Power measuring method without torque sensor

Abstract

The invention discloses a dynamometer method without a torque sensor. The dynamometer method comprises the following steps: 1) obtaining an id and iq relation table of an alternating current motor at each rotating speed and torque; (2) the alternating-current motor and the power source to be tested are dragged oppositely, the power source to be tested is started, the alternating-current motor works in a rotating speed closed-loop mode, and the rotating speed is n; 3) after the power source to be measured operates stably, measuring three-phase currents ia, ib and ic and an electrical angle theta e of the alternating current motor; coordinate transformation is carried out to obtain idn and iqn of the AC motor at the moment; 4) looking up the table according to the rotating speed n idn and iqn of the alternating current motor at the moment to obtain a torque value T at the moment; and 5) calculating the power of the to-be-measured power source at the moment according to the torque value T and the rotating speed n. According to the power measuring method based on the table look-up method, when the torque is measured again, a torque sensor is not needed, the cost and the installation time of the whole testing system are reduced, and the low-cost, efficient and convenient power measuring function is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of power system testing, and particularly to a dynamometer method without a torque sensor. Background Art

[0002] In the field of power system testing, a dynamometer is a key device for measuring performance parameters such as the output power and torque of a power system. Classified by different energy processing methods, dynamometers are divided into hydraulic dynamometers, eddy current dynamometers, and electric dynamometers, among which electric dynamometers are further divided into DC electric dynamometers, AC motor dynamometers, and magnetic powder dynamometers. AC electric dynamometers generally use permanent magnet synchronous motors or asynchronous motors, and have advantages such as high precision, wide speed regulation range, and fast dynamic response, support four-quadrant operation and intelligent control, and are widely used in the testing of new energy, industrial, and scientific research experimental fields.

[0003] When a dynamometer is in use, it needs to be connected to the device under test. The traditional method of using an AC electric dynamometer usually relies on a torque sensor to directly measure the torque of the power output shaft, and then combines the rotational speed signal to calculate the power of the device under test. However, this dynamometer technology based on a torque sensor has many disadvantages: 1. The price of a high-precision torque sensor is expensive. Especially when used for testing a high-power power system, the cost of the sensor may account for more than 50% of the entire test system. At the same time, installing a torque sensor requires additional mechanical connection components such as couplings and bearings, further increasing the hardware cost. 2. The installation requirements of the torque sensor are stringent. It is necessary to ensure strict coaxiality between the torque sensor and the rotating shaft of the device under test. A deviation exceeding 0.05 mm will cause a significant increase in measurement error, resulting in a large increase in installation time. In addition, a special coupling needs to be designed to transmit torque and isolate radial and axial vibrations. Some high-precision sensors require a working environment temperature change rate <5°C / h. Summary of the Invention

[0004] Aiming at the above deficiencies existing in the prior art, the technical problem to be solved by the present invention is: how to provide a dynamometer method without a torque sensor that can reduce the cost and installation time of the entire test system.

[0005] To solve the above technical problems, the present invention adopts the following technical solutions:

[0006] A dynamometer method without a torque sensor, comprising the following steps:

[0007] Step 1) Obtain the relationship table of the direct-axis component current i d and the quadrature-axis component current i q of an AC motor at various rotational speeds and torques;

[0008] Step 2) Drag the AC motor against the power source to be measured, start the power source to be measured, and make the AC motor operate in the speed closed-loop mode at a speed of n;

[0009] Step 3) After the power source to be measured runs stably, measure the three-phase current i a , i b , i c and the electrical angle θ e of the AC motor at this time; and perform coordinate transformation to obtain the direct-axis component current i dn and the quadrature-axis component current i qn of the AC motor at this time;

[0010] Step 4) According to the rotational speed n, direct-axis component current i dn and quadrature-axis component current i qn of the AC motor at this time, look up the torque value T at this time in the table;

[0011] Step 5) Calculate the power of the power source to be measured at this time according to the torque value T and the rotational speed n.

[0012] Preferably, in Step 2), connect the AC motor to the computer through the motor controller, and send instructions to the motor controller through the computer so that the alternating current operates in the speed closed-loop mode at a speed of n.

[0013] Preferably, in Step 3), perform coordinate transformation according to the following formula to obtain the direct-axis component current i dn and the quadrature-axis component current i qn of the AC motor at this time:

[0014]

[0015] Preferably, in Step 4), when the torque value corresponding to the rotational speed n, direct-axis component current i dn and quadrature-axis component current i qn of the AC motor at this time can be found in the relationship table in Step 1), this torque value is the torque value T on the rotating shaft of the power source to be measured at this time; when the torque value corresponding to the rotational speed n, direct-axis component current i dn and quadrature-axis component current i qn of the AC motor at this time cannot be found in the relationship table in Step 1), determine the torque value T on the rotating shaft of the power source to be measured at this time by interpolating the relationship table in Step 1).

