CN111682553B - SVG-based control system and control method for inhibiting transient overvoltage of direct current system - Google Patents
SVG-based control system and control method for inhibiting transient overvoltage of direct current system Download PDFInfo
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- CN111682553B CN111682553B CN202010627538.0A CN202010627538A CN111682553B CN 111682553 B CN111682553 B CN 111682553B CN 202010627538 A CN202010627538 A CN 202010627538A CN 111682553 B CN111682553 B CN 111682553B
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- 238000000034 method Methods 0.000 title claims abstract description 16
- 230000002401 inhibitory effect Effects 0.000 title abstract description 3
- 238000002955 isolation Methods 0.000 claims abstract description 64
- 239000003990 capacitor Substances 0.000 claims abstract description 41
- 238000001914 filtration Methods 0.000 claims abstract description 24
- 230000003993 interaction Effects 0.000 claims abstract description 21
- 230000009471 action Effects 0.000 claims description 14
- 238000006243 chemical reaction Methods 0.000 claims description 7
- 238000005259 measurement Methods 0.000 claims description 6
- 101100489717 Saccharomyces cerevisiae (strain ATCC 204508 / S288c) GND2 gene Proteins 0.000 claims description 4
- 230000000670 limiting effect Effects 0.000 claims description 4
- 230000000087 stabilizing effect Effects 0.000 claims description 4
- 101100489713 Saccharomyces cerevisiae (strain ATCC 204508 / S288c) GND1 gene Proteins 0.000 claims description 3
- 230000015556 catabolic process Effects 0.000 claims description 2
- 230000003287 optical effect Effects 0.000 claims description 2
- 230000000630 rising effect Effects 0.000 claims description 2
- 230000001629 suppression Effects 0.000 abstract description 2
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Classifications
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/12—Circuit arrangements for ac mains or ac distribution networks for adjusting voltage in ac networks by changing a characteristic of the network load
- H02J3/16—Circuit arrangements for ac mains or ac distribution networks for adjusting voltage in ac networks by changing a characteristic of the network load by adjustment of reactive power
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/18—Arrangements for adjusting, eliminating or compensating reactive power in networks
- H02J3/1821—Arrangements for adjusting, eliminating or compensating reactive power in networks using shunt compensators
- H02J3/1835—Arrangements for adjusting, eliminating or compensating reactive power in networks using shunt compensators with stepless control
- H02J3/1842—Arrangements for adjusting, eliminating or compensating reactive power in networks using shunt compensators with stepless control wherein at least one reactive element is actively controlled by a bridge converter, e.g. active filters
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/36—Arrangements for transfer of electric power between ac networks via a high-tension dc link
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
- Y02E40/10—Flexible AC transmission systems [FACTS]
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
- Y02E40/30—Reactive power compensation
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/60—Arrangements for transfer of electric power between AC networks or generators via a high voltage DC link [HVCD]
Abstract
The invention belongs to the technical field of power automation, and particularly relates to a transient overvoltage suppression method and a control system of a direct current system based on SVG, wherein the system comprises the following components: the system comprises a voltage and current measuring module, a signal calculating and filtering module, a PWM control module, a man-machine interaction module, a switch control module, a switch selecting and driving module and a secondary system isolation module. Based on the working characteristics of the SVG direct-current side capacitor, when the effective value of the bus voltage of the SVG access point is higher than a setting value, the purpose of rapidly reducing SVG output reactive power is achieved by reducing the capacitance value of the direct-current side capacitor or increasing the resistance value of the direct-current side capacitor and the series capacitor; and after the voltage is recovered below the setting value, the capacitance value or the resistance value is recovered, and the SVG returns to the normal working state. Compared with the conventional SVG, the method has the advantages of quick response, capability of inhibiting transient overvoltage, simplicity and easiness in implementation.
Description
Technical Field
The invention relates to a control system and a control method for restraining transient overvoltage of a direct current system based on SVG (static var generator) applied to an alternating current-direct current transmission system, and belongs to the technical field of power automation.
Background
The energy and load distribution of China are unbalanced, and trans-regional and remote power transmission is an important means for optimizing and configuring resources of China. The high-voltage direct-current power transmission (line commutated converter based high voltage direct current, LCC-HVDC) of the grid converter has the advantages of large transmission capacity, rapid and controllable active power, no stability problem of alternating-current power transmission, capability of realizing asynchronous grid connection of a grid and the like, and is widely applied to the occasions of long-distance large-capacity power transmission in China. But the converter elements of LCC-HVDC converters are thyristors without self-turn-off capability, with the following drawbacks: the commutation is realized by depending on an alternating current power grid with certain strength, so that the commutation failure problem exists when the LCC-HVDC is connected with a weak alternating current system; the two-end converter equipment needs to consume a large amount of reactive power, needs a large amount of reactive compensation and the like. The reactive compensation equipment is arranged at the alternating current bus of the LCC-HVDC system, is an important measure for improving the operation characteristic of the system, can provide reactive support for the system, and improves the stability and reliability of the system. The static var generator (Static Var Generator, SVG) has significant advantages over conventional reactive compensation devices in suppressing bus voltage oscillations and increasing the transient voltage stability level of the system. To improve the operating characteristics of LCC-HVDC systems, to enhance their resistance to commutation failure, more and more SVG devices are applied to LCC-HVDC systems.
