阅读说明：本技术 一种适用于大功率电压源型变流器的快速保护电路 (Quick protection circuit suitable for high-power voltage source type converter ) 是由 陈晓娇 王震 黄连生 张秀青 何诗英 于 2021-06-23 设计创作，主要内容包括：本发明公开了一种适用于大功率电压源型变流器的快速保护电路,包括并联的熔断支路和泄能支路,所述熔断支路包括第一熔断支路、第二熔断支路；所述泄能支路包括第一泄能支路、第二泄能支路；第一熔断支路包括与直流侧电容C-1串联的第一快速熔断器Fuse1；第一泄能支路由晶闸管开关V-1和续流二极管D-1反并联后,再与泄能电阻R-1串联组成；第二熔断支路包括与直流侧电容C-2串联的第二快速熔断器Fuse2；第二泄能支路由晶闸管开关V-2和续流二极管D-2反并联后,再与泄能电阻R-2串联组成。通过直流侧电容支路串联快速熔断器,同时并联泄能支路。本发明技术方案能够有效减小快速熔断器常规保护电路中的弧前时间,降低故障支路的电流峰值,达到保护变流器功率器件的目的。(The invention discloses a quick protection circuit suitable for a high-power voltage source type converter, which comprises a fusing branch and an energy-releasing branch which are connected in parallel, wherein the fusing branch comprises a first fusing branch and a second fusing branch; the energy leakage branch comprises a first energy leakage branch and a second energy leakage branch; the first fuse branch comprises a capacitor C on the DC side 1 A first fast Fuse1 in series; the first energy-discharging branch is switched by a thyristor 1 And a freewheeling diode D 1 After being connected in inverse parallel, the energy leakage resistor R is connected with the energy leakage resistor 1 Are connected in series; the second fuse branch comprises a capacitor C on the DC side 2 A second fast Fuse2 in series; second energy-discharging branch route thyristor switch V 2 And a freewheeling diode D 2 After being connected in inverse parallel, the energy leakage resistor R is connected with the energy leakage resistor 2 Are connected in series. The direct current side capacitor branch is connected with the fast fuse in series and is connected with the energy discharge branch in parallel. The technical scheme of the invention can effectively reduceThe small fast fuse protects the time before arc in the circuit conventionally, reduces the current peak value of the fault branch, and achieves the purpose of protecting the power device of the converter.)

1. A fast protection circuit suitable for a high-power voltage source type converter is characterized in that:

the fuse protector comprises a fusing branch and an energy discharging branch which are connected in parallel, wherein the fusing branch comprises a first fusing branch and a second fusing branch; the energy leakage branch comprises a first energy leakage branch and a second energy leakage branch;

the first fuse branch comprises a capacitor C on the DC side₁A first fast Fuse1 in series;

the first energy-discharging branch is switched by a thyristor₁And a freewheeling diode D₁After being connected in inverse parallel, the energy leakage resistor R is connected with the energy leakage resistor₁Are connected in series;

the second fuse branch comprises a capacitor C on the DC side₂A second fast Fuse2 in series;

second energy-discharging branch route thyristor switch V₂And a freewheeling diode D₂After being connected in inverse parallel, the energy leakage resistor R is connected with the energy leakage resistor₂Are connected in series.

2. The fast protection circuit for high power voltage source type current transformer as claimed in claim 1, wherein:

each group of direct current side capacitors of each high-power voltage source type converter is provided with a group of fusing branch circuits and energy discharging branch circuits which are connected in parallel; upper bridge arm thyristor switch V₁The positive pole is connected with the positive bus of the voltage source type converter, R₁A thyristor switch V connected with the midpoint potential of the voltage source converter and arranged on the lower bridge arm₂The positive pole is connected with the midpoint potential of the voltage source type converter, R₂Is connected with the negative bus of the voltage source type converter.

3. The fast protection circuit for high power voltage source type current transformer as claimed in claim 1, wherein: the fusing branch is used for timely cutting off the capacitor branch under the condition of a fault; the energy discharge branch circuit is used for sharing a part of capacitor fault current, improving the current initial value of the capacitor at the initial moment of the fault and reducing the time before the arc of the fast fuse.

