CN106707081A - Flexible DC power distribution network monopolar grounding fault identification and fault protection method - Google Patents

Abstract

The invention relates to a flexible DC power distribution network monopolar grounding fault identification and fault protection method. Positive and negative DC bus voltage to the ground is acquired, and the interpolar voltage change rate of positive and negative DC buses is acquired; and when the absolute value of the interpolar voltage change rate of the positive and negative DC buses is greater than a first comparison limit, pulse broadens t1 millisecond and the absolute value of the sum of the positive DC bus voltage to the ground and the negative DC bus voltage to the ground is greater than a second comparison limit and the time of duration exceeds a time limit, the judgment result indicates a monopolar grounding fault. According to the method, the monopolar grounding fault bus can be rapidly identified, and rapid isolation of the fault bus can be realized by tripping the DC circuit breaker of the grounding fault DC bus so as to enhance the power supply reliability of a DC power distribution network.

Description

The identification of flexible direct current power distribution network monopolar grounding fault, fault protecting method

Technical field

The invention belongs to Power Electronic Technique and DC distribution field, and in particular to the ground connection event of flexible direct current power distribution network monopole Barrier identification, fault protecting method.

Background technology

Multiterminal flexible direct current distribution system refers under same direct current rack, to contain more than 2 VSC (voltage source converters Device), the flexible direct current distribution system that change of current port DC side is connected with each other and constitutes by the way of in parallel or series.Modularization Relative to two traditional level or three level VSC, with being easy to, extension, harmonic distortion be small, switch is damaged for multilevel converter (MMC) The advantages of consumption is low, troubleshooting capability is strong, one of preferred transverter topology as flexible direct current power distribution network.

At present, the identification of direct current monopolar grounding fault and exclusion is realized by differential protection, when bus occurs monopole During metallic earthing failure, failure pole DC voltage is changed into 0, and non-faulting pole DC voltage is changed into 2 times of rated values, the electricity at failure Stream is smaller, influences the accuracy of fault detect.Also, the time for starting differential protection in the prior art is slower, if can not be fast Fast isolated fault bus, be likely to result in equipment overvoltage, start overvoltage protection, locking transverter and transverter it is out of service, shadow Ring the reliability of power supply.

The content of the invention

It is an object of the invention to provide a kind of identification of flexible direct current power distribution network monopolar grounding fault, fault protecting method, use In solving the problems, such as that prior art cannot accurately detect monopolar grounding fault.

In order to solve the above technical problems, the present invention proposes a kind of flexible direct current power distribution network monopolar grounding fault recognition methods, Including following five solutions：

Scheme one, comprises the following steps：

1) positive and negative dc bus voltage-to-ground is obtained, the voltage across poles rate of change of positive and negative dc bus is obtained；

2) when the absolute value of the voltage across poles rate of change of positive and negative dc bus compares limit value, pulse stretching t more than first₁ Millisecond, and positive direct-current Bus Voltage and negative dc bus voltage-to-ground and absolute value compare limit value more than second, institute When stating the duration over-time limit value for comparing limit value more than second, judge that current positive and negative dc bus occurs monopole ground connection Failure.

Scheme two, on the basis of scheme one, described first compares limit value is drawn by following formula：

dU_dcset=k_rel1dU_{dc_max_o}

In formula, dU_dcsetCompare limit value, dU for first_{dc_max_o}For monopolar grounding fault voltage change ratio absolute value is most outside area Big value, k_rel1It is the first setting safety factor.

Scheme three, on the basis of scheme two, described first compares limit value carries out sensitivity verification by following formula：

In formula, dU_{dc_min_i}It is monopolar grounding fault voltage change ratio absolute value minimum value, k in area_sen1It is the first sensitive system Number.

Scheme four, on the basis of scheme one, described second compares limit value is drawn by following formula：

dU_dcunbalset=k_rel2dU_{dcunbal_max_o}

In formula, dU_dcunbalsetCompare limit value, dU for second_{dcunbal_max_o}It is voltage caused by non-monopolar grounding fault outside area Uneven maximum absolute value value, k_rel2It is the second setting safety factor.

Scheme five, on the basis of scheme four, described second compares limit value carries out sensitivity verification by following formula：

In formula, dU_{dcunbal_min_i}It is monopolar grounding fault Voltage unbalance absolute value minimum value, k in area_sen2It is the second spirit Quick coefficient.

