WO2017131541A1 - Decentralized process and regulation system for microgenerators to mitigate permanent overvoltages in low voltage electrical networks - Google Patents

Abstract

This invention presents the decentralized process and local regulation system, to mitigate voltage swells (overvoltages) due to the increasing integration of microgenerators in low voltage distribution networks. The process is based on a local voltage controller, acting on the leading angle of the injected current and simultaneously controlling the active power: - to maintain the microgenerator at its maximum power point, except if the physical limit of the current value is exceeded, which allows in most situations to adjust the voltage profiles along the network to values within the limits established in the EN 50160 standard; - to reduce the injected active power, proportionally to the value of the leading angle of the injected current, if the physical limitation of the current value is exceeded; - to reduce the active power injected using a closed-loop regulator of the local site neutra1 voltage.

Description

ΏΈSCR1S IOH

^^Decentr lize process arid regulation system for microgenerators to mitigate perm ent ©vervoltages in low

v l age elect ical network "

ΓO O0rh CU .1 -t;-^; ..Jit ::.:!::: JJ.rhJi: i^::

The present invention efe s to the process and systss of decent liz d lygaX n si ) reguXat on to mitigate avo voit ges i,n ioa voltage (Ltd gistributiQt netoorha, caused fey the increasing inte ration of mietogeneration cysteras_, us ng renewable energies sooh as solar otoealt ic, in weak ioa orthtage no v.coris . spage op JJ_.pp_.iyPl

In the last years;, roue ta L ohanges haoa occurred in most countriea electric systems, namely the liberal aat ion of the electrical energy naariret and its opening to competition in the areas of energy production and oaaaiietciaiiraition . The concept of inte tat Xny the decant rail tad productinn of electric energy has emerged, and is character i red b electrical energy production in dispersed sites, neat the coneumption locations, oai:ng mierogenetatton systems, often based, on eaB¾¾ .ls energies. Hoot govartn ents endorsed incsntlees to this type of production p-d , 1 2 } virion correlated with the clean renanahle sources eneray production, lad many electricity ooneoiaaro to embrace this raw ¾ay of uenerating electrical energy^■>

Microgeaeration enables lit netoork gonsnaars to produce electricity enough for all or part of their energy consumption needs, and/or t.he inieetion and sale to the

~t~ public utility grid of the generated energy unde econoTsicaliy adv nt geous conditions, in particular in contracts still valla cue to government past r g lati ns .

Current ly, in th scope o ne^:w applicable legislation (Decree-Law n.° 153/2014 of .20 October [2] in fertugai) > the energy produced is elected to self-consumption (auto- consumption) , as an electrical generation activity aimed to satisfy the producers needs of electric energy in a given period, without preventing tha possible momentarily production surplus be injected i the public utility grid. In the self-consumption case, electrical energ production may be based on renewable or non-renevabie production technologies, known as production units for self- consumption,, where there is no imposed limit to the Portuguese installed capacity |3]

Legislation also applies to the production. of electricity from renewable energy sources using small production units, to be totally sold to the grid.

The small-prodaction unit is based on a single production technology whose nominal network connecting power is equal to or less than 2S0kW and whose installed system maximum power cannot e¾ceed the maximum powe at the point of consumption defined in the deliver contract [3j .

The main dif erences between the two types of production units, in terms of customer benefits, in the: case of production units for self-consumption, are related to the fact that the consumer stops consuming energ from an energ supplier, since the consumer uses a renewable production technology, and can also be paid for the produced excess energy injected in the electrical public network.. In the small production units case, the oostume earnings are determined by he sale of all energy to the public utility grid, during 15 years, at a tariff resulting from a .bidding process defined, in the: decree-law [2j [3] »

These advantages m ke generation systems with photovoltaic panels interesting, especially in isolated houses or buildings in rural networks, generally in places relatively far from the transformer secondary substation (weak local network) .

Due to the: transformer: distance, as th impedance of LV lines is directly proportional, to: that distance, in situations .of very lo« consumption (off-peak} and on---peak solar production, the injection of the power produced by a single-phase microgeneratnr in LV network cause a voltage rise (overvoitage} , which may exceed the maximum limit allowed by the standard EM 50160 [4, 5J - scenario for this occurrence could be some hot weekend days, although it can occur whenever the low consumption coincides with the peak of solar production, since, in the case of photovoltaic solar energy, the simultaneity facto- of the solar microgeneration is unity. In the situation of ovetvoltage, the microgenerator usual iy turns off as a result of its m ximum voltage protection, stopping the production of electrical energyy whic is translated in a loss of revenue- Additionally, if the overveitag is partially allowed, other equipme t connected to the sam bus may he affected b the ov-ervoltage, being the most benign disadvantage the accelerated aging of such equipment,

.A number of centralized end/or distributed solutions have been proposed to: solve the over vol togo issue due to photovoltaic micregeneration in long (weak) networks [6] , I l_t [B], [161 ill) . These include solutions like the deterrfdnat.ion of the maximum power tha car: be installed in a certain network bus [9], which requires an estimated model of the network and. can limit the penetratio of the photovoltaic energy in the electric network, to the requirement to change the trans rme taps at the low voitage transformer or regulate their own voltage [15],· [IS], but can also require the change of the L? power grid [18] and/o communication of the network operator with the mierogena ator for active and reactive o er control [§], [13] , [ISO [17] .

In addition to centralized and/or distributed solutions using communication between ricrogenerators and network operators, several local (in situ) solutions to the overvoitage problem have been proposed. The most normal would be to consume the surplus energy injected in the grid by total or partial connection of resistive loads controlled by the microgenerator itself [10]» Thes dissipative loads could be used to heat sanitary waters, or pools, or in. absorption based ai conditioning equipment _f among other applications. This solution requires monitoring and control systems external, to the microgenerator, and may not optimize the active power injected or inject harmonic disturbances in, the network, voltage [10], if that optimisation is done,

Another solution is: to replace the usual single-phase inverter microgenerator, by a three-phase inverter microgenerator controlling the active power and, in a, limite range, the reactive power [8.] , ibis solution has additional costs in the microgenerator to be used, in the electrical h¥ network connectio in the microprodaction location, as well as in the communication, monitoring and control systems,

& solution with almost no: investment consist of slightly reducing the active power in cted by the micrcgen.era.tOr, actuating in the tracking system of the m imum power point of the photovoltaic panels (Maximum Power Point Tracking ~ MPP )T11 _>. [7], This process may only require updating the microgenerator program [11], although it cannot guarantee the maxim zation of revenues, which may require coordination of microgenarators with the network operator [7.1♦

The solution consisting of temporarily storing, locally or in a distributed form, the excess energy [12] , which would, be posteriorly injected in the LV network, eventually at a more advantageous reveng [141, r qui res a real time tariff system, has a higher cost and a relatively long return/payback time.

