LLC in simulari

[Vizitator]

Diferente la sarcini in raport 1/2:

 

Diferente la grupul rezonant 1/2:

[Vizitator]

Ca sa nu mai caut prin calculator pun aici o selectie din cartea lui Xiang Fang:

 

Xiang Fang ian19

Series Resonant Converter
The SRC circuit is illustrated in Figure 1.7. The resonant tank of SRC consists of a
resonant capacitor and a resonant inductor connected in series. The output load resistance is
in series with the resonant tank and the impedance of the resonant tank is a function of the
switching frequency, and hence the voltage across the output impedance can be modulated by the
switching frequency. At resonant frequency ( √ ), the resonant impedance
reaches its minimum and the normalized output voltage gain ( , the transformer turns
ratio is included as if is equal to 1) becomes unity. It is the max gain of SRC, since
magnitude becomes larger for the switching frequency above or below resonance and the voltage
divided to output accordingly will decrease. The DC characteristic plot is shown in Figure 1.8.

For the frequency region above the resonance, the total input impedance will appear
inductive, which makes the input current lag the input voltage, and thus ZVS condition is
attainable. ZVS is preferable for converters that use MOSFETs and diodes, since it minimizes the
switching losses and the EMI effect. On the other hand, below the resonant frequency is the
capacitive impedance region, where ZCS can be achieved. ZCS condition is more favorable for
reducing the switching losses for IGBT devices, but cannot reduce the switching loss in MOSFET
converters. Also, the resonant behavior in the ZCS region of SRC is more complicated than in
ZVS due to the sub-harmonic effect. The resonant tank responds to the signal with the resonant
frequency component more strongly than other frequency, and it is possible that some high order
harmonic of a low switching frequency input coincides with the resonance. In this case, the gain
and frequency relationship is no longer monotonic for low switching frequency and therefore
these operation regions should be generally avoided.
It can be observed from the DC characteristic plot (Figure 1.8) that the gain curves are less
steep for lighter load condition. In other words, in order to regulate an increased input voltage, the
required frequency variation range will be wider for light load comparing to heavy load. In theory,
the gain curve becomes flat for zero load condition, which makes SRC incapable of zero load
regulation. Another problem for the high frequency operation (above the resonance) is that the
turn-off switching loss is increased. Therefore, SRC is not suitable for wide input and load
applications.

Parallel Resonant Converter
The parallel resonant converter (PRC) topology is shown in Figure 1.9. Its resonant tank
also has two resonant components as SRC, but the capacitor is in parallel with the output
rectifier. Another difference is that the output stage is an L-C filter rather than a capacitor filter,
which is an inductively coupled output and equivalent to a current source.
The peak gain of PRC is affected by the load resistance, whereas for SRC the peak gain at
resonance is unity and load-independent. The peak gains occur at a frequency below the resonant
frequency, and the peak frequency will be lower for a heavier load condition. The peak value can
be larger or smaller than 1, which allows the converter to work in a wider gain range if properly
designed. The DC gain plot is shown in Figure 1.10.
The same analysis can be applied to PRC that in order to achieve ZVS the converter
should be limited in the above peak gain frequency region. However, the peak frequency is
variable depending on the load condition and the tank parameters: the peak point shifts to lower
frequency and smaller gain value as the load increases. Another notable feature of the DC gain is
that the curve slope is steeper for lighter load condition in contrary to SRC. Provided the same
input and load range, the required frequency variation to regulate the voltage is narrower for PRC
than for SRC. The drawback of PRC is the same circulating current problem causing high
conduction loss and poor efficiency for light load condition, since the input impedance is
inductive for ZVS condition, which is dominated by the inductive part and less affected by the
load resistance resulted in a relatively large resonant current even for large load resistance.

