Soft start and soft deceleration method for electromechanical system

Abstract

The invention belongs to the technical field of electromechanical control, and discloses an electromechanical system soft start and soft deceleration method, which comprises the following steps of: setting a speed set value, a start or deceleration working condition moment value and a time constant; monitoring the actual operation time of the system; calculating an expected tracking signal according to the following formula; and controlling the dynamic response speed of the electromechanical system based on the expected tracking signal to realize soft start or soft deceleration. According to the invention, the impact current in the starting or deceleration process of the system can be effectively eliminated, and the impact torque of load machinery is reduced, thereby achieving the purpose of prolonging the service life of the machine.

Description

Technical Field

[0001] This application relates to the field of electromechanical control technology, and in particular to a soft-start and soft-deceleration method for electromechanical systems. Background Technology

[0002] In industrial automation and electrical drive systems, electric motors have become the primary power actuators due to their simple structure, reliable operation, and convenient maintenance. However, their traditional starting method—direct starting—can trigger a series of severe electromechanical problems at the moment of circuit closure, seriously restricting system performance, reliability, and intelligence.

[0003] In direct starting, the motor stator windings are directly connected under the grid voltage. At this time, the rotor is stationary due to inertia, resulting in extremely high slip, causing the starting current to reach 5-8 times the rated current. This huge inrush current, and the resulting electromechanical transients, constitute the core defect of traditional starting methods. Therefore, seeking a smooth and controllable starting method—i.e., soft starting—has become a crucial and continuously evolving technical issue in the field of industrial control.

[0004] Analysis of the technical defects and impacts of traditional direct starting The enormous impact of direct starting poses a multifaceted threat to electromechanical systems, primarily at the electrical and mechanical levels: (1) Electrical shock and its consequences Inrush Current: Voltage Drop in Power Grid: The huge starting current will generate a significant voltage drop on the power grid lines, especially when the power supply capacity is relatively small. This may cause other sensitive equipment on the same grid to malfunction or even shut down, and cause lighting fixtures to flicker. Power Quality Deterioration: The instantaneous large current leads to an increase in harmonic content, polluting the power grid. Increased Equipment Selection and Costs: To withstand the inrush current, the capacity of upstream electrical components such as circuit breakers, contactors, and cables must be increased, leading to increased system costs. Thermal Stress Damage: The Joule heat generated by frequent starting will accelerate the aging of the motor winding insulation and shorten the motor's lifespan.

[0005] (2) Mechanical impact and its consequences Impact Torque: Although the starting current is large, the starting torque of a motor is typically only 1.0-1.8 times its rated torque. However, this torque is applied to the transmission system instantaneously. Damage to Transmission Components: The instantaneous high torque can cause severe impact stress on mechanical transmission components such as couplings, gearboxes, belts, and chains, leading to fatigue, wear, and even breakage. Product Process Damage: In applications such as pumps, fans, compressors, and conveyor belts, mechanical impact can cause pipeline vibration, product displacement, detachment, or damage, affecting production process quality.

[0006] The Position and Advantages of Soft Starters in Automated Control Systems: In modern automated systems, soft starters are no longer just independent motor starting devices, but rather key intelligent nodes in the drive layer, integrated with the upper-level PLC or DCS system through communication interfaces (such as Profibus, Modbus, Ethernet / IP, etc.). Their comprehensive advantages are reflected in: System protection: Significantly reduces inrush current and mechanical stress, extending the lifespan of motors and transmission equipment.

[0007] Intelligent integration: Enables remote setting of start / stop curves, real-time monitoring of operating status (current, voltage, power factor, etc.) and fault diagnosis, thereby improving the intelligence level of the entire control system.

[0008] Process optimization: Through precise torque and speed control, the special requirements of complex production processes for the start-up process are met.

[0009] Economic benefits: Although soft starters themselves have costs, their overall economic benefits over their entire life cycle are significant by reducing equipment downtime, lowering maintenance costs, and optimizing power grid quality.

