Method and system for offline identification of motor rotor resistance and elimination of identification errors

Abstract

The present invention relates to induction motor parameter identification technology, specifically a method and system for offline identification of motor rotor resistance and elimination of identification errors. The method comprises: establishing an asymmetric T-type equivalent circuit in the steady state of an asynchronous motor to obtain the loop impedance when a single-phase, low-frequency AC voltage is input; designing the input single-phase, low-frequency current, performing zero-error control on the input AC current through a proportional resonant controller, and outputting a duty cycle to adjust the state of the power switch tube of a voltage-type inverter to achieve the desired identification voltage output; sampling the inverter bus voltage and duty cycle, and performing a fast Fourier transform to obtain a reconstructed identification voltage, analyzing the reconstructed identification voltage imaginary part; and calculating the precise identification value of the asynchronous motor rotor resistance based on the reconstructed identification voltage imaginary part, the input AC current amplitude, and the input loop impedance imaginary part. The present invention solves the technical problem of the prior art in which identification values ​​have large deviations due to stator resistance identification errors and inverter nonlinear errors.

Description

Technical Field

[0001] The present invention belongs to the technical field of induction motor parameter identification, and particularly relates to a method and system for offline identification of motor rotor resistance and elimination of identification errors. Background Art

[0002] In induction motor vector control systems, both control parameter adjustment and control performance depend on the motor model parameters. Rotor flux observation particularly requires an accurate rotor time constant. If the rotor time constant is inaccurate, errors will occur in flux estimation, leading to an offset in the calculated slip. This will directly lead to inaccurate magnetic field orientation, failure of d / q axis decoupling, and a significant degradation of the excellent speed regulation performance of vector control. In severe cases, it can even cause abnormal operation and damage the motor. Therefore, vector control requires the most accurate motor parameters possible, and the rotor time constant, specifically the rotor resistance and inductance, requires even more precise identification.

[0003] Current offline parameter identification methods typically excite the asynchronous motor with single-phase AC power. The current output voltage is reconstructed based on the bus voltage and PWM duty cycle, and the actual identification value is derived from the current circuit impedance. However, due to the non-ideal nature of power devices, their switching characteristics are nonlinear. Dead time and switching delays of the switching transistors can lead to a certain difference between the reference value applied to the winding voltage and the reconstructed voltage. Different inverters have different dead time and switching characteristic parameters, making compensation based on these parameters less universal. The use of high-frequency current in the rotor identification process can lead to skin effect, and the static error of the AC current PI controller also affects parameter identification accuracy. Summary of the Invention

[0004] The present invention proposes a method and system for offline identification of motor rotor resistance and elimination of identification errors, thereby eliminating the identification errors of rotor resistance and leakage inductance caused by static errors in a PI controller used for identification of the alternating current, and solving the technical problem of large deviations in the identification value of the existing rotor resistance caused by stator resistance identification errors and inverter nonlinear errors.

[0005] The method for offline identification of motor rotor resistance and elimination of identification error adopted by the present invention comprises the following steps:

[0006] Establish an asymmetric T-type equivalent circuit of the asynchronous motor in steady state, obtain the theoretical data parameters of the motor system, and analyze the loop impedance when inputting a single-phase low-frequency AC voltage;

[0007] The design inputs a single-phase low-frequency current, uses a proportional resonant controller to perform zero-static error control on the input AC current, and uses the SVPWM output duty cycle to adjust the state of the voltage-type inverter power switch tube to achieve the output of the required identification voltage;

[0008] The reconstructed identification voltage is obtained by sampling the inverter bus voltage and SVPWM duty cycle through fast Fourier transform, and the imaginary part of the reconstructed identification voltage that is not affected by the inverter nonlinear error is obtained through analysis.

[0009] The accurate identification value of the asynchronous motor rotor resistance is calculated based on the reconstructed imaginary part of the identification voltage, the input AC current amplitude and the imaginary part of the input loop impedance.

[0010] Preferably, in the asymmetric T-type equivalent circuit of the asynchronous motor in steady state, when the single-phase low-frequency AC voltage required for identification is input to the asynchronous motor, its excitation inductance is connected in parallel with the rotor resistance, and the input loop impedance of the asynchronous motor is:

[0011]

[0012] Among them, R s is the stator resistance, R r is the rotor resistance, L 1s is the leakage inductance, L m is the excitation inductance, U s is the motor phase voltage, i s is the motor phase current.

