Introduction

A single-stage remoted converter, akin to a bidirectional capacitor-inductor-inductor-inductor-capacitor (CLLLC), is a well-liked converter sort in power storage programs (ESSs) to avoid wasting system prices and enhance energy density. The achieve curve of an CLLLC is flatter, nevertheless, when the switching frequency (f_s) is increased than the collection resonant frequency (f_r) the achieve curve might be undesirably flat. The parasitic capacitance of the transformer and MOSFETs would additionally considerably affect the converter achieve [1], which can lead the converter’s output voltage out of regulation. On this energy tip, I’ll introduce a CLLLC management algorithm and a synchronous rectifier (SR) management technique to eradicate this nonlinearity, utilizing a 3.6-kW prototype converter to confirm the efficiency. Determine 1 is a block diagram of a residential ESS.

Determine 1 Residential ESS block diagram with bidirectional energy issue correction (PFC)/inverter, bidirectional DC/DC converter, and most energy level monitoring (MPPT). Supply: Texas Devices

Design issues within the management stage

Determine 2 exhibits the circuit topology of the full-bridge CLLLC resonant converter with the parasitic capacitors. This topology consists of a symmetric resonant tank and full-bridge construction.

Determine 2 The circuit topology of the full-bridge CLLLC converter with parasitic capacitors. Supply: Texas Devices

Determine 3 exhibits the perfect achieve curve of the CLLLC. Much like an LLC converter, variable frequency management is a well-liked management scheme for a CLLLC resonant converter.

Determine 3 A really perfect CLLLC achieve curve that makes use of variable frequency management. Supply: Texas Devices

As talked about earlier, the achieve curve is flat when f_s exceeds f_r. Furthermore, with the ability stage rising, the converter must parallel extra FETs on the battery aspect to deal with extra present, which implies that the output capacitance (C_oss) on the output full-bridge FETs might be extraordinarily giant. Contemplating the parasitic parameters of transformer interwinding capacitance and C_oss, the non-monotonic achieve curve at excessive frequency is critical, which corresponds to a light-load situation, as proven in Determine 4.

Determine 4 The CLLLC achieve curve contemplating parasitic parameters such because the transformer interwinding capacitance and C_oss. Supply: Texas Devices

On this case, frequency management is ineffective. Hiccup mode is a well-liked technique for addressing CLLLC resonant converter nonmonotonic options, however this technique just isn’t appropriate in battery functions as a result of the converter must ship excessive present when the battery voltage is low. Pulse-width modulation (PWM) and phase-shift management may resolve this problem, however PWM management will make the transistors work at a hard-switching state, which decreases effectivity and limits the operational frequency. Subsequently, phase-shift management is a more sensible choice.

Management logic

Determine 5 exhibits the frequency and phase-shift mixed-control scheme diagram. The battery voltage is low throughout startup, so the converter must gentle begin with low charging present to restrict the excessive present spike and delay the battery life. It’s a restricted impact to gentle begin from a excessive frequency if the resonant inductor worth or frequency just isn’t excessive sufficient. When the battery prices to close full capability, it is going to trickle cost with a small present and keep a continuing voltage. Each circumstances correspond to a light-load situation for the converter. At mild load, the output voltage tends to rise due to the parasitic capacitance and will finally exit of regulation primarily based on earlier evaluation; phase-shift management might help regulate the output voltage on this state. The controller’s calculation end result decides whether or not the converter must enter phase-shift mode or not.

Determine 5 The management scheme in several cost states. Word, the battery voltage is low throughout startup, so the converter must gentle begin with low charging present to restrict the excessive present spike and delay the battery life. Supply: Texas Devices

Determine 6 exhibits the modulation change between frequency and part shift. When the load decreases, the frequency will improve to control the output voltage. If the calculated most frequency is increased than the setting worth, the converter will enter phase-shift modulation; then when the load will increase, the phase-shift angle will lower with a view to regulate the output voltage. The converter will enter frequency mode once more when the phase-shift angle decreases to zero.

Determine 6 The management scheme between frequency and phase-shift modes. When the load decreases and the phase-shift angle is zero, the frequency will improve to control the output voltage (frequency mode). If the utmost frequency is increased than the setting worth, the part shift angle decreases to control output voltage (part shift mode). Supply: Texas Devices

Issues attributable to parasitic capacitance

The MOSFETs’ C_oss additionally has this impact beneath phase-shift mode; the tank present will oscillate with these capacitors, as proven in Determine 7.

