CONTROL METHOD FOR BALANCING SCALING ERRORS OF MULTIPLE CURRENT SENSORS FOR PMSM

Abstract

The invention discloses a control method for balancing scaling errors of multiple current sensors for PMSM. An impedance network is set between a direct current power supply and a three-phase inverter connected to a PMSM to avoid positive and negative poles of the direct current power supply being short-circuited under actions of shoot-through vectors. Under actions of two shoot-through vectors in a PWM cycle, three-phase current sensors are used to respectively sample the sum of currents in each branch of three-phase output branches of the three-phase inverter and a branch of the same bridge arm of the three-phase inverter, according to the sampled currents, operating to obtain the relationship between the scaling error coefficients of the three-phase current sensors. Then, correction coefficients are calculated. The correction of the scaling errors of the current sensors is implemented using correction coefficient feedback control.

Claims

1. A control method for balancing scaling errors of a plurality of current sensors for PMSM, comprising: step 1) setting an impedance network between a direct current power supply and a three-phase inverter connected to a permanent magnet synchronous motor to avoid positive and negative poles of the direct current power supply being short-circuited under actions of shoot-through vectors; step 2) under the actions of two shoot-through vectors in one PWM cycle of the three-phase inverter, respectively sampling a sum of currents in each branch of three-phase output branches of the three-phase inverter and a branch of a same bridge arm of the three-phase inverter using the current sensors being three-phase to obtain a sampled current of each of three phases, and then performing operations according to the sampled currents to obtain a relationship between scaling error coefficients of the current sensors being three-phase; step 3) calculating correction coefficients through the relationship between the scaling error coefficients of the current sensors being three-phase, and implementing correction of scaling errors of the current sensors using a correction coefficient feedback control.

2. The method for balancing the scaling errors of the current sensors sampled under the actions of the shoot-through vectors according to claim 1, wherein: the impedance network in the step 1) comprises a first inductor L.sub.1, a second inductor L.sub.2, a first capacitor C.sub.1, a second capacitor C.sub.2, and a switching transistor S.sub.0, the direct current power supply u.sub.in is connected in parallel to the three-phase inverter, the first capacitor C.sub.1 is connected in parallel to two ends of the direct current power supply u.sub.in, the first inductor L.sub.1, and the switching transistor S.sub.0 connected in series, the first inductor L.sub.1, the switching transistor S.sub.0, and the second inductor L.sub.2 are sequentially connected in series between the positive pole of the direct current power supply u.sub.in and one of bridge arm branches of the three-phase inverter, the second capacitor C.sub.2 is connected in parallel to two ends of the switching transistor S.sub.0 and the second inductor L.sub.2 connected in series.

3. The method for balancing the scaling errors of the current sensors sampled under the actions of the shoot-through vectors according to claim 1, wherein: in the step 2), a bridge arm branch of the three-phase inverter refers to a branch between a node after connecting lower bridge arms of two phases and a lower bridge arm of a remaining phase.

