multilevel voltage space vector generation for induction motor drives using conventional two-level...

Multilevel Voltage Space Vector Generation for Induction Motor Drives using Conventional Two-

level Inverters and H-bridge cells

K. Siva Kumar

CEDT, IISc, Bangalore

CEDT, Indian Institute of Science Bangalore 1

Overview of the presentation

Introduction Proposed three-level inverter scheme Experimental results Proposed Five-level inverter schemes Experimental results Conclusion


INTRODUCTION



The induction motor is called as a work horse of the industry

The induction motor requires a variable voltage magnitude and frequency to control the rotor speed

Conventional two-level inverter


Inverter pole voltage (sine-triangle PWM)Normalized harmonics spectrum of pole voltage

The harmonic components in the inverter pole voltage are present at higher (switching) frequencies

The popular PWM control scheme is space vector pulse width modulation (SVPWM) technique

Space vector (Vr) is nothing but a resultant representation of all three phase voltage phasors and it is defined as

j120° j240°r AO BO COV =v +v e +v e


space vector diagram of conventional two-level inverter

The symbols ‘+’ and ‘-’ respectively indicate that the top switch and the bottom switch in a given phase leg are turned on

The conventional two-level inverter has to switch at higher frequencies to get a better harmonic profile at the inverter output voltage

But in high power applications, high switching frequency is generally not preferred because of the high switching losses and large dv/dt.


This dv/dt effect causes EMI problem in the motor and increases stress on the motor winding

To overcome these disadvantages, many multilevel inverter configurations and associated analysis of PWM techniques have been suggested

The most significant advantages of the multi-level inverters compared to two-level inverters

It is possible to use power semiconductor devices of lower voltage ratings to realize high voltage levels at inverter output

It is possible to obtain refined output voltage waveforms and reduced total harmonic distortion (THD)

It is possible to reduce the EMI problems by reducing the switching dv/dt


Multilevel Voltage Source Inverter

One phase leg of general n-level inverter

The most popular topologies to realize the multilevel inverters are

Neutral Point Clamped (NPC) topology Cascaded H-bridge (CHB) topology Flying capacitor (FC) topology


Multi-level Inverter topologies feeding from one side of the induction motor

NPC inverte

r

FC inverte

r

H-Bridge inverter


Multi-level inverters with open-end winding induction motor

The concept of multilevel inverters with open-end winding is introduced by H. Stemmler and P. Guggenbach in the year 1993

The three-level inverter topology can be realized by feeding an open-end winding induction motor with two two-level inverter from both sides of the winding

Three-level inverter topology for open-end winding induction motor


The triplen harmonic voltage introduced by the PWM inverters will cause triplen harmonic currents in the motor phase windings, because of the lake of isolated neutral

This topology requires either harmonic filter or isolated dc-link voltages to prevent triplen harmonic currents flowing through the motor phase windings

The dc-link voltage requirement for each inverter Vdc/2, which is half the dc-link voltage of conventional three-level inverter fed IM drive

But the radii of the combined voltage vector hexagon will be Vdc

This multilevel inverter topology is free from capacitor voltage balancing issues


Many interesting multi level inverter topologies are proposed by various research groups across the world from industry and academic institutions

Apart from the conventional 3-level NPC and H-bridge topology, others are not yet highly preferred for general high and medium power drives applications

In this respect, two different five-level inverter topologies and one three-level inverter topology for high power induction motor drive applications are proposed

Motivation


A Dual Two-Level Inverter scheme for a Four-Pole Induction Motor Drive with a single voltage

source

Part - 1


Induction machine stator winding arrangement Stator winding of an induction machine is an arrangement of

conductors in the machine slots to produce nearly sinusoidal air gap MMF

Four pole induction motor stator winding (full pitch) diagram The conductors in the slots 1 to 3 and 19 to 21 should have the

same voltage profile to produce identical magnetic poles Similarly the conductor in the slots 10 to 12 and 28 to 30 should

have the same voltage profile


In a four pole induction motor, two sets of identical voltage profile coils will be present in the total phase winding, at a phase displacement of 360o (electrical)

The identical voltage profile winding coils (or pole pair winding coils) in the stator winding will equally share the applied voltage vector

