Five, embodiment
The present invention is described in further detail below in conjunction with embodiment that accompanying drawing and inventor provide.
Before introducing particular content of the present invention, at first introduce the characteristics of output power of inverter in parallel, afterwards labor automatic host-slave parallel networking control strategy and implementation thereof again.5.1 inverter power output in parallel is analyzed
The distributed generation system or the ups system that compose in parallel by inverter, it is the system of a complexity, the alternating voltage of each inverter output can equivalence be a controllable voltage source, its frequency, phase place, amplitude be cooperation mutually, common burden load current promptly will be realized the balanced control of load current.For the ease of analyzing, below be that example is analyzed with two inverters group net operations in parallel.Equivalent circuit diagram when Fig. 1 is two inverters group net operations in parallel comprises two ideal inverse variable power source modules in parallel and is connected on load on the AC bus, wherein Z
1, Z
2Be line impedance, Z
0Be load impedance.
In distributed generation system, the resistance of circuit is less, and line impedance mainly is perception, i.e. Z
1≈ j ω L
1, Z
2≈ j ω L
2, and the output voltage of inverter of two parallel operations among the hypothesis figure
1,
2Be standard sine, and their capacity is respectively S
1, S
2, and S
2=nS
1, then:
The complex power of inverter 1 supply load is:
The output current of inverter 1 is:
Draw by formula (1), (2):
Because the output voltage of general inverter
1With system voltage
0Between phase difference very little, sin then
1≈
1If make U
1=k
1U
0Then draw by formula (3):
In the formula:
Be the active power coefficient;
Be the reactive power coefficient;
The power output that in like manner draws
inverter 2 is:
Can draw the power characteristic of each inverter output in parallel according to formula (4), (5):
1) active power of inverter output depends primarily on phase angle , and proportional with phase difference, and phase difference surpasses the former and sends active power, otherwise absorbs active power; The big more active power of sending or absorbing of phase difference is big more.The adjusting of inverter phase angle realizes by the fine setting frequency f, therefore, regulate the active power of each inverter output, only needs the frequency of output voltage is done corresponding the adjustment.
2) reactive power of inverter output then depends primarily on the voltage magnitude U of output, and the high person of amplitude sends reactive power, on the contrary absorbing reactive power; The output voltage amplitude difference is big more, send or the reactive power that absorbs big more.
The frequency of the output voltage by changing inverter control output active power, control the reactive power of output by the output voltage amplitude that changes inverter, thereby the approximate decoupling zero that the frequency of inverter (phase place) and two key elements of amplitude active power P and reactive power Q by output carries out non-strictness is controlled.This power characteristic that just is being based on the automatic host-slave parallel networking of the relevant inverter of the present invention synchronous operation control strategy and no interconnected holding wire independence control strategy realizes.5.2 the automatic automatic host-slave parallel control principle of host-slave parallel networking control strategy 5.2.1
Automatically principal and subordinate's control technology is a kind of parallel system of redundancy, it is based on, and the power characteristic of inverter output in parallel controls, that is: the active power of inverter output in parallel depends primarily on phase angle , and phase difference surpasses the former and sends active power, otherwise absorbs active power; The reactive power of parellel inversion power output then depends primarily on the voltage magnitude U of output, and the high person of amplitude sends reactive power, on the contrary absorbing reactive power.The adjusting of inverter phase angle realizes by the fine setting frequency f, regulate the active power of each inverter output, only needs the frequency of output voltage is done corresponding the adjustment.The frequency of output voltage that therefore, can be by changing inverter is controlled the active power of output; Control the reactive power of output by the output voltage amplitude that changes inverter, thereby can be similar to decoupling zero control to the frequency of inverter (phase place) and two key elements of amplitude by the active power P and the reactive power Q of output.Inverter is when parallel running, and each power module can be according to capacity and the meritorious regulated quantity Δ P of output, the idle regulated quantity Δ Q of self, then to the given f of its frequency
r, the given U of voltage magnitude
rRegulate the inhibition with circulation of dividing equally that realizes load current accordingly.
