Asymmetric cooperative control three-phase balance motor soft starter

Abstract

The utility model discloses an asymmetric cooperative control three-phase balance motor soft starter, comprising a three-phase AC power supply input end, a power adjusting unit, an output end connected to a three-phase asynchronous motor, and a main controller which are connected in sequence. The power adjusting unit comprises an A-phase control module which is internally provided with a first thyristor at least controlled by a main controller; the B-phase control module is internally provided with a pair of antiparallel second thyristors controlled by the main controller; and the C-phase control module is internally provided with a pair of third thyristors which are controlled by the main controller and are reversely connected in parallel. The main controller cooperatively controls the conduction angles of the first thyristor, the second thyristor pair and the third thyristor pair in the starting process of the motor by outputting a control signal so as to adjust the voltage applied to the motor and improve the balance of the three-phase output voltage. According to the utility model, the three phases are controlled, so that the three-phase balance during starting is effectively improved, and the vibration and noise of the motor are reduced.

Description

Technical Field

[0001] This utility model belongs to the field of power electronics technology, specifically relating to an asymmetric cooperative control three-phase balanced motor soft starter. Background Technology

[0002] Three-phase asynchronous motors are widely used in industrial and civil applications, but their direct starting generates a starting current several times higher than the rated current, which can impact the power grid and potentially damage the motor and the driven equipment. Therefore, soft-start technology for motors is widely adopted.

[0003] Traditional motor soft starters, especially thyristor-based soft starters, achieve soft starting by smoothly adjusting the voltage output to the motor by controlling the conduction angle of the thyristors. Common high-performance soft starters typically employ a pair of anti-parallel thyristors for full-phase control in the three-phase input (i.e., a three-phase six-thyristor scheme), which achieves good starting performance and three-phase balance. However, for small to medium power motors (such as 18.5kW and below), the six-thyristor scheme is relatively expensive.

[0004] To reduce costs, some simplified solutions have emerged, such as using thyristor control only for phases B and C, while phase A is directly connected to the power supply or controlled by a simple switch. As mentioned in the original technical document, due to the size limitations of thyristors, the production cost difference for soft starters for motors below 18.5kW is generally not significant, resulting in high costs for traditional thyristor-based motor soft starters. This original solution reduces costs by reducing the number of thyristors in phase A, but this "two-phase control, one-phase direct connection" approach has inherent drawbacks: during soft starting, the voltage of phase A differs significantly from the controlled voltages of phases B and C, leading to severe three-phase voltage and current imbalance. This imbalance causes significant vibration and noise in the motor, generates negative sequence torque, increases motor losses, and may adversely affect the long-term stable operation and lifespan of the motor. Therefore, its applicability is limited, making it difficult to meet the requirements of applications with certain requirements for smooth starting and vibration control.

[0005] Therefore, how to effectively reduce the cost of soft starters for small and medium power motors while improving their starting performance as much as possible, especially solving the three-phase imbalance problem during the starting process, is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] Purpose of the invention: The purpose of this utility model is to provide an asymmetric cooperative control three-phase balanced motor soft starter, which aims to overcome the above-mentioned defects in the background technology, that is, while maintaining the advantage of low cost, significantly improve the three-phase balance during the motor starting process, reduce vibration and noise, and improve soft start performance.

[0007] Technical Solution: The motor soft starter provided by this utility model includes a three-phase AC power input terminal (L1, L2, L3), a power regulation unit, and an output terminal (U, V, W) connected in sequence to a three-phase asynchronous motor, as well as a main controller (MCU). The main controller (MCU) is used to generate control signals. The power regulation unit includes:

[0008] The A-phase control module has its input terminal connected to the A-phase power input terminal (L1) and its output terminal connected to the A-phase output terminal (U) of the motor. The A-phase control module is equipped with at least one first thyristor (TRIAC1; SCR1) controlled by the main controller. The control electrode of the first thyristor receives a first control signal from the main controller.

[0009] The B-phase control module has its input terminal connected to the B-phase power input terminal (L2) and its output terminal connected to the B-phase output terminal (V) of the motor. The B-phase control module contains a pair of anti-parallel second thyristors (VT1, VT3) controlled by the main controller. The control electrode of the second thyristor pair receives a second control signal from the main controller.

