SENSORLESS FIELD ORIENTED CONTROL OF BRUSHLESS ...

Figure 4.11 – Ideal voltage waveforms for 120° six-step squarewave inverter with resistive load.
.............................................................................................................................................169
Figure 4.12 – Commutation and PWM configurations in 120° inverter...................................... 170
Figure 4.13 – Concept of PWM for one phase leg; not to scale. .................................................170
Figure 4.14 – Sine-triangle PWM................................................................................................171
Figure 4.15 – Ramp-comparison current regulator for one phase. .............................................. 172
Figure 4.16 – Hysteresis CRPWM...............................................................................................173
Figure 4.17 – Overmodulation in carrier-based SPWM; not to scale. .........................................174
Figure 4.18 – Fundamental gain and operating modes of carrier-based SPWM. ........................175
Figure 4.19 – Adding the third harmonic reduces peak amplitude. .............................................176
Figure 4.20 – Third harmonic injection can produce larger fundamental than SPWM. ..............176
Figure 4.21 – Inverter states and neutral voltages. ......................................................................179
Figure 4.22 – Voltage relationships. ............................................................................................179
Figure 4.23 – Voltage waveforms for 180° six-step squarewave inverter...................................180
Figure 4.24 – Instantaneous phase-A line-neutral voltage in SPWM inverter.............................181
Figure 4.25 – Direct selection of inverter state............................................................................181
Figure 4.26 – Base SVs showing the states of a 180° inverter. ...................................................183
Figure 4.27 – Transformed voltage waveforms for six-step 180° squarewave inverter. .............185
Figure 4.28 – Magnitudes and trajectories of some important SVs.............................................186
Figure 4.29 – Base SVs................................................................................................................189
Figure 4.30 – Synthesis of SV by time-averaging base SVs........................................................190
Figure 4.31 – Temporal limit of inverter output. .........................................................................191
Figure 4.32 – α-projection of hexagon trajectory. .......................................................................191
Figure 4.33 – SVM overmodulation region: SV locus. ............................................................... 192
Figure 4.34 – SVM overmodulation region: locus of fundamental SV. ......................................193
Figure 4.35 – One period in a simple switching scheme. ............................................................193
Figure 4.36 – One period in an improved switching scheme.......................................................194
Figure 4.37 – One period on a second improved switching scheme............................................194
Figure 4.38 – Leg control signals; commanded SV in sextant s12. ..............................................196
Figure 4.39 – Phase-A line-neutral voltage; commanded SV in sextant s12. ...............................196
Figure 4.40 – SVM inverter.........................................................................................................197
Figure 4.41 – Generating leg switch commands..........................................................................198
Figure 4.42 – Dead-time insertion. ..............................................................................................198
Figure 4.43 – Average pole voltages for THI and SVM inverter. ...............................................199
x