energies Article
Active, Reactive and Harmonic Control for Distributed Energy Micro-Storage Systems in Smart Communities Homes Maria-Isabel Milanes-Montero 1, *, Fermin Barrero-Gonzalez 1 , Jaime Pando-Acedo 1 , Eva Gonzalez-Romera 1 , Enrique Romero-Cadaval 1 and Antonio Moreno-Munoz 2 1
2
*
Department of Electrical, Electronic and Automation Engineering, University of Extremadura, Badajoz 06006, Spain;
[email protected] (F.B.-G.);
[email protected] (J.P.-A.);
[email protected] (E.G.-R.);
[email protected] (E.R.-C.) Department of Computer Architecture, Electronics and Electronic Technology, Universidad de Córdoba, Córdoba 14071, Spain;
[email protected] Correspondence:
[email protected]; Tel.: +34-924-289600
Academic Editor: Rodolfo Araneo Received: 8 February 2017; Accepted: 24 March 2017; Published: 1 April 2017
Abstract: This paper aims to provide control strategies for distributed micro-storage energy systems at the residential level to contribute to smart grid goals. A simulation model of an energy storage system (ESS) charger has been implemented to test these proposed control strategies. The smart community energy management system (SCEMS), acting as an aggregator of resources in the community according to the expected demand and production, sends to each individual home the active and reactive power set-points. Besides, in case the ESS has available capacity, once the SCEMS requirements are satisfied, it is used to absorb the harmonic current components demanded by the household circuitry. It allows a local improvement in the power quality of the demanded current, and thus contributes to the global power quality consumption of the community. Simulation results showing the operation of a local ESS at a home in a Smart Community are presented to validate the proposed control strategies. Keywords: energy storage systems (ESSs); energy management systems; smart communities; micro-storage systems; active control; reactive control; harmonic control
1. Introduction The idea of the so called Smart Communities [1,2] is supported by the following facts: the rising trend in electricity demand, the increase of distributed generation based on renewable resources and the great advance in energy storage systems research. The energy demanded by a community could be provided by the generators owned by the consumers themselves. This can be done either directly (if the time period of consumption match that of the non-manageable energy production) or indirectly by means of an energy storage system. With a proper management, an important savings in the electricity bill will be achieved [3]. Owners of distributed generators, usually non-manageable (photovoltaic or wind units) located in the vicinity of consumers, could take advantage of selling their energy locally, or they can sell electrical energy to the market at time periods in which the price is higher, regardless of the generation timetable [4]. From the point of view of the grid, demand side management and smoothing of the power injected into the grid by the distributed generators, facilitate the distribution grid operation [5]. In this situation, energy storage systems (ESSs) are essential for the energy management system of the smart community [6]. Most of the attention in the technical literature has been paid to the research
Energies 2017, 10, 448; doi:10.3390/en10040448
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on the design of large storage capacity (10–100 MWh) equipment. However, in the last years, research has been focused on the use of distributed micro-storage systems with a smaller capacity (few kWh). These micro-storage systems, shared by several homes in a community, allow consumers to keep stored a small amount of energy to take over the peaks in its demand and to smooth the variability of their own renewable energy supply. A central smart community energy management system (SCEMS) is responsible for the control of these equipment, acting as an aggregator of resources and coordinating them to assure benefits for the whole community. The SCEMS generates and sends to each local ESS the set-points for both active and reactive power for charging/discharging, according to the demand and production. Additionally, these systems should not get worse the power quality. Indeed, most battery chargers for ESS on the market demand harmonic currents and reactive power and, as a consequence, the massive installation of battery chargers leads to a deterioration of power quality in the distribution grid [7]. This shows the need for research into new control strategies applicable to the energy storage management system (ESMS) to guarantee that these chargers operate according to the smart grid goals and policies [8]. The objective of this work is to contribute to this line of research. Thus, control strategies for the ESMS to meet the active and reactive power set-points received from the SCEMS have been proposed. These strategies will improve the performance of the ESS and the quality of the current waveform demanded by the charger. Besides, in case the ESS has got available capacity, once the SCEMS requirements are satisfied, it is used to absorb the harmonic current components demanded by the household circuitry. It allows a local improvement in the power quality of the demanded current, and so contributes to the global power quality consumption of the community. Most bidirectional chargers found in the technical literature focus on the active power flow control and few works address a reactive power flow control. However, the benefits of including a local harmonic control strategy, operating simultaneously with the active and reactive controllers, have not been further investigated. The main contributions of the paper are:
• • •
The proposal of a strategy to control fundamental reactive power, able to operate properly under distorted grid voltage, The harmonic control strategy with saturated function, to assure the charger safety, The combination of the active, reactive and harmonic control in a global control strategy which allows the charger to operate simultaneously with P, Q and H control, and the validation by simulation of this global strategy.
