How to develop AC-AC automatic voltage regulators more efficiently?

【Introduction】An Automatic Voltage Regulator (AVR), also commonly referred to as a voltage regulator, regulates the supply voltage level by compensating for fluctuations in the input voltage and is common in many industrial and residential applications. For example, AVRs are used in marine generator sets, emergency power supplies and oil rigs to stabilize voltage levels during fluctuations in power demand.

Voltage regulation of the distribution network is critical for utility companies as it determines the quality of electricity service provided to end consumers. To do this, utilities must ensure proper short- and long-term planning, maintenance of electrical equipment, and deployment of voltage stabilizers on distribution lines. However, this task is quite challenging, especially for many South Asian countries such as Pakistan, India and Bangladesh. Power distribution systems in these areas are fragile, often resulting in intermittent and other types of outages, due to power theft and power shortages. As a result, end users may face problems with power line voltage fluctuations. To ensure the safety and proper operation of valuable equipment such as air conditioners, refrigerators and TVs, small portable AVRs are very common. AVR devices are easy to use and typically operate over a predetermined range of voltage levels (eg 150V to 240V, or 90V to 280V).

Functionally, AVRs typically use a tapped autotransformer to keep the AC output within an acceptable range. It utilizes a feedback mechanism to control the position of the tap, switching the appropriate relay to regulate the output voltage. AVRs usually consist of two units: a sensing unit and a conditioning unit. The job of the sensing unit is to determine the input and output voltage levels of the regulator, while the conditioning unit is responsible for keeping the output voltage within an acceptable predetermined range.

Traditionally, relay-based AVR designs have typically used an op-amp IC combined with an analog comparator to implement the control function. In the latest digitally controlled commercial AVRs, designs using 8-bit microcontrollers (MCUs) for control have increased significantly. The method described in this paper uses a low-cost GreenPAK programmable mixed-signal ASIC (application-specific integrated circuit) from Dialog semiconductor to achieve similar functions and features. Not only does it reduce cost and space requirements, it also eliminates the need to program the MCU.

In this article, we will describe how developers can develop AVRs using a programmable ASIC such as the GreenPAK SLG46537V IC, and will describe the overall system design and GreenPAK design in detail. To verify the feasibility and operability of this AVR, we will also present the experimental results obtained through the prototype.

system design

How to develop AC-AC automatic voltage regulators more efficiently?

Figure 1: Functional block diagram of the AVR design (Image credit: BarqEE)

The functional block diagram of this AVR design is shown in Figure 1. The system is mainly based on a feedback mechanism. The AC voltage at the AVR output is regulated to be within the operating DC voltage limits of the SLG46537V IC. Based on the sensed voltage, the IC drives the appropriate relay to select the appropriate tap winding on the autotransformer.

The specifications of the AVR depend on the specific application. The AVRs described in this article have the following characteristics:

● The input voltage range is 125V to 240V.

● The output voltage is regulated between 200V and 240V.

● Provide undervoltage and overvoltage protection functions. When the AVR output voltage is lower than 180V (undervoltage) or higher than 255V (overvoltage), the output power supply is disconnected.

● Four electromechanical relays are used in the design.

● Autotransformer is used for boosting, it has 0V neutral connection and four extra taps (135V, 174V, 196V and 220V).

● The output waveform and frequency are the same as the input.

● AVR (controller) is designed with low cost.

● Provide LED indicators to indicate normal, overvoltage or undervoltage conditions.

Note that these parameters can be set arbitrarily. Depending on the actual application, the given parameters can be easily adjusted in the GreenPAK IC configuration.

feature design

Figure 2: AVR design recommendations (Image credit: BarqEE)

Figure 2 shows the AVR functional design recommendations using the SLG46537V IC.

power regulation

The power conditioning module powers the GreenPAK IC. It takes live AC as input and steps it down to 12V, which is then further converted to 5VDC using a suitable voltage regulator IC.

