Analog closed loop enhanced soft starter

Abstract

The utility model belongs to the technical field of soft starter, specifically relates to a simulation closed loop enhanced type soft starter, and the thyristor in power main bridge realizes the smooth rise of motor voltage and current limit under the control of simulation slope and current closed loop control unit, after the completion of soft start, the solid state bypass unit that is composed of low conducting resistance SiC MOSFET is driven to conduct, and bypass power main bridge is used to reduce operating loss, the hardware protection logic unit can carry out microsecond level fast detection to overcurrent and other faults and immediately seals the power output, realizes fast protection, and the microcontroller unit is responsible for parameter setting, starting control, bypass switching and fault management. The utility model realizes the motor soft start of starting stable, current-limiting accurate, running efficient and protection quick and reliable through the combination of simulation control and fast hardware protection.

Description

Technical Field

[0001] This utility model belongs to the field of soft starter technology, specifically relating to a simulated closed-loop enhanced soft starter. Background Technology

[0002] Three-phase asynchronous motors are widely used in industrial production and civil facilities due to their advantages such as simple structure, reliable operation, and low cost. However, when an asynchronous motor is started directly, it generates a starting current several times the rated current. This huge inrush current not only causes a voltage drop in the power grid, affecting the stability of the power grid and the normal operation of other electrical equipment, but also causes mechanical shock that damages the motor itself and the load equipment it drives, shortening its service life.

[0003] To address the problems associated with direct starting, various reduced-voltage starting methods have been developed, such as star-delta starting and autotransformer reduced-voltage starting. However, these traditional stepped reduced-voltage starting methods do not have a smooth starting process, still suffer from secondary impacts, and have poor starting torque characteristics.

[0004] With the development of power electronics technology, electronic soft starters using power electronic devices such as thyristors have become mainstream due to their ability to achieve stepless and smooth voltage regulation. These soft starters typically use a microcontroller (MCU) or digital signal processor (DSP) to control the conduction angle of the thyristors, thereby achieving a smooth rise in the motor terminal voltage and effectively limiting the starting current. After the soft-start process is complete, to reduce losses caused by thyristor conduction and improve system operating efficiency, a mechanical bypass contactor is usually used to short-circuit the thyristors.

[0005] However, existing electronic soft starters based on MCU / DSP control still have some shortcomings:

[0006] First, current closed-loop control typically relies on software algorithms (such as PID control) of MCUs / DSPs. The execution of the software, data sampling and conversion, and the output of the control signal all involve a certain delay, resulting in insufficient response to rapid changes in motor current. This can lead to current overshoot or control instability, affecting the smoothness of startup and the accuracy of current control. Furthermore, the parameter tuning of the software algorithm is relatively complex, and its adaptability to different operating conditions is limited.

[0007] Secondly, traditional mechanical bypass contactors may generate electric arcs during switching, and their contacts also suffer from wear. Especially in situations with frequent start-stop cycles, their reliability and lifespan will decrease significantly, increasing maintenance costs and the risk of failure.

[0008] Third, software-implemented protection functions are also limited by the MCU's scan cycle and processing speed. For some sudden and severe faults, such as a sharp rise in current caused by an output short circuit or motor stall, the response speed of software protection may not be sufficient to effectively protect power devices and motors in a very short time.

[0009] Fourth, the complex control algorithms and real-time requirements place higher demands on the performance of the MCU, increasing the design complexity and hardware cost of the soft starter.

[0010] Therefore, how to design a soft starter with faster response speed, more precise control, higher operating efficiency, more reliable protection, and relatively simplified control is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0011] Purpose of the invention: The purpose of this utility model is to address the shortcomings of the existing technology by providing an analog closed-loop enhanced soft starter, which solves the problems mentioned in the background art such as slow current closed-loop response, low reliability of bypass contactor, insufficient and untimely hardware protection, and complex MCU control.

[0012] Technical solution: The analog closed-loop enhanced soft starter of this utility model includes a power main bridge, a solid-state bypass unit, an analog ramp and current closed-loop control unit, a thyristor trigger drive circuit, a SiCMOSFET bypass drive circuit, a hardware protection logic unit, and a microcontroller unit.

