阅读说明：本技术 基于双有源桥结构的固态变压器故障电流限流拓扑及限流方法 (Double-active-bridge-structure-based fault current limiting topology and current limiting method for solid-state transformer ) 是由 卓超然 杨旭 张笑天 张�雄 马鑫 黄燕飞 于 2019-07-25 设计创作，主要内容包括：本发明公开了一种基于双有源桥结构的固态变压器故障电流限流拓扑及限流方法,包括变压器T和全桥电路,所述全桥包括连接在电压器T原边的全桥逆变电路和副边的全桥整流电路,所述全桥逆变电路和全桥整流电路分别连接有一支路,所述支路由一电力电子开关和一支撑电容连接组成,本发明相比于其它外加专用直流限流器设备型的方案,本发明具有造价低廉,电路简单且控制方法容易等优点；因为本发明具有对称的电路拓扑,因此本发明不受电网潮流方向的影响。通过调节H桥间移相角以及输入侧半桥的移相角,可以实现直流电力电子变压器输出电流的宽范围连续控制,因此具有宽范围的适应性,满足直流回路发生短路故障时不同程度的短路状况。(The invention discloses a fault current limiting topology and a current limiting method of a solid-state transformer based on a double-active-bridge structure, which comprises a transformer T and a full-bridge circuit, wherein the full-bridge circuit comprises a full-bridge inverter circuit connected to the primary side of the transformer T and a full-bridge rectifier circuit connected to the secondary side of the transformer T, the full-bridge inverter circuit and the full-bridge rectifier circuit are respectively connected with a branch circuit, and the branch circuit is formed by connecting a power electronic switch and a supporting capacitor; because the invention has a symmetrical circuit topology, the invention is not influenced by the power flow direction of the power grid. By adjusting the phase shift angle between the H bridges and the phase shift angle of the half bridge at the input side, the wide-range continuous control of the output current of the direct current power electronic transformer can be realized, so that the wide-range adaptability is realized, and the short circuit conditions of different degrees when the direct current loop has short circuit faults are met.)

1. Solid-state transformer fault current-limiting topology based on two active bridge structures, its characterized in that, including transformer T and full-bridge circuit, the full-bridge is including connecting the full-bridge inverter circuit on transformer T primary side and the full-bridge rectifier circuit on secondary, full-bridge inverter circuit and full-bridge rectifier circuit are connected with a branch road respectively, it forms to prop up to connect by a power electronic switch and a support capacitor, and wherein, power electronic switch's collecting electrode links to each other with the positive pole that supports capacitor, and support capacitor's negative pole is connected to the full-bridge circuit negative terminal, and power electronic switch's projecting pole is connected to the positive terminal of full-bridge circuit.

2. The dual-active-bridge-architecture-based solid-state transformer fault current-limiting topology of claim 1, wherein the full-bridge inverter circuit is comprised of four power electronic switches.

3. The dual-active-bridge-based solid-state transformer fault current-limiting topology of claim 1, wherein two ends of one full-bridge circuit are connected to the input end, and two ends of the other full-bridge circuit are connected to the output end.

4. The dual-active-bridge-structure-based solid-state transformer fault current-limiting topology of claim 1, wherein the power electronic switch is comprised of an IGBT and an anti-parallel diode.

5. The dual-active-bridge-structure-based solid-state transformer fault current limiting topology of claim 1, further comprising an inductor L connected between the full-bridge inverter circuit and the primary side of the transformer T, wherein the inductor L is a sum of a transformer leakage inductance and a line and power electronic switch equivalent inductance.

