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Study of a low voltage reactive power dynamic compensation device with continuously adjustable capacity

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A dynamic reactive power compensation device with continuously adjustable capacity is designed for low voltage power grid. According to the time requirement of reactive power dynamic compensation for capacitor switching, a signal generating circuit of voltage/current zero-crossing triggering switching is designed. A capacitor combination method to improve the compensation accuracy and the control strategy to change the compensation power of capacitor by adjusting voltage are put forward. The hardware structure of compensation device, reactive power compensation control mode, capacitor switching control method and capacitor output power regulation method are designed. Using Matlab/Simulink, the simulation results show that the proposed method can realize continuous reactive power adjustment according to the set power factor.
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Study of a low voltage reactive power dynamic compensation device
with continuously adjustable capacity
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4th International Symposium on Resource Exploration and Environmental Science
IOP Conf. Series: Earth and Environmental Science 514 (2020) 042064
IOP Publishing
doi:10.1088/1755-1315/514/4/042064
1
Study of a low voltage reactive power dynamic compensation
device with continuously adjustable capacity
Zifu Zhou, Jun Long*
School of Electrical Engineering, Guangxi University, Nanning, China
*Corresponding author e-mail: gxnnlj161@163.com
Abstract. A dynamic reactive power compensation device with continuously adjustable
capacity is designed for low voltage power grid. According to the time requirement of
reactive power dynamic compensation for capacitor switching , a signal generating
circuit of voltage/current zero-crossing triggering switching is designed. A capacitor
combination method to improve the compensation accuracy and the control strategy to
change the compensation power of capacitor by adjusting voltage are put forward. The
hardware structure of compensation device, reactive power compensation control mode,
capacitor switching control method and capacitor output power regulation method are
designed. Using Matlab /Simulink, the simulation results show that the proposed
method can realize continuous reactive power adjustment according to the set power
factor.
1. Introduction
The inductive loads in power grid leads to the increase of line loss and voltage drop, the power factor
also decreases [1]. Therefore, reactive power compensation must be used to improve the above situation.
There are many options for reactive power compensation technologies, such as FC fixed capacitor [2],
TCR thyristor switching reactor [3], TSC thyristor switching capacitor [4], SVG static var generator [5],
etc. There are two problems in the low-voltage network with capacitor as the main reactive power supply.
One is the timing of capacitor switching. When the capacitor is put into operation, if the voltage at both
ends of the switch is not equal, inrush current will be generated; if the current is not equal to zero at the
moment of capacitor removal, flashover will be generated. The other one is over or under compensation.
Although the access state of the capacitor bank is determined by the reactive power of the load, it will
still lead to under or over compensation due to the difference of capacitance magnitude of the capacitor
bank, and even produce switching oscillation [6]. The first problem can be solved by controlling the
thyristor and other electronic switching elements, putting the capacitor into work when the grid voltage
crossing zero, and cutting off the capacitor when the capacitor current crossing zero. However, the above
method needs to consider the discharge of capacitors, so the switching interval is long. The second
problem can be solved by adjusting the voltage of the capacitor so as to continuously adjust the reactive
power. Reference [7, 8] used auto-transformer or inductive voltage regulator to change capacitor voltage,
but they failed to achieve continuous and step less regulation of reactive power. In reference [9], SVC
is used in low-voltage power grid to realize accurate and continuous compensation of reactive power,
but it is too expensive. In reference [10], capacitor is connected in parallel with reactor, and then
connected between the output end of inverter and compensation node, and the nature and size of
4th International Symposium on Resource Exploration and Environmental Science
IOP Conf. Series: Earth and Environmental Science 514 (2020) 042064
IOP Publishing
doi:10.1088/1755-1315/514/4/042064
2
compensation reactive power are changed by switching and adjusting the output voltage of inverter, but
the method is only applicable to three-phase balance load.
In this paper, a kind of reactive power dynamic compensation device with continuously adjustable
compensation power and low cost is developed. A capacitor configuration scheme with high
compensation precision is presented, a capacitor voltage/current zero-crossing switching device is
designed, a circuit topology and control strategy for continuously adjusting capacitor power are designed
to realize continuous adjustment of reactive power.
