Soft start control circuit structure with frequency conversion soft start and non-frequency conversion soft start being standby for each other

Abstract

The utility model provides a soft start control circuit structure with mutual standby frequency conversion soft start and non-frequency conversion soft start, which relates to the technical field of motor soft start and high-voltage frequency conversion soft start and comprises a high-voltage bus, a non-frequency conversion soft start device and a high-voltage frequency conversion soft start device. The non-variable-frequency soft start device adopts a step-down start device of a motor stator or rotor series resistor, or adopts a solid-state soft start device or a liquid-state soft start device; the high-voltage variable-frequency soft start device comprises a first power switch, a frequency converter, an electric reactor and a first wire outlet switch. The frequency converter comprises a phase-shifting transformer, a power unit and a control system which are connected with one another. The first power switch is connected to a high-voltage bus, the phase-shifting transformer is connected with the first power switch in series, the electric reactor is connected with the power unit and the control system in series, the first outlet switch is connected with the electric reactor in series, and the first outlet switch is further used for being connected with a non-variable-frequency soft start device. According to the utility model, the two groups of soft start devices are redundant standby for each other, so that the reliability and the safety of the motor soft start system can be improved.

Description

Technical Field

[0001] The utility model relates to the technical field of motor soft starting and high-voltage variable frequency soft starting, and in particular to a soft starting control circuit structure in which variable frequency soft starting and non-variable frequency soft starting serve as backup for each other. Background Art

[0002] With the widespread application of high-voltage motors, especially high-voltage and high-power AC motors, their starting problem has gradually become a major contradiction in the user's internal power grid. The choice of starting method not only affects the one-time investment of the project, but also affects the long-term safe and stable operation of the factory's internal power grid in the later period.

[0003] There are basically two ways to start a high-voltage motor before installing a high-voltage inverter, namely direct starting and voltage reduction soft starting. When the motor is started directly, the starting current will reach 7-8 times the rated current of the motor, especially for large-power motors, which will cause current shock and mechanical shock to the power grid and electrical equipment. As for voltage reduction soft starting, there are solid-state soft starters and liquid resistance voltage reduction soft starting. Both squirrel cage asynchronous motors and wound-rotor asynchronous motors can be connected in series with solid-state soft starters in the stator circuit (such as Figure 1 As shown in the figure), when liquid soft start is used, the squirrel cage asynchronous motor stator series liquid resistance voltage reduction soft start, while the wound-rotor asynchronous motor uses rotor series liquid resistance soft start (as shown in the figure). Figure 2 As shown). Whether it is a solid-state soft starter or a series liquid resistance step-down starter, the starting current is 3-4 times the rated current. The variable frequency soft starter uses a variable frequency variable voltage starting method, which is a non-slip starting method. The starting current generally does not exceed the rated current. In addition, the liquid water resistance starting device is easily affected by the ambient temperature. When starting in winter, the water resistance value changes greatly, and the starting current fluctuates, affecting the starting efficiency.

[0004] From a technical point of view, the use of high-voltage inverter soft start motor (such as Figure 3 As shown in the figure, it has technical advantages that other starting methods cannot match, such as: no impact on the unit and the power grid, greater starting torque can be obtained while limiting the current, the system is relatively simple, maintenance is relatively convenient, excellent control performance is easy to realize automatic control, and when using cascaded high-voltage inverters, there is no harmonic impact on the power grid and motor. However, from an economic point of view, non-frequency conversion liquid or solid soft starters have obvious price advantages over inverters, so frequency conversion speed regulation and water resistance speed regulation have their own advantages and disadvantages. Users should choose a suitable soft start device according to the actual conditions on site.

[0005] From the perspective of technical transformation, when the frequency converter replaces the non-frequency converter soft start device as the motor soft start, in order to save the subsequent maintenance cost of the original soft start equipment, the original equipment is usually dismantled, resulting in a certain amount of waste. In addition, when a fault occurs during the operation of the frequency converter, there is no spare starting equipment, and there is not enough grid capacity to start the high-power motor directly. The process can only be stopped and the frequency converter can only be started after maintenance and recovery, which will cause certain production losses.

