CN110336470B

CN110336470B - Power electronic transformer system, transformer and fault ride-through control method thereof

Info

Publication number: CN110336470B
Application number: CN201910616077.4A
Authority: CN
Inventors: 曹建博; 黄辉; 安昱; 王林; 牛化鹏; 吴金龙; 辛德锋; 黎阳; 郜亚秋; 肖飞; 陈雪; 龚培娇; 赵建荣
Original assignee: China Electric Power Research Institute Co Ltd CEPRI; XJ Electric Co Ltd; Xian XJ Power Electronics Technology Co Ltd
Current assignee: China Electric Power Research Institute Co Ltd CEPRI; XJ Electric Co Ltd; Xian XJ Power Electronics Technology Co Ltd
Priority date: 2019-07-09
Filing date: 2019-07-09
Publication date: 2021-09-03
Anticipated expiration: 2039-07-09
Also published as: CN110336470A

Abstract

The invention relates to a power electronic transformer system, a transformer and a fault ride-through control method thereof, belonging to the technical field of bidirectional isolation direct-current voltage conversion, wherein the power electronic transformer comprises: the high-voltage half-bridge module comprises a high-voltage upper arm branch and a high-voltage lower arm branch; the self-blocking module comprises a low-voltage half-bridge module, the low-voltage half-bridge module comprises a low-voltage upper arm branch and a low-voltage lower arm branch, the low-voltage lower arm branch is used for being connected with a low-voltage side direct-current power grid, and a total branch connected by the low-voltage upper arm branch and the low-voltage lower arm branch is connected with the low-voltage side of each module in parallel. Through the matching control of the half-bridge module arranged on the high-voltage side of the module and the half-bridge module in the self-blocking module, the power electronic transformer has fault ride-through capability, and the reliability and the stability of the operation of a power grid are improved.

Description

Power electronic transformer system, transformer and fault ride-through control method thereof

Technical Field

The invention belongs to the technical field of bidirectional isolation direct-current voltage conversion, and particularly relates to a power electronic transformer system, a transformer and a fault ride-through control method thereof.

Background

At present, power electronic transformers applied to direct-current distribution networks, new energy grid connection and energy internet have many advantages, such as: the weight and the volume are reduced; the voltage and the current are accurate and controllable, and the quality of electric energy is improved; the modular design is convenient for system capacity expansion, disassembly and maintenance; has the advantages of low pollution, high efficiency, intellectualization and the like. However, when the power electronic transformer fails, the whole system where the power electronic transformer is located may fail and stop, which may seriously affect the reliability and stability of the dc distribution network power supply.

Disclosure of Invention

The invention aims to provide a power electronic transformer, which is used for solving the problem of providing execution hardware for the power electronic transformer with fault ride-through capability;

the fault ride-through control method of the power electronic transformer is also provided, and is used for solving the problem that the reliability and the stability of the operation of the power grid are reduced because the power electronic transformer in the prior art breaks down, namely the system stops when a high-voltage side direct-current power grid (a direct-current power grid connected with the high-voltage side of the power electronic transformer) has a short-circuit fault;

the other fault ride-through control method of the power electronic transformer is used for solving the problem that the reliability and the stability of the operation of a power grid are reduced due to the fact that a power electronic transformer in the prior art breaks down, namely a system stops when a low-voltage side direct-current power grid (a direct-current power grid connected with the low-voltage side of the power electronic transformer) has a short-circuit fault;

the power electronic transformer system is used for solving the problem that the reliability and the stability of a power grid are reduced when the power electronic transformer in the prior art breaks down, namely the system stops.

Based on the above purpose, the technical scheme of the power electronic transformer of the invention is as follows:

the high-voltage half-bridge module comprises a high-voltage upper arm branch and a high-voltage lower arm branch which are connected, and the high-voltage lower arm branch is used as the high-voltage side of the module;

the bidirectional direct current conversion unit comprises a primary side semiconductor current conversion unit, a primary side resonance network, a transformer, a secondary side resonance network and a secondary side semiconductor current conversion unit which are sequentially connected, wherein the secondary side semiconductor current conversion unit is positioned on the low-voltage side of the module;

the self-blocking module comprises a low-voltage half-bridge module, the low-voltage half-bridge module comprises a low-voltage upper arm branch and a low-voltage lower arm branch, the low-voltage lower arm branch is used for being connected with a low-voltage side direct-current power grid, and a total branch connected by the low-voltage upper arm branch and the low-voltage lower arm branch is connected with the low-voltage side of each module in parallel.

The beneficial effects of the above technical scheme are:

the invention designs a hardware device of a power electronic transformer, wherein a high-voltage half-bridge module is arranged on the high-voltage side of a module, a bidirectional direct current conversion unit is arranged on the low-voltage side of the module, the bidirectional direct current conversion unit of each module is connected with a low-voltage side direct current power grid through a self-blocking module, and the high-voltage half-bridge module arranged on the high-voltage side of the module and a low-voltage half-bridge module in the self-blocking module are matched for control, so that the power electronic transformer has fault ride-through capability, and effective hardware support is provided for the power electronic transformer to have the fault ride-through capability.