[0010] In conclusion, the traditional direct starting method for electromechanical systems, due to its inherently large impact characteristics, can no longer meet the stringent requirements of modern industry for equipment reliability, system intelligence, and energy efficiency management. Summary of the Invention

[0011] To address the aforementioned problems, this application provides a soft-start and soft-deceleration method for electromechanical systems. Based on power electronics technology and microprocessor intelligent control, this soft-start technology offers an efficient, smooth, and controllable solution. This method solves the classic electromechanical shock problem and, as a key component of automation architecture, lays a solid technical foundation for building efficient, reliable, and intelligent modern drive systems.

[0012] This application provides a method for soft starting and soft deceleration of an electromechanical system, the method comprising the following steps: Set speed setting value Start-up or deceleration time values and time constant ; Monitoring system actual running time ; The desired tracking signal is calculated using the following formula. : ; Based on the desired tracking signal It controls the dynamic response speed of the electromechanical system to achieve soft start or soft deceleration.

[0013] As a preferred technical solution, the time constant is set based on the speed, current, voltage and electromagnetic torque curves of the soft-start PI control.

[0014] As a preferred technical solution, the time constant .

[0015] As a preferred technical solution, the method is applicable to electromechanical systems, wherein the desired tracking signal Used to control the dynamic response speed, current, voltage, and electromagnetic torque of electromechanical systems.

[0016] As a preferred technical solution, during the soft deceleration process, the voltage is gradually reduced to avoid water hammer effect or mechanical impact.

[0017] As a preferred technical solution, the method is applied to trapezoidal velocity trajectory tracking, wherein the velocity setpoint Dynamic adjustments are made based on a preset speed sequence.

[0018] As a preferred technical solution, the trapezoidal speed trajectory includes a transition process from low speed to high speed and then back to low speed.

[0019] As a preferred technical solution, during soft start-up or soft deceleration, the motor speed trajectory is a trapezoidal trajectory, and the speed change of the trapezoidal trajectory is 200rpm→600rpm→1000rpm→600rpm in sequence.

[0020] The soft-start and soft-deceleration methods for electromechanical systems according to the various schemes of this application have at least the following technical effects: At the electrical level, it effectively eliminates the inrush current during the startup process of the electromechanical system, avoiding impact on the power grid, ensuring power supply reliability, and improving power quality. At the mechanical level, it significantly reduces the impact torque of the load machinery, extending the service life of the motor and transmission system. At the system level, it achieves energy saving and consumption reduction, resulting in significant overall economic benefits. Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0021] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the following description of the embodiments taken in conjunction with the accompanying drawings, wherein: Figure 1 A flowchart of a soft-start and soft-deceleration method for an electromechanical system provided in this application embodiment; Figure 2 The time constant provided for the embodiments of this application Curves of speed, current, voltage and electromagnetic torque under PI-SS control with different selected values; Figure 3 The rotation speed of the PMSM servo system provided in the embodiments of this application Various response curves of rpm. Detailed Implementation

[0022] To enable those skilled in the art to better understand the technical solution of this application, the application will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0023] Example 1: To address the issue that traditional direct starting methods for motors, due to their inherently large impact characteristics, cannot meet the stringent requirements of modern industry for equipment reliability, system intelligence, and energy efficiency management, this application provides a soft starting and soft deceleration method for electromechanical systems, such as... Figure 1 As shown, the method includes the following steps S10-S40.

[0024] S10: Set speed setting value Start-up or deceleration time values and time constant ; Step S10 involves setting the initialization parameters for the control process. Speed ​​setpoint. This is the target speed that the motor needs to achieve. The time value during starting or deceleration. It is the starting timing point of the control process, such as the moment a start or stop command is received. Time constant. This is the core control parameter of this method, which directly determines the speed and smoothness of the dynamic process of the motor accelerating from a standstill to the target speed or decelerating from the target speed to a standstill.

