Method for dead-time compensation of frequency converter

Abstract

The application discloses a variable frequency device dead zone compensation method, which acquires real-time data of a load current, obtains characteristic harmonics of dead zone generated current according to the real-time data of the load current, inputs the characteristic harmonics after taking the opposite to a regulator, then obtains a characteristic harmonic control quantity, and finally obtains a compensation time point or a compensation amplitude of the dead zone compensation according to the characteristic harmonic control quantity. The application improves the precision of the dead zone compensation, further reduces the harmonics of the system, has low sensitivity to the load characteristic change, and does not need to acquire a special dead zone compensation table.

Description

Technical Field

[0001] This invention relates to the field of frequency converters, and more specifically to a method for dead-time compensation in frequency converters. Background Technology

[0002] Voltage source inverters typically employ PWM modulation technology, where the upper and lower switches in a single-phase bridge arm circuit are complementary in their switching action. To prevent shoot-through of these switches, a dead time needs to be artificially introduced during the switching process. While this dead time effectively prevents shoot-through, it also causes a discrepancy between the inverter's output voltage and the desired voltage, leading to current distortion. This distortion results in unnecessary losses and may cause torque ripple, vibration, noise, or even oscillation. Therefore, effectively compensating for dead time to minimize its impact is a crucial issue in high-performance frequency conversion technology.

[0003] Dead zone causes a close relationship between the harmonic voltage and current characteristics and the direction of the fundamental current. Current dead zone compensation methods generally employ open-loop compensation, which determines the polarity of the compensation voltage and the compensation timing based on the direction of the fundamental current, while using a fixed compensation amplitude. Since the optimal compensation timing and amplitude vary under different loads and operating conditions, different preset tables need to be designed for different loads and operating conditions to improve the compensation effect. The inputs to the preset table are generally the magnitude of the fundamental current and the frequency of the output current, and the outputs are the dead zone compensation timing and amplitude. This preset table requires a large amount of data, and the acquisition process is cumbersome and complex. Moreover, with hardware aging and temperature effects, the preset table may lead to significant deviations.

[0004] In short, there are problems such as difficulty in obtaining the pre-set tables for dead zone compensation and environmental influences. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method for dead-zone compensation of frequency converters, which eliminates the need to obtain a special dead-zone compensation table, and further reduces system harmonics while improving the accuracy of dead-zone compensation.

[0006] To address the aforementioned technical problems, this invention discloses a method for dead-zone compensation in a frequency converter. The method acquires real-time load current data, obtains the characteristic harmonics of the dead-zone current based on the real-time load current data, inverts the characteristic harmonics and inputs them into the regulator, then obtains the characteristic harmonic control quantity, and finally obtains the compensation time point or compensation amplitude of the dead-zone compensation based on the characteristic harmonic control quantity.

[0007] Preferably, it includes the following steps:

[0008] Step 1: Detect the three-phase current of the actuator connected to the main circuit of the frequency converter;

[0009] Step 2: Transform the three-phase currents to the dq coordinate system through coordinate transformation to obtain the d-axis current and q-axis current;

[0010] Step 3: Use coordinate transformation to obtain the m-axis current and t-axis current in the mt coordinate system;

[0011] Step 4: Filter the m-axis current and t-axis current to obtain the m-axis filtered current and t-axis filtered current;

[0012] Step 5: Invert the m-axis filter current and the t-axis filter current and input them to the PI controller. Then, obtain the PI controller output control quantity for the m-axis and the PI controller output control quantity for the t-axis according to the preset formula.

[0013] Step 6: Obtain the three-phase dead zone control quantity using inverse coordinate transformation;

[0014] Step 7: Limit the three-phase dead zone control quantity to obtain the dead zone compensation quantity.

[0015] Preferably, it further includes:

[0016] Step 8: Add the three-phase dead zone compensation calculated in Step 7 to the control voltage to complete the closed loop.

[0017] Preferably, the actuating device is a drive motor.

[0018] Preferably, the execution device is a PWM rectifier.

[0019] Preferably, in step two, the three-phase current is transformed into the dq coordinate system through coordinate transformation A6, which is the angle of the motor magnetic pole angle θ.

