【正文】 . In this case, the instantaneous amplitude of the AC mains is a time variant CD signal. Due to the above and to the necessity to have a good voltage regulation, aP1controller is proposal to improve the dynamic response of the singlephase ACAC converter. Fig. 8 shows the closed loop block diagram of the singlephase ACAC converter. yo Fig8 Closed loop block diagram of the singlephase ACAC converter. The PI controller transfer function is: VII, SIMULATION RESULTS In order to verify the operation of the singlephase ACAC converter, several simulations of the converter in open and closed loop were performed. In these simulations it is used a load of 5kW with a nominal voltage of 127 VIUIs, 60 Hz. The mutation frequency is equal to 20 KHz, the output low pass filter has a cutoff frequency of 91 8 Hz and the selected transformation relation is 3:l. The electric scheme used is shown in Fig. 1. Fig. 9 shows open loop simulation results when a voltage swell occurs. Waveform ) is the voltage of the AC mains. The converter generates vout = 0 while the voltage maintains its nominal value. When there is an amplitude disturbance in the time P, (corresponding to voltage swell) the converter reproduces the necessary ponent to pensate the load voltage. The fast system response can be noticed. Simulation results from the singlephase ACAC converter (change from 180 to 220 Vamp。 the voltage fast variation effects are function of the amplitude and the duration of the event. Some studies show that 92% of all disturbances in the electrical power distribution systems are produced by voltage sags [ 11. It is important to eliminate the voltage fast variations because they are the most frequently cause of disrupted operations for many industrial processes, particularly those using modem electronic equipment, which are highly sensitive to short duration source variations [2]. Dynamic Voltage Restorer (DVR) and Uninterrupted Power Supply (UPS) systems had been researched and developed along the last decades and they are capable to pensate voltage sugs and swells. Nevertheless, they depend on devices to store energy, like large capacitors or batteries bank. The nominal power operation is a function of size and capacity of those devices。. (a) AC mains, (b) Coqensatlon voltage generated by the converter, (c) Load voltage. A closed loop simulation taking account the presence of harmonic content in the AC mains is shown in Fig. 12. 4 I 1% P Eamp。 and 0 respectively. % I % V. COUPLING TRANSFORMER DESIGN From Fig. 1, the pensated voltage measured in the load is: Using electrical system equations and considering a factor a that represents an amplitude percent of increment or decrement of the AC mains when the voltage sag or swelZ occur: Fig. 7 shows different values of u and n obtained from the equation (1 1). It is noted that there are two values of a for each a。 if the power is increased, This work was sponsored by Mexican Council for Science and Technology (CONACyT), with the project J37670A. the size of the devices will increase. In spite of the above, the UPS systems are capable to support energy interruptions. Other option developed, which is able to pensate voltage sags is based on PWM ACAC converter [3], [4]. This solution uses an autotransformer posed by one primary side and two secondary windings presenting a good performance. The system pensates until 50% voltage sags and swells and can continuously shape the output voltage to be sinusoidal (with low THD). Nevertheless, the autotransformer drives all the load power due to it is connected between the load and the AC mains. In this paper a PWM ACAC converter is presented, in order to pensate voltage sags and swells simultaneously in critical loads, and to maintain a continuous regulation in the output voltage. The system consists in a singlephase ACAC converter in a matrix arrangement, and energy storage devices are not required. A four step switching technique is used to drive ACAC converter switches, executing snubberless operations. The reference signal is generated using singlephase dq theory, obtaining a fast response time and continue regulation, with a high efficiency. One of the adva