energies Article
Development of a Novel Bidirectional DC/DC Converter Topology with High Voltage Conversion Ratio for Electric Vehicles and DC-Microgrids Ching-Ming Lai Department of Vehicle Engineering, National Taipei University of Technology, 1, Sec. 3, Chung-Hsiao E. Rd., Taipei 106, Taiwan;
[email protected]; Tel.: +886-2-2771-2171 (ext. 3612); Fax: +886-2-2731-4990 Academic Editor: Neville Watson Received: 3 February 2016; Accepted: 19 May 2016; Published: 26 May 2016
Abstract: The main objective of this paper was to study a bidirectional direct current to direct current converter (BDC) topology with a high voltage conversion ratio for electric vehicle (EV) batteries connected to a dc-microgrid system. In this study, an unregulated level converter (ULC) cascaded with a two-phase interleaved buck-boost charge-pump converter (IBCPC) is introduced to achieve a high conversion ratio with a simpler control circuit. In discharge state, the topology acts as a two-stage voltage-doubler boost converter to achieve high step-up conversion ratio (48 V to 385 V). In charge state, the converter acts as two cascaded voltage-divider buck converters to achieve high voltage step-down conversion ratio (385 V to 48 V). The features, operation principles, steady-state analysis, simulation and experimental results are made to verify the performance of the studied novel BDC. Finally, a 500 W rating prototype system is constructed for verifying the validity of the operation principle. Experimental results show that highest efficiencies of 96% and 95% can be achieved, respectively, in charge and discharge states. Keywords: bidirectional dc/dc converter (BDC); electric vehicle (EV); dc-microgrid; high voltage conversion ratio
1. Introduction In recent years, to reduce fossil energy consumption, the development of environmentally friendly dc-microgrid technologies have gradually received attention [1–7]. As shown in Figure 1, a typical dc-microgrid structure includes a lot of power electronics interfaces such as bidirectional grid-connected converters (GCCs), PV/wind distributed generations (DGs), battery energy systems (BES), electric vehicles (EVs), and so on [4]. They connect together with a high-voltage dc-bus, so that dc home appliances can draw power directly from the dc-bus. In this system, the main function of GCCs is to maintain the dc-bus voltage constant, while in order to ensure the reliability of operation for dc-microgrids, a mass of BES can usually be accessed into the system. Electric vehicles (EVs) can also provide auxiliary power services for dc-microgrids, which makes clean and efficient battery-powered conveyance possible by allowing EVs to power and be powered by the electric utility. Usually, in dc-microgrid systems, when the voltage difference between the EV battery, BES and the dc-bus is large, a bidirectional dc/dc converter (BDC) with a high voltage conversion ratio for both buck and boost operations is required [4,7]. In the previous literatures, BDCs circuit topologies of the isolated [8–10] and non-isolated type [11–23] have been described for a variety of system applications. Isolated BDCs use the transformer to implement the galvanic isolation and to comply with the different standards. Personnel safety, noise reduction and correct operation of protection systems are the main reasons behind galvanic isolation. In contrast with isolated BDCs, non-isolated BDCs lack the galvanic isolation between two sides, however, they offer the benefits of smaller volume, high reliability, etc., so they have been widely used for hybrid power system [24,25]. Energies 2016, 9, 410; doi:10.3390/en9060410
www.mdpi.com/journal/energies
Energies 2016, 9, 410
2 of 25
Energies2016, 2016,9,9,410 410 Energies
2 of 24 24 2 of
ElectricUtility Utility Electric Point of common Point of common coupling (PCC) coupling (PCC)
EV EV SST SST
Bidirectional Bidirectional DC/DC DC/DC Converter Converter
DC home DC home appliances appliances
Bidirectional Bidirectional Grid-Connected Grid-Connected Converter (GCC) Converter (GCC)
DC-Bus DC-Bus
DC/DC Converter DC/DC Converter
AC/DC Converter AC/DC Converter
Bidirectional DC/DC Bidirectional Converter DC/DC Converter
PV PV
Wind Turbine Wind Turbine
Battery Storage Battery Storage
BES BES
DGs DGs
Figure 1. A typical dc-microgrid structure [4]. Figure Figure 1. 1. A A typical typical dc-microgrid dc-microgrid structure structure [4]. [4].