[0010] The C-phase control module has its input terminal connected to the C-phase power input terminal (L3) and its output terminal connected to the C-phase output terminal (W) of the motor. The C-phase control module is equipped with a pair of anti-parallel third thyristors (VT2, VT4) controlled by the main controller. The control electrode of the third thyristor pair receives a third control signal from the main controller.

[0011] The main controller (MCU) outputs the first, second, and third control signals to coordinately control the conduction angles of the first thyristor pair, the second thyristor pair, and the third thyristor pair during motor startup, thereby adjusting the voltage applied to the motor and improving the balance of the three-phase output voltage.

[0012] Furthermore, the first thyristor in the A-phase control module is a bidirectional thyristor (TRIAC1).

[0013] Furthermore, the first thyristor in the A-phase control module is a unidirectional thyristor (SCR1), and the A-phase control module is also provided with a diode (D1) connected in reverse parallel with the unidirectional thyristor (SCR1).

[0014] Furthermore, it also includes a bypass contactor module (K1), the input terminals of which are connected to the three-phase AC power input terminals (L1, L2, L3) respectively, and the output terminals of which are connected to the output terminals (U, V, W) of the motor respectively, thereby forming a parallel structure with the power regulation unit; the main controller (MCU) is also used to output a bypass control signal to the bypass contactor module (K1) to make it engage after the motor soft start is completed, and to stop outputting the first, second and third control signals.

[0015] Furthermore, the main controller (MCU) controls the conduction angle of the first thyristor to rapidly decrease from a relatively large initial value to near zero degree within a preset short period of time through the first control signal, so that the A-phase control module can quickly reach the full conduction state.

[0016] Furthermore, before the voltage output by the B-phase control module and the C-phase control module reaches a preset intermediate voltage value, the main controller (MCU) maintains the first thyristor in the off state or at a minimum conduction angle state through the first control signal, and after the voltage output by the B-phase and C-phase control modules reaches the intermediate voltage value, it controls the first thyristor to quickly conduct through the first control signal.

[0017] Furthermore, the main controller (MCU) internally stores preset voltage start-up curve data; it also includes a zero-crossing detection circuit, whose input terminal is connected to the three-phase AC power input terminal and whose output terminal is connected to the main controller (MCU) to provide a power synchronization signal; the main controller (MCU) calculates and generates trigger pulse parameters in the first, second and third control signals based on the voltage start-up curve data and the power synchronization signal.

[0018] Furthermore, it also includes at least one current sensor, the sensing end of which is connected in series in the current path between the power regulation unit and the output terminal of the motor, and the signal output terminal of which is connected to the main controller (MCU) to provide a current feedback signal; the main controller (MCU) is also used to adjust the first, second and third control signals according to the current feedback signal to limit the starting current of the motor.

[0019] Furthermore, when calculating the parameters of the first control signal, the main controller (MCU) will refer to or coordinate with the current or target parameters of the second and third control signals to achieve coordinated control of the outputs of the A-phase, B-phase and C-phase control modules.

[0020] Beneficial Effects: This utility model, by equipping all three-phase inputs with controllable thyristors and implementing a coordinated control strategy by the main controller, particularly employing a weak control strategy for phase A, offers the following significant advantages compared to existing technologies:

[0021] Significantly improves three-phase balance and reduces vibration and noise: Because phase A also participates in voltage regulation during startup, it is no longer a constant full voltage input. This results in a much smaller imbalance between three-phase voltage and current during startup compared to two-phase schemes with phase A directly connected or simply controlled. This effectively suppresses the negative sequence current component and the torque pulsation it generates, thereby significantly reducing vibration and noise during motor startup, improving the operating environment of the equipment, and helping to extend the service life of the motor and related mechanical components.

