CN103051279A - Vector control-based prediction method for uncontrollability of electric current of induction machine - Google Patents

Abstract

The invention discloses a vector control-based prediction method for the uncontrollability of an electric current of an induction machine. The method specifically comprises the following steps of: repeatedly adopting two-phase electric current within a single PWM (pulse-width modulation) period, and decoupling a d/q axis to obtain electric current ids and iqs under the d/q axis; computing deviation delta ids and delta iqs between the ids, the iqs and the set value of the d/q axis electric current; computing the allowed change range delta i'ds and delta i'qs of the d/q axis electric current under the current voltage margin according to a motor electric parameter and a motor model; and comparing the delta ids and the delta i'ds as well as the delta iqs and the delta i'qs, and comparing the electric current uncontrollability threshold value delta d with the electric current uncontrollability threshold value delta q of the d/q axis electric current to predict whether the electric current is uncontrollable or not. According to the method, the saturation degree of the electric current adjuster, the voltage use margin and the electrical characteristics of the motor are comprehensively considered, and the prediction method for the possible uncontrollability of the electric current is given, so that the running reliability of the motor and a driving device can be obviously improved, and the damage of a power device or the motor caused by overcurrent can be avoided.

Description

A kind of induction machine electric current Forecasting Methodology out of control based on vector control

Technical field

The invention belongs to AC induction motor and control technology field thereof, be specifically related in a kind of vector control situation the Forecasting Methodology that the induction machine electric current is out of control.

Background technology

The ac motor speed control by variable frequency method mainly comprises open loop V/f speed governing and closed-loop drive, and the closed-loop drive vector control method that is otherwise known as specifically comprises indirectly rotor field-oriented, direct rotor field-oriented, direct stator flux orientation etc.Its indirect is rotor field-oriented because the hardware that needs is few, and control performance is high and be widely used.

The principle of the indirect rotor flux-orientation vector control of induction machine is: rotating coordinate system is based upon on the direction of rotor field, and by this coordinate, stator current is decomposed into torque current (q shaft current) and exciting current (d shaft current) component, and the product of actual output level of torque and torque current and exciting current is linear.

Induction Motor Vector Control System comprises two current regulators, respectively q shaft current adjuster and d shaft current adjuster, owing to have cross-couplings between the d/q shaft current, so that conventional pi regulator bandwidth can descend along with the raising of power frequency, and when motor speed is higher, because the continuous rising of back electromotive force, so that d/q shaft current adjuster is easier to be saturated, therefore, current regulator may be difficult to reach designing requirement, thereby cause electric current out of control, even damage power device and motor.Therefore, be necessary to predict the induction machine electric current is out of control, in order to before out of control, take measures, avoid the power device that causes owing to electric current is out of control and the damage of motor.

Summary of the invention

The purpose of this invention is to provide a kind of faster induction machine electric current Forecasting Methodology out of control, put according to voltage margin, electric parameter and the setting ground stability margin valve of motor, the situation that electric current is out of control is predicted.

A kind of induction machine electric current Forecasting Methodology out of control based on vector control is specially:

In single PWM cycle biphase current is repeatedly sampled, and sample rate current is carried out the d/q decoupler shaft, obtain d shaft current i _DsWith q shaft current i _Qs

Calculate d shaft current i _DsWith d shaft current set-point

Between deviation delta i _Ds, q shaft current i _QsWith q shaft current set-point

Between deviation delta i _Qs

According to motor electric parameter and motor model, to calculate under the current voltage nargin, the d shaft current allows variation range delta i ' _DsAllow variation range delta i ' with the q shaft current _Qs

Calculate | Δ i _Ds| with | Δ i ' _Ds| between difference DELTA i _d, and | Δ i _Qs| and | Δ i ' _Qs| between difference DELTA i _q

If difference DELTA i _dLess than d shaft current threshold values Δ out of control d, illustrate that then the d shaft current is out of control, if difference DELTA i _qLess than q shaft current threshold values Δ out of control q, illustrate that then the q shaft current is out of control.

Further, also calculate Y _Dq=λ _d(Δ i _d-Δ d)+λ _q(Δ i _q-Δ q), 0＜λ _d≤ 1,0＜λ _q≤ 1, if Y _Dq＜0, illustrate that then current regulator is out of control.

