The proposed FCSMPC provides the
excellent of gridconnected of PV system with the
changes of injected power into grid, the low THD
of grid current and the good DClink capacitor
voltage balance. Using the proposed FCSMPC
can achieve flexible to choose the switching
frequency for the threelevel TType NPC to
enhance the efficiency of system while still
guaranteeing about the problems concerned with
the power quality as: DClink capacitor voltage
balance and THD of grid current. The proposed
FCS–MPC only uses 27 switching states to
calculate the cost function, considerably reduces
the computation amount to enhance the efficiency
of the proposed FCSMPC. In addition, the
proposed FCS–MPC is simple and easy to control
in comparison with the traditional PWM for the
control of DClink capacitor voltage balance with
the constant switching frequency [3].
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TAÏP CHÍ PHAÙT TRIEÅN KH&CN, TAÄP 18, SOÁ K6 2015
Finite control set model predictive control to
balance DClink capacitor voltage for T
Type NPC inverter of gridconnected
photovoltaic systems
. Phan Quoc Dzung
. Nguyen Dinh Tuyen
. Nguyen Minh Nhat
Ho Chi Minh city University of Technology, VNUHCM, Vietnam
(Manuscript Received on July 15, 2015, Manuscript Revised August 30, 2015)
ABSTRACT
This paper proposes the Finite control set function of the proposed FCSMPC uses the
Model Predictive Control (FCSMPC) with 27 possible switching states generated by T
delay compensation for threephase three Type NPC, the optimal switching state is
level TType NPC inverter (TType NPC) of selected in each sampling time that
gridconnected photovoltaic systems (PV). minimizes the cost function. The proposed
The proposed FCSMPC controls the FCSMPC has also proposed the delay
objectives: current tracking control, DClink compensation with twostep prediction
capacitor voltage balance, the reduction of horizon at time k+2 to reduce the total
switching frequency to ensure issues of the harmonic distortion (THD) of the grid current.
power quality and improve the efficiency of The proposed FCSMPC is verified by using
gridconnected of PV system. The cost Matlab/Simulink.
Keywords: Finite control set Model predictive control, reduction of switching frequency, DC
link Capacitor voltage balance, TType NPC, PV system.
1. INTRODUCTION
In the recent decades, photovoltaic system these disadvantages, the threephase threelevel
(PV system) quickly has been developed about the TType Neutral Point Clamp inverter (TType
installed power, as well as the penetration into the NPC), shown in Figure 1, is proposed, which has
electrical grid. Photovoltaic is the distributed the advantages about the low THD of output
generation, thus the stability when connecting the current, high efficiency with switching frequency
grid with the photovoltaic is a problem that worth in 4kHz30kHz, small size, low investment cost
to concern about at this moment. Due to the [1], [2], [3].
restrict of the twolevel inverter is the output The structure of a TType NPC includes two
current with high THD distortion, the large size DClink capacitors connected in series, thus the
filters is chosen, however which causes some small voltage vectors and medium voltage vectors
problems: reduction of the efficiency of PV of TType NPC produce the voltage oscillations
system, high cost, bulky system [1], [2]. To solve
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SCIENCE & TECHNOLOGY DEVELOPMENT, Vol.18, No.K6  2015
of the midpoint “O” of dclink capacitor, making FCSMPC has presented with the limited
the unbalanced DClink capacitors [5], [6]. The switching states of the converter for solving the
voltage oscillations of the midpoint of dclink optimization problem from a discrete model of the
capacitor voltage causes the voltage stress on the system [8], [10], [11], [14], [15]. Many researches
capacitors and the semiconductor devices [4], [5]. with FCSMPC have been presented for current
Namely the failure in switching and the increase tracking control and DClink capacitor voltage
of THD of output current, due to the loworder balance [10], [13], [21], [14]; current tracking
harmonics of output voltage [3], [5], [6]. Pulse control and reduce switching frequency [7]. The
width modulation (PWM) is used to balance FCSMPC with delay compensation (twostep
prediction horizon) has presented to reduce the
capacitor voltage with threelevel NPC inverter
THD of current [8], [11], [14], [15]. The FCS
[4]; threelevel TType NPC [2], [3], [5].
MPC with delay compensation will cause a big
However, the PWM algorithm has the complex
quantity of switching states due to twostep
calculation and is not easy to implement for the
prediction horizon: k+1, k+2, for threelevel T
controlled objects that are nonlinearities and have
Type NPC, number of the switching states can
many constraints [7], [8].
correspond to 272 = 729, the computation amount
to select optimal switching state is massive.
This paper focuses on the control for the
objectives of gridconnected of PV system:
current tracking control, balancing dclink
capacitor voltage, the reduction of switching
frequency by using the proposed FCSMPC with
delay compensation. In order to reduce the
computation amount, this paper proposes that the
values of current and dclink capacitor voltages at
Figure 1. Threelevel TType NPC inverter for three
time k+1, will be estimated based on the optimal
phase gridconnected of PV system
switching state at time k1, then use these
Model predictive control (MPC) bases on the estimated values to predict the values at time k+2.
good mathematical model of system to support the Therefore, the proposed FCSMPC only chooses
exact and complete the prediction about the future 27 switching states of TType NPC for twostep
behaviors of system in control. In addition, the prediction horizon for the reduction of the
development of the microprocessor’s speed computation amount in comparison [8], [15]. The
allows calculating quickly the MPC [9], [10]. This optimal switching state is selected that minimizes
makes MPC more and more popular in many the cost function of the proposed FCSMPC. The
fields of the power electronics. MPC have distinct change of weighting factor in the interrelationship
advantages: simple, easy to implement, well between the objectives of cost function, will prove
control with the systems that are nonlinear and the flexibility of the proposed FCSMPC for
have many constraints, fast responds with solving the problems of power quality and
changing of the system, sustainable when enhancing efficiency of gridconnected for PV
compared to the classic control uses the system via the reduction of switching frequency.
proportional  integral controller (PI) and the 2. MODEL OF TTYPE NPC FOR GRID
PWM modulators [8], [9], [11], [12]. CONNECTED OF PV SYSTEM
2.1 Model of the system
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TAÏP CHÍ PHAÙT TRIEÅN KH&CN, TAÄP 18, SOÁ K6 2015
TType NPC for gridconnected of PV Grid current and grid voltage vector are
system using Lfilter is illustrated in Figure 1, the defined [14], [17]:
dclink voltage is assumed constant, we have the 2 2
i() ia ai b a i c (5)
relation between voltage and current of grid 3
connected of PV system in (1) [11], [14], [17]:
2 2
e() ea ae b a e c (6)
di 3
v La Ri e v
aodt a a No With,
2 2
di (v av a2 v ) v (1 a a 2 ) 0 (7)
v Lb Ri e v (1) 3No No No 3 No
bodt b b No
From (4) (5) (6) (7), mathematical model of
di
v Lc Ri e v the gridconnected for PV system is rewritten:
codt c c No di
v L Ri e (8)
ia, ib, ic : grid current dt
Equation (8) demonstrates the mathematical
ea, eb, ec : grid voltage
model of the gridconnected for PV system with
L,R : filter inductance and filter resistance of
TType NPC inverter. With the voltage vector is
Lfilter
defined by (2), there are totally 19 separate
vao, vbo, vco : output voltage of TType NPC voltage vectors for corresponding to 27 switching
The voltage vector of TType NPC is defined: combinations of TType NPC as Figure 2.
2 2
v() Vao aV bo a V co (2) 2.2 Gridconnected control for PV system
3j2π/3
Where, a = e Voltage oriented control (VOC) method is
Considering a constant dclink voltage, and proposed to control gridconnected for PV
balanced capacitor voltages, the voltages system. According to [16], the instantaneous
generated by the TType NPC at the inverter active and reactive powers in the rotating dq frame
terminals are obtained in (3) and Table 1 [14]. injected into the grid by PV system are given in
V
VS dc (3) (9):
xo x 2
Table 1. Switching state of TType NPC,
with x = a, b, c [1]
Switching status Output
Switching states
voltage
(Sx)
Sx1 Sx2 Sx3 Sx4 (Vxo)
1 1 1 0 0 Vdc/2
0 0 1 1 0 0
1 0 0 1 1 Vdc/2 Figure 2. Voltage vectors and switching states can be
generated by a TType NPC
From (2), equation (1) is rewritten: 3
P() e i e i (9)
d 2 2 2 d d q q
vL( ( iaiai 2 )) R ( ( iaiai 2 ))
a b c a b c 3
dt 3 3 (4) Q() e i e i
2 2 2 q d d q
()()e ae a2 e v av a 2 v
3a b c 3 No No No
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SCIENCE & TECHNOLOGY DEVELOPMENT, Vol.18, No.K6  2015
ed, eq: grid voltage in the rotating dq frame The proposed FCSMPC for TType NPC of
id, iq : grid current in the rotating dq frame the gridconnected of PV system is illustrated in
Figure 4. The proposed FCSMPC for TType
Assuming that the d axis is perfectly aligned
NPC of the gridconnected of PV system uses 27
with the grid voltage, thus eq = 0. The active
switching states corresponding to 19 separate
power and reactive power are rewritten:
voltage vectors as Figure 2. The optimal switching
3
P e i state is selected that minimizes the cost function.
2 d d
(10) The proposed FCSMPC for gridconnected of PV
3
Q e i system produces the optimized switching state
2 d q
From (10), we can independently control directly to the TType NPC, without using the
modulation techniques such as CBPWM or
between active and reactive powers with id and iq
currents. We assume that: the dclink voltage is Space Vector Modulation (SVM).
constant, delivering symmetrical and balanced ac The proposed FCSMPC for gridconnected
currents to the grid, so we can skip the calculation of PV system has two main assumptions: keeping
*
of the reference grid current (i dq) [13]. In this the stable DClink voltage, symmetrical and
* *
paper, we only choose i dq as an external reference balanced grid voltages, so we treat only i dq(k) for
for implementing the proposed FCSMPC, as controlling the gridconnected of PV system, not
shown in Figure 4. operating in islanded case with grid systems.
3. THE PROPOSED FCSMPC From Figure 4, grid voltage and grid current are
measured at time k, which are used for predicting
3.1 Finite control set model predictive
the grid current at time k+2 and the predicted grid
control (FCSMPC) with delay
current shows in stationary αβ frame. The
compensation
reference grid current in the dq frame have to
FCSMPC for the current tracking control show in stationary αβ frame for implementing the
presented in [11], [14]. x*(k) represents the proposed FCSMPC, so we use PhaseLocked
reference values of the desired control object, x(k) Loop block (PLL) to synchronize the phase angle
is the measured value at time k, x(k+2) is the (θ) between the grid system and the PV systems
predicted value for possible switching states of T [16]. We use Park and Clark transformations for
Type NPC inverter at time k+2 (twostep the conversion between the abc, αβ, dq frames
prediction horizon). The error between x(k+2) and with phase angle (θ) calculated by PLL blocks.
x*(k) is obtained to minimize the cost function The costfunction of the proposed FCSMPC
and the switching state that minimizes the cost produces the optimal switching state based on the
function will be chosen. FCSMPC block diagram reference grid current and the predicted grid
is illustrated in Figure 3 [9]. current, or other controlled objectives. In this
paper, x(k) presents for the desired control
objectives: grid current, DClink voltage,
switching frequency.
Figure 3. FCSMPC block diagram
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TAÏP CHÍ PHAÙT TRIEÅN KH&CN, TAÄP 18, SOÁ K6 2015
Figure 4. The proposed FCSMPC applies for TType NPC of gridconnected of PV System
3.2 Current tracking control According to the proposed FCSMPC with
Applying a sampling period Ts, the derivative delay compensation, the grid current at k+1 time
of grid current in (8) will be approximated by is estimated based on the grid current and voltage
Euler forward method [14], [17], as follows: current measured at time k, thus the estimated grid
current has the value as (12), meaning ip(k+1) =
di i( k 1) i(k) (11)
i^(k+1), with i^(k+1) is the estimated value at time
dt Ts
k + 1 and v(k) is the optimal voltage vector which
i(k+1) is the predicted grid current at time was calculated at time k1. The estimation value
k+1, i(k) is the value of grid current measured at i^(k+1) will be used for predicting the grid current
time k. From (8), (11) and grid voltage e(k) ip(k+2) at time k+2, considering all possible
measured at time k, the equation of the predicted switching states of TType NPC [14]. The
grid current at time k+1 is rewritten: prediction of grid current at time (k+2) is defined:
RT T p RTs T s
ip ( k 1)(1 s )() i k s (() v k e ()) k (12) i( k 2) (1 ) i ( k 1) ( v ( k 1) e ( k 1))(13)
LL LL
v(k+1) is voltage vector of TType NPC for
v(k) is voltage vector of inverter and considering all possible switching states
depending on the switching states of TType NPC generated by the inverter. e(k+1) is the grid
inverter as (2) and (3), so the predicted grid voltage at time k+1. The value e(k+1) can be
current i(k+1) at each time will vary and depends determined by Lagrange extrapolation formula as
on the switching states. follows [14]:
e( k 1) 3() e k 3( e k 1) e (k2) (14)
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SCIENCE & TECHNOLOGY DEVELOPMENT, Vol.18, No.K6  2015
For a small enough Ts, we can approximate time k1 to thereby calculate switching instants for
e(k+1) ≈ e(k), equation (13) is rewritten: each switching state. The cost function for
RT T
ip ( k 2) (1 s ) i ( k 1) s ( v ( k 1) e ( k )) (15) reducing the switching frequency is defined:
LL g . N
From equation (15) shows that the different 2s w k 2 (22)
switching states of TType NPC inverter will λsw : weighting factor of the reduction of
produce the different values of predicted grid switching frequency
current at time k+2. The cost function for current Nk+2 : the total switching instants is calculated
tracking control is defined with the predicted grid by the change between of each expected switching
current and the reference grid current at time k+2, state of the 27 possible switching states generated
gives in (16): by TType NPC with optimal switching state was
*p 2 * p 2 (16) chosen at time k1.
g1 ( i ( k 2) i ( k 2)) ( i ( k 2) i ( k 2))
p p p (17) 3.4 Balancing DClink capacitor voltages
i( k 2) i ( k 2) ji ( k 2)
*** (18) Assuming the DClink capacitor voltage is
i( k 2) i ( k 2) ji ( k 2)
p p
i α(k+2), i β(k+2) of the predicted grid current constant. From Figure 1, the prediction for the
* * voltage of each capacitor at the time k+1 is [14]:
and i α(k+2), i β(k+2) of the reference grid current
TT
show in αβ frame at time k+2. v( k 1) v (k) s i ( k ) v (k) s i ( k )
C1 C1CC C 1 C1 2 o
The i*(k+2) at time k+2 can be determined by (23)
TT
Lagrange extrapolation formula as follows [14]: v( k 1) v (k) s i ( k ) v (k) s i ( k )
C2 C2CC C 2 C2 2 o
****
i( k 2) 6() i k 8( i k 1) 3i(k 2) (19) vC1, vC2 : DClink capacitor voltage
For a small enough Ts, we can approximate C : capacitance of each DClink capacitor
i*(k+2) ≈ i*(k) [14], [17]. The cost function for
io : current at the midpoint of dclink
current tracking control is rewritten:
capacitor “O”
*p 2 * p 2
g1 (() i k i ( k 2)) (() i k i ( k 2)) (20)
The current at the midpoint of dclink
3.3 Reduction of switching frequency
capacitor “O” can be defined from currents ia, ib,
The switching frequency for MPC is limited ic on each phase at the current time and switching
to half the sampling frequency (fs) [14], [17]. The state depended function Sxo , with switching state
switching frequency is the average switching Sx in Table 1 [14]:
frequency value of power semiconductors of (24)
iko()()()()()()() Skik ao a Skik bo b Skik co c
inverter. Switching frequency for FCSMPC for
Sxo = 1 if Sx=0; Sxo = 0 if Sx = 1 or 1; (25)
TType NPC with 12 power semiconductors
with x = a,b,c
(IGBTs) is calculated [11], [17]:
N (21) The proposed FCSMPC will delay 01
fsw
12*t sampling period (Ts), thus we will predict the
N : the total switching instants of 12 IGBTs
future value k+2 based on the estimated value at
during period of t
the time k+1. DClink capacitor voltage is
t : time of simulation or experiment predicted at time k+2 [14]:
The total switching instants N should be
TTs s
decreased to reduce the switching frequency. vC1( k 2) v C 1 ( k 1) i C 1 ( k 1) v C 1 ( k 1) i o ( k 1)
CC2 (26)
Comparing the 27 switching states of TType TTs s
vC2( k 2) v C 2 ( k 1) i C 2 ( k 1) v C 2 ( k 1) i o ( k 1)
NPC inverter with optimum switching state at CC2
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TAÏP CHÍ PHAÙT TRIEÅN KH&CN, TAÄP 18, SOÁ K6 2015
v(k+1) is the voltage vector corresponding to link=Vdc=700V; fgrid = 50Hz; C1 = C2 = 5mF. To
27 the possible switching states in the proposed demonstrate the flexibility for controlling grid
FCSMPC. The current at the midpoint of dclink connected of PV systems, the reference grid
capacitor “O” at time k+1 is written: current of daxis of the rotating dq frame will have
(27) the different values at different times, and the
iko( 1) Skik ao ( 1)( a 1) Skik bo ( 1)( b 1) Skik co ( 1)( c 1)
reference grid current of qaxis with iqref = 0A;
io(k+1) is defined based on the estimated grid
sample time Ts = 25µs with sampling frequency
current i(k+1) at the time k+1, and Sao(k+1),
fs = 1/Ts = 40kHz applies the proposed FCSMPC:
Sbo(k+1), Sco(k+1) correspond to all of the
switching states of inverter as (25). + t = 0s – 0.2s; idref = 4A, iqref = 0A
The differentiation of DClink capacitor + t = 0.2s – 0.3s; idref = 10A, iqref = 0A
voltage is defined: + t = 0.3s – 0.5s; idref = 6A, iqref = 0A
VDC( k 2) v C1 (k 2) V C2 (k 2) (28) In this paper, weighting factor of the
From the (26) and (28), we have: capacitor voltage balance with λDC = 8 and
Ts weighting factor of the reduction of switching
VDC( k 2) v C1 (k 1) V C2 (k 1) i o ( k 1) (29)
C frequency with λsw = 0.1 và λsw = 1.5 are used to
Cost function for DClink capacitor voltage
compare the responses of the gridconnected of
balance is defined in (34):
PV system.
g ( V ( k 2))2
3 DC DC (30)
The proposed FCS–MPC for TType NPC of
λDC: weighting factor of capacitor voltage gridconnected of PV system provides the fast
balance. response to the power change of system with
3.5 Cost function of the proposed FCS – decoupled control active power (P) and reactive
MPC power (Q) in the rotating dq frame via the current
From (20), (22), (30), the proposed FCS – tracking control. At the time t = 0.2s, the reference
MPC for controlling many objectives: current grid current is ordered to change from idref = 4A
tracking control, balancing the DClink capacitor to idref = 10A, and at the time t = 0.3s, the reference
voltage, reduction of switching frequency with the grid current is ordered to change from idref = 10A
cost function is defined: to idref = 6A, system’s response is fast, as shown
in Figure 5 and Figure 6. Corresponding to the
g g g g
1 2 3 change of power supply, the grid current in abc
*p 2 * p 2 2
(ikik ( ) ( 2)) ( ikik ( ) ( 2)) DC .( Vk DC ( 2)) sw . N k 2 frame in Figure 8, at the time of t = 0.2s and t =
Depending on the priority of the controlled 0.3s, has a fast response and a good current
objectives, we can adjust the weighting factors tracking control.
(λDC, λsw) represented for objectives to obtain the For the proposed FCS – MPC, the reduction
optimal switching state. Some guidelines on of switching frequency shows the interrelation
choosing weighting factor for the desired between the weighting factor of the reduction of
objectives may refer in [18]. switching frequency and weighting factor of
The optimal switching state is selected by the capacitor voltage balance. The switching
minimized of cost function g. frequency of PWM is constant. FCS–MPC
4. SIMULATION RESULTS chooses the optimal voltage vector, minimizes the
cost function, hence there is a independence
The specifications for the system in Figure 1
between sampling frequency and switching
are: R=0.5Ω; L=5mH; Vgrid = 220V; Vdc
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SCIENCE & TECHNOLOGY DEVELOPMENT, Vol.18, No.K6  2015
frequency [7], [14]. We can see that the switching the THD of grid current is higher than
frequency depends on the weighting factors λsw in implemented by λDC = 8, λsw = 0.1, shown in
the cost function. With the same capacitor balance Figure 5(a) and Figure 5(b).
weighting factor λDC = 8, and λsw = 1.5 produces
(A)
(A)
abc
abc
i
i


Grid current current Grid
Grid current current Grid
Time Time (s)
(A)
(A)
ia
abc
abc
i
i

 ib
ic
Grid current current Grid
Grid current current Grid
Time (s) Time
THD = 11.20% THD = 2.81%
(a)
Figure 5. Waveform and THD of grid current in abc frame: (a) λDC = 8, λsw = 1.5; (b) λDC = 8, λsw = 0.1
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TAÏP CHÍ PHAÙT TRIEÅN KH&CN, TAÄP 18, SOÁ K6 2015
(A)
dq
dq
i
i


Grid current current Grid
Grid current current Grid
Time (s) id,P iq,Q Time (s)
(a) (b)
Figure 6. Waveform of grid current in the rotating dq frame: (a) λDC = 8, λsw = 1.5; (b) λDC = 8, λsw = 0.1
(V)
(V)
C2
C2
V
V


C1
C1
= V
= V
DC
DC
ΔV
ΔV
(V)
(V)
C2
C2
V
V


C1
C1
= V =
= V
DC
DC
ΔV
ΔV
C2 (V) C2 (V) C2
Voltage of C1, C1, of Voltage C1, of Voltage
Time (s) Time (s)
VC1 VC2
(a) (b)
Figure 7. The differentiation of DClink capacitor voltage ΔVDC, capacitor voltage of C1
and C2 capacitor: (a) λDC = 8, λsw = 1.5 ; (b) λDC = 8, λsw = 0.1
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SCIENCE & TECHNOLOGY DEVELOPMENT, Vol.18, No.K6  2015
(V)
AB
AB
V

V

Line to line line voltage to Line
Line to line line voltage to Line
Time (s) Time (s)
(a) (b)
Figure 8. Wave form of output voltage of TType NPC inveter  VAB (Line to line voltage  VAB) and VAN
(Voltage of phase A): (a) λDC = 8, λsw = 1.5; (b) λDC = 8, λsw = 0.1
The increasing weighting factor of the
reduction of switching frequency will make the
reduction of switching frequency and the increase
of THD of grid current, as shown in Figure 5,
Figure 9 and Table 2.
Similarly, the increasing weighting factor of
the reduction of switching frequency, the priority
of DClink capacitor voltage balance will
decrease, so the voltage oscillations of the mid
point of dclink capacitor “O” will increase, as
shown in Table 2. With λDC = 8 and λsw = 1.5
produces ΔVDC = 1.2V, as shown in Figure 7(a);
with λDC = 8 and λsw = 0.1 only produces ΔVDC =
Figure 9. The effects of weighting factor of the
0.27V as shown in Figure 7(b). From Table 2 and
reduction switching frequency to: The DClink
Figure 9 (using Microsoft Excel to sketch), with
capacitor voltage balance and THD of grid current
the λDC = 8, the increasing weighting factor of
reduction of switching frequency corresponds to Table 2 shows the independence between the
reduce the switching frequency and increase the sampling frequency and the switching frequency
voltage oscillations of the midpoint of dclink via the control of the interrelation between
capacitor, and the correlation between the voltage objectives: grid current, DClink capacitor
oscillations of the midpoint of dclink capacitor voltage, switching frequency by the cost function
and weighting factor of reduction of switching
of the proposed FCSMPC. With λDC = 8, λsw =
frequency is almost linear. Waveforms of lineto 0,1, the THD of grid current is only 2,81%, the
line voltage of TType NPC is illustrated in Figure DClink capacitor voltage is the best value with
8, which comply with wave forms of output
ΔVDC = 0,27V and the switching frequency is
voltage of TType NPC. 4.99kHz, complying with the switching
frequency for TType NPC with high efficiency
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TAÏP CHÍ PHAÙT TRIEÅN KH&CN, TAÄP 18, SOÁ K6 2015
[1]. The proposed FCSMPC provides the THD of 5. CONCLUSION
grid current to meet the requirements for grid The proposed FCSMPC provides the
connected of PV system as IEEE 1547 and IEC excellent of gridconnected of PV system with the
61727. changes of injected power into grid, the low THD
of grid current and the good DClink capacitor
Table 2. The quantitative of the desired objectives, voltage balance. Using the proposed FCSMPC
with Ts = 25µs, fs = 40kHz can achieve flexible to choose the switching
DClink
Weighting Weighting Switching
THD capacitor frequency for the threelevel TType NPC to
factor of factor of frequency
(%) voltage  enhance the efficiency of system while still
the λDC λsw fsw (kHz)
ΔVDC (V) guaranteeing about the problems concerned with
8 0 6.961 3.07 0.35
8 0.1 4.99 2.81 0.27 the power quality as: DClink capacitor voltage
8 0.3 3.428 3.53 0.4 balance and THD of grid current. The proposed
8 0.5 2.477 4.54 0.55 FCS–MPC only uses 27 switching states to
8 0.7 1.77 5.86 0.8
calculate the cost function, considerably reduces
8 0.9 1.414 7.07 1
8 1.1 1.151 8.95 1.1 the computation amount to enhance the efficiency
8 1.3 0.973 9.82 1.15 of the proposed FCSMPC. In addition, the
8 1.5 0.871 11.2 1.2 proposed FCS–MPC is simple and easy to control
8 1.7 0.781 13.47 1.3
8 1.9 0.712 14.12 1.45 in comparison with the traditional PWM for the
control of DClink capacitor voltage balance with
the constant switching frequency [3].
Giải thuật finite control set model predictive
control để cân bằng điện áp tụ DClink cho
nghịch lưu TType NPC của hệ thống năng
lượng mặt trời kết nối lưới
. Phan Quốc Dũng
. Nguyễn Đình Tuyên
. Nguyễn Minh Nhật
Trường Đại học Bách Khoa, ĐHQGHCM, Việt Nam
TÓM TẮT:
Bài báo này đề xuất giải thuật điều khiển Control (FCSMPC) có bù trễ cho nghịch lưu
dự báo Finite control set Model Predictive 3 pha 3 bậc TType NPC (TType NPC) của
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SCIENCE & TECHNOLOGY DEVELOPMENT, Vol.18, No.K6  2015
hệ thống năng lượng mặt trời kết nối lưới. cắt tối ưu được chọn trong mỗi thời gian lấy
FCSMPC được đề xuất cho điều khiển nhiều mẫu là trạng thái mà ở đó hàm mục tiêu có
đối tượng: điều khiển bám dòng điện, cân giá trị bé nhất. Giải thuật FCSMPC được đề
bằng điện áp tụ DClink, giảm tần số đóng cắt xuất là có bù trễ với hai thời khoảng dự báo
để qua đó đảm bảo các vấn đề chất lượng tại thời điểm k+2 để qua đó giúp giảm méo
điện năng và hiệu suất của hệ thống năng dạng sóng hài của dòng điện lên lưới. FCS
lượng mặt trời kết nối lưới. Hàm mục tiêu của MPC được đề xuất sử dụng phần mềm
FCSMPC sử dụng 27 trạng thái đóng cắt Matlab/Simulink để kiểm chứng.
khác nhau của TType NPC, trạng thái đóng
Từ khóa: Finite control set Model predictive control, giảm tần số đóng cắt, cân bằng điện áp
tụ DClink, nghịch lưu TType NPC, hệ thống năng lượng mặt trời.
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