In order to adapt to specific voltage classes, the high-voltage side of each module of the power electronic transformer is connected in series and the low-voltage side of each module of the power electronic transformer is connected in parallel.

In order to timely remove a fault module when a module in the power electronic transformer fails, a bypass switch is connected in parallel to the high-voltage side of a high-voltage half-bridge module of each module, and the removal and the input of the corresponding module are realized by controlling the on-off of the bypass switch.

In order to absorb energy released by a high-voltage side inductor when a high-voltage side power grid is subjected to load shedding, a high-voltage side absorption loop is connected between a positive electrode and a negative electrode of the high-voltage side of the module; be equipped with the second inductance between low pressure underarm branch road and the low pressure side direct current electric wire netting for play the filtering action, in order to absorb the energy of low pressure side inductance release when the low pressure side electric wire netting gets rid of the load, be connected with the low pressure side absorption loop between the positive negative pole of the low pressure side of module.

Specifically, the low-voltage side absorption circuit comprises a first absorption circuit and a second absorption circuit which are connected in parallel, and a first resistor and a first capacitor are arranged on the first absorption circuit; the second absorption loop is provided with a second resistor, a second capacitor and a diode, and when short-circuit faults occur to the low-voltage side power grid, the diode can prevent the capacitor circuit on the second absorption loop from being damaged due to discharging, and meanwhile, the effect of limiting short-circuit current is achieved.

Based on the above purpose, a first technical scheme of a fault ride-through control method for a power electronic transformer is as follows:

the high-voltage side of the power electronic transformer is provided with a high-voltage half-bridge module, the low-voltage side of the power electronic transformer is provided with a low-voltage half-bridge module, the high-voltage half-bridge module comprises a high-voltage upper arm branch and a high-voltage lower arm branch, the high-voltage upper arm branch is connected with the high-voltage lower arm branch, and the high-voltage lower arm branch is used for being connected with a high-voltage side direct-; the low-voltage half-bridge module comprises a low-voltage upper arm branch and a low-voltage lower arm branch, the low-voltage upper arm branch is connected with the low-voltage lower arm branch, and the low-voltage lower arm branch is used for being connected with a low-voltage side direct-current power grid;

when a short-circuit fault occurs to a high-voltage side direct-current power grid, switching tubes of the high-voltage half-bridge module and the low-voltage half-bridge module are controlled to be turned off; and after the short-circuit fault in the high-voltage side direct-current power grid is cleared, controlling the corresponding switching tubes of the high-voltage half-bridge module to normally operate, and controlling the low-voltage upper arm branch in the low-voltage half-bridge module to be switched on and the low-voltage lower arm branch in the low-voltage half-bridge module to be switched off.

The first technical scheme of the fault ride-through control method has the beneficial effects that:

aiming at the hardware device of the power electronic transformer provided by the invention, when short-circuit fault occurs in a high-voltage side direct current power grid, fault ride-through can be realized by only controlling the switching tubes of the high-voltage half-bridge module and the low-voltage half-bridge module to be switched off without switching off the switching tubes in the working bidirectional direct current conversion unit, so that the power electronic transformer does not stop working and can not be damaged when short-circuit fault occurs, and the hardware device has a fault ride-through function, and improves the reliability and stability of power grid operation.

Based on the above purpose, the second technical scheme of the fault ride-through control method implemented by the power electronic transformer of the present invention is as follows:

the high-voltage side of the power electronic transformer is provided with a high-voltage half-bridge module, the low-voltage side of the power electronic transformer is provided with a low-voltage half-bridge module, the high-voltage half-bridge module comprises a high-voltage upper arm branch and a high-voltage lower arm branch, the high-voltage upper arm branch is connected with the high-voltage lower arm branch, and the high-voltage lower arm branch is used for being connected with a high-voltage side direct-current power grid; the low-voltage half-bridge module comprises a low-voltage upper arm branch and a low-voltage lower arm branch, the low-voltage upper arm branch is connected with the low-voltage lower arm branch, and the low-voltage lower arm branch is used for being connected with a low-voltage side direct-current power grid;

when a low-voltage side direct-current power grid has a short-circuit fault, controlling an upper switching tube of a high-voltage half-bridge module to be switched on and a lower switching tube of the high-voltage half-bridge module to be switched off, and controlling the switching tube of the low-voltage half-bridge module by adopting a voltage outer ring current inner ring to stabilize the low-voltage side direct-current voltage of the power electronic transformer at a set direct-current voltage instruction value;

and after the short-circuit fault in the low-voltage side direct-current power grid is cleared, controlling the upper switch tube of the low-voltage half-bridge module to be switched on and the lower switch tube to be switched off, and controlling the corresponding switch tube of the high-voltage half-bridge module to normally operate.

