A voltage regulator is designed to automatically maintain a constant voltage level. A voltage regulator may be a simple "feed-forward" design or may include negative feedback control loops. It may use an electromechanical mechanism, or electronic components. Depending on the design, it may be used to regulate one or more AC or DC voltages.
Electronic voltage regulators are found in devices such as computer power supplies where they stabilize the DC voltages used by the processor and other elements. In automobile alternators and central power station generator plants, voltage regulators control the output of the plant. In an electric power distribution system, voltage regulators may be installed at a substation or along distribution lines so that all customers receive steady voltage independent of how much power is drawn from the line.
Feedback voltage regulators operate by comparing the actual output voltage to some fixed reference voltage. Any difference is amplified and used to control the regulation element in such a way as to reduce the voltage error. This forms a negative feedback control loop; increasing the open-loop gain tends to increase regulation accuracy but reduce stability. (Stability is avoidance of oscillation, or ringing, during step changes.) There will also be a trade-off between stability and the speed of the response to changes. If the output voltage is too low (perhaps due to input voltage reducing or load current increasing), the regulation element is commanded, up to a point, to produce a higher output voltage–by dropping less of the input voltage (for linear series regulators and buck switching regulators), or to draw input current for longer periods (boost-type switching regulators); if the output voltage is too high, the regulation element will normally be commanded to produce a lower voltage. However, many regulators have over-current protection, so that they will entirely stop sourcing current (or limit the current in some way) if the output current is too high, and some regulators may also shut down if the input voltage is outside a given range (see also: crowbar circuits).
In electromechanical regulators, voltage regulation is easily
accomplished by coiling the sensing wire to make an electromagnet. The magnetic field
produced by the current attracts a moving ferrous core held back under
spring tension or gravitational pull. As voltage increases, so does the
current, strengthening the magnetic field produced by the coil and
pulling the core towards the field. The magnet is physically connected
to a mechanical power switch, which opens as the magnet moves into the
field. As voltage decreases, so does the current, releasing spring
tension or the weight of the core and causing it to retract. This closes
the switch and allows the power to flow once more.
If the mechanical regulator design is sensitive to small voltage fluctuations, the motion of the solenoid core can be used to move a selector switch across a range of resistances or transformer windings to gradually step the output voltage up or down, or to rotate the position of a moving-coil AC regulator.
Early automobile generators and alternators had a mechanical voltage regulator using one, two, or three relays and various resistors to stabilize the generator's output at slightly more than 6 or 12 V, independent of the engine's rpm or the varying load on the vehicle's electrical system. Essentially, the relay(s) employed pulse width modulation to regulate the output of the generator, controlling the field current reaching the generator (or alternator) and in this way controlling the output voltage produced.
The regulators used for DC generators (but not alternators) also disconnect the generator when it was not producing electricity, thereby preventing the battery from discharging back into the generator and attempting to run it as a motor. The rectifier diodes in an alternator automatically perform this function so that a specific relay is not required; this appreciably simplified the regulator design.
More modern designs now use solid state technology (transistors) to perform the same function that the relays perform in electromechanical regulators.
Electromechanical regulators are used for mains voltage stabilisation — see AC voltage stabilizers below.
To control the output of generators (as seen in ships and power
stations, or on oil rigs, greenhouses and emergency power systems)
automatic voltage regulators are used. This is an active system. While
the basic principle is the same, the system itself is more complex. An
automatic voltage regulator (or AVR for short) consists of several
components such as diodes, capacitors, resistors and potentiometers or
even microcontrollers, all placed on a circuit board. This is then
mounted near the generator and connected with several wires to measure
and adjust the generator.
How an AVR works: In the first place the AVR monitors the output voltage and controls the input voltage for the exciter of the generator. By increasing or decreasing the generator control voltage, the output voltage of the generator increases or decreases accordingly. The AVR calculates how much voltage has to be sent to the exciter numerous times a second, therefore stabilizing the output voltage to a predetermined setpoint. When two or more generators are powering the same system (parallel operation) the AVR receives information from more generators to match all output.
This is an older type of regulator used in the 1920s that uses the
principle of a fixed-position field coil and a second field coil that
can be rotated on an axis in parallel with the fixed coil, similar to a variocoupler.
When the movable coil is positioned perpendicular to the fixed coil, the magnetic forces acting on the movable coil balance each other out and voltage output is unchanged. Rotating the coil in one direction or the other away from the center position will increase or decrease voltage in the secondary movable coil.
This type of regulator can be automated via a servo control mechanism to advance the movable coil position in order to provide voltage increase or decrease. A braking mechanism or high ratio gearing is used to hold the rotating coil in place against the powerful magnetic forces acting on the moving coil.