[0013] The power bridge has an input terminal for connecting to a three-phase AC power supply and an output terminal for connecting to a motor. The power bridge uses a three-phase anti-parallel thyristor module, which is used to control the voltage output from its output terminal to the motor by adjusting the conduction angle of the thyristor module during the soft start phase.

[0014] The solid-state bypass unit has its input terminal connected to the three-phase AC power supply and its output terminal connected to the motor and connected in parallel with the power main bridge. The solid-state bypass unit uses a three-phase SiCMOSFET AC switching module to be turned on after soft start-up to bypass the power main bridge.

[0015] The simulated ramp and current closed-loop control unit is used to receive the start control signal and current limiting reference signal from the microcontroller unit, and to receive the current feedback signal from the current sensor used to detect the phase current of the motor (M) to output the phase shift control voltage.

[0016] The thyristor trigger drive circuit has its input terminal connected to the output terminal of the analog ramp and current closed-loop control unit and receives the grid synchronization signal. Its output terminal is connected to the gate of the thyristor module in the power main bridge. The thyristor trigger drive circuit is used to generate and amplify the thyristor trigger pulse according to the phase shift control voltage and the grid synchronization signal.

[0017] The SiCMOSFET bypass drive circuit receives a bypass control signal at its input terminal and its output terminal is connected to the gate of the SiCMOSFET AC switch module in the solid-state bypass unit, which is used to drive the SiCMOSFET to turn on and off.

[0018] The hardware protection logic unit operates independently of any microcontroller unit. It monitors operating parameters, including at least the motor current, in real time through hardware circuitry. When the operating parameters exceed a preset hardware threshold, it generates a hardware blocking signal within a time frame less than a predetermined microsecond. The hardware blocking signal is connected to the thyristor trigger drive circuit and the SiCMOSFET bypass drive circuit, respectively, to forcibly stop the generation of the thyristor trigger pulse and forcibly turn off the SiCMOSFET when the hardware blocking signal is valid.

[0019] The microcontroller unit is configured to provide the start-up control signal and the current-limiting reference signal to the analog ramp and current closed-loop control unit, provide the bypass control signal to the SiCMOSFET bypass drive circuit, and receive and respond to status signals from the hardware protection logic unit.

[0020] To further improve the above technical solution, the simulated ramp and current closed-loop control unit includes:

[0021] An analog voltage ramp generating circuit is used to respond to the received start control signal and output a linearly changing voltage ramp signal.

[0022] The analog current error processing and phase-shift voltage generation circuit has its input terminal connected to a current sensor for detecting the motor current and receiving a current limiting reference signal. The analog current error processing and phase-shift voltage generation circuit is used to process the difference between the current feedback signal output by the motor current sensor and the current limiting reference signal, and combine it with the voltage ramp signal to output a phase-shift control voltage for controlling the conduction angle of the thyristor module.

[0023] Furthermore, the analog voltage ramp generation circuit includes an integrator circuit composed of an operational amplifier, the integration rate of which is controlled by the microcontroller unit by changing the parameters of its input resistance or integrating capacitor.

[0024] Furthermore, the analog current error processing and phase-shifting voltage generation circuit includes:

[0025] A current error amplifier circuit is used to amplify the difference between the current feedback signal and the current limiting reference signal to generate a current error signal;

[0026] A signal synthesis circuit is used to superimpose the current error signal and the voltage ramp signal or select them through priority logic to generate the phase-shift control voltage. When the current feedback signal indicates that the motor current exceeds the current value limited by the current limiting reference signal, the current error signal preferentially controls the phase-shift control voltage to reduce the conduction angle of the thyristor module.

[0027] Furthermore, the hardware protection logic unit (600) includes at least one high-speed analog comparator, the input of which is connected to the current sensor, and its reference input is connected to a reference voltage representing a hardware threshold for instantaneous overcurrent. The output signal of the high-speed analog comparator is directly or after being processed by logic gate circuits to trigger the generation of the hardware blocking signal.

[0028] Furthermore, in the solid-state bypass unit (200), each phase AC switch in the three-phase SiCMOSFET AC switch module is composed of two SiCMOSFET devices with an on-resistance of less than 10 milliohms connected back to back in series, so that the power loss of the soft starter in the bypass operation state is lower than the power loss of the power bridge (100) in the fully on state.

