CN100576688C - Current converter parallel system and control method thereof - Google Patents

Abstract

The application means a kind of current converter parallel system and control method thereof of not having the communication bus-bar, wherein current converter parallel system comprises the converter of at least two tool instantaneous voltage control kenels that are connected in parallel to each other, each this converter comprises an output voltage waveforms controller and a load allocating controller, output voltage waveforms controller system is electrically connected on the waveform of the output of converter with one of control converter output voltage, load allocating controller system is electrically connected on the load allocating (load-sharing) of this output voltage waveforms controller with the control converter, makes that each converter can have identical phase place under the situation of not having communication, real power (active power) and fictitious power (reactive power).

Description

Current converter parallel system and control method thereof

[technical field]

The present invention means a kind of converter (INVERTER) parallel system and control method thereof, especially refer between the converter of parallel connection, not have the current converter parallel system and the control method thereof of communication bus-bar, distribute (WIRELESS LOAD-SHARING) in order to reach radio bearers.

[background technology]

Along with increasing day by day for the excellent properties of uninterruptible power supply provider (UPS) and the requirement of reliability, the radio bearers of parallel inverter (WIRELESS LOAD-SHARING) technology of distributing just is being widely used on each described product; So-called radio bearers is distributed, mean the converter that is connected in parallel to each other need not by the communication bus-bar can realize each converter between the real merit and the virtual work pro-rata that provide to load.

In order to reach actual redundancy (redundancy) state, several controlled in wireless technology have been proposed in the located by prior art, describe in detail and see also citing document [1] ~ [7], 5,745, No. 356 cases of United States Patent (USP) and United States Patent (USP) 6,381,157B2 case.

In known wireless parallel system, the control method of its use all stems from traditional sagging method (droop method); United States Patent (USP) 6,803, the 679B1 case is an example.And in order to obtain good power division, control loop system is sagging at the frequency and the amplitude of the output voltage of converter, to reach the purpose of load allocating.Yet, exist a great problem in the wireless parallel technology of this class at least: promptly each converter between device parameters inconsistent will influence converter between the precision of load allocating.

[summary of the invention]

The application proposes wireless parallel system of a kind of converter and control method thereof, tie up to converter in parallel between need not connect the communication bus-bar, distribute to reach desirable radio bearers.

The application at first explains the notion of unifying to control at the load allocating of parallel inverter, according to this notion, the main difference between so-called wireless parallel system and traditional wired parallel system just be how to obtain the reference active power of each power converter cells with reference to reactive power; If wireless parallel system can equally obtain identical and correct reference power with wired parallel system, just wireless parallel system can have the load allocating effect identical with wired parallel system.

The application proposed wireless parallel technology system according to the root-mean-square value of load voltage and frequency by so-called static receiver error adjuster (static-error regulator) to obtain real merit and virtual power reference.And Active Power Controller and reactive power controller system design in the mode with higher gain, and be all the more so when stable state especially; This can make the active power stream and the reactive power flow that stem from each converter all correctly follow its reference value.

In the application's wireless parallel system, the root-mean-square value of load voltage and the detection accuracy of frequency are depended in the accuracy of load allocating system.And converter between the inconsistent of device parameters will can the load allocating of converter not exerted an influence.In addition, the application and propose to analyze and experimental result with confirm the validity of the parallel system that proposed and control method thereof.

The application must pass through following graphic and detailed description, in order to do getting more deep understanding:

[description of drawings]

Fig. 1: the schematic diagram of current converter parallel system;

Fig. 2: the schematic diagram of the power circuit control method of current converter parallel system;

Fig. 3: the schematic diagram of the wireless parallel system of converter;

Fig. 4: the schematic diagram of sagging method (droop method) calculation reference power;

Fig. 5: the calcspar of the application's current converter parallel system one embodiment;

Fig. 6: the application is the schematic diagram of the current converter parallel system of basic institute construction with the static receiver error adjuster;

Fig. 7: the schematic diagram of two current converter parallel systems.

