High-voltage ac switching composite switch with complete zero-voltage closing and turning-off

Abstract

A high-voltage AC switching composite switch with complete zero-voltage closing conduction and turning off, relates to the field of high-voltage AC power grid switch, uses N groups of unidirectional thyristors in series with N groups of diodes to replace the original N groups of bidirectional thyristors in series, AC power passes through a voltage reduction circuit to input voltage waveform signals to an optical coupler, the output of the optical coupler is connected to the I / O interface of a single-chip microcomputer, after receiving an external conduction signal, the single-chip microcomputer identifies the half wave in which the diode string of the auxiliary circuit of the power grid is cut off, delays for 3 ms, and outputs a signal for controlling the conduction of the unidirectional thyristor, all unidirectional thyristors will be turned on in this half wave, until the next half wave, the diode group is naturally turned on, the auxiliary conduction circuit is turned on, after identifying the negative half wave, the single-chip microcomputer delays for 7.5 ms from zero point, and sends a command to turn on the AC vacuum contactor, the auxiliary conduction circuit is a group of multiple strings of thyristors and a group of the same number of strings of diodes in series that can meet the voltage level.

Description

Technical Field

[0001] This invention relates to the field of high-voltage AC power grid switches. More precisely, it is a high-voltage AC switching composite switch that conducts an auxiliary circuit in a current-free state, waits for current to flow through the auxiliary circuit after the auxiliary circuit is turned on, and then connects to the main circuit (vacuum contactor). After the main circuit is turned on, the auxiliary circuit is disconnected. This switch is used in AC power grids and is a high-voltage AC switching composite switch with completely zero-voltage closing conduction and disconnection. Background Technology

[0002] In the AC high-voltage field, switches include vacuum contactors, vacuum circuit breakers, and oil switches. When these switches are directly switched on and off with a load, the inrush current is large, which has a great impact on the power grid, and the number of switching operations is small.

[0003] Another approach uses multiple sets of thyristor valves connected in series as an auxiliary switching circuit. This circuit conducts at the zero-voltage point of the AC mains, and then a vacuum contactor or vacuum circuit breaker follows suit. This type of switch experiences almost no inrush current when connected at zero voltage. However, it still has drawbacks. While the microsecond-level response speed of the thyristors is sufficient to achieve zero-voltage conduction at 50Hz AC mains, the sequential conduction of multiple valves still presents a challenge. Theoretically, the last valve to conduct must still bear the entire voltage. Therefore, this structure has significant limitations in high-voltage applications, and the problem is particularly severe with very high voltage levels or capacitive loads. Summary of the Invention

[0004] The purpose of this invention is to provide a high-voltage AC switching composite switch with completely zero-voltage closed-loop conduction and cutoff. Utilizing the sinusoidal wave characteristics of the 50Hz high-voltage power grid, it replaces the original N sets of series-connected bidirectional thyristor valves with N sets of unidirectional thyristor valves connected in series with N sets of diodes. As an auxiliary circuit for the high-voltage composite switch, the main circuit also uses a vacuum contactor such as... Figure 5 Current technology uses N sets of bidirectional thyristors in series in the auxiliary circuit, and a vacuum tube in the main circuit. Figure 4 The specific number N in the N groups corresponds to the voltage level of the application. For example, if each group is used at a voltage of 350Vac and the rated voltage of the diode and thyristor is >2000V, then for a voltage level of 35KVac, N = 35KVac / 0.35Vac = 100, and N groups are 100 series.

[0005] The working principle of this invention is as follows: In the 50Hz power grid sine wave, during the half-wave when the diode valve group is not conducting, all unidirectional thyristor valve groups are triggered to conduct. Because the diodes are in the off state at this time, the conduction of multiple thyristor valve groups is completed in a state without current, so no current flows. When the next half-wave arrives, the auxiliary conduction circuit naturally conducts.

[0006] During the half-wave of diode conduction, the vacuum switch in the main circuit completes conduction. This is because the voltage drop across the main circuit switch at this time is the sum of the voltage drops of each diode plus the sum of the voltage drops of each unidirectional thyristor. For example, the sum of the voltage drops of 100 diodes is 0.7 * 100 = 70 Vac. If we calculate the voltage drop of 100 thyristors as 1.4 V after each string is turned on, the sum of the voltage drops of the 100 unidirectional thyristor valves is 140 Vac. The total voltage of the auxiliary circuit when the main circuit is closed is 140 + 70 = 210 V. This voltage is negligible for the voltage level of 100 valves.

[0007] The signal is drawn from the high-voltage line L of the power grid, passing through a high-voltage voltage divider capacitor and a current-limiting resistor, as follows: Figure 6 The input of the optocoupler is connected to the power supply (N). The output of the optocoupler is the opto-isolated signal I0, which is connected to the microcontroller's I / O input pin. The microcontroller's default input is high level. When the optocoupler is turned on, it changes to a high level. When the optocoupler is turned off, it returns to a high level. Obviously, the microcontroller can distinguish between the positive and negative half-waves by the change in high and low levels.

[0008] Based on the positive and negative half-wave patterns, the microcontroller can control the unidirectional thyristors, turning on all the thyristors during the half-wave when the diode string is not conducting. Because the diode string is in the off state at this time, the thyristors do not have a specific order of conduction; even the last thyristor to conduct does not need to bear additional voltage. After all the unidirectional thyristors have conducted, the auxiliary circuit formed by the diodes waits for the next half-wave to conduct naturally.

