{"id":32146,"date":"2025-06-05T07:27:33","date_gmt":"2025-06-05T07:27:33","guid":{"rendered":"https:\/\/imperix.com\/doc\/?p=32146"},"modified":"2025-07-24T13:30:46","modified_gmt":"2025-07-24T13:30:46","slug":"active-power-filters-for-harmonics-mitigation","status":"publish","type":"post","link":"https:\/\/imperix.com\/doc\/implementation\/active-power-filters-for-harmonics-mitigation","title":{"rendered":"Active power filters for harmonics mitigation"},"content":{"rendered":"<div id=\"ez-toc-container\" class=\"ez-toc-v2_0_82_2 ez-toc-wrap-right-text counter-hierarchy ez-toc-counter ez-toc-grey ez-toc-container-direction\">\n<div class=\"ez-toc-title-container\">\n<p class=\"ez-toc-title\" style=\"cursor:inherit\">Table of Contents<\/p>\n<span class=\"ez-toc-title-toggle\"><\/span><\/div>\n<nav><ul class='ez-toc-list ez-toc-list-level-1 ' ><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-1\" href=\"https:\/\/imperix.com\/doc\/implementation\/active-power-filters-for-harmonics-mitigation\/#Software-resources\" >Software resources<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-2\" href=\"https:\/\/imperix.com\/doc\/implementation\/active-power-filters-for-harmonics-mitigation\/#What-is-an-Active-Power-Filter-APF\" >What is an Active Power Filter (APF)<\/a><ul class='ez-toc-list-level-3' ><li class='ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-3\" href=\"https:\/\/imperix.com\/doc\/implementation\/active-power-filters-for-harmonics-mitigation\/#Topologies-of-Active-Power-Filters\" >Topologies of Active Power Filters<\/a><\/li><\/ul><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-4\" href=\"https:\/\/imperix.com\/doc\/implementation\/active-power-filters-for-harmonics-mitigation\/#Control-strategies-of-a-shunt-APF\" >Control strategies of a shunt APF<\/a><ul class='ez-toc-list-level-3' ><li class='ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-5\" href=\"https:\/\/imperix.com\/doc\/implementation\/active-power-filters-for-harmonics-mitigation\/#Estimation-of-the-compensation-signals\" >Estimation of the compensation signals<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-6\" href=\"https:\/\/imperix.com\/doc\/implementation\/active-power-filters-for-harmonics-mitigation\/#Active-front-End\" >Active front End<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-7\" href=\"https:\/\/imperix.com\/doc\/implementation\/active-power-filters-for-harmonics-mitigation\/#Current-control-for-an-active-power-filter\" >Current control for an active power filter<\/a><\/li><\/ul><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-8\" href=\"https:\/\/imperix.com\/doc\/implementation\/active-power-filters-for-harmonics-mitigation\/#Implementation-of-a-shunt-APF-with-a-TPI8032\" >Implementation of a shunt APF with a TPI8032<\/a><ul class='ez-toc-list-level-3' ><li class='ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-9\" href=\"https:\/\/imperix.com\/doc\/implementation\/active-power-filters-for-harmonics-mitigation\/#Experimental-setup\" >Experimental setup<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-10\" href=\"https:\/\/imperix.com\/doc\/implementation\/active-power-filters-for-harmonics-mitigation\/#Experimental-results\" >Experimental results<\/a><\/li><\/ul><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-11\" href=\"https:\/\/imperix.com\/doc\/implementation\/active-power-filters-for-harmonics-mitigation\/#Academic-references\" >Academic references<\/a><\/li><\/ul><\/nav><\/div>\n\n<p>This technical note provides an overview of Active Power Filters (APFs) designed for harmonic mitigation and specifically targeting three-phase grid-connected inverters.