CN110365008B - Power electronic transformer direct current port current transformer position optimization configuration method - Google Patents
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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
- 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
- H02J3/36—Arrangements for transfer of electric power between ac networks via a high-tension dc link
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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
- H02J3/36—Arrangements for transfer of electric power between ac networks via a high-tension dc link
- H02J2003/365—Reducing harmonics or oscillations in HVDC
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- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/60—Arrangements for transfer of electric power between AC networks or generators via a high voltage DC link [HVCD]
Abstract
The invention discloses a position optimization configuration method for a current transformer at a direct current port of a power electronic transformer, which comprises the following steps of firstly, obtaining specific parameters of power electronic transformer equipment and a circuit; calculating the resonant current of the discharge loop by using the specific parameters of the equipment and the line; and step three, comparing the resonance current peak values of the discharge loop, and determining the position of the current transformer at the direct current port of the power electronic transformer. According to the invention, through carrying out analysis on the current oscillation current waveform of the direct current side of the power electronic transformer, the method for optimally selecting the installation position of the direct current side sensor is provided, the direct current line current protection caused by the response oscillation current at the moment of closing the direct current line switch can be effectively avoided, and the normal and reliable grid connection work of the direct current port of the power electronic transformer is ensured.
Description
Technical Field
The invention relates to the technical field of new energy power generation and micro-grids, in particular to a position optimization configuration method for a direct current port current transformer of a power electronic transformer.
Background
Under the driving of green energy-saving efficient energy transformation, the alternating current and direct current energy intelligent configuration technology gives full play to the advantages of optimal configuration of a power grid, efficiently utilizes clean energy to meet the increasing diversified energy consumption requirements of people, and is one of the important trends of development of the future intelligent power distribution network. A new ac/dc distribution network with a Power Electronic Transformer (PET) as a core is an innovative research and development to adapt to this trend.
Compared with the traditional transformer, the power electronic transformer can realize alternating current-direct current power conversion, and also has multiple functions of flexible energy regulation and control, flexible resource access, power quality management, fault monitoring isolation and the like. The interconnection and intercommunication of the AC/DC net racks in the region are realized, the flexible access of various distributed power supplies and AC/DC loads is supported, and the AC/DC conversion links of the multi-converter are reduced.
In order to ensure that the output voltage of a direct current port of a power electronic transformer is stable, a large voltage stabilizing capacitor generally exists, and the fault removal quick response of the power electronic transformer is ensured. When the voltage of a direct current port of the power electronic transformer is established, a voltage stabilizing capacitor of the direct current port of the power electronic transformer can charge a bus at the closing moment of a solid-state switch, under the condition of considering the impedance characteristic of a line, the voltage stabilizing capacitor is also arranged in the direct current port solid-state switch, the solid-state switch capacitor can firstly charge the bus, and then the voltage stabilizing capacitor of the direct current port of the power electronic transformer charges the solid-state switch capacitor.
The invention relates to a power electronic transformer research which mainly focuses on the field of topological mode and control, and at present, the positions of current sensors of a power electronic direct current port line are researched by few scholars at home and abroad.
Disclosure of Invention
In order to solve the defects in the prior art, the invention provides a position optimization configuration method for a direct current port current transformer of a power electronic transformer, which solves the problems that a voltage stabilizing capacitor of a direct current port of the power electronic transformer and a solid-state switch capacitor are inconsistent in charging speed and may oscillate, and the whole machine is locked and a contactor is opened due to line current error protection caused by incorrect arrangement position of a direct current port current sensor.
In order to achieve the above purpose, the invention adopts the following technical scheme: a method for optimally configuring the position of a current transformer at a direct current port of a power electronic transformer is characterized by comprising the following steps:
the method comprises the following steps of firstly, obtaining specific parameters of power electronic transformer equipment and lines;
calculating the resonant current of the discharge loop by using the specific parameters of the equipment and the line;
and step three, comparing the resonance current peak values of the discharge loops, and determining the position of the current transformer at the direct current port of the power electronic transformer.