Fig. 2 is the schematic diagram of automatic principal and subordinate's control technology.As can be seen from the figure, every inverter in parallel has oneself oscillator, voltage waveform controller, and active power is selected main control unit automatically, reactive power is selected main control unit automatically.System is by selecting the control of master unit automatically, automatically the big module of active power of output as meritorious primary module, all the other modules then for meritorious from module, active power bus P
BUSValue by the active power of output power decision of meritorious primary module; System is by selecting the control of master unit automatically, and exporting the big module of reactive power as idle primary module, all the other modules then are idle from module, reactive power bus Q automatically
BUSValue by the reactive power decision of idle primary module output, all desirable reactive powers from module output all should be Q
BUSValue.Therefore there are meritorious primary module and idle primary module in the system simultaneously.
If a certain inverter active power of output P
iAnd reactive power Q
iNot desirable P
BUSSum Q
BUSValue, then its deviation is:
The active power deviation and the reactive power deviation that can be drawn inverter i output by formula (4) are:
Therefore to make every inverter realize the consistent of power output and primary module, as long as every electric current I and output voltage V that inverter oneself is exported by sampling from module from module
0Calculate the active power P of output
iAnd reactive power Q
i, and respectively with active power bus P
BUSWith reactive power bus Q
BUSRelatively, obtain deviation delta P
iWith Δ Q
i, again with Δ P
iAs phase place
iCompensation rate, Δ Q
iAs amplitude U
iCompensation rate is adjusted the voltage of output, realizes each inverter load-sharing power in parallel, thereby has realized high-precision sharing control between inverter.
If the capacity of inverter in parallel does not wait in system, then to the active power and the reactive power of its output be marked the change processing according to the capacity of inverter, thereby make each inverter can bear the active power and the reactive power of load by its capacity, be the more power of inverter output capacious, the inverter output less power that capacity is little.Mark is changed relational expression:
Before promptly should sending the active power value of reality output and reactive power value by the power calculation unit of every inverter, should be with they rated capacity S divided by inverter
iMark and change processing.5.2.2 select the principle and the implementation thereof of main control unit automatically
Automatically selecting main control unit is a key link of automatic host-slave parallel controlling schemes, meritorious primary module and idle primary module that it determines system according to the active power and the reactive power of the output of each inverter module of parallel connection.The module that active power of output is big is designated as meritorious primary module, and meritorious primary module competition automatically obtains active power bus P
BUSAnd the value of own active power of output outputed to active power bus P
BUSOn, gaining merit that other are all then abandoned active power bus P automatically from module
BUSCompetition, and active power bus P
BUSValue as the benchmark of own active power of output, promptly all meritorious from module according to P
BUSValue regulate oneself output active power; In like manner, the big module of output reactive power is designated as idle primary module, and idle primary module competition automatically obtains reactive power bus Q
BUS, and oneself output reactive power value output to reactive power bus Q
BUSOn, other all idlely then abandons automatically reactive power bus Q from module
BUSCompetition, and reactive power bus Q
BUSValue as the own benchmark of exporting reactive power, promptly all idle from module according to Q
BUSValue regulate oneself output reactive power.
Automatically select main control circuit, as shown in Figure 3.In the drawings, because the unilateral conduction of diode has only meritorious (idle) prominent module, just conducting of diode, the value of meritorious (idle) power generatrix equals meritorious (idle) performance number of meritorious (idle) the prominent module of output.Under normal circumstances, meritorious (idle) of each module output equates, if i
#Meritorious (idle) power of module output increases suddenly, becomes one maximum in n the module, so, P
i(Q
i) rise, this module becomes meritorious (idle) primary module automatically, and other module is from module, at this moment, P
BUS=P
i(Q
BUS=Q
i), the Δ P of primary module
i=0 (Δ Q
i=0), and respectively from the P of module
k(Q
k) and P
BUS(Q
BUS) relatively, produce meritorious (idle) power error Δ P
k(Δ Q
k), error is adjusted the frequency (amplitude) of its output voltage thus, thereby realizes automatic load-sharing power.
Because the diode among Fig. 3 is included in the inside of voltage follower, therefore the power-sharing error that does not exist the forward voltage drop of diode to bring, does not exist the power-sharing error in theory.In the practical circuit, proportional control is all adopted in choosing master and power-sharing control automatically, and this makes the stability of a system good, the rapid dynamic response speed of power-sharing control.This another advantage of selecting main control circuit automatically is active power bus P
BUSWith reactive power bus Q
BUSBe low-impedance, to insensitive for noise.
