IEEE Power Electronics Magazine Compendium - March 2018 - 38

.
θg

50.55

.
θ
Voltage (V)

Frequency (Hz)

50.5

50
49.75
49.5

0

1

2
3
4
Time (Seconds)
(a)

5

6

Frequency (Hz)

P (kW)

Vref

0

1

2

3
4
Time (Seconds)
(b)

Vo

5

6

5

12
8

4
0

800
700
600
500
400
300
200
100
0

0

1

2
3
4
Time (Seconds)
(c)

5

6

Qref

Q

2.5
0
-2.75
-5

0

1

2
3
4
Time (Seconds)
(d)

5

6

FIG 4 The simulation results of a rectifier operated as a VSM [8]. (a) Frequency. (b) Vref and Vo (V). (c) P (W). (d) Q (Var).

mainly based on the vector control approach in the d-q
reference frame. However, vector control techniques are
very sensitive to parameter variations and mismatches
because of the decoupling terms used for achieving the
desired field orientation. The VSM technologies described
in the "Operation of Inverters as a VSM" and "Operation of
Rectifiers as a VSM" sections can be adopted to integrate
wind energy, because the back-to-back converter consists
of a rectifier and an inverter [12].
The rotor-side converter can be operated as a virtual synchronous motor, as shown in Figure 6, because it receives
power from the permanent magnet synchronous generator
(PMSG) at the ac side and injects it to the dc link. The main
tasks of the rotor-side converter are to regulate the dc link
voltage to the desired level and to achieve unity power factor operation at the ac side. In contrast to the existing vector control techniques, the synchronverter technology is
completely independent from the parameters of the PMSG,
providing significant advantages.

The grid-side converter can be operated as a virtual synchronous generator to inject real and reactive power to the
grid, as shown in Figure 7. The main tasks of the grid-side
converter are to achieve maximum power point tracking (MPPT), that is, maximum power extraction from
the wind, and also to regulate the reactive power. As a
result, the whole system behaves as a rotor-generator/
motor-generator system, which leads to a compact and
effective system with the potential of utilizing the inertia
of the wind turbine.
Figure 8 shows the real-time simulation results of the
rotor-side performance of such a system. Note that the dcbus voltage is always maintained around the desired value,
even when the wind speed changed at 6 seconds.

Integration of solar Power

A VSM control strategy can also be applied to the integration of solar power. In [13], a synchronverter-based singlephase transformerless photovoltaic (PV) inverter is
proposed. The topology of the inverter
is shown in Figure 9. The PV inverter
can be formed by adding a neutral leg
LCL Filter
Grid
into the conventional half-bridge
inverter. The added neutral leg conPMSG
sists of two switches and one inductor. The two switches are connected
Three-Phase
Three-Phase
in series and then put between the
Rectifier
Inverter
positive and negative poles of the dc
bus. The neutral inductor is put
FIG 5 The connection of a wind-power generation system to the grid through a backbetween the midpoint of the switches
to-back converter.

38

IEEE PowEr ElEctronIcs MagazInE

z	December 2016
Table of Contents for the Digital Edition of IEEE Power Electronics Magazine Compendium - March 2018