2. Function of dynamic reactive power compensation device
The reactive power compensation device includes two parts: the mutual compensation part and the split-
phase compensation part, the schematic diagram is shown in figure 1.The mutual compensation part is
composed of three capacitors with equal reactive capacity connected by 󰅿,each phase of the split-phase
compensation part is composed of three capacitors with proportional distribution capacity in parallel,
and at the end of each phase of the split-phase compensation part is connected with an inverter for
voltage regulation. Each capacitor of the split-phase compensation part is equipped with a switch, which
can independently turn on/off the capacitor; the inverter device is equipped with a bypass switch to
control whether the voltage regulation is carried out.
Ua
Uc
UbLoad
The mutual
compensation part
the split-phase
compensation part
Figure 1. Wiring diagram of reactive power compensation device.
2.1. Response speed
The capacitor switching circuit as shown in figure 2.
4th International Symposium on Resource Exploration and Environmental Science
IOP Conf. Series: Earth and Environmental Science 514 (2020) 042064
IOP Publishing
doi:10.1088/1755-1315/514/4/042064
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Figure 2. Schematic diagram of voltage detection and capacitor switching
Voltage detection and capacitor switching circuits work as follows. Start MSP430 and two voltage
transmitters. The main program of capacitor switching is executed after the self-check of single-chip
microcomputer (SCM). LV25-p module is adopted for the voltage sensor, and the output ports of the
sensor are respectively converted into voltage values through resistors R1 and R2. The SCM samples
the voltage values of resistors R1 and R2 in real time and makes a subtraction to the two sampling values.
When the difference value is 0, the P4.4 pin of SCM sends the switch-on signal, and the capacitor is put
into operation. As the phase difference between the current flowing through the capacitor and its
terminal voltage is 90°, when the terminal voltage reaches the maximum value, the current is 0A. At
this time, the capacitor can be cut off to avoid flashover. Using Proteus Software to analyze the above
capacitor switching circuit, the switching signal is as shown in figure 3.
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1
-300
-200
-100
0
100
200
300
trigger
static
t/s
Connection signal Voltage/V
Cut-off signal
trigger
static
Figure 3. Output signal of switching circuit
When the instantaneous value of AC voltage is equal to the instantaneous value of capacitor voltage,
the signal of connecting capacitor will be generated, when the instantaneous value of AC voltage reaches
MSP430F149
GND Voltage
sensor 2
-15V
+15V
R2
Voltage
sensor 1
-15V
+15V
R1
P6.3/A3
P6.4/A4
Phase A line
voltage
A-phase capacitance
voltage
Capacitor switching
signal output
P4.4
1 2
6 5 4
5V
GND
U1
U2
U4
U3
4th International Symposium on Resource Exploration and Environmental Science
IOP Conf. Series: Earth and Environmental Science 514 (2020) 042064
IOP Publishing
doi:10.1088/1755-1315/514/4/042064
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the peak value, the signal of cutting-off capacitor will be generated. According to the national standard,
the time requirement for dynamic compensation is that the time interval of repeated switching capacitor
should not be more than 1 second, this circuit can capture the switching time of capacitor within 100ms,
which meets the requirement.
2.2. Compensation accuracy
2.2.1. Capacitor capacity combination. The capacitor combination of the device is as follows:
1) The capacitors of mutual compensation part is triangle connection, three phase capacitor switching
at the same time, to provide basic reactive power demand for the load, the capacitors of split-phase
compensation part operates separately according to the reactive load of each phase. Because the
capacitance of mutual compensation part is connected to the line voltage, its compensation power is 3
times to which is applied phase voltage.
2) In split-phase compensation part, each phase has 3 capacitors, they are called Ck(k=1, 2, 4), their
capacity ratio is 1:2:4, so they can realize the capacity combination of 1~7 levels, the capacitors of
mutual compensation are called Ccom, which is divided into n parts, Each part has a capacity ratio of 1.
The capacity of each capacitor can be determined according to the combination proportion of the
capacitors:
1) Suppose the total compensation capacity to be configured for each phase is, and the weight
sum of capacitor capacity is ( ), the compensation capacity of the minimum capacitor
can be calculated as
󰇛󰇜 (1)
2) The capacity of the minihmum capacitor is
 (2)
3) The capacity of split-phase compensation part and the capacity of the mutual compensation part
can be determined according to the weight proportion.
According to the above capacity combination method, the compensation deviation can be controlled
within [-Qmin/2, Qmin/2]. Suppose n=1, the minimum compensation capacity Qmin is 1 / 10 of QΣ, and
the compensation deviation is about ±5%. If the reactive load of each phase is large, the number of
capacitor groups of the mutual compensation part can be increased.
