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Chapter 3 — Power generation - Coggle Diagram

- - - - Gasoline engine (OTTO) MEASURES:
        
        optimize mixture creation
        
        optimize ignition
        
        optimize ignition timing
        
        reducing NOx by high air surplus (trade-off with CmHn because y=1.2 is ignition threshold). To reduce this CmHn emissions we can use Stratified charge engine -> not having homogeneous mix anymore (like in diesel)
        stratified charge engine, lean-burn engine, exhaust gas recirculation not enough. Exhaust gas after-treatment with three-way catalytic converter required!
      - DIESEL MEASURES:
        
        Cumbustion methods
        -- pre or vortex chamber instead of direct injection
        -- injection start later
        -- high injection pressure
        
        Exhaustion gas recirculation
        -- reduction of NOx when precisely dosed quantity (up to 30%) of gas is recirculated because the 02 concentration decreases and also combustion temperature decreases because of higher thermal capacity of CO2
        
        To deal with soot
        -- piston wall distribution of the injection
        -- good turbulance in combustion chamber
        -- high lambida
        -- high injection pressure
        at present, the engine-based measures are partially still sufficient to stay below emission limits. In future, after-treatment of NOx combined with oxidation catalyst and particle filter required!
    - - Gasoline engine w/ catalytic converter
        3-way catalytic converter that promotes oxidation of CO and CmHn, and reduction of NOx
        
        y=1 (stecheometric):, ~90% conversion
        
        y<1 (air defficiency): increase CO & CmHn
        
        y>1 increase NOx due to air surplus
        
        Uses a closed loop control with feedback of y to ECU. Exhaust gas passes through catalyst before going into the atmosphere
        
        Optimal temperature 300-900ºC
        
        using y-control up to 90% reduction
        
        y sthechometricsal increases be up to 5%
      - Diesel engine w/ catalytic converter
        
        Conventional catalytic converter only used as oxidation catalyst because the y is from 1.2 to 10
        -- CO and CmHn oxidies but NOx do not reduce
        -- Using NOx adsorber - stores NOx at working temperatures > 150ºC, don't work on startup with cold engine. It also increases the consumption up to 2%. The NO2 is trapped until it is full and than regenerated into N2 + H2O with diesel injection
        
        SCR catalyst
        -- working temperature > 200ºC problem at startup cold eng
        -- reduces consumption up to 5%
        AdBlue is sprayed in before the SCR catalyst, first step creates ammonia in the catalyst, second step amonia and NOx converted into H2O + N2.
        
        SOOT is a problem even with the catalyst, but can be overcomed with filters.
      - Comparison of catalysts on DIESEL and on OTTO
        diesel is only better on CO2 and be. It is way worse on NOx
- - - - Parallel shaft drive
        motor diameter limited for space reasons. Suitable for high-speed drives.
        E.g. Tesla, Renault Zoe, BMW i3, VW ID.3 and many more
      - Coaxial drive
        Due to the required hollow shaft, the applicable motor technology is limited. On the other hand, the space requirement is minimal. Only permanent magnet synchronous machines can be used here.
        E.g. Honda (Fit EV, FCX Clarity) and the Audi e-tron
      - Angular drive
        offers the maximum degrees of freedom in electrical design from the point of view of the electric motor
        E.g. Porsche e-Ruf Greenster
  - - - Parallel hybrid system
        Operation optional or simultaneous
        
        The mechanical addition of both power sources is possible
        
        Manual gearbox needed
        
        closely modelled upon existing drive trains
        
        One electric motor needed
        
        Often also as a plug-in hybrid vehicle
        
        Implementation:
        
        microhybrid
        
        mild hybrid
        
        full hybrid
        
        Mounting positions:
        
        P0 Hybrid - Belt-driven starter-generator BSG
        
        P1 Hybrid - Transmission integrated starter-generator
        
        P2 & P3 Hybrids - Integral part off transmission
      - Serial hybrid system
        Operation with motor
        
        No mechanical coupling between combustion engine and wheels.
        
