CN106849720A - One kind is used for Modular UPS parallel power control method in a balanced way - Google Patents

Abstract

It is used for Modular UPS parallel power control method in a balanced way the invention discloses one kind, specifically includes following steps：Two single-phase uninterrupted power source Converting Units equivalent control model in parallel is set up, inverter uses half-bridge structure；Two parallel UPSs flow equal power using virtual resistance feedback control strategy, and by the equivalent suppression for realizing parallel connection circulation of virtual resistance of connecting, the equal power capability of stream of strengthening system is specifically included：The suppression of active circulation, reactive circular power flow and DC loop-current.The present invention is directed to two single-phase UPS Converting Units and associated load electric power system, using the control method of equivalent series virtual resistance, by adding virtual resistance feed-forward loop in UPS contravarianter voltage current loop control block diagrams, greatly reduce circulation caused by being had differences due to each parallel UPS, so as to realize the suppression to active circulation and reactive circular power flow, so balanced parallel system power output；The suppression of overall circulation is realized, the stream ability of parallel system is improve.

Description

One kind is used for Modular UPS parallel power control method in a balanced way

Technical field

Patent of the present invention is related to a kind of for Modular UPS parallel power control method in a balanced way.

Background technology

With continuing to develop for modern industry, electrical equipment is increasingly enriched, and substantial amounts of sensitive instrument and equipment is appeared in In modern industry occasion, in communications and transportation, information communication, industrial automation production field, the effect that can not be substituted is played.And These equipment whether can safe and reliable lasting running, be directly connected to people into produce and live, equipment whether can be reliable The operation of stabilization, except being decided by equipment technology and quality level in itself, whether the safety for being also dependent upon to provide stabilization can The electric energy for leaning on.

With continuing to develop for Power Electronic Technique, transformation of electrical energy technology causes that AC-DC, DC-AC are for conversion into possibility, no Uninterruptible power (UPS) can both make to continue to power to the load during municipal power failure, ensure the normal operation of load, isolation can be played again and is made With to the high-quality power supply of load offer stabilization.Its major function is for load provides continual power supply, it is to avoid powers off and causes System failure problem, it can effectively solve the problems, such as to have influence on power supply quality, it is ensured that load running it is reliable and stable.

Thus, in the power quality that can ensure to load supplying of being powered using UPS, but real system with separate unit UPS come Its reliability of powering is difficult to be guaranteed, if the UPS module breaks down, still may result in being powered to load equipment It is disconnected, and in the key equipment of some important application scenarios or system, such failure occur can bring about great losses. If several UPS modules are connected in parallel as an entirety, the UPS parallel systems of redundancy properties are formed, powered to the load When, all UPS in parallel running of whole system can realize flowing, if a UPS breaks down, can voluntarily exit parallel connection Repaired, without influence whole system operation, loaded normal power supply, improve the stability and reliability of ups power.

Although parallel UPS can improve electric power system stability, connect due to the difference of each UPS device property and with load Wire length is different, and different unit output internal impedances have differences in parallel system, even if amplitude, the phase of each UPS output voltages Position is identical with frequency, and the difference can also cause power and not divide equally to output current is loaded, and causes between each parallel UPS Circulation is produced, the output characteristics of UPS is influenceed.Thus, in order to realize the equal power of stream of parallel UPS, seeking one kind is not increasing Suppressing the control strategy of parallel system circulation on the premise of power attenuation is worth exploring.

The present invention is established based on two single-phase uninterrupted power source (UPS) Converting Units equivalent control model in parallel, inversion Device uses half-bridge structure, flows equal power using virtual resistance feedback control strategy, is realized simultaneously by the way that virtual resistance of connecting is equivalent It is associated with the suppression of work(circulation reactive circular power flow and DC loop-current, the equal power capability of stream of strengthening system.It is bicyclic based on voltage x current Control block diagram, adds virtual resistance feed-forward loop, and the relation that circulation resists with inverter equivalent internal resistance is obtained according to equivalent-circuit model, Consider the power output that line resistance in DC loop-current equivalent model brings UPS inverters to be lost, it is suitable by selection Virtual resistance realize the optimal inhibition effect of circulation, improve the stream ability of parallel system.The method is for based on many lists Phase uninterrupted power source (UPS) Converting Unit equal Power Control of stream in parallel is significant.

