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Cascaded multilevel inverter thesis paper

Apr 29, 2018


A 7-Level Single Electricity Source Cascaded H-Bridge Multilevel Inverter getting an altered DTC Request Induction Motor-Based Electric Vehicle Propulsion

1 College of Brest, EA 4325 LBMS, Kergoat Street, CS 93837, 29238 Brest Cedex 03, France
2 Ecole Militaire Polytechnique, UER ELT, 16111 Algiers, Algeria

Received 1 September 2012 Revised 15 The month from the month of the month of january 2013 Recognized 16 The month from the month of the month of january 2013

Academic Editor: Lingyang Song

2013 Farid Khoucha et al. It is really an open access article distributed underneath the Creative Commons Attribution License. which helps unrestricted use, distribution, and reproduction in almost any medium, provided the very first jobs are correctly reported.

This paper presents a totally new hybrid cascaded H-bridge multilevel inverter motor drive DTC request electric vehicles where each phase within the inverter may be implemented having a single Electricity source. Typically, each phase within the inverter requires

output current levels. During this paper, an idea is suggested that enables employing a single Electricity source because the first Electricity source which may be accessible from batteries or fuel cells, while using the remaining (

) Electricity sources being capacitors. This course of action can concurrently take proper care of the capacitors of Electricity current level and supply a virtually sinusoidal output current because of its many output levels. During this context, high performances and efficient torque and flux control are acquired, enabling a DTC solution for hybrid multilevel inverter powered induction motor drives meant for electric vehicle propulsion. Simulations and experiments show the suggested multilevel inverter and control plan work effectively and very attractive for embedded systems for example automotive applications.

Presently, automotive applications for example EV’s appear to constitute an more and more more efficient option to conventional vehicles, allowing vehicle manufacturers to satisfy users needs (dynamic performances and fuel consumption) and ecological constraints (pollutant emissions reduction) [1 ].

The electrical propulsion technique is the center of EV. It provides the motor drive, transmission device, and wheels. Really, the motor drive, like the motor unit, the ability ripping tools, along with the electronic controller, may be the core within the EV propulsion system. The motor drive is configured to solve a torque demand set using the driver [2 ].

The induction motor appears to get very useful solution for EV’s propulsion. FOC and DTC emerged because the standard industrial strategies to achieve high dynamic performance [3 –5 ]. However, some drawbacks of each and every method have motivated important research efforts within the last decades. Produced for DTC, the very best torque ripple along with the variable switching frequency created with the hysteresis comparators are really extensively addressed [6. 7 ]. In addition, several contributions that combine DTC concepts along with PWM and SVM are really reported to correct these problems. This method draws on the duty position control, the current reference vector is computed that’s finally modulated using the inverter [8 ].

Although one major feature of classic DTC is having less modulators and straight line controllers, this method has proven significant enhancements and achieves similar dynamic performance.

However, power ripping tools technologies are continuously developing, and cascaded multilevel inverters have become a really attractive solution for EV applications, because of its modular structure, greater current capacity, reduced common mode voltages, near sinusoidal outputs, and smaller sized sized sized or even no output filter [9 –12 ]. Generally, cascaded multilevel inverter might be classified by 50 % groups. The initial means amplitude of isolated Electricity sources centered on supply each H-bridge cell. When the amplitude of sources is equal, your inverter is known as symmetrical otherwise, if a number of within the sources presents different amplitude, then it will be known as asymmetrical. The 2nd classification labels the multilevel inverter whether hybrid otherwise. When the ripping tools is implemented with some other semiconductor device technologies, different nature of Electricity sources (fuel cells, batteries, and supercapacitors) and/or even it presents a hybrid modulation strategy, then it’s considered hybrid [13 –15 ]. This structure greatly simplifies the ripping tools complexity.