However, SVG also has problems in improving the regulation capability of ac voltage at a converter station in LCC-HVDC system, especially when connecting weak ac systems, which may cause transient overvoltage at the converter station: when commutation fails, the alternating-current side voltage drops, the SVG control system sends out an reactive power increasing instruction, when the voltage returns to a normal level, the control system instruction cannot be changed instantaneously, the SVG still sends out reactive power, the voltage continues to rise, then, the control system sends out an instruction to reduce the reactive power increasing amount of the SVG until the reactive power is not increased any more, at the moment, the reactive power of the alternating-current system is excessive, and a transient overvoltage phenomenon occurs. The occurrence of transient overvoltage is unfavorable for the safe and stable operation of the system, so that corresponding inhibition measures are necessary for the transient overvoltage generated by the LCC-HVDC system added with SVG.
Disclosure of Invention
Aiming at the problems, the invention provides a transient overvoltage control system and a control method of a direct current system based on SVG.
According to one aspect of the present invention, there is provided a transient overvoltage control system for a SVG-based dc system, the control system comprising: the system comprises a voltage and current measuring module (1), an isolation module I (2), a Hall reactive power transmitter module (3), a signal calculating and filtering module (4), a PWM (pulse-width modulation) control module (5), an isolation module II (6), a man-machine interaction module (7), a switch control module (8), an isolation module III (9), a switch selecting and driving module (10), a switch I (11) and a switch II (12);
the voltage and current measuring module (1) is connected with the Hall reactive power transmitter module (3) and the signal calculating and filtering module (4) through the first isolation module (2) at the same time; the signal calculation and filtering module (4), the PWM control module (5) and the isolation module II (6) are connected in sequence; the switch control module (8) is connected with the signal calculation and filtering module (4); the man-machine interaction module (7), the switch control module (8), the isolation module III (9) and the switch selection and driving module (10) are connected in sequence; the first switch (11) and the second switch (12) are respectively connected with the switch selecting and driving module (10).
The voltage and current measurement module (1) is used for acquiring an SVG access point bus instantaneous voltage value and an instantaneous current value between the SVG and a power grid, and transmitting the instantaneous voltage value and the instantaneous current value to the isolation module I (2) and the Hall reactive power transmitter module (3);
the first isolation module (2) is used for isolating the first and second systems, converting a strong voltage current signal of the first system into a weak voltage current signal of the second system, and transmitting the weak voltage current signal to the signal calculation and filtering module (4);
the Hall reactive power transmitter module (3) uses the measurement data of the voltage and current measurement module (1) to obtain reactive power exchanged between the SVG and the power grid, and plays a role in isolating a primary system and a secondary system at the same time;
the signal calculation and filtering module (4) adopts abc-dq conversion to instantly obtain voltage and current effective values, further calculates a voltage reference value, a current reference value and a reactive reference value, and transmits calculation results of the voltage reference value, the current reference value and the reactive reference value to the PWM control module (5) after filtering, and transmits the obtained voltage effective values to the switch control module (8) after filtering;
the PWM control module (5) is used for calculating the trigger angle of the inverter bridge thyristor, generating trigger pulse and outputting the trigger pulse to the isolation module II (6);
the second isolation module (6) is used for isolating the first and second systems, converting weak signals of the second system into strong signals of the first system and outputting the strong signals to the SVG inverter bridge;
the man-machine interaction module (7) comprises a keyboard, a display and a conversion interface, and is used for setting parameters and displaying data and states of the system in real time, so that serial communication between the system and an upper computer is realized; the parameter setting comprises the steps of manually setting a trigger counting result N to zero, setting a voltage threshold value for comparison with a voltage effective value, setting a counting threshold value for comparison with N and manually selecting an action switch, and finally outputting data of the parameter setting to a switch control module (8);
the switch control module (8) is used for calculating and judging whether the system meets the action conditions of the first switch (11) and the second switch (12), realizing the selection of an action switch according to the parameter setting of the man-machine interaction module (7), and outputting a switch control instruction to the isolation module III (9);
the isolation module III (9) is used for isolating the primary system and the secondary system, converting weak signals of the secondary system into strong signals of the primary system and outputting the strong signals to the switch selection and driving module (10);
the switch selection and driving module (10) realizes the selection and the opening and the closing of a switch I (11) for controlling the resistor and a switch II (12) for controlling the capacitor according to the output of the isolation module III (9).
