CN105406790A - Frequency converter three-resistance current sampling method based on current prediction - Google Patents

Abstract

The invention provides a frequency converter three-resistance current sampling method based on current prediction. In each PWM (Pulse-Width Modulation) period, current closed loop PID (Proportion Integration Differentiation) control and SVGEN modulation are performed, and PWM comparison values T<1>, T<2> and T<3> of three phases A, B and C are obtained; the sizes of the T<1>, the T<2> and the T<3> and the shortest time T<min> required by complete sampling are compared in real time; and different current obtaining modes are used according to different size relationships. The method provided by the invention solves the problem that the three-phase current cannot be accurately sampled due to zero-voltage vector duration insufficiency at a high modulation ratio of the conventional three-resistance sampling technology of a three-phase frequency converter. The wide region current closed loop control under the three-resistance sampling can be realized; the modulation ratio is improved; the motor load capability is improved; the cost is low; and the sampling is simple and reliable.

Description

Based on the frequency converter three resistor current method of sampling of current forecasting

Technical field

The present invention relates to electrical engineering technical field, particularly, relate to a kind of frequency converter three resistor current method of sampling based on current forecasting.

Background technology

Within 1971, German scholar F.Blaschke proposes alternating current machine principle of vector control, and vector control is used to rapidly in engineer applied with the superiority of himself, and the important indicator affecting motor vector control is electric machine phase current.Use the three-phase current of Hall element sample motor, use simple, but its cost is higher; For reducing costs, scholar utilizes DC bus current list resistance sampling, reconstruct electric machine phase current, and its method is complicated, and there is non-viewing district; Also there is brachium pontis under three-phase inverter to connect three resistance samplings, but there is the problem that high modulation cannot sample than some phase lower.

Beijing Information Science & Technology University's journal (natural science edition) the 1st phase 28 volume 18-21 page in 2013, " door-inverter three resistor current sampling and synthetic method ", for some low cost application scenario, proposes three resistor current sample modes of brachium pontis under door-inverter.Electric automatization the 1st phase 36 volume 64-66 page in 2014, " realization of low capacity frequency converter three resistance sampling electric current synthetic method " describes three resistance sampling implementations of low capacity frequency converter.AppliedPowerElectronicsConference meeting 1701-1706 page in 2007, " ACurrentReconstructionSchemeforLow-CostPMSMDrivesUsingSh untResistors " describe a kind of low cost PMSM drive three resistance sampling technology, utilization state observer realize high modulation than under electric current reconstructing.

Above-mentioned article " sampling of door-inverter three resistor current and synthetic method " and " realization of low capacity frequency converter three resistance sampling electric current synthetic method ", although propose the implementation of three resistance samplings, but the problem cannot do not sampled than some phase that lower zero vector time deficiency causes for high modulation makes analysis and research, can not meet the needs that real electrical machinery controls." ACurrentReconstructionSchemeforLow-CostPMSMDrivesUsingSh untResistors " is although analyze three resistance sampling Problems existing and study, and utilization state observer realizes the motor current reconstruction in wide region, but can only be used on PMSM motor (permagnetic synchronous motor), and not be suitable for ACIM motor (AC induction motor).

Summary of the invention

The present invention is directed to three phase converter tradition three resistance sampling technology Problems existing, namely there will be under high modulation ratio that Zero voltage vector duration deficiency causes cannot the problem of accurate sampling three-phase electric current, a kind of frequency converter three resistor current method of sampling based on current forecasting is provided, requires that the wide zone current closed-loop vector of some equipment such as lower asynchronous machine controls to realize low cost.

For realizing above object, the invention provides a kind of frequency converter three resistor current method of sampling based on current forecasting, in each PWM cycle, being controlled by current closed-loop PID and after SVGEN modulation, obtaining A, B, C three-phase PWM comparison value T ₁, T ₂and T ₃, three comparison values represent brachium pontis switch conduction times under inverter A, B, C three-phase respectively, compare T in real time ₁, T ₂and T ₃with the required shortest time T that samples completely _minsize, and according to different magnitude relationship, take different electric current acquisition patterns; Wherein:

As three-phase PWM comparison value T ₁, T ₂and T ₃in, there is a value and be less than the required shortest time T of sampling completely _mintime, resistance sampling electric current only has two-phase effective, utilizes motor three-phase current sum to be 0 to be reconstructed an other phase motor, after obtaining effective three phase electric machine current value, is realized the closed-loop current control of motor by Clark and Park conversion;

As three-phase PWM comparison value T ₁, T ₂and T ₃in, there are two values and be less than the required shortest time T of sampling completely _mintime, resistance sampling electric current only has a phase effective, carries out discretization, obtains current forecasting model, utilized the stator current i of current control period by this model to the state equation of asynchronous machine _sd(k), i _sqk () dopes the stator current i of next control cycle _sd(k+1), i _sq, and use stator current i (k+1) _sd(k+1), i _sq(k+1) closed-loop current control of motor is realized.