[0025] In a typical implementation scenario, these parameters can be sent from a host computer (such as a PLC or industrial PC) to the servo drive via a fieldbus. The operator can then set the target speed on the human-machine interface. For example, set it to 200 rpm. Time constant. The start / deceleration smoothness can be preset according to the load's inertia and the process requirements. For example, for systems with high inertia and sensitivity to mechanical shock, a larger preset value should be selected. A value, such as 0.5 seconds; for systems requiring a fast response, a smaller value can be selected. Values, such as 0.05 seconds. Extensive experimental verification shows that when... When the value is 0.1, the optimal balance between dynamic response speed and impact suppression can be achieved.

[0026] S20: Monitoring system actual running time .

[0027] Step S20 is fundamental to achieving closed-loop tracking control. The system requires a unified time base to calculate the desired rotational speed and position in real time. Actual running time Timing typically begins at the start of a control cycle or the instant a start / deceleration command is received. For example, step S20 can be implemented by a microprocessor within the driver. The timer / counter in the microprocessor starts at zero and increments at fixed control cycles, thus providing a high-precision, continuous system time. .

[0028] S30: Calculate the desired tracking signal according to the following formula. : ; Step S30 is the core of this algorithm. It utilizes the sigmoid smoothness and monotonicity of the hyperbolic tangent function tanh to construct the desired tracking signal. The function shown in this formula is... t = t s The time value is zero, making It rises smoothly from zero; as time progresses, the function value asymptotically approaches 1, making... Smoothly approximation The derivative of the curve is zero at both the start and end points, meaning that the acceleration changes from zero and eventually returns to zero, thus fundamentally avoiding sudden changes in rotational speed and suppressing the generation of inrush current and inrush torque.

[0029] In one specific embodiment, the microprocessor reads the current system time in each control cycle. t and set the preset speed value Start-up or deceleration time values and time constant Substitute the values ​​into the above formula for real-time calculation. For soft-start conditions, Calculated at the start command time It is a line that smoothly rises from 0 to The S-shaped curve. For soft deceleration conditions, This is the moment of the deceleration command, in order to smoothly reduce the speed from the current speed to zero or a lower target speed.

[0030] S40: Based on the desired tracking signal It controls the dynamic response speed of the electromechanical system to achieve soft start or soft deceleration.

[0031] Step S40 is the process of converting the calculated ideal smooth trajectory into the actual motion of the motor. This is the desired tracking signal. The speed loop receives a command and compares it with the actual speed fed back from the motor encoder. The deviation is adjusted by the controller, which outputs a control quantity (such as the q-axis current reference value). This output is then used by the power electronic converter to drive the motor, forcing the motor's actual speed to precisely follow the speed output. The trajectory changes.

[0032] In a typical permanent magnet synchronous motor (PMSM) vector control system, the result calculated in step S30 is... The current is fed into the speed PI regulator. The PI regulator outputs a q-axis current reference value based on the speed deviation. The current loop controller then tracks the current reference value and generates a drive signal using space vector pulse width modulation (SPWM) technology to control the power switching devices of the inverter bridge, thereby regulating the voltage applied to the motor so that the motor's actual speed smoothly and without overshoot tracks the speed. The curve enables smooth, soft starts and deceleration without any impact.

[0033] Example 2: Based on the soft start and soft deceleration method for electromechanical systems provided in Embodiment 1, this application further demonstrates the feasibility and progressiveness of the method through specific experiments.

