A three-phase alternating current motor speed control device

Abstract

This utility model relates to the field of motor speed control technology and discloses a three-phase AC motor speed control device. The device connects a "frequency converter speed control branch" and a "contactor-relay full-voltage branch" in parallel within the main circuit of the same motor. The two branches are electrically interlocked via normally closed contacts KM1 and KM2. The control circuit includes segmented speed control circuits for frequency converter start / stop, fault indication, power indication, and time control, and adds an energy feedback circuit to invert the motor's regenerated electrical energy into AC power with the same frequency and voltage as the power grid before feeding it back to the grid, with a feedback rate ≥95%. The device can seamlessly switch to full-voltage power frequency operation in case of frequency converter failure, ensuring continuous production. It has protection functions such as overcurrent, overvoltage, undervoltage, phase loss, short circuit, and stall protection. The motor efficiency is ≥90%, and the power factor is ≥0.97, significantly reducing power consumption and maintenance. It has a simple structure, is easy to operate, and is suitable for applications requiring variable flow operation, such as water treatment.

Description

Technical Field

[0001] This utility model relates to the field of motor speed control technology, and in particular to a three-phase AC motor speed control device. Background Technology

[0002] Concentrated sulfuric acid in water treatment workshops is a crucial product for ore recovery in metal smelting plants. During actual operation, as the concentrated sulfuric acid in the tank is gradually extracted from shallow to deep depths, the output decreases, and the load on the alloy pump correspondingly reduces, eventually leading to a light-load or no-load operation. Since the motor is directly controlled by three-phase AC power, it operates at its rated speed whenever the alloy pump starts, resulting in near-idle operation and causing the sulfuric acid tank to experience dry-running. Because the equipment uses a traditional contactor-relay control system, manual adjustment of the motor speed based on the pump's flow rate is impossible. This significantly reduces the actual load rate and power factor of the alloy pump motor, causing its operating efficiency to consistently remain below 30%, ultimately resulting in substantial energy loss during operation. Furthermore, the constant speed operation under consistently low load conditions can damage the motor's insulation, shorten its lifespan, and sometimes even cause motor failure, leading to malfunctions in various control circuits, ultimately resulting in frequent system failures, mid-operation shutdowns, or equipment paralysis. Utility Model Content

[0003] The purpose of this invention is to provide a three-phase AC motor speed control device to solve the problems mentioned in the background art.

[0004] To achieve the above objectives, the technical solution adopted by this utility model is as follows:

[0005] A three-phase AC motor speed control device includes a main circuit and a control circuit, wherein:

[0006] The main circuit includes: fuse FU, main circuit breaker QF, surge protector, branch circuit breaker QF2 and energy meter connected in sequence after the three-phase power supply;

[0007] The output terminal of the energy meter is connected in parallel with two paths:

[0008] The first path connects to the main motor M of the alloy pump via the frequency converter, the main contacts of the frequency converter AC contactor KM1, and the thermal relay FR1.

[0009] The second path, via the main contacts of the main contactor KM2 and the thermal relay FR2, is also connected to the main motor M of the alloy pump.

[0010] The inverter's DC bus side is connected to a parallel energy feedback circuit, which is used to invert the motor's regenerative energy into AC power that is in the same frequency and phase as the power grid and feed it back to the power grid.

[0011] The control loop includes:

[0012] The inverter speed control system control circuit includes an inverter system control circuit stop button SB1, an inverter system control circuit start button SB2, an inverter AC contactor KM1 coil, an inverter system control circuit run indicator L1, an inverter system control circuit stop indicator L2, an inverter system control circuit fault indicator L3, an inverter system control circuit power indicator L4, and a time controller. The time controller automatically switches the inverter output frequency within a set time period through an interlocking circuit of intermediate relay coils KA1, KA2, and KA3.

[0013] The contactor-relay speed control system control circuit includes a contactor-relay system control circuit stop button SB9, a contactor-relay system control circuit start button SB10, a main contactor KM2 coil, a contactor-relay system control circuit run indicator L5, a contactor-relay system control circuit stop indicator L6, a contactor-relay system control circuit fault indicator L7, and a contactor-relay system control circuit power indicator L8.

[0014] The inverter speed control system control circuit and the contactor-relay speed control system control circuit are respectively connected in series with the normally closed contact of the main contactor KM2 and the normally closed contact of the inverter AC contactor KM1 to form an electrical interlock, so that the two speed control modes cannot be put into operation at the same time.