[0016] Preferably, in Step 4), when the torque value corresponding to the rotational speed n, direct-axis component current i dn and quadrature-axis component current i qn of the AC motor at this time cannot be found in the relationship table in Step 1), calculate the torque value on the rotating shaft of the power source to be measured at this time by the following formula:

[0017]

[0018] where: T(n, i dn / i qn ) is the torque value on the rotating shaft of the power source to be measured when the rotational speed is n, the direct-axis component current is i dn , and the quadrature-axis component current is i qn ; n0 is the starting rotational speed in the relational table, i d0 is the starting direct-axis component current in the relational table, i q0 is the starting quadrature-axis component current in the relational table, a ij is a coefficient.

[0019] Preferably, in step 4), the torque value on the rotating shaft of the power source to be measured can also be calculated using the following formula:

[0020]

[0021] where: p is the number of pole pairs of the AC motor, L dn is the direct-axis inductance of the AC motor when the rotational speed is n, L qn is the quadrature-axis inductance of the AC motor when the rotational speed is n, is the permanent magnet flux linkage.

[0022] Preferably, in step 5), the following formula is used to calculate the power of the power source to be measured:

[0023]

[0024] where: P is the power of the power source to be measured.

[0025] Preferably, in step 1), a relational table of the AC motor at different temperatures under various rotational speeds, torques, direct-axis component current i d and quadrature-axis component current i q is established.

[0026] Preferably, the motor controller uses the PID algorithm to implement rotational speed closed-loop control on the AC motor, so that it stably operates at the target rotational speed n.

[0027] Preferably, an encoder is installed on the AC motor, and the encoder acquires the rotational speed signal of the AC motor in real time and feeds it back to the motor controller.

[0028] Compared with the prior art, the present invention pre-establishes the direct-axis component current i d and quadrature-axis component current i qDatabase of the correspondence table. During the actual torque measurement process, the AC motor is controlled to stably operate at the target speed value n, and the direct-axis component current i of the AC motor is collected in real time dn and the quadrature-axis component current i qn . By combining the current speed n to query the database of the preset correspondence table, the actual output torque value of the rotating shaft can be obtained, and then the power of the power source to be measured can be calculated by combining the speed. Therefore, when measuring the torque again in this solution, a torque sensor is not required, reducing the use of the torque sensor, and thus also reducing the cost and installation time of the entire test system, realizing the low-cost, efficient and convenient dynamometer function. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] APPENDIX Figure 1 is a flowchart of the dynamometer method without a torque sensor according to the present invention;

[0030] APPENDIX Figure 2 is a schematic diagram of the principle of the dynamometer method without a torque sensor according to the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0031] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. The components of the embodiments of the present invention described and illustrated herein can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0032] In this specific embodiment, a dynamometer method without a torque sensor is provided. As shown in APPENDIX Figure 1 and APPENDIX Figure 2 , the method specifically includes the following steps:

[0033] Step 1) Obtain the direct-axis component current i of the AC motor at various speeds and torques d and the quadrature-axis component current i q relationship table.

[0034] Specifically, the AC motor is pre-calibrated through a bench test to obtain the correspondence table of the direct-axis component current i d and the quadrature-axis component current i q under different speed n and output torque T conditions; this correspondence table is stored in the database of the computer for current comparison and control in subsequent test processes.

[0035] In addition, since the mechanical resistances such as the bearing friction and the seal friction inside an AC motor are positively correlated with the rotational speed during operation, the above corresponding relationship table should be measured at different rotational speeds, and the internal mechanical resistance of the AC motor under different operating conditions has been taken into account. Therefore, no additional calculation of the mechanical internal resistance is required when referring to the power measurement table later.

[0036] Meanwhile, temperature has a great influence on the parameters of an AC motor. Since temperature changes will cause changes in parameters such as the winding resistance and the permanent magnet flux of the AC motor, thereby affecting the accuracy of the output torque of the AC motor. To ensure the reliability and repeatability of the rotational speed-torque-current corresponding relationship table, the operating temperature should be marked in the relationship table during testing or the relationship corresponding tables at different temperature points should be obtained through multi-temperature point testing. Specifically, through multi-temperature point testing, the relationship tables of the AC motor at various rotational speeds, torques, direct-axis component current i d and quadrature-axis component current i q at different temperatures can be established.

