A variable frequency starting circuit capable of automatically switching between line frequency and variable frequency

Abstract

The utility model discloses a kind of frequency conversion starting circuit of automatic switching power frequency, belong to the technical field of alternating current motor frequency conversion circuit.It includes: main circuit;Speed regulation circuit, including the same phase speed regulation switching device HSP connected with the analog quantity input end of frequency converter VFD;Secondary control circuit, including the starting control circuit of control frequency converter VFD soft-starting alternating current motor M, and switching control circuit.This frequency conversion starting circuit is equipped with speed regulation circuit and switching control circuit, when alternating current motor starts, the frequency conversion starting power supply output by frequency converter is used as starting power supply, when meeting the same frequency, same phase, same amplitude condition, switching control circuit switches the power supply of alternating current motor from frequency conversion output power supply to bypass power frequency power grid power supply, frequency converter stops operation, does not consume additional electric energy, improve the overall working efficiency of alternating current motor, also avoid the additional loss caused by high-order harmonic generated in the operation process of frequency converter to reduce the energy efficiency of power system, long-term operation cost significantly decreases.

Description

Technical Field

[0001] This utility model relates to a variable frequency starting circuit that automatically switches power frequency, belonging to the technical field of AC motor variable frequency circuits. Background Technology

[0002] An AC motor is a device that converts mechanical energy into alternating current (AC) electrical energy through electromagnetic induction and is widely used in various industries. AC motor starting methods are mainly classified according to motor power, load characteristics, and power grid conditions: direct full-voltage starting, star-delta starting, soft starter, and frequency converter starting. Currently, the common practice for starting high-power, heavy-load AC motors is to use a frequency converter for soft starting. While this method reduces the impact on the power grid and avoids voltage drops affecting other equipment, the frequency converter continues to operate after the AC motor starts. The high-order harmonics generated during frequency converter operation increase copper and iron losses in the motor stator and rotor, leading to decreased efficiency and increased temperature rise. Harmonics can also cause motor vibration, overheating, and even accelerate insulation aging, resulting in a decrease in the overall operating efficiency of the AC motor.

[0003] Therefore, an automatic switching frequency converter starting circuit is designed. When starting an AC motor, it can switch the power supply of the AC motor from the frequency converter output power supply to the bypass power grid, thus avoiding the adverse effects caused by the frequency converter constantly being involved in operation. Summary of the Invention

[0004] The technical problem to be solved by this utility model is to provide a variable frequency starting circuit that automatically switches the power frequency, which solves the problem of how to reduce the impact of the frequency converter on the whole system when using the current method of soft starting AC motor.

[0005] The technical problem to be solved by this utility model is achieved by the following technical solution:

[0006] A variable frequency start-up circuit that automatically switches power frequency includes:

[0007] The main circuit includes circuit breaker QF, fast fuse FU, frequency converter VFD, isolating contactor KM1, and AC motor M, which are connected sequentially to the incoming power supply L1-L3. The motor side of circuit breaker QF is also connected to AC motor M through bypass contactor KM2 and thermal relay FR.

[0008] Speed ​​control circuit, including synchronous speed control switching device HSP connected to the analog input terminal of frequency converter VFD;

[0009] The secondary control circuit includes a starting control circuit for controlling the VFD soft start of the AC motor M, and a switching control circuit. The switching control circuit includes an intermediate relay K5 and a synchronous contact of the synchronous speed control switching device HSP. The coil of the intermediate relay K5 is connected in series with the synchronous contact of the synchronous speed control switching device HSP. When the normally open contact of the intermediate relay K5 is closed, it triggers the main contact of the isolation contactor KM1 in the main circuit to open and the main contact of the bypass contactor KM2 to close.

[0010] Preferably, the synchronous speed control switching device HSP consists of a synchronous device and an electronic potentiometer. The input terminal of the synchronous device is connected to the input power supply L1 and L2, the motor input terminal of the synchronous device is connected to the input lines L11 and L13 of the AC motor M, the relay output terminal of the synchronous device is connected to the input terminal of the electronic potentiometer, and the analog output terminal of the electronic potentiometer is connected to the analog input terminal of the frequency converter VFD.

[0011] Preferably, the start-up control circuit includes a main power supply, an auxiliary power supply AUX powered by the main power supply, intermediate relays K1-K3, a closing button HA, a tripping button TA, a bypass operation indicator light HR2, a frequency converter operation indicator light HR1, and a fault indicator light HY1. The operating status output contact, fault status output contact, and closing button HA of the frequency converter VFD are connected in parallel to the auxiliary power supply AUX, and the bypass operation indicator light HR2, the frequency converter operation indicator light HR1, and the fault indicator light HY1 are connected in parallel to the main power supply.

