CN103595324B - A kind of mixed excitation electric machine field weakening control method - Google Patents

Abstract

The invention discloses a kind of mixed excitation electric machine field weakening control method, when motor speed is higher than rated speed, motor enters invariable power district, weak magnetic algorithm is now adopted to improve motor speed further, concrete grammar is: ignore armature resistance, and keeping motor synthesis back electromotive force constant is motor terminal voltage maximum, utilizes exciting current to weaken air-gap flux and carries out motor raising speed, distribute armature supply and exciting current accordingly, motor torque fan-out capability can be improved.The inventive method can realize mixed excitation electric machine high speed wide speed regulating range and run, and effectively improves the torque output capability of motor simultaneously, has a good application prospect in the straight drive system of Wheel hub for electric automobile formula.

Description

A kind of mixed excitation electric machine field weakening control method

Technical field

The present invention relates to a kind of mixed excitation electric machine field weakening control method, belong to electric machines control technology.

Background technology

Permanent magnet motor has that structure is simple, power density is high, torque mass ratio is large and efficiency advantages of higher, but the main air-gap field of permanent magnet motor is produced by the permanent magnet be arranged on rotor or stator, is difficult to regulate in motor operation course.Mixed excitation electric machine has two kinds of excitation sources, and one is permanent magnet, and another kind is electric excitation, has very strong flux control ability; The exciting current passing into forward in the electric motor starting stage produces positive electromagnetic torque can increase electric motor starting torque, passes into reverse exciting current and effectively can improve motor weak magnetic speed-up ability during high-speed cruising.Mixed excitation electric machine has the advantage of the large and speed-regulating range width of Driving Torque compared to permanent magnet motor, has a good application prospect in the straight drive system of Wheel hub for electric automobile formula.

Current mixed excitation electric machine mostly adopts the vector control algorithm based on zonal control, it is permanent torque district below rated speed, more than rated speed be invariable power district, invariable power district takes to keep q axle back-emf to be the control strategy of steady state value more, utilizes the weak magnetic of DC excitation electric current; Utilize the method for the weak magnetic of d shaft current compared to common permagnetic synchronous motor, adopt the mixed excitation electric machine of such algorithm to have wider speed adjustable range.But the cost of weak magnetic speed-raising is the carrying load ability of sacrificing motor, along with the rising of rotating speed, the torque output capability inverse ratio of motor declines.

In practical application, electric motor car travels rear cell voltage for a long time and declines to a great extent, and can reduce the velocity interval in permanent torque district; In addition, when load is larger, the forward exciting current of increase can produce extra back-emf, can reduce permanent torque district velocity interval equally; On the other hand, in high speed weak magnetic area, when load is less, d axle back-emf is also relatively little, traditional maintenance q axle back-emf is now adopted to be the current weighting algorithm of steady state value, can guarantee that synthesis back-emf is no more than DC bus-bar voltage, but when load is larger, d axle back-emf can significantly increase, and uses this algorithm to there will be comparatively big error.

Summary of the invention

Goal of the invention: in order to overcome the deficiencies in the prior art, the invention provides a kind of mixed excitation electric machine field weakening control method, takes to keep synthesizing the weak magnetics detect strategy that back-emf is steady state value, realizes the object that mixed excitation electric machine high-speed wide-region runs.

Technical scheme: for achieving the above object, the technical solution used in the present invention is:

A kind of mixed excitation electric machine field weakening control method, when motor speed is higher than rated speed, motor enters invariable power district, weak magnetic algorithm is now adopted to improve motor speed further, concrete grammar is: ignore armature resistance, and keeping motor synthesis back electromotive force constant is motor terminal voltage maximum, utilizes exciting current to weaken air-gap flux and carries out motor raising speed, distribute armature supply and exciting current accordingly, motor torque fan-out capability can be improved.