The second technical scheme of the fault ride-through control method has the beneficial effects that:

aiming at the hardware device of the power electronic transformer provided by the invention, when short-circuit fault occurs in a low-voltage side direct-current power grid, by interchanging the control strategies of the switch tube of the high-voltage half-bridge module and the switch tube of the low-voltage half-bridge module (during normal operation, the switch tube of the high-voltage half-bridge module is controlled by a voltage outer ring current inner ring, the upper switch tube of the low-voltage half-bridge module is switched on, the lower switch tube of the low-voltage half-bridge module is switched off, during short-circuit fault, the upper switch tube of the high-voltage half-bridge module is switched on, the lower switch tube of the high-voltage half-bridge module is switched off, the switch tube of the low-voltage half-bridge module is controlled by the voltage outer ring current inner ring), the power electronic transformer can realize fault ride-through without switching off a switching tube in a working bidirectional direct current conversion unit, so that the power electronic transformer cannot be damaged without shutdown when short-circuit faults occur, has a fault ride-through function, and improves the reliability and stability of power grid operation.

Based on the above purpose, a technical scheme of a power electronic transformer system is as follows:

including above-mentioned power electronic transformer to and the controller of control connection switch tube among the power electronic transformer, this controller is used for:

when a short-circuit fault occurs in a high-voltage side direct-current power grid, switching tubes of the high-voltage half-bridge module and the low-voltage half-bridge module are controlled to be turned off; and after the short-circuit fault in the high-voltage side direct-current power grid is cleared, controlling the corresponding switching tubes of the high-voltage half-bridge module to normally operate, and controlling the low-voltage upper arm branch in the low-voltage half-bridge module to be switched on and the low-voltage lower arm branch in the low-voltage half-bridge module to be switched off.

when a short-circuit fault occurs in a low-voltage side direct-current power grid, controlling an upper switching tube of a high-voltage half-bridge module to be switched on and a lower switching tube of the high-voltage half-bridge module to be switched off, and controlling the switching tube of the low-voltage half-bridge module by adopting a voltage outer ring current inner ring to stabilize the low-voltage side direct-current voltage of the power electronic transformer at a set direct-current voltage instruction value; and after the short-circuit fault in the low-voltage side direct-current power grid is cleared, controlling the upper switch tube of the low-voltage half-bridge module to be switched on and the lower switch tube to be switched off, and controlling the corresponding switch tube of the high-voltage half-bridge module to normally operate.

The beneficial effects of the above technical scheme are as follows:

according to the hardware device of the power electronic transformer, the high-voltage half-bridge module is arranged on the high-voltage side of each module, the bidirectional direct-current conversion unit is arranged on the low-voltage side of each module, the bidirectional direct-current conversion unit of each module is connected with the low-voltage side power grid through the self-blocking module, and the power electronic transformer has fault ride-through capability through the matched control of the high-voltage half-bridge module of each module and the low-voltage half-bridge module in the self-blocking module, namely when the high-voltage side direct-current power grid has a short-circuit fault, the switching tubes of the high-voltage half-bridge module and the low-voltage half-bridge module are only controlled to be turned off so as to realize fault ride-through; when a short-circuit fault occurs in a low-voltage side direct current power grid, fault ride-through is realized by interchanging control strategies of switching tubes of the high-voltage half-bridge module and the low-voltage half-bridge module, so that the reliability and the stability of the operation of the power grid are improved.

Drawings

FIG. 1 is a schematic diagram of a power electronic transformer according to an embodiment of the present invention;

FIG. 2 is a schematic diagram of a module topology of an embodiment of a transformer system of the present invention;

FIG. 3 is a block diagram of the 750V side voltage source control in an embodiment of the transformer system of the present invention;

FIG. 4 is a high side current waveform of the fault module bypassing and switching phase shift angle in the transformer system embodiment of the present invention (bypass fault module at 0.15 s);

FIG. 5 is a diagram of a high side current waveform with a fault module bypassing and without switching phase shifting angles (bypass fault module at 0.15 s) in an embodiment of a transformer system of the present invention;

FIG. 6(a) is a PWM pulse waveform diagram for switching on light in a high voltage half bridge module in an embodiment of a transformer system of the present invention;

FIG. 6(b) is a PWM pulse waveform diagram of the switching tube in the self-blocking module in an embodiment of the transformer system of the present invention; in the figure, the upper column is a PWM pulse waveform of an upper switching tube of a low-voltage half-bridge module in a self-blocking module; the lower column is a PWM pulse waveform of a lower switching tube of the low-voltage half-bridge module in the self-blocking module;

FIG. 7(a) is a waveform illustrating the self-blocking and fast recovery of 750V side load current during a DC short-circuit fault ride-through in an embodiment of a transformer system according to the present invention;

