The overtone produces the basic reason is because the non-linear load is the result of. When the electric current flows after the load, with the voltage which adds does not assume the linear relations, forms the non-sinusoidal current, thus produces the overtone. The harmonic frequency is the base frequency integral multiple, (M. Fourier) analyzes the principle according to French mathematician Fourier to prove, any redundant profile all may decompose for includes the base frequency and a series of for the fundamental wave multiple overtone sine wave component. The overtone is a sine wave, each overtone all has the different frequency, the scope and the angle. The overtone may I discrimination be inferior and wonderful for the partner, 3rd, 5, 7 serial numbers are 奇次谐波, but 2, 14, 6, 8 and so on for 偶次谐波, when the fundamental wave is 50Hz, 2 次谐�?is lOOHz, 3 次谐�?is 150Hz. Generally speaking, 奇次谐波 causes the harm 偶次谐波 more is bigger than. In the balanced three-phase system, as a result of the symmetric relation, 偶次谐波 was already eliminated, only has 奇次谐波 the existence. Regarding the three-phase rectification load, the harmonic current which appears is 6n±1 次谐�? for example 5, 7, 11, 13, 17, 19 and so on, the frequency changer mainly produces 5, 7 次谐�? Overtone definition schematic drawing like chart 1 shows.

1.2 overtones governments related standard

The frequency changer overtone governs should pay attention to following several standards, the antijamming standard: EN50082-1, -2, EN61800-3: Radiation standard: EN5008l-1, -2, EN61800-3. Specially IECl0003, IECl800-3 (EN61800-3), IEC555 (EN60555) and IEEE519-1992.

Ordinary antijamming standard EN50081 and EN50082 as well as (1ECl800-3) defined the equipment in view of frequency changer standard EN61800 to move the time radiation in the different environment and the antijamming level. The above standard defined has been possible to accept the radiation rank under the different environmental condition: L level, non- radiation limit. Is suitable to in under the environment which disturbs is not used the frequency changer the user and own processes the radiation limit the user. H level, according to EN61800-3 determination limit, first environment: Has the limit distribution, with second environment. As chooses the RFI filter, disposes the RFI filter to be allowed to enable the frequency changer to achieve the commercial level, usually uses in the non- industry environment. Related overtone government EMC standard schematic drawing like table 1 shows.

2 overtones government measures

The government overtone question, the suppression radiated interference and the power supply system disturbance, may adopt the shield, the isolation, technical method and so on earth and filter. (1) Uses the passive filter or the active filter: (2) increases the transformer the capacity, reduces the return route the impedance and shuts off the transmission line law; (3) uses the green frequency changer which the non- overtone pollutes.

2.1 uses passive filters or active filter

Uses passive filter it mainly is the change under the special frequency the power source impedance, is suitable to the system which is stable, does not change. But uses the active filter mainly is uses in to compensate the non-linear load.

The traditional way selects the passive filter much, the passive filter appears most early, because its structure simple, invests few, the movement reliability higher as well as the operating cost is lower, until now was still the harmonic suppression main method. The LC filter is the traditional passive harmonic suppression installment, it by the filter capacitor, the reactor and the resistor suitable combination becomes, is parallel with the harmony wave source, besides has the filter function, but also has the function which the idle work compensates. This kind of equipment has the shortcoming which some is more difficult to overcome, mainly is easy to overload, when overload can 烧损, possibly create the power factor to direct, to recompense is fined; Moreover, the passive filter cannot receive controls, therefore along with time passing, the fitting gets older or the electrical network load change, can cause the resonance frequency to have the change, the filter effect drops. More importantly the passive filter only can filter one kind of overtone ingredient (for example some filters only to be able to filter triple frequency), if filters the different harmonic frequency, then must separately use the different filter, increases the equipment investment.

Domestic and foreign has the many kinds of active filters, this kind of filter can the overtone which all changes to the frequency and the peak-to-peak value carry on the track to compensate, also compensates the characteristic not the electrical network impedance influence. The active electric power filter (APF) the theory in 20th century 60's formations, afterwards the major and medium power all controlling semiconductor device maturity, the pulse width modulation (PWM) was controlling technical the progress as well as based on instant reactive power theory harmonic current instant examination method proposing, the active electric power filter could rapidly develop. Its basic principle is from compensates in the object to examine the harmonic current, produces by the compensation system to be equal but the polarity opposite bucking current frequency spectrum with this harmonic current size, counterbalances the overtone which the original line harmony wave source produces, thus enable the electrical network electric current only to include the fundamental wave component. Core part is the harmonic current generator and the control system, namely its work depends on the digital signal processing (DSP) the technical control fast insulation bipolar transistor (1GBT) to complete.