The content of the invention

The technical problems to be solved by the invention are, defeated to loading for two single-phase uninterrupted power source (UPS) parallel systems Go out the requirement of electric current and Power balance control, there is provided a kind of parallel power control method in a balanced way, suppress due to each parallel UPS Internal impedance difference and the inconsistent caused parallel system circulation of DC bus-bar voltage, it is ensured that load current during UPS parallel runnings With the equilibrium assignment of power, the equal properties of flow and stability of whole system are improved, improve current sharing control accuracy.

In order to solve the above technical problems, the technical solution adopted in the present invention is：One kind is used for Modular UPS Parallel power control method in a balanced way, the method is derived using based on the bicyclic series connection virtual resistance control method of voltage x current The relation of circulation and two shunt chopper internal impedances in continuous domain, and it is produced in inverter circuit to combine DC loop-current Power attenuation, choose optimal virtual resistance value, circulation is reached minimum value with power attenuation, optimal circulation is reached with this Inhibition.

The technical scheme that the present invention solves above-mentioned technical problem is comprised the following steps：

1) basic structure powered to the load based on two single-phase UPS Converting Units parallel connections, according to KCL theorems, foundation side Journey is as follows：

Wherein, i_oAnd i_hCirculation respectively between the load current of parallel system and two single-phase UPS, i_o1And i_o2Respectively It is two output currents of UPS, i_LAnd i_cRespectively output inductor electric current and capacitance current, due to inverter output circuit It is LC parallel filtering circuits, according to circuit structure, the relational expression of each magnitude of current is as shown in above formula.According to the pass of each magnitude of current of above formula System can set up the equivalent control block diagram of separate unit UPS voltage x current rings；

2) the equivalent control block diagram based on separate unit UPS voltage x current rings in 1), adds virtual resistance feed-forward loop, that is, choose filter Ripple inductive current is multiplied by virtual resistance (feed-forward coefficients), the input of the inverter output voltage controller that is added to, and obtains New voltage x current ring control block diagram, calculates and contrasts expression of the parallel connection circulation in s domains before and after virtual resistance feed-forward loop is added Formula.For separate unit UPS, inverter output voltage can be respectively relative to the closed loop transfer function, of output order voltage and output current It is expressed as

Wherein, U_o(s), U_ref(s) and I_oS () represents UPS output voltages, output order voltage and output electricity in s domains respectively The expression formula of stream, G_v(s) and Z_oS () is respectively UPS output voltages and is transmitted relative to the closed loop of output order voltage and output current Function, Z_oS () is regarded as output impedance.

According to principle of stacking, UPS output voltages are represented by s domains

U_o(s)=U_ref(s)G_v(s)-I_o(s)Z_o(s)

Then two output currents of parallel UPS can be expressed as in s domains

Wherein, I_o1(s), I_o2(s) and U_o1(s), U_o2S () is respectively the output current and output voltage of two UPS in s domains In expression formula, then system parallel connection circulation be represented by

I_hS () is expression formula of the parallel connection circulation in s domains, compare the Z added before and after virtual resistance feedforward_oS (), checking adds Enter validity of the virtual resistance to loop current suppression, the controlling unit in control block diagram is converted in s domains and obtained.