4. The fast protection circuit for high power voltage source type current transformer as claimed in claim 1, wherein: the first and the second fast fuses Fuse1 and Fuse2 are selected, and the rated voltage U is_NThe calculation is performed by equation (1), where: u shape_NCIs a capacitor C₁Or C₂The rated voltage of (3).

U_N≥U_NC (1)

Rated current I thereof_NThe calculation is performed by equation (2):

wherein: i is_RMSRepresenting the current root mean square value of the capacitor branch circuit in a steady state; g represents an unbalance coefficient; k_tRepresenting the correction coefficient of the ambient temperature, K if the ambient temperature exceeds 30 DEG C_tCalculated from equation (3):

θ_αrepresents the ambient temperature; k_vRepresents a cooling correction coefficient; k_bRepresenting a connection coefficient;

according to the rated voltage U of the fast fuse_NAnd rated current I_NAnd determining the specific model of the fast fuse.

5. The fast protection circuit for high power voltage source type current transformer as claimed in claim 1, wherein: the protection circuit is used for verifying, and respectively carrying out on the breaking capacity of the fast fuse and the square time product I of the current of the fast fuse²And t, verifying surge current of the IGCT device and arcing overvoltage of the quick fuse.

Technical Field

The invention relates to the field of high-power voltage source type converter systems, and mainly applies the technology to the design of a quick protection circuit under the condition of short-circuit fault of a high-power voltage source type converter.

Background

Due to the existence of the direct-current side capacitor, when a bridge arm of the converter has a short-circuit fault, the direct-current side capacitor and the short-circuit bridge arm form a closed loop, so that huge short-circuit impact current is caused, the influence of the fault condition is the worst, and irreversible damage is caused to an equipment structure and a semiconductor power device. The design of the protection circuit is therefore particularly important.

A high-power voltage source type converter short-circuit protection circuit based on a fast fuse mainly comprises the fast fuse connected in series at a bridge arm, the fast fuse connected in series on a direct current bus and a direct current side capacitor series fast fuse. The conventional protection circuits are commonly used for converter systems with medium and small power levels, when the converter power level is high, the capacitance value of a direct-current side capacitor is high, the change rate and the peak value of fault current are high, the critical time of damage of a semiconductor power device is short, and the pre-arc time of a fast fuse in the conventional protection circuit is long, so that the semiconductor power device of the converter cannot be effectively protected.

Disclosure of Invention

The invention aims to provide a novel protection circuit based on a fast fuse, and aims to solve the problems that the fast fuse in the prior art is long in pre-arc time and large in current peak value of a fault branch.

The invention provides a rapid protection circuit suitable for a high-power voltage source type converter,

the fuse protector comprises a fusing branch and an energy discharging branch which are connected in parallel, wherein the fusing branch comprises a first fusing branch and a second fusing branch; the energy leakage branch comprises a first energy leakage branch and a second energy leakage branch;

the first fuse branch comprises a capacitor C on the DC side₁A first fast Fuse1 in series;

first branch of energy dischargeRoute thyristor switch V₁And a freewheeling diode D₁After being connected in inverse parallel, the energy leakage resistor R is connected with the energy leakage resistor₁Are connected in series;

the second fuse branch comprises a capacitor C on the DC side₂A second fast Fuse2 in series;

second energy-discharging branch route thyristor switch V₂And a freewheeling diode D₂After being connected in inverse parallel, the energy leakage resistor R is connected with the energy leakage resistor₂Are connected in series.

The fast fuses Fuse1 and Fuse2 are selected and have rated voltage U_NRated current I_NThe theoretical calculation formula of (1) is as follows:

U_N≥U_NC (1)

wherein: u shape_NCThe rated voltage of the capacitor.

Wherein: i is_RMSRepresenting the current root mean square value of the capacitor branch circuit in a steady state; g represents an unbalance coefficient; k_tWhich represents an ambient temperature correction coefficient, if the ambient temperature exceeds 30 c,

θ_αrepresents the ambient temperature; k_vRepresents a cooling correction coefficient; k_bRepresenting the connection coefficient.

