Power Quality Issues in Traction Power Systems - Control of Power Inverters in Renewable Energy and Smart Grid Integration - page 174

π /6

-

sin( ω t)

sin

i sa

u ab

sin( ω t-2 π /3) ω t+ π /6

-

sin

STA

i ra PWM S1

K D

-

×

5 π /6

PWM S2

sin

-

i sc

-

-

PWM S3
PWM S4
PWM S5
PWM S6

2

i L

i L

×

LPF

3

-

+

i sb

- +

i rb

V cref × K D

PI

-

− Ts

V c

1 − e

2

Ts / 2

DC-bus voltage controller

Figure 9.3 Control strategy to compensate negative-sequence, reactive and harmonic currents

The major control problem is for the SPC to track the calculated reference compensation
currents i ra , i rb and i rc . This can be done with many control strategies. For example, the
repetitive controller discussed in other chapters is a very good candidate that works with a
fixed switching frequency. In this chapter, three hysteresis controllers are adopted to generate
PWM signals to drive the converter switches, as shown in Figure 9.3.

9.4 Special Case: cos 1

Nowadays, many high-speed trains are equipped with four-quadrant converters and the power
factor of the load is nearly 1. In this case, the load current is

θ =

I L 1 ∠ 6

I L =

and the grid currents before compensation are
⎧
⎨

I L 1

K V ∠ 6 ,

I A =

I L 1
K V ∠ −

5
6 π,

I B =

⎩

I C =

.

0

After compensation, the grid currents are
⎧
⎨

I L 1
√ 3 K V ∠

I A =

0 ,

I L 1
√ 3 K V ∠ −

2
3 π,

I B =

⎩

I L 1
√ 3 K V ∠

2
3 π.

I C =