AC Voltage Sensing

The voltage sensing section steps down and rectifies the output AC voltage (Live_out) using a diode and resistor divider network to obtain a low voltage DC level. Then, an output filter (electrolytic capacitor) is employed to minimize ripple and obtain a constant smooth DC voltage. A bypass capacitor is then used to filter out transients. Finally, the filtered DC voltage (Vsense) is obtained. To ensure that the DC voltage level is compatible with this chip, a step-down factor of approximately 0.01 is used (ie 200VAC Û 2VDC).

GreenPAK

The GreenPAK IC takes Vsense as input and drives the desired relay (via BJT) action based on the GreenPAK logic (see Section 2). The IC’s digital output is also used to toggle LED indicators to notify the user of the AVR’s normal and over/under voltage status. The schematic diagram of GreenPAK IC and its IO connections are shown in Figure 2 for reference.

relay actuation

Three electromechanical relays (RL1, RL2 and RL3) are used to switch the input AC voltage (Live_in) connection between the 135V, 174V, 196V and 220V taps of the autotransformer. A fourth electromechanical relay (RL4) is used to disconnect the AVR output in undervoltage or overvoltage conditions, preventing any damage to the load connected to the AVR output.

GreenPAK Logic

Complete design files created by GreenPAK Designer software (available free of charge), please copy the link below to open the download in your browser:

https://www.dialog-semiconductor.com/an-cm-314-gp

Figure 3: GreenPAK design schematic (Image credit: BarqEE)

Figure 3 is a schematic diagram of the design of GreenPAK. Vsense is fed to different comparators via pin 6. Within the normal operating range of the AVR, voltage regulation is performed by analog comparators ACMP0 and ACMP1, while ACMP2 and ACMP3 are used for overvoltage and undervoltage detection. Since the maximum internal reference voltage of the comparator can be set to no greater than 1.2V, a gain of 0.33 is used to ensure that the output voltages can be compared and classified correctly across different ranges. The reference voltage settings of the comparators meet the specifications mentioned in Section 1.2. The Asynchronous State Machine (ASM) block is used to build a finite state machine for voltage regulation.

Figure 4: Finite State Machine (Image credit: BarqEE)

Figure 4 describes the five states used. In each state, relays 1, 2, and 3 use ASM to output OUT3, OUT2, and OUT1, respectively, to select the associated autotransformer tap, and the corresponding autotransformer turns ratio. A change from state 0 to state 4 results in a stepwise reduction in the autotransformer turns ratio. Table 1 shows how each state corresponds to the turns ratio.

Table 1: Relationship between AT turns ratio and each state (Source: BarqEE)

If Live_out is greater than the upper limit (about 240VAC, set by the reference of ACMP1) or less than the lower limit (about 200VAC, set by the reference of ACMP0), voltage regulation is achieved through a state transition. If either state fails to produce the desired regulated output voltage level (200V

To ensure the normal operation of the electromechanical relay, the sudden state transition is controlled by the delay in the feedback of the ASM module. For this purpose, the OUT3, OUT4, OUT5, OUT6 and OUT7 outputs of the ASM block are fed to delay blocks DLY2, DLY3, DLY4, DLY5 and DLY6 respectively. Figure 5 depicts the RAM module configuration of the ASM, showing the state of each binary output OUT0 to OUT7.

Figure 5: RAM module (Image credit: BarqEE)

The state is held for a predefined time period tp (about 0.5s) set in the delay. A state transition occurs only after Live_out remains outside the desired range for at least tp time. The delayed outputs are fed back to different LUTs (and AND blocks) along with the outputs of ACMP0 and ACMP1, as shown in Figure 4. This ensures that state transitions only happen after the tp time period has elapsed and Live_out is out of the desired range. Specific state transitions depend on the outputs of ACMP0 and ACMP1. For example, if state 1 remains during the tp period, it is not possible to transition to state 0 and state 2. State 1 is maintained if the desired voltage level has been reached. Otherwise, depending on whether Live_out is greater than the upper bound or less than the lower bound, transitions to state 0 and state 2 occur.