According to the rated voltage U of the fast-acting fuse_NAnd rated current I_NThe specific model of the fast fuse is determined.

The novel protection circuit is used for verifying and respectively carrying out on-off capacity of the fast fuse and current square time product I of the fast fuse²And t, verifying surge current of the IGCT device and arcing overvoltage of the quick fuse.

The invention has the beneficial effects that:

by adopting the novel protection circuit of the quick fuse, the time before the arc of the quick fuse can be effectively reduced, and the current peak value of a fault branch circuit is reduced to be lower than the critical point of the damage of a semiconductor power device, so that the protection purpose is achieved.

Drawings

FIG. 1 is a topology diagram of a single-phase bridge arm of a three-level voltage source type converter;

FIG. 2 is a schematic diagram of the novel protection circuit of the fast fuse of the present invention;

FIG. 3 is an equivalent circuit diagram of the protection circuit of the present invention;

FIG. 4 is a schematic diagram of an experimental circuit of the protection circuit of the present invention;

FIG. 5 is a fault current waveform diagram of the protection circuit of the present invention;

FIG. 6 is a waveform diagram of a fault in a conventional protection circuit of the fast fuse of the present invention;

FIG. 7 is a fault waveform diagram of the novel protection circuit of the fast fuse of the present invention.

Detailed Description

The technical solutions in the embodiments of the present invention will be described clearly and completely with reference to the accompanying drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, rather than all embodiments, and all other embodiments obtained by a person skilled in the art based on the embodiments of the present invention belong to the protection scope of the present invention without creative efforts.

As shown in FIG. 1, the single-phase bridge arm of the three-level voltage source type converter is composed of four fully-controlled devices IGCT (T)_a1、T_a2、T_a3And T_a4) And its anti-parallel diode (D)_a1、D_a2、D_a3And D_a4) In series, D_a5And D_a6To clamp a diode, L_a1-D_a7-R_a1-C_a1And L_a2-D_a8-R_a2-C_a2To buffer the absorption circuit, C₁And C₂Is a midpoint clamp capacitance. When the converter is working normally, T_a1、T_a2、T_a3And T_a4Two adjacent IGCTs are conducted in sequence, when one IGCT is conducted in error, three adjacent IGCTs of the same bridge arm are conducted simultaneously and are connected with the direct current sideThe capacitor forms a closed loop and generates a great pulse current in a short time.

As shown in FIG. 1, three IGCTs (T) are arranged on a single-phase upper bridge arm of a three-level voltage source type converter_a1、T_a2And T_a3) Simultaneous conduction, assuming current flow is through capacitor C₁The direction of the flow direction positive bus is positive. When the capacitance C₁When discharging in the forward direction, the fault current path is C₁-L_a1-T_a1-T_a2-T_a3-D_a6-C₁As shown in dashed lines in fig. 1; when the capacitance C₁When discharging reversely, the fault current path is C₁-D_a5-D_a1-L_a1-C₁As shown in solid lines in fig. 1.

As shown in FIG. 2, a fast protection circuit for a high power voltage source converter, a DC side capacitor C₁The protection circuit is composed of a fusing branch and an energy-discharging branch in parallel, wherein the first fusing branch is composed of a fast Fuse1 and a direct-current side capacitor C₁Are connected in series; the first energy-discharging branch is switched by a thyristor₁And a freewheeling diode D₁After being connected in inverse parallel, the energy leakage resistor R is connected with the energy leakage resistor₁Are connected in series. DC side capacitor C₂The same applies to the protection circuit. Wherein, the energy leakage resistor R₁Connected in parallel to a capacitor C₁Two ends of branch, thyristor V₁Is connected in series to R₁Branch line, V₁Positive electrode connected to positive bus-bar, V₁Negative electrode and R₁Connected, diode D₁And thyristor V₁And are connected in anti-parallel.

The Fuse1 selection of the fast Fuse in the protection circuit mainly relates to 2 parameters.