LCC Resonant Converter
The SPRC, also known as the LCC resonant converter, is a combination of SRC and PRC
as seen in Figure 1.11[36-38]. The resonant tank has three resonant elements: and in series,
in parallel with the rectifier input. Consequently, the converter has two resonant frequencies:
( √ ) is the short circuit resonant frequency, and ( √ ) is the
open circuit resonant frequency, where ( )
The DC gain of the SPRC is illustrated in Figure 1.12 (where ). It can be seen that
at it is the load-independent operating point similar to the SRC where all the gain curves cross
the unity point. However, affected by the presence of the gain may reach its peak at a higher
frequency above . As aforementioned, in order to operate in the preferable ZVS region, the
converter with MOSFET switches should be working on the right slope of a gain curve.
Therefore, the LCC cannot operate at the open circuit resonant frequency, which is the highest
efficacious point for the series part of the resonant tank impedance is at its minimum magnitude
with the inductance and capacitance canceled each other.
The LCC possesses the advantages of PRC that it is capable of handling zero load
condition and the gain-frequency curves have steep slope for light load condition. In the
meantime, the resonant current is not as large as PRC and thus the circulating energy is limited,
which is one of the merits of SRC.
LLC Resonant Converter
The LLC resonant converter is also a three-resonant-component converter as shown in
Figure 1.13. Unlike the LCC, the LLC resonant tank has an inductor in parallel to the
transformer primary side (or rectifier input) instead of a capacitor. The parallel inductor is denoted
as for the reason that it is usually implemented by the magnetizing inductor of the transformer.
Although the magnetizing inductor exists for every transformer, which makes SRC look the same
as LLC, in SRC is much larger than the resonant inductor and will not participate in the
resonance, while in the LLC has comparable inductance with and can no longer be ignored
in the resonance. Since the magnetizing inductor is embodied in the transformer and the resonant
inductor can be implemented by the leakage inductance of the transformer as well, the SRC
circuit structure can be converted to the LLC topology at no extra costs [39-41].
The LLC converter has likewise two resonant frequencies: ( √ ) is the short
circuit resonant frequency, and ( √( ) ) is the open circuit resonant
frequency. But is larger than , which indicates that the load-independent unity gain point
occurs at a higher frequency than the peak gain point based on the previous LCC analysis as
shown in Figure 1.14 (where ). This feature of the LLC grants the highest efficiency
operation point reachable within ZVS region to the converter, which is given up by the LCC in
consideration of ensuring ZVS. Besides, the LLC combines the advantages of SRC and PRC: the
range of gain is wide as the gain can be above or below 1; the span of operation frequency is
contracted as different gain curves for different load condition converge to the unity gain point
at .
1.3 Objectives and Outline
The primary objective of this dissertation is to give a thorough and systematic analysis of
the operation of the resonant converter, particularly the LLC resonant converter, whose topology
has the potential to achieve high power density and high power efficiency for wide input range
applications.
 

Editat Ianuarie 15, 2019 de Vizitator

[Vizitator]

Pe care sa te bazezi, la aceeasi simulare diferenta de 4:1

[Vizitator]

Am zis, ce atatea comenzi, tranzistoare...Am folosit un generator sinusoidal si verific raspunsul circuitului LC serie functie de frecventa sau de valorile L si C din tancul rezonant.

[gsabac]

Este o diferenta la modul de reprezentare a marimilor, Tina are semnal din generator "virf la virf" si LTspice doar "virf",

deci in exemplu Tina are doar 500Vv fata de LTSpice care are 1000Vv, dar asta nu explica diferentele.

Deoarece ati ales 4900uS vedeti doar coada tranzitorie a pornirii simularii simultan cu terminarea ei, adica ati ales valori "imposibile"

La Tina nu cunosc, scrie Axis label nu este gradat in volti si care ar fi scala de masura a osciloscopului virtual?

La LTspice daca folositi .tran 0 5m 200u 10n, adica sa anulati tranzitia simularii inainte de 200uS si sa ramina doar regimul stationar si 10nS pentru a forta simularea cu un timp de 10nS, mult mai mic decit perioada semnalului de 70,5KHz, obtineti urmatoarea curba sinusoidala pentru tensiunea din punctul RC.

 

Pentru ca schema sa fie cit mai lamuritoare am introdus 3 puncte de masura (Label alese iesiri) si cu click se evidentiaza in simulare pentru ce punct al schemei este curba respectiva.

 

 

@gsabac

Editat Ianuarie 16, 2019 de gsabac

[Vizitator]

CITAT:    Este o diferenta la modul de reprezentare a marimilor, Tina are semnal din generator "virf la virf" si LTspice doar "virf",

imagehost

[gsabac]

OK, am gresit, ambebe au volti la virf.

Tensiunea pe bobina V(l):

  

 Are cam 450V, se deduce ca poate circuitul este in apropiere de rezonanta.