3) it is logical to carry the Balance route of active power that virtual resistance exports to inverter and reactive power in realizing 2) The Balance route for crossing analysis watt current and reactive current realizes dividing equally for power, and all voltage x current amounts are s in the step Expression formula in domain, according to step 1) in two single-phase UPS inversions bands carry the basic structures of parallel system, it is assumed that two UPS are inverse Become output voltage equal, and inverter equiva lent impedance is expressed as：

U₁=U₂=U

Z₁=R₁+jX₁,Z₂=R₂+jX₂

Wherein, U₁And U₂The amplitude of the equivalent output voltage of inverter is represented respectively, and the two is equal, is set to U, Z₁And Z₂Point Not Biao Shi inverter equivalent internal resistance resist, R₁And R₂Resistance, X in representing respectively₁And X₂Internal reactance is represented respectively；

According to Dai Weinan equivalent theorems and circuit add-up principle, active component and idle point in load voltage and system circulation Amount is expressed as follows with the relation of two inverter output voltages and internal impedance：

Wherein, U_oAnd I_hThe amplitude of load voltage and circulation, I are represented respectively_phAnd I_qhThe active component of circulation is represented respectively And reactive component.By taking active circulation as an example, by U_oExpression formula substitute into I_ph, two inverter internal impedances after analysis addition virtual resistance The relation that difference changes with circulation, by virtual resistance R_vSubstitute into above formula equivalent internal resistance R₁And R₂In, expression formula is as follows：

R_1eq=R₁+R_v

R_2eq=aR₁+R_v

Wherein, R_1eqAnd R_2eqThe equivalent internal resistance after two UPS addition virtual resistances is represented respectively, and a is R₂Relative to R₁'s Interior resistance ratio coefficient, for representing two internal resistance differences of parallel UPS, considers interior in the case where virtual resistance changes respectively The influence of resistance and internal reactance to parallel connection circulation, inhibitory action of the analysis virtual resistance to active circulation.

4) the DC loop-current equivalent circuit for adding virtual resistance control strategy is set up, in DC loop-current circuit, virtual electricity Resistance is equivalent to and is series in inverter outlet line, it is considered to which the power output loss that line resistance brings to UPS, selection makes power Feedforward amount of the virtual resistance value minimum with circulation absolute value sum as filter inductance electric current is lost, line power loss can table It is shown as

Wherein, P_lossRepresent line power loss, i_o1And i_o2Two output currents of parallel UPS, r are represented respectively₁And r₂ The line resistance that two parallel UPSs are connected with load is represented respectively, and J represents the valuation functions for choosing virtual resistance, | i_h| for simultaneously Join the absolute value of circulation, then should choose makes J be minimum value J_minVirtual resistance as virtual feed-forward loop optimization design scheme, f (R_v) it is the function expression of virtual resistance.Comprehensive analysis line power loses and step 3) in active circulation and virtual resistance Relation curve chooses optimum virtual resistance value, it is ensured that the loop current suppression effect of parallel system is improved on the premise of minimum power line loss Really.

Compared with prior art, the advantageous effect of present invention is that：One kind proposed by the present invention is used for modularization not Uninterruptible power parallel power control method in a balanced way, for separate unit UPS, using voltage x current dual-loop controller respectively to its inversion Output voltage and output current are analyzed and control in s domains；To suppress the circulation that parallel system is produced, with two UPS machines As a example by group parallel connection, the comprehensive voltage x current control of the two, using the control strategy feedovered in outer voltage addition virtual resistance, is led to Cross active circulation and the influence of reactive circular power flow of the analysis virtual resistance to parallel UPS system, suppression of the checking virtual resistance to circulation Effect processed；Further, it is contemplated that the power line loss that line resistance is produced in DC loop-current loop, comprehensive analysis power line loss and circulation are exhausted Minimum value to being worth sum, chooses optimum virtual resistance value to reach the optimal loop current suppression effect of overall parallel system.

Brief description of the drawings

Fig. 1 is for two Modular UPS (UPS) parallel system structure charts of the invention and equivalent-circuit model.

Fig. 2 is the voltage electricity before and after one embodiment of the invention is based on the separate unit UPS of s domain analysis addition virtual resistance feed-forward loops Stream double -loop control block diagram.

Fig. 3 is the relation song of one embodiment of the invention virtual resistance and two parallel UPS internal impedance differences and active circulation Line.

Fig. 4 is two equivalent-circuit models in UPS parallel system DC loop-currents loop of one embodiment of the invention.