The position optimization configuration method for the current transformer at the direct current port of the power electronic transformer is characterized by comprising the following steps of: the specific parameters of the power electronic transformer equipment and the lines comprise: a DC port capacitor C1 of the electronic transformer, an internal capacitor C2 of the solid-state switch, an equivalent resistor R of a DC line, an equivalent inductor L of the DC line and a PET port voltage U c1 Direct current port load R load 。
The position optimization configuration method for the current transformer at the direct current port of the power electronic transformer is characterized by comprising the following steps of: the second step comprises the following specific processes:
through a KVL equation of a discharge circuit 1 consisting of a power electronic transformer direct current port capacitor C1, a direct current circuit equivalent inductor L, a direct current circuit equivalent resistor R and a solid-state switch internal capacitor C2 and an instantaneous voltage-current relation of the solid-state switch internal capacitor C2, the resonant current i (t) of the discharge circuit 1 and the instantaneous voltage u of the solid-state switch internal capacitor C2 are obtained C2 (t) load R by solid-state switch internal capacitance C2 and DC port load The current of the discharge circuit 2 is u C2 (t)/R load 。
The position optimization configuration method for the current transformer at the direct current port of the power electronic transformer is characterized by comprising the following steps of: the power electronic transformer dc port C1 is equivalent to a dc power supply.
The position optimization configuration method for the current transformer at the direct current port of the power electronic transformer is characterized by comprising the following steps of: resonant current i (t) of the discharge circuit 1 and instantaneous voltage u of the internal capacitance C2 of the solid-state switch C2 (t), the concrete solving process is as follows:
the KVL equation for discharge loop 1 is:
Ri(t)+u L (t)+u C2 (t)＝u C1 (t) (1)
in the formula (1), u L (t) is the instantaneous value of the voltage across the equivalent inductance of the line, u C2 (t) is the instantaneous value of the capacitor voltage in the solid state switch, u C1 (t) is the equivalent DC power supply instantaneous value;
substituting formula (2) for formula (1) to obtain:
the zero input response equation is formula (4):
the characteristic equation of the formula (4) is formula (5):
LC 2 s 2 +RC 2 s+1＝0 (5)
the characteristic root that gives formula (5) is formula (6):
wherein s is a complex variable in Laplace transform, α is a current attenuation coefficient of the discharge circuit 1, and ω is 0 For the resonant angular frequency, omega, of the discharge circuit 1 d Damping the resonance angular frequency, s, for the discharge circuit 1 1 、s 2 Is a characteristic root, j is an imaginary number;
the solution of formula (4) is formula (11):
in formula (11), K and
is represented by formula (12) and formula (13):
k in the formulae (12) and (13) 1 、K 2 From initial conditions i (0) and u C2 (0) Determining:
K 1 ＝u C2 (0) (14)
assume that initial conditions are that i (0) is 0, u C2 (0) When the value is 0, then:
K 1 ＝0 (16)
u is obtained by solving the formula (11) and the formula (2) C2 (t) and i (t).
The position optimization configuration method for the current transformer at the direct current port of the power electronic transformer is characterized by comprising the following steps of: the third step comprises the following specific processes:
comparing two discharge loop resonant current peaks Max | i (t) | and Max | u C2 (t)/R load The value of | when Max | i (t) | does not calculation>Max|u C2 (t)/R load If not, the current sensor is arranged between the direct current port of the power electronic transformer and the solid-state switch.
The invention has the following beneficial effects: according to the invention, through current oscillation analysis possibly formed on the direct current port of the power electronic transformer, RLC series resonance theory analysis is established on a discharge circuit between the power electronic transformer and the solid-state switch, and an optimal selection method for the installation position of the direct current side sensor is provided, so that direct current circuit current protection caused by response to oscillation current at the moment of closing of the direct current circuit switch can be effectively avoided, and the normal and reliable grid-connected work of the direct current port of the power electronic transformer is ensured.
Drawings
FIG. 1 is a power electronic transformer topology;
FIG. 2 is a schematic diagram of a DC port of a power electronic transformer;
FIG. 3 is a solid state switching topology;
FIG. 4 is a schematic diagram of a DC port discharge circuit;
FIG. 5 is a simplified circuit diagram of the DC side;
FIG. 6 is a schematic diagram of the series response of the discharge circuit 1;
FIG. 7 is a schematic diagram of the positions of current measurement points on the DC side.
Detailed Description
The invention is further described below with reference to the accompanying drawings. The following examples are only for illustrating the technical solutions of the present invention more clearly, and the protection scope of the present invention is not limited thereby.
