The necessity for cost-effective options to enhance energy issue correction (PFC) at mild masses and with peak effectivity whereas shrinking passive elements is changing into tough with standard steady conduction mode (CCM) management. Engineers are conducting vital analysis into complicated multimode options to handle these considerations [1], [2], and these approaches are engaging in that they permit you to shrink the scale of the inductor whereas concurrently bettering effectivity with mushy switching at lighter masses.
However on this energy tip, I’ll current a brand new strategy to attaining excessive effectivity and low complete harmonic distortion (THD) that doesn’t require the usage of a fancy multimode management algorithm and achieves zero switching losses underneath all working situations. This strategy makes use of a high-performance gallium-nitride (GaN) change with an built-in flag that signifies whether or not the change activates with zero voltage switching (ZVS). This strategy allows high-efficiency ZVS underneath all working situations whereas concurrently forcing the THD very low.
Topology
The topology used for this method is the built-in triangular present mode (iTCM) totem-pole PFC [3]. For prime-power and high-efficiency programs, the totem-pole PFC presents a definite benefit for conduction losses. The TCM model of this topology enforces ZVS by ensuring that the inductor present all the time goes sufficiently unfavourable earlier than the change activates [4]. Determine 1 illustrates the iTCM model of totem-pole PFC.
Determine 1 The iTCM topology, displaying AC line frequency present envelopes.
The distinction between the TCM converter and the iTCM converter is the presence of Lb1, Lb2 and Cb. Throughout regular operation, the voltage throughout Cb is the same as the enter voltage Vac. Two phases working 180 levels out of section reap the benefits of ripple present cancellation and scale back the root-mean-square present stress in Cb. Lb1 and Lb2 are sized to solely course of the high-frequency AC ripple present mandatory for TCM operation. This removes the DC bias required for the inductor utilized in TCM, as outlined in [4]. Ferrite cores for Lb1 and Lb2 assist guarantee low losses within the presence of the excessive flux swings mandatory for ZVS. Lg1 and Lg2 are bigger in worth (as a lot as 10 instances bigger) than Lb1 and Lb2, which prevents a lot of the high-frequency present from flowing into the enter supply and subsequently reduces electromagnetic interference (EMI). As well as, the lowered ripple present in Lg1 and Lg2 allows the doable use of lower-cost core supplies. Determine 1 additionally illustrates the ripple present envelopes for a number of key branches.
Management
Management is facilitated by the Texas Devices (TI) TMS320F280049C microcontroller and LMG3526R030 GaN field-effect transistors (FETs). These FETs have an built-in zero-voltage-detection (ZVD) sign that’s asserted anytime the change activates with ZVS. The microcontroller makes use of the ZVD info to regulate the change timing parameters to show the change on with simply sufficient present to attain ZVS. For simplicity, Determine 2 illustrates a one-phase iTCM PFC converter. Desk 1 defines the important thing variables used on this determine. The microcontroller makes use of an algorithm that solves the precise set of differential equations for the system. These equations use situations that implement ZVS on each switches and power the present to be equal to the present command. The equations are correct, supplied that the system is working with the correct amount of ZVS for each switches. When working appropriately, the algorithm yields the timing parameters for 0% THD and an optimum quantity of ZVS. To facilitate the ZVS situation, every change (S1 and S2) stories their respective ZVS turnon standing on a cycle-by-cycle foundation again to the microcontroller. In Determine 2, Vhs,zvd and Vls,zvd denote the ZVD reporting.
Determine 2 A single-phase iTCM schematic with management indicators.
Desk 1 Swap timing parameters and definitions.
Determine 3 illustrates the ZVD timing adjustment course of. Throughout each switching cycle, the microcontroller calculates the change timing parameters (ton, toff, trp, and trv) primarily based on the ZVD sign’s cumulative historical past. Determine 3b exhibits the system working on the ideally suited frequency. By ideally suited, I imply that the THD is 0%, and you’ve got the proper quantity of ZVS for the high- and low-side FETs. Determine 3a exhibits what occurs when the working frequency is 50 kHz decrease than the perfect. Discover that the high-side FET loses ZVS (as indicated by the lack of the high-side ZVD sign), whereas the low-side FET has extra unfavourable present than is important to attain ZVS. The result’s a lack of effectivity and a distorted energy issue. Determine 3c happens when the working frequency is 50 kHz larger than the perfect. On this case, the high-side FET has ZVS however the low-side FET loses ZVS. Once more, there’s a clear lack of effectivity and distortion.
Determine 3 ZVD habits with low fs (a); ideally suited fs (b); and excessive fs (c).
Based mostly on the presence or absence of the ZVD sign, the controller can improve or lower the frequency to push the system to the optimum working level. On this manner, the management effort acts like an integrator that makes an attempt to search out the most effective working frequency. The optimum will happen when the system is hovering proper on the brink of simply barely getting ZVS each cycle.
Prototype efficiency
Determine 4 exhibits a prototype constructed with the topology and algorithm I’ve mentioned to date.
Determine 4 A 400-V, 5-kW prototype with an influence density of 120 W/in3.
Desk 2 summarizes the specs and necessary element values for the prototype.
Desk 2 System specs and necessary elements
Determine 5 exhibits the prototype’s measurement nodes and Determine 6 illustrates the system waveforms of the prototype working underneath full energy (5 kW). The switch-node currents, IL,A and IL,B, are the sum of the present in Lg and Lb for his or her respective department. The zoom part of the plot exhibits the waveform element in the course of the constructive half cycle. The present waveforms have an excellent triangular form, with simply sufficient unfavourable present to attain ZVS as demonstrated by switch-node voltages VA and VB. Moreover, the sinusoidal envelope of the present waveform suggests a low THD.
Determine 5 Prototype measurement nodes
Determine 6 System waveforms of the prototype working underneath full energy (Vin = Vout/2, load = 5 kW, Vin = 230 Vac, Vout = 400 V).
Determine 7 exhibits the measured effectivity and THD throughout the load vary. The effectivity peaks above 99% and is above 98.5% for nearly the complete load vary. The THD has a most of 10% and is under 5% for a lot of the load vary. To be able to optimize efficiency, the unit section sheds or provides phases at roughly 2 kW.
Determine 7 The prototype effectivity and THD throughout the load vary.
Reaching a excessive effectivity and low THD for a totem-pole PFC
You should utilize the ZVD sign to regulate the working frequency of a totem-pole PFC converter to attain excessive effectivity and low THD. For extra details about this strategy, in addition to a simulation mannequin for the system, see the Variable-Frequency, ZVS, 5-kW, GaN-Based, Two-Phase Totem-Pole PFC Reference Design.
Brent McDonald is system engineer for the Texas Devices Energy Provide Design Providers crew. He acquired a bachelor’s diploma in electrical engineering from the College of Wisconsin-Milwaukee, and a grasp’s diploma, additionally in electrical engineering, from the College of Colorado Boulder.
Associated Content material
References
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