[0006] Therefore, there is room for improvement, and the utility model provides a soft start control circuit structure in which a variable frequency soft start and a non-variable frequency soft start serve as backup for each other. Utility Model Content

[0007] In view of the shortcomings of the prior art, the utility model aims to propose a soft start control circuit structure in which variable frequency soft start and non-variable frequency soft start serve as backup for each other. The specific scheme is as follows:

[0008] A soft start control circuit structure in which a variable frequency soft start and a non-variable frequency soft start are mutually backup, the circuit structure comprising a high voltage bus, a non-variable frequency soft start device, and a high voltage variable frequency soft start device, wherein the non-variable frequency soft start device and the high voltage variable frequency soft start device are respectively connected to the high voltage bus;

[0009] The non-variable frequency soft start device adopts a step-down starting device with a resistor in series with the motor stator or rotor, or a solid-state soft start device, or a liquid soft start device;

[0010] The high-voltage frequency conversion soft start device includes a power switch, a frequency converter, a reactor, and an outlet switch. The frequency converter includes a phase-shifting transformer, a power unit, and a control system that are interconnected.

[0011] The power switch 1 is connected to the high-voltage bus, the phase-shifting transformer is connected in series with the power switch 1, the reactor is connected in series with the power unit and the control system, the outgoing line switch 1 is connected in series with the reactor, and the outgoing line switch 1 is also used to connect with the non-frequency conversion soft start device.

[0012] Furthermore, when the non-frequency conversion soft start device adopts a liquid soft start device, it is set as a water resistance pressure reduction start device;

[0013] The water resistance voltage reduction starting device includes a power frequency switch, a motor, a water resistance, and a short-circuit switch;

[0014] The power frequency switch 1 is connected to the high voltage bus, the motor is connected in series with the power frequency switch 1, the water resistor is connected in series with the motor, the short-circuit switch is connected in parallel with the water resistor, and the outlet switch 1 is connected between the motor and the power frequency switch 1.

[0015] Furthermore, when the high-voltage variable frequency soft-start device is in operation, before closing the power switch, the short-circuit switch in the liquid soft-start device must be in a closed state.

[0016] Furthermore, during the operation of the high-voltage frequency conversion soft-start device, after the outgoing line switch 1 is closed, when the motor is accelerated to the point where the phases on the motor side and the power supply side are basically consistent, the industrial frequency switch 1 is closed, and then the outgoing line switch 1 is opened with a delay until the frequency converter stops working, completing the frequency conversion soft-start process.

[0017] Further, when the non-frequency conversion soft start device adopts a solid-state soft start device;

[0018] The solid-state soft start device includes a second power frequency switch, a motor, a thyristor valve group, a second power switch, a bypass switch, and a second outlet switch;

[0019] The power frequency switch 2 is connected to the high voltage bus, and the motor is connected in series with the power frequency switch 2;

[0020] The power switch 2 is connected to the high voltage bus, the thyristor valve group is connected in series with the power switch 2, the bypass switch is connected in parallel to both ends of the thyristor valve group, and the outlet switch 2 is connected in series with the thyristor valve group;

[0021] The outgoing line switch 2 is connected between the power frequency switch 2 and the motor, and the outgoing line switch 1 is also connected between the power frequency switch 2 and the motor.

[0022] Furthermore, when the high-voltage frequency conversion soft start device is running, power switch 1 is closed. When the frequency converter receives the start command, the output switch 1 is closed until the motor is accelerated to the point where the phases of the motor side and the power supply side are basically consistent. The power frequency switch 2 is closed. At this time, the frequency converter and the power grid supply power to the motor at the same time. When it is detected that the power frequency switch 2 is closed, the output switch 1 is opened with a delay, the frequency converter stops working, and the frequency conversion soft start process is completed.