Fig. 8: with the dynamic response figure of load current converter parallel system of the application when zero increases to the impedance load suddenly; And

Fig. 9: with the dynamic response figure of load current converter parallel system of the application when zero increases to full rectification load suddenly.

[embodiment]

The load allocating basic skills of ◎ parallel inverter of the present invention

(a) power circuit control rule

See also Fig. 1, it is the schematic diagram of current converter parallel system.Wherein, converter INV1 and INV2 system is connected in a load Z via a filter inductance (X1 and X2) separately.As have the knack of as described in this known to operator also, the active power stream and the reactive power flow that stem from i converter (i=1 or 2) can be represented with (1) formula and (2) formula respectively

(1) formula and (2) formula in, Vi is the amplitude of the output voltage of i converter, ψ i is the phase angle of the output voltage of i converter, Vo then is the amplitude of the terminal voltage of load Z.

Hence one can see that, in order to control the power circuit of each converter in the parallel system, must measure and control at the amplitude and the phase angle of the output voltage of all converters.

See also Fig. 2, it is a kind of schematic diagram of converter power method of flow control.Wherein, no matter be that converter INV1 or INV2 utilize active power and reactive power controller and a sinusoidal reference baud generator to carry out the control of power circuit.Because the high-gain of active power and reactive power controller, it is as follows that the power circuit system that therefore is derived from each converter follows reference value fully

P ₁＝P _ref1 Q ₁＝Q _ref1

P ₂＝P _ref2 Q ₂＝Q _ref2

In wired parallel system, all converters all have identical reference power because of communication to each other, that is

P _ref1＝P _ref2 Q _ref1＝Q _ref2

Simultaneously, also can reach excellent converter load allocating by the power circuit control method, that is

P ₁＝P ₂ Q ₁＝Q ₂

(b) in wireless system, obtain reference power

Clearly, the key point of reaching load allocating is how to make that all parallel inverters obtain identical reference power; Is yet problem how we obtain identical reference power under the situation that does not communicate to connect (wireless)?

See also Fig. 3, it is the schematic diagram of the wireless parallel system of converter in the located by prior art.Wherein, do not have any bus-bar of communicating by letter between converter INV1 and INV2, but still be connected in same load Load jointly.The information system of load voltage vo is common to all converters; In other words, converter INV1 and the INV2 live of all can thinking highly of oneself is pressed and is obtained identical information.Hence one can see that, if converter INV1 and INV2 can obtain reference power by same calculation rule from the information of load voltage vo, just the reference power of converter INV1 and INV2 can be identical so.

In general, load voltage can be represented by following formula

v ₀＝V ₀sinω ₀t

From the information of load voltage vo, can determine the amplitude V0 and the frequencies omega 0 of load voltage, so the reference power of each converter just can be derived according to following calculation rule

P _ref＝f ₁(V ₀，ω ₀)

Q _ref＝f ₂(V ₀，ω ₀)

If V0 and ω 0 are known,,, and reach excellent load allocating so converter INV1 just can obtain identical reference power from load voltage vo with INV2 just then Pref and Qref can be determined onlyly.

For instance, Fig. 4 is the schematic diagram of sagging method calculation reference power.Sagging method shown in the figure is a kind of in order to obtain the calculation rule of reference power, and this rule can be represented by the following relationship formula:

P _ref＝P _set-k ₁V ₀

Q _ref＝Q _set-k ₂ω ₀

Wherein, Pref is with reference to active power, and Qref is with reference to reactive power, and Pset and Qset are constant, and k1 and k2 are respectively the slope of active power function (left figure) and reactive power function (right figure).

Certainly, though this sagging method is simple, its non-only or the most handy method.In fact, if f ₁(V ₀, ω ₀) and f ₂(V ₀, ω ₀) be the monotonic function of V0 and ω 0, then all converters just can reach identical reference power; In this case, function f ₁(V ₀, ω ₀) and f ₂(V ₀, ω ₀No matter) construction just can so that each converter in stable state with dynamically down all have a good response.