In a general wa , the: solutions proposed eithe need: information about the Model and state of the network, transmitted b the network, operator,, or can only avoid overvoitages toy reducing the active power and/or using three- phase inverters, that is, distributing the i.e ected power equally by the 3 phases, tony existing solutions are set to restore the voltage (V«240V} well within th range of limit values (between 20?V e 2S3V1 , requiring a very tight control of the injected power, with the loss of a signifleant fraction of the .active power available. This, lost . nergy could be injected, if the candidate solution only trie©: to restore the voltage to the upper limit of the operating range (V 253V) .

The cent ail ted solutions can also reduce the active power of all microgenerators in the network, either globally or individuall , in vie of a less pronounced reduction, in the active power of the mierogenerators located far from the (transformer) secondary substation, as well as in their efficiency, especially in the case of a reactive power being imposed to c m ns te the voltage iocreaee due to t e injection or the active power.

In this invention, a decentralized s o l ution needing no 5 cororun i a ion networks is created to mitigate the problem of existing permanent ovorvoitages in a radial electric power distribution netwo k, especially in the scPorogenerators farthest from the secondary substation. S is solution is based on the local measurement of the phase and neutral 10 voltages at the point of microgenerator coupling to the network and on: specific regulators for phase and: neutral volt ges >

The measurement of the hase voltage at the network r¾ coupling point is made in all current Taieroqenerators or aynchfonination purposes_., r quency range and for maximum and minimum voltage protection®. In addi ion, the microgenerators incorporate a maximum current protection for immunity to short circuits.

20

Measuring also the neutral voltage, in this invention migrogener tor systems will be operated using new regulation systems, so that the value of the voltage at the connection point is kept below 253V (being the reference voltage

2S ' ^/~ S>2\'} t that is, below the maximum value allowed by the standard EP 50160 [ , maximizing the energy transferred to the LV network. Therefore, the regulation systems of the maximum injecting power in the network, when the phase voltage is above the reference (V>2S2V} must:

30 ^■■· Inject a current in the LV network with a determined leading angle relative to the phase voltage;

- Maintain the active power corresponding to the maximum power point, except after the point at which said leading current relatively to the phase voltage, reaches a value corresponding t the apparent power: limit of the mic ocenerater.

- Peg ) at: simultaneously the active power injected to, a value that de r ases proportionally to the value of the cosine of the in ected cu rant leading angle, when the mierogsnerafor current limit is reached;

~ Regulate simultaneously the active power iniected to a value that decreases proportionally to the root mean square ( ms) neutral voltage value.

I moat situations, this approac allows the voltages profile adjustment along the network to values within the limits established in standards (EN 50160) » It differs from the state of the art proposals, since it:

- Injects a leading current relative to the phase voltage to regulate the voltages profile along the network, instead of reducing the active power while increasing the reactive power (which may reduce the rKicrogenerator efficiency);

- Maintains the injected power at the maximum power point. The active power reduction only occurs if the current limit of the mierogenera or is exceeded. This limit can foe conveniently specified to maximize the economic profit;

- Usee the local neutral voltage that is regulated in closed- loop in order to obtain the value of power to be injected, which guarantees the non-existence of o etvoitages along the .network,, in the :;u.c regenerator phase and in other phases, wgen the system is unbalanced, without information f ojs the netWork ope£ator »

This .method is not mentioned in any known publication.

This invention presents the decent ali ed process and local regulation system, to mitigate voltage swells {overva!cages) due to the increasing integration of icrogeneration systems in low voltage distribution networks ,

To solve the oyer ol age issue a decentralioed regulation process is created, that is based on a closed- loop cootroller of the loca (point of coupling; phase and neutral vol lages . Analysing the neutral voltage, the system of this inven ion drives the nulcr ogenerator using new phase and neutral voltage regulators, maximising the power delivered to the !,¥ network_* In the evervoltage ituation (V>tt3V, maximum value permissible by standard .E.E4 50160 j) , the control sys ems of the m xinsun! power i.o bo injected in the network operate so that th value of the phase voltage, in th 3 phases of the system, is maintained below 253 i?¾¾y -2S V) , foy regulating;

- the leading angle of the LV network injected current, relatively to the phase voltage. This angle could go up to 60°· or more, by properly sizing the miexogenerato ;

- the value of the active power to foe injected in the network, which starts to be the maximum power point power, decreasing when the said current, leading the phase voltage, reaches a value corresponding to the physical curren limit of the microgenerator »

~ the value of the active power to be injected in the network, which decreases proportionally to the local neutral voltage. The process described in. this invention can foe used in centralized L or distribution network operator systsims, in isolated or islanded networks, in networks with distributed energy storage,- to mitigate udervoltages or voltage dips, or in electrical networks embedded in aircrafts, in shipboard elect rioei networks, or in emergency power or signalling equipment, or in energ storage. The system described is this invention by measuring local phase and neutral voltages can be used in centralized LV or distribution network operator' systems, in isolated or islanded networks, in networks with distributed energy storage_:, to mit ga e, ndervoXia.ges or voltage dips, or in electrical networks embedded in aircr ft-s, in shipboard electrical networks, or in emergency power or signalling equipment* or in energy storage, .Detai 1ed description of the in.yentlon.

L w voltage electrical networks in semi-urban o rural areas, are deployed radially, from a medium voltage network {15₁ being the m dium, voltage busbar (2) connected to the primary of a voltage step-down transformer (3), whose secondary feeds the main low voltage busbar (4) {fig. 1)„ In. this embodiment, three feeders are connected to the main low voltage busbar (4), which start in busbar (4), and follow respectively to busbar (8) , busbar (20) and busbar (21) , The busbars (8), (20) and (21 ) are located 70m away from the main low voltage busbar {4}„. The busbar {8} successively connects to several load coupling busbars along the line, being also in this embodiment th busbar (3) at 90m away from the busbar (8), the busbar {10} at 100m away iron? busbar (9) the busbar {1.1} at 110m away from, busbar {10} and the busbar (1,2.) t 130m away from th busbar {11} .

The .said v lues are only on example of an embodiment, as distances between busbars can b any positive value. The electrical loads {13} are also connected to the busbar feeder (8), being the electrical loads {14}, (15), < 1 ) and (17} connected respectively to the busbars {9}, (101 , (11) and (12) . The busbar (9) is also connected to a photovoltaic mictogenerator system hereinafter referred to as microqenerator {5} being the microgenerators (S) , {?}, {18} and (19) connected respectively to busbars {.11}^' , (12) , (£0) and (21;. Busbars (20} and (21} have a further connection to loads (22) and {23} respectively.