Determine 7 The tank present waveforms beneath phase-shift mode in open loop. Supply: Texas Devices

Determine 8 plots a achieve comparability of a CLLLC converter with and with out contemplating MOSFET C_oss. In accordance with the determine, there might be fluctuation within the achieve curve. On this case, the controller could modify the phase-shift angle to the mistaken course beneath closed-loop management, leading to a big present spike.

Determine 8 The achieve curve beneath phase-shift mode with and with out C_OSS. Supply: Texas Devices

Answer for the achieve downside

To eradicate the non-monotonic of achieve, using SR management as proven in Determine 9 may resolve this problem. Turning on both two higher or two decrease SR switches on the identical time through the tank present oscillation interval will quickly brief the transformer’s secondary-side winding, such that C_oss is not going to contain the resonant.

Determine 9 Proposed SR management scheme to eradicate the non-monotonic of achieve. Supply: Texas Devices

Determine 10 exhibits the take a look at end result; there isn’t a oscillation in comparison with Determine 8. For extra detailed evaluation and take a look at outcomes, see reference [2].

Determine 10 Achieve curve beneath phase-shift mode utilizing the proposed management scheme (gray line). Supply: Texas Devices

Experimental outcomes

A prototype [3] makes use of this management scheme to confirm the efficiency. Determine 11 exhibits the soft-start waveform and Determine 12 exhibits the tank present waveforms beneath phase-shift mode with the proposed management scheme.

Determine 11 The phase-shift gentle begin with 750 W of output energy. Supply: Texas Devices

Determine 12 The tank present waveforms beneath phase-shift mode with the proposed scheme. Supply: Texas Devices

Determine 13 and Determine 14 present the frequency/phase-shift modulation change take a look at. From the take a look at waveforms, the startup present is restricted inside 28 A with 750 W of output energy. There is no such thing as a oscillation within the tank present and the converter may change the modulation easily in several working circumstances.

Figure 13 The phase-shift and frequency modulation change: frequency mode with a 5-A load. Supply: Texas Devices

Figure 14 The phase-shift and frequency modulation change: phase-shift mode with a 1-A load. Supply: Texas Devices

Conclusion

The proposed frequency and phase-shift mixed-control scheme limits the inrush present through the startup stage and makes the achieve linear at a light-weight load situation. The converter may change between frequency modulation and part shift modulation easily. Apart from, phase-shift management additionally introduces the non-monotonic achieve problem and makes the present oscillate within the designs which have giant C_OSS. The proposed SR management technique might help clear up the present oscillation problem and makes the achieve monotonic.

Guangzhi Cui is a System Engineer at Texas Devices, the place he’s chargeable for creating energy provide design. Guangzhi earned his M.S. diploma in Electrical Engineering from Hong Kong College of Science and Expertise in 2016; and his B.S. diploma of Engineering from Hunan College in 2014.

Associated Content material

• Energy Ideas #102: CLLLC vs. DAB for EV onboard chargers
• Energy Ideas #92: Excessive-frequency resonant converter design issues, Half 2
• Energy Ideas #134: Don’t change the exhausting approach; obtain ZVS with a PWM full bridge
• Energy Ideas #117: Measure your LLC resonant tank earlier than testing at full working circumstances
• Energy Ideas #97: Form an LLC-SRC achieve curve to fulfill battery charger wants
• Energy Ideas #94: How an upside-down buck provides a topology different to the non-isolated flyback

 References

1. Lee, Byoung-Hee, Moon-Younger Kim, Chong-Eun Kim, Ki-Bum Park, and Gun-Woo Moon, “Evaluation of LLC Resonant Converter Contemplating Results of Parasitic Elements.” Revealed in INTELEC 2009 – thirty first Worldwide Telecommunications Vitality Convention, Incheon, Korea (South), Oct. 18-22, 2009, pp. 1-6.
2. Tai, Will, Guangzhi Cui, and Sheng-Yang Yu, “Achieve Optimization Management Methodology for CLLLC Resonant Converters Underneath Part Shift Mode.” Revealed in PCIM Europe 2024; Worldwide Exhibition and Convention for Energy Electronics, Clever Movement, Renewable Vitality and Vitality Administration, Nürnberg, Germany, June 11-13, 2024, pp. 2513-2518.
3. Cui, Guangzhi. n.d. “3.6kW Bidirectional CLLLC Resonant Converter Reference Design.” Tex as Devices reference design No. PMP41042. Accessed Nov. 6, 2024.

The publish Energy Ideas #135: Management scheme of a bidirectional CLLLC resonant converter in an ESS appeared first on EDN.

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