Compared with isolated types, BDCs with coupled-inductors for non-isolated applications Compared isolated types, BDCs withwith coupled-inductors for non-isolated applications possess Compared with isolated types, BDCs coupled-inductors forFurthermore, non-isolated possess simplerwith winding structures and lower conduction losses [12–17]. theapplications coupledsimpler winding structures and lower conduction losses [12–17]. Furthermore, the coupled-inductor possess simpler winding structures andthe lower losses [12–17]. Furthermore, coupledinductor techniques can achieve easily highconduction voltage conversion ratio by adjusting thethe turn ratio techniques can achieve theeasily high voltage conversion ratio by adjusting the turnthe ratio the inductor techniques caneasily achieve the high voltage conversion ratio byofadjusting turnofratio of the coupled-inductor. However, the energy stored in the leakage inductor the coupled inductor coupled-inductor. However, thepower energy stored in et the leakage inductor ofcauses the coupled-inductor. However, the energy stored inal. the leakage inductorofaofthe thecoupled coupled inductor inductor a high voltage spike in the devices. Wai [12,13] investigated high-efficiency BDC, causes a high voltage spike in the power devices. Wai et al. [12,13] investigated a high-efficiency whichautilizes only three to achieve the objective of bidirectional power flow. Also, BDC, the causes high voltage spikeswitches in the power devices. Wai et al. [12,13] investigated a high-efficiency BDC, which utilizes only three to recycle achieve theleakage objective of bidirectional power Also, voltage-clamped technique wasswitches adopted to so that the low-voltage stress which utilizes only three switches to achieve the the objective ofenergy bidirectional power flow.flow. Also, the the voltage-clamped technique was adopted to recycle the leakage energy so that the low-voltage on power switches can be ensured. To reduce the switching losses, Hsieh et al. proposed a high voltage-clamped technique was adopted to recycle the leakage energy so that the low-voltage stress stress on power switches canensured. be ensured. To reduce switching losses, Hsieh al. proposed proposed efficiency BDC with coupled inductor andreduce active-clamping circuitlosses, [16]. InHsieh this reference, a low-power on power switches can be To thethe switching etetal. aa high high efficiency and prototypeBDC waswith built coupled to verifyinductor the feasibly. efficiency BDC with coupled inductor and active-clamping active-clamping circuit circuit [16]. [16]. In In this this reference, reference, aa low-power low-power prototype was to the As shown in Figure 2, Liang et al. [17] proposed a bidirectional double-boost cascaded topology prototype was built built to verify verify the feasibly. feasibly. shown in Figure 2, Liang et proposed aa bidirectional double-boost cascaded topology for aAs renewable energy hybrid supply system, in which the energy is transferred from one stage to As shown in Figure 2, Liang et al. al. [17] [17] proposed bidirectional double-boost cascaded topology another stage toenergy obtain hybrid ahybrid high voltage Hence their conduction are high and requires for aa renewable supply system, in the is from stage for renewable energy supplygain. system, in which which the energy energylosses is transferred transferred fromitone one stageato to large number of components. another stage to obtain a high voltage gain. Hence their conduction losses are high and it requires another stage to obtain a high voltage gain. Hence their conduction losses are high and it requires aa Chen et al. proposed a reflex-based BDC to achieve the energy recovery function for batteries large of components. large number number of[18] components. connected to a low-voltage micro dc-bus system. In [18], a traditional BDC wasfor adopted, Chen proposed reflex-based BDC achieve the energy energybuck-boost recovery function batteries Chen et et al. al. [18] [18] proposed aa reflex-based BDC to to achieve the recovery function for batteries however, the voltage conversion ratio is limited because of the equivalent series resistance (ESR) of connected to a low-voltage micro dc-bus system. In [18], a traditional buck-boost BDC was adopted, connected to a low-voltage micro dc-bus system. In [18], a traditional buck-boost BDC was adopted, the inductors and capacitors and effect of the active switches [19]. however, because of of thethe equivalent series resistance (ESR) of the however,the thevoltage voltageconversion conversionratio ratioisislimited limited because equivalent series resistance (ESR) of inductors and capacitors and effect of the active switches [19]. the inductors and capacitors and effect of the active switches [19]. +