[0029] Beneficial effects: Compared with the prior art, the advantages of this utility model are:

[0030] Fast and precise current closed-loop control: Because the core voltage ramp generation and current closed-loop limiting functions are implemented by analog circuits, their response speed is much faster than traditional MCU-based software closed-loop control. The bandwidth of the analog circuits can be designed to be higher, enabling timely responses to rapid changes in current, effectively suppressing current overshoot during startup, making the startup current more stable, the startup process smoother, and improving the protection of the motor and load.

[0031] High-efficiency and high-reliability solid-state bypass: Utilizing SiCMOSFETs as the bypass switch, the extremely low on-resistance significantly reduces the power loss of the soft starter during bypass operation, improving overall operating efficiency. Simultaneously, the solid-state switch has no mechanical contacts, eliminating arcing and wear issues, resulting in an extremely long switch lifespan. This greatly enhances the reliability of the bypass unit and the overall lifespan of the soft starter, reducing maintenance requirements.

[0032] Instantaneous and reliable hardware-level protection: The hardware protection logic unit, which operates independently of the MCU, can respond to severe faults such as overcurrent, overvoltage, undervoltage, and phase loss in microseconds. It can forcibly shut down power devices in the very short time after the fault occurs, thereby protecting the power bridge, solid-state bypass unit, and motor from damage to the greatest extent. Its timeliness and reliability are far superior to software protection that relies on the MCU software scan cycle.

[0033] Simplified MCU Tasks and Enhanced System Stability: Since the core real-time, high-speed control and protection functions are handled by dedicated analog circuits and hardware logic, the microcontroller unit (MCU) is freed from heavy real-time calculations and interrupt handling. It primarily handles relatively low-speed and non-critical tasks such as parameter setting, state coordination, and human-machine interaction. This not only reduces the performance requirements of the MCU, allowing for the selection of lower-cost MCUs, but also significantly simplifies the complexity of MCU software design and debugging, reduces the risk of system instability due to software defects, and improves the overall stability and reliability of the soft-start device.

[0034] Excellent adaptability to power grid and load: The fast analog current closed-loop control enables the soft starter to better adapt to fluctuations in grid voltage and sudden changes in load, maintaining current stability during startup and avoiding startup failure or current surges caused by external disturbances.

[0035] In summary, this utility model provides a novel and high-performance analog closed-loop enhanced soft starter, which has significant value for widespread application. Attached Figure Description

[0036] Figure 1 This is a block diagram of the overall structure of a simulated closed-loop enhanced soft starter.

[0037] Figure 2 This is a block diagram of the principle of the simulated ramp and current closed-loop control unit.

[0038] Figure 3 This is a block diagram of the hardware protection logic unit. Detailed Implementation

[0039] The technical solution of this utility model will be described in detail below with reference to the accompanying drawings, but the protection scope of this utility model is not limited to the described embodiments.

[0040] Example 1: Refer to Figure 1 The present invention discloses an analog closed-loop enhanced soft starter, comprising a power main bridge 100, a solid-state bypass unit 200, an analog ramp and current closed-loop control unit 300, a thyristor trigger drive circuit 400, a SiCMOSFET bypass drive circuit 500, a hardware protection logic unit 600, and a microcontroller unit 700.

[0041] The input terminals of the power main bridge 100 are connected to a three-phase AC power supply (e.g., via input terminals L1, L2, L3), and its output terminals are connected to the motor M to be started (e.g., via output terminals T1, T2, T3). The power main bridge 100 internally consists of three anti-parallel thyristor modules, for example, two thyristors per phase connected in anti-parallel, or an integrated three-phase thyristor power module. During the soft-start phase, by adjusting the conduction angle α of the thyristors, the effective voltage value output from the power main bridge 100 to the motor M can be smoothly changed, thereby achieving a soft start for the motor.

[0042] The solid-state bypass unit 200 is also connected in parallel between the three-phase AC power supply and the motor M. Its input terminal shares the same power supply as the input terminal of the power main bridge 100, and its output terminal shares the same power main bridge 100 as the output terminal of the motor M. The solid-state bypass unit 200 is constructed using a three-phase SiCMOSFET AC switching module. For example, each phase can be composed of two SiCMOSFET devices connected back-to-back in series to form a bidirectional AC switch. Preferably, the SiCMOSFET has an extremely low on-resistance RDS(on), for example, less than 10 milliohms. After the soft-start process is completed, the SiCMOSFET AC switching module is driven to fully conduct, bypassing the main current from the power main bridge 100. At this time, the motor M is mainly powered by the solid-state bypass unit 200, thereby significantly reducing power loss during operation.