 

@gsabac

Editat Ianuarie 16, 2019 de gsabac

[gsabac]

In LTSpice generatorul are posibilitatea setarii rezistentei interne si a capacitatii in paralel.

  

In simulare eu am folsit un generator cu impedanta aproape zero si am obtinut circa 8V la 70,500KHz

 si ma intreb daca si Tina nu are cumva aceste proprietati predefinite si cu ce valori, deci care este rezistenta interna a generatorului din Tina.

Daca Rg din LTSpice il setez la 500 ohmi, atunci rezultatele sunt identice.

In continuare cred ca ar fi bine sa folositi numai LTSpice, deoarece programul este standard pe toate forumurile si printre useri si mai ales pentru ca este

 versiunea completa care accepta scheme si circuite oricit de complexe.

In poza este setata o analiza AC, pentru circuitul RLC cu generator de 1000Vv si rezistenta zero, intre 30K si 200K cu 1000 de puncte .

 

La rulare generatorul este baleat si in poza sunt marcate tensiunile de pe generator,  bobina si grupul RC.

 

Rezonanta se obtine la 71,180KHz (valoare calculata) si care este si pe simulare.

Daca baleajul se face intre 70,000KHz si 72,000KHz, atunci apar detalii precise despre tensiuni.

  

De fapt circuitul analizat are un factor de calitate subunitar si este mai greu de inteles cum functioneaza.

Pentru circuitul de forta cu sau fara transformator, se poate folosi acest procedeu de analiza globala pe AC, apoi detaliat pe analiza tranzitorie la frecventele

 de interes, ZCS in stinga rezonantei si ZVS in dreapta, desigur cu generator sinusoidal pentru AC si generator dreptunghilar cu dead time pentru tranzitoriu.

 

@gsabac

Editat Ianuarie 17, 2019 de gsabac

[Vizitator]

[Vizitator]

Daca esti mai atent si ai timp de pierdut vezi ca nu difera prea mult cele 2 programe. Insa LT vede un max in jur de 71,2kHz in timp ce TINA il vede la 71kHz.

EDIT1:  am reusit si cu gen de curent al TINA

 

Editat Ianuarie 17, 2019 de Vizitator

[gsabac]

Cu Tina nu inteleg cum ati descoperit frecventa de rezonanta, prin incercari sau cum?

Frecventa exacta prin calcul este 71,17625KHz si cu LTSpice am verificat-o prin baleajul frecventei

 si puteti incerca acest procedeu cu ajutorul fisierului din atasament, pentru orice valori, circuit sau puteri, bineinteles in regim sinusoidal.

 

@gsabac

RLC rezonanta.asc

[Vizitator]

 

Editat Ianuarie 17, 2019 de Vizitator

[gsabac]

Adica ultimul rezultat este 71,2KHz adica la precizie cu calculul.

 

@gsabac

Editat Ianuarie 17, 2019 de gsabac

[FRobert]

      Felicitari Dl. @miticamy si Dl. Sabac pentru acest topic si totodata multumiri pentru informatiile pretioase si simularile indelungate facute pentru comunitate. Intradevar este o provocare de a realiza o sursa LLC care sa lucreze cu o alimentare de la retea intre 180V - 265V. Am cuparat inca din decembrie niste controlere UCC25600 si driver IRS21867 si as dori sa realizez o sursa rezonanta cu stabilizare pentru tensiune de intrare 180V-265V, dupa ce scap de actuala provocare care nu este altceva decat de realizat o retea pentru 452 de calculatoare, pentru care trebuie sa intind 20.7km de cablu.....

Am descarcat calculatorul excel pentru UCC25600 de pe siteul Texas Instruments, doar ca mai am multe necunoscute in jurul alegerii factorului de calitate a tancului rezonant respectiv alegerea  valorii castigului si din acest motiv obtineam niste valori aiurea sau cel putin asa mi se pareau.

   Pana ajung la proba practica citesc cu interes realizarile dumneavoastra.

Cu respect Robert

[Vizitator]

Daca PFC-ul este cam obligatoriu de ce vrei un LLC pt asa variatie a intrarii? Am gasit a aplicatie in care PFC-ul era de 420V dar LLC-ul era calculat pt intrare 400-440V (riplul de la PFC?) AN4930 daca nu gresesc.