Design method of multifunctional motor loading device

Abstract

The invention discloses a design method of a multifunctional motor loading device, and the method comprises the steps: firstly connecting a loading device to a test motor, and calculating the rotating speed of the test motor; secondly, calculating the energy loss of the internal resistance of the test motor and the loss of a three-phase rectification circuit, and calculating the torque TL of the test motor; and then recording load resistance RL and TL, changing the rotating speed and RL of the motor, and establishing a three-dimensional relational graph by taking RL, TL and rotating speed as three coordinate axes of the three-dimensional relational graph. And finally, when the motor is loaded, the value of the corresponding load resistance is obtained through the three-dimensional relational graph, PID control is carried out according to the error between the user expected torque and the actual torque TL, the sum of the output of a PID controller and the corresponding load resistance serves as the value of the load resistance RL of the three-phase rectification circuit, and loading of the braking torque is achieved. According to the invention, loading with low cost and simple calculation is realized, the rotating speed, the torque and the mechanical power of the motor are measured and tested in real time, and an accurate loading effect is realized.

Description

Technical Field

[0001] The invention belongs to the field of permanent magnet synchronous motor parameter measurement, and in particular relates to a design method of a multifunctional motor loading device. Background Art

[0002] In the electrical industry, it is often necessary to perform performance tests on motors or motor controllers. During the test, the test motor is connected to a motor loading device, which provides different load effects for the test motor, thereby achieving the purpose of motor or motor controller performance testing. According to different loading principles and application scenarios, motor loading devices can be divided into many types. The following are some common classifications of motor loading devices:

[0003] 1. Mechanical loading device: Mechanical loading device is the earliest invented load simulation technology. It mainly connects the external load to the motor shaft and uses mechanical devices to provide a certain torque resistance. There are two common forms: cantilever beam type and torsion bar type. The load structure simulated by this method is simple, with wide adaptability and large load range, but it is difficult to achieve complex loading modes and has limited control accuracy.

[0004] 2. Electro-hydraulic loading device: Electro-hydraulic loading device is mainly based on the synergy of hydraulic transmission and electrical signal control. It uses the movement of actuators such as hydraulic cylinders or hydraulic motors to convert pressure into the required loading torque, and achieves precise loading effect by adjusting the pressure, flow and other parameters of the hydraulic system. However, this loading device has time-varying and nonlinear characteristics, such as leakage, sealing friction and large inertia. Due to the large elastic modulus of the oil, once the loading system is disturbed externally, it will generate very large excess force, which will affect the loading accuracy and stability.

[0005] 3. Magnetic powder brake loading device. The magnetic powder brake loading device uses the electromagnetic principle to transfer torque through magnetic powder to achieve the loading function. There is an excitation coil on the stator of the magnetic powder brake, and there is magnetic powder in the gap between the stator and the rotor. When the appropriate voltage is applied to the excitation coil, the generated magnetic field will magnetize the magnetic powder material. When the rotor rotates, the friction and bonding force between the magnetic powder and the surface of the stator and rotor must be overcome. These forces together constitute the braking torque that hinders the rotation of the rotor, thereby achieving the loading purpose. This loading device has the advantages of fast response speed, high control accuracy, and stable loading, but it also has problems such as large temperature rise, insufficient stability, and poor durability.

[0006] 4. Electric loading device system. The electric loading device realizes loading by controlling the load motor, using the motor as the power source and converting the rotational motion of the motor into the load force exerted on the loaded object through the transmission mechanism. The electric loading device has excellent dynamic and static performance, and has the advantages of fast response speed and complex simulated working conditions, but it is accompanied by complex control algorithms and hardware systems.

[0007] Each of the above-mentioned loading devices has its own advantages and disadvantages. In practical applications, it is necessary to select a suitable loading device according to experimental conditions and performance requirements. Summary of the invention

[0008] The purpose of the present invention is to provide a design method for a multifunctional motor loading device, which has the advantages of simple calculation and low cost. While meeting the motor loading requirements, it also has the functions of speed measurement, torque measurement, and mechanical power measurement.

