A DC system AC inrush protection device and protection method

Abstract

The present invention discloses a DC system AC inrush protection device, the protection device is connected in series with the protected load into the branch; the protection device includes a capacitor, an inductor and a circuit breaker; the inductor is arranged in the branch and connected in series with the load in the branch; the capacitor is connected in parallel with the branch, one end of the capacitor is connected to the inductor and the other end is grounded; based on the needs of the protected load, the circuit breaker has two placement methods to be set in the circuit, when the protected load only needs alarm protection, the circuit breaker adopts two 1P circuit breakers to be set in the circuit in series with the capacitor; when the protected load needs to cut off the branch protection, the circuit breaker adopts a single 2P circuit breaker to be placed in the branch in series with the load. The device of the present invention has a simple structure and convenient parameter determination. It can choose to directly short-circuit or perform AC inrush alarm according to needs, effectively avoiding the impact of AC inrush on the load in the DC system.

Description

Technical Field

[0001] The present invention relates to an AC inrush protection device for a DC system, and also relates to a protection method for the protection device. Background Art

[0002] In recent years, the DC power distribution system has been widely used and studied because it can easily accept distributed power generation and has the advantages of high efficiency, low loss and high reliability. However, some problems have also appeared in the actual operation of the DC power distribution system. Since DC and AC form a hybrid AC / DC distribution network, AC may enter the DC power supply and load due to various reasons. The AC enters the DC fault and is difficult to detect and requires rapid protection.

[0003] There are already some methods for detecting AC inrush faults in DC systems, including finders and ground voltage detection. However, the accuracy of finders is poor and they are not easy to operate. The speed of ground voltage detection is slow and needs to be coordinated with other devices to achieve protection. Summary of the invention

[0004] Purpose of the invention: One of the purposes of the present invention is to provide an AC inrush protection device for a DC system with high search accuracy and fast detection speed; another purpose of the present invention is to provide a protection method for the above protection device, which can choose to directly disconnect the circuit or perform an AC inrush alarm according to needs, thereby effectively avoiding the impact of AC inrush on the load in the DC system.

[0005] Technical solution: The DC system AC inrush protection device described in the present invention is connected in series with the protected load into the branch, and the protection device includes a capacitor, an inductor and a circuit breaker; the inductor is arranged in the branch and is connected in series with the load in the branch, the capacitor is connected in parallel with the branch, one end of the capacitor is connected to the inductor and the other end is grounded; based on the needs of the protected load, the circuit breaker has two placement methods in the circuit, when the branch needs to be cut off when AC inrushes, the circuit breaker is placed in the branch in series with the load in the form of a single 2P circuit breaker; when only an alarm is required when AC inrushes, the circuit breaker is placed in the circuit in series with the capacitor in the form of two 1P circuit breakers.

[0006] Among them, when only an alarm is required when AC is injected, the circuit breaker adopts the form of two 1P circuit breakers and is connected in series with a capacitor, and the circuit breaker is connected to a circuit breaker detection device; the circuit breaker detection device collects the short-circuit status of the circuit breaker in real time, and issues an audible and visual alarm when it is detected that the circuit breaker is disconnected.

[0007] Among them, the circuit breaking detection device includes a circuit breaking sensor, a central processing unit and an audible and visual alarm device; the circuit breaking sensor collects the switching status of the circuit breaker in real time and transmits the status information to the central processing unit, and the central processing unit collects the switching status of the circuit breaker in real time, and controls the audible and visual alarm device to operate when the circuit breaker is disconnected, and sends out an audible and visual alarm signal.

[0008] Among them, the parameters of capacitance and inductance are determined by the following formula:

[0009]

[0010] Where L is the inductance value, C is the capacitance value, and f is the frequency of the system AC source;

[0011] Among them, the withstand voltage values ​​of capacitors, inductors and circuit breakers are determined by the voltage level of the branch;

[0012] The DC system AC inrush protection method of the above device comprises the following steps:

[0013] (1) Determine the system AC source frequency f, then the angular frequency is ω = 2πf;

[0014] (2) Calculate the resonant parameters of inductance L and capacitance C. When resonance occurs, the following formula is used:

[0015]

[0016] The calculation can be obtained:

[0017]