FIG. 7(b) is a waveform diagram of a 750V side voltage droop and snap-back during a DC short-circuit fault ride-through in an embodiment of a transformer system of the present invention;

FIG. 8 is a block diagram illustrating control strategy switching during a DC short fault on the low side of an embodiment of a transformer system of the present invention;

FIG. 9 is a waveform diagram of the output current at 750V during a DC short-circuit fault ride-through on the low-side of an embodiment of a transformer system of the present invention;

FIG. 10 is a graph of the output voltage waveform at 750V side during a DC short-circuit fault ride-through on the low-side of an embodiment of a transformer system of the present invention;

fig. 11 is a schematic diagram of a push-pull circuit and primary tap transformer in the prior art.

Detailed Description

The following further describes embodiments of the present invention with reference to the drawings.

Transformer system embodiment:

the embodiment provides a power electronic transformer system, which comprises a power electronic transformer and a controller for controlling a switching tube connected with the power electronic transformer, for example, as shown in fig. 1, the high-voltage side and the low-voltage side of the power electronic transformer both determine specific voltage levels, which are respectively +/-10 kV (or 20kV) and 750V, and the total power of the system is 1.5 MW. In order to adapt to the voltage class requirements, the power electronic transformer comprises 24 modules (1# module, …, 24# module, and two additional redundant standby modules, not shown in the figure) connected between the high-voltage side and the low-voltage side of the direct-current power grid, wherein the high-voltage side of each module is connected in series, and the low-voltage side of each module is connected in parallel.

Each module comprises a high-voltage half-bridge module and a bidirectional direct-current conversion unit, taking a 1# module as an example, as shown in fig. 2, the high-voltage half-bridge module comprises a high-voltage upper arm branch and a high-voltage lower arm branch, the high-voltage upper arm branch is connected with the high-voltage lower arm branch, and the high-voltage lower arm branch is used as a high-voltage side of the module; an upper switching tube Q9 is arranged in the high-voltage upper arm branch, a lower switching tube Q10 is arranged in the high-voltage lower arm branch, a midpoint is arranged between the high-voltage upper arm branch and the high-voltage lower arm branch, and the midpoint is used for being connected with a high-voltage side direct-current power grid through a high-voltage side filter inductor L1.

The bidirectional direct current conversion unit comprises a primary side semiconductor commutation unit (comprising upper switching tubes Q1 and Q3 and lower switching tubes Q2 and Q4), a primary side resonance network (comprising Lr1, Cr1 and Lm), a high-frequency transformer, a secondary side resonance network (comprising Lr2 and Cr2) and a secondary side semiconductor commutation unit (comprising upper switching tubes Q5 and Q7 and lower switching tubes Q6 and Q8) which are connected in sequence. Wherein the primary side resonance network and the secondary side resonance network have symmetrical structures, L_mThe high-frequency transformer is an excitation inductor of the high-frequency transformer, the high-frequency transformer works at the resonant frequency of 10kHz, the transformation ratio of the high-frequency transformer is 4:3, the primary side semiconductor converter unit is connected with a high-voltage upper arm branch and a high-voltage lower arm branch of a high-voltage half-bridge module, and the secondary side semiconductor converter unit is used for being connected with a low-voltage side direct-current power grid through a self-blocking module. The bidirectional direct current conversion unit realizes the functions of electric isolation and voltage conversion of high and low voltage sides through a high-frequency transformer. Bypass switch K in the module is used for realizing amputation trouble module when the module breaks down, and fuse FV is used for carrying out fusing protection when the module is inside to take place short-circuit fault.

As shown in fig. 1, the self-blocking module connected to the secondary side semiconductor commutation unit includes three low-voltage half-bridge modules connected in parallel, wherein, the upper switching tubes Q11, Q13, Q15 are disposed in the low-voltage upper arm branches of the respective low-voltage half-bridge modules, the lower switching tubes Q12, Q14, Q16 are disposed in the low-voltage lower arm branches of the respective low-voltage half-bridge modules, the low-voltage lower arm branches of the respective low-voltage half-bridge modules are used for connecting to a low-voltage side dc grid, and the total branch formed by connecting the low-voltage upper arm branches and the low-voltage lower arm branches is connected in parallel with the low-voltage side of each module.

In fig. 1, KM1 is a high-voltage side main contactor, and KR1 is a high-voltage side soft start contactor; l1 is a high-voltage side filter inductor which plays a role in limiting current, a resistor R1 and a capacitor C1 are connected in series to form a high-voltage side absorption loop which is arranged between an anode and a cathode of the high-voltage side of the module and used for absorbing energy released by the high-voltage side inductor when the high-voltage side direct-current power grid is used for load shedding; l2 is a low-voltage side filter inductor, a resistor R2 and a capacitor C2 are connected in series to form a low-voltage side absorption loop (a first absorption loop), and the low-voltage side absorption loop is arranged between the positive electrode and the negative electrode of the low-voltage side of the module and used for absorbing energy released by the low-voltage side inductor when the low-voltage side direct-current power grid is used for load shedding; c4 is the low side bus capacitance; KM2 is low-voltage side main contactor, KR2 is low-voltage side soft start contactor.