2.2.2. Switching strategy. The switching strategy is:
1) During operation, if the reactive power of each phase is larger than the capacity of the mutual
compensation part, the mutual compensation part shall be put into operation, and then the appropriate
capacitance of the split-phase compensation part shall be put into each phase, and the power factor shall
meet the requirements through voltage regulation.
2) During operation, if the reactive power of single-phase load is less than the capacity of the mutual
compensation part, the capacitors of mutual compensation part shall be cut off, and then appropriate
capacitance of the split-phase compensation part shall be put into each phase, and the power factor shall
meet the requirements through voltage regulation.
3) In case of over/under compensation of reactive power due to load change, the voltage can be
directly adjusted to make the power factor meet the requirements, or it can be resolved by
cutting/switching the capacitor and adjust the voltage.
4th International Symposium on Resource Exploration and Environmental Science
IOP Conf. Series: Earth and Environmental Science 514 (2020) 042064
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doi:10.1088/1755-1315/514/4/042064
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2.2.3. The method of continuous adjustment of compensation capacity. It can be seen from formula (2)
that the capacitance power Q is proportional to, so the capacitor voltage can be changed to adjust the
output of reactive power.
The continuous regulation device of split-phase compensation capacitors is composed of inverter
and capacitor in series. Its single-phase topology is shown in Fig. 4, and the control block diagram is
shown in Fig. 5.
+
-~
PWM
Circuit breaker
Capacitor bank
PLL
Amplitude
control
PWM
drive
Single phase bus
Load
C
L
Inverter
inverter control
Idc
Us
UVSD
Udc
PCC
PI
Us
Is
Pulse
generator
Phase
control
Figure 4. Topological diagram of subpart control
Calculation formula of reactive power of capacitor is:
Q=fC󰇛
󰇗
󰇗󰇜 (3)
Where f is the frequency,
󰇗 is the phase voltage,
󰇗 is the output voltage of the inverter, and the
reactive power value can be adjusted by adjusting the voltage
󰇗
PWM
generation Inverter main
circuit
PI
controller
Line voltage
and current
detection
PLL
Power
factor
calculation US
0.99
-+
IS
AC voltage
signal
generation
Figure 5. Block diagram of inverter control
According to the difference of power factor, PWM duty cycle is calculated and the output voltage
󰇗is controlled. The reactive power can be changed by continuously adjusting
󰇗, so as to change
4th International Symposium on Resource Exploration and Environmental Science
IOP Conf. Series: Earth and Environmental Science 514 (2020) 042064
IOP Publishing
doi:10.1088/1755-1315/514/4/042064
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the potential difference between the two ends of the capacitor. When the phases both
󰇗 and
󰇗 are
the same, the voltage difference between both ends of capacitor decreases and the reactive power
generated decreases; when the phases both
󰇗 and
󰇗 are opposite, the voltage difference increases
and the reactive power generated increases.
3. Controller of compensation device
The compensation device controller is shown in figure 6. The device includes a reactive power
compensation controller, a switching control unit and a power regulating unit.
LPC1768 32-bit SCM is selected as the central processor of the reactive power compensation
controller, the MSP430F149 microcontroller is selected as the switching control unit, and the adopts
TMS320F2802 digital processor is selected as the inverter controller chip.
Figure 6. Schematic diagram of controller of reactive power compensation device
4. Control software design
4.1. Main process of reactive compensation control mode
When the compensation device is started, the lower limit value cosφA and the upper limit value cosφB
of the power factor shall be set first, and the mark D of the capacitor shall be initialized (if the capacitor
is not put into operation, D is 0, put into operation is 1). The controller shall collect the voltage and
current data of the access point in real time, and calculate the active, reactive and power factor cosφ.
When the cosφ is lower than cosφA, the capacitor connected sub process shall be executed, and
appropriate amount of capacitance shall be connected according to the difference between cosφA and
cosφ, or (and) raise the capacitor voltage to make the power factor meet the requirements. When the
reactive power is inverted (Qs<0) after the capacitor is put into operation, the capacitor cut-off
subprocess is started to reduce the compensation power; if the reactive power direction is positive
(Qs>0) and the power factor exceeds the upper limit cosφB, the capacitor voltage is reduced to stabilize
the power factor between cosφA and cosφB. Reactive compensation control flow is shown in figure 7.
4th International Symposium on Resource Exploration and Environmental Science
IOP Conf. Series: Earth and Environmental Science 514 (2020) 042064
IOP Publishing
doi:10.1088/1755-1315/514/4/042064
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Start
Measuring
line voltage
and current
Calculation Ps
Qscosφ
QL
cosφ<cosφA&
Qs>0 or not
Qs<0 or not?
cosφ>cosφB or
not?