Further, the d shaft current allows variation range delta i ' _DsAllow variation range delta i ' with the q shaft current _QsComputational methods be:

$\mathrm{\Δ}{i}_{\mathrm{ds}}^{\′}=\frac{{\mathrm{\σL}}_s{R}_s{\mathrm{\ω}}_e\mathrm{\Δ}{V}_{\mathrm{qs}}+(1-\mathrm{\σ}{L}_s^2{\mathrm{\ω}}_e^2)\mathrm{\Δ}{V}_{\mathrm{ds}}}{R_s^3+{\mathrm{\σL}}_s^2{R}_s{\mathrm{\ω}}_e^2},$ ${\mathrm{\Δi}}_{\mathrm{qs}}^{\′}=\frac{R_s\mathrm{\Δ}{V}_{\mathrm{qs}}-L_s{\mathrm{\ω}}_e\mathrm{\Δ}{V}_{\mathrm{ds}}}{R_s^2+{\mathrm{\σL}}_s^2{\mathrm{\ω}}_e^2},$

Wherein, Δ V _Ds=V _{Ds_limit}-V _Ds(k), Δ V _Qs=V _{Qs_limit}-V _Qs(k),

V _Ds(k) and V _Qs(k) be respectively d axle and the q shaft voltage of k sampled point, V _{Ds_linit}And V _{Qs_limit}Be respectively the output saturation value of d axle and q shaft current adjuster, L _sBe stator inductance, R _sBe stator phase resistance, ω _eBe synchronous angular velocity, σ is total leakage inductance coefficient, and k is the sampled point sequence number.Concrete technique effect of the present invention embodies as follows:

1) improves the current sample method, improved the current sample frequency, shortened the time of electric current prediction out of control;

2) improve the reliability of Current Control, effectively avoided the power device that causes owing to electric current is out of control and the damage of motor;

3) compare with existing software overcurrent protection, this method can realize overcurrent protection faster, and can reduce the misoperation cause owing to disturbing;

4) compare with existing hardware overcurrent protection, can reach similar rapidity, and save hardware cost;

5) this method is considered degree of saturation and the voltage margin of current regulator, and is more accurate to the judgement that electric current is out of control.

In sum, the present invention considers the electrical characteristic of current regulator degree of saturation, voltage use nargin and motor self, provided the Forecasting Methodology that electric current may be out of control, significantly lifting motor and drive unit reliability of operation are avoided the power device or the motor damage that cause owing to overcurrent.

Description of drawings

Fig. 1 is vector control current regulator block diagram;

Fig. 2 is current sample method of the present invention, and Fig. 2 (a) is the conventional current method of sampling, and Fig. 2 (b) is the method for sampling proposed by the invention;

Fig. 3 is the inventive method flow chart;

Fig. 4 uses Physical Experiment oscillogram of the present invention.

Embodiment

In the vector control system, the voltage under the d/q axle, electric current satisfy following relation:

V _ds＝i _dsR _s-i _qsσL _sω _e (1)

V _qs＝i _qsR _s+i _dsL _sω _e (2)

Wherein: R _s: the stator phase resistance; L _s: stator inductance; σ: total leakage inductance coefficient; i _Ds: the d shaft current; i _QsThe q shaft current; V _Ds: the d shaft voltage; V _Qs: the q shaft voltage; ω _e: synchronous angular velocity.

Formula (1) and (2) illustrate between d/q shaft current and the voltage and have cross-couplings, therefore, the conventional employed pi regulator 1 of vector control and 2 is difficult to guarantee design bandwidth, its bandwidth descends along with the rising of power frequency, and with reference to formula (2), owing to the rising of back electromotive force along with frequency raises, current regulator 1 and 2 is easier to be saturated, thereby so that current regulator 1 and 2 regulating powers for electric current further descend, high-speed cruising district at induction machine, very easily cause electric current out of control in the quick respective process of electric current, even damage drive unit and motor.

For fear of the damage of the power device that causes owing to electric current is out of control and motor, the present invention proposes a kind of electric current based on vector control Forecasting Methodology out of control.