Np
S2
S2
V+L
CL
NpS1
V-L
CL
S1
- Charge State
Ns C2
C2
+
S3
NDs 4 D4
C S3H
CH
VH+ -VH
Discharge State -
Discharge State topology [17]. State Figure 2. Circuit Charge structure of the bidirectional double-boost cascaded
double-boost cascaded topology [17]. Figurethe 2. Circuit theconverter, bidirectional cascaded topology To increase voltagestructure gain ofofthe thedouble-boost capacitors are switched and [17]. it will act as a charge-pump. The main advantage of the switched capacitor-based boost converter is that there is no To increase the voltage gain of the converter, the capacitors are switched and it will act as a charge-pump. The main advantage of the switched capacitor-based boost converter is that there is no
Energies 2016, 9, 410
3 of 25
To increase the voltage gain of the converter, the capacitors are switched and it will act as a of 24 main advantage of the switched capacitor-based boost converter is that 3there is no need of a transformer or inductors. The main drawbacks of this topology are the complexity need of a transformer or inductors. The main drawbacks of this topology are the complexity of the of the topology, high cost, low power level and high pulsating current in the input side [11,21]. topology, high cost, low power level and high pulsating current in the input side [11,21]. In order to In order to increase the conversion efficiency and voltage conversion ratio, multilevel combined the increase the conversion efficiency and voltage conversion ratio, multilevel combined the switchedswitched-capacitor techniques have been proposed to achieve lower stress on power devices [20–23]. capacitor techniques have been proposed to achieve lower stress on power devices [20–23]. As shown As shown in Figure 3, in [22,23] two converters regulated the reasonable voltage conversion ratio with in Figure 3, in [22,23] two converters regulated the reasonable voltage conversion ratio with a simple a simple pulse-width_modulation (PWM) control. However, if a high voltage conversion ratio must pulse-width modulation (PWM) control. However, if a high voltage conversion ratio must be be provided, more power switches and capacitors are indeed required. Furthermore, although the provided, more power switches and capacitors are indeed required. Furthermore, although the extreme duty cycle can be avoided, the input current ripple is large due to their single-phase operation extreme duty cycle can be avoided, the input current ripple is large due to their single-phase which renders these BDCs unsuitable for high current and low ripple applications. operation which renders these BDCs unsuitable for high current and low ripple applications. Energies 2016, 9, 410 The charge-pump.
L1
+
S1 VL
+
S3
L1
+
S3
CH1
CL
L2 VH
VL
S2 S4
-
Discharge State
Charge State
(a)
CL
CH S1
CH2
-
+
S4
VH
S2 C
-
Discharge State
Charge State
(b)
Figure 3. Two multilevel combined the switched-capacitor topologies: (a) circuit structure in [22]; Figure 3. Two multilevel combined the switched-capacitor topologies: (a) circuit structure in [22]; (b) circuit structure in [23]. (b) circuit structure in [23].
The objective of this paper is to study and develop a novel BDC for applications involving EVs The objective of this paper is to study and develop a novel BDC for applications involving connected to dc-microgrids. To meet the high current, low current ripple, and high voltage EVs connected to dc-microgrids. To meet the high current, low current ripple, and high voltage conversion ratio demands, the studied topology consists of an unregulated level converter (ULC) conversion ratio demands, the studied topology consists of an unregulated level converter (ULC) cascaded with a two-phase interleaved buck-boost charge-pump converter (IBCPC). In discharge cascaded with a two-phase interleaved buck-boost charge-pump converter (IBCPC). In discharge state, state, the topology acts as a two-stage cascaded two-phase boosting converter to achieve a high stepthe topology acts as a two-stage cascaded two-phase boosting converter to achieve a high step-up ratio. up ratio. In charge state, the topology acts as two-stage cascaded two-phase bucking converter to In charge state, the topology acts as two-stage cascaded two-phase bucking converter to achieve a high achieve a high