A method for suppressing motor oscillation in VF control of asynchronous motor

Abstract

The present invention discloses a method for suppressing motor oscillation of an asynchronous motor VF control, comprising the following steps: a frequency converter samples three-phase output current, obtains instantaneous reactive current of the asynchronous motor, extracts reactive current oscillation components, outputs an oscillation suppression calculation angle, and then outputs an oscillation suppression adjustment angle; at the same time, the frequency converter samples bus voltage, obtains bus voltage variation, and then outputs an oscillation suppression adjustment voltage; finally, the oscillation suppression adjustment angle and the frequency instruction are calculated by a second angle integrator to obtain an angle, and the oscillation suppression adjustment voltage and the frequency instruction are calculated by a VF curve calculation unit to obtain an output voltage, which is used for SVPWM modulation output. The present invention simultaneously detects the output current and bus voltage, adds an adjustment angle output controller and a universal adjustment unit, effectively speeds up the control response, realizes the optimal control adjustment output, and has an obvious suppression effect, which can meet the needs of parameter consistency for asynchronous motors of different capacities.

Description

Technical Field

[0001] The present invention belongs to the technical field of VF control methods for asynchronous motors, and in particular relates to a VF control method for asynchronous motors to suppress motor oscillation. Background Art

[0002] VF control is a commonly used inverter control mode. Its advantages are simple control method, no dependence on motor parameters, and adaptability to most applications. VF control is an open-loop control, which cannot suppress the inherent instability characteristics of a specific operating frequency when running at light load or no load, resulting in torque fluctuations, causing the motor to oscillate continuously. At the same time, the motor current also oscillates significantly, causing the inverter to report a fault and shut down. Long-term continuous oscillation will shorten the service life of the motor and other motor equipment, and it cannot operate normally within a specific oscillation frequency range, which also limits the speed regulation range of the VF control method.

[0003] It is generally believed that VF control motor oscillation is usually related to the modulation method, inverter dead zone effect, reactive power exchange between the inverter and the motor, and mechanical frequency resonance of the motor. Since VF control is an open-loop control, when current oscillation occurs, there is no effective feedback to adjust the current output, which can easily lead to further deterioration of the oscillation until the motor or inverter becomes abnormal.

[0004] For the problem of motor oscillation in VF control of asynchronous motors, the output current is usually detected, the oscillation factor is extracted, the output frequency is adjusted, and the output torque is stabilized to suppress the motor oscillation. Motor oscillation will also cause fluctuations in bus voltage, resulting in instability in output voltage. Therefore, by detecting bus voltage, adjusting and stabilizing output voltage, further deterioration of motor oscillation can be effectively avoided. Usually, motor oscillation presents irregular periodicity. If the control response is not timely, or the adjustment amount and motor oscillation form a chase, not only can the motor oscillation not be suppressed, but it may even cause the motor oscillation to further intensify.

[0005] Therefore, a method for suppressing motor oscillation in VF control of asynchronous motors is urgently needed. Summary of the invention

[0006] In order to solve the defects in the prior art, the present invention provides an asynchronous motor VF control motor oscillation suppression method.

[0007] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0008] The present invention provides an asynchronous motor VF control motor oscillation suppression method, comprising the following steps:

[0009] S1. The frequency converter samples the three-phase output current, obtains the instantaneous reactive current of the asynchronous motor through the current coordinate converter, and extracts the reactive current oscillation component through the first filter and the subtractor;

[0010] S2. The reactive current oscillation component is output by a first oscillation suppression calculation unit to calculate an oscillation suppression angle, and the oscillation suppression calculation angle is output by an adjustment angle output controller to adjust the oscillation suppression angle;

[0011] S3. The frequency converter samples the bus voltage, and obtains the bus voltage variation through the bus voltage sampling value holder and the subtractor, and the bus voltage variation is outputted by the second oscillation suppression calculation unit to adjust the oscillation suppression voltage;

[0012] S4. Add the angle obtained by calculating the oscillation suppression adjustment angle and the frequency command through the second angle integrator, and add the output voltage obtained by calculating the oscillation suppression adjustment voltage and the frequency command through the VF curve calculation unit for SVPWM modulation output.

