Rising the ability density of a GaN-based PFC

Introduction

Fashionable digital programs want small, light-weight, high-efficiency energy provides. These provides require cost-effective strategies to take energy from the AC energy distribution grid and convert it to a kind that may run the required electronics.

Excessive switching frequencies are among the many greatest enablers for small dimension. To that finish, gallium nitride (GaN) switches present an efficient technique to obtain these excessive frequencies given their low parasitic output capacitance (C_OSS) and speedy turn-on and turn-off instances. It’s potential, nonetheless, to amplify the high-power densities enabled by GaN switches by means of the usage of superior management strategies.

On this article, I’ll look at a sophisticated management technique used inside a 5-kW energy issue corrector (PFC) for a server. The design makes use of high-performance GaN FETs to function the ability provides on the highest sensible frequency. The facility provide additionally makes use of a novel management expertise that extracts extra efficiency out of the GaN FETs. The tip result’s a high-efficiency, small-form-factor design with greater energy density.

03.21.2024

03.18.2024

03.18.2024

System overview

It’s well-known that the totem-pole PFC is the workhorse of a high-power, high-efficiency PFC. Determine 1 illustrates the topology.

Determine 1 Primary totem-pole PFC topology the place S₁ and S₂ are high-frequency GaN switches and S₃ and S₄ are low-frequency-switching Si MOSFETs. Supply: Texas Devices

S₁ and S₂ are high-frequency GaN switches working with a variable frequency between 70 kHz and 1.2 MHz. S₃ and S₄ are low-frequency-switching silicon MOSFETs working on the line frequency (50 to 60 Hz).

In the course of the optimistic half cycle of the AC line, S₂ operates because the management FET and S₁ is the synchronous rectifier. S₄ is at all times on and S₃ is at all times off. Determine 2 exhibits the interval when the inductor present is rising as a result of management FET S₂ is on. Determine 3 exhibits the interval when the inductor present is discharging by means of synchronous rectifier S₁.

Determine 2 Constructive one-half cycle inductor present cost interval. Supply: Texas Devices

Determine 3 Constructive one-half cycle inductor discharge interval. Supply: Texas Devices

Determine 4 and Determine 5 illustrate the identical behaviors for the unfavourable one-half cycle.

Determine 4 Destructive one-half cycle inductor present cost interval. Supply: Texas Devices

Determine 5 Destructive one-half cycle inductor discharge interval. Supply: Texas Devices

ZVS

The usage of GaN switches for S₁ and S₂ allows the converter to run at greater switching frequencies given the decrease turn-on and turn-off losses of the swap. It’s potential to realize even greater frequencies, nonetheless, if the GaN switches can activate with zero voltage switching (ZVS). The target for this design is to realize ZVS on each switching cycle for all line and cargo circumstances. With the intention to do that, you have to two issues:

• Suggestions to inform the controller if ZVS has been achieved
• An algorithm {that a} microcontroller can execute in actual time to realize low complete harmonic distortion (THD)

You possibly can accomplish the primary merchandise by means of an built-in zero voltage detection (ZVD) sensor contained in the GaN switches [1]. The ZVD flag works by asserting a excessive sign if the swap activates with ZVS; if it doesn’t obtain ZVS at turn-on, the ZVD sign stays low. Determine 6 and Determine 7 illustrate this habits.

Determine 6 ZVD suggestions block diagram with the LMG3425R030 GaN FET with an built-in driver, safety and temperature reporting in addition to the TMS320F280049C MCU. Supply: Texas Devices

Determine 7 ZVD sign with ZVS (left) and ZVD sign with out ZVS (proper). The built-in ZVD sensor allows a ZVD flag that may be seen if the swap activates with ZVS. Supply: Texas Devices

Integrating this operate contained in the GaN swap offers an a variety of benefits: minimal part rely, low latency and dependable detection of ZVS occasions.

Along with the ZVD sign, you additionally want an algorithm able to calculating the swap timing parameters such that you would be able to obtain ZVS and low THD concurrently. Determine 8 is a block diagram of the {hardware} wanted to implement the algorithm.