[0012] The branch where the closing button HA is located is connected in series with the opening button TA, the normally closed contact of the intermediate relay K3, the coil of the intermediate relay K1, and the normally open contact of the intermediate relay K1 connected in parallel across the opening button TA.

[0013] The coil of intermediate relay K2 is connected in series on the branch where the operating status output contact of the frequency converter VFD is located.

[0014] The branch where the fault status output contact of the frequency converter VFD is located is connected in series with the coil of intermediate relay K3 and thermal relay FR1.

[0015] The bypass operation signal light HR2 is connected in series with the auxiliary normally open contact of the bypass contactor KM2;

[0016] The normally open contact of the intermediate relay K2 is connected in series on the branch where the inverter operation indicator light HR1 is located;

[0017] The normally open contact of the intermediate relay K3 is connected in series on the branch where the fault signal light HY1 is located.

[0018] Preferably, the switching control circuit further includes an intermediate relay K4, the coils of the intermediate relay K4 and intermediate relay K5 are connected in parallel to the auxiliary power supply AUX, and the coils of the isolation contactor KM1 and the bypass contactor KM2 are connected in parallel and then connected to the main power supply through the normally open contact of the common intermediate relay K1.

[0019] The normally open contacts of intermediate relays K1 and K5 are connected in series on the branch where the coil of intermediate relay K4 is located, and the normally open contacts of intermediate relay K4 are connected in parallel across the two ends of the contacts of intermediate relay K5.

[0020] The branch where the coil of the intermediate relay K5 is located is also connected in series with the synchronous contact of the synchronous speed control switching device HSP.

[0021] The branch circuit where the coil of the isolating contactor KM1 is located is also connected in series with the auxiliary normally closed contact of the bypass contactor KM2 and the normally closed contact of the intermediate relay K4.

[0022] The bypass contactor KM2's coil is connected in series with the auxiliary normally closed contact of the isolation contactor KM1 and the normally open contact of the intermediate relay K4. The two ends of the normally open contact of the intermediate relay K4 are connected in parallel with the auxiliary normally open contact of the bypass contactor KM2.

[0023] Preferably, in the speed control circuit, the start / stop terminal of the frequency converter VFD is connected to the 24V DC control power supply provided inside the frequency converter VFD through the auxiliary normally open contact of the isolation contactor KM1, and the emergency stop terminal of the frequency converter VFD is connected to the 24V DC control power supply in sequence through the normally open contact of the intermediate relay K3 and the normally closed contact of the intermediate relay K4.

[0024] The beneficial effects of this utility model are as follows: This variable frequency starting circuit is equipped with a speed regulation circuit and a switching control circuit. When the AC motor starts, the variable frequency starting power supply output by the frequency converter is used as the starting power supply. When the conditions of same frequency, same phase, and same amplitude are met, the switching control circuit switches the power supply of the AC motor from the frequency converter output power supply to the bypass power grid power supply. The frequency converter stops running and does not consume additional power, which improves the overall working efficiency of the AC motor. It also avoids the additional losses caused by high-order harmonics generated during the operation of the frequency converter, which reduces the energy efficiency of the power system and significantly reduces long-term operating costs. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the main circuit of this utility model;

[0026] Figure 2 This is a schematic diagram of the speed regulation circuit of this utility model;

[0027] Figure 3This is a schematic diagram of the secondary control loop circuit of this utility model. Detailed Implementation

[0028] To facilitate a clear understanding of the technical means, creative features, objectives, and effects of this utility model, the following description, in conjunction with specific illustrations, further elaborates on this utility model.

[0029] like Figures 1-3 As shown, this automatic frequency switching inverter start circuit includes a main circuit, a speed regulation circuit, and a secondary control circuit.

[0030] like Figure 1 The diagram shows the main circuit. It includes circuit breaker QF, fast-acting fuse FU, frequency converter VFD, isolating contactor KM1, and AC motor M, which are connected sequentially to the incoming power supply L1-L3. The motor side of circuit breaker QF is also connected to AC motor M through bypass contactor KM2 and thermal relay FR.

[0031] The incoming lines L11, L12, and L13 of the AC motor M are connected to the terminals U1, V1, and W1 of the AC motor M via the incoming lines L11, L12, and L13, respectively.

[0032] like Figure 2 The diagram shows a circuit diagram of the speed control loop. It includes a synchronous speed control switching device (HSP) connected to the analog input terminal of the frequency converter (VFD).