[0013] Preferably, the first oscillation suppression calculation unit includes a first proportional coefficient, a universal adjustment unit, an adjustment frequency calculation unit, an adjustment frequency limiting unit, and a first angle integrator; the first proportional coefficient is a user-adjustable parameter; the reactive current oscillation component is multiplied by the first proportional coefficient and the universal adjustment unit to obtain an equivalent voltage adjustment amount; the adjustment frequency calculation unit obtains the oscillation suppression adjustment frequency by inverse calculation of the equivalent voltage adjustment amount according to the slope of the VF curve; the oscillation suppression adjustment frequency is output as an oscillation suppression calculation angle through the adjustment frequency limiting unit and the first angle integrator.

[0014] Preferably, the universal adjustment unit automatically calculates the adjustment parameters according to the current rated output current of the inverter, and is used to adjust the user adjustment parameters of asynchronous motors of different capacities.

[0015] Preferably, the adjustment angle output controller accumulates the oscillation suppression calculation angle. If the accumulated oscillation suppression calculation angle reaches a preset angle threshold, the oscillation suppression adjustment angle is output according to the preset angle threshold. If the accumulated oscillation suppression calculation angle does not reach the preset angle threshold, the oscillation suppression adjustment angle is not output.

[0016] Preferably, the second oscillation suppression calculation unit includes a second proportional coefficient and a first adjustment voltage calculation unit; the second proportional coefficient is a user-adjustable parameter; the first adjustment voltage calculation unit calculates the oscillation suppression adjustment voltage according to the bus voltage change.

[0017] Preferably, after the frequency converter samples the bus voltage in step S3, the bus voltage is also calculated through a second filter and a subtractor to obtain a bus voltage oscillation component, and the bus voltage oscillation component is output as an oscillation suppression adjustment voltage through a third oscillation suppression calculation unit; the third oscillation suppression calculation unit includes a third proportional coefficient, a second adjustment voltage calculation unit, and an adjustment voltage limiting unit; the third proportional coefficient is a user-adjustable parameter; the second adjustment voltage calculation unit calculates the oscillation suppression adjustment voltage based on the bus voltage oscillation component; the adjustment voltage limiting unit limits the maximum and minimum values ​​of the oscillation suppression adjustment voltage.

[0018] Preferably, the first filter reduces the filtering effect in the low-frequency stage to avoid startup abnormalities; the frequency adjustment limit unit reduces the frequency limit value in the low-frequency stage to avoid abnormalities caused by excessive output oscillation suppression adjustment frequency.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] First, the present invention detects the output current and bus voltage simultaneously, and adds links such as an adjustment angle output controller and a universal adjustment unit, which can effectively speed up the control response, achieve the best control adjustment output, have a significant suppression effect, and can meet the needs of parameter consistency for asynchronous motors of different capacities, and has good practical value.

[0021] Second, the present invention adds a universal adjustment unit to automatically calculate the corresponding adjustment parameters based on easily obtained parameters such as the rated output current and rated output voltage of the current inverter. Without the need to adjust or only need to fine-tune the user parameters, the oscillation suppression of asynchronous motors of different capacities can be achieved, and the parameter consistency is good.

[0022] Third, the present invention avoids the oscillation suppression adjustment amount chasing the motor oscillation and failing to effectively suppress the motor oscillation by adding a link for accumulating and outputting the oscillation suppression calculation angle. It also avoids the problem of a single adjustment amount being too small under high carrier conditions, resulting in poor suppression effect.