According to above analysis, made the automatic master-slave control method of sinusoidal pulse width modulation inverter, system is as shown in Figure 4.In conjunction with Fig. 4, further specify the course of work of the automatic principal and subordinate's control of inverter.Suppose i
#The active power of output P of inverter module
iGreater than all the other each modules, then active power bus P
BUSBy amplifier A
PiDrive, then P
BUS=P
i, i
#The inverter module from module, draws for meritorious for meritorious primary module, all the other modules
Δ P
j=P
i-P
j>0, (j ≠ i) wherein
So Δ f
j>0,
Thereby f
j=f
Rj+ Δ f
j
Be j
#The frequency of inverter module output voltage is in its given frequency f
RjThe basis on compensation Δ f
j, the frequency of its output voltage is improved, the phase place of output voltage moves forward, thereby makes j
#The active power of output P of inverter module
jIncrease gradually; At P
jIn the process that increases, i
#The frequency of inverter module remains unchanged, and its phase place is relative to moving backward, i.e. P
iReduce gradually.Finally, the active power of each inverter module output of parallel running is tending towards equal.In meritorious balanced adjustment process, the frequency of each inverter, the Synchronization Control of phase place have also been realized simultaneously.In like manner, can realize dividing equally of reactive power.
In the automatic host-slave parallel operation control procedure of inverter, there are meritorious primary module and idle primary module, the frequency of system is by the given reference frequency decision of meritorious primary module, the voltage magnitude of system is by output voltage (given reference voltage) decision of idle primary module, therefore the frequency and the voltage magnitude of system are stable, and it is very high that the frequency accuracy of system and amplitude precision can be done.Simultaneously, the consistency of the consistency of the active power of each inverter output and reactive power is all fine.5.2.3 the realization circuit of automatic host-slave parallel networking controlling schemes
According to above analysis, the present invention proposes the automatic host-slave parallel controlling schemes of a kind of high performance digital-analog mixed type inverter, its control block diagram is as shown in Figure 5.It adopts high speed digital signal processor TMS320F240 and extends out voltage, electric current, the active power bus P that 12 A/D detect output
BUSAnd reactive power bus Q
BUSAnd based on instantaneous reactive power theory, calculate active power of output P, the reactive power Q of inverter, calculate frequency f and amplitude U then, synthetic more given voltage instruction, after deliver to the high-performance inverter after 12 D/A conversions, inverter will be according to given voltage instruction output sinusoidal voltage.
Realize dividing equally of active current and reactive current, reduce the circulation between the inverter, must improve the resolution of control resolution, the especially frequency of inverter frequency and amplitude.In the controlling schemes of the present invention, the frequency adjustment resolution of the voltage instruction that DSP sends is 200,000/, this is enough to guarantee the dividing equally of active power of inverter; It is four one thousandths that the amplitude of the voltage instruction that DSP sends is regulated resolution, is enough to guarantee that the reactive power of inverter divides equally, and makes the operation of system stability in parallel.
The high-performance inverter is as the actuator of voltage given instruction, and it has high stability, high voltage stability precision, the high sinusoidal degree of output.It adopts a kind of controlling schemes of novelty, and this scenario-frame is simple, two simple PI adjustable rings is only arranged: instantaneous voltage waveform outer shroud, high speed capacitive current inner ring.The instantaneous voltage outer shroud guarantees the tracking accuracy of output voltage, at a high speed, the capacitive current inner ring of low steady-state error can overcome because of the influence to output waveform of the fluctuation of load or disturbance voltage, make inverter realize that output voltage is near pure sinusoid, and the nonlinear load adaptive capacity is strong, harmonic wave of output voltage resultant distortion rate is little under the diode rectification loading condition, rapid dynamic response speed, adjustment process was short when the impact Reduction of Students' Study Load was carried, output voltage precision height.