Preferably, the switch control module (8) completes judgment on whether the system accords with the switch action condition and switch selection according to the voltage effective value output by the signal calculation and filtering module (4) and the voltage threshold value, the counting threshold value and the switch selection instruction input by the manual interaction module (7), and outputs a control instruction to the switch driving module (10) through the isolation module III (9) to drive the switch I (11) or the switch (12).
The switch control module (8) comprises the following components:
a voltage comparator: inputting a voltage effective value and a voltage threshold value, comparing the voltage effective value and the voltage threshold value, and outputting a comparison result to a trigger condition counter;
triggering condition counter: the output ends are connected with the voltage comparator and the trigger pulse generator, each pulse period operates once for counting or setting zero, and the result is output to the switch trigger judgment device;
trigger pulse generator: the trigger condition counter is used for generating a pulse with a certain period and outputting the pulse to the trigger condition counter;
a switch trigger determiner: the output of the trigger condition counter and the manual interaction module 7 is received and used for judging whether the condition of the switching action is met or not and sending out a control instruction;
a monostable output delay; and receiving the output of the switch trigger judgment device, and inputting a steady-state output signal to the repeatedly-triggerable monostable trigger after delay time.
Repeatedly triggerable monostable trigger: and receiving an output signal of the monostable output delayer, and inputting a switch control signal to the switch driving module.
According to another aspect of the present invention, there is provided a method for controlling transient overvoltage using the above control system, comprising the steps of:
the first step: setting the switch triggering condition counting result N to be zero;
and a second step of: collecting an SVG access point bus voltage instantaneous value, and instantly obtaining an effective value of the voltage by adopting abc-dq conversion;
and a third step of: judging whether the effective voltage value is larger than a voltage threshold value or not;
fourth step: if the effective voltage value is smaller than the voltage threshold value, setting N to be 0; if the voltage effective value is greater than the voltage threshold, n=n+1;
fifth step: comparing the value of N with a set counting threshold value;
sixth step: if the value of N is greater than or equal to the counting threshold value, a switch-off instruction is sent out; if the value of N is smaller than the counting threshold value and is not equal to 0, the switch state is kept unchanged; if the value of N is equal to 0, a switch closing instruction is sent out; and ending the control and returning to the second step.
Preferably, the voltage threshold is 1.2Un, wherein Un is the rated voltage of the control system.
Preferably, the count threshold is 5.
Drawings
FIG. 1 is a block diagram of a transient overvoltage control system of a SVG-based DC system according to the present invention;
FIG. 2 is a circuit diagram of a first isolation module in the control system of the present invention;
FIG. 3 is a circuit diagram of a Hall reactive power transmitter in the control system of the present invention;
FIG. 4 is a functional block diagram of a switch control module in the control system of the present invention;
FIG. 5 is a circuit diagram of a voltage comparator in the control system of the present invention;
FIG. 6 is a circuit diagram of a pulse generator in the control system of the present invention;
FIG. 7 is a circuit diagram of a switch trigger condition counter in the control system of the present invention;
FIG. 8 is a circuit diagram of a monostable output delay in the control system of the present invention;
FIG. 9 is a circuit diagram of a re-triggerable monostable flip-flop in the control system of the present invention;
FIG. 10 is a circuit diagram of a second isolation module in the control system of the present invention;
fig. 11 is a circuit diagram of a isolator module three in the control system of the present invention.
Fig. 12 is a flowchart of a transient overvoltage control method to which the control system of the present invention is applied.
Detailed Description
The embodiments are described in detail below with reference to the accompanying drawings.
Fig. 1 shows a control system for suppressing transient overvoltage of a dc system based on SVG according to the present invention, as shown in fig. 1, the control system includes: the system comprises a voltage and current measuring module (1), an isolation module I (2), a Hall reactive power transmitter module (3), a signal calculating and filtering module (4), a PWM (pulse-width modulation) control module (5), an isolation module II (6), a man-machine interaction module (7), a switch control module (8), an isolation module III (9), a switch selecting and driving module (10), a switch I (11) and a switch II (12); the voltage and current measuring module (1) is connected with the Hall reactive power transmitter module (3) and the signal calculating and filtering module (4) through the first isolation module (2) at the same time; the signal calculation and filtering module (4), the PWM control module (5) and the isolation module II (6) are connected in sequence; the switch control module (8) is connected with the signal calculation and filtering module (4); the man-machine interaction module (7), the switch control module (8), the isolation module III (9) and the switch selection and driving module (10) are connected in sequence; the first switch (11) and the second switch (12) are respectively connected with the switch selecting and driving module (10).
Fig. 2 is a circuit diagram of an isolation module one (2) in the control system according to the present invention, where the isolation module one (2) includes a photo-coupler TLP521-4 and resistors R201, R202, R203, and a 1 st pin of the photo-coupler TLP521-4 is connected to a switch through a resistor R203 with 250 ohms, and the other end of the switch is connected to a power supply Vcc 1; the 2 nd leg of the TLP521-4 is connected to GND1, the 16 th leg of the TLP521-4 is connected to the power supply Vcc2 through a resistor R201 of 10-100 ohms, the 15 th leg of the TLP521-4 is connected to the power supply ground GND2 through a resistor R202 of 100 kiloohms, and the 15 th leg of the TLP521-4 is the output terminal.
