PEE401- SOLID STATE DRIVES AND CONTROL UNIT-1 Review of Electric Drives 4/22/2017 PALANISAMY MTech.,(PhD)
REVIEW OF ELECTRIC DRIVES (Syllabus) Electric Drives-Advantage of Electric Drives Selection of Motor power rating Thermal model of motor for heating and cooling Classes of duty cycle & Determination of motor rating Control of Electric drives- modes of operation Speed control and drive classifications Closed loop control of drives 4/22/2017 PALANISAMY MTech.,(PhD)
Definition of Electrical Drives 4/22/2017 PALANISAMY MTech.,(PhD)
Advantages of Electrical Drives 4/22/2017 PALANISAMY MTech.,(PhD)
Block Diagram of Electric Drive System 4/22/2017 PALANISAMY MTech.,(PhD)
Why Power Electronic Devices? 4/22/2017 PALANISAMY MTech.,(PhD)
PALANISAMY MTech.,(PhD) Components in electric drives Motors DC motors - permanent magnet – wound field AC motors – induction, synchronous brushless DC Applications, cost, environment Natural speed-torque characteristic is not compatible with load requirements Power sources DC – batteries, fuel cell, photovoltaic - unregulated AC – Single- three- phase utility, wind generator - unregulated Power processor To provide a regulated power supply Combination of power electronic converters More efficient Flexible Compact AC-DC, DC-DC, DC-AC, AC-AC 4/22/2017 PALANISAMY MTech.,(PhD)
PALANISAMY MTech.,(PhD) Power Converters 4/22/2017 PALANISAMY MTech.,(PhD)
PALANISAMY MTech.,(PhD) Power Converters 4/22/2017 PALANISAMY MTech.,(PhD)
PALANISAMY MTech.,(PhD) Components in electric drives Control unit Complexity depends on performance requirement analog- noisy, inflexible, ideally has infinite bandwidth. DSP/microprocessor – flexible, lower bandwidth - DSPs perform faster operation than microprocessors (multiplication in single cycle), can perform complex estimations Electrical isolation between control circuit and power circuit is needed: Malfunction in power circuit may damage control circuit Safety for the operator Avoid conduction of harmonic to control circuit 4/22/2017 PALANISAMY MTech.,(PhD)
PALANISAMY MTech.,(PhD) Components in electric drives Sensors Sensors (voltage, current, speed or torque) is normally required for closed-loop operation or protection. Electrical isolation between sensors and control circuit is needed. The term ‘sensorless drives’ is normally referred to the drive system where the speed is estimated rather than measured. 4/22/2017 PALANISAMY MTech.,(PhD)
Modern Electrical Drive System 4/22/2017 PALANISAMY MTech.,(PhD)
PALANISAMY MTech.,(PhD) 4/22/2017 PALANISAMY MTech.,(PhD)
Choice (or) selection of Electrical Drives 4/22/2017 PALANISAMY MTech.,(PhD)
PALANISAMY MTech.,(PhD) AC and DC Drives 4/22/2017 PALANISAMY MTech.,(PhD)
Torque equation for Rotating system 4/22/2017 PALANISAMY MTech.,(PhD)
PALANISAMY MTech.,(PhD) J – Moment of inertia of the motor-load system referred to the motor shaft (kg-m2) ωm - Instantaneous angular velocity of motor shaft (rad/sec) T - Instantaneous value of developed motor torque (Nm) Tl - Instantaneous value of load torque referred to motor shaft (Nm) Variable Moment of inertia of the motor-load system 4/22/2017 PALANISAMY MTech.,(PhD)
PALANISAMY MTech.,(PhD) 4/22/2017 PALANISAMY MTech.,(PhD)
Torque equation for Rotating system with Gears 4/22/2017 PALANISAMY MTech.,(PhD)
Torque equation for Rotating system with Gears 4/22/2017 PALANISAMY MTech.,(PhD)
Four quadrant (multiquadrant) operation of motor using hoist load
Four quadrant (multiquadrant) operation of motor using hoist load Direction of positive (forward) speed is arbitrary chosen Te m m Te Direction of positive torque will produce positive (forward) speed Quadrant 2 Forward braking Quadrant 1 Forward motoring T Quadrant 3 Reverse motoring Quadrant 4 Reverse braking Te Te m m 4/22/2017 PALANISAMY MTech.,(PhD) 22
PALANISAMY MTech.,(PhD) Torque-speed quadrant of operation 1 2 T -ve +ve Pm -ve T +ve +ve Pm +ve Quadrant of operation is defined by the speed and torque of the motor. Most rotating electrical machines can operate in 4 quadrants. Not all converters can operate in 4 quadrants. T 3 4 T -ve -ve Pm +ve T +ve -ve Pm -ve 4/22/2017 PALANISAMY MTech.,(PhD)
1st Quadrant (Forward Motoring): The torque and speed of the motor are in the same direction. Of course, the load torque is opposite to the machine torque. The electrical machine in this case is operating as a motor. The flow of power is from the machine to the load. 2nd Quadrant (Forward Braking): The speed direction is unchanged while the direction of the torque is reversed. Since the load torque direction is in the same direction of speed, the mechanical load is delivering power to the machine. The machine then receives mechanical energy, converting it in to electrical energy and returning it back to the electric source. The electric machine is thus acting as a Generator.
PALANISAMY MTech.,(PhD) 3rd Quadrant (Reverse Motoring): Compared to the first quadrant, the system speed and torque are reversed in the third quadrant. Since the torque and speed of the machine are in the same direction, the power flow is from the machine to the load. The machine is therefore acting as a motor rotating in the reverse direction to the speed of the first quadrant. Bidirectional grinding machine is the good example of the 1st and 3rd quadrant operation. The direction of the load torque of the grinding load is reversed when the speed is reversed (3rd quadrant). A horizontal conveyor belt is another example of this type of operation. 4/22/2017 PALANISAMY MTech.,(PhD)
PALANISAMY MTech.,(PhD) 4th Quadrant (Reverse Braking): The torques remains unchanged as compared to the first quadrant. The speed, however, changes the direction. From the load perspective, the load torque and the speed are in the same direction. Hence the power flow is from the load to the machine. The machine is in this case acting as generator delivering the electric power to the source. The first and fourth quadrant of operation can be explained with the elevator. When the elevator is going upward or downward, the direction of the load torque remains unchanged but the direction of the speed only reversed. 4/22/2017 PALANISAMY MTech.,(PhD)
Four quadrant operation of a drive Parameters I quadrant II quadrant III quadrant IV quadrant Operation of the Hoist The hoisting up of the loaded cage The hoisting up of the unloaded cage The downward motion of the unloaded cage The downward motion of the loaded cage Te +VE -VE TL WM Power Operation of the Drive forward motoring Forward Braking Reverse motoring Reverse Braking 4/22/2017 PALANISAMY MTech.,(PhD)
Selection of Motor Power Rating Selection of power rating is important to achieve economy with reliability. Improper selection of motor power rating results extra initial cost and extra loss of energy due to operation below rated power makes the choice uneconomical. Furthermore, induction and synchronous motors operate at a low power factor when operating below the rated power. During operation of the machine, heat is produced due to losses and temperature rises. An amount of developed heat is dissipated into the atmosphere. When the dissipation of heat is equal to the developed heat, then it is said to be equilibrium condition. Motor temperature then reaches a steady state value. .