[0043] The simulated ramp and current closed-loop control unit 300 is one of the core control components of this invention, and its specific structure can be found in [reference needed]. Figure 2This unit is primarily composed of analog circuitry. It includes an analog voltage ramp generation circuit 301 and an analog current error processing and phase-shift voltage generation circuit 302. The analog voltage ramp generation circuit 301 can be implemented using a precision integrator circuit composed of an operational amplifier. When a start control signal is received from the microcontroller unit 700, the integrator circuit starts operating, outputting a linearly rising or falling (for soft stop) voltage ramp signal V_ramp. The rise rate of this voltage ramp signal (i.e., the soft start time) can be adjusted by the microcontroller unit 700 by controlling the input resistance or integrating capacitor value of the integrator circuit, for example, by selecting different resistive and capacitive components using a digital potentiometer or analog switch. The input of the analog current error processing and phase-shift voltage generation circuit 302 is connected to the output of a current sensor (e.g., a Hall current sensor) used to detect the M-phase current of the motor, acquiring the current feedback signal V_I_fb, and receiving a current-limiting reference signal V_I_limit_ref from the microcontroller unit 700 (e.g., output from the MCU's DAC). Internally, this circuit, for example, uses a differential amplifier to process the difference between the current feedback signal V_I_fb and the current limiting reference signal V_I_limit_ref to obtain the current error signal V_I_err. Then, through a signal synthesis circuit (such as an adder composed of operational amplifiers, or priority selection logic implemented using analog switches and diode clamping circuits), the current error signal V_I_err is dynamically combined with the voltage ramp signal V_ramp, ultimately outputting a phase-shift control voltage V_phase_ctrl. Its core logic is that when the current is within the limit, V_phase_ctrl is mainly controlled by V_ramp, achieving a smooth voltage rise; when the current feedback signal indicates that the motor current is trending towards exceeding the current limiting reference signal, the current error signal V_I_err will intervene first, rapidly adjusting V_phase_ctrl to increase the thyristor's trigger delay angle (reduce the conduction angle), thereby limiting the motor current within the set range.

[0044] The thyristor trigger drive circuit 400 receives the phase-shift control voltage V_phase_ctrl output from the analog ramp and current closed-loop control unit 300 and obtains a grid synchronization signal (e.g., a zero-crossing signal or a sawtooth / cosine wave synchronized with the grid) from the grid (or an input voltage sensor). Internally, the circuit compares the phase-shift control voltage V_phase_ctrl with the synchronized sawtooth / cosine wave using a comparator, for example. When they are equal, a grid-synchronized and phase-controllable pulse is generated. This pulse, after pulse shaping, amplification, and isolation via a pulse transformer or high-speed optocoupler, drives the gate of the corresponding thyristor in the power main bridge 100, causing it to conduct at a controlled moment.

[0045] The SiCMOSFET bypass drive circuit 500 is responsible for driving the SiCMOSFET in the solid-state bypass unit 200. It receives bypass turn-on / turn-off control signals from the microcontroller unit 700. Since SiCMOSFETs typically require specific gate drive voltages (e.g., +15V / -5V) and large instantaneous drive currents, this drive circuit usually includes a high-speed isolated driver chip (such as an optocoupler-based or magnetically isolated driver) and corresponding auxiliary power supply and protection circuitry to ensure that the SiCMOSFET can be turned on and off quickly and reliably.