The paper is structured in the following manner: first, the control strategies to control active power (P mode) and reactive power (Q mode) are presented. Then, the harmonic control (H mode) is added with the aim of compensating the harmonic consumption of the homes, contributing to improve the power quality of the network. These strategies have been implemented in a simulation model of an energy micro-storage system located at a home of a smart community. A set of simulation tests has been carried out showing the effectiveness of the strategies in different practical situations. 2. Control Strategies The control strategies are the general rules that must be followed by the control system in order to achieve the desired converter behavior. 2.1. Active Power The SCEMS will manage the local ESS at homes, by sending an active power set-point to each individual ESS, according to previous market negotiations. Two modes of operation can be distinguished: Grid to battery mode (G2B-P mode) when the ESS is extracting active power to charge the batteries, and Battery to grid mode (B2G-P mode), when the ESS is injecting active power from the
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batteries into the grid. The sign criterion for the set-point is positive in the G2B-P mode (Pref > 0), and negative in the B2G-P mode (Pref < 0). A Direct Sinusoidal Current (DSC) control strategy is proposed [9]. This strategy aims to do that the current demanded or injected into the grid to be in phase with the fundamental component of the grid voltage. It guarantees, on the one hand, that the ESS will operate with unity displacement power factor (dPF), and on the other hand, that the charger current will have no harmonic content. The reference charger current is [9]: ich− P,re f =
Pre f 2 US1
uS1d
(1)
where US1 is the fundamental component of the grid voltage and uS1d is the instantaneous value of the fundamental component of the grid voltage. A single-phase Second-order Generalized Integrator Phase-Locked-Loop (SOGI-PLL) system [10] is employed to extract the fundamental component of the grid voltage. 2.2. Reactive Power Local ESS at homes of smart communities can be used as distributed storage sources to provide voltage control or to improve globally the power factor of the community. Thereby, the SCEMS is responsible for calculating a fundamental reactive power set-point, Q1ref , for each individual ESS. The modes of operation are G2B-Q mode, when the ESS is absorbing fundamental reactive power from the grid (Q1ref > 0) and B2G-Q mode, when it is injecting fundamental reactive power to the grid (Q1ref < 0). A novel quadrature sinusoidal current (QSC) control strategy is proposed in this case, equivalent to the previous SC strategy, but taking over the reactive power, instead of the active power set-point. This strategy assures that the current demanded or injected into the grid will be sinusoidal and in quadrature with the fundamental component of the grid voltage. The reference charger current with this strategy is obtained as: Q1re f uS1q (2) ich−Q,re f = 2 US1 where uS1q is the instantaneous value of the fundamental source voltage, being +90◦ phase shifted from uS1d . This component can be calculated by using the SOGI-PLL proposed in [10], since the output signals of this single-phase PLL are the fundamental component of the input signal and another component with the same amplitude but with a phase shift of 90◦ . 2.3. Additional Harmonic Control Strategy If the ESS is below 100% capacity, it can be in charge of an additional function concerning the power quality improvement of the current demanded by each home and so, contributing to the global power quality consumption of the community. This harmonic control function has only a unidirectional operation mode, from the charger to the load: Battery to load mode (B2L-H mode). It is important to note that this control strategy does not receive a set-point from the SCEMS, since it proposes a local compensation of the harmonic content demanded by the household circuitry. Since each home in the community has an ESS, this local compensation contributes to achieve a global compensation in the community. A total harmonic compensation (THC) control strategy is proposed. It aims to provide as a harmonic reference charger current the whole harmonic spectrum of the current demanded by the house, neglecting the fundamental frequency. The advantage of this strategy comparing to selective harmonic compensation strategies [11] is that it can be applied for loads with unknown harmonic spectrum and requires more simplified control algorithms.
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If the harmonic reference current added to the current for P and Q control exceeds the nominal 4 of 11 current of the charger, Ich ,n , the reference current has to be limited to prevent overload. The maximum Root Mean Square (RMS) harmonic charger current is obtained from:
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2 2 2 I ch − H , m ax =q I ch (3) ,n − I ch − P − I ch − Q 2 2 2 Ich− H,max = Ich,n − Ich (3) − P − Ich− Q where Ich-P and Ich-Q are the RMS charger current components responsible for the P and Q control, where Ich-P and Ich-Q into are the RMSthis charger components responsible for the P and control, respectively. Taking account limit,current the reference harmonic charger current will beQobtained respectively. Takingexpression: into account this limit, the reference harmonic charger current will be obtained from the following from the following expression: ich − H ,ref = −(iL − iL1 ) if (iL − iL1 )RMS ≤ I ch − H ,max
ich− H,re f = −(i L −IichL1−)H ,max if (i L − i L1 ) RMS ≤ Ich− H,max ich − H if (i − i ) > I ch − H ,max I − H,max ,ref = −(i L − i L1 ) −−ii L1))RMS if (i LL− iLL11 )RMS ich− H,re f = −(i L − i L1 )(i(Li ch RMS > Ich− H,max L
(4) (4)
L1 RMS
where, demanded by by the the house, house, iiL1 its fundamental component, obtained from where, iiLL is is the the load load current current demanded L1 its fundamental component, obtained from the SOGI-PLL and (i L − iL1)RMS is the RMS value of (iL − iL1). the SOGI-PLL and (i − i ) is the RMS value of (i − i ). L
L1 RMS
L
L1
3. 3. ESS ESS Power Power Structure Structure and and Control Control System System A A single-phase single-phase energy energy micro-storage micro-storage system, system, based based on on batteries, batteries, located located at at aa home home of of aa smart smart community has been developed. It receives P and Q set-points from the SCEMS and controls community has been developed. It receives P and Q set-points from the SCEMS and controls the the current current demanded/injected demanded/injectedfrom/into from/intothe thegrid gridusing usingthe theenergy energystored storedininthe thebattery. battery. Topology 3.1. Topology
The ESS has aa single-phase single-phase topology topology (Figure (Figure 1). 1). It It uses uses two two power power converters: converters: one one DC/DC DC/DC the battery and to adapt thethe battery voltage ubat utobatthe converter to manage managethe thecharge chargeand anddischarge dischargeofof the battery and to adapt battery voltage to DC-link voltage UDC ; U and AC/DC converter to interface with thewith AC grid. The grid. DC/DC the DC-link voltage DC; an and an AC/DC converter to interface the AC Theconverter DC/DC −+ has a half has bridge bidirectional buck-bustbuck-bust DC/DC topology, consistingconsisting of two transistors (Sc + and S(S converter a half bridge bidirectional DC/DC topology, of two transistors c c) − inductor L2 (with Lresistance R2 ). TheRAC/DC converter is a full-bridge Voltage Voltage Source Inverter and Sone c ) and one inductor 2 (with resistance 2). The AC/DC converter is a full-bridge Source + , S − , SSa++,, Sa−− +, San − and (VSI) formed four switches and inductor L (with resistance R ). The current Inverter (VSI)by formed by four Sswitches , S b b an inductor L 1 (with resistance R 1). The a a 1 1 b b current drawn grid ich and the current absorbed by the battery drawn from thefrom gridthe is ich andisthe current absorbed by the battery is ibat . is ibat. Sa+
i s ich R1
L1
A
+ us
Sa-
+
Sb+
B Sb-
+
Sc
R2
L2
U DC –
ibat u bat
Sc-
iL House load
Figure 1. Two-stage topology for the ESS bidirectional charger. Figure 1. Two-stage topology for the ESS bidirectional charger.
It is considered a typical consumer having 4.6 kVA contracted power (one of the standard values It is considered a typical consumer having kVA contracted power (oneisofrated the standard values in Spain). It is estimated the ESS to be rated at a4.6 half of that value, so the ESS at 2.3 kVA, 230 in Spain). It is estimated the ESS to be rated at a half of that value, so the ESS is rated at 2.3 kVA, 230 V. V. Therefore, the RMS nominal charger current Ich,n is 10 A and the main parameter values are shown Therefore, the RMS nominalvalues charger current Ich ,n is 10according A and thetomain parameter values are shown in in Table 1. These parameter has been selected the design criteria proposed in [12]. Table 1. These parameter values has been selected according to the design criteria proposed in [12]. Table 1. Main parameter values for the ESS. Parameter R1 L1 C R2 L2 UiBat
Description AC/DC converter’s resistance AC/DC converter’s inductance DC bus capacitor DC/DC converter’s resistance DC/DC converter’s inductance Battery’s initial voltage
Value 1 × 10-3 30 × 10-3 1.1 × 10-3 1 × 10-3 15.6 × 10-3 48
Unit Ω H F Ω H V
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Table 1. Main parameter values for the ESS. Parameter
Description
R1 L1 C R2 L2 UiBat
Value
Ω H F Ω H V
1× 30 × 10-3 1.1 × 10-3 1 × 10-3 15.6 × 10-3 48
AC/DC converter’s resistance AC/DC converter’s inductance DC bus capacitor DC/DC converter’s resistance DC/DC converter’s inductance Battery’s initial voltage
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Unit
10-3
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3.2. Global Global Control Control Strategy Strategy 3.2. The block blockdiagram diagramofofthe thegeneral general control strategy is displayed in the left side of Figure The control strategy is displayed in the left side of Figure 2. The2. The control algorithm requires the measurement of several variables: the source voltage, uSload , the control algorithm requires the measurement of several variables: the source voltage, uS, the load current demanded by the house, i , the battery voltage, U and the DC-link voltage, UDC . L current demanded by the house, iL, the battery voltage, Ubat and thebat DC-link voltage, UDC. In addition, In addition, the other inputs are the set-points P and Q provided by the SCEMS and the RMS ref ref SCEMS and the RMS nominal charger the other inputs are the set-points Pref and Qref provided by the nominal charger current, I which has a known value. controlare or not Q control are the not ,n ch current, Ich,n which has a known value. In case P controlInorcase Q P control required, required, the corresponding set-points are void. If harmonic control is not precise, the i measurement L is cancelled. corresponding set-points are void. If harmonic control is not precise, the iL measurement is cancelled. UDC DC UDC, ref
PI DSC ich-P,ref
Pref
us
iL
SOGI PLL
Qref
U2s1 us1d us1q θ
ich,ref
ich-Q,ref
PLL
iL1
ich UDC
THC
u bat
DBC1
d1
S -a
PWM
S +b S -b
ich-H,ref u bat UDC
BC Pref
S +a
us
QSC
ibat, ref
DBC2
d2
S +c
PWM
ibat
S -c
Figure Figure 2. 2. Block Blockdiagram diagramof of the the control control system system for for both both converters. converters.
One One can can notice notice that that there there are are no no potential potential conflicts conflicts among among the the active, active, reactive reactive and and harmonic harmonic compensation, since each control is devoted to a different component of the charger current. compensation, since each control is devoted to a different component of the charger current.Indeed, Indeed, the the lack lack of of interaction interaction is is one one of of the the advantages advantagesof ofthe theproposed proposedglobal globalcontrol controlstrategy, strategy, which which allows allows the charger to operate simultaneously with P, Q and H control. the charger to operate simultaneously with P, Q and H control. The block obtains obtains U US1,, u S1d and uS1q from the grid voltage uS. The DSC block The SOGI-PLL SOGI-PLL block S1 uS1d and uS1q from the grid voltage uS . The DSC block implements the active power from Equation and adds a signal the control DC control This implements the active power from Equation (1)(1) and adds a signal fromfrom the DC block.block. This block block has the objective of maintain a constant it is constituted (see of the has the objective of maintain a constant DC-linkDC-link voltage;voltage; it is constituted (see at the topatofthe thetop figure) by figure) by a proportional-integral (PI) controller, whose input is the difference between real and a proportional-integral (PI) controller, whose input is the difference between real and desired DC-link desired voltage. QSC and THC blocks below the DSC) the reactive power voltage.DC-link QSC and THC blocks (shown below (shown the DSC) implement theimplement reactive power control from control from (2) and the harmonic from (4), respectively. outputs of Equation (2) Equation and the harmonic control fromcontrol Equation (4),Equation respectively. The outputsThe of these three these three blocks are added to obtain the reference for the AC/DC converter: the reference charger blocks are added to obtain the reference for the AC/DC converter: the reference charger current ich,ref . current ich,ref. The BC block (at the bottom on the figure) divides the Pref by ubat, obtaining the reference current for the DC/DC converter: the reference battery current ibat,ref. 3.3. Switching Signal Generation A dead-beat control technique is used to follow the reference currents ich,ref for the DC/AC converter and ibat,ref for the DC/DC converter. Dead-beat technique is a well-known discrete control
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The BC block (at the bottom on the figure) divides the Pref by ubat , obtaining the reference current for the DC/DC converter: the reference battery current ibat,ref . 3.3. Switching Signal Generation A dead-beat control technique is used to follow the reference currents ich,ref for the DC/AC converter and ibat,ref for the DC/DC converter. Dead-beat technique is a well-known discrete control technique based on the idea of reduce to zero the error in the controlled variable at the end of the control period. Figure 3 illustrates the operation principle applied to follow ich,ref in one switching period TS . At the beginning, ich,ref is compared with the measured or real charger current ich . The evolution of ich is determined by the states of the switches Sa and Sb . Indeed, when Sa + and Sb − are turned on (Sa on-state) UAB = UDC and when Sa − and Sb + are on (Sa off-state) UAB = −UDC ; of course the Energiesof 2017, 448switches of one leg is complementary. Two approximation are considered: on one 6 of 11 operation the10, two hand, voltage across R1 can be ignored compared to uL and, on the other hand, the grid voltage uS can one hand, constant voltage across 1 can be ignored compared to uL and, on the other hand, the grid voltage be considered duringRthe switching period TS . Therefore, an approximately constant voltage u S can be considered constant during the switching period TS. Therefore, an approximately constant is applied to inductance L1 : uS − UDC in the Sa on-state and uS + UDC in the Sa off-state. Taking into voltage to inductance L1: uS − UDC in the Sa on-state and uS + UDC in the Sa off-state. Taking account thatisuapplied L1 = L1 dich /dt, the current ich will be a positive ramp in the first case and a negative into account that u L1 = L1 dich/dt, the current ich will be a positive ramp in the first case and a negative ramp in the second case; in both cases the slope value is 1/L1 . The duty cycle (d1 = Ton /TS ) necessary ramp in the second case; in both cases theofslope value is 1/L1. Thefrom dutythe cycle 1 = Ton/TS) necessary to to achieve ich to be equal to ich,ref at the end TS can be calculated fact(dthat the following achieve i ch to be equal to ich,ref at the end of TS can be calculated from the fact that the following equality equality must be satisfied: must be satisfied: (u − U )d1 TS (uS + UDC )(1 − d1 ) TS − U DC )d+ ( u + U DC )(1 − d1 )TS ich,re f − ich = S ( uDC (5) 1TS ich ,ref − ich = LS1 + S L1 (5) L1
L1
and the resulting expression for d1 will be: and the resulting expression for d1 will be: d1 =
(uS + U ) TS − (ich,re f − ich ) L1 (uDC S + U DC )TS − ( ich ,ref − ich ) L1 d1 = 2 · TS2U⋅ TDCU S
(6) (6)
DC
ThisThis operation is executed by the DBC1 (Dead-Beat Controller 1) in1) Figure 2, whose inputs operation is executed byblock the block DBC1 (Dead-Beat Controller in Figure 2, whose inputs are uare , i , i and U and whose output signal is d . S ch uS, ich,ref ch, ich,ref andDC UDC and whose output signal is1d1.
iCh, ref ich TON
TOFF TS
Figure 3. Dead-beat control technique to follow a reference current. Figure 3. Dead-beat control technique to follow a reference current.
Analogously, the duty forDC/DC the DC/DC converter is obtained, resulting: Analogously, the duty cyclecycle d2 ford2the converter is obtained, resulting: u T − (i
−i
) L2
bat (iS bat ,r ef bat udbat =TS − bat,re f − ibat ) L2 d2 = 2 TSU DC TS UDC
(7) (7)
operation is executed by block the block DBC2 (Dead-Beat Controller in Figure 2, whose inputs ThisThis operation is executed by the DBC2 (Dead-Beat Controller 2) in2)Figure 2, whose inputs are u bat, ibat, ibat,ref and UDC; and whose output signal is d2. Finally, both values d1 and d2 are converted into are ubat , ibat , ibat,ref and UDC ; and whose output signal is d2 . Finally, both values d1 and d2 are converted switches byby means of of thethe Pulse Width into the the corresponding correspondingswitching switchingsignals signalsfor forthe thegates gatesofofthe theconverter converter switches means Pulse Modulation (PWM) blocks: S a+, Sa−,+Sb+, S b− for+the AC/DC converter and S c+, Sc− for the DC/DC converter. − − + − Width Modulation (PWM) blocks: S , S , S , S for the AC/DC converter and S , S for the a
a
b
b
c
c
DC/DC converter. 4. Simulation Results
A simulation model of the ESS has been developed in Matlab-Simulink according to the topology and control system described before. For 10 kHz switching frequency (switching period TS = 10−4 s), the time step for the simulation was taken Tm = 10−6 s. The nominal RMS value of the fundamental grid voltage is 230 V, and the harmonic components are 5% 3rd harmonic, 4.5% 5th harmonic and 4%
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4. Simulation Results A simulation model of the ESS has been developed in Matlab-Simulink according to the topology and control system described before. For 10 kHz switching frequency (switching period TS = 10−4 s), the time step for the simulation was taken Tm = 10−6 s. The nominal RMS value of the fundamental grid voltage is 230 V, and the harmonic components are 5% 3rd harmonic, 4.5% 5th harmonic and 4% 7th harmonic. The total harmonic distortion (THD) is 7.83%, complying with the limits proposed in IEC 61000-2-2:2002 [13]. To demonstrate the behaviour of the system, the simulation has been conducted in four cases:
•
Case A. Charging the battery and demanding fundamental reactive power: Pref = 1800 W and Q1ref = 1400 VAr. House demand without harmonics: IL = 10 A (perfectly sinusoidal, i.e., iLh = 0).
•
Case B. Discharging the battery and injecting fundamental reactive power: Pref = −1800 W and Q1ref = −1400 VAr. House demand without harmonics. IL = 10 A (perfectly sinusoidal, i.e., iLh = 0).
•
Case C. Charging the battery and injecting reactive power: Pref = 1000 W and Q1ref = −600 VAr. House demand with usual odd harmonics contents [14] below 11th order specified in Table 2; with RMS value of load current IL = 4.996 A. Case D. Discharging the battery and demanding reactive power: Pref = −1800 W, Q1ref = 1100 VAr. House demand with the same usual harmonics contents; now with IL = 19.98 A.
•
Table 2. Typical harmonic of house current. Individual Harmonic Distortion (%)
Total Harmonic Distortion THD (%)
HD3
HD5
HD7
HD9
25.3
9.99
12.41
6.83
30.67
Figures 4–7 show the simulation results for every case. From top to bottom and from left to right the figures present: uS , ich , iL , ich-H,ref and iS in steady state and ubat , ibat , ibat-ref , UDC and UDC-ref from their initial values to steady state. It is supposed that the battery is initially charged at its nominal value (48 V). On the other hand, the AC/DC converter is supposed to operate √ initially as a rectifier, so as the DC-link voltage is initially at the corresponding rectified voltage (230 2 = 325 V). Simulation starts at t = 0 and at t = 0.05 s the DC block starts to operate leading the DC-link voltage to its nominal value (600 V); this objective is achieved and then, at t = 0.2 s the all three modes (P, Q and H) are activated. To ease the visualization of transient behavior, the evolution of UDC and UDC-ref are shown from t = 0 to steady state and ubat , ibat and ibat-ref are shown from t = 0.18 to steady state (in this last case to show in more detail the evolution around t = 0.2 s). On the other hand, the evolution of uS , ich , iL , ich-H,ref and iS are shown for two cycles (40 ms) from 2.96 s to 3 s, when the steady state condition is reached. In all cases, the charger current ich follows the reference ich-ref accurately although the source voltage is distorted, so the ESS complies with the limits for harmonic currents produced by equipment connected to public low-voltage systems [15].
200
0
-200
-20 -40 2.96
2.965
2.97
2.975
2.98 t(s)
2.985
2.99
2.995
20
-400 3
-20 2.965
2.97
2.975
2.98 t(s)
2.985
2.99
2.995
3
60
60
Current A
20
Current A
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0
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40
40
,
20
20 0 0.18
3
0.2
0.22
0.24 t(s)
0.26
Voltage V
400
20
Voltage V
40
Current A
Current A
activated. To ease the visualization of transient behavior, the evolution of UDC and UDC-ref are shown from t = 0 to steady state and ubat, ibat and ibat-ref are shown from t = 0.18 to steady state (in this last case to show in more detail the evolution around t = 0.2 s). On the other hand, the evolution of uS, ich, iL, ichH,ref and iS are shown for two cycles (40 ms) from 2.96 s to 3 s, when the steady state condition is reached. In all cases, the charger current ich follows the reference ich-ref accurately although the source voltage Energies 2017, 10, 448 is distorted, so the ESS complies with the limits for harmonic currents produced by equipment connected to public low-voltage systems [15].
0
0.28
Voltage V
Current A
10
,
0
-10 2.96
2.965
2.97
2.975
2.98 t(s)
2.985
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2.995
600 400
,
200 0 0
3
0.2
0.4
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t(s)
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0 0
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2.965 2.965
2.97 2.97
2.975 2.975
10 10 Current A A Current
2.985 2.985
Current A A Current
20 20
2.98 2.98 t(s) t(s)
2.985 2.985
2.99 2.99
2.995 2.995
2.965 2.965
2.97 2.97
2.975 2.975
2.98 2.98 t(s) t(s)
2.985 2.985
2.99 2.99
2.995 2.995
0 0 -20 -20 2.96 2.96
2.965 2.965
3 3
2.97 2.97
2.975 2.975
50 50 0 0