◎ the application's preferred embodiment

According to above-mentioned analysis, the application proposes a kind of current converter parallel system, can reach converter between radio bearers distribute; See also Fig. 5, it is the calcspar of the application's current converter parallel system one embodiment.

In Fig. 5, device calculates by a loop control unit, a rms voltage calculator, a frequency calculator, an active power and reactive power in current converter parallel system system and a sinusoidal reference baud generator is constituted.

In Fig. 5, loop control unit is to make the output voltage floating voltage reference of converter, rms voltage calculator and frequency calculator with the root-mean-square value Vo of this output voltage V o and frequency (phase angle) ω o calculate respectively after it is delivered to active power and reactive power is calculated device, active power and reactive power calculate device calculate respectively again a reference amplitude Vamp and a reference frequency fref after, the two is delivered to the sinusoidal reference baud generator to produce one of may command loop control unit sinusoidal reference ripple Vref.

The ◎ radio bearers is distributed

See also Fig. 6, it is the schematic diagram of the current converter parallel system of basic institute construction with the static receiver error adjuster for the application.Wherein, current converter parallel system mainly is by representing one of inner looping output voltage waveforms controller and represent one of external loop load allocating controller to be constituted, have more a sinusoidal reference baud generator between inner looping and external loop.Represent the output voltage waveforms controller system of inner looping to be constituted, and the load allocating controller system that represent external loop is made of one of responsible active power distribution root mean square adjuster and one of an Active Power Controller and the distribution of responsible reactive power system frequency adjuster and a reactive power controller by a voltage controller VR and a current controller CR.

In Fig. 6, in order to reach good load allocating, Active Power Controller and reactive power controller system design in the mode with higher gain, and be all the more so when stable state especially; This can make the active power stream and the reactive power flow that stem from each converter all correctly follow its reference value.What deserves to be mentioned is, active power and reactive power controller system usually are designed to proportional integral (PI) kenel, except that this, it also can be designed to the controller of other kind, for example: smooth mode (slide mode), ambiguity type (fuzzy), adaptability (adaptive) or gamma controller.

In Fig. 6, root mean square adjuster and system frequency adjuster as reference power generator are in order to guarantee the pinpoint accuracy of load voltage root-mean-square value and frequency respectively, in general, both are very accurate on design concept, so can be so that load voltage dynamically and aspect the stable state two all has good response for root-mean-square value and frequency.

In wireless parallel system, root mean square adjuster and system frequency adjuster are most criticals, they not only can guarantee the pinpoint accuracy of root-mean-square value and frequency, also can obtain the active power and the idle reference power of each converter, to reach load allocating good in the wireless system.

In located by prior art, root mean square adjuster and system frequency adjuster system are designed to the kenel of astatic error, yet, in the application's wireless current converter parallel system, but be designed to the kenel of static receiver error, this makes and to determine onlyly that with reference to active power Pref with reference to root-mean-square value V0 and frequencies omega 0 that reactive power Q ref is output voltage respectively therefore all converters just can obtain identical reference power.

Aspect the active power distribution, Vref is the reference of load voltage root-mean-square value, and Vo is the load voltage root-mean-square value, wherein

Verr＝Vref-Vo

Root mean square adjuster by voltage can obtain with reference to active power Pref

Pref＝f(Verr)

Po is an active power stream, deducts Po with reference to active power Pref and can produce an active power error Perr, can be produced the input amplitude Vamp of sinusoidal reference baud generator by Active Power Controller.

Because the existence of Active Power Controller, active power stream Po begins just can closely follow with reference to active power Pref from the root mean square adjuster of voltage, that is

Po＝f(Verr)

Can find out that from this equation active power of output Po just can change with the variable quantity of output voltage root-mean-square value Vo.

