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107 | Maddu & Bhasme
period to another and require toggling two switches. Since C. Hardware implementation
these switches are not ideal cause more switching losses dur- In this work, The MATLAB/Simulink software results are
ing on and off and vice versa. To overcome the transition validated and verified using an FPGA-based Wavect controller.
problem, keeping the null vector in the middle position and The schematic hardware implementation of various PWM
simultaneously switching periods should be arranged. Since techniques for a two-level inverter is shown in Fig. 1
the sequence of applied voltages doesn’t matter unless the
timings are kept the same. In this, the net reference vector The most popular category of FPGA controllers is highly
is rotating from one sector to another. This causes a double required for accurate response and position estimation [20].
transition problem. To rectify it, the switching states would Here, Fig. 2 represents the real-time experimental setup and,
be swapped which is termed an alternate reverse sequence. Fig. 3, shows the block diagram for a three-phase, two-level
This method of implementation is complex and switching PWM inverter. The SVPWM switching states are represented
losses are also higher [18]. The SVPWM method can also be as shown in Fig. 4. The experimental system consists of
realized as below with reduced computation time in real-time a Three-phase bridge rectifier, Autotransformer, Semikron
digital implementation: inverter, Induction motor with load, and Wavect controller.
DC capacitor bank serves to maintain the constant DC volt-
In the Min-Max method, the main objective is to enhance age at the inverter input side. The PWM signals and ADC
the magnitude of the inverter output voltage by simply adding interface is made through the Wavect Control board. The
an offset to the reference signal. The resultant modulating control algorithm can be implemented using HDL block sets
signals can be written as [19], of MATLAB/Simulink. After the implementation, the control
algorithm is converted into HDL code generation using the
?vam? = Vm sin(wt) + offset (18) HDL workflow advisor. The hardware implementation work-
flow and PI controller using HDL blocks in the WAVECT
?vbm? = Vm sin(wt - 2p/3) + offset (19) design suite are shown in Fig. 5 and Fig. 6 respectively. In
this work, a V/f control algorithm is used to control the IM
and its implementation is as shown in Fig. 7.
?vcm? = Vm sin(wt + 2p/3) + offset (20) III. RESULT ANALYSIS
Here, Offset = -Vmax +Vmin ;
For high-frequency applications, advanced control techniques
2 (Field oriented control (FOC) and Direct torque control (DTC))
are often used PWM techniques in motor control drives. In
Vmax = Max {vam, vbm, vcm} , Vmin = Min {vam, vbm, vcm} General, a Six-step (Square) inverter produces more losses at
(21) the output of the inverter side.
In Direct Injection of third harmonic PWM (THPWM), The PWM techniques are more popular for AC drives due
phase waveforms with no third harmonics can be created by to their power loss in the switching devices being very low in
adding third harmonics to the sinusoidal reference waveform. the case of high-frequency applications. In this work, SPWM,
The modulating waves can be written as follows [8, 18], Square Wave, SVPWM (Min-Max), and THPWM methods
are implemented with the help of MATLAB/Simulink soft-
?vam? = Vm1 sin(wt) +Vm3 sin(3wt) (22) ware. The results obtained in Simulink have shown phase
voltage, line voltage, and load current without filter in Fig. 7,
?vbm? = Vm1 sin(wt - 2p/3) +Vm3 sin(3wt) (23) Fig. 8, Fig. 9, Fig. 10, and Fig. 11. Also, the FFT tool is used
to analyze the performance of the motor by calculating the To-
?vcm? = Vm1 sin(wt + 2p/3) +Vm3 sin(3wt) (24) tal Harmonic Distortion (THD). The performance parameter,
THD is calculated without filter for line and phase voltages
The obtained modulation index can be written as, of SPWM, Square wave type, THPWM, and SVPWM meth-
ods respectively. The Square wave type produces 61 % THD
|vam| = Vm1 sin(wt ) - 1 Vm1 cos p sin(3wt) = 0.5Vdc whereas other methods such as THPWM and SVPWM pro-
3 3 duce 53.47% THD approximately. From this, the SVPWM
method produces less harmonic distortion compared to the
(25) SPWM method. The Comparative analysis is carried out for
the PWM techniques at different switching frequencies. Ta-
ble III and Table IV show %THD in-phase voltage and line
voltage with fundamental phase and line voltages at 5 kHz