A method for optimally configuring the position of a current transformer at a direct current port of a power electronic transformer comprises the following steps:
the method comprises the following steps of firstly, obtaining specific parameters of power electronic transformer equipment and lines;
as shown in fig. 4, a power electronic transformer dc port capacitor C1, a solid-state switch internal capacitor C2, a dc line equivalent resistor R, a dc line equivalent inductor L, a PET port voltage Uc, and a dc port load R are obtained load 。
Calculating the resonant current of the discharge loop by using the specific parameters of the equipment and the line;
the method comprises the following specific steps: the resonant current of a discharge loop 1 consisting of a power electronic transformer DC port capacitor C1, a DC circuit equivalent inductor L, a DC circuit equivalent resistor R and a solid-state switch internal capacitor C2 is i (t), and the KVL (kirchhoff voltage law) equation of the discharge loop 1 is utilized: ri (t) + u L (t)+u C2 (t)＝u C1 (t) and
the current i (t) in the discharge circuit 1 and the instantaneous voltage u of the internal capacitance C2 of the solid-state switch can be determined C2 (t), wherein t is time; by anti-parallel connection of solid state switchesDiode (anti-parallel connected at outlet of solid switch line), mechanical switch, DC port load R load The current of the discharge loop 2 is u C2 (t)/R load (ii) a Since the anti-parallel diode is a pass, it can be disregarded when its losses are disregarded.
And step three, comparing the resonance current peak values of the discharge loop, and determining the position of the current transformer at the direct current port of the power electronic transformer.
The method comprises the following specific steps: comparing two discharge loop resonant current peaks Max | i (t) | and Max | u C2 (t)/R load The value of | when Max | i (t) | does not calculation>Max|u C2 (t)/R load If not, the current sensor is arranged between the direct current port of the power electronic transformer and the solid-state switch, namely the position of a measuring point 1 in fig. 7.
The power electronic transformer can freely and flexibly convert alternating current and direct current voltage, and can convert a low-voltage 10kV alternating current distribution network in commercial power into low-voltage 750V direct current.
As shown in fig. 1, in a Power Electronic Transformer (PET) topology structure according to the present invention, a PET ac side is connected to a 10kV ac, a dc side is connected to a ± 750V dc, wherein an H Bridge is a single-phase full Bridge, devices adopt IGBTs (insulated gate bipolar transistors), and DAB is a bidirectional Active Bridge (DAB) composed of two H bridges and a high frequency transformer connected in series. It can be seen that the topology is actually an Input Series Output Parallel (ISOP) structure, and is used for equally dividing voltage by connecting H bridges on an alternating current side in Series, each H bridge bears voltage stress and is reduced, voltage level on a direct current side is low, and therefore the H bridges are Output in Parallel, power is increased under the condition that Output voltage is ensured to be constant, and DAB current stress is reduced.
The dc side port of the power electronic transformer is typically regulated by a large capacitor C1, as shown in fig. 2. In order to ensure the fault isolation capability of the direct-current port of the power electronic transformer, because the mechanical switch has slow action time, a solid-state switch is usually installed on the direct-current port, the topology of the solid-state switch in the topology is shown in fig. 3, the capacitance value of a capacitor C2 is 4mF, VT is a power electronic switch, an IGBT device is adopted, and V is a freewheeling diode. During normal operation, the VT is always in an on state, and the VT is turned off under a fault condition, wherein the turn-off time is only determined by the characteristics of the device, and the fault isolation time can be generally controlled within 50 us.
Because the direct current port of the power electronic transformer is usually a voltage stabilizing capacitor, when two power electronic transformers are directly connected on the direct current side (referring to the parallel connection condition, and directly connected (in parallel) and then simultaneously supplying power to a load), a discharge loop exists between the two capacitors due to the fact that the initial voltages are unequal. As shown in fig. 4, the power electronic transformer 750V dc port load is directly connected to the solid-state switch, when the power electronic transformer is switched on after the power electronic transformer is started to charge, the voltage stabilizing capacitor C1 forms a discharge loop 1 to the capacitor C2, and the capacitor C2 forms a discharge loop 2 to the 750V port load, when the discharge time constants τ 1 and τ 2 of the discharge loop 1 and the discharge loop 2 are not equal, the discharge loop 1 may form a series resonance with the solid-state switch dc port capacitor C2 through the line inductance L, and the oscillating current may be measured by two current sensors on the discharge loop 1 and the discharge loop 2 in fig. 4, that is, two current sensors between the power electronic transformer dc port and the solid-state switch, and between the solid-state switch and the dc load. When the peak value of the oscillation current is too large, the misoperation of the line current protection can be caused, and the whole machine is locked.