<\/p>\n\n\n\n<p>The note begins by introducing various APF topologies and control schemes. Then, it presents a practical implementation and experimental validation of a shunt active power filter using the <a href=\"https:\/\/imperix.com\/products\/power\/programmable-inverter\/\">TPI8032<\/a>. This example adresses the case of a nonlinear load connected to a three-phase grid.<\/p>\n\n\n\n<p>Additionally, ready-to-use Simulink and PLECS files are available for <a href=\"#APF-download\">download<\/a>.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"APF-download\"><span class=\"ez-toc-section\" id=\"Software-resources\"><\/span>Software resources<span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<p>The implementation of an shunt active power filter in Simulink and PLECS can be found below.<\/p>\n\n\n\n<div class=\"wp-block-file\"><a id=\"wp-block-file--media-703c1e29-4f1a-43a1-83dc-5e3e20ea9456\" href=\"https:\/\/imperix.com\/doc\/wp-content\/uploads\/2025\/06\/TN163_Active_Power_Filter_Simulink_powerlib.zip\">TN163_Active_Power_Filter_Simulink_powerlib<\/a><a href=\"https:\/\/imperix.com\/doc\/wp-content\/uploads\/2025\/06\/TN163_Active_Power_Filter_Simulink_powerlib.zip\" class=\"wp-block-file__button wp-element-button\" download aria-describedby=\"wp-block-file--media-703c1e29-4f1a-43a1-83dc-5e3e20ea9456\">Download<\/a><\/div>\n\n\n\n<div class=\"wp-block-file\"><a id=\"wp-block-file--media-165c4c4b-888b-432e-b128-c6f3260ffe57\" href=\"https:\/\/imperix.com\/doc\/wp-content\/uploads\/2025\/06\/TN163_Active_Power_Filter_PLECS.plecs\">TN163_Active_Power_Filter_PLECS<\/a><a href=\"https:\/\/imperix.com\/doc\/wp-content\/uploads\/2025\/06\/TN163_Active_Power_Filter_PLECS.plecs\" class=\"wp-block-file__button wp-element-button\" download aria-describedby=\"wp-block-file--media-165c4c4b-888b-432e-b128-c6f3260ffe57\">Download<\/a><\/div>\n\n\n\n<h2 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"What-is-an-Active-Power-Filter-APF\"><\/span><strong>What is an Active Power Filter (APF)<\/strong><span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<p>Ideally, an electrical grid should supply loads with a&nbsp;purely sinusoidal voltage. However, many&nbsp;nonlinear loads draw&nbsp;distorted currents. Such as variable-speed drives, computer power supplies and industrial converters. As these non-ideal currents flow through the&nbsp;line impedance, they create&nbsp;voltage drops at specific frequencies (harmonics), leading to&nbsp;voltage distortion&nbsp;at the load terminals. This phenomenon degrades power quality&nbsp;and&nbsp;increases energy losses. This is illustrated below.<\/p>\n\n\n<div class=\"wp-block-image\">\n<figure class=\"aligncenter size-full\"><img loading=\"lazy\" decoding=\"async\" width=\"366\" height=\"142\" src=\"https:\/\/imperix.com\/doc\/wp-content\/uploads\/2025\/02\/harmonics_distortion.png\" alt=\"harmonics in a power line\" class=\"wp-image-32417\" srcset=\"https:\/\/imperix.com\/doc\/wp-content\/uploads\/2025\/02\/harmonics_distortion.png 366w, https:\/\/imperix.com\/doc\/wp-content\/uploads\/2025\/02\/harmonics_distortion-300x116.png 300w\" sizes=\"auto, (max-width: 366px) 100vw, 366px\" \/><figcaption class=\"wp-element-caption\">Harmonics generated at the PCC<\/figcaption><\/figure>\n<\/div>\n\n\n<p>To mitigate these issues,&nbsp;active power filters provide a dynamic and effective solution by injecting compensating currents, which sum-up with the nonlinear load current as to create a sinusoidal current at the point of common coupling (PCC) <a href=\"#references\">[1]<\/a>. This mitigate the total amount of harmonics distortion and enhancing the overall&nbsp;power quality&nbsp;of the grid. Moreover, unlike traditional passive filters, APFs can dynamically adapt to varying load conditions and act as a <a href=\"https:\/\/imperix.com\/doc\/example\/static-synchronous-compensator-statcom\">STATCOM<\/a>, providing&nbsp;reactive power compensation&nbsp;when needed.