Present-mode management LLC concerns
Inductor-inductor-capacitor (LLC) serial resonant circuits, as proven in Determine 1, can obtain each zero voltage switching on the first aspect and nil present switching on the secondary aspect with a purpose to enhance effectivity and allow a better switching frequency. Normally, an LLC converter makes use of direct frequency management, which has just one voltage loop and stabilizes its output voltage by adjusting the switching frequency. An LLC with direct frequency management can not obtain excessive bandwidth as a result of there’s a double pole within the LLC small-signal switch operate that may range below totally different load situations [1] [2]. When together with the entire nook situations, the compensator design for a direct frequency management LLC turns into tough and sophisticated.
Present-mode management can remove the double pole with an inside management loop, attaining excessive bandwidth below all working situations with a easy compensator. Hybrid hysteretic management is a technique of LLC current-mode management that mixes cost management and ramp compensation [3]. This methodology maintains the nice transient efficiency of cost management, however avoids the associated stability points below no- or light-load situations by including slope compensation. The UCC256404 LLC resonant controller from Texas Devices proves this methodology’s success.
Determine 1 LLC serial resonant circuits that obtain each zero voltage switching on the first aspect and nil present switching on the secondary aspect. Supply: Texas Devices
Rules of LLC current-mode management
Just like pulse-width modulation (PWM) converters equivalent to buck and increase, peak current-mode management controls the inductor present in every switching cycle and simplifies the inside management loop right into a first-order system. Reference [2] proposes LLC cost management with the resonant capacitor voltage.
In an LLC converter, the resonant tank operates like a swing. The high- and low-side switches are pushing and pulling the voltage on the resonant capacitor: when the high-side change activates, the voltage on the resonant capacitor will swing up after the resonant present turns constructive; conversely, when the low-side change activates, the voltage on the resonant capacitor will swing down after the resonant present turns detrimental.
Vitality flows into the resonant converter when the high-side change activates. Should you take away the enter decoupling capacitor, the facility delivered into the resonant tank equals the combination of the product of the enter voltage and the enter present. Should you neglect the lifeless time, Equation 1 expresses the vitality in every switching cycle.
In Equation 1, the enter voltage is fixed, and the enter present equals absolutely the of the resonant present. So, you possibly can modify Equation 1 into Equation 2.
Wanting on the resonant capacitor, the combination of the resonant present is proportional to the voltage variation on the resonant capacitor (Equation 3).
Equation 4 deduces the vitality delivered into the resonant tank.
From Equation 4, it’s apparent that the vitality delivered in a single switching cycle is proportional to the voltage variation on the resonant capacitor when the high-side change activates. That is similar to peak present management in a buck or increase converter, by which the vitality is proportional to the height present of the inductor.
LLC current-mode management controls the vitality delivered in every switching cycle by controlling the voltage variation on the resonant capacitor, as proven in Determine 2.
Determine 2 The LLC current-mode management precept that manages the vitality delivered in every switching cycle by controlling the voltage variation on the resonant capacitor. Supply: Texas Devices
LLC current-mode management with MCUs
Determine 3 reveals the logic of a current-mode LLC applied with the TMS320F280039C C2000
32-bit microcontroller (MCU) from Texas Devices, which features a hardware-based delta voltage of resonant capacitor (ΔVCR) comparability, pulse technology and most interval limitation [4].
In LLC current-mode management, sign Vc comes from the voltage loop compensator, and sign VCR is the voltage sense of the resonant capacitor. A C2000 comparator subsystem module has an inner ramp generator that may routinely present downsloped compensation to Vc. You simply must set the preliminary worth of the ramp generator; the digital-to-analog converter (DAC) will present the downsloped VCR limitation (Vc_ramp) primarily based on the slope setting. The comparator subsystem module compares the analog sign of VCR with the sloped limitation, and generates a set off occasion (COMPARE_EVT) to set off enhanced PWM (ePWM) by means of the ePWM X-bar.
The motion qualifier submodule in ePWM receives the evaluate occasion from the comparator subsystem and pulls low the excessive aspect of PWM (PWMH) in every switching cycle. The configurable logic block then duplicates the identical pulse width to the low aspect of PWM (PWML) after PWMH turns low. After PWML turns low, the configurable logic block generates a synchronous pulse to reset the entire associated modules and resets PWMH to excessive. The method repeats with a brand new switching cycle.