Because the high-performance inverter adopts the voltage waveform control technology, in inverter parallel system, line impedance is indispensable, otherwise the voltage waveform ring of inverter can lose efficacy, and makes the inverter cisco unity malfunction.In the inverter parallel system of reality, the output of every inverter has sealed in a suitable resistance.Seal in line impedance and can make the voltage waveform of nonlinear load that certain distortion is arranged, but it can suppress the harmonic circulating current between parellel inversion power, make the distortion power of inverter load-sharing, and needn't consider dividing equally of distortion power from controlling.5.2.4 the experimental result of automatic host-slave parallel control
The automatic host-slave parallel control method of digital-analog mixed type inverter that proposes according to the present invention; made the parallel system of two inverters; the major parameter of every inverter is as follows: capacity is 1.5kVA; switching frequency is 20kHz; unloaded output voltage is 110V; unloaded output voltage frequency is 50Hz, and the series circuit impedance is 0.2mH.Fig. 6~9 are relevant experimental waveform.
Fig. 6 is output voltage waveforms and the output current wave of separate unit high-performance inverter when impact subtracts bridge rectifier filtering load.As can be seen from Figure 6: when the high-performance inverter subtracts bridge rectifier filtering load at impact, output voltage waveforms remains unchanged (the output voltage effective value when actual measurement zero load and loading all is about 110V) substantially, and when the impact Reduction of Students' Study Load is carried, the dynamic adjustment process of output voltage very of short duration (the actual measurement adjusting time is 200 μ s), the THD that loads the back output voltage is 0.17%.
Unloaded circulation waveform when Fig. 7 is two inverters parallel connections, the effective value of the unloaded circulation of actual measurement is about 0.05A, only is 0.4% of output-current rating.
The output current wave of two parellel inversion powers when Fig. 8 is the load of impact drag reduction, the current peak of two inverter outputs is respectively 5.4A, 5.5A.
The output current wave of two parellel inversion powers when Fig. 9 subtracts bridge rectifier filtering load for impact, the electric current peak-to-peak value of two inverter outputs is respectively 33.8A and 32.2A.From Fig. 9,10 as can be seen, the load current effect of dividing equally is fine.
5.3 invention effect
In the automatic host-slave parallel operation control procedure of inverter, the frequency of system is given by meritorious primary module Decide reference frequency and determine that the voltage magnitude of system is by the output voltage (given reference voltage) of idle primary module Determine, so the frequency of system and voltage magnitude be stable that frequency accuracy and the amplitude precision of system can That does is very high; Simultaneously, because the power-sharing ring is outer shroud, can overcome the inverter that is included in the ring All errors (comprise that each inverter is because detecting, control frequency, phase place and the width of cloth of the output voltage that brings The error of value, and the fluctuation of the fluctuation of dc bus, load etc.), thereby each inverter output The uniformity of active power and the uniformity of reactive power are all fine, and the current-sharing effect between inverter is fine.
The Parallel Control that automatic principal and subordinate controls parallel system does not detect the electric current of load, so load can be branch Cloth. Each of parallel running inverter can come according to its capacity the active power, idle of load sharing Power, and be not subjected to the impact of line impedance.
The networking control in parallel of system is what to finish under the control of automatically selecting main control unit. Automatically select master control Built in there not being in theory the power-sharing error, and the main and power-sharing of choosing is controlled equal adoption rate control automatically System, this is so that the stability of a system is good, the rapid dynamic response speed of power-sharing control. This selects master control automatically Another advantage of circuit processed is active power bus PBUSWith reactive power bus QBUSLow-impedance, right Insensitive for noise, no matter power bus be open circuit or short circuit, do not affect the performance of each module.
Though there is meritorious power bus P in the system
BUSWith reactive power bus Q
BUSReduced the reliability of system to a certain extent, increased the cost of system, but compare with centralized control, traditional principal and subordinate control, the signal that these two buses are transmitted is direct current signal substantially, and the pass band of holding wire does not need too high, if some filtering links of suitable increase, eliminate and disturb, then these two buses can long distance be laid.And in centralized control, principal and subordinate's control, current command signal line between the inverter module, what transmit under the situation of linear load is the AC signal of a fundamental frequency, under the situation of nonlinear load, what this command signal line transmitted is a fundamental signal that comprises high-frequency harmonic, therefore the current command signal line is difficult for long distance and lays, otherwise signal attenuation, serious interference.
Automatically principal and subordinate's control is the system of a redundancy, every inverter module status on physical structure is equal to, during any inverter (comprising primary module) fault, just do not influence the normal operation of whole system as long as it can log off fast, the reliability of system is very high.
In sum, in systems such as distributed power generation, UPS, the automatic host-slave parallel control method of sinusoidal pulse width modulation inverter of the present invention has a good application prospect.