MODULATION TECHNIQUES COMPARISON FOR THREE LEVELS VSI CONVERTERS

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1 IECON MODULATION TECHNIQUES COMPARISON FOR THREE LEVELS VSI CONVERTERS Emilio J. Bueno, Roberto García, Marta Marrón, Felipe Espinosa, Jesús Ureña Departamento e Electrónica. Universia e Alcalá [email protected] November

2 Inex. Introuction.. PWM moulation techniques for NPC converters. 3. NP unbalancing in NPC. 4. Simulation results. 5. Conclusions. November

3 . Introuction (/3) NPC ouble converter block iagram INVERSOR P V P INVERSOR S a S b S c RED ELÉCTRICA V a I a C D S a S b S c I u V u MÁQUINA AC ASÍNCRONA I b I c V b V c NP V NP I v I w V v V w IM S a S b S c C D S a S b S c V N N A/D Meia e variables Control inversor. Generación señales SVPWM A/D Meia e variables Control inversor. Generación señales SVPWM A/D Meia e variables CPU principal November 3

4 . Introuction (/3) Comparison between a NPC VSI an a two-level VSI NPC VSI line voltage levels 3 levels U DC (V) 484,6 483,4 I DCBUS (A) 7,395 7,4 P DC (W) P out activa (W) 83,4 799,3 P inv = P DC P out activa (W) 97,6 337,7 P IGBT (W) 49,6 8,4 Harmonics to the conmutation frequency -level VSI line voltage Loa: R =Ω y L = mh f S = Khz November 4

5 . Introuction (3/3) Dioe rectifier/npc inverter system: System use to simulate P Sa Sb Sc C V P Sa Sb Sc R L D NP I NP Sa Sb Sc C D V N Sa Sb Sc Line voltage 4V/5Hz C = 47μF IGBT s are simulate by ieal- switches. R =.Ω an L =.H November N The simulations have been evelope with the Matlab Power System Blockset 5

6 . PWM moulation techniques for NPC converters (/8). Cosinusoial moulation function (/3) F O = cos ( α ) Reference signal Harmonic components of v ab. Sa s carrier Sa s carrier November 6

7 . PWM moulation techniques for NPC converters (/8). Cosinusoial moulation function (3/3) DC-bus voltage an variation of NP voltage I NP current V NP = V P V N November 7

8 . PWM moulation techniques for NPC converters (3/8). Vectorial moulation function (/3) Switching-state vectors of the three-level VSI β Vectores cero: How oes it obtain the PWM signals? V REF : m y θ Placing V REF insie in once of the 6 sectors of 6º V REF α Placing V REF in the triangles,, 3, or 4 of the once of the sectors of 6º Computing of the three uty cycles November 6 sectors of 6º 4 subsectors (each one equilateral triang. ) Choosing of the conmutation-sequence 8

9 . PWM moulation techniques for NPC converters (4/8). 3 In which subsector is the reference vector?. The reference vector is place insie una e las 6 regiones e 6º.. How m is equal to: VREF VREF m = = VDC.35 VLL 3 3 se obtiene el subsector en el que está. V DC Vectorial moulation function (/3): V REF synthesis 3 V DC θ 4 Space-vectors for θ 6º (phase volltages) November V REF 3 3 V DC m < m > m > 3 cos 3 cos 3 cos m < sin ( θ ) + sin( θ ) ( θ ) + sin( θ ) ( θ ) sin( θ ) ( θ ) = m 3. Duty cycles calculation = m ( 3 cos( θ ) + sin( θ )) cos( θ ) sin( θ ) ( θ ) sin( θ ) sin( θ ) + 3 cos( θ ) sin( θ ) 3 cos( θ ) ( 3 ) = m sin = m = + m = + m ( ) ( ) 3 V REF θ = m = + m ( 3 cos( θ ) sin( θ )) 3 cos( θ ) sin( θ ) ( θ ) ( 3 cos( θ ) sin( θ )) m ( 3 cos( θ ) + sin( θ )) + m sin( θ ) = m sin = m = = ( ) 9

