Chapter 2 Literature Review Research has been carried out in two ways one is on the track of an AC-AC converter and other is on track of an AC-DC converter. Researchers have worked in AC-AC conversion and have tried to remove drawbacks in AC AC conversion system. They have also worked in AC-DC conversion area and have used different topologies and have overcome many drawbacks in existing converters. 2.1 AC/AC conversion In many industrial applications AC-AC power conversion is used.ac/ac converters take power from one AC system and deliver it to another with waveforms of different amplitude, frequency, or phase. The AC/AC converters are commonly classified into two types, a) Indirect converter which utilizes a DC link between the two AC systems b) Direct converter that provides direct conversion. Disadvantages of existing AC-AC converters 1. Large number of semiconductors are required in a cyclo-converter (AC-AC converter), and its control circuitry becomes more complex 2. Reasonable power output and efficiency, but the output frequency is limited to one-third of the input frequency. 3. The power factor is low particularly at reduced output voltages 4. Two stage Conversion is required. 5. Energy storage element such as capacitor/inductor required 2.2 AC to DC converter AC to DC converters are employed in i) DC drives ii) As a front end converter in voltage source and current source inverter fed induction synchronous motor drives. and 1
iii) Slip power recovery control of induction motor iv) HVDC transmission, and many other applications such as electrolysis, electroplating, welding and so on. The line commutated thyristor converters, which are presently used in these applications, suffer from three common drawbacks a) They produce low frequency harmonics at the source terminals b) Operate at low power factor for large firing angles c) Output voltage consists of ripple or low frequency harmonics In order to, overcome drawbacks in existing AC-AC converters and AC-DC converters a new system has been developed which is the multi output (multimode) converter. Multi output (Multimode) converter operates in two modes as both AC-AC converter and AC-DC converter simultaneously. In AC-AC mode frequency variation is obtained and AC-DC conversion variable voltage across the load. Matrix topology is used to implement multi output converter. The matrix converter (MC) concept, introduced by Venturini and Alessina in 1979, seems to be the most advanced concept for static energy conversion. The MC, which is mainly an AC/AC direct converter (without DC link) is also capable of rectifying and inverting. The theoretical characteristics of the circuit are satisfactory output current waveforms, bidirectional energy flow, minimal energy storage passive elements and adjustable input power factor. All published studies have dealt with single-.phase circuit topologies, their control and power switch protection All published studies deal with either AC to AC conversion or AC to DC conversion. The main purpose of this research topic was to investigate multimode operation of multimode converter using matrix topology which works in two modes-direct AC-AC converters and AC-DC converter with a single circuit. The well-known sinusoidal pulse width modulation (SPWM) scheme can be used to synthesize the output, which simplifies the control strategy. These converters are useful for industrial applications. So this important idea was been selected for further research. Recently there has been considerable interest in the use of matrix converter technology for motor drive applications, with particular interest being shown by Siemens, Rockwell, International Rectifiers, and Yaskawa in published literature an introduction to matrix converter technology is given and the suitability and design of matrix converters for industrial an 2
application is reviewed. The potential advantages of matrix converter technology are examined and the factors that have so far prevented commercial exploitation of the circuits are discussed. The remaining technical challenges are defined and the works in progress to meet these challenges are highlighted. Switching is important for matrix topology. It introduces behaviour of converter for low frequency modulation using switching Matrix. The new ac-ac converter provides output higher than input (boost) or lower than input (buck).it varies amplitude, phase, power factor of input to output. So it is called a generalized transformer [1]. A paper we have referred to describes input-output voltage transformation ratio of direct ac-ac converter using pulse width modulation technique. [2]. Single-phase to single-phase matrix Converter can be realized. Input is directly transferred to output. Another paper describes a matrix converter that gives fixed input frequency to variable output frequency. The paper idea describes limited application in traction.[3].ac regulator based on a PWM matrix downconverter is economical. this converter works over a wide range of load power factors, with relatively simple control logic.[4].process of current commutation technique in matrix converter which not require snubber circuit is discussed in another paper.[5].the matrix converter is an array of controlled switches that connects directly source to load. This converter has several important features that have been investigated in the last two decades. In the last few years, matrix converter topology is closer to the industrial application. The most important practical implementation problem in the matrix converter circuit is the commutation between two controlled bidirectional switches.the solution has been done with the development of highly intelligent commutation strategies [6]. Pulse Width Modulation control scheme is used to matrix converters for reducing the output voltage harmonics. This control scheme is based on the direct AC/AC conversion approach and the carrier-based PWM control to obtain the constant switching frequency. [7].One paper has described basic AC-AC converter topologies in industrial electronics-voltage regulators, induction motor drives, wind power conversion systems and other. A comparison between Matrix converters and with DC-link converter is given in another. [8] The next paper refereed describes single phase matrix converter used as AC-DC converter. It provides regenerative capabilities.[9] Active Input Current Shaper (AICS) Topology is used in AC-DC converter. This 3