In general, existing raicrogenerato s (5) , {&}, (?) , (18} and (19), inject a current with the same phase as the phase-to-neutrai voltage at the point of connection to the network coupling busbar, respectively {9} _f (11}., (12) , (20) and {21} _r

In this invention, in order to mitigate permanent overvoitages caused b the simudtaneous injection of th power of the mlcrogenerators considered (5) , {$) (?) (18) and (19,), a process is defined In which the current injected, in the network by the ierogeneraters leads the phase to neutral voltage with a- certain angle and the local neutral voltage is simultaneously regulated originating a cotr-penaatt an voltage and possibly a regulation of the injected power which promotes a s;r:a i 1 busbar voltage drop, just enough to bring the voltage back into the E 50160 limits, so that there: is no overvoltage. Equipment connected i the network; will, no be sub ect to voltages outside their working range and the overvoltage protection relay of the microgenerator will not operate.

The process herein described can. be used in centrai operated distribution, or low voltage network operator systems, in isolated or islanded networks, i .networks with distributed energy storage, to mitigate unaervoitages o voltage dips, or in electrical networks embedded in ad craf s, in shipboard electrical networks, or in emergency power or signalling equipment, or in energy storage systems. The system described in the present invention, neasu ring the location phase and neutral, voltages, can he used in centralized operating subsystems distribution or io¾? voltage network opcratcr systems, in isolated or islanded s networks, in. networks with dis ributed energy storage, to mitigate undervoitages. or voltage di s, or in electrical networks embedded in aircrafts, in shipboard electrical networks, or in emergency power or signalling equipment, or in energy storage systems.

Establishing the leading angle of tile current

Th system contains devices that measure the root mean square (r s] _t or the peak value, the frequenc and the phase is of the phase to neutral voltage V¾s( and local neutral, rms voltage V¾?,_: a sensor that measures the injected current I it) in the network and a microcomputer for mathematical operations on those values and to control the microgenerator conve ter .

»·\ ,·"·,

v

The time evolution of the phase to neutral alternating voltage at the input of the raicro-gen.e-.rator ( t) can be described by the equation (i) , where a temporal referential is used so that the phase to neutral V { t) voltage phase is 2¾ ero at the origin:

½s(t) ~ 2- V_mef ^< $η(ωΙ) i}

In this equation %¾sf is the rms voltage value and ω is the angular frequency.

3D The time evolution of the alternating current injected

Imit) in the network with rms value IV is described by equation iiid, for the generality of the current mierogenerators operating at nearl unitary power factor:: _m(t) ~ v2 · t_ef · si n(mt) ₁1j,₃

In order to appl the leading angle <j>_JC to the current the equation of this current, with a phase shift of φ_Μ(. in relation to ¾s(t) is;

IMG(i) ~ V2 ^« Igf · s!n(c£ +

i£|.}

Developing the term 5ΐη(ώ.ί 4-≠_MG) and considering that :

1} The quadrature component to& ioi can e obtained from:

cos (ω t) s= ~ ωjsi n(ωί) d t i i v^* }

2) The i:n-phase cocs onent, in pe unit values {pa} , of the mio egener tor phase¹ to neutral, ac voltage can: he obtained f om ( ) ;

Sin(ii^') - -~ r-™—— -^y./

The a o e process will generate reference sinusoid leading by angle fe the ac phase to neutral voltage. Using blocks (.26), (27), (28.), (29} , {30}, (31) , (32) and (33) shown in fig, ^'2_t the system to create the leading angle _Μΰ of. the injected current is obtained.

Measuring the voltage ¾sit) on busbar (12}, i aclag the resul of (v) of the busbar (12) , (fig, .2} , and introducing the value of the leading angle _Μ(1 (phase-shift) cf the current in block {26} , equation (iv) is physically realised using negative gain blocks (32} and a limited integrator

-it - block Ϊ33·> The sine and coeine of φ_Μΰ (2^'6) e calculated respectively in the operators {ill} and (2?; , The operator- blocks (2bb, (30) and. pi) perform the operations to obtain sm(&>t ¾_S) .

Establishing the cur ent rms value

The tma value ? of the ac current in eered in the network is obtained from equation (el.) , where ly represents the power available from the mioregenera or and is the maximum, rms current limit value that th mierogenerator cat physically handle, or the maximum rms: current limit value that eliminates the overvoltage in case the leading angle _ν.. has reached its ioa/xi um limit vai e.

The process ¾iii generate the rms value of the leading current to be injeered in the network, being the leading angle regarding the voltage angle in the coupling busbars of the network micro-generators , y dividing the value of the available power in the mierogenerator by the product of the ros< voltage: in the bv.e,a r ¾c_i? value, by the cosine of the angle and 1 redding the r.oo current generated :! _xz to the maximum permissible value by the physical design of the mierogenerator _t thus reducing the value of the power to be injected in the networky or limi i g the current to the maximum rms current limit value that eliminates the overvoltage,.; in case the leading angle φ_Μΰ has reached its max i o.o limit value, except in ease the network voltage does not reach the value of 201 Vd De ermination of the ef e t; of h cxrreti leading angle on the local phase to ne ttral voltage

Considering the feeder f the busbar (8) hich starts at the .oain low voltage busbar {¾}, in situations of very ss a i 1 consuniption (off-peak) in all loads {13}, (14}, {15} (15}, (1?) , (22} and (23) (aboat 21 o the norrinai consumption} , and in steady state, the electrical bahaodour of the busbar (5} do¾rvs rears feeders can be represented fey the sioipiifled rroxaei of fd.ge.re 3 that includes the resistance .hitr (24^') an the induc ive reactsfic¾ X {25} _f which are equivalents: of both the phase and neutral lina conductors,. Gdeee the phase voltage ¾ at the main low voltage busbar hi}, and the voltage V¾t(t} , intended to be regulated, at the rcicrogensrstor couplrng terednal s _f the local react rai roltage 1% in the isicrcqeHsrs sr ( ? ) and the direct loo of the current &c, the vo.l ge vari t on &¥ in this line section la giteo as :

AF - V_MG -id,- !_m (_R(:;: - jX_e ) ( v i i }

Aa the KYicroqenerafor output or; .·; rout , given by (vi), In the nor--d.iTsitir.g situation, car: be also be written as in oiix}, froit the expression (old can be received the module &¥, denoted \&V\ in (ixb.

{ _¾ :¾ _e

^! ' VUG cosine)

Neglecting in iix) the contribution of the square roo since its value is nearly unitary for the practical, values of χβ, it is written:

Since ί& _Μΰ increases with _Ηβ or - _m 6jo, -J, then the modulus of the voltage variation AV decreases with the increase of the current leading angle,.

