Detection circuit for real-time state of relay of APF or SVG

Abstract

A relay real-time state detection circuit of an APF or an SVG comprises a filtering unit, a soft start unit, an output current detection unit, an IGBT power unit and a direct current voltage source unit, the input end of the filtering unit is connected with a three-phase power grid, the soft start unit comprises three relays and a relay starting circuit, and the output current detection unit is connected with the IGBT power unit. The output current detection unit comprises three current transformers, first pins and second pins of three relays are all connected with a relay starting circuit, third pins are respectively connected with three phases of the output end of the filtering unit, and fourth pins are respectively connected with input ends of the three current transformers of the output current detection unit; the output ends of the three current transformers are respectively connected with three phases of the output end of the filtering unit through a current-limiting resistor, one end of the IGBT power unit is connected with the output ends of the three current transformers, and the other end of the IGBT power unit is connected with the direct-current voltage source unit.

Description

Technical Field

[0001] The utility model relates to the field of power grid harmonic control, and particularly relates to a detection circuit for the real-time state of a relay of an APF or an SVG. Background Art

[0002] The extensive use of modern power electronic devices and nonlinear loads results in a large amount of harmonics and reactive power in the power grid, seriously polluting the power quality, interfering with the normal operation of power equipment, and even causing equipment failures and accidents in severe cases. Active power filters (APFs) or static var generators (SVGs) can compensate for harmonics and reactive power in the power grid and improve the power quality.

[0003] In the main circuit of an APF or an SVG, when the device is first put into operation and connected to the power grid, the power grid will charge the energy storage capacitor of the active power filter through the rectifier circuit of the IGBT power module of the APF or SVG. Since the instantaneous impact current is very large, a pre-charge protection method of connecting a current-limiting resistor and a relay in parallel is required in the main circuit of the APF or SVG. When the voltage of the energy storage capacitor is charged to a certain value, the APF or SVG will drive the relay to turn on the circuit through the relay control signal and bypass the current-limiting resistor. However, if the relay fails and interrupts, it will cause the current-limiting resistor to burn out, and even cause short circuits and fire accidents in severe cases. At present, for the detection of the relay state in existing APFs or SVGs, voltage or current sampling is generally added on both sides of the relay. This not only causes interference to the sampling voltage or sampling current for detecting the relay state, making it unclear and prone to misjudgment of the relay state, but also increases the cost of voltage or current sampling, as well as the driving circuit or DSP control chip.

[0004] In the invention patent "A Relay State Detection System and Method Applied to APF / SVG" with the authorization announcement number CN114035041B, the detection system proposed by this patent cannot detect the relay state in real time. The detection system of this patent can only be used during the maintenance of the APF or SVG. Moreover, under actual operating conditions, even if the relay of this patent fails and interrupts, it can still maintain a certain current through the current-limiting resistor until the current-limiting resistor burns out. Therefore, the circuit of this patent is difficult to effectively achieve real-time circuit protection. Summary of the Invention

[0005] Aiming at the above problems, the utility model provides a real-time state detection system and method for a relay of an APF or an SVG, which can detect the state of the relay in the circuit in real time, judge whether the relay has an interruption fault, so as to achieve real-time protection of the circuit and prevent the current-limiting resistor from being burned out.

[0006] The technical solution of the present utility model is: a detection circuit for the real-time state of a relay of an APF or SVG, characterized in that it includes a filtering unit, a soft start unit, an output current detection unit, an IGBT power unit, and a DC voltage source unit. The input end of the filtering unit is connected to a three-phase power grid. The soft start unit includes three relays and a relay start circuit. The output current detection unit includes three current transformers. The first and second feet of the three relays are both connected to the relay start circuit. The third feet are respectively connected to the three phases of the output end of the filtering unit. The fourth feet are respectively connected to the input ends of the three current transformers of the output current detection unit. The output ends of the three current transformers are respectively connected to the three phases of the output end of the filtering unit through a current limiting resistor. One end of the IGBT power unit is connected to the output ends of the three current transformers, and the other end is connected to the DC voltage source unit.

