System for protecting power electronic equipment in direct-current micro-grid

Abstract

The invention discloses a system for protecting power electronic equipment in a direct-current micro-grid, relates to the field of micro-grid control, and aims to solve the problem that an existing low-voltage direct-current micro-grid protection technology lacks rapid fault point removal and inductive current oscillation suppression characteristics. The active current limiter is arranged between the DC-DC converter and the DC bus, and is used for limiting the current output by the DC-DC converter and then sending the current to the DC bus; and the controller is used for detecting the output current after current limiting of the active current limiter, comparing the output current with a preset current, controlling the IGBT switching tubes Q1-Q2 of the DC-DC converter to be switched off when the output current is higher than the preset current, and keeping the IGBT switching tubes Q1-Q2 to be switched on when the output current is not higher than the preset current. The invention is used for protecting the power electronic equipment.

Description

Technical Field

[0001] The invention relates to the field of microgrid control and belongs to switch tube control. Background Art

[0002] Low-voltage DC microgrids show obvious advantages in efficiently utilizing distributed energy and meeting the development needs of diversified loads. For low-voltage DC microgrids, the bus voltage is mainly controlled by the converter connected to the bus. Once a DC fault occurs, even if the pulse is blocked in time after the fault, the boost DC / DC converter will still provide short-circuit current through the diode. In this process, the anti-parallel diode will be severely impacted by the fault current and even damaged. Therefore, if effective measures are not taken when a DC bus fault occurs, it will cause great damage to power electronic equipment. Fault protection in DC microgrids is crucial.

[0003] For the protection of low-voltage DC microgrid faults, passive protection is difficult to solve the contradiction between protection speed, selectivity and economy caused by the vulnerability of power electronic devices. Active current limiting protection schemes using power electronic converters or external controllable components have attracted widespread attention from scholars at home and abroad.

[0004] The existing method combines the fault control and protection of power electronic converters, adds a fault control module, and cooperates with the DC protection device to achieve the identification and rapid isolation of the fault location. However, it does not take into account the fault current oscillation caused by the existence of DC lines and DC bus capacitors, which will threaten the safety of equipment.

[0005] In summary, the existing low-voltage DC microgrid protection technology lacks the problem of rapid fault point removal and suppression of inductor current oscillation characteristics. Summary of the invention

[0006] The purpose of the present invention is to solve the problem that the existing low-voltage DC microgrid protection technology lacks rapid fault point removal and suppression of inductive current oscillation characteristics, and proposes a system for protecting power electronic equipment in a DC microgrid.

[0007] A system for protecting power electronic equipment in a DC microgrid, wherein the DC / DC converter includes IGBT switch tubes Q1-Q2, and the system includes an active current limiter and a controller;

[0008] The active current limiter is arranged between the DC-DC converter and the DC bus, and is used to limit the output current of the DC / DC converter and then send it to the DC bus;

[0009] The controller is used to detect the output current after the active current limiter limits the current, and compare the output current with the preset current. When the output current is higher than the preset current, the IGBT switch tubes Q1-Q2 of the DC / DC converter are controlled to be turned off; when the output current is not higher than the preset current, the IGBT switch tubes Q1-Q2 are kept closed.

[0010] Preferably, the active current limiter includes capacitors C1-C2, diodes D1-D2, inductors L1-L2, resistors R d and diode D d ;

[0011] DC power supply U dc The positive output terminal of the capacitor C1 is connected to the drain of the IGBT switch Q1. dc The negative electrode of is connected to the source of the IGBT switch tube Q2 and one end of the capacitor C2 at the same time, and the other end of the capacitor C1 is connected to the other end of the capacitor C2, the anode of the diode D1 and the cathode of the diode D2 at the same time;

[0012] The cathode of diode D1 is connected to the source of IGBT switch tube Q1 and one end of inductor L1 at the same time, the anode of diode D2 is connected to the drain of IGBT switch tube Q2 and one end of inductor L2 at the same time, and the other end of inductor L2 is connected to diode D d The anode of and the negative input terminal of the DC bus;

[0013] Diode D d The cathode connection resistance R d One end of the resistor R d The other end of the inductor L1 is connected to the positive input end of the DC bus at the same time.

