CN113595040A - Annular direct-current micro-grid single-ended current type distance measurement method based on control and protection cooperation - Google Patents
Annular direct-current micro-grid single-ended current type distance measurement method based on control and protection cooperation Download PDFInfo
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- CN113595040A CN113595040A CN202110761198.5A CN202110761198A CN113595040A CN 113595040 A CN113595040 A CN 113595040A CN 202110761198 A CN202110761198 A CN 202110761198A CN 113595040 A CN113595040 A CN 113595040A
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
- H02H7/26—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured
- H02H7/268—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured for dc systems
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H1/00—Details of emergency protective circuit arrangements
- H02H1/0007—Details of emergency protective circuit arrangements concerning the detecting means
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H1/00—Details of emergency protective circuit arrangements
- H02H1/0061—Details of emergency protective circuit arrangements concerning transmission of signals
Abstract
The invention relates to a single-ended current type distance measurement method for an annular direct current microgrid based on control and protection cooperation, which comprises the following steps: a hybrid current limiter consisting of a hybrid direct current breaker and a current limiting resistor is connected in series at the VSC outlet; adding a boundary inductor and a boundary resistor in the annular direct-current micro-grid; configuring a current break variable and a voltage break variable of a direct-current side capacitor branch of each converter as starting criterion conditions of protection; when detecting that the annular direct-current micro-grid has an inter-electrode fault, realizing single-end fault location; when the fault distance measurement result is smaller than the length of the local line, the fault can be judged to be in the area, and then a tripping signal is sent to the second quick isolating switch, so that the fault is cleared, and power supply is recovered; if judge that the trouble takes place outside the district, when the electric current is zero, close the first quick isolator in the hybrid quick isolator, resume normal condition, after can't detect the fault current in the circuit, recover VSC, resume the power supply.
Description
Technical Field
The invention belongs to the field of relay protection of power systems, and particularly relates to a single-ended current type distance measurement technology of an annular direct-current micro-grid based on control and protection cooperation.
Background
The direct-current microgrid based on Pulse Width Modulation (PWM) has the advantages of low network loss, large transmission capacity, few conversion links, high electric energy quality and the like, is a power distribution mode that effectively utilizes distributed power sources, and becomes one of important networking modes of future smart power grids. However, in the low-voltage dc system, there are still more critical problems to be solved, and there are also many technical difficulties in fault current limiting, positioning and isolating.
At present, the research schemes for protecting the direct current system at home and abroad are mainly divided into two types. The first type is a protection scheme based on single-end quantity, and accurate fault location cannot be realized due to the problem that the electrical quantity of the opposite end is unknown. The second type is a protection scheme based on communication, which can effectively overcome the defects of a single-end quantity protection principle in a multi-end power supply system, has strong resistance to transition resistance, but has higher requirement on the synchronism of communication, and also can not meet the requirement on economy when a large number of communication devices are laid.