[0009] First, the braking torque of the loading device comes from a three-phase brushless motor (hereinafter referred to as the loading motor). When the loading device is in operation, it should be connected to the motor to be tested (hereinafter referred to as the test motor) through a mechanical coupling. The test motor drives the loading motor to rotate through the coupling. The loading motor works in generator mode. When running in this state, a voltage will be generated at the stator end of the loading motor. Then, the DC voltage obtained after rectification is connected to the load resistor. Finally, the current generated in the loop will generate a braking torque in the motor. According to the speed of the loading motor and the target loading torque, the specific value of the resistor can be obtained by looking up the table. After adjusting the load resistance to this value, the motor loading function of the target torque can be achieved.

[0010] The steps of the present invention are as follows:

[0011] Step 1: The loading device is connected to the test motor through a mechanical coupling. When the test motor rotates, it drives the loading motor to run. At this time, the stator end of the loading motor will generate three back electromotive forces with a phase difference of 120°. The back electromotive force is rectified by a three-phase rectifier circuit to obtain a pulsating DC voltage. The average value of the DC voltage is measured by a voltage sensor and recorded as U dc .

[0012] Step 2: According to the average DC voltage U dc The speed of the loading motor can be calculated based on the relevant parameters of the loading motor. Since the loading motor and the test motor are connected through a mechanical coupling, the speed is the test motor speed n. The speed calculation formula is as follows.

[0013]

[0014] Where U emf is the back electromotive force of the loading motor, n is the motor speed in r / min, p nis the number of motor pole pairs, λ pm The motor flux constant, in units of Wb, can be found on the motor nameplate or in the manufacturer's technical manual. r This is the voltage loss of the rectifier device. This loss is generally a fixed value and can be confirmed in the device technical manual.

[0015] Step 3: Calculate the energy loss P of the test motor internal resistance s And the loss P of the three-phase rectifier circuit r .

[0016] The three-phase rectifier circuit in step 1 forms a loop through a load resistor, which is denoted as R L , the loop load current is recorded as i L , the three-phase current on the stator side of the loading motor is recorded as i a 、i b 、i c , the two-phase current i of the motor is measured by the current sensor a 、i b Since the sum of the three-phase currents of the motor is zero, the third-phase current i c According to the motor phase current and resistance, the energy loss P of the motor internal resistance can be calculated. s and the loss of the rectifier circuit P r , the loss of the rectifier circuit mainly comes from the rectifier diode, including the conduction loss of the diode and the recovery loss P rec The calculation formula is as follows.

[0017]

[0018] Where P s , P r , P rec The unit is watt (W), R s To load the motor phase resistance, restore the loss P rec It is a curve function related to current, which can be fitted according to the curve in the device manual. x When x is 1, 2, or 3, it corresponds to the current i a 、i b 、i c , U F It represents the conduction voltage drop of a single diode. It is generally a fixed value and can be confirmed in the device manual.

[0019] Step 4: Energy loss P according to the motor internal resistance s and the loss of the rectifier circuit P r , obtain the mechanical power of the test motor, and calculate the actual torque T of the test motor through the mechanical power of the test motor L .

[0020] Step 4.1: Test the motor mechanical power measurement function:

[0021] Energy loss according to internal resistance P s and the loss of the rectifier circuit P r , according to the energy conservation of the entire device, calculate the mechanical power P input by the loading device m Since the input mechanical power of the loading motor is approximately equal to the output mechanical power of the test motor, P m That is to test the current output mechanical power of the motor, and its calculation method is as follows:

[0022]

[0023] Step 4.2: Test the motor torque measurement function:

[0024] The torque measurement function of the test motor is based on the speed measurement function and the mechanical power measurement function. The rotor speed n and mechanical power P of the test motor are obtained through the operation of step 4.1. m , thus calculating the load torque T corresponding to the current power of the test motor L , the calculation method is as follows:

[0025]

[0026] Step 5: Record the R at this time L and the corresponding T L , change the test motor speed n and load resistance R L Repeat the above steps and record, and change the load resistance R L , Braking torque T L And speed n are used as the three coordinate axes of the three-dimensional relationship diagram to establish a three-dimensional relationship diagram.