In fig. 1, an RCD absorption circuit (a second absorption circuit) is formed by a resistor R3, a capacitor C3 and a diode D, and is used for absorbing excess energy and preventing voltage shock when a rated load is suddenly thrown by a low-voltage side dc grid; the diode D prevents the capacitor C3 from being damaged by short-circuit discharge when the low-side dc power grid has a short-circuit fault, and prevents the occurrence of an uncontrollable condition due to a large short-circuit current. In addition, the capacitance value of the capacitor C2 is small, so that current is limited by the resistor R2 during short circuit, and short circuit damage is avoided.

The power electronic transformer shown in fig. 1 has two starting modes and three operating modes, wherein the starting modes are respectively: starting from high pressure to low pressure and starting from low pressure to high pressure; the three working modes are respectively as follows: the current source at the +/-10 kV side is controlled in a working mode; controlling a voltage source at the +/-10 kV side in a +/-10 kV side voltage source working mode; and (3) an 750V side voltage source working mode, and 750V side voltage source control is carried out.

Taking the power electronic transformer operating in the 750V side voltage source operating mode as an example, when operating in the 750V side voltage source operating mode, the high voltage side connects to the grid, and the low voltage side connects to the load, as shown in fig. 3, the specific control method of the 750V side voltage source includes the following steps:

firstly, detecting 750V side direct current voltage Udc _ fdb _750V, comparing with 750V side direct current voltage command value Udc _ ref _750V (issued in the background), calculating an error signal obtained by comparison through a PI regulator, and outputting a current command value Idc _ ref _10kV of a current inner loop at the +/-10 kV side.

Detecting direct current Idc _ fdb _10kV at the +/-10 kV side, comparing the direct current Idc _ fdb _10kV with a current command value Idc _ ref _10kV (the value is output by a 750V voltage outer ring), calculating an error signal obtained by comparison through a PI regulator, outputting a modulation wave M _ Buck _ Boost, and comparing the modulation wave M _ Buck _ Boost with 24 phase-shifted carriers respectively, wherein the phases of the 24 carriers are sequentially different from each other by 360 degrees/24 degrees to 15 degrees; the comparison method is as follows: if the modulation wave is larger than or equal to the carrier wave, outputting a high level; if the modulated wave is smaller than the carrier wave, a low level is output. And obtaining upper switch tube control pulse signals of 24 high-voltage half-bridge modules at the +/-10 kV side according to the comparison mode, and obtaining lower switch tube control pulse signals of the high-voltage half-bridge modules by inverting the upper switch tube control pulse signals.

The bidirectional direct current conversion unit adopts the following fixed frequency synchronous control method:

PWM driving pulses of the primary side semiconductor commutation unit and the secondary side semiconductor commutation unit are constant frequency (the frequency is 10kHz of series resonance frequency of LLC) and 50% fixed duty ratio, driving pulses of power devices Q1, Q4, Q5 and Q8 in the circuit board 2 are controlled to be in the same frequency and the same phase, driving pulses of power devices Q2, Q3, Q6 and Q7 are in the same frequency and the same phase, and driving pulses of an upper power device and a lower power device (namely switching tubes) of the same bridge arm are complementary.

When a certain module fails, the fault self-cutting method is as follows:

1) after the module is detected to be in fault, a control system (the control system controls and connects the control ends of all the switch tubes) blocks the driving PWM pulses of all the switch tubes (such as IGBTs) (Q1-Q10) of the module immediately;

2) then, issuing a closing command of a bypass switch K of the module, and removing the fault module;

3) the control system needs to recalculate the phase shift angles of the carriers 1 to 24 in fig. 3 according to the total number of the currently operating modules and the positions of the faulty modules, and perform phase shift angle switching to reduce the current ripple on the high-voltage side (as shown in fig. 4), otherwise the current ripple on the high-voltage side is increased, as shown in fig. 5.

The carrier phase shift angle calculation principle is as follows:

a) when no module fails, the phases of 24 carriers are sequentially different from each other by 360 °/24 to 15 °, that is: the carrier phase shift angle of the 1# module is 0 degree, the carrier phase shift angle of the 2# module is 15 degrees, … … degrees and the carrier phase shift angle of the 24# module is 345 degrees;

b) when a module has a fault, the carrier phase shift angle of the fault module is distributed to the next adjacent module without the fault, all driving pulses of the fault module are blocked, and the fault module exits from operation after bypassing through a bypass switch;

c) for both principle a) and principle b), it must be satisfied: the real-time running modules are numbered in sequence from small to large, the carrier phase shift angles of the modules sequentially differ by 360 degrees/N, and N is the total number of the modules in normal running (in this embodiment, N is 24).