In order to solve the above technical problems, the present invention also proposes a kind of flexible direct current power distribution network monopolar grounding fault protection side Method, including following five solutions：

Scheme one, comprises the following steps：

1) positive and negative dc bus voltage-to-ground is obtained, the voltage across poles rate of change of positive and negative dc bus is obtained；

2) when the absolute value of the voltage across poles rate of change of positive and negative dc bus compares limit value, pulse stretching t more than first₁ Millisecond, and positive direct-current Bus Voltage and negative dc bus voltage-to-ground and absolute value compare limit value more than second, institute When stating the duration over-time limit value for comparing limit value more than second, judge that current positive and negative dc bus occurs monopole ground connection Failure；

3) trip command is sent to the dc circuit breaker of the positive and negative dc bus that monopolar grounding fault occurs, is disconnected described Positive and negative dc bus.

Scheme two, on the basis of scheme one, described first compares limit value is drawn by following formula：

dU_dcset=k_rel1dU_{dc_max_o}

In formula, dU_dcsetCompare limit value, dU for first_{dc_max_o}For monopolar grounding fault voltage change ratio absolute value is most outside area Big value, k_rel1It is the first setting safety factor.

Scheme three, on the basis of scheme two, described first compares limit value carries out sensitivity verification by following formula：

In formula, dU_{dc_min_i}It is monopolar grounding fault voltage change ratio absolute value minimum value, k in area_sen1It is the first sensitive system Number.

Scheme four, on the basis of scheme one, described second compares limit value is drawn by following formula：

dU_dcunbalset=k_rel2dU_{dcunbal_max_o}

In formula, dU_dcunbalsetCompare limit value, dU for second_{dcunbal_max_o}It is voltage caused by non-monopolar grounding fault outside area Uneven maximum absolute value value, k_rel2It is the second setting safety factor.

Scheme five, on the basis of scheme four, described second compares limit value carries out sensitivity verification by following formula：

In formula, dU_{dcunbal_min_i}It is monopolar grounding fault Voltage unbalance absolute value minimum value, k in area_sen2It is the second spirit Quick coefficient.

The beneficial effects of the invention are as follows：The present invention proposes a kind of flexible direct current power distribution network monopolar grounding fault identification, failure Guard method, can accurately detect monopolar grounding fault, and quickly recognize fault bus, and earth fault direct current occurs by tripping Dc circuit breaker where bus, realizes quickly isolating for fault bus, improves the power supply reliability of DC distribution net.

Brief description of the drawings

Fig. 1 is the flexible direct current power distribution network A stations monopolar grounding fault protection sketch of bus 1；

Fig. 2 is flexible direct current power distribution network monopolar grounding fault positioning logic block diagram.

Specific embodiment

Specific embodiment of the invention is further described below in conjunction with the accompanying drawings.

A kind of embodiment of flexible direct current power distribution network monopolar grounding fault guard method of the invention, comprises the following steps：

1) positive and negative dc bus voltage-to-ground is obtained, the voltage across poles rate of change of positive and negative dc bus is obtained；

2) when the absolute value of the voltage across poles rate of change of positive and negative dc bus compares limit value, pulse stretching t more than first₁ Millisecond, and positive direct-current Bus Voltage and negative dc bus voltage-to-ground and absolute value compare limit value more than second, institute When stating the duration over-time limit value for comparing limit value more than second, judge that current positive and negative dc bus occurs monopole ground connection Failure；

3) trip command is sent to the dc circuit breaker of the positive and negative dc bus that monopolar grounding fault occurs, is disconnected described Positive and negative dc bus.

Tetra- current conversion stations of A, B, C and D as shown in Figure 1 constitute a direct current by bus 1, bus 2, bus 3 and bus 4 Looped network.The two ends of dc bus install border of the direct current reactor as bus additional, and dc bus two ends are provided with dc circuit breaker, energy Enough in protection exit, powered rapid tripping, isolated fault bus.Control protective unit is arranged on the current conversion station at bus two ends It is interior, the dc circuit breaker for controlling dc bus two ends.