Though be that converter with two parallel connections illustrates (as the schematic diagram of the current converter parallel system of Fig. 7) as an example, yet the application also can promote under the deriving of haveing the knack of this described operator and can be applicable to plural current converter parallel system herein.In Fig. 7, the in parallel mutually and any communication line of tool not to each other of converter INV1 and converter INV2 system, because two converters all are to be connected in load Load, therefore the root mean square output voltage values Vo1 of converter INV1 equals the root mean square output voltage values Vo2 of converter INV2, and the active power of output value Po2 of the active power of output value Po1 of converter INV1 and converter INV2 also is equal to each other.Hereat, two converters can be reached correct active power distribution.

Please return Fig. 6, similarly, aspect the reactive power distribution, fsys is the output frequency of being asked, and fo is the load voltage frequency, wherein

ferr＝fsys-fo...............

Can obtain with reference to reactive power Q ref by the system frequency adjuster.

Qo is a reactive power flow, and Qref deducts Qo can produce a reactive power error Qerr, can be produced the reference frequency fref of converter by reactive power controller.

The reference reactive power Q ref that the system frequency adjuster is produced can represent by following formula

Qref＝f(ferr)

Wherein f (ferr) is the function representation of system frequency adjuster.

Because the existence of reactive power controller, reactive power flow Qo begins just can closely follow with reference to reactive power Q ref from the system frequency adjuster, that is

Qo＝f(ferr)

From this equation, parallel system just can correctly be reached the distribution of reactive power.

◎ obtains reference power by the static receiver error adjuster

Equation (3) is a kind of calculation rule that widely is used in converter control.

u(k)＝λu(k-1)+αe(k)-βe(k-1) (3)

Wherein, u (k) is k the instantaneous sample output controlled variable constantly of controller, and e (k) is the error originated from input of k instantaneous sample, and α and β are coefficients, usually α＞β＞0.

λ is decline coefficient (decay factor), 0＜λ≤1 in general.When λ=1, equation (3) just is traditional proportional integral (PI) calculation rule, and it becomes a kind of astatic error controller, can guarantee that output error is zero when stable state, that is

e(+∞)＝0

When 0＜λ＜1, controller just becomes a kind of digit delay (lag) controller, and it is compared with traditional PI calculation rule has higher phase boundaries and preferable dynamic response usually, but it is a static receiver error controller, and the stable state output error is

$e(+\∞)=\frac{1-\mathrm{\λ}}{\mathrm{\α}-\mathrm{\β}}u(+\∞)---\left(4\right)$

Clearly, when λ hour, controller just has higher phase boundaries but bigger steady-state error; And when λ was big, controller just had lower phase boundaries but less steady-state error.When λ steady-state error just approaching more zero near 1 time more.Therefore, by design parameter λ suitably just can reach phase boundaries and steady-state error between balance (trade-off).

In this application, postpone control calculation rule system be applied to root mean square adjuster and system frequency adjuster in, by design parameter λ suitably, make parallel system not only have the pinpoint accuracy of load voltage root-mean-square value and frequency, the well loaded that also has active power stream and reactive power flow is distributed.

(a) active power is distributed

Rms voltage regulated device can design by following formula

P _ref(k+1)＝λ ₁P _ref(k)+α ₁V _err(k+1)-β ₁V _err(k) (5)

When n 〉=1,

$P_{\mathrm{ref}}(k+n)={{\mathrm{\λ}}_1}^n{P}_{\mathrm{ref}}\left(k\right)+{\mathrm{\α}}_1\underset{i=1}{\overset{n}{\mathrm{\Σ}}}{{\mathrm{\λ}}_1}^{i-1}{V}_{\mathrm{err}}(k+n-i+1)-{\mathrm{\β}}_1\underset{i=1}{\overset{n}{\mathrm{\Σ}}}{{\mathrm{\λ}}_1}^{i-1}{V}_{\mathrm{err}}(k+n-i)---\left(6\right)$