Fig. 5 is line resistance power line loss in one embodiment of the invention DC loop-current loop and circulation absolute value and virtually The relation curve of resistance.

Specific embodiment

Fig. 1 is shown for two Modular UPS (UPS) parallel system structure charts of the invention and its equivalent electric Road model.Left figure is parallel system structure chart, is powered to the load using single-phase inverter parallel connection, and two parallel-connection structures are provided for circulation Loop, load meets resistive load R_L, L₁, L₂And C₁, C₂It is respectively the output inductor electric capacity of UPSI and UPSII, T₁~T₂According to Secondary is the power switch pipe up and down of UPSI and UPSII, here using IGBT；E is DC voltage, i_L1And i_L2Respectively UPS is filtered Ripple inductive current, i_C1And i_C2It is filter capacitor electric current, i_o1And i_o2It is the output current of UPSI and UPSII flow direction loads, i_oIt is negative Carry electric current, i_hIt is the circulation between UPSI and UPSII.Right figure is the equivalent-circuit model of the parallel system structure, Z₁=R₁+jX₁ And Z₂=R₂+jX₂The equivalent output internal impedance of respectively UPSI and UPSII, U₁And U₂It is equivalent output voltage, I_o1And I_o2For defeated Go out electric current, I_oIt is load current.

According to the parallel equivalent model, the current relationship between parallel UPS electric current and load is represented by：

Fig. 2 is the voltage x current double -loop control frame before and after the separate unit UPS based on s domain analysis adds virtual resistance feed-forward loop Figure.Wherein, u_refIt is the reference value of each parallel UPS output voltage, i_refIt is output current reference value, i_LIt is filter inductance electric current, i_C It is capacitance current, i_oIt is UPS output currents, that is, flows to the supply current of load；G_PIS () is outer shroud voltage controller, be defined as G_iRing controller in (s) output current, G_pwmS () is inverter equivalent model, it is contemplated that inverter Can be considered first order inertial loop, it is believed thatK_pwmIt is control gain, T is time constant, and L is filtered for output Inductance, C is filter capacitor, capacitance voltage u_cThe as output voltage of UPS.UPS output voltages relative to output order voltage and The closed loop transfer function, of output current is respectively

Control section identical table before and after virtual resistance can be added after voltage x current double -loop control block diagram equivalent transformation Up to formula G₁(s) and G₂(s), it is as follows：

Wherein, U_o(s), U_ref(s) and I_oS () represents output voltage, output order voltage and the output of UPS in s domains respectively The expression formula of electric current.

According to principle of stacking, UPS output voltages are represented by s domains

U_o(s)=U_ref(s)G_v(s)-I_o(s)Z_o(s) (4)

Then two output currents of parallel UPS can be expressed as in s domains

Wherein, I_o1(s), I_o2(s) and U_o1(s), U_o2S () is respectively the output current and output voltage of two UPS in s domains In expression formula, then system parallel connection circulation be represented by

The expression formula of output impedance is before addition virtual resistance feed-forward loop

The expression formula of output impedance is after addition virtual resistance feed-forward loop

It is evident that Z_{o_Rv}(s) ＞ ＞ Z_{o_woRv}S (), illustrates the ring for adding virtual resistance effectively to suppress parallel system Stream.

Fig. 3 is the relation curve of virtual resistance and two parallel UPS internal impedance differences and active circulation.According to Fig. 1 Equivalent-circuit model, it is assumed that the output voltage of two parallel UPSs is equal, and amplitude is U, i.e. U₁=U₂=U, according to Dai Weinan etc. Effect theorem, obtains load voltage as follows with UPS output voltages and its anti-relational expression of equivalent internal resistance：

Then parallel connection circulation can be obtained according to superposition theorem is

Formula (9) is substituted into formula (10) and obtains active circulation I_phFor

By virtual resistance R_vSubstitute into above formula equivalent internal resistance R₁And R₂In, expression formula is as follows：

