CN114123337B - Hybrid multifunctional grid-connected converter of power distribution network and optimal operation control method thereof - Google Patents
Hybrid multifunctional grid-connected converter of power distribution network and optimal operation control method thereof Download PDFInfo
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- CN114123337B CN114123337B CN202111451667.XA CN202111451667A CN114123337B CN 114123337 B CN114123337 B CN 114123337B CN 202111451667 A CN202111451667 A CN 202111451667A CN 114123337 B CN114123337 B CN 114123337B
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- 230000008878 coupling Effects 0.000 claims abstract description 20
- 238000010168 coupling process Methods 0.000 claims abstract description 20
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Classifications
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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
- H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
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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
- H02J3/28—Arrangements for balancing of the load in a network by storage of energy
- H02J3/32—Arrangements for balancing of the load in a network by storage of energy using batteries with converting means
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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
- H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
- H02J3/46—Controlling of the sharing of output between the generators, converters, or transformers
- H02J3/48—Controlling the sharing of the in-phase component
-
- 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
- H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
- H02J3/46—Controlling of the sharing of output between the generators, converters, or transformers
- H02J3/50—Controlling the sharing of the out-of-phase component
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Abstract
The invention provides a hybrid multifunctional grid-connected converter of a power distribution network, which consists of a power grid, a single-phase full-bridge converter, LC filtering, a three-winding transformer T and a coupling capacitor C 0 And a load composition; wherein one end of the primary side of the three-winding transformer T is connected with a power grid, the other end is connected with a load, the secondary side of the three-winding transformer T is connected with a single-phase full-bridge converter, and the tertiary side of the secondary side of the three-winding transformer T is connected with a coupling capacitor C 0 The common ground of the secondary side and the tertiary side of the three-winding transformer T is grounded; LC filtering inductance L 1 The end is connected with the secondary side of the three-winding transformer T, and the filter capacitor C 1 End-connected single-phase full-bridge converter, in which the filter inductance L 1 And filter capacitor C 1 And (3) connecting in series. The problems that in the prior art, active power consumption exists in the power electronic converter during operation, the capacity of direct-current side configuration is often limited, and continuous active power output is difficult to meet the long-time power quality control requirement are solved.
Description
Technical Field
The invention belongs to the technical field of electric power, and relates to a hybrid multifunctional grid-connected converter of a power distribution network and an optimal operation control method thereof.
Background
With the wide access of new energy sources and the gradual increase of nonlinear loads in a power grid, the problems of electric energy quality and the risks of short circuit faults are increased increasingly. In order to effectively improve the electric energy quality of the power grid and suppress short-circuit fault current, the power electronic converter is increasingly applied to the power grid. This mainly comprises series-connected and parallel-connected converters, which perform their respective functions by means of voltage injection and current injection, respectively. In view of the fact that various power electronic converters have certain commonalities in topology and control, the method has important significance in further improving the utilization rate of various converters, optimizing the asset configuration of a power grid and promoting the economic and reliable operation of the power grid, integrating the advantages of various converters and developing the research of the multifunctional converters.
Aiming at a power distribution network mixed type multifunctional grid-connected converter containing a multi-winding transformer, the power distribution network mixed type multifunctional grid-connected converter has certain advantages in the aspects of functional diversity and module multiplexing rate. However, conventional control strategies may cause the converter to continuously output active power during operation, which may be detrimental to maintaining long-term operation of the converter and to address longer-lasting power quality issues, given limited dc-side energization. Therefore, it is necessary to study the minimum active power output method of the down-converter in this structure.
At present, for a power electronic converter, the energy mainly comes from various energy storage devices or depends on online power supply of a power grid, and the energy can be divided into an energy storage type and a back-to-back type. In both modes, if the active power is continuously output by the control device, the long-time operation requirement of the device is difficult to meet, and the problem of power quality with longer duration is difficult to solve. Therefore, to meet the long-term operation requirements of the device, it is important to study the minimum active output method of the converter. Under the method, when the energy provided by the DC side of the converter is obviously insufficient, the converter is switched to the minimum active output mode, so that the running time of the converter can be effectively prolonged, and the continuous safe and stable running of the system is ensured.