2.98 2.98 t(s) t(s)
2.985 2.985
2.99 2.99
2.995 2.995
3 3
50 50 0 0
, ,
-50 0.18 -50 0.18
3 3
, ,
0 0
-10 2.96 -10 2.96
2.98 2.98 t(s) t(s)
20 20
0.2 0.2
0.22 0.22
0.24 t(s)0.24 t(s)
0.26 0.26
0.28 0.28
Voltage V V Voltage
2.97 2.97
Voltage V V Voltage
Current A A Current
2.965 2.965
-200 -200 -400 3-400 3
Current A A Current
400 400 200 200
Current A A Current
40 40 20 20 0 0 -20 -20 -40 2.96 -40 2.96
Voltage V V Voltage
ref = 1800 W W and 1ref = 1400 VAr. House demand without Figure 4. Simulation Figure 4. Simulation result. result. CaseCase A. PA.refP= 1800 andQQ 1ref = 1400 VAr. House demand without harmonics: IL = 10 A (perfectly sinusoidal). Energies 2017, 10,A 448 8 of 11 harmonics: I = 10 (perfectly sinusoidal). EnergiesL2017, 10, 448 8 of 11
-50 -50
600 600 400 400 200 200 0 00 0
, ,
0.2 0.2
0.4 0.4
t(s) t(s)
0.6 0.6
0.8 0.8
1 1
2.985 2.985
2.99 2.99
2.995 2.995
2.965 2.965
2.97 2.97
2.98 2.98 t(s) t(s)
2.985 2.985
2.99 2.99
2.995 2.995
2.965 2.965
2.97 2.97
2.975 2.975
2.98 2.98 t(s) t(s)
2.985 2.985
2.99 2.99
2.995 2.995
3 3
0 0 -20 -20 2.96 2.96 60 60 40 40 20 20 0 0.18 0 0.18
3 3
, ,
0 0
-10 2.96 -10 2.96
2.975 2.975
20 20
600 600 400 400 200 200 0 00 0
2.965 2.965
2.97 2.97
2.975 2.975
2.98 2.98 t(s) t(s)
2.985 2.985
2.99 2.99
2.995 2.995
3 3 60 60
40 40
, ,
20 20 0.2 0.2
0.22 0.22
0.24 t(s)0.24 t(s)
0.26 0.26
0.28 0.28
0 0
Voltage VV Voltage
2.98 2.98 t(s) t(s)
Current Current AA
2.975 2.975
Voltage VV Voltage
Current Current AA
2.97 2.97
0 0
-20 2.96 -20 2.96 10 10
Current Current AA
2.965 2.965
-200 -200 -400 3 -400 3
Current AA Current
400 400 200 200
Current Current AA
40 40 20 20 0 0 -20 -20 -40 2.96 -40 2.96 20 20
Voltage VV Voltage
Figure 5. Simulation Case B. = Pref = −1800 W W and QQ 1ref = −1400 VAr. House demand demand without Figure 5. Simulation result. result. Case Pref = −1400 VAr. House without Figure 5. Simulation result. B. Case B. Pref−=1800 −1800 W and and Q1ref1ref = −1400 VAr. House demand without harmonics. IL = 10 A (perfectly sinusoidal). harmonics. harmonics. IL = 10 AIL(perfectly sinusoidal). = 10 A (perfectly sinusoidal).
, , 0.2 0.2
0.4 0.4
t(s) t(s)
0.6 0.6
0.8 0.8
1 1
Figure 6. Simulation result. Case C. Pref = 1000 W and Q1ref = −600 VAr. House demand with usual
Figure 6. Simulation Case C. Pref = 1000 W and Q1ref = −600 VAr. House demand with usual Figure 6. Simulation result.IL =result. Case harmonics content; 4.996 C. A. Pref = 1000 W and Q1ref = −600 VAr. House demand with usual harmonics content; IL = 4.996 A. harmonics content; IL = 4.996 A.
9 of 11
400
40
20
200
20
-200
-20 -40 2.96
-400 2.965
2.97
2.975
2.98 t(s)
2.985
2.99
2.995
20 0
-20 2.965
2.97
2.975
2.98 t(s)
2.985
2.99
2.995
2.97
2.975
2.98 t(s)
2.985
2.99
2.995
3
50
,
0
2.965
2.97
2.975
2.98 t(s)
2.985
2.99
2.995
0
0
, -50 0.18
3
Voltage V
Current A
10
-10 2.96
2.965
50
Current A
Current A
40
-40 2.96
0 -20 -40 2.96
3
9 of 11
0.2
0.22
0.24 t(s)
0.26
Voltage V
0
Current A
40
Voltage V
Current A
Energies 2017,Energies 10, 448 2017, 10, 448
-50
0.28
600 400
,
200 0 0
3
0.2
0.4
0.6
0.8
1
t(s)
Figure 7. Simulation ref = = 1100 VAr.VAr. HouseHouse demanddemand with usual Figure 7. Simulation result.result. CaseCase D. PD.refP= −−1800 1800 W, W,QQ1ref1ref = 1100 with usual IL = 19.98 A. harmonicsharmonics contents;contents; IL = 19.98 A.