[0018] (3) According to the LC value in step (2), select the parameter values ​​of the inductor and capacitor, and determine the withstand voltage values ​​of the inductor, capacitor and circuit breaker according to the voltage level of the branch; and construct a protection circuit based on the parameter values ​​of the inductor and capacitor;

[0019] (4) According to the requirement of alarm or protection when AC intrusion occurs, the circuit breaker is configured in the corresponding position. When alarm only is selected, the circuit breaker and the branch are connected in parallel; when protection trip is selected, the circuit breaker is connected in series in the branch;

[0020] (5) When AC is introduced, series resonance occurs. At this time, the current will pass through the inductor, circuit breaker, and capacitor to the ground in sequence. The resistance of the resonant circuit is equal to the line resistance R0 + the circuit breaker resistance R. At this time, the expression of the resonant current I is as follows:

[0021]

[0022] Among them, U is the voltage value of the AC input; since the resistance of the resonant circuit is extremely small, the current value will be very high, causing the circuit breaker to trip.

[0023] Among them, in step (5), when the circuit breaker is connected in series in the branch, the tripping action realizes the circuit disconnection; when the circuit breaker and the branch are connected in parallel, the tripping action is used as a switch signal alarm or as a switch signal output or directly observed.

[0024] Beneficial effects: The present invention adopts the method of series resonance in conjunction with a circuit breaker to achieve protection against AC intrusion in a DC system; the protection device can quickly determine parameters without the need for sensors, measuring circuits, power supplies, etc., and is a passive protection; compared with a finder, the protection device is rapid and accurate in positioning; compared with a ground voltage detection method, the protection device omits the steps of voltage sampling and signal conversion, further improving reliability, and can simultaneously achieve detection and protection against AC intrusion; in addition, when the circuit breaker is connected in series in a branch, the presence of a series resonant circuit directly achieves tripping at the input end of the branch, preventing AC from intruding into DC, and avoiding the impact of AC intrusion in the DC system on the load. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a schematic diagram of the application of the protection device of the present invention in the power grid system;

[0026] Figure 2 is a circuit schematic diagram of the protection device of the present invention;

[0027] Figure 3 is a flow chart of the device protection method of the present invention;

[0028] Figure 4 This is the schematic diagram of the circuit breaker detection device. DETAILED DESCRIPTION

[0029] like Figure 1-3 As shown, the present invention uses a series resonant circuit in conjunction with a circuit breaker to detect and protect the AC intrusion in the DC system. A protection device is installed in the branch that needs to be protected from AC intrusion. The protection device includes three main parts: an inductor, a capacitor, and a circuit breaker. The inductor is arranged in the branch, and the capacitor is connected in parallel with the branch and grounded. The circuit breaker can be placed in position 1 or position 2 according to whether the branch is cut off when AC intrudes. When placed in position 1, a single 2P circuit breaker can be used. When AC intrudes, the circuit breaker trips and the branch is cut off; when placed in position 2, two 1P circuit breakers can be used. When AC intrudes, the circuit breaker of the corresponding polarity of the intrusion trips. The trip signal can be output in the form of a switch quantity, or it can be directly observed to find the position of the AC intrusion (that is, whether it is intruded into the positive or negative pole).

[0030] The implementation steps of this method are as follows:

[0031] (1) Determine the system AC source frequency f (the conventional mains frequency is 50 Hz), then the angular frequency ω = 2πf;

[0032] (2) Calculate the resonant parameters of inductance L and capacitance C. When resonance occurs, the following formula is used:

[0033]

[0034] Calculation can be obtained

[0035]

[0036] (3) According to the LC value in step (2), the parameter values ​​of the inductor and capacitor are selected, and the withstand voltage values ​​of the inductor, capacitor and circuit breaker are determined according to the voltage level of the branch; and a protection circuit is constructed based on the parameter values ​​of the inductor and capacitor;

[0037] (4) According to the requirement of alarm or protection when AC intrusion occurs, the circuit breaker is configured in the corresponding position. When alarm only is selected, the circuit breaker and the branch are connected in parallel; when protection trip is selected, the circuit breaker is connected in series in the branch;

[0038] (5) When AC is introduced, series resonance occurs. At this time, the current will pass through the inductor, circuit breaker, and capacitor to the ground in sequence. The resistance of the resonant circuit is equal to the line resistance R0 + the circuit breaker resistance R. At this time, the expression of the resonant current I is as follows:

[0039]

[0040] Among them, U is the voltage value of the AC inrush. Since the resistance of the resonant circuit is extremely small, the current value will be very high, causing the circuit breaker to trip. The tripping action can be connected in series in the branch to cut off the circuit, or it can be connected in parallel in the branch as a switch signal alarm, can be output as a switch signal, or can be directly observed.