<\/p>\n\n\n\n<p>Finally, active power filters are also crucial for ensuring compliance with harmonic standards such as IEEE 519 or IEC 6100.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"Topologies-of-Active-Power-Filters\"><\/span>Topologies of Active Power Filters<span class=\"ez-toc-section-end\"><\/span><\/h3>\n\n\n\n<p>Active Power Filters can be classified based on their hardware configurations and the objectives of their application <a href=\"#references\">[2]<\/a>. The main topologies include the following ones :<\/p>\n\n\n\n<h4 class=\"wp-block-heading\">1.&nbsp;<strong>Shunt Active Power Filter (SAPF)<\/strong><\/h4>\n\n\n\n<p>This is the most widely used topology, designed to&nbsp;eliminate current harmonics,&nbsp;compensate reactive power, and, in some cases,&nbsp;equilibrate unbalanced currents. In addition, this topology makes it easy to scale the output power. SAPF are installed&nbsp;in parallel with the load and injects&nbsp;compensating currents&nbsp;of equal magnitude but&nbsp;opposite phase&nbsp;to the harmonic currents generated by the load. This method is highly effective in&nbsp;damping harmonic propagation&nbsp;within power systems. The figure below illustrates a&nbsp;shunt active power filter connected to the grid.<\/p>\n\n\n<div class=\"wp-block-image\">\n<figure class=\"aligncenter size-full\"><img loading=\"lazy\" decoding=\"async\" width=\"391\" height=\"162\" src=\"https:\/\/imperix.com\/doc\/wp-content\/uploads\/2025\/02\/sAPF-1.png\" alt=\"shunt active power filter schematic\" class=\"wp-image-32412\" srcset=\"https:\/\/imperix.com\/doc\/wp-content\/uploads\/2025\/02\/sAPF-1.png 391w, https:\/\/imperix.com\/doc\/wp-content\/uploads\/2025\/02\/sAPF-1-300x124.png 300w\" sizes=\"auto, (max-width: 391px) 100vw, 391px\" \/><figcaption class=\"wp-element-caption\">Shunt active power filter<\/figcaption><\/figure>\n<\/div>\n\n\n<h4 class=\"wp-block-heading\">2.&nbsp;<strong>Series Active Power Filter<\/strong><\/h4>\n\n\n\n<p>This topology connects in series with the power line through a transformer and primarily addresses voltage-related issues such as harmonics, negative-sequence voltage, and flicker. Series APF are generally placed close to electrical installations in order to attenuate voltage harmonics propagated by line resonances. The figure below shows a serie active power filter connected to a grid.<\/p>\n\n\n<div class=\"wp-block-image\">\n<figure class=\"aligncenter size-full\"><img loading=\"lazy\" decoding=\"async\" width=\"391\" height=\"162\" src=\"https:\/\/imperix.com\/doc\/wp-content\/uploads\/2025\/02\/serieAPF.png\" alt=\"serie active power filter schematic\" class=\"wp-image-32413\" srcset=\"https:\/\/imperix.com\/doc\/wp-content\/uploads\/2025\/02\/serieAPF.png 391w, https:\/\/imperix.com\/doc\/wp-content\/uploads\/2025\/02\/serieAPF-300x124.png 300w\" sizes=\"auto, (max-width: 391px) 100vw, 391px\" \/><figcaption class=\"wp-element-caption\">Serie active power filter<\/figcaption><\/figure>\n<\/div>\n\n\n<h4 class=\"wp-block-heading\">3.&nbsp;<strong>Hybrid Active Power Filter<\/strong><\/h4>\n\n\n\n<p>Hybrid APFs combine active and passive filtering elements to achieve cost-effective harmonic mitigation. For instance, a passive filter can handle lower-order harmonics, while the active component compensates for higher-order harmonics and dynamic conditions. This topology is widely used for high-power applications due to its reduced cost and improved efficiency. The figure below shows a hybrid active power filter connected to a grid.<\/p>\n\n\n<div class=\"wp-block-image\">\n<figure class=\"aligncenter size-full\"><img loading=\"lazy\" decoding=\"async\" width=\"386\" height=\"213\" src=\"https:\/\/imperix.com\/doc\/wp-content\/uploads\/2025\/02\/hybrid_APF.png\" alt=\"hybrid active power filter schematic\" class=\"wp-image-32416\" srcset=\"https:\/\/imperix.com\/doc\/wp-content\/uploads\/2025\/02\/hybrid_APF.png 386w, https:\/\/imperix.com\/doc\/wp-content\/uploads\/2025\/02\/hybrid_APF-300x166.png 300w\" sizes=\"auto, (max-width: 386px) 100vw, 386px\" \/><figcaption class=\"wp-element-caption\">Hybrid Active Power Filter<\/figcaption><\/figure>\n<\/div>\n\n\n<h4 class=\"wp-block-heading\">4.