Solid state ac load switch device for an electric energy meter

Abstract

The application discloses a solid-state alternating current load switch device of an electric energy meter. The device is mainly composed of a SiC MOSFET power switch, a switch side control unit and a wireless power supply communication unit. The device mainly utilizes near-field magnetic coupling technology to wirelessly transmit energy and control signals, and completely solves the power supply and electrical isolation problems of the high-voltage side circuit. The application realizes arcless, super-long life, miniaturization and intelligentization of the alternating current load switch, and provides a solid-state switch solution which is superior to a traditional magnetic latching relay in the field of intelligent electric energy meters and the like.

Description

Technical Field

[0001] This invention relates to the field of power electronics technology and smart electrical equipment, specifically to a solid-state switching device used in smart energy meters to achieve safe switching of circuits. Background Technology

[0002] In low-voltage AC power management equipment, load switches are the control and execution components. For example, in smart meters, load switches enable remote fee control. Currently, this function is almost exclusively used by magnetic latching relays. These relays utilize pulsed current to change the state of a permanent magnet, achieving circuit switching through mechanical contacts. They have the advantage of low static power consumption, but suffer from the following fundamental drawbacks: 1) Arc hazard: When interrupting current, an arc is generated between the mechanical contacts, burning the contacts, leading to increased contact resistance, abnormal temperature rise, and even adhesion failure. Their electrical life is limited (typically around 100,000 cycles); 2) Poor anti-interference capability: The internal magnetic circuit is susceptible to interference from strong external magnetic fields; 3) Large size and slow response: The mechanical structure and arc-extinguishing requirements result in a large size, and the millisecond-level action speed is insufficient to meet precise control needs; 4) Existence of mechanical failure modes.

[0003] Replacing mechanical contacts with semiconductor solid-state switches (such as SiC MOSFETs) can physically eliminate electric arcing, achieving ultra-long lifespan and fast response. However, directly using SiC devices in AC circuits, with their drive circuits at a floating high potential, presents a significant engineering challenge in providing stable and isolated power and control signals. Traditional approaches, such as drawing power from current transformers (CTs), fail when the load is unloaded; while solutions using isolated DC-DC power supplies with optocoupler communication suffer from numerous components, large size, and high cost. Therefore, a highly integrated, low-cost, and highly reliable integrated power and signal isolation transmission solution is needed, combined with innovative soft-switching control strategies, to make SiC solid-state switches practically applicable in cost-sensitive fields such as energy meters. Summary of the Invention

[0004] The technical problem this invention aims to solve is to provide a novel solid-state AC load switch device that addresses the inherent defects of magnetic latching relays and the shortcomings of existing solid-state switching solutions in terms of cost, power supply, and isolated communication. This device, through wireless power supply and communication technology, completely solves the power supply and signal isolation problems of the high-voltage side circuit, enabling SiC power devices to operate under near-zero stress conditions. This achieves the goals of arc-free operation, long lifespan, and small size while significantly reducing system cost and complexity.

[0005] Technical solution of the present invention A solid-state AC load switch for an electricity meter, comprising: The power switching module consists of two SiC MOSFETs connected in reverse parallel to form a bidirectional switch, which is connected in series in the AC circuit. The switch-side control unit shares the same potential as the power switch module, and is used to receive control commands and output trigger signals to control the on / off state of the power switch module according to the control commands. The wireless power supply communication unit is used to provide isolated operating power to the switch-side control unit and power switch module through near-field electromagnetic coupling, and to realize bidirectional isolated communication between the switch-side control unit and the energy meter MCU. The wireless power supply communication unit includes: The main circuit, located on the main control circuit board of the energy meter, includes a high-frequency oscillator and a transmitting coil controlled by the energy meter MCU, which are used to generate a high-frequency alternating magnetic field and modulate and send control commands. The secondary circuit, located on the switch-side circuit board, includes a receiving coil magnetically coupled to the transmitting coil, a rectifier and voltage regulator circuit, and a signal demodulation circuit, used to acquire the operating power supply and demodulate the control command.

[0006] Preferably, both the main and secondary circuits are equipped with ASK modulation drive and detection circuits to achieve bidirectional communication. The ASK modulation of the main circuit is directly controlled by the MCU of the energy meter to send control commands via PWM. The ASK modulation of the secondary circuit is achieved by controlling the impedance change between its receiving coil and floating ground through the peripheral circuit of transistors, resistors, and capacitors. The switching on and off of the transistors achieves ASK modulation. This change is fed back to the main circuit, causing its amplitude to change. Both the main and secondary circuits achieve signal demodulation through detection circuits.

[0007] This invention achieves isolated power supply and isolated communication for the switch-side circuit through a power switch module, a switch-side control unit, and a wireless power supply communication unit. It achieves the goals of arc-free, long-life, and small-size AC load switches while significantly reducing system cost and complexity.

