CN104897041A - PWM active control type magnetic suspension mechanism air gap length measuring system and method - Google Patents

Abstract

The invention discloses a PWM active control type magnetic suspension mechanism air gap length measuring system and method. The measuring system is composed of a suspension mechanism, an electromagnet power driving unit, a phase lock amplification unit and a digital signal processing unit. The suspension mechanism is composed of an electromagnet and a suspension body; the electromagnet power driving unit comprises an H-bridge type circuit and a Hall current sensor; the phase lock amplification unit comprises a front filtering amplifier, a phase sensitive detector and a low-pass filter; the digital signal processing unit employs a CPU processor; and the digital signal processing unit is connected with the suspension mechanism through a cable for driving an electromagnet coil. According to the invention, under the condition that a position sensor is not used, the air gap length of a magnetic suspension mechanism can be calculated simply by use of electromagnet current information and pulse width modulation information; and the system is simplified to two parts in terms of overall structure, i.e., a magnetic suspension mechanism and a driving control circuit board, and additional installation of the position sensor on the magnetic suspension mechanism is unnecessary.

Description

The measuring system of PWM active control type magnetic suspension mechanism gas length and method

Technical field

The present invention relates to the field of position-sensor-free magnetic suspension system, be specifically related to a kind of measuring system and method for PWM active control type magnetic suspension mechanism gas length.

Background technology

PWM active control type magnetic levitation technology is the electromagnet apparatus utilizing pwm signal to drive, and adopts closed-loop control means to regulate magnetic field force, makes to keep certain gap between suspended matter and electromagnet, realize the object suspended.Magnetic levitation can effectively avoid contact friction between object, therefore has broad application prospects.Magnetic levitation technology is widely used in a lot of fields, as magnetic suspension train, magnetic suspension bearing, high speed magnetic suspension motor etc.

Current most of active control type magnetic suspension mechanism adopts position transducer to measure gas length.Sensor is divided into two classes substantially, laser range sensor, eddy current displacement sensor.Due to the existence of position transducer, add the cost of system and the difficulty of assembling, be unfavorable for miniaturization and the cost degradation of magnetic suspension mechanism.

Summary of the invention

For solving the problem, the invention provides a kind of measuring system and method for PWM active control type magnetic suspension mechanism gas length, when non-use position sensor, only utilize electromagnet current information and pulse width modulated information just can calculate the gas length of magnetic suspension mechanism; System is reduced to two parts from one-piece construction, magnetic suspension mechanism and Drive and Control Circuit plate, without the need to extra installation site sensor on magnetic suspension mechanism.

For achieving the above object, the technical scheme that the present invention takes is:

A kind of measuring system of PWM active control type magnetic suspension mechanism gas length, described measuring system is by suspension mechanism, power of electromagnet driver element, lock-in amplify (LIA) unit and digital signal processing unit are formed, described suspension mechanism is made up of electromagnet and suspended matter, described power of electromagnet driver element comprises H bridge type circuit and Hall current sensor, described lock-in amplify (LIA) unit, comprise pre-filtering amplifier, phase sensitive detector (PSD) and low-pass filter (LPF), described digital signal processing unit adopts CPU processor, described digital signal processing unit is connected with suspension mechanism by the cable for drive magnetic coil.

Wherein, described lock-in amplify (LIA) unit adopts AD630 chip; The output of Hall current sensor is through signal condition, after filter and amplification, be input to (network label is Sig_Input) in 1 pin of phase demodulation chip AD630, CPU will with PWM ripple with frequently simultaneously, and through the square wave of phase shift process, be input in 9 pin of AD630, as the reference signal of lock-in amplify; Sig_Input signal is by lock-in amplify in AD630, and the output signal of AD630, after low-pass filtering, obtains the signal Output of the amplitude information containing electric current fundamental component; This signal, after simple signal conditioning, is input in digital signal processing unit.

For solving the problem, present invention also offers a kind of measuring method of PWM active control type magnetic suspension mechanism gas length, comprising the steps:

S1, CPU send PWM drive singal, magnet coil generation current to sending power drive unit, and suspended matter motion under electromagnetic force controls makes air gap x change, and then changes magnetic resistance and the coil current of magnetic circuit;

S2, utilize lock-in amplify (LIA) technology, the change in location information be submerged in current harmonics signal is extracted;

S3, according to the amplitude of fundamental frequency driving voltage component in pwm signal and the relation of electric current, in CUP processor, calculate gas length.

Wherein, described motion makes the computing formula of air gap x be:

$x=\frac{1}{2}(\frac{\mathrm{\π}{\mathrm{\μ}}_0{\mathrm{\ω}}_0{N}^{2}A{U}_l}{4U\sin \left(\mathrm{\π\α}\right)}-\frac{l}{{\mathrm{\μ}}_r})$

In formula, N is the number of turn of magnet coil, μ ₀represent permeability of vacuum, A represents the sectional area of electromagnet core, ω ₀represent pulse-width signal first-harmonic angular frequency, U _lrepresent the amplitude of the current first harmonics signal measured, U represents H bridge supply voltage, and α represents pwm signal dutycycle, and l represents the length of iron core in magnetic circuit, μ _rrepresent iron core relative permeability.

The present invention has following beneficial effect:

Utilize phase lock amplifying technology, process magnetic suspension mechanism measurement of air gap problem, compared with other position-sensor-free methods based on common rectifying and wave-filtering demodulation, measures more accurate; Consider the impact of control signal dutycycle on measurement of air gap, improve measuring accuracy; Electromagnet is namely as topworks, and again as the Sensitive Apparatus that magnetic resistance is measured, compared with the existing scheme utilizing laser position sensors and electric eddy current measurement, this method cost is lower, is easier to integrated, is more suitable for installment and debugging.

Accompanying drawing explanation

The structural drawing of a kind of PWM active control type of Fig. 1 embodiment of the present invention magnetic suspension mechanism gas length system.

Fig. 2 is the reduced graph of Fig. 1.

Fig. 3 is the equivalent magnetic circuit modeling schematic diagram of magnetic levitation system in the embodiment of the present invention.

Fig. 4 is the equivalent circuit diagram of the equivalence of magnetic levitation system in the embodiment of the present invention.

Fig. 5 is the PWM driving voltage waveform figure of embodiment of the present invention coil input.

Fig. 6 is AD630 lock-in amplify circuit in the embodiment of the present invention.

Embodiment

In order to make objects and advantages of the present invention clearly understand, below in conjunction with embodiment, 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.

As shown in Figure 1-2, embodiments provide a kind of measuring system of PWM active control type magnetic suspension mechanism gas length, described measuring system is by suspension mechanism, power of electromagnet driver element, lock-in amplify (LIA) unit and digital signal processing unit are formed, described suspension mechanism is made up of electromagnet and suspended matter, described power of electromagnet driver element comprises H bridge type circuit and Hall current sensor, described lock-in amplify (LIA) unit, comprise pre-filtering amplifier, phase sensitive detector (PSD) and low-pass filter (LPF), described digital signal processing unit adopts CPU processor, described digital signal processing unit is connected with suspension mechanism by the cable for drive magnetic coil.

As shown in Figure 6, described lock-in amplify (LIA) unit adopts AD630 chip; The output of Hall current sensor, through signal condition, after filter and amplification, is input in 1 pin of phase demodulation chip AD630, CPU will with PWM ripple with frequently simultaneously, and through the square wave of phase shift process, be input in 9 pin of AD630, as the reference signal of lock-in amplify; Sig_Input signal is by lock-in amplify in AD630, and the output signal of AD630, after low-pass filtering, obtains the signal Output of the amplitude information containing electric current fundamental component; This signal, after simple signal conditioning, is input in digital signal processing unit.

The embodiment of the present invention additionally provides a kind of measuring method of PWM active control type magnetic suspension mechanism gas length, comprises the steps:

S1, CPU send PWM drive singal, magnet coil generation current to sending power drive unit, and suspended matter motion under electromagnetic force controls makes air gap x change, and then changes magnetic resistance and the coil current of magnetic circuit;

S2, utilize lock-in amplify (LIA) technology, the change in location information be submerged in current harmonics signal is extracted;

S3, according to the amplitude of fundamental frequency driving voltage component in pwm signal and the relation of electric current, in CUP processor, calculate gas length.

Described motion makes the computing formula of air gap x be:

$x=\frac{1}{2}(\frac{\mathrm{\π}{\mathrm{\μ}}_0{\mathrm{\ω}}_0{N}^{2}A{U}_l}{4U\sin \left(\mathrm{\π\α}\right)}-\frac{l}{{\mathrm{\μ}}_r})$

In formula, N is the number of turn of magnet coil, μ ₀represent permeability of vacuum, A represents the sectional area of electromagnet core, ω ₀represent pulse-width signal first-harmonic angular frequency, U _lrepresent the amplitude of the current first harmonics signal measured, U represents H bridge supply voltage, and α represents pwm signal dutycycle, and l represents the length of iron core in magnetic circuit, μ _rrepresent iron core relative permeability.

