Configuring a two-phase drive for automotive applications


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The 48V two-phase motor is a suitable choice for a low-cost micro-mobility or compact hybrid drive system1 because the overall frame is efficient and cost-effective. Since the dc correlation voltage is low, the operating current is relatively high for the proposed frame. Since it is a current capacitor system, bulky capacitors are required to reduce the DC-link voltage ripple. To ensure a reliable framework, studying the modulation scheme, DC-link capacitance, and thermal response of the transducer is a must. This article will discuss three different diagrams of a two-phase voltage source transformer. Moreover, it will compare and analyze modulation schemes, modulation ratio, current stress, and DC-link voltage ripple for the topology under discussion. Figure 1 illustrates the target diagrams that will be discussed in this article. The diagrams are classified as follows: a three-legged configuration two-legged configuration with a separate DC-link capacitor Four-legged configuration without a neutral line Since the neutral current is 1.414 × higher than the phase current, a large DC-link capacitor in a two-legged configuration is required to stabilize the point voltage Neutral. On the other hand, a four-legged configuration has a higher adjustment ratio, compared to a two-legged configuration, but each additional part increases the cost and complexity of the system. The two-phase machine used in the four-legged frame must have open ended coils. The three-legged configuration is similar to a conventional three-phase voltage source transformer, but the third-station current is 1.414 × higher than other legs in a two-phase configuration. In order to improve the overall efficiency, overall cost and power density, there is a competition between silicon switches and wide band gap devices. Although wide band gap devices, such as GaN HEMTs, are widely adopted in many power electronics applications, high cost, high dV / dt, and reliability issues limit their implementation in a 48V motor system. The advantages of low cost, low stray inductance, and good heat dissipation capacity, which are attractive to the low cost 48V motor system 6-8. Comparing these two transformers, the silicon based MOSFET inverters offer more advantages. This article will discuss silicon MOSFETs in two-phase transducer design. Two-phase transducer operation: different topologies of two-phase voltage sources covered in this article are shown in Fig. 1. All of these structures have different modulation diagrams, current pressures, and DC junction capacitor requirements. It is important to consider the advantages and disadvantages of these structures. Space conveyor pulse modulation is commonly included in engine drive systems. The modulation diagrams for the topology discussed in Fig. 2. The maximum phase voltage is achieved when the reference voltage is tangent to the polygon. In a two phase system, the neutral current is 1.414 × higher than the phase current. This is because the current pressure is high in the three-legged structure, compared to the other two topologies, where the third leg is used as the return path for the neutral line current. In both two-legged and four-legged configurations, the peak phase current is the maximum current of the switches. However, due to the third rib, the current pressure in a three-legged configuration is 1.414 × higher than the peak phase current. For voltage ripple analysis on a DC-link capacitor, a stray capacitor is assumed between a DC voltage source and a DC-link capacitor, as shown in Fig 1. In most applications, there is reasonable stray inductance between the DC-voltage source and the DC-link capacitor. Due to this stray inductance, the input current of the DC source is constant. The DC link output current contains high-frequency pulsating components, which are determined by the switching modes of the SVPWM system. The purpose of the DC-link capacitor is to absorb the high-frequency ripple current, and the capacitance of the DC link should be large enough to stabilize the DC link voltage. The waveform and DC junction capacitance are fully examined in Ref. 9.) The DC junction voltage is directly proportional to the phase current and inversely proportional to the switching frequency of a constant DC junction capacitance. Generally, high value DC-link capacitors are required in large phase currents to reduce voltage ripple. Design process This section discusses the design of a 6.8 kW three-legged transducer