stage, and the preceding-stage voltage source converter CV1Detecting three-phase mains voltage variations and regulating auxiliary winding vca、vcb、vccA voltage peak of 353V, which is equal to the three-phase supply voltage Vga、vgb、vgcThe phases are opposite to each other. The transformation ratio of the coupling transformer winding adopted by the embodiment is 3:1, the peak voltage of the high-voltage side winding is 816V. The user side voltage peak rapidly stabilized from 280V to 311V after 0.01 s. The pre-stage voltage source converter CV can be improved by reasonably designing the winding turn ratio of the coupling transformer1The three-phase power supply voltage compensation depth and the voltage calculation formula of the low-voltage side of the preceding-stage voltage source converter are as follows:
the expression of the control signal for generating the compensation voltage by the preceding-stage voltage source converter is as follows:
as shown by CV in FIG. 42Showing a subsequent voltage source converter CV for an intelligent distribution substation combined system architecture2. In this embodiment, the subsequent voltage source converter CV2And the three-phase PWM rectifier is adopted to realize the functions of direct-current bus voltage stabilization, user side harmonic compensation and the like. CV of2Comprising A, B, C three bridge arms containing VD1、VD2、VD3、VD4、VD5、VD6Six Insulated Gate Bipolar Transistors (IGBT) and anti-parallel diodes, where VD1、VD4Form the A-phase bridge arm of the post-stage voltage source converter, VD2、 VD5B-phase bridge arm of the voltage source converter of the rear stage, VD3、VD6And forming a C-phase bridge arm of the rear-stage voltage source converter. Rear stage voltage source converter CV2A, B, C three phases in (1) are filtered by 2mHInductor Lsha、 Lshb、LshcAnd then are respectively and correspondingly connected to the three-phase bus at the user side in parallel. Rear stage voltage source converter CV2And functions of harmonic current compensation, reactive compensation and the like are realized.
The subsequent voltage source converter CV shown in FIGS. 7 and 82And a direct current bus voltage stabilization and harmonic current compensation control strategy block diagram. Phase and frequency of voltage at network side are tracked by phase-locked loop (PLL), and three-phase current i at user side is acquiredLa、iLb、iLcThrough Clark transformation formula (5), two-phase current i can be obtainedɑAnd iβ. The instantaneous active current i can be calculated by the instantaneous power formula (6)pAnd instantaneous reactive current iqNumerical values. Instantaneous active current ipAnd instantaneous reactive current iqObtaining a DC component by a Low Pass Filter (LPF)
And
the three-phase current fundamental component i can be obtained through Clark inverse transformation formula (8)fa、ifb、ifc. Will adopt the nonlinear current i on the user sideLa、iLb、iLcFundamental component i of three-phase currentfa、ifb、ifcThe difference is shown as formula (9), so that the harmonic current i can be obtainedha、ihb、ihc. In order to realize the voltage control on the direct current side and the accurate compensation of the harmonic current, the harmonic current i is usedha、ihb、ihcAnd a subsequent voltage source converter CV2Port output current isha、 ishb、ishbObtaining a harmonic current reference value i under a d-q coordinate axis by performing park transformationdref、iqrefAnd the compensation current i actually output by the port of the post-stage voltage source converterd2、iq2. Wherein the DC bus voltage is related to the active current and the DC side voltage VdcAfter the difference is made between the acquisition quantity and the expected voltage 800V of the direct current bus, the value obtained by proportional integral control (PI) is converted into the d-axis reference value of the harmonic currentidrefAnd adding the currents to realize harmonic current compensation and direct current side voltage stabilization control. Harmonic current i when d-q axis conversion is performedd、iqThe coupling quantity exists, and decoupling control is added in the current inner ring, so that accurate compensation of harmonic current is realized. Duty ratio reference value d of current loop outputd、dqObtaining the required duty ratio d through park inverse transformationa、db、dc。
FIG. 9 shows an SPWM control block diagram of the on and off of an Insulated Gate Bipolar Transistor (IGBT) of an A, B, C three-phase bridge arm, in this example, a bipolar modulation strategy is adopted, and a reference modulation wave d is obtaineda、 db、dcCompared with carrier wave (frequency of 20kHz)And if the obtained value is larger than 0, the selector outputs a high level 1, otherwise, the selector outputs a low level 0, SPWM pulse waves are formed, and the switching-on and switching-off of the transistor IGBT forming the A, B, C three-phase bridge arm are modulated.
Fig. 10 shows the current at the user side after harmonic compensation is added to the voltage source converter at the later stage at 0.1s, and it can be seen that the main harmonic component of the current at the output port of the main winding at the low-voltage side of the power frequency transformer is eliminated.