Determine 8 {Hardware} wanted for the ZVD-based management technique that permits an algorithm able to calculating the swap timing parameters to realize ZVS and a low THD concurrently. Supply: Texas Devices

Fixing the state airplane for ZVS of the resonant transitions of the GaN FET’s drain-to-source voltage (V_DS) gives you the algorithm for this design. Determine 9 illustrates the GaN FET V_DS, inductor present, and management indicators, together with each the time-domain and state-plane plots.

Determine 9 Resonant transition state-plane resolution with the GaN FET V_DS, inductor present, and management indicators, together with each the time-domain and state-plane plots. Supply: Texas Devices

In Determine 9’s state-plane plot:

• “j” is the normalized present firstly and finish of every dead-time interval
• “m” is the normalized voltage
• “θ” is used for the normalized timing parameters

The determine additionally exhibits the normalization relationships. The microcontroller in Determine 8 solves the state-plane system equations proven in Determine 9 such that the system achieves each ZVS and a really perfect energy issue. The ZVD sign offers suggestions to instruct the microcontroller on the right way to regulate the switching frequency to fulfill ZVS.

Determine 10 exhibits the working waveforms when the utilized frequency is simply too low (left), perfect (middle) and too excessive (proper). You possibly can see that each ZVD indicators are current solely when the utilized frequency is on the perfect worth; thus, various the frequency till each FETs obtain ZVD will reveal the best working level.

Determine 10 ZVD management waveforms when the utilized frequency is simply too low (left), perfect (middle) and too excessive (proper). Supply: Texas Devices

{Hardware} efficiency

Determine 11 is a photograph of a two-phase 5-kW design instance utilizing GaN and the beforehand described algorithm.

Determine 11 Two-phase 5 kW GaN-based PFC with the {hardware} required to use algorithms to realize even greater frequencies and improve the effectivity of the general resolution. Supply: Texas Devices

Desk 1 lists the specs for the design instance.

 Desk 1 Design specs for {hardware} instance utilized in Determine 11.

Determine 12 exhibits the inductor present waveforms (I_LA and I_LB) and GaN FET V_DS waveforms for each phases (V_A and V_B). The plots are at full energy and illustrate three totally different working circumstances. In every case, you may see ZVS and a sinusoidal present envelope. The circumstances for all three plots are V_IN = 230V_RMS, V_OUT = 400V, P = 5kW, and 200V/div, 20A/div and 2µs/div.

Determine 12 The inductor present waveforms (I_LA and I_LB) and GaN FET V_DS waveforms taken at full energy for: (a) V_IN≪V_OUT/2, (b) V_IN=V_OUT/2, and (c) V_IN≫V_OUT/2. Supply: Texas Devices

Determine 13 exhibits the measured effectivity and THD for a system working with a 230V_AC enter throughout the load vary.

Determine 13 Effectivity and THD of a two-phase PFC working with a 230V_AC enter throughout the load vary. Supply: Texas Devices

 Lowering the footprint of a GaN energy provide

GaN switches can enhance the ability density of all kinds of functions by enabling sooner switching frequencies. Nevertheless, the addition of applied sciences comparable to superior management algorithms can considerably scale back the footprint of an influence provide even additional. For extra details about the reference design instance mentioned on this article, see reference [2].

Brent McDonald works as a system engineer for the Texas Devices Energy Provide Design Providers workforce, the place he creates reference designs for a wide range of high-power functions. Brent 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. Texas Devices. n.d. LMG3526R030 650-V 30-mΩ GaN FET with Built-in Driver, Safety and Zero-Voltage Detection. Accessed Jan. 22, 2024.
2. Texas Devices. n.d. “Variable-Frequency, ZVS, 5-kW, GaN-Primarily based, Two-Part Totem-Pole PFC Reference Design.” Texas Devices reference design No. PMP40988. Accessed Jan. 22, 2024.