The suggested control formula eliminates involve additional isolated Electricity sources. The control strategy regulates the ability link voltages of capacitors attached to the tiniest voltages of the-cell 7-level cascaded H-bridge inverter [16 ]. Particularly and in comparison with previous works [17. 18 ], the suggested control doesn’t work by having an position for capacitor current regulation however an assessment current level. This might facilitate a DSP implementation.

The transported out simulations and experiments validate the current control strategy and make certain the very best dynamic performance within the suggested method, presenting small torque ripple.

The ability circuit within the cascaded H-bridge multilevel inverter is highlighted in Figure 1. The inverter consists using the series connection of power cells, each one of these containing an H-bridge inverter along with an isolated Electricity source. Within the particular situation of uneven inverters these sources aren’t equal (

). The asymmetry within the input voltages is effective in reducing or, when correctly designed, eliminate redundant output levels, maximizing the amount of different levels generated using the inverter. Therefore, this topology is able to do exactly the same output current quality with less amount of semiconductors, space, costs, and internal fault probability in comparison with symmetric given topology.

Figure 1: Hybrid cascaded multilevel ripping tools topology.

A specific cell

If both flux magnitudes are stored constant in (4 ), the torque may be controlled directly by altering the duty position. This can be frequently easily achieved, since variations within the stator flux vector modify the load position because of slower rotor flux dynamics.

Thinking about (3 ) and (4 ) it seems sensible the stator current vector allows you to manipulate the duty position and so to handle torque.

In traditional DTC, the influence within the load position of each current vector generated using the inverter is made a decision and stored in the lookup table, using the stator flux position within the complex plane. This is often hard to extend for multilevel inverter given drives, in which the complexity increases in huge proportions based on the amount generated using the inverter. Therefore, it’s better to consider the problem diversely: the torque error allows you to produce a reference load position

essential to correct the torque behavior. Your chosen load position allows you to compute the particular current vector that make the needed flux variation. This principle is highlighted in Figure 3. Understand that once provided the reference load position. the reference stator flux vector may be computed by

may be the fixed stator flux amplitude reference, the rotor flux vector position. Understand that ( ) matches the reference stator flux vector position .

Figure 3: Stator current vector influence within the stator flux vector.

Your chosen stator current vector may be acquired by

Finally should be generated using the inverter. This is often generally performed with PWM or SVM for 2 primary-level inverters [19 ]. Employing a multilevel inverter will reduce the torque ripple amplitude because of the decrease in the speed of change from typically the most popular-mode current (amount of step variations within the fixed time period), and, during this situation, when using the hybrid modulation method [20 ], a group-frequency output current will most likely be acquired concentrating the current spectrum over the carrier frequency within the small power cell. Therefore, the key drawbacks of traditional DTC are remedied. A simplified control diagram within the suggested technique is proven in Figure 4. The outer speed control loop is overlooked.

Figure 4: Hybrid multilevel inverter-given DTC motor drive getting only one Electricity source.

The hybrid modulation is especially created for the uneven multilevel H-bridge inverter structure [14 ].

The fundamental idea could be to benefit from the different power rates one of the cells to lessen switching losses and raise the ripping tools efficiency. From Figure 5 it may be observed the inverter generates an oblong waveform, that is within the same frequency within the reference (turn-on and -off just once inside a half reference cycle). All individuals other within the output current, second trace in Figure 5. is synthesized using the auxiliary inverter at high switching frequency (with sinusoidal PWM). This completes the generation in the multilevel walked waveform obtaining a greater-frequency component (much like a multicarrier-based PWM), although the primary difference that less switching losses are created to attain it. Typical output waveform within the inverter employing this modulation is proven within the third trace of Figure 5. Understand that the output has 7 different current levels provided by all of the possible mixtures in the series connection of (

Figure 5: Preferred output, auxiliary and primary inverter current waveforms.