PALANISAMY MTech.,(PhD) Steady state temperature depends on power loss, which in turn depends on the output power of the machine. Since temperature rise has a direct relation with the output power, it is termed thermal loading on the machine. Steady state temperature varies in different parts of the machine. It is usually high is the windings because loss density in conductors is high and dissipation is slow; the conductors which are wrapped in insulating material are partly embedded in slots and thus are not directly exposed to the cooling air. 4/22/2017 PALANISAMY MTech.,(PhD)
Thermal model of motor for Heating and Cooling when an electrical motor and drive operates, there is a generation of heat inside the motor. The amount of heat generated inside the motor should - accurately as possible. That’s why thermal modeling of motor is necessary. The material of the motors and the shapes and size of the motors are not unique but the generation of heat does not alter very much depending on these characteristics. So, a simple thermal model of any motor can be obtained assuming it to be a homogeneous body. Aim of this modeling is to choose the appropriate rating of a motor so that the electric motor does not exceed its safe limit during operation. 4/22/2017 PALANISAMY MTech.,(PhD)
PALANISAMY MTech.,(PhD) 4/22/2017 PALANISAMY MTech.,(PhD)
PALANISAMY MTech.,(PhD) 4/22/2017 PALANISAMY MTech.,(PhD)
Speed control and Drive Classifications Drives - driving motor runs at a nearly fixed speed Constant speed or single speed drives. Multi speed drives are those which operate at discrete speed settings- Variable speed drives. When a no. of motors are fed from a common converter or when a load is driven by more than one motor – multi motor drive. A variable speed drive is called constant torque drive if the drive’s maximum torque capability does not change with a change in speed setting – constant torque mode. Speed regulation = (no load speed – full load speed)/ (full load speed)*100% 4/22/2017 PALANISAMY MTech.,(PhD)
Closed-Loop Control of Drives: Feedback loops in an electrical drive may be provided to satisfy one or more of the following requirements: Protection Immediate Speed response Improvement in steady state accuracy Efficiency 4/22/2017 PALANISAMY MTech.,(PhD)
Current – limit Control - Threshold logic circuit Controller Converter Current Sensor Motor Load Imax I If If* + 4/22/2017 PALANISAMY MTech.,(PhD)
Closed loop torque control - Torque Controller Converter Torque Sensor Motor Load T T* + 4/22/2017 PALANISAMY MTech.,(PhD)
Closed loop speed control Δm - + Speed Controller Current Sensor Motor Load m m* Converter Current Controller Speed Sensor I* I Current Limiter 4/22/2017 PALANISAMY MTech.,(PhD)
Closed loop speed control of multi motor Drives 4/22/2017 PALANISAMY MTech.,(PhD)
Phase locked loop (PLL) control 4/22/2017 PALANISAMY MTech.,(PhD)
Closed loop position control Current sensing Speed sensing 4/22/2017 PALANISAMY MTech.,(PhD)
PALANISAMY MTech.,(PhD) Modes of Operation An electric drive operates in three modes, Steady state Acceleration including starting Deceleration including stopping 4/22/2017 PALANISAMY MTech.,(PhD)
PALANISAMY MTech.,(PhD) Steady state Load torque is equal to motor torque Change in speed is achieved by varying the steady state motor speed torque curve so that Load torque is equal to motor torque at desired new speed. The motor works as a motor operating in quadrant 1 or 3. 1. frequent maintenance 2. lower life 3. braking power is always wasted as heat 4/22/2017 PALANISAMY MTech.,(PhD)
Acceleration and deceleration Drive depends on the values of T and Tl. T > Tl – Acceleration T < Tl – deceleration During acceleration, the motor torque not only overcome the load torque but it supplies to dynamic torque J(dωm/dt) to overcome drive inertia. In drives with larger inertia, like electric trains, motor torque must exceed the load torque by a large amount in order to get sufficient acceleration. When fast transient response required, motor torque should be maintained at larger rate and the system should be designed with lowest inertia 4/22/2017 PALANISAMY MTech.,(PhD)