[0020] Preferably, in step three, the motor adopts a control method where the d-axis current is zero, and the q-axis current is transformed by coordinate transformation to -6θ or -12θ.

[0021] Preferably, in step three, the motor adopts a control mode in which the d-axis current is zero, and the q-axis current is transformed by coordinate transformation to 6θ or 12θ.

[0022] Preferably, in step three, the motor adopts a control method in which the d-axis current is not zero, and coordinate transformation is used to transform the d-axis and q-axis currents by -6θ or -12θ.

[0023] Preferably, in step three, the motor adopts a control method in which the d-axis current is not zero, and coordinate transformation is used to transform the d-axis and q-axis currents into 6θ or 12θ coordinates.

[0024] Preferably, in step two, the three-phase current is transformed to the dq coordinate system by a coordinate transformation with an angle of θ, which is the angle of the grid voltage vector angle.

[0025] Preferably, in step three, the current control adopts a unity power factor control method, and the d-axis current is transformed by a 6θ or 12θ coordinate.

[0026] Preferably, in step three, the current control adopts a unity power factor control method, and the d-axis current is transformed by a coordinate of -6θ or -12θ.

[0027] Preferably, in step three, the current control adopts a non-unity power factor control method, and the d-axis and q-axis currents are transformed by 6θ or 12θ coordinates.

[0028] Preferably, in step three, the current control adopts a non-unity power factor control method, and the d-axis and q-axis currents are transformed by coordinates of -6θ or -12θ.

[0029] Preferably, the three-phase current of the actuator connected to the main circuit of the frequency converter is detected by a current sensor.

[0030] This invention improves the accuracy of dead-zone compensation and further reduces system harmonics; it has low sensitivity to changes in load characteristics and does not require a dedicated dead-zone compensation table. Attached Figure Description

[0031] Figures 1-2 This is a basic schematic diagram of Embodiment 1 of the present invention;

[0032] Figure 3 The current spectrum when there is no dead zone compensation;

[0033] Figure 4 This refers to the current spectrum when dead-zone compensation is performed using a specific compensation amplitude in existing technologies.

[0034] Figure 5 This is the current spectrum corresponding to Embodiment 1 of the present invention. Detailed Implementation

[0035] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0036] Example 1

[0037] like Figure 1-2 As shown, the first embodiment of the present invention relates to a closed-loop control method for the dead-time compensation voltage compensation timing and compensation amplitude of a frequency converter. This embodiment is based on a scenario where the frequency converter drives a motor, and includes the following steps:

[0038] Step 1: Detect the three-phase currents ia, ib, and ic of the drive motor A11 using the first current sensor A8, the second current sensor A9, and the third current sensor A10;

[0039] Step 2: Transform the three-phase currents into the dq coordinate system using coordinate transformation A6, which is the angle of the motor magnetic poles θ, to obtain the d-axis current id and the q-axis current iq.

[0040] Step 3: The motor adopts the control mode of id=0. Using coordinate transformation A51, iq is transformed by -6θ to obtain the m-axis current im and t-axis current it in the mt coordinate system; of course, a -12θ coordinate transformation can also be performed.

[0041] Step 4: After filtering im and it through the first filter unit A52 and the second filter unit A53, the m-axis filtered current imf and the t-axis filtered current itf are obtained;

[0042] Step 5: Invert the imf value using A54 and input it to the PI controller A56 on the m-axis. The PI controller A56 on the m-axis outputs the control value um. Invert the itf value using A55 and input it to the PI controller A57 on the t-axis. The PI controller A57 on the t-axis outputs the control value ut.

[0043] Specifically, multiplying A54 by A56 yields the formula for calculating the value from IMF to UM:

[0044]

[0045] Multiplying A55 by A57 gives the formula for calculating from imt to ut:

[0046]

[0047] In the above two equations, kp and ki are parameters that are calculated or adjusted, and s is the Laplace operator.

[0048] Step 6: Use the output iqs of the speed loop speed regulator A1, the magnetic pole angle θ, the output control quantity um of the PI regulator A56 on the m axis, and the coordinate inverse transformation to obtain the three-phase dead zone control quantities ica, icb, and icc.

