Dead zone compensation method based on three-phase current estimation

Abstract

The invention provides a dead zone compensation method based on three-phase current estimation, and the method comprises the following steps: carrying out the preprocessing and estimation of three-phase current: filtering harmonic components of three-phase current ia, b and c, and obtaining three-phase current ia, b and cBase only containing a fundamental component; calculating the three-phase current ia, b and cT0 at the starting moment and the three-phase current ia, b and cT1 at the ending moment of the next control period by using ia, b and cBase; current polarity judgment: according to ia, b, cT0 and ia, b, cT1, utilizing a sign function to judge the polarity of the three-phase current; compensation mode selection and calculation: selecting a dead-zone voltage compensation mode or a dead-zone duty ratio compensation mode through a dead-zone compensation mode selector according to requirements, and calculating a voltage compensation value or a duty ratio compensation value; and taking the obtained voltage compensation value or duty ratio compensation value as the input of ia, b and cBase. Through filtering harmonic current, on the basis of estimating three-phase current values at the starting moment and the ending moment of the next control period, accurate determination of phase current polarity is realized, and accurate compensation of a dead zone effect can be further realized.

Description

Technical Field

[0001] The present invention relates to the technical field of dead zone compensation methods for motor control systems, and in particular to a dead zone compensation method based on three-phase current estimation. Background Art

[0002] With the continuous development of new energy vehicle technology, the requirements for torque control stability of the motors used are becoming higher and higher. At present, motor control mainly uses PWM modulation. In order to avoid the upper and lower bridges of the motor controller being directly connected, a control period in which the upper and lower bridges are closed at the same time, that is, the dead zone, is added during PWM modulation.

[0003] Although the increase in dead zone effectively protects the motor controller, it also causes a deviation between the actual output voltage and the control target voltage. After analyzing the three-phase current, it can be seen that the increase in dead zone increases the 5th and 7th harmonic current components of the three-phase current, which in turn affects the torque stability and NVH performance of the motor.

[0004] In order to solve the impact of increasing the dead zone on the motor control system, there are two existing dead zone compensation methods:

[0005] The first category is the dead zone compensation solution based on hardware circuit.

[0006] The dead zone compensation scheme of the hardware circuit mainly completes the dead zone compensation by adding hardware circuits to detect the current polarity and the actual output voltage waveform. The hardware compensation scheme detects the current polarity more accurately, is less affected by zero current clamping and noise interference, and can achieve better compensation effects.

[0007] The drawback of the dead zone compensation solution of the hardware circuit is that it requires the addition of an additional hardware circuit, which inevitably leads to an increase in cost.

[0008] The second type is the dead zone compensation solution based on software algorithm.

[0009] There are many dead zone compensation schemes in existing software algorithms, mainly the following three:

[0010] 1. Perform dead zone compensation according to the polarity of the currently collected three-phase current.

[0011] 2. The three-phase current is calculated inversely according to the target values ​​idDes and iqDes of the AC and DC axis currents, and then the dead zone compensation is performed according to the polarity of the three-phase current obtained inversely.

[0012] 3. The three-phase current is calculated inversely according to the actual values ​​idAct and iqAct of the AC and DC axis currents after filtering, and then the dead zone compensation is performed according to the polarity of the three-phase current obtained by inverse calculation.

[0013] It can be seen that the dead zone compensation scheme based on software algorithm mainly determines the current polarity through software. Since the judgment of current polarity is greatly affected by zero current clamping and high-order harmonic current, how to determine the polarity of three-phase current is the most important point of dead zone compensation based on software algorithm.

[0014] The defects of the dead zone compensation solution of the software algorithm are:

[0015] First, since the dead zone compensation value performed by the software algorithm in the current cycle needs to be reflected in the next control cycle, the solution of performing dead zone compensation based on the polarity of the currently collected three-phase current can basically not be applied in actual engineering.

[0016] Secondly, since the actual current may not reach the target current after a control cycle, it is also inaccurate to reversely calculate the three-phase current of the next cycle based on the target values ​​idDes and iqDes of the AC and DC axis currents and then determine the polarity of the three-phase current.

[0017] Furthermore, since the actual values ​​idAct and iqAct of the AC and DC axis currents may change suddenly within a control cycle, using these values ​​to reversely calculate the three-phase currents in the next control cycle and determine the polarity may also result in deviations.

