UPS: Inverters provide control alternating current (AC):

supply of a DC or AC source.

There are two broad classes of applications:
Providing a fixed output from a variable source UPS designed to provide regulated supply lines from sources that may have a variable input voltage (AC or DC) or if the electricity network, an input variable frequency. These applications include May standby generators, power supplies (UPS) or distributed power generation from wind and other intermittent resources. All must issue a fixed output voltage and frequency to the load since the applications expect and depend on it in May.
Providing a variable flow from a stationary source Moreover, many applications require inverters to accept a fixed voltage and frequency AC voltage area and provide a different voltage or variable frequency for applications such as control of motor speed. .
In both models, a bridge rectifier is used to provide power through DC with a current link "to a standard AC inverter.
The circuit below shows the principle of such an inverter designed for three phase applications.
Three frequency inverter variable phase
The third phase sinusoidal input is sent to a simple diode full wave bridge rectifier block issuing a fixed voltage to the UPS. The connection between the rectifier and the inverter is known as the current link. The transistors are switched inverter in the sequence of numbers as shown in the diagram with a time difference if T / 6 and each transistor is kept for a period of T / 4, where T is the period of time for each complete cycle. Line output waveform voltage of each phase is presented below.
This reference frequency converter may simply be a voltage applied to the input of a Voltage Controlled Oscillator (VCO), examples of which are usually available as integrated circuit chips, or it may be derived from a microprocessor clock. Digital logic circuits are used to obtain trigger pulses programmed to the UPS source of reference frequency. In the case of generators supplying AC power, the value of the reference frequency will be set.
The amplitude of the output waveform is determined by the voltage level DC power inverter block but can be modified by thyristor (SCR) control of the rectifier circuit to provide variable voltage to the current link .
Instead of transistor switches, the inverter May use MOSFET, IGBT or CSIS.
Free-wheeling diodes connected to the terminals of the transistors to protect them against wave reverse bias due to inductive motor rot on the ground that occurs when the transistors turn up freewheeling paths for stored energy.
The waveforms for applications such as traction is often reinforced waves rather than pure sine waves because they are easier to produce and engine smooth waves.
Variable frequency drives are used when the variable speed control is required. The wave frequency is controlled by a variable frequency clock which triggers impulses.
For speed control in machines ac voltage and frequency must vary in unison. See AC speed control motor. In open loop systems the operating point is set by a speed reference and speed of equilibrium is determined by the load torque. A closed loop system allows a fixed speed to define. This requires a tachometer to provide feedback of the actual speed comparison with the desired speed. If there is a difference, an error signal is generated to bring the actual speed in accordance with the reference speed by adjusting both the voltage and frequency to eliminate the speed difference.
Volts / Hertz Control Volts / Hertz control is required to control the speed of induction motors. In a system open loop control system converts the desired speed to a reference input frequency to a variable frequency, variable voltage inverter. At the same time, it multiplies the reference frequency by the Volts / Hertz characteristic ratio of the engine to provide the reference voltage corresponding to the UPS. Change the reference speed will then cause the voltage and frequency output of the inverter to change in unison.
In a closed loop system response to the treatment provided from a tachometer signal on the output shaft of the engine is used in the control loop to derive an error signal speed to drive a Volts / Hertz function control similar to that described above.
As for large DC motors, cruise control is normally accompanied by current control.
Cycloconverter:
The Cycloconverter converts AC supply frequency directly to an AC variable frequency without the stage of the DC intermediate link.
The system is complex and operates by sampling the voltage of each phase of AC power and synthesize the desired output signal by switching on the responsibility for the duration of the sampling period, the phase whose voltage is closer to the desired voltage at the instant of sampling. The waveform output is severely distorted and the ability of induction motors to deal with the harmonic content of extra high frequencies within which the system can be used.
Cycloconverters only suitable for very low frequencies up to 30% of the input frequency. They are used for drives at low speed high power to eliminate the need for a gearbox in heavy rolling and crushing plant and the uses pulling trains and ships.
Vector Control - RSS or field oriented control (FOC) All engines require a magnetizing current and torque producing current. In a dc motor brushed, these two trends are connected to two different windings. The magnetizing current is supplied to the stator or field coil and torque producing current is fed into the rotor winding. This allows independent control of both the stator and rotor fields. However in motors such as brushless permanent magnet or induction motors, it is not possible to control the rotor field directly because there are no connections to it. Because the parameters to be checked can not be measured, their value is derived from parameters that can be measured and monitored. Admission only on which control is possible is the input current supplied to the stator.
The stator current interest is the vector sum of two current vectors, induction (delayed phase) vector magnetizing current produces the flux in the gap and in phase, producing a torque, power. To change the torque we need change in phase, producing a torque, current, but because we want the gap airflow remains constant at its optimum level, the magnetizing current should also remain unchanged at change of torque.
Vector control or field-oriented control is a more or less independently of the magnitude and phase of the stator current vectors to adapt to the instantaneous speed and torque applications on the engine.
It allows the parameters on which no direct control can be changed by changing the position, parameters which can be measured and monitored.
To control many applications vector is not necessary, but control precision and maximum efficiency and rapid response, control field of the rotor is necessary and other methods of indirect control were developed. Given the low cost of computing power, vector control is used in automotive applications increasingly brushless.
Vector Control Summary Objectives Maximum current-torque power conversion, fast transient response, precise control of torque, speed and position. Rotating flux need to be maintained at 90 degrees to the flow of the rotor. Inputs of information (state voltages and currents of the stator and the rotor position and / or speed). Uses two independent control loops for control of the magnetization and torque producing current vectors. Calculates mathematical error transforms to analyze the input signals of the stator and calculate any deviation from the desired conditions of the rotor. Calculates correct mathematical inverse transform to convert the error signal rear rotor command signals applied to the stator to counter the error. Active pulse width modulated (PWM) inverter supplying power to the engine.