Apart from the evaluate actions, the time base submodule limits the utmost pulse width of PWMH and PWML, which determines the minimal switching frequency of the LLC converter. If the evaluate occasion hasn’t appeared till the timer counts to the utmost setting, the time base submodule will reset the AQ submodule and pull down PWMH, changing the evaluate occasion motion from the comparator subsystem module.
This {hardware} logic kinds the inside VCR variation management, which controls the vitality delivered to the resonant tank in every switching cycle. You possibly can then design the outer voltage loop compensator, utilizing the normal interrupt service routine to calculate and refresh the setting of the VCR variation amplitude to Vc.
For a extra detailed description of the hybrid hysteretic management logic, see Reference [1].
Determine 3 LLC current-mode management logic with a C2000 MCU the place the sign Vc comes from the voltage loop compensator, and the sign VCR is the voltage sense of the resonant capacitor. Supply: Texas Devices
Experimental outcomes
I examined the current-mode management methodology described right here on a 1-kW half-bridge LLC platform with the TMS320F280039C MCU. Determine 4 reveals the Bode plot of the voltage loop below a 400 V enter and 42 A load, proving that the LLC can obtain 6 kHz of bandwidth with a 50-degree section margin.
Determine 4 The Bode plot of a current-mode management LLC with a 400 V enter and 42 A load. Supply: Texas Devices
Determine 5 compares the load transient between direct frequency management and hybrid hysteretic management with a 400-V enter and a load transient from 10 A to 80 A with a 2.5 A/µs slew fee. As you possibly can see, the hybrid hysteretic management current-mode management methodology can obtain higher a load transient response than a conventional direct frequency management LLC.
For extra experimental check knowledge and waveforms, see Reference [5].
Determine 5 Load transient with direct frequency management (a) and hybrid hysteretic management (b), from 10 A to 80 A with a 2.5 A/µs slew fee below a 400 VDC enter. Inexperienced is the first present; gentle blue is the output voltage, with DC coupled; purple is the output voltage, with AC coupled; and darkish blue is the output present. Supply: Texas Devices
Digital current-mode managed LLC
The digital current-mode managed LLC can obtain increased management bandwidth than direct frequency management and maintain very low voltage variation throughout load transition. In N+1 redundancy and parallel functions, this management methodology can maintain the bus voltage inside the regulation vary throughout sizzling swapping or defending. So, this management methodology has been extensively adopted in knowledge heart energy and AI server energy with this quick response characteristic and digital programable capacity.
Desheng Guo is a system engineer at Texas Devices, the place he’s liable for growing energy options as a part of the facility supply industrial section. He has created a number of reference designs and is aware of AC-DC energy provide, digital management, and GaN merchandise. He obtained a grasp’s diploma from the Harbin Institute of Know-how in energy electronics in 2007, and beforehand labored for Huawei Know-how and Delta Electronics earlier than becoming a member of TI.
Associated Content material
- Energy Ideas #84: Suppose outdoors the LLC collection resonant converter field
- Energy Ideas #117: Measure your LLC resonant tank earlier than testing at full working situations
- Energy Ideas #122: Overview of a planar transformer utilized in a 1-kW high-density LLC energy module
- Energy Ideas #97: Form an LLC-SRC acquire curve to satisfy battery charger wants
- Energy Ideas #92: Excessive-frequency resonant converter design concerns, Half 2
References
- Hu, Zhiyuan, Yan-Fei Liu, and Paresh C. Sen. “Bang-Bang Cost Management for LLC Resonant Converters.” Revealed in IEEE Transactions on Energy Electronics 30, no. 2, (February 2015): pp. 1093-1108. doi: 10.1109/TPEL.2014.2313130.
- McDonald, Brent, and Yalong Li. “A novel LLC resonant controller with best-in-class transient efficiency and low standby energy consumption.” Revealed in 2018 IEEE Utilized Energy Electronics Convention and Exposition (APEC), San Antonio, Texas, March 4-8, 2018, pp. 489-493. doi: 10.1109/APEC.2018.8341056.
- “UCC25640x LLC Resonant Controller with Extremely-Low Audible Noise and Standby Energy.” Texas Devices knowledge sheet, literature No. SLUSD90E, February 2021.
- Li, Aki, Desheng Guo, Peter Luong, and Chen Jiang. “Digital Management Implementation for Hybrid Hysteretic Management LLC Converter.” Texas Devices software observe, literature No. SPRADJ1A, August 2024.
- Texas Devices. n.d. “1-kW, 12-V HHC LLC reference design utilizing C2000 real-time microcontroller.” Texas Devices reference design No. PMP41081. Accessed Jan. 16, 2025.
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