AC-driven three-phase solid state relay with very low leakage current and active spike protection

Abstract

This invention relates to a three-phase AC-driven solid-state relay consisting of six thyristors in an anti-parallel configuration and incorporating control circuits to reduce leakage current, eliminate noise, and prevent unwanted switching. An internal thermal protection circuit also ensures safe operation of the device. The relay is used for precision switching in industrial, medical, and instrumentation systems.

Description

Description of the invention Title of the invention AC-driven three-phase solid state relay with very low leakage current and active spike protection Technical background of the relevant invention This invention is in the field of power electronic equipment and switching systems and specifically relates to the design and manufacture of three-phase solid state relays (Solid State Relay - SSR) with AC excitation and advanced technical features to reduce leakage current and increase operational safety in industrial environments and sensitive equipment. Technical problem and statement of invention objectives Traditional electromechanical relays, due to their moving parts, face challenges in industrial environments such as electrical noise, wear, limited lifespan, and unstable performance. Although existing solid state relays (SSRs) have overcome these disadvantages, they often have the following disadvantages: High current leakage in off mode, which can cause unwanted load operation in sensitive systems such as medical equipment and precision instruments; lack of thermal protection and if the internal temperature increases beyond the permissible range, they are completely destroyed and become permanently connected, which is very dangerous; lack of active protection against voltage spikes that burn semiconductors. Another problem with existing SSRs is their spontaneous and uncontrolled switching during rapid changes in input voltage. This phenomenon occurs when the voltage applied to the SSR input power terminals suddenly increases sharply. The most common case for this to occur is the sudden switching of the voltage by an upstream switch or fuse in the three-phase SSR input power path. In this situation, the input voltage may change from 0 to a peak of 600 volts in a fraction of a microsecond (depending on the moment of switching, which may be a number between 0 and 600 volts). This rapid rate of voltage change causes the SSR to switch on unintentionally. The purpose of this invention is to design and manufacture a three-phase AC-excited SSR relay that overcomes the above disadvantages by utilizing inverse-parallel thyristors, active protection against transient voltages, a low-pass filter circuit, and a thermal shutdown system. A description of the state of the prior art and the history of developments related to the claimed invention. Existing technologies use triac or thyristor-based SSR relays, but they have a leakage current higher than 1 mA and lack integrated protection. Existing models also do not use active circuitry to eliminate spikes or limit the rate of voltage change. As a result, this invention provides a higher level of performance by significantly reducing leakage current and adding active protection. Providing a solution to an existing technical problem along with an accurate, sufficient, and integrated description of the invention The designed relay consists of six thyristors in a back-to-back configuration to switch three-phase AC loads. Key technical features include: 1. Reduced leakage current: The excitation circuit and gate driver are designed to reduce the leakage current to less than 10 microamperes in the off state. 2. Active spike protection: The active clamping circuit at the input of the thyristors neutralizes voltage spikes and prevents semiconductor damage. 3. Low-pass filter: An RC network is used to remove high-frequency noise at the control input. 4. Protection against unwanted connection: A special circuit limits the rate of voltage change at the power terminals and prevents the SSR from turning on unintentionally when the power is suddenly connected. 5. Internal thermal protection: The circuit is turned off at temperatures above 90°C and reactivated at temperatures below 80°C. 6. Compact physical structure: The body is made of durable thermal-electrical insulation materials that are suitable for industrial and medical environments. Explanation of shapes, maps and diagrams Figure 1: Gate driver circuit and input isolation Figure 2: Internal thermal protection circuit Figure 3: Active clamping circuit against voltage spike Figure 4: Reverse-parallel arrangement of two thyristors for each phase Figure 5: Input voltage rate of change limiting circuit Figure 6: Physical view and insulating body of the relay. A clear and precise statement of the advantages of the claimed invention over prior inventions. The present invention has the following outstanding technical advantages over existing examples on the market: 1. Much lower leakage current than similar models, less than 10 microamperes 2. Active protection against voltage spikes with active clamping circuit 3. Has a circuit to reduce the rate of voltage changes and prevent unwanted connection 4. Built-in thermal protection with automatic recovery after temperature drop 5. Stability of control circuit performance independent of input voltage changes 6. Compact physical structure with high thermal and electrical insulation 7. Long life and high reliability without mechanical components Description of at least one implementation method for implementing the invention For practical use of the designed relay in industrial, medical or instrumentation control systems, it is sufficient to place the relay in series with the load supply path. The relay control input is supplied with an AC signal in the range of 160 to 250 V. By stimulating this input, the gate driver circuit is activated and the thyristors establish the current path to the load. If the temperature exceeds the permissible limit or dangerous spikes occur, the relay automatically activates active protection. Explicit mention of the industrial application of the invention This three-phase solid state relay with AC excitation and advanced protections is used in the following industries: Medical equipment sensitive to leakage current Laboratory instruments requiring complete power cut in stand-by mode Industrial automation systems with fast and safe switching Military and isolated applications with high safety and stability requirements Precise control of AC loads on production lines or sensitive equipment

Claims

Claims What is claimed: Claim 1: A three-phase AC-excited solid-state relay comprising six thyristors in an inverse-parallel configuration designed to have a leakage current of less than 10 microamperes in the open state while providing fast and safe switching of three-phase AC loads. Claim 2: As claimed in claim 1, including an active voltage spike protection circuit that prevents thyristors from being damaged by neutralizing momentary peaks. Claim 3: According to claim 1, including an input voltage slew rate reduction circuit that prevents the relay from being turned on unintentionally when power is suddenly applied to the power input. Claim 4: According to claim 1, having a constant input current control circuit for driving the thyristors and the LED indicator such that its operation remains independent of input voltage variations. Claim 5: According to claim 1, an RC low-pass filter is used in the control circuit to eliminate high-frequency noise. Claim 6: According to the above claims, it has an internal thermal protector that turns off the relay at a temperature of more than 90 degrees Celsius and activates it after the temperature returns to less than 80 degrees.