For further research on the current oscillation characteristics of the dc port of the power electronic transformer, fig. 4 can be simplified to 5, and it can be seen that the discharge circuit 1 is an RLC series oscillation circuit.
When the solid-state switch capacitor C2 is incorporated into a 750V DC port of the power electronic transformer, the voltage-stabilizing capacitor C1 of the power electronic transformer can be equivalent to a DC source u c1 As shown in fig. 6, RLC circuit series response analysis is performed on the discharge circuit 1, and the dc side simplified circuit of the power electronic transformer includes: voltage stabilizing capacitor C1 equivalent direct current power supply u of power electronic transformer connected in series in sequence c1 Line equivalent inductance L, line equivalent resistance R and solid-state switch capacitance C2.
From fig. 6, the KVL (kirchhoff voltage law) circuit equation can be given:
Ri(t)+u L (t)+u C2 (t)＝u C1 (t)(1)
in the formula (1), R is the equivalent resistance of the line, i (t) is the instantaneous value of the line current, u L (t) is the instantaneous value of the voltage across the equivalent inductance of the line, U c2 (t) is the instantaneous value of the capacitor voltage in the solid state switch, u c1 (t) is an equivalent DC power supply u a Instantaneous value.
The discharge loop 1 current can be obtained by the capacitor voltage in the solid-state switch:
by substituting formula (2) for formula (1):
it can be seen that equation (3) is a constant coefficient non-homogeneous linear second order differential equation, and the zero input response equation is equation (4):
the characteristic equation of the formula (4) is formula (5):
LC 2 s 2 +RC 2 s+1＝0(5)
the characteristic root equation (6) of equation (5) can be obtained:
wherein s is a complex variable in Laplace transform, alpha is a current attenuation coefficient of the discharge circuit 1, omega 0 is a resonance angular frequency of the discharge circuit 1, and omega d Damping the resonance angular frequency, s, for the discharge circuit 1 1 、s 2 Is a characteristic root, j is an imaginary number; s 1 ＝-α+jω d ，s 2 ＝-α-jω d ，s 1, 2 is a generic notation of two characteristic roots;
see formula (7) -formula (9):
because the outlet of the power electronic transformer is directly connected with the solid-state switch, the line distance is short, the resistance is small and is generally less than 0.1 omega, and the discharge loop 1 can be judged to present the under-damped oscillation characteristic by the formula (10):
the solution of formula (4) can be solved into formula (11)
In formula (11), K and
is a general formula (12) and a general formula (13)
K in the formulae (12) and (13) 1 、K 2 From initial conditions i (0) and u C2 (0) Determining:
K 1 ＝u C2 (0)(14)
assume that initial conditions are that i (0) is 0, u C2 (0) When the value is 0, then:
K 1 ＝0(16)
u is obtained by solving the formula (11) and the formula (2) C2 (t) and i (t). The currents for points 1 and 2 in FIG. 7 are i (t) and u, respectively C2 (t)/R load (ii) a When t is 0, the time 0 is the switch closing time;
comparing two measuring points in FIG. 7, in order to avoid the malfunction of line current protection caused by the series resonance current, the peak value of the resonance current in the discharge loop is compared, when Max | i (t) is not conducted>Max|u C2 (t)/R load In |, the oscillating current of the discharge loop 1 is larger, so as to avoid the protection misjudgment caused by the oscillating current, the current sensor should be designed and installed at the measuring point 2, that is, the current of the discharge loop 2 represents the port current. On the contrary, the oscillation current of the discharge loop 2 is larger, so as to avoid protection misjudgment caused by the oscillation current, the current sensor should be designed and installed at the measuring point 1, that is, the current of the discharge loop 1 represents the port current.
When the voltage of the direct current port of the power electronic transformer is already established, the capacitor of the direct current port of the power electronic transformer charges the bus at the closing moment of the solid-state switch, and the direct current port oscillates under the condition of considering the impedance characteristic of the line. The invention establishes RLC series resonance theory analysis on the discharge circuit between the power electronic transformer and the solid-state switch by analyzing the current oscillation possibly formed at the direct current port of the power electronic transformer, provides an optimal selection method for the installation position of the direct current side sensor, can effectively avoid the direct current line current protection caused by the response oscillation current at the moment of closing the direct current line switch, and ensures the normal and reliable grid-connected work of the direct current port of the power electronic transformer.
