Method of loading asynchronous motors during their testing by the mutual loading method

Abstract

FIELD: electrical engineering.SUBSTANCE: invention can be used as a method for loading asynchronous motors, including braking the tested asynchronous motor, which is powered by an alternating current source, with a loading asynchronous machine. This is achieved by stepwise reducing the frequency of the alternating voltage generated by the controlled inverter, together with the effective value of this voltage, by monitoring the electrical power of the load asynchronous machine and the effective value of the voltage at the output of the controlled inverter using electrical sensors, the output of which is connected to the input of the control system; the stepwise reduction of the frequency of the alternating voltage and its effective value is carried out in such a way that, as a result of the reduction in the effective value of the voltage (at each step of the change in the voltage frequency), the nominal torque on the shaft is ensured, and by reducing the voltage frequency, the maximum value of the electrical power generated by the load machine is ensured.EFFECT: loading machine is brought to a mode with maximum power, which ensures the system operates with minimal losses of electrical energy.1 cl, 4 dwg

Description

[0001] The invention relates to the field of electrical engineering and can be used as a method for loading asynchronous motors when testing them using the mutual load method.

[0002] An analogue of the proposed invention is a circuit for testing asynchronous electric motors using the method of their mutual loading, consisting of two uncontrolled rectifiers supplied from a three-phase network, two DC links electrically interconnected, the inputs of which are connected to the outputs of the uncontrolled rectifiers, two identical controlled inverters, the inputs of which are connected to the outputs of the DC links, a clutch mechanically connecting the tested asynchronous motors supplied from the controlled inverters, equipped with a control system, the outputs of which are connected to the inputs of the controlled inverters, and the inputs of which are connected to the outputs of the following devices: two current sensors, the inputs of which are connected to the outputs of the controlled inverters, a speed sensor connected to the rotors of the tested asynchronous motors, two supply voltage frequency calculators, the inputs of which are connected to the outputs of the controlled inverters,and the setter of network parameters and tested asynchronous motors (RU 163996 U1, 20.08.2016) [1].,

[0003] The disadvantage of the given analog is that this test circuit implements a method for controlling the magnitude of the load torque on the shaft by changing the voltage frequency without optimizing the magnitude of the effective value of this voltage in order to reduce losses.

[0004] Another analogue of the proposed invention is a test bench for testing asynchronous machines consisting of a clutch mechanically connecting the shafts of two asynchronous machines, a frequency converter with a DC link and two controlled rectifier-inverters that allow electrical energy to be transmitted through the frequency converter not only from the industrial network to the asynchronous motor, but also in the opposite direction; the power input of the first controlled rectifier-inverter is connected to the network, and the output to the DC link, the power input of the second controlled rectifier-inverter is connected to the same DC link, and the output is connected to the stator winding of the first asynchronous machine, equipped with a parameter setter, a contactor, a supply voltage frequency calculator, a control system, a current sensor, a rotation speed sensor;the outputs of the control system are connected to the control inputs of the controlled rectifier-inverters and the control input of the contactor, the inputs of the control system are connected to the output of the parameter setter, the output of the supply voltage frequency calculator, the input of which is connected to the output of the controlled inverter; the output of the current sensor, the input of which is connected to the output of the controlled rectifier-inverter, the output of the rotation speed sensor connected to the shafts of the asynchronous machines; the stator winding of the second asynchronous machine is connected to the network through a contactor (RU 186188 U1, 11.01.2019) [2].;

[0005] The disadvantage of the given analog is that this test circuit implements a method for controlling the magnitude of the load torque on the shaft by changing the voltage frequency without optimizing the magnitude of the effective value of this voltage in order to reduce losses.

[0006] The prototype of the proposed invention is a method for testing asynchronous motors using a mutual loading method, which includes loading the tested asynchronous motor, which is powered by an alternating current source, with a braking torque created by a load asynchronous machine operating in generator mode, the shaft of which is rigidly connected to the shaft of the tested asynchronous motor by a clutch; the stator winding of the load asynchronous machine is connected to a controlled inverter, the control input of which is connected to the output of a control system, the inputs of which are connected to the output of a rotational speed sensor connected to the shafts of the asynchronous machines, and the output of a voltage frequency calculator, the input of which is connected to the output of the controlled inverter;the load torque is created by reducing the frequency of the alternating voltage generated by the controlled inverter, characterized in that in the process of reducing the frequency of the alternating voltage generated by the controlled inverter, its effective value is also reduced to the minimum required to create its rated torque on the shaft of the tested asynchronous motor (RU 2706449 C1, 11 / 19 / 2019) [3].;

[0007] The disadvantages of the prototype are: with some nominal parameters of the machines, the point after reaching the nominal load mode may be at a higher rotation speed and a higher effective value of the voltage of the loading machine, and also due to the nonlinearity of the dependencies of the mechanical power loss in asynchronous machines on the effective value of the voltage and rotation speed, the principle proposed in the prototype may not give the highest value of the electrical power of the loading machine.

