What is an automatic voltage regulator

As an advancement of the traditional relay-type voltage regulator, the modern thyristor automatic voltage regulator uses high-performance digital control circuits and thyristor thyristors, which do not require the adjustment of potentiometers, do not require manual operation to set the voltage, and have output start and stop functions to automatically complete the work of stabilizing the voltage.

This also makes the voltage stabilization time and response speed of the voltage regulator very fast, usually less than a few milliseconds, and this can be adjusted through variable settings. Today, automatic voltage regulators have become the optimized power supply solution for many electronic devices that are sensitive to voltage fluctuations, and they have found use with many devices such as CNC machines, air conditioners, televisions, medical equipment, computers, telecommunication equipment, etc.

1. What is an automatic voltage regulator:

It is an electrical appliance designed to provide a constant voltage to the load at its output terminals regardless of changes in the input or input power supply voltage. It protects the device or machine from overvoltage, undervoltage and other voltage surges.

It is also called an automatic voltage regulator (AVR). Voltage regulators are the first choice for expensive and precious electrical equipment to protect them from harmful low/high voltage fluctuations. Some of these devices are air conditioners, offset printing machines, laboratory equipment, industrial machines, and medical equipment.

A voltage regulator regulates the fluctuating input voltage before feeding it to the load (or a device that is sensitive to voltage variations). The output voltage of an automatic voltage regulator is maintained within the range of ±1% within the rated input voltage fluctuation range. This regulation is performed by buck and boost operations performed by internal circuits.

There are a wide variety of automatic voltage regulators available in the market today. These can be single-phase or three-phase units, depending on the type of application and capacity (KVA) required. Three-phase voltage regulators are available in two versions, namely, balanced load models and unbalanced load models.

These can be either dedicated units for an appliance or large stabilizer units for an entire appliance in a particular place, such as an entire house. Furthermore, these can be either analog or digital type stabilizer units.

Common types of voltage stabilizers include manual or switchable stabilizers, thyristor thyristor stabilizers, automatic relay type stabilizers, solid-state or static stabilizers, and servo-controlled stabilizers. In addition to the voltage stabilization function, most voltage stabilizers also have additional functions such as input/output low voltage cutoff, input/output high voltage cutoff, overload cutoff, output start and stop function, manual/automatic start, voltage cutoff display, zero voltage switch, etc.

2. Why do we need a voltage stabilizer:

Generally, each electrical device or device is designed for a wide range of input voltages. Depending on the sensitivity, the operating range of the device is limited to a specific value, for example, some devices can withstand ±10% of the rated voltage, while others can withstand ±5% or less.

Voltage fluctuations (increases or decreases in the magnitude of the rated voltage) are common in many fields, especially in terminal wiring circuits. The most common causes of voltage fluctuations are lighting, electrical faults, wiring faults, and regular shutdown of equipment. These fluctuations can cause accidents to electrical equipment or appliances.

1). It will cause long-term overvoltage;

2). Permanent damage to the equipment;

3). Damage to the winding insulation;

4). Unnecessary interruptions in the load;

5). Increased losses in cables and related equipment;

6). Reduced service life of the equipment;

7). Long-term undervoltage will lead to;

8). Equipment failure;

9). Longer working time (such as resistance heater);

10). Degradation of equipment performance;

11). Absorption of large current, further leading to overheating;

12). Calculation errors;

13). Reduced motor speed.

Therefore, voltage stability and accuracy determine the correct operation of the equipment. Therefore, the voltage regulator ensures that the voltage fluctuation of the input power supply does not affect the load or electrical appliances.

3. The working principle of the voltage regulator is:

The basic principle of the voltage regulator is used to perform step-down and step-up operations.

In the voltage regulator, voltage correction under overvoltage and undervoltage conditions is performed by two basic operations, namely step-up and step-down operations. These operations can be performed manually by switches or automatically by electronic circuits. Under undervoltage conditions, the step-up operation increases the voltage to the rated level, while the step-down operation reduces the voltage level under overvoltage conditions.

The concept of stabilization involves adding or subtracting the voltage of the main power supply. To perform such tasks, the voltage regulator uses a transformer, which is connected with a switching relay in different configurations. Some voltage stabilizers use transformers with taps on the windings to provide different voltage corrections, while servo stabilizers use automatic transformers for a wide range of corrections.

4. Types of automatic voltage stabilizers:

Voltage stabilizers have become an integral part of many household, industrial, and commercial system appliances. Previously, manually operated or switchable voltage stabilizers were used to step up or step down the input voltage in order to provide an output voltage within the required range. Such stabilizers were made with electromechanical relays as switching devices.

