Direct Power and Torque Control of AC/DC/AC Converter-Fed ...

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5. Passive Components Design mainly depends on quality of the used DC-link voltage and input/output power flow control methods. 80 70 60 |eUdc| [V] 50 40 30 3 4 with PF C=470uF with PF C=47uF 20 10 3 0.2 0.1 0.05 0.02 0.01 Ts [ms] 4 Fig. 5. 7. Module of the DC-link voltage fluctuation eU dc as a function of sampling time T S , during load change from 0 to 3kW with command DC-link voltage U dcc = 560 [ V] for a case when in control structure the active power feedforward – PF is implemented. Simulated results in Saber model of DPTC-SVM. 5.2.3.1. Consideration of Operation with Reduced DC-link Capacitor The minimum value of the DC-link capacitor is limited by a maximal acceptable switching ripple level and fluctuation during load power steps. In case of small DClink capacitor that phenomena can not be reduced by the reactive component (DClink capacitor), but have to be compensated by the other way. One alternative is to use a load itself e.g. induction motor. The VSI-fed IM can be controlled in such a way that, all energy which intent to drown or especially inject to the DC-link can be dissipated in the IM itself. It is necessary because in a typical motor drive, the mechanical energy is several times higher then electrical energy stored in the DC-link capacitor of the AC/DC/AC converter-fed IM. In cost effective case the diode rectifier with reduced DC-link capacitor can be used. However, in such application line current is still distorted (Fig. 5. 8a). Moreover, the fluctuation of the DC-link voltage (Fig. 5. 8b) is significant for life time of the capacitor. Regenerative energy has to be wasted in IM (this increase the temperature of the 102
5. Passive Components Design motor too) or in DC-link chopper. While the energy during braking is not dissipated in the motor (or chopper) the DC-link voltage grown fast (see Fig. 5. 9a). Mag(A) Mag(V) (A) (V) Fig. 5. 8. Simulated AC/DC/AC converter with diode rectifier and reduced DC-link capacitor. Steady state at nominal load; a) line current and its harmonics spectrum, b) DC-link voltage and its harmonics spectrum Fig. 5. 9. Simulated AC/DC/AC converter with diode rectifier and reduced DC-link capacitor. Transient to: a) start up, loading (20Nm), and speed reversal +/- 71% of nominal speed, b) load torque +/- 100% of nominal torque at zero speed. From the top: DC-link voltage [V], mechanical speed of IM [rpm], torque [Nm] Another solution is just transfer all fluctuations from the load power to the supply line power. It can be realized by active power feedforward – PF (see Chapter 4). However, in the case when the DC-link capacitor has a minimized value its capacity 103
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POLITECHNIKA WARSZAWSKA WARSAW UNIV
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Acknowledgements The work presented
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Contents 4.2.2. Energy of the DC-li
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Chapter 1 1. Introduction 1.1. AC/D
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1. Introduction Tab. 1. 1. Current
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1. Introduction DC-link voltage to
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1. Introduction then nominal speed
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1. Introduction [69]. From that tim
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Chapter 2 2. Voltage Source Convert
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2. Voltage Source Converters - VSC
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Chapter 3 3. Vector Control Methods
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3. Vector Control Methods of AC/DC/
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Page 133 and 134: References [18] G. Buja, M. P. Kazm
Page 135 and 136: References [58] J. G. Kassakian, M.
Page 137 and 138: References [96] H. Mao, D. Boroyevi
Page 139 and 140: References [133] A. Tripathi, A. M.
Page 141 and 142: References [167] M. Jasiński, D.
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Appendices Tab. A. 4. 6. Data of th
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Direct Power and Torque Control of AC/DC/AC Converter-Fed ...

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