[0022] Effective cost reduction while maintaining good starting performance: Compared to the traditional three-phase six-thyristor fully controlled scheme, this invention adopts a simplified structure in phase A using a single bidirectional thyristor or a unidirectional thyristor plus a diode, using a total of 5 thyristors (or equivalently 4 bidirectional plus 1 unidirectional power switching element). This reduces the number of power devices, the corresponding trigger circuit complexity, and heat dissipation requirements, thereby effectively reducing hardware costs and device size. Simultaneously, since all three phases participate in the voltage regulation process, its starting smoothness and surge suppression capability are superior to the two-phase scheme with phase A directly connected, achieving a good balance between cost and performance.

[0023] Lower starting shock, protecting the power grid and equipment: Through three-phase coordinated voltage control, the output voltage smoothly rises from a lower initial value to the rated value, effectively limiting the peak starting current, reducing the impact on the power grid, and avoiding interference to other equipment on the same grid caused by a sudden drop in grid voltage due to high starting current. At the same time, the smooth torque build-up also reduces the mechanical shock to the motor itself and the driven load, extending the service life of the mechanical transmission system.

[0024] The application scope of low-cost soft starters has been expanded: Due to the improvement in starting performance, especially the improvement in three-phase balance, the present invention enables low-cost soft starters with fewer thyristors to be applicable to some occasions with certain requirements for vibration and noise, or slightly complex load characteristics, which are difficult to meet by the simple A-phase direct two-phase control scheme.

[0025] Improved system reliability and operating efficiency (when a bypass contactor is included): The use of a bypass contactor allows the thyristor to operate only during the brief starting process. After starting, the contactor takes over the main current, avoiding conduction losses and heat generation of the thyristor during long-term motor operation, thus improving the overall operating efficiency and long-term reliability of the system. Attached Figure Description

[0026] Figure 1This is a schematic diagram of the main circuit structure of the motor soft starter of this utility model;

[0027] Figure 2 This is a block diagram of the control system for the motor soft starter of this utility model. Detailed Implementation

[0028] 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.

[0029] Example 1: Refer to Figure 1 and Figure 2 The motor soft starter shown includes three-phase AC power input terminals L1, L2, and L3 for connecting to an external three-phase AC power source. The output terminals U, V, and W of the soft starter are used to connect to a three-phase asynchronous motor M. The core control unit is the main controller MCU, such as an STM32 series microcontroller.

[0030] The soft starter also includes a power regulation unit, which is connected in series between the power input terminals L1, L2, L3 and the motor output terminals U, V, W. This power regulation unit is specifically composed of the following modules:

[0031] Phase A control module 10: Its input terminal is connected to the Phase A power input terminal L1, and its output terminal is connected to the Phase A output terminal U of the motor. The Phase A control module 10 internally houses a first thyristor. In a preferred embodiment, the first thyristor can be a bidirectional thyristor TRIAC1. In another preferred embodiment, the first thyristor can be a unidirectional thyristor SCR1, with a diode D1 connected in reverse parallel with it. The control electrode (gate) of the first thyristor is connected to the main controller MCU, receiving the first control signal from the MCU.

[0032] B-phase control module 20: Its input terminal is connected to the B-phase power input terminal L2, and its output terminal is connected to the B-phase output terminal V of the motor. The B-phase control module 20 has a pair of anti-parallel second thyristors, namely thyristors VT1 and VT3. The control terminals of VT1 and VT3 are both connected to the main controller MCU to receive the second control signal from the MCU.

[0033] C-phase control module 30: Its input terminal is connected to the C-phase power input terminal L3, and its output terminal is connected to the C-phase output terminal W of the motor. The C-phase control module 30 has a pair of anti-parallel third thyristors, namely thyristors VT2 and VT4. The control terminals of VT2 and VT4 are both connected to the main controller MCU to receive the third control signal from the MCU.

[0034] The main controller (MCU) is the core of the entire soft starter. It controls the conduction angles of the thyristors in the A-phase, B-phase, and C-phase control modules by outputting the first, second, and third control signals, respectively. During motor starting, the MCU coordinates the control of the conduction angles (i.e., trigger delay times) of these three-phase thyristors, ensuring that the three-phase voltage applied to the motor M smoothly rises from a lower initial value to the rated value, while maintaining the balance of the three-phase voltages as much as possible.