[0023] Furthermore, the power switch 1, the outlet switch 1, the power frequency switch 1, the short-circuit switch, the power switch 2, the outlet switch 2, and the power frequency switch 2 all use withdrawable vacuum circuit breakers or vacuum contactors.

[0024] Furthermore, the bypass switch adopts a fixed vacuum circuit breaker or a vacuum contactor.

[0025] Compared with the prior art, the beneficial effects of the utility model are as follows:

[0026] The utility model retains the original non-frequency conversion soft-start device and only needs to add a set of high-voltage frequency conversion soft-start device, combined with the adjustment control logic, so that it can complete the automatic input or removal of the high-voltage frequency conversion soft-start device or the non-frequency conversion soft-start device in the circuit according to relevant instructions, and realize the mutual interlocking switching of the high-voltage frequency conversion soft-start device and the original starting device, so that the two sets of soft-start devices are redundant and standby to each other. Under the premise of meeting the soft starting of the high-voltage AC motor, the electrical impact on the power grid and the motor caused by the direct starting of the motor and the mechanical impact on the motor load are avoided, and the reliability and safety of the motor soft-start system are greatly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 A primary wiring diagram showing a solid-state soft start circuit in the background technology;

[0028] Figure 2 A primary wiring diagram showing a liquid soft start circuit in the background technology;

[0029] Figure 3 The primary wiring diagram of the variable frequency soft start circuit shown in the background technology;

[0030] Figure 4 This is a primary wiring diagram of a soft start system in which the frequency conversion soft start and the liquid hydropower group soft start serve as backup for each other in the utility model;

[0031] Figure 5 The utility model is a primary wiring diagram of a soft start system in which a variable frequency soft start and a solid state soft start serve as backup for each other.

[0032] Figure numerals: 1. high-voltage bus; 2. power switch 1; 3. outgoing line switch 1; 4. power frequency switch 1; 5. short-circuit switch; 6. frequency converter; 61. phase-shifting transformer; 62. power unit and control system; 7. reactor; 8. motor; 9. water resistor; 10. power frequency switch 2; 11. power switch 2; 12. outgoing line switch 2; 13. bypass switch; 14. thyristor valve group. DETAILED DESCRIPTION

[0033] The present invention will be further described in detail below in conjunction with the embodiments and drawings, but the implementation methods of the present invention are not limited thereto.

[0034] The utility model provides a soft start control circuit structure in which a variable frequency soft start and a non-variable frequency soft start serve as backup for each other, which is particularly suitable for a technical transformation project of motor equipment. The original non-variable frequency solid-state soft start device or liquid soft start device is retained, a set of high-voltage variable frequency soft start device is added, and the user's process DCS control logic is adjusted so that the high-voltage variable frequency soft start device or the original starting device in the circuit is automatically put into or removed according to relevant instructions, and the interlocking switching between the high-voltage variable frequency soft start device and the original starting device is realized, so that the two sets of soft start devices serve as redundant backup for each other.

[0035] Under the premise of meeting the soft start of the high-voltage AC motor 8, the electrical impact on the power grid and the motor 8 caused by the direct start of the motor 8 and the mechanical impact on the load of the motor 8 are avoided, and the reliability and safety of the soft start system of the motor 8 are greatly improved.

[0036] In this regard, the above circuit structure includes a high-voltage bus 1, a non-frequency conversion soft start device, and a high-voltage frequency conversion soft start device. The non-frequency conversion soft start device and the high-voltage frequency conversion soft start device are respectively connected to the high-voltage bus 1, and the bus is used to access a 10kV voltage.

[0037] It should be noted that the non-frequency conversion soft start device in the present invention can be a step-down starting device with a resistor in series with the stator or rotor of the motor 8, or a non-frequency converter 6 soft start device such as a solid-state soft starter or a liquid soft starter.