Another important feature of the proposed GreenPAK design is protection under overvoltage and undervoltage conditions. Comparators ACMP2 and ACMP3 are used for overvoltage and undervoltage conditions, respectively. The output of ACMP2 and the inverted output of ACMP3 are passed to delay blocks DLY0 and DLY1 to ensure that any transient overvoltage and undervoltage conditions are not detected. The outputs of DLY0 and DLY1 are then fed to the LUT block, which decides whether it is a normal, overvoltage or undervoltage condition. Under normal conditions, RLY4 remains powered and the AVR regulates the voltage; otherwise the voltage will not be regulated and RLY4 trips. Additionally, GreenPAK provides the user with an indication of normal, overvoltage and undervoltage conditions.

Experimental results

Experimental hardware

Figure 6: Experimental setup (Image credit: BarqEE)

Figure 6 shows the experimental setup for the designed prototype. The Variac is used to control the input AC voltage supplied to the AVR. The AVR contains an autotransformer and a PCB that contains the control circuitry.

The GreenPAK development board is connected to the PCB to control the electromechanical relays. Simultaneously use an oscilloscope to record the input and output voltages.

Figure 7: PCB circuit (Image credit: BarqEE)

Figure 7 is a PCB circuit with electromechanical relays, BJTs and other auxiliary components installed.

AVR performance data

The performance data of the AVR is summarized as follows:

● Load range: 450VA-550VA

● Input voltage range: 125V-240V

● Output voltage: 200V-240V

● Frequency: 50Hz-60Hz

● Insulation resistance: >5MΩ

● Response time: 10ms-15ms

● Transformer temperature rise: 65°C-70°C (1.2 times full rated load)

● System efficiency: >95%

● Ambient temperature: 0℃-40℃

Oscilloscope output

The following pictures are all oscilloscope records in the experiment. The yellow and blue markers represent the input and output voltages, respectively.

Figure 8: Summary of quantitative experiments (Image source: BarqEE)

Figure 8 depicts a quantitative summary of the experimental results for normal AVR function. Sweeping the input voltage from low to high voltage range and observing the corresponding output voltage, you can see that the IC successfully drives the relay to change the autotransformer tap, reducing the turns ratio from 1.63 to 1, achieving voltage regulation.

Figure 9: Normal function (Image credit: BarqEE)

Figure 9 shows the normal function of the AVR, which successfully determines and selects a tap with a turns ratio of 1.63.

Figure 10: Approaching overvoltage (Image credit: BarqEE)

Figure 11: Overvoltage condition (Image credit: BarqEE)

Figure 10 depicts the input and output voltage waveforms as they approach an overvoltage condition. Both have similar waveforms because the tap turns ratio is 1.

Figure 11 shows the overvoltage condition. It can be seen that the output voltage has slumped as the AVR has successfully tripped RL4 for protection.

Figure 12: Approaching undervoltage (Image credit: BarqEE)

Figure 13: Undervoltage condition (Image credit: BarqEE)

Figure 12 depicts the input and output voltage waveforms as they approach a brownout condition. In this case, the AVR chose the maximum turns ratio (1.63) tap.

Figure 13 shows the undervoltage condition. It can be observed that the output voltage drops due to the RL4 trip protection.

Note that while the AVR regulates the voltage, neither the input nor the output voltage has a frequency change or phase shift.

in conclusion

AVRs are popular in residential and industrial applications, and this article describes how to use a programmable ASIC such as the GreenPAK SLG46537V IC as a controller for an AVR. ASICs can replace the discrete components and MCUs currently used in these applications. This article describes the role of the SLG46537V in the proposed AVR design and clarifies the design of the GreenPAK in detail. In addition, experimental details of an AVR prototype are given to validate the proposed design.

It can be seen that this circuit has sufficient capability as a controller, especially in a residential AVR. Therefore, it is feasible to use low-cost IC to design the control unit of AVR while reducing the PCB space. Also, by using other ASICs to provide more states to the ASM, we can also design more complex controllers.