[0015] When the frequency converter fails, it can be manually or automatically switched to contactor-relay full-voltage operation to ensure uninterrupted operation of the main motor M.

[0016] The energy feedback circuit consists of an inverter circuit and a filter circuit, and can feed back ≥95% of the motor's regenerated energy to the power grid.

[0017] The time controller achieves automatic switching of multiple speeds through an interlocking circuit of intermediate relay coils KA1, KA2, and KA3, so that the main motor M of the alloy pump operates at a preset frequency during the flow rate change period, thereby reducing power consumption.

[0018] The frequency converter has built-in overcurrent, overvoltage, undervoltage, phase loss, short circuit, and stall protection functions, and outputs corresponding fault signals to illuminate the fault indicator L3 of the frequency converter system control circuit and the fault indicator L7 of the contactor-relay system control circuit.

[0019] The main motor M of the alloy pump has a power of 30kW, and the overall motor operating efficiency of the device is ≥90%, with a power factor ≥0.97.

[0020] In summary, due to the adoption of the above technical solution, the beneficial effects of this utility model are:

[0021] This utility model features a simple overall structure, convenient operation, and stable running, solving the problems of difficult speed adjustment, low power factor, and low operating efficiency of the alloy pump motor in sulfuric acid tank wells. It also significantly reduces energy loss, saving a substantial amount of electrical energy. Statistical testing results after using this device show that the alloy pump motor's operating efficiency can reach over 90%, and the power factor can reach over 0.97. Furthermore, because the device's frequency converter speed control system circuit also has overcurrent, overvoltage, undervoltage, short circuit, phase loss, and stall protection functions, the alloy pump motor will not burn out during operation. This solves many long-standing problems such as frequent equipment failures, frequent maintenance, and excessively long repair times, and greatly improves the company's production costs and economic profits. Attached Figure Description

[0022] Figure 1 This is the electrical schematic diagram of this utility model.

[0023] Figure 2 This is the control circuit diagram of this utility model.

[0024] Attached Figure Numbers and Names: 1-Normally closed contact of thermal relay FR1; 2-Stop button SB1 of inverter system control circuit; 3-Start button SB2 of inverter system control circuit; 4-Normally open contact of inverter AC contactor KM1; 5-Normally closed contact of main contactor KM2; 6-Coil of inverter AC contactor KM1; 7-Run indicator light L1 of inverter system control circuit; 8-Normally closed contact of inverter AC contactor KM1; 9-Stop indicator light L2 of inverter system control circuit; 10-Normally open contact EA of inverter relay; 11-Fault indicator light L3 of inverter system control circuit; 12-Normally open contact RC of inverter multi-function relay output; 13-Time controller; 14-Stop button SB3 of time control circuit; 15-Time controller... The circuit includes the following components: SB4 (start button), SB5 (stop button), SB6 (start button), SB7 (start button), SB8 (start button), SB8 (start button), SB9 ...9 (start button), SB8 (start button), SB9 (start button), SB9 (start button), SB8 (start button), SB9 (start button), SB9 (start button), SB8 (start button), SB9 (start button), SB9 (start button), SB9 (start button), SB9 (start button), SB8 (start button), SB9 (start button), SB9 (start button), SB9 (start button), SB9 (start button), SB9 (start button), SB9 (start button), SB9 (start button), SB9 (start button), SB9 (start button), SB9 (start button), SB9 (start button), SB9 (start button), SB9 (start button), SB9 (start button), SB9 (start button), SB9 (start button), SB9 (start button), SB9 (start button), SB9 (start button), SB9 (start button), SB9 (start button), SB9 (start button), 31-Intermediate relay KA3 coil; 32-Inverter system control circuit power indicator L4; 33-Thermal relay FR2 normally closed contact; 34-Contactor-relay system control circuit stop button SB9; 35-Contactor-relay system control circuit start button SB10; 36-Main contactor KM2 normally open contact; 37-Variable frequency AC contactor KM1 normally closed contact; 38-Main contactor KM2 coil; 39-Contactor-relay system control circuit run indicator L5; 40-Main contactor KM2 normally closed contact; 41-Contactor-relay system control circuit stop indicator L6; 42-Thermal relay FR2 normally open contact; 43-Contactor-relay system control circuit fault indicator L7; 44- - Contactor-relay system control circuit power indicator L8, 45- Inverter system control running circuit, 46- Inverter system control stop circuit, 47- Inverter system control fault circuit, 48- Inverter system control time control circuit, 49- Inverter system control power supply circuit, 50- Contactor-relay system control running circuit, 51- Contactor-relay system control stop circuit, 52- Contactor-relay system control fault circuit, 53- Contactor-relay system control power supply circuit, 54- Inverter speed control system control circuit, 55- Contactor-relay speed control system control circuit, 100- Fuse FU, 200- Main circuit breaker QF1, 300- Energy meter, 400- Energy feedback circuit.500 - Frequency converter, 600 - Time control circuit, 700 - Surge protector, 800 - Circuit breaker QF2, 900 - Variable frequency AC contactor KM1, 1000 - Main contactor KM2, 1100 - Thermal relay FR1, 1200 - Thermal relay FR2, 1300 - Alloy pump main motor M, 1400 - Three-phase AC motor speed control device system main circuit. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of the embodiments of this utility model clearer, the technical solutions of the embodiments of this utility model will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this utility model, and not all embodiments. The components of the embodiments of this utility model described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0026] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0027] To better understand this utility model, the following description is provided:

[0028] This utility model provides a three-phase AC motor speed control device. The final speed control method is to use a combination of frequency converter and contactor-relay to adjust the speed of the alloy pump motor, thereby achieving the purpose of saving energy. The equipment required for modification is: one alloy pump, and accessories include: one motor (power: 30kW).

[0029] The electrical components of the frequency converter speed control system of this device include: 1 frequency converter, 1 set of frequency conversion AC contactor, 1 energy meter, 1 set of energy feedback circuit module, 1 set of time controller module, 4 start buttons, 4 stop buttons, 3 intermediate relays, 1 thermal relay, 4 system control circuit indicator lights, and several control wires, etc.

[0030] The electrical components of the contactor-relay speed control system of this device include: 3 sets of fuses, 1 main circuit breaker, 1 surge protector, 1 branch circuit breaker, 1 set of AC contactors, 1 start button, 1 stop button, 1 thermal relay, 4 indicator lights for the system control circuit, 1 main motor, and several control wires, etc.

[0031] like Figure 1As shown, this circuit is the main circuit of the speed control device of this utility model, and is described in detail below:

[0032] A 380V three-phase power supply (U, V, and W phases) is introduced into the circuit. First, a fuse 100 is installed to protect the circuit. The output of fuse 100 is connected to the input of the main circuit breaker QF1200. The output of the main circuit breaker QF1200 is then connected to the inputs of the energy meter 300, surge protector 700, and branch circuit breaker QF2800. The outputs of the energy meter 300 and branch circuit breaker QF2800 are then connected to the inputs of the frequency converter 500 and main contactor KM21000, respectively. The output of the frequency converter 500 is connected to the input of the variable frequency AC contactor KM1900, and its output is connected to the input of the thermal relay FR11100. The output of the main contactor KM21000 is connected to the input of the thermal relay FR21200. Finally, the output terminals of thermal relays FR11100 and FR21200 are all connected to the wiring terminals of the alloy pump main motor M1300. Specifically, three wires are separately led out from the output terminal of the energy meter 300 and directly connected to the energy feedback circuit 400, then to the frequency converter 500, and finally the frequency converter 500 is directly connected to the time control circuit 600.

[0033] like Figure 2 As shown, this circuit is the control circuit of the speed control device, mainly composed of two parts: the speed control system control circuit and the contactor-relay speed control system control circuit. Details are as follows:

[0034] The first part of the circuit is the inverter speed control system control circuit 54, as follows:

[0035] The circuit introduces a 220V two-phase power supply (U and N phases). It first draws power from the live wire (U phase) and then branches into five paths: Path 1 connects to a thermal relay FR1 with its normally closed contact 1. Its output is connected to a stop button 2 and a start button 3. Then, a main contactor KM2 with its normally closed contact 5 and a frequency converter AC contactor KM1 coil 6 are connected in series. Simultaneously, a frequency converter AC contactor KM1 with its normally open contact 4 is connected in parallel across the start button 3. Finally, a running indicator light 7 is connected in series across the other end of KM1's normally open contact 4. Path 2 connects a stop indicator light 9 and a frequency converter AC contactor KM1 with its normally closed contact 8. Path 3 connects a fault indicator light 11 and a frequency converter multi-function relay output normally open contact 12. Simultaneously, a frequency converter relay normally open contact 10 is connected in parallel across the frequency converter multi-function relay output normally open contact 12. The fourth path connects to a set of time controllers 13, and three paths branch off from the output of the time controllers 13. These three paths are respectively configured as self-locking circuits for intermediate relay coils 19, 25, and 31. In each of these three self-locking circuits, two other sets of normally closed contacts of intermediate relays are connected in series, ultimately forming an interlocking circuit. The fifth path directly connects to a set of power indicator lights 32.

