Biến đổi hình học tô pô bộ biến áp nguồn điện ba pha hiệu quả cao với không gian véc tơ PWM

Journal of Science & Technology 101 (2014) 041-046 The Modified High Efficient Three-Phase Voltage Source Inverter Topology with Space Vector Pwm Phan Quae Dzung*, Le Chi Hiep, Nguyen Bao Anh, To Huu Phuc, Nguyen Dinh Tuyen Ho Chi Minh University of Technology 268, Ly Thuong Kiet 10 District Ho Chi Minh City Received September 03 2013, accepted April 22 2014 Abstract This paper proposes the modified Space vector PWfA tor the modified topology of high efficient threephase voltage source inverter (HE-VSI3) which consists of traditional six switches voltage source inverter and three bidirectional free-wheeling switches for creating the ac decoupling circuit This topology has the advantages such as the ability to improve the efficiency based on the principle of decoupling, the ability of applying to the conventional VSI scheme, the simplicity of the control algorithm and can widely applied to many applications The HE-VSI3 topology and modified space vector PWM method are simulated by using Matlab/Simulink software and implemented in the experimental prototype The high efficiency is obtained very promising in the proposed scheme with modified SVPWf^ Keywords Three-Phase VSI Topology, Space Vector PWM, LCL Filter Galvanic Isolated Transformer Introduction Con vent ion al'three-phase voltage source inverter (VSI) is now widely used in industrial and energy systems, in order to convert electrical energy from dc to ac This scheme is particularly applied in the electric motor drive systems and renewable energy systems such as photovoltaic, fuel-cell conversion systems The recent study on improving the efficiency of three-phase inverters is based on the structural changes of the VSI, therefore the principal scheme and control method for generating pulse pattems become more complex and it is difficult to be implemented for the existmg VSI [1,2], Recently, many research papers have been published for single phase VSI scheme for transformerless grid connected system The efficiency improvement is based on the principle of ac or dc decoupling, when the zero state occurs [3-7] In these works, some topologies, based on the H-bndge with a ac bypass circuit consisting of a bidirectional switch (HERIC topology) [3] or a diode rectifier and a switch with clamping to the dc midpoint (HB-2VR topology) [4], are proposed In case of dc decoupling cfrcuit, some topologies are invented, which consists one extra switch (H5 topology) [5] or two extra switches (H6 topology) [6,7] High conversion efficiency in these schemes is obtained In order to mcrease the efficiency, the researchers usually pay attention to the use of multi' Conesponding Author, Tel; (-I-84) 903.657 486 Email; phan_quoc_dung@yahoo.com level principles [8,9] This leads to a change in configuration and availability of PWM methods such as space vector PWM of the we 11-developed three phase two-level inverter This paper analyses the topology of high efficient three-phase VSI (HE-VSI3), which consists of six fraditional switches for converting power and three bidirectional free-wheeling switches for creatmg the ac decoupling circuit (Fig I) In this topology, the DC common point is separated from the gnd neutral point or common point of stand-alone three-phase load The modified SVPWM algorithm is developed for this topology This topology has the advantages such as the ability of improving the efficiency based on the principle of decoupling, the ability of applying to the conventional VSI scheme, the possibility of implementing the Space Vector PWM algorithm So, it can he applied to many industrial field widely ~-J i Fig The modified three phase voltage source inverter with ac decoupling circuit (HE-VS13) Journal of Science & Technology 101 (2014)041-046 Fig The HE-VSI3 with an output LCL fiher The filter parameter (Table I) is calculated using the method which is shown in [9] Table Table of designed parameters for Id filter 'f-i-f -iJJSfW' ~ Fig The HE- VSI3 PV Grid-Connected System This topology can he applied to' - The application of conversion from DC to AC: zero space vector occurs (S1, S3, S5 or S2 S6 are m on-state in conventional VSI scheme), i lie output current of the modified configuration flow.