Reference text: Amore effective approach for developing AC-AC automatic voltage regulators

By Aamir Hussain Chughtai, Muhammad Saqib

This article is translated by the editorial team of “EET Electronic Engineering Album”, editor in charge: Amy Guan

【Introduction】An Automatic Voltage Regulator (AVR), also commonly referred to as a voltage regulator, regulates the supply voltage level by compensating for fluctuations in the input voltage and is common in many industrial and residential applications. For example, AVRs are used in marine generator sets, emergency power supplies and oil rigs to stabilize voltage levels during fluctuations in power demand.

Voltage regulation of the distribution network is critical for utility companies as it determines the quality of electricity service provided to end consumers. To do this, utilities must ensure proper short- and long-term planning, maintenance of electrical equipment, and deployment of voltage stabilizers on distribution lines. However, this task is quite challenging, especially for many South Asian countries such as Pakistan, India and Bangladesh. Power distribution systems in these areas are fragile, often resulting in intermittent and other types of outages, due to power theft and power shortages. As a result, end users may face problems with power line voltage fluctuations. To ensure the safety and proper operation of valuable equipment such as air conditioners, refrigerators and TVs, small portable AVRs are very common. AVR devices are easy to use and typically operate over a predetermined range of voltage levels (eg 150V to 240V, or 90V to 280V).

Functionally, AVRs typically use a tapped autotransformer to keep the AC output within an acceptable range. It utilizes a feedback mechanism to control the position of the tap, switching the appropriate relay to regulate the output voltage. AVRs usually consist of two units: a sensing unit and a conditioning unit. The job of the sensing unit is to determine the input and output voltage levels of the regulator, while the conditioning unit is responsible for keeping the output voltage within an acceptable predetermined range.

Traditionally, relay-based AVR designs have typically used an op-amp IC combined with an analog comparator to implement the control function. In the latest digitally controlled commercial AVRs, designs using 8-bit microcontrollers (MCUs) for control have increased significantly. The method described in this paper uses a low-cost GreenPAK programmable mixed-signal ASIC (application-specific integrated circuit) from Dialog semiconductor to achieve similar functions and features. Not only does it reduce cost and space requirements, it also eliminates the need to program the MCU.

In this article, we will describe how developers can develop AVRs using a programmable ASIC such as the GreenPAK SLG46537V IC, and will describe the overall system design and GreenPAK design in detail. To verify the feasibility and operability of this AVR, we will also present the experimental results obtained through the prototype.

system design

Figure 1: Functional block diagram of the AVR design (Image credit: BarqEE)

The functional block diagram of this AVR design is shown in Figure 1. The system is mainly based on a feedback mechanism. The AC voltage at the AVR output is regulated to be within the operating DC voltage limits of the SLG46537V IC. Based on the sensed voltage, the IC drives the appropriate relay to select the appropriate tap winding on the autotransformer.

The specifications of the AVR depend on the specific application. The AVRs described in this article have the following characteristics:

● The input voltage range is 125V to 240V.

● The output voltage is regulated between 200V and 240V.

● Provide undervoltage and overvoltage protection functions. When the AVR output voltage is lower than 180V (undervoltage) or higher than 255V (overvoltage), the output power supply is disconnected.

● Four electromechanical relays are used in the design.

● Autotransformer is used for boosting, it has 0V neutral connection and four extra taps (135V, 174V, 196V and 220V).

● The output waveform and frequency are the same as the input.

● AVR (controller) is designed with low cost.

● Provide LED indicators to indicate normal, overvoltage or undervoltage conditions.

Note that these parameters can be set arbitrarily. Depending on the actual application, the given parameters can be easily adjusted in the GreenPAK IC configuration.

feature design

Figure 2: AVR design recommendations (Image credit: BarqEE)

Figure 2 shows the AVR functional design recommendations using the SLG46537V IC.

power regulation

The power conditioning module powers the GreenPAK IC. It takes live AC as input and steps it down to 12V, which is then further converted to 5VDC using a suitable voltage regulator IC.