&nbsp;<strong>Unified Power Quality Conditioner (UPQC)<\/strong><\/h4>\n\n\n\n<p>This advanced topology integrates both series and shunt APFs into a single system. The UPQC compensates for both voltage and current distortions simultaneously, offering comprehensive power quality solutions. While highly effective, UPQCs are more complex and costly, making them suitable for critical applications requiring superior power quality. The figure below shows an UPQC connected to a grid.<\/p>\n\n\n<div class=\"wp-block-image\">\n<figure class=\"aligncenter size-full\"><img loading=\"lazy\" decoding=\"async\" width=\"510\" height=\"162\" src=\"https:\/\/imperix.com\/doc\/wp-content\/uploads\/2025\/02\/UPQC_APF.png\" alt=\"Unified Power Quality Conditioner schematic\" class=\"wp-image-32414\" srcset=\"https:\/\/imperix.com\/doc\/wp-content\/uploads\/2025\/02\/UPQC_APF.png 510w, https:\/\/imperix.com\/doc\/wp-content\/uploads\/2025\/02\/UPQC_APF-300x95.png 300w\" sizes=\"auto, (max-width: 510px) 100vw, 510px\" \/><figcaption class=\"wp-element-caption\">Unified Power Quality Conditioner<\/figcaption><\/figure>\n<\/div>\n\n\n<div class=\"wp-block-simple-alerts-for-gutenberg-alert-boxes sab-alert sab-alert-info\" role=\"alert\">Since the\u00a0Shunt Active Power Filter\u00a0is the most commonly used topology in\u00a0low-voltage grids, the rest of this technical note will focus exclusively on Shunt Active Power Filters.<\/div>\n\n\n\n<h2 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"Control-strategies-of-a-shunt-APF\"><\/span><strong>Control strategies of a shunt APF<\/strong><span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<p>The&nbsp;control strategy of Active Power Filters&nbsp;often consists of three key steps in order to achieve a proper harmonic mitigation. The figure below illustrates these processes, and the following sections describe them.<\/p>\n\n\n<div class=\"wp-block-image\">\n<figure class=\"aligncenter size-full is-resized\"><img loading=\"lazy\" decoding=\"async\" width=\"417\" height=\"99\" src=\"https:\/\/imperix.com\/doc\/wp-content\/uploads\/2025\/03\/Process_SAPF.png\" alt=\"control sheme active power filter\" class=\"wp-image-32597\" style=\"width:417px;height:auto\" srcset=\"https:\/\/imperix.com\/doc\/wp-content\/uploads\/2025\/03\/Process_SAPF.png 417w, https:\/\/imperix.com\/doc\/wp-content\/uploads\/2025\/03\/Process_SAPF-300x71.png 300w\" sizes=\"auto, (max-width: 417px) 100vw, 417px\" \/><figcaption class=\"wp-element-caption\">Main processes of an APF control strategy<\/figcaption><\/figure>\n<\/div>\n\n\n<p>The first and most important step is the&nbsp;generation of compensation current signals. These signals correspond to the corrective currents that, when combined with the&nbsp;nonlinear load currents, produce a&nbsp;sinusoidal current&nbsp;on the grid side. Careful attention to the estimation of compensation signals is important, as this step directly influences the APF&#8217;s ability to reduce harmonic distortion.<\/p>\n\n\n\n<p>The second step is the&nbsp;control of the DC bus voltage. This step acts as an <a href=\"https:\/\/imperix.com\/doc\/implementation\/active-front-end\">Active Front End (AFE)<\/a> and generates an&nbsp;additional current reference, which ensures that the&nbsp;DC bus voltage remains at the desired level. However, if the&nbsp;DC bus is powered by an external source, this regulation is unnecessary, as the voltage is already maintained independently. Together with the first step, the total current reference that the converter must follow are defined.