Wherein, R_1eqAnd R_2eqThe equivalent internal resistance after two UPS addition virtual resistances is represented respectively, and a is R₂Relative to R₁'s Interior resistance ratio coefficient, for representing two internal resistance differences of parallel UPS, only considers active circulation, even X₁=X₂=0, in R₁ Under conditions of constant, R is obtained during formula (12) is substituted into formula (11)_v, a and I_phRelation curve, i.e. I_ph=f (R_v,a)。

By curved line relation as can be seen that with virtual resistance R_vBe continuously increased, by two parallel UPS equivalent internal resistances it Between the active circulation that produces of difference constantly decline, it was demonstrated that the validity of virtual impedance control strategy, proving by the same methods is bright, by etc. The active circulation that effect internal reactance difference is produced also can be with R_vIncrease and decline.The proof procedure of reactive circular power flow is complete with active circulation Exactly the same, the present invention is no longer unnecessary.

Fig. 4 is two equivalent-circuit models in UPS parallel system DC loop-currents loop.Only consider that two is in parallel in straight-flow system The equivalent internal resistance of UPS, DC voltage and outlet line resistance, virtual resistance is in DC loop equivalent to being connected on UPS In outlet line, in figure, U_dc1And U_dc2Respectively the DC side electromotive force of UPSI and UPSII units, R₁And R₂It is equivalent interior electricity Resistance, R_v1And R_v2It is series connection virtual resistance, r₁And r₂It is outlet line resistance, i_dc1And i_dc2Respectively line resistance r₁And r₂Electricity Stream, i_dcIt is DC load current.

Then line resistance electric current i_dc1And i_dc2Expression formula be

Then DC loop-current is

Because load resistance is much larger than line resistance, i.e. R_L＞ ＞ r₁,R_L＞ ＞ r₂, formula (13) negligible r₁r₂Product , simplification can be obtained

Fig. 5 is that the line resistance power line loss in DC loop-current loop is bent with the relation of circulation absolute value and virtual resistance Line.Consider virtual resistance of being connected in outlet line, virtual resistance is with the relation of line resistance and UPS equivalent internal resistances

Formula (16) is substituted into formula (15) can add the line resistance electric current after virtual resistance to be

Wherein,It is the ratio of equivalent internal resistance and the line resistance sum of UPSI and UPSII units,It is the ratio between the two direct electromotive force., then the expression formula of DC loop-current is

Wherein, A=m_u(R₂+r₂+R_v2)+(m_u- 1), B=m_R(R₂+r₂+R_v2)+(1-m_u)R_L, C=m_R(R₂+r₂+R_v2)²+(1 +m_R)(R₂+r₂+R_v2)R_L。

Convolution (17), the power output line loss of two parallel UPSs is represented by

The optimized evaluation function of virtual resistance can be expressed as

J=P_loss+|i_hdc|=f (R_v2) (20)

Can be obtained getting minimum value, i.e. J=J when optimized evaluation function according to Fig. 5_minWhen, selected virtual resistance is to be The optimization design scheme of system.

Claims (3)

1. it is a kind of to be used for Modular UPS parallel power control method in a balanced way, comprise the following steps：

1) basic structure of parallel system is carried based on two single-phase UPS inversions bands, according to KCL theorems, equation is set up, it is as follows：

$\left\{\begin{array}{c}{i}_o=i_{o1}+i_{o2}\\ i_h=\frac{i_{o1}-i_{o2}}{2}\\ i_o=i_L-i_c\end{array}\right.;$

Wherein, i_oAnd i_hCirculation respectively between the load current of parallel system and two single-phase UPS, i_o1And i_o2Respectively two The output current of platform UPS, i_LAnd i_cRespectively output inductor electric current and capacitance current；According to the relation of each magnitude of current of above formula Set up the equivalent control block diagram of separate unit UPS voltage x current rings；

2) on the basis of the equivalent control block diagram of the separate unit UPS voltage x current rings set up in 1), virtual resistance feedforward is added Ring, calculates and contrasts expression formula of the parallel connection circulation in s domains before and after virtual resistance feed-forward loop is added, and checking adds the virtual resistance , to the validity of loop current suppression, the controlling unit in the equivalent control block diagram of separate unit UPS voltage x current rings is in s domains for feed-forward loop Conversion is obtained；

