The requirements for electric energy quality of modern industrial development are higher and higher, how to offer the safe and reliable green power to energy consumer is a focus of area research of the power at present. UPS, as a kind of incessant power supply equipment, it is one of the important measures which improves electric energy quality, also the important insurance that the key equipment must use normal operation. At present there are reserve type, online, and dual converter bunches – several kinds of types of connecting in parallel compensating typely etc. that three ports are online and interdynamic type in the structure of U PS. Dual converter bunch – connect in parallel compensating typely and can already be compensated not to be wattless current and harmonic current in the linear loads among them, can also compensate harmonic wave and fundamental wave deflection of the mains voltage at the same time, have synthetic electric energy quality modulability, it is a new kind of UPS appearing recently. There is this kind of material object products in the foreign A PC Company at present, China is in theoretical research state.

This text has introduced one pair of converters bunch – connect the compensating type operating principle in parallel, discuss the compensating type U PS cascade converter control method of the multiple-series connection on this basis, and through artificial operating characteristic of verification system, result indicate exactness of control strategy withdrawn, compensating type UPS cascade converter parts of multiple-series connection studied can guarantee all the time the total distortion rate of input current of the electric wire netting invites 3, input the system performance that the power factor approaches 1, has verified it improves significance of the side electric energy quality of electric wire netting.

A pair of converters bunch- Connect the compensating type UPS operating principle in parallel

Fig. 1 provides the principle of one pair of changer multiple-series connections compensating type UPS, current transformer device, are two-way SPWM AC/ DC converters in the picture, its straight flow side connects the storage battery, the current transformer device passes inductance L1, electric capacity C1 and voltage transformer Ts, output voltage V electric current I s Tandem connection calls it the series compensation converter between mains voltage, v s and load voltage vL. Its compensating voltage outputted is made up of two parts: v = v 1 v H, Uh is the harmonic compensating voltage, the harmonic voltage vsh in it and AC supply is equal, vh =Vsh, but the direction is opposite; V1 is a fundamental wave voltage compensation, compensate the fundamental component vs l of the mains voltage and deflection of the load voltage rated value vR, so the compensating voltage that the current transformer device offers v Have already offsetted harmonic vsh in the mains voltage vs, compensate the fundamental wave voltage vsl again, make the load voltage vL become with the nominal voltage of fundamental wave and voltage vs in-phase sine wave of the power.

Bunch – connect compensating type UPS in parallel of a pair of converters of Fig.

The converter joining-up in parallel after L2, C2 filter is or connected at the load both ends to support by the output transformer Tp, call it and compensate the converter in parallel. Support for a linear load, then the load current iL is made up of fundamental wave active current iLP, fundamental wave wattless current iLQ and harmonic current iLh three parts. Carry on real-time, appropriate control to the converter , can make it output until the voltage that is supported is the sine wave nominal voltage vR, and to the output current i3 of load =i LQ iLh iLP-is ,Among them iLQ, iLh compensate and support idle work and harmonic current, makes the power output the fundamental wave active current is only to load, the active current iLP supported is by the AC supply is And converter i2d Offer together. Active current i2d= iLP-is that the converter outputs to load. When it is not that a linear load, mains voltage are higher than or lower than the rated value vR and contain the harmonic voltage, the system compensates the converter to act on together through this kind of multiple-series connection, can make the load voltage vL compensate to with the in-phase specified sinusoidal voltage vR of the mains voltage, the AC supply only inputs the fundamental wave active current is at the same time, the power factor is 1.

By above-mentioned analysis being knowing, U PS this overcome the intersection of tradition and pair vary online U PS input the intersection of input and the intersection of power factor and lower shortcoming brought partly to commutate. Usually the voltage of fundamental wave of the power deviates from the rated value and less than 15, so the current transformer device only compensates the nominal voltage that v % is less than or equal to 15V, its capacity, only for about 20 of the system capacity. City power and converter supply power to load together when being normal, the intensity of maximum power of two converters is only 20% of the load power, vary online UPS as to the tradition pair working under 100′s load power all the time, not merely the complete machine is with high efficiency, the power device losses small, longe-lived, reliability is high, have sufficient the intersection of power and margin deal with special load ‘ Impact load, over load of twinkling of an eye,etc. ,So fan-out capability gets very great enhancement, the products fabrication cost of same capability has been reduced.