And work as | λ ₁|＜1 and n →+∞, λ ₁ ⁿ→ 0 o'clock,

$P_{\mathrm{ref}}(k+n)={\mathrm{\α}}_1\underset{i=1}{\overset{n}{\mathrm{\Σ}}}{{\mathrm{\λ}}_1}^{i-1}{V}_{\mathrm{err}}(k+n-i+1)-{\mathrm{\β}}_1\underset{i=1}{\overset{n}{\mathrm{\Σ}}}{{\mathrm{\λ}}_1}^{i-1}{V}_{\mathrm{err}}(k+n-i)---\left(7\right)$

Hence one can see that, and in parallel system, even the reference active power of all converters is also inequality at certain instantaneous moment, but after passing through certain period, the reference active power of all converters also much at one.

According to equation (5), the root mean square adjuster is a kind of static receiver error adjuster, under static situation,

$P_{\mathrm{ref}}=\frac{{\mathrm{\α}}_1-{\mathrm{\β}}_1}{1-{\mathrm{\λ}}_1}{V}_{\mathrm{err}}---\left(8\right)$

In other words, the reference active power of converter system is one to one corresponding to the error of VRMS voltage root mean square under the static state.

${\mathrm{<figure-callout\; id="1"\; label="K\; droop"\; filenames="C2005100778660018H1.png,C2005100778660020H1.png"\; state="\{\{state\}\}">K</figure-callout>}}_{\mathrm{droop}}=\frac{{\mathrm{\&alpha;}}_1-{\mathrm{\&beta;}}_1}{1-{\mathrm{\&lambda;}}_1}---\left(9\right)$

P _ref＝K _droop1(V _ref-V _o) (10)

Certainly, the root mean square adjuster can also be designed to other pattern, for example: sliding mode controller, ambiguity type control and gamma controller etc., but the root mean square adjuster is necessary for a static receiver error adjuster, and its output (effective reference power of converter) is one to one corresponding to the error of VRMS voltage root mean square under the static state, so just can reach the load allocating of system.

Be load voltage indifference all of each converter of being detected of hypothesis in above-mentioned analysis, yet in fact, because the difference of line impedence and testing circuit, the load voltage of each converter that is detected also can be not identical.

For instance, when load voltage is V0, and the detection voltage among converter INV1 and the INV2 is when being respectively V01 and V02, according to above-mentioned analysis, and when stable state,

P _ref1＝K _droop1(V _ref-V ₀₁)

P _ref2＝K _droop1(V _ref-V _o2)

ΔP _ref＝P _ref1-P _ref2＝K _droop1(V ₀₂-V ₀₁) (11)

Therefore to distribute error mainly be that the detection error of load voltage root-mean-square value produces to active power.

(b) reactive power is distributed

Similarly,

The system frequency adjuster can design by following formula

Q _ref(k+1)＝λ ₂Q _ref(k)+α ₂f _err(k+1)-β ₂f _err(k) (12)

And the reactive power distribution result is shown in equation (13)

Q _ref＝K _droop2(f _sys-f _o)

ΔQ _ref＝Q _ref1-Q _ref2＝K _droop2(f ₀₂-f ₀₁) (13)

Can draw the assignment accuracy that the wireless parallel system of the application's converter can not influence real merit and virtual power because of the inconsistent of device parameters between each converter via above-mentioned analysis.

The ◎ experimental result

For the usefulness performance of the current converter parallel system that proves the application and control method thereof, experiment system one of is constituted parallel system with two converters and is carried out; Experimental result sees also Fig. 8 and Fig. 9, Fig. 8 is the dynamic response figure with load current converter parallel system of the application when zero increases to the impedance load suddenly, and Fig. 9 is the dynamic response figure with load current converter parallel system of the application when zero increases to full rectification load suddenly.Show that by the experimental result among the figure the application's radio bearers distribution technique has been brought into play great effect, among the figure, i _L1And i _L2System is respectively the inductive current of two converters, and U is a load voltage.