Disclosure of Invention
In order to achieve the above purpose, the invention provides a hybrid multifunctional grid-connected converter of a power distribution network and an optimized operation control method thereof, which solve the problems that in the prior art, the power electronic converter consumes active power when working, the capacity of direct-current side configuration is often limited, and the continuous active power output is difficult to meet the long-time power quality control requirement.
The invention adopts the technical scheme that the mixed multifunctional grid-connected converter of the power distribution network comprises a power grid, a single-phase full-bridge converter, an LC filter, a three-winding transformer T and a coupling capacitor C 0 And a load composition; wherein one end of the primary side of the three-winding transformer T is connected with a power grid, the other end is connected with a load, the secondary side of the three-winding transformer T is connected with a single-phase full-bridge converter, and the tertiary side of the secondary side of the three-winding transformer T is connected with a coupling capacitor C 0 The common ground of the secondary side and the tertiary side of the three-winding transformer T is grounded; LC filtering inductance L 1 The end is connected with the secondary side of the three-winding transformer T, and the filter capacitor C 1 End-connected single-phase full-bridge converter, in which the filter inductance L 1 And filter capacitor C 1 And (3) connecting in series.
Further, the single-phase full-bridge converter comprises 4 IGBT modules and a direct-current side energy storage capacitor C; one end of the alternating current side of the single-phase full-bridge converter passes through a second IGBT module T 2 Emitter and fourth IGBT module T 4 The node of the collector passes through the filter inductance L 1 The other end of the alternating-current side of the single-phase full-bridge converter is connected with a power grid through a first IGBT module T 1 Emitter and third IGBT module T 3 The node of the collector is connected to the non-grounding end of the secondary side of the three-winding transformer T; one end of the direct current side of the single-phase full-bridge converter passes through a first IGBT module T 1 Collector and second IGBT module T 2 The node of the collector electrode is connected to the positive electrode of the direct-current side energy storage capacitor C, and the other end of the direct-current side of the single-phase full-bridge converter passes through the third IGBT module T 3 Emitter and fourth IGBT module T 4 The node of the emitter is connected to the negative electrode of the direct-current-side energy storage capacitor C.
The invention also provides an optimized operation control method of the hybrid multifunctional grid-connected converter of the power distribution network, which comprises the following steps:
step 1: detecting the running state of the grid voltage by using the detection moduleObtaining the voltage drop coefficient d of the power grid s The value of d s Judging that the grid voltage has a sag fault if the power grid voltage is more than 10%;
step 2: according to d s Calculating to obtain a load voltage control phase a corresponding to the minimum active power output of the single-phase full-bridge converter, wherein the load voltage control phase a and a load voltage amplitude U Lm Obtaining a reference value of the load voltageThereby obtaining the reference value of the compensation voltage>Wherein ω is angular velocity, t is time, U s Is the power supply voltage of the power grid;
step 3: according to the reference value of the compensation voltageObtain the filter capacitor C of the output port of the single-phase full-bridge converter 1 Reference value>And collecting the filter capacitor voltage U of the output port of the single-phase full-bridge converter C1 As a feedback quantity, will->And U C1 Difference is made, and a filter inductance current reference value +.>
Step 4: will beAnd filter inductance L 1 Real-time feedback quantity I of current L1 Difference is made, and modulated wave u is obtained through PI regulation r The drive signal of the bridge arm IGBT module of the single-phase full-bridge converter is obtained through SPWM modulation, and is input to the single-phase full-bridge converter to realize the driveAnd controlling the topological structure optimization operation of the hybrid multifunctional grid-connected converter of the power distribution network.
Further, in the step 1Wherein U is SM And->The power grid voltage amplitude detection value and the rated value are respectively.
Further, the load voltage control phase a in the step 2 is obtained according to the following formula:
primary side compensation voltage U of three-winding transformer T dvr The size of (2) is:
primary side compensation voltage U of three-winding transformer T dvr Phase b of (a) is:
at this time, the secondary side coupling capacitor branch current I of the three-winding transformer T cn The size of (2) is:
I cn ＝ωC 0 U dvr
I cn the phase q of (2) is:
grid current I s The size of (2) is:
I S ＝I cn ＝ωC 0 U dvr
grid current I s The phase m of (2) is:
assuming that the power factor angle of the load is j, the active power P output by the single-phase full-bridge converter under the condition in And reactive power Q in The method comprises the following steps:
wherein U is L For the load voltage, C 0 For coupling capacitance, I s For the power supply current of the power grid, I L Is the load current.