[0007] Preferably, the filtering unit includes three LCL filtering circuits. Each LCL filtering circuit is composed of two inductors, a filtering capacitor, and a damping resistor. After the two inductors are connected in series, one end is connected to one phase of the three-phase power grid, and the other end is connected to the third foot of a relay of the soft start unit. One end of the filtering capacitor is connected between the two inductors, and the other end is connected to one end of the damping resistor. The other ends of the damping resistors of each LCL filtering circuit are connected to each other.

[0008] Preferably, the IGBT power unit includes six IGBT switching tubes. Among them, the emitter of the first IGBT switching tube is respectively connected to the collector of the second IGBT switching tube and the output end of a current transformer of the output current detection unit. The emitter of the third IGBT switching tube is respectively connected to the collector of the fourth IGBT switching tube and the output end of a current transformer of the output current detection unit. The emitter of the fifth IGBT switching tube is respectively connected to the collector of the sixth IGBT switching tube and the output end of a current transformer of the output current detection unit. The collectors of the first, third, and fifth IGBT switching tubes are connected to one end of the DC voltage source unit. The emitters of the second, fourth, and sixth IGBT switching tubes are connected to the other end of the DC voltage source unit. The gates of the first, second, third, fourth, fifth, and sixth IGBT switching tubes are all connected to the main control board.

[0009] Preferably, the DC voltage source unit is composed of electrolytic capacitors. The positive electrode of the electrolytic capacitor is connected to the collectors of the first, third, and fifth IGBT switching tubes of the IGBT power unit, and the negative electrode of the electrolytic capacitor is connected to the emitters of the second, fourth, and sixth IGBT switching tubes of the IGBT power unit.

[0010] Preferably, the relay startup circuit includes a first resistor, a second resistor, and a triode. The base of the triode is connected to the main control board through the first resistor for receiving a relay control signal. The collector is respectively connected to the first pins of three relays and one end of the second resistor. The other end of the second resistor is respectively connected to the second pins of the three relays and the power supply. The emitter of the triode is grounded.

[0011] The beneficial effects of the present utility model are as follows: By first connecting the relay in series with the current transformer and then connecting a current-limiting resistor in parallel, the present utility model ensures that during the actual operation of the APF or SVG circuit, the relay status can be checked in real time. When the relay fails and interrupts, the APF or SVG circuit can be protected in a timely manner, preventing the current-limiting resistor from being burned out, greatly improving the reliability and safety of the APF or SVG circuit, and without the need to add additional devices and costs. Description of the Drawings

[0012] Figure 1 is the circuit schematic diagram of the present utility model;

[0013] Figure 2 is the flowchart for detecting the relay status of the present utility model. Detailed Embodiments