Capacitor current control within the auxiliary inverter could be a challenging task [14. 21 ]. The suggested control method draws on a hybrid modulation including modifying the primary inverter turn-on. This indeed matches modifying the active and reactive forces the primary inverter injects for that load (if

is selected to obtain exactly 18°, the primary inverter injects only active power). By shifting the current waveform synthesized using the primary inverter (Figure 6 ), you may inject some reactive power, that can be used to charge or discharge the auxiliary inverter capacitor.

Figure 6: Variation however inverter conduction position by

Therefore, the suggested formula, highlighted by Figure 7. regulates the capacitor up-to-date with a appropriate adjustment being provided through the PI regulator and procedures round the variation within the comparison level that controls the primary inverter turn-on and -off. The closed loop regulation for every phase is completed by calculating the capacitor current. Inside the capacitors current error, the PI regulator gives directly the appropriate to get incorporated for the first comparison level which results in altering the conduction position however inverter that enables the secondary inverter capacitor charging.

Figure 7: Closed-loop charge of the capacitor voltages.

The above mentioned pointed out stated-discussed hybrid modulation strategy remains experimentally implemented (Figure 8 ). The suggested hybrid modulation strategy primary solutions are highlighted by Figure 9. As abovementioned, the inverter generates an oblong waveform, that is within the same frequency within the reference (Figure 9(a) ). All individuals other within the output current is synthesized using the auxiliary inverter at high switching frequency with sinusoidal PWM (Figure 9(b) ). Figure 9(c) shows the conventional output waveform within the 7-level inverter under hybrid modulation.

Figure 8: 7-level single Electricity source cascaded H-bridge multilevel inverter.

Figure 9: Preferred output, primary, auxiliary, and inverter current and current waveforms within the recognized 7-level inverter under hybrid modulation.

To judge the dynamic performances within the suggested control strategy, record simulations are really transported by having an EV propelled by an induction motor provided with 7-level single Electricity source cascaded multilevel inverter (Figure 4 ).

Simulations were done when using the standardized ECE-15 and EUDC driving cycle [22 ]. The achieved performances are highlighted by Figures ten to fifteen .

Figure 10: Speed while using the ECE-15 + EUDC driving cycle.

The simulation results show the rate reference needed using the driver is well-tracked as proven by Figure 10. You are able to understand that the induction motor developed torque presents less ripples around the traditional DTC (Figure 11 ). For the reason that the standard of the current supplying the inverter (Figure 12 ). Consequently, the stator currents are nearly sinusoidal (Figure 13 ) and dynamics are acquired operating practically with constant flux (Figure 14 ).

Figure 11: Reference and developed torques.

Figure 12: Output current waveform.

Figure 13: Stator currents waveforms.

Figure 14: Magnitude and locus within the stator flux within the DTC-PWM.

Figure 15: Capacitor current waveforms.

Figure 15 shows the capacitor voltages waveforms that offer each auxiliary H-bridge within the three phase hybrid multilevel inverter. You can put the oscillations over the reference. Additionally, these voltages are quiet identical. However, their difference becomes large when there’s a considerable acceleration or deceleration requested using the driver. Indeed, in such instances, different stamina are crucial because of the induction motor operating point fast variation.

The above mentioned pointed out stated-presented simulation results ensure, individually within the requested speed and torque, the capacitor voltages are controlled along with the validity within the suggested control approach is proven.

During this paper a control strategy remains suggested for almost any hybrid cascaded multilevel inverter getting an altered DTC plan meant for induction motor-based EV propulsion. During this situation, the primary inverter uses single Electricity current source, along with the auxiliary inverter capacitor voltages are controlled in every single phase. In addition, DTC-PWM enables the operation obtaining a set switching frequency, the decrease in the torque ripple without output filter, and-performance torque and flux control.

The suggested control method simplifies the DTC application in embedded systems by reduction in the inverter cost and complexity (by decrease in the semiconductor along with the source figures). Additionally, there’s no dependence on hysteresis comparators and lookup tables. Each one of these key features make suggested control approach very attractive for embedded systems for example automotive applications.

Table 2: Rated data within the simulated induction motor.


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