[0035] Example 2: As Figure 2 As shown, the soft starter also includes a zero-crossing detection circuit 40. The input terminals of the zero-crossing detection circuit 40 are connected to the three-phase AC power input terminals L1, L2, and L3, and are used to detect the zero-crossing point of the power supply voltage. Its output terminal transmits a zero-crossing synchronization signal to the main controller MCU. The MCU uses this synchronization signal as a reference for calculating the firing angle of each phase thyristor.

[0036] The main controller MCU can store preset voltage start-up curve data. Based on this data and the zero-crossing synchronization signal, the MCU calculates the conduction angle of the three-phase thyristors at each moment during the start-up process and generates corresponding trigger pulses as control signals to send to the control electrode of each thyristor.

[0037] The main controller MCU implements a weak control strategy for the first thyristor of the A-phase control module 10. For example, at the initial stage of motor startup, the MCU controls the conduction angle of the first thyristor to rapidly decrease from a relatively large initial value (corresponding to a lower output voltage) to near zero (full conduction state) within a preset short time (e.g., 0.5 seconds to 1.5 seconds) using the first control signal. At the same time, the MCU implements a strong control strategy for the second thyristor pair of the B-phase control module 20 and the third thyristor pair of the C-phase control module 30 using the second and third control signals, so that their conduction angles decrease smoothly throughout the preset soft-start time (e.g., 5 seconds to 30 seconds), thereby achieving a smooth rise in the voltages of phases B and C. This coordinated control method, in which phase A quickly reaches full conduction while phases B and C slowly rise, can better balance the three-phase voltages at the initial stage of startup, avoiding the severe imbalance of the traditional A-phase direct-through scheme throughout the startup process.

[0038] Another weak control strategy for phase A can be as follows: Before the voltage output by the phase B and phase C control modules (achieved by controlling their conduction angle) reaches a certain preset intermediate voltage value (e.g., 20%-40% of the rated voltage), the MCU maintains the first thyristor in the off state or a very small conduction angle state through the first control signal. When the phase B and phase C voltages reach this intermediate value, the MCU then controls the first thyristor to quickly conduct to the fully conducting state through the first control signal.

[0039] To further improve performance and protect the motor, the soft starter may also include a current sensor 50. The current sensor 50 can be installed on the U, V, and W lines at the motor output terminals to detect the current flowing through the motor and transmit a current feedback signal to the main controller MCU. The MCU can use this current feedback signal to implement a current-limiting function during startup; that is, when the starting current exceeds a preset limit, the MCU will temporarily increase the firing angle of the three-phase (or the phase with the most severe imbalance) thyristors to reduce the output voltage, thereby limiting the current.

[0040] In a preferred embodiment, the soft starter further includes a bypass contactor module K1 (such as...). Figure 1 (As shown). The input terminals of the main contacts of the bypass contactor K1 are connected to the three-phase AC power input terminals L1, L2, and L3, respectively, and the output terminals of its main contacts are connected to the output terminals U, V, and W of the motor, thus forming a parallel structure with the power regulation unit (including the A, B, and C phase control modules). After the main controller MCU determines that the motor soft-start process is complete (for example, the output voltage reaches the rated value and the current stabilizes, or the preset start-up time is reached), it outputs a bypass control signal to drive the bypass contactor K1 to engage, and its main contacts close. At the same time, the MCU stops sending trigger pulses to all thyristors. After this, the motor M is directly powered from the grid by the bypass contactor K1, and the thyristors are deactivated, thus avoiding the power consumption and heat generation caused by the thyristors being on for a long time, and improving the system efficiency and reliability.

[0041] When the main controller MCU calculates the parameters (such as the firing angle) of the first control signal of phase A, it can refer to or link the current or target parameters of the second and third control signals of phases B and C to achieve dynamic coordinated control of the three-phase output and further optimize the three-phase balance.

[0042] Through the above structure and control method, the motor soft starter of this utility model can achieve the following working process: Upon receiving a start command, the MCU, according to a preset strategy and (optional) feedback signal, coordinates the conduction angles of the three-phase thyristors A, B, and C, so that the voltage output to the motor rises smoothly and the current is controlled until the motor reaches a stable operating state. Then, (optional) the bypass contactor is put into operation.