[0009] The advantages of this invention are: It utilizes a series diode group in the auxiliary circuit. During the half-wave when the diodes are off, the thyristor is triggered to conduct. Because the diodes are off, no current flows when the thyristor conducts, resulting in no inrush current. In the next half-wave, the diodes naturally conduct, and the thyristor valve group also conducts, thus completing the entire auxiliary circuit. At this point, the vacuum contactor closes. As long as the vacuum contactor conducts within this half-wave, the voltage across the vacuum contactor is the sum of the voltage drops across all the thyristors and diodes in the auxiliary circuit. Assuming N diodes and N thyristors, the voltage across the contactor is 2N * 0.7. Taking a voltage drop of 0.7V after the diodes and thyristors conduct, and using N=100 as an example, the voltage drop across the vacuum contactor is only 140Vac, so the inrush current when the vacuum contactor closes can be ignored.

[0010] The existing bidirectional thyristor, used as an auxiliary circuit, is triggered to conduct under high voltage. It needs to be ensured that the conduction occurs when the voltage of the sine wave crosses zero. Even a slight deviation will result in a large inrush current because the load is a capacitor. Since the resistance of the capacitor load is zero at the moment of conduction, a large inrush current will occur as long as the voltage is not exactly zero at the moment of conduction.

[0011] This patent utilizes the characteristic of diodes being half-wave conduction and half-wave cutoff in sinusoidal alternating current. As long as the thyristor is conducting during the half-wave cutoff of the diode, no inrush current can be guaranteed. It provides a time range of 10ms (half a cycle), which can completely guarantee that the thyristor will complete the conduction without any inrush current. Attached Figure Description

[0012] Figure 1 This is a diagram of the diode string assembly of the present invention.

[0013] Figure 2 This is a series diagram of the unidirectional thyristor valve of the present invention.

[0014] Figure 3 This is a diagram of a bidirectional thyristor valve connected in series.

[0015] Figure 4 It is existing technology.

[0016] Figure 5 This is a diagram of an auxiliary conduction circuit composed of unidirectional thyristor valves connected in series, as described in this invention.

[0017] Figure 6 It is a control signal circuit diagram that can identify the zero point of the sine wave in a high-voltage AC circuit and determine the origin of the signal's time coordinate.

[0018] Figure 7 It is a diagram showing the control signal received by the thyristor and vacuum contactor under high voltage 50Hz AC and the coordinates of the closed point. Detailed Implementation

[0019] Building circuits, such as Figure 4 Through secondary circuit Figure 6 The alternating current (AC) is stepped down and its voltage waveform signal is input to the optocoupler. The output of the optocoupler is connected to the I / O interface of the microcontroller. After receiving the external conduction signal, the microcontroller identifies the negative half-wave of the power grid (the half-wave in which the diode string in the auxiliary circuit is cut off), delays for 3ms, and outputs a signal to control the conduction of the unidirectional thyristors. All unidirectional thyristors will conduct within this half-wave. When the next half-wave arrives, the diode group will naturally conduct, and the auxiliary circuit will conduct. After identifying the negative half-wave, the microcontroller delays for 7.5ms from zero point and issues a command to turn on the AC vacuum contactor. Because the AC vacuum contactor closes in 7.5ms, its closing point will fall at the center point of the half-wave in which the auxiliary circuit is conducting. This solves the problem of some dispersion in the closing time of the vacuum contactor contacts, and the given inrush-free error range is ±5ms.

Claims

1. A high-voltage AC switching composite switch with complete zero-voltage closing, conduction and turning off, the main circuit using a vacuum contactor, N sets of unidirectional thyristors in series with N sets of diodes to replace the original N sets of bidirectional thyristors in series, AC power passing through a voltage reduction circuit to input voltage waveform signals to an optical coupler, the output of the optical coupler connected to the I / O interface of a single-chip microcomputer, the single-chip microcomputer after receiving an external conduction signal, identifying the half wave in which the diode string of the power grid auxiliary circuit is cut off, delaying for 3 ms, outputting a signal to control the conduction of the unidirectional thyristors, all the unidirectional thyristors being turned on in this half wave, until the next half wave, the diode string being naturally turned on, the auxiliary circuit being turned on, the single-chip microcomputer after identifying the negative half wave, delaying for 7.5 ms from zero, sending a command to turn on the AC vacuum contactor, because the AC vacuum contactor is closed for 7.5 ms, so the closing point will fall on the center point of the half wave in which the auxiliary circuit is turned on, characterized in that: The auxiliary conducting loop is a group of thyristors and a group of diodes in series, which can meet the voltage level. The specific number of N in the N groups corresponds to the applied voltage level. The applied voltage of each group is 350 Vac, and the rated voltage of the diodes and thyristors is >2000V. For the voltage level of 35KVac, N=35KVac / 0.35Vac=100, and the N groups are 100 series.

2. A high voltage AC throw over composite switch with zero voltage closure and turn off as claimed in claim 1 wherein: The auxiliary loop conducting condition is the rising edge of the grid voltage, and can maintain a high level for 3ms, thereby excluding harmonic interference.

Images