Electric Drives:

Motor Controllers and Control Systems (Description and Applications):
Purpose For many years the controller engine was a box which provides control of engine speed and allowed the engine to adapt to variations in load. Projects were often at a loss or provided only slow increases in the control of parameters.
Modern controllers can integrate both power electronics and microprocessors, allowing the check to take on many more tasks and apply them more accurately. These tasks include:
Monitoring the dynamics of the machine and its response to applied loads. (speed, torque and efficiency of the machine or the position of the moving parts.) Providing electronic conversion. Turn yourself starting the engine. The protection of the engine and the controller itself from harm or abuse. Matching the power sources available to meet the engine requirements (voltage, frequency, number of phases).

This is an example of "Power Conditioning" whose purpose is to provide pure sinewave power DC or without harmonics or interference. Although it could be an integral part of the generator control system in general, conditioning could also be provided by a separate autonomous unit operating on any energy source.
Control System Principles:

Open Loop Systems (manual control) In an open loop control system are the control parameters specified or operator and the system finds its own equilibrium.

In the case of an engine balance desired function may be the motor speed or angular position. The controlling parameters such as the supply voltage or load may or may not be under the control of the operator.
If any of the parameters such as load or supply voltage changed the engine will find a new equilibrium, in this case will settle at different speeds. The true equilibrium can be changed by forcing a change in parameters on which the operator has control.

Closed Loop Systems (Automatic Control):

Just set the initial operating parameters, an open loop system can not respond to subsequent changes or disturbances in the system operating environment such as temperature and pressure, or different requirements for the system, such as power supply or load conditions.
For monitoring and control mode of a system without operator intervention, for greater accuracy and faster response, require automatic control.
Negative feedback
To meet these requirements "closed loop" systems are needed. Also called the control feedback or negative feedback, allowing the user to specify a desired running object or reference and control system will automatically move the system to the desired operating point and maintain it at this point then.
A sensor used to monitor the effective running of the system and feed back to the input of the controller analog or digital signal representing the state exit. The actual and desired or reference than ever if the reality is different from the baseline, an error message is created that the auditor uses to force the change of parameters checked to eliminate errors in driving the system back in the desired operating point.
Gain Loop:

The error signal is usually very small so the control circuit or mechanism must include a high gain "amp error" to provide the controlling signal with the power to influence change.
The aid provided for in the loop called the loop gain.
Loop Delay:

The answer is not always instantaneous as there is usually a delay between sensing the error, or targeted at a new location, and correcting errors or moving in the desired new location. This delay is called delay loop.
In mechanical systems the delay may be due to the inertia associated with the lowest possible speed to get a large mass to move when a force is applied.
Electrical circuits the delay may be associated with the inductive circuit elements that may reduce the rate of current build up in the circuit when the voltage is applied.

The closed loop control systems should act quickly to implement error correction without delay before the system has time to change to a different situation. Otherwise, the system may become unstable.
When there is a time lag between sensing the error and completion of remedial measures and the loop gain is large enough system the system can be exceeded. If this occurs, the error will then be in the opposite direction and control system will be reversed also the direction of action to fix this new error. The result is that the actual position will vary around the desired position. This instability is called hunting, and the system hunts to find the point of view.
At worst, the slow reaction to correct the error will reach 180 degrees outside stage with the disorder try to eleiminate. When this occurs, the direction of the system response will not act to eliminate the error, instead will increase the error. Thus, the delay has changed the system's response to negative feedback to positive feedback and the system is critically unstable.

If the loop gain is ot greater unity in the frequency of an input sinusoid if the delay time the system is equal to half the period of the cycle, the sytem will be unstable.
In practical terms, a system with high electrical or mechanical inertia will have a slow response (long delay). With a small, correcting errors of action (mechanical power or voltage), the system will slow in responding (acceleration), but because they are slow, will also have a little momentum and will tend to settle to the desired operating point when the error correcting power is removed.
The delay in implementation of corrective measures, but depends on the loop gain.
If, on the same system, the error correcting power is high (amplified / higher gain loop), as in a fast-acting, the system will respond (alert) faster (less delay), but has higher sprint (faster response). When the error correcting power is removed, and any system of high inertia, momentum of the system will keep moving and it will overshoot the target position. Applying the error message in the opposite direction to bring the system back in order, will cause it to excess in the opposite direction.
Nyquist shows how delay can be tolerated in a system with unity gain loop, and determining the point at which the system becomes unstable
In the example of a DC electric motor, the desired mode can be a particular speed. A tachometer is used to measure the actual speed in comparison with the reference speed. If different, an error message, the size and polarity of which corresponds to the difference between the reference and actual speed, is supplied with a voltage controller to change the engine speed to reduce the error message. With the engine at the desired speed signal error is zero and the engine will maintain the speed.
The three different types of treatment commonly used in error control, P, I and D, named after three main ways to manipulate the error information. Analog - Analog error correction multiplies the error of a (negative) constant P, and adds that the controlled quantity. Integral - Integral error correction incorporates past experience. Integrates the error over a period and then multiply by a (negative) constant I and adds that the controlled quantity. Balance is based on the average error and avoid excess vibration and a more stable system. - Production debugging based on the rate of change of error and reflect future expectations. Used in so-called "Predictive Controllers". The first derivative of the error over time is calculated and multiplied by another (negative) constant D, and also added the controlled quantity.