[0038] It should be noted that the power configuration of the high-voltage variable frequency soft-start device in the utility model is not configured according to the full power of the motor 8, but is calculated based on the rotational inertia of the motor 8 load, the starting process resistance torque curve (or maximum resistance torque), the load rated speed, the inertia of the motor 8, the rated speed of the motor, the starting time and other parameters. Therefore, the soft-start power is usually light power, which is far less than the rated power of the motor. The variable frequency soft-start power for no-load starting of non-variable frequency fan loads is only about 30% of the rated power of the motor 8.

[0039] In order to better illustrate the utility model, taking the blast furnace blower motor in the metallurgical industry as an example, the current starting method of the blower is a set of independent water resistance voltage reduction starting device, that is, a liquid soft starting device, which has a certain current impact on the power grid and requires two sections of single bus working system bus combination gates to run in parallel. By adding variable frequency soft start technology to the motor starting method, not only the large starting current is reduced, the start is smooth, the impact on the power grid is small, and there is no need for parallel operation of the power grid system. Moreover, when the seasonal ambient temperature is affected, the use of variable frequency soft start is not restricted by environmental factors, which improves the starting efficiency of the blower.

[0040] This new type of one-to-one variable frequency soft start solution is used, and a set of high-voltage variable frequency soft start devices is added. The water resistance voltage reduction starting device of the fan motor is still retained during the transformation. The structure and working performance of the water resistance voltage reduction starting device are not changed after the transformation, and the water resistance voltage reduction starting device can still work normally and reliably. When the unit is started by variable frequency, the water resistance voltage reduction starting device is isolated. When the inverter 6 is overhauled or fails to start, it can be switched to the water resistance voltage reduction starting device in time to achieve voltage reduction starting. One in use and one in reserve improves the starting efficiency. After the frequency conversion transformation, the starting current is reduced, the fan is started smoothly, and the grid voltage does not fluctuate significantly during startup. After the transformation, the control system automatically switches the starting signal to ensure that the starting signal is accurate and reliable.

[0041] Among them, the high-voltage variable frequency soft start device of the utility model adopts the form of a cascaded high-voltage frequency converter 6, which is composed of a phase-shifting transformer 61, a power unit and control system 62, a reactor 7 synchronization device, etc. The excitation inrush current suppression device (also called a current limiting device or a pre-charging device) can be configured or not according to the size of the power selection of the frequency converter 6 and the grid capacity of the starting bus as a judgment basis. The excitation inrush current suppression device here can be in the form of high-voltage pre-charging or low-voltage pre-charging.

[0042] The primary wiring diagram of the soft start system in the above case project is as follows: Figure 4 shown.

[0043] exist Figure 4 Among them, QFa-QFd are withdrawable vacuum circuit breakers, QFa is a power switch 2 for providing power to the frequency converter 6, QFb is an output switch 3 of the frequency converter 6, QFc is an industrial frequency switch 4 for providing industrial frequency power to the motor 8, and QFd is a short-circuit switch 5 of the water resistor 9 short-circuit cabinet.

[0044] TM is the phase-shifting transformer 61 of the inverter 6, VFD is the power unit and control system 62 of the inverter 6, and the power of the inverter 6 is a light-power high-voltage variable-frequency soft-start device configured according to the starting data such as the load resistance torque curve.

[0045] L is the synchronous reactor 7 of the frequency converter 6, which is used to limit the power grid circulating current when the frequency converter switches to the power frequency, so as to avoid the impact on the frequency converter 6 and the power grid.

[0046] M is a wound-rotor high-voltage asynchronous motor 8.

[0047] Rs is the water resistor 9 in the water resistor 9 cabinet, and together with the short-circuit switch 5 forms a water resistor 9 short-circuit cabinet.

[0048] The high-voltage bus 1 is used to access a voltage of 10 kV.

