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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The filter’s design parameters are shown in Table IV. Finally, the converter state is selected applying the set of rules from the expert knowledge based SVM technique. These are shown below.

1.  At every sampling interval, calculate the harmonic error ei, the phase error eγ, the input phase voltage vector’s (Vin) phase α, and the output current vector’s phase β. When indicated by the fuzzy controller, select the converter state following the next steps.
2.  Assign Vx and Vy considering the input line current vector Ii zone in the complex plane (Figure 10), and the time zone of the output line current vector Ilo. Vx is the space vector leading the line current vector, and Vy is the one lagging it, with Vx and Vy in {V1, V2,..., V18} as shown in Table I. The output line current vector’s phase β determines six time zones for each vector cycle [0°-60°, 60°-120°,...,300°-360°]. Each time zone denotes the current space vectors with bigger modules in each zone in the complex plane (Figure 10b). For example, in case the load current vector zone is I, then Vx will be in {V3, V6, V9, V12, V15, V18} (Figure 5), depending on the time zone given by β.

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

where,


ei =
eγ =
St = converter’s state.

6. Results

The previous sections of this chapter have described the modeling, operation, and control of the presented XDFC. However, the advantages of the proposed converter have yet to be shown. In this section, results of the converter operation are given. For this purpose computer simulations were performed to validate the control algorithm presented.

The XDFC is evaluated in an Adjustable Speed Drive (ASD) like the one shown in Figure 4. The converter is controlled to produce a constant V/f characteristic up to 50 Hz, and constant power in the field weakening region. The load’s current distortion is set to a maximum of 6%, and the input current harmonic distortion is reduced. The load considered is a 20 kVA squirrel cage induction machine. The test circuit parameters are shown in Table V.

Table V Test Circuit Parameters

Parameters Values

Input rms phase voltage 120 V
Input frequency 50 Hz
Power rating 20 KVA
Squirrel cage induction machine phase parameters X=2.4 Ω/phase
R=6 Ω /phase
Input capacitive filter (Wye connected, ungrounded) 86 μF/phase

Computer simulations of the XDFC were performed using Matlab under Windows environment. Although Matlab is a computer language and not a circuit simulator, it offers multiple advantages due to its graphics interface and matrix-like functions which are proper for circuit representations. The converter’s transfer function can be extensively employed when simulating under these conditions, being a powerful tool for modeling static power converters.

Example-Computer simulation using Matlab

As an example for simulating under Matlab environment, the rectifying system depicted in Figure 2 will be analyzed, but with a resistive-inductive (R-L) load instead of the current source. In order to simulate any circuit, all its equations must be written in the time domain. The equations for the circuit in Figure 2 are the following.

Now, if a time step of Δt is used to discretize the time variable t, Equation (34) can be rewritten as shown in (36) using a first order approximation for the current derivative.

The load current io may be determined at time instant t.

Finally, to simulate the circuit the following steps are required:

1.  Create voltages va, vb, vc as time vectors of length n, where n is given by (38).

2.  Create transfer functions (Figure 3b) Ha, Hb, Hc as time vectors of length n.
3.  Run the following loop n times.

a)  Determine vo(t) using (33).
b)  Determine io(t) using (37).
c)  Determine ia(t), ib(t), ic(t) using (35).

Figure 11a) shows the input phase voltage va and input line current ia, and Figure 11b) shows the output voltage vo and load current io. The simulations results were obtained using the following load parameters.

Initial io = 0 A;
Load Resistance = 5 Ω;
Load Inductance = 10 mH.


Figure 11  Simulation results of rectifying-system shown in Figure 2 using an R-L load instead of a current source.


Figure 12  Input phase voltage Vr, input line current Ir, output line voltage Vab, and output line current Ia of the XDFC operating at 70 Hz.


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