Further, in the step 3, the filter capacitor C 1 Reference value of voltageThe method is based on the following formula:
wherein U is tr1 Is the voltage of the secondary side of the three-winding transformer T, U tr2 Is the voltage of the three-time side of the three-winding transformer T, I 1 For flowing into the secondary side current of the three-winding transformer T, I cn For flowing through the three-winding transformer T coupling capacitor C 0 Branch current, U s Is the power supply voltage of the power grid.
The invention has the beneficial effects that
(1) The invention provides a control method of the minimum active power output of a power distribution network mixed type multifunctional grid-connected converter with a multi-winding transformer. The method can enable the converter to realize minimum active power output under different working conditions, and further enable the converter to run for a longer time so as to cope with the problem of longer-duration electric energy quality. The method has important significance for ensuring continuous and stable operation of the system.
(2) The short-circuit current when the load side has short-circuit fault can be effectively limited, and the equipment and the system are protected to run safely.
Drawings
In order to more clearly illustrate the embodiments of the invention or the technical solutions in the prior art, the drawings that are required in the embodiments or the description of the prior art will be briefly described, it being obvious that the drawings in the following description are only some embodiments of the invention, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
Fig. 1 is a topology structure diagram of a multifunctional grid-connected inverter according to an embodiment of the present invention.
FIG. 2 is a graph of phasor relationship under normal and sag conditions of a grid voltage according to an embodiment of the present invention; wherein (a) is a phasor relationship diagram under the condition of normal voltage, and (b) is a phasor relationship diagram under the condition of voltage sag.
Fig. 3 is a waveform diagram of the output active power of the single-phase full-bridge inverter under multiple factors in accordance with an embodiment of the present invention.
FIG. 4 is a diagram of an embodiment d of the present invention s =0.8 and d s When=0.6, the single-phase full-bridge converter outputs an active power waveform, wherein (a) is d s When the wave form of the active power outputted by the single-phase full-bridge converter is=0.8, (b) is d s When=0.6, the single-phase full-bridge converter outputs an active power waveform.
Fig. 5 is a schematic topology diagram of a load side short circuit fault in an embodiment of the present invention.
Fig. 6 is a control strategy diagram of the minimum active output of a single-phase full-bridge inverter according to an embodiment of the present invention.
Fig. 7 is a simulated waveform diagram of a single-phase full-bridge converter according to an embodiment of the invention in a minimum active power output method. Wherein (a) is a voltage waveform diagram and (b) is a power waveform diagram.
Fig. 8 is a waveform diagram of load current when dealing with a short-circuit fault according to an embodiment of the present invention.
FIG. 9 shows the output voltage, current and secondary voltage U of the three-winding transformer T of the single-phase full-bridge inverter in the case of short-circuit fault according to the embodiment of the invention tr1 Is a waveform diagram of (a).
FIG. 10 shows the three secondary sides of the three-winding transformer T in the case of a short circuit fault according to an embodiment of the present inventionSecondary side voltage U tr2 Coupling capacitor C 0 Current I of the branch cn Load current I L Is a waveform diagram of (a).
Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
Active power consumption exists in the working process of the power electronic converter, the capacity of the direct current side configuration is often limited, and the continuous active power output is difficult to meet the long-time power quality management requirement. Therefore, the invention provides an optimized operation control method, which can realize the minimum active power output of the converter under the condition of insufficient energy at the direct current side so as to meet the longer treatment requirement and ensure the safe and stable operation of the system. Fig. 1 is a topological structure diagram of a multifunctional grid-connected transformer with a multi-winding transformer, which is researched by the invention.