If the output saturation value of current regulator 1 is V _{Qa_limit}, the output saturation value of current regulator 2 is V _{Ds_limit}, current d/q shaft voltage is V _Ds(k) and V _Qs(k), then according to formula (1) and formula (2), obtain:

V _{ds_limit}-V _ds(k)＝Δi′ _dsR _s-Δi′ _qsσL _sω _e (3)

V _{qs_limit}-V _qs(k)＝Δi′ _qsR _s+Δi′ _dsL _sω _e (4)

Wherein: Δ i ' _Ds: the d shaft current allows excursion; Δ i ' _Qs: the q shaft current allows excursion.

According to formula (3) and (4), can obtain Δ i ' _DsWith Δ i ' _Qs:

$\mathrm{\Δ}{i}_{\mathrm{ds}}^{\′}=\frac{{\mathrm{\σL}}_s{R}_s{\mathrm{\ω}}_e\mathrm{\Δ}{V}_{\mathrm{qs}}+(1-\mathrm{\σ}{L}_s^2{\mathrm{\ω}}_e^2)\mathrm{\Δ}{V}_{\mathrm{ds}}}{R_s^3+{\mathrm{\σL}}_s^2{R}_s{\mathrm{\ω}}_e^2}---\left(5\right)$

${\mathrm{\Δi}}_{\mathrm{qs}}^{\′}=\frac{R_s\mathrm{\Δ}{V}_{\mathrm{qs}}-L_s{\mathrm{\ω}}_e\mathrm{\Δ}{V}_{\mathrm{ds}}}{R_s^2+{\mathrm{\σL}}_s^2{\mathrm{\ω}}_e^2}---\left(6\right)$

Wherein, Δ V _Ds=V _{Ds_limit}-V _Ds(k), Δ V _Qs=V _{Qs_limit}-V _Qs(k)

Conventional current sample is shown in Fig. 2 (a), underflow in each PWM (pulse width modulation) cycle starts the AD conversion constantly, each PWM periodic sampling once, perhaps at underflow and the middle point sampling in each PWM cycle, twice of each PWM periodic sampling.The speed of the operational capability of this method considering processor and AD conversion, single PWM cycle is divided into several less sampling and computing cycles, shown in Fig. 2 (b), the conversion speed of considering processor and AD converter part, the PWM cycle is divided into N (N 〉=1) individual sampling and the change-over period, can significantly improves system to the response speed of overcurrent by this method of sampling.

If a phase current that obtains by Fig. 2 (b) sampling is i _As, the b phase current is i _Bs, the c phase current can obtain by following formula:

i _cs＝-i _as-i _bs (7)

By coordinate transform, be converted to the d/q shaft current:

Wherein,

Be the anglec of rotation of rotor field, can obtain by the field orientation algorithm.Given in conjunction with current regulator d/q shaft current can get:

$\mathrm{\Δ}{i}_{\mathrm{ds}}=i_{\mathrm{ds}}^{*}-i_{\mathrm{ds}}---\left(9\right)$

$\mathrm{\Δ}{i}_{\mathrm{qs}}=i_{\mathrm{qs}}^{*}-i_{\mathrm{qs}}---\left(10\right)$

Be d shaft current set-point,

Be q shaft current set-point,

According to motor electric parameter and motor model, calculate d shaft current permission variation range delta i ' under the current voltage nargin _DsAllow variation range delta i ' with the q shaft current _Qs,

If Y _d=| Δ i _Ds|-| Δ i ' _Ds|-Δ d (11)

Y _q＝|Δi _qs|-|Δi′ _qs|-Δq (12)

Δ d is d shaft current threshold values out of control, and Δ q is q shaft current threshold values out of control.

If Y _d＜0 d shaft current may be out of control, if Y _q＜0 q shaft current may be out of control.Regulate the sensitivity that d/q shaft current threshold values Δ d out of control and Δ q can change this method of discrimination, Δ d and Δ q are less, and sensitivity is higher, otherwise then sensitivity is lower.

Because have cross-couplings between the d/q shaft current, shown in (1) and formula (2), therefore, the meeting out of control of d axle or q shaft current influences each other, and therefore, increases by two weight coefficient λ _dAnd λ _q, then have:

Y _dq＝λ _dY _d+λ _qY _2q (13)

And 0＜λ _d≤ 1,0＜λ _q≤ 1.

Under the different operating modes, design different λ _dAnd λ _q, then through type (13) is obtained Y _DqIf, Y _Dq＜0, but then the decision-making system current regulator may be out of control, and then can boot make corresponding measure.