FIG. 3 is a circuit diagram of a Hall reactive power transmitter (3) in the control system of the invention, wherein a voltage input signal is connected with a low-pass filter formed by a resistor R301 and a capacitor C301 through a transformer, and the output end of the low-pass filter is connected with a potentiometer R302, the capacitor C302 and a Hall element in series; the current signal is input into the coil to form a magnetic field, and the magnetic field is injected into the Hall element, and the output of the Hall element is output after being connected in series with a second-order filter formed by resistors R304 and R305 and capacitors C303 and 304 through a resistor R303.
The switch control module of the invention comprises the following components:
a voltage comparator: inputting a voltage effective value and a voltage threshold value, comparing the voltage effective value and the voltage threshold value, and outputting a comparison result to a trigger condition counter;
triggering condition counter: the output ends are connected with the voltage comparator and the trigger pulse generator, each pulse period operates once for counting or setting zero, and the result is output to the switch trigger judgment device;
trigger pulse generator: the trigger condition counter is used for generating a pulse with a certain period and outputting the pulse to the trigger condition counter;
a switch trigger determiner: and the output of the trigger condition counter and the manual interaction module 7 is received and used for judging whether the condition of the switching action is met or not and sending out a control instruction.
A monostable output delay; and receiving the output of the switch trigger judgment device, and inputting a steady-state output signal to the repeatedly-triggerable monostable trigger after delay time.
Repeatedly triggerable monostable trigger: and receiving an output signal of the monostable output delayer, and inputting a switch control signal to the switch driving module.
Fig. 4 is a functional block diagram of the switch control module according to the present invention. The input signal of the switch control module (8) comes from the signal calculation and filtering module (4) and the man-machine interaction module (7), and the specific process is that the voltage effective value and the voltage reference value are compared instantly by a level comparator and output to a trigger condition counter in real time, and the counting time interval of the counter is generated and controlled by a trigger pulse module; the counting result is output to a switch trigger judging device in real time and is used for comparing with a counting threshold value to judge the control to be implemented by the corresponding switch, and the man-machine interaction module can manually select the switch and set the numerical value of the counting threshold value of the switch trigger judging device; and finally, outputting the switch control signal to a switch driving module through a repeatedly triggerable monostable trigger.
FIG. 5 is a circuit diagram of a voltage comparator in a switch control module of the present invention, the voltage comparator including an operational amplifier, a non-re-triggerable monostable flip-flop;
the non-repeatable triggering monostable trigger consists of CMOS gate circuits G1 and G2, wherein G1 is a NOR gate of 'more than or equal to 1', G2 is a NOT gate of '1', the output of G1 is connected to the input end of G2 through an isolation capacitor C502, the input end of G2 is connected to a voltage Vcc through a resistor R502, and the capacitor C502 is connected in parallel with the resistor R502; the output signal of the operational amplifier is connected to one input end of G1 after passing through an isolation capacitor C501, the output signal of G2 is connected to the other input end of G1, the input voltage of the voltage comparator is connected to the positive electrode of the operational amplifier after passing through a resistor R501, and the threshold voltage of the voltage comparator is connected to the negative electrode of the operational amplifier after passing through a resistor R502.
Fig. 6 is a circuit diagram of a trigger pulse generator in a switch control module of the present invention, wherein the trigger pulse generator is a clock pulse generator with an adjustable duty ratio, and is composed of a 555 timing chip, two diodes D601 and D602, two capacitors C601 and C602, and three resistors R601, R602 and R603, wherein a pin 7 of the 555 timing chip leads out a slide sheet to be connected to the resistor R602, and the R602 is divided into an upper part and a lower part of the R602;
in the trigger pulse generator, after two diodes D601 and D602 are connected, a charge and discharge loop of a capacitor C601 is separated, the discharge loop is composed of D602, R603 on R602, an internal triode and the capacitor C601, and the discharge time is equal to 0.7 (R603 on R602) C601; charging loop D601, R602 lower +R601, C601, charging time equal to 0.7 (R602 lower +R601) C601.
The frequency of the output pulse of the trigger pulse generator is as follows:
wherein R601, R602, R603 refer to the resistance values of the resistors R601, R602, R603, respectively, in ohm, and C601 refers to the capacitance value of the capacitor C601 in law. The duty ratio of the output pulse can be changed by adjusting the potentiometer, but the frequency is unchanged, and the size of the frequency f can be adjusted by setting the resistance values of the resistors R601, R602 and R603 and the capacitance value of the capacitor C601.