[0027] Step 6: When the motor is loaded, according to the user's expected torque T r , the speed n of the loaded motor can be checked by looking up the three-dimensional relationship diagram to get the corresponding load resistance value, according to the user's expected torque T r and the actual torque T L The error is PID controlled, and the sum of the output of the PID controller and the corresponding load resistance obtained from the table is used as the final load resistance R L The load resistance of the three-phase rectifier is adjusted to this value to achieve the loading function of the corresponding braking torque. The above steps are repeated in this way to complete the purpose of motor loading.

[0028] Beneficial effects of the present invention:

[0029] Compared with the electric loading device, this device does not need to provide the motor controller and high-power power supply required for the drive motor. While saving the speed sensor and torque sensor, it realizes a low-cost and simple loading method. At the same time, it can measure the motor speed, torque and mechanical power in real time. This method obtains the braking resistance by table lookup, has a wide range of applications, and performs closed-loop control through the PID link to achieve a relatively accurate loading effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is the overall structure diagram of the loading method;

[0031] Figure 2 is the structural diagram of the rectifier circuit;

[0032] Figure 3 It is the relationship diagram between torque, speed and resistance;

[0033] Figure 4 Load the speed waveform at time zero;

[0034] Figure 5 The waveform diagram of the loading torque at time zero;

[0035] Figure 6 Load speed waveform for runtime;

[0036] Figure 7 Load the torque waveform diagram for the running time;

[0037] Figure 8 This is the waveform diagram of the mechanical power of the tested motor and load. DETAILED DESCRIPTION

[0038] Next, the present invention will be further described in conjunction with the accompanying drawings.

[0039] A design method of a multifunctional motor loading device proposed by the present invention comprises the following steps:

[0040] Step 1: The loading device is connected to the test motor through a mechanical coupling and the average DC voltage U is measured. dc .

[0041] Step 2: According to the average DC voltage U dc , calculate the test motor speed n.

[0042] Step 3: Calculate the energy loss P of the test motor internal resistance s And the loss P of the three-phase rectifier circuit r .

[0043] Step 4: Energy loss P according to the motor internal resistance s and the loss of the rectifier circuit P r, obtain the mechanical power of the test motor and calculate the actual torque T of the test motor L .

[0044] Step 5: Record the load resistance R L and the corresponding T L , change the test motor speed n and load resistance R L , R L 、T L And speed n are used as the three coordinate axes of the three-dimensional relationship diagram to establish a three-dimensional relationship diagram.

[0045] Step 6: When the motor is loaded, according to the user's expected torque T r , load the motor speed n, obtain the corresponding load resistance value through the three-dimensional relationship diagram, and calculate the torque T according to the user's expected torque r and the actual torque T L The error is PID controlled, and the sum of the output of the PID controller and the corresponding load resistance is used as the load resistance R of the three-phase rectifier circuit. L The value of is used to realize the loading function of the corresponding braking torque.

[0046] Example:

[0047] Step 1: As attached Figure 1 As shown on the right, the test motor and the loading motor are connected through a mechanical coupling. When the test motor rotates, it drives the loading motor to run. At this time, the stator end of the loading motor will generate a back electromotive force, which is a three-phase alternating current with a phase difference of 120°. After rectifying the back electromotive force, a pulsating DC voltage is obtained. The average value of the voltage is measured by a voltage sensor and recorded as U dc .

[0048] Step 2: According to U dc The speed of the loading motor can be calculated based on the relevant parameters of the loading motor. Since the loading motor and the test motor are connected through a mechanical coupling, the speed is the test motor speed n.