[0023] Fourth, since the motor oscillation causes unstable energy exchange between the inverter and the motor, causing bus voltage fluctuations, the present invention also adjusts the output voltage by detecting bus voltage changes, and stabilizes the output voltage to avoid further deterioration of motor oscillation caused by output voltage fluctuations. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a flow chart of a method for suppressing motor oscillation by VF control of an asynchronous motor in the first embodiment of the present invention;

[0025] Figure 2 4 is a framework diagram of a first oscillation suppression calculation unit in the first embodiment of the present invention;

[0026] Figure 3 is a framework diagram of a second oscillation suppression calculation unit in the first embodiment of the present invention;

[0027] Figure 4 This is a workflow framework diagram of a method for suppressing motor oscillation by VF control of an asynchronous motor in Embodiment 2 of the present invention;

[0028] Figure 5 It is a framework diagram of the third oscillation suppression calculation unit in the second embodiment of the present invention;

[0029] Figure 6 This is a current comparison diagram of a 7.5Kw asynchronous motor driven by a frequency converter at 25Hz when the inverter does not adopt the suppression method of the present invention and adopts the suppression method of the present invention. DETAILED DESCRIPTION

[0030] The preferred embodiments of the present invention are described below in conjunction with the accompanying drawings. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention. Specific implementation method one:

[0032] This embodiment provides an asynchronous motor VF control motor oscillation suppression method, comprising the following steps:

[0033] S1. The inverter samples the three-phase output current, obtains the instantaneous reactive current of the asynchronous motor through the current coordinate converter, and extracts the reactive current oscillation component through the first filter and the subtractor of the instantaneous reactive current;

[0034] like Figure 1 As shown, the output current sampling unit samples the three-phase output current, and obtains the instantaneous reactive current i_d and the instantaneous active current i_q through the current coordinate converter; the instantaneous reactive current i_d can obtain the reactive current DC component i_d_lpf through the first filter, and the reactive current oscillation component Δi_d=i_d_lpf-i_d is calculated through the subtractor.

[0035] S2. The reactive current oscillation component is output by the first oscillation suppression calculation unit to calculate the oscillation suppression angle, and the oscillation suppression calculation angle is output by the adjustment angle output controller to adjust the oscillation suppression angle;

[0036] like Figure 2 As shown, the first oscillation suppression calculation unit includes a first proportional coefficient, a universal adjustment unit, an adjustment frequency calculation unit, an adjustment frequency limiting unit, and a first angle integrator;

[0037] The first proportionality coefficient is a user-adjustable parameter, denoted as K_p1;

[0038] The universal adjustment unit automatically calculates the adjustment parameter based on the current rated output current of the inverter, which is recorded as K_a; K_a=V_m / I_m*K_m, where V_m is the inverter input voltage, I_m is the rated output current of the inverter, and K_m is the built-in model identification coefficient of the inverter; the universal adjustment unit can be used to adjust the user-adjustable parameter k_p1 of asynchronous motors of different capacities to meet consistency requirements;

[0039] The reactive current oscillation component is multiplied by the first proportional coefficient and the universal adjustment unit to obtain an equivalent voltage adjustment amount, which is recorded as V_Δid;

[0040] The frequency adjustment calculation unit calculates the oscillation suppression adjustment frequency f_adj by inverse calculation based on the slope of the VF curve for the equivalent voltage adjustment V_Δid, that is, f_adj=V_Δid×f_base / V_base, where f_base is the base frequency of the VF curve, and V_base is the base voltage of the VF curve;

[0041] The oscillation suppression adjustment frequency f_adj is outputted as an oscillation suppression calculation angle through the adjustment frequency limiter unit and the first angle integrator;

[0042] The frequency limiter unit is adjusted to set the maximum limit value f_adj_max of the oscillation suppression adjustment frequency. Generally speaking, when operating at a low frequency, f_adj_max needs to be reduced accordingly to avoid abnormal operation caused by a large oscillation suppression adjustment frequency.

[0043] The first angle integrator is used to perform angle integration on the oscillation suppression adjustment frequency f_adj to obtain an oscillation suppression calculation angle θ_cal;

[0044] The adjustment angle output controller accumulates the oscillation suppression calculation angle θ_cal. If the accumulated oscillation suppression calculation angle reaches the preset angle threshold θ_thr, the output oscillation suppression adjustment angle θ_adj=θ_thr is output. If the accumulated oscillation suppression calculation angle does not reach the preset angle threshold θ_thr, the output oscillation suppression adjustment angle θ_adj=0 is output.