1. Introduction of topology
As shown in figure 1, the hybrid multifunctional grid-connected converter of the power distribution network comprises a power grid, a single-phase full-bridge converter, LC filtering, a three-winding transformer T and a coupling capacitor C 0 And a load. Wherein, one end of the primary side of the three-winding transformer T (the primary side of the three-winding transformer T is the primary side, the other side is the secondary side) is connected with a power grid, the other end is connected with a load, the secondary side of the three-winding transformer T is connected with a single-phase full-bridge converter, and the secondary side of the three-winding transformer T is connected with a coupling capacitor C 0 The common ground of the secondary side and the tertiary side of the three-winding transformer T is grounded; LC filtering inductance L 1 The end is connected with the secondary side of the three-winding transformer T, and the filter capacitor C 1 End-connected single-phase full-bridge converter, in which the filter inductance L 1 And filter capacitor C 1 And (3) connecting in series.
Further, the single-phase full-bridge converter includes4 full-control device-insulated gate bipolar transistor (Insulated Gate Bipolar Transistor, IGBT) modules and a direct-current side energy storage capacitor C. The single-phase full-bridge converter comprises a first IGBT module T 1 Second IGBT module T 2 Third IGBT module T 3 And a fourth IGBT module T 4 The method comprises the steps of carrying out a first treatment on the surface of the One end of the alternating current side of the single-phase full-bridge converter passes through a first IGBT module T 2 Emitter and third IGBT module T 4 The node of the collector passes through the filter inductance L 1 The other end of the alternating-current side of the single-phase full-bridge converter is connected with a power grid through a second IGBT module T 1 Emitter and fourth IGBT module T 3 The node of the collector is connected to the non-grounding end (secondary end) of the secondary side of the three-winding transformer T; one end of the direct current side of the single-phase full-bridge converter passes through a first IGBT module T 1 Collector and second IGBT module T 2 The node of the collector electrode is connected to the positive electrode of the direct-current side energy storage capacitor C, and the other end of the direct-current side of the single-phase full-bridge converter passes through the third IGBT module T 3 Emitter and fourth IGBT module T 4 The node of the emitter is connected to the negative electrode of the direct-current-side energy storage capacitor C.
In FIG. 1, U s For the mains supply voltage, I s For mains supply current, U C1 Is a filter capacitor C 1 Voltage at two sides, I 2 Via inductance L for single-phase full-bridge converter 1 Output current of U dc Is the voltage of two ends of the direct-current side energy storage capacitor C, U dvr For compensating the voltage at the primary side (primary side) of a three-winding transformer T, U tr1 Is the voltage of the secondary side of the three-winding transformer T, U tr2 Is the voltage of the three-time side of the three-winding transformer T, I 1 For flowing into the secondary side current of the three-winding transformer T, I nn For the common ground branch current flowing through the secondary side, the secondary side and the tertiary side of the three-winding transformer T, I cn For flowing through the three-winding transformer T coupling capacitor C 0 Branch current, U L Is the load voltage, I L Is the load current.
2. Working principle and optimal operation control method
2.1 principle of operation
The multifunctional grid-connected converter disclosed by the invention has normal and wave voltage of a power gridCan effectively work under dynamic conditions, thereby realizing multiple functions. FIG. 2 is a graph showing the phasor relationship between the normal and sag conditions of the grid voltage according to an embodiment of the present invention, in FIG. 2, U is taken S The phase of (a) is a reference phase, and alpha and gamma respectively represent the control phase of the load voltage and the current I 1 Is a phase of (a) of (b). As can be seen from fig. 2, under this condition, the single-phase full-bridge converter outputs power S in The method meets the following conditions:
S in ＝U C1 I 1 ＝|U C1 I 1 |cos(α-γ)+|U C1 I 1 |sin(α-γ) (1)
as can be seen from equation (1), the single-phase full-bridge inverter output power is related to the load voltage control phase α. When the power grid voltage is normal, the amplitude of the load voltage is controlled to be unchanged, the phase is changed, the output power of the single-phase full-bridge converter can be effectively adjusted, and further the regulation and control of the power flow in the system are realized, and a phasor relation diagram under the normal condition of the power grid voltage is shown as (a) of fig. 2; when the power grid voltage is reduced, under the same control strategy, the stability of the load voltage can be effectively ensured, meanwhile, the power regulation and control can be performed, and a phasor relation diagram under the condition of the power grid voltage is shown as (b) of fig. 2. In addition, when a short-circuit fault occurs at the load side, the active part of the equipment can be effectively protected, the short-circuit current is limited, and the safety of the system is protected.