The ferroresonant approach is attractive due to its lack of active components, relying on the square loop saturation characteristics of the tank circuit to absorb variations in average input voltage. Saturating transformers provide a simple rugged method to stabilize an AC power supply.
Older designs of ferroresonant transformers had an output with high harmonic content, leading to a distorted output waveform. Modern devices are used to construct a perfect sine wave. The ferroresonant action is a flux limiter rather than a voltage regulator, but with a fixed supply frequency it can maintain an almost constant average output voltage even as the input voltage varies widely.
The ferroresonant transformers, which are also known as Constant Voltage Transformers (CVTs) or ferros, are also good surge suppressors, as they provide high isolation and inherent short-circuit protection.
A ferroresonant transformer can operate with an input voltage range ±40% or more of the nominal voltage.
Output power factor remains in the range of 0.96 or higher from half to full load.
Because it regenerates an output voltage waveform, output distortion, which is typically less than 4%, is independent of any input voltage distortion, including notching.
Efficiency at full load is typically in the range of 89% to 93%. However, at low loads, efficiency can drop below 60%. The current-limiting capability also becomes a handicap when a CVT is used in an application with moderate to high inrush current like motors, transformers or magnets. In this case, the CVT has to be sized to accommodate the peak current, thus forcing it to run at low loads and poor efficiency.
Minimum maintenance is required, as transformers and capacitors can be very reliable. Some units have included redundant capacitors to allow several capacitors to fail between inspections without any noticeable effect on the device's performance.
Output voltage varies about 1.2% for every 1% change in supply frequency. For example, a 2 Hz change in generator frequency, which is very large, results in an output voltage change of only 4%, which has little effect for most loads.
It accepts 100% single-phase switch-mode power supply loading without any requirement for derating, including all neutral components.
Input current distortion remains less than 8% THD even when supplying nonlinear loads with more than 100% current THD.
Drawbacks of CVTs are their larger size, audible humming sound, and the high heat generation caused by saturation.
Voltage regulators are used in devices like air conditioners, refrigerators, televisions etc. in order to protect them from fluctuating input voltage. The major problem faced is the use of relays in voltage regulators. Relays create sparks which result in faults in the product.
If the stabilizer must provide more power, the shunt regulator output is only used to provide the standard voltage reference for the electronic device, known as the voltage stabilizer. The voltage stabilizer is the electronic device, able to deliver much larger currents on demand.
Entire linear regulators are available as integrated circuits. These chips come in either fixed or adjustable voltage types.
Like linear regulators, nearly complete switching regulators are also available as integrated circuits. Unlike linear regulators, these usually require an inductor that acts as the energy storage element.
Electronic voltage regulators are found in devices such as computer power supplies where they stabilize the DC voltages used by the processor and other elements. In automobile alternators and central power station generator plants, voltage regulators control the output of the plant. In an electric power distribution system, voltage regulators may be installed at a substation or along distribution lines so that all customers receive steady voltage independent of how much power is drawn from the line.
Electronic voltage regulators
A simple voltage regulator can be made from a resistor in series with a diode (or series of diodes). Due to the logarithmic shape of diode V-I curves, the voltage across the diode changes only slightly due to changes in current drawn or changes in the input. When precise voltage control and efficiency are not important, this design may work fine.Feedback voltage regulators operate by comparing the actual output voltage to some fixed reference voltage. Any difference is amplified and used to control the regulation element in such a way as to reduce the voltage error. This forms a negative feedback control loop; increasing the open-loop gain tends to increase regulation accuracy but reduce stability. (Stability is avoidance of oscillation, or ringing, during step changes.) There will also be a trade-off between stability and the speed of the response to changes. If the output voltage is too low (perhaps due to input voltage reducing or load current increasing), the regulation element is commanded, up to a point, to produce a higher output voltage–by dropping less of the input voltage (for linear series regulators and buck switching regulators), or to draw input current for longer periods (boost-type switching regulators); if the output voltage is too high, the regulation element will normally be commanded to produce a lower voltage. However, many regulators have over-current protection, so that they will entirely stop sourcing current (or limit the current in some way) if the output current is too high, and some regulators may also shut down if the input voltage is outside a given range (see also: crowbar circuits).
Electromechanical regulators
Circuit design for a simple electromechanical voltage regulator.
A voltage stabilizer using electromechanical relays for switching.
Graph of voltage output on a time scale.
If the mechanical regulator design is sensitive to small voltage fluctuations, the motion of the solenoid core can be used to move a selector switch across a range of resistances or transformer windings to gradually step the output voltage up or down, or to rotate the position of a moving-coil AC regulator.
