Abstract: Introduced the matrix form converter inputs filter’s design method. Trades the class and the optimized switch order using half soft electric current can reduce the breakover to lose, simultaneously improves the profile quality. The input filter design’s difficulty lies in the EMC laws and regulations which must tally extant and is going to appear. Compared with the use software simulation and the actual survey obtained DSP control’s power transformer’s perturbation voltage, and to has conducted the research with the input filter design’s relations.
Key word: Input filter design; Electromagnetic compatibility; Matrix form converter; Four steps trades the class
1 outline
The matrix form converter is one kind of force phase change junction - hands over the converter, it by 9 controllable double throw switches, will exchange the live pressure frequency conversion power source which using the PWM control the electric power supply direct transform load needs, its structure as shown in Figure 1. The double throw switch uses two IGBT common-collector series-opposing, prevents the reverse voltage using the component internal after flow diode, the structure is compact, facilitates simply, the switching loss is also low. The input side L-C filter may reduce the input current effectively the turn-on frequency overtone.
Figure 1
2 EMI analyses
The matrix form converter will be the AC/AC direct transform, the electrical network and the load immediate influence, electrical network’s fluctuation (for example asynchronous machine) will have the disturbance directly mutually to the load; Double throw switch which and the counter-parallel diode constitutes with IGBT, as well as their control circuit DSP and CPLD and so on high speed integrated circuit, has high di/dt, they cause the transient state electromagnetism noise through the line or primary device’s lead inductance, its frequency is several thousand Hz, becomes the unnegligible noise source; The PWM modulating technology in each kind of electric power electronic installation’s widespread application, in theirs main power electric circuit, will usually wind through a series of PWM power pulse, its recurrence rate will regard the application situation to be possible to reach several thousand Hz, thus in these pulse current will contain the overtone may achieve several MHz and even several dozens MHz scopes, moreover they will produce the electromagnetism noise intensity will be very big; But the periphery equipment and the equipment will also radiate the electromagnetic wave, they will also become the noticeable noise source. These noise sources through ways and so on conduction and radiation to output with the input current, the voltage have the influence, must try to find solution to suppress it or the reduction in the acceptable scope.
Various countries have formulated the corresponding standard to electrical equipment’s electromagnetic compatibility, specially Western Europe, started from January, 1996 to force to fulfil exactly its standard, our country also has the corresponding standard and the laws and regulations, therefore, must use inputs the filter to reduce the turn-on frequency overtone which the matrix form converter produces, this article introduced with emphasis inputs filter’s design.
3 reduction switching process disturbance
In order to guarantee between switch’s safe cut, identical outputs two cluster switches cannot willfully simultaneously the breakover, will otherwise create inputs two short-circuits has the electric current peak value; The three-phase switch cannot also separate, otherwise causes the perceptual load opening to induce the high voltage. But actual uses semiconductor switch component IGBT is impossible to achieve the ideal instantaneous breakover and the shutdown, before soon shuts off the component withdraws from the breakover, soon the breakover component cannot achieve the ideal condition the instant conducting state, trades when the class the avoidless short clear overlaps or the shutdown dead area, therefore, to reduce the switching process the disturbance, safe trades the class usually not to be able one step to complete.
Four step security trades the dangerous on-off state which the class the thought is reduces as far as possible short-circuits and leads the way. Trades class process as shown in Figure from switch S1 to switch S2 2.
When iL>0, four step switch orders are: Closes S1n, opens S2p, closes S1p, opens S2n.
When iL<0, four step switch orders are: Closes S1p, opens S2n, closes S1n, opens S2p.
Obviously, four steps traded the class to constitute successfully to two double throw switch’s reverse controls, both prevented possibly to cause the power source to have the short circuit switch combination, and had guaranteed provided at least a circulation way in the random time to the load, moreover soon shut off the component when the component serve back pressure which soon cleared might realize zero current breaker, therefore, used four steps trades the class plan to be possible to reduce 50% average switching loss.
The optimized switch order is the switch order establishment is S1, S2, S3, S0, S3, S2, S1, namely uses the hemihedry PWM switch order, after using optimized the switch order may reduce 33% average switching loss.
