【正文】 singlephase ACAC converter and shows a fast response to pensation. x. REFERENCES D. Sabin, An Assessment of Distribution System Power Quality, Vol. 2: Statistical Summy Report, Palo Alto, CA. EPRl Final Report TR106294V2, May 1996. E. Randolph Collins Jr, Arshad Mansoor, “Effects of Voltage Sags on AC Motor Drives”, IEEE 1997 Annucd Textile? Fiber and Film Industry Technical Confzrence, 68 May 1997. E. C. Aeloiza, P. N. Enjeti, L. A. Morin, I. Pitel, “Next Generation Distribution Transformer: To Address power Quality for Critical Loads”, Power Electronics Specialists Conference PESC 2020, Vol. 3, June 2020, pp. 12661271. E. C. Aeloiza, P. N. Enjeti, 0. C. Montero, L. A. Morin, “A~lysis and Design of a New Voltage Sag Compensator for Critical Loads in Electrical Power Distribution Systems”, Industrid Applifionr Cun]erenceL4SZUO2,Vol. 2, 1318de ,pp. 911916. Patrick W. Wheeler, Jon C. Clare, Lee Empringha, Michael Bland, “Matrix Converters: The Technology and Potential for Exploitation”, The Drives and Controls Power Electronics Conference, London, Section 5, March 2020. Patrick W. Wheeler, JOG Rodriguez, Jon C. CLare, Lee Etnpringha, Alejandro Weinstein, “Matrix Converter: A Technology Review”, IEEE Transactions on IndustrirrI Electronics, Vol. 49, Aprit 2020. pp. 276288. J. Adamek, W. Hofmann, M. Ziegler, “Fast Commutation Process and Demand of Bidirectional Switches in Matrix Converters”, Power Electronics Specidisamp。dDo is the peak voltage related to the singlephase dq transfonnation of v!,. Equation (8) shows that V, V~Q for a voltage sag and Ynom Vap for a voltage swell. This allows that D stays within 1 y 1. B. Four sfep switching technique The four step switching technique offers a safe transition of inductive load current fiom one bidirectional switch to another, and ensures a safe PWM operation. This technique controls independently each switching device within a bidirectional switch element that depends on the input voltage and load current polarity. In the case of the ACAC converter, operation state of Si, SI, S3 and S4 wilt depend on the input voltage polarity, the pensation to realize (a sag or swell) and the control signal of the switching devices. The diagram of the operation sequence for voltage sags is shown in Fig. 4. To pensate a swell it is just necessary to change SI by Sj and S4 by S,. The switching pattern as much for sags as for swells turns on two switching devices in altemated form to offer a safe transition for inductive load current, that is, it is used S, and S, during the first pulse control and SI and S, during the second one. The above guarantee that switch mutation and conduction looses are equilibrated. . State machine representation for voltagesags. Fig. 5 shows the operation sequence of singlephase ACAC converter: Operation sequence of the ACAC converter. A Field Programmable Gate Arrays (FPGA) is used to program the state machine and to generate a dead time between the turn on and the turn off for the bidirectional switches. The FPGA permits to reduce the processing time of the DSP. In this case, The DSP only generates the voltage reference and the switching pattem. 1v. REFERENCE GENERATION The singlephase dq theory is used to realize the pensation process and to select the duty cycle. The dq theory transforms fundamental frequency signals into DC ponents, allowing a fast transient response to pensate voltage sags and swells. To achieve the singlephase dg transformation, an imaginary orthogonal system concept is introduced. The main idea is that the imaginary orthogonal variable keeps exactly the same system ponents and parameters, keeping always 90 phase shift with respect to real ponents [9]. In this paper, it is employed the proposal in [lo] which is based on the concept that the imaginary orthogonal circuit has a 90 lag. Fig. 6 shows the real and orthogonal imaginary variable used to determine the dq transformation from the AC mains. I Real and imaginary variables. 1613 The matrix transformation from real and imaginary circuit to the dq rotating frame is expressed by: 5:l (9) % I % where: Vd = Voltage of the real circuit. Vq = Voltage of the imaginary.