As will be appreciated by one skilled in the art, embodiments of the present application may be provided as a method, system, or computer program product. Accordingly, the present application may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present application may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and so forth) having computer-usable program code embodied therein.
The present application is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the application. It will be understood that each flow and/or block of the flowchart illustrations and/or block diagrams, and combinations of flows and/or blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
The above description is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, several modifications and variations can be made without departing from the technical principle of the present invention, and these modifications and variations should also be regarded as the protection scope of the present invention.
Claims (3)
1. A method for optimally configuring the position of a current transformer at a direct current port of a power electronic transformer is characterized by comprising the following steps: the method comprises the following steps of obtaining specific parameters of power electronic transformer equipment and lines, wherein the specific parameters comprise: a power electronic transformer DC port capacitor C1, a solid-state switch internal capacitor C2, a DC line equivalent resistor R, a DC line equivalent inductor L and a PET port voltage U c1 Direct current port load R load ；
Calculating the resonant current of the discharge loop by using the specific parameters of the equipment and the line; the specific process is as follows: through a KVL equation of a discharge circuit 1 consisting of a power electronic transformer direct current port capacitor C1, a direct current circuit equivalent inductor L, a direct current circuit equivalent resistor R and a solid-state switch internal capacitor C2 and an instantaneous voltage-current relation of the solid-state switch internal capacitor C2, the resonant current i (t) of the discharge circuit 1 and the instantaneous voltage u of the solid-state switch internal capacitor C2 are obtained C2 (t) internal capacitance C2 of solid-state switch and DC port load R load The current of the discharge circuit 2 is u C2 (t)/R load ；
Comparing the resonance current peak values of the discharge loop, and determining the position of a current transformer at a direct current port of the power electronic transformer; the specific process is as follows: comparing two discharge loop resonant current peaks Max | i (t) | and Max | u C2 (t)/R load The value of | when Max | i (t) | does not calculation>Max|u C2 (t)/R load If not, the current sensor is arranged between the direct current port of the power electronic transformer and the solid-state switch.
2. The method for optimally configuring the position of the current transformer at the direct current port of the power electronic transformer as claimed in claim 1, wherein the method comprises the following steps: the power electronic transformer DC port capacitor C1 is equivalent to a DC power supply.
3. The method for optimizing and configuring the position of the current transformer at the direct current port of the power electronic transformer as claimed in claim 2, wherein the method comprises the following steps: resonant current i (t) of the discharge circuit 1 and instantaneous voltage u of the internal capacitance C2 of the solid-state switch C2 (t), the concrete solving process is as follows:
the KVL equation for discharge loop 1 is:
Ri(t)+u L (t)+u C2 (t)＝u C1 (t) (1)
in the formula (1), u L (t) is the instantaneous value of the voltage across the equivalent inductance of the line, u C2 (t) is the instantaneous value of the capacitor voltage in the solid state switch, u C1 (t) is the equivalent DC power supply instantaneous value;
substituting formula (2) for formula (1) to obtain:
the zero input response equation is formula (4):
the characteristic equation of the formula (4) is formula (5):
LC 2 s 2 +RC 2 s+1＝0 (5)
the characteristic root that gives formula (5) is formula (6):
wherein s is a complex variable in Laplace transform, α is a current attenuation coefficient of the discharge circuit 1, and ω is 0 For resonant angular frequency, omega, of the discharge circuit 1 d Damping the resonance angular frequency, s, for the discharge circuit 1 1 、s 2 Is a characteristic root, j is an imaginary number;
the solution of formula (4) is formula (11):
in formula (11), K and
formula (12) and formula (13):
k in formula (12) and formula (13) 1 、K 2 From initial conditions i (0) and u C2 (0) Determining:
K 1 ＝u C2 (0) (14)
assume that the initial condition is that i (0) is 0, u C2 (0) When the value is 0, then:
K 1 ＝0 (16)
u is obtained by solving the formula (11) and the formula (2) C2 (t) and i (t).
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|---|---|---|---|---|
| CN108832825A (en) * | 2018-07-06 | 2018-11-16 | 华北电力大学 | A kind of multiport electric power electric transformer topology of high power density |
| CN108957307A (en) * | 2018-07-12 | 2018-12-07 | 国网湖北省电力有限公司电力科学研究院 | A kind of direct current change-over switch parameter of oscillation measurement method based on many reference amounts |
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