FIG. 7 is a circuit diagram of a switch trigger condition counter in the switch control module of the present invention, which is composed of a 74LS161 chip, and outputs a voltage comparator to a zero clearing end of the chip, so that the effective voltage value is higher than the voltage threshold value, and the function of zero clearing is achieved; the pulse trigger is output to the clock end of the chip, the rising edge is triggered, and the counting time interval can be controlled by controlling the pulse generator.
Fig. 8 is a circuit diagram of a monostable output delay in a switch control module of the present invention, the monostable output delay including two operational amplifiers IC1, IC2, two diodes D801, D802, resistors R801, R802, R803, R804, R805, R806, a not gate, isolation capacitors C801, C802, and a switch S;
the input voltage Ui of the monostable output delay is connected to the positive electrode of the operational amplifier IC1, the negative electrode of the operational amplifier IC1 is grounded through a resistor R801, the output end of the operational amplifier IC1 is connected with the negative electrode of the operational amplifier IC1 through a resistor R802, the output end of the operational amplifier IC1 is sequentially connected with a NOT gate, a resistor R803 and an isolation capacitor C801 and then connected with the negative electrode of the operational amplifier IC2, the negative electrode of the operational amplifier IC2 is grounded through the isolation capacitor C802 and sequentially grounded through resistors R806, R805 and R804, and the capacitors C801 and C802 are connected in parallel and connected in parallel with a serial branch formed by the resistors R806, R805 and R804; two ends of the resistor R806 are connected with a diode D801 in parallel, and the positive electrode of the diode D801 is connected to the negative electrode of the operational amplifier IC 2; the positive electrode of the operational amplifier IC2 is connected to the positive electrode of the diode D802 through the switch S, the negative electrode of the diode D802 is grounded, and the output voltage Uo of the monostable output delay is output by the operational amplifier IC 2.
FIG. 9 is a circuit diagram of a re-triggerable monostable flip-flop in the switch control module of the present invention, the re-triggerable monostable flip-flop comprising a 555 timer chip, a PNP triode, resistor R901, isolation capacitors C901, C902;
the 1 st pin of the 555 timing chip is grounded and connected to the collector of the PNP triode, the 2 nd pin is connected to the base of the PNP triode and connected to the input voltage Ui, the 3 rd pin is the output end Uo of the repeatedly triggerable monostable trigger, the 4 th pin and the 8 th pin are connected to the positive bias voltage Vcc, the 5 th pin is connected to the collector of the triode through an isolation capacitor C902, the 6 th pin and the 7 th pin are connected to the emitter of the PNP triode together and connected to the collector of the PNP triode through an isolation capacitor C901, and a resistor R901 is connected between the 7 th pin and the 4 th pin.
Fig. 10 is a circuit diagram of a second isolation module in the control system of the present invention, which is a MOSFET driving circuit, and selects a chip TLP250 to perform photoelectric isolation on the main circuit and the driving circuit, wherein pin No. 3 of the chip TLP250 is connected to an optical isolation digital output port of a lower computer; the pin 2 of the chip TLP250 is connected with a power interface on a lower computer through a current limiting resistor R1101; the pin 6 and the pin 5 of the chip TLP250 are connected to the gate and the source of the MOSFET through the current limiting resistor R1102 and the voltage stabilizing tube D of 10V, respectively; when the low level is input, the gate-source voltage of the MOSFET is clamped at the breakdown voltage of the voltage stabilizing tube, so that the MOSFET can be stably turned off.
FIG. 11 is a circuit diagram of a third isolation module in the control system of the present invention, wherein one end of the switch is connected to the power supply Vcc1, and the other end is connected to the 3 rd leg of the photo-coupler TLP521-4 through a resistor R1103 of 150 ohms; the power ground GND1 is connected with the 2 nd pin of the TLP521-4, the power Vcc2 is connected with the 14 th pin of the TLP521-4 through a resistor R1101 of 100 kiloohms, the power ground GND2 is connected with the 13 th pin of the TLP521-4 through a resistor R1102 of 500 kiloohms, and the upper end of the resistor R1102 of 500 kiloohms is an output end.
In another embodiment of the present invention, the control of the transient overvoltage of the dc system is achieved by applying the above-mentioned SVG-based dc system transient overvoltage control system, and the specific method is that the control system is controlled by a switch (including a switch (11) and a switch (12)), so as to achieve the control (suppression) of the transient overvoltage of the dc system.
Fig. 12 is a flowchart of a transient overvoltage control method applying the control system of the present invention, and the specific steps are as follows:
the first step: setting the trigger condition counting result N of the switch to zero;
and a second step of: collecting an SVG access point bus voltage instantaneous value, and instantly obtaining an effective value Urms of the voltage by adopting abc-dq conversion;
and a third step of: judging whether the voltage effective value Urms is larger than a voltage threshold value or not;
fourth step: if the effective voltage value is smaller than the voltage threshold value, setting N to be zero; if the voltage effective value is greater than the voltage threshold, n=n+1;
fifth step: manually setting a selection action switch according to the man-machine interaction module (7);
sixth step: comparing the value of N with a set counting threshold value;
seventh step: if the value of N is greater than or equal to the counting threshold value, a switch-off instruction is sent out; if the value of N is smaller than the counting threshold value and is not equal to 0, the switch state is kept unchanged; if the value of N is equal to 0, a switch closing instruction is sent out; and ending the control and returning to the second step.
