Department of Electrical Engineering Southern Taiwan University of Science and Technology Robot and Servo Drive Lab. 2016/2/10 Novel PWM Technique Without Causing Reversal DC- link Current For Brushless DC Motor Drives With Bootstrap Driver Industry Applications Conference, VOL. 3, Page. 2182~Page. 2188, October 2005, By Yen-Shin Lai, Fu-San Shyu, and Yong-Kai Lin Professor ： Ming-Shyan Wang Student ： Chih-Hung Wang

Department of Electrical Engineering Southern Taiwan University of Science and Technology 2016/2/10 Robot and Servo Drive Lab. 2 Outline Abstract Driver Circuit and PWM Techniques PWM Techniques1 PWM Techniques2 PWM Techniques3 PWM Techniques4 Reversal DC-link Current Novel PWM Technique without Causing Reversal DC-Link Current Experimental System Experimental Results

Department of Electrical Engineering Southern Taiwan University of Science and Technology 2016/2/10 Robot and Servo Drive Lab. 3 Abstract The speed of BLDM is controlled by the frequency and duty of the Pulse-Width Modulation (PWM) technique, which is one of the key technologies for the development of BLDM drives. This paper will present a novel PWM technique for BLDM drives with bootstrap driver circuit. As compared with existing PWM techniques for BLDM drives the presented technique doesn ’ t cause any reversal DC-link current and thereby reducing the DC-link voltage fluctuation of the drives.

Department of Electrical Engineering Southern Taiwan University of Science and Technology 2016/2/10 Robot and Servo Drive Lab. 4 Driver Circuit and PWM Techniques The inverter consists of MOSFET and driver circuit.There are three types of driver circuits: photo coupler, isolation transformer, and bootstrap circuit.. For small power applications, bootstrap driver dominates the market for cost down consideration and requiring no extra independent DC source.

Department of Electrical Engineering Southern Taiwan University of Science and Technology 2016/2/10 Robot and Servo Drive Lab. 5 Driver Circuit and PWM Techniques The capacitor “ ” provides a power source to high-side driver and is charged when the low-side MOSFET is turned on. Since no extra power source is required, the isolation circuit is therefore no more needed.

Department of Electrical Engineering Southern Taiwan University of Science and Technology 2016/2/10 Robot and Servo Drive Lab. 6 PWM Techniques1 As shown in Fig. 2 the high-side power device is controlled by chopper signal every consecutive 120 degrees in a fundamental period. The associated low-side control signal is shifted by 180 degrees, as compared to its high-side one, to clamp the related inverter output to the negative dc-link rail.

Department of Electrical Engineering Southern Taiwan University of Science and Technology 2016/2/10 Robot and Servo Drive Lab. 7 PWM Techniques2 PWM technique 2 shown in Fig. 3 turns high-side power device on and lasts for 1/6 fundamental period. In the following 60 degrees, the high- side power device is controlled by chopper signal. The same control signal is applied to the associated low-side power device except 180-degre phase shift.

Department of Electrical Engineering Southern Taiwan University of Science and Technology 2016/2/10 Robot and Servo Drive Lab. 8 PWM Techniques3 For the PWM technique shown in Fig. 4, the high-side power device is chopped in 1/6 fundamental period and the duty ratio is derived from the speed reference. Moreover, the high-side power device is clamped to the positive dc-link rail in the consecutive 1/6 fundamental period.

Department of Electrical Engineering Southern Taiwan University of Science and Technology 2016/2/10 Robot and Servo Drive Lab. 9 PWM Techniques4 Fig. 5 shows the control signals for PWM technique reported in [11]. The chop-controlled area for high- side power device is divided into two parts, each lasts for 30 degrees. This division solves the circulating current issue of the floating phase.

Department of Electrical Engineering Southern Taiwan University of Science and Technology 2016/2/10 Robot and Servo Drive Lab. 10 Reversal DC-link Current PWM technique 1 shown in Fig. 2 is very popular for low power MOSFET-driven BLDCM drives because the bootstrap driver circuit can be adopted. However, it invokes reversal DC-link current The current in the conducting phase flows back to the DC link and thereby significant DC-link voltage fluctuation.

Department of Electrical Engineering Southern Taiwan University of Science and Technology 2016/2/10 Robot and Servo Drive Lab. 11 Reversal DC-link Current This issue occurs at the commutation instance for PWM technique 1 and 2. Fig. 7 illustrates the current path using as an example. During the first several choppers around, the energy of floating phase has not yet been fully released.