4. The method for balancing the scaling errors of the current sensors sampled under the actions of the shoot-through vectors according to claim 1, wherein: in the step 2), in the one PWM cycle of the three-phase inverter, inserting one shoot-through vector when an upper bridge arm and a lower bridge arm of a phase A are respectively turned on: using a state of upper bridge arms and lower bridge arms of a phase B and a phase C being all turned on and only the upper bridge arm of the phase A being turned on as a shoot-through vector VAPsh, using a state of the upper bridge arms and the_lower bridge arms of the phase B and the phase C being all turned on and only the lower bridge arm of the phase A being turned on as a shoot-through vector VANsh; in cases of the shoot-through vector V.sub.APsh and the shoot-through vector V.sub.ANsh, respectively collecting and obtaining sampled current values through the current sensors being three-phase, obtaining the relationship between the scaling error coefficients of the current sensors being three-phase according to a following formula expressed as:
k.sub.A:k.sub.B:k.sub.C=Δi.sub.AM:Δi.sub.BM:Δi.sub.CM
Δi.sub.AM=i.sub.AMP−i.sub.AMN,Δi.sub.BM=i.sub.BMP−i.sub.BMN,Δi.sub.CM=i.sub.CMP−i.sub.CMN where Δi.sub.AM is a difference between the sampled current values of the current sensor of the phase A under the shoot-through vectors V.sub.APsh and V.sub.ANsh, i.sub.AMP is the sampled current value of the current sensor of the phase A under the shoot-through vector V.sub.APsh, i.sub.AMN is the sampled current value of the current sensor of the phase A under the shoot-through vector V.sub.ANsh; Δi.sub.BM is a difference between the sampled current values of the current sensor of the phase B under the shoot-through vectors V.sub.APsh and V.sub.ANsh, i.sub.BMP is the sampled current value of the current sensor of the phase B under the shoot-through vector V.sub.APsh, i.sub.BMN is the sampled current value of the current sensor of the phase B under the shoot-through vector V.sub.ANsh; Δi.sub.CM is a difference between the sampled current values of the current sensor of the phase C under the shoot-through vectors V.sub.APsh and V.sub.ANsh, i.sub.CMP is the sampled current value of the current sensor of the phase C under the shoot-through vector V.sub.APsh, i.sub.CMN is the sampled current value of the current sensor of the phase C under the shoot-through vector V.sub.ANsh; k.sub.A, k.sub.B, k.sub.C are respectively the scaling error coefficients of the current sensors of the phase A, the phase B, and the phase C.

5. The method for balancing the scaling errors of the current sensors sampled under the actions of the shoot-through vectors according to claim 1, wherein: in the step 3), substituting the relationship between the scaling error coefficients of the current sensors being three-phase into a following formula: $\{\begin{array}{c}x.Math.k_A=y.Math.k_B=z.Math.k_C\\ x.Math.y.Math.z=1\end{array}$ obtaining three correction coefficients x, y, and z: $\{\begin{array}{c}x=\sqrt[3]{{\Delta i}_{\mathrm{BM}}.Math.{\Delta i}_{\mathrm{CM}}/{{\Delta i}_{\mathrm{AM}}}^2}\\ y=\sqrt[3]{{\Delta i}_{\mathrm{AM}}.Math.{\Delta i}_{\mathrm{CM}}/{{\Delta i}_{\mathrm{BM}}}^2}\\ z=\sqrt[3]{{\Delta i}_{\mathrm{AM}}.Math.{\Delta i}_{\mathrm{BM}}/{{\Delta i}_{\mathrm{CM}}}^2}\end{array}$ where x, y, and z are respectively the correction coefficients of the current sensors of a phase A, a phase B, and a phase C; processing using a following formula according to the correction coefficients to obtain corrected three-phase currents: $\{\begin{array}{c}{i}_{\mathrm{Ao}}=x.Math.i_{\mathrm{AMP}}-x.Math.i_{\mathrm{AMN}}\\ i_{\mathrm{Bo}}=y.Math.i_{\mathrm{BMP}}-x.Math.i_{\mathrm{AMN}}\\ i_{\mathrm{Co}}=z.Math.i_{\mathrm{CMP}}-x.Math.i_{\mathrm{AMN}}\end{array}$ where i.sub.Ao, i.sub.Bo, and i.sub.Co are the corrected currents of the phase A, the phase B, and the phase C; finally feeding the corrected three-phase currents back to a current loop of the permanent magnet synchronous motor for control to eliminate imbalance issue of three-phase currents caused by a difference of the scaling error coefficients of three-phase sensors.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] FIG. 1 is a structural block diagram of a method of the disclosure.

[0029] FIG. 2 is a schematic diagram of an installation position of a current sensor.

[0030] FIG. 3 is a schematic diagram of current flow during shoot-through of two phases.