[0033] The synchronous speed control switching device HSP consists of a commercially available synchronizing device and an electronic potentiometer. The input terminal of the synchronizing device is connected to the incoming power supply L1 and L2 via fuses FU1 and FU2. The motor-side input terminal of the synchronizing device is connected to the incoming lines L11 and L13 of the AC motor M via fuses FU3 and FU4. The relay output terminal of the synchronizing device is connected to the input terminal of the electronic potentiometer: the UP speed-up output is connected to the UP side of the electronic potentiometer IN; the DOWN speed-down output is connected to the DOWN side of the electronic potentiometer IN. The analog output terminal of the electronic potentiometer is connected to the analog input terminal of the frequency converter VFD.

[0034] The synchronizing device detects the voltage, frequency, and phase angle of the upper end (input power supply L1, L2) and lower end (input lines L11, L13 of AC motor M) of the frequency converter VFD, and adjusts the speed of the frequency converter VFD by dynamically adjusting the output analog quantity of the electronic potentiometer.

[0035] In the speed control circuit, the start / stop terminals of the frequency converter VFD are connected to the 24V DC control power supply provided inside the frequency converter VFD through the auxiliary normally open contact of the isolation contactor KM1. The emergency stop terminals of the frequency converter VFD are connected to the 24V DC control power supply sequentially through the normally open contact of intermediate relay K3 and the normally closed contact of intermediate relay K4. This connection is used to automatically stop the operation of the frequency converter VFD when switching to bypass mode.

[0036] like Figure 3 The diagram shows a schematic of the secondary control circuit. It includes a starting control circuit for controlling the VFD soft-start AC motor M, and a switching control circuit. The switching control circuit includes an intermediate relay K5 and the synchronizing contact of the synchronizing speed control switching device HSP. The coil of the intermediate relay K5 is connected in series with the synchronizing contact of the synchronizing speed control switching device HSP. When the normally open contact of the intermediate relay K5 closes, it triggers the main contact of the isolation contactor KM1 in the main circuit to open and the main contact of the bypass contactor KM2 to close.

[0037] I. Start-up Control Circuit. This includes the main power supply (AC220V), an auxiliary power supply AUX (DC24V) powered by the main power supply, intermediate relays K1-K3, closing button HA, opening button TA, bypass operation indicator HR2, inverter operation indicator HR1, fault indicator HY1, the inverter VFD's operating status output contacts and fault status output contacts, and the closing button HA connected in parallel to the auxiliary power supply AUX. The bypass operation indicator HR2, inverter operation indicator HR1, and fault indicator HY1 are connected in parallel to the main power supply. The auxiliary power supply AUX input is connected to the main power supply via circuit breaker QF1, and the main power supply powers the auxiliary power supply AUX. The auxiliary power supply AUX output is connected to other subsequent components via a fuse. The main power supply is connected to subsequent components via circuit breaker QF2.

[0038] The branch where the closing button HA is located has a normally closed opening button TA, a normally closed contact of intermediate relay K3, a coil of intermediate relay K1, and a normally open contact of intermediate relay K1 connected in parallel across the opening button TA.

[0039] The coil of intermediate relay K2 is connected in series on the branch where the VFD operating status output contact is located.

[0040] The branch where the fault status output contact of the frequency converter VFD is located has the coil of intermediate relay K3 and thermal relay FR1 connected in series.

[0041] The bypass operation signal light HR2 is connected in series with the auxiliary normally open contact of the bypass contactor KM2.

[0042] The normally open contact of intermediate relay K2 is connected in series on the branch where the inverter operation indicator light HR1 is located.

[0043] The normally open contact of intermediate relay K3 is connected in series on the branch where the fault indicator light HY1 is located.

[0044] II. Switching control circuit. This includes intermediate relay K5 and the synchronizing contact of the synchronizing speed control switching device HSP, as well as intermediate relay K4. The coils of intermediate relays K4 and K5 are connected in parallel to the auxiliary power supply AUX. The coils of isolation contactor KM1 and bypass contactor KM2 are connected in parallel and then connected to the main power supply through the normally open contact of the common intermediate relay K1.

[0045] The normally open contacts of intermediate relays K1 and K5 are connected in series on the branch where the coil of intermediate relay K4 is located, and the normally open contacts of intermediate relay K4 are connected in parallel across the normally open contacts of intermediate relay K5.

[0046] The branch where the coil of intermediate relay K5 is located is also connected in series with the synchronous contact of synchronous speed control switching device HSP.

[0047] The branch circuit where the coil of isolating contactor KM1 is located is also connected in series with the auxiliary normally closed contact of bypass contactor KM2 and the normally closed contact of intermediate relay K4.