According to the above principle of calculating the phase shift angle of the carrier, when the number of the module faults and the positions of the fault modules randomly change, the calculation of the phase shift angle of the carrier is more complicated, and needs to be performed by a uniform method, which is specifically as follows:

a. defining a module operation array and assigning an initial value:

A_Run[24]＝{1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1}

(Note: 24 in A _ Run [24] indicates the number of elements in the array A _ Run, which is the format specified in the C language. when A _ Run [24] is used in conjunction with the following assignments {1,1,1,1,1,1,1,1,1,1,1,1,1, 1} it indicates that an array of 24 elements is defined and does not indicate an element in A _ Run [ i ])

The array element A _ Run [ i ] represents the meaning as follows:

b. defining a module phase shift angle array and assigning an initial value:

A_Theta[24]＝{0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0}

c. the fault information of each module is detected in real time in the operation process, and the elements in the module operation array are assigned according to the existence of faults:

d. calculating the total number Run _ Num of the operation modules in real time according to the numerical values of the array elements of the module operation:

e. according to the total number Run _ Num of the modules and the element value A _ Run [ i ] in the module running array, calculating the carrier phase shift angle (note: when two modules have faults) of the 2# module to the 24# module, the rest 22 modules do not need to be numbered again, the original number is unchanged, the calculated carrier phase shift angle of the 2# module to the 24# module is also the phase shift angle corresponding to the original number module at the moment, the carrier phase shift angle of the 1# module is always 0 degrees, the initial value is given as 0 degrees, and the calculation is as follows:

when the number of the faults of the module is larger than 2, a controller of the system issues a shutdown command and blocks PWM (pulse width modulation) pulses of all the IGBT modules, and the system enters a fault shutdown state.

In the following, still taking the power electronic transformer operating in the 750V side voltage source operating mode as an example, a fault ride-through control method implemented by the power electronic transformer when a short-circuit fault occurs is described:

1) when a +/-10 kV side has a short-circuit fault, a 750V side is connected with a normal load, and the fault ride-through control method comprises the following specific steps:

firstly, when short-circuit fault on a high-voltage side (namely a +/-10 kV side) is detected, a controller issues a blocking pulse command to switching tubes (Q9 and Q10) of all high-voltage half-bridge modules and switching tubes (Q11, Q12, … and Q16) of low-voltage half-bridge modules in a self-blocking module to block pulses, and PWM driving pulses of the switching tubes in a bidirectional direct current conversion unit are not blocked;

and secondly, after the short-circuit fault at the high-voltage side is detected to be cleared, the controller sends an unlocking pulse instruction to the switching tubes of all the high-voltage half-bridge modules and the low-voltage half-bridge modules to perform pulse unlocking, and the power electronic transformer is rapidly put into operation according to the operation state before the fault, namely a double-loop control algorithm (voltage outer loop and current inner loop control for short) of a voltage outer loop and a current inner loop at +/-10 kV side shown in the figure 3.

According to the above steps, the blocking and unblocking pulses of the switch tube in the high-voltage half-bridge module are shown in fig. 6(a), and the blocking and unblocking pulses of the switch tube in the self-blocking module are shown in fig. 6 (b). During a short-circuit fault ride-through, the 750V side load current self-blocking and snap-back waveforms are shown in fig. 7(a), and the 750V side voltage droop and snap-back waveforms are shown in fig. 7 (b).

2) When a direct-current short-circuit fault occurs on the 750V side, the fault ride-through control method comprises the following specific steps:

firstly, when a short-circuit fault of a direct-current power grid at a 750V side is detected, in order to meet the requirement that a system provides 1.2 times of rated short-circuit current for a load side, the modulation waves of switching tubes in all high-voltage half-bridge modules at a +/-10 kV side are output and switched to be a fixed value of 1.0 from a high-voltage side current loop, and an upper switching tube (Q9) and a lower switching tube (Q10) of the high-voltage half-bridge modules are ensured to be always connected and disconnected during the fault period;

during the short-circuit fault, the self-blocking module is switched on from the upper switching tubes (Q11, Q13 and Q15) and switched off from the lower switching tubes (Q12, Q14 and Q16) before the fault, and is switched into a double-loop control algorithm of a voltage outer loop (750V side voltage loop) and a current inner loop (750V side current loop), and a control strategy switching block diagram is shown in FIG. 8;

after detecting that the short-circuit fault in the low-voltage side direct-current power grid is cleared, the controller switches the modulation wave of the switching tube in the high-voltage half-bridge module and the modulation wave of the switching tube in the self-blocking module to a normal operation state, and the power electronic transformer is put into operation rapidly according to the operation state before the fault, as shown in fig. 8.