[0018] Therefore, the dead zone compensation currently implemented by software algorithms inevitably leads to erroneous compensation, resulting in abnormal torque fluctuations introduced into the motor system. Summary of the invention

[0019] The technical problem to be solved by the present invention is how to improve the effect of dead zone compensation achieved by software algorithm.

[0020] In order to solve the above technical problems, the present invention provides a dead zone compensation method based on three-phase current estimation, the method comprising the following steps:

[0021] Three-phase current preprocessing and estimation: Filtering the three-phase current i a,b,c The harmonic components of the three-phase current i containing only the fundamental component are obtained. a,b,cBase ; Use the i a,b,cBase Calculate the three-phase current i at the start of the next control cycle a,b,cT0 and the three-phase current i at the end time a,b,cT1 ;

[0022] Current polarity judgment: According to the i a,b,cT0 and the i a,b,cT1 , and use the sign function to determine the polarity of the three-phase current;

[0023] Compensation method selection and calculation: According to the needs, the dead zone voltage compensation or dead zone duty cycle compensation is selected through the dead zone compensation method selector, and the voltage compensation value or the duty cycle compensation value is calculated; and the obtained voltage compensation value or the duty cycle compensation value is used as the i a,b,cBase Input.

[0024] Further, using the i a,b,cBase Calculate the three-phase current i at the start time of the next control cycle a,b,cT0 and the three-phase current i at the end time a,b,cT1 ,include:

[0025] According to the electrical angle θ collected at the start of the current control cycle, the control cycle T and the angular frequency ω, the electrical angle θ0 at the start of the next control cycle and the electrical angle θ1 at the end of the next control cycle are calculated:

[0026] θ0=θ+ωT

[0027] θ1=θ+2ωT

[0028] Use the i a,b,cBase Calculate the three-phase current i at the start time of the next control cycle a,b,cT0 and the three-phase current i at the end time a,b,cT1 :

[0029]

[0030] Further, according to the i a,b,cT0 and the i a,b,cT1 , and use the sign function to determine the polarity of the three-phase current, including:

[0031]

[0032] Among them, 1 represents that the polarity of the three-phase current is positive; -1 represents that the polarity of the three-phase current is negative; and 0 represents that the three-phase current passes through the zero point in the current control cycle.

[0033] Furthermore, the voltage compensation value calculation method includes:

[0034] According to the dead time t d , control period T and DC bus voltage u dc , calculate the dead zone error voltage u d :

[0035]

[0036] The dead zone error voltage u d The three-phase compensation voltage u is calculated a,b,ccmp :

[0037] uacmp = sing(i a ) d ,u bcmp = sing(i b ) d ,u ccmp = sing(i c ) d .

[0038] Furthermore, the calculation method of the duty cycle compensation value includes:

[0039] According to the dead time t d , control period T, calculate dead zone error duty cycle dyc d :

[0040]

[0041] The dead-band error duty cycle dyc d Calculate the three-phase compensation duty cycle dyc a,b,ccmp :

[0042] udyc acmp = sing(i a )dyc d ,dyc bcmp = sing(i b )dyc d ,dyc ccmp = sing(i c )dyc d .

[0043] Furthermore, the three-phase current i is filtered out. a,b,c Methods for removing the harmonic content include using a low-pass filter or a second-order integrator.

[0044] Compared with the prior art, the present invention has the following beneficial effects:

[0045] The present invention filters out harmonic currents and estimates the three-phase current values ​​at the start and end of the next control cycle to accurately determine the polarity of the phase current, thereby accurately compensating for the dead zone effect. It effectively suppresses the fluctuation of the fundamental current, reduces the content of higher harmonics in the system, improves the distortion of the three-phase current, and makes the system run more stably. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 A flowchart of the disclosed embodiment of the present invention;

[0047] Figure 2 The current waveform diagram of the experimental results of the present invention when the dead zone compensation is turned off;

[0048] Figure 3 The current waveform diagram of the experimental results of the present invention when the dead zone compensation is turned on;

[0049] Figure 4 The experimental results of the present invention are the FFT analysis diagram of the three-phase current when the dead zone compensation is turned off;

[0050] Figure 5 This is the FFT analysis diagram of the three-phase current when the dead zone compensation is turned on according to the experimental results of the present invention. DETAILED DESCRIPTION

[0051] In order to make the technical scheme and technical effect of the present invention clearer, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments.

[0052] The present invention aims to provide a dead zone compensation method based on three-phase current estimation, the principle of which is as follows:

[0053] On the one hand, since the permanent magnet synchronous motor is an inductive load, according to Faraday's law of electromagnetic induction, it will produce impedance to the current change. This characteristic causes the current to change continuously in time without sudden jumps, that is, the three-phase current cannot change suddenly.