Further, described according to different magnitude relationship, take different electric current acquisition patterns, be specially:

For convenience of representing, replace three comparison value T respectively with X, Y, Z ₁, T ₂and T ₃, and making X≤Y≤Z, definition motor three-phase current is i _a, i _band i _c, direction outflow motor is just; Corresponding inverter three-phase sample rate current is defined as i _{a_m}, i _{b_m}and i _{c_m}, it is just that direction flows to DC negative pole;

(I) X>=T _min, represent in the Zero voltage vector duration, accurately can complete the sampling of three-phase current; Pass through i _a=i _{a_m}, i _b=i _{b_m}and i _c=i _{c_m}, Synthetic motor three-phase current, after Clark and Park conversion, obtains the stator current i under d-q coordinate system needed for closed loop _sd, i _sq;

(II) X<T _min, Y>=T _min, represent in the Zero voltage vector duration, accurately can only complete the sampling of biphase current; Comprising following situation:

A () works as T ₁<T _min, T ₂, T ₃>T _mintime, B, C two-phase inverter current sample is accurate, there is i _b=i _{b_m}, i _c=i _{c_m}; By formula (1), obtain motor A phase current i _aas follows:

i _a＝-i _b-i _c＝-(i _{b_m}+i _{c_m})(1)

B () works as T ₂<T _min, T ₁, T ₃>T _mintime, A, C two-phase inverter current sample is accurate, has:

$\left\{\begin{array}{c}{i}_a=i_{a\_m}\\ i_c=i_{c\_m}\\ i_b=-(i_{a\_m}+i_{c\_m})\end{array}\right.---\left(2\right)$

C () works as T ₃<T _min, T ₁, T ₂>T _mintime, A, B two-phase inverter current sample is accurate, has:

$\left\{\begin{array}{c}{i}_a=i_{a\_m}\\ i_b=i_{b\_m}\\ i_c=-(i_{a\_m}+i_{b\_m})\end{array}\right.---\left(3\right)$

According to formula (1), (2), (3) Synthetic motor three-phase current, after Clark and Park conversion, obtain the stator current i under d-q coordinate system needed for closed loop _sd, i _sq;

(III) X<T _min, Y<T _min, Z>=T _minrepresent in the Zero voltage vector duration, accurately can only complete the sampling of a phase current, now utilize the voltage in current control period, electric current and tachometer value, the stator current i under current forecasting model obtains the d-q coordinate system that in next control cycle, closed loop needs _sd, i _sq, current forecasting model is as follows:

$\begin{array}{c}{i}_{sd}(k+1)=(1-\frac{R_s{T}_s}{{\mathrm{\&sigma;L}}_s})i_{sd}\left(k\right)+{\mathrm{\&omega;}}_1\left(k\right)T_s{i}_{sq}\left(k\right)+\frac{T_s}{{\mathrm{\&sigma;L}}_s}{u}_{sd}\left(k\right)\\ i_{sq}(k+1)=-{\mathrm{\&omega;}}_1\left(k\right)T_s{i}_{sd}\left(k\right)-\frac{L_m^2\mathrm{\&omega;}\left(k\right)T_s}{{\mathrm{\&sigma;L}}_s{L}_r}{i}_{sd}\left(k\right)+(1-\frac{R_s{L}_r^2+R_r{L}_m^2}{{\mathrm{\&sigma;L}}_s{L}_r^2}{T}_s)i_{sq}\left(k\right)+\frac{T_s}{{\mathrm{\&sigma;L}}_s}{u}_{sq}\left(k\right)\end{array}---\left(4\right)$

In formula: T _sfor system communication cycle, σ is motor flux leakage coefficient, σ=1-L _m ²/ L _sl _r; R _sfor stator resistance, R _rfor rotor resistance, L _mfor motor mutual inductance, L _sfor stator inductance, L _rfor inductor rotor, i _sd, i _sqbe respectively stator current direct axis component and quadrature axis component under rotating coordinate system, u _sd, u _sqbe respectively stator voltage direct axis component and quadrature axis component under rotating coordinate system, ω ₁motor in synchrony rotating speed and rotor speed is respectively with ω.