Algorithm realization flow figure as shown in Figure 3.According to the susceptibility requirement, Δ d and Δ q are set; Any biphase current that utilizes transducer to obtain, through type (7) calculates another phase current, and then through type (8) obtains the d/q shaft current; Δ i is calculated in through type (9) and (10) _DsWith Δ i _QsThrough type (3) and formula (4) are calculated Δ i ' _DsAnd Δ ' i _QsThrough type (11) and formula (12) are calculated Y _dAnd Y _qDifferent according to operating mode, different weight λ is set _dAnd λ _q, and then according to formula (13) calculating Y _Dq, according to Y _DqSize judge whether electric current can be out of control.

Fig. 4 is the physical results.In this physical test, for the validity of verification algorithm, when out-of-control signal provides, control program is not taked treatment measures, and the result causes current of electric further to be dispersed, if take certain measure when out-of-control signal provides, for example carry out tube sealing, then can avoid further dispersing of electric current.

Those skilled in the art will readily understand; the above only is preferred embodiment of the present invention; not in order to limiting the present invention, all any modifications of doing within the spirit and principles in the present invention, be equal to and replace and improvement etc., all should be included within protection scope of the present invention.

Claims (3)

1. induction machine electric current Forecasting Methodology out of control based on vector control is specially:

In single PWM cycle biphase current is repeatedly sampled, sample rate current is carried out the d/q decoupler shaft, obtain d shaft current i _DsWith q shaft current i _Qs

Calculate d shaft current i _DsWith d shaft current set-point Between deviation delta i _Ds, q shaft current i _QsWith q shaft current set-point

Between deviation delta i _Qs

According to motor electric parameter and motor model, to calculate under the current voltage nargin, the d shaft current allows variation range delta i ' _DsAllow variation range delta i ' with the q shaft current _Qs

Calculate | Δ i _Ds| with | Δ i ' _Ds| between difference DELTA id, and | Δ i _Qs| and | Δ i ' _Qs| between difference DELTA i _q

If difference DELTA i _dLess than d shaft current threshold values Δ out of control d, illustrate that then the d shaft current is out of control, if difference DELTA i _qLess than q shaft current threshold values Δ out of control q, illustrate that then the q shaft current is out of control.

2. induction machine electric current according to claim 1 Forecasting Methodology out of control is characterized in that, also calculates synthetic determination value Y _Dq=λ _d(Δ i _d-Δ d)+λ _q(Δ i _q-Δ q), 0＜λ _d≤ 1,0＜λ _q≤ 1, if Y _Dq＜0, illustrate that then current regulator is out of control.

3. induction machine electric current according to claim 1 and 2 Forecasting Methodology out of control is characterized in that, the d shaft current allows variation range delta i ' _DsAllow variation range delta i ' with the q shaft current _QsComputational methods be:

${\mathrm{\Δi}}_{\mathrm{ds}}^{\′}=\frac{\mathrm{\σ}{L}_s{R}_s{\mathrm{\ω}}_e{\mathrm{\ΔV}}_{\mathrm{qs}}+(1-\mathrm{\σ}{L}_s^2{\mathrm{\ω}}_e^2){\mathrm{\ΔV}}_{\mathrm{ds}}}{R_s^3+{\mathrm{\σL}}_s^2{R}_s{\mathrm{\ω}}_e^2},$ ${\mathrm{\Δi}}_{\mathrm{qs}}^{\′}=\frac{R_s{\mathrm{\ΔV}}_{\mathrm{qs}}-L_s{\mathrm{\ω}}_e{\mathrm{\ΔV}}_{\mathrm{ds}}}{R_s^2+{\mathrm{\σL}}_s^2{\mathrm{\ω}}_e^2},$

Wherein, Δ V _Ds=V _{Ds_limit}-V _Ds(k), Δ V _Qs=V _{Qs_limit}-V _Qs(k),

V _Ds(k) and V _Qs(k) be respectively d axle and the q shaft voltage of k sampled point, V _{Ds_limit}And V _{Qs_limit}Be respectively the output saturation value of d axle and q shaft current adjuster, L _sBe stator inductance, R _sBe stator phase resistance, ω _eBe synchronous angular velocity, σ is total leakage inductance coefficient, and k is the sampled point sequence number.

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