A soft switching control circuit and control method for a power conversion device

Abstract

This invention discloses a soft-switching control circuit and method for a power conversion device, electrically connected to both the power conversion device and an AC power supply. It includes a first relay and a second relay, with the power conversion device electrically connected to the AC power supply sequentially via either the first relay and the second relay or sequentially via the second relay and the first relay. The two ends of the second relay are connected in parallel to the two pins of a thyristor. The invention also includes a controller electrically connected to the first relay, the second relay, and the thyristor. The beneficial effect is that it ensures that both series-connected relays are in a zero-current or near-zero-current state at the instant of closing and opening. This fundamentally eliminates the huge surge current and arc erosion and impact on the contacts caused by traditional switching methods.

Description

Technical Field

[0001] This invention relates to the field of power conversion device control, and more particularly to a soft-switching control circuit and control method for power conversion devices. Background Technology

[0002] Power conversion devices, such as grid-connected inverters, uninterruptible power supplies (UPS), and frequency converters, commonly use mechanical relays or contactors as switching actuators when connecting to or disconnecting from the AC power grid (or AC power source). This approach is widely used due to its simple structure and relatively low cost. However, with the increasing demands for system reliability, lifespan, and safety, the inherent technical shortcomings of traditional relay switching methods are becoming increasingly apparent, mainly in the following aspects:

[0003] First, direct switching of a single relay presents a significant electrical surge problem. The mechanical action time of a relay (such as closing and opening time) typically exhibits a dispersion of several milliseconds or even greater, making it difficult to precisely control its closing at the zero-crossing point of the AC voltage. If closing occurs at the peak of the mains voltage or a high instantaneous value, a huge surge current (inrush current) will be generated due to the charging of the load-side capacitor or sudden changes in circuit impedance. This inrush current will severely erode the relay contact surface, leading to increased contact resistance and accelerated temperature rise, greatly shortening the relay's electrical life. In extreme cases, it may even cause the contacts to weld together, causing relay failure and triggering system malfunctions.

[0004] Secondly, to suppress the electric arc generated when the relay disconnects an inductive load and to mitigate the closing impact to some extent, existing technologies often connect an RC absorption circuit (also known as a buffer circuit or arc-extinguishing circuit) composed of a resistor and a capacitor in parallel across the relay contacts. Although this circuit can absorb some energy and suppress arc propagation, it also introduces new problems: First, after the relay closes, the RC circuit is always connected in parallel in the current-carrying loop, and its capacitive component will lead to continuous capacitive leakage current, generating a significant amount of standby power consumption, which does not conform to the current design trend of high-efficiency electronic products; Second, in applications such as photovoltaics and energy storage, where electrical safety isolation (such as reinforced insulation) is extremely important, the presence of this RC circuit may change the overall insulation structure of the equipment, and its own insulation performance may become an obstacle to meeting high-standard safety specifications. Summary of the Invention

[0005] Purpose of the invention: The purpose of this invention is to solve the technical problems in the prior art and provide a soft-switching control circuit and control method for power conversion devices.

[0006] Technical solution: This application proposes a soft-switching control circuit for a power conversion device, which is electrically connected to both the power conversion device and the AC power supply. Its features are as follows:

[0007] The device includes a first relay and a second relay, and the power conversion device is electrically connected to the AC power supply in sequence through the first relay and the second relay or in sequence through the second relay and the first relay.

[0008] The two ends of the second relay are connected in parallel to the two pins of the thyristor;

[0009] It also includes a controller, which is electrically connected to the first relay, the second relay and the thyristor respectively.

[0010] Preferably, an RC circuit is connected in parallel across the two ends of the second relay.

[0011] Preferably, the power conversion device is a grid-connected inverter, an uninterruptible power supply, or a frequency converter.

[0012] Preferably, the first relay is connected between the power conversion device and the second relay, or between the second relay and the AC power supply.

[0013] Preferably, the two poles of the AC power supply are electrically connected to the AC voltage zero-crossing detection circuit, and the AC voltage zero-crossing detection circuit is electrically connected to the controller.