[0049] refer to Figure 4The high-voltage frequency conversion soft start device includes the above-mentioned power switch 2, frequency converter 6, reactor 7, and outgoing line switch 3. The frequency converter 6 includes a phase-shifting transformer 61, a power unit and a control system 62 that are connected to each other; the power switch 2 is connected to the high-voltage bus 1, the phase-shifting transformer 61 is connected in series with the power switch 2, the reactor 7 is connected in series with the power unit and the control system 62, the outgoing line switch 3 is connected in series with the reactor 7, and the outgoing line switch 3 is also used to be connected to the non-frequency conversion soft start device.

[0050] The water resistance voltage reduction starting device includes the above-mentioned power frequency switch 4, motor 8, water resistor 9, and short-circuit switch; the power frequency switch 4 is connected to the high-voltage bus 1, the motor 8 is connected in series with the power frequency switch 4, the water resistor 9 is connected in series with the motor 8, the short-circuit switch is connected in parallel with the water resistor 9, and an outlet switch 3 is connected between the motor 8 and the power frequency switch 4.

[0051] exist Figure 4 In the case project, the operation logic of the inverter 6 soft start motor is as follows:

[0052] Before starting, cut off the water resistor 9 system and confirm that the short-circuit switch (QFd) in the water resistor 9 short-circuit cabinet is in the closed state;

[0053] Close the power switch 2 (QFa) of the inverter 6, and the 10kV power supply is sent to the inverter 6. After the inverter 6 is charged and self-checked without fault, it sends a "ready" command to the superior control system. After receiving the start command, the inverter 6 closes the output switch 3 (QFb) and starts to output and drive the motor 8 to run. When the motor 8 is accelerated to a frequency close to the rated frequency, the phase of the motor side and the power supply side is automatically detected under the condition of satisfying the voltage difference and frequency difference. When the phases on both sides are basically consistent, the inverter 6 closes the power frequency switch 4 (QFc) of the motor 8. At this time, the inverter 6 and the power grid supply power to the motor 8 at the same time. When it is detected that the power frequency switch 4 (QFc) is closed, the output switch 3 (QFb) is opened with a delay, and the inverter 6 stops working, completing the variable frequency soft start process.

[0054] Afterwards, the operation logic of the water resistance pressure reduction starting device starting the motor 8 is as follows:

[0055] Before starting, cut off the inverter 6 system and confirm that the inverter 6 power switch 2 (QFa) and the output switch 3 (QFb) are in the open state; when the water resistance voltage reduction starting device is selected, the switch logic of the inverter 6 starting system will automatically fail;

[0056] Check that the water level and water temperature of the water resistor 9 short-circuit cabinet are in a reasonable state. After the water resistor 9 short-circuit cabinet self-checks and has no faults and is ready, it accepts the background DCS start-up command. The water resistor 9 short-circuit cabinet automatically adjusts the resistance value of the liquid resistor during the start-up process of the motor 8, so that it gradually decreases from a large resistance value to close to zero within a predetermined time, and finally disconnects the water resistor 9 through the short-circuit switch (QFd) to achieve full start-up of the motor 8.

[0057] In order to ensure the safety and reliability of the motor soft start system, the control logic of the two soft start systems is described as follows:

[0058] (1) Add the system interlocking signal and switch cabinet protection function when the inverter 6 is started without changing the starting mode of the raw water resistance cabinet.

[0059] (2) The start-up and operation signals of the inverter 6 and the water resistance cabinet are interlocked and do not interfere with each other, ensuring that the start-up mode is unique during startup;

[0060] (3) The fault tripping signal of inverter 6 has both hard contact tripping and communication signal tripping. When the startup is abnormal, the hard contact signal directly trips the main switch cabinet, and the communication tripping signal can be transmitted to the main control DCS system to achieve tripping synchronization. The inverter 6 cabinet is also equipped with an on-site emergency stop to ensure that the main switch is stopped nearby when the startup is abnormal.

[0061] (4) During variable frequency starting, the motor 8 can automatically exit the differential protection function, and automatically enter the differential protection function after starting, to ensure that the protection function before and after starting is reliable.