According to the above steps, the current and voltage simulation waveforms when the low-voltage side direct-current power grid has a short-circuit fault are respectively shown in fig. 9 and fig. 10, the short-circuit fault occurs at 0.1s, and the fault is cleared at 0.3s, as shown in fig. 9, 1.2 times of rated short-circuit current is provided to the load side and maintained for a period of time (0.2s), and after the fault is cleared, the operation state before the fault can be quickly recovered, so that fault ride-through is realized.

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. For example, the power electronic transformer in the embodiment includes 24 modules and 2 standby redundant modules, and as another embodiment, when the voltage level of the high-voltage side is lower, for example, 1kV, only one module and one standby redundant module may be provided in the power electronic transformer, but only one module is put into operation when the power electronic transformer is in normal operation.

For another example, the fault ride-through control method of the invention is not only suitable for the 750V side voltage source working mode, but also suitable for the working modes in the prior art, such as the ± 10kV side current source working mode and the ± 10kV side voltage source working mode.

The three operation modes, i.e. the 750V side voltage source operation mode, the ± 10kV side current source operation mode and the ± 10kV side voltage source operation mode, are included in the prior art regardless of which mode fails. In three modes of operation: if the +/-10 kV side fails, performing fault ride-through according to the control strategy in the 1) when the +/-10 kV side has a short-circuit fault; if the 750V side has a fault, the fault ride-through is carried out according to the control strategy when the 750V side has a direct current short-circuit fault in the 2).

For another example, the self-blocking module in fig. 1 is provided with three low-voltage half-bridge modules, as another embodiment, the number of the low-voltage half-bridge modules may be set according to the current range of the low-voltage side dc power grid, and if the conditions allow, the self-blocking module may also be provided with only one low-voltage half-bridge module.

For another example, the controller for controlling the switching tube in the power electronic transformer may be configured with only a fault-ride-through control method in which the high-voltage side dc network has a short-circuit fault, or only a fault-ride-through control method in which the low-voltage side dc network has a short-circuit fault.

For another example, the primary/secondary side semiconductor converter unit may be implemented by using a push-pull circuit and a primary tap transformer in the prior art, as shown in fig. 11, in addition to the full-bridge module shown in fig. 2. Besides the symmetrical structure shown in fig. 2, the primary/secondary resonant network may also adopt a medium-asymmetrical structure (which is prior art and is not illustrated).

For another example, the processor in this embodiment may be a computer, a microprocessor, such as an ARM, or a programmable chip, such as an FPGA, a DSP, or the like.

Therefore, any modification, equivalent replacement, improvement or the like made within the spirit and principle of the present invention should be included in the scope of the claims of the present invention.

The embodiment of the control method comprises the following steps:

the high-voltage side of the power electronic transformer is provided with a high-voltage half-bridge module, the low-voltage side of the power electronic transformer is provided with a low-voltage half-bridge module, the high-voltage half-bridge module comprises a high-voltage upper arm branch and a high-voltage lower arm branch, the high-voltage upper arm branch is connected with the high-voltage lower arm branch, and the high-voltage lower arm branch is used for being connected with a high-voltage side direct-current power grid; the low-voltage half-bridge module comprises a low-voltage upper arm branch and a low-voltage lower arm branch, the low-voltage upper arm branch is connected with the low-voltage lower arm branch, and the low-voltage lower arm branch is used for connecting a low-voltage side direct-current power grid.

Based on the power electronic transformer with the high-voltage half-bridge module and the low-voltage half-bridge module, the embodiment provides a fault ride-through control method, which includes the following steps:

when a short-circuit fault occurs to a high-voltage side direct-current power grid, switching tubes of the high-voltage half-bridge module and the low-voltage half-bridge module are controlled to be turned off; after the short-circuit fault in the high-voltage side direct-current power grid is cleared, the corresponding switching tubes of the high-voltage half-bridge module are controlled to normally operate, the low-voltage upper arm branch in the low-voltage half-bridge module is controlled to be switched on, and the low-voltage lower arm branch in the low-voltage half-bridge module is controlled to be switched off, so that fault ride-through of the high-voltage side direct-current power grid with the short-circuit fault can be realized.

When the low-voltage side direct-current power grid has a short-circuit fault, the upper switching tube of the high-voltage half-bridge module is controlled to be switched on and the lower switching tube of the high-voltage half-bridge module is controlled to be switched off, and the switching tube of the low-voltage half-bridge module is controlled by adopting a voltage outer ring current inner ring to enable the low-voltage side direct-current voltage of the power electronic transformer to be stabilized at a set direct-current voltage instruction value. After the short-circuit fault in the low-voltage side direct-current power grid is cleared, the upper switching tube of the low-voltage half-bridge module is controlled to be switched on and the lower switching tube of the low-voltage half-bridge module is controlled to be switched off, and the corresponding switching tube of the high-voltage half-bridge module is controlled to normally operate, so that fault ride-through of the short-circuit fault of the low-voltage side direct-current power grid can be realized.