6. The solid-state transformer fault current limiting method based on the double-active-bridge structure is characterized by comprising the following steps of:

step one, when the direct current power grid is in a normal operation state, the transformer part is in an inter-bridge phase-shifting control method, d₁Defining the duty ratio as the phase difference of H bridges at two sides of the intermediate frequency transformer to be 0.5 working cycles, selecting an output voltage closed-loop control system or a voltage current double closed-loop control system on a controller, outputting the phase shift angle between the two H bridges and the duty ratio d₁The function for the average output active power P is shown in equation (1):

wherein d is₁Has a value range of [ -1,1 [)]；P(d₁) Is an odd function with respect to point (0,0) and at duty cycle d₁A maximum value at 0.5 and a minimum value at-0.5;

step two, when any point of two end points of the direct current transformer has short-circuit fault, the transformer changes the control method, when the transformer normally operates, the transformer is started and normally operates according to the SPS (single phase shift), at the normal operation time, whether the short-circuit fault occurs at the output side is detected, if not, the transformer continues to normally operate, when the line short-circuit fault is detected, firstly, the SPS method debugging is tried to be continued, the inner shift angle of the H bridge of the inverter bridge is forcibly set to zero, at the moment, whether the fault current is limited is judged again, and if the fault current is limited, the current limiting control is carried out according to the method; if the voltage is not limited, forcibly controlling the phase shift angle between the H bridges to be set to zero, and independently modulating the phase shift angle in the inversion H bridge to reduce the output voltage of the inversion side;

when a short-circuit fault occurs in a direct-current power grid, firstly, a supporting capacitor at the fault side is disconnected, a phase shift angle in an H bridge at the input side is started, the output current at the short-circuit moment is limited by limiting the input voltage of the intermediate-frequency transformer, and meanwhile, the phase difference between bridges is forced to be 0 according to the formula (2);

at this time, the corresponding duty ratio d of the power electronic transformer₂The function of the average output active power P is shown in formula (2);

wherein d is₂Has a value range of [ -1,1 [)]Its characteristics are in combination with₁The same is true.

7. The method for limiting fault current of solid-state transformer based on double active bridge structure as claimed in claim 1, wherein in step one, the controller uses the form of voltage and current double closed loop;

the whole closed-loop control input is a reference voltage Uout, the difference Uerr between the reference voltage and the actual measured voltage Uout is the input of a controller PI1, the output of the PI1 is connected with a boundary controller (hard limiter) to obtain a reference current output Iout _ ref, and the difference between the reference current output Iout _ ref and the actual current output value Iout is an output current error value Iout _ err and is also the input of a regulator PI 2; the PI2 output is the input to transfer function 1, which is the reference output Power _ ref; the output of the transfer function 1 is the control angle δ; the control angle δ is an input of the transfer function 2, an output of the transfer function 2 is an output voltage Uout, the output voltage Uout is connected to an input of the transfer function 3, and an output of the transfer function 3 is an output current value Iout.

8. The method for limiting the fault current of the solid-state transformer based on the dual-active-bridge structure according to claim 1, wherein in the second step, at the time of the short-circuit fault, the system provides a fault current limiting reference value I_{limit_ref}The current-limiting reference value of the fault current is subtracted from the actual value to obtain the current error I_errObtaining a control angle delta through a PI regulator by using the current error, taking the control angle as the input of a transfer function, wherein the transfer function is the relation between the output current and the control angle, and the output of the transfer function is the actual value I of the output current_out。

Technical Field

The invention belongs to the technical field of fault current ride-through control, and particularly relates to a fault current limiting topology and a fault current limiting method of a solid-state transformer based on a double-active-bridge structure.

Background

Direct current transmission and distribution systems began in the last 20 th century because of limited technical reserves at that time, which is not enough to realize functions of direct current voltage conversion, power flow control, fault circuit breaking and current limiting. This has largely restricted the development of dc transmission grids. Nowadays, with the rapid development of power electronic semiconductor devices and related control technologies, dc systems are once again mentioned and increasingly used in new construction projects of power transmission and distribution systems due to their unique advantages over ac systems. However, as the scale of the dc transmission system increases, dc lines of different voltage classes are connected by a dc power electronic transformer, and fault ride-through is an unavoidable problem, and various solutions for current limitation of the existing medium-high voltage dc fault are mostly solved by using a current limiting device.

Disclosure of Invention

In order to solve the problems in the prior art, the invention aims to provide a fault current limiting topology and a fault current limiting method of a solid-state transformer based on a double-active-bridge structure.

