Fusion of Neural Networks, Fuzzy Systems and Genetic Algorithms: Industrial Applications Fusion of Neural Networks, Fuzzy Systems and Genetic Algorithms: Industrial Applications
by Lakhmi C. Jain; N.M. Martin
CRC Press, CRC Press LLC
ISBN: 0849398045   Pub Date: 11/01/98
  

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With these space vectors, the XSVM can be realized. Basically, the converter state is selected applying the following set of rules.

1.  At every sampling interval, calculate the current error ei, the phase error eθ, the input phase voltage vector’s phase α, and the load current vector module mi. When indicated by the fuzzy controller, select the converter state as follows.
2.  Determine the converter’s output line voltage vector zone in the complex plane using the filtered line voltage vector Vlf defined in (30), (Figure 10 a).
3.  Assign space vectors Vx and Vy according to the zone determined in 2 (Figure 10 b), and the time zone given by α. Vx is the space vector leading the line voltage vector, and Vy is the one lagging it. Vx and Vy are in { V1, V2, ..., V18) as shown in Table I. The input phase voltage vector’s phase α determines six time zones for each vector cycle [330°-30°, 30°-90°, ...,270°-330°]. Each time zone denotes the voltage space vectors with bigger modules in each zone in the complex plane (Figure 10a). For example, if the voltage vector zone is I, then Vx will be in { V1, V2, V3, V10, V11, V12}, depending on the time zone given by α.
4.  If M>0.9, then

a)  If eθ >0 then the next state is St= Vy.
b)  If eθ <0 then the next state is St= Vx.

5.  If M<.09, then

a)  If mi>mref and eθmin then the next state is St = V25, V26 or V27. The null state is chosen to minimize switch commutations based on the actual converter state,
b)  else i) If eθ >0 then the next state is St= Vy.
            ii) If eθ <0 then the next state is St= Vx.

where,


ei =
eθ =
mref = reference current vector’s module;
θmin = minimum lagging angle for null state connection;
M = modulation index;
St = converter’s state.


Figure 10  a) Complex plane zones defined by the converter. b) Space vectors Vx and Vy during commutation instant, i.e., Il is out of Iref’s error zone.

5.4 Input’s Line Current Control

This controller is in charge of the converter’s input line currents. It has a single objective which is to reduce the input current’s harmonic distortion. To accomplish this goal it must keep the magnitude of the input harmonic currents restrained to a specified maximum. This is done by appropriately choosing the next converter state using the XSVM technique presented in Section 4.

The controller acts, just as the load’s line current controller, upon reception of the order coming from the fuzzy controller. Once that this controller has decided that the input port has higher priority, it will pass command of the converter to the input’s line current control. After the decision has been made, the input controller will select the converter state that will reduce the converter’s input current distortion, which also improves the converter’s power factor.

The input current control requires measurement of the input and output line currents, and the input voltages in order to select the next converter state according to the control’s objective. The output line currents and input phase voltages are already measured by the load’s line current control, thus leaving only the input line currents Iin unknown. These are obtained by software waveform reconstruction, using the converter’s current transfer function Hi for this purpose. The actual operation is shown in (31).

The converter input currents are also pulse-like waveforms, just like the output line voltages of the converter, therefore, they require filtering in order to produce a space vector with constant magnitude when transformed using Park’s matrix. Taking advantage of the design characteristics of digital filters, two digital IIR filters are employed, a low pass filter and a band pass filter tuned to pass from the 3rd to 19th harmonic currents. With them the input line currents Iin are filtered, obtaining the filtered input line currents Iinf and Ih of the converter. The filtered waveforms are then used to obtain two current space vectors (17) and (32).


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