[0014] Preferably, the controller is implemented using a chip of model STM32F103VET6.

[0015] The beneficial effects of the present invention are:

[0016] When the DC bus fails, the capacitor C3 is connected to the line , R f and R load R load Short circuit, the current i on inductor L1 L rises, the voltage u0 on both sides of capacitor C3 decreases; when the current i L When the current rises above the preset current value, Q1 is controlled to be locked. Therefore, the present invention limits the reverse voltage phenomenon that occurs when a short circuit occurs between poles of the DC bus, and can quickly cut off the fault point to prevent the current from spreading. The present invention also increases the energy dissipation branch (resistance R d and diode D d), effectively solving the problem of inductor current oscillation. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is the structural diagram of low voltage DC microgrid system;

[0018] Figure 2 Schematic diagram of the system for protecting power electronic equipment in a DC microgrid. DETAILED DESCRIPTION

[0019] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0020] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0021] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments, but they are not intended to limit the present invention.

[0022] Example:

[0023] Combination Figure 1 and Figure 2 This embodiment is described, for a system for protecting power electronic equipment in a DC microgrid, the DC-DC converter includes IGBT switches Q1-Q2, and the system includes an active current limiter and a controller;

[0024] The active current limiter is arranged between the DC-DC converter and the DC bus, and is used to limit the output current of the DC-DC converter and then send it to the DC bus;

[0025] The controller is used to detect the output current after the active current limiter limits the current, and compare the output current with the preset current. When the output current is higher than the preset current, the IGBT switch tubes Q1-Q2 of the DC-DC converter are controlled to be turned off; when the output current is not higher than the preset current, the IGBT switch tubes Q1-Q2 are kept closed.

[0026] Specifically, the DC bus voltage of the low-voltage DC microgrid system is 750V, and its topology is as follows: Figure 1As shown in the figure, the low-voltage DC microgrid system includes intermittent distributed generation (DG) such as photovoltaics, energy storage and DC loads; each DG and energy storage unit is connected to the DC bus through a DC / DC converter; and considering that in the actual system, each unit in the DC microgrid is connected to the DC bus through lines (L1-L4); the DC microgrid can also be connected to the AC system through a DC / AC converter.

[0027] Figure 2 In the DC system shown, the DC / DC converter operates under constant DC bus voltage control. When a short circuit occurs between the poles of the DC bus, reverse voltage will occur, and the current-limiting inductor current will also oscillate. The reverse voltage on the DC bus may cause the electrolytic capacitor on the bus side of some equipment (such as uncontrolled rectifier power electronic loads) to be damaged. Figure 2 The fault development process can be decomposed as follows: ① The DC bus fails, and the capacitor C3 is connected to the capacitor C3 through L line , R f and R load R load Short circuit, the current i on inductor L1 L The voltage u0 on both sides of capacitor C3 decreases; ② The current i on inductor L1 L When the current rises above the preset current value, Q1 is controlled to be locked; ③ After the voltage on both sides of capacitor C3 drops to 0, a reverse voltage u0<0 will appear due to the freewheeling effect of the line inductance, and under the action of this voltage, the current i on the inductor L1 L Continue to rise; ④ After u0=0, i L It stops rising and starts to charge capacitor C3 under the action of freewheeling, and u0 starts to gradually become greater than 0.