[0054] On the other hand, in motor control systems, the control frequency usually refers to the frequency of the PWM (pulse width modulation) signal, while the current frequency refers to the period of the current waveform. Since the current frequency is relatively small, that is, the change period of the current waveform is long, the change of the current in a short time (within a control cycle) is limited compared to the control frequency. Due to the small current frequency, the polarity (positive and negative direction) of the three-phase current changes at most once in a control cycle. Therefore, by determining the polarity of the three-phase current at the start and end of the next control cycle, the direction of current flow in the entire cycle can be determined. Since the current polarity changes at most once in a control cycle, the polarity of these two time points is sufficient to represent the current polarity of the entire cycle, that is, the polarity of the three-phase current in the next control cycle can be correctly determined, thereby achieving accurate compensation for the dead zone effect.

[0055] refer to Figure 1 , the specific method includes the following steps:

[0056] Step 1: Filter out harmonic current

[0057] The unfiltered three-phase current i a,b,c Filter out the harmonic components and obtain the three-phase current i containing only the fundamental component a,b,cBase Preferably, the three-phase current i is filtered out. a,b,cMethods for eliminating harmonic components include using a low-pass filter or a second-order integrator.

[0058] Step 2: Three-phase current estimation

[0059] First, according to the electrical angle θ collected at the start of the current control cycle, the control cycle T and the angular frequency ω, the electrical angle θ0 at the start of the next control cycle and the electrical angle θ1 at the end of the next control cycle are calculated:

[0060] θ0=θ+ωT

[0061] θ1=θ+2ωT

[0062] Use the three-phase current i after filtering out harmonics a,b,cBase Calculate the three-phase current i at the start of the next control cycle a,b,cT0 and the three-phase current i at the end of the next control cycle a,b,cT1 :

[0063]

[0064] Step 3: Determine the current polarity

[0065] Use the current i obtained in step 2 a,b,cT0 and i a,b,cT1 , and use the sign function to determine the polarity of the three-phase current:

[0066]

[0067] Among them, "1" represents that the polarity of the three-phase current is positive; "-1" represents that the polarity of the three-phase current is negative; and "0" represents that the three-phase current passes through the zero point in the current control cycle.

[0068] Step 4: Select compensation method

[0069] You can choose dead zone voltage compensation or dead zone duty cycle compensation according to your needs. The two methods are equivalent in effect.

[0070] 4.1 Dead zone voltage compensation method

[0071] It is suitable for applications with high voltage accuracy requirements. By directly compensating the voltage, it ensures that the output voltage closely follows the set value, thereby improving the overall control accuracy.

[0072] 4.2 Dead zone duty cycle compensation method

[0073] Suitable for systems where current control is more critical, duty cycle compensation mainly adjusts the proportion of the time the switch tube is turned on. It is more suitable for those occasions with higher requirements for current control. In the motor control system, the duty cycle is adjusted to optimize the current waveform, reduce harmonic interference, and improve the stability and reliability of the motor system.

[0074] Step 5: Compensation value calculation

[0075] 5.1. Calculation of voltage compensation value

[0076] According to the dead time t d , control period T and DC bus voltage u dc , calculate the dead zone error voltage u d :

[0077]

[0078] The dead zone error voltage u d The three-phase compensation voltage u is calculated a,b,ccmp :

[0079] u acmp = sing(i a ) d ,u bcmp = sing(i b ) d ,u ccmp = sing(i c ) d

[0080] 5.2. Calculation of duty cycle compensation value

[0081] According to the dead time t d , control period T, calculate dead zone error duty cycle dyc d :

[0082]

[0083] The dead-band error duty cycle dyc d Calculate the three-phase compensation duty cycle dyc a,b,ccmp :

[0084] udyc acmp = sing(i a )dyc d ,dyc bcmp = sing(i b )dyc d ,dyc ccmp = sing(i c )dyc d

[0085] Step 6: The compensation voltage u obtained in step 5 a,b,ccmp or compensate duty cycle dyc a,b,ccmp As the input of fundamental wave control, motor control is performed.

[0086] In order to verify the effectiveness of the above dead zone compensation method, the present invention also conducts experimental verification through a physical motor test bench, and the specific experiment is as follows:

[0087] Experimental method: The DC bus voltage is given as 400V, the motor speed is given as 1000rpm, and the motor torque is given as 20Nm. An oscilloscope is used to collect the three-phase currents when the dead zone compensation is turned off and on.

