CN105024614A - Method for sampling current of motor stator - Google Patents

Abstract

The invention discloses a method for sampling a current of a motor stator in motor vector control, and the method comprises the steps: firstly defining the switching states of an inverter bridge arm as Sa, Sb, and Sc, wherein the switching state is '1' when the bridge arm is connected, or else the switching state is '1'; secondly carrying out the collection of two-phase stator currents when upper bridge arms are completely switched off and the lower bridge arms are completely switched on; carrying out the changing of the collected two-phase stator currents from a static three-phase coordinates to a static two-phase orthogonal coordinate system through a constraint condition (ia+ib+ic=0), thereby achieving the accurate collection of the stator currents, wherein ia, ib and ic are the stator currents of A, B and C phases of a motor. According to the invention, a specific sampling method is employed, and the method can reduce the complexity of collection. The method can obtain the stator currents of A and B phases at a time, and can save cost.

Description

A kind of method of sampling of motor stator electric current

Technical field

The invention belongs to the technical field of motor vector control, particularly stator current detects and the method for sampling.

Background technology

The correct sampling of stator current is the basis realizing motor vector control.In the middle of vector control, the indices of the direct influential system of capability of fast response of current inner loop, it is very crucial that coordinate transform is carried out in correct stator current collection.

Such as patent application 201410474695.7, disclose a kind of double-fed aerogenerator stator current diagnostic method of impeller imbalance fault, the method specifically comprises: gather doubly-fed generation machine stator monophase current, utilize fft analysis to extract the fundamental frequency of this stator monophase current; The fault signature component of stator phase currents under the fundamental frequency calculating impeller imbalance fault that utilization obtains; Gather impeller of wind turbine set tach signal, calculate stator current impeller imbalance fault characteristic frequency; The fault signature component of FFT to the stator phase currents obtained is utilized to carry out spectrum analysis, according to fault characteristic frequency now, extract the amplitude at this frequency place, and during with same wind speed operating mode, Wind turbines characteristic frequency amplitude is under normal circumstances made comparisons the failure judgement order of severity.The method utilize frequency characteristic to carry out breakdown judge, sampling and calculate all rather complicated, and frequency easily receives many factors interference, is difficult to the accurate sampling done.

Therefore, in the middle of motor stator current control system, conventional current sample mainly contains: the two-phase phase current 1) utilizing two current sensor device sample motor; 2) utilize the electric current of single resistance sampling DC bus, reconstruct the phase current of motor with this.

Utilize that the cost of current sensor method is higher, volume is comparatively large, be often restricted at the more sensitive electric machine speed regulation product of cost ratio.At single resistance sampling, in order to gather bus current and phase current reconstruction, adopt space voltage vector modulation method.In practice, the delayed meeting of part of hardware causes single resistance sampling can not carry out electric current reconstructing in non-viewing district, and the double sampling in a sector also can increase complexity in control, as depicted in figs. 1 and 2, in the first sector, double sampling process switch conduction situation and electric current flow to situation.

Summary of the invention

For solving the problem, the object of the present invention is to provide a kind of method of sampling of motor stator electric current, the method both can reduce the complexity of collection, again can be cost-saving.

For achieving the above object, technical scheme of the present invention is as follows.

A method of sampling for motor stator electric current, the method comprises:

101, the on off state defining inverter leg is S _a, S _b, S _c, when upper brachium pontis conducting, on off state is ' 1 ', otherwise state is ' 0 ';

102, upper brachium pontis is all in shutoff, the moment that lower brachium pontis is all opened, i.e. S _as _bs _c=' 000 ', carry out collection two-phase stator current;

103, the two-phase stator current collected, utilizes i _a+ i _b+ i _c=0 this constraints, then carry out the change of static three phase coordinates to the static orthogonal coordinate system of two-phase, wherein, i _a, i _band i _cit is the stator current of motor A phase, B phase and C phase.

In described step 102, the resistance of sample circuit is precision resistance R ₁and R ₂, be arranged between lower brachium pontis and ground, and A and B is amplifier, be used as conditioning stator current, DC bus side is voltage is V _dc, GND is ground.

In the first sector, A phase stator current is through precision resistance, through diode continuousing flow, flow to the neutral point in the middle of motor again, for B phase stator current, flow out from the neutral point of electric current and flow to the negative terminal of power supply after precision resistance again, as long as gather the stator current that once just can draw A and B phase like this, the acquisition mode of sector is also similar in addition.

In described method, can not conducting simultaneously between any time upper and lower bridge arm, otherwise power supply is straight-through then can damage inverter.