Early automobile generators and alternators had a mechanical voltage regulator using one, two, or three relays and various resistors to stabilize the generator's output at slightly more than 6 or 12 V, independent of the engine's rpm or the varying load on the vehicle's electrical system. Essentially, the relay(s) employed pulse width modulation to regulate the output of the generator, controlling the field current reaching the generator (or alternator) and in this way controlling the output voltage produced.
The regulators used for DC generators (but not alternators) also disconnect the generator when it was not producing electricity, thereby preventing the battery from discharging back into the generator and attempting to run it as a motor. The rectifier diodes in an alternator automatically perform this function so that a specific relay is not required; this appreciably simplified the regulator design.
More modern designs now use solid state technology (transistors) to perform the same function that the relays perform in electromechanical regulators.
Electromechanical regulators are used for mains voltage stabilisation — see AC voltage stabilizers below.
Automatic voltage regulator
Voltage regulator for generators.
How an AVR works: In the first place the AVR monitors the output voltage and controls the input voltage for the exciter of the generator. By increasing or decreasing the generator control voltage, the output voltage of the generator increases or decreases accordingly. The AVR calculates how much voltage has to be sent to the exciter numerous times a second, therefore stabilizing the output voltage to a predetermined setpoint. When two or more generators are powering the same system (parallel operation) the AVR receives information from more generators to match all output.
AC voltage stabilizers
Coil-rotation AC voltage regulator
Basic design principle and circuit diagram for the rotating-coil AC voltage regulator.
When the movable coil is positioned perpendicular to the fixed coil, the magnetic forces acting on the movable coil balance each other out and voltage output is unchanged. Rotating the coil in one direction or the other away from the center position will increase or decrease voltage in the secondary movable coil.
This type of regulator can be automated via a servo control mechanism to advance the movable coil position in order to provide voltage increase or decrease. A braking mechanism or high ratio gearing is used to hold the rotating coil in place against the powerful magnetic forces acting on the moving coil.
Magnetic mains regulator
Electromechanical
Electromechanical regulators called voltage stabilizers or tap-changers, have also been used to regulate the voltage on AC power distribution lines. These regulators operate by using a servomechanism to select the appropriate tap on an autotransformer with multiple taps, or by moving the wiper on a continuously variable auto transfomer. If the output voltage is not in the acceptable range, the servomechanism switches the tap, changing the turns ratio of the transformer, to move the secondary voltage into the acceptable region. The controls provide a dead band wherein the controller will not act, preventing the controller from constantly adjusting the voltage ("hunting") as it varies by an acceptably small amount.PWM static voltage regulator
This is the latest technology of voltage regulation to provide real-time control of voltage fluctuation, sag, surge and also to control other power quality issues such as spikes and EMI/RFI electrical noises. This uses an IGBT regulator engine generating pulse width modulated (PWM) AC voltage at high switching frequency. This AC PWM wave is superimposed on the main incoming wave through a buck-boost transformer, to provide precisely regulated AC voltage. The regulation in this technology is instantaneous, thus making it suitable for electronic machines which need precise regulated power.Constant-voltage transformer
The ferroresonant transformer, ferroresonant regulator or constant-voltage transformer is a type of saturating transformer used as a voltage regulator. These transformers use a tank circuit composed of a high-voltage resonant winding and a capacitor to produce a nearly constant average output voltage with a varying input current or varying load. The circuit has a primary on one side of a magnet shunt and the tuned circuit coil and secondary on the other side. The regulation is due to magnetic saturation in the section around the secondary.The ferroresonant approach is attractive due to its lack of active components, relying on the square loop saturation characteristics of the tank circuit to absorb variations in average input voltage. Saturating transformers provide a simple rugged method to stabilize an AC power supply.
Older designs of ferroresonant transformers had an output with high harmonic content, leading to a distorted output waveform. Modern devices are used to construct a perfect sine wave. The ferroresonant action is a flux limiter rather than a voltage regulator, but with a fixed supply frequency it can maintain an almost constant average output voltage even as the input voltage varies widely.
The ferroresonant transformers, which are also known as Constant Voltage Transformers (CVTs) or ferros, are also good surge suppressors, as they provide high isolation and inherent short-circuit protection.
A ferroresonant transformer can operate with an input voltage range ±40% or more of the nominal voltage.
Output power factor remains in the range of 0.96 or higher from half to full load.
Because it regenerates an output voltage waveform, output distortion, which is typically less than 4%, is independent of any input voltage distortion, including notching.