The fault ride-through control method of the present embodiment is not only applicable to the power electronic transformer shown in fig. 1, but also applicable to the fault ride-through control method of the present embodiment as long as the high-voltage half-bridge module is disposed on the high-voltage side and the low-voltage half-bridge module is disposed on the low-voltage side of the existing power electronic transformer.

As will be appreciated by one skilled in the art, embodiments of the present invention may be provided as a method, system, or computer program product. Accordingly, the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present invention 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 the like) having computer-usable program code embodied therein.

The present invention is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each flow and/or block of the flow diagrams and/or block diagrams, and combinations of flows and/or blocks in the flow diagrams 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.

While preferred embodiments of the present invention have been described, additional variations and modifications in those embodiments may occur to those skilled in the art once they learn of the basic inventive concepts. Therefore, it is intended that the appended claims be interpreted as including preferred embodiments and all such alterations and modifications as fall within the scope of the invention.

It will be apparent to those skilled in the art that various modifications and variations can be made in the embodiments of the present invention without departing from the spirit or scope of the embodiments of the invention. Thus, if such modifications and variations of the embodiments of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to encompass such modifications and variations.

Claims

1. A power electronic transformer, comprising:

the high-voltage half-bridge module comprises a high-voltage upper arm branch and a high-voltage lower arm branch which are connected, and the high-voltage lower arm branch is used as the high-voltage side of the module; the high-voltage side of the high-voltage half-bridge module of each module is connected with a bypass switch in parallel;

the self-blocking module is connected with the low-voltage side of each module in parallel, and comprises a low-voltage half-bridge module, wherein the low-voltage half-bridge module comprises a low-voltage upper arm branch and a low-voltage lower arm branch, the low-voltage lower arm branch is used for being connected with a low-voltage side direct-current power grid, and a total branch formed by connecting the low-voltage upper arm branch and the low-voltage lower arm branch is connected with the low-voltage side of each module in parallel;

when a certain module fails, the fault self-cutting method comprises the following steps:

1) the control system immediately blocks the driving pulses of all the switching tubes of the fault module;

2) issuing a bypass switch closing command of the fault module, and removing the fault module;

3) the control system recalculates the phase shifting angles of the carriers 1-N according to the total number of the currently operated modules and the positions of the fault modules, and switches the phase shifting angles;

the calculation principle of the phase shift angle of the carrier wave is as follows:

a) when no module fails, the phases of N carriers are sequentially different by 360 degrees/N;

b) when a module fails, the carrier phase shift angle of the failed module is respectively distributed to the next adjacent module without failure, all driving pulses of the failed module are blocked, and the failed module exits from operation after bypassing through a bypass switch; numbering the modules running in real time in sequence;

define module operation array A _ Run [ N ]]And assigning an initial value; defining a modular phase shift angle array A _ Theta [ N ]]And assigning an initial value; the fault information of each module is detected in real time in the operation process, the values of elements in the module operation array are updated according to the existence of faults, and the updating mode is as follows: the module runs the elements of the array A _ Run [ i ]]Means are as：

A_Run[i]The ith element in the module operation array is represented, i is 0,1,2, …, N-1; calculating the total number Run _ Num of the operation modules in real time according to the numerical values of the array elements of the module operation:

according to the total running number Run _ Num of the module and the element A _ Run [ i ] in the running array of the module]Calculating the carrier phase shift angle of each module, the carrier phase shift angle A _ Theta [ i ]]Comprises the following steps:

2. a power electronic transformer according to claim 1, characterised by a power electronic transformer consisting of more than two modules, each module having its high voltage side connected in series and its low voltage side connected in parallel.

3. A power electronic transformer according to claim 2, characterized in that a high-voltage side absorption loop is connected between the positive and negative poles of the high-voltage side of the series module; and a second inductor is arranged between the low-voltage lower arm branch and a low-voltage side direct-current power grid, and a low-voltage side absorption loop is connected between the positive electrode and the negative electrode of the output end of the low-voltage half-bridge module in the self-blocking module.

4. A power electronic transformer according to claim 3, characterized in that the low-voltage side absorption loop comprises a first absorption loop and a second absorption loop which are connected in parallel, and a first resistor and a first capacitor are arranged on the first absorption loop; and a second resistor, a second capacitor and a diode are arranged on the second absorption loop.

5. A fault-ride-through control method applied to the power electronic transformer in claim 1, characterized by comprising the following steps:

6. A fault-ride-through control method applied to the power electronic transformer in claim 1, characterized by comprising the following steps:

7. A power electronic transformer system, comprising a power electronic transformer according to any one of claims 1-4, and a controller connected to the switching tube of the power electronic transformer, the controller being configured to:

8. A power electronic transformer system, comprising a power electronic transformer according to any one of claims 1-4, and a controller connected to the switching tube of the power electronic transformer, the controller being configured to: