第1章 能量储存

Fx
xW
1 C Vd2c 2d
xˆ
➢Discharging the capacitor results in a force that is opposite in sign to the direction the current is flowing
➢Dielectric is being compressed and pulled away from the metallic conductors
Dielectric Breakdown
Dielectric Strength of Insulating Film Decreases With Thickness
Capacitor Design Parameters
User Electrical Requirements Capacitance
Capacitor – Self Healing
➢Non-metallized design: Separate sheets of metal foil as electrodes.
Foils extend alternately out of each end of the capacitor roll beyond the dielectric; leads are attached by welding or soldering.
Common Dielectrics and Their Ability to Store Energy
Decreasing relative K Vb2
Energy stored in parallel plate capacitor:
W
1 2
e Vd2c
L W d
with e = K e0 .
电位移： D D0 cos(t ) D1 cost D2 sin t
电流密度：
j=
dq dt
dD dt
(D1
sin t
D2
cos t )
绝缘介质单位体积和单位时间损耗的能量密度 W:
W
2
2 / 0
jEdt
2
E0D0 sin
2
E0 D0
tan
定义：tan 为介损
电容器使用寿命
where Vb is the breakdown voltage of dielectric by a continuous voltage, Vc the capacitor voltage, and ɷ the radian frequency.
must be considered in the application.
Advantages of a Metallized Unit: 1. The self-healing feature of a metallized design enables the metallized unit to remain
Limitations of a Metallized Unit: 1. Under a clearing operation situation,
sufficient energy must be present to accomplish this function. 2. During a clearing operation, the resulting transient drop in voltage
its non-metallized equivalent unit. 4. The maximum AC voltage-frequency capability of a metallized unit is
slightly less than its non-metallized equivalent unit.
Capacitor Failure
Capacitor Failure
Internal short circuit (Breakdown of insulation)
100 kJ capacitor
Observed damage
Capacitor Basics
Force during discharging for non-conducting (very high dc-resistance) dielectric
Before
After
➢Note: Metallized capacitors have smaller volume than standard caps. (e.g. factor ½ for polyester dielectric 10 mF, 200 V)
Non-Metallized or Metallized?
➢In case of local fault of the dielectric due to flaw or weak spot, the energy stored in the capacitor is used to vaporize the thin metallic electrode.
Circuit Model for a Real Capacitor:
ESR and ESL measurement*
课后作业：如何从放电波形得到未知电容器参数？
Capacitor Selection – Lifetime 电容充电电压一般为其额定电压的80%
电容器绝缘材料损耗
设交流电场：E E0 cost
operational after a short condition develops. In a non-metallized unit, the short condition results in a catastrophic permanent failure. 2. The volumetric efficiency of a metallized unit is higher than its non-metallized equivalent unit. 3. In direct proportion to the volumetric efficiency is the weight savings realized with a metallized unit. 4. The cost of a metallized unit in the higher microfarad ratings (above 0.1 Mfd) is less than its non-metallized equivalent unit.
Non-metallized
ቤተ መጻሕፍቲ ባይዱ
Metallized
Capacitor – Self Healing
➢Metallized capacitors (thin metal film as electrode between dielectric rely on the “thinness” of the metallized electrode material).
Capacitor Selection
High energy cap (300 J/kg)
low number of shots ~103
Self healing cap for laser market
High Energy Capacitor
Maxwell Type C
Extended Foil Capacitor
第一章 储能技术 （Energy Storage）
1. 电容器（Capacitors） 2. 电感（Inductors） 3. 蓄电池（Batteries） 4. 旋转电机（Rotating Machines） 5. 应用与研究方向（Application /
Research）
Typical Discharge Time vs. Energy Density
➢Metallized: Thin layer of 99% pure Al vapor-deposited directly onto dielectric.
The two sheets of metallized dielectric are positioned properly relative to a right and left margin and wound into a roll; end terminations of the metallized unit by application of a fine molten metal spray.
➢Possible rupture damage to the dielectric bulk
➢Possible destruction of the intimate bond between the dielectric and the rigid metal conductors
Capacitor – Recent Development
Disadvantages of a Metallized Capacitor: 1. The dissipation factor is slightly higher than that of a non-metallized unit. 2. The insulation resistance is slightly lower than a non-metallized unit. 3. The metallized unit maximum current limitation is lower than
Super caps:
2.3 V, 100 F, 125 A peak current Size: 35 x 60 x 20 mm Weight: 35 g ESR: 15 mOhm Energy/weight: 7.5 J/g
(Peak electrical output comparable to a Li-Ion battery with ten times the weight.)
(J/cm3)
• 电容器储能 • （Capacitive Energy Storage）
Capacitive/Inductive Energy Discharge Circuits
Capacitive Energy Discharge Circuit
Inductive Energy Discharge Circuit
Voltage Rating Tolerance
Stray inductance
Manufacturer Design Parameters Capacitance variation
Dissipation factor Insulation resistance
Residual charge Temperature coefficient
Simple Capacitor – Parallel Plate Capacitor
terminal
Stored Energy: ½ C V2
“Problem”: e0 = 8.85 10–12 As/Vm
Range: 50 kJ/Can (Top Left) down to a few 100 Joules (Front Row) Metal and Plastic Cases Low Inductance
➢The energy required for an average or "normal" clearing: approx. 10 microJoules clearing may be questionable if insufficient energy stored in the capacitor
User Geometry Dimensions
Dimensional tolerance Terminal location
Terminal dimensions Mounting means Case materials
User Environment Temperature range Frequency Repetition rate Duty cycle Wave shape Life expectancy Humidity Altitude Shock Vibration Storage temperature