PDF | This paper discusses the speed and torque control of a shunt DC motor through MATLAB Simulink simulations. The DC shunt motor is Vdc with rated . PDF | Speed of a dc series motor can be controlled using diverter in the field circuit of motor. This paper derives an equation which shows the. 𝗣𝗗𝗙 | he speed of separately excited DC motor (SEDM) can be controlled above rated speed using field control method. The chopper circuit is used to control.
|Language:||English, Spanish, Japanese|
|ePub File Size:||23.52 MB|
|PDF File Size:||17.51 MB|
|Distribution:||Free* [*Sign up for free]|
armature control method. (iii) By varying the applied voltage V. This is known as voltage control method. Speed Control of D.C. Shunt Motors. The speed of a. In this lesson aspects of starting and speed control of d.c motors are discussed and explained. At The problems of starting d.c motors with full rated voltage. 2. Speed Control of Shunt motor: (i) Variation of Flux or Flux Control Method: By decreasing the flux, the speed can be increased and vice versa. The flux of a dc.
This intentional change of drive speed is known as speed control of a DC motor. Speed control of a DC motor is either done manually by the operator or by means of an automatic control device. The speed of a DC motor N is equal to: Therefore of the 3 types of DC motors — shunt, series and compound — can be controlled by changing the quantities on the right-hand side of the equation above. Hence the speed can be varied by changing: The terminal voltage of the armature, V. The external resistance in armature circuit, Ra.
The trained neural network is then used for controller design.
Rotor inertia Nm2 K. All are based on standard linear control architecture. It is to train a neural network to represent the forward dynamics of the plant. Tapped Delay Lines that stores previous values of the input signal IW i. The prediction error between the plant output and the neural network output is used as the neural network training signal.
Model Reference Control Architecture 4. DBP gets applied to a larger class of plant and hence the controller requires minimal online computation.
Generally indirect MRAC is preferred. The controller training is done separately and requires the use of dynamic back-propagation. This architecture consists of two neural networks. The discrete time model speed equation governing the system dynamics is given by. Controller network Plant model network After SI. The equation can be manipulated to the form.
The following second order reference model is chosen. Wp k-1 ] where the function g[. The objective of the control system is to drive the motor so that its speed Wp k. An ANN is trained to emulate the unknown function g[. This result can be fed to the ANN to estimate the control input at kth time step using.
Wp k-2 ]. Wp k Following parameter values are associated with it. Using the given values of the system parameters in the above stated equations we get.
While in addition to being functions of the above parameters are also functions of. A separately excited dc motor with name plate ratings of 1 hp. The value k denotes the kth time step. La and the sampling period T. The system equation becomes. Substituting the values of the motor parameters in the above two equations along with the initial conditions.
Actual And Estimated Rotor Speeds Where the function f[. Wp k-1 ] is given by above equation. The values Wp k and Wp k. The 3-layer feed-forward ANN used: The corresponding ANN output target f [Wp k. The choice of Wp k.
Where N[. ANN topology and the training effort are briefly described by the following statistics: Wp k-1 ]. The ANN is trained off-line using randomly generated input patterns of [Wp k. Wp k-1 ] and the corresponding target f [Wp k.
Wp k-1 has to satisfy the constraints as specified earlier. A single neuron i. The performance of the trained ANN identifier is evaluated by comparing the actual and estimated speeds as calculated from the afore mentioned equations above for the following arbitrarily selected terminal voltage sequence. This has the effect of squashing the infinite range of In into the range 0 to 1.
It is convenient to think of the activations flowing through layers of neurons. Remember that in C the array indices start from zero. Each neuron will also have a bias. I find that keeping a separate index i. For obvious reasons. Target[p][k] labelled by the index p. For example. The network learns by minimizing some measure of the error of the network's actual outputs compared with the target outputs.