is not exactly single phase because a part of energy is proceed twice that is in two stages. Energy storage element inductor and capacitor connected across output discussed in another work. [10]. This paper discusses AC-DC-AC matrix converter with boost circuit. The design increased voltage transfer ratio. Two stage conversions is used. It requires storage element like inductor or capacitor [11].One cycle control ac-dc converter implemented. It kept power factor constant. [12]It represents paralleling three phase ac to dc converter using CUK rectifier module for dc distribution power module. Control strategy is developed for fast output regulation for two parallel connected Three phase three switch AC-DC converter [13].Author suggests the modification of the sinusoidal pulse-width modulation (SPWM) switching technique.using this modified method operation of a power electronic converter to control the power and to optimize the power factor (PF) [14].An 18-pulse ac dc converter with various auto connected transformer configurations has been developed for SMPS. It reduces the THD [15].Paper presents threephase ac-to-dc converter using CUK rectifier modules. It provides nearly unity power factor and fast dynamic transient response based on power balance control technique. [16].A bidirectional AC DC DC converter with a simple and efficient control strategy has been presented. It is having a wide adjustable voltage range from zero to any rated value for DC voltage or current. It consists of a three-phase AC DC converter (CSC I) plus a DC DC converter (CSC II and VSC I). Using a single switch to provide a bypass for the inductor current, the voltage spikes are reduced and the safety of current flow is realized. [17].The present direct ac-to-dc low voltage converter used in energy harvesting. It achieves higher efficiency. It avoids the bridge rectification and directly converts the low ac input voltage to the required high dc output voltage at a higher efficiency [18].Here the author describes comparison Matrix Converter, Converter, and a Voltage DC-Link Back-to-Back Converter for motor drive. Another work describes here in the low-voltage and low-power ac-ac converter segment the MC technology performance is restricted.[19].three single-phase AC-to-AC converters with inductor coupling implemented in another work. It improves input power factor. [20].Power converters are designed with multi physic and multi domain constraints. The presented system is an ac/dc-dc fly back converter. [21].Two reversible single-phase-to-three-phase ac drive systems have been developed. They are composed of an induction motor fed by two parallel single-phase-to-three-phase dc-link converters without any isolation transformers. The configurations have been generalized to include multiple single-phase-to-three-phase dc-link converters in parallel. [22] 4
Z-source converter for ac-ac conversion can be presented. In this converter input ground and output ground are same. [23].In this paper a three-level three-leg AC-DC-AC converter for single-phase applications discussed. This is a three level converter with several advantages one is lower harmonics. [24] Synchronization technique is used to reduce the ac power and voltage fluctuation in the dc-link of single-phase full-bridge converters. This technique can be directly adapted to be used for three-leg and two-leg AC-AC dc-link converters, in order to reduce the ac dc link capacitor.[25]. Author presents automatic voltage regulator by three arm power converter in a paper. For lower voltage it acts as buck converter while for higher voltage it acts as boost converter.[26].it represents single-stage capacitor-clamped ac choppers (ac-ac converter). This converter can directly transfer unsteady high ac voltage with distortion into regulated sinusoidal voltage with low THD. [27] Direct AC-AC converters that focus on buck, half bridge, fullbridge, and push pull converters are the subject in the next paper. These converters were used to implement a voltage restorer that can be supplied either on the line side or on the load side.[28]author presents a direct power control (DPC) for three-phase matrix converters operating as unified power flow controllers (UPFCs). Matrix converters (MCs) allow the direct ac/ac power conversion without dc energy storage element. [29]Finite state model predictive control (FSMPC) method is developed for ac voltage regulator with LC filter to regulate the load voltage [30] and it also helps to reduce the output THD and increase the efficiency of converter. The matrix converter drive has been developed for a 30 hp induction motor. Control strategy was developed and the design used in lower distortion and achieved almost unity power factor. Limitations of naturally commutated cyclo converter are overcome in another matrix converter design [31]. Design of matrix converter was by using bi-directional switches for ac motor drive. Switching control was developed using space vector modulation method to get four quadrant operations [32]. Commutation strategy describes the switching of bi-directional switches four quadrant operation to convert three phase to a two phase matrix converter supplying a series resonant load. Normally four step commutation is used in the matrix converter; main advantage of switching strategy is reducing the commutation steps [50]. Author describes the conduction and commutation losses in direct ac-ac converter. For analysis four step or two step commutation methods are used. Complete loss calculation model using individual commutation loss has developed along with a numerical model of modulation process [84]. Using offset voltage and changing slope of carrier wave the sinusoidal input voltage has been synthesized and desired 5