[0014] This application also proposes a soft-switching control method for a power conversion device, applicable to a soft-switching control circuit for a power conversion device as described in the above embodiments, comprising the following steps:

[0015] This includes the switching on control process and the switching off control process;

[0016] The switching and connection control process includes:

[0017] Step S1a: When the power conversion device and the AC power supply need to be electrically connected, the first relay is closed and the second relay is opened, while the controller does not send a trigger signal to the thyristor.

[0018] Step S2a: Perform zero-crossing detection on the AC power supply voltage;

[0019] Step S3a: When the voltage of the AC power supply is detected to reach the zero-crossing point, a trigger signal is sent to the thyristor to turn on the thyristor;

[0020] Step S4a: After the thyristor is turned on, the controller controls the closing of the second relay;

[0021] Step S5a: When the AC current flowing through the thyristor naturally crosses zero, the thyristor automatically disconnects, allowing the AC current to flow to the second relay, thus completing the connection process;

[0022] The cut-off control process includes:

[0023] Step S1b: When it is necessary to disconnect the power conversion device from the AC power supply, control the second relay to disconnect;

[0024] Step S2b: Set a preset delay time through the controller to disconnect the first relay and complete the disconnection process.

[0025] Preferably, the second relay is closed immediately after the thyristor is turned on, or the process is performed at any time within the same AC half-wave cycle before the thyristor turns off at the next zero current crossing.

[0026] Preferably, the preset time is 10 milliseconds to 50 milliseconds.

[0027] Preferably, in the stage after step S1b is executed and before step S2b is executed, the first relay remains closed to isolate the power conversion device from the AC power supply side and the RC circuit.

[0028] Beneficial effects:

[0029] This invention ensures that both series relays are in a zero-current or near-zero-current state at the moment of closing and opening by using a turn-on sequence of "closing K1 first, then triggering the thyristor at the voltage zero-crossing point, and finally closing K2" and a turn-off sequence of "opening K2 first (with RC protection), then opening K1". This fundamentally eliminates the erosion and impact on the contacts caused by the huge surge current and disconnection arc in traditional switching methods, changing the relay failure mode from "electrical life exhaustion" to "mechanical life exhaustion" as the dominant factor, thereby increasing the service life and reliability of the relay and even the entire switching system by multiples or even orders of magnitude.

[0030] By connecting two standard relays (K1 and K2) in series, a double insulation barrier is formed. When the system is disconnected, the insulation voltage between the AC power supply and the power conversion device is shared by both relays, allowing this structure to easily meet stringent safety standards such as "reinforced insulation." Compared to solutions using a single special high-voltage relay, this invention achieves the same standard using a combination of conventional low-voltage relays, significantly reducing hardware costs and design complexity.

[0031] The RC absorption circuit in this invention only functions at the instant the second relay (K2) is disconnected, absorbing energy and suppressing the arc to achieve a "soft disconnect." During normal system operation, current flows through the main contacts of the relay, the RC circuit is short-circuited, and no longer forms a leakage current path. This avoids the capacitive leakage current and standby power consumption caused by the continuous parallel connection of the RC circuit in traditional solutions, conforming to the design direction of green and high-efficiency power supply products.

[0032] In the intermediate state of the switching process (K2 is off, K1 is not off), since the first relay (K1) remains closed, it physically isolates the internal circuitry of the power conversion device (typically including filter capacitors, etc.) from the grid side and the RC snubber circuit. This design effectively prevents grid-side interference or noise from coupling into the sensitive power conversion device through the RC circuit, and also avoids the possibility of internal capacitors discharging to the grid side through the RC circuit, thus improving system safety during faults or maintenance. Attached Figure Description

[0033] Figure 1 This invention provides a schematic diagram of the switching and connection control process framework.

[0034] Figure 2 This invention provides a schematic diagram of the control process framework for the cutting-off and opening process;

[0035] Figure 3 A schematic diagram of an example control circuit is provided for this invention;

[0036] Figure 4 This invention provides another example of a control circuit schematic diagram;

[0037] Figure 5 This invention provides a schematic flowchart of the switching and connection control process.