Compared with prior art, the present invention has following beneficial effect:

There will be under the invention solves the high modulation ratio that three phase converter tradition three resistance sampling technology exist that Zero voltage vector duration deficiency causes cannot the problem of accurate sampling three-phase electric current, wide zone current closed-loop control under can realizing three resistance samplings, improve modulation ratio, increase motor load ability, cost is low, sampling is simple, reliably.

Accompanying drawing explanation

By reading the detailed description done non-limiting example with reference to the following drawings, other features, objects and advantages of the present invention will become more obvious:

Fig. 1 is based on two general level converter three resistance sampling circuits;

Fig. 2 is the control flow chart of one embodiment of the invention.

Embodiment

Below in conjunction with specific embodiment, the present invention is described in detail.Following examples will contribute to those skilled in the art and understand the present invention further, but not limit the present invention in any form.It should be pointed out that to those skilled in the art, without departing from the inventive concept of the premise, some distortion and improvement can also be made.These all belong to protection scope of the present invention.

In one embodiment of this invention: based on two general level converter three resistance sampling circuits (as shown in Figure 1), provide a kind of frequency converter three resistor current method of sampling based on current forecasting, its control flow as shown in Figure 2:

In each PWM cycle, controlled by current closed-loop PID and after SVGEN modulation, obtain A, B, C three-phase PWM comparison value T ₁, T ₂and T ₃, three comparison values represent the ON time of brachium pontis switch under inverter A, B, C three-phase respectively, for convenience of representing, representing three comparison values respectively, and have X≤Y≤Z with X, Y, Z; Compare X, Y, Z in real time and the required shortest time T that samples completely _minsize, and according to different magnitude relationship, take different electric current acquisition patterns, concrete:

(I) X>=T _min, represent in the Zero voltage vector duration, accurately can complete the sampling of three-phase current, pass through i _a=i _{a_m}, i _b=i _{b_m}and i _c=i _{c_m}, Synthetic motor three-phase current, after Clark and Park conversion, obtains the stator current i under d-q coordinate system needed for closed loop _sd, i _sq;

(II) X<T _min, Y>=T _min, represent in the Zero voltage vector duration, accurately can only complete the sampling of biphase current; Comprising following several situation:

A () works as T ₁<T _min, T ₂, T ₃>T _mintime, B, C two-phase inverter current sample is accurate, there is i _b=i _{b_m}, i _c=i _{c_m}; By formula (1), obtain motor A phase current i _aas follows:

i _a＝-i _b-i _c＝-(i _{b_m}+i _{c_m})(1)

B () works as T ₂<T _min, T ₁, T ₃>T _mintime, A, C two-phase inverter current sample is accurate, has:

$\left\{\begin{array}{c}{i}_a=i_{a\_m}\\ i_c=i_{c\_m}\\ i_b=-(i_{a\_m}+i_{c\_m})\end{array}\right.---\left(2\right)$

C () works as T ₃<T _min, T ₁, T ₂>T _mintime, A, B two-phase inverter current sample is accurate, has:

$\left\{\begin{array}{c}{i}_a=i_{a\_m}\\ i_b=i_{b\_m}\\ i_c=-(i_{a\_m}+i_{b\_m})\end{array}\right.---\left(3\right)$

According to formula (1), (2), (3) Synthetic motor three-phase current, after Clark and Park conversion, obtain the stator current i under d-q coordinate system needed for closed loop _sd, i _sq;

(III) X<T _min, Y<T _min, Z>=T _min, represent in the Zero voltage vector duration, accurately can only complete the sampling of a phase current, now utilize the voltage in current control period, electric current and tachometer value, obtain through current forecasting model (shown in formula 4) i that in next control cycle, closed loop needs _sd, i _sq:

$\begin{array}{c}{i}_{sd}(k+1)=(1-\frac{R_s{T}_s}{{\mathrm{\&sigma;L}}_s})i_{sd}\left(k\right)+{\mathrm{\&omega;}}_1\left(k\right)T_s{i}_{sq}\left(k\right)+\frac{T_s}{{\mathrm{\&sigma;L}}_s}{u}_{sd}\left(k\right)\\ i_{sq}(k+1)=-{\mathrm{\&omega;}}_1\left(k\right)T_s{i}_{sd}\left(k\right)-\frac{L_m^2\mathrm{\&omega;}\left(k\right)T_s}{{\mathrm{\&sigma;L}}_s{L}_r}{i}_{sd}\left(k\right)+(1-\frac{R_s{L}_r^2+R_r{L}_m^2}{{\mathrm{\&sigma;L}}_s{L}_r^2}{T}_s)i_{sq}\left(k\right)+\frac{T_s}{{\mathrm{\&sigma;L}}_s}{u}_{sq}\left(k\right)\end{array}---\left(4\right)$