[0031] FIG. 4 is a schematic diagram of switching signals of a modulation method of shoot-through of two phases B and C.

[0032] FIG. 5 is a schematic diagram of modulation of shoot-through of two phases B and C.

[0033] FIG. 6 is a waveform diagram of influence of scaling errors of three-phase current sensors on torque.

DETAILED DESCRIPTION OF DISCLOSED EMBODIMENTS

[0034] The disclosure will be further described in detail below with reference to the drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the disclosure, but not to limit the disclosure.

[0035] The embodiments of the disclosure and the implementation processes thereof are as follows:

[0036] 1. Layout System

[0037] As shown in FIG. 2, the entire system implemented is composed of a direct current power supply, a symmetrical impedance network, a three-phase inverter, and a permanent magnet synchronous motor PMSM.

[0038] In the drawing, u.sub.in is the direct current power supply, i.sub.A, i.sub.B, and i.sub.C are three-phase currents of the permanent magnet synchronous motor PMSM, L.sub.1=L.sub.2=L are respectively a first inductor, a second inductor, and an inductance value thereof of the impedance network, and C.sub.1=C.sub.2=C are a first capacitor, a second capacitor, and a capacitance value thereof of the impedance network.

[0039] The system allows upper and lower bridge arms of the same phase of the three-phase inverter to be turned on at the same time, and the state is a shoot-through vector. The shoot-through vector is a voltage vector, and a duty cycle of the shoot-through vector in one PWM cycle is d.sub.sh.

[0040] FIG. 2 shows the structures of the symmetrical impedance network and the three-phase inverter. The pumping of a bus voltage may be implemented through adjusting the duty cycle of the shoot-through vector. At this time, the magnitude of an output voltage of the three-phase inverter may be increased without increasing a modulation coefficient. The feature provides another sampling window for motor control.

[0041] 2. Sampling Errors of Current Sensors and Installation of Current Sensors to Suppress Sampling Errors

[0042] One current sensor is installed at an intersection between each of the three-phase output branches of the three-phase inverter and the same bridge arm branch of the three-phase inverter, and three current sensors are installed at three intersections corresponding to the three-phase output branches. Each current sensor simultaneously collects the sum of the current in the respective one-phase output branch and the current of the bridge arm branch.

[0043] After the current sensors are installed, considering current sampling errors, sampling values of the current sensors are expressed as:

[00004]$\begin{array}{cc}\{\begin{array}{c}{i}_{\mathrm{AM}}=k_A\left(i_A-i_{\mathrm{br}}\right)+e_A\\ i_{\mathrm{BM}}=k_B\left(i_B-i_{\mathrm{br}}\right)+e_B\\ i_{\mathrm{CM}}=k_C\left(i_C-i_{\mathrm{br}}\right)+e_C\end{array}& \left(1\right)\end{array}$

[0044] where i.sub.br is the current of the bridge arm branch of the three-phase inverter, i.sub.AM, i.sub.BM, and i.sub.CM are the sampled current values of the three-phase current sensors, k.sub.A, k.sub.B, and k.sub.C are the scaling error coefficients of the three-phase current sensors, and e.sub.A, e.sub.B, and e.sub.C are the offset errors of the three-phase current sensors.

[0045] 3. Balance of Shoot-Through Vector Sampling-Scaling Errors of Current Sensors

[0046] The system allows the three-phase inverter to work in various shoot-through states, which include three-bridge arm shoot-through, two-bridge arm shoot-through, and single-bridge arm shoot-through. Considering the implementation of current sampling and the current stress of the three-phase inverter comprehensively, the disclosure implements shoot-through vector current sampling by selecting a manner of simultaneous shoot-through of phases B and C. The shoot-through vector when only an upper bridge arm of a phase A is turned on is defined as V.sub.APsh and the shoot-through vector when only a lower bridge arm of the phase A is turned on is defined as V.sub.ANsh. The states of the three-phase inverter corresponding to V.sub.APsh and V.sub.ANsh are shown in FIG. 3. In FIG. 3, i.sub.sh is the shoot-through current when the three-phase inverter is shoot-through.