In cases A (Figure 4) and B (Figure 5) ich-H,ref is null, so H function is not needed and, therefore, the charger draws a current (is) that differs from sinusoid only is in not the switching In cases A (Figure 4)from andthe B grid (Figure 5) ich-H,ref is null, soaH function neededripple. and, therefore, In case C (Figure 6) the requirements from the SCEMS and the harmonic content of the house is the charger draws from the grid a current (is ) that differs from a sinusoid only in the switching ripple. compatible with the ESS nominal current, so the ESS performs a full compensation and the current In case C demanded (Figure 6)from thethe requirements SCEMSonly and harmonic content of the house is grid (iS) differsfrom from athe sinusoidal in the the switching ripple. Its harmonic content shown Table 3. Ascurrent, one can see, reduced from 30.67% to compensation 2.94%. On the otherand hand, compatible withisthe ESSinnominal soTHD the isESS performs a full the current case D (Figure 7) the requirements are such that itonly is notinpossible to fully attend to the harmonic demandedinfrom the grid (i ) differs from a sinusoidal the switching ripple. Its harmonic content S compensation requirement, so ESS performs a partial compensation and in this case the current is shown in Table 3. As one can see, THD is reduced from 30.67% to 2.94%. On the other hand, in case D demanded from the grid (iS) is not sinusoidal. Its harmonic content is shown in Table 4. As one can (Figure 7) the are14.56%. such that it is not possible to fully attend to the harmonic compensation see, requirements THD is reduced to
requirement, so ESS performs a partial compensation and in this case the current demanded from the 3. Load and grid current harmonic content for case C. grid (iS ) is not sinusoidal. ItsTable harmonic content is shown in Table 4. As one can see, THD is reduced Total RMS Value (A) Individual RMS Value (A) to 14.56%. Variable THD (%) Load current iL Table 3. Grid current iS
Variable
Load
I 4.996 and grid 9.244
I1 I3 I5 I7 I9 4.78 1.21 0.48 0.59 0.33 current harmonic content for case 30.67% C. 9.24 0.19 0.09 0.14 0.1 2.94%
Total RMSTable Value4.(A) Individual RMS Value (A) Load and grid current harmonic content for case D. I Variable
I
Total RMS Value1 (A) I 4.78 19.98 13.405
I
I
I
3 5 Value (A) 7 Individual RMS I1 I3 I5 I7 I9 1.21 0.48 0.59 19.11 4.83 1.91 2.37 1.31 13.26 1.56 0.62 0.82 0.49
THD (%) I9 THD (%)
Load 4.996 0.33 30.67% current iL Load current iL 30.67 Grid Grid current iS 14.56 9.244 9.24 0.19 0.09 0.14 0.1 2.94% current iS Power terms according to power definitions proposed in Std. IEEE-1459:2010 [16] are collected in Table 5 for the four cases. S is the apparent power, P is the active power, N is the non-active power, Table 4. Load and grid current harmonic content for case D. Q1 is the fundamental reactive power, PF is the power factor and dPF is the displacement power factor. Total RMS Value (A) Individual RMS Value (A) THD (%) Variable I I1 I3 I5 I7 I9 Load current iL Grid current iS
19.98
19.11
4.83
1.91
2.37
1.31
30.67
13.405
13.26
1.56
0.62
0.82
0.49
14.56
Power terms according to power definitions proposed in Std. IEEE-1459:2010 [16] are collected in Table 5 for the four cases. S is the apparent power, P is the active power, N is the non-active power, Q1 is the fundamental reactive power, PF is the power factor and dPF is the displacement power factor.
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Table 5. Power terms according to Std. IEEE-1459:2010. Case
S (VA)
P (W)
N (VA)
Q1 (VAr)
PF
dPF
A B C D
2349 2335 1228 2273
1804 −1796 1002 −1797
1504 1493 709.4 1391
1503 −1503 −593.6 1072
0.768 0.769 0.8162 0.7907
0.774 0.773 0.866 0.8602
5. Conclusions Control strategies for local energy micro-storage systems regarding active power and reactive power control in the homes of smart communities have been proposed. Additionally, a control strategy to reduce harmonic content in the current demanded by the houses is presented. This control only comes into operation once the ESMS verifies that the ESS has available capacity and, if necessary, saturates the harmonic load current compensation to ensure that the charger does not exceed its nominal parameters. The main contributions of the paper are the proposal of the QSC strategy to control fundamental reactive power and the saturated THC strategy, to assure the charger safety. A 2.3 kVA single-phase energy micro-storage system based on batteries, located at a home of a smart community, has been implemented by simulation to test the proposed strategies. Simulation results showing the currents injected/demanded by the ESS charger following the set-points provided by the SCEMS with active, reactive and harmonic control are presented under distorted source conditions. These results validate the correct operation of the proposed control strategies and demonstrate that local ESS in smart communities can contribute to the smart grid goals, providing ancillary services and improving the power quality locally, thanks to the performance of the SCEMS. Acknowledgments: This work was supported by the Spanish Ministerio de Economía y Competitividad and Fondo Social Europeo, FEDER, under Project TEC2013-47316-C3-3-P. Author Contributions: Maria Isabel Milanes-Montero and Fermin Barrero-Gonzalez conceived, designed and supervised the simulation tests and wrote the paper, Jaime Pando-Acedo performed the simulation model and tests, Eva Gonzalez-Romera analyzed the data and simulation results, Enrique Romero-Cadaval contributed analysis tools and supervised the simulation model, and Antonio Moreno-Munoz collaborated with the paper review. Conflicts of Interest: The authors declare no conflict of interest.
Nomenclature di ibat ich ich-P ich-Q, ich-H Ich,n Ich-H,max iL iS Pref Q1ref TS Tm Ubat UDC uS uS1d uS1q
Duty cycle obtained from the dead-beat controller number i Battery current Charger current Charger current with P mode control Charger current with Q mode control Charger current with H mode control Nominal current of the charger Maximum RMS charger current available for H mode control Load current demanded by the house Source or grid current Active power set-point Fundamental reactive power set-point Switching period Time step for simulation Battery voltage DC bus voltage Source or grid voltage Fundamental component of the grid voltage Fundamental component of the grid voltage, +90 degrees phase shifted
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