Power Quality Conditioners in Smart Grid

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A power quality conditioner is nothing but a device used in smart grid networks for maintaining power quality characteristics within the specified limits. The primary function of power quality conditioners is to improve the quality of power delivered to the electrical load equipment.

Power quality conditioners improve the power quality in smart grid systems by reducing various disturbances and improving the overall performance of the networks. These devices are essential for developing a stable and high-quality power supply system.

In this chapter of smart grid tutorial, we will learn about power quality conditioners, their functions, types, and advantages in the field of smart grid technology.

What is a Power Quality Conditioner?

In the context of modern electric grid or smart grid, a power quality conditioner is a device designed and used for improving the quality of power delivered to the end-users electrical load equipment. A power quality conditioner works by continuously monitoring and regulating the electrical power supply flowing in the grid. It is capable in automatically compensating the power quality issues like waveform distortion, voltage sags/swells, harmonic distortions, interruptions, etc.

Power quality conditioners are also known by other names like line conditioners or power conditioners. Although, there is no official definition of the power quality conditioners, but they are devices that can maintain the supply voltage within proper levels required for proper functioning of load equipment.

Some of the common examples of power quality conditioners include voltage regulators, power factor correction devices, noise suppressors, transient impulse protectors, etc.

Functions of Power Quality Conditioners

In smart grid systems, the following are key functions of power quality conditioners −

• Power quality conditioners are provided to deliver voltage and current of the proper levels and characteristics, so that the load equipment can function properly.
• Power quality conditioners improve the power transfer efficiency between utility grid and micro grid.
• Power quality conditioners also isolate the utility grid and micro grid from their respective disturbances and noises.
• Power quality conditioners provide seamless integration with distributed energy resources and energy storage systems.

Types of Power Quality Conditioners

The following are some most commonly used types of power quality conditioners −

• Distribution Static Compensators (DSTATCOM)
• Active Power Filters Shunt, Series, and Hybrid
• Unified Power Quality Conditioners

Let us discuss about these different types of power quality conditioners in detail.

1. Distribution Static Compensator (DSTATCOM)

The distribution static compensator (DSTATCOM) is a voltage source converter based custom power device designed to precisely regulate the system voltage. It is connected in parallel to the distribution networks. The primary functions of DSTATCOM include voltage profile improvement, reduced harmonics, and load compensation.

This power quality conditioner can also reduce the voltage dips and can improve the magnitude and phase angle of the voltage by injecting active or reactive power into the grid.

Therefore, DSTATCOM can perform three different functions in smart grid networks which are voltage regulation, reactive power compensation, and power factor correction. Additionally, it can also reduce or eliminate the current harmonics.

The block diagram of the distribution static compensator is shown in the following figure −

The voltage source converter of the DSTATCOM converts the direct voltage across the storage device into a set of 3-phase AC output voltage. These voltages are in-phase and coupled with the AC system through a coupling transformer. This arrangement allows the DSTATCOM to absorb or generate controllable active and reactive powers.

2. Active Power Filters

Active power filters are advanced power electronic devices designed and used for power quality conditioning. These devices are capable in providing compensation for harmonics distortion, reactive power, and neutral current. Additionally, the active filters can also used for voltage regulation, eliminate voltage flicker, and load balancing in a 3-phase system.

The active power filters offer dynamic compensation through continuous monitoring of the electrical grid.

Depending on the configuration and application, the active power filters can be classified into the following three types −

• Shunt Active Power Filter
• Series Active Power Filter
• Hybrid Active Power Filter

These three types of active power filters are explained here.

Shunt Active Power Filter

These active power filters are connected in parallel with the load as shown in the following figure −

The shunt active power filters cancel out the harmonic currents by injecting equal-but-opposite harmonic compensating currents into the electrical system. These power quality conditioners are ideal for compensating all current related issues like reactive power compensation, power factor improvement, current harmonics, and unbalance load compensation.

Series Active Power Filter

Series active power filters are used in smart grid networks to compensate power quality problems caused by non-linear loads. These filters are connected in series with the load as shown in the following figure −

The series active power filters work by generating a compensating voltage of the same frequency as that of the voltage harmonic component that has to be cancelled out.

These active power filters are ideal for compensating all voltage related power quality issues like voltage harmonics, voltage sags, voltage swells, or voltage flickers, in smart grid networks.

Hybrid Active Power Filter

Hybrid active power filters are those that combine both active and passive filter components in a single circuit. The primary aim of designing hybrid active filters is to reduce the cost of static compensation.

Passive filters are provided to cancel out the most relevant harmonics to the load, while the active filters are used to improve the performance of the passive filters or to cancel out other harmonic components.

3. Different Hybrid Topologies

Different hybrid topologies are shown in the following figures.

Hybrid Filter with Shunt Passive Filter and Shunt Active Filter

The following diagram shows the topology of a Hybrid Filter with Shunt Passive Filter and Shunt Active Filter −

Hybrid Filter with Shunt Passive Filter and Series Active Filter

The following diagram shows the topology of a Hybrid Filter with Shunt Passive Filter and Series Active Filter −

Hybrid Filter with Series Active Filter in Series with Shunt Passive Filter

The following diagram shows the topology of a Hybrid Filter with Series Active Filter in Series with Shunt Passive Filter −

The main characteristics of these three hybrid filter topologies are summarized in the following table −

Unified Power Quality Conditioner (UPQC)

Unified Power Quality Conditioner (UPQC) is an advanced power electronic device that combines both series active power filter and shunt active power filter in a single unit. Therefore, it is capable in compensating the voltage and current disturbances and reactive power simultaneously.

The hardware structure of the unified power quality conditioner is depicted in the following figure.

In this type of power quality conditioner, the series active power filter compensates the source voltage disturbances like voltage harmonics, voltage spikes and dips, etc. Whereas the shunt active power filter compensates the load current disturbances like current harmonics, power factor correction, reactive power, unbalance load currents, etc.

The shunt active power filter also provides control over the DC bus voltage to ensure the compensation capability of the UPQC.

Advantages of Power Quality Conditioners

Listed below are some major advantages of using power quality conditioners in smart grid networks −

• Power quality conditioners reduce the voltage fluctuations and disturbances in the electrical network and therefore improve the reliability of power supply.
• Power quality conditioners improve the power factor and minimize the energy losses in the grid. This results in enhanced efficiency and reduced operating cost.
• Power quality conditioners improve the overall performance of power supply to comply with standards of power quality.
• Power quality conditioners make the grid stable and reduce the risks of malfunctions of equipment.

Conclusion

Power quality conditioners are important components of a modern smart grid system because these make the system reliable and stable to meet the requirements of power quality standards.

The primary function of power quality conditioners is to compensate the power quality issues like voltage disturbances, current harmonics, waveform distortions, poor power factor, and more in the smart grids.