[0043] This invention provides a motor soft starter with a relatively simple structure, low cost, and significantly improved starting performance, which is particularly suitable for soft starting applications of small and medium power three-phase asynchronous motors.

[0044] 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 asymmetric cooperative control three-phase balanced motor soft starter, comprising a three-phase alternating current power input end, a power regulating unit and an output end connected to a three-phase asynchronous motor connected in sequence, and a main controller MCU, the three-phase alternating current power input end comprises an A-phase power input end L1, a B-phase power input end L2 and a C-phase power input end L3, the output end comprises a motor A-phase output end U, a motor B-phase output end V and a motor C-phase output end W, and the main controller MCU is used to generate a control signal, characterized in that, The power regulation unit includes: The A-phase control module has its input terminal connected to the A-phase power input terminal L1 and its output terminal connected to the A-phase output terminal U of the motor. The A-phase control module is equipped with at least one first thyristor, and the control electrode of the first thyristor receives a first control signal from the main controller. The B-phase control module has its input terminal connected to the B-phase power input terminal L2 and its output terminal connected to the B-phase output terminal V of the motor. The B-phase control module contains a pair of anti-parallel second thyristors, whose control electrodes receive a second control signal from the main controller. The C-phase control module has its input terminal connected to the C-phase power input terminal L3 and its output terminal connected to the C-phase output terminal W of the motor. The C-phase control module is equipped with a pair of anti-parallel third thyristors. The control electrode of the third thyristor pair receives a third control signal from the main controller. The main controller MCU outputs the first, second, and third control signals to coordinately control the conduction angles of the first thyristor pair, the second thyristor pair, and the third thyristor pair during motor startup, thereby adjusting the voltage applied to the motor and improving the balance of the three-phase output voltage.

2. The motor soft starter of claim 1, wherein, The first thyristor in the A-phase control module is a bidirectional thyristor TRIAC1.

3. The motor soft starter of claim 1, wherein, The first thyristor in the A-phase control module is a unidirectional thyristor SCR1, and the A-phase control module also has a diode D1 connected in reverse parallel with the unidirectional thyristor SCR1.

4. The motor soft starter of claim 1, wherein, It also includes a bypass contactor module K1, whose main contact input terminals are respectively connected to the three-phase AC power input terminals, and whose main contact output terminals are respectively connected to the output terminals of the motor, thereby forming a parallel structure with the power regulation unit; the main controller MCU is also used to output a bypass control signal to the bypass contactor module K1 to make it engage after the motor soft start is completed, and to stop outputting the first, second and third control signals.

5. The motor soft starter of claim 1, wherein, The main controller MCU controls the conduction angle of the first thyristor to rapidly decrease from its initial value to near zero within a preset time through the first control signal, so that the A-phase control module can quickly reach the full conduction state.

6. The motor soft starter of claim 1, wherein, The main controller MCU controls the second thyristor of the B-phase control module and the third thyristor of the C-phase control module through the second and third control signals. Before the output voltage of the B-phase control module and the C-phase control module reaches the preset intermediate voltage value, the first control signal keeps the first thyristor in the off state or at a minimum conduction angle. After the output voltage of the B-phase control module and the C-phase control module reaches the intermediate voltage value, the first control signal controls the first thyristor to quickly turn on.

7. The motor soft starter of claim 1, wherein The main controller MCU stores preset voltage start-up curve data; it also includes a zero-crossing detection circuit, whose input is connected to the three-phase AC power input and whose output is connected to the main controller MCU to provide a power synchronization signal. The main controller MCU calculates and generates the trigger pulse parameters in the first, second, and third control signals based on the voltage start-up curve data and the power synchronization signal.

8. The motor soft starter of claim 1, wherein, It also includes at least one current sensor, whose sensing end is connected in series in the current path between the power regulation unit and the motor output end, and whose signal output end is connected to the main controller MCU to provide a current feedback signal; the main controller MCU is also used to adjust the first, second and third control signals according to the current feedback signal to limit the starting current of the motor.

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