system. Gate driver design The boot circuit, due to its simplicity and low cost, has been used in gate drives of silicon MOSFET based transducer. Figure 5 illustrates a boot gate driver circuit. In this circuit, the voltage on the capacitor is affected by the voltage drop on the semiconductor, which in turn makes the operating voltage unstable. Moreover, this circuit cannot provide the necessary safety feature to shut down the electrical semiconductor safely. The above problems made the reliability of the boot circuit-based gate driver questionable. A reliable gate driver is critical in a capacitive current system. For this purpose, an unregulated push-pull transformer is used to produce a 5V floating voltage. In order to drive the silicon MOSFET, a step-up transformer has been incorporated to increase the floating voltage to 15V. To turn off, a buck boost is performed to invert the 5V to -5V floating voltage. The isolated gate driver is shown in Fig. 3. Power phase design DC link capacitors and power semiconductors are included in the power phase of a two-phase three-leg transformer. The FM 400TU-07A silicon MOSFET is specified for the transducer design. 10 The specified switching frequency is 25KHz so the loss is not too high. The capacitance of the DC junction should be high enough to suppress the voltage ripple on the DC junction. Control stage design The control part of the transformer includes a microcontroller, sensors and signal conditioning circuits. The cost effective TMS320F280049C microcontroller is used in designing two-phase 48V inverters as they are cost effective and operate at a CPU frequency of 100MHz. Hall current sensors are used to measure the phase current. But in the case of large current measurements, the magnetic core of the Hall effect current sensor uses a very large area, causing the volume to increase. In order to reduce the size, shunt resistors are implemented with an isolated amplifier to measure the phase current, as shown in Figure 4. Conclusion This article has discussed in detail the design of a 48V two-phase transducer. The voltage ripple produced by the DC connection is compared in three different topologies. After analyzing three different topologies, the three-legged configuration was chosen to illustrate the design process. The design process describes in detail the design of the gate driver, power and control stages. After trying the proposed design, the waveform and heat coil validated the design and reliability of the proposed system. References 1 Design of a 6.8 kW two-phase transformer for 48V automotive applications. Tianyu Chen, Carlos Caicedo-Narvaez, Pingyuan Chen, Prince of Parsapur, Babak Fahmi Electrical and Computer Engineering, University of Texas at Dallas, Richardson, Texas, USA [email protected] 2K. Shane. “Future prospects for wide-band semiconductor (WBG) power switches.” IEEE Transactions on Electronic Devices 62, No. 2 (2014): 248–257. 3e. a. Jones, G. Zhang, and F. Wang. “A dV / dt transient analysis of enhanced mode GaN FETs.” IEEE 2017 Applied Energy Electronics Conference and Exhibition (APEC), Pages 2692-2699. IEEE, 2017. 4J. Lu, and Dr. Chen. Parallel GaN E-HEMTs in 10kW – 100kW systems. IEEE 2017 Applied Energy Electronics Conference and Exhibition (APEC), Pages 3049-3.056. IEEE, 2017.5M. Tapajna, O. Hilt, E. Bahat-Treidel, J. Wurfl, and J. Kuzmik. “Achieving gate reliability in typically non-switched p-type-GaN / AlGaN / GaN HEMTs under forward bias stress.” IEEE Electron Device 37 Letters, # 4 (2016): 385-388. 6O. Muhlfeld and F.W. Fuchs. “Improvement of stray inductance in three-phase MOSFET power units with the help of PEEC simulation.” 2009 Thirteenth European Conference on Power Electronics and its Applications, Pages 1-7. IEEE, 2009.7B. Yang, c. Wang, S. Zhou, J. Couric, and ZJ Shin. “Advanced low-power MOSFET technology for power supply in package applications.” IEEE Transactions on Power Electronics 28, No. 9 (2012): 4,202-4,215. 8 S. C. Gerstenmaier, A. Castellazzi, and GKM Wachutka. “Electrothermal simulation of multi-chip modules with a new thermal transient model and time-dependent boundary conditions.” IEEE Transactions on Power Electronics 21, No. 1 (2006): 45-5 9T. Chen, S. Me, and b. Fahmi. “DC-Link Voltage Ripple Analysis in Capacitor-Free Voltage Source Transformers.” 44th IECON 2018 Annual Conference of IEEE Industrial Electronics Association, Pages 1,041 to 1,048. IEEE, 2018.10Mitsubishi Electric. “FM400TU-07A High Power Switching Use Insulated Package”, FM200TU-07A Datasheet, May 2006.


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