        No need for manual gearbox
        
        Combustion engine only for generation of electricity
        
        Two high powered electric motors are needed
        Plug-in electric vehicles
      - Serial-Parallel hybrid system
        
        Division of power between combustion engine and electric motor
        
        Summing transmission (Planet gears transmission) to:
        -- Split the mechanical and electrical power
        -- Combining the mechanical and electrical power
        -- Stepless conversion of torque and rotational speed
        
        Two high power electric motors needed (sometimes as mutual power supply)
    - - Full power
        More power at hill and for overtaking
        
        The battery supplies additional energy for the system if needed
        
        Therefore additional power for electric drive
        
        By combining the gasoline engine and electric motor, we have an acceleration like a vehicle of the next higher class
      - Deceleration / Energy recovery
        Recovering energy while braking
        
        Electric motor functions as generator while decelerating
        
        Kinetic energy of vehicle is converted into electric energy
        
        Storage in battery
      - Regular operation
        Energy saving operation with gasoline engine as main power source
        
        Operation with gasoline engine at higher speeds
        
        Planetary gears as power switch:
        -- Partially direct power to the wheels by gasoline engine
        -- Partial operation of wheels over the path generator – control unit – electric motor
        
        Therefore implementation of a stepless transmission.
      - Stand still
        All drive elements are turned off
        
        Gasoline engine and electric motor as well as generator are all automatically turned off
        
        No energy loss while idling
        
        The gasoline engine keeps running (in some cases) to charge the battery when the battery is low on charge or the AC unit is running.
      - Slow to medium speed
        Energy efficient operation with the electric drive
        
        No optimal efficiency for gasoline engine in the partial load range
        
        High efficiency of electric motor at low speeds
        
        Therefore operation with electric motor from the electric energy stored in the battery
        
        When the battery is low on charge, the gasoline engine kicks in and powers the generator which in turn produces electricity.
      - Regular operation / Battery charging
        Charging of battery with spillover energy
        
        Optimal workload of gasoline engine
        
        Resulting power spillover is converted into electric power
        
        Storage in battery
      - Start
        When starting the vehicle, the high torque of the electric motor at a slow speed is used
        
        Operation with electric motor
        
        Energy from battery
        
        Gasoline engine stays off
        
        Gasoline engine runs only until it is warmed up.
  - - - PM syncronous
        In a synchronous machine, the rotor always follows the stator field. The speed of the rotor is therefore the same as that of the rotating field, i.e. the rotor and stator field run synchronously
        
        The higher the number of grooves, the smoother the torque (no ripples) because there are more sinosoids to sum up.
        
        Serial or parallel connection of the coils of each phase possible, depending on the available battery voltage.
        
        Small system voltages (48 V, 120 V)
        -- Parallel connection preferred
        -- Higher currents (for the same machine power)
        
        High system voltages (400 V, 800 V)
        -- Serial connection preferred
        -- Lower currents (at same machine power)
        
        2 magnets in the rotor premagnetized in direction S → N
        
        Even if the rotor follows the stator at the same speed, there is an angular offset depending on the load, the so-called pole wheel angle. In the unloaded state (no-load operation), the north pole of the rotor and the south pole of the stator field are exactly aligned with each other. If one increases the load on the machine, the increasing stator current generates a counter field, which leads to a rotation of the rotor relative to the stator field. The rotor thus follows the stator field with a load-dependent pole wheel angle.
        
        Pole wheel angle 0° to < 90° (motor operation, increases with load)
        
        Pole wheel angle 0° to < -90° (regenerative operation, increases with load - in direction to -90)
        
        Pole wheel angle = 90° or = -90°.(breakdown point of the motor, maximum power)
        
        Pole wheel angle < -90° or > 90°. (motor out off step, rotor can no longer follow the stator, strong torque pulsations which can damage the motor and the gearbox, must never occur.)
      - Separately excited synchronous machines (SESM)
        The difference between a separately excited synchronous machine, also called electrically excited synchronous machine EESM, and a permanent magnet synchronous machine is the design of the rotor. The stators of both machine types do not differ. In the stator, as in the PMSM, a uniform rotating magnetic field is generated.
        