End
Yes
Yes
Yes
No
No
No
Reduce the
capacitor voltage
Set cosφAcosφB
capacitor switching mark
DC=0 , Dk=0
Capacitor cutted
subprocess
Capacitor Connected
subprocess
Figure 7. Flow chart of reactive power compensation control
4.2. Capacitor switching control sub process
As shown in figure 8 (a), when power factor cosφ< cosφA and Qs>0, the compensation power needs
to be increased to make cosφ rises to cosφA. The capacitor connected sub process judge whether the
mutual compensation part has been put into operation, and then judge either to put in split-phase
compensation part or (and) raise the capacitor voltage to make the power factor meet the requirement.
As shown in figure 8 (b), when reactive power is inverted (QS<0), the compensation power needs
to be reduced. The capacitor cut-off sub process judge whether to exit the mutual compensation part,
and then judge either to exit capacitor of split-phase compensation part; or (and) reduce the capacitor
voltage to make the power factor meet the requirement.
4th International Symposium on Resource Exploration and Environmental Science
IOP Conf. Series: Earth and Environmental Science 514 (2020) 042064
IOP Publishing
doi:10.1088/1755-1315/514/4/042064
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Start of capacitor connected
QL>QC or not
Connect the mutual
compensation part
DC=1
No
Yes
QL=QL-QC
DC=0 or not
Yes
No
J=Dk·k
J=0 or not
QL>Q4 or
|Q4-QL|<Q1 or not?
QL>Q2 or
|Q2-QL|<Q1/2 or not?
Connect the
capacitance C4
D4=1
Connect the
capacitance C2
D2=1
Connect the
capacitance C1
D1=1
J=7 or not
Increase the
capacitor
voltage
Yes
QL<1.5Qk·D
No
Q=QL-Qk·D k
End
Q>Q4 and
D4=0 or not
Connect the
capacitance C4
D4=1
Q>Q2 and
D2=0 or not
Connect the
capacitance C2
D2=1
Connect the
capacitance C1
D1=1
Yes
Yes No
No
Yes
No
No
Yes
Yes
Yes
No
Start of capacitor cut-off
D1+D2+D4=0 or not
Cut The
capacitance
C4
D4=0
End
-QS>Q4/2&
D4=1 or not?
Cut the mutual
compensation
Part
DC=0
-QS>Q2/2&
D2=1 or not?
Cut The
capacitance
C2
D2=0
-QS>Q1/2&
D1=1 or not?
Cut The
capacitance
C1
D1=0
Reduce the
capacitor voltage
DC=0 or not
No
Yes
Yes
Yes
Yes
No
No
No
No
Yes
(a) Capacitor sub process (b) Capacitor cutting sub process
Figure 8. Capacitor switching control flow chart.
4.3. Dynamic regulation sub process of capacitor power
The device calculates the power and power factor cosφ by sampling the bus voltage and current value,
calculates cosφA-cosφ and cosφ-cosφB, and decides to increase or decrease the output power of the
capacitor according to the calculation result, and drives the inverter to change the output voltage, thus
changes the capacitor compensation power, so that the power factor meets the set range. The
regulation flow of capacitor output power is shown in figure 9.
4th International Symposium on Resource Exploration and Environmental Science
IOP Conf. Series: Earth and Environmental Science 514 (2020) 042064
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doi:10.1088/1755-1315/514/4/042064
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Initialize system
clock
Start
increase the voltage
and output power of
capacitor
Calculated power
and cosφ
Bus voltage
and current
sampling
End
cosφA-cosφ>0 or
not?
No
Yes
cosφ-cosφB>0 or
not?
Reduce the voltage and
output power of
capacitor
No
Yes
Figure 9. Flow chart of capacitor output power regulation
5. Simulation verification
Matlab / Simulink platform is used to build the system model based on figure 1 and the control system
model based on figure 4, and the examples of putting capacitor into operation, increasing the capacitor
voltage and reducing the capacitor voltage are simulated respectively. The parameters involved in the
examples are shown in Table 1.
Table 1. Simulation model parameters.