[0034] It should be noted that the core of this method lies in addressing the issue that traditional direct starting generates large inrush currents or voltages in electromechanical systems, potentially damaging components. A novel soft starting (SS) method is proposed to solve this problem. ; in For the desired tracking signal, Set the speed value. These are the time values ​​for starting or decelerating operation. This refers to the actual system runtime. The time constant is used. This soft-start technology replaces traditional starting methods, achieving smooth starting, effectively reducing starting current, reducing impact torque on the load machinery, extending machine life, minimizing the impact of motor starting on the power grid, and improving power quality and supply reliability. Furthermore, the soft-start concept can also achieve soft deceleration (stop), allowing for smooth deceleration. This overcomes the drawbacks of instantaneous deceleration, such as reducing impact on heavy machinery and avoiding water hammer effects in elevated water supply systems, minimizing equipment damage and improving economic efficiency. However, most existing methods do not incorporate the soft-start and soft deceleration (stop) concepts into engineering applications.

[0035] This embodiment uses a permanent magnet synchronous motor speed control system as an example to discuss different time constants. Effects on soft start: time constant The speed, current, voltage, and electromagnetic torque curves based on soft-start PI (PI-SS) control with different selected values ​​are shown below. Figure 2 As shown. When the time constant Choosing a smaller value results in faster starting speed, but also significant overshoot in the speed response curve, and higher starting current and torque. Conversely, a larger time constant... A larger value results in a slower speed response and greater chattering amplitude in the current and torque curves during startup. The appropriate time constant is selected based on the performance changes under different time constants. This choice not only achieves faster dynamic response but also avoids inrush current and high torque, resulting in smooth start-up and better control performance.

[0036] To better align with actual production needs, a soft-start method is discussed for trapezoidal trajectories ( Tracking performance (Revolutions per minute, rpm). Figure 3 The images show the speed trajectory tracking responses using the PI and PI-SS methods, along with magnified local images. Using the PI method, a noticeable speed drop occurs when transitioning from high to low speed, with drop ranges of 48 rpm and 38 rpm, respectively. Using the PI-SS method, the speed drop during the transition from high to low speed is weaker, with a drop range of only 5 rpm, demonstrating the advantages of soft start and soft deceleration. The proposed strategy not only effectively achieves rapid tracking of the trapezoidal trajectory but also avoids the speed drop phenomenon.

[0037] In summary, the method proposed in this application eliminated the inrush current during system startup, reduced the impact torque of the load machinery, extended the machine's lifespan, avoided adverse effects on the power grid during motor startup, ensured reliable power supply, improved power quality, and thus promoted energy conservation.

[0038] The above embodiments are only used to illustrate this application and are not intended to limit this application. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of this application. Therefore, all equivalent technical solutions also fall within the scope of this application, and the patent protection scope of this application should be defined by the claims.

Claims

1. A method for soft starting and soft decelerating an electromechanical system, comprising: The method comprises the following steps: Set speed set value , start or deceleration operating condition time value and time constant ; Monitoring system actual run time ; The expected tracking signal is calculated according to the following equation : ； based on the desired tracking signal , control the dynamic response speed of the electromechanical system, realize soft start or soft deceleration.

2. The method of claim 1, wherein, The time constant is set based on the soft start PI control speed, current, voltage and electromagnetic torque curve.

3. The method of claim 2, wherein, the time constant .

4. The method of claim 1, wherein, The method is applicable to electromechanical systems, wherein the desired tracking signal for controlling the dynamic response speed, current, voltage and electromagnetic torque of electromechanical systems.

5. The method of claim 1, wherein, In the soft deceleration process, the water hammer effect or mechanical impact is avoided by gradually reducing the control voltage.

6. The method of claim 1, wherein, The method is applied to trapezoidal trajectory tracking control of permanent magnet synchronous motor speed regulation system, wherein a speed setting value Dynamic adjustment is performed according to a preset rotation speed sequence.

7. The method of claim 6, wherein, The trapezoidal speed trajectory includes a conversion process from low speed to high speed and then to low speed.

8. The method of claim 6, wherein, In the soft start or soft deceleration process, the motor speed trajectory is a trapezoidal trajectory, and the speed change of the trapezoidal trajectory is 200 rpm→600 rpm→1000 rpm→600 rpm in turn.

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