Pfam (vii) we have V_ua " + whereby neglecting, the contribution of &Ϋ, sohstrtuting in (x) and solving the resulting equatio for AV we obtains

To^: zero this A V voltage variation., om ix) o iron; (xi) it is concl ded::

Low voltage networks usually present i¼ > ¾< For this reason attending to ; xii 5 it is easi ly concluded that the curIenv. leading ngle can only slightly reduce the voltage vatration:.

Assuming ¾«3.5k , Vt *2iOV, ¾*2χ0.δΩ and B_¾/¾-7 e obtain for tan (fks) ===ø AV *16.2V, which const itutes an overvoltage {V ∞2S6.2V (see figure 4} . For $ - 31" it is obtained Δ¥*14 ν, but for -60" it is AW*12>4V, which is no longer an overvoltage {Vm <253V) . Regarding the case where there is no current lead (t n{^}~0t a reduction of almost 4V is achieved without reducing the pow¾-r .in ected in the network.

It is also concluded that if _Λ?ί·_; S ] then the voltage variation will increase Ifig. 4} , so using a negative angle for the current lead, (corresponding to a lagging current) is a way to mitigate undercoltages « & voltage increase of about 4V can foe obtained provided that the active power is not reduced, thus possibly configuring the removal of an undervoltage situation , which happens for voltages below 207VC

However, reducing the voltage V from the overvoltage threshold (¾s 2S3V) to the nominal value 230V (i^Oi , or even to 240 ^" would imply a current leading angle outside the microgenerator specifications. To cojnpicteiy cancel the voltage variation the value s;¾^:S * is necessary but it has no practical interest because it originates very expensive microgenerators and mainly hig losses in the network and microgenerator, due to the high values of reactive power,

Consequently, according to (vi.) the current in this process is lie iced, by construction of microgenerator, to il- , being the injected power l¾ in the network proportional to cos ¾y, therefore decreasing with the increase of the leading angle i¾¾v. This limitation usually occurs only if φ<;-; > iί ^:'·' in conventional microgenerators A microgenerator ensures greater if it is designed for higher currents.

¾ ~ V_m e_r-lmaxCQs _m {xi ii )

If there was no power limitation, for ^";2° the current to be injected would be too high for the physical capability of the microgenerator. Being ^™: I * a limited current, the process described herein reduces the injected, power by limiting the Imx arid by increasing <k- _f but only when the physical limitation of the rms current value is exceeded,

Closed loop regttlafciors of the cur ent le ding angle

The process of this invention regulates the leading angle m of the inicrogenerator output current regarding the phase to neutral coupling voltage,, to mitigate overvoltages (or undervoitages) . For this goal a closed loop regulation process is created_* This process- (figure 5 will generate the value of the angle ;α proportional to the^' integral compensato (36) (negative proportional constant .- {35) ) of the deviation, obtained in the subtracter (34) , f.x the referenc valu of the phase voltage, of the present value of that voltage in the networh coupling busbars of the microganer s s .

Its operation, shown in figure 5, is baaed on the determination of th deviation (or difference) in the subtractox: (34) , between the rras; voltage phase to neutral value ¾en measured at the terminals of the miorogenerator coupling point and a reference value ^':¾■^■.;·»>^■, generally less than .253V, if this devia ion has a negative value it means that the network: voltage at the connection point is higher than, the value predetermined in the reference,, and therefore there is an overvoicage.

An integral compensator (36) with Ki gain (.35) is used to obtain. «¾·_·:- in the closed-loop regulation, he use of an φ_Μ(; value proportional to the integral of the voltage deviation has the advantage of guaranteeing the tracking of the reference (null deviation) _f while the control input i.s bounded {X *$ I ) t ^'5>-.r thereafter by reducing th powe according to xiii) and (vi.) . The integral compensator (36) allows a relatively high voltage «252 V to be established at the point f connection of the microgenerator, the voltage tracking without deviation (regulation for the reference value) avoiding the need to lower th reference voltage .{¾&¾r<2 2 v) , or to operate with, a h steresis cycle, which does not maximize the injected, power.

If it is found that the deviation in the subtracter (34) is positive, the operation point of the miorogenerator is maintained, i.e., the integral compensator (36) is limited to have _Μ(, ~ ϋ, being maintained the state of injectio of the maxiisnm niorogeneratiori power available for voltages over 20 V, For voltages below this value the limitation of the integral compensator (36} is removed by the process to show ~π/3 < φ_Μΰ < 0 while there is no decrease in the active power due to current limitation, in which case the decrease of φ _r will stop- Thus, the angle will be:

~ positive if the voltage in a busbar ((8), (9), { 1.0 ; , (11) , : 12 } , {20 } or (21) } of the microgenerator f(5), (6), {?^■) , (18) or (19^'}) coupling to the grid exceeds 252 V;

·- negative if the voltage in a doshar (^'{8}^', {$} , (ID), (11). , (12) , (20) or (21.}) of the microgenerator ( (5), (6) , (7), (18) or (19); coupling to the grid does not reach the valee of 207 V;

To estimate the ¾. gain (35}, first it is considered that the miorogenerator is represented, by a model consisting of an incremental gain % (37} and a delay represented by the time constant ¾ (37) ,

By solving (x) in order to v¼o, the phase l¾. ca foe obtained at the terminals of the ierDgenerate :

Deriving

in orcier to the leading angle it .is obtained (.p) which defines a value for the incremental gain ¾¾ of the itucrogenerator .

The numerical value of this incremental gain is negative withi the range ¾ 6 [-§; -2,1] for the values of interest of f_m, i.e. 0<φ_Μ6< 60° (Figure 6).

The determination of the · gain (35} still requires the definition of the closed-loop transfer function of the output voltage VMS on the busba (12) fig. 5 which is given by;

This result, can be: compared wit the canonical forrn of a second-order svstea ——™ -,. where;

1 1 (xvii)

2 v¾ ~r w ·»„„ ,^■

•2 (xviii)

½

From where i can. be obtained: as:

Assatdng a darn ieg factor < -^:: ---·, a ti.se cons nt Τ_α ~

100 ms arid K_(; ^■■■■■ corresponding to t e sort interesting values of the isadicg aegis froru the point of view of the regulation range : 0 - < _w.. < Site .. ¾e obtain the vales; · « - i h¾x,;

This ft value .being negative, ensures the stability e the rsiiorogenerator and allows to define the leading angle Μ_€ . The process guarantees the riaeiriue; available powe rejection, unless the recrogsnetator carrent j¾e etceebs the .oexi¾u¾ value b-., - . ponssquently, from an angle of about 35° , the process decreases the value of the output wer, which is given by {xiii} bsi.ng _j < ¾ ,