[0049] Specifically, the calculation formulas for the phase A dead zone control quantity ica, phase B dead zone control quantity icb, and phase C dead zone control quantity icc are as follows:

[0050] ica=-k1*iqs*sin(θ+k2*um)

[0051] icb=-k1*iqs*sin(θ+k2*um-120°)

[0052] icc=-k1*iqs*sin(θ+k2*um+120°)

[0053] Both k1 and k2 are parameters obtained through calculation or adjustment.

[0054] Step 7: Use the PI controller A57 on the t-axis to output the control quantity ut, and limit the three-phase dead zone control quantities ica, icb, and icc from -ut to ut, i.e., module A59, to obtain the dead zone compensation quantities uca, ucb, and ucc.

[0055] Specifically, for phase a, if the dead zone control quantity ica is greater than ut, then the dead zone compensation quantity uca is equal to ut; if ica < -ut, then uca = -ut; otherwise, uca is equal to ica.

[0056] For phase b, if the phase b dead zone control quantity icb is greater than ut, then the dead zone compensation quantity ucb is equal to ut; if icb < -ut, then ucb = -ut; otherwise, ucb is equal to icb.

[0057] For phase C, if the phase C dead zone control value ICC is greater than UT, then the dead zone compensation value UCC is equal to UT; if ICC < -UT, then UCC = -UT; otherwise, UCC is equal to ICC.

[0058] Step 8: Add the three-phase dead zone compensation values ​​uca, ucb, and ucc calculated in the previous step to the control voltages ua, ub, and uc to complete the closed loop.

[0059] The current harmonic simulation results of the present invention and the existing dead zone compensation method are shown in the figure below. The frequency of the fundamental current is 58.2Hz and the effective value is 12.18A. Figure 3 The current spectrum without dead-zone compensation. Figure 4 This is the current spectrum when dead-zone compensation is performed using a specific compensation amplitude in existing technologies. Figure 5 This is the current spectrum corresponding to this embodiment. Figures 3-5 The magnitudes of the corresponding major harmonic values ​​are:

[0060]

[0061] Example 2

[0062] The second embodiment of the present invention relates to a closed-loop control method for the dead-time compensation voltage compensation timing and compensation amplitude of a frequency converter. This embodiment is based on a PWM rectifier and includes the following steps:

[0063] Step 1: Detect the three-phase currents ia, ib, and ic of the power grid using current sensors;

[0064] Step 2: Transform the three-phase currents to the dq coordinate system using coordinate transformation with the grid voltage vector angle θ to obtain id and iq;

[0065] Step 3: The current control adopts the unity power factor control method, and the id is transformed by 6θ coordinates to obtain im and it in the mt coordinate system; of course, a 12θ coordinate transformation can also be performed.

[0066] Step 4: Filter im and it to obtain imf and itf;

[0067] Step 5: Invert the imf value and input it into the PI controller of the m-axis. The PI controller of the m-axis outputs the control quantity um. Invert the itf value and input it into the PI controller of the t-axis. The PI controller of the t-axis outputs the control quantity ut.

[0068] The specific calculation formula is the same as in Example 1, and will not be repeated here.

[0069] Step 6: Use the d-axis current feedback value id, the grid voltage vector angle θ, the t-axis PI regulator output control quantity ut, and the coordinate inverse transformation to obtain the three-phase dead zone control quantity;

[0070] Specifically, the calculation formulas for the phase A dead zone control quantity ica, phase B dead zone control quantity icb, and phase C dead zone control quantity icc are as follows:

[0071] ica=k1*id*cos(θ+k*ut)

[0072] icb=k1*id*cos(θ+k*ut-120°)

[0073] icc=k1*id*cos(θ+k*ut+120°)

[0074] Both k1 and k2 are parameters obtained through calculation or adjustment.

[0075] Step 7: Limit the amplitude based on the output control quantity um of the PI regulator on the m-axis to obtain the three-phase dead zone compensation quantity.

[0076] Specifically, for phase a, if the dead zone control quantity ica is greater than um, then the dead zone compensation quantity uca is equal to um; if ica < -um, then uca = -um; otherwise, uca is equal to ica.

[0077] For phase b, if the phase b dead zone control quantity icb is greater than um, then the dead zone compensation quantity ucb is equal to um; if icb < -um, then ucb = -um; otherwise, ucb is equal to icb.