output voltage obtained. This method is called as carrier based modulation and is used for matrix converter. This method is s equivalent to space vector pulse width modulation method in its working [36]. The instantaneous effective power control (IEPC) algorithm has been developed for the maintaining instantaneous effective power constant by controlling input current and stability of the system [37]. Comparison of Alesina-Venturini methods and space vector modulation has been investigated. Alesina-Venturini method represents time domain and space vector represents frequency domain. Mathematical dynamic state space model has been presented by author and it includes control variable as power factor [38][39[54]].Input power clamp method is developed to avoid regeneration form matrix converter in an aerospace application. Combining input current space vector modulation and three phase 120 degree conduction a method has been developed for matrix converter system [41][42]. Sinusoidal pulse width modulation scheme is used for single phase matrix converter [44][85].The auxiliary resonant commutated pole (ARCP) method is developed to reduce the noise and improve the quality of output waveform and has been applied to a matrix converter [51]. The PWM control strategy designed for the output frequency control of matrix converter. Single pulse operation is used to increase the power factor and voltage transformation ratio. The space vector modulation method is used for multilevel indirect matrix converters. This method reduces the harmonic and good quality of output voltage is got [52][53] [79] [84] [86].Matrix converter protection issues are described by author[56] and a researcher has developed a simulation model of matrix converter using MATLAB Simulink[58]. The structure of three phase to two phase topology and development control of a scheme for the same based on space vector modulation is discussed by researchers [57]. Soft switching technique has been presented for three phase low frequency to three phase high frequency direct converter with PFC function for industrial heating by same. It can regulate output power with a constant frequency and zero voltage soft switching based on the PWM control scheme [60]. Researchers were described modulation techniques used to reduce the switching losses in the Matrix converter systems [48, 65, 72, 43, 52]. The new structure of three phase to single phase ac-ac converter has been presented in earlier work [89]. Some other related work is listed in this paragraph. The IGBT based a three-phase variable voltage and frequency to a single phase constant voltage and frequency converter has been discussed. This converter consists of three-phase rectifier (AC-DC) and single phase inverter (DC-AC) that is two stage conversions [90]. Three phase ac-ac matrix converter can be 6
implemented using 15 devices based on sparse matrix converter (SMC) method. It is based on zero current commutation method [91]. To increase the efficiency of generator and converter three phase to single phase matrix converter has been developed. It can realize increase power factor to reduce reactive current and harmonic torque and reduce the power losses in the converter [92]. Author has discussed the Application of three phase to single phase converter. It is used for Induction Heating application and gas engine cogeneration system [93] [94]. Low frequency switching function modulation strategy based on Alsena - Venturini theory has been developed [95]. A three-phase to single-phase matrix converter is investigated mathematically based on the state matrix vector. Mathematical analysis of the converter is used for realizing the relation between line voltage and the output voltage is described in a work [96]. Optimal Pulse width Modulation scheme for nine switch converter has been presented [97]. Active filter configuration presented for single phase to three phase converters by researchers. This active filter reduces IGBT losses and cost of system [98]. Single phase to three phase four leg converter have been used for distribution systems. It operates unlike the full bridge converter. Advantages of the four leg converter are reduced number of switches and increased efficiency. The circuit configuration and control algorithm for a single phase to three phase converter with power decoupling between input and output has been developed. It can improve voltage transfer ratio to 0.707. [99][100]A power-conversion system for converting three phase power into single-phase power is developed. This power conversion system consists of power converter, zero sequence transformer and filter capacitor. SPWM strategy and ISPWM strategy developed for single phase to three phase matrix converter. It improves harmonic distortion as compare to prior methods [101][102]. Control algorithm has been developed for single phase to three phase matrix converter to drive synchronous motor [103]. A control strategy for a reactor-free converter has been developed to apply in a square-wave operation with an adjustable speed drive motor [104]. Using Sic devices matrix converter-based IPT system has been developed SiC devices are used to improve the overall efficiency of system through the reduction of power conversion stages [105]. All previous work was focused on AC-AC converter, AC-DC converter, and matrix converter. Also researchers were focused on different control methods such as Space Vector Modulation(SVM),Pulse Width Modulation(PWM),Sinusoidal Pulse Width Modulation(SPWM) to improve quality of output and increase efficiency of converter. All 7
above converters are connected to a single load across output. No converter is available to give multiple outputs across the loads. No researcher has done any work in the way of implementation of multi output (Multimode) converter concepts. There was scope to do research in the area of the Multi output (Multimode) converter concepts. 2.3. Definition of Problem To design, analyse, build and test a Multimode (Multi output) Converter Using Matrix Topology in order to meet the requirement of producing multiple outputs, without having a multiple number of standalone power supplies thus reducing the cost and space requirements. The words multimode and multi output are used in this thesis synonymously. 8