[0008] Beneficial effects of the present invention 1. A revolutionary power supply and communication solution: Based on a near-field magnetic coupling wireless power supply and communication unit, this solution solves the two major challenges of isolated power supply and isolated communication in high-voltage switchgear circuits. This solution is independent of load current and can operate reliably even under no-load conditions; moreover, its high integration eliminates the need for multiple optocouplers and isolated DC-DC modules, significantly reducing system cost, size, and complexity.

[0009] 2. Significant cost advantages: Allows for the use of more cost-effective low- and medium-voltage components. Wireless integration reduces the number of isolation components. Combined, these factors optimize the overall cost of solid-state switches, providing an economical alternative to magnetically latched relays.

[0010] 3. High reliability, small size and intelligence: The all-solid-state design is resistant to vibration and magnetic field interference; the module size can be greatly reduced; the built-in intelligent control and wireless two-way communication capabilities provide the hardware foundation for realizing advanced functions such as status monitoring and fault diagnosis. Attached Figure Description

[0011] Figure 1 This is a system overall configuration block diagram of the device of the present invention.

[0012] Figure 2 This is a connection diagram of the power switch module.

[0013] Figure 3 This is a schematic diagram of the principle of a wireless power communication unit.

[0014] Figure 4 This is a schematic diagram of the main circuit. Detailed Implementation

[0015] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0016] Example: Figure 1-4 As shown, a 120A load switch device is used for a single-phase 220V / 60Hz smart energy meter.

[0017] • Power Switching Module: Two domestically produced 650V / 75A SiC MOSFETs (e.g., B3M0175065D, TO-247-4L package) are selected and connected in reverse parallel on the PCB board on the switch side to form a bidirectional symmetrical switch, which is connected in series to the controlled AC circuit (such as the live wire). Specifically, the drain of Q1 and the source of Q2 are directly connected through PCB copper foil, and the source of Q1 and the drain of Q2 are also directly connected through PCB copper foil, forming a back-to-back reverse parallel connection between Q1 and Q2. One end of the parallel connection is connected to the live wire input, and the other main terminal is connected to the live wire output. In this structure, the parasitic diodes of Q1 and Q2 are in reverse parallel. When a low-level drive signal is applied to the gates of Q1 and Q2, Q1 and Q2 are turned off as a whole, and cannot conduct regardless of whether the AC current is in the positive or negative half-cycle. When a high-level drive signal is applied to the gates of Q1 and Q2, Q1 and Q2 are turned on as a whole. At this time, Q1 and Q2 are equivalent to diodes connected in reverse parallel, one conducting in the positive half-cycle of the current and the other conducting in the negative half-cycle.

[0018] The voltage rating of SiC MOSFETs is selected based on the AC system voltage (e.g., 650V for a 220V system). The nominal continuous current is selected based on half of the effective value of the load current (e.g., ≥60A for a 120A system), because only one of Q1 and Q2 is conducting at a time, meaning the heating time is only half, thus optimizing costs.

[0019] • Switch-side control unit: Sharing the same voltage as the power switch module, it consists of a microcontroller and its peripheral circuits. It receives control commands and outputs trigger signals to control the on / off state of the power switch module according to the control commands. Control commands include "closing" and "opening". When a "opening" command is received, a drive signal is output to turn off Q1 and Q2. When a "closing" command is received, a drive signal is output to open Q1 and Q2.

[0020] Specifically, it uses a low-power MCU (such as STM32G031) as the core, responsible for driving timing generation and instruction decoding. It controls two isolated gate drivers (such as UCC5350) through the MCU's GPIO to drive the SiC MOSFET.

[0021] • Wireless power supply communication unit: Used to provide isolated operating power to the switch-side control unit and power switch module via near-field electromagnetic coupling, and to achieve bidirectional isolated communication between the switch-side control unit and the energy meter MCU. The wireless power supply communication unit includes: Main circuit: Located on the main control circuit board of the energy meter, it includes a high-frequency oscillator controlled by the energy meter MCU and a transmitting coil L1, used to generate a high-frequency alternating magnetic field and modulate and send control commands. Specifically, the energy meter MCU controls a driver to drive a transmitting coil L1 (approximately 10μH) resonating at 125kHz and a resonant capacitor C1. The radio frequency signal can be generated by the PWM function of the energy meter MCU.

[0022] Secondary circuitry: Located on the switch-side circuit board, it includes a receiving coil L2 magnetically coupled to the transmitting coil, a resonant capacitor C2, a rectification and voltage regulation circuit, and a signal demodulation circuit, used to acquire the operating power and demodulate the control commands. Specifically, a receiving coil L2 and a resonant capacitor C2 of the same frequency are integrated on the switch-side PCB, coupled to L1 via a magnetic field. The AC current induced by L2 is rectified by a Schottky diode bridge, filtered by an LC filter, and regulated by an LDO to generate +5V to power the switch-side MCU. This power is then supplied to the gate driver via a miniature isolated DC-DC module (input +5V, output +18V / -5V).

[0023] Both the main-side circuit and the secondary-side circuit include ASK modulation drive and detection circuits.