Closed-loop egulati £ fcfee locally saeasti ed neutral voltage

The process previously described avoids the existence of overvoitages (end gives support to the uncervoitages) when tee three phases of the electrical network are almost balanced fro;¾ the point of viee of coneusption and ricroprodaction In the case of a rice ogenerator connected to one phase, but not to others, the maeirb.Si^:rt^:i.on. of. the power injected by the isicrogeeerator ieplies the increase of the local neutral vol sage _* This Increase i s^: vector!ally added to the voltage of another phase which, aided by the rota c loo of the voltage vector due to the inductive voltage drop and the negative currest, causes ae eve voXtape in one of the rema i.e.1r■g ehasee ,

In this in.v¾n ion_f the ayateo. seasarea the rma value of the local central voltage ht, a no. adda to the previously described process a proportional regulator with gain fhu ouch that the p er to be injected by the ¾.ietogenerator is reduced by hi? for each volt of the local neutral voltage, Considering the process previously described and Cxi 11} _f the power to he injected lie is the valae of the following; expression :

The value of ¾ was estroated at about 250 ¾Vv {reduction of power per volt of the local neutral voltage;, hut in practice it. is guaranteed that using the value hi ™ 500 fPV_f overvoitages in networks el th heavily unbalanced tuleroproduction are avoided.

Thne_f the prooess will tower the value of the power ho be injected in the network, regarding the available power, by a. vai.ee proportional to the nine loeal neutral voltage _f with proportionality constant between 250¾/v and 500¾/¥, but ::. nor values ooeid be u&ed depending on the irspedanoe of the ne work ,

Advantages of the decentralized process and regulation sys em for micr generators

Regarding the process/keyaterea that temporarily reduce the t¾a¾iteta owe injected by edorogeneratora In the electrical netwerk and/or centrally regelate the reactive power [6-9,. 13, IS, 16, 17, 18], the advantages of the proposed process/system are;

- Th power reduction achieved by the proposed process/system, may be smaller in the case of a balanced set of microganerators, and much smalle in the case of an unbalanced set;

~ No need to know the model of the network;

~ o need to rtionitor the whole network, only the voltage at the location, of the icrogenerato ;

- Mo need for eom unications between microgenerator and network operators ;

-- No need of transformers allowing variation of the transformer ratio, electronics swa/tc ing tap changers in secondary substa ions, or topological changes in the network;

- It has a faster response because it is not dependent on the latency of cor^anicat ion networks between the nodes of the power network: _:n_:eifher on the comput tion in a central, proc ssor.

Regarding the processes/systems that consume surplus energ injected into the network, to total or partial connection of resistive loads controlled by the microgenera or itself [101 , the advantages of the proposed process/system are:

- No need for investment in these loads;

- o wasted energy i the load is not needed or the energy cannot be used;

- No need for communications between the microgenerator and load,

Regarding the processes /systems that reduce the power injected in the network [lij, removing the microgenerator frors the saxisura po¾¾r point,, the advantages of the proposed rosess_./system a e

~ Does not wast the avail ble energya hlegarding the processes/systems that replace the .;nieregenerator canal ly with a single- hase Inve e , by a three-phase inverter sdcfegensrator _f with or with cent rail red or dece t liz d control of the active and reactive power [ , 13], the advantages of the proposed: process/system are.:

- he need of iavesfrntet in new three-phaae inverters;

~ Mo reed to knew the .model of the network

- ho need to itopitor all network nodes, only the local voltage in the jsierogenerator;

- No need for' eoavaanication between nnorogeaerator and network o erators ;

- 1 ·;. has a raste response as it is net dependent on the latency of ootvauri tion net O Ps between the nodes of the power network neither on the compocatioo. tree in a central processor <

Regarding; processes/systems that store locally and temporarily the exces energy [12, 13] which will, be inaected in the .L^'V network later_f the advantages of the proposed process / spatem are :

Does not regoire investatent in electrical energy storage systems;

- Does not regnire m i te.nan.ee or energy storage systems.

Performance ass ssmen of decentralized process and regulation system of microgeaerators

A worst case scenario is consid re to assess the performance of the described process and system The line has a total length of 500m and the consumption in this scenario is in the off-peak period at only 2% of th nominal value. The voltage at the main low voltage (4) is 242V, well above the nominal value of 23QV, but typical in a secondary substation at off-peak periods. In this scenario figure 7 shows the voltage profile along the busbar (8) downstream feeders if there is no microgeneration connected i the network and the off-peak load distribution, is unbalanced. £s expected- the voltages in the three phases V¾, v«, Vr remain ver close to the value of 242V, decreasing only very slightly along the li e.

Subsequently, micropreduction is in rod ced in the busbars following busbar (81 and busbars 20) and (21) in a total equal to the aoeepced maximum of 25% f the t ansformer nominal ower_* It is considered that the microgenerators all simultaneously inject the maximum power, The microgenerators considered hav a power of 3, ¾k¾ or multiple of this value.

The voltage profiles are shown along the busbar (8) downstream feeders which was taken as representative, figure 8 presents the voltage profile along the busbar (85 downstream feeders in the considered ©££:---peak period;, unbalanced load distribution and without voltage reguiation in. any of the microgenerators . Consequently, it is observed that the voltages in the busbar (22), the farthest and most prone to voltage variations due to line impedance,, exceed the limit of EN 50160 in the three phases ¾¾, ½,

Using the regulators described its this invention, figure 9 shows the voltage profile along the busbar (8) downstream feeders in the described scenario, with 3 microgenerators in the busba (12) , controlled with $ and ?.i : «3k.W limited by the mierogenerators physical maximum current limit of 16.6&_* If the liiaximum permissible current is 19.6Ά the leading angle is ®-^«51° and ¾.¾ -3.2kvv. It is observed th t the voltages in the three hases t¾, Vr in the busbar (,.12 ) do not exceed the limit of m 50168 being exactl at the value of - ®_?*™2.52 V as intended.

Figur 10 shows that the vol cages an the bus (12) fed fro;r the busbar (8) in the described scenario, with 3 sicrogenetato in the busbar (12) still tracks the value V rsi -252 V even though the physical maximu current limit of icrogerierators is increased to 23.6Ά, by microgenerator design, to ensure j~3. SkW with >& «55°

Corns idering unbalanced. mioroprodactioHi figure 11 shows the voltage profile along the busbar {8) downstream feeders in the described scenario bat using only 2 svicrogenerators i the busbar f 12) in the R and S phases without voltage regulation in any of the TR.iG.toge.nerators . It is seen that voltages V¾ and % exceed the limit of EN 50160.

