Digital Totem-Pole & Interleaved PFC: HP1010 & HP1011 new performance for motor drives

Motors drive applications of a huge array of products, ranging from hair driers, refrigerators or even conveyor systems in manufacturing facilities. The technical nature of such applications demands the power flow from 1-phase of AC supply to 3-phase motor rotor, as shown in Figure 1. Power Factor Correction (PFC) in between plays a vital role linking two distinct systems of  the dynamic load and power grid, where a set of technical issues must be tackled. In general, there are two schools of engineering endeavour mitigating these challenges, integrated or discrete, using either one or two chips for operations of both PFC and motor inverter. In this reading, we delve into the advantages of Totem-Pole and interleaved PFC from HyCtrl® family of Hynetek, HP1010 and HP1011 (HP101X) exploring how their innovative features can significantly enhance the efficiency and performance of motor applications. This article focuses on digital controller, neither analogue solutions like FAN9672, NCP1631 and UCC28070, nor single chip like F28035, whose complicated algorithm consumes significant engineering effort on resource conflict and control programming.

Figure 1: A Typic Motor System

HP1010 and HP1011 are the latest digital PFC controllers introduced by Hynetek, both packaged in a 4mm x 4mm QFN-24L, as Figure 2. HP1010 is the industry's first dedicated digital Totem-Pole PFC controller, while HP1011 is the first dual-phase interleaved PFC digital controller operating in CCM mode. As the first of its kind, the digital architecture of both chips is based on a high-speed state machine with integrated high-performance analogue front-end including high-speed comparators. Thus real-time control of PFC is assured. In sleep mode, the chip's supply current reduces to 1 mA. Meanwhile, advanced performance is insured through a rich set of programmable protection features, including cycle-by-cycle current limit protection, surge protection, overvoltage/undervoltage protection, open circuit protection, and more. The flexible design process empowers these two controllers suitable for a wide range of applications, including air conditioners, white goods, high-performance computers, 5G/telecom power supplies, industrial power supplies, ultra-high-density (UHD) power supplies, and IGBT-based PFC power supplies.

Figure 2: HP1010 & HP1011

In addition, each of the two ICs has its own prominent traits. The surge protection of HP1010 allows for the rapid shutdown of slow synchronous rectifiers, even at challenging scenarios of out-of-phase events（e.g. positive AC input with negative strike）. This effectively enhances the stability and reliability of the Totem-Pole bridgeless PFC. HP1011 supports automatic channel management and dynamic balance of two inductor currents, effectively achieving less than 5% deviations.

I²C & UART ensuring optimal efficiency of motor systems

I²C and UART enables intelligent efficiency optimization of motor systems. In such systems, the motor speed changes based on the application dynamics. Therefore, ensuring the timely matching between the PFC output voltage and the motor load is crucial for further enhancement of system efficiency. Assuming that the motor load decreases leads to a slower spinning speed, it is essential to adjust the PFC output voltage promptly. If the PFC maintains the original high voltage output, mismatch would  result in unnecessary power consumption, hence a decrease in efficiency. On the contrary, through the communication interface, adjusting the output voltage promptly in response to the motor speed variations could help avoid such power waste and additionally preventing potential damage to the rotor's mechanical structure.

Similar considerations also apply to motor fault events, where instantaneous intelligent interaction between PFC control and the motor irregularity is invaluable. To achieve smart coordination, the motor controller can dynamically configure three registers of the HP101X. Using address 0X00[2], you can choose whether to enable the PFC function. Addresses 0X23 and 0X24 represent the reference voltages for low and high voltage inputs, respectively. The HP101X's high-precision analogue front-end supports fine adjustments in 0.27V increments within the range of 0V to 560V. Additionally, based on specific requirements of the designed motor system, various operating parameters of the PFC can be fed back to the secondary controller via these very interfaces. Information for further system intelligence optimization includes protection status, output current, input voltage frequency, system status, and more. For more details, you can refer to the HP101x GUI user manual available on the Hynetek Semiconductor official website(Hynetek-HyCtrl).

Fast response on dynamic load

Intelligent coordination is undoubtedly beneficial, but system reliability and stability is a priority, especially in handling unforeseen where planned communication is unrealistic.

Motor inherently drives load of being nonlinear and inductive. Correspondingly system power consumption varies with the load and rotating speed. This nonlinear behaviour makes it challenging to design a PFC system that can adapt to the alternating conditions while maintaining a high-power factor across a wide range of operating points. Normally, striving for a unit power factor, PFC algorithm comprises of fast current loop and slow voltage loop. The bandwidth of voltage loop is specifically designed as narrow as tens Hertz to decouple from higher rectified line frequency.  As a result of this narrow bandwidth, handling of fast load transition is disadvantaged. Mishandling of load variation could further stresses the capacitor placed in front of the inverter, hence risk the system reliability. This is the challenge from the load side.  

Moreover, bus voltage fluctuations could also come from AC side as well. Any disturbance on the AC line, such as a drop or lighting strikes, could potentially yield damage on the very same capacitor mentioned above.

HP1010 and HP1011 have been tested with both quick and robust transition response. This excellent performance can be viewed from two aspects: AC input and motor load.

Tacking the stresses from the AC side, HP101x offers cycle by cycle current projection and patented control algorithm to guarantee an agile response. Figure 3 presents when inductor current shooting to higher level, PWM latches off at once and then recovered based on adjustable threshold, debounce time and blanking time. All these three parameters can be set via graphic user interface (GUI) according to the system design.

Figure 3: 100 Vac, 400V, Light Load To High Load, Latch (Right), Recover (Left)

Figure 4: 100 Vac, 90° Drop, 5ms (Left) / 10ms(Right)

The superb performance of load transition of HP101x can also be observed from Figure 4, the measurement proved a smooth and fast transition when input voltage dropped at 90° for both 5 ms and 10 ms. The current intelligently reinstates itself to the normal condition in a few cycles once the drop occurred.

Fast loop mode is another feature of HP101x, designed to react quickly towards load transitions. From Figure 5, maintaining output voltage of 400 volts, the difference with and without fast loop feature is more than 10%. More flexibility to benefit the design specifics, reference voltage and response time again could be customised through simple register setting.

Figure 5: 100 Vac, 60 Hz, Open-Full Load, Vout 334V ( Fast Loop Enable, Left), Vout 290V ( Disable, Right)

Low Electromagnetic Interference (EMI)

Motor and PFC control operate on two distinct clocks, hundreds kilo Hertz and tens kilo Hertz respectively. These two beats excite the system boards with distinct rhythms, hence deteriorated system electromagnetic interference (EMI), potential total harmonic distortions of current (THDi) as well.

Frequency dithering is an effective function to this issue. Once enabled, HP101x alters the switching frequency through a set number of cycles given in the relevant register. There are eight value steps available to satisfy the design requirement.

Figure 6: EMI And Thdi With (Bottom) & Without (Top) Dithering

From Figure 6, It is rather salient that EMI performance is improved to a large degree with dithering enabled. The harmonic components have been supressed and reduced through the entire spectrum.

Insofar, there are three aforementioned improvements anchoring how the performance of motor system could benefit from HP101x: intelligent cooperation, dynamic response and  EMI performance. In fact, HP101x offers a set of advanced features to ensure flexible and reliable design experience. For instance, affluent protections, X-cap discharge, power metering, inrush current protection and much more. The detailed information can be found in here (Hynetek-HyCtrl).