[0062] (5) The power cabinet of the inverter 6 is equipped with a protective device to protect the incoming cable of the inverter 6 and the inverter 6 body. The inverter 6 body has a protective function.

[0063] The utility model can also be a soft start system control circuit in which a high voltage variable frequency soft start device and a solid state soft start device are used as backup for each other. The primary wiring diagram is as follows: Figure 5 shown.

[0064] exist Figure 5 Among them, QFa, QFb, QFe-QFg are all withdrawable vacuum circuit breakers, QFa is a power switch 2 for providing power to the frequency converter 6, QFb is an outlet switch 3 for the frequency converter 6, QFe is an industrial frequency switch 10 for providing industrial frequency power to the motor 8, QFf is a power switch 11 for providing power to the solid-state soft starter, and QFg is an outlet switch 12 for the solid-state soft starter;

[0065] QFh is a fixed vacuum circuit breaker, which is a bypass switch 13 of the solid-state soft-start internal thyristor valve group 14;

[0066] TM is the phase-shifting transformer 61 of the frequency converter 6, VFD is the power unit and control system 62 of the frequency converter 6, and the power of the frequency converter 6 is a light-power high-voltage variable frequency soft-start device configured according to the starting data such as the load resistance torque curve;

[0067] L is the synchronous reactor 7 of the frequency converter 6, which is used to limit the power grid circulating current when the frequency converter switches to the power frequency, so as to avoid the impact on the frequency converter 6 and the power grid;

[0068] SCR is a thyristor valve group 14 inside a solid-state soft start device, used for soft starting the motor 8;

[0069] M is a high voltage asynchronous motor 8.

[0070] refer to Figure 5 , combined with the aforementioned high-voltage variable frequency soft start device, the solid-state soft start device includes a power frequency switch 2 10, a motor 8, a thyristor valve group 14, a power switch 2 11, a bypass switch 13, and an outlet switch 2 12;

[0071] The power frequency switch 2 10 is connected to the high voltage bus 1, and the motor 8 is connected in series with the power frequency switch 2 10;

[0072] The power switch 11 is connected to the high voltage bus 1, the thyristor valve group 14 is connected in series with the power switch 11, the bypass switch 13 is connected in parallel to both ends of the thyristor valve group 14, and the outlet switch 12 is connected in series with the thyristor valve group 14;

[0073] The outgoing line switch 12 is connected between the power frequency switch 10 and the motor 8, and an outgoing line switch 3 is also connected between the power frequency switch 10 and the motor 8.

[0074] exist Figure 5 In the case project, the operation logic of the inverter 6 soft start motor is as follows:

[0075] Before starting, cut off the solid-state system and confirm that the circuit breakers QFf and QFg are in the closed state;

[0076] Close the power switch 2 (QFa) of the inverter 6, and the 10kV power supply is sent to the inverter 6. After the inverter 6 is charged and self-checked without fault, it sends a "ready" command to the superior control system. After receiving the start command, the inverter 6 closes the output switch 3 (QFb) and starts to output and drive the motor 8 to run. When the motor 8 is accelerated to a frequency close to the rated frequency, it automatically detects the phase between the motor side and the power supply side under the condition of satisfying the voltage difference and frequency difference. When the phases on both sides are basically consistent, the inverter 6 closes the power frequency switch 10 (QFe) of the motor 8. At this time, the inverter 6 and the power grid supply power to the motor at the same time. When it is detected that the power frequency switch 10 (QFe) is closed, the output switch 3 (QFb) is opened with a delay, and the inverter 6 stops working, completing the variable frequency soft start process.