So that A stations bus 1 occurs monopolar grounding fault as an example, the positive DC voltage and negative pole of the A stations collection head end of bus 1 are straight Stream voltage, sample frequency is 10kHz.As shown in Fig. 2 Control protection system is according to the bus positive and negative electrode DC voltage for collecting, The rate of change of positive and negative electrode interpolar DC voltage is calculated, when the absolute value of voltage change ratio compares limit value more than first, shows this Bus there may be failure, and this signal is transient based protection signal, pulse stretching t₁Millisecond.Determining type is as follows：

Wherein, U_pIt is positive DC voltage, U_NIt is negative DC voltage, dt is the step-length of sampling, dU_dcsetCompare for first Limit value, adjusts first when comparing limit value, it should should avoid DC voltage change rate response caused by monopolar grounding fault outside area, lead to Following formula is crossed to be adjusted：

dU_dcset=k_rel1dU_{dc_max_o}

In formula, dU_dcsetCompare limit value, dU for first_{dc_max_o}For monopolar grounding fault voltage change ratio absolute value is most outside area Big value, k_rel1It is the first setting safety factor, k_rel1＞ 1.

Above-mentioned first compares after limit value adjusts, and sensitivity verification is carried out by following formula：

In formula, dU_{dc_min_i}It is monopolar grounding fault voltage change ratio absolute value minimum value, k in area_sen1It is the first sensitive system Number, k_sen1＞ 1.3.

Then bus positive and negative electrode DC voltage is sued for peace, and asks for absolute value, if this value compares limit value more than second and surpasses Cross time limit value t₂During millisecond, show that bus 1 there occurs monopolar grounding fault, this road signal is Voltage unbalance signal.Judge Formula is as follows：

|U_p+U_N| ＞ U_dcunbalset

In formula, U_dcunbalsetFor second compares limit value, adjust second when comparing limit value, non-monopole ground connection outside area should be avoided therefore DC voltage unbalance response, is adjusted by following formula caused by barrier：

dU_dcunbalset=k_rel2dU_{dcunbal_max_o}

In formula, dU_dcunbalsetCompare limit value, dU for second_{dcunbal_max_o}It is voltage caused by non-monopolar grounding fault outside area Uneven maximum absolute value value, k_rel2It is the second setting safety factor, k_rel2＞ 1.

Above-mentioned second compares after limit value adjusts, and sensitivity verification is carried out by following formula：

In formula, dU_{dcunbal_min_i}It is monopolar grounding fault Voltage unbalance absolute value minimum value, k in area_sen2It is the second spirit Quick coefficient.

After detecting the generation monopolar grounding fault of circuit 1, Control protection system sends trip signal to dc circuit breaker K1. Control protection system program performs the cycle for 100 μ s.

The flexible direct current power distribution network monopolar grounding fault guard method that the present invention is provided, can accurately detect monopole ground connection event Barrier, it is not necessary to rely on interior communication, quickly position and cut off faulty line, it is ensured that the power supply reliability of DC distribution net.

A kind of embodiment of flexible direct current power distribution network monopolar grounding fault recognition methods of the invention, comprises the following steps：

1) positive and negative dc bus voltage-to-ground is obtained, the voltage across poles rate of change of positive and negative dc bus is obtained；

2) when the absolute value of the voltage across poles rate of change of positive and negative dc bus compares limit value, pulse stretching t more than first₁ Millisecond, and positive direct-current Bus Voltage and negative dc bus voltage-to-ground and absolute value compare limit value more than second, institute When stating the duration over-time limit value for comparing limit value more than second, judge that current positive and negative dc bus occurs monopole ground connection Failure.

Monopolar grounding fault recognition methods of the invention is in a kind of above-mentioned flexible direct current power distribution network monopolar grounding fault It is described in detail in the embodiment of guard method, here no longer to flexible direct current power distribution network monopolar grounding fault identification side The embodiment of method is repeated.

The preferred embodiments of the present invention are the foregoing is only, is not intended to limit the invention, for those skilled in the art For member, the present invention can have various modifications and variations.All any modifications within the spirit and principles in the present invention, made, Equivalent, improvement etc., within the scope of should be included in claim of the invention.

Claims (10)

1. a kind of flexible direct current power distribution network monopolar grounding fault recognition methods, it is characterised in that comprise the following steps：

1) positive and negative dc bus voltage-to-ground is obtained, the voltage across poles rate of change of positive and negative dc bus is obtained；

2) when the absolute value of the voltage across poles rate of change of positive and negative dc bus compares limit value, pulse stretching t more than first₁Millisecond, And positive direct-current Bus Voltage and negative dc bus voltage-to-ground and absolute value compare limit value more than second, it is described to be more than Second compare limit value duration over-time limit value when, judge that current positive and negative dc bus occurs monopolar grounding fault.