[0036] The second part of the circuit is the contactor-relay speed control system control circuit 55, as detailed below:

[0037] The circuit continues from the live U phase, and then branches into four paths: The first path connects to a set of normally closed contacts 33 of a thermal relay FR2. Its output is connected to the stop button SB934 and the start button SB1035 of the contactor-relay system control circuit. Then, a set of normally closed contacts 37 of a frequency converter AC contactor KM1 and the coil 38 of a main contactor KM2 are connected in series. Simultaneously, a set of normally open contacts 36 of the main contactor KM2 are connected in parallel across the start button SB1035. Finally, a set of running indicator lights L539 of the contactor-relay system control circuit is connected in series from the other end of the normally open contacts 36. The second path connects to a set of stop indicator lights 41 and a set of normally closed contacts 40 of the main contactor KM2. The third path connects to a set of fault indicator lights L743 of the contactor-relay system control circuit and a set of normally open contacts 42 of the thermal relay FR2. The fourth path directly connects to a set of power indicator lights L844 of the contactor-relay system control circuit. Finally, all five output terminals from the first part of the circuit and the four output terminals from the second part of the circuit are connected to the neutral line (N phase), thus forming a closed loop for the control circuit of the device.

[0038] The working principle of this utility model is as follows: When the device is in use, a three-phase 380V power supply is first connected. After passing through the main circuit breaker QF1200, the power is transmitted to the energy meter 300, the surge protector 700, and the branch circuit breaker QF2800. The energy meter 300 is an energy metering instrument used to accurately measure the power consumption of a single device. The surge protector 700 is a protection unit used to prevent high voltage and high current from lightning strikes from entering the device. Then, the energy meter 300 transmits the power to the frequency converter 500. After the frequency converter is powered on, it first converts the AC power with a fixed frequency into DC power. The DC power is then converted back into AC power with a fixed frequency through an inverter circuit and transmitted to the frequency converter AC contactor KM1900 and the thermal relay FR11100. After that, it reaches the alloy pump main motor M1300. After the alloy pump main motor M1300 is powered on and starts, it changes its frequency according to the flow rate, and then adjusts its speed according to the frequency. Finally, it reaches the preset frequency and speed and then operates stably. The device incorporates a time control circuit 600, which mainly consists of a time controller module and three intermediate relays. Its primary function is to automatically adjust the motor's speed within segmented time periods. During speed adjustment, a selector switch chooses the appropriate frequency converter for the site conditions, allowing the frequency converter to automatically adjust to a reasonable frequency during peak electricity consumption and when the flow rate is constantly changing. The motor speed also changes with the frequency; the lower the frequency, the lower the speed, and the less power the motor consumes. This not only achieves automatic speed adjustment but also eliminates significant energy loss, greatly reducing the load on the power grid and ultimately ensuring the safe and reliable operation of the power grid. Meanwhile, when the frequency converter controls the motor to run, it generates high-voltage pulses. These pulses can remain in the cables. Sometimes, in the event of a sudden power outage or power failure, the inertia of the motor rotor will generate a large amount of back-generated electricity. This back-generated electricity will be released into the frequency converter 500 along the cable. If the back-generated voltage is too high, it will directly pass through the DC bus of the frequency converter and break down the rectifier tubes and inverter tubes, thus causing the frequency converter to burn out. Therefore, the common protection method is to use energy dissipation resistors to consume this excess electrical energy, which results in this excess electrical energy being wasted. In view of this problem, the device also designed an energy feedback circuit 400. This circuit module mainly consists of 8 diodes and 3 sets of filter capacitors, etc. The main circuit board consists of an inverter circuit and a filter circuit. Because the energy feedback circuit 400 can automatically detect the DC bus voltage of the inverter 500, it can convert the detected excess generated electricity into AC power with the same phase, voltage, and frequency as the grid through the inverter circuit. After filtering by the filter circuit, clean AC power is obtained and fed back to the grid, thus achieving the goal of energy feedback. Test data shows that the energy fed back to the grid can reach over 95% of the generated electricity, significantly saving energy.After the device was designed, its speed control system has two modes: one is the frequency converter speed control system, and the other is the contactor-relay speed control system. In the control circuits of these two systems, a set of normally closed contacts of the contactor is connected in series to form an interlock. Therefore, if the frequency converter system fails during equipment operation, it can switch to the contactor-relay system control mode. At this time, the circuit breaker QF2800 is activated, the main contactor KM21000 is energized, and the alloy pump main motor M1300 continues to run. This function is to ensure uninterrupted operation of the equipment, so as not to cause midway shutdown or equipment paralysis, so as not to affect production efficiency.