[0077] Afterwards, the operation logic of the solid-state soft start device starting the motor 8 is as follows:

[0078] Before starting, cut off the inverter 6 system and confirm that the inverter 6 power switch 2 (QFa) and the output switch 3 (QFb) are in the open state; when the solid-state soft start is selected, the switch logic of the inverter 6 starting system will automatically fail;

[0079] When the load needs to be started, the control circuit receives a start signal and controls the conduction angle of the thyristor valve group 14 inside the solid-state soft start device to gradually increase the input voltage of the motor 8 according to the preset start curve and parameters. The corresponding starting torque and speed of the motor 8 also gradually increase until the start is completed and the full voltage is given to the motor 8. At this time, the bypass switch 13 (QFh) is controlled to be closed to stop the soft starter from running.

[0080] The power circuit inside the solid-state soft start device of the utility model is mainly composed of power semiconductor devices, such as thyristors (GTOs), insulated gate bipolar transistors (IGBTs), etc. The working principle of the power circuit is to achieve smooth start and regulation of the power grid system by reasonably triggering and controlling the power semiconductor devices after receiving the signal of the control circuit.

[0081] In order to ensure the safety and reliability of the motor soft start system, the control logic of the two soft start systems is described as follows:

[0082] (1) Add the system interlock signal and switch cabinet protection function without changing the starting mode of the solid-state soft start system after the inverter 6 is started.

[0083] (2) The inverter 6 startup and solid-state soft start and operation signals are interlocked and do not interfere with each other, ensuring that the startup mode is unique during startup;

[0084] (3) The fault tripping signal of inverter 6 has both hard contact tripping and communication signal tripping. When the startup is abnormal, the hard contact signal directly trips the main switch cabinet, and the communication tripping signal can be transmitted to the main control DCS system to achieve tripping synchronization. The inverter 6 cabinet is also equipped with an on-site emergency stop to ensure that the main switch is stopped nearby when the startup is abnormal.

[0085] (4) During variable frequency starting, the motor 8 can automatically exit the differential protection function, and automatically enter the differential protection function after starting, to ensure that the protection function before and after starting is reliable.

[0086] (5) The power cabinet of the inverter 6 is equipped with a protective device to protect the incoming cable of the inverter 6 and the inverter 6 body. The inverter 6 body has a protective function.

[0087] It should be noted that DCS is the abbreviation of the existing distributed control system (Distributed Control System).

[0088] It should be noted that the switch used in the control circuit of the utility model is not limited to a high-voltage vacuum circuit breaker, but may also be a switch such as a high-voltage vacuum contactor that can automatically control the opening and closing of the switch.

[0089] It should be noted that the variable frequency soft start device in the control circuit of the utility model adopts a cascaded high-voltage frequency converter 6. The purpose is that the frequency converter 6 has no harmonic impact on the power grid and the motor. When other forms of frequency converters 6 are used, it is necessary to consider adding input and output filters to avoid harmonic impacts on the power grid and the motor 8.

[0090] The above is only a preferred embodiment of the present invention. The protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, some improvements and modifications without departing from the principle of the present invention should also be regarded as the protection scope of the present invention.

Claims

1. A soft start control circuit structure in which variable frequency soft start and non-variable frequency soft start are mutually backup, characterized in that: The circuit structure comprises a high-voltage bus (1), a non-frequency conversion soft-start device, and a high-voltage frequency conversion soft-start device, wherein the non-frequency conversion soft-start device and the high-voltage frequency conversion soft-start device are respectively connected to the high-voltage bus (1); The non-frequency conversion soft start device adopts a voltage reduction starting device with a resistor in series with the stator or rotor of the motor (8), or adopts a solid-state soft start device, or a liquid soft start device; The high-voltage variable-frequency soft-start device comprises a power switch (2), a frequency converter (6), a reactor (7), and an outlet switch (3); the frequency converter (6) comprises a phase-shifting transformer (61), a power unit, and a control system (62) which are connected to each other; A power switch (2) is connected to the high-voltage bus (1), a phase-shifting transformer (61) is connected in series with the power switch (2), a reactor (7) is connected in series with the power unit and the control system (62), an outlet switch (3) is connected in series with the reactor (7), and the outlet switch (3) is also used to connect to a non-frequency conversion soft start device.