In a specific embodiment of the present invention, the voltage threshold is 1.2un, un is the rated voltage of the control system, and the count threshold is 5.
In the control method, the voltage pre-count, the counting result threshold and the selective action switch can be manually set or changed in a man-machine interaction mode, when the power grid side fails, dynamic reactive support can be provided, when the SVG dynamic reactive compensation has transient overvoltage, the switching switch of the SVG auxiliary capacitor or resistor can be automatically controlled, and the influence of the SVG auxiliary transient overvoltage is effectively reduced.
In summary, the invention has the following beneficial effects:
1. through man-machine interaction mode, can set for change voltage threshold, count result threshold and select action switch by personnel.
2. The method can rapidly judge the effective value of the power grid voltage and effectively shorten the instruction sending time.
3. When the power grid side fails, dynamic reactive power support can be provided, and system stability is improved.
4. When the SVG dynamic reactive power compensation has the transient overvoltage condition, the switching switch of the SVG auxiliary capacitor or resistor can be automatically controlled, and the influence of the SVG auxiliary transient overvoltage is effectively reduced.
It should be understood by those skilled in the art that the embodiments of the present invention are only used to describe preferred embodiments of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions easily conceivable by those skilled in the art within the technical scope of the present invention should be covered by the scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.
Claims (15)
1. Control system for suppressing transient overvoltage of direct current system based on SVG, which is characterized by comprising: the system comprises a voltage and current measuring module (1), an isolation module I (2), a Hall reactive power transmitter module (3), a signal calculating and filtering module (4), a PWM (pulse-width modulation) control module (5), an isolation module II (6), a man-machine interaction module (7), a switch control module (8), an isolation module III (9), a switch selecting and driving module (10), a switch I (11) and a switch II (12);
the voltage and current measuring module (1) is connected with the Hall reactive power transmitter module (3) and the signal calculating and filtering module (4) through the first isolation module (2) at the same time; the signal calculation and filtering module (4), the PWM control module (5) and the isolation module II (6) are connected in sequence; the switch control module (8) is connected with the signal calculation and filtering module (4); the man-machine interaction module (7), the switch control module (8), the isolation module III (9) and the switch selection and driving module (10) are connected in sequence; the first switch (11) and the second switch (12) are respectively connected with the switch selection and driving module (10);
the voltage and current measurement module (1) is used for acquiring an SVG access point bus instantaneous voltage value and an instantaneous current value between the SVG and a power grid, and transmitting the instantaneous voltage value and the instantaneous current value to the isolation module I (2) and the Hall reactive power transmitter module (3);
the first isolation module (2) is used for isolating the first and second systems, converting a strong voltage current signal of the first system into a weak voltage current signal of the second system, and transmitting the weak voltage current signal to the signal calculation and filtering module (4);
the Hall reactive power transmitter module (3) uses the measurement data of the voltage and current measurement module (1) to obtain reactive power exchanged between the SVG and the power grid, and plays a role in isolating a primary system and a secondary system at the same time;
the signal calculation and filtering module (4) adopts abc-dq conversion to instantly obtain voltage and current effective values, further calculates a voltage reference value, a current reference value and a reactive reference value, and transmits calculation results of the voltage reference value, the current reference value and the reactive reference value to the PWM control module (5) after filtering, and transmits the obtained voltage effective values to the switch control module (8) after filtering;
the PWM control module (5) is used for calculating the trigger angle of the inverter bridge thyristor, generating trigger pulse and outputting the trigger pulse to the isolation module II (6);
the second isolation module (6) is used for isolating the first and second systems, converting weak signals of the second system into strong signals of the first system and outputting the strong signals to the SVG inverter bridge;
the man-machine interaction module (7) comprises a keyboard, a display and a conversion interface, and is used for setting parameters and displaying data and states of the system in real time, so that serial communication between the system and an upper computer is realized; the parameter setting comprises the steps of manually setting a trigger counting result N to zero, setting a voltage threshold value for comparison with a voltage effective value, setting a counting threshold value for comparison with N and manually selecting an action switch, and finally outputting data of the parameter setting to a switch control module (8);
the switch control module (8) is used for calculating and judging whether the system meets the action conditions of the first switch (11) and the second switch (12), realizing the selection of an action switch according to the parameter setting of the man-machine interaction module (7), and outputting a switch control instruction to the isolation module III (9); the switch control module (8) comprises the following components:
a voltage comparator: inputting a voltage effective value and a voltage threshold value, comparing the voltage effective value and the voltage threshold value, and outputting a comparison result to a trigger condition counter;
triggering condition counter: the output ends are connected with the voltage comparator and the trigger pulse generator, each pulse period operates once for counting or setting zero, and the result is output to the switch trigger judgment device;
trigger pulse generator: the trigger condition counter is used for generating a pulse with a certain period and outputting the pulse to the trigger condition counter;
a switch trigger determiner: the output of the trigger condition counter and the man-machine interaction module (7) is received and used for judging whether the trigger condition counter meets the condition of the switch action or not and sending out a control instruction;
a monostable output delay; receiving the output of the switch trigger judgment device, and inputting a steady-state output signal to the repeatedly-triggerable monostable trigger after delay time;
repeatedly triggerable monostable trigger: receiving an output signal of the monostable output delayer, and inputting a switch control signal to the switch driving module;
the isolation module III (9) is used for isolating the primary system and the secondary system, converting weak signals of the secondary system into strong signals of the primary system and outputting the strong signals to the switch selection and driving module (10);
the switch selection and driving module (10) realizes the selection and the opening and the closing of a switch I (11) for controlling the resistor and a switch II (12) for controlling the capacitor according to the output of the isolation module III (9).