A standard way to do this is by 'gradient descent' on the error function. The factor of 0. If we insert the above code for computing the network outputs into the p loop of this. We can compute how much the The complete training process will consist of repeating the above weight updates for a number of epochs using another for loop until some error crierion is met. Fixing good values of the learning parameters eta and alpha is usually a matter of trial and error.
Having it too large will cause the weight changes to oscillate wildly. If we put the NumPattern training pattern indices p in random order into an array ranpat. If it is set too low. It is therefore generally a good idea to use a new random order for the training patterns for each epoch. Finding a good value for eta will depend on the problem. Certainly alpha must be in the range 0 to 1. If rando is your favourite random number generator function that returns a flat distribution of random numbers in the range 0 to 1.
It is normal to initialize all the weights with small random values. Starting all the weights at zero is generally not a good idea. Generating the random array ranpat is not quite so simple. Let's for a moment assume that the tracking error Ec k is zero. The following second order reference model is selected. The objective of the control system is to drive the motor so that its speed. The controller topology trained in the previous chapter is now used to estimate the motor terminal voltage Vt k which enables accurate trajectory control of the shaft speed Wp k.
The coefficients are selected to ensure that its poles are within the unit circle and has the type of response that can be achieved by the dc motor. For a given desired sequence Wm k trajectory. Performance of the controller is simulated for arbitrarily selected speed tracks Wm k. This is done by letting the dc motor follow the output of a selected reference model throughout the trajectory.
A graphical comparison of the specified and actual speed trajectories are hence presented. The matrix corresponds to the reference model coefficients [0. Only a specific result is shown for brevity.
In a motor, the magnitude of this Lorentz force a vector represented by the green arrow , and thus the output torque,is a function for rotor angle, leading to a phenomenon known as torque ripple Since this is a two-pole motor, the commutator consists of a split ring, so that the current reverses each half turn degrees.
The brushed DC electric motor generates torque directly from DC power supplied to the motor by using internal commutation, stationary magnets permanent or electromagnets , and rotating electromagnets.
Advantages of a brushed DC motor include low initial cost, high reliability, and simple control of motor speed. Disadvantages are high maintenance and low life-span for high intensity uses. Maintenance involves regularly replacing the carbon brushes and springs which carry the electric current, as well as cleaning or replacing the commutator. These components are necessary for transferring electrical power from outside the motor to the spinning wire windings of the rotor inside the motor.
Brushes are usually made of graphite or carbon, sometimes with added dispersed copper to improve conductivity. In use, the soft brush material wears to fit the diameter of the commutator, and continues to wear. A brush holder has a spring to maintain pressure on the brush as it shortens. For brushes intended to carry more than an ampere or two, a flying lead will be molded into the brush and connected to the motor terminals.
Very small brushes may rely on sliding contact with a metal brush holder to carry current into the brush, or may rely on a contact spring pressing on the end of the brush. The brushes in very small, short-lived motors, such as are used in toys, may be made of a folded strip of metal that contacts the commutator. Main articles: Brushless DC electric motor and Switched reluctance motor Typical brushless DC motors use one or more permanent magnets in the rotor and electromagnets on the motor housing for the stator.
A motor controller converts DC to AC. This design is mechanically simpler than that of brushed motors because it eliminates the complication of transferring power from outside the motor to the spinning rotor.
The motor controller can sense the rotor's position via Hall effect sensors or similar devices and can precisely control the timing, phase, etc. Advantages of brushless motors include long life span, little or no maintenance, and high efficiency.
Disadvantages include high initial cost, and more complicated motor speed controllers. Some such brushless motors are sometimes referred to as "synchronous motors" although they have no external power supply to be synchronized with, as would be the case with normal AC synchronous motors.
Uncommutated[ edit ] Other types of DC motors require no commutation. Homopolar motor — A homopolar motor has a magnetic field along the axis of rotation and an electric current that at some point is not parallel to the magnetic field. The name homopolar refers to the absence of polarity change.