3) analysis of power is realized by analyzing the Balance route of watt current and reactive current, according to two single-phase UPS in 1) Inversion band carries the basic structure of parallel system, obtains the relation of circulation and inverter internal resistance, and two are reinvented after adding virtual resistance The impedance model of parallel UPS, obtains the relation of the active component, reactive component and virtual resistance in circulation；

4) the DC loop-current equivalent circuit for adding virtual resistance control strategy is set up, it is considered to which inverter parallel system output end is connected The power output loss that line resistance brings to UPS during virtual resistance, comprehensive analysis power loss and circulation absolute value sum Minimum value, according to step 3) in the relation curve of circulation active component and virtual resistance choose optimum virtual resistance value.

2. one kind according to claim 1 is used for Modular UPS parallel power control method in a balanced way, described Step 3) comprise the following steps：

Assuming that two UPS inverter output voltages are equal, and inverter equiva lent impedance is expressed as：

U₁=U₂=U

Z₁=R₁+jX₁,Z₂=R₂+jX₂

Wherein, U₁And U₂The amplitude of the equivalent output voltage of inverter is represented respectively, and the two is equal, is set to U, Z₁And Z₂Represent respectively Inverter equivalent internal resistance resists, R₁And R₂Resistance, X in representing respectively₁And X₂Internal reactance is represented respectively；

According to Dai Weinan equivalent theorems and circuit add-up principle, load voltage and system circulation be expressed as follows for：

$\left\{\begin{array}{c}{U}_o=U\frac{(R_1+R_2)+j(X_1+X_2)}{\[(R_1+R_2)+(R_1{R}_2-X_1{X}_2)/R_L\]+j\[(X_1+X_2)+(R_1{X}_2+R_2{X}_1)/R_L\]}\\ I_h=I_{ph}+j{I}_{qh}=\frac{U\[(R_2-R_1)+j(X_2-X_1)\]+U_o\[(R_1-R_2)+j(X_1-X_2)\]}{2(R_1+{\mathrm{jX}}_1)(R_2+{\mathrm{jX}}_2)}\end{array}\right.$

Wherein, U_oAnd I_hThe amplitude of load voltage and circulation, I are represented respectively_phAnd I_qhThe active component and nothing of circulation are represented respectively Work(component；

By virtual resistance R_vSubstitute into above formula equivalent internal resistance R₁And R₂In, expression formula is as follows：

R_1eq=R₁+R_v

R_2eq=aR₁+R_v

Wherein, R_1eqAnd R_2eqThe equivalent internal resistance after adding virtual resistance is represented respectively, and a is R₂Relative to R₁Interior resistance ratio Coefficient.

3. one kind according to claim 1 is used for Modular UPS parallel power control method in a balanced way, described Step 4) comprise the following steps：

The DC loop-current equivalent circuit for adding virtual resistance control strategy is set up, for DC loop-current circuit, virtual resistance is suitable In inverter outlet line is connected on；

Selection makes the power loss virtual resistance value minimum with circulation absolute value sum as the amount of feedback loop, wherein, circuit work( Rate loss is expressed as：

$P_{loss}=i_{o1}^2{r}_1+i_{o2}^2{r}_2$

$\left\{\begin{array}{c}J=P_{loss}+\left|i_h\right|\\ J_{\min }=f\left(R_v\right)\end{array}\right.;$

Wherein, P_lossRepresent line power loss, r₁And r₂The line resistance that two parallel UPSs are connected with load, J are represented respectively The valuation functions for choosing virtual resistance are represented, | i_hdc| it is circulation absolute value, selection makes J be minimum value J_minVirtual resistance conduct The optimization design scheme of virtual feedback ring, f (R_v) it is the function expression of virtual resistance, it is as follows：

J_min=f (R_v2)=(P_loss+|i_hdc|)_min。