2. The control system according to claim 1, wherein the switch control module (8) completes the judgment of whether the system meets the switch action condition and the switch selection according to the voltage effective value output by the signal calculation and filtering module (4) and the voltage threshold value, the counting threshold value and the switch selection instruction input by the man-machine interaction module (7), and outputs the control instruction to the switch driving module (10), the driving switch one (11) or the switch (12) through the isolation module three (9).
3. The control system according to any one of claims 1-2, wherein the isolation module one (2) comprises a photo-coupler TLP521-4, a resistor R201, R202, R203; wherein the 1 st pin of the photoelectric coupler TLP521-4 is connected with one end of a switch through a resistor R203, and the other end of the switch is connected with a power supply V cc1 Connecting;
the 2 nd pin of the photoelectric coupler TLP521-4 is connected with GND 1;
the 16 th pin of the photoelectric coupler TLP521-4 is connected with a power supply V through a resistor R201 cc2 Are connected;
the 15 th pin of the photo coupler TLP521-4 is connected to the power ground GND2 through a resistor R202, and the 15 th pin is the output terminal of the isolation module one (2).
4. A control system according to claim 3, characterized in that the resistor R201 is set to 10-100 ohms, the resistor R202 is set to 100 kiloohms, and the resistor R203 is set to 250 ohms.
5. The control system according to claim 1 or 2, characterized in that in the hall reactive power transmitter (3), a voltage input signal is connected to a low-pass filter composed of a resistor R301 and a capacitor C301 through a transformer, and an output end of the low-pass filter is connected in series with a potentiometer R302, the capacitor C302 and a hall element; the current signal is input into the coil to form a magnetic field, and the magnetic field is injected into the Hall element, and the output of the Hall element is output after being connected in series with a second-order filter formed by resistors R304 and R305 and capacitors C303 and 304 through a resistor R303.
6. The control system of claim 1, wherein the voltage comparator comprises an operational amplifier, a non-re-triggerable monostable trigger;
the non-repeatable triggering monostable trigger consists of CMOS gate circuits G1 and G2, wherein G1 is a NOR gate, G2 is a NOT gate, the output of G1 is connected to the input end of G2 through an isolation capacitor C502, the input end of G2 is connected to voltage Vcc through a resistor R502, and the capacitor C502 is connected in parallel with the resistor R502; the output signal of the operational amplifier is connected to one input end of G1 after passing through an isolation capacitor C501, the output signal of G2 is connected to the other input end of G1, the input voltage of the voltage comparator is connected to the positive electrode of the operational amplifier after passing through a resistor R501, and the threshold voltage of the voltage comparator is connected to the negative electrode of the operational amplifier after passing through a resistor R502.
7. The control system according to claim 1, wherein the trigger pulse generator is a duty cycle adjustable clock pulse generator, and is composed of a 555 timing chip, two diodes D601 and D602, two capacitors C601 and C602, and three resistors R601, R602 and R603, wherein a pin 7 of the 555 timing chip leads out a slide sheet to be connected to the resistor R602, and divides the R602 into an upper part and a lower part of the R602, and the slide sheet and the R602 form a potentiometer;
the frequency f of the output pulse of the trigger generator is calculated by the following equation:
wherein R601, R602, R603 refer to the resistance values of the resistors R601, R602, R603, respectively, in ohm, and C601 refers to the capacitance value of the capacitor C601 in law.
8. The control system of claim 1, wherein the trigger condition counter is comprised of a 74LS161 chip, and when the voltage comparator outputs a voltage effective value to a zero clearing terminal of the 74LS161 chip, zero clearing is performed if the voltage effective value is lower than a voltage threshold count;
the trigger pulse generator outputs to the clock end of the 74LS161 chip, the rising edge triggers, and the counting time interval is controlled by controlling the trigger pulse generator.