Later, additional electronic circuits automated the voltage regulation process and gave rise to tap-switch automatic voltage stabilizers. Another popular type of voltage stabilizer is the servo stabilizer, in which voltage correction is performed continuously without any switches. Let us discuss the three main types of voltage stabilizers.

1). Relay type voltage stabilizer:

In this type of voltage stabilizer, voltage regulation is achieved by switching relays so that one of the multiple taps of the transformer is connected to the load (as mentioned above), whether for step-up or step-down operation.

In addition to the transformer, it also has an electronic circuit and a relay group (which can be a toroidal or iron core transformer with taps on its secondary). The electronic circuit includes a rectifier circuit, an operational amplifier, a microcontroller unit, and other tiny components.

The electronic circuit compares the output voltage with a reference value provided by a built-in reference voltage source. Whenever the voltage rises or falls beyond the reference value, the control circuit switches the corresponding relay to connect the required shunt to the output.

These regulators typically change the voltage by ±15% to ±6% based on the input voltage change, and the output voltage accuracy is ±5% to ±10%. This type of regulator is most commonly used in low-rated appliances in residential, commercial, and industrial applications because they are lightweight and low cost. However, they have some limitations such as slow voltage correction, poor durability, low reliability, interruption of the power path during regulation, and inability to withstand high voltage surges.

2). Servo Control Regulators:

These are simply called servo regulators (the work of a servo mechanism, also known as negative feedback), and the name suggests that it uses a servo motor to achieve voltage correction. They are mainly used for high output voltage accuracy, typically ±1%, with input voltage changes of up to ±50%.

In this voltage stabilizer, one end of the primary of the buck-boost transformer is connected to the fixed tap of the autotransformer while the other end is connected to the moving arm controlled by the servo motor. The secondary of the buck-boost transformer is connected in series with the input supply which is nothing but the stabilizer output.

The electronic control circuit detects voltage sags and voltage swells by comparing the input with the built-in reference voltage source. When the circuit finds an error, it operates the motor which in turn moves the arm on the autotransformer. This feeds the primary of the buck-boost transformer so that the voltage across the secondary should be the desired voltage output. Most of the servo stabilizers use an embedded microcontroller or processor as the control circuit to achieve intelligent control.

These stabilizers can be single-phase, three-phase balanced type or three-phase unbalanced devices. In the single-phase type, a servo motor connected to a variable transformer enables voltage correction. In the case of the three-phase balanced type, the servo motor is coupled with three autotransformers to provide a stable output by adjusting the output of the transformer during fluctuations. In the unbalanced type of servo stabilizer, three independent servo motors are coupled with three autotransformers which have three independent control circuits.

There are several advantages of using a servo stabilizer compared to a relay type stabilizer. Some of these are higher correction speed, high precision stable output, ability to withstand surge current, and high reliability. However, these require regular maintenance due to the presence of the motor.

3). Static voltage stabilizer:

As the name suggests, a static voltage stabilizer does not have any moving parts as a servo motor mechanism in the case of a servo voltage stabilizer. It uses a power electronic converter circuit to achieve voltage regulation instead of a variation of a conventional voltage stabilizer. This type of voltage stabilizer can produce higher accuracy and excellent voltage regulation compared to a servo stabilizer, typically with a regulation rate of ±1%.

It mainly consists of a buck-boost transformer, an IGBT power converter (or AC to AC converter), and a microcontroller, microprocessor, or DSP-based controller. The microprocessor-controlled IGBT converter generates the right amount of voltage through pulse width modulation technology and provides this voltage to the primary of the buck-boost transformer. The IGBT converter generates voltage in a way that it can be in-phase or 180 degrees out-of-phase with the input line voltage so that it can perform addition and subtraction of voltage during fluctuations.

Whenever the microprocessor detects a voltage sag, it sends PWM pulses to the IGBT converter so that it produces a voltage equal to the deviation from the nominal value. This output is in phase with the input supply and is provided to the primary of the buck-boost transformer. Since the secondary is connected to the input line, the induced voltage is added to the input supply and this corrective voltage is provided to the load.

Similarly, a voltage rise causes the microprocessor circuit to send PWM pulses in such a way that the converter will output a voltage of the deviation amount, which is 180 degrees out of phase with the input voltage. The voltage at the secondary of the buck-boost transformer is subtracted from the input voltage, thereby performing a step-down operation.

These stabilizers are very popular as compared to tap changers and servo-controlled stabilizers because of their various advantages such as small size, very fast correction speed, excellent voltage regulation, no maintenance due to the absence of moving parts, high efficiency, and high reliability.