-, in a path with ac decoupling circuit via three extra fi^ewheeling switches (SSI-SS3) and therefore the energy consumption of DC link and the temperature of switches Si-Sft are reduced, i.e increasing the efficiency of inverter electrical energy • for providing the ac voltage with variable frequency and variable effective value to the load (such as induction motor), without the output LCL filter (Fig 1) • for providing the ac voltage with fixed frequency and effective value to the load (such as RL) with the output LCL filter for obtaining the tme sinusoidal wave, (Fig 2) - Photovoltaic panels three-phase gridconnected applications with an isolation LV transformer (Fig 3) Almost the network configurations are divided mto two groups: with galvanic isolated fransformer and transformerless The grid connected configuration with isolated fransformer has advantages such as safety, no leakage cunent, and no dc cunent injection In contrast, fransformerless topology has higher efficiency, but it has more complex control algorithms and some related issues such as leakage cunent and dc current injection into the grid Filter parameter Li, |mH| Lg, |mH| C, IllFI 0.462 3.29 3.306 0.231 6.58 1653 0.154 9.87 1.102 0.116 13.2 0.863 Scheme Power load,[W] 5000 10000 15000 20000 Semiconductor losses in voltage source IGBT converters can be calculated using method in [10], The efficiency of the VSI and the modified HE-VSI3 is calculated by the formula: where Pm is the input dc power, Poui is the output ac power according to I" voltage harmonic 'ouJ " '\RMS IRMS > ' 2.2 Modified Space Vector PWM algorithm for the High Efficient VSIS The space vector modulation is based on the formation of three voltage vectors in sequence in one sampling interval Ts so that the average output voltage meets the requirement The calculations of the switching states in VSI are as follows for /i Ts [11]: Modified he-vsi topology 2.1 Structure and principle of the High Efficient VSI3 t =— M r s i n T/2-f_ ir/3- •RMT sin Q ; -t^ Modified topology, called the High Efficient Voltage Source Inverter (HE-VSI3), uses a modified version of the three-phase bridge VSI, by adding an ac-decoupling circuit, which composes of three exfra bidirectional switches as shown in Fig I DC common point is separated from grid or load common point and the common point of bidirectional switches (4) where: t, • duration for vector V„ i^ -duration for vector Vy, 1^ - duration for vector Vi, M - the index of modulation M = VVV,™ (V" - amplitude of the required voltage vector, V,.„ - peak value of six step voltage) The purpose of the HE-VS13 scheme is the isolation of AC output from DC-link input when the Fig shows the space vectors ii the modified HE-VSI3 inverters Journal of Science & Technology 10! (2014) 041-046 The algorithm of modified space vector PWM is proposed in Fig The switchmg process of modified algonthm when the zero voltage occurs and finishes in sector is shown in Fig The difference of this modified SVPWM from the conventional one is when the zero space vector occurs, in the modified topology (HE-VS13), all switches SSI, SS2 and SS3 are mm on and all SI, S2, S3, S4, S5 and S6 are frim off with the inserted blank time (DT! - Dead time interval) between complementary switches This way, using SSI - SS3 as shown m Fig.l, the zero-voltage space vector is realized by short-circuiting the output of the inverter, during which period the DC-lmk is separated from die load or the grid, because all S1-S6 are turned off This modified SVPWM is very simple and easily to implement by using DSP or FPGA confroller for generating pulse pattems J Simulation of the modified he-vsi with svpwm The simulation model is built Matlab/Simulink with SimPowerSystem Toolbox 3.1 Case study 1: Reference output voltage is fixed, power load is changeable (for application such as stand-alone load or grid power system) The simulation model includes (Fig.7): - DC link voltage: Vd = 800V - HE-VSB inverter (Fig.I) - Filter: LCL type - Reference output voltage: Vp = 22 QV^s, fi= 50Hz - Modified SVPWM : modulation index M= 7881; switchmg frequency fs^v ^ 10 kHz - Switch parameters: IGBT on-state resislance=0.02 £1, IGBT forward voltage =2.5 V, Diode on-state resistance=0.01 Q, Diode forward voltage-0.8 V - Load : RL (5 kW, 10 kW, 15 kW, 20 kW) The simulation results of output phase voltage and cunent waveform are shown in Fig, Fig, shows the power and efficiency The comparison of efficiency between VSI and HE-VSI3 versus power load is presented in Table 4, S.Table 2, 3, Fig The flowchart of modified Space Vector PWM for HE-VS13 ^ J L TLL i n I l_ - Fig Pulse pattern of SVPWM (a) and Modified SVPWM (b) Table Table of simulation re suits fo VSI VSI |kW| V,