Acceleration and deceleration 4/22/2017 PALANISAMY MTech.,(PhD)
PALANISAMY MTech.,(PhD) Motor steady state torque-speed characteristic Synchronous mch Induction mch Separately / shunt DC mch Series DC SPEED TORQUE By using power electronic converters, the motor characteristic can be change 4/22/2017 PALANISAMY MTech.,(PhD) 48
PALANISAMY MTech.,(PhD) Synchronous or Reluctance motor: They exhibit constant speed characteristics as shown in block curve. At steady state conditions, these motors operate at constant speed irrespective of the value of load torque. DC Shunt/Separately excited motor: The characteristic green curve shows that the speed is slightly reduced when the load torque increases. DC Series Motor: The speed is high at light load and low at heavy loading condition as shown in the Blue curve . 4/22/2017 PALANISAMY MTech.,(PhD)
Induction Motors: They exhibit complex characteristics as shown in red curve. During steady state, they operate at the linear proportion of speed torque characteristic, which resembles the characteristic of a DC shunt motor. The maximum developed torque of induction motors is limited to Tmax. In electric drive applications, the selection of the motor should match with the required performance of the loads. For example, the synchronous motor is probably the best option for the constant speed applications. Other motors, such as induction or DC shunt motors can also be used in constant speed applications, provided that feedback circuits are used to compensate for the change in speed when load torque changes.
PALANISAMY MTech.,(PhD) Load steady state torque-speed characteristic Exist in all motor-load drive system simultaneously In most cases, only one or two are dominating Exists when there is motion. Frictional torque (passive load) SPEED T~ C Constant torque load T~ 2 Fan type load T~ Generator type load TORQUE 4/22/2017 PALANISAMY MTech.,(PhD) 51
PALANISAMY MTech.,(PhD) Load steady state torque-speed characteristic Constant torque, e.g. gravitational torque (active load) SPEED TORQUE Gravitational torque TL Te Vehicle drive FL gM 4/22/2017 PALANISAMY MTech.,(PhD) 52
PALANISAMY MTech.,(PhD) Load steady state torque-speed characteristic Hoist drive Speed Torque 4/22/2017 PALANISAMY MTech.,(PhD) 53
Load and motor steady state torque At constant speed, Te= Tl Steady state speed is at point of intersection between Te and Tl of the steady state torque characteristics Tl Te Torque r2 r3 r1 Steady state speed r Speed 54
PALANISAMY MTech.,(PhD) Classes of motor duty 4/22/2017 PALANISAMY MTech.,(PhD)
PALANISAMY MTech.,(PhD) Paper mills compressors Conveyers fans 4/22/2017 PALANISAMY MTech.,(PhD)
Continuous duty (constant load and variable load) Load torque is constant over extended period multiple Steady state temperature reached Nominal output power chosen equals or exceeds continuous load Losses due to continuous load t L 4/22/2017 PALANISAMY MTech.,(PhD)
PALANISAMY MTech.,(PhD) Operation considerably less than time constant, Motor allowed to cool before next cycle Motor can be overloaded until maximum temperature reached Crane drives Household appliances Machine tools for position control 4/22/2017 PALANISAMY MTech.,(PhD)
PALANISAMY MTech.,(PhD) Cutting Drilling Machines 4/22/2017 PALANISAMY MTech.,(PhD)
PALANISAMY MTech.,(PhD) Periodic intermittent duty Load cycles are repeated periodically Motors are not allowed to completely cooled p1 heating coolling t Fluctuations in temperature until steady state temperature is reached 4/22/2017 PALANISAMY MTech.,(PhD)
PALANISAMY MTech.,(PhD) Metal cutting Drilling tool drives Mine hoists 4/22/2017 PALANISAMY MTech.,(PhD)
PALANISAMY MTech.,(PhD) Billet Mill drive Manipulator drive Machine tools 4/22/2017 PALANISAMY MTech.,(PhD)