[0037] Step 2) Connect the AC motor in a counter-rotation mode with the power source to be measured, start the power source to be measured, and make the AC motor operate in a rotational speed closed-loop mode at a rotational speed of n.

[0038] Specifically, the output shaft of the power source to be measured is coaxially and rigidly connected to the rotor shaft of the AC motor through a coupling to form a mechanical transmission system for counter-rotation; meanwhile, the AC motor establishes a data communication connection with the computer through the motor controller, and the computer sends instructions to the motor controller to control the motor to form a closed-loop control system; among them, the motor controller is configured to receive computer instructions and the operating state of the AC motor, and at the same time, it collects motor operating parameters in real time and feeds them back to the computer.

[0039] During operation, start the power source to be measured, and at the same time, send a rotational speed control instruction to the motor controller through the computer. The motor controller uses the PID algorithm to implement rotational speed closed-loop control on the AC motor according to the instruction, so that it stably operates at the target rotational speed n; among them, an encoder is installed on the AC motor, and the encoder obtains the rotational speed signal of the AC motor in real time and feeds it back to the motor controller.

[0040] Step 3) After the power source to be measured operates stably, measure the three-phase current i a 、i b 、i c and the electrical angle θ e of the AC motor at this time; and perform coordinate transformation to obtain the direct-axis component current i dn and the quadrature-axis component current i qn of the AC motor at this time.

[0041] Specifically, when the system is in a stable operating state, the three-phase stator current i of the AC motor is collected through a current sensora 、i b 、i c and synchronously obtain the electrical angle θ e ; Then, perform Clarke transformation and Park transformation on the collected current signals in sequence, and calculate the actual values of the direct-axis component current i dn and the quadrature-axis component current i qn of the AC motor at this time; This transformation process is completed in real time through the algorithm module built in the motor controller.

[0042] The specific transformation formula is:

[0043]

[0044] Step 4) According to the rotational speed n, direct-axis component current i dn and quadrature-axis component current i qn of the AC motor at this time, look up the torque value T at this time in the table.

[0045] Specifically, according to the rotational speed n, direct-axis component current i dn and quadrature-axis component current i qn of the AC motor at this time, find the corresponding torque value in the relationship table in Step 1). At this time, the torque value in the table is the torque on the rotating shaft of the power source to be measured, thereby achieving the goal of measuring torque without a torque sensor. If there is no corresponding rotational speed n, direct-axis component current i dn and quadrature-axis component current i qn when looking up the relationship table, interpolate the table of rotational speed-torque-current relationship to refine the calibration data and improve the resolution of rotational speed and current. At this time, calculate the torque value on the rotating shaft of the power source to be measured at this time through the following formula:

[0046]

[0047] In the formula: T(n, i dn / i qn ) is the torque value on the rotating shaft of the power source to be measured when the rotational speed is n, the direct-axis component current is i dn , and the quadrature-axis component current is i qn ; n0 is the starting rotational speed in the relationship table, i d0 is the starting direct-axis component current in the relationship table, i q0 is the starting quadrature-axis component current in the relationship table, a ij is a coefficient determined by the data T(n i , i dj / i qj ) = T ij and the continuity condition. T(n i , i dj / i qj ) = Tij are the data substituted into the rotational speed - current - torque relationship correspondence table, where a rotational speed n i and i dj 、i qj correspond to a torque T ij , after substituting all the data and combining with the continuity condition, all the undetermined coefficients a ij can be obtained.

[0048] In addition, the torque value of the power source to be measured on the rotating shaft at this time can also be directly calculated using the following formula:

[0049]

[0050] In the formula: p is the number of pole pairs of the AC motor, L dn is the direct-axis inductance when the rotational speed of the AC motor is n, L qn is the quadrature-axis inductance when the rotational speed of the AC motor is n, is the magnetic flux of the permanent magnet.

[0051] Step 5) Calculate the power of the power source to be measured at this time according to the torque value T and the rotational speed n.

[0052] Specifically, the following formula is used to calculate the power of the power source to be measured:

[0053]

[0054] In the formula: P is the power of the power source to be measured.