        Replacement of magnets by excitation coils
        
        Rotor field is generated by direct current (DC) in the excitation coils
        
        PROS:
        
        Exciter field can be adjusted independently of load and speed
        
        Thus, depending on the operating point, better efficiency than with PMSM possible
        
        Good field weakening capability → high speeds (wide speed range) possible
        
        CONS:
        
        Additional losses due to current in the rotor
        
        Thus, depending on the operating point, poorer efficiency than with PMSM is also possible
        
        Complicated transmission of electrical energy to the rotating rotor
      - Transverse flux machine
        The transverse flux motor is actually an outer pole synchronous motor, but the rotating field spools are placed in peripheral direction. The magnetic flux proceeds in a meandering pattern through the stator and rotor. The drive power is generated like in every electromagnetic machine through the change of the energy density in the air gap (dW/dx).
      - Asynchronous machines (ASM)
        The asynchronous machine also uses the same stator design as the PMSM. However, the rotor functions fundamentally differently from the PMSM or SESM.
        
        A large number of bars (yellow) made of a conductive material (usually aluminum or copper) are embedded in the laminated core of the rotor
        
        At the axial ends, the bars are connected to each other by a ring (see Fig. 3-79)
        
        Operating principle
        
        The rotating stator field induces a voltage in the rotor bars
        
        By connecting the bars at the ends, these voltages lead to currents
        
        The currents now generate their own magnetic field, the rotor field
        
        The rotor field has the same number of poles as the stator field, since it is generated by the stator field.
        
        The rotor is now rotated by the stator and rotor field due to the principle of magnetic attraction.
        
        The voltage induction only works as long as the stator field and the rotor have different speeds. If the rotor turns slower, the rotor sees a changing stator field. Only then does the voltage induction work. If the rotor were rotating at the same speed as the stator field, an observer on the rotor would always see the same stator field. However, since no voltage is induced without a change in the field and thus no current can flow in the rotor, the rotor would lose its magnetic field and consenquentlu could not be pulled along further by the stator field. Therefore, the rotor must always turn a little slower than the stator fifeld. This speed difference is called slip s. It indicates the percentage of deviation of the rotor speed n from the speed of the stator field n1
        
        Idle speed - slip-s ~= 0
        
        With load - slip increases successively with load. Continuous operation with slip from 3 to 10%. Max torque (breakdown torque) s~=20%. A further increase in torque over the breakdown torque causes the machine to stop. However, this is prevented in controlled traction drives by the power electronics.
        
        Since an asynchronous machine does not contain any magnets, no voltage is generated at open terminals when it is rotated from the outside. In order to operate the machine as a generator nevertheless, a rotary voltage must always be applied. Only then a field is also generated and a current can be driven back into the battery. Recuperation is therefore only possible with an external voltage source. Since this is always provided in the car by the battery, there are no disadvantages here compared with the other machine types.
      - Switched reluctance machine
        The reluctance machines have different numbers of teeth on rotor and stator. The rotor consists of a sheet metal package that forms some kind of gear. The teeth of the stator are winded with spools and carry a current. Through the current, a cog of the rotor is pulled to a cog of the stator which carries the current. By switching certain teeth on and off, the rotor starts to turn.
    - - Rotor
        
        Cylindrical, partially hollow design (weight reduction)
        
        Consists of layered sheets (0.2 to 1.0 mm thick) electrically insulated from each other
        
        Depending on the machine, provided with grooves for wire winding or pockets for magnets
        
        The distance between stator and rotor is called air gap (from 0.5 to 2mm)
        
        Bearing arrangement
        
        Usually fixed-loose bearing
        
        Fixed bearing on the output side (A-side)
        
        Floating bearing on the rear side (B-side)
        
        Sensor (position encoder) on the B-side, for detection of the angular position of the rotor by the power electronics
        
        Depending on requirements, shaft seals to protect against dirt or gearbox oil
        
        Separately excited synchronous machine
        
        No magnets
        
        Rotor with grooves for excitation winding
        
        Transmission of excitation current via slip rings
        
        Asynchronous machine
        
        Internal bars are inserted into the rotor by die casting and directly connected by shorting ring (especially with aluminum).
        
        Other possibility: hammer in copper bars and weld them with attached end rings (e.g. Tesla Motors)
        
        Permanent magnet synchronous machines
        
        TYPE I
        
        Mostly used in starter generators and transmission-integrated machines
        
        Primarily used in hybrid vehicles
        
        Cost effective
        
        Plenty of space inside the rotor (for clutches, etc.)
        