In the situation of figure 11, the regulation process described in. this invention was applied, bat the local neutral voltage regulation was removed. The results are shown in figure 12,,. the regulation reduces the power of the mierogenerators, in phase R to 2.2k¾ with ffe -60° and maintains the power of the microgenerato of phase S in 3>4Sk¾v with ά:ΰ^{■■■■■}20°, In this unbalanced case as there is no local neutral voltage regulation in the phase B, the voltage % fo ^:::212V is not regulated, exceeding thi reference value, although not the limit of 253V.

Figure 13 shows the voltage profile along th busbar (8) downstream feeders with 2 microgenerators in the busbar (12) now controlled so that the injected power decreases with co iffe) even if the current limit is not exceeded, but without the neutral voltage regulation. In phase H a slight reduction of the voltage previously exceeding the reference value of 252V is observed with the lowest injected power (1.73 kW, f -; ^¾0°; while in phase S 3.QlkM are injected with G -27-,

Figure 14 shows the voltages profile along the busbar (8) downstream feeders in the described scenario, with 2 microgenetatots in the busbar {1.2}, containing leading current and loc l neutral voltage regulation with power reduction of 500 /V. Ά power of 2,2Sk is obtained in each rsierogenetstor with of 58" and 0* respectively in phases R and It is observed that no voltage exceeds 252 V, although the voltage of phase S is not nud.ntained at 252 v because the local neutral voltage regulator is proportional and cannot sho oero deviation in steady state.

Figure IB shows the voltages profile along the busbar (8 } downstream feeders in the described scenario, now only with 1 microgenerator in the busbar (12), in phase R, without any network voltage regulation in the mierogener&tar , t is observed that the voltage of the phase in which the microgenerator ia connected exceeds widely the limit of E 50160.

Figure 16 shows the voltages profile along the busbar (8) downstream feeders in the described conditions, with control of power injected by the single microgenerator., but with no injected current leading angl , where P - .lkW to reduce the voltage to 252V,

Figure 1? shows the voltages profile along the busbar id) downstream feeders in the scenario of a single microgenerator on the busbar (12} in phase H_f controlled with current leading angle hut without neutral voltag regulation, with <fe at 65* and power at 1 , -k (by current limitation to J€ .6A. to lower to 252V the phase voltage of the microgeneratot » The voltage on phase T approaches the limit but doss not exceed t. This demonstrates that the current leading angle regulator allows injecting i . SkW instead of l.lleW (figure 16) .

Figure 18 shews the voltages profile along the busbar {8} downstream feeders in the described scenario with a raierogenerator on the busbar (12.) in phase R controlled with current leading angle, power reduction and local neutral voltage regulation, power reduction constant of SOG /V local neutral ol age, where P ~1.6 k not -exceeding 2S2V in any ot the three phases. This proves that the local neutral voltage regulation allows the phase voltage to be set to the desired value or below, at a slight decrease (from 1..S kw to i. k ) of the injected powe which is still greater than the permitted (1.1 kW) without the current leading angl regulato .

Preferred and alternative embodiments :

The preferred emnod im n of the system which concretises the method of this invention comprises:

- A device with digital output (38} which measures the rms or peak value, frequency and phase voltage ½d t) between the phase of the busbar (12} and the neutral;

- A device with digital output .(39) which measures the cms neutral voltage value ¾;

- A device with digital output which measures the current .¾¾{£.5 injected by the converter (42} of the lcrogenerator connected to the network betw en the busbar phase (12) and the local, neutral; A microcomputer {Al} for mathematical operations on measu d voltages and current values and to execute the method, namely aquations (iix) , (iv), (v), {-vi ) , (κίϋ) and XK } , and for supplying the S¾. drive to the .coriverf r i42) of the microgenerator;

- ¾ converter {42} and its protections, controlled by a microcomputer ( 41} , fed b a renewable energy source (4.3) , whic injects the current Ie it) in. the network between the phase voltage in the busbar {12} and local neutral.

Alternativ embodiments may include the use of phase- locked loops, zero crossing detectio of quan i ies, sBcasurement of quantities by indirect processes using form factors and peak or average values, either in digital or analog form, using or not multiplexer .

The microcomputer (41 may also be completely replaced by an analogue system with operations, regulators, 1 i.miters and generators constructed with operational amplifiers or dedicated circuits.

The method referred in this invention may also be performed centrall by the distribution network; operator, which from the measured voltages and phase currents- on each bus, ca estimate the local neutral voltage and calculate the c rrent leading angle and the power reduction needed in each of the microgenerator. These reference values can be sent via telecommunications network for each individual microgenerator s to inject currents with the leading angle defined arid amplitude so obtain the estimated ower.

Description o£ the figures

Figure 1 represents the typicai network configuration under study where: - (1) represents th medi m voltage network;

- (2) represents the .medium, voltage bus;

- (3) represents the voltage step-down transformer;

- (4) represents the ^'mairi low voltage basher;

lb), (6), f?l, (185 and (19} represent microgenerators;

- .(8), (20) arid {2.1) represen the busbars irrsrsediatei after the main low voltage bu (4) of each of three feeders;

~ {3} _r (1Q) , (11), _.{_.12) represent the busbars of the busbar (8) downstream feeders;

~ (13) , (14) _f (15 ), i ) , ill)_r (22) and (23} represent the eleetrieal loads cormected respectively to busbars (8), (.9), (10), (11), (12), I2m and (21} ;

Figure 2 represents the implementa ion scheme of the current leading angle regulator, foeing

(12 the busbar to which the raicrogenerator is connected;

- (26) the input value of the leading angle

- (27), {28), ( 9} , (30) and (31) operator blocks;

- (32) the eega ive gain, block;

- (33) the limited integrate* block.

Figure 3 shows the equivalent model of the busbar (85 downstream feeders, whe e:

- (4) represents the ma I n low voltage busbar;

- (7) represents a microgenerator

- (24) represents the equivalent resistance of the phase and neutral conductors;

- (25; represents the equivalent inductive reactance of the phase and neutral conductors.

Figure 4 shows the graph of the voltage drop as a function of the leading angle fm of the current , Figure 5 shows the closeb-"loop block diagram of the local phase vol.tafe regulator where:

- (12} represents the busbar to which miorogenerator is connected

~ (34) represents the subtracter;

{35). represents the gai rh .of the integral compensator;

- (36) represents the integral, compensator.;

^« (37} represents the dela with time constant :/h. fig e 6 shows the graph of the iTiicrogenerator incremental gain as a function of the leading angle κ¾; of the- current.

Figure shows the vol cage profiles along the busbar (8) hewnat re n feeders in a scenario without rRicrbproductioK in the network in off-peak period and unbalanced situation.