In formula: T _sfor system communication cycle, σ is motor flux leakage coefficient, σ=1-L _m ²/ L _sl _r; R _sfor stator resistance, R _rfor rotor resistance, L _mfor motor mutual inductance, L _sfor stator inductance, L _rfor inductor rotor, i _sd, i _sqbe respectively stator current direct axis component and quadrature axis component under rotating coordinate system, u _sd, u _sqbe respectively stator voltage direct axis component and quadrature axis component under rotating coordinate system, ω ₁motor in synchrony rotating speed and rotor speed is respectively with ω.

In the present invention, current forecasting model (formula 4) is based on ACIM, is therefore applicable to ACIM asynchronous induction machine.But similar, utilize same thought, PMSM motor mathematical model discretization is obtained current forecasting model, be applicable to three resistance sampling strategies of PMSM motor equally.

The present embodiment is through verification experimental verification, and result meets expection; In test, non-synchronous motor parameter is as follows:

Stator resistance R _sbe 1.2 Ω, rotor resistance R _rbe 1.22 Ω, motor mutual inductance L _mfor 71.33e-3H, stator inductance L _sfor 78.86e-3H, inductor rotor L _rfor 78.86e-3H, motor number of pole-pairs is 2, and rated power is 1.5kW, and rated speed is 1500rpm; The rotational speed setup arranging motor is rated speed, and load torque is 9.55N.m (namely motor full power 1.5kW exports).

Test is verified by three aspects: 1) use actual motor current (accurately being obtained by current sensor) to carry out closed-loop vector control.Export the three phase electric machine resultant current under novel three resistance sampling technology, contrast with actual motor current, its current error is maximum only has 0.290A.Show that motor resultant current and the actual current of novel three resistance sampling technology acquisitions are very close.2) the motor resultant current using novel three resistance sampling technology to obtain carries out closed-loop vector control.Resultant current and actual motor current are contrasted, its current error is maximum only has 0.363A, and show that novel three resistance sampling technology have reasonability, control effects is good.3) use described in based on after the novel three resistance sampling methods of current forecasting, motor run can stable operation in rated condition, namely rotating speed is 1500rpm, and torque is 9.55N.m, now motor modulation ratio is 1, increases than the modulation ratio of traditional three resistance samplings.For investigating the impact of current prediction method on electric machine phase current waveform further, respectively to 1) and 2) A phase current of electric under two kinds of control modes carries out fft analysis.When using actual motor current to do closed-loop control, fundamental voltage amplitude is 12.03A, THD is 3.21%; When using novel three resistance sampling technology Synthetic motor electric currents to do closed-loop control, fundamental voltage amplitude is 11.89A, THD is 4.53%, and both only have 0.14A at fundamental voltage amplitude error, shows the correctness of the three resistance sampling strategies based on current forecasting.

From experimental result, use that of the present invention current of electric THD only increases to 4.53% based on after the frequency converter three resistor current method of sampling of current forecasting, motor operating state is good, and Absorbable organic halogens is at given state; Compared with traditional three resistance sampling modes, in test, modulation ratio increases to 1 from 0.82, and maximum (top) speed and the carrying load ability of motor all increase.Result describes the correctness of theory analysis, and current forecasting is to the feasibility solving traditional three resistance sampling problems.

Above specific embodiments of the invention are described.It is to be appreciated that the present invention is not limited to above-mentioned particular implementation, those skilled in the art can make various distortion or amendment within the scope of the claims, and this does not affect flesh and blood of the present invention.

Claims (2)

1. based on a frequency converter three resistor current method of sampling for current forecasting, it is characterized in that, in each PWM cycle, controlled by current closed-loop PID and after SVGEN modulation, obtain A, B, C three-phase PWM comparison value T ₁, T ₂and T ₃, compare T in real time ₁, T ₂and T ₃with the required shortest time T that samples completely _minsize, and according to different magnitude relationship, take different electric current acquisition patterns; Wherein:

As three-phase PWM comparison value T ₁, T ₂and T ₃in, there is a value and be less than the required shortest time T of sampling completely _mintime, resistance sampling electric current only has two-phase effective, utilizes motor three-phase current sum to be 0 to be reconstructed an other phase motor, after obtaining effective three phase electric machine current value, is realized the closed-loop current control of motor by Clark and Park conversion;

As three-phase PWM comparison value T ₁, T ₂and T ₃in, there are two values and be less than the required shortest time T of sampling completely _mintime, resistance sampling electric current only has a phase effective, carries out discretization, obtains current forecasting model, utilized the stator current i of current control period by this model to the state equation of asynchronous machine _sd(k), i _sqk () dopes the stator current i of next control cycle _sd(k+1), i _sq, and use stator current i (k+1) _sd(k+1), i _sq(k+1) closed-loop current control of motor is realized.