2.2 method for minimum energy operation (minimum active Power output) of Single-phase full-bridge inverter
Definition when grid voltage dropsIs the power grid voltage drop coefficient (d when the power grid voltage is normal s ＝1)，U SM And->The power grid voltage amplitude detection value and the rated value are respectively. The phase of the power grid voltage is the reference phase, the control phase of the load voltage is a, and then the primary side compensation voltage U of the three-winding transformer T is obtained under the condition dvr The size of (2) is:
the phase b of the primary compensation voltage of the three-winding transformer T is as follows:
for convenience of analysis, the transformation ratio of the three-winding transformer T is set to be 1:1:1. At this time, the secondary side coupling capacitor branch current I of the three-winding transformer T cn The size of (2) is:
I cn ＝ωC 0 U dvr (4)
I cn the phase q of (2) is:
further, the grid current I is available s The size of (2) is:
I S ＝I cn ＝ωC 0 U dvr (6)
grid current I s The phase m of (2) is:
assuming that the power factor angle of the load is j, the active power P output by the single-phase full-bridge converter under the condition in And reactive power Q in The method comprises the following steps:
according to the formulas (2) to (8), the active power waveform output by the single-phase full-bridge converter is obtained under the influence of the double factors of the falling degree of the power grid and the control phase of the load voltage, and is shown in fig. 3. In fig. 3, the grid voltage drop coefficient d S In the range of (0.5-1)The control phase a of the load voltage varies within the (0, pi) range. As can be seen from fig. 3, the power curve intersects the zero plane over a wide voltage dip. This means that by controlling the phase of the load voltage in this case, the single-phase full-bridge converter pure reactive power output can be effectively achieved. When the falling degree continues to deepen and the curve and the zero plane have no intersection point, the phase corresponding to the position of the curve with the closest distance from the zero plane can realize the minimum active output of the single-phase full-bridge converter.
To further embody the output conditions of the active power of the single-phase full-bridge converter under different conditions, the values shown in FIG. 4 are shown as d s =0.8 (fig. 4 (a)) and d s Active power P output by single-phase full-bridge converter when=0.6 (fig. 4 (b)) in Waveform. As can be seen from FIG. 4, when d s When=0.8, the single-phase full-bridge converter has two load voltage control phases a and B with pure reactive power output, and further analysis finds that the power grid cannot realize unit power factor operation when the point B is found, so when d s When=0.8, the load voltage phase is controlled to be a; d, d s When=0.6, the single-phase full-bridge converter cannot realize pure reactive power output, but can realize minimum active power output when the phase of the control load voltage is C.
2.3 analysis of ability to cope with short-circuit faults
When a short-circuit fault occurs on the load side, as shown in fig. 5. As can be seen from FIG. 5, there will be U when a short circuit fault occurs dvr ＝-U S . If the T transformation ratio of the three-winding transformer is 1:1:1 at the moment, U is as follows tr1 ＝U S ，U C1 =0, directly protecting the active part of the device. On the other hand, U tr2 ＝U S ，I cn Will be of the size ωC 0 U S ，I L Will also be of size ωC 0 U S Wherein ω is angular velocity, which can effectively suppress the damage of the short-circuit current to the whole system.
2.4 control strategy
According to the analysis, the topological structure optimization operation control method of the power distribution network hybrid multifunctional grid-connected converter is obtained, and is shown in fig. 6. First, the grid voltage is detected by a detection moduleThe running state is used for obtaining the voltage drop coefficient d of the power grid s The value of d s And if the power grid voltage is more than 10%, judging that the power grid voltage has a sag fault. Then d is carried out s Substituting formula (3) -formula (8) to calculate to obtain d s Load voltage control phase a corresponding to the minimum active power output of the lower single-phase full-bridge converter, wherein the load voltage control phase a and load voltage amplitude U Lm Obtaining a reference value of the load voltageOmega is angular velocity and t is time, and then the reference value of the compensation voltage is obtained>Then, the reference value of the compensation voltage is +.>Substituting (9) to obtain the filter capacitor C of the output port of the single-phase full-bridge converter 1 Reference value>And collecting the filter capacitor voltage U of the output port of the single-phase full-bridge converter C1 As a feedback quantity, will->And U C1 Difference is made, and a filter inductance current reference value +.>Will->And filter inductance L 1 Real-time feedback quantity I of current L1 Difference is made, and modulated wave u is obtained through PI regulation r The driving signal of the bridge arm IGBT module of the single-phase full-bridge converter is obtained through SPWM modulation, and is input into the single-phase full-bridge converter to control the topological structure operation of the hybrid multifunctional grid-connected converter of the power distribution network.