[0048] The bypass contactor KM2's coil is connected in series with the auxiliary normally closed contact of the isolation contactor KM1 and the normally open contact of the intermediate relay K4. The bypass contactor KM2's auxiliary normally open contact is connected in parallel across the normally open contact of the intermediate relay K4.

[0049] The control power supply for the coils of isolating contactor KM1, bypass contactor KM2, and indicator lights HR1, HR2, and HY1 is AC220V (main power). The power supply for the remaining secondary control circuits is DC24V (auxiliary power AUX).

[0050] The working principle of variable frequency starting of AC motor:

[0051] S1. With both the inverter VFD and the bypass thermal relay FR functioning correctly, in the secondary control circuit, the coil of intermediate relay K3 is de-energized, and the normally open contacts 6 and 10 of intermediate relay K3 open, causing the fault indicator HY1 to fail to illuminate. The normally closed contacts 5 and 9 of intermediate relay K3 close, preparing for subsequent startup.

[0052] S2. In the secondary control circuit, when the closing button HA is closed, the coil of intermediate relay K1 is energized. This self-holding is achieved by closing the normally open contacts 7 and 11 of intermediate relay K1. At the same time, the normally open contacts 6 and 10 and contacts 5 and 9 of intermediate relay K1 also close synchronously, causing the coil of isolation contactor KM1 to be energized, and the frequency converter VFD in the main circuit to start. Simultaneously, the operating status output contact of the frequency converter VFD closes, the coil of intermediate relay K2 is energized and energized, the normally open contacts 8 and 12 of intermediate relay K2 close, and the frequency converter operation indicator light HR1 illuminates.

[0053] S3. After the VFD is started, in the speed control circuit, the synchronization device in the synchronization speed control switching device HSP starts to detect the synchronization status of the incoming power supply L1, L3 and the AC motor M side power supply L11, L13. It automatically adjusts the AI ​​input of the VFD through the AO output of the electronic potentiometer, thereby adjusting the speed of the VFD.

[0054] The working principle of switching power frequencies:

[0055] Synchronization Judgment: During speed regulation, when the synchronization speed control switching device HSP detects that the upper end (incoming power supply L1, L2) and lower end (incoming lines L11, L13 of AC motor M) of the frequency converter VFD meet the conditions of same frequency, same phase, and same amplitude within the allowable deviation range:

[0056] In the secondary control circuit, when the synchronous contact of the synchronous speed regulation switching device HSP closes, the coil of intermediate relay K5 is energized and closes, and the normally open contacts 7 and 11 of intermediate relay K5 close. When the coil of intermediate relay K4 is energized and closes, the normally open contacts 5 and 9 of intermediate relay K4 close, thus achieving self-holding.

[0057] Power Frequency Switching: In the secondary control circuit, normally open contacts 6 and 10 of intermediate relay K4 close, and normally closed contacts 3 and 11 open. The coil of bypass contactor KM2 is energized, and the coil of isolation contactor KM1 is de-energized. In the main circuit, the main contacts of bypass contactor KM2 close, and the main contacts of isolation contactor KM1 open, switching the AC motor M in the main circuit from the frequency converter VFD to the power grid (incoming power supply L1-L3). In the secondary control circuit, self-holding is achieved by closing the auxiliary normally open contacts 13 and 14 of bypass contactor KM2, and the auxiliary normally open contacts 33 and 34 of bypass contactor KM2 close, illuminating the bypass operation indicator HR2. The operating status output contact of the frequency converter VFD opens, the coil of intermediate relay K2 is de-energized, the normally open contacts 8 and 12 of intermediate relay K2 open, and the frequency converter operation indicator HR1 goes out.

[0058] This variable frequency starting circuit has a speed regulation circuit and a switching control circuit. When the AC motor starts, the variable frequency starting power supply output by the frequency converter is used as the starting power supply. When the conditions of same frequency, same phase, and same amplitude are met, the switching control circuit switches the power supply of the AC motor from the frequency converter output power supply to the bypass power grid power supply. The frequency converter stops running and does not consume additional power, which improves the overall working efficiency of the AC motor and avoids the additional losses caused by high-order harmonics generated during the operation of the frequency converter, which reduces the energy efficiency of the power system and significantly reduces long-term operating costs.

[0059] The foregoing has shown and described the basic principles, main features, and advantages of this utility model. Those skilled in the art should understand that this utility model is not limited to the above embodiments. Various changes and modifications can be made to this utility model without departing from its spirit and scope, and all such changes and modifications fall within the scope of protection claimed by this utility model. The scope of protection of this utility model is defined by the appended claims and their equivalents.