[0008] The purpose of the proposed invention is to ensure that the load machine is brought to a mode with maximum power, which ensures the system operates with minimal losses of electrical energy.

[0009] The stated objective is achieved by the fact that the method of loading asynchronous motors during their testing by the mutual loading method includes braking the tested asynchronous motor, which is powered by an alternating current source, with a torque created by a loading asynchronous machine operating in generator mode, the shaft of which is rigidly connected to the shaft of the tested asynchronous motor by a clutch;the stator winding of the load asynchronous machine is connected to a controlled inverter, the control input of which is connected to the output of the control system, the inputs of which are connected to the output of the rotation speed sensor connected to the shaft of the asynchronous machine, and the output of the voltage frequency calculator, the input of which is connected to the output of the controlled inverter, is ensured by the fact that the frequency of the alternating voltage generated by the controlled inverter is stepwise reduced together with the effective value of this voltage, monitoring the electrical power of the load asynchronous machine and the effective value of the voltage at the output of the controlled inverter with the help of electrical sensors connected to its output, the output of which is connected to the input of the control system;a step-by-step reduction in the frequency of the alternating voltage and its effective value is carried out in such a way that, as a result of the reduction in the effective value of the voltage, carried out at each step of changing the frequency of the voltage, the nominal torque on the shaft is ensured, and due to the reduction in the frequency of the voltage, the maximum value of the electrical power generated by the loading machine is ensured.

[0010] There are various schemes for mutual loading of asynchronous machines: 1) schemes in which energy exchange is carried out via a DC link; 2) schemes in which energy exchange is carried out via a three-phase network.

[0011] Fig. 1 shows a block diagram of the mutual loading of asynchronous machines, implementing a method of energy exchange along a DC link.

[0012] The block diagram consists of the tested asynchronous motor 1, clutch 2, load asynchronous machine 3, two-link frequency converter 4, consisting of controlled rectifier-inverters 4.1 and 4.3, DC link 4.2 (RU 143348 U1, 02.04.2014) [4].

[0013] Fig. 2 shows a block diagram of the mutual loading of asynchronous machines, implementing a method of energy exchange over a three-phase network.

[0014] The block diagram consists of the tested asynchronous motor 1, clutch 2, load asynchronous machine 3, first controlled inverter 5 and second controlled inverter 6 (RU 145998 U1, 09 / 27 / 2014) [5].

[0015] All these circuits have a common part shown in Fig. 3.

[0016] Fig. 3 shows a block diagram explaining the proposed method for testing asynchronous motors using the mutual load method.

[0017] The block diagram shows the tested asynchronous motor 1, clutch 2, load asynchronous machine 3, controlled inverter 7, control system 8, voltage frequency calculator 9, rotation speed sensor 10, electrical sensors 11.

[0018] Coupling 2 connects the shafts of the tested asynchronous motor 1 and the load asynchronous machine 3, the stator winding of which is supplied with power from the output of the controlled inverter 7. A speed sensor 10 is also installed on this shaft, the output of which is connected to the control system 8. The output of the control system 8 is connected to the control input of the controlled inverter 7. The outputs of the voltage frequency calculator 9 and electrical sensors 11, connected to the output of the controlled inverter 7, are also connected to the inputs of the control system 8. DC voltage is supplied to the power input of the controlled inverter 7, and an alternating three-phase voltage is supplied to the stator winding of the tested asynchronous motor 1.

[0019] Fig. 4 shows a block diagram of the algorithm implementing the proposed method for testing asynchronous motors using the mutual load method, which corresponds to the test scheme for asynchronous motors shown in Fig. 3.

[0020] The frequency of voltage ƒ2 supplied to the load asynchronous machine 3 is regulated by a controlled inverter 7, which is controlled by a control system 8, based on signals received from a voltage frequency calculator 9 (e.g., part of the electronic part of frequency converters and autonomous voltage inverters), a rotation speed sensor 10 (e.g., an incremental encoder), and electrical sensors 11 (current and voltage sensors in each phase). The effective value of voltage U2 supplied to the load asynchronous machine 3 is regulated by a controlled inverter 7, which is controlled by a control system 8, based on signals received from sensors 10. The electrical power at the generator output P2 эл is controlled using sensors 11. During the loading of the tested asynchronous motor 1, it is considered that the power value on its shaft P мехreaches the nominal value P н at a shaft speed n equal to the nominal value for a given engine n н The shaft rotation speed is measured using the rotation speed sensor 10.