4 input filter design
4.1 turn-on frequency overtone
May obtain the three-phase input current frequency spectrum using the simulation and experiment’s method, may compare in the simulation and the experiment profile the turn-on frequency and the overtone peak value and the position, and by this achievement filter design basis.
Is 30Hz input current frequency spectrum as shown in Figure 3 using the Matlab simulation’s output frequency. Figure 4 is the actual turn-on frequency is 20kHz, the power is the 3.5kW matrix form converter not filter’s input current frequency spectrum. Obviously, has many relevances between the simulation and the experiment profile, they the harmonic components are very big nearby the turn-on frequency.
In the matrix form converter actuates in asynchronous machine’s system, electrical machinery startup procedure’s electromagnetism torque profile as shown in Figure 5. May know by Figure 5, the asynchronous machine starts when the torque is biggest, from this produces the disturbing voltage is also biggest. Had known disturbing voltage’s frequency spectrum, might start to design satisfies the request the input filter.
4.2 design methods
May use the heterogeneity LC filter circuit or the belt overtone choice single-phase LC filter, but increased system’s complexity obviously. This experiment uses the single-phase LC filter circuit to satisfy the design requirements.
Inputs filter’s design to satisfy the cut-off frequency to be lower than the turn-on frequency, the volume and the weight should be as far as possible small, should be as far as possible small in the filter inductance’s pressure drop, the power factor should be as far as possible big. In order to reduce to electrical network’s disturbance, the matrix form converter must guarantee the close 1 power factor as far as possible, therefore, the matrix form converter must compensate as far as possible by the introduction inputs filter’s detention, because the electric capacity is creates the detention the primary factor, therefore the input current ratio input voltage has one to lag. In order to guarantee that the space vector modulation strategy the correct execution, we establish in a big way π/6 to lag acceptable.
Input filter design basis shown in Figure 6, the matrix form converter regards as is a current supply, to obtain the power factor is 1, must guarantee input current iL and the input voltage Ui synchronism as far as possible.
May result in by Figure 6
The matrix form converter lags (electric current backwardness) to limit for π/6, then
In the formula: ωc=1/[(LC)] for filter closure angular frequency.
The filter inductance causes the voltage retards may neglect [5], filter’s cut-off frequency compared to mains frequency high number magnitude [6], the filter electric capacity’s maximum value is decided by input current peak value [7] or ideal output [8][9]. These values when matrix form converter low input current work especially important. Considers the type (5) and the type (6)
Or
Using the Jierhuofu electric current theorem, obtains the electric capacity voltage pulsation is
Electric capacity voltage hunting when low input/output voltage transmission compared to and low power factor changes big.
By type (9), when the power is 3.3kW, the limit is C<38.3μF here takes to the electric capacity 5μF/630V.
Filter’s cut-off frequency fc should choose in the mains frequency
(50Hz) and the turn-on frequency (20kHz), usually and the mains frequency and the turn-on frequency have 10 time of relations, therefore, here we take fc are about 1kHz.
According to the above definite capacitance value, may obtain the L value scope, here takes L is 5mH.
4.3 experimental verifications
After designing filter’s parameter, may examine the parameter through the experiment the choice whether to meet the requirement.
When full load in the inductance greatest voltage reduces to
In the formula: Un is the fixed input phase voltage;
In is the fixed input interphase current.
May know by the computation, when full load the greatest voltage reduces to 0.01%.
After addition filter, input current’s frequency spectrum as shown in Figure 7, obviously in the input current the fundamental wave content has occupied absolutely partially, the turn-on frequency and the harmonic content already obviously reduced, moreover may know the input current and the voltage basic sine and the synchronism by Figure 8, therefore, the filter have realized the design requirements well.
5 conclusions
The electric power electronic installation’s EMI pollution received all quarters more and more attention, various countries one after another has also released the related EMC laws and regulations. The matrix form converter (MC) takes one kind to have the superiority extremely the electrical energy use technology, must have the good EMC performance. Electrical network’s fluctuation to the matrix form converter (MC) the work will have the influence, MC will also have the pollution to the electrical network, therefore, must adopt the measure reduction switching process disturbance, and will increase inputs the filter. This article introduced in detail MC input filter’s design process, the simulation and the experimental result has proven this kind of design reliability and the usability.