Voltage vector distribution in the four pole induction machine winding


These identical voltage profile winding coils can be disconnected from a conventional four pole induction machine without any design change

Modified four pole induction motor stator winding diagram

Coil connection after the identical pole pair winding disconnection


These two identical voltage profile coil groups can be connected in parallel instead of series, thereby the voltage vector Vr/2 is sufficient to drive the four pole induction motor with the same air gap flux profile

With this arrangement the dc-link voltage magnitude requirement will come down to half compared to the conventional arrangement

From the above discussion one can observe that, it is sufficient to feed the disconnected pole pair winding coils with the same fundamental voltage to get a performance similar to the conventional induction motor


Three-level voltage space vector generation for an open-end winding induction motor

drive with single voltage source using decoupled space-vector PWM strategy

Proposed three-level inverter with one active source for four-pole induction motor drive

Cont..


The two identical voltage profile, pole pair winding coils, in each phase of a four pole induction motor, is connected in two star groups

These two star connected winding coil groups are fed from two inverters

But these two inverters should produce the same fundamental voltage on the motor pole pair winding to generate uniform air gap flux

So a decoupled space-vector PWM scheme is used to drive the inverters

inverter-I and inverter-II are operated with a reference voltage space vector of Vr/2 and –Vr/2


Space vector diagram of the two inverters

Space vector diagram of three-level inverter


Using the decoupled PWM technique the voltage reference is equally divided in to two new reference vectors for two two-level inverters to generate the same fundamental voltage

In a switching time period Ts the voltage vectors OA and OA’ can be generated with a sequence of switching states 8-1-2-7 for inverter-I and 8’-5’-4’-7’ for inverter-II

The resultant switching sequence is 88’-15’-25’-24’-77’

Timing distribution of the switching states for two inverters in one sampling interval


Maximum modulation index

1 ( ) max

2* (max)

3 2r

A O Avg

Vv

1 ( )

2* *cos(30) 0.289

3 2dc

A O Avg DC

Vv V

Similarly

4 ( )

2*( )*cos(30) 0.289

3 2dc

A O Avg DC

Vv V

1 4 10 40 0.289 ( 0.289 ) 0.577A A A A dc dc dcv v v V V V

The proposed topology is capable of producing a maximum phase voltage of 0.577Vdc in linear modulation with a single dc link voltage of Vdc/2

So in the proposed scheme, the dc-bus utilization is increased by 15% compared to the earlier schemes presented with a single voltage source

Resultant Phase voltage


Experimental results

The proposed topology are experimentally verified on a 5 H.P four pole induction motor (pole pair winding disconnected) drive

The drive is operated in open loop V/f control for different voltage reference covering the entire speed range

A decoupled space vector PWM scheme is used to generate the switching pulses

The inverter switching frequency is kept at 1 kHz for the entire speed range

The controller is implemented on TMS320F2812 DSP platform


Block diagram of V/f control scheme used for the proposed three-level inverter topology

The modulation index (M) given by the Vr/Vdc, so at the end of linear modulation M equal is to 0.866


Experimental results for modulation index 0.4 (i.e. 20Hz operation)

pole voltages

phase voltage

Phase currents

[Y-axis: 100V/div]

[Y-axis: 200V/div]

[Y-axis: 2A/div, X-axis: 10ms/div]

Normalized harmonic spectrum of the two inverters pole voltages

CKT DIG


Phase voltage [Y-axis: 200V/div]

common mode voltage [Y-axis:

100V/div]

Effective phase voltage [Y-axis: 200V/div, X-axis:

10ms/div]

Normalized harmonic spectrum of the effective phase voltage

phase currents

effective phase current

The first center band harmonics are completely eliminated



pole voltages

phase voltage

Phase currents

[Y-axis: 100V/div]

[Y-axis: 200V/div]



The first centre band harmonics appear at 25 (1000Hz/40Hz) times the fundamental frequency

The isolated neutral presented in the proposed topology will not allow the triplen currents to flow through the motor phase windings




100V/div]


10ms/div]