2. The soft start control circuit structure in which the variable frequency soft start and the non-variable frequency soft start are mutually backup according to claim 1, characterized in that: When the non-frequency conversion soft start device adopts a liquid soft start device, it is set as a water resistance pressure reduction starting device; The water resistance voltage reduction starting device comprises an industrial frequency switch (4), a motor (8), a water resistance (9), and a short-circuit switch; The power frequency switch (4) is connected to the high voltage bus (1), the motor (8) is connected in series with the power frequency switch (4), the water resistor (9) is connected in series with the motor (8), the short-circuit switch is connected in parallel with the water resistor (9), and the outlet switch (3) is connected between the motor (8) and the power frequency switch (4).

3. The soft start control circuit structure in which the variable frequency soft start and the non-variable frequency soft start are mutually backup according to claim 2, characterized in that: When the high-voltage variable frequency soft start device is in operation, the short-circuit switch in the liquid soft start device must be in the closed state before closing the power switch 1 (2).

4. The soft start control circuit structure in which the variable frequency soft start and the non-variable frequency soft start are mutually backup according to claim 3, characterized in that: During the operation of the high-voltage variable frequency soft-start device, after the outgoing line switch 1 (3) is closed, when the motor (8) is accelerated to the point where the phases of the motor side and the power supply side are substantially consistent, the industrial frequency switch 1 (4) is closed, and then the outgoing line switch 1 (3) is opened with a time delay until the frequency converter (6) stops working, thereby completing the variable frequency soft-start process.

5. The soft start control circuit structure in which the variable frequency soft start and the non-variable frequency soft start are mutually backup according to claim 1, characterized in that: When the non-frequency conversion soft start device adopts a solid-state soft start device; The solid-state soft start device comprises a second power frequency switch (10), a motor (8), a thyristor valve group (14), a second power switch (11), a bypass switch (13), and a second outlet switch (12); The second power frequency switch (10) is connected to the high voltage bus (1), and the motor (8) is connected in series with the second power frequency switch (10); The second power switch (11) is connected to the high voltage bus (1), the thyristor valve group (14) is connected in series with the second power switch (11), the bypass switch (13) is connected in parallel to both ends of the thyristor valve group (14), and the second output switch (12) is connected in series with the thyristor valve group (14); The second outgoing line switch (12) is further connected between the second power frequency switch (10) and the motor (8), and the first outgoing line switch (3) is also connected between the second power frequency switch (10) and the motor (8).

6. The soft start control circuit structure in which the variable frequency soft start and the non-variable frequency soft start are mutually backup according to claim 5, characterized in that: When the high-voltage variable frequency soft start device is in operation, the power switch 1 (2) is closed, and when the frequency converter (6) receives a start command, the outgoing line switch 1 (3) is closed until the motor (8) is accelerated to a point where the phases of the motor side and the power side are substantially consistent, and the power frequency switch 2 (10) is closed. At this time, the frequency converter (6) and the power grid simultaneously supply power to the motor (8). When it is detected that the power frequency switch 2 (10) is closed, the outgoing line switch 1 (3) is opened with a time delay, and the frequency converter (6) stops working, completing the variable frequency soft start process.

7. The soft start control circuit structure in which the variable frequency soft start and the non-variable frequency soft start are mutually backup according to claim 2 or 5, characterized in that: The power switch 1 (2), the outlet switch 1 (3), the power frequency switch 1 (4), the short-circuit switch, the power switch 2 (11), the outlet switch 2 (12), and the power frequency switch 2 (10) all adopt withdrawable vacuum circuit breakers or vacuum contactors.

8. The soft start control circuit structure in which the variable frequency soft start and the non-variable frequency soft start are mutually backup according to claim 5, characterized in that: The bypass switch (13) adopts a fixed vacuum circuit breaker or a vacuum contactor.

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