Ideal mains voltage 2 plays the control of the cascade converter

Mains voltage will certainly when,it control that input current effectively fast and last speed and magnitude that energy flow. The cascade converter can neglect the influence of 0 axles and be regarded as the three phase three wire system PWM rectifier in fact at this moment, adopt the intersection of dq and axle cross control technique of decoupling, can obtain the ideal converter and input the current control result. Neglect the converter, reactor and capacitor power consumption in Fig. 1, if the storage battery does not charge discharge as well as, the active power Psdc of power input should be equal to the loaded active power P Ldc. As the cascade converter is made the sine fundamental wave current source I s, and co s=1. At 0 o’clock, there is power P sdc:

In the type, I s is and the voltage VS1 in-phase electric current of fundamental wave of power, it is a order electric current I *s of power that should choose this electric current:

Measure three-phase A, B, the load current, load voltage and mains voltage of C system, get the DC component V Ld, VLq, I Ld, I Lq, VSd, VSq of corresponding to fundamental wave after coordinator transformation and low-pass filtering LPF, pressing type 2 Find I *s and electric current control command to regard this value as cascade converter, control PWM to the output current I s on the sine current source converter, enable the power electric current I s tracing I *s, can realize, regard as the intersection of sine and cascade converter of current source to the intersection of power and control function of electric current and to the intersection of power and compensation of harmonic voltage ‘ Isolate The function, as shown in Fig. 2.

Fig. 2 ideal electric wire netting makes the cascade converter and controls the block diagram

Artificial waveform under ideal voltage 3

The system simulation parameter is as follows: Exchange the electric wire netting and input the amplitude VR of voltage rating =100 V, frequency f =50 Hz; Amplitude VL of the nominal voltage of load =100 V, the nominal capacity 500 VA of load, cos=0. 8; The sectional three phases connect the voltage transformer nominal capacity 500 VA, turns ratio N1 / N2 in series =1/ 1. 5; The cascade converter inputs the inductance L =4 mH, the resistance R of the inductance =0. 1, the Filtering capacitance C1 of the output =1 F; Connect the converter in parallel and export the filtering inductance L =1 mH, the resistance R of the inductance =0. 1 ; Filtering capacitance C1 of the output =90 F. Battery E =86 V, internal resistance R =0. 1, the direct-flow bus wire electric capacity Cdc =6 800 F; Switching frequency f of the converter =9 kHz. The artificial waveform is shown as Figs. 3, 4, 5.

The pure resistor of Fig. 3 is supported

Fig. 4 sense hindering type is supported

The commutator type of Fig. 5 is supported

Can be seen by the artificial waveform, under the three-phase symmetric ideal electric wire netting, the control action of the cascade converter is very good, the three-phase electric wire netting input current is the compensating sinusoidal current, the ripple of the direct-flow busbar voltage is very little, subharmonic alternating component 2 hardly exists to fluctuate; The distortion rate of the electric current of the electric wire netting invites 3.

Control strategy and artificial waveform under non-ideal voltage 4

When the input voltage of the cascade converter is asymmetric, if PWM switch function includes the harmonic wave, will influence and can not produce desiredly the harmonic wave in the direct-current volts, especially 2 subharmonics make the voltage ripple of dc output serious. Still influence the input voltage of bridge end of the cascade converter conversely, enable the harmonic wave including grades 3, 5, 9 in the bridge end input voltage, thus has increased the total harmonic distortion rate of the input current.