Normalized harmonic spectrum of the effective phase voltage

phase currents

effective phase current

The first center band harmonics are completely eliminated

the ripple content in the two currents are approximately equal in magnitude with opposite direction


Experimental results for over modulationpole voltages

phase voltage

Phase currents

[Y-axis: 100V/div]

[Y-axis: 200V/div]



The first center band harmonics appear at approximately 21 (1000Hz/47Hz) times the fundamental frequency

Because of this square wave operation fifth and seventh harmonic will be presented in the inverter pole voltages




100V/div]


10ms/div]

Normalized harmonic spectrum of the effective

phase voltage

From the above results it is clear that, for full modulation range the first center band harmonics are suppressed in the effective motor phase voltage


The identical voltage profile winding coils are disconnected and connected in two star groups

These star connected phase windings are fed from independently controlled inverters

The two inverters are fed from a single dc-link voltage source (The isolated neutrals provided by two star winding groups will not allow the triplen currents to flow through the motor phase windings)

The first center band harmonics are at two times the carrier frequency

The implementation of the proposed scheme does not necessitate any special design requirements for the induction motor

It can be extended to induction motor with number of poles more than four

Salient features


A Five Level Inverter Scheme for a Four Pole Induction Motor Drive by

Feeding the Identical Voltage Profile Windings from Both Sides

Part - 2


The advantages of the open-end winding structure along with identical voltage profile winding coils for a four pole induction motor are effectively utilized to realize multilevel structures using conventional two-level inverters

Proposed Five-level Inverter Power circuit


In the proposed topology, three isolated voltage source with a magnitude of Vdc/4 (where Vdc is the dc-bus voltage required for a conventional NPC three-level inverter) is used to deny the path for zero sequence currents

The switches S11 to S46, in the above figure, are part of the two level inverters which are fed from the voltage source magnitude of Vdc/4

So the maximum voltage blocking capacity of the switches (labelled as Sxy, where x= 1 to 4 and y= 1 to 6) is Vdc/4

With the proposed topology, it is possible to switch four two-level inverters independently and thereby each inverter will have eight switching states

Therefore a total of 4096 (8x8x8x8) switching combinations are possible, which are spread over 61 locations


Voltage space vector locations for a Five-level inverter

Note that each voltage level can be realized in a number of ways


Voltage

magnitude (level)S11 S21 S31 S41

+Vdc/2 (2) ON OFF ON OFF

+Vdc/4 (1)

ON OFF OFF OFF

OFF OFF ON OFF

ON ON ON OFF

ON OFF ON ON

0 (0)

OFF OFF OFF OFF

OFF OFF ON ON

ON ON OFF OFF

ON ON ON ON

ON OFF OFF ON

OFF ON ON OFF

-Vdc/4 (-1)

OFF OFF OFF ON

OFF ON OFF OFF

ON ON OFF ON

OFF ON ON ON

-Vdc/2 (-2) OFF ON OFF ON

All switching combinations for the five voltage levels for a-phase

Presently, the bi-directional switches S1 to S6 , in the power circuit, are assumed to be shorted


Schematic of possible voltage levels across the A-phase winding

Voltage level at Vdc/2

Voltage level at Vdc/4

Voltage level at 0

Voltage level at -Vdc/4

Voltage level at -Vdc/2

As mentioned above turning on the bidirectional switches (S1 to S6) permanently will cause a short circuit at the middle of motor phase windings


It will create an unequal voltage sharing between the same winding groups and this is explained using with switching state combinations 110 and 20-1

(a)Phase winding connection to the voltage sources for switching state 110 (b) Phase winding connection to the voltage sources

for switching state 20-1


One group of windings (i.e. A1-A2, B1-B2 and C1-C2) is fed from a voltage vector (110) and the other group of windings (i.e. A3-A4, B3-B4 and C3-C4) is fed from a zero voltage vector (000)

part of the A-phase and B-phase winding group (A1A2

& B1-B2) has a voltage of Vdc/4 across it and the other phase group has zero voltage across it

Similarly for switching state 20-1 it can be observed that, one group of windings (i.e. A1-A2, B1-B2 and C1-C2) is fed from a voltage vector (100) and the other group of windings (i.e. A3-A4, B3-B4 and C3-C4) is fed from a voltage vector (10-1)