[0088] Experimental results: Reference Figure 2-5 , which are the current waveform and FFT analysis diagram when the dead zone compensation is turned off, and the current waveform and FFT analysis diagram when the dead zone compensation is turned on.

[0089] Experimental analysis: On the one hand, Figure 2-3 From the waveforms shown, the distortion of the three-phase current is significantly reduced after the dead zone compensation is turned on. Figure 4-5 From the displayed FFT analysis chart, when the dead zone compensation is turned off, the total harmonic distortion of the three-phase current is 5.62%; when the dead zone compensation is turned on, the total harmonic distortion of the three-phase current is 1.62%, that is, the harmonic content of the three-phase current is significantly reduced.

[0090] In summary, by using the dead zone compensation method provided by the present invention, the distortion degree of the three-phase current can be significantly reduced, and the harmonic content of the three-phase current can be significantly reduced.

[0091] The present invention explores the optimization of the dead zone compensation algorithm by filtering out harmonic currents from the software algorithm level, and proposes a current polarity determination method based on three-phase current estimation to achieve dead zone compensation. If, without considering the cost, a three-phase current hardware filtering circuit is added to improve the quality of three-phase current sampling, and then the three-phase current polarity determination method in the method provided by the present invention is used, this can not only improve the effect of dead zone compensation, but also play a positive role in the control effect of the system fundamental current loop.

[0092] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A dead zone compensation method based on three-phase current estimation, characterized in that: The method comprises the following steps: Three-phase current preprocessing and estimation: Filtering the three-phase current i a,b,c The harmonic components of the three-phase current i containing only the fundamental component are obtained. a,b,cBase ; Use the i a,b,cBase Calculate the three-phase current i at the start time of the next control cycle a,b,cT0 and the three-phase current i at the end time a,b,cT1 ; Current polarity judgment: According to the i a,b,cT0 and the i a,b,cT1 , and use the sign function to determine the polarity of the three-phase current; Compensation method selection and calculation: According to the needs, the dead zone voltage compensation or dead zone duty cycle compensation is selected through the dead zone compensation method selector, and the voltage compensation value or the duty cycle compensation value is calculated; and the obtained voltage compensation value or the duty cycle compensation value is used as the i a,b,cBase Input.

2. The dead zone compensation method based on three-phase current estimation according to claim 1, characterized in that: Use the i a,b,cBase Calculate the three-phase current i at the start time of the next control cycle a,b,cT0 and the three-phase current i at the end time a,b,cT1 ,include: According to the electrical angle θ collected at the start of the current control cycle, the control cycle T and the angular frequency ω, the electrical angle θ0 at the start of the next control cycle and the electrical angle θ1 at the end of the next control cycle are calculated: θ0=θ+ωT θ1=θ+2ωT Use the i a,b,cBase Calculate the three-phase current i at the start time of the next control cycle a,b,cT0 and the three-phase current i at the end time a,b,cT1 :

3. The dead zone compensation method based on three-phase current estimation according to claim 2, characterized in that: According to the a,b,cT0 and the i a,b,cT1 , and use the sign function to determine the polarity of the three-phase current, including: Among them, 1 represents that the polarity of the three-phase current is positive; -1 represents that the polarity of the three-phase current is negative; and 0 represents that the three-phase current passes through the zero point in the current control cycle.

4. The dead zone compensation method based on three-phase current estimation according to claim 3, characterized in that: The calculation method of the voltage compensation value includes: According to the dead time t d , control period T and DC bus voltage u dc , calculate the dead zone error voltage u d : The dead zone error voltage u d The three-phase compensation voltage u is calculated a,b,ccmp : u acmp =sing(i a )u d ,u bcmp =sing(i b )u d ,u ccmp =sing(i c )u d 。 5. The dead zone compensation method based on three-phase current estimation according to claim 3, characterized in that: The calculation method of the duty cycle compensation value includes: According to the dead time t d , control period T, calculate dead zone error duty cycle dyc d : The dead-band error duty cycle dyc d Calculate the three-phase compensation duty cycle dyc a,b,ccmp : udyc acmp =sing(i a )dyc d ,dyc vcmp =sing(i b )dyc d ,dyc ccmp =sing(i c )dyc d 。 6. The dead zone compensation method based on three-phase current estimation according to claim 1, characterized in that: The three-phase current i a,b,c Methods for removing the harmonic content include using a low-pass filter or a second-order integrator.

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