Department of Electrical Engineering Southern Taiwan University of Science and Technology 2016/2/10 Robot and Servo Drive Lab. 12 Reversal DC-link Current There is a current path between “ W ” phase and “ U ” phase when the high side of “ W ” phase is “ On. When the high side of “ W ” phase is “ Off ” there is no current path between “ U ” phase and “ W ” phase, “ U ” phase and “ V ” phase. W = High Side Chopper On, V = Low Side On

Department of Electrical Engineering Southern Taiwan University of Science and Technology 2016/2/10 Robot and Servo Drive Lab. 13 Reversal DC-link Current Therefore, “ U ” phase discharges through DC link, and thereby producing reversal DC-link current. W = High Side Chopper Off, V = Low Side On

Department of Electrical Engineering Southern Taiwan University of Science and Technology 2016/2/10 Robot and Servo Drive Lab. 14 Novel PWM Technique without Causing Reversal DC-Link Current Using as an example, ‘‘ W ’’ phase is clamped to positive DC-link rail to provide a current path for ‘‘ U ’’ phase to release its energy. Therefore, there is no reversal DC- link current. This clamped period is decided by the stored energy in the floating phase.

Department of Electrical Engineering Southern Taiwan University of Science and Technology 2016/2/10 Robot and Servo Drive Lab. 15 Novel PWM Technique without Causing Reversal DC-Link Current The terminal voltage of floating phase is higher than V DC once the upper free wheeling diode is flowing current. When the floating phase releases its stored energy completely, the terminal voltage of floating phase is lower than V DC. WU W = High Side Chopper On, V = Low Side On

Department of Electrical Engineering Southern Taiwan University of Science and Technology Novel PWM Technique without Causing Reversal DC-Link Current 2016/2/10 Robot and Servo Drive Lab. 16 W = High Side Chopper On, V = Low Side OFF W = High Side Chopper OFF, V = Low Side ON

Department of Electrical Engineering Southern Taiwan University of Science and Technology 2016/2/10 Robot and Servo Drive Lab. 17 Experimental System

Department of Electrical Engineering Southern Taiwan University of Science and Technology 2016/2/10 Robot and Servo Drive Lab. 18 Experimental Results Fig. 10 shows the experimental results for PWM technique “ 1 ”

Department of Electrical Engineering Southern Taiwan University of Science and Technology 2016/2/10 Robot and Servo Drive Lab. 19 Experimental Results The presented PWM technique doesn ’ t cause any reversal DC- link current as shown in Fig. 11.

Department of Electrical Engineering Southern Taiwan University of Science and Technology 2016/2/10 Robot and Servo Drive Lab. 20 Experimental Results The reversal DC-link current will cause fluctuation of DC-link voltage. For the same converter switching frequency, the fluctuation of DC- link voltage depends upon the value of output capacitor, current supplied by the adapter and reversal DC-link current.

Department of Electrical Engineering Southern Taiwan University of Science and Technology 2016/2/10 Robot and Servo Drive Lab. 21 Experimental Results

Department of Electrical Engineering Southern Taiwan University of Science and Technology 2016/2/10 Robot and Servo Drive Lab. 22 Experimental Results

Department of Electrical Engineering Southern Taiwan University of Science and Technology 2016/2/10 Robot and Servo Drive Lab. 23 Experimental Results From these experimental results some remarks can be derived as follows. 1. The presented PWM technique can cope with the reversal DC-link current issue and thereby reducing the DC-link voltage fluctuation. 2. The DC-link voltage fluctuation caused by reversal DC-link current decreased when the value of DC-link capacitor increased. 3. The DC-link voltage fluctuation caused by reversal DC-link current increased when the load is increased.

Department of Electrical Engineering Southern Taiwan University of Science and Technology 2016/2/10 Robot and Servo Drive Lab. 24 Conclusion This paper contributes to the presentation of a novel PWM technique for widely used small power brushless DC motor drives driven by bootstrap driver circuit which has been widely used in small power applications. Experimental results derived from an FPGA based controller show that the presented PWM technique can cope with the reversal DC-link current issue and thereby reducing the DC- link voltage fluctuation.

Department of Electrical Engineering Southern Taiwan University of Science and Technology 2016/2/10 Robot and Servo Drive Lab. 25 Thanks for listening!