Parameter 1: rated voltage U_N. The voltage rating of the fast fuse should be chosen to be slightly greater than the voltage rating of the capacitor with some margin left. The rated voltage theoretical calculation of the fast fuse is determined by the formula (1);

U_N≥U_NC (1)

wherein: u shape_NCThe rated voltage of the capacitor.

Parameter 2: rated current I_N. In practical application, the rated current of the fast fuse needs to be consideredFor simplicity, the theoretical calculation of the rated current of the fast fuse is determined by equation (2) for the effects of factors such as ambient temperature, heat dissipation conditions, connector size, etc.:

wherein: i is_RMSRepresenting the current root mean square value of the capacitor branch circuit in a steady state; g represents an unbalance coefficient; k_tWhich represents an ambient temperature correction coefficient, if the ambient temperature exceeds 30 c,

θ_αrepresents the ambient temperature; k_vRepresents a cooling correction coefficient; k_bRepresenting the connection coefficient.

The equivalent circuit of the protection circuit of the present invention is shown in FIG. 3, wherein u_dcRepresenting the capacitor voltage; c₁Represents the dc side capacitance; r₁Representing a discharge resistance; l represents the equivalent resistance of the short circuit bridge arm; r represents the equivalent inductance of the short circuit bridge arm; i.e. i_CRepresents the capacitor discharge current; i.e. i₁Indicating the flow of energy through the dump resistor R₁The fault current of (2); i.e. i_fIndicating a fault current flowing through the short-circuit leg IGCT device. Neglecting to let out can branch circuit thyristor turn-on time, carry out the check-up to novel protection circuit, specifically as follows:

step 1: and (6) fault simulation.

The fault was simulated in MATLAB/Simulink, set to start at time 0, with a crystal simulation time of 10ms, and the simulation results are shown in fig. 4. Wherein: i.e. i_CRepresenting the current flowing through the capacitor C₁Processing a fault current waveform; i.e. i₁Representing the current flowing through the energy discharge resistor R₁A branch fault current waveform; i.e. i_fAnd the waveform of the fault current flowing through the IGCT device of the short-circuit bridge arm is shown.

Step 2: and checking the breaking capability of the fast fuse.

The breaking capability of the fast fuse should be greater than the maximum effective value of the fault current, i.e.:

I_break＞I_p (4)

wherein, I_breakIs the rated breaking current value of the fast-acting fuse, and comes from a device manual; i is_pIs the maximum expected fault current effective value.

And step 3: square time product of current I of fast fuse²And (t) checking.

For IGCT semiconductor devices, there is a critical parameter current squared time product I²t, which is also a criterion for damage to IGCT devices. The judgment standard is as follows:

I²t_Fuse1＝k₁×I²t_Fuse1＜0.9×I²t_IGCT (5)

wherein: k is a radical of₁Indicating the total of the flash fuses I²t correction coefficients, from device handbook; 0.9 is a safety margin and the subscript Fuse1 represents the calculation for the first Fuse, Fuse1, and the same for the second Fuse.

And 4, step 4: and checking the surge current of the IGCT device.

For IGCT semiconductor device, there is a critical parameter of on-state unrepeated surge current I_TSMThis is also the criterion for damage to IGCT devices. The judgment standard is as follows:

I_fmax(tp)＜I_TSM (6)

wherein: i is_fmax(tp)Indicating the pre-arc time t of the fast-acting fuse_pA short-circuit bridge arm fault current peak value corresponding to the moment;

and 5: and (4) checking the arcing overvoltage of the fast fuse.

The flash-fuse arcing generates an overvoltage exceeding the supply voltage, which must be less than the off-repeat peak voltage V of the IGCT device_DRMAnd the IGCT device is prevented from being damaged. The judgment standard is as follows:

V_arc＜V_DRM (7)

wherein: v_arcThe arcing overvoltage corresponding to the actual operating voltage of the fast fuse is indicated from the device manual.

Step 6: and (5) experimental verification.