[0038] Figure 6 This invention provides a schematic flowchart of the process for controlling the switching on and off of devices. Detailed Implementation

[0039] To make the technical solution of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0040] Example 1

[0041] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention. Unless otherwise defined, the technical or scientific terms used herein should have the ordinary meaning understood by those skilled in the art. The terms "including" and similar expressions used herein mean that the element or object preceding the term covers the element or object listed after the term and its equivalents, but do not exclude other elements or objects.

[0042] In response to the problems existing in the current technology, such as Figure 3-4As shown, this invention proposes a soft-switching control circuit for a power conversion device, which is electrically connected to both the power conversion device and the AC power supply.

[0043] Including a first relay K1 and a second relay K2, the power conversion device sequentially passes through the first relay K1 and the second relay K2 (e.g., Figure 3 ) or sequentially connected to the AC power supply via the second relay K2 and the first relay K1 (e.g. Figure 4 );

[0044] The two pins of the thyristor TR1 are connected in parallel across the two ends of the second relay K2 to provide a temporary current path during the switching and connection phase, thereby achieving zero-current closing of the second relay K2.

[0045] It also includes a controller, which is electrically connected to the first relay K1, the second relay K2 and the thyristor TR1 respectively, and is used to output control signals to precisely control the on and off timing of each component.

[0046] An RC circuit is connected in parallel across the two ends of the second relay K2 to absorb the induced electromotive force generated when the contacts separate during the switching phase, suppress the arc, and achieve soft disconnection of the second relay K2.

[0047] The power conversion device is a grid-connected inverter, uninterruptible power supply, or frequency converter, which can be adapted to different power electronics application scenarios.

[0048] The first relay K1 is connected between the power conversion device and the second relay K2, or between the second relay K2 and the AC power supply.

[0049] The two poles of the AC power supply are electrically connected to the AC voltage zero-crossing detection circuit, and the AC voltage zero-crossing detection circuit is electrically connected to the controller.

[0050] This application also provides a soft-switching control method for a power conversion device, applicable to a soft-switching control circuit for a power conversion device as described in the above embodiments, comprising the following steps:

[0051] This includes the switching on control process and the switching off control process;

[0052] Combination Figure 1 , Figure 5 The switching and connection control process includes:

[0053] Step S1a: When the power conversion device and the AC power supply need to be electrically connected, the first relay K1 is closed and the second relay K2 is opened, and the controller does not send a trigger signal to the thyristor TR1. At this time, the main circuit is in an open circuit state, and the first relay K1 closes under zero current conditions to avoid the influence of inrush current;

[0054] Step S2a: Detect the zero-crossing point of the AC power supply voltage and feed the detection data back to the controller in real time;

[0055] Step S3a: When the AC power supply voltage reaches zero-crossing, a trigger signal is sent to thyristor TR1 to turn it on. At this time, the current path is: AC power supply → thyristor TR1 → first relay K1 → power conversion device, and a stable current path is formed in the main circuit (e.g., Figure 3 (under what circumstances)

[0056] Step S4a: After the thyristor TR1 is turned on, the controller controls the closing of the second relay K2; since the thyristor TR1 is turned on, the two ends of the second relay K2 are short-circuited, the voltage difference across the contacts is approximately zero, and almost no current flows during the closing process, thus achieving zero-current closing of the second relay K2.

[0057] Step S5a: When the AC current flowing through thyristor TR1 naturally crosses zero, thyristor TR1 automatically disconnects, allowing the AC current to flow to the second relay K2, completing the connection process; the power conversion device is stably connected to the AC power supply and enters normal operation.

[0058] Combination Figure 2 , Figure 6 The cut-off control process includes:

[0059] Step S1b: When it is necessary to disconnect the power conversion device from the AC power supply, control the second relay K2 to disconnect; at this time, the RC circuit connected in parallel across the second relay K2 immediately starts, absorbs the induced electromotive force generated when the contacts separate, suppresses the generation of electric arc, and realizes the soft disconnection of the second relay K2.

[0060] Step S2b: Set a preset delay time through the controller to disconnect the first relay K1 and complete the disconnection process.