Stator produces waveforms of input voltage correct amplitude, frequency and phase for the change. Method 1 Direct Control position sensors and uses complex mathematical transforms Method 2 indirect control "sensorless" Use more complex mathematical transforms (Both methods above use current sensors for monitoring current stator windings) Control signals status Samples repeats and provides 20 kHz for ongoing monitoring. Additional benefits low speed control, improved efficiency, smaller engines.
The good news is that detailed knowledge of the process involved is not necessary since most of these tasks are performed in integrated circuits and incorporated into the design of the engine. But read on to find out how the overall system is used.
Transient Response Despite its many advantages, the venerable induction motor is relatively slow to react to changing load conditions or user commands to change speed. This is mainly because the current rotor can not follow instantaneously the applied voltage due to the delay caused by the inductance of the motor windings.
During the transition period the amplitude of the flux and its angle relative to the rotor must be maintained so that the desired torque can be developed.
Torque also depends on the importance of the flow, but it depends on the inductive current component and can be changed instantly. In any case, the flux density is set to its optimum point before saturation occurs.
Vector control is a way to change the current vector in phase without changing the magnetization vector inductive current so that the response time of the machine is not subject to delay induction.

Efficiency:

The inductive phase shift noted above also results in an immediate loss of torque and the low efficiency because of the torque producing stator flux is not acting 90 degrees to the electric field of the rotor.
Torque on the rotor of a motor at its maximum when the magnetic field due to the rotor is perpendicular to the field due to the stator. View Interactive Fields
The system of vector control provides instant adjustments stator currents to control the rotor position relative to the wave of displaced flow thereby avoiding losses due to the lag phase.
Implementation Both control methods described below describe each processing a sample of engine condition and how the error correction occurs. They both involve a lot of processing power of mathematics. The engine requires however continuous real time control to regulate the speed and torque and it takes sampling rate of 20 kHz or more to increase the processing load of the signal dramatically. This task is well within the scope of digital signal processors (DSP) integrated circuits designed for special applications of supercomputing.
Once the engine has a computer on board other functions such as communications and network (CAN bus) can be integrated with the motor controllers.
The system of vector control is essentially an indirect system using information on the system gain knowledge of voltages and currents of the stator and position. Both the "direct" and "indirect" methods of checks to indicate below the details of the rotor position is obtained.
For further information about stator currents in a three phase system, it suffices to measure two of the three phase currents supplied to the engine because the sum of the currents flowing in two windings must equal the course of the third winding.
Direct control:

This method uses a position sensor to determine the angular position of the rotating shaft. The angle between the rotor flux and the wave rotating flux is the sum of the angular position of the shaft and drift angle can be derived from the rotor current. The position error (difference of 90 degrees) is able to produce the necessary torque component of stator current. This signal can then be used as a basis for a classical loop current control.
The component of current flow in the stator must be calculated using a mathematical model of the engine. A mathematical transformation (Clarke-Park transformation) is performed on the actual stator currents to derive a measure of actual flow and a representation of the deviation from the desired value. The inverse transform is used to derive the correction signals corresponding error to be applied to the input of a frequency variable to generate appropriate stator current (amplitude, frequency and phase) to correct the error.
The mathematical processes require specific inputs on the mechanical and electrical machine which are often difficult to measure or estimate. Self-learning adaptive control systems have come to the rescue to generate baseline data from measurements of actual performance.
Control algorithms must also take account of environmental conditions. For example, the motor winding resistance (and therefore the L / R time constant of the engine) depends on the temperature and the effect of temperature changes to be incorporated into the model.
Indirect - Sensorless Control Sensorless control refers only to the elimination of the position of the detector used in the diagram above. The control system may have several other sensors. The position information provided by the position sensor can also be derived from mathematical transformations on stator currents and voltages along the stream is in the direct system. Since the physical sensor adds to the complexity and cost of the machine, and the cost of computing power is continually reduced, the replacement of the sensor by mathematical techniques is now economically justified.
The method of sensorless control can be used to control the motor speed to near zero.
Actuators Many of the techniques involved in vector control applicable to systems of oppression and therefore controlled vector system are the replacement of some traditional servo systems.

Ward Leonard Controller:

The Ward Leonard speed controller allows for variable speed drive of the fixed voltage and frequency of AC mains power. It uses three machines, induction motor ac driven at a fixed speed AC power, driving a DC generator which in turn is a dc motor shunt wound, generally of similar construction to generator. The generator output current is directly connected to the armature of the DC motor. The motor speed is adjusted using a rheostat to adjust the excitation current in the winding of the generator to vary the output voltage of the generator. Ward Leonard controllers can still see in lifts (elevators) throughout the world as well as electric cranes, winding gear coal mine machinery and industrial processes, although they were largely replaced by auditors thyristor speed.
Position Control Stepper motors:

It is generally used when the precise position control is necessary. Precise positioning is possible with an open-loop system by counting pulses applied to the motor. Potentiometers can be used to provide position feedback in closed loop systems, but shaft encoders provide more detailed comments Travel counting pulses.
When long distances to the target or engine revolutions many are involved, it may be desirable to accelerate the engine during the trip. In this case speed control may be provided by a feedback loop.
Electronic switching:

The function of the switch is to change the direction of the motor excitation current as the rotor poles pass the alternative poles of the stator. In brushless DC motors, the mechanical switch is eliminated and the current remote power is supplied by the stator coils. Switching is performed by electronic switches which reverse the stator current as the rotor poles alternate through the poles of the stator. This requires a position sensor feedback from the angular position of the rotor controller engine to enable them to change the direction of current when the rotor poles are in the correct position relative to the poles of the stator.
From Some engine models are not independent start when power is applied. These problems are usually treated by the manufacturer of machines using auxiliary windings or other methods and are usually not visible to the user.
One problem encountered by the user is only from many machines, comes with a high inrush current which is potentially damaging to the engine or food. Current control systems described above are used to overcome this problem.
Regenerative Braking:

The battery can capture energy from regenerative braking when maximum volts regen exceed the volt battery. With a DC motor, DC needs a variable - DC converter whose output is based on engine speed to convert the pulses of high voltage low at low speed braking high voltage low current pulses . The control system must also withdraw any voltage regen that exceeds the burden of high-voltage battery to avoid damaging the battery and it must dump excess energy into a resistive load when the battery reaches its full state of charge (SOC) of 100% or the current reaches the battery recommended charge current limit. This is particularly important for lithium batteries.
To capture energy from regenerative braking induction motors synchronous speed required to be reduced below the engine speed by reducing the frequency of supply. See generator action.
Power Factor:

Correction To avoid unnecessary losses, or to meet the load requirements acceptable to the utility of energy supply, correcting the power factor is often needed for induction motors, particularly for large machines or in facilities being implementing many machines.
The most common factor correction power is through capacitors added, however, under certain conditions, the motor controller can also be used for this purpose
In low load conditions the magnetization current in an induction motor is relatively high compared to the current load causing low power factor. (See Induction Motors). Because the charge is increased, the load increases in the current phase with respect to the magnetizing current, thus improving (increasing) the power factor.
The motor controller can be used to treat the problem of low power factor in lightly loaded machines. If the voltage is reduced to levels of light load, the airflow gap will be reduced accordingly and the current (and sliding) must increase to produce the same torque. The effect is to increase the charge current with respect to the magnetizing current, reducing the current weakness and increasing the power factor. Thyristor simple control of the supply voltage is sufficient to provide the control voltage necessary to implement this plan.
The control method of power factor is only practical for lightly loaded machines. Heavily loaded with power factor of the machinery is normally quite high and the effect of control voltage is not significant.
Protection Control systems described above are also designed to ensure that the electrical machine does not exceed its voltage and current. In addition, the machine in May incorporate several protection devices simple.
When overheated, a temperature sensor or thermistor causes power to be switched off or cooling systems to be turned on. If it exceeds a speed limit of safety, a centrifugal switch interrupting the current.
Sensors:

Examples of many types of sensors used in electronic engine control are given below.
Current -- Current Shunt - economic risk of loss. Current Transformer - Efficient, AC only - can not measure DC. Hall effect sensor. Voltage - A to D converters Frequency - pulse counting. Phase - derivative time difference between measured and reference sources. Temperature - thermistors, thermocouples. Light - opto-electronic and optical fibers. Magnetic flux - Hall effect sensor. Position - linear and angular. Optical encoders (based on a light source, a code wheel and an optical detector). Pulse counters - Linear and angular displacements. Pulses may be magnetic or optical. Potentiometers - Limited range, low accuracy. Speed - Tachometer based on different principles. Rotary DC generator - Provides a voltage output. Pulse counters - Legumes may be magnetic or optical. Centrifugal switch (limit switch). Torque - usually from motor current. Time - Microprocessor clock.
Practice Controllers Simple and low cost, low-power machines are usually open systems simple loop. Commons brushed DC motor, for example, needs only one simple voltage controller to control speed, low cost, integrated circuit controllers are available for this purpose. Machines with higher power, however, tend to use closed-loop controllers more complex are generally tailored to each particular machine, often incorporated into the machine itself. Electronic circuits in the motor controller must be able to handle the maximum engine power and this may be a limiting factor in designing a train driving.

The main variable influencing the peak power current, because it defines the cost of power electronics for a maximum voltage given. It is often necessary to use liquid cooling to accommodate high power levels required by the engine.
Polyphase machines need a set of circuits of power and control phase. The cost of the controller often limits the number of motor phases practices typically 3 or 4. Safety features also play a greater role in larger machines because in case of machine failure the damage potential is greater. Inverters, converters and collector circuits used in motor controllers needles all very high currents are therefore likely to be a source of radio interference (RFI).

The system designer must also be aware of the consequences of high frequency current high loads pulsed inverters and choppers May have on battery life in systems of dc traction, such as hybrid electric vehicles. Similarly, the regulated voltage generator on the board and the regenerative braking pulse of charge can also impair the battery if left unchecked.