[0045] S3. The inverter samples the bus voltage, calculates the bus voltage change through the bus voltage sampling value holder and the subtractor, and the bus voltage change is output through the second oscillation suppression calculation unit to adjust the oscillation suppression voltage;

[0046] like Figure 1As shown, the bus voltage sampling unit samples the DC bus voltage V_pn, reads the bus voltage V_pn_last sampled in the previous cycle through the bus voltage sampling value holder, and obtains the bus voltage change ΔV_pn1=V_pn_last-V_pn through the subtractor. The bus voltage change ΔV_pn1 passes through the second oscillation suppression calculation unit to obtain the oscillation suppression adjustment voltage V_d_adj1;

[0047] like Figure 3 As shown, the second oscillation suppression calculation unit includes a second proportional coefficient and an adjustment voltage calculation unit;

[0048] The second proportional coefficient is a user-adjustable parameter, denoted as K_p2;

[0049] The first voltage adjustment calculation unit determines the relationship between the bus voltage and the inverter output voltage based on the inverter mathematical model. Taking the common SVPWM modulation as an example, the oscillation suppression adjustment voltage ;

[0050] Through the second oscillation suppression calculation unit, the problem of deviation between the calculated value and the actual value of the modulated output voltage caused by the oscillation of the bus voltage can be corrected. When the bus voltage wave is caused by the motor oscillation, the output voltage can be kept stable, thus avoiding further deterioration of the motor oscillation due to the fluctuation of the output voltage.

[0051] S4. The oscillation suppression adjustment angle and the frequency command are calculated by an angle integrator to obtain an angle addition, and the oscillation suppression adjustment voltage and the frequency command are calculated by a VF curve calculation unit to obtain an output voltage addition for SVPWM modulation output;

[0052] like Figure 1 As shown, the current frequency command f_ref is calculated by the speed curve, the output voltage V_ref is calculated by the frequency command f_ref according to the VF curve, and the voltage vector angle θ_ref is obtained by the frequency command f_ref through the angle integrator 2; the output voltage V_ref is added to the oscillation suppression adjustment voltage V_d_adj1 to obtain the final output voltage, the voltage vector angle θ_ref is added to the oscillation suppression adjustment angle θ_adj to obtain the final output voltage vector angle, and the final output voltage and the final output voltage vector angle are used for calculation and output by the SVPWM modulation unit;

[0053] like Figure 6 As shown, not adopted ( Figure 6 The left half of the Figure 6 (right half of the figure) According to the control method of this embodiment, the current comparison diagram of the inverter driving a 7.5Kw asynchronous motor when running at 25Hz. Through comparison, it can be seen that the control method provided by the present invention can quickly and effectively suppress motor oscillation. Specific implementation method 2:

[0055] As another preferred embodiment, the rest is the same as embodiment one, except that, in this embodiment, after the inverter samples the bus voltage, the bus voltage is calculated through a second filter and a subtractor to obtain a bus voltage oscillation component, and the bus voltage oscillation component is output through a third oscillation suppression calculation unit to output an oscillation suppression adjustment voltage.

[0056] like Figure 4 As shown, the bus voltage sampling unit samples the DC bus voltage V_pn, and the bus voltage V_pn_lpf is obtained through the second filter. The bus voltage fluctuation ΔV_pn2=V_pn_lpf-V_pn is calculated by the subtractor, and the bus voltage fluctuation ΔV_pn2 is passed through the third oscillation suppression calculation unit to obtain the oscillation suppression adjustment voltage V_d_adj2;

[0057] like Figure 5 As shown, the third oscillation suppression calculation unit includes a third proportional coefficient, a second adjustment voltage calculation unit, and an adjustment voltage limiting unit;

[0058] The third proportional coefficient is a user-adjustable parameter, denoted as K_p3;

[0059] The second voltage adjustment calculation unit determines the relationship between the bus voltage and the inverter output voltage based on the inverter mathematical model. Taking the common SVPWM modulation as an example, the oscillation suppression adjustment voltage ;

[0060] The voltage limiting unit is used to limit the output range of the oscillation suppression adjustment voltage V_d_adj2, wherein the minimum value of V_d_adj2 is set to avoid normal bus voltage fluctuations, and at the same time, oscillation suppression based on output reactive current can be prioritized, and the maximum value of V_d_adj2 is set to avoid abnormal output voltage adjustment causing motor abnormality.