[0046] The hardware protection logic unit 600 is another core part of this utility model, and its structure can be referred to as follows. Figure 3 This unit is entirely composed of hardware circuitry and operates independently of the microcontroller unit 700. It monitors key operating parameters in real time, such as enabling rapid transient overcurrent detection by connecting the output of a current sensor to a high-speed analog comparator (e.g., LM311 or LT1720). The comparator's reference terminal is connected to a reference voltage representing a hardware threshold for the transient overcurrent (this threshold can be set via a hardware potentiometer or by the MCU via a DAC before startup). When the motor current exceeds this hardware threshold, the comparator immediately flips, and its output signal, after necessary logic processing (e.g., latched by a NAND gate or D flip-flop), generates a valid hardware blocking signal. Similarly, the unit may also include hardware comparator circuitry for detecting input voltage over / undervoltage, phase loss, and excessively high power device heatsink temperatures. The response time of all these hardware detection circuits is designed in the microsecond range, for example, less than 50 microseconds. The generated hardware blocking signal is simultaneously sent to the thyristor trigger drive circuit 400 and the SiCMOSFET bypass drive circuit 500. Once the hardware blocking signal is valid, it immediately forces the thyristor's trigger pulse output to stop and forcibly turns off the SiCMOSFET, thereby cutting off the power supply to the motor in a very short time and achieving rapid protection. The hardware protection logic unit 600 also typically latches the fault status and displays it through LED indicators, while simultaneously sending the fault status signal to the microcontroller unit 700 for reading.

[0047] In this invention, the microcontroller unit 700 primarily plays a role in coordination, management, and human-machine interaction. It reads user settings (e.g., via buttons, knobs, or a touchscreen) and provides start-up control signals (e.g., a start-up enable signal) and current-limiting reference signals (e.g., setting the reference point of the current feedback loop by outputting a DC voltage via a DAC or controlling a digital potentiometer via SPI / I2C) to the analog ramp and current closed-loop control unit 300. During soft-start, the MCU monitors changes in motor voltage or current (through its own ADC sampling). When the conditions for soft-start completion are met (e.g., the output voltage reaches 90%-95% of the rated voltage and stabilizes for a period of time), the MCU sends an on-state command to the SiCMOSFET bypass drive circuit 500, driving the solid-state bypass unit 200 to conduct. After the solid-state bypass unit 200 is reliably turned on, the MCU stops the operation of the power bridge 100 by stopping the start-up control signal or directly disabling the output of the thyristor trigger drive circuit 400. In addition, the MCU is also responsible for reading the fault status reported by the hardware protection logic unit 600, displaying and recording it accordingly, and sending a reset signal to the hardware protection logic unit 600 after the operator confirms that the fault has been resolved. The MCU can also implement some auxiliary software protection functions, such as start-up timeout protection and sensor fault detection.

[0048] Example 2: The workflow of this utility model is as follows: System initialization. After the user sets the start-up parameters, the MCU issues a start-up command. The simulated ramp and current closed-loop control unit 300 starts working, controlling the thyristor conduction angle, the motor voltage rises smoothly, and the current is controlled. The hardware protection logic unit 600 monitors in parallel throughout the process. After start-up is completed, the MCU control switches to SiCMOSFET solid-state bypass operation. In the event of a hardware fault, the hardware protection logic unit 600 immediately activates, blocking the power output.

[0049] Taking a specific startup process as an example: Assume the user sets the startup time to 10 seconds and the current limit to 300% of the motor's rated current. After pressing the start button, the MCU unit 700 enables the analog voltage ramp generation circuit 301 and sets its integration parameters to output a voltage ramp signal V_ramp from 0V to, for example, 5V within 10 seconds. Simultaneously, the MCU outputs a current-limiting reference signal V_I_limit_ref corresponding to 300% of the rated current to the analog current error processing and phase-shifting voltage generation circuit 302 via a DAC. Initially, V_ramp is low, the thyristor conduction angle is small, and the output voltage is low. As V_ramp increases linearly, the thyristor conduction angle gradually increases, and the output voltage increases accordingly. During this process, if the motor current attempts to exceed 300% of the rated current, the current feedback signal V_I_fb will be greater than V_I_limit_ref. The current error processing part in circuit 302 will immediately respond, adjusting the phase-shifting control voltage V_phase_ctrl to reduce the thyristor conduction angle, thereby pulling the current back to near the limit value. When the motor voltage rises to, for example, 95% of the rated voltage, the MCU determines that the start-up is complete, drives the solid-state bypass unit 200 to conduct, and stops the operation of the power main bridge 100. If at any time, for example, the motor current momentarily exceeds the hardware-set threshold of 500% of the rated current, the hardware protection logic unit 600 will immediately (for example, within 20 microseconds) issue a hardware blocking signal to stop the driving of all power devices.

[0050] As described above, although the present invention has been shown and described with reference to specific preferred embodiments, it should not be construed as limiting the present invention itself. Various changes in form and detail may be made to the present invention without departing from the spirit and scope of the appended claims.