Efficiency at full load is typically in the range of 89% to 93%. However, at low loads, efficiency can drop below 60%. The current-limiting capability also becomes a handicap when a CVT is used in an application with moderate to high inrush current like motors, transformers or magnets. In this case, the CVT has to be sized to accommodate the peak current, thus forcing it to run at low loads and poor efficiency.
Minimum maintenance is required, as transformers and capacitors can be very reliable. Some units have included redundant capacitors to allow several capacitors to fail between inspections without any noticeable effect on the device's performance.
Output voltage varies about 1.2% for every 1% change in supply frequency. For example, a 2 Hz change in generator frequency, which is very large, results in an output voltage change of only 4%, which has little effect for most loads.
It accepts 100% single-phase switch-mode power supply loading without any requirement for derating, including all neutral components.
Input current distortion remains less than 8% THD even when supplying nonlinear loads with more than 100% current THD.
Drawbacks of CVTs are their larger size, audible humming sound, and the high heat generation caused by saturation.
Commercial use
Voltage regulators or stabilizers are used to compensate for voltage fluctuations in mains power. Large regulators may be permanently installed on distribution lines. Small portable regulators may be plugged in between sensitive equipment and a wall outlet. Automatic voltage regulators are used on generator sets on ships, in emergency power supplies, on oil rigs, etc. to stabilize fluctuations in power demand. For example, when a large machine is turned on, the demand for power is suddenly a lot higher. The voltage regulator compensates for the change in load. Commercial voltage regulators normally operate on a range of voltages, for example 150–240 V or 90–280 V. Servo stabilizers are also manufactured and used widely in spite of the fact that they are obsolete and use out-dated technology.Voltage regulators are used in devices like air conditioners, refrigerators, televisions etc. in order to protect them from fluctuating input voltage. The major problem faced is the use of relays in voltage regulators. Relays create sparks which result in faults in the product.
A three-phase bank of voltage regulators used to control the voltage on
long AC power distribution lines. This bank is mounted on a wooden pole
structure. Each regulator weighs about 2600 lbs and is rated 576 kVA.
DC voltage stabilizers
Many simple DC power supplies regulate the voltage using either series or shunt regulators, but most apply a voltage reference using a shunt regulator such as a Zener diode, avalanche breakdown diode, or voltage regulator tube. Each of these devices begins conducting at a specified voltage and will conduct as much current as required to hold its terminal voltage to that specified voltage by diverting excess current from a non-ideal power source to ground, often through a relatively low-value resistor to dissipate the excess energy. The power supply is designed to only supply a maximum amount of current that is within the safe operating capability of the shunt regulating device.If the stabilizer must provide more power, the shunt regulator output is only used to provide the standard voltage reference for the electronic device, known as the voltage stabilizer. The voltage stabilizer is the electronic device, able to deliver much larger currents on demand.
Active regulators
Active regulators employ at least one active (amplifying) component such as a transistor or operational amplifier. Shunt regulators are often (but not always) passive and simple, but always inefficient because they (essentially) dump the excess current not needed by the load. When more power must be supplied, more sophisticated circuits are used. In general, these active regulators can be divided into several classes:- Linear series regulators
- Switching regulators
- SCR regulators
Linear regulators
Main article: Linear regulator
Linear regulators are based on devices that operate in their linear
region (in contrast, a switching regulator is based on a device forced
to act as an on/off switch). In the past, one or more vacuum tubes were commonly used as the variable resistance. Modern designs use one or more transistors instead, perhaps within an integrated circuit.
Linear designs have the advantage of very "clean" output with little
noise introduced into their DC output, but are most often much less
efficient and unable to step-up or invert the input voltage like
switched supplies. All linear regulators require a higher input than the
output. If the input voltage approaches the desired output voltage, the
regulator will "drop out". The input to output voltage differential at
which this occurs is known as the regulator's drop-out voltage. Low-dropout regulators (LDOs) allow an input voltage that can be much lower (i.e., they waste less energy than conventional linear regulators).Entire linear regulators are available as integrated circuits. These chips come in either fixed or adjustable voltage types.
Switching regulators
Main article: Switched-mode power supply
Switching regulators rapidly switch a series device on and off. The duty cycle of the switch sets how much charge
is transferred to the load. This is controlled by a similar feedback
mechanism as in a linear regulator. Because the series element is either
fully conducting, or switched off, it dissipates almost no power; this
is what gives the switching design its efficiency. Switching regulators
are also able to generate output voltages which are higher than the
input, or of opposite polarity — something not possible with a linear
design.Like linear regulators, nearly complete switching regulators are also available as integrated circuits. Unlike linear regulators, these usually require an inductor that acts as the energy storage element.
Do you recommend using avr at home?
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