[0049] Step 3: Attach Figure 2 The left side is the schematic diagram of the rectifier circuit. The right side is the schematic diagram of the test motor circuit. The right side is the schematic diagram of the general three-phase brushless motor drive. It consists of three groups of bridge arms. Each group of bridge arms consists of two upper and lower switch tubes. 1-6 Indicates six switch signals, and the right side is a schematic diagram of the loading motor rectifier circuit. The rectifier circuit is connected to the load resistor R L When the load resistor and the loaded motor winding are connected, a current will be formed. The three-phase rectifier circuit is provided with three-phase sampling resistors R1 and R2 on the motor side. The two-phase current i of the circuit can be obtained by calculating the voltage on both sides of the sampling resistor and the resistor. a 、i b According to Kirchhoff's law, the sum of the three-phase currents is zero, so the third-phase current ic , calculate the motor internal resistance loss P s and the loss of the rectifier circuit P r .

[0050] Step 4: Since the energy of the entire device is conserved, according to the P obtained in step 3 s , P r and U obtained in step 1 dc The current input power of the loading device can be calculated, that is, the output mechanical power P of the test motor m .

[0051] Step 5: The speed and mechanical power of the test motor have been obtained in the above steps. Calculate the current torque T of the test motor L .

[0052] Step 6: Record the R of the above steps L 、T L , speed n, change the speed of the test motor, brake resistance R L Repeat the above steps and set the recorded load resistance R L , Braking torque T L and speed n as the three coordinate axes of the three-dimensional relationship diagram to establish a three-dimensional relationship diagram, as shown in the attached figure. Figure 3 As shown, when the motor is loaded, the loading torque T is calculated according to the user's target r , the speed n of the loaded motor can be obtained by looking up the table to obtain the current load resistance R L The value of can be adjusted by adjusting the load resistance of the three-phase rectifier circuit to this value to realize the loading function of the corresponding braking torque.

[0053] Step 7: Since the nonlinearity of the motor, the temperature drift of the resistor, the mechanical friction and other factors may cause errors in the actual braking torque, closed-loop control is required. Step 5 has calculated the load torque of the test motor, the target loading torque T r With load torque T L The error is controlled by the PID controller, and the sum of the output of the PID controller and the resistance obtained by the table lookup is used as the braking resistance R L , and repeat the above steps to complete the purpose of motor loading.

[0054] The present invention establishes a simulation model based on the parameters of the loading motor and the rectifier circuit, and constructs a three-dimensional relationship table between the loading speed, the braking torque, and the load resistance. When the motor is loaded, according to the user's target loading torque T r , the speed n of the loaded motor can be obtained by looking up the table to obtain the current load resistance R LThe load resistance of the rectifier bridge can be adjusted to this value to achieve the corresponding braking torque loading function. Due to the existence of factors such as motor nonlinearity, resistance temperature drift, and mechanical friction, the actual braking torque will produce errors. Here, according to the target torque T r and the actual torque T L The error is controlled by PID to achieve accurate torque loading.

[0055] The feasibility of the method has been verified by simulation in MATLAB. The test motor and the loading motor are selected as permanent magnet synchronous motors. In the constant torque zero speed loading mode, the speed and torque waveforms of the test motor and the loading motor are as follows: Figure 4 , Attachment Figure 5 , within two seconds, the target speed is 1000rpm, it can be seen that the torques of the two motors are roughly the same after the speed stabilizes. In the constant torque operation loading mode, the speed and torque waveforms of the test motor and the loading motor are as follows Figure 6 , Attachment Figure 7 After adding a load of 1.8 N·m at 1 second, the speeds of the two motors dropped slightly and then quickly adjusted back to the target value. After the speed stabilized, the load torque was generally maintained in constant torque mode. Figure 8 The waveform diagram of the test motor and the loading mechanical power is shown. During the motor acceleration phase, the loading motor power is less than that of the test motor. After the speed stabilizes, the mechanical power of the loading motor is very close to that of the test motor, which is consistent with theoretical expectations.