step-down ratio. The extreme duty cycle of power devices will not occur for step-down ratio. The extreme duty cycle of power devices will not occur for bidirectional power flow bidirectional power flow conditions, thus not only can the output voltage regulation range be further conditions, thus not only can the output voltage regulation range be further extended but also the extended but also the conduction losses can be reduced. In addition, the two-stage structure benefits conduction losses can be reduced. In addition, the two-stage structure benefits reducing the voltage reducing the voltage stress of active switches, which enables one to adopt the low-voltage rating and stress of active switches, which enables one to adopt the low-voltage rating and high performance high performance devices, thus the conversion efficiency can be improved. The remainder of this devices, thus the conversion efficiency can be improved. The remainder of this paper is organized as paper is organized as follows: first, the converter topology and the operation principles of the studied follows: first, the converter topology and the operation principles of the studied BDC are illustrated in BDC are illustrated in Section 2. Then, steady-state characteristic analyzes are presented in Section 3. Section 2. Then, steady-state characteristic analyzes are presented in Section 3. A 500 W laboratory A 500 W laboratory prototype is also constructed, and the corresponding simulation results, as well prototype is also constructed, and the corresponding simulation results, as well as experimental results, as experimental results, are provided to verify the feasibility of the studied BDC in Section 4. Finally, are provided to verify the feasibility of the studied BDC in Section 4. Finally, some conclusions are some conclusions are offered in the last section. offered in the last section. 2.2.Proposed ProposedBDC BDCTopology Topologyand andOperation OperationPrinciples Principles The The system system configuration configuration for for the the studied studied BDC BDC topology topology is is depicted depicted in in Figure Figure 4. 4. The The system system contains two parts, including a ULC and a two-phase IBCPC. The major symbol representations contains two parts, including a ULC and a two-phase IBCPC. The major symbol representationsare are summarized as follows: V H and VL denote the high-side voltage and low-side voltage, respectively. L1 summarized as follows: VH and VL denote the high-side voltage and low-side voltage, respectively. and L2 represent two-phase inductors of IBCPC. CB denotes the charge-pump capacitor. CH and CL are L1 and L2 represent two-phase inductors of IBCPC. CB denotes the charge-pump capacitor. CH and CL the high-side and low-side capacitors, respectively. The symbols, Q 1~Q4, and S1~S4, respectively, are are the high-side and low-side capacitors, respectively. The symbols, Q1 ~Q4 , and S1 ~S4 , respectively, the switches of the and and ULC. arepower the power switches of IBCPC the IBCPC ULC.
Energies 2016, 9, 410 Energies 2016, 9, 410
4 of 25 4 of 24
Bidirectional Power Flow
S1 La
+ VL
+
Q1
+
S2 VM S3 S4
CB
CH VH
Q3
-
Unregulated Level Converter (ULC) Low-Side Stage
L2 Q4
CM2 Lb
Q2
CM1
CL
-
L1
Two-Phase Interleaved Buck-Boost Charge-Pump Converter (IBCPC) High-Side Stage
Figure 4. System configuration of the novel BDC topology. Figure 4. System configuration of the novel BDC topology.
In this study, as the low-side stage, a high efficiency magnetic-less ULC with bidirectional power In this study, as the low-side stage, a high efficiency magnetic-less ULC with bidirectional power flow is adopted to output a fixed voltage for a given input voltage. Because only a small sized high flow is adopted to output a fixed voltage for a given input voltage. Because only a small sized high frequency line filter (L , L ) is required, it can substantially boost the power density of the low-side frequency line filter (Laa, Lbb) is required, it can substantially boost the power density of the low-side stage. Furthermore, by leaving the voltage regulation to another high-side stage, the studied BDC for stage. Furthermore, by leaving the voltage regulation to another high-side stage, the studied BDC for the low-side stage with fixed 2:1 under charge state operation or 1:2 conversion ratio under discharge the low-side stage with fixed 2:1 under charge state operation or 1:2 conversion ratio under discharge state operation, can achieve high efficiency with a relatively low-side voltage in whole load