        TYPE V
        
        Application in powerful main drives
        
        Variants with multiple layers of magnets possible
        
        TYPE U
        
        Similar to V-arrangement, with further magnet in the middle
        
        Same points as V
      - Windings
        
        Distributed windings
        
        The coil sides of the three phases are evenly distributed over the slots
        
        The windings of one coil exit at the end of the stack of laminations and reenter on the
        opposite side
        
        The coil width depends on the number of poles
        
        PROS:
        
        Magnetic field in air gap is sinusoidal
        
        Number of poles freely selectable = independent of the number of grooves
        
        CONS:
        
        Complex manufacturing → higher costs
        
        Very difficult to automate depending on the design
        
        Large winding heads (= a lot of installation space)
        
        Concentrated windings
        
        Each coil is wound around one tooth at a time
        
        Also called single tooth winding
        
        PROS:
        
        Compact winding head, space saving
        
        Simple construction
        
        Simple manufacturing
        
        Cost effective
        
        CONS
        
        Coil width = distance between two grooves
        
        For electromagnetic reasons, the coil width should correspond approximately to the pole
        width
        
        Larger machine diameter = more teeth
        
        More magnetic poles necessary
        
        Speed and thus power density decreases
        
        Magnetic field in the air gap is strongly distorted (= many harmonics)
        
        Harmonics on torque more pronounced
        
        Stronger noise excitation, machine becomes louder
        
        Formed coil windings
        In traction drives, so-called shaped coil windings have been used more and more frequently in recent years. These represent a compromise between distributed windings and single-tooth windings and attempt to combine the advantages of both types:
        STRUCTURE: Winding consists of individual, preformed rectangular conductors. Preformed wire pieces are pushed into the grooves from one side. Bending of the wires on the other side of the stator. Welding (= interconnection to form coils). Between 2 and 8 conductors per groove. 4 variants: Hairpin, D-pin, I-pin and wave winding.
        
        PROS
        
        Manufacturing can be fully automated
        
        Same good electromagnetic properties as distributed windings
        
        CONS
        
        Only economical from higher quantities (costly tools for forming the wires)
        
        Low flexibility with regard to changing the number of windings
        
        Only practicable for mass production in automotive segment
      - Stator
        
        Designed as a hollow cylinder (stator yoke with teeth)
        
        Consists of laminated, electrically insulated sheets (usually 0.2 to 1.0 mm thick)
        
        The winding of copper wire is located in the grooves
        
        Surrounded by a housing
        
        Housing takes over the cooling
        
        Air cooling
        
        Liquid cooling (mostly spiral cooling channels)
    - - Basic speed range
        
        Constant magnetic flux range 𝜙
        
        Magnetic flux = ratio of applied voltage 𝑈 and rotational frequency 𝑓
        
        Constant 𝑘1 is given by the construction of the machine
        (𝜙 = k1 x U/ƒ)
        
        Torque is given by the product of flux and coil current
        
        k2 is given by the design of the machine (M = k2 x 𝜙 x I)
        
        GOAL: keep magnetic flux constant
        
        Increase voltage proportional to speed
        
        Optimal magnetic utilization
        
        Torque is proportional to current
        
        Max. torque (at max. current) is constant over speed
        
        Power increases linearly
      - Field weakening range
        
        Power electronics generates AC voltage for the motor from the battery voltage
        
        Rotation frequency (=speed) is freely adjustable
        
        Amplitude of output voltage limited by max. battery voltage
        
        Speed limit is reached when the inverter must set the maximum available output voltage to keep the magnetic flux constant
        
        limit is called corner speed n[eck]
        
        Further increase in speed at constant voltage leads to:
        
        Decrease of magnetic flux inversely proportional to speed
        
        𝜙 ~ 1/ƒ
        
        Drop of flux = flux weakening
        
        Torque also falls inversely proportional to speed
        
        M ~ 1/ƒ
        
        Power remains constant
        
        Field weakening range = constant power range
        
        Current limit given by inverter and not speed-dependent
        
        Current I[max] remains constant
  - - - Crash safety:
        
        Corrosion resistant, crash proof battery housing
        
        System to discharge reaction gases in case of malfunction
        
        Controlled discharge reaction of cell for the case of a destroyed separator (nail test)
      - Operation safety:
        
        Cell monitoring, automatic disable before crossing critical threshold value
        
        Thermo management (cold start properties)
        
        Safety against overcharging
        
        Cell balancing
      - Service safety:
        
        Cable labeling
        
        Contact protection (isolation, plug)
        
        Partition in partial batteries with connecting safety switches