Claims

1. A design method for a multifunctional motor loading device, characterized in that: The following steps are involved: Step 1: The loading device is connected to the test motor through a mechanical coupling and the average DC voltage U is measured. dc ; Step 2: According to the average DC voltage U dc , calculate the test motor speed n; Step 3: Calculate the energy loss P of the test motor internal resistance s And the loss P of the three-phase rectifier circuit r ; Step 4: Energy loss P according to the motor internal resistance s and the loss P of the rectifier circuit r , obtain the mechanical power of the test motor and calculate the actual torque T of the test motor L ; Step 5: Record the load resistance R L and the corresponding T L , change the test motor speed n and load resistance R L , R L , T L and the speed n as the three coordinate axes of the three-dimensional relationship diagram to establish a three-dimensional relationship diagram; Step 6: When the motor is loaded, according to the user's expected torque T r , load the motor speed n, obtain the corresponding load resistance value through the three-dimensional relationship diagram, and calculate the torque T according to the user's expected torque r and the actual torque T L The error is PID controlled, and the sum of the output of the PID controller and the corresponding load resistance is used as the load resistance R of the three-phase rectifier circuit. L The value of is used to realize the loading function of the corresponding braking torque.

2. The design method of a multifunctional motor loading device according to claim 1, characterized in that: The specific process of measuring the average value of the DC voltage in step 1 is as follows: the loading device is connected to the test motor through a mechanical coupling. When the test motor rotates, it drives the loading motor to run. At this time, three back electromotive forces with a phase difference of 120° are generated at the stator end of the loading motor; the back electromotive force is rectified by a three-phase rectifier circuit to obtain a pulsating DC voltage, and the average value of the DC voltage is measured by a voltage sensor and recorded as U dc .

3. The design method of a multifunctional motor loading device according to claim 2 is characterized in that: The specific implementation process of step 2 is as follows: According to U dc The speed of the loading motor is calculated based on the relevant parameters of the loading motor. Since the loading motor and the test motor are connected through a mechanical coupling, the speed is the test motor speed. The speed calculation formula is as follows: Where U emf is the back electromotive force of the loading motor, n is the motor speed in r / min, p n is the number of motor pole pairs, λ pm is the motor flux constant, in Wb, U r is the voltage loss of the rectifier device.

4. The design method of a multifunctional motor loading device according to claim 3 is characterized in that: The specific implementation process of step 3 is as follows: The three-phase rectifier circuit in step 1 forms a loop through a load resistor, which is denoted as R L , the loop load current is recorded as i L , the three-phase current on the stator side of the loading motor is recorded as i a 、i b 、i c , the two-phase current i of the motor is measured by the current sensor a 、i b Since the sum of the three-phase currents of the motor is zero, the third-phase current i c , according to the motor phase current and resistance, calculate the energy loss P of the motor internal resistance s and the loss of the rectifier circuit P r , the loss of the rectifier circuit comes from the rectifier diode, including the conduction loss of the diode and the recovery loss P rec , the calculation formula is as follows: Where P s , P r , P rec The unit is watt, R s To load the motor phase resistance, restore the loss P rec is a curve function related to current, i x When x is 1, 2, or 3, it corresponds to the current i a 、i b 、i c , U F Represents the forward voltage drop of a single diode.

5. The design method of a multifunctional motor loading device according to claim 4, characterized in that: The specific implementation process of step 4 is as follows: Step 4.1: Test the motor mechanical power measurement function: Energy loss P according to internal resistance s and the loss P of the rectifier circuit r , calculate the mechanical power P input by the loading device m Since the input mechanical power of the loading motor is equal to the output mechanical power of the test motor, P m That is to test the current output mechanical power of the motor, and its calculation method is as follows: Step 4.2: Test the motor torque measurement function: The torque measurement function of the test motor is based on the speed measurement function and the mechanical power measurement function. The rotor speed n and mechanical power P of the test motor are obtained through the operation of step 4.

1. m , thus calculating the load torque T corresponding to the current power of the test motor L , the calculation method is as follows:

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