Claims

1. A variable frequency start-up circuit that automatically switches power frequency, characterized in that, include: The main circuit includes circuit breaker QF, fast fuse FU, frequency converter VFD, isolating contactor KM1, and AC motor M, which are connected sequentially to the incoming power supply L1-L3. The motor side of circuit breaker QF is also connected to AC motor M through bypass contactor KM2 and thermal relay FR. Speed ​​control circuit, including synchronous speed control switching device HSP connected to the analog input terminal of frequency converter VFD; The secondary control circuit includes a starting control circuit for controlling the VFD soft start of the AC motor M, and a switching control circuit. The switching control circuit includes an intermediate relay K5 and a synchronous contact of the synchronous speed control switching device HSP. The coil of the intermediate relay K5 is connected in series with the synchronous contact of the synchronous speed control switching device HSP. When the normally open contact of the intermediate relay K5 is closed, it triggers the main contact of the isolation contactor KM1 in the main circuit to open and the main contact of the bypass contactor KM2 to close.

2. The variable frequency start-up circuit for automatically switching power frequency according to claim 1, characterized in that, The synchronous speed control switching device HSP consists of a synchronizing device and an electronic potentiometer. The input terminal of the synchronizing device is connected to the input power supply L1 and L2. The motor-side input terminal of the synchronizing device is connected to the input lines L11 and L13 of the AC motor M. The relay output terminal of the synchronizing device is connected to the input terminal of the electronic potentiometer. The analog output terminal of the electronic potentiometer is connected to the analog input terminal of the frequency converter VFD.

3. The variable frequency start-up circuit for automatically switching power frequency according to claim 1, characterized in that, The start-up control circuit includes a main power supply, an auxiliary power supply AUX powered by the main power supply, intermediate relays K1-K3, a closing button HA, a tripping button TA, a bypass operation indicator light HR2, a frequency converter operation indicator light HR1, and a fault indicator light HY1. The operating status output contact, fault status output contact, and closing button HA of the frequency converter VFD are connected in parallel to the auxiliary power supply AUX. The bypass operation indicator light HR2, the frequency converter operation indicator light HR1, and the fault indicator light HY1 are connected in parallel to the main power supply. The branch where the closing button HA is located is connected in series with the opening button TA, the normally closed contact of the intermediate relay K3, the coil of the intermediate relay K1, and the normally open contact of the intermediate relay K1 connected in parallel across the opening button TA. The coil of intermediate relay K2 is connected in series on the branch where the operating status output contact of the frequency converter VFD is located. The branch where the fault status output contact of the frequency converter VFD is located is connected in series with the coil of intermediate relay K3 and thermal relay FR1. The bypass operation signal light HR2 is connected in series with the auxiliary normally open contact of the bypass contactor KM2; The normally open contact of the intermediate relay K2 is connected in series on the branch where the inverter operation indicator light HR1 is located; The normally open contact of the intermediate relay K3 is connected in series on the branch where the fault signal light HY1 is located.

4. The variable frequency start-up circuit for automatically switching power frequency according to claim 3, characterized in that, The switching control circuit also includes an intermediate relay K4. The coils of the intermediate relays K4 and K5 are connected in parallel to the auxiliary power supply AUX. The coils of the isolation contactor KM1 and the bypass contactor KM2 are connected in parallel and then connected to the main power supply through the normally open contact of the common intermediate relay K1. The normally open contacts of intermediate relays K1 and K5 are connected in series on the branch where the coil of intermediate relay K4 is located, and the normally open contacts of intermediate relay K4 are connected in parallel across the two ends of the contacts of intermediate relay K5. The branch where the coil of the intermediate relay K5 is located is also connected in series with the synchronous contact of the synchronous speed control switching device HSP. The branch circuit where the coil of the isolating contactor KM1 is located is also connected in series with the auxiliary normally closed contact of the bypass contactor KM2 and the normally closed contact of the intermediate relay K4. The bypass contactor KM2's coil is connected in series with the auxiliary normally closed contact of the isolation contactor KM1 and the normally open contact of the intermediate relay K4. The two ends of the normally open contact of the intermediate relay K4 are connected in parallel with the auxiliary normally open contact of the bypass contactor KM2.

5. The frequency converter starting circuit for automatic switching of power frequency according to claim 4, characterized in that, In the speed control circuit, the start / stop terminal of the frequency converter VFD is connected to the 24V DC control power supply provided inside the frequency converter VFD through the auxiliary normally open contact of the isolation contactor KM1. The emergency stop terminal of the frequency converter VFD is connected to the 24V DC control power supply in sequence through the normally open contact of the intermediate relay K3 and the normally closed contact of the intermediate relay K4.

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