Disclosure of Invention
The invention aims to provide a single-ended current type distance measurement method for an annular direct-current microgrid, which can improve the power supply reliability of a direct-current microgrid system. The invention is based on the control and protection cooperation idea, the converter and an external controllable element are controlled to be changed into a single-ended alternating current power supply system, accurate distance measurement can be realized only by using single-ended current magnitude, direct current breakers are not required to be configured at two ends of a line, and fault isolation can be realized only by using a rapid isolating switch and a fault control strategy to carry out mutual coordination in time sequence logic, so that the reliability of power supply of the direct current microgrid system is improved. The technical scheme of the invention is as follows:
a single-ended current type distance measurement method for an annular direct-current micro-grid based on control and protection cooperation comprises the following steps:
(1) when the system normally operates, a hybrid current limiter consisting of a hybrid direct current breaker and a current limiting resistor is connected in series at the VSC outlet, and after a fault occurs, the hybrid current limiter is put into operation to play a role in limiting current and shortening alternating current follow current time;
(2) a boundary inductor and a boundary resistor are additionally arranged in the annular direct-current micro-grid, and the method comprises the following steps: the hybrid isolating switch is arranged at the head end of the positive pole and the tail end of the negative pole of each section of circuit, each hybrid isolating switch comprises a first fast isolating switch and a second fast isolating switch which are connected in parallel, and the second fast isolating switch is also connected with a boundary inductor and a boundary resistor in series; when the circuit works normally, the two quick isolating switches are both in a closed state;
(3) configuring a current break variable and a voltage break variable of a direct-current side capacitor branch of each converter as starting criterion conditions of protection;
(4) when detecting that the annular direct-current microgrid has an interelectrode fault, protecting the starting device, entering a fault control stage, at the stage, protecting and starting and locking the IGBT of the VSC in the system, simultaneously locking all DC/DC in the system, cutting off the load, and putting the current limiter into operation; the method comprises the steps that when current crosses zero, a first quick isolating switch is switched off, a boundary resistor and a boundary inductor are connected in series into a line, positive and negative currents in the line are not equal any more, accordingly, distance measurement is conducted, whether a fault occurs in a positive direction or not is determined through the current direction, if the current is in the reverse direction, locking is protected, if the current is in the positive direction, the inductance ratio from a fault point to the positive and negative lines at a VSC outlet is calculated through obtaining the ratio of the positive and negative currents, then the fault position can be solved according to the inductance ratio, and single-ended fault distance measurement is achieved;
(5) when the fault distance measurement result is smaller than the length of the local line, the fault can be judged to be in the area, and then a tripping signal is sent to the second quick isolating switch, so that the fault is cleared, and power supply is recovered; if judge that the trouble takes place outside the district, when the electric current is zero, close the first quick isolator in the hybrid quick isolator, resume normal condition, after can't detect the fault current in the circuit, recover VSC, resume the power supply.
Preferably, the boundary inductor and the boundary resistor additionally arranged in the ring-shaped direct-current microgrid are respectively 10% of the resistance and the inductance of the whole line.
Compared with the prior art, the invention has the following advantages:
1. the protection principle belongs to single-ended quantity protection, communication is not needed, accurate fault location can be achieved only by means of positive and negative electrode currents measured at a protection installation position, and the principle is simple and reliable.
2. In the calculation process of the fault distance, the transition resistance is eliminated, so that the ranging result is not influenced by the transition resistance in principle, and the practicability is high.
3. Compared with the original differential equation solving algorithm, the principle only utilizes single-ended current magnitude, does not need to collect voltage magnitude, and does not have calculation errors brought by solving differential, so the measurement precision is very high.
4. In the fault isolation scheme, a direct-current breaker is not needed, fault isolation can be achieved only by using a quick isolating switch, the cost of the direct-current microgrid is further reduced, and the economy is good.
Drawings
Fig. 1 is a four-terminal ring-shaped direct-current microgrid topology;
FIG. 2 is a schematic diagram of a VSC topology conversion process;
FIG. 3 is a hybrid isolator topology;
FIG. 4 is a schematic diagram of a fault current loop;
FIG. 5 is a fault loop equivalent diagram;
FIG. 6 is a timing diagram of a protection action policy.
Detailed Description
Because a large number of controllable elements exist in the direct-current microgrid, a physical implementation foundation is laid for the protection scheme provided by the invention. The method is based on the control and protection coordination idea, the control strategy of the current converter in the system is tightly combined with the protection scheme, the interference of opposite-end current in single-end fault location of the loop system is eliminated, direct-current circuit breakers are not needed to be arranged at two ends of a line, and fault isolation can be realized only by utilizing the mutual coordination of the quick isolating switch and the fault control strategy in time sequence logic, so that the reliability of power supply of the direct-current microgrid system is improved.