Fig. 11 shows a dc-side regulated waveform that quickly settles to the desired voltage amplitude of 800V when both a voltage surge and a voltage dip occur in the three-phase supply voltage.
Fig. 12 shows a schematic diagram of the voltage variation of the dc side of the rear-stage voltage source converter.
Through the mode, the intelligent distribution area combined system provided by the invention can be used for carrying out comprehensive control on the electric energy quality and providing a low-voltage direct-current distribution interface without changing the traditional distribution network system framework condition, integrates the electric energy quality control functions of voltage regulation, harmonic control, three-phase load unbalance and the like, and simultaneously provides a stable and reliable low-voltage direct-current bus so as to realize plug and play of distributed renewable energy sources, an energy storage system and novel direct-current loads.
Claims (5)
1. An intelligent distribution area combined system is characterized by comprising three high-voltage side independent windings which are respectively connected with different phases of a three-phase power supply in series, wherein each high-voltage side independent winding is connected with one high-voltage side winding, the three high-voltage side windings are mutually connected, the three low-voltage side windings are connected with one end in a star connection mode, the other end of each low-voltage side winding is connected with a three-phase nonlinear load, the star connection position of the three low-voltage side windings is connected with the central line of the three-phase nonlinear load, each high-voltage side winding and one low-voltage side winding are magnetically and reactively coupled through a wound iron core, each high-voltage side independent winding is connected with a bypass switch in parallel, each high-voltage side independent winding is magnetically and reactively coupled with one low-voltage side independent winding through a wound iron core, one end of each low-voltage side independent winding is respectively connected with the alternating current side of a preceding-stage voltage source converter through a filter, the other end of the three-phase direct current bus is connected with a neutral line of an alternating current side of the front-stage voltage source converter, the three-phase direct current bus further comprises a rear-stage voltage source converter, the neutral line of the alternating current side of the rear-stage voltage source converter is connected with a neutral line of a three-phase nonlinear load, three phases of the alternating current side of the rear-stage voltage source converter are respectively connected with a three-phase bus of a load side, and the direct current side of the front-stage voltage source converter and the direct current side of the rear-stage voltage source converter are both connected with a low-voltage direct current distribution port.
2. An intelligent distribution substation combined system according to claim 1, wherein three said high side windings are interconnected specifically as: the three high-voltage side windings are connected in an angle mode to form a triangle, each angle of the triangle is connected with one high-voltage side independent winding, one high-voltage side winding corresponding to the three-phase power supply A is connected with a low-voltage side winding of the three-phase nonlinear load A phase in a magnetic reaction coupling mode through a wound iron core, the high-voltage side winding corresponding to the three-phase power supply B is connected with a low-voltage side winding of the three-phase nonlinear load B phase in a magnetic reaction coupling mode through the wound iron core, and the high-voltage side winding corresponding to the three-phase power supply C is connected with a low-voltage side winding of the three-phase nonlinear load C phase in a magnetic reaction coupling mode through the wound iron core.
3. An intelligent distribution substation combined system according to claim 1, wherein three said high side windings are interconnected specifically as: one end of each of the three high-voltage side windings is star-connected, the other end of each of the three high-voltage side windings is connected with a high-voltage side independent winding, the high-voltage side winding corresponding to the three-phase power supply A is connected with a low-voltage side winding of the three-phase nonlinear load A phase through a wound iron core in a magnetic reaction coupling mode, the high-voltage side winding corresponding to the three-phase power supply B is connected with a low-voltage side winding of the three-phase nonlinear load B phase through a wound iron core in a magnetic reaction coupling mode, and the high-voltage side winding corresponding to the three-phase power supply C is connected with a low-voltage side winding of the three-phase nonlinear load C phase through a wound iron core in a magnetic reaction coupling mode.
4. The intelligent distribution substation combined system of claim 1, wherein the dc side of the preceding stage voltage source converter and the dc side of the following stage voltage source converter are both connected in parallel with a separation capacitor.
5. The intelligent distribution substation combination system of claim 1, wherein each filter comprises a filter inductor and a filter capacitor, the filter inductor is connected in series between the low-voltage side independent winding and the different phase of the ac side of the preceding voltage source converter, and the filter capacitor is connected in parallel between the different phase of the ac side of the preceding voltage source converter and the neutral line.
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| CN105119290A (en) * | 2015-07-21 | 2015-12-02 | 河南行知专利服务有限公司 | Power compensation system for uninterrupted power supplies and control method |
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