Described static three phase coordinates to the expression formula of the change of the static orthogonal coordinate system of two-phase are:

$\left[\begin{array}{c}{i}_{\mathrm{\α}}\\ i_{\mathrm{\β}}\end{array}\right]=\left[\begin{array}{cc}\sqrt{\frac{3}{2}}& 0\\ \frac{1}{\sqrt{2}}& \sqrt{2}\end{array}\right]\left[\begin{array}{c}{i}_A\\ i_B\end{array}\right].$

Be connected to lifting circuit after described sample circuit, because the stator current collecting motor is bipolarity, and the signal of ramp metering device is unipolarity and be between 0V-3.3V, needs one to promote circuit.

Further, described lifting circuit has amplifying circuit simultaneously, and when motor is in zero load or load is less, the value of stator current is less, needs to amplify, and the multiple of amplification is unsuitable excessive, and the peak value of the voltage signal after amplification is preferably between 0V-3.3V.

The present invention, by the specific method of sampling, can reduce the complexity of collection, as long as gather the stator current that once just can draw A and B phase, and again can be cost-saving.

Accompanying drawing explanation

Fig. 1 is the design frame chart of single resistance sampling mode one.

Fig. 2 is the design frame chart of single resistance sampling mode two.

Fig. 3 is space voltage vector and sector division figure.

Fig. 4 is that the invention process stator current gathers block diagram.

Fig. 5 is the current direction figure of sampling instant.

Fig. 6 is the circuit diagram that the invention process promotes circuit.

Fig. 7 is the circuit diagram of the invention process amplifying circuit.

Fig. 8 is the process schematic of the invention process stator current modulation.

Embodiment

In order to make object of the present invention, technical scheme and advantage clearly understand, below in conjunction with drawings and Examples, the present invention is further elaborated.Should be appreciated that specific embodiment described herein only in order to explain the present invention, be not intended to limit the present invention.

Please refer to shown in Fig. 4, the method for sampling of the motor stator electric current that the present invention realizes, the method comprises:

101, the on off state defining inverter leg is S _a, S _b, S _c, when upper brachium pontis conducting, on off state is ' 1 ', otherwise state is ' 0 '; Here adopt the mode of SVPWM equally, the principle of which is: by controlling non-zero voltage basic voltage vectors U ₀(100), U ₆₀(110), U ₁₂₀(010), U ₁₈₀(011), U ₂₄₀(011), U ₃₀₀and zero vector 0 (101) ₀₀₀(000), 0 ₁₁₁(000) action time, the control to alternating current machine voltage waveform is realized.Space voltage vector plane is divided into 6 sectors by the voltage vector of 6 non-zeros, as shown in Figure 3.Motor is M, and resistance is precision resistance R ₁and R ₂, be arranged between lower brachium pontis and ground, and A and B is amplifier, be used as conditioning stator current, DC bus side is voltage is V _dc, GND is ground.

102, when brachium pontis on inverter is all in shutoff, the moment that lower brachium pontis is all opened carries out collection two-phase stator current; In any one sector, only 0 ₀₀₀(000) this moment gathers, and as shown in Figure 4, because the coil of motor winding is in perception, the phase current flow through on coil can not suddenly change, and now flows through precision resistance R ₁and R ₂electric current be the electric current of stator afterflow, the diode in parallel with lower brachium pontis can play the effect of afterflow, is the stator current of motor.

Shown in composition graphs 5, gather in the first sector, A phase stator current through precision resistance, through diode continuousing flow, flow to the neutral point in the middle of motor again, for B phase, flow out from the neutral point of electric current and flow again after precision resistance to the negative terminal of power supply, in different sectors, the current direction of A and B phase as shown in Figure 5, as long as gather the stator current that once just can draw A and B phase in any one sector, in other sector, current direction as shown in Figure 5.

103, the two-phase stator current collected, utilizes i _a+ i _b+ i _c=0 this constraints, then carry out the change of static three phase coordinates to the static orthogonal coordinate system of two-phase, wherein, i _a, i _band i _cit is the stator current of motor A phase, B phase and C phase.

Expression formula is now: $\left[\begin{array}{c}{i}_{\mathrm{\α}}\\ i_{\mathrm{\β}}\end{array}\right]=\left[\begin{array}{cc}\sqrt{\frac{3}{2}}& 0\\ \frac{1}{\sqrt{2}}& \sqrt{2}\end{array}\right]\left[\begin{array}{c}{i}_A\\ i_B\end{array}\right].$

For the P75NF75 that the above-mentioned inverter mentioned can be ST (STMicw Electronics) company, precision resistance can be 0.5 Ω, and power is 1W, 1% precision, and encapsulated type is 2512.Integrated transporting discharging chip can be LM358.For motor, it can be permagnetic synchronous motor, four pairs of poles, rated power is 30W, controller can be the EP3C25Q240C8N of the Cyclone type III that altera corp provides, here AD conversion chip can be AD9201, and the square wave rising edge that this chip is exported by FPGA and trailing edge trigger, and can change two-way stator current simultaneously.