AC Voltage Sensing

The voltage sensing section steps down and rectifies the output AC voltage (Live_out) using a diode and resistor divider network to obtain a low voltage DC level. Then, an output filter (electrolytic capacitor) is employed to minimize ripple and obtain a constant smooth DC voltage. A bypass capacitor is then used to filter out transients. Finally, the filtered DC voltage (Vsense) is obtained. To ensure that the DC voltage level is compatible with this chip, a step-down factor of approximately 0.01 is used (ie 200VAC Û 2VDC).

GreenPAK

The GreenPAK IC takes Vsense as input and drives the desired relay (via BJT) action based on the GreenPAK logic (see Section 2). The IC’s digital output is also used to toggle LED indicators to notify the user of the AVR’s normal and over/under voltage status. The schematic diagram of GreenPAK IC and its IO connections are shown in Figure 2 for reference.

relay actuation

Three electromechanical relays (RL1, RL2 and RL3) are used to switch the input AC voltage (Live_in) connection between the 135V, 174V, 196V and 220V taps of the autotransformer. A fourth electromechanical relay (RL4) is used to disconnect the AVR output in undervoltage or overvoltage conditions, preventing any damage to the load connected to the AVR output.

GreenPAK Logic

Complete design files created by GreenPAK Designer software (available free of charge), please copy the link below to open the download in your browser:

https://www.dialog-semiconductor.com/an-cm-314-gp

Figure 3: GreenPAK design schematic (Image credit: BarqEE)

Figure 3 is a schematic diagram of the design of GreenPAK. Vsense is fed to different comparators via pin 6. Within the normal operating range of the AVR, voltage regulation is performed by analog comparators ACMP0 and ACMP1, while ACMP2 and ACMP3 are used for overvoltage and undervoltage detection. Since the maximum internal reference voltage of the comparator can be set to no greater than 1.2V, a gain of 0.33 is used to ensure that the output voltages can be compared and classified correctly across different ranges. The reference voltage settings of the comparators meet the specifications mentioned in Section 1.2. The Asynchronous State Machine (ASM) block is used to build a finite state machine for voltage regulation.

Figure 4: Finite State Machine (Image credit: BarqEE)

Figure 4 describes the five states used. In each state, relays 1, 2, and 3 use ASM to output OUT3, OUT2, and OUT1, respectively, to select the associated autotransformer tap, and the corresponding autotransformer turns ratio. A change from state 0 to state 4 results in a stepwise reduction in the autotransformer turns ratio. Table 1 shows how each state corresponds to the turns ratio.

Table 1: Relationship between AT turns ratio and each state (Source: BarqEE)

If Live_out is greater than the upper limit (about 240VAC, set by the reference of ACMP1) or less than the lower limit (about 200VAC, set by the reference of ACMP0), voltage regulation is achieved through a state transition. If either state fails to produce the desired regulated output voltage level (200V

To ensure the normal operation of the electromechanical relay, the sudden state transition is controlled by the delay in the feedback of the ASM module. For this purpose, the OUT3, OUT4, OUT5, OUT6 and OUT7 outputs of the ASM block are fed to delay blocks DLY2, DLY3, DLY4, DLY5 and DLY6 respectively. Figure 5 depicts the RAM module configuration of the ASM, showing the state of each binary output OUT0 to OUT7.

Figure 5: RAM module (Image credit: BarqEE)

The state is held for a predefined time period tp (about 0.5s) set in the delay. A state transition occurs only after Live_out remains outside the desired range for at least tp time. The delayed outputs are fed back to different LUTs (and AND blocks) along with the outputs of ACMP0 and ACMP1, as shown in Figure 4. This ensures that state transitions only happen after the tp time period has elapsed and Live_out is out of the desired range. Specific state transitions depend on the outputs of ACMP0 and ACMP1. For example, if state 1 remains during the tp period, it is not possible to transition to state 0 and state 2. State 1 is maintained if the desired voltage level has been reached. Otherwise, depending on whether Live_out is greater than the upper bound or less than the lower bound, transitions to state 0 and state 2 occur.