However, for a four pole induction machine, two parts of the winding groups should have identical voltage profile for a uniform flux distribution

Therefore the present sequence with turning on the bidirectional switches will result in a distorted flux profile

From the Phase winding connection to the voltage sources for switching state 110, shown above, it can be observed that


(a) Phase winding connection to the voltage sources with equal voltage distribution across the phase winding groups for switching state 110 using the bidirectional switches. (b) Phase winding connection to the voltage sources with equal voltage distribution across the phase winding groups for switching state 20-1 using the bidirectional switches


Based on the above considerations it is not possible to realize all the switching combinations presented in the above table

Voltage

magnitude

(level)

S11 S21 S31 S41 S1 S2

+Vdc/2 (2) ON OFF ON OFF ON ON

+Vdc/4 (1)ON OFF OFF OFF OFF OFF

ON ON ON OFF OFF OFF

0 (0)

OFF OFF OFF OFF OFF OFF

ON ON ON ON OFF OFF

ON OFF OFF ON OFF OFF

OFF ON ON OFF OFF OFF

-Vdc/4 (-1)OFF OFF OFF ON OFF OFF

OFF ON ON ON OFF OFF

-Vdc/2 (-2) OFF ON OFF ON ON ON

Possible switching combinations


All the voltage vector locations inside the first and second innermost hexagon can be realized with the voltage levels ‘-1’, ‘0’ and ‘1’

By using the switching state redundancy, it is possible to clamp inverter-2 and inverter-3 up to modulation index of 0.433

Where the maximum radius of the reference voltage vector within the second innermost hexagon is achieved at a modulation index of 0.433

Both the bi-directional switches, in corresponding phases, are completely turned off for the voltage levels ‘-1’, ‘0’ and ‘1’

The bi-directional switches are also need not to switch up to the modulation index 0.433 like inverter-2 and inverter-3

So in case of any switch failure in inverter-2 or inverter-3, the proposed five-level inverter can still be operated as a three-level inverter for lower modulation indices


voltage rating of the bidirectional switches

Phase winding connection to the voltage sources for switching state 22-2, with bi-directional switches

the voltage equation for the loop (using Kirchhoff’s voltage Law) (B1 B2 X C2 C1 B1)

dcV2* 0

4 2 2b c

s

e eV

dcV1

2 4 2 2b c

s

e eV

The maximum voltage across the switch is half the voltage difference between Vdc/4 and the difference between the back emf’s of two phases

Maximum voltage appears across the bidirectional switches is Vdc/8


Switching strategy Space vector pulse width modulation (SVPWM)

technique is used to generate gating pulses for the proposed inverter

The voltage space vector reference (Vr*) can be

generated from the motor speed requirement using V/f control

, where va, vb and vc are three phase voltages

The individual phase voltage references (va*,vb

* and vc*)

can be derived from voltage space vector To have maximum utilization of dc-bus voltage, in linear

modulation, an offset voltage is added to the three reference voltages

Voffset = -[max(va*,vb

* and vc*) + min(va

*,vb* and vc

*)]/2

van*= va*+Voffset

o oj120 j240r a b cV =v +v e +v e


The A-phase reference voltage Van*

modulation index (M= Vr/Vdc) equal to 0.8

In actual experimental verification using a DSP it is difficult to generate four level shifted triangles


The modified A-phase reference voltage and triangle carriers

The voltage level required by the load is released by comparing the reference wave form with carrier wave

The switching state can be select from the above mentioned table


EXPERIMENTAL RESULTS

The proposed five-level inverter topology is experimentally verified on a 5hp four pole induction motor

The motor is run at no load condition to show the effect of changing PWM patterns on the motor current

Open loop V/f control is used to test the drive for the full modulation range

Throughout the speed range, the switching frequency is kept at 1 kHz

The controller is implemented in TMS320F2812 DSP platform

The gating signals generated from GAL22V10B


Block diagram of V/f control scheme used for the proposed five-level inverter

topology



Total phase voltage

voltage across the one phase winding coils

phase current

[X-axis: 20ms/div, Y-axis: 100V/div, 1A/div]