Figur 8 shows the voltage profiles along the busbar (8) downstream feeders when the microgeneration power equals: 25% of the nominal power of the secondary substation, 3 nic regener tors i the busbar {12} without control, off- eak period and unbalanced distri ution si uation..

Figure 9 shows the v ltage profiles along the busbar (8) downstrears, feeders when the rsicrogeneration power equals 25% of th nominal power of the secondary substation, off- peak period_f unbalanced load distribution, 3 mioro eneratorS: in the busbar (12] controlled with - 7° and Pi_$ -Ikw limited, by the raxifaum curren of 1 .6A (if the maxi um current is i¾,6¾ comes *:i~Sl^G and ~3t 2k¾d <

Figure 10 shows the voltage profiles along the busbar (8) downstream feeders when the mlorogeneration power equals 25% of the nominal power of the secondary substation, off- peak period, unbalanced load distribution, 3 m crogeoerators in the busbar (12) controlled with ¾y-55^c and ^» j .4$kW being the maximum current increased- to 2it 6¾,

Figure 11 shows the voltage profiles along the busbar {8} downstream feeders when the microgeneration power equals 25% of the nominal power of the secondary substation, off- peak period, unbalanced load distribution, 2 mierogenerators in th busbar (1.2} without network voltage regulation in any of the mierogenerators.

Figure 12 shows the voltage profiles along the busbar (8) downstream feeders when the micrOgeneration power egualo 25 of the nominal power of the secondary substation, off- peak period, unbalanced load distribution,. 2 mierogenerators in the busbar (12) controlled but without regulation of the local neutral voltage, ;Vu -2.2k¾, *·.·.; -6C°, I¾ur »3. 5k¾, -2ϋ^& (exceeds the reference value of 252V but not the 253V limit) -

Figure 13 shows the voltage profiles along the busbar {8} downstream feeders when: the microgeneration power equals 25% of the nominal power of the secondary substation, off- peak period, unbalanced load distribution, 2 mierogenerators in the busbar (12) controlled with a decrease in P ith even if the current limit is not exceeded, without regulation of the local neutral voltage (exceeds the reference value of 252V but not the limit value), Pi_:o -1.73k , -60°·,

Figure 14 shows the voltage profiles along the busbar iS) downstream, feeders when the microgeneration power equals 251 of the nominal power of the secondary substation, off- peak period; unbalanced load dist ibution, 2 microgenerators n the busbar {12} with, current leading angle and .local- neutral vol ge regulation,: pow reduction per neutral volt

SDO V, Prl^«=2.2Sk in -each. *i. r6¾s.neratQ jta* ~56.^*, =0⁵.

Figure 15 shows the voltage profiles along the busba (S j downstream feeders when the microgeneratio power- equals. 25% of the nominal power of the secondary substation, off- peak period, unbalanced load distribution, 1 mic.r©generator i the busbar (12) without network voltage regulation in the nicrogenerator .

Figure 16 shows the voltage profiles alon the busbar (8) downstream feeders wjnen the -microgeneration power equals 25 of the nominal power of the secondary substation, off- peak period, unbalanced load distribution, 1 microgenerator in the busbar {12} with P control but without current leading angle regulation, being P -1.1kW to be able to reduce to 252V.

Figure 17 shows the voltage profiles along the busbar (8) downstream feeders when the raicrogeneration power equals 25% of the nominal power of the secondary substation, off- peak period, unbalanced load distribution, 1 itlcregene ator in the busbar (125 controlled with . of 65° and with id i i .9 k (fey current limitation to 16i6Af to be able to reduce to 252V in the phase of the miorogenerator, but with the voltage in the phase 1 approaching the limit.

Figure 18 shows the voltage profiles along the busbar {8} downstream feeders when the TfuerogeneratXDn powe equals 25% of the nominal power of the secondary substation, off- peak period, unbalanced load distribution, 1 rareregonerarer in the busbar (12) with current leading angle and with local neutral vol ag gul tion, power reduction per neutral volt 500 /V, it; ==d . Oka, s<=58^c not exceeding 252V^' i an phase .

Figure 13 shows the preferred embodiment of the .system eontairririg the^■ .^■meas r ment evic s ( 36-5. , (3S) and ( 01 of the voltages at connections [Y, H_t. T) of the busba (125, the microco puter (41) _r the converter (42) and the renewable energy source {435

Bibliographic References

[1] Decreto-Lei n,° 363/2007 de 2 de ^ovemforo, Diario da Repubiica, 1. * serie - N. ° 211, Hinisterio da Economia e da ln.ova?ao.

[2] Decreto-Lei 153/2014 de 20 de Outubro, Diario da

Bepubiiea, 1.¹ serie - N.*202^' _jf Ministerlo do Aauvien e, Ordenamentc do erritdrio e Energia,

[3 Perguntas frequentes sobre produtos e ssrvigos, EDP, [OnI ine ] .

Avai1ab1e : ht1 s : //energi , edp , /part icuia s /pergun as- frequeB.tes/prod tos-e~:Se:rvicos _* aspx _* {Acedido em Feveraira 2015]

[if So ma Portugueaa d 50160 / £S 50x60, Caraterlsticas da_: ten.sao forneelda pelas reces de distrihuigao publica. de energia eietrica, Bomoiogasav© em Diario da Bep blica, 111 Serie n,°170, de 25 d Julbo de 1 95, Institute Pgrtugues da Qualidade, (EDP e DGE) /..IE?-

[5] EOF, Manual d Qualidade da Energi Eletrica, Dereiabro 2 05, [61 Pedro M.. S, Oa rvai^'no, Pedro F. Cor eia Luis A. F. F rreira, Distributed Reactive Power Generation Control fo Voltage Rise Mitigation in Distribution Networks, IEEE TRANSACTIONS ON POWER SYSTEMS, VOL, 23, NO . 2, MAY 2008,

[7] Reinaldo Tonkoski, Luis A.,. €. Lopes, and Tarek .H. M. El-Fouly, Coordinated Active Power Curtailment of GriaConnscted PV Inverters for Overvoitage Prevention, IEEE TRANSACTIONS O SUSTAINABLE ENERGY, VOL. 2, HO. 2, APRIL 2011.

Γ8] Erh n Demitok, Pablo Casado Gonzale , Kenri H. B. Frederiksen, De so Sera, P d o Rodriguez, IEEE, and Remus Teodorescu, Local Reactiv Power Control Methods for Overvoitage Prevention of Distributed Solar Inverters in Low-Voltage Grids, IEEE. IEEE JOURNAL OF PHOTO OLTAICS, VOL. 1, NO. 2, DECEMBER 2011. ¾j Pedro M. S. Carvaiho, Luis A.. F. . Ferreira, and doao J. E. Santana, Single-Ph s Generation Headroom in Low- Voltage Distribution. Networks Under Reduced Circui Characterization, IEEE TRANSACTIONS OS POWER STEMS , VOL. 30, NO. 2, MARCH 2015.