Another important feature of the proposed GreenPAK design is protection under overvoltage and undervoltage conditions. Comparators ACMP2 and ACMP3 are used for overvoltage and undervoltage conditions, respectively. The output of ACMP2 and the inverted output of ACMP3 are passed to delay blocks DLY0 and DLY1 to ensure that any transient overvoltage and undervoltage conditions are not detected. The outputs of DLY0 and DLY1 are then fed to the LUT block, which decides whether it is a normal, overvoltage or undervoltage condition. Under normal conditions, RLY4 remains powered and the AVR regulates the voltage; otherwise the voltage will not be regulated and RLY4 trips. Additionally, GreenPAK provides the user with an indication of normal, overvoltage and undervoltage conditions.

Experimental results

Experimental hardware

Figure 6: Experimental setup (Image credit: BarqEE)

Figure 6 shows the experimental setup for the designed prototype. The Variac is used to control the input AC voltage supplied to the AVR. The AVR contains an autotransformer and a PCB that contains the control circuitry.

The GreenPAK development board is connected to the PCB to control the electromechanical relays. Simultaneously use an oscilloscope to record the input and output voltages.

Figure 7: PCB circuit (Image credit: BarqEE)

Figure 7 is a PCB circuit with electromechanical relays, BJTs and other auxiliary components installed.

AVR performance data

The performance data of the AVR is summarized as follows:

● Load range: 450VA-550VA

● Input voltage range: 125V-240V

● Output voltage: 200V-240V

● Frequency: 50Hz-60Hz

● Insulation resistance: >5MΩ

● Response time: 10ms-15ms

● Transformer temperature rise: 65°C-70°C (1.2 times full rated load)

● System efficiency: >95%

● Ambient temperature: 0℃-40℃

Oscilloscope output

The following pictures are all oscilloscope records in the experiment. The yellow and blue markers represent the input and output voltages, respectively.

Figure 8: Summary of quantitative experiments (Image source: BarqEE)

Figure 8 depicts a quantitative summary of the experimental results for normal AVR function. Sweeping the input voltage from low to high voltage range and observing the corresponding output voltage, you can see that the IC successfully drives the relay to change the autotransformer tap, reducing the turns ratio from 1.63 to 1, achieving voltage regulation.

Figure 9: Normal function (Image credit: BarqEE)

Figure 9 shows the normal function of the AVR, which successfully determines and selects a tap with a turns ratio of 1.63.

Figure 10: Approaching overvoltage (Image credit: BarqEE)

Figure 11: Overvoltage condition (Image credit: BarqEE)

Figure 10 depicts the input and output voltage waveforms as they approach an overvoltage condition. Both have similar waveforms because the tap turns ratio is 1.

Figure 11 shows the overvoltage condition. It can be seen that the output voltage has slumped as the AVR has successfully tripped RL4 for protection.

Figure 12: Approaching undervoltage (Image credit: BarqEE)

Figure 13: Undervoltage condition (Image credit: BarqEE)

Figure 12 depicts the input and output voltage waveforms as they approach a brownout condition. In this case, the AVR chose the maximum turns ratio (1.63) tap.

Figure 13 shows the undervoltage condition. It can be observed that the output voltage drops due to the RL4 trip protection.

Note that while the AVR regulates the voltage, neither the input nor the output voltage has a frequency change or phase shift.

in conclusion

AVRs are popular in residential and industrial applications, and this article describes how to use a programmable ASIC such as the GreenPAK SLG46537V IC as a controller for an AVR. ASICs can replace the discrete components and MCUs currently used in these applications. This article describes the role of the SLG46537V in the proposed AVR design and clarifies the design of the GreenPAK in detail. In addition, experimental details of an AVR prototype are given to validate the proposed design.

It can be seen that this circuit has sufficient capability as a controller, especially in a residential AVR. Therefore, it is feasible to use low-cost IC to design the control unit of AVR while reducing the PCB space. Also, by using other ASICs to provide more states to the ASM, we can also design more complex controllers.

Reference text: Amore effective approach for developing AC-AC automatic voltage regulators

By Aamir Hussain Chughtai, Muhammad Saqib

This article is translated by the editorial team of “EET Electronic Engineering Album”, editor in charge: Amy Guan

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