2. flexible direct current power distribution network monopolar grounding fault recognition methods according to claim 1, it is characterised in that described One compares limit value is drawn by following formula：

dU_dcset=k_rel1dU_{dc_max_o}

In formula, dU_dcsetCompare limit value, dU for first_{dc_max_o}It is monopolar grounding fault voltage change ratio maximum absolute value value outside area, k_rel1It is the first setting safety factor.

3. flexible direct current power distribution network monopolar grounding fault recognition methods according to claim 2, it is characterised in that described One compares limit value carries out sensitivity verification by following formula：

$k_{sen1}=\frac{{\mathrm{dU}}_{dc\_\min \_i}}{{\mathrm{dU}}_{dcset}}$

In formula, dU_{dc_min_i}It is monopolar grounding fault voltage change ratio absolute value minimum value, k in area_sen1It is the first sensitivity coefficient.

4. flexible direct current power distribution network monopolar grounding fault recognition methods according to claim 1, it is characterised in that described Two compare limit value is drawn by following formula：

dU_dcunbalset=k_rel2dU_{dcunbal_max_o}

In formula, dU_dcunbalsetCompare limit value, dU for second_{dcunbal_max_o}For voltage is uneven caused by non-monopolar grounding fault outside area Weighing apparatus maximum absolute value value, k_rel2It is the second setting safety factor.

5. flexible direct current power distribution network monopolar grounding fault recognition methods according to claim 4, it is characterised in that described Two compare limit value carries out sensitivity verification by following formula：

$k_{sen2}=\frac{{\mathrm{dU}}_{dcunbal\_\min \_i}}{{\mathrm{dU}}_{dcunbalset}}$

In formula, dU_{dcunbal_min_i}It is monopolar grounding fault Voltage unbalance absolute value minimum value, k in area_sen2It is the second sensitive system Number.

6. a kind of flexible direct current power distribution network monopolar grounding fault guard method, it is characterised in that comprise the following steps：

1) positive and negative dc bus voltage-to-ground is obtained, the voltage across poles rate of change of positive and negative dc bus is obtained；

2) when the absolute value of the voltage across poles rate of change of positive and negative dc bus compares limit value, pulse stretching t more than first₁Millisecond, And positive direct-current Bus Voltage and negative dc bus voltage-to-ground and absolute value compare limit value more than second, it is described to be more than Second compare limit value duration over-time limit value when, judge that current positive and negative dc bus occurs monopolar grounding fault；

3) trip command is sent to the dc circuit breaker of the positive and negative dc bus that monopolar grounding fault occurs, is disconnected described positive and negative Dc bus.

7. flexible direct current power distribution network monopolar grounding fault guard method according to claim 6, it is characterised in that described One compares limit value is drawn by following formula：

dU_dcset=k_rel1dU_{dc_max_o}

In formula, dU_dcsetCompare limit value, dU for first_{dc_max_o}It is monopolar grounding fault voltage change ratio maximum absolute value value outside area, k_rel1It is the first setting safety factor.

8. flexible direct current power distribution network monopolar grounding fault guard method according to claim 7, it is characterised in that described One compares limit value carries out sensitivity verification by following formula：

$k_{sen1}=\frac{{\mathrm{dU}}_{dc\_\min \_i}}{{\mathrm{dU}}_{dcset}}$

In formula, dU_{dc_min_i}It is monopolar grounding fault voltage change ratio absolute value minimum value, k in area_sen1It is the first sensitivity coefficient.

9. flexible direct current power distribution network monopolar grounding fault guard method according to claim 6, it is characterised in that described Two compare limit value is drawn by following formula：

dU_dcunbalset=k_rel2dU_{dcunbal_max_o}

In formula, dU_dcunbalsetCompare limit value, dU for second_{dcunbal_max_o}For voltage is uneven caused by non-monopolar grounding fault outside area Weighing apparatus maximum absolute value value, k_rel2It is the second setting safety factor.

10. flexible direct current power distribution network monopolar grounding fault guard method according to claim 9, it is characterised in that described Second compares limit value carries out sensitivity verification by following formula：

$k_{sen2}=\frac{{\mathrm{dU}}_{dcunbal\_\min \_i}}{{\mathrm{dU}}_{dcunbalset}}$

In formula, dU_{dcunbal_min_i}It is monopolar grounding fault Voltage unbalance absolute value minimum value, k in area_sen2It is the second sensitive system Number.