3. Simulation analysis
In order to verify the effectiveness and feasibility of the invention, a simulation model is built in MATLAB/Simulink for simulation analysis, and simulation parameters are shown in Table 1.
TABLE 1 Main simulation parameters
| Parameters (parameters) | Numerical value |
| Effective value of power distribution network voltage | 220V |
| Frequency of | 50Hz |
| Filter inductance L 1 | 4mH |
| Filter capacitor C 1 | 100uF |
| Three-winding transformer T secondary side coupling capacitor C 0 | 540uF |
| DC side voltage | 400V |
| T transformation ratio of three-winding transformer | 1:1:1 |
| Load impedance | 8Ω+0.0191H |
| Load power factor | 0.8 |
(1) Simulation verification of minimum active power output of single-phase full-bridge converter
The simulation waveform of the single-phase full-bridge converter in the minimum active power output method is shown in FIG. 7, wherein P s For active power, P, output by the network L For the active power required by the load Pinv is zero active power output by the converter. Two falling conditions are set in the simulation, wherein the power grid voltage generates d when 0.06-0.14s s Dip = 0.8; at 0.18-0.26s, the power grid voltage generates d s Dip=0.9. The voltage waveform shows that under different sag degrees, the single-phase full-bridge converter can effectively compensate, and the continuous stability of load voltage is ensured. Meanwhile, as can be seen from the power waveform, during the voltage sag period, the phase a is adjusted, so that the single-phase full-bridge converter can be effectively controlled to realize minimum active power output under different working conditions. The zero active power output of the single-phase full-bridge converter is realized under the working condition shown in fig. 7, and the correctness and the effectiveness of the optimized operation method provided by the invention are verified.
(2) Simulation verification of capability of multifunctional grid-connected converter for coping with short-circuit fault
When a short-circuit fault occurs on the load side, the load current waveform is as shown in fig. 8. Therefore, the short circuit fault occurs in 0.1s, and the researched multifunctional grid-connected converter is provided with a current limiting branch capable of circulating current during the short circuit fault, so that the short circuit current can be limited in a safety range, and the safety of equipment and a system is further protected.
Meanwhile, under the working condition, the output voltage and the output current of the single-phase full-bridge converter and the secondary side voltage U of the secondary side of the T-shaped winding transformer tr1 The waveform of (2) is shown in fig. 9. As can be seen from fig. 9, after the short-circuit fault occurs, the secondary side voltage U of the secondary side of the three-winding transformer T tr1 Equal to U s The output voltage of the port of the single-phase full-bridge converter is 0, and the output current is 0, so that the active part of the device is effectively protected. In addition, the secondary side three-time side voltage U of the three-winding transformer T tr2 Coupling capacitor C 0 Current I of the branch where cn And the load current waveform is shown in fig. 10. As can be seen from fig. 10, when the structure has a short circuit fault, the secondary side coupling capacitor branch of the three-winding transformer T plays a role in limiting short circuit current: at this point the branch is conducting and a current flows, which is equal to the load current.
The foregoing description is only of the preferred embodiments of the present invention and is not intended to limit the scope of the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention are included in the protection scope of the present invention.