The derivative term provides a quick response to the climate system. The combinations of three treatments of error are often used simultaneously "PID" Those responsible for dealing with different priorities of system performance. Where noise can be a problem, the derivative term is not used.
Four Quadrant Operation When an electric motor is required to work as both an engine and generator, both forward and reverse directions is said to be four quadrant operation. A simple engine operates only in one direction and never driven a generator is an example of a single application quadrant. An engine designed for automotive use which must run forward and reverse directions, which should provide regenerative braking in both directions, the needs of four quadrant controller.
Control systems for four quadrant applications will obviously be more complex than single quadrant of the controls.

Basic Motor Control functions and applications Auditors may have some or all of the following functions many of which have been applied to integrated circuits.

Speed DC machines One of the main attractions of brushed DC motors is the simplicity of the controls. The speed is proportional to the voltage and the torque is proportional to the current.
Speed control used in brushed DC motors to be achieved by varying the voltage supply, using lossy rheostats in voltage. The speed shunt wound DC motors can be controlled through the weakened area. Today electronic control voltage is employed. See below.
Simple open-loop voltage control is adequate when the engine has a fixed load, however, open loop voltage control can not respond to changes in load on the engine. If the load, engine speed will change. If the load increases, the engine has to deliver more torque to reach an equilibrium position and it needs more power. The engine slows down accordingly, reducing the back EMF, so that more current flows.

To maintain the desired speed, the voltage change is necessary to provide the necessary current required by the new load conditions. Automatic speed control can be achieved only in a closed loop. This uses a tachogenerator on the output shaft to a feedback measure the actual speed. When this is compared with the desired speed, a "velocity error" signal is produced which is used to change the input voltage to the motor lead to the desired speed. Note - This is essentially a system voltage control since the tachogenerator usually provides a dc output that is compared with an input voltage reference.
Voltage control alone may be insufficient to cover the broad, rapidly changing load on the engine after the voltage controller may request currents in excess of the limits of the design of motors. A separate current feedback loop may be required to provide automatic current control. The current control loop must be nested within the voltage control loop. This allows the voltage control loop to provide more modern, but can not override the current control which ensures that the current stays within the limits set by the current control loop.
The Brushless DC motor powered by a pulsed DC supply create a rotating field and the speed is synchronous with the frequency of rotating field. Speed is controlled by varying the frequency of supply. Inverters see below.
AC machines The speed of AC depends generally on the frequency of the voltage supply and the number of magnetic poles per phase in stator. Early speed controllers depends on the transition to a different number of poles and control was only available with manual and slow steps. Modern electronic converters make continuously variable frequency supply may enable closed-loop speed control. To control the speed induction motors, but the supply voltage must change in harmony with the frequency. This requires a special Volts / Hertz control.
Torque Control If the application requires direct control of torque rather than speed, in simple machines can be achieved by controlling the flow, which is proportional to torque, and omitting the loop speed control. For more precise control, the auditors used the disease entities.

Voltage Control It is no longer necessary to use energy wasting rheostats to provide a variable voltage.

Voltage Choppers Modern controllers use switching regulators or channels helicopter to provide a variable DC voltage supply from a fixed DC. The dc power supply is switched on and off at high frequency (typically 10 kHz or more) with the use of electronic switching devices such as MOSFETs, IGBTs or GTOS providing wave form of pulsed DC. The average output current can be controlled by changing the duty cycle of the helicopter.

Pulse Width Modulation (PWM):

AC voltages can be controlled in the same way bi-directional pulses to represent the sine wave.
The PID controller are also called "3 term controllers:

Motor controllers can be simple or open loop systems may include various inserts closed loop systems operating simultaneously. For example, closed-loop controls can be used to synchronize the excitation of stator poles in the angular position of the cursor or simply to control the motor speed or angular position of the cursor.