From the phase voltage it can be noted that, the proposed inverter is operating in two-level mode


Voltage between the point A2,A3

Inverter-1 pole voltage


phase current

Voltage across the bidirectional switch


The inverter 1 and 4 are switching half of the period in a fundamental cycle

The negative and positive voltage peaks (across the bidirectional switch) are less than half of the inverter pole voltage peak

So the maximum voltage appear across the bidirectional switch is Vdc/8


Total phase voltage


phase current


From the phase voltage it can be noted that, the proposed inverter is operating in three-level mode






phase current



Here also the inverter 1 and 4 are switching half of the period in a fundamental cycle

The middle inverters (i.e. Inverter 3 and 4) are not switching for full fundamental cycle

The negative and positive voltage peaks (across the bidirectional switch) are less than half of the inverter pole voltage peak



Total phase voltage


phase current


From the phase voltage it can be noted that, the proposed inverter is operating in four-level mode





phase current



Inverters (inv-2 and inv-3) are switching when the other two inverters (inv-1 and inv-4) are clamped

This indicates that, at a time only two inverters are switching, in a fundamental cycle of operation



Total phase voltage


phase current


From the phase voltage it can be noted that, the proposed inverter is operating in five-level mode





phase current



Here also inverters (inv-2 and inv-3) are switching when the other two inverters (inv-1 and inv-4) are clamped

This indicates that, at a time only two inverters are switching, in a fundamental cycle of operation


Experimental results for over modulationTotal phase voltage

voltage across the one phase winding coilsphase current




phase current

Throughout the modulation range, at a time only two inverters are switched

This will result in less switching losses, and it will increase the overall efficiency of the drive system


Transient performance of the proposed drive

Phase voltage

Phase current

The transient performance of the proposed drive is tested by accelerating induction motor from 10Hz operation (i.e. 300rpm) to 47Hz (i.e. 1410rpm)

The smooth transition of the voltage profile from two-level to five-level can be seen from the waveforms


Comparison between the proposed topology and conventional topologies

NPC Topology

Flying capacitor topology

H-bridge topology

Proposed topology

Switches(with a voltage rating of

Vdc/4)24 24 24 24

Clamping diodes

Voltage rating of 3*Vdc/4

6 0 0 0

Vdc/2 6 0 0 0

Vdc/4 6 0 0 0

Isolated voltage sources (voltage magnitude)

1* (Vdc) 1* (Vdc) 6 (Vdc/4) 3 (Vdc/4)

Number of capacitor banks (with a voltage

rating of Vdc/4)4 18 0 0

Bi-directional switches (voltage rating )

0 0 0 6 (Vdc/8)


Two identical voltage profile winding coils in each phase of a four pole induction motor are disconnected

The dc bus voltage magnitude requirement is one-fourth compared to a conventional five-level NPC inverter

All the inverters are switching for a maximum period of half, in a fundamental cycle

In lower modulation indices (M<0.43) the middle two inverters can be clamped for the entire period of fundamental cycle

Only conventional two-level inverters are used so this will eliminate all capacitor voltage unbalance issues normally encountered in NPC inverters

This concept can be easily extended to induction motor with number of poles more than four and thereby the number of levels on the phase winding can be further increased

Salient features


A Hybrid Five level Inverter Topology for an Open-end winding Induction Motor Drive Using Two-

Level Inverters in series with a Capacitor fed H-Bridge Cell

Part - 3


In this circuit, only one voltage source is used with a magnitude of Vdc/2 where Vdc is the dc-link voltage requirement for the conventional NPC inverter

Proposed Five-level Inverter Power circuit


This topology is similar to an open-end winding multilevel inverter structure

In the open-end winding multilevel inverter structure, it is possible to generate a three voltage levels on phase winding by connecting two two-level inverters from both sides of the motor phase windings

This concept is further extended by introducing an additional flying capacitor with H-bridge cell in series with motor phase windings

For the present study, the flying capacitors (Ca, Cb and Cc) are charged to a voltage Vdc/4

If the two level inverters are now clamped to zero voltage, then the H-bridge cell can produce voltage levels of Vdc/4, 0 and –Vdc/4 on the motor phase winding

