# How to raise electric machinery electric current to gather capability of circuit interference rejection

The sampling of electric machinery phase current is controlled to FOC for it is indispensable, in the design**Electric machinery control**When circuit, for can accurate sampling is worth to the electric current in electric machinery winding, need those who collect to increase electric current**Interference rejection**Ability. So the design that how assures us is reasonable, small make up 3 when take everybody to discuss next electric machinery electric current to collect circuit main essential factor.

One, foreword

Because the wide range timing of electric machinery and high speed are characteristic, add electrify machine oneself to cannot acquire magnetic field of perfect sine air gap, bring about the phase current in the sampling when the system is controlled to contain irregular Gao Cixie wave and random interference, change the existence of unit deviation plus the instability of voltaic sampling circuit and A/D, it is the voltaic error that increased actual sampling to arrive more.

Well-known, voltaic sampling is very important to control of electric machinery vector. Voltaic sampling means basically has 3 kinds.

Express kind of sampling of 1.1 electric current

To application of major electric machinery, the method that uses sampling of double resistor phase current has definite advantage, so small make up here to discuss next double resistor means to fall with everybody mainly, how to increase the interference rejection capacity of phase current sampling.

2, interference rejection design

1, sampling resistor

Sampling resistor is basic resistor yuan parts of an apparatus, at the same time the choice of its parameter also is main influencing factor to sampling accuracy.

Electric machinery controller is right of electric machinery among them two-phase electric current undertakes sampling through sampling resistor, if the graph is shown 1 times, the voltage signal that gets from sampling resistor slants through voltage buy and enlarge, the A/D that inputs microprocessor is unit, get thereby among them two-phase electric current, again according to Kirchhoff law, vector of three-phase electric current and for 0, push the value that calculates the electric current that gives three-phase.

Graph sampling of 1 pair of resistor

To compressor of air conditioning of 320V power supply, 0.2Ω of electric machinery internal resistance, if sampling resistor is appropriate, do not have what influence to loop. If the block value of sampling resistor is too great, can cause the loss of voltage, make energy efficiency becomes low, greater block value can make laden voltage produces deflection, generate electromagnetism interference, produce the issue with sensitive to noise system. The steady performance that still needs to consider resistance after deciding good block is worth and block are worth an error.

2, carry puts a design

Needing to consider the design of carry discharge road again in the circuit design process of electric machinery, the design that circuit of phase current sampling is below explains. The carry of NCV20034 car class that what use in the article is ON company puts chip, have the gain bandwidth that is as high as 7MHz, compositive 4 independent movement are put at a suit.

Carry puts chip itself to be opposite in all modular interference has counteractive effect, and the counteractive working that disturbs in wrong standard is a bit young, when be being designed so, wanting to raise the on-line that need branch to need capability of modular interference rejection again. If the graph is shown 2 times, c2 capacitance disturbs ability to raise the standard that fight difference namely. Resistor of the on-line that need branch (R34, R35) with feedback resistor (R39) the resistor that should use high accuracy, make the parameter that theoretical calculation gets is accurate and reliable. With the output that carry puts connective AD mouth brings a foot to go up and connect filter of circuit of a RC to drop Gao Cixie next wave interference and random pulse interference, promote interference rejection capability thereby.

Graph 2 electric current are measured

3, PCB is decorated

For can accurate sampling electric current, the position that should put fortune chip to go up in PCB approachs sampling resistance as far as possible, want to make carry puts chip to cannot be far from MCU again at the same time, carry the ground of put land and MCU should draw close as far as possible. If the graph is shown 3 times, sampling resistor (R98, R99, R100) what two end go poor to divide a line to carry to put is inphase and turn over photograph port, difference divides a line to answer equidistant and as far as possible short, arise in order to avert other interference. Compressor involves high pressure and low-pressure share, be in ground of layout electric current when, the sheet that should make ground of big electric current and ground of small electric current can very good nods segregation.

Graph 3 carry put poor cent to take a line

After above passes hardware filter wave, if the graph is shown 4 times, weaveform of 3 phase current gets be optimizinged significantly.

Graph 4 three-phase electric current is undee