The ◎ conclusion

According to the application's current converter parallel system, distribute for desiring to reach radio bearers, how obtaining identical reference power at each converter from load voltage is one of most important ring.Based on this point, the application proposes a kind of radio bearers distribution system that is applied to parallel inverter especially; In this system, root mean square adjuster and system frequency adjuster system are designed to the static receiver error adjuster, and also being discussed among the embodiment, so-called digit delay controls algorithm, by choosing the parameter of delay controller, not only good load allocating be can reach, excellent stable state and dynamic response also can on load voltage, be obtained.Certainly, in the application's wireless parallel system, can also use the usefulness of the static receiver error adjuster of other kenels as root mean square adjuster and system frequency adjuster.

The application must be thought and is to modify right neither taking off as Protector that attached claim is desired as all by the personage Ren Shi craftsman who is familiar with this skill.

Claims (13)

1. the control method of a current converter parallel system, this current converter parallel system have at least two converters with instantaneous voltage control kenel that are connected in parallel to each other, and these converters are to supply power to load by bus-bar, and this control method comprises the following steps:

The first step, the voltage signal of this bus-bar of taking a sample;

Second step, the power signal of each this converter of taking a sample;

In the 3rd step, this voltage signal that processing is taken a sample is to obtain power reference signal, and wherein this power reference signal is by the root-mean-square value and the unique decision of frequency of bus bar voltage; And

The 4th step, relatively this power reference signal and each this power signal of being taken a sample, and output converter control signal makes each this power signal follow this power reference signal to each this converter.

2. control method according to claim 1 is characterized in that, the 4th step made each this power signal follow this power reference signal for the output voltage waveforms controller of this converter control signal of output to each this converter.

3. control method according to claim 1 is characterized in that, this voltage signal is a VRMS voltage root mean square, and each this power signal is the active power signal.

4. control method according to claim 1 is characterized in that, this voltage signal is the system frequency value, and this power signal is a reactive power signals.

5. current converter parallel system, comprise at least two converters that are connected in parallel to each other with instantaneous voltage control kenel, these converters are to supply power to load by bus-bar, each this converter comprises output voltage waveforms controller and load allocating controller at least, and wherein this load allocating controller comprises:

The voltage sampling device is in order to the voltage signal of this bus-bar of taking a sample;

The power sampler is in order to the power signal of this converter of taking a sample;

The reference power generator, in order to handle this voltage signal taken a sample to obtain power reference signal, wherein this power reference signal is by the root-mean-square value and the unique decision of frequency of bus bar voltage; And

Power controller in order to receive this power reference signal and itself and this power signal of being taken a sample are compared, to this output voltage waveforms controller, makes this power signal follow this power reference signal with output converter control signal.

6. current converter parallel system according to claim 5 is characterized in that, this voltage signal is a VRMS voltage root mean square, and this power signal is the active power signal.

7. current converter parallel system according to claim 6 is characterized in that, this reference power generator is a voltage root mean square adjuster.

8. current converter parallel system according to claim 7 is characterized in that, this power controller is an Active Power Controller.

9. current converter parallel system according to claim 8 is characterized in that, this Active Power Controller be selected from pi controller, sliding mode controller, ambiguity type controller, Adaptive Control device and gamma controller one of them.

10. current converter parallel system according to claim 5 is characterized in that, this voltage signal is the system frequency value, and this power signal is a reactive power signals.

11. current converter parallel system according to claim 10 is characterized in that, this reference power generator is the system frequency adjuster.

12. current converter parallel system according to claim 11 is characterized in that, this power controller is a reactive power controller.

13. current converter parallel system according to claim 12 is characterized in that, this reactive power controller be selected from pi controller, sliding mode controller, ambiguity type controller, Adaptive Control device and gamma controller one of them.

Images