9. The control system of claim 1, wherein the monostable output delay comprises two operational amplifiers IC1, IC2, two diodes D801, D802, resistors R801, R802, R803, R804, R805, R806, a not gate, isolation capacitors C801, C802, a switch S;
the input voltage Ui of the monostable output delay is connected to the positive electrode of the operational amplifier IC1, the negative electrode of the operational amplifier IC1 is grounded through a resistor R801, the output end of the operational amplifier IC1 is connected with the negative electrode of the operational amplifier IC1 through a resistor R802, the output end of the operational amplifier IC1 is sequentially connected with a NOT gate, a resistor R803 and an isolation capacitor C801 and then connected with the negative electrode of the operational amplifier IC2, the negative electrode of the operational amplifier IC2 is grounded through the isolation capacitor C802 and sequentially grounded through resistors R806, R805 and R804, and the capacitors C801 and C802 are connected in parallel and connected in parallel with a serial branch formed by the resistors R806, R805 and R804; two ends of the resistor R806 are connected with a diode D801 in parallel, and the positive electrode of the diode D801 is connected to the negative electrode of the operational amplifier IC 2; the positive electrode of the operational amplifier IC2 is connected to the positive electrode of the diode D802 through the switch S, the negative electrode of the diode D802 is grounded, and the output voltage Uo of the monostable output delay is output by the operational amplifier IC 2.
10. The control system of claim 1, wherein the re-triggerable monostable flip-flop consists of a 555 timer chip, a PNP transistor, resistor R901, isolation capacitors C901, C902;
the 1 st pin of the 555 timing chip is grounded and connected to the collector of the PNP triode, the 2 nd pin is connected to the base of the PNP triode and connected to the input voltage Ui, the 3 rd pin is the output end Uo of the repeatedly triggerable monostable trigger, the 4 th pin and the 8 th pin are connected to the positive bias voltage Vcc, the 5 th pin is connected to the collector of the triode through an isolation capacitor C902, the 6 th pin and the 7 th pin are connected to the emitter of the PNP triode together and connected to the collector of the PNP triode through an isolation capacitor C901, and a resistor R901 is connected between the 7 th pin and the 4 th pin.
11. The control system according to claim 1 or 2, wherein the second isolation module (6) adopts a MOSFET driving circuit, the main circuit and the driving circuit are photoelectrically isolated by the chip TLP250, and pin No. 3 of the chip TLP250 is connected to an optical isolation digital output port of the lower computer; the pin 2 of the chip TLP250 is connected with a power interface on a lower computer through a current limiting resistor R1101; the pin 6 and the pin 5 of the chip TLP250 are connected to the gate and the source of the MOSFET through the current limiting resistor R1102 and the voltage stabilizing tube D of 10V, respectively; when the low level is input, the gate-source voltage of the MOSFET is clamped at the breakdown voltage of the voltage stabilizing tube, so that the MOSFET is turned off.
12. The control system according to claim 1 or 2, wherein the isolation module three (9) comprises a switch, a photo coupler TLP521-4, and resistors R1101, R1102, R1103, one end of the switch being connected to the power supply Vcc1, and the other end being connected to the 3 rd leg of the photo coupler TLP521-4 through a resistor R1103 of 150 ohms; the power ground GND1 is connected with the 2 nd pin of the TLP521-4, the power Vcc2 is connected with the 14 th pin of the TLP521-4 through a resistor R1101 of 100 kiloohms, the power ground GND2 is connected with the 13 th pin of the TLP521-4 through a resistor R1102 of 500 kiloohms, and the upper end of the resistor R1102 of 500 kiloohms is an output end.
13. A control method for suppressing transient overvoltage of a direct current system using the control system according to any one of claims 1 to 12, characterized by comprising the steps of:
the first step: setting the trigger condition counting result N of the switch to zero;
and a second step of: collecting an SVG access point bus voltage instantaneous value, and instantly obtaining an effective value Urms of the voltage by adopting abc-dq conversion;
and a third step of: judging whether the voltage effective value Urms is larger than a voltage threshold value or not;
fourth step: if the effective voltage value is smaller than the voltage threshold value, setting N to be zero; if the voltage effective value is greater than the voltage threshold, n=n+1;
fifth step: comparing the value of N with a set counting threshold value;
sixth step: if the value of N is greater than or equal to the counting threshold value, a switch-off instruction is sent out; if the value of N is smaller than the counting threshold value and is not equal to 0, the switch state is kept unchanged; if the value of N is equal to 0, a switch closing instruction is sent out; and ending the control and returning to the second step.
14. The control method of claim 13, wherein the voltage threshold is 1.2Un, where Un is a rated voltage of the control system.
15. The control method of claim 14, wherein the count threshold is 5.
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