[0013] Preferably, the three-phase voltage-type inverter is connected to the three-phase asynchronous motor through a plurality of power switching tubes, wherein the plurality of power switching tubes are divided into three groups, and the plurality of power switching tubes in each group of switching tubes are connected in series. The three groups of switching tubes are connected in parallel at both ends of the output voltage of the three-phase asynchronous motor, and the three-phase windings of the three-phase voltage-type inverter are respectively connected to the series nodes of the power switching tubes in the three groups of switching tubes; the phase voltage output required for identification is achieved by controlling the state of the corresponding power switching tubes, and the identification current is input using a current closed-loop PR regulation method.

[0014] Further preferably, the AC current amplitude I is set A , the AC current frequency f0 is the same as the identification voltage frequency, then the single-phase input AC current is constructed In ideal condition, the input identification voltage is For input AC current and the current feedback value i s A proportional resonant PR controller is used to track and control the single-phase AC current to obtain the required identification voltage.

[0015] Preferably, the real part U of the reconstructed identification voltage re and the imaginary part U im They are as follows:

[0016]

[0017] U im =U A sinθ

[0018] Among them, U A is the AC voltage amplitude, θ is the initial phase angle of the AC voltage, U DC is the inverter DC bus voltage, T d is the inverter dead zone and switch delay time, f c is the carrier frequency.

[0019] Further preferably, the imaginary part of the identified voltage U is reconstructed im , input AC current amplitude I A And the imaginary part of the input loop impedance, we get the input loop equation:

[0020]

[0021] Obtain the asymmetric T-type rotor resistance R r for:

[0022]

[0023] where R r is the rotor resistance, L 1s is the leakage inductance, L m is the excitation inductance, f0 is the AC current frequency.

[0024] The system for offline identification of motor rotor resistance and elimination of identification errors according to an embodiment of the present invention includes the following modules:

[0025] The loop impedance acquisition module establishes an asymmetric T-type equivalent circuit of the asynchronous motor in steady state, obtains the theoretical data parameters of the motor system, and analyzes and obtains the loop impedance when a single-phase low-frequency AC voltage is input;

[0026] The identification voltage output module is designed to input single-phase low-frequency current, and uses a proportional resonant controller to perform zero-error control on the input AC current. The SVPWM output duty cycle is used to adjust the state of the voltage-type inverter power switch tube to achieve the output of the required identification voltage.

[0027] The identification voltage reconstruction module obtains the reconstructed identification voltage by sampling the inverter bus voltage and SVPWM duty cycle through fast Fourier transform, and analyzes the reconstructed identification voltage imaginary part;

[0028] The rotor resistance identification module calculates the accurate identification value of the asynchronous motor rotor resistance based on the reconstructed imaginary part of the identification voltage, the input AC current amplitude and the imaginary part of the input loop impedance.

[0029] Compared with the prior art, the motor rotor resistance identification method and system of the present invention do not need to consider the influence of stator resistance error, inverter nonlinear error and static error of AC current PI controller. They can eliminate the identification errors of rotor resistance and leakage inductance caused by static error of PI controller used for identification of AC current, and can achieve more accurate identification accuracy of rotor resistance and leakage inductance parameters, thus solving the technical problem of large deviation of identification value of existing rotor resistance caused by stator resistance identification error and inverter nonlinear error. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 : is an asymmetric T-type equivalent circuit diagram of an asynchronous motor in steady state according to an embodiment of the present invention;

[0031] Figure 2 1 is a connection diagram of a three-phase voltage source inverter and a three-phase asynchronous motor in an embodiment of the present invention;

[0032] Figure 3 This is a schematic diagram of the single-phase AC experimental control principle in an embodiment of the present invention. DETAILED DESCRIPTION

[0033] The technical solution of the present invention is further described in detail below with reference to the embodiments and drawings, but the embodiments of the present invention are not limited thereto.