In order to achieve the purpose, the invention adopts the technical scheme that: the utility model provides a power electronic transformer trouble short-circuit current limiting topology based on two active bridge structures, includes transformer T and full-bridge circuit, the full-bridge is including connecting the full-bridge inverter circuit on transformer T primary side and the full-bridge rectifier circuit on secondary, full-bridge inverter circuit and full-bridge rectifier circuit are connected with a branch road respectively, and the branch road is connected to form by a power electronic switch and a support capacitor, and wherein, power electronic switch's collecting electrode links to each other with the positive pole that supports capacitor, and the negative pole that supports capacitor is connected to the full-bridge circuit negative terminal, and power electronic switch's projecting pole is connected to the positive end of full-bridge circuit.

Further, the full-bridge inverter circuit is composed of four power electronic switches.

Furthermore, in the full-bridge circuit, two ends of one full-bridge circuit are used for connecting the input end, and two ends of the other full-bridge circuit are used for connecting the output end.

Further, the power electronic switch is composed of an IGBT and an anti-parallel diode.

The transformer T further comprises an inductor L connected between the full-bridge inverter circuit and the primary side of the transformer T, wherein the inductor L is the sum of leakage inductance of the transformer and equivalent inductance of a circuit and a power electronic switch.

The solid-state transformer fault current limiting method based on the double-active-bridge structure is characterized by comprising the following steps of:

step one, when the direct current power grid is in a normal operation state, the transformer part is in an inter-bridge phase-shifting control method, d₁Defining the duty ratio as the phase difference ratio of H bridges on two sides of the intermediate frequency transformer to be 0.5 working cycles, selecting an output voltage closed-loop control system or a voltage current double closed-loop control system on a controller, outputting the phase shift angle between the two H bridges and the duty ratio d₁The function for the average output active power P is shown in equation (1):

wherein d is₁Has a value range of [ -1,1 [)]；P(d₁) Is an odd function with respect to point (0,0) and at duty cycle d₁A maximum value at 0.5 and a minimum value at-0.5;

step two, when any point of two end points of the direct current transformer has short-circuit fault, the transformer changes the control method, when the transformer normally operates, the transformer is started and normally operates according to the SPS (single phase shift), at the normal operation time, whether the short-circuit fault occurs at the output side is detected, if not, the transformer continues to normally operate, when the line short-circuit fault is detected, firstly, the SPS method debugging is tried to be continued, the inner shift angle of the H bridge of the inverter bridge is forcibly set to zero, at the moment, whether the fault current is limited is judged again, and if the fault current is limited, the current limiting control is carried out according to the method; if the voltage is not limited, forcibly controlling the phase shift angle between the H bridges to be set to zero, and independently modulating the phase shift angle in the inversion H bridge to reduce the output voltage of the inversion side;

when a short-circuit fault occurs in a direct-current power grid, firstly, a supporting capacitor at the fault side is disconnected, a phase shifting angle in an H bridge at the input side is started, the output current at the short-circuit moment is limited by limiting the input voltage of a medium-frequency transformer, and meanwhile, the phase difference between bridges is forced to be 0 according to the formula (2);

at this time, the corresponding duty ratio d of the power electronic transformer₂The function of the average output active power P is shown in formula (2);

wherein d is₂Has a value range of [ -1,1 [)]Its characteristics are in combination with₁The same is true.

Further, in the first step, the controller uses a voltage and current double closed loop form;

the whole closed-loop control input is a reference voltage Uout, the difference Uerr between the reference voltage and the actual measured voltage Uout is the input of a controller PI1, the output of the PI1 is connected with a boundary controller (hard limiter) to obtain a reference current output Iout _ ref, and the difference between the reference current output Iout _ ref and the actual current output value Iout is an output current error value Iout _ err and is also the input of a regulator PI 2; the PI2 output is the input to transfer function 1, which is the reference output Power _ ref; the output of the transfer function 1 is the control angle δ; the control angle δ is the input of the transfer function 2, the output of the transfer function 2 is the output voltage Uout, the output voltage Uout is connected to the input of the transfer function 3, and the output of the transfer function 3 is the output current value Iout.