[0061] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for suppressing oscillation of an asynchronous motor VF control motor, characterized in that: The steps include: S1. The frequency converter samples the three-phase output current, obtains the instantaneous reactive current of the asynchronous motor through the current coordinate converter, and extracts the reactive current oscillation component through the first filter and the subtractor; S2. The reactive current oscillation component is output by a first oscillation suppression calculation unit to calculate an oscillation suppression angle, and the oscillation suppression calculation angle is output by an adjustment angle output controller to adjust the oscillation suppression angle; S3. The frequency converter samples the bus voltage, and obtains the bus voltage variation through the bus voltage sampling value holder and the subtractor, and the bus voltage variation is outputted by the second oscillation suppression calculation unit to adjust the oscillation suppression voltage; S4. The oscillation suppression adjustment angle and the frequency command are calculated by the second angle integrator to obtain the angle addition, and the oscillation suppression adjustment voltage and the frequency command are calculated by the VF curve calculation unit to obtain the output voltage addition for SVPWM modulation output; The first oscillation suppression calculation unit includes a first proportional coefficient, a universal adjustment unit, an adjustment frequency calculation unit, an adjustment frequency limiting unit, and a first angle integrator; the first proportional coefficient is a user-adjustable parameter; the reactive current oscillation component is multiplied by the first proportional coefficient and the universal adjustment unit to obtain an equivalent voltage adjustment; the adjustment frequency calculation unit is the equivalent voltage adjustment to obtain an oscillation suppression adjustment frequency by reverse calculation according to the slope of the VF curve; the oscillation suppression adjustment frequency is output through the adjustment frequency limiting unit and the first angle integrator to output an oscillation suppression calculation angle; After the frequency converter samples the bus voltage in step S3, the bus voltage is also calculated through a second filter and a subtractor to obtain a bus voltage oscillation component, and the bus voltage oscillation component is output through a third oscillation suppression calculation unit to output an oscillation suppression adjustment voltage; the third oscillation suppression calculation unit includes a third proportional coefficient, a second adjustment voltage calculation unit, and an adjustment voltage limiting unit; the third proportional coefficient is a user-adjustable parameter; the second adjustment voltage calculation unit calculates the oscillation suppression adjustment voltage according to the bus voltage oscillation component; the adjustment voltage limiting unit limits the maximum and minimum values ​​of the oscillation suppression adjustment voltage.

2. The method for suppressing oscillation of an asynchronous motor VF controlled motor according to claim 1, characterized in that: The universal adjustment unit automatically calculates the adjustment parameters according to the current rated output current of the inverter, and is used to adjust the user adjustment parameters of asynchronous motors of different capacities.

3. The method for suppressing oscillation of an asynchronous motor VF controlled motor according to claim 1, characterized in that: The adjustment angle output controller accumulates the oscillation suppression calculation angle. If the accumulated oscillation suppression calculation angle reaches a preset angle threshold, the oscillation suppression adjustment angle is output according to the preset angle threshold. If the accumulated oscillation suppression calculation angle does not reach the preset angle threshold, the oscillation suppression adjustment angle is not output.

4. The method for suppressing oscillation of an asynchronous motor VF controlled motor according to claim 1, characterized in that: The second oscillation suppression calculation unit includes a second proportional coefficient and a first adjustment voltage calculation unit; the second proportional coefficient is a user-adjustable parameter; the first adjustment voltage calculation unit calculates the oscillation suppression adjustment voltage according to the bus voltage change.

5. The method for suppressing oscillation of an asynchronous motor VF controlled motor according to claim 1, characterized in that: The first filter reduces the filtering effect in the low-frequency stage to avoid startup abnormalities; the frequency adjustment limit unit reduces the frequency limit value in the low-frequency stage to avoid abnormalities caused by excessive output oscillation suppression adjustment frequency.

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