Introduction
Fashionable digital techniques 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 mandatory electronics.
Excessive switching frequencies are among the many greatest enablers for small dimension. To that finish, gallium nitride (GaN) switches present an efficient method to obtain these excessive frequencies given their low parasitic output capacitance (C_{OSS}) and speedy turn-on and turn-off instances. It’s doable, nevertheless, to amplify the high-power densities enabled by GaN switches via using superior management methods.
On this article, I’ll look at a complicated management methodology used inside a 5-kW energy issue corrector (PFC) for a server. The design makes use of high-performance GaN FETs to function the facility 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 top result’s a high-efficiency, small-form-factor design with increased energy density.
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 S_{1} and S_{2} are high-frequency GaN switches and S_{3} and S_{4} are low-frequency-switching Si MOSFETs. Supply: Texas Devices
S_{1} and S_{2} are high-frequency GaN switches working with a variable frequency between 70 kHz and 1.2 MHz. S_{3} and S_{4} are low-frequency-switching silicon MOSFETs working on the line frequency (50 to 60 Hz).
Throughout the optimistic half cycle of the AC line, S_{2} operates because the management FET and S_{1} is the synchronous rectifier. S_{4} is at all times on and S_{3} is at all times off. Determine 2 exhibits the interval when the inductor present is growing as a result of management FET S_{2} is on. Determine 3 exhibits the interval when the inductor present is discharging via synchronous rectifier S_{1}.
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 Unfavourable one-half cycle inductor present cost interval. Supply: Texas Devices
Determine 5 Unfavourable one-half cycle inductor discharge interval. Supply: Texas Devices
ZVS
Using GaN switches for S_{1} and S_{2} permits the converter to run at increased switching frequencies given the decrease turn-on and turn-off losses of the change. It’s doable to attain even increased frequencies, nevertheless, if the GaN switches can activate with zero voltage switching (ZVS). The target for this design is to attain ZVS on each switching cycle for all line and cargo circumstances. So as to do that, you will have two issues:
- Suggestions to inform the controller if ZVS has been achieved
- An algorithm {that a} microcontroller can execute in actual time to attain low whole harmonic distortion (THD)
You’ll be able to accomplish the primary merchandise via 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 change activates with ZVS; if it doesn’t obtain ZVS at turn-on, the ZVD sign stays low. Determine 6 and Determine 7 illustrate this conduct.
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 permits a ZVD flag that may be seen if the change activates with ZVS. Supply: Texas Devices
Integrating this perform contained in the GaN change supplies an a variety of benefits: minimal element rely, low latency and dependable detection of ZVS occasions.
Along with the ZVD sign, you additionally want an algorithm able to calculating the change timing parameters such which you can 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 methodology that permits an algorithm able to calculating the change timing parameters to attain ZVS and a low THD concurrently. Supply: Texas Devices
Fixing the state aircraft for ZVS of the resonant transitions of the GaN FET’s drain-to-source voltage (V_{DS}) provides you with 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 answer 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 originally 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 perfect energy issue. The ZVD sign supplies suggestions to instruct the microcontroller on methods to alter the switching frequency to satisfy ZVS.
Determine 10 exhibits the working waveforms when the utilized frequency is just too low (left), splendid (middle) and too excessive (proper). You’ll be able to see that each ZVD indicators are current solely when the utilized frequency is on the splendid 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 just too low (left), splendid (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 attain even increased frequencies and improve the effectivity of the general answer. Supply: Texas Devices
Desk 1 lists the specs for the design instance.
Parameters |
Worth |
AC enter |
208V-264V |
Line frequency |
50-60Hz |
DC output |
400V |
Most energy |
5kW |
Holdup time at full load |
20ms |
THD |
OCP v3 |
Electromagnetic interference |
European Norm 55022 Class A |
Working frequency |
Variable, 75kHz-1.2MHz |
Microcontroller |
TMS320F280049C |
Excessive-frequency GaN FETs |
LMG3526R030 |
Low-frequency silicon FETs |
IPT60R022S7XTMA1 |
Inner dimensions |
38mm x 65mm x 263mm |
Energy density |
120W/in^{3} |
Switching frequency |
70kHz-1.2MHz |
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 completely different working circumstances. In every case, you’ll be able to 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 facility density of all kinds of purposes by enabling quicker switching frequencies. Nonetheless, the addition of applied sciences corresponding to superior management algorithms can considerably cut 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 Companies workforce, the place he creates reference designs for a wide range of high-power purposes. Brent obtained 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
- Texas Devices. n.d. LMG3526R030 650-V 30-mΩ GaN FET with Built-in Driver, Safety and Zero-Voltage Detection. Accessed Jan. 22, 2024.
- Texas Devices. n.d. “Variable-Frequency, ZVS, 5-kW, GaN-Based mostly, Two-Section Totem-Pole PFC Reference Design.” Texas Devices reference design No. PMP40988. Accessed Jan. 22, 2024.