The parameter
Parameter selection
The parameter
Parameter selection
Rated voltage of power supply
400
Filter capacitor
10μF
Rated voltage of three-phase load
380
cosφA, cosφB
260
DC supply voltage
100V
kp, ki
0.737, 32.2349
switching frequency
50 kHz
Single phase minimum
compensation capacity
5kVar
Filter inductance
2mH
1) In the case of absence of reactive power, the device automatically connects the compensation
capacitor and adjusts the capacitor voltage to increase the reactive power. The simulation scenario 1
is set: the initial active power of load is 50kW and the reactive power is 33kVar. The load power
remains unchanged, and the device automatically adjusts the compensation power. Among them, the
mutual compensation part is put into operation at 1.5s, and the compensation capacity is 15kVar. The
simulation results are shown in figure 10:
4th International Symposium on Resource Exploration and Environmental Science
IOP Conf. Series: Earth and Environmental Science 514 (2020) 042064
IOP Publishing
doi:10.1088/1755-1315/514/4/042064
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(a) Voltage variation curve (b) Power factor variation curve
t/s
QC/kvar
0
5
10
15
20
11.5 2 2.5
(c) Variation curve of reactive power (d) Variation curve of capacitor power in
on supply side split-phase compensation part
(e) Variation curve of capacitor voltage of split-phase compensation part
Figure 10. Simulation results of scenario 1
From the simulation results in figure 10, it can be seen that:
The compensation device is not started before 1.5s, and the reactive power required by the load is
completely provided by the power supply, resulting in a lower power factor.At 1.5s, the 15kVar
compensation power is provided by the mutual compensation part, so that the power factor rises to
0.94. At 1.7s, split-phase compensation part put 10kVar capacitance in, and the power factor rises to
0.988. At 2s, the device automatically adjusts the capacityors voltage of split-phase compensation part,
so that its peak voltage rises from 311V to 353V, the output power of the capacitor increases to 13kVar,
and the power factor reaches 0.99.
2) The reduction of load power causes the power factor to cross the upper limit, and the device
adjusts the capacitor voltage to reduce the reactive output. The simulation scenario 2 is set: At 3s,
active power reduction to 43kW and reactive power reduction to 30kVar.At 4s, the active power is
reduced to 36kW and the reactive power to 26kVar. The simulation results are shown in figure 11:
t/s
cos
φ
2.5 3 3.5 4 4.5 5
0.98
0.99
1
0.999 0.9957
(a) Voltage variation curve (b) Power factor variation curve
(c) Variation curve of reactive power (d) Variation curve of capacitor power in
on supply side split-phase Compensation part
t/s
1
204
208
212
216
220
U/V
1.5 2 2.5
t/s
cos
φ
0.99
11.5 2 2.5
0.8
0.85
0.9
0.95
1
t/s
QC/kvar
0
7
14
21
28
35
1 1.5 2 2.5
t/s
UC/V
1 1.5 2 2.5
-400
-200
0
200
400
t/s
U/V
2.5 3 3.5 4 4.5 5
212
216
220
224
228
t/s
QS/kvar
2.5 3 3.5 4 4.5 5
-3
0
3
6
9
t/s
QC/kvar
2.5 3 3.5 4 4.5 5
0
5
10
15
20
4th International Symposium on Resource Exploration and Environmental Science
IOP Conf. Series: Earth and Environmental Science 514 (2020) 042064
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doi:10.1088/1755-1315/514/4/042064
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(e) Variation curve of capacitor voltage of split-phase compensation part
Figure 11. Simulation results of scenario 2
It can be seen from figure 11 that after the reactive power of the load is reduced to 30kVar, the
compensation device remains in the previous working state, and the power factor rises to 0.9965;
because the power factor exceeds the upper limit value of 0.996, voltage regulating device is out of
operation the at 3.2s, and the power factor drops to 0.994. At 4s, reactive power of the load reduce to
26kVar, as can be seen from figure 11 (b), the power factor is larger than 0.996, therefore, the
capacitor voltage of split-phase compensation part is reduced by the inverter, and the compensation
power is reduced from 10.8kVar to 6.7kVar, and the power factor is reduced to 0.9957.
3) The change of load causes reactive power to be reversed. The device removes the capacitor and
adjusts the voltage to make the power factor meet the requirements. The simulation scenario 3 is set:
The active power of the load is 77kW, and the reactive power is 35kVar, and the capacitors of mutual
compensation part and C1, C2 which belong to split-phase compensation part are put into operation.