[0034] Example 1

[0035] This embodiment provides a method for offline identification of motor rotor resistance. The method first establishes a steady-state asymmetric T-type equivalent circuit for an asynchronous motor to obtain theoretical parameters of the motor system, specifically including phase voltage, phase current, stator resistance, rotor resistance, magnetizing inductance, leakage inductance, and the like. The loop impedance is then analyzed to obtain the input single-phase, low-frequency AC voltage. The input single-phase, low-frequency current is then designed, and a proportional resonant controller is used instead of a PI controller to perform zero-error control of the input AC current to reduce identification error. The SVPWM output duty cycle is then used to adjust the state of the voltage-type inverter power switch to achieve the desired identification voltage output. Finally, the inverter bus voltage and SVPWM duty cycle are sampled and fast Fourier transformed to obtain a reconstructed identification voltage. The imaginary part of the reconstructed identification voltage, which is unaffected by inverter nonlinearities, is analyzed and obtained. The precise identification value of the asynchronous motor rotor resistance is obtained based on the reconstructed imaginary part of the identification voltage, the input AC current amplitude, and the imaginary part of the input loop impedance.

[0036] The asymmetric T-type equivalent circuit of the asynchronous motor in steady state is as follows Figure 1 As shown, R s is the stator resistance, R r is the rotor resistance, L 1s is the leakage inductance, L m is the excitation inductance, U sis the motor phase voltage, i s is the motor phase current. When the single-phase low-frequency AC voltage required for identification is input to the asynchronous motor, its excitation inductance is connected in parallel with the rotor resistance, so the input circuit impedance of the asynchronous motor is:

[0037]

[0038] From (1), we can know that the imaginary part of the input impedance is:

[0039]

[0040] Where f0 is the input AC voltage frequency.

[0041] The three-phase voltage inverter is connected to the three-phase asynchronous motor as follows Figure 2 As shown in the figure, VT1-VT6 are power switches. The six power switches are divided into three groups, with the two power switches in each group connected in series. The three groups are connected in parallel across the output voltage of the three-phase asynchronous motor. The three-phase windings of the three-phase voltage-source inverter are connected to the series connection nodes of the power switches in the three groups. Taking the (a, b) phase windings as an example, power switch VT1 is kept normally closed, while power switches VT2, VT3, VT4, and VT5 are normally open. Inputting an excitation pulse signal from power switch VT6 achieves the voltage output required for identification. At this point, only the (a, b) phase windings form a loop, resulting in a pulsating magnetic field but no electromagnetic torque. Similarly, by controlling the states of the corresponding switches, the voltage output required for identification of phases (b, c) and (a, c) can be achieved.

[0042] Since direct injection of AC voltage into an asynchronous motor is prone to current surge or overcurrent, current closed-loop regulation is generally used to input the identification current. Figure 3 shown.

[0043] Taking the (a, b) phase winding circuit as an example, set the AC current amplitude I A , AC voltage amplitude U A , the AC current frequency f0 is the same as the identification voltage frequency, then a single-phase input AC current can be constructed In ideal condition, the input identification voltage is Since the PI controller has static error, it is impossible to achieve error-free tracking of the AC signal. Based on this, the present invention uses the input AC current and the current feedback value i s A proportional resonant (PR) controller is used for single-phase AC current tracking control, and the regulator output is the required identification voltage. The transfer function of the proportional resonant controller is:

[0044]

[0045] Where K p is the proportionality coefficient, K r is the resonance coefficient, ω0=2πf0 is the input AC angular frequency.

[0046] The resonance coefficient can be increased without changing the stability, so that the PR controller has better frequency selection characteristics and can achieve zero static error tracking of the AC input signal.

[0047] In the stator two-phase stationary coordinate system, let the α-phase stator voltage U alfa is the input excitation voltage, β-phase stator voltage U beta =0, at this time (b, c) phase line current is 0, only (a, b) phase winding forms a loop, and the corresponding duty cycle signal T is obtained after SVPWM modulation. a 、T b 、T c By adjusting the state of the power switch tube of the voltage-type inverter, the identification voltage output of the asynchronous motor (a, b) phase winding circuit can be achieved.

[0048] Due to the limitation of hardware circuit, there is no phase voltage sampling, and the DC bus voltage U DC Combined with the duty cycle signal T a 、T b 、T c To maintain synchronous calculation of current and voltage, this embodiment samples and calculates the voltage at the same time when the current phase is zero, and calculates the output voltage through Fast Fourier Transform (FFT) within one current cycle. Real part of fundamental component U re and the imaginary part U im , as shown in formula (4) and (5), where is the fundamental period of the output current.