On the other hand, by clamping the H-Bridge cells to zero voltage, the two two-level inverters, with a voltage source magnitude of Vdc/2, can independently generate voltage levels of Vdc/2, 0 and –Vdc/2 on the phase winding

When both of them are operated together, it is possible to have five voltage levels on the motor phase windings


ALL POSSIBLE SWITCHING COMBINATIONS FOR THE FIVE VOLTAGE LEVELS FOR PHASE-A

Phase voltage

Vdc/2 Vdc/4 0 -Vdc/4 -Vdc/2

Sa1 ON ON OFF OFF ON OFF OFF OFF

Sa2 * ON OFF * * OFF ON *

Sa3 * OFF ON * * ON OFF *

Sa4 OFF OFF OFF OFF ON ON OFF ON

Capacitor Ca status Ideal

ia>0: charging

ia<0: discharging

ia>0: discharging

ia<0: charging

Ideal

ia<0: charging

ia>0: discharging

ia<0: discharging

ia>0: charging

ideal

Due to the complementary nature of the two-level inverter switches, switch Sa1 ‘ON’ automatically implies that switch S’a1 ‘OFF’

The current from A to A’ is assumed to be the positive direction of current and is shown as ia>0


There are 14 possible switching combinations for one phase to realize the five voltage levels

Therefore a total of 2744 (14x14x14) switching combinations are possible for the present work

The flying capacitors can be charged or discharged independent of the phase current direction for the voltage levels Vdc/4 and –Vdc/4 (it can be observed from the previous table)

The other voltage levels (i.e. Vdc/2, 0 and -Vdc/2) on the phase winding is achieved by bypassing the flying capacitors, so it will not affect the capacitor voltages


Common Mode Voltage

It is known that inverters controlled by conventional two-dimensional SVPWM will produce a common mode (triplen) voltage along with the fundamental voltage on the motor phase windings

The triplen harmonic content in the phase voltage would cause a high triplen harmonic current to flow through the motor phases and power semi-conductor devices

To suppress the triplen harmonic current, either harmonic filter or isolated power supplies should be used

In this proposed topology two isolated voltage sources are used to deny the path for triplen current


Modified Five-level inverter topology

The proposed topology can be operate as a dual inverter fed open-end winding Induction motor drive (i.e. three-level operation) for full modulation range, by properly clamping the H-bridge cells


Flying Capacitor Design The performance of the proposed topology is dependent on

flying capacitor ripple voltage The capacitors can be designed properly to restrict the

ripple voltage within acceptable limits The capacitance required by the flying capacitor can be

calculated by using the formula

sp p

TTC I * I *

V V

Where C is flying capacitor (Ca, Cb or Cc)Ip is peak phase currentTs is switching time period∆V is the peak-to-peak voltage ripple allowed in the flying capacitor.


EXPERIMENTAL RESULTS

The proposed five-level inverter topology is experimentally verified on a 5hp open-end winding induction motor

The motor is run at no load condition to show the effect of changing PWM patterns on the motor current

Open loop V/f control is used to test the drive for the full modulation range

Throughout the speed range, the switching frequency is kept at 1 kHz

The flying capacitor value is chosen as 1100μF

The controller is implemented in TMS320F2812 DSP platform

The gating signals generated from SPARTAN XC3S200 FPGA


The V/f controller block schematic for proposed five-level inverter scheme

The symbols vca, vcb and vcc represents the voltage across the flying capacitors (Ca, Cb and Cc)


Experimental results for modulation index 0.2

The proposed topology is operating in three-level mode

The flying capacitor peak to peak voltage ripple is less than 1V

Flying capacitor ripple voltage [2V/div]

phase voltage [Y-axis: 50V/div]

phase current [Y-axis: 1A/div] [X-axis: 20ms/div]


inverter-1 pole voltage[Y-axis: 50v/div]

inverter-1 pole voltage

H-bridge cell output voltage


High voltage fed inverters (i.e. inverter-1 and inverter-2) are switching half of the period in fundamental cycle







The flying capacitor peak to peak voltage ripple is less than 1V



inverter-1 pole voltage

H-bridge cell output voltage


High voltage fed inverters (i.e. inverter-1 and inverter-2) are switching half of the period in fundamental cycle