range. state operation, can achieve high efficiency with a relatively low-side voltage in whole load range. As As to the high-side stage, the structure of two-phase IBCPC is similar to a conventional buck-boost to the high-side stage, the structure of two-phase IBCPC is similar to a conventional buck-boost converter except two active switches in series and a charge-pump capacitor (C ) employed in the converter except two active switches in series and a charge-pump capacitor (CBB) employed in the power path. The circuit structure is simple and it can reach the high voltage conversion ratio with a power path. The circuit structure is simple and it can reach the high voltage conversion ratio with a reasonable duty cycle. Therefore, it can reduce the conduction loss of the switch, to further upgrade reasonable duty cycle. Therefore, it can reduce the conduction loss of the switch, to further upgrade the efficiency of the whole bidirectional converter. the efficiency of the whole bidirectional converter. The studied BDC topology can deliver energy in both directions. When the energy flows from The studied BDC topology can deliver energy in both directions. When the energy flows from V to V , it operates in charge state (i.e., buck operation); Q and Q are controlled to regulate the VHH to VLL, it operates in charge state (i.e., buck operation); Q11 and Q22 are controlled to regulate the output. Thus, Q and Q are defined as the active switches, while Q and Q are the passive switches. output. Thus, Q11and Q22are defined as the active switches, while Q33and Q44are the passive switches. The passive switches work as synchronous rectification (SR). When the energy flows from V to V , The passive switches work as synchronous rectification (SR). When the energy flows from VLL to VHH, it operates in discharge state (i.e., boost operation); Q and Q are controlled to regulate the output. it operates in discharge state (i.e., boost operation); Q33 and Q44are controlled to regulate the output. Thus, Q3 and Q4 are defined as the active switches, while Q1 and Q2 are the passive switches. Thus, Q3 and Q4 are defined as the active switches, while Q1 and Q2 are the passive switches. In this study, the following assumptions are made to simplify the converter analyzes as follows: In this study, the following assumptions are made to simplify the converter analyzes as follows: (1) the converter is operated in continuous conduction mode (CCM); (2) capacitors CH and CL is large (1) the converter is operated in continuous conduction mode (CCM); (2) capacitors CH and CL is large enough to be considered as a voltage source; (3) the middle-link voltage V = V + VM2 is treated enough to be considered as a voltage source; (3) the middle-link voltage VMM= VM1M1 + VM2 is treated as as a pure dc and considered as constant; (4) the two inductor L and L have the same inductor L ; a pure dc and considered as constant; (4) the two inductor L1 and1L2 have2 the same inductor Ls; (5) alls (5) all power semiconductors are ideal; (6) charge-pump the charge-pump voltage is treated puredc dc and and CB treated power semiconductors are ideal; (6) the voltage VCBVis as as a apure considered as as constant. constant. considered 2.1. Charge State Operation 2.1. Charge State Operation Figures 5 and 6 show the circuit configuration and characteristic waveforms of the studied BDC Figures 5 and 6 show the circuit configuration and characteristic waveforms of the studied BDC in charge state, respectively. It can be seen that switches Q1 and Q2 are driven with the phase shift in charge state, respectively. It can be seen that switches Q1 and Q2 are driven with the phase shift angle of 180˝ ; Q3 and Q4 work as synchronous rectification. In charge state, when S1 , S3 are turned on angle of 180°; Q3 and Q4 work as synchronous rectification. In charge state, when S1, S3 are turned on and S2 , S4 are turned off; or else S2 , S4 are turned on and S1 , S3 are turned off. The low-side voltage VL and S2, S4 are turned off; or else S2, S4 are turned on and S1, S3 are turned off. The low-side voltage VL is half the middle-link voltage VM , i.e., VL = 0.5VM . In this state, one can see that, when duty ratio of is half the middle-link voltage VM, i.e., VL = 0.5VM. In this state, one can see that, when duty ratio of Q1 Q1 and Q2 are smaller than 50%, there are four operating modes according to the on/off status of the and Q2 are smaller than 50%, there are four operating modes according to the on/off status of the active switches. active switches.