[0061] Immediately after thyristor TR1 is turned on, the controller controls the closing of the second relay K2, or at any time within the same AC half-wave cycle before the next zero-current turn-off of thyristor TR1. This ensures a zero-current closing effect.

[0062] The preset time is 10 to 50 milliseconds. This delay ensures that the second relay K2 is completely disconnected and the circuit state is stable, avoiding current surges when the first relay K1 is disconnected.

[0063] During the stage after step S1b is executed and before step S2b is executed, the first relay K1 remains closed, isolating the power conversion device from the AC power supply side and the RC circuit, preventing grid-side noise from coupling into the power conversion device through the RC circuit, thereby improving the system's anti-interference capability and operational safety.

[0064] Throughout the process, both relays achieved soft switching with zero or near-zero current, with no arc erosion at the contacts, significantly extending their lifespan. Simultaneously, the series connection of K1 and K2 provided a double insulation barrier for the system, effectively meeting the safety specifications for enhanced insulation.

[0065] The above description is merely a specific implementation of the embodiments of the present invention, but the protection scope of the embodiments of the present invention is not limited thereto. Any changes or substitutions within the technical scope disclosed in the embodiments of the present invention should be covered within the protection scope of the embodiments of the present invention. Therefore, the protection scope of the embodiments of the present invention should be determined by the protection scope of the claims.

Claims

1. A soft-switching control circuit for a power conversion device, electrically connected to both the power conversion device and an AC power supply, characterized in that, The device includes a first relay and a second relay, and the power conversion device is electrically connected to the AC power supply in sequence through the first relay and the second relay or in sequence through the second relay and the first relay. The two ends of the second relay are connected in parallel to the two pins of the thyristor; It also includes a controller, which is electrically connected to the first relay, the second relay and the thyristor respectively.

2. The soft-switching control circuit for a power conversion device according to claim 1, characterized in that, An RC circuit is connected in parallel across the two ends of the second relay.

3. The soft-switching control circuit for a power conversion device according to claim 1, characterized in that, The power conversion device is a grid-connected inverter, an uninterruptible power supply, or a frequency converter.

4. A soft-switching control circuit for a power conversion device according to claim 1, characterized in that, The first relay is connected between the power conversion device and the second relay, or between the second relay and the AC power supply.

5. A soft-switching control circuit for a power conversion device according to claim 1, characterized in that, The two poles of the AC power supply are electrically connected to the AC voltage zero-crossing detection circuit, and the AC voltage zero-crossing detection circuit is electrically connected to the controller.

6. A soft-switching control method for a power conversion device, applicable to the soft-switching control circuit for a power conversion device as described in any one of claims 1-5, characterized in that, Includes the following steps: This includes the switching on control process and the switching off control process; The switching and connection control process includes: Step S1a: When the power conversion device and the AC power supply need to be electrically connected, the first relay is closed and the second relay is opened, while the controller does not send a trigger signal to the thyristor. Step S2a: Perform zero-crossing detection on the AC power supply voltage; Step S3a: When the voltage of the AC power supply is detected to reach the zero-crossing point, a trigger signal is sent to the thyristor to turn on the thyristor; Step S4a: After the thyristor is turned on, the controller controls the closing of the second relay; Step S5a: When the AC current flowing through the thyristor naturally crosses zero, the thyristor automatically disconnects, allowing the AC current to flow to the second relay, thus completing the connection process; The cut-off control process includes: Step S1b: When it is necessary to disconnect the power conversion device from the AC power supply, control the second relay to disconnect; Step S2b: Set a preset delay time through the controller to disconnect the first relay and complete the disconnection process.

7. A soft-switching control method for a power conversion device according to claim 6, characterized in that, Immediately after the thyristor is turned on, the controller closes the second relay, or at any time within the same AC half-wave cycle before the thyristor turns off at the next zero current crossing.

8. A soft-switching control method for a power conversion device according to claim 6, characterized in that, The preset time is 10 milliseconds to 50 milliseconds.

9. A soft-switching control method for a power conversion device according to claim 6, characterized in that, During the stage after step S1b is executed and before step S2b is executed, the first relay remains closed, isolating the power conversion device from the AC power supply side and the RC circuit.

Images