[0041] When used as a switch signal, a circuit breaker detection device is used to detect the switch signal, collect the short-circuit status of the circuit breaker in real time, and issue an audible and visual alarm when the circuit breaker is detected to be disconnected. Figure 4 As shown, the circuit breaker detection device includes a circuit breaker sensor, a central processing unit and an audible and visual alarm device; the circuit breaker sensor collects the switch status of the circuit breaker in real time and transmits the status information to the central processing unit, the central processing unit collects the switch status of the circuit breaker in real time, and controls the audible and visual alarm device to operate when the circuit breaker is disconnected, and sends out an audible and visual alarm signal.

Claims

1. A DC system AC inrush protection device, characterized by: The protection device is connected in series with the protected load into the branch; the protection device includes a capacitor, an inductor and a circuit breaker; the inductor is arranged in the branch and is connected in series with the load in the branch; the capacitor is connected in parallel with the branch, one end of the capacitor is connected to the inductor and the other end is grounded; based on the needs of the protected load, the circuit breaker has two placement methods to be set in the circuit, when the protected load only needs alarm protection, the circuit breaker is set in the circuit in series with the capacitor in the form of two 1P circuit breakers; when the protected load needs to cut off the branch protection, the circuit breaker is placed in the branch in series with the load in the form of a single 2P circuit breaker; when AC is introduced, only an alarm is required, and the circuit breaker is in the form of two 1P circuit breakers and is connected in series with the capacitor, and the circuit breaker is connected to the circuit breaking detection device; the circuit breaking detection device collects the circuit breaker closing state in real time, and performs an audible and visual alarm when the circuit breaker is detected to be disconnected; The DC system AC inrush protection method of the above device comprises the following steps: (1) Determine the system AC source frequency f, then the angular frequency is ω = 2πf; (2) Calculate the resonant parameters of inductance L and capacitance C. When resonance occurs, the following formula is used: The calculation can be obtained: (3) According to the LC value in step (2), the parameter values ​​of the inductor and the capacitor are selected, the withstand voltage values ​​of the inductor, the capacitor and the circuit breaker are determined according to the voltage level of the branch, and the protection circuit is constructed based on the parameter values ​​of the inductor and the capacitor; (4) According to the requirement of alarm or protection when AC intrusion occurs, the circuit breaker is configured in the corresponding position. When alarm only is selected, the circuit breaker and the branch are connected in parallel; when protection trip is selected, the circuit breaker is connected in series in the branch; (5) When AC is introduced, series resonance occurs. At this time, the current will pass through the inductor, circuit breaker, and capacitor to the ground in sequence. The resistance of the resonant circuit is equal to the line resistance R0 + the circuit breaker resistance R. At this time, the expression of the resonant current I is as follows: Among them, U is the voltage value of AC inrush; since the resistance of the resonant circuit is extremely small, the current value will be very high, causing the circuit breaker to trip; when the circuit breaker is connected in series in the branch, the tripping action realizes the circuit cutoff; when the circuit breaker and the branch are connected in parallel, the tripping action is used as a switch signal alarm or as a switch signal output or directly observed; the above method adopts the method of series resonance and circuit breaker to realize the protection of DC system from AC inrush.

2. The AC inrush protection device for a DC system according to claim 1, characterized in that: The circuit breaker detection device includes a circuit breaker sensor, a central processing unit and an audible and visual alarm device; the circuit breaker sensor collects the switch status of the circuit breaker in real time and transmits the status information to the central processing unit, the central processing unit collects the switch status of the circuit breaker in real time, and controls the audible and visual alarm device to operate and send out an audible and visual alarm signal when the circuit breaker is disconnected.

3. The AC inrush protection device for a DC system according to claim 1, characterized in that: The parameters of the capacitor and inductor are determined by the following formula: Where L is the inductance value, C is the capacitance value, and f is the frequency of the system AC source.

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