Energies 2016, 9, 410 Energies 2016, 9, 410 Energies 2016, 9, 410
5 of 25 5 of 24 5 of 24
Charge State Charge State
iL iL + + VL VL -
iLa La iLa La iCL iCLCL CL
Lb Lb
iQ2 - vQ2+ iQ2 - vQ2+ Q2 Q2
iL1 L1 iLt iL1 L- 1vL1 + iLt - vL1 + iCM1
S1 S1 + +vM1 iCM1CM1 vM1- CM1 -S2 S2 S3
iQ1 - vQ1 + iQ1 - vQ1 + Q1 Q1 iCH
CB iCB CB iCB - vCB + i-Q3vCB +
iL2 L2 iL2 L- 2vL2 +
iCM2 S3 + +vM2 iCM2 CM2 vM2CM2 -S4 S4
- vL2 +
iCH+
+
CH VH CH VH
+ iQ4 + + vQ4iQ4 + vQ3iQ3 vQ4 - Q vQ3 Q3 4 - Q4 Q3 SR Operation SR Operation
-
-
Figure Circuit configuration thestudied studiedBDC BDCinincharge chargestate. state. Figure 5. 5. Circuit configuration ofofthe Figure 5. Circuit configuration of the studied BDC in charge state. TSW TSW DdTSW DdTSW
Q1 Q1
on on
off off
on off on off (VH/2-V -VM/L1 M)/L1 (VH/2-VM)/L1 -VM/L1
iL1 iL1
t t IL1 IL1 t t
VH/2-VM VH/2-VM
vL1 vL1
-VM t -VM t (VH/2-VM)/L2 -V /L (VH/2-V -VM/LM2 2 M)/L2
i iL2 L2
VH/2-VM VH/2-V M
v vL2 L2
IL2
IL2 t
t
t Mt -VM-V
iL1+iL2 iL1+i L2
iLtiLt iL2iL2
iCBiCB
-iL1-iL1
t
t
t
t
VCBVCB
vCB vCB
t
t
iL2iL2
iQ1iQ1
t t VH/2 VH/2
vQ1 vQ1
t
t
t
t
iL1 iL1
iQ2iQ2
VHVH
VH/2 VH/2
vQ2 vQ2 iL1iL1
iQ3iQ3
VHV /2H/2
vQ3 vQ3
iL1+i iL1L2 +iL2
iQ4iQ4 VHV /2H/2
vQ4 vQ4
t
t
t
t
t
t
t
t
t
t
t
t
TSW TSW
S1S1 S3S 3
S2S 2 S4S 4
vM1 v
t
t
Q2 Q2
ILaI-ILt-I/CM1 /C La Lt
ILt/C I M1 /C
M1
Lt
M1
ILt/CM2 ILt/CM2
vM2 vM2 t0
t VM1V t M1
M1
t0
t1
t1
t2
t2
t3
ILa-ILt/CM2 ILa-ILt/CM2
t3
t4
t4
t VM2 t VM2 t
t
Figure Characteristic waveforms ofof studied BDC in in state. Figure Characteristic waveforms the studied BDC charge state. Figure 6.6.6. Characteristic waveforms of the the studied BDC incharge charge state.
Energies 2016, 9, 410
6 of 25
Energies 2016, 9, 410
6 of 24
Referring to to the the equivalent equivalent circuits circuits shown shown in in Figure Figure 7, 7, the the operating operating principle principle of of the the studied studied BDC BDC Referring can be explained briefly as follows. can be explained briefly as follows. Charge State iLt S1 iL +
iLa La iCL
S3 Lb
-
- vL1 +
+ vM2 S4
iQ1 - vQ1 +
Q2
iCM1
Q1 iCH
CM1 CB
iL2 L2
CL
VL
+ vM1 S2
iQ2 - vQ2+
iL1 L1
- vL2 + iCM2
iCB
CH VH
- vCB +
+ iQ4 + iQ3 vQ4 vQ3 - Q4 Q3
CM2
+
-
SR Operation
(a) Charge State iLt S1 iL + VL
+ vM1 S2
iLa La iCL
- vL1 +
S3
+ vM2 S4
Lb
iQ1 - vQ1 +
Q2
iCM1
Q1 iCH
CM1 CB iCB
iL2 L2
CL
-
iQ2 - vQ2+
iL1 L1
- vL2 + iCM2
CH VH
- vCB +
+ iQ4 + iQ3 vQ4 vQ3 - Q4 Q3
CM2
+
-
SR Operation
(b) Charge State
S1 iL + VL
iLa La iCL
- vL1 +
S3 Lb
+ vM2 S4
iQ1 - vQ1 +
Q2
iCM1
Q1 iCH
CM1 CB iCB
iL2 L2
CL
-
+ vM1 S2
iQ2 - vQ2+
iL1 L1
iLt
- vL2 + iCM2
- vCB +
+ iQ4 + iQ3 vQ4 vQ3 - Q4 Q3
CM2
+
CH VH
-
SR Operation
(c) Figure 7. Equivalent circuits of the modes during different intervals in charge state: (a) Mode 1; (b) Figure 7. Equivalent circuits of the modes during different intervals in charge state: (a) Mode 1; Mode 2, Mode 4; (c) Mode 3. (b) Mode 2, Mode 4; (c) Mode 3.
2.1.1. 2.1.1. Mode Mode 11 [t [t00