[0021] Before loading the tested asynchronous motor 1 and the load asynchronous machine 3, connected by the coupling 2, they are started. For this, for example, the following actions are performed. Starting the tested asynchronous motor 1 and the load asynchronous machine 3 without a load on the shaft is carried out by increasing the frequencies of the supply voltages ƒ1 and ƒ2 (supplied to the tested asynchronous motor 1 and the load asynchronous machine 3, respectively) with a step of Δƒ1 and increasing the effective values ​​of the voltage U1 and U2 (supplied to the tested asynchronous motor 1 and the load asynchronous machine 3, respectively) with a step of ΔU1 until the condition is no longer met: ƒ1<ƒ1 н , where ƒ1 н- the nominal value of the frequency of the supply voltage of the tested motor (failure to meet this condition means that the frequencies are equal ƒ1=ƒ1 н ). Steps Δƒ1 and ΔU1 must be calculated so that the cycle providing an increase in the supply voltage frequencies ƒ1 and ƒ2 ends with the equalities ƒ1=ƒ1 н , U1=U1 н Each step of increasing the supply voltage frequencies ƒ1 and ƒ2 is performed with a time delay Δt1 necessary for the stator current to decrease to the value kI1 1н , to ensure the condition: I11 <kI1 1н The coefficient k>1 can be taken to be approximately 1.2 to 1.5, depending on how smooth the regulation process needs to be. If the current I11 has not had time to drop to the value kI1 during the delay time 1H , the time delay Δt1 is repeated until the condition is met: I11 <kI1 1H . After reaching ƒ1=ƒ1 н the test engine 1 and the loading machine 3 are operating in idle mode.

[0022] The proposed method of loading the test engine 1 is implemented as follows.

[0023] In order to load the tested motor 1, the frequency of the supply voltage ƒ2 is gradually reduced in increments of Δƒ2 until the condition is met: |nn н |≤Δn. Each step of reducing the supply voltage frequency ƒ2 is performed with a time delay of Δt2. After the condition |nn is met н |≤Δn (which corresponds to the output of the tested engine 1 to the mode with the rated load) the electrical power P2 is measured эл. изм and assigning the value of the electrical power of the load motor P2 эл P2 values эл. изм .

[0024] Then the frequency of the supply voltage ƒ2 is reduced in step Δƒ2. At each step of reducing the frequency ƒ2, the effective value of the voltage U2 is reduced in step ΔU2 until the condition |nn is met н|≤Δn. Each step of reducing the effective value of voltage U2 is performed with a time delay of Δt3. After the condition |nn is met н |≤Δn, the value of P2 is measured эл. изм and condition P2 is checked эл. изм >P2 эл When the condition is met, the effective value of voltage U2 and the frequency of the supply voltage ƒ2 are recorded and assigned to the value P2 эл P2 values эл. изм , after which the next step of reducing the frequency of the supply voltage ƒ2 occurs. The process of reducing the frequency of the supply voltage ƒ2 is carried out until the condition P2 is no longer satisfied эл. изм >P2 эл . Each step of reducing the frequency of the supply voltage ƒ2 is performed with a time delay of Δt4. After failure to meet the condition P2 эл. изм >P2 элThe supply voltage frequency ƒ2 is assigned its previous value ƒ2'. Next, the effective value of voltage U2 is increased in increments of ΔU2 until the condition |U2-U2'|≤ΔU is met. Each step of increasing the effective value of voltage U2 is performed with a time delay of Δt3. After the condition |U2-U2'|≤ΔU is met, the load asynchronous machine in generator mode delivers the maximum value of electric power to the tested asynchronous motor at the supply voltage frequency ƒ2' and the effective value of voltage U2'.

[0025] Thus, the proposed invention makes it possible to ensure that the load machine is brought to a mode with maximum power, which ensures the system operates with minimal losses of electrical energy.

[0026] Sources of information

[0027] 1. Patent for utility model of the Russian Federation No. 163996, IPC G01R 31 / 34, 2016.

[0028] 2. Patent for utility model of the Russian Federation No. 186188, IPC G01R 31 / 34, H02K 15 / 02, 2018.

[0029] 3. Patent for utility model of the Russian Federation No. 2706449, IPC G01R 31 / 34, 2019.

[0030] 4. Patent for utility model of the Russian Federation No. 143348, IPC G01R 31 / 34, 2014.

[0031] 5. Patent for utility model of the Russian Federation No. 145998, IPC G01R 31 / 34, 2014.

Claims

A method of loading asynchronous motors during their testing by the mutual loading method, which includes braking the asynchronous motor being tested, which is powered by an alternating current source, with a torque created by a load asynchronous machine operating in generator mode, the shaft of which is rigidly connected to the shaft of the asynchronous motor being tested by a clutch;the stator winding of the load asynchronous machine is connected to a controlled inverter, the control input of which is connected to the output of a control system, the inputs of which are connected to the output of a rotation speed sensor connected to the shaft of the asynchronous machine, and the output of a voltage frequency calculator, the input of which is connected to the output of the controlled inverter, characterized in that the frequency of the alternating voltage generated by the controlled inverter is stepwise reduced together with the effective value of this voltage, monitoring the electrical power of the load asynchronous machine and the effective value of the voltage at the output of the controlled inverter with the help of electrical sensors connected to its output, the output of which is connected to the input of the control system;a step-by-step reduction in the frequency of the alternating voltage and its effective value is carried out in such a way that, as a result of the reduction in the effective value of the voltage, carried out at each step of changing the frequency of the voltage, the nominal torque on the shaft is ensured, and due to the reduction in the frequency of the voltage, the maximum value of the electrical power generated by the loading machine is ensured.

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