The three-phase influence symmetrical and including some k subharmonic of the input voltage of the converter is: Make in the direct-flow output voltage including k- 1 And k 1 The subharmonic, included the harmonic wave of k time by this converter of input current, the harmonic wave of the input voltage has been totally transmitted to the three-phase input current also, thus has increased the total distortion rate of the input current and increased the sine difficulty of control of input current.

The three-phase electric wire netting input current is uneven seriously in Fig. 6, B phase current obviously goes beyond the amplitude of other two phase current, and the electric wire netting electric current and inputting the mains voltage of A, C quarter-phase has obvious phase shift, it is not totally 1 to input the power factor, but the direct-flow busbar voltage obviously has a fluctuation of the alternating component of 2 subharmonics. The three-phase electric wire netting input current poises in Fig. 7, but the harmonic composition of the input voltage makes the sine of the input current influenced much, harmonic content 5 times is serious, the total distortion rate is great; The direct-flow busbar voltage fluctuates bigger too, especially harmonic component 4 times.

Fig. 6 inputs the artificial waveform under the voltage imbalance, voltage unbalance of the electric wire netting

Fig. 7 inputs the artificial waveform when the mains voltage include the harmonic wave

The artificial waveform of preceding paragraphs proves, control dq axle decoupling under the ideal electric wire netting a pair of close cycle control scheme of electric current of voltage under

The requirements for electric energy quality of modern industrial development are higher and higher, how to offer the safe and reliable green power to energy consumer is a focus of area research of the power at present. UPS, as a kind of incessant power supply equipment, it is one of the important measures which improves electric energy quality, also the important insurance that the key equipment must use normal operation. At present there are reserve type, online, and dual converter bunches – several kinds of types of connecting in parallel compensating typely etc. that three ports are online and interdynamic type in the structure of U PS. Dual converter bunch – connect in parallel compensating typely and can already be compensated not to be wattless current and harmonic current in the linear loads among them, can also compensate harmonic wave and fundamental wave deflection of the mains voltage at the same time, have synthetic electric energy quality modulability, it is a new kind of UPS appearing recently. There is this kind of material object products in the foreign A PC Company at present, China is in theoretical research state.

This text has introduced one pair of converters bunch – connect the compensating type operating principle in parallel, discuss the compensating type U PS cascade converter control method of the multiple-series connection on this basis, and through artificial operating characteristic of verification system, result indicate exactness of control strategy withdrawn, compensating type UPS cascade converter parts of multiple-series connection studied can guarantee all the time the total distortion rate of input current of the electric wire netting invites 3, input the system performance that the power factor approaches 1, has verified it improves significance of the side electric energy quality of electric wire netting.

A pair of converters bunch- Connect the compensating type UPS operating principle in parallel

Fig. 1 provides the principle of one pair of changer multiple-series connections compensating type UPS, current transformer device, are two-way SPWM AC/ DC converters in the picture, its straight flow side connects the storage battery, the current transformer device passes inductance L1, electric capacity C1 and voltage transformer Ts, output voltage V electric current I s Tandem connection calls it the series compensation converter between mains voltage, v s and load voltage vL. Its compensating voltage outputted is made up of two parts: v = v 1 v H, Uh is the harmonic compensating voltage, the harmonic voltage vsh in it and AC supply is equal, vh =Vsh, but the direction is opposite; V1 is a fundamental wave voltage compensation, compensate the fundamental component vs l of the mains voltage and deflection of the load voltage rated value vR, so the compensating voltage that the current transformer device offers v Have already offsetted harmonic vsh in the mains voltage vs, compensate the fundamental wave voltage vsl again, make the load voltage vL become with the nominal voltage of fundamental wave and voltage vs in-phase sine wave of the power.

Bunch – connect compensating type UPS in parallel of a pair of converters of Fig.