[0055] Compared with the prior art, the present invention pre - establishes a database of the correspondence table of the direct - axis component current i d and the quadrature - axis component current i q of the AC motor under different rotational speeds and output torque conditions. During the actual torque measurement process, the AC motor is controlled to stably operate at the target rotational speed value n, and by real - time collecting the direct - axis component current i dn and the quadrature - axis component current i qn of the AC motor, and querying the preset correspondence table database in combination with the current rotational speed n, the actual output torque value of the rotating shaft can be obtained, and then the power of the power source to be measured can be calculated in combination with the rotational speed. Therefore, the power measurement method based on the look - up table method in this solution does not require a torque sensor when measuring the torque again, reducing the use of the torque sensor, and thus reducing the cost and installation time of the entire test system. It is applicable to AC dynamometer motors, can effectively save the test cost and test installation time of the power system, and realizes the power measurement function of low - cost, high - efficiency and convenience.

[0056] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than limiting them. Those of ordinary skill in the art should understand that any modifications or equivalent replacements made to the technical solutions of the present invention without departing from the spirit and scope of the present technical solutions shall be covered by the scope of the claims of the present invention.

Claims

1. A dynamometer method without a torque sensor, characterized in that, Including the following steps: Step 1) Obtain the relationship table of the direct-axis component current i d and the quadrature-axis component current i q at various speeds and torques of the AC motor; Step 2) Drag the AC motor in tandem with the power source to be measured, start the power source to be measured, and make the AC motor operate in a speed closed-loop mode at a speed of n; Step 3) After the power source to be measured operates stably, measure the three-phase currents i a 、i b 、i c and the electrical angle θ e ; and perform coordinate transformation to obtain the direct-axis component current i dn and the quadrature-axis component current i qn ; Step 4) According to the rotational speed n of the AC motor at this time, the direct-axis component current i dn and the quadrature-axis component current i qn look up the torque value T at this time in the table; Step 5) Calculate the power of the power source to be measured at this time according to the torque value T and the speed n.

2. The dynamometer method without a torque sensor according to claim 1, characterized in that In step 2), connect the AC motor to the computer through the motor controller, and send instructions to the motor controller through the computer so that the alternating current operates in a speed closed-loop mode at a speed of n.

3. The dynamometer method without a torque sensor according to claim 1, characterized in that, In step 3), coordinate transformation is performed according to the following formula to obtain the direct-axis component current i dn and the quadrature-axis component current i qn :

4. The dynamometer method without a torque sensor according to claim 3, characterized in that, In step 4), when the corresponding torque value can be found in the relationship table of step 1) based on the current rotational speed n of the AC motor, the direct-axis component current i dn and the quadrature-axis component current i qn , this torque value is the torque value T on the rotating shaft of the power source to be measured at this time; when the corresponding torque value cannot be found in the relationship table of step 1) based on the current rotational speed n of the AC motor, the direct-axis component current i dn and the quadrature-axis component current i qn , the torque value T on the rotating shaft of the power source to be measured at this time is determined by interpolating the relationship table in step 1).

5. The dynamometer method without a torque sensor according to claim 4, characterized in that, In step 4), when the corresponding torque value cannot be found in the relationship table of step 1) based on the current rotational speed n of the AC motor, the direct-axis component current i dn and the quadrature-axis component current i qn , the torque value on the rotating shaft of the power source to be measured at this time is calculated by the following formula: Where: T(n,i dn / i qn ) is the torque value on the rotating shaft of the power source to be measured when the rotational speed is n, the direct-axis component current is i dn , and the quadrature-axis component current is i qn ; n0 is the starting rotational speed in the relationship table, i d0 is the starting direct-axis component current in the relationship table, i q0 is the starting quadrature-axis component current in the relationship table, and a ij is a coefficient.

6. The dynamometer method without a torque sensor according to claim 5, characterized in that In step 4), the following formula can also be used to calculate the torque value on the rotating shaft of the power source to be measured at this time: Where: p is the number of pole pairs of the AC motor, L dn is the direct-axis inductance when the rotational speed of the AC motor is n, L qn is the quadrature-axis inductance when the rotational speed of the AC motor is n, is the permanent magnet flux linkage.

7. The dynamometer method without a torque sensor according to claim 6, characterized in that, In step 5), the following formula is used to calculate the power of the power source to be measured: In the formula: P is the power of the power source to be measured.

8. The dynamometer method without a torque sensor according to claim 1, characterized in that, In step 1), a relationship table of an AC motor at different temperatures with respect to each rotational speed, torque, direct-axis component current i d and quadrature-axis component current i q is established.

9. The dynamometer method without a torque sensor according to claim 2, characterized in that, The motor controller uses the PID algorithm to implement speed closed-loop control on the AC motor so that it stably operates at the target speed n.

10. The dynamometer method without a torque sensor according to claim 2, characterized in that, An encoder is installed on the AC motor, and the encoder obtains the speed signal of the AC motor in real time and feeds it back to the motor controller.

Images