As shown in fig. 5, a comparative experiment circuit is designed to verify the effectiveness of the protection circuit of the present invention. Wherein: e.g. of the type_sIndicating the charging machine by controlling the thyristor switch V₃Conducting to charge the capacitor bank; c₁Represents a capacitor bank; fuse1 denotes a fast-acting Fuse; l, R denote inductive and resistive loads, respectively; r₁Indicating the energy leakage resistance. Respectively at Fuse1 and energy-discharging resistor R₁The branch circuit and the load branch circuit are provided with current sensors for measuring the current of the three places as i_C、i₁、i_f(ii) a Connecting high-voltage differential probe at two ends of capacitor, and measuring its voltage as u_dc. By controlling thyristor switch V₁The connection and disconnection of the energy discharge resistance branch can be realized.

The experimental parameters are shown in tables 1 and 2.

TABLE 1 Experimental Circuit related parameters

TABLE 2Ferraz Corp 70 tube fast fuse parameters

Experiment 1: the fast fuse conventional protection circuit.

First of all, the thyristor switch V is controlled₁Disconnecting, wherein the energy leakage resistance branch is not connected; then charger e_sTo the capacitor bank C according to a predetermined voltage₁Charging is carried out, and charging is waited to be completed; finally the thyristor switch V is switched off₃Turn-on thyristor switch V₂Capacitor bank C₁And a load branch resistance inductor RL form a second-order discharge loop. The Fuse1 will normally blow, and the capacitance voltage u at this stage is measured_dcAnd fault current i_f(i_f＝i_C) Can obtain the pre-arc time t of the fast fuse_p1And t_p1Fault current peak value I corresponding to time_f1(max)。

Experiment 2: novel protection circuit of fast acting fuse.

First of all, the thyristor switch V is controlled₁The energy leakage resistance branch is connected to the main circuit at the moment; then charger e_sTo the capacitor bank C according to a predetermined voltage₁Charging is carried out, and charging is waited to be completed; finally the thyristor switch V is switched off₃Turn-on thyristor switch V₂Capacitor bank C₁And simultaneously discharging the load branch RL and the energy leakage resistance branch. Measuring the capacitor voltage u at this stage_dcAnd fault current i_C、i₁、i_fCan obtain the pre-arc time t of the fast fuse_p2And t_p2Fault current peak value I corresponding to time_f2(max)。

As shown in fig. 6, the conventional protection circuit fault waveform of the fast fuse. At the initial stage of the occurrence of a fault, a fault current i_fRapidly rising, capacitor voltage u_dcRapidly decreases to the pre-arc time t of the fast fuse_p1Time, fault current i_fDecays rapidly and eventually falls to zero. The pre-arc time t of the fast fuse can be obtained by observing the experimental waveform_p1260us, fault current peak I_f1(max)＝6.15kA。

As shown in fig. 7, the novel protection circuit of the fast fuse has a fault waveform. At the initial stage of failure, the capacitor voltage u_dcRapidly decreasing, fault current i_fRapidly increasing from zero, fault current i₁Starting from a maximum value of 3.53kA, the fault current i_CIs i₁And i_fDue to the energy-discharging resistance R₁Shunting of the branch, fault current i_CThe initial value increased, rising rapidly from 3.53 kA. Before arc time t of fast fuse_p2At that time, since the fast fuse becomes a high resistance state, a fault current i_CAnd i_fDecays rapidly to zero. The inductor L is operated by follow current, and the capacitor bank C₁Form a closed loop 1, and a discharge resistor R₁Diode D₁Form a closed loop 2, so that the fault current i_fGradually decreases to zero, and the fault current i₁First, the increase is reversed, and finally, the synchronization is reduced to zero. The pre-arc time t of the fast fuse can be obtained by observing the experimental waveform_p2140us, fault current peak I_f2(max)＝4.05kA。

Therefore, compared with the conventional protection circuit, the protection circuit of the invention has the advantage that the pre-arc time t of the fast fuse_pChanging from 260us to 140us, the fault current peak value I of the load branch_f(max)The change from 6.15kA to 4.05kA was significant.

The present invention has been described in detail with reference to the specific embodiments and examples, but these are not intended to limit the present invention. Without departing from the principles of the present invention, those skilled in the art may change and apply the structure and parameters of different voltage source converter systems, and may also perform the changes and applications according to the actual situation.