At 7.5s, active power and reactive power are reduced to 67kw and 27kVar respectively. The
simulation results are shown in figure 12:
(a) Voltage variation curve (b) Power factor variation curve
(c) Variation curve of reactive power (d) Variation curve of capacitor power in
on supply side split-phase compensation part
(e) Variation curve of capacitor voltage of split-phase compensation part
Figure 12. Simulation results of scenario 3
It can be seen from figure 12 that the load power is reduced at 7.5s, and the compensation power
is larger than the reactive power of the load, resulting in a 2.8kVar reverse power, device automatically
t/s
UC/V
2.5 3 3.5 4 4.5 5
-400
-200
0
200
400
t/s
U/V
7 7.5 8 8.5
210
212
214
216
218
220
t/s
cos
φ
0.993
0.994
0.995
0.996
0.997
0.998
0.999
1
7 7.5 8 8.5
t/s
QS/kvar
-4
-2
0
2
4
6
8
10
77.5 8 8.5
t/s
QC/kvar
22.5 3 3.5
2
4
6
8
10
12
14
16
t/s
UC/V
7 7.5 8 8.5
-400
-200
0
200
400
4th International Symposium on Resource Exploration and Environmental Science
IOP Conf. Series: Earth and Environmental Science 514 (2020) 042064
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doi:10.1088/1755-1315/514/4/042064
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cuts off the capacitor C1, and no reverse power is generated, at this time, the power factor is 0.9995.
At 7.9s, the device reduces the capacitor voltage, and the power factor is reduced to 0.9959.
6. Conclusion
The reactive power dynamic compensation device designed for low-voltage power grid can quickly and
effectively reduce the energy loss and improve the quality of power supply.
1) By using the zero-crossing switching circuit and strategy, the switching response time of the
capacitor is less than 100ms, and the inrush current and flashover arc are avoided.
2) The compensation capacity of reactive power can be adjusted continuously by voltage regulation,
which can effectively stabilize the power factor, avoid switching oscillation of capacitor and expand the
compensation range.
3) By changing the output of reactive power through voltage regulation, the switching times can be
reduced and the service life of the switch can be improved.
4) The reactive power that changed by voltage regulation is less, the cost of voltage regulation device
can be controlled.
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When connecting a large number of generating sets into power grid, there will be the harmonic wave generated in power grid causing voltage and current distortion, which affects power quality seriously. Based on the instantaneous reactive power theory, the active current, reactive current and harmonic current can be real-time monitored. The P–Q method can be adopted to control reactive power compensation. By building the converter control model, the variation of reactive power of power grid between photovoltaic grid-connected inverter working under stand-alone mode and grid-connected mode can be analysed via a simulation system. The experimental analysis of reactive power compensation and harmonic suppression, the availability of the control strategy of the photovoltaic grid-connected inverter system can be proved. Using this novel strategy, the photovoltaic grid-connected power system can not only provide active power but also compensate reactive power and suppress harmonic, which will improve power quality.
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A reactive power compensation scheme along with harmonic reduction technique for an unbalanced four-wire system has been addressed in this study. The proposed compensation scheme can mitigate a wider range of thyristor controlled reactor (TCR) injected harmonics and load harmonics up to specified range. The scheme is realised by using a combination of thyristor controlled delta (Δ)-connected and star (Y)-connected static VAr compensator (SVC). Each SVC consists of a TCR and a tuned-thyristor switched capacitor (t-TSC). The proposed SVC scheme can eliminate negative sequence current with source power factor improvement through Δ-SVC and zero sequence current caused by unbalanced load is removed by Y-SVC. For harmonic compensation, the tuned-TSC is used to filter harmonics generated by the non-linear load or due to TCR switching in SVC. An optimised switching function is also adopted in the proposed scheme to minimise TCR harmonic injection in the SVC which reduces the required filter size. The optimised switching angles are computed off-line using gravitational search algorithm and stored in microcontroller memory for on-line applications. The proposed scheme has been validated through proper simulations using MATLAB software backed by suitable experimental results on a practical system.
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A control scheme is proposed for the combined system with the roles of power factor compensation, unbalanced load compensation and harmonic current filtering, which is composed of SVC (Static Var Compensator) mode control and APF (Active Power Filter) control. In SVC mode control, the negative sequence fundamental extractor is used to detect the negative sequence fundamental current of grid and the improved voltage controller is used to realize the voltage stability of PCC. The harmonic components of grid are detected by specified harmonics detection and phase compensation while the frequency dividing compensation for specified harmonics is implemented with the neural cell generalized integrator control. With simple structure and good robustness, the proposed controller adjusts parameters adaptively to improve the tracking performance. Simulative and experimental results show its feasibility and effectiveness.
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