10 . PWM moulation techniques for NPC converters (5/8). Vectorial moulation function (4/5): Conmutation sequence P Asymmetrical moulation Asymmetrical moulation withour con. V NP N I NP C O C S a S b S c i a i b i c a b c c b a c b a Example: V REF is in the subsector 3 of the first sector of 6º. Insie of this subsector there is one conmutation sequence: --- After choose the conmutation sequence, the PWM signals are obtaine. Chosen option: Symmetrical PWM November Symmetrical Moulation c b a 4

11 . PWM moulation techniques for NPC converters (6/8). Vectorial moulation function (3/3): Results Line voltage signal an its harmonic components V REF (phase voltage) Out line voltage November

12 . PWM moulation techniques for NPC converters (7/8). Cosinusoial moulation function with zero-sequence component (/) Cosinusoial moulation function is very easy to implement but has two isavantages: the maximum linear moulation inex is.79, an. the current istortion is not minimize. Both factors can be improve aing a zero-sequence of the reference signals containing only thir orer harmonics, an aing it to the original cosinusoial reference signals. In this work the following continuous zero-sequence has been chosen: max{ Va, Vb, Vc } + mínv { a, Vb, Vc } VZ = The zero-sequences can to generate moulation functions:. continuous, an. iscontinuous November

13 . PWM moulation techniques for NPC converters (8/8). Cosinusoial moulation function with zero-sequence component (/): Results Line voltage harmonic components PWM generator circuit Zero-sequence generator moule Offset November 3

14 3. NP unbalacing in NPC (/3). P NP Voltage: V NP = V P V N C S a i a a V NP I NP O C S b S c i b i c b c N I NP current Thir orer component harmonic. Unbalance between the voltages of the two capacitor banks of the DC-bus (low frequency ripple). November 4

15 3. NP unbalacing in NPC (/3). It s epen on... (/) V NP with para R=Ω an L=mH, m a =.45 V NP with R=Ω an L=mH, m a =.9 November 5

16 3. NP unbalacing in NPC (3/3). It s epen on... (/) V NP with R=mΩ an L=mH, m a =.9 Same conitions, except C = mf CONCLUSIONS: V NP is a function of the amplitue moulation inex. V NP is a function of the loa, that is to say, of the loa power factor. November 6

17 4. Simulation results (/3) NPC Inverter.- Regenerative circuit C U DC DC L I a u a (t) L u b (t) L u c (t) e a (t) e b (t) e c (t) Loa: R =.Ω y L =.mh Phase = 5º U DC = 75V SVM with zero-sequence. FILTER GRID NPC VSI V ab δ = 5º u a α e a i a November 7

18 4. Simulation results (/3) e a (t) eb (t) e c (t) NPC Rectifier.- Controlle rectifier (active filter) e a i a u a L u a (t) L u b (t) L u c (t) NPC VSI C DC LOAD U DC Loa: R =.Ω y L =.mh Phase = 5º SVM with zero-sequence. i a e a δ = 5º u a November 8

19 4. Simulation results (3/3) NPC ouble converter Inverter.- RECTIFIER Inverter.- INVERTER e a (t) e b (t) e c (t) L L L u a (t) u b (t) u c (t) C DC U DC L R Loa: R =.Ω y L =.mh Gri : R =.Ω y L =.mh November 9

20 5. Conclusions Moulation tecniques comparison Cosinusoial Vectorial Cosinusoial with zero-seq. Maximum m a V NP variation δ Conmutation sequence δ Implementation Easy Difficult Easy NP unbalancing Loas with a low power factor generate high ripple currents in NP. Cosinusoial moulation functions: Moify the offset of the reference signals. Vectorial moulation functions: Choose of other reunant vectors. November

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