ABSTRACT:
This
paper presents the study, analysis and practical implementation of a versatile
unified power quality conditioner (UPQC), which can be connected in both
three-phase three-wire or three-phase four-wire distribution systems for
performing the series-parallel power-line conditioning. Thus, even when only a
three-phase three-wire power system is available at a plant site, the UPQC is
able to carry out power-line compensation for installed loads that require a
neutral conductor to operate. Different from the control strategies used in the
most of UPQC applications in which the controlled quantities are
non-sinusoidal, this UPQC employs a dual compensation strategy, such that the
controlled quantities are always sinusoidal. Thereby, the series converter is
controlled to act as a sinusoidal current source, whereas the parallel
converter operates as a sinusoidal voltage source. Thus, because the controlled
quantities are sinusoidal, it is possible to reduce the complexity of the
algorithms used to calculate the compensation references. Therefore, since the
voltage and current controllers are implemented into the synchronous reference
frame, their control references are continuous, decreasing the steady-state
errors when traditional proportional-integral controllers are employed. Static
and dynamic performances, as well as the effectiveness of the dual UPQC are
evaluated by means of experimental results.
KEYWORDS:
1. Active filter
2. Dual control strategy
3. Power
conditioning
4. Three-phase distribution systems
5. UPQC
SOFTWARE: MATLAB/SIMULINK
CIRCUIT DIAGRAM:
Fig.
1. 3P4W distribution system based on UPQC topology connected to 3P3W power
system.
EXPECTED SIMULATION RESULTS:
Fig.
2. Experimental results for the loads presented in Table III: (a) UPQC currents
for unbalanced three-phase -phase load (1) (20 A/div, 5 ms/div): Load currents
(𝑖𝐿𝑎, 𝑖𝐿𝑏, 𝑖𝐿𝑐) and 𝑖𝐿𝑛, Compensated source currents (𝑖𝑠𝑎, 𝑖𝑠𝑏, 𝑖𝑠𝑐), and Currents of the parallel
converter (𝑖𝑐𝑎, 𝑖𝑐𝑏, 𝑖𝑐𝑐) and 𝑖𝑐𝑛; (b) Currents and voltages of
phase “a” of the UPQC for the unbalanced three-phase load (2) (20 A/div,
100V/div, 5 ms/div): Load currents (𝑖𝐿𝑎, 𝑖𝐿𝑏, 𝑖𝐿𝑐); Currents of
phase “a”: load 𝑖𝐿𝑎, parallel
converter 𝑖𝑐𝑎 and source 𝑖𝑠𝑎; voltages and currents of phase
“a”: load current 𝑖𝐿𝑎 , source
current 𝑖𝑠𝑎, utility
voltage 𝑣𝑠𝑎 and load
voltage 𝑣𝐿𝑎, (c) UPQC
currents for three-phase load (1) (2.5 ms/div): Load currents (𝑖𝐿𝑎, 𝑖𝐿𝑏, 𝑖𝐿𝑐) (5 A/div), Source compensated
currents (𝑖𝑠𝑎, 𝑖𝑠𝑏, 𝑖𝑠𝑐) (10 A/div),
Parallel converter currents (𝑖𝑐𝑎, 𝑖𝑐𝑏, 𝑖𝑐𝑐) (10 A/div).
Fig.
3. Voltages of the UPQC under utility harmonics and unbalances for the
unbalanced three-phase load (1): (a) Utility voltages (𝑣𝑠𝑎, 𝑣𝑠𝑏, 𝑣𝑠𝑐) (50 V/div, 2,5ms/div), Load
voltages (𝑣𝐿𝑎, 𝑣𝐿𝑏, 𝑣𝑠𝐿) (50 V/div,
2,5ms/div) and series compensating voltages (𝑣𝐶𝑎, 𝑣𝐶𝑏 and 𝑣𝐶𝑐) (50 V/div, 2,5ms/div); (b) (a)
Utility voltages (𝑣𝑠𝑎, 𝑣𝑠𝑏, 𝑣𝑠𝑐) (50 V/div,
2,5ms/div), Load voltages (𝑣𝐿𝑎, 𝑣𝐿𝑏, 𝑣𝑠𝐿) (50 V/div, 2,5ms/div)
and series compensating voltages (𝑣𝐶𝑎, 𝑣𝐶𝑏 and 𝑣𝐶𝑐) (50 V/div, 2,5ms/div)
Fig.
4. Voltages and current of the UPQC for the unbalanced three-phase load 1: (a)
DC-bus voltage (𝑉𝐷𝐶) (100 V/div,
500ms/div) and load currents (𝑖𝐿𝑎, 𝑖𝐿𝑏, 𝑖𝐿𝑐) (20 A/div,
500ms/div); (b) DC-bus voltage (𝑉𝐷𝐶) (100 V/div,
500ms/div) and source currents (𝑖𝑠𝑎, 𝑖𝑠𝑏, 𝑖𝑠𝑐) (20 A/div,
500ms/div); (c) DC-bus voltage (𝑉𝐷𝐶) (100 V/div,
5ms/div) and details of the source currents (𝑖𝑠𝑎, 𝑖𝑠��, 𝑖𝑠𝑐) after the first load transient
(20 A/div, 5ms/div).
Fig.
5. UPQC under voltage sag disturbance (phase ‘a’): utility voltage (𝑣𝑠𝑎), load voltage (𝑣𝐿𝑎) and series compensating voltage
(𝑣𝐶𝑎) (200 V/div,
25ms/div).
CONCLUSION:
This paper
presents a practical and versatile application based on UPQC, which can be used
in three-phase three-wire (3P3W), as well as three-phase four-wire (3P4W)
distribution systems. It was demonstrated that the UPQC installed at a 3P3W
system plant site was able to perform universal active filtering even when the
installed loads required a neutral conductor for connecting one or more
single-phase loads (3P4W). The series-parallel active filtering allowed
balanced and sinusoidal input currents, as well as balanced, sinusoidal and
regulated output voltages. By using a dual control compensating strategy, the
controlled voltage and current quantities are always sinusoidal. Therefore, it
is possible to reduce the complexity of the algorithms used to calculate the
compensation references. Furthermore, since voltage and current SRF-based
controllers are employed, the control references become continuous, reducing
the steady-state errors when conventional PI controllers are used. Based on
digital signal processing and by means of extensive experimental tests, static
and dynamic performances, as well as the effectiveness of the dual UPQC were
evaluated, validating the theoretical development.
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