[0047] Three phases of the three-phase inverter are divided into the phase A, the phase B, and the phase C.

[0048] In one PWM cycle of the three-phase inverter, one shoot-through vector is inserted when the upper bridge arm and the lower bridge arm of the phase A are respectively turned on: a state of upper bridge arms and lower bridge arms of the phase B and the phase C being all turned on and only the upper bridge arm of the phase A being turned on is used as the shoot-through vector V.sub.APsh, a state of the upper bridge arms and the lower bridge arms of the phases B and C being all turned on and only the lower bridge arm of the phase A being turned on is used as the shoot-through vector V.sub.ANsh.

[0049] In the specific implementation of the disclosure, the offset errors of the current sensors are compensated when the motor is not working, and the sampling offset errors of the current sensors have been compensated.

[0050] Then, in the cases of the shoot-through vector V.sub.APsh and the shoot-through vector V.sub.ANsh, sampled current values are respectively collected and obtained through the three-phase current sensors. Then, the relationship between the scaling error coefficients of the three-phase current sensors is obtained according to the following formula, which is expressed as:

k.sub.A:k.sub.B:k.sub.C=Δi.sub.AM:Δi.sub.BM:Δi.sub.CM  (2)

Δi.sub.AM=i.sub.AMP−i.sub.AMN,Δi.sub.BM=i.sub.BMP−i.sub.BMN,Δi.sub.CM=i.sub.CMP−i.sub.CMN

[0051] where Δi.sub.AM is the difference between the sampled current values of the current sensor of the phase A under the shoot-through vectors V.sub.APsh and V.sub.ANsh twice, i.sub.AMP is the sampled current value of the current sensor of the phase A under the shoot-through vector V.sub.APsh, i.sub.AMN is the sampled current value of the current sensor of the phase A under the shoot-through vector V.sub.ANsh;

[0052] Δi.sub.BM is the difference between the sampled current values of the current sensor of the phase B under the shoot-through vectors V.sub.APsh and V.sub.ANsh twice, i.sub.BMP is the sampled current value of the current sensor of the phase B under the shoot-through vector V.sub.APsh, i.sub.BMN is the sampled current value of the current sensor of the phase B under the shoot-through vector V.sub.ANsh;

[0053] Δi.sub.CM is the difference between the sampled current values of the current sensor of the phase C under the shoot-through vectors V.sub.APsh and V.sub.ANsh twice, i.sub.CMP is the sampled current value of the current sensor of the phase C under the shoot-through vector V.sub.APsh, i.sub.CMN is the sampled current value of the current sensor of the phase C under the shoot-through vector V.sub.ANsh; k.sub.A, k.sub.B, k.sub.C are respectively the scaling error coefficients of the current sensors of the phase A, the phase B, and the phase C.

[0054] In the specific implementation, the corresponding modulation manner is set to implement the insertion of the shoot-through vectors V.sub.APsh and V.sub.ANsh in one PWM cycle. Taking a reference shoot-through vector being located in a sector I as an example, the diagram of switching signals after inserting the shoot-through vectors V.sub.APsh and V.sub.ANsh is shown in FIG. 4, where S.sub.AP, S.sub.BP, and S.sub.CP are respectively the switching signals of the upper bridge arms of the three phases of the three-phase inverter, and S.sub.AN, S.sub.BN, and S.sub.CN are respectively the switching signals of the lower bridge arms of the three phases of the three-phase inverter.

[0055] The implementation of the modulation manner of the switching signals is shown in FIG. 5.