[0078] For phase C, if the phase C dead zone control value icc is greater than um, then the dead zone compensation value ucc is equal to um; if icc < -um, then ucc = -um; otherwise, ucc is equal to icc.

[0079] Step 8: Add the three-phase dead zone compensation calculated in step 7 to the control voltage to complete the closed loop.

Claims

1. A method for dead-time compensation in a frequency converter, characterized in that, The method obtains real-time load current data, obtains the characteristic harmonics of the dead zone current based on the real-time load current data, inverts the characteristic harmonics and inputs them into the regulator, then obtains the characteristic harmonic control quantity, and then obtains the compensation time point or compensation amplitude of the dead zone compensation based on the characteristic harmonic control quantity. Includes the following steps: Step 1: Detect the three-phase current of the actuator connected to the main circuit of the frequency converter; Step 2: Transform the three-phase currents to the dq coordinate system through coordinate transformation to obtain the d-axis current and q-axis current; Step 3: Use coordinate transformation to obtain the m-axis current and t-axis current in the mt coordinate system; Step 4: Filter the m-axis current and t-axis current to obtain the m-axis filtered current and t-axis filtered current; Step 5: Invert the m-axis filter current and the t-axis filter current and input them to the PI controller. Then, obtain the PI controller output control quantity for the m-axis and the PI controller output control quantity for the t-axis according to the preset formula. Step 6: Use the output of the speed regulator, the single magnetic pole angle, the PI regulator output of the m-axis, and the coordinate inverse transformation to obtain the three-phase dead zone control quantity; Step 7: Use the PI controller output control quantity on the t-axis to limit the three-phase dead zone control quantity to obtain the dead zone compensation quantity. Step 8: Add the three-phase dead zone compensation calculated in Step 7 to the control voltage to complete the closed loop.

2. The inverter dead-time compensation method as described in claim 1, characterized in that, The execution device is a drive motor.

3. The inverter dead-time compensation method as described in claim 1, characterized in that, The execution device is a PWM rectifier.

4. The inverter dead-time compensation method as described in claim 2, characterized in that, In step two, the three-phase current is transformed into the dq coordinate system through coordinate transformation A6, which is the angle of the motor magnetic pole angle θ.

5. The inverter dead-time compensation method as described in claim 4, characterized in that, In step three, the motor adopts a control method where the d-axis current is zero, and the q-axis current is transformed by coordinate transformation to -6θ or -12θ.

6. The inverter dead-time compensation method as described in claim 4, characterized in that, In step three, the motor adopts a control method where the d-axis current is zero, and the q-axis current is transformed into 6θ or 12θ coordinates using coordinate transformation.

7. The inverter dead-time compensation method as described in claim 4, characterized in that, In step three, the motor adopts a control method in which the d-axis current is not zero, and coordinate transformation is used to transform the d-axis and q-axis currents by -6θ or -12θ.

8. The inverter dead-time compensation method as described in claim 4, characterized in that, In step three, the motor adopts a control method in which the d-axis current is not zero, and coordinate transformation is used to transform the d-axis and q-axis currents into 6θ or 12θ coordinates.

9. The inverter dead-time compensation method as described in claim 3, characterized in that, In step two, the three-phase current is transformed into the dq coordinate system through coordinate transformation with the grid voltage vector angle θ.

10. The inverter dead-time compensation method as described in claim 9, characterized in that, In step three, the current control adopts a unity power factor control method, which transforms the d-axis current into a 6θ or 12θ coordinate system.

11. The inverter dead-time compensation method as described in claim 9, characterized in that, In step three, the current control adopts a unity power factor control method, and the d-axis current is transformed by a coordinate transformation of -6θ or -12θ.

12. The inverter dead-time compensation method as described in claim 9, characterized in that, In step three, the current control adopts a non-unity power factor control method, which transforms the d-axis and q-axis currents into 6θ or 12θ coordinates.

13. The inverter dead-time compensation method as described in claim 9, characterized in that, In step three, the current control adopts a non-unity power factor control method, which transforms the d-axis and q-axis currents by -6θ or -12θ coordinates.

14. The inverter dead-time compensation method as described in claim 1, characterized in that, The three-phase current of the actuator connected to the main circuit of the frequency converter is detected by a current sensor.

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