The necessity for cost-effective options to enhance energy issue correction (PFC) at mild hundreds and with peak effectivity whereas shrinking passive parts is turning into troublesome with typical steady conduction mode (CCM) management. Engineers are conducting vital analysis into complicated multimode options to deal with these issues [1], [2], and these approaches are engaging in that they allow you to shrink the scale of the inductor whereas concurrently bettering effectivity with delicate switching at lighter hundreds.

However on this energy tip, I’ll current a brand new method to attaining excessive effectivity and low complete harmonic distortion (THD) that doesn’t require using a posh multimode management algorithm and achieves zero switching losses beneath all working circumstances. This method 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 method permits high-efficiency ZVS beneath all working circumstances 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 top-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 at all times goes sufficiently adverse 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 L_b1, L_b2 and C_b. Throughout regular operation, the voltage throughout C_b is the same as the enter voltage V_ac. Two phases working 180 levels out of section make the most of ripple present cancellation and scale back the root-mean-square present stress in C_b. L_b1 and L_b2 are sized to solely course of the high-frequency AC ripple present crucial for TCM operation. This removes the DC bias required for the inductor utilized in TCM, as outlined in [4]. Ferrite cores for L_b1 and L_b2 assist guarantee low losses within the presence of the excessive flux swings crucial for ZVS. L_g1 and L_g2 are bigger in worth (as a lot as 10 occasions bigger) than L_b1 and L_b2, which prevents many of the high-frequency present from flowing into the enter supply and subsequently reduces electromagnetic interference (EMI). As well as, the diminished ripple present in L_g1 and L_g2 permits the potential 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 data to regulate the change timing parameters to show the change on with simply sufficient present to realize 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 circumstances that implement ZVS on each switches and drive 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 accurately, 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) studies their respective ZVS turnon standing on a cycle-by-cycle foundation again to the microcontroller. In Determine 2, V_hs,zvd and V_ls,zvd denote the ZVD reporting.

Determine 2 A single-phase iTCM schematic with management alerts.

Desk 1 Change timing parameters and definitions.

Determine 3 illustrates the ZVD timing adjustment course of. Throughout each switching cycle, the microcontroller calculates the change timing parameters (t_on, t_off, t_rp, and t_rv) primarily based on the ZVD sign’s cumulative historical past. Determine 3b reveals 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 reveals 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 adverse present than is critical to realize ZVS. The result’s a lack of effectivity and a distorted energy issue. Determine 3c happens when the working frequency is 50 kHz greater 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 conduct with low f_s (a); ideally suited f_s (b); and excessive f_s (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 very best 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 reveals a prototype constructed with the topology and algorithm I’ve mentioned up to now.

Determine 4 A 400-V, 5-kW prototype with an influence density of 120 W/in³.

Desk 2 summarizes the specs and essential part values for the prototype.

Desk 2 System specs and essential parts

Determine 5 reveals the prototype’s measurement nodes and Determine 6 illustrates the system waveforms of the prototype working beneath full energy (5 kW). The switch-node currents, I_L,A and I_L,B, are the sum of the present in L_g and L_b for his or her respective department. The zoom part of the plot reveals the waveform element throughout the constructive half cycle. The present waveforms have a great triangular form, with simply sufficient adverse present to realize ZVS as demonstrated by switch-node voltages V_A and V_B. 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 beneath full energy (V_in = V_out/2, load = 5 kW, V_in = 230 V_ac, V_out = 400 V).

Determine 7 reveals 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 many of the load vary. With the intention 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 need to use the ZVD sign to manage the working frequency of a totem-pole PFC converter to realize excessive effectivity and low THD. For extra details about this method, 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 group. 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

1. Fernandes, Ryan, and Olivier Trescases. “A Multimode 1-MHz PFC Entrance Finish with Digital Peak Present Modulation.” Revealed in IEEE Transactions on Energy Electronics 31, no. 8 (August 2016): pp. 5694-5708. doi: 10.1109/TPEL.2015.2499194.
2. Lim, Shu Fan, and Ashwin M. Khambadkone. “A Multimode Digital Management Scheme for Increase PFC with Larger Effectivity and Energy Issue at Mild Load.” Revealed in 2012 Twenty-Seventh Annual IEEE Utilized Energy Electronics Convention and Exposition (APEC), Feb. 5-9, 2012, pp. 291-298. doi: 10.1109/APEC.2012.6165833.
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4. Liu, Zhengyang. 2017. “Characterization and Utility of Broad-Band-Hole Units for Excessive Frequency Energy Conversion.” Ph.D. dissertation, Virginia Polytechnic Institute and State College. http://hdl.handle.net/10919/77959.