The method specifically comprises the steps:

(1) when motor enters invariable power district, keeping motor synthesis back electromotive force constant is motor terminal voltage maximum, and armature supply and exciting current meet following formula:

$E_{\mathrm{back}}={\mathrm{\ω}}_e\sqrt{{({\mathrm{\ψ}}_{\mathrm{pm}}+M_{\mathrm{sf}}{i}_f+L_d{i}_d)}^2+{\left(L_q{i}_q\right)}^2}=U_{\max }---\left(1\right)$

Wherein, E _backfor motor synthesis back-emf, ω _efor motor angular rate, ψ _pmfor motor permanent magnet flux, M _sffor mutual inductance between armature winding and excitation winding, i _ffor exciting current, L _dfor d axle inductance, L _qfor q axle inductance, i _dfor the d axle component of armature supply, i _qfor the q axle component of armature supply, U _maxfor motor terminal voltage maximum.

(2) i _qfor the q axle component of armature supply, armature supply composite value can not overrate, makes i _d=0 can make armature supply have larger torque component; On the other hand, for salient pole machine, reverse d shaft current can produce negative reluctance torque, reduces the fan-out capability of motor torque; Therefore, for make armature supply torque component as far as possible Datong District time avoid occurring negative reluctance torque, keep i _d=0, utilize exciting current to carry out weak magnetic speed-up, motor torque T _ecalculated by following formula:

$T_e=\frac{3}{2}{\mathrm{pi}}_q({\mathrm{\ψ}}_{\mathrm{pm}}+M_{\mathrm{sf}}{i}_f)---\left(2\right)$

Wherein, p is motor number of pole-pairs;

(3) under the prerequisite being no more than respective rated value, the i of formula (1) will be met _qand i _fsubstitution formula (2), tries to achieve T _efor armature supply set-point corresponding during maximum and exciting current set-point are:

$\left\{\begin{array}{c}{i}_{\mathrm{fref}}=\frac{{\mathrm{\ψ}}_{\mathrm{pm}}-\frac{U_{\max }}{\sqrt{2}{\mathrm{\ω}}_e}}{M_{\mathrm{sf}}}\\ i_{\mathrm{dref}}=0\\ i_{\mathrm{qref}}=\frac{U_{\max }}{\sqrt{2}{\mathrm{\ω}}_e{L}_q}\end{array}\right.---\left(3\right)$

Using the armature supply set-point arrived calculated and exciting current set-point as the controlled quentity controlled variable of mixed excitation electric machine.

Beneficial effect: mixed excitation electric machine field weakening control method provided by the invention, for mixed excitation electric machine own structural characteristics, takes to keep synthesizing the weak magnetics detect strategy that back-emf is steady state value, achieves the object that mixed excitation electric machine high-speed wide-region runs; Q axle back-emf is kept to be the algorithm of steady state value compared to tradition, the drive system of one's duty A Ming has higher control precision and stability, weak magnetic area is that optimization aim formulates Current Assignment Strategy with Driving Torque, improves torque output capability during high speed operation of motor.

Accompanying drawing explanation

Fig. 1 is control system block diagram of the present invention;

Fig. 2 is torque-excitation current waveform;

Fig. 3 is torque-speed waveform.

Embodiment

Below in conjunction with accompanying drawing, the present invention is further described.

A kind of mixed excitation electric machine field weakening control method, when motor speed is higher than rated speed, motor enters invariable power district, weak magnetic algorithm is now adopted to improve motor speed further, concrete grammar is: ignore armature resistance, and keeping motor synthesis back electromotive force constant is motor terminal voltage maximum, utilizes exciting current to weaken air-gap flux and carries out motor raising speed, distribute armature supply and exciting current accordingly, motor torque fan-out capability can be improved.