Claims

1. A three-phase AC motor speed control device, comprising a main circuit and a control circuit, characterized in that: The main circuit includes: fuse FU (100), main circuit breaker QF (200), surge protector (700), branch circuit breaker QF2 (800) and energy meter (300) connected in sequence after the three-phase power supply; The output terminals of the energy meter (300) are connected in parallel with two circuits: The first path connects to the main motor M (1300) of the alloy pump via the main contacts of the frequency converter (500), the frequency converter AC contactor KM1 (900), and the thermal relay FR1 (1100); The second path is also connected to the main contactor KM2 (1000) and thermal relay FR2 (1200) of the alloy pump main motor M (1300); The inverter (500) is connected in parallel with an energy feedback circuit (400) on the DC bus side, which is used to convert the regenerated energy of the motor into AC power with the same frequency and phase as the power grid and feed it back to the power grid; The control loop includes: The inverter speed control system control circuit (54) includes an inverter system control circuit stop button SB1 (2), an inverter system control circuit start button SB2 (3), an inverter AC contactor KM1 coil (6), an inverter system control circuit running indicator L1 (7), an inverter system control circuit stop indicator L2 (9), an inverter system control circuit fault indicator L3 (11), an inverter system control circuit power indicator L4 (32), and a time controller (13). The time controller (13) automatically switches the inverter output frequency within a set time period through an interlocking circuit of intermediate relay KA1 coil (19), intermediate relay KA2 coil (25), and intermediate relay KA3 coil (31). The contactor-relay speed control system control circuit (55) includes a contactor-relay system control circuit stop button SB9 (34), a contactor-relay system control circuit start button SB10 (35), a main contactor KM2 coil (38), a contactor-relay system control circuit running indicator L5 (39), a contactor-relay system control circuit stop indicator L6 (41), a contactor-relay system control circuit fault indicator L7 (43), and a contactor-relay system control circuit power indicator L8 (44). The inverter speed control system control circuit (54) and the contactor-relay speed control system control circuit (55) are respectively connected in series with the normally closed contact (5) of the main contactor KM2 and the normally closed contact (37) of the inverter AC contactor KM1 to form an electrical interlock, so that the two speed control modes cannot be put into operation at the same time. When the frequency converter (500) fails, it can be manually or automatically switched to contactor-relay full-voltage operation to ensure that the main motor M (1300) works continuously.

2. The three-phase AC motor speed control device according to claim 1, characterized in that: The energy feedback circuit (400) consists of an inverter circuit and a filter circuit, which can feed back ≥95% of the motor's regenerated energy to the power grid.

3. The three-phase AC motor speed control device according to claim 1, characterized in that: The time controller (13) achieves automatic switching of multiple speeds through the interlocking circuit of intermediate relay KA1 coil (19), intermediate relay KA2 coil (25), and intermediate relay KA3 coil (31), so that the alloy pump main motor M (1300) runs at a preset frequency during the flow rate change period to reduce power consumption.

4. The three-phase AC motor speed control device according to claim 1, characterized in that: The inverter (500) has built-in overcurrent, overvoltage, undervoltage, phase loss, short circuit, and stall protection functions, and outputs corresponding fault signals to light up the inverter system control circuit fault indicator L3 (11) and the contactor-relay system control circuit fault indicator L7 (43).

5. The three-phase AC motor speed control device according to claim 1, characterized in that: The main motor M(1300) of the alloy pump has a power of 30kW, and the overall motor operating efficiency of the device is ≥90%, with a power factor ≥0.97.

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