Claims (5)
1. A hybrid multifunctional grid-connected converter of a power distribution network is characterized by comprising a power grid, a single-phase full-bridge converter, LC filtering, a three-winding transformer T and a coupling capacitor C 0 And a load composition; wherein one end of the primary side of the three-winding transformer T is connected with a power grid, the other end is connected with a load, the secondary side of the three-winding transformer T is connected with a single-phase full-bridge converter, and the tertiary side of the secondary side of the three-winding transformer T is connected with a coupling capacitor C 0 The common ground of the secondary side and the tertiary side of the three-winding transformer T is grounded; LC filtering inductance L 1 The end is connected with the secondary side of the three-winding transformer T, and the filter capacitor C 1 End-connected single-phase full-bridge converter, in which the filter inductance L 1 And filter capacitor C 1 Serial connection;
the single-phase full-bridge converter comprises 4 IGBT modules and a direct-current side energy storage capacitor C; one end of the alternating current side of the single-phase full-bridge converter passes through a second IGBT module T 2 Emitter and fourth IGBT module T 4 The node of the collector passes through the filter inductance L 1 The other end of the alternating-current side of the single-phase full-bridge converter is connected with a power grid through a first IGBT module T 1 Emitter and third IGBT module T 3 The node of the collector is connected to the non-grounding end of the secondary side of the three-winding transformer T; one end of the direct current side of the single-phase full-bridge converter passes through a first IGBT module T 1 Collector and second IGBT module T 2 The node of the collector electrode is connected to the positive electrode of the direct-current side energy storage capacitor C, and the other end of the direct-current side of the single-phase full-bridge converter passes through the third IGBT module T 3 Emitter and fourth IGBT module T 4 The node of the emitter is connected to the negative electrode of the direct-current-side energy storage capacitor C.
2. A method for controlling the optimal operation of a hybrid utility grid-connected inverter of claim 1, comprising the steps of:
step 1: detecting the running state of the power grid voltage by using a detection module to obtain a power grid voltage drop coefficient d s The value of d s Judging that the grid voltage has a sag fault if the power grid voltage is more than 10%;
step 2: according to d s Calculating to obtain a load voltage control phase a corresponding to the minimum active power output of the single-phase full-bridge converter, wherein the load voltage control phase a and a load voltage amplitude U Lm Obtaining a reference value of the load voltageThereby obtaining the reference value of the compensation voltage>Wherein ω is angular velocity, t is time, U s Is the power supply voltage of the power grid;
step 3: according to the reference value of the compensation voltageObtain the filter capacitor C of the output port of the single-phase full-bridge converter 1 Reference value>And collecting the filter capacitor voltage of the output port of the single-phase full-bridge converterU C1 As a feedback quantity, will->And U C1 Difference is made, and a filter inductance current reference value +.>
Step 4: will beAnd filter inductance L 1 Real-time feedback quantity I of current L1 Difference is made, and modulated wave u is obtained through PI regulation r The driving signal of the bridge arm IGBT module of the single-phase full-bridge converter is obtained through SPWM modulation, and is input into the single-phase full-bridge converter to realize the control of the topological structure optimized operation of the hybrid multifunctional grid-connected converter of the power distribution network.
3. The method for controlling the optimal operation of a hybrid utility grid-connected inverter according to claim 2, wherein in step 1Wherein U is SM And->The power grid voltage amplitude detection value and the rated value are respectively.
4. The method for controlling the optimal operation of a hybrid-type multifunctional grid-connected inverter of claim 2, wherein the load voltage control phase a in step 2 is obtained according to the following formula:
primary side compensation voltage U of three-winding transformer T dvr The size of (2) is:
primary side compensation voltage U of three-winding transformer T dvr Phase b of (a) is:
at this time, the secondary side coupling capacitor branch current I of the three-winding transformer T cn The size of (2) is:
I cn ＝ωC 0 U dvr
I cn the phase q of (2) is:
grid current I s The size of (2) is:
I S ＝I cn ＝ωC 0 U dvr
grid current I s The phase m of (2) is:
assuming that the power factor angle of the load is j, the active power P output by the single-phase full-bridge converter under the condition in And reactive power Q in The method comprises the following steps:
wherein U is L For the load voltage, C 0 For coupling capacitance, I s For the power supply current of the power grid, I L Is the load current.
5. The optimal operation control method for a hybrid-type multifunctional grid-connected converter of a power distribution network according to claim 2, which is characterized in thatCharacterized in that the filter capacitor C in the step 3 1 Reference value of voltageThe method is based on the following formula:
wherein U is tr1 Is the voltage of the secondary side of the three-winding transformer T, U tr2 Is the voltage of the three-time side of the three-winding transformer T, I 1 For flowing into the secondary side current of the three-winding transformer T, I cn For flowing through the three-winding transformer T coupling capacitor C 0 Branch current, U s Is the power supply voltage of the power grid.
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