ClOj Oliveira, P., Es do e controlo da resposca da inversores fotovoltaicos ao a¾¾ento da tsnslo em f acas redes de baixa tens o, Dissertaeao de Mestrado em Engenharia Eietrotecnica e de Computadores, Insti u o Superior Tecnico, Abril de 201

[11] Bernardes-, E. , Ccmpensacao de sobretensdes oriainadas ©or sistemas de microgsra^S© «m redes de foaixa tensao, Dissertaeao: de Mestrado em Engao.har,ia Eietrotecniea, « de ^•Comp tadores , Institutes Superior tecnico, Lisboa, Abrll 2014.

[12] Perdigao, Joao f. ^'G. , Seguidores de Potencia Maxima 5 para Sisrernas de Microgeracao Fotovoltaica na Presence de Sobretsnsoes, Dissertacao de Mestrado em Engenharia Eletrotecriioa e de Computadores _r Instituto Superior Tecnl.co, Lisboa, Dezembro 2013.

10 [13] Bus.sam Alatrash, Methods and Systems for Mitigation of Intermittent Generation Impact on Electrical Power Systems, US PAT 20140097807 (Ai) , 2014. f 141 Sergio Ramos, AGREGAC Q E GES a INTEL IGEHTE DE CONSUMOS 15 DE SKERGIA ELETRICA EM MERCADOS LIBERALIE.ADOS, Tase de DoutoramentG em Engenharia Eietrotecnica e de Co putadores, Instituto Superior Tecnico, Lisboa, 2015,

[15] .Gonialves., P., "Con^ersores com.utad.os^· para a itiga ao ■ de sobretensd s originadas po eiste as de microgexacao- na rede de distribnicao¹ de foai«a tens o," Di.sseriacSode Mestrado em Eng nhari.a Eletrotaenica e de Compubadores, Instituto Superior Tecrdeo, Lisboa, Abril 0-1 »

25 [26] Kenichi vvatanafoe, Cu , Juni IKondoh, I,, Voltage control apparatus, Voltage control method and power adjustment apparatus, DS201SQ69978 1, 2015. ill] Nobuhiko Itaya, C. , Voltage moni t^arin - control device, 30 Voltage control device and Voltage monitoring control method, US2015233975A1, 2015. [18] Daniel Prefers, , , Claus Al ert, K . , eontrol of operating q i ment by influencing a grid voltage:, US201501234? 5 i i l } , 2015.

January, 20^" 201?

Claims

CIA-CMS

1, Process of decentralised regulation for ird.croceneratore ·{5 ) , (6). , (?) , (IS) , (19) to mitigate permanent overvoltagas and undervoitages in low voltage electrical networks by regulating local phase and neutral voltages respectively in busbars (9), (11), (12), (20) and (21), characterized by.: a) The generation of a sinusoidal reference signal, with a leading angle «k>, using the value of the current leading angle _Μ& in rad/s (26) , th sine (29) of _Μΰ multiplied (30} by th cosine (33) of the phase scaled symmetrical sine value (321, and added. (3Ϊ; to the cosine of _Μ6 (.27 } multiplie (28} by the input of (32); b) The generation of the value of the angle proportionally, being the proportional gain Ki {35} negative, to the integral compensator (36.) ox the deviation in. the subtraction (34) of the reference value of the phase voltage minus the current value o that voltage in busbars (8), (9), (10) , {111, U2 , (20 or (21) of the coupling of the miorogenerators (5), (6) , (7), (18) or (19) to the network, being the angle

- positive if the voltage at the microgenerator network coupling busbar (8), (9), (105, (11), (12), (20) o (21) exceeds 252 V;

·- negative if the voltage at the coupling busbars {8}, (9), (10), (11), (12; , (20) or {21} of the TRicrogenerators (5} , (6), (7), (18} or (IS) to the network does not reach the value of 207 V; c) The generation of the rms v lue of the current to be injected in the network with leading angle regarding the voltage in the busbar {(8), (9), (10), (11), (12), (20) or (21) by dividing the available power in the microgenerator i {5} _f (6), (7) , (18} or {19) ) toy the product of the rms value of the us voltage times the cosine of the angle

d) The limitation of the current rrns value generated in c) to: the maximum ermissible value allowed by the physical construction of th microgenerator reducing the value of the power to be injected in the network, or to the maximum: rms current limit value that eliminates the overvoitage in the case the leading angle Μ_ΰ has reached its maximum limit value, except if the network voltage does not reach the value of 20^"? V;

a; The reduction of the value of the power to be injected in the network, regarding the available power, fay a value proportional to the local neutral voltage, being the proportionality constant between 250W/V and 500W/V, while othe values are feasible depending of the netwo k impedance,

2, System for the decentralized regulation of microgenerators (5), {6}, (7), (18), (191 to mitigate permanent overvoitages and nndervoltages in low voltage electrical networks int rconnected in one of the busbars ( ¾} , (11} , (12), (201 and (21} executing the process of regulating the local phase and neutral voltages, described in claim. I, characterized by having:

a) a device (38) for measuring the root mean square value:, the frequency and the phase of the voltage at the microgenerater coupling bus;

b) a devic {.39} to measure the rms value of the neutral voltage of the microgenerator coupling bus;

c) a device {40} to measure the current injected by the microgenerator; d) a microcomputer (41) or computing system for the operators (26; , { ^' 21 } _f (28} , {29}, { 30} , (31), {32}, { 33 , (34}, {35} , 36) , actuating in the eas red values to execute the logic of the process described in clai

5 1 and to drive the converter (42);

e) a. converter (42) to: inject in the network the leading current etermined by the regulators and by the power supplied by the generation system (43), 0

3. Use of the process defined in claim 1, characteri ed by its use in centralized: low voltage or dist ibutiors. network operator systems, in isolated ox islanded networks, in networks ^■with distributed energy storage, to mitigate undervoltages or voltage dips, or in electrical networks5 embedded in. sir-crafts, in shipboard electrical networks, or in emergency power or signalling equipment, or in energy storage «

4. Use of the. system defined in claim 2 characterised by the0 measurement of local phase and neutr l voltages, in centralised .low voltage or distribution network operator systems, in isolated or islanded networks, in networks with distributed, energy storage, to mitigate undervoitages or voltage dips, or in electrical networks embedded inb aircrafts, in shipboard electrical networks, or in emergenc power or signalling equipment, or in energ storage.

January, 2Cr" 2017