The technical scheme of the invention is divided into the following three stages:
1. fault control phase
When the annular direct-current microgrid detects that an inter-electrode fault occurs, the protection is started, the system enters a fault control stage, the IGBT of the VSC in the system is started and locked in a protection mode, all DC/DC in the system are locked at the same time, loads are removed, and the current limiter is put into the system to operate. And the topology conversion of the system is completed, and the annular direct-current micro-grid is equivalent to an alternating-current power supply to discharge to a fault point. Due to the unidirectional conductivity of the diodes in the VSC, the current is conducted in the time when the equivalent voltage source is positive, and the line current crosses zero after freewheeling due to the action of the inductance in the line in the time when the equivalent voltage source is negative. In order to shorten the follow current time, a resistance current limiter is additionally arranged at the VSC outlet. By adjusting the selection value of the resistor, the time of the circuit current being zero in one power frequency period (20ms) can be 10 ms.
2. Protection enforcement phase
The artificial boundary inductance and resistance are added in the looped network, and the size of the artificial boundary inductance and resistance is 10% of the whole line resistance and inductance. As shown in figure 1, in a clockwise direction, a hybrid isolating switch as shown in figure 3 is arranged at the head end of the positive pole and the tail end of the negative pole of each section of circuit, QS1 and QS2 are both quick isolating switches, and only the quick isolating switches are arranged at other positions. In normal operation both QS1 and QS2 are in a closed state. After a fault occurs, the QS1 is disconnected when the current crosses zero, the resistor and the reactor are connected in series in the circuit, so that the currents of the positive electrode and the negative electrode in the circuit are unequal, whether the fault occurs in the positive direction or not is determined according to the current direction, and then the fault position is determined according to the ratio of the currents of the positive electrode and the negative electrode measured at the protection installation position.
3. Fault isolation phase
If the fault occurs in the area, the QS2 is tripped in 10ms of the zero crossing of the current, and then fault isolation can be realized; if not, when the current is zero, QS1 in the hybrid fast isolating switch is switched on, and the switch returns to a normal state. When no fault current is detected in the line, fault isolation may be verified to be complete. Can restore the VSC this moment, make the system resume normal to resume the power supply.
Fig. 1 shows a four-terminal ring-shaped dc microgrid topology, and the damage of the inter-pole fault is more serious compared to the single-pole ground fault, so the inter-pole fault is only considered in the present invention, fig. 6 is a protection action strategy diagram, and the present invention is further described in detail with reference to the attached drawings. The specific protection scheme is as follows:
1. the mixed isolating switch as shown in figure 3 is arranged at the head end of the positive pole and the tail end of the negative pole of each section of the circuit in a clockwise direction; and configuring a current sudden change amount and a voltage sudden change amount of a direct-current side capacitor branch of each converter as a starting criterion condition of protection.
2. After the protection device is started, the load is disconnected, and short-time load crossing is realized. Meanwhile, all DC/DC converters and IGBTs and thyristors in the VSC are locked, and fig. 2 is a schematic diagram of a VSC topology conversion process.
3. When the system normally operates, the resistance and the inductance in the hybrid quick isolating switch are not put into the circuit. After a fault occurs, within a time period of 10ms when the fault current of the line is zero, the QS1 in the figure 3 is disconnected, the resistor and the inductor are connected in series into the line, so that the positive and negative currents at the protection installation position are not equal, whether the fault occurs in the positive direction is determined by the current direction, and then whether the fault occurs in the area is determined according to a single-ended distance measurement method. If yes, jumping off QS2 within 10ms of current zero crossing, and then realizing fault isolation; if not, when the current is zero, QS1 in the hybrid fast isolating switch is switched on, and the switch returns to a normal state. The ranging is specifically described as follows.
Taking the inter-electrode fault of the line 2 as an example, assuming that the distance between the fault point and the protection device PD32 is x, if the fault occurs in the positive direction of the protection installation, the positive-negative current ratio i measured by the protection device PD32 is2/i4Will be shown below.
From the above formula, the positive-negative current ratio i measured by the protection device PD322/i4Will increase with increasing x, the fault distance can be uniquely calculated from the value of i2/i4, and the protection is able to accurately distinguish between internal and external faults in the positive direction zone due to the presence of the boundary elements. If the fault occurs in the opposite direction, the fault direction can be accurately judged according to the positive and negative currents, so that the protection scheme can accurately distinguish the internal fault from the external fault.