[0014] See Figure 1, taking an APF with 400V / 60A as an example, a detection circuit for the real-time state of a relay of an APF or SVG, including a filtering unit, a soft start unit, an output current detection unit, an IGBT power unit, and a DC voltage source unit. The soft start unit includes a relay KY1, a relay KY2, a relay KY3, and a relay start circuit. In this embodiment, the relays KY1, KY2, and KY3 all use Hongfa relays 90A. The filtering unit includes three LCL filtering circuits. Among them, the first LCL filtering circuit includes an inductor L1, an inductor L2, a filtering capacitor C2, and a damping resistor R1. After the inductors L1 and L2 are connected in series, one end is connected to the U phase in the three-phase power grid, and the other end is connected to the third pin of the relay KY1 in the soft start unit. One end of the filtering capacitor C2 is connected between the inductors L1 and L2, and the other end is connected to one end of the damping resistor R1. The second LCL filtering circuit includes an inductor L3, an inductor L4, a filtering capacitor C3, and a damping resistor R2. After the inductors L3 and L4 are connected in series, one end is connected to the V phase in the three-phase power grid, and the other end is connected to the third pin of the relay KY2 in the soft start unit. One end of the filtering capacitor C3 is connected between the inductors L3 and L4, and the other end is connected to one end of the damping resistor R2. The third LCL filtering circuit includes an inductor L5, an inductor L6, a filtering capacitor C4, and a damping resistor R3. After the inductors L5 and L6 are connected in series, one end is connected to the W phase in the three-phase power grid, and the other end is connected to the third pin of the relay KY3 in the soft start unit. One end of the filtering capacitor C4 is connected between the inductors L5 and L6, and the other end is connected to one end of the damping resistor R3. The other ends of the damping resistors R1, R2, and R3 are connected to each other. In this embodiment, the inductance values of the inductors L1, L3, and L6 are all 100uH, the inductance values of the inductors L2, L4, and L5 are all 1mH, the capacitance values of the filtering capacitors C2, C3, and C4 are all 20uF, and the damping resistors R1, R2, and R3 all use 5 20W 1Ω cement resistors in parallel, and the overall resistance value of each damping resistor is 0.2 Ω; The relay startup circuit includes a first resistor R4, a second resistor R5, and a triode Q1. The base of the triode Q1 is connected to the main control board through the first resistor R4 for receiving a relay control signal. The collector of the triode Q1 is respectively connected to the first pins of relays KY1, KY2, and KY3 and one end of the second resistor R5. The other end of the second resistor R5 is respectively connected to the second pins of relays KY1, KY2, and KY3 and the power supply. The emitter of the triode Q1 is grounded. In this embodiment, the resistance value of the first resistor R4 is 1 kΩ, and the resistance value of the second resistor R5 is 10 kΩ. The output current detection unit includes current transformers CT1, CT2, and CT3. In this embodiment, the current transformers CT1, CT2, and CT3 all adopt LEM LA-130_P, with a rated current of 130 A and an accuracy of 0.5%, the input end of the current transformer CT1 is connected to the fourth pin of the relay KY1, and the output end of the current transformer CT1 is connected between the inductor L2 and the relay KY1 through the current-limiting resistor R8. The input end of the current transformer CT2 is connected to the fourth pin of the relay KY2, and the output end of the current transformer CT2 is connected between the inductor L4 and the relay KY2 through the current-limiting resistor R7. The input end of the current transformer CT3 is connected to the fourth pin of the relay KY3, and the output end of the current transformer CT3 is connected between the inductor L5 and the relay KY3 through the current-limiting resistor R6. In this embodiment, the current-limiting resistors R6, R7, and R8 all adopt 50W 100Ω metal oxide film resistors. The IGBT power unit includes a first IGBT switch tube T1, a second IGBT switch tube T2, a third IGBT switch tube T3, a fourth IGBT switch tube T4, a fifth IGBT switch tube T5, and a sixth IGBT switch tube T6. The emitter of the first IGBT switch tube T1 is respectively connected to the collector of the second IGBT switch tube T2 and the output end of the current transformer CT1 of the output current detection unit. The emitter of the third IGBT switch tube T3 is respectively connected to the collector of the fourth IGBT switch tube T4 and the output end of the current transformer CT2 of the output current detection unit. The emitter of the fifth IGBT switch tube T5 is respectively connected to the collector of the sixth IGBT switch tube T6 and the output end of the current transformer CT3 of the output current detection unit. The collectors of the first, third, and fifth IGBT switch tubes are connected to one end of the DC voltage source unit, and the emitters of the second, fourth, and sixth IGBT switch tubes are connected to the other end of the DC voltage source unit. The gates of the first, second, third, fourth, fifth, and sixth IGBT switch tubes are all connected to the main control board. The DC voltage source unit is composed of an electrolytic capacitor C1. The positive electrode of the electrolytic capacitor C1 is connected to the emitters of the first, third, and fifth IGBT switch tubes of the IGBT power unit, and the negative electrode of the electrolytic capacitor is connected to the emitters of the second, fourth, and sixth IGBT switch tubes of the IGBT power unit. In this embodiment, the electrolytic capacitor C1 adopts 20 450V / 820uF electrolytic capacitors. The 20 electrolytic capacitors are divided into two groups, with 10 electrolytic capacitors in each group connected in parallel, and then the two groups are connected in series.

[0015] See Figure 2 , the relay state of the APF with a rated current of 60A is detected in real time by using the above detection circuit, including the following steps:

[0016] 1) When powering on and starting the APF, after the three-phase power grid is rectified by the filtering unit, the electrolytic capacitor C1 of the DC voltage source unit is charged through the current-limiting resistors R6, R7, and R8. When the voltage of the electrolytic capacitor C1 is greater than 500V, the main control board outputs a relay control signal KY_CTL to drive the relays KY1, KY2, and KY3 to turn on the circuit through the relay drive circuit until the relays are closed, bypassing the current-limiting resistors R6, R7, and R8.

[0017] 2) After the relays are closed, the APF starts to work. The effective values of the external harmonic and reactive currents Ia are detected through the current transformers of the external load or the power grid current transformers, and the output current Ib is detected through the current transformer of the output current detection unit.