Continuous duty with intermittent periodic loading Consists of periodic duty cycles, each consisting of a period of running at a constant load and period of running at a no load. Load period and no load period being too short for respective temperatures to be obtained. This duty distinguished from the intermittent periodic duty by period of running by constant load and period of running by no load instead of rest condition. Pressing, cutting and drilling machine drives 4/22/2017 PALANISAMY MTech.,(PhD)
Continuous duty with starting and braking Consists of periodic duty cycles, each consisting of a period of starting, period of running at a constant load and period of braking, there is no rest condition. Continuous duty with periodic speed changes Consists of periodic duty cycles, each consisting of a period of running at one load and speed, and another period of running at different load and speed. There is no period of rest. 4/22/2017 PALANISAMY MTech.,(PhD)
Determination of motor Rating Broadly classified into, Continuous Duty Fluctuating loads Short time and intermittent duty 4/22/2017 PALANISAMY MTech.,(PhD)
PALANISAMY MTech.,(PhD) Continuous Duty A motor with next higher power rating from commercially available ratings is selected. Motor speed should also match load’s speed requirements. Necessary to check whether the motor can fulfill starting torque requirement and can continue to drive load. Losses due to continuous load t L 4/22/2017 PALANISAMY MTech.,(PhD)
Fluctuating loads & intermittent loads Motor loss P1 consists of two components- constant loss Pc which is independent of load and contains core & friction loss; and load dependent copper loss. This fluctuating load consisting of n values of motor currents I1, I2, I3, …In for the durations of t1, t2, t3,...tn respectively. Then the equivalent current is, load diagram of Fluctuating load
Equivalent current is, If the current varies smoothly over a period T, When torque is directly proportional to current and power is directly proportional to torque,
PALANISAMY MTech.,(PhD) In DC motor- allowed to carry larger current than the rated current for short duration- short time overload capacity of load. Normally DC motor designed to carry up to 3 times of rated current. Because the higher currents sparking between the brushes and commutator. λ >= (Imax / Irated) 4/22/2017 PALANISAMY MTech.,(PhD)
PALANISAMY MTech.,(PhD) Short Time Duty In short time duty, time of motor operation considerably less than the heating time constant & motor is allowed to cool down to ambient temperature. If a motor with continuous duty power rating of Pr is subjected to a short time duty load of magnitude Pr’ - then motor temp rise will be far below the maximum permissible value & motor can be overloaded by a factor K (K>1). 4/22/2017 PALANISAMY MTech.,(PhD)
PALANISAMY MTech.,(PhD) When the duration of running period in a duty cycle with power KPr is tr, If the motor losses for powers Pr and (KPr) be P1r nd P1s respectively. Pc is the load independent loss and Pcu load dependent loss. Then, The overloading factor for short time duty, 4/22/2017 PALANISAMY MTech.,(PhD)
Intermittent periodic duty During a period of operation, if the speed changes in wide limits, leading to changes in heating and cooling conditions, equ. current, torque or power are not employed. Temp rise will fluctuate between a maximum value Tmax and a minimum value Tmin. Temp at the end of the working interval will be given by, fall in Temp rise at the end of standstill interval ts will be 4/22/2017 PALANISAMY MTech.,(PhD)
PALANISAMY MTech.,(PhD) Time constants of motor for working and standstill conditions Tmax= Tmin, then P1r and P1s will be, The overloading factor for intermittent periodic duty is, 4/22/2017 PALANISAMY MTech.,(PhD)
PALANISAMY MTech.,(PhD) Applications of Electric Drives Transportation Systems Rolling Mills Paper Mills Textile Mills Machine Tools Fans and Pumps Robots Washing Machines etc 4/22/2017 PALANISAMY MTech.,(PhD)
PALANISAMY MTech.,(PhD) 4/22/2017 PALANISAMY MTech.,(PhD)
PALANISAMY MTech.,(PhD) 4/22/2017 PALANISAMY MTech.,(PhD)
PALANISAMY MTech.,(PhD) 4/22/2017 PALANISAMY MTech.,(PhD)