[0056] 4. Correction Processing

[0057] When the scaling error coefficients of the current sensors are different, the relationship between the scaling error coefficients of the three-phase current sensors is substituted into the following formula to balance the scaling error coefficients of the current sensors:

[00005]$\begin{array}{cc}\{\begin{array}{c}x.Math.k_A=y.Math.k_B=z.Math.k_C\\ x.Math.y.Math.z=1\end{array}& \left(3\right)\end{array}$

[0058] Three correction coefficients x, y, and z are obtained:

[00006]$\begin{array}{cc}\{\begin{array}{c}x=\sqrt[3]{{\Delta i}_{\mathrm{BM}}.Math.{\Delta i}_{\mathrm{CM}}/{{\Delta i}_{\mathrm{AM}}}^2}\\ y=\sqrt[3]{{\Delta i}_{\mathrm{AM}}.Math.{\Delta i}_{\mathrm{CM}}/{{\Delta i}_{\mathrm{BM}}}^2}\\ z=\sqrt[3]{{\Delta i}_{\mathrm{AM}}.Math.{\Delta i}_{\mathrm{BM}}/{{\Delta i}_{\mathrm{CM}}}^2}\end{array}& \left(4\right)\end{array}$

[0059] where x, y, and z are respectively the correction coefficients of the current sensors of the phase A, the phase B, and the phase C.

[0060] Corrected three-phase currents are obtained by processing using the following formula according to the correction coefficients:

[00007]$\begin{array}{cc}\{\begin{array}{c}{i}_{\mathrm{Ao}}=x.Math.i_{\mathrm{AMP}}-x.Math.i_{\mathrm{AMN}}\\ i_{\mathrm{Bo}}=y.Math.i_{\mathrm{BMP}}-x.Math.i_{\mathrm{AMN}}\\ i_{\mathrm{Co}}=z.Math.i_{\mathrm{CMP}}-x.Math.i_{\mathrm{AMN}}\end{array}& \left(5\right)\end{array}$

[0061] where i.sub.Ao, i.sub.Bo, and i.sub.Co are the corrected currents of the phase A, the phase B, and the phase C.

[0062] Finally, the corrected three-phase currents are fed back to a current loop of the permanent magnet synchronous motor for control to eliminate the issue of imbalance of the three-phase currents caused by the scaling error coefficients of the three-phase sensors.

[0063] FIG. 6 shows the waveforms of the torque of the motor when the three-phase current sensors have no scaling errors and have scaling errors when the motor runs at 1000 r/min and the torque of the motor is respectively 20 N.Math.m, 40 N.Math.m, and 60 N.Math.m. (a) of FIG. 6 shows the waveform of the torque of the motor when the three-phase current sensors have no scaling errors; and (b) of FIG. 6 shows the waveform of the torque of the motor when the three-phase current sensors have scaling errors. In the drawings, T is the torque, which is measured and obtained through using a torque sensor. It can be seen from FIG. 6 that through adopting the technical solution of the disclosure to correct the issue of imbalance of the scaling errors of multiple current sensors, current distortion and torque fluctuations of the motor caused by the imbalance of the scaling errors of the current sensors can be eliminated.

[0064] In summary, the embodiments of the disclosure can implement the correction of imbalance of the scaling errors of multiple current sensors through the above steps, thereby eliminating current distortion and torque fluctuations of the motor caused by the imbalance of the scaling errors of the current sensors.

[0065] In the embodiments of the disclosure, except for the special description for the model of each device, the models of other devices are not limited, as long as the devices can complete the above functions.

[0066] Persons skilled in the art can understand that the drawings are only schematic diagrams of a preferred embodiment, and the serial numbers of the embodiments of the disclosure are only for description and do not represent the ranking of the embodiments.

[0067] The disclosure is not limited to the embodiments described above. The above description of the specific embodiments is intended to describe and illustrate the technical solution of the disclosure, and the specific embodiments are only illustrative and not restrictive. Without departing from the spirit of the disclosure and the protection scope of the claims, persons skilled in the art can also make many specific transformations under the teachings of the disclosure, which all fall within the protection scope of the disclosure.