[0024] The ASK modulation of the main circuit is directly implemented by the PWM control of the energy meter MCU. For example, it is implemented in 8-cycle units, stopping transmission for 8 cycles when outputting "1" and transmitting for 8 cycles when outputting "0". By defining the bit stream of various instructions and transmitting them in ASK modulation mode, instructions can be transmitted to the secondary side, such as sending "open" or "close" instructions.

[0025] The ASK modulation of the secondary circuit is achieved by controlling the impedance change between its coil and floating ground through an external circuit consisting of a transistor, resistor, and capacitor. This change is fed back to the primary circuit, causing its amplitude to change. In other words, ASK modulation can be achieved by controlling the transistor's on and off states. For example, in 8-cycle units, an output of "1" means stopping transmission for 8 cycles, and an output of "0" means transmitting for 8 cycles.

[0026] Both the main and auxiliary circuits have detection circuits. Signal demodulation uses simple envelope detection (diode, RC) plus Schmitt trigger shaping to restore the ASK signal to digital instructions, which are then sent to the UART of the MCUs in both the main and auxiliary circuits. Because the ASK modulated signal transmitted by the main circuit is stronger than that transmitted by the auxiliary circuit, the strength of the ASK signal received by the other side is reversed, resulting in different parameter configurations for the detection circuits on both sides. like Figure 4 As shown, this is the main circuit. The leftmost 125kHz output is generated by the MCU via PWM.

[0027] When no command is issued, MODE=0, CARDOUT=0, Q2 and Q3 on the main side are turned off, L1 and C4 resonate, and electromagnetic waves are emitted outward to wirelessly transmit power. At the same time, the card reading circuit after D1 can detect the status fed back from the secondary side.

[0028] When a command is issued, the 125kHz signal will stop, MODE=1, and Q2 on the main side will be turned on. CARDOUT will output a modulated frequency signal, whose carrier frequency is still 125kHz. The command encoding will change the duty cycle of the output. The secondary circuit can sense this change and detect the corresponding signal.

[0029] Workflow: 1. Power-on: The electricity meter is powered on, the main wireless power supply circuit of the wireless power supply communication unit is working, the switch side circuit is powered on and started, and the power switch is initialized to the off state.

[0030] 2. Closing: The energy meter's MCU sends a "closing" command wirelessly. After decoding, the switch-side MCU immediately controls the gate driver to output +18V, turning on the two SiC MOSFETs.

[0031] 3. Circuit Breaker Tripping: The energy meter MCU sends a "Break" command. Upon receiving this command, the switch-side MCU immediately controls the gate driver to output -5V, turning off the two SiC MOSFETs.

[0032] 4. Protection and Feedback: If the MCU on the switch side detects an overcurrent (through the sampling resistor), it can immediately perform a protective shutdown and encode the status, returning the status code in a manner equivalent to the RFID card returning the card number.

[0033] In the circuit described above, a zero-crossing detection circuit can also be added. By controlling the MCU on the switching side circuit, the SiC MOSFET can be turned on or off at the zero-crossing point of the voltage waveform when the circuit is closed or opened, so as to reduce the impact on the SiC MOSFET and eliminate interference.

[0034] The above embodiments are merely illustrative of the technical concept and implementation of the present invention. Those skilled in the art can make modifications or equivalent substitutions based on the principles disclosed in the present invention. For example, the power switch can be an integrated package module; wireless communication can use other modulation methods such as FSK; these transformations should all be included within the protection scope of the present invention.

Claims

1. A solid-state AC load switch device for an electricity meter, characterized in that, include: The power switching module consists of two SiC MOSFETs connected in reverse parallel to form a bidirectional switch, which is connected in series in the AC circuit. The switch-side control unit shares the same potential as the power switch module, and is used to receive control commands and output trigger signals to control the on / off state of the power switch module according to the control commands. The wireless power supply communication unit is used to provide isolated operating power to the switch-side control unit and power switch module through near-field electromagnetic coupling, and to realize bidirectional isolated communication between the switch-side control unit and the energy meter MCU. The wireless power supply communication unit includes: The main circuit, located on the main control circuit board of the energy meter, includes a high-frequency oscillator and a transmitting coil controlled by the energy meter MCU, which are used to generate a high-frequency alternating magnetic field and modulate and send control commands. The secondary circuit, located on the switch-side circuit board, includes a receiving coil magnetically coupled to the transmitting coil, a rectifier and voltage regulator circuit, and a signal demodulation circuit, used to acquire the operating power supply and demodulate the control command.

2. The solid-state AC load switching device for an electricity meter according to claim 1, characterized in that, Both the main and secondary circuits are equipped with ASK modulation drive and detection circuits to achieve bidirectional communication. The ASK modulation of the main circuit is directly controlled by the MCU of the energy meter to send control commands via PWM. The ASK modulation of the secondary circuit is achieved by controlling the impedance change between its receiving coil and floating ground through the external circuit of transistors, resistors, and capacitors. The switching on and off of the transistors achieves ASK modulation. This change is fed back to the main circuit, causing its amplitude to change. Both the main and secondary circuits achieve signal demodulation through detection circuits.

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