Homopolar motors necessarily have a single-turn coil, which limits them to very low voltages. This has restricted the practical application of this type of motor. Ball bearing motor — A ball bearing motor is an unusual electric motor that consists of two ball bearing -type bearings, with the inner races mounted on a common conductive shaft, and the outer races connected to a high current, low voltage power supply.
An alternative construction fits the outer races inside a metal tube, while the inner races are mounted on a shaft with a non-conductive section e. This method has the advantage that the tube will act as a flywheel. Therefore series motors are widely used in all types of electric vehicles, eletrictrains, streetcars, battery powered tools, automotive starter motors etc.
With the increase in the load speed of the machine decreases. DC shunt motor maintains almost constant speed from no load to full load.. Therefore such type of compound motors are used for loads requiring heavy starting torque which are likely to be reduced to zero A compound motor with weak series field has its characteristics approaching that of a shunt motor. Weak series field causes more drooping speed torque characteristics than with an ordinary shunt motors.
Such compound motors with steeper characteristics, are used where load fluctuates between wide limits intermittently. They are also used in feedback and the freewheeling functions of converters and snubbers. Fig 2. In the forward biased condition, the diode can be represented by a junction offset drop and a series-equivalent resistance that gives a positive slope in the V-I characteristics.
The typical forward conduction drop is 1. This drop will cause conduction loss, and the device must be cooled by the appropriate heat sink to limit the junction temperature. In the reverse-biased condition, a small leakage current flows due to minority carriers, which gradually increase with voltage. If the reverse voltage exceeds a threshold value, called the breakdown voltage, the device goes through avalanche breakdown, which is when reverse current becomes large and the diode is destroyed by heating due to large power dissipation in the junction.
Thyristors or silicon-controlled rectifiers SCRs have been the traditional workhorses for bulk power conversion and control in industry. The modern era of solid- state power electronics started due to the introduction of this device in the late s. Basically, it is a trigger into conduction device that can be turned on by positive gate current pulse but once the device is on, a negative gate pulse cannot turn it off. The thyristors have been widely used in dc and ac drives, lighting, heating and welding control.
The dc current gain of a power transistor is low and varies widely with collector current and temperature. The gain is increased to a high value in the Darlington connection, as shown in Fig2. The shunt resistances and diode in the base-emitter circuit help to reduce collector leakage current and establish base bias voltages. A transistor can block voltage in the forward direction only asymmetric blocking.
The feedback diode, as shown, is an essential element for chopper and voltage-fed converter applications. Double or triple Darlington transistors are available in module form with matched parallel devices for higher power rating. Power transistors have an important property known as the second breakdown effect. This is in contrast to the avalanche breakdown effect of a junction, which is also known as first breakdown effect. When the collector current is switched on by the base drive, it tends to crowd on the base-emitter junction periphery, thus constricting the collector current in a narrow area of the reverse-biased collector junction.
This tends to create a hot spot and the junction fails by thermal runaway, which is known as second breakdown. The rise in junction temperature at the hot spot accentuates the current concentration owing to the negative temperature coefficient of the drop, and this regeneration effect causes collapse of the collector voltage, thus destroying the device.
Two stage Darlington transistor with bypass diode 2. If the gate voltage is positive and beyond a threshold value, an N-type conducting channel will be induced that will permit current flow by majority carrier electrons between the drain and the source. Although the gate impedance is extremely high at steady state, the effective gate-source capacitance will demand a pulse current during turn-on and turn-off. The device has asymmetric voltage- blocking capability, and has an integral body diode, as shown, which can carry full current in the reverse direction.
The diode is characterized by slow recovery and is often bypassed by an external fast-recovery diode in high-frequency applications. Many designers view IGBT as a device with MOS input characteristics and bipolar output characteristic that is a voltage-controlled bipolar device. It combines the best attributes of both to achieve optimal device characteristics.
The IGBT is suitable for many applications in power electronics, especially in Pulse Width Modulated PWM servo and three-phase drives requiring high dynamic range control and low noise. IGBT improves dynamic performance and efficiency and reduced the level of audible noise. It is equally suitable in resonant-mode converter circuits.
