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 three- phase 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 1. 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; [email protected]
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. 1. The modified three phase voltage source inverter with ac decoupling circuit (HE-VS13)
Journal of Science & Technology 101 (2014)041-046
Fig. 2. The HE-VSI3 with an output LCL fiher
'f-i-f
-iJJSfW' ~
Fig. 3. The HE- VSI3 PV Grid-Connected System This topology can he applied to'
- The application of electrical energy conversion from DC to AC:
• 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 grid- connected 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.
2. Modified he-vsi topology
2.1. Structure and principle of the High Efficient VSI3
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.
The purpose of the HE-VS13 scheme is the isolation of AC output from DC-link input when the
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.
The filter parameter (Table I) is calculated using the method which is shown in [9].
Table 1 Table of designed parameters for Id filter Scheme
Power load,[W]
5000 10000 15000 20000
Filter parameter Li, |mH|
3.306 1653 1.102 0.863
Lg, | m H | 0.462 0.231 0.154 0.116
C, IllFI 3.29 6.58 9.87 13.2 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
' o u J " '\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]:
t = — M r s i n i r / 3 - . T / 2 - f _ -t^
•R
MT sin Q ;(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).
Fig. 4 shows the space vectors ii
HE-VSI3 inverters. the modified
Journal of Science & Technology 10! (2014) 041-046 The algorithm of modified space vector PWM
is proposed in Fig 5. The switchmg process of modified algonthm when the zero voltage occurs and finishes in sector 1 is shown in Fig. 6. 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= 0 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, 8. Fig, 9 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. 5. The flowchart of modified Space Vector PWM for HE-VS13
^ . T L L J L .- i n
I l_
Fig. 6. Pulse pattern of SVPWM (a) and Modified SVPWM (b)
V,<0DI-OIIO) ViflOI-OOO)
Fig. 4. Space vectors in the HE-VS13
Table 2 Table o f simulation re suits fo VSI VSI
|kW|
5
!0 15 20
Pdc, [W]
6442 11550 16650 21740
Pout, 5037 10060 15070 20070
n 0.78 0.87 0.90 0.92
Id, |A1 8.05 14,43 20.81 27.17
VlHMS
IV]
220-8 220,7 220 5 220 4
THD 1,03
|%|
1-04 1 04 1,04
Journal of Science & Technology 101 (Z014) 041-046
Fig. 7. The simulation model of HE-VSI3 witli tile modified SVPWM
5
Fig. 8. Output voltage and cunent waveform of HEVSI3 (when Picad = 20kW)
Fig. 9. Input, output power (W) and efficiency Table 3. Table of simulation results for HE-VS13 (Fig 1)
HE-VSI3 Power
[kW|
5 10 15 20
Pdc, 1W|
6008 11140 16280 21410
Pout,
|W]
5082 IOI60 15240 20320
Tl 0.84 0.91 0.93 0.94
Id, |A|
751 13,93 20,35 26.77
VI 221 8 221 8 221,8 221,7
THD
|%J 1-03 I 03 1 03 1 04
;e and such as 3.2. Case study 2: Reference output v frequency are changeable (for appUcatio induction motor drive)
The simulation model mcludes' - Load : Pio.d_n,=. = 5 kW, Qtod_n,ax = 1 kvar The simuladon resuhs of output phase voltage and cunent waveform are shown in Fig. 10, I I . The comparison of efficiency between VSI and HE-VSIS versus modulafron index (or base frequency) is presented in Table 4, 5.
The output voltage has modified shape and the output cunent has sine shape. The efficiency of HE- VSI3 is also higher than VSI in the frequency levels,
The load cunent is m phase with the output voltages with sinusoidal waveforms (Fig. 11). In case of HE-VS13 topologies, the higher efficiency is obtained in whole the power load range.
The output voltage and current have sine shape and low THD index. Besides, the efficiency of HE-VSI3 is always higher than VSI in the power levels.
Fig. 10. Output phase voltage waveform of HE-VSI3 (when f= 40Hz, M=0.63)
Fig. 11 Output cunent waveform of HE-VSI3 (when f = 40 Hz, M = 0.63)
Table 4 ^able of simulation results for VSI VSI fl, | H z |
10 20 30 40 50
M 0.157 0.315 0.472 0.630 0.788
Pd.,
| W | 2140 4462 6657 6636 6440
P.., 1407 3154 4865 5004 5036
1 0.65 0.70 0.73 0.75 0.78
Id,
|A|
8.172 8.509 8 457 8.295 8.049
Vi,
|V| 40.79 86.31 131.2 176,1 220.8 Table 5. Table of simulation results for HE-VS13
HE-VSI3
n,
IHil 10 20 30 40 50
M 0.157 0.315 0 472 0 630 0.788
Pdc,
|W1 1573 3606 5687 5924 5970
Pout
| W | 1299 3066 4796 4964 5013
1 0.82 0.85 0.84 0.83 0.83
Id,
|A|
6 01 6.877 7 224 7,405 7,463
VI,
|V1 39.29 84 95 130.3 175.4 220.2
Journal of Science & Technology 101 (2014) 041-046 t . Experimental results for he-vsi3 topology
A prototype is used to verify the modified topology with SVPWM confrol algonthm. The expenmental model (Fig. 12) includes:
- DC Source: 130 V - Confroller: Card FPGA Virtex 5 - VSI and AC Decoupling Circuit. 12 IGBTs FGL60N100
- Dnver' HCPL A3020 - Switching frequency: 10 Hz - Deadtime duration. 2ps - RL Load: R - 3 3 i l , L = 5mH
Table 6. Table of experimental results for the conventional VSI (Averaged values for 11 measures)
Fig. 12. Experimental model of HE-VSI3
Fig. 13. Output phase voltage wavefonn of HE-VSI3 TMt J L •Stop M(*K-i60DllH
VSI ToDOloEV M
0.8 DC Voltage
(V) 132.93 Average Temperature
CC) DC Current
(A) 5.15
Input Power (W) 685.53
Output Power (W) 633.64
(%)
1 92,43 .lain switches: 62.04 "C Sidirectional switches. 28.33 °C Table 7. Table of experimental results for the HE- VSB (Averaged values for 11 measures)HE-VSI3 ToDoloEV M
0,8 DC Voltage
132 74 Average Temperature
rc)
DC Current
(A) 5,10
Input Power (W) 676.54
Output Power (W) 628 27
(%)
92.86 vlain switches. 55 83 "C Bidirectional switches: 38 33 °C The experimental results demonsfrale the feasibility of modified HE-VS13 scheme with SVPWM algorithm (Fig 13, 14), The comparison of efficiency and average temperature between VSI and HE-VS13 IS presented m Table 6, 7. The higher efficiency of HE-VSI topology is obtained.
:?. Conclusions
The modified topology of high efficient three- phase voltage source inverter (HE-VS13) with Space Vector PWM is presented. The HE-VS13 topology consists of conventional six switches two level voltage source inverter and auxiliary three bidirectional switches in order to create the ac decoupling circuit- The modified Space Vector PWM for generating pulse pattems is also shown in details.
The proposed HE-VS13 topology with modified space vector PWM method is simulated by using Matlab/Siraulmk software and implemented in the experimental prototype. The high efficiency is obtained very promising.
Acknowledgments
This research is funded by Vietnam National University - HCMC University of Technology, Viemam under grant number B2012-20-04TD.
Fig, 14. Output phase current waveform of HE-VSI3
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