[0018] 3) The main control board calculates the duty cycle based on the effective values of the external harmonic and reactive currents Ia and the output current Ib. The main control board controls the IGBT power unit to compensate the output current Ib according to the duty cycle. The output current Ib compensated by the IGBT power unit is opposite in direction and equal in amplitude to the effective values of the external harmonic and reactive currents Ia.

[0019] 4) The current transformer of the output current detection unit continuously detects the output current Ib compensated by the IGBT power unit. If Ia ≤ 1A and Ib ≤ 0.1A, or 1A ≤ Ia ≤ 30A and Ib ≤ 0.1Ia, or 30A ≤ Ia ≤ 60A and Ib ≤ 0.2Ia, it is determined that the relay is faulty, and the main control board controls the IGBT power unit to stop compensating the output current Ib. Otherwise, the relay is in a normal closed state.

[0020] 5) When the relay is in a normal closed state, steps 2) to 4) are repeated.

[0021] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. Those skilled in the art, without departing from the spirit of the present invention, any modifications made to the present invention fall within the protection scope of the present invention.

Claims

1. A detection circuit for the real-time status of an APF or SVG relay, characterized in that: It comprises a filtering unit, a soft starting unit, an output current detection unit, an IGBT power unit and a DC voltage source unit. The input end of the filtering unit is connected to a three-phase power grid. The soft starting unit comprises three relays and a relay starting circuit. The output current detection unit comprises three current transformers. The first and second pins of the three relays are connected to the relay starting circuit, the third pins are respectively connected to the three phases of the output end of the filtering unit, the fourth pins are respectively connected to the input ends of the three current transformers of the output current detection unit, the output ends of the three current transformers are respectively connected to the three phases of the output end of the filtering unit through a current limiting resistor, one end of the IGBT power unit is connected to the output ends of the three current transformers, and the other end is connected to the DC voltage source unit.

2. The detection circuit of the real-time state of the relay of an APF or SVG according to claim 1, characterized in that: The filtering unit includes three LCL filtering circuits, each of which is composed of two inductors, a filtering capacitor, and a damping resistor. After the two inductors are connected in series, one end is connected to one phase of the three-phase power grid, and the other end is connected to the third pin of a relay of the soft start unit. One end of the filtering capacitor is connected between the two inductors, and the other end is connected to one end of the damping resistor. The other ends of the damping resistors of each LCL filtering circuit are connected to each other.

3. The detection circuit of the real-time state of the relay of an APF or SVG according to claim 1, characterized in that: The IGBT power unit includes six IGBT switching tubes, wherein the emitter of the first IGBT switching tube is respectively connected to the collector of the second IGBT switching tube and the output end of a current transformer of the output current detection unit, the emitter of the third IGBT switching tube is respectively connected to the collector of the fourth IGBT switching tube and the output end of a current transformer of the output current detection unit, the emitter of the fifth IGBT switching tube is respectively connected to the collector of the sixth IGBT switching tube and the output end of a current transformer of the output current detection unit, the collectors of the first, third and fifth IGBT switching tubes are connected to one end of a DC voltage source unit, the emitters of the second, fourth and sixth IGBT switching tubes are connected to the other end of the DC voltage source unit, and the gates of the first, second, third, fourth, fifth and sixth IGBT switching tubes are all connected to the main control board.

4. The detection circuit of the real-time state of the relay of an APF or SVG according to claim 3, characterized in that: The DC voltage source unit is composed of an electrolytic capacitor, the positive electrode of the electrolytic capacitor is connected to the collectors of the first, third and fifth IGBT switch tubes of the IGBT power unit, and the negative electrode of the electrolytic capacitor is connected to the emitters of the second, fourth and sixth IGBT switch tubes of the IGBT power unit.

5. The detection circuit of the real-time state of the relay of an APF or SVG according to claim 1, characterized in that: The relay starting circuit includes a first resistor, a second resistor, and a transistor. The base of the transistor is connected to the main control board through the first resistor for receiving a relay control signal. The collector is respectively connected to the first pins of the three relays and one end of the second resistor. The other end of the second resistor is respectively connected to the second pins of the three relays and a power supply. The emitter of the transistor is grounded.

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