At present, in the concrete overtone government aspect, appeared the passive filter (the LC filter) with the active filter supplementary mix use way, fully displays the LC filter structure simply, is easy to realize, the cost lowly, the active electric power filter compensates the performance good merit, overcomes the active electric power filter capacity to be big, the cost high shortcoming, two unions uses, thus causes the overall system to obtain the good performance.

2.2 reduces the return route the impedance and shuts off the transmission line law

The overtone produces the basic reason is because has used the non-linear load, therefore, solution basic is produces the overtone load supply line and separates to the overtone sensitive load supply line (like chart 2 to show). Because the non-linear load causes the distortion electric current has a distortion loss of voltage in the electric cable impedance, but synthesizes the distortion voltage waveform adds to other loads which meets with this identical line on, causes the harmonic current (like chart 3 to show) in its upper reaches. Therefore, reduces the overtone harm the measure also to be possible from to enlarge the electric cable cross-sectional area, reduces the return route the impedance way to realize. At present, the home comparatively uses enhances the transformer capacity, increases the electric cable cross-sectional area, specially enlarges the neutral axis electric cable section, as well as selects an entire definite value bigger circuit breaker, the fuse and so on protects means and so on part, but this way could not fundamentally the harmonic cancellation, instead reduce the protection characteristic and the function, also has enlarged the investment, the increase power supply system hidden danger. May know from chart 2, may the linear load and the non-linear load from the identical power source

Connection (PCC) starts the electric circuit power supply which distinguishes, like this may cause the distortion voltage which produces by the non-linear load not to be able to conduct to the linear load comes up. This is at present governs the overtone question more ideal solution.

2.3 uses the green frequency changer which the non- overtone pollutes

The green frequency changer quality standard is: The input and the output current all are the sine wave, the power input factor controllable, when belt any load all can cause the power factor is 1, may obtain about the labor frequency wilfully the controllable output frequency. In the frequency changer sets the exchange reactor, it can the very good suppression overtone, simultaneously be allowed to protect the rectification bridge the supply voltage instantaneous sharp wave influence, the practice was not indicated that, does not bring the reactor the harmonic current obviously to be higher than the harmonic current which the belt reactor produces. In order to reduce the disturbance which the overtone pollution creates, installs the noise filter in the frequency changer output circuit. And situation which permits in the frequency changer, reduces the frequency changer the carrier frequency. Moreover, in the high efficiency frequency changer, usually uses 12 pulses or 18 pulses rectification, like this in the power source, reduces the harmonic content through the elimination 低次overtone. For example 12 pulses, the lowest overtone is 11, 13, 23, 25 次谐�? Analogizes in turn, regarding 18 pulses, the lowest overtone is 17 and 19 次谐�?

In the frequency changer the application low overtone technology may, the induction as follows: (1) Contravariant unit parallel multiple, uses 2 or many contravariant units is parallel, through profile superimposition counterbalance harmonic component. (2) Levelling circuit multiple, uses 121 pulses, 18 pulses or 24 pulses rectification in the PWM frequency changer, reduces the overtone. (3) Contravariant unit series multiple, uses 30 pulses the series inversion unit multiple lines, its overtone may reduce to is very small. (4) uses the new frequency conversion modulation method, like voltage vector diamond modulation and so on. At present, many frequency changers manufactures merchant extremely has taken the overtone question, when design has guaranteed the frequency changer green from the technical method, thus in on basic solves the overtone problem.

3 conclusions

In summary, may clearly understand the overtone produces the reason, may use the passive filter, the active filter in the concrete government, reduces the return route impedance, shuts off the overtone transmission route and the development uses non- overtone pollution method and so on green frequency changer, produces the frequency changer the overtone control in the smallest scope, achieved the science reasonably uses electricity, suppresses the electrical network pollution, improves the power source quality.