4. When no fault current is detected in the line, fault isolation may be verified to be complete. Can restore the VSC this moment, make the system resume normal to resume the power supply. The total time from the occurrence of the fault to the restoration of the power supply is less than 55 ms.
In summary, a timing diagram of the protection action strategy is shown in FIG. 6. The distance measuring method provided by the invention only needs to collect a 1ms data window at the shortest time. During simulation, factors such as action reliability, engineering practice and the like are comprehensively considered, and the data sampling frequency can be 20 kHz.
Claims (2)
1. A single-ended current type distance measurement method for an annular direct-current micro-grid based on control and protection cooperation comprises the following steps:
(1) when the system normally operates, a mixed current limiter consisting of a mixed direct current breaker and a current limiting resistor is connected in series at the VSC outlet, and after a fault occurs, the mixed current limiter is put into operation to play a role in limiting current and shortening alternating current follow current time.
(2) A boundary inductor and a boundary resistor are additionally arranged in the annular direct-current micro-grid, and the method comprises the following steps: the hybrid isolating switch is arranged at the head end of the positive pole and the tail end of the negative pole of each section of circuit, each hybrid isolating switch comprises a first fast isolating switch and a second fast isolating switch which are connected in parallel, and the second fast isolating switch is also connected with a boundary inductor and a boundary resistor in series; when the circuit works normally, the two quick isolating switches are both in a closed state;
(3) configuring a current break variable and a voltage break variable of a direct-current side capacitor branch of each converter as starting criterion conditions of protection;
(4) when detecting that the annular direct-current microgrid has an interelectrode fault, protecting the starting device, entering a fault control stage, at the stage, protecting and starting and locking the IGBT of the VSC in the system, simultaneously locking all DC/DC in the system, cutting off the load, and putting the current limiter into operation; the method comprises the steps that when current crosses zero, a first quick isolating switch is switched off, a boundary resistor and a boundary inductor are connected in series into a line, positive and negative currents in the line are not equal any more, accordingly, distance measurement is conducted, whether a fault occurs in a positive direction or not is determined through the current direction, if the current is in the reverse direction, locking is protected, if the current is in the positive direction, the inductance ratio from a fault point to the positive and negative lines at a VSC outlet is calculated through obtaining the ratio of the positive and negative currents, then the fault position can be solved according to the inductance ratio, and single-ended fault distance measurement is achieved;
(5) when the fault distance measurement result is smaller than the length of the local line, the fault can be judged to be in the area, and then a tripping signal is sent to the second quick isolating switch, so that the fault is cleared, and power supply is recovered; if judge that the trouble takes place outside the district, when the electric current is zero, close the first quick isolator in the hybrid quick isolator, resume normal condition, after can't detect the fault current in the circuit, recover VSC, resume the power supply.
2. The single-ended current type distance measurement method for the annular direct-current microgrid according to claim 1, characterized in that the boundary inductor and the boundary resistor additionally installed in the annular direct-current microgrid are respectively 10% of the whole line resistor and inductor.
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN114720902A (en) * | 2022-04-07 | 2022-07-08 | 国网黑龙江省电力有限公司佳木斯供电公司 | Direct-current power supply fault rapid isolation system for transformer substation |
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Patent Citations (6)
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| CN109188188A (en) * | 2018-07-10 | 2019-01-11 | 国网浙江省电力有限公司杭州供电公司 | The single-ended method of discrimination of Multi-end flexible direct current transmission line fault based on voltage monitoring |
| CN109950884A (en) * | 2019-03-14 | 2019-06-28 | 天津大学 | A kind of annular direct current micro-grid system distance measuring type guard method for protecting collaboration based on control |
| CN110148929A (en) * | 2019-06-10 | 2019-08-20 | 天津大学 | A kind of single-ended guard method of annular direct-current micro-grid for protecting collaboration based on control |
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| CN114720902A (en) * | 2022-04-07 | 2022-07-08 | 国网黑龙江省电力有限公司佳木斯供电公司 | Direct-current power supply fault rapid isolation system for transformer substation |
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