Claims

1. An analog closed loop enhanced soft starter, characterized by, include: The power bridge (100) has an input terminal for connecting to a three-phase AC power supply and an output terminal for connecting to a motor. The power bridge uses a three-phase anti-parallel thyristor module to control the voltage output from its output terminal to the motor by adjusting the conduction angle of the thyristor module during the soft start phase. A solid-state bypass unit (200) is connected to the three-phase AC power supply at its input and to the motor at its output. The solid-state bypass unit uses a three-phase SiCMOSFET AC switching module to bypass the power bridge (100) after soft start is completed. The simulated ramp and current closed-loop control unit (300) is used to receive the start control signal and current limiting reference signal from the microcontroller unit (700), and to receive the current feedback signal from the current sensor used to detect the phase current of the motor (M) to output the phase shift control voltage. The thyristor trigger drive circuit (400) is used to receive the phase shift control voltage and grid synchronization signal output by the analog ramp and current closed-loop control unit (300) to generate and output trigger pulses to drive the thyristors in the power bridge (100); SiCMOSFET bypass drive circuit (500) is used to receive a bypass control signal from the microcontroller unit (700) to drive the SiCMOSFET in the solid-state bypass unit (200) to turn on or off. The hardware protection logic unit (600) is used to monitor key operating parameters, including motor current, in real time. When any parameter exceeds the preset hardware threshold, it immediately generates a hardware blocking signal and sends it to the thyristor trigger drive circuit (400) and the SiCMOSFET bypass drive circuit (500) to forcibly stop the thyristor trigger pulse output and forcibly turn off the SiCMOSFET. The microcontroller unit (700) is used to provide the start-up control signal and the current limiting reference signal to the analog ramp and current closed-loop control unit (300), send the bypass turn-on / turn-off control signal to the SiCMOSFET bypass drive circuit (500), and receive the fault status signal from the hardware protection logic unit (600).

2. The analog closed loop boost soft-starter of claim 1, wherein, The simulated ramp and current closed-loop control unit (300) includes: An analog voltage ramp generating circuit (301) is used to respond to the received start control signal and output a linearly changing voltage ramp signal; The analog current error processing and phase-shift voltage generation circuit (302) has its input terminal connected to a current sensor for detecting the motor current and receiving a current limiting reference signal. The analog current error processing and phase-shift voltage generation circuit is used to process the difference between the current feedback signal output by the motor current sensor and the current limiting reference signal, and combine it with the voltage ramp signal to output a phase-shift control voltage for controlling the conduction angle of the thyristor module.

3. The analog closed loop boost soft-starter of claim 2, wherein, The analog voltage ramp generation circuit (301) comprises an integrator circuit composed of an operational amplifier, the integration rate of which is controlled by the microcontroller unit (700) by changing the parameters of its input resistance or integration capacitance.

4. The analog closed loop boost soft-starter of claim 2, wherein, The analog current error processing and phase-shifted voltage generation circuit (302) comprises: a current error amplification circuit for amplifying the difference between the current feedback signal and the current-limiting reference signal to generate a current error signal; a signal synthesis circuit for superimposing or selecting by priority logic the current error signal and the voltage ramp signal to generate the phase-shifted control voltage, wherein when the current feedback signal indicates that the motor current exceeds the current value defined by the current-limiting reference signal, the current error signal has priority to control the phase-shifted control voltage to reduce the conduction angle of the thyristor module.

5. The analog closed loop boost soft-starter of claim 1, wherein, The hardware protection logic unit (600) comprises at least one high-speed analog comparator, the input end of which is connected to the current sensor, the reference input end of which is connected to a reference voltage representing the instantaneous overcurrent hardware threshold, and the output signal of the high-speed analog comparator directly or after logic gate circuit processing triggers the generation of the hardware lockout signal.

6. The analog closed loop boost soft-starter of claim 1, wherein, Each phase AC switch in the three-phase SiC MOSFET AC switch module in the solid-state bypass unit (200) is composed of two SiC MOSFET devices with a conduction resistance of less than 10 milliohms in back-to-back series connection, so that the soft starter has a self-power loss lower than that of the power main bridge (100) in the full conduction state in the bypass running state.

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