Be illustrated in figure 1 based on control system block diagram of the present invention, this system is made up of main circuit, testing circuit and control circuit; Main circuit is made up of hidden pole type mixed excitation electric machine (HESM motor), PWM inverter, distributing switch, field regulator, exciter inverter; Testing circuit is made up of voltage, current sensor and incremental optical-electricity encoder.Position transducer detects the angular signal θ obtaining motor, and θ obtains motor actual speed n through differentiation element.Motor given rotating speed n _reftorque set-point T is obtained through PI link with actual speed n _ref.By T _refsend into distributing switch with n and calculate armature supply dq axle component set-point i _drefand i _qrefand exciting current set-point i _fref.Current sensor measurement A phase, B phase armature and exciting current actual value are respectively i _a, i _band i _freal, wherein i _aand i _barmature supply dq axle component actual value i is obtained through changes in coordinates _drealand i _qreal, by dq shaft current set-point i _drefand i _qrefwith respective actual value i _drealand i _qrealthree-phase duty cycle signals can be generated respectively through PI link, coordinate die change block and space vector module SVPWM, described three-phase duty cycle signals is acted on mixed excitation electric machine through three-phase inverter.Exciting current set-point i _frefwith actual value i _frealthe duty cycle signals generated by field regulator acts on mixed excitation electric machine through exciter inverter.

The main body of the inventive method is in lower distributing switch part, and our bright method can also be referred to as the operation principle of distributing switch, mainly comprises the following steps:

(1) when motor enters invariable power district, keeping motor synthesis back electromotive force constant is motor terminal voltage maximum, and armature supply and exciting current meet following formula:

$E_{\mathrm{back}}={\mathrm{\ω}}_e\sqrt{{({\mathrm{\ψ}}_{\mathrm{pm}}+M_{\mathrm{sf}}{i}_f+L_d{i}_d)}^2+{\left(L_q{i}_q\right)}^2}=U_{\max }---\left(1\right)$

Wherein, E _backfor motor synthesis back-emf, ω _efor motor angular rate, ψ _pmfor motor permanent magnet flux, M _sffor mutual inductance between armature winding and excitation winding, i _ffor exciting current, L _dfor d axle inductance, L _qfor q axle inductance, i _dfor the d axle component of armature supply, i _qfor the q axle component of armature supply, U _maxfor motor terminal voltage maximum.

(2) i _qfor the q axle component of armature supply, armature supply composite value can not overrate, makes i _d=0 can make armature supply have larger torque component; On the other hand, for salient pole machine, reverse d shaft current can produce negative reluctance torque, reduces the fan-out capability of motor torque; Therefore, for make armature supply torque component as far as possible Datong District time avoid occurring negative reluctance torque, keep i _d=0, utilize exciting current to carry out weak magnetic speed-up, motor torque T _ecalculated by following formula:

$T_e=\frac{3}{2}{\mathrm{pi}}_q({\mathrm{\ψ}}_{\mathrm{pm}}+M_{\mathrm{sf}}{i}_f)---\left(2\right)$

Wherein, p is motor number of pole-pairs;

(3) under the prerequisite being no more than respective rated value, the i of formula (1) will be met _qand i _fsubstitution formula (2), tries to achieve T _efor armature supply set-point corresponding during maximum and exciting current set-point, be specially:

I is obtained by formula (1) _qexpression formula be:

$i_q=\frac{\sqrt{{\left(\frac{U_{\max }}{{\mathrm{\ω}}_e}\right)}^2-{({\mathrm{\ψ}}_{\mathrm{pm}}+M_{\mathrm{sf}}{i}_f)}^2}}{L_q}---\left(3\right)$

By i _qexpression formula bring formula (2) into, obtain T _eexpression formula be:

$T_e=\frac{3}{2}p({\mathrm{\ψ}}_{\mathrm{pm}}+M_{\mathrm{sf}}{i}_f)\frac{\sqrt{{\left(\frac{U_{\max }}{{\mathrm{\ω}}_e}\right)}^2-{({\mathrm{\ψ}}_{\mathrm{pm}}+M_{\mathrm{sf}}{i}_f)}^2}}{L_q}---\left(4\right)$

Formula (4) is an One-place 2-th Order function that Open Side Down, has maximum, as shown in Figure 2; At T _eduring for maximum, corresponding armature supply set-point and exciting current set-point are:

$\left\{\begin{array}{c}{i}_{\mathrm{fref}}=\frac{{\mathrm{\ψ}}_{\mathrm{pm}}-\frac{U_{\max }}{\sqrt{2}{\mathrm{\ω}}_e}}{M_{\mathrm{sf}}}\\ i_{\mathrm{dref}}=0\\ i_{\mathrm{qref}}=\frac{U_{\max }}{\sqrt{2}{\mathrm{\ω}}_e{L}_q}\end{array}\right.---\left(5\right)$

Using calculate the armature supply set-point arrived and exciting current set-point as the controlled quentity controlled variable of mixed excitation electric machine, mixed excitation electric machine is controlled.

