phase a phase b phase c dc - princeton
TRANSCRIPT
Turbo-MMC: Minimizing the Submodule Capacitor Size in Modular Multilevel Converters with a Matrix Charge Balancer
Yenan Chen, Youssef Elasser, Ping Wang, Jaeil Baek, Minjie ChenPower Electronics Research Lab, Princeton University
Background & Motivation
Control Strategy for Turbo Operation
Turbo MMC with a Matrix Charge Balancer
➢ Submodule Capacitors in Modular Multilevel Converters
• Buffer pulsating power at low frequencies
• The voltage ripple of submodule capacitors: Vpp 1/fo and Io
➢ Modular Multilevel Converter based Motor Drive
• Design submodule capacitor for maximum Io and lowest fo.
• Capacitors take more than 50% of total size and weight.
Pulsating Power in MMC
Simulation and Experiments
Fig. 3: Three ways of balancing the pulsating power.
Simulation Parameters
Vdc 700V
Po 6kW
fmmc 10kHz
fmab 100kHz
Larm 4mH
Csm 1mF
Lb 5H
Cb 0.1mF
SM Number 4
Fig. 1: Typical startup process of a 3- ac induction motor: (a) phase current amplitude (b) phase current waveform and motor speed.
Fig. 2: Schematic of a 3- MMC and Voltage ripple and pulsating power of the submodule capacitors in Phase A.
SM
SM
SM
SM
SM
SM
SM
SM
SM
SM
SM
SM
SM
SM
SM
SM
SM
SM
0.5Vdc
0.5Vdc
Larm
Larm
Larm
Larm
Larm
Larm
Lo Ro
Phase A Phase B Phase C
ioa
iob
ioc
iua
ila
PUA1
NUA1
PUA2
NUA2
PUAn
NUAn
PLA1
NLA1
PLA2
NLA2
PLAn
NLAn
PUB1
NUB1
PUB2
NUB2
PUBn
NUBn
PLA1
NLA1
PLA2
NLA2
PLAn
NLAn
PUC1
NUC1
PUC2
NUC2
PUCn
NUCn
PLC1
NLC1
PLC2
NLC2
PLCn
NLCn
Eua
vcua
vcla
pua
pla
0
0
ioa iob ioc
ft
Voltage ripple: vcua, vcla
Ac circulating current: iza
Pulsating power: pua, pla
Output current: ioa
➢ Pulsating power = ac output power + circulating power
➢ Reduce the voltage ripple in SM capacitors:
• Sophisticated control strategy for power management
• Active pulsating power balancing
Matrix
Power
Balancing
pua
pua
pla
pla
pub
pub
plb
plb
puc
puc
plc
plc
Phase A Phase B Phase C
Upper Arm
Lower Arm
Vertical
Power
Balancing
Horizontal Power Balancing
Fig. 5: A matrix charge balancer implemented as a multi-active-bridge converter with a single magnetic core.
0 ft
100
0
-100
p.u
. [%
]
0
0
-0
p.u
. [%
]
0.0
0
-0.0
p.u
. [%
]
Ev
Eh
Em
pv
ph2
pm
ph1
Fig. 4: Percentage of residual unbalanced pulsating power.
➢ Vertical: partially balance power
➢ Horizontal: completely balance the
output power, partially balance the
circulating power
➢ Matrix: completely balance power
➢ Balance energy among submodule capacitorsVertical
Horizontal
Matrix
MMC Central
Controllervsm MCB
Port
+
_
MMC
SM
Hi
GPI_i
Φivref
Delay
Global Synchronize Clock
Global Enable Signal
Distributed Phase
Shift Controller
Fig. 7: Distributed phase-shift control with a ripple voltage hysteresis for submodule capacitor voltage.
V#1 V#j
V#k
Nw:1 1:Nw
1:Nw
L1j
Ljk
L1k
V#n
Nw:1
Fig. 6: Simplified ac power flow model of a matrix charge balancer.
➢ Power flow controlled by
modulating the phase-shift:
𝑃𝑖 =𝑉𝑖
2𝜋𝑓𝑚𝑎𝑏𝑁𝑤2
𝑗≠𝑖
𝑉𝑗
𝐿𝑖𝑗Φ𝑗 −Φ𝑖 1 −
Φ𝑗 −Φ𝑖
𝜋
v
0
Vpp/2
— Vpp/2
Vh
Vh
➢ Deliver energy from/to a submodule capacitor by closed-loop
control with hysteresis in voltage ripple
Fig. 8: Simulated capacitor voltage ripple of the Turbo-MMC in five operating modes: (1) 0.0s -- 0.3s, low frequency (10 Hz) startup with Turbo mode ON, 20% load (1200 W); (2) 0.3s -- 0.6s, light load operation with Turbo mode OFF; (3) 0.6s -- 0.9s, output frequencyincreased to 50Hz with Turbo mode OFF; (4) 0.9s -- 1.2s, output load steps up to 100% (6000 W); (5) 1.2s -- 1.5s, high frequency heavy load operation with Turbo mode ON.
Experiment Parameters
Vdc 24V
Po 30W
fmmc 50kHz
fmab 200kHz
Larm 7mH
Csm 1mF
Lb 0.1H
Cb 0.1mF
SM Number 4 Fig. 9: A Turbo-MMC prototype
Fig. 10: Measured waveforms of the prototype Turbo-MMC with fo = 50 Hz. High voltage ripple even causes arm inductor saturation without Turbo operation.
➢ Summary: Turbo-MMC operation for startup process can
1. Reduce the submodule capacitor and arm inductor size.
2. Reduce the voltage ripple in submodule capacitors for low
frequency and high power operation;
➢ Power flow controlled by
time domain multiplexing.
3Φ - MMC
Matrix Charge
Balancer
Half-bridge Module
BranchInductor Lb
12-Winding Transformer
One Portof MCB