Optimized IGBT is available for both low conduction loss and low switching loss. It has a very low on-state voltage drop due to conductivity modulation and has superior on-state current density. So smaller chip size is possible and the cost can be reduced. Low driving power and a simple drive circuit due to the input MOS gate structure.
It can be easily controlled as compared to current controlled devices thyristor, BJT in high voltage and high current applications. Wide SOA. It has superior current conduction capability compared with the bipolar transistor. It also has excellent forward and reverse blocking capabilities. The collector current tailing due to the minority carrier causes the turnoff speed to be slow. There is a possibility of latchup due to the internal PNPN thyristor structure. The IGBT is suitable for scaling up the blocking voltage capability.
In case of Power MOSFET, the on-resistance increases sharply with the breakdown voltage due to an increase in the resistively and thickness of the drift region required to support the high operating voltage. In contrast, for the IGBT, the drift region resistance is drastically reduced by the high concentration of injected minority carriers during on-state current conduction. The forward drop from the drift region becomes dependent upon its thickness and independent of its original resistivity.
Pulse-width modulation PWM or duty-cycle variation methods are commonly used in speed control of DC motors. Thus by varying the pulse-width, we can vary the average voltage across a DC motor and hence its speed. Ymax The circuit of a simple speed controller for a mini DC motor, such as that used in tape recorders and toys, is shown in Fig2.
The heat dissipation problem often results in large heat sinks and sometimes forced cooling. PWM amplifiers greatly reduce this problem because of their much higher power conversion efficiency. The PWM power amplifier is not without disadvantages. The desired signal is not translated to a voltage amplitude but rather the time duration or duty cycle of a pulse. This is obviously not a linear operation. But with a few assumptions, which are usually valid in motor control, the PWM may be approximated as being linear i.
The linear model of the PWM amplifier is based on the average voltage being equal to the integral of the voltage waveform. The duty cycle must be recalculated at each sampling time. Pulse width modulation technique PWM is a technique for speed control which can overcome the problem of poor starting performance of a motor. PWM for motor speed control works in a very similar way. Instead of supplying a varying voltage to a motor, it is supplied with a fixed voltage value such as 12v which starts it spinning immediately.
The wave forms in the below figure to explain the way in which this method of control operates. In each case the signal has maximum and minimum voltages of 12v and 0v. By varying the mark space ratio of the signal over the full range, it is possible to obtain any desired average output voltage from 0v to12v.
The motor will work perfectly well, provided that the frequency of the pulsed signal is set correctly, a suitable frequency being 30Hz. Pulse Width Modulation Waveforms 2. Block Diagram of an Analogue PWM Generator The simplest way to generate a PWM signal is the intersective method, which requires only a saw tooth or a triangle wave form easily generated using a simple oscillator and a comparator.
When the value of the reference signal is more than the modulation wave form, the PWM signal is in the high state, otherwise it is in the low state. Digital Method: The digital method involves incrementing a counter, an comparing the counter value with a pre-loaded register value, or value set by an ADC. They normally use a counter that increments periodically and is reset at the end very period of the PWM.
When the counter value is more than the reference value, the PWM output will change state from high to low. PWM generator chips: Many of these are designed for use in switch mo power supplies. The Power Supply is a Primary requirement for the project work. The can be used to provide time delays, as an oscillator, and as a flip-flop element. Derivatives provide up to four timing circuits in one package. Fig 3. In phase with output. The trigger and reset inputs pins 2 and 4 respectively on a are held high via pull-up resistors while the threshold input pin 6 is simply floating.
Thus configured, pulling the trigger momentarily to ground acts as a 'set' and transitions the output pin pin 3 to Vcc high state. Pulling the reset input to ground acts as a 'reset' and transitions the output pin to ground low state.
No timing capacitors are required in a bistable configuration.