Further, in the second step, at the time of short-circuit fault, the system provides a fault current limiting reference value I_{limit_ref}The current-limiting reference value of the fault current is subtracted from the actual value to obtain the current error I_errThe current error is adjusted by a PI regulator to obtain a control angle delta, and the control angle is used as a transfer functionThe transfer function is the relation between the output current and the control angle, and the output of the transfer function is the actual value I of the output current_out。

Compared with the prior art, the invention has at least the following beneficial effects, compared with other schemes of adding special direct current limiter equipment types, the invention has the advantages of low manufacturing cost, simple circuit, easy control method and the like; because the invention has a symmetrical circuit topology, the invention is not influenced by the power flow direction of the power grid. The wide-range continuous control of the output current of the direct current power electronic transformer can be realized by adjusting the phase shift angle between the H bridges and the phase shift angle of the half bridge at the input side, so that the wide-range adaptability is realized, and the short circuit conditions of different degrees when the direct current loop has short circuit faults are met; in addition, based on various solutions of the existing medium-high voltage direct current fault current limiting, the current limiting of direct current short-circuit fault current on a high-voltage side or a low-voltage side and the ride-through of low-voltage fault current are realized by applying a corresponding control method to the direct current transformer under the condition of not additionally adding current limiting equipment; besides the energy transmission of the direct current loops, the invention can also protect the short-circuit fault current possibly generated by the direct current lines at the two ends of the transformer, limit the short-circuit fault current at the two ends of the direct current and maintain the fault ride-through function of the low-voltage short-circuit.

The direct current transformer topology disclosed by the invention applies an electronic power control technology, has the characteristic of fast response to fault current and good fault current control performance, and has a very good application prospect in a future direct current transmission network.

Drawings

Fig. 1 shows a dc transformer topology with current limiting function according to the present invention.

Fig. 2 shows a typical application example of a dc transformer with current limiting function.

Fig. 3 is a waveform diagram of the transformer at the time of normal operation.

Fig. 4 is a control block diagram of the transformer at the time of normal operation.

Fig. 5 is a logic decision block diagram for a short-circuit fault of a transformer.

Fig. 6 is a working waveform diagram of phase shift in an input side H-bridge of the power electronic transformer at the time of short circuit.

Fig. 7 is a block diagram of the fast control of the operation time of the short-circuit fault of the power electronic transformer.

Fig. 8 is a simulation waveform diagram before and after a short-circuit fault of a power electronic transformer without a current limiting function.

Fig. 9 is a simulation waveform diagram before and after a short-circuit fault of the power electronic transformer with a current limiting function according to the present invention.

Detailed Description

The present invention will be described with reference to specific embodiments.

Fig. 1 shows a dc transformer topology with current limiting function according to the present invention, wherein ABCD is an output or input port. The topology mainly comprises power electronic switches Q1-Q8, Q_cpriAnd Q_csecSupporting capacitor C_priAnd C_secAnd a medium frequency transformer T. The homonymous ends of the transformer T are all on the same side. For convenience of demonstration, L in fig. 1 is mainly the sum of the leakage inductance of the transformer and the equivalent inductance of the line and the power electronic switch. The power electronic switch is composed of an IGBT and an anti-parallel diode, so that the power electronic switch has a function of unidirectional disconnection.

Q_cpriCollector and supporting capacitor C_priIs connected to the anode of (a) and the emitter is connected to point N. And Q_cpriAlso connected to the emitter are collectors for Q1 and Q3. The emitters of Q1 and Q3 are connected to the collectors of Q2 and Q4 at point P and point Q, respectively. Support capacitor C_priThe cathode is connected to the emitters of Q2 and Q4 at point S. The P point is connected with the anode of the transformer and is connected in series with the inductor L, and the cathode of the transformer is connected with the point Q. The topology in fig. 1 is symmetrical about the primary and secondary sides of the transformer, and therefore the connection method about the secondary side of the transformer is consistent with that described above and will not be described in detail here.

Fig. 2 shows an example of a dc transmission network with dc transformers connected between two dc voltage levels. The four points of the transformer ABCD correspond to the four points in fig. 1. DC1 and DC2 represent different voltages, respectively, which are positive-negative at the top and negative at the bottom, and the power flow can be from port AB to CD or vice versa. The numbers 1-4 represent locations where short circuits may occur, where 1 is equivalent to 2 and 3 is equivalent to 4. The invention can be applied to the condition that any place of 1-4 is short-circuited.