According to system shown in Figure 1, under MATLAB/SIMULINK environment, build simulation model, the parameter of electric machine is as table 1:

Table 1 parameter of electric machine

Parameter	Numerical value
		Permanent magnet flux linkage amplitude ψ pm（Wb）	0.11348
Number of pole-pairs p	4
		Armature winding resistance R s（Ω）	2.7
Excitation winding resistance R f（Ω）	10
		D-axis inductance L d（mH）	24.1
Quadrature axis inductance L q（mH）	19.6
		Armature and excitation winding mutual inductance M sf（mH）	52
Nominal torque T e（N）	3.4
		Rated speed N(rpm)	1500
Busbar voltage U dc（V）	300
		Armature supply rated value (A)	5
Exciting current rated value (A)	1

Simulation result as shown in Figure 3.

Fig. 3 is the maximum output torque waveform of motor under different rotating speeds, as seen from the figure, adopts this algorithm effectively can increase the torque output capability of mixed excitation electric machine.

The above is only the preferred embodiment of the present invention; be noted that for those skilled in the art; under the premise without departing from the principles of the invention, can also make some improvements and modifications, these improvements and modifications also should be considered as protection scope of the present invention.

Claims (1)

1. a mixed excitation electric machine field weakening control method, it is characterized in that: when motor speed is higher than rated speed, motor enters invariable power district, weak magnetic algorithm is now adopted to improve motor speed further, concrete grammar is: ignore armature resistance, keeping motor synthesis back electromotive force constant is motor terminal voltage maximum, utilizes exciting current to weaken air-gap flux and carries out motor raising speed, distribute armature supply and exciting current accordingly; The method specifically comprises the steps:

(1) when motor enters invariable power district, keeping motor synthesis back electromotive force constant is motor terminal voltage maximum, and armature supply and exciting current meet following formula:

$E_{back}={\mathrm{\ω}}_e\sqrt{{({\mathrm{\ψ}}_{pm}+M_{sf}{i}_f+L_d{i}_d)}^2+{\left(L_q{i}_q\right)}^2}=U_{max}---\left(1\right)$

Wherein, E _backfor motor synthesis back-emf, ω _efor motor angular rate, ψ _pmfor motor permanent magnet flux, M _sffor mutual inductance between armature winding and excitation winding, i _ffor exciting current, L _dfor d axle inductance, L _qfor q axle inductance, i _dfor the d axle component of armature supply, i _qfor the q axle component of armature supply, U _maxfor motor terminal voltage maximum.

(2) i is kept _d=0, utilize exciting current to carry out weak magnetic speed-up, motor torque is calculated by following formula:

$T_e=\frac{3}{2}{\mathrm{pi}}_q({\mathrm{\ψ}}_{pm}+M_{sf}{i}_f)---\left(2\right)$

Wherein, p is motor number of pole-pairs;

(3) i of formula (1) will be met _qand i _fsubstitution formula (2), tries to achieve T _efor armature supply set-point corresponding during maximum and exciting current set-point are:

$\left\{\begin{array}{c}{i}_{fref}=\frac{{\mathrm{\ψ}}_{pm}-\frac{U_{\max }}{\sqrt{2}{\mathrm{\ω}}_e}}{M_{sf}}\\ i_{fref}=0\\ i_{qref}=\frac{U_{\max }}{\sqrt{2}{\mathrm{\ω}}_e{L}_q}\end{array}\right.---\left(3\right)$

Using the armature supply set-point arrived calculated and exciting current set-point as the controlled quentity controlled variable of mixed excitation electric machine.