The converter joining-up in parallel after L2, C2 filter is or connected at the load both ends to support by the output transformer Tp, call it and compensate the converter in parallel. Support for a linear load, then the load current iL is made up of fundamental wave active current iLP, fundamental wave wattless current iLQ and harmonic current iLh three parts. Carry on real-time, appropriate control to the converter , can make it output until the voltage that is supported is the sine wave nominal voltage vR, and to the output current i3 of load =i LQ iLh iLP-is ,Among them iLQ, iLh compensate and support idle work and harmonic current, makes the power output the fundamental wave active current is only to load, the active current iLP supported is by the AC supply is And converter i2d Carry together. Active current i2d= iLP-is that the converter outputs to load. When it is not that a linear load, mains voltage are higher than or lower than the rated value vR and contain the harmonic voltage, the system compensates the converter to act on together through this kind of multiple-series connection, can make the load voltage vL compensate to with the in-phase specified sinusoidal voltage vR of the mains voltage, the AC supply only inputs the fundamental wave active current is at the same time, the power factor is 1.

By above-mentioned analysis being knowing, U PS this overcome the intersection of tradition and pair vary online U PS input the intersection of input and the intersection of power factor and lower shortcoming brought partly to commutate. Usually the voltage of fundamental wave of the power deviates from the rated value and less than 15, so the current transformer device only compensates the nominal voltage that v % is less than or equal to 15V, its capacity, only for about 20 of the system capacity. City power and dual converters supply power to load together when being normal, the intensity of maximum power of two converters is only 20% of the load power, vary online UPS as to the tradition pair working under 100′s load power all the time, not merely the complete machine is with high efficiency, the power device losses small, longe-lived, reliability is high, have sufficient the intersection of power and margin deal with special load ‘ Impact load, over load of twinkling of an eye,etc. ,So fan-out capability gets very great enhancement, the products fabrication cost of same capability has been reduced.

Ideal mains voltage 2 plays the control of the cascade converter

Mains voltage will certainly when,it can control when controlling that input current effectively fast speed and magnitude that energy flow. The cascade converter can neglect the influence of 0 axles and be regarded as the three phase three wire system PWM rectifier in fact at this moment, adopt the intersection of dq and axle cross control technique of decoupling, can obtain the ideal converter and input the current control result. Neglect the converter, reactor and capacitor power consumption in Fig. 1, if the storage battery does not charge discharge as well as, the active power Psdc of power input should be equal to the loaded active power P Ldc. As the cascade converter is made the sine fundamental wave current source I s, and co s=1. At 0 o’clock, there is power P sdc:

In the type, I s is and the voltage VS1 in-phase electric current of fundamental wave of power, it is a order electric current I *s of power that should choose this electric current:

Measure three-phase A, B, the load current, load voltage and mains voltage of C system, get the DC component V Ld, VLq, I Ld, I Lq, VSd, VSq of corresponding to fundamental wave after coordinator transformation and low-pass filtering LPF, pressing type 2 Find I *s and electric current control command to regard this value as cascade converter, control PWM to the output current I s on the sine current source converter, enable the power electric current I s tracing I *s, can realize, regard as the intersection of sine and cascade converter of current source to the intersection of power and control function of electric current and to the intersection of power and compensation of harmonic voltage ‘ Isolate The function, as shown in Fig. 2.

Fig. 2 ideal electric wire netting makes the cascade converter and controls the block diagram

Artificial waveform under ideal voltage 3

The system simulation parameter is as follows: Exchange the electric wire netting and input the amplitude VR of voltage rating =100 V, frequency f =50 Hz; Amplitude VL of the nominal voltage of load =100 V, the nominal capacity 500 VA of load, cos=0. 8; The sectional three phases connect the voltage transformer nominal capacity 500 VA, turns ratio N1 / N2 in series =1/ 1. 5; The cascade converter inputs the inductance L =4 mH, the resistance R of the inductance =0. 1, the Filtering capacitance C1 of the output =1 F; Connect the converter in parallel and export the filtering inductance L =1 mH, the resistance R of the inductance =0. 1 ; Filtering capacitance C1 of the output =90 F. Battery E =86 V, internal resistance R =0. 1, the direct-flow bus wire electric capacity Cdc =6 800 F; Switching frequency f of the converter =9 kHz. The artificial waveform is shown as Figs. 3, 4, 5.