2. a kind of frequency converter three resistor current method of sampling based on current forecasting according to claim 1, is characterized in that, described according to different magnitude relationship, takes different electric current acquisition patterns, is specially:

For convenience of representing, replace three comparison value T respectively with X, Y, Z ₁, T ₂and T ₃, and making X≤Y≤Z, definition motor three-phase current is i _a, i _band i _c, direction outflow motor is just; Corresponding inverter three-phase sample rate current is defined as i _{a_m}, i _{b_m}and i _{c_m}, it is just that direction flows to DC negative pole;

(I) X>=T _min, represent in the Zero voltage vector duration, accurately can complete the sampling of three-phase current; Pass through i _a=i _{a_m}, i _b=i _{b_m}and i _c=i _{c_m}, Synthetic motor three-phase current, after Clark and Park conversion, obtains the stator current i under d-q coordinate system needed for closed loop _sd, i _sq;

(II) X<T _min, Y>=T _min, represent in the Zero voltage vector duration, accurately can only complete the sampling of biphase current; Comprising following situation:

A () works as T ₁<T _min, T ₂, T ₃>T _mintime, B, C two-phase inverter current sample is accurate, there is i _b=i _{b_m}, i _c=i _{c_m}; By formula (1), obtain motor A phase current i _aas follows:

i _a＝-i _b-i _c＝-(i _{b_m}+i _{c_m})(1)

B () works as T ₂<T _min, T ₁, T ₃>T _mintime, A, C two-phase inverter current sample is accurate, has:

$\left\{\begin{array}{c}{i}_a=i_{a\_m}\\ i_c=i_{c\_m}\\ i_b=-(i_{a\_m}+i_{c\_m})\end{array}\right.---\left(2\right)$

C () works as T ₃<T _min, T ₁, T ₂>T _mintime, A, B two-phase inverter current sample is accurate, has:

$\left\{\begin{array}{c}{i}_a=i_{a\_m}\\ i_b=i_{b\_m}\\ i_c=-(i_{a\_m}+i_{b\_m})\end{array}\right.---\left(3\right)$

According to formula (1), (2), (3) Synthetic motor three-phase current, after Clark and Park conversion, obtain the stator current i under d-q coordinate system needed for closed loop _sd, i _sq;

(III) X<T _min, Y<T _min, Z>=T _minrepresent in the Zero voltage vector duration, accurately can only complete the sampling of a phase current, now utilize the voltage in current control period, electric current and tachometer value, the stator current i under current forecasting model obtains the d-q coordinate system that in next control cycle, closed loop needs _sd, i _sq, current forecasting model is as follows:

$\begin{array}{c}{i}_{sd}(k+1)=(1-\frac{R_s{T}_s}{{\mathrm{\&sigma;L}}_s})i_{sd}\left(k\right)+{\mathrm{\&omega;}}_1\left(k\right)T_s{i}_{sq}\left(k\right)+\frac{T_s}{{\mathrm{\&sigma;L}}_s}{u}_{sd}\left(k\right)\\ i_{sq}(k+1)=-{\mathrm{\&omega;}}_1\left(k\right)T_s{i}_{sd}\left(k\right)-\frac{L_m^2\mathrm{\&omega;}\left(k\right)T_s}{{\mathrm{\&sigma;L}}_s{L}_r}{i}_{sd}\left(k\right)+(1-\frac{R_s{L}_r^2+R_r{L}_m^2}{{\mathrm{\&sigma;L}}_s{L}_r^2}{T}_s)i_{sq}\left(k\right)+\frac{T_s}{{\mathrm{\&sigma;L}}_s}{u}_{sq}\left(k\right)\end{array}---\left(4\right)$

In formula: T _sfor system communication cycle, σ is motor flux leakage coefficient, σ=1-L _m ²/ L _sl _r; R _sfor stator resistance, R _rfor rotor resistance, L _mfor motor mutual inductance, L _sfor stator inductance, L _rfor inductor rotor, i _sd, i _sqbe respectively stator current direct axis component and quadrature axis component under rotating coordinate system, u _sd, u _sqbe respectively stator voltage direct axis component and quadrature axis component under rotating coordinate system, ω ₁motor in synchrony rotating speed and rotor speed is respectively with ω.