[0049]

[0050]

[0051] Due to the existence of nonlinear factors such as dead zone, the output voltage reconstructed by bus voltage and duty cycle can be expressed as:

[0052]

[0053] Where U dt (t)=±T d f c U DC is the average error voltage, whose value depends only on the current direction and has nothing to do with the current amplitude; T dis the inverter dead zone and switch delay time, f c is the carrier frequency. The average error voltage U is obtained by Fourier series expansion. dt (t) is:

[0054] Ignore the higher harmonics that account for a smaller proportion and obtain the real part U of the output voltage reconstruction value (i.e., the reconstructed identification voltage) re and the imaginary part U im They are as follows:

[0055]

[0056] It can be seen that the error voltage only affects the real part of the reconstructed value of the output voltage U re ; The imaginary part of the output voltage reconstruction value U im It is not affected and is equal to the imaginary part of the actual output voltage. Due to the phase voltage reconstruction and phase current tracking without static error, it can be considered that U s 、i s Equivalent to In summary, the imaginary part of the identified voltage U im , input AC current amplitude I A And the imaginary part of the input loop impedance, the input loop equation is as follows:

[0057]

[0058] The asymmetric T-type rotor resistance R can be obtained r for:

[0059]

[0060] The rotor resistance of phases (b, c) and (a, c) can be obtained in the same way. The average rotor resistance can be obtained by adding the rotor resistances of phases (a, b), (b, c), and (a, c). 1s and the magnetizing inductance L m It can be obtained through single-phase AC experiment and no-load equivalent experiment.

[0061] Example 2

[0062] This embodiment is based on the same inventive concept as the first embodiment, and provides a system for offline identification of motor rotor resistance and elimination of identification errors, specifically including the following modules:

[0063] The loop impedance acquisition module establishes an asymmetric T-type equivalent circuit of the asynchronous motor in steady state, obtains the theoretical data parameters of the motor system, and analyzes and obtains the loop impedance when a single-phase low-frequency AC voltage is input;

[0064] The identification voltage output module is designed to input single-phase low-frequency current, and uses a proportional resonant controller to perform zero-error control on the input AC current. The SVPWM output duty cycle is used to adjust the state of the voltage-type inverter power switch tube to achieve the output of the required identification voltage.

[0065] The identification voltage reconstruction module obtains the reconstructed identification voltage by sampling the inverter bus voltage and SVPWM duty cycle through fast Fourier transform, and analyzes the reconstructed identification voltage imaginary part;

[0066] The rotor resistance identification module calculates the accurate identification value of the asynchronous motor rotor resistance based on the reconstructed imaginary part of the identification voltage, the input AC current amplitude and the imaginary part of the input loop impedance.

[0067] The above modules of this embodiment are used to implement the steps of Example 1. The specific implementation process is shown in Example 1 and will not be described in detail.

[0068] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and deform the above embodiments within the scope of the present invention without departing from the principles and purpose of the present invention.

Claims

1. A method for offline identification of motor rotor resistance and elimination of identification error, characterized in that: The following steps are involved: Establish an asymmetric T-type equivalent circuit of the asynchronous motor in steady state, obtain the theoretical data parameters of the motor system, and analyze the loop impedance when inputting a single-phase low-frequency AC voltage; The design inputs a single-phase low-frequency current, uses a proportional resonant controller to perform zero-static error control on the input AC current, and uses the SVPWM output duty cycle to adjust the state of the voltage-type inverter power switch tube to achieve the output of the required identification voltage; The reconstructed identification voltage is obtained by sampling the inverter bus voltage and SVPWM duty cycle through fast Fourier transform, and the imaginary part of the reconstructed identification voltage that is not affected by the inverter nonlinear error is obtained through analysis. The accurate identification value of the asynchronous motor rotor resistance is calculated based on the reconstructed imaginary part of the identification voltage, the input AC current amplitude and the imaginary part of the input loop impedance. The real part of the reconstructed identification voltage U re and the imaginary part U im They are as follows: U im =U A sinθ Among them, U A is the AC voltage amplitude, θ is the initial phase angle of the AC voltage, U DC is the inverter DC bus voltage, T d is the inverter dead zone and switch delay time, f c is the carrier frequency; By reconstructing the imaginary part of the identified voltage U im , input AC current amplitude I A And the imaginary part of the input loop impedance, we get the input loop equation: Obtain the asymmetric T-type rotor resistance R r for: where R r is the rotor resistance, L 1s is the leakage inductance, L m is the excitation inductance, f0 is the AC current frequency.