Described motion makes the computing formula of air gap x be obtained by following steps:

As shown in Figure 3-4, getting N is coil turn, and i is coil current, then Ni is the mmf of system, R _mfor the magnetic resistance of system; If ignore leakage field and effect of end surface, then the magnetic resistance of system can be expressed as:

$R_m=\frac{l}{{\mathrm{\μ}}_0{\mathrm{\μ}}_{r}A}+\frac{2x}{{\mathrm{\μ}}_{0}A}---\left(1\right)$

Wherein l represents core length in magnetic circuit (containing suspended matter), and x represents gas length, μ ₀for permeability of vacuum, μ _rfor the relative permeability of core material, A represents the area of iron core

According to the relation of magnetic resistance and inductance, have:

$L=\frac{N^2}{R_m}---\left(2\right)$

The magnetic linkage of electromagnet is: ψ=Li (3)

As shown in Figure 5, if electromagnet two ends making alive u, magnet coil resistance is R, then can list the ferroelectric loop equation of electromagnetism and be:

$u=\frac{\mathrm{d\ψ}}{\mathrm{dt}}+\mathrm{iR}=L\frac{\mathrm{di}}{\mathrm{dt}}+i\frac{\mathrm{dL}}{\mathrm{dt}}+\mathrm{iR}---\left(4\right)$

If ignore the back-emf item of electromagnet, that is, then have

$u\≈L\frac{\mathrm{di}}{\mathrm{dt}}+\mathrm{iR}---\left(5\right)$

By L and R _mrelation (2) bring (5) formula into, have

$\frac{\mathrm{di}}{\mathrm{dt}}=\frac{R_m}{N^2}(u--\mathrm{iR})=\frac{1}{N^2{\mathrm{\μ}}_{0}A}(\frac{l}{{\mathrm{\μ}}_r}+2x)(u-\mathrm{iR})---\left(6\right)$

Wherein, u is the pulse-width signal be input in coil, and its cycle is T, and its dutycycle is

Pulse-width signal is carried out Fourier analysis can obtain:

$u\left(t\right)=U(2\mathrm{\α}-1)+4\mathrm{U\α}\underset{n=1}{\overset{\∞}{\mathrm{\Σ}}}\frac{\sin \left(\mathrm{n\π\α}\right)}{\mathrm{n\π\α}}\cos \left(n{\mathrm{\ω}}_{0}t\right)---\left(7\right)$

Wherein, U is bridge power supply voltage,

The fundametal compoment of u (t) is: $u_{\mathrm{\ω}0}\left(t\right)=\frac{4U}{\mathrm{\π}}\sin \left(\mathrm{\π\α}\right)\cos \left({\mathrm{\ω}}_{0}t\right)---\left(8\right)$

As follows according to the system voltage current relationship that electromagnet system loop equation obtains:

$\frac{\mathrm{di}}{\mathrm{dt}}=\frac{R_m}{N^2}(u-\mathrm{iR})=\frac{1}{N^2{\mathrm{\μ}}_{0}A}(\frac{l}{{\mathrm{\μ}}_r}+2x)(u-\mathrm{iR})---\left(9\right)$

The frequency arranging fundamental frequency signal in system is more than 10KHz, has under this frequency therefore have, u > > iR, namely

$\frac{\mathrm{di}}{\mathrm{dt}}\≅\frac{1}{N^2{\mathrm{\μ}}_{0}A}(\frac{l}{{\mathrm{\μ}}_r}+2x)u---\left(10\right)$

For (10) formula, consider the situation of fundamental frequency excitation, have:

$\begin{array}{c}\frac{{\mathrm{di}}_{\mathrm{\ω}0}}{\mathrm{dt}}=\frac{1}{N^2{\mathrm{\μ}}_{0}A}(\frac{l}{{\mathrm{\μ}}_r}+2x)u_{\mathrm{\ω}0}\\ =\frac{1}{N^2{\mathrm{\μ}}_{0}A}(\frac{l}{{\mathrm{\μ}}_r}+2x)\·\frac{4U}{\mathrm{\π}}\sin \left(\mathrm{\π\α}\right)\cos \left({\mathrm{\ω}}_{0}t\right)\end{array}---\left(11\right)$

(11) formula integration is obtained:

$i_{\mathrm{\ω}0}\left(t\right)=\frac{1}{N^2{\mathrm{\μ}}_{0}A{\mathrm{\ω}}_0}(\frac{l}{{\mathrm{\μ}}_r}+2x)\·\frac{4U}{\mathrm{\π}}\sin \left(\mathrm{\π\α}\right)\sin \left({\mathrm{\ω}}_{0}t\right)---\left(12\right)$

If i _{ω 0}the amplitude U of (t) _lknown, then gas length can be expressed as:

$x=\frac{1}{2}(\frac{\mathrm{\π}{\mathrm{\μ}}_0{\mathrm{\ω}}_0{N}^{2}A{U}_l}{4U\sin \left(\mathrm{\π\α}\right)}-\frac{l}{{\mathrm{\μ}}_r})---\left(13\right).$

This concrete enforcement adopts phase lock amplifying technology to measure the amplitude U of electric current fundamental component _l.Adopt phase sensitivity amplifying technique, the reason extracting gas length information in current signal is as follows:

A) electromagnet produces electromagnetic force by pwm pulse signal excitation, and PWM fundamental frequency signal is carrier signal, and positional information is modulated in PWM fundamental frequency signal, therefore directly utilizes fundamental component in pwm signal as with reference to signal;

B) utilize phase sensitive detector to realize the demodulating process of modulation signal, frequency and phase place can be utilized simultaneously to detect, interference noise and signal are with the probability of homophase is very low again frequently;

C) compare conventional demodulator, lock-in amplifier adopts low-pass filtering, and its passband can be done very narrow, and its bandwidth is not by modulation frequency influence, has good stability

In this concrete implementation procedure implemented, the processor that CPU is used can be single-chip microcomputer, DSP, ARM, FPGA, PC104, PC etc.; Reference signal can be sent by CPU processor, also can adopt special phaselocked loop (PLL) circuit, generates the reference signal being used for lock-in amplify; Lock-in amplify unit can adopt AD630 to be the lock-in amplify circuit of core, also can adopt the lock-in amplify circuit built by high-speed analog switch circuit, or directly realizes lock-in amplify function by digital servo-control mode of amplifying; The function of Hall current sensor can replace with sampling resistor, a copper-manganese Low Drift Temperature sampling resistor of namely connecting in H bridge lower end, then measures resistive voltage with differential amplifier circuit, and then the mode of calculating current is measured.

The above is only the preferred embodiment of the present invention; it should be pointed out 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 (4)

1. the measuring system of a PWM active control type magnetic suspension mechanism gas length, it is characterized in that, described measuring system is by suspension mechanism, power of electromagnet driver element, lock-in amplify unit and digital signal processing unit are formed, described suspension mechanism is made up of electromagnet and suspended matter, described power of electromagnet driver element comprises H bridge type circuit and Hall current sensor, described lock-in amplify unit, comprise pre-filtering amplifier, phase sensitive detector and low-pass filter, described digital signal processing unit adopts CPU processor, described digital signal processing unit is connected with suspension mechanism by the cable for drive magnetic coil.

2. the measuring method of PWM active control type magnetic suspension mechanism gas length according to claim 1, is characterized in that, described lock-in amplify unit adopts AD630 chip; The output of Hall current sensor, through signal condition, after filter and amplification, is input in 1 pin of phase demodulation chip AD630, CPU will with PWM ripple with frequently simultaneously, and through the square wave of phase shift process, be input in 9 pin of AD630, as the reference signal of lock-in amplify; Sig_Input signal is by lock-in amplify in AD630, and the output signal of AD630, after low-pass filtering, obtains the signal Output of the amplitude information containing electric current fundamental component; This signal, after simple signal conditioning, is input in digital signal processing unit.

3. a measuring method for PWM active control type magnetic suspension mechanism gas length, is characterized in that, comprise the steps:

S1, CPU send PWM drive singal, magnet coil generation current to sending power drive unit, and suspended matter motion under electromagnetic force controls makes air gap x change, and then changes magnetic resistance and the coil current of magnetic circuit;

S2, utilize phase lock amplifying technology, the change in location information be submerged in current harmonics signal is extracted;

S3, according to the amplitude of fundamental frequency driving voltage component in pwm signal and the relation of electric current, in CUP processor, calculate gas length.

4. the measuring method of PWM active control type magnetic suspension mechanism gas length according to claim 3, is characterized in that, described motion makes the computing formula of air gap x be:

$x=\frac{1}{2}(\frac{\mathrm{\π}{\mathrm{\μ}}_0{\mathrm{\ω}}_0{N}^{2}A{U}_l}{4U\sin \left(\mathrm{\π\α}\right)}-\frac{l}{{\mathrm{\μ}}_r})$

In formula, N is the number of turn of magnet coil, μ ₀represent permeability of vacuum, A represents the sectional area of electromagnet core, ω ₀represent pulse-width signal first-harmonic angular frequency, U _lrepresent the amplitude of the current first harmonics signal measured, U represents H bridge supply voltage, and a represents pwm signal dutycycle, the length of iron core in/expression magnetic circuit, μ _rrepresent iron core relative permeability.