[0028] The active current limiter mainly uses the energy dissipation branch (resistance R d and diode D d ) to limit the inductor current oscillation phenomenon. To verify the robustness of the active current limiter, the system parameters are fixed and the energy dissipation branch resistance is changed. The active current limiter outlet voltage, current limiting inductor current and energy dissipation branch current are observed. The active current limiter can effectively suppress the inductor current oscillation phenomenon, and with R d The decrease of the current flowing through the energy dissipation branch increases, and the peak value of the inductor current decreases. In addition, in order to verify the effectiveness of the active current limiter in different working conditions, the hardware parameters of the active current limiter are fixed and the line inductance L is changed. line , equivalent bus capacitance C3 and short-circuit resistance R f, the other system parameters remain unchanged, and the change of the inductor current limited by the active current limiter is observed. It can be seen that under various working conditions, the active current limiter can effectively suppress the oscillation of the inductor current, which also shows that the active current limiter has good robustness.

[0029] The following is an introduction to the active current limiter structure: The active current limiter includes capacitors C1-C2, diodes D1-D2, inductors L1-L2, resistors R d and diode D d ;

[0030] DC power supply U dc The positive output terminal of the capacitor C1 is connected to the drain of the IGBT switch Q1. dc The negative electrode of is connected to the source of the IGBT switch tube Q2 and one end of the capacitor C2 at the same time, and the other end of the capacitor C1 is connected to the other end of the capacitor C2, the anode of the diode D1 and the cathode of the diode D2 at the same time;

[0031] The cathode of diode D1 is connected to the source of IGBT switch tube Q1 and one end of inductor L1 at the same time, the anode of diode D2 is connected to the drain of IGBT switch tube Q2 and one end of inductor L2 at the same time, and the other end of inductor L2 is connected to diode D d The anode of and the negative input terminal of the DC bus;

[0032] Diode D d The cathode connection resistance R d One end of the resistor R d The other end of the inductor L1 is connected to the positive input end of the DC bus at the same time.

[0033] The controller model is introduced below: The controller is implemented using a chip model STM32F103VET6.

[0034] Although the present invention is described herein with reference to specific embodiments, it should be understood that these embodiments are merely examples of the principles and applications of the present invention. It should therefore be understood that many modifications may be made to the exemplary embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims. It should be understood that the various dependent claims and features described herein may be combined in a manner different from that described in the original claims. It should also be understood that features described in conjunction with individual embodiments may be used in other described embodiments.

Claims

1. A system for protecting power electronic equipment in a DC microgrid, wherein the DC / DC converter includes IGBT switch tubes Q1-Q2, and is characterized in that: The system includes an active current limiter and a controller; The active current limiter is arranged between the DC-DC converter and the DC bus, and is used to limit the output current of the DC / DC converter and then send it to the DC bus; The controller is used to detect the output current after the active current limiter limits the current, and compare the output current with the preset current. When the output current is higher than the preset current, the IGBT switch tubes Q1-Q2 of the DC / DC converter are controlled to be turned off; when the output current is not higher than the preset current, the IGBT switch tubes Q1-Q2 are kept closed.

2. The system for protecting power electronic equipment in a DC microgrid according to claim 1, characterized in that: The active current limiter includes capacitors C1-C2, diodes D1-D2, inductors L1-L2, resistors R d and diode D d ; DC power supply U dc The positive output terminal of the DC power supply U is connected to one end of the capacitor C1 and the drain of the IGBT switch Q1. dc The negative electrode of is connected to the source of the IGBT switch tube Q2 and one end of the capacitor C2 at the same time, and the other end of the capacitor C1 is connected to the other end of the capacitor C2, the anode of the diode D1 and the cathode of the diode D2 at the same time; The cathode of diode D1 is connected to the source of IGBT switch tube Q1 and one end of inductor L1 at the same time, the anode of diode D2 is connected to the drain of IGBT switch tube Q2 and one end of inductor L2 at the same time, and the other end of inductor L2 is connected to diode D d The anode of and the negative input terminal of the DC bus; Diode D d The cathode connection resistance R d One end of the resistor R d The other end of the inductor L1 is connected to the positive input end of the DC bus at the same time.

3. The system for protecting power electronic equipment in a DC microgrid according to claim 1, characterized in that: The controller is implemented using a chip called STM32F103VET6.

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