2. The method for offline identification of motor rotor resistance and elimination of identification error according to claim 1, characterized in that: In the asymmetric T-type equivalent circuit of an asynchronous motor in steady state, when the single-phase low-frequency AC voltage required for identification is input to the asynchronous motor, its excitation inductance is connected in parallel with the rotor resistance, and the input circuit impedance of the asynchronous motor is: Among them, R s is the stator resistance, R r is the rotor resistance, L 1s is the leakage inductance, L m is the magnetizing inductance, U s is the motor phase voltage, i s is the motor phase current.

3. The method for offline identification of motor rotor resistance and elimination of identification error according to claim 1, characterized in that: The three-phase voltage-type inverter is connected to the three-phase asynchronous motor through several power switching tubes. The several power switching tubes are divided into three groups. The multiple power switching tubes in each group are connected in series. The three groups of switching tubes are connected in parallel at both ends of the output voltage of the three-phase asynchronous motor. The three-phase windings of the three-phase voltage-type inverter are respectively connected to the series nodes of the power switching tubes in the three groups of switching tubes. The phase voltage output required for identification is achieved by controlling the state of the corresponding power switching tubes, and the identification current is input using a current closed-loop regulation method.

4. The method for offline identification of motor rotor resistance and elimination of identification error according to claim 3, characterized in that: Set the AC current amplitude I A , the AC current frequency f0 is the same as the identification voltage frequency, then the single-phase input AC current is constructed In ideal condition, the input identification voltage is For input AC current and the current feedback value i s A proportional resonant PR controller is used to track and control the single-phase AC current to obtain the required identification voltage.

5. The method for offline identification of motor rotor resistance and elimination of identification error according to claim 4, characterized in that: The transfer function of the proportional resonant controller is: Where K p is the proportionality coefficient, K r is the resonance coefficient, ω0=2πf0 is the input AC angular frequency.

6. A system for offline identification of motor rotor resistance and elimination of identification errors, characterized in that: Includes the following modules: The loop impedance acquisition module establishes an asymmetric T-type equivalent circuit of the asynchronous motor in steady state, obtains the theoretical data parameters of the motor system, and analyzes and obtains the loop impedance when a single-phase low-frequency AC voltage is input; The identification voltage output module is designed to input single-phase low-frequency current, and uses a proportional resonant controller to perform zero-error control on the input AC current. The SVPWM output duty cycle is used to adjust the state of the voltage-type inverter power switch tube to achieve the output of the required identification voltage. The identification voltage reconstruction module obtains the reconstructed identification voltage by sampling the inverter bus voltage and SVPWM duty cycle through fast Fourier transform, and analyzes the reconstructed identification voltage imaginary part; The rotor resistance identification module calculates the accurate identification value of the asynchronous motor rotor resistance based on the reconstructed imaginary part of the identification voltage, the input AC current amplitude, and the imaginary part of the input loop impedance; The real part of the reconstructed identification voltage U re and the imaginary part U im They are as follows: U im =U A sinθ Among them, U A is the AC voltage amplitude, θ is the initial phase angle of the AC voltage, U DC is the inverter DC bus voltage, T d is the inverter dead zone and switch delay time, f c is the carrier frequency; By reconstructing the imaginary part of the identified voltage U im , input AC current amplitude I A And the imaginary part of the input loop impedance, we get the input loop equation: Obtain the asymmetric T-type rotor resistance R r for: where R r is the rotor resistance, L 1s is the leakage inductance, L m is the excitation inductance, f0 is the AC current frequency.

7. The system for offline identification of motor rotor resistance and elimination of identification errors according to claim 6, characterized in that: A three-phase voltage-source inverter is connected to a three-phase asynchronous motor via a plurality of power switching tubes. The plurality of power switching tubes are divided into three groups, with multiple power switching tubes in each group connected in series. The three groups of switching tubes are connected in parallel across the output voltage of the three-phase asynchronous motor. The three-phase windings of the three-phase voltage-source inverter are respectively connected to the series connection nodes of the power switching tubes in the three groups of switching tubes. The phase voltage output required for identification is achieved by controlling the states of the corresponding power switching tubes, and the identification current is input using a current closed-loop regulation method. Set the AC current amplitude I A , the AC current frequency f0 is the same as the identification voltage frequency, then the single-phase input AC current is constructed In ideal condition, the input identification voltage is For input AC current and the current feedback value i s A proportional resonant PR controller is used to track and control the single-phase AC current to obtain the required identification voltage.

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