So this will reduce the switching losses of the drive




phase current [Y-axis: 1A/div] [X-axis: 10ms/div]inverter-1 pole voltage[Y-axis: 50v/div]

inverter-1 pole voltageH-bridge cell output voltagephase current [Y-axis: 1A/div] [X-axis: 10ms/div]





The flying capacitor voltage is well balanced (since, ripple voltage magnitude is less) when the inverter is operating at five-level mode







Normalized harmonic spectrum of the motor phase voltage

The first centre band harmonics is present at 25 (1000Hz/40Hz) times the fundamental frequency

the peak harmonic voltage magnitude is around 8% and it is placed at 50 times of the fundamental frequency, thereby the effect of this harmonic voltage on motor phase current is insignificant







Experimental results for over modulation

The H-bridge capacitor voltage is well balanced (since, ripple voltage magnitude is less) when the inverter is operating at over modulation


Transient performance of the proposed drive

Transient performance of the proposed scheme during speed reversal operation of the drive

The capacitor voltage is balanced for the full modulation range Even though the accelerating and decelerating the motor draws

current much more than the steady state operation, yet the capacitor voltage is balanced for the full modulation range


Comparison between the proposed topology and conventional topologies

NPC Topology

Flying capacitor topology

H-bridge topology

Proposed topology

Switches

voltage rating of

Vdc/424 24 24 12

Vdc/2 0 0 0 12

Clamping diodes

Voltage rating of 3*Vdc/4

6 0 0 0

Vdc/2 6 0 0 0Vdc/4 6 0 0 0

Isolated voltage sources (voltage magnitude)

1* (Vdc) 1* (Vdc) 6 (Vdc/4) 2 (Vdc/2)

Number of capacitor banks (with a voltage

rating of Vdc/4)4 18 0 3


The concept of open-end winding structure is extended by adding a flying capacitor in series with motor phase winding

This results in a five level inverter topology It does not require any clamping diodes as in a

conventional five-level NPC inverter It requires only one capacitor bank for each phase,

whereas five-level flying capacitor require 6 additional capacitor banks for each phase

this proposed topology reduces the power circuit complexity compared to NPC or flying capacitor topologies

In case of any switch failure in the H-bridge cell, the proposed inverter topology can be operated as a three-level inverter for full modulation range using open-end winding concept

Salient features


Overall experimental setup


List of publications

1. K. Sivakumar, A. Das, R. Ramchand, C. Patel, K. Gopakumar, “A Five Level Inverter Scheme for a Four Pole Induction Motor Drive by Feeding the Identical Voltage Profile Windings from Both Sides”, IEEE Trans. on Industrial Electronics(accepted for publication)

2. K. Sivakumar, A. Das, R. Ramchand, C. Patel, K. Gopakumar, “A Hybrid Multilevel Inverter Topology for an Open-end winding Induction Motor Drive Using Two-Level Inverters in series with a Capacitor fed H-Bridge Cell”, IEEE Trans. on Industrial Electronics(accepted for publication)

3. K.Sivakumar, Rijil Ramchand, Anadarup das, Chintan Patel, K.Gopakumar, “Two different Schemes for Three-level Voltage Space Vector Generation for Induction Motor drives with Reduced DC-Link Voltage”, EPE( European power electronics journal),(accepted for publication and scheduled on march 2010)

4. K. Sivakumar, Anandarup Das, Rijil Ramchand, Chintan Patel, K.Gopakumar, “A Simple Five-Level Inverter Topology for Induction Motor Drive Using Conventional Two-Level Inverters and Flying Capacitor Technique”, IEEE IECON 2009, 3-5 November 2009 at Porto, Portugal.

5. K. Sivakumar, Anandarup Das, Rijil Ramchand, Chintan Patel, K.Gopakumar, “A Three Level Voltage Space Vector Generation for Open End Winding IM Using Single Voltage Source Driven Dual Two-Level Inverter”, IEEE TENCON 2009, 23-26 November 2009 at Singapore.

THANK YOU


multilevel voltage space vector generation for induction motor drives using conventional two-level...

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