PWM is modulated in the middle of fpga chip internal procedure, the carrier wave used is triangular wave, here adopt Voltage space vector PWM (SVPWM) control technology, modulating wave is saddle ripple, triangular wave start counting, be exactly now gather the moment, at this moment on inverter, brachium pontis turns off, and lower brachium pontis is opened, and control synchronization exports a pulse signal on FPGA, thus trigger peripheral A/D chip, make it start conversion.

The stator current collecting motor is bipolarity, and the signal of ramp metering device is unipolarity and be between 0V-3.3V, needs one to promote circuit, as shown in Figure 6.In addition, motor be in zero load or load less when, the value of stator current is less, needs to amplify, and as shown in Figure 7, the multiple of amplification is unsuitable excessive, and its peak value is between 0-3.3V for amplifying circuit.

Above-mentioned circuit 6 is known: generally speaking, R is had ₁=R ₂, now V _ref=1.65V.

The amplifying circuit of stator current A phase as shown in Figure 7, by the V of above-mentioned output _refvoltage be connected to R in the middle of figure ₈, work as R ₃=R ₆, R ₄=R ₇, R ₅=R ₈time, the multiplication factor obtained is: obtain a suitable correct multiplication factor to need constantly to adjust R ₃, R ₄and R ₅value.When pulse exports triggering signal from FPGA, AD9201 carries out analog-to-digital conversion after receiving the pulse signal from FPGA, directly delivers to follow-up coordinate transform computing after the correct digital quantity obtained.

Equally, the conditioning for the stator current of B phase is also analyzed based on above.

Figure 8 shows that the stator current that motor reads is after ovennodulation, is finally sent to the schematic diagram of controller, inside controller what obtain is all digital quantity, the is-symbol position of 0 of its highest order and 1 representative, 1 represents negative, and 0 is just representing.

The present invention, by the above-mentioned method of sampling, can reduce the complexity of collection, as long as gather the stator current that once just can draw A and B phase, and again can be cost-saving.

The foregoing is only preferred embodiment of the present invention, not in order to limit the present invention, all any amendments done within the spirit and principles in the present invention, equivalent replacement and improvement etc., all should be included within protection scope of the present invention.

Claims (6)

1. a method of sampling for motor stator electric current, is characterized in that the method comprises:

101, the on off state defining inverter leg is S _a, S _b, S _c, when upper brachium pontis conducting, on off state is ' 1 ', otherwise state is ' 0 ';

102, when brachium pontis on inverter is all in shutoff, the moment that lower brachium pontis is all opened, i.e. S _as _bs _c=' 000 ', carry out collection two-phase stator current;

103, the two-phase stator current collected, utilizes i _a+ i _b+ i _c=0 this constraints, then carry out the change of static three phase coordinates to the static orthogonal coordinate system of two-phase, wherein, i _a, i _band i _cit is the stator current of motor A phase, B phase and C phase.

2. the method for sampling of motor stator electric current as claimed in claim 1, it is characterized in that in described step 102, the resistance of sample circuit is precision resistance R ₁and R ₂, be arranged between lower brachium pontis and ground, DC bus side is voltage is V _dc, GND is ground.

3. the method for sampling of motor stator electric current as claimed in claim 1, is characterized in that in described method, can not conducting simultaneously between any time upper and lower bridge arm.

4. the method for sampling of motor stator electric current as claimed in claim 1, is characterized in that described static three phase coordinates to the expression formula of the change of the static orthogonal coordinate system of two-phase are:

$\left[\begin{array}{c}{i}_{\mathrm{\α}}\\ i_{\mathrm{\β}}\end{array}\right]=\left[\begin{array}{cc}\sqrt{\frac{3}{2}}& 0\\ \frac{1}{\sqrt{2}}& \sqrt{2}\end{array}\right]\left[\begin{array}{c}{i}_A\\ i_B\end{array}\right].$

5. the method for sampling of motor stator electric current as claimed in claim 2, is connected to lifting circuit after it is characterized in that described sample circuit.

6. the method for sampling of motor stator electric current as claimed in claim 2, it is characterized in that described after be connected to amplifying circuit, and the peak value of voltage signal after amplifying is between 0V-3.3V.