The pure resistor of Fig. 3 is supported

Fig. 4 sense hindering type is supported

The commutator type of Fig. 5 is supported

Can be seen by the artificial waveform, under the three-phase symmetric ideal electric wire netting, the control action of the cascade converter is very good, the three-phase electric wire netting input current is the compensating sinusoidal current, the ripple of the direct-flow busbar voltage is very little, subharmonic alternating component 2 hardly exists to fluctuate; The distortion rate of the electric current of the electric wire netting invites 3.

Control strategy and artificial waveform under non-ideal voltage 4

When the input voltage of the cascade converter is asymmetric, if PWM switch function includes the harmonic wave, will influence and can not produce desiredly the harmonic wave in the direct-current volts, especially 2 subharmonics make the voltage ripple of dc output serious. Still influence the input voltage of bridge end of the cascade converter conversely, enable the harmonic wave including grades 3, 5, 9 in the bridge end input voltage, thus has increased the total harmonic distortion rate of the input current.

The three-phase influence symmetrical and including some k subharmonic of the input voltage of the converter is: Make in the direct-flow output voltage including k- 1 And k 1 The subharmonic, by the harmonic wave including k time in this converter of input current, the harmonic wave of the input voltage has been totally transmitted to the three-phase input current also, thus has increased the total distortion rate of the input current and increased the sine difficulty of control of input current.

The three-phase electric wire netting input current is uneven seriously in Fig. 6, B phase current obviously goes beyond the amplitude of other two phase current, and the electric wire netting electric current and inputting the mains voltage of A, C quarter-phase has obvious phase shift, it is not totally 1 to input the power factor, but the direct-flow busbar voltage obviously has a fluctuation of the alternating component of 2 subharmonics. The three-phase electric wire netting input current poises in Fig. 7, but the harmonic composition of the input voltage makes the sine of the input current influenced much, harmonic content 5 times is serious, the total distortion rate is great; The direct-flow busbar voltage fluctuates bigger too, especially harmonic component 4 times.

Fig. 6 inputs the artificial waveform under the voltage imbalance, voltage unbalance of the electric wire netting

Fig. 7 inputs the artificial waveform when the mains voltage include the harmonic wave

The artificial waveform of preceding paragraphs explains, the results are unsatisfactory while controlling a pair of loop-locked control strategy of electric current of voltage under to applying dq axle decoupling under the ideal electric wire netting to the non-ideal electric wire netting. So direct against the non-ideal electric wire netting, seek a kind of control strategy suitable for its special property, dq 0 axle with harmonic feedforward of the mains voltage controls, makes the output voltage of bridge end of the converter include the harmonic component of equidimension, there is no harmonic current in the input current to exchange. Fig. 8 is that dq 0 axle with harmonic feedforward of the mains voltage control the system block diagram, Fig. 9 is its artificial waveform.

Fig. 8 dq 0 axles with harmonic feedforward of mains voltage control the system block diagram

Fig. 9 dq 0 axles with harmonic feedforward control the harmonic analysis of artificial waveform and Isa

We can see from artificial waveform, waveform and unbalance degree of the three-phase electric wire netting input current get good control, the total harmonic distortion rate of I s a is 1 respectively. 74, waveform distortion has got very great improvement; And the direct-current volts is steady, the ripple is minor, the harmonic wave in the straight flow side is reduced to some extent.

5 conclusions

The simulation result shows: Dq 0 axle control method with harmonic feedforward of the mains voltage adopted can obtain the fine control result. It is the sine current source of fundamental wave to connect the converter in series controlledly, the electric current I s of the power is and the in-phase sine active current of voltage of fundamental wave of power, harmonic wave and the intersection of fundamental wave and deflection in the mains voltage connect in series into converter, compensate ‘ Or isolate .