<\/p>\n\n\n\n<p>The&nbsp;third and final step is the&nbsp;application of the current control to ensure that the APF tracks the current references calculated in the previous steps. The selection and tuning of the controller require special attention, as APF current references have a distinct waveform that includes high-order harmonics (i.e., high-frequency components).<\/p>\n\n\n\n<h3 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"Estimation-of-the-compensation-signals\"><\/span>Estimation of the compensation signals<span class=\"ez-toc-section-end\"><\/span><\/h3>\n\n\n\n<p>The estimation of compensation signals plays a key role in active power filter control, directly impacting performance and computational complexity. Different methods exist to estimate these signals, which can be broadly classified into two main approaches: time-domain methods and frequency-domain methods.<\/p>\n\n\n\n<p>Frequency-domain methods&nbsp;use spectral analysis to identify and eliminate harmonics but require&nbsp;high computational resources, making them difficult to use for real-time applications. Consequently, these methods are out of the scope of this article.<\/p>\n\n\n\n<p>Time-domain techniques extract compensation signals instantly from distorted waveforms, offering fast response and simple implementation but are limited to single-point corrections . In practice, these algorithms measure the&nbsp;current drawn by the nonlinear load, isolate harmonics using a&nbsp;high-pass filter, and inject the&nbsp;high-frequency components (&gt;50 Hz) back into the grid with same amplitude but opposit phase. As a result, the APF supplies the&nbsp;non-sinusoidal and high-frequency currents drawn by the nonlinear load. This prevents the grid from bearing these distortions.<\/p>\n\n\n\n<p>Among the various&nbsp;time-domain techniques, the most widely used is the&nbsp;instantaneous P-Q strategy <a href=\"#references\">[3]<\/a>, which is detailed in the section below.<\/p>\n\n\n\n<h4 class=\"wp-block-heading\">Instantaneous P-Q theory for active power filters<\/h4>\n\n\n\n<p>The&nbsp;Instantaneous P-Q theory, also known as the&nbsp;P-Q strategy, aims to ensure that the&nbsp;active and reactive powers drawn from the grid do not oscillate. This implies that the currents drawn from the grid must be&nbsp;perfectly sinusoidal, assuming the voltage is also ideal. To achieve this, the P-Q strategy first calculates the&nbsp;instantaneous active and reactive powers&nbsp;consumed by the nonlinear load using Eq. (1).<\/p>\n\n\n\n<p>$$ (1) \\quad \\begin{bmatrix} p_L\\\\ q_L \\end{bmatrix} = \\begin{bmatrix}<br>v_{g,\\alpha}&amp;v_{g,\\beta}\\\\<br>-v_{g,\\beta} &amp; v_{g,\\alpha}<br>\\end{bmatrix} \\begin{bmatrix}<br>i_{L,\\alpha}\\\\<br>i_{L,\\beta} <br>\\end{bmatrix} $$<\/p>\n\n\n\n<p>As a result, when the load currents are not purely sinusoidal at the fundamental frequency (i.e., they contain&nbsp;negative-sequence components or harmonics), the instantaneous&nbsp;active and reactive powers&nbsp;fluctuate instead of remaining constant. Consequently, the formulation expresses the active and reactive powers as the sum of a constant and an oscillating component, as follows :<\/p>\n\n\n\n<p>$$ (2) \\quad p_L = \\tilde{p}_L + \\bar{p}_L \\quad \\quad q_L = \\tilde{q}_L + \\bar{q}_L$$<\/p>\n\n\n\n<p>To ensure that the grid supplies only a&nbsp;constant power, the role of the APF&nbsp;is to inject the oscillating power components consumed by the nonlinear load. This compensation corresponds to :<\/p>\n\n\n\n<p>$$ (3) \\quad  p^*_{APF} = -\\tilde{p} _{L} \\quad \\quad q^*_{APF} = -\\tilde{q} _{L} $$<\/p>\n\n\n\n<p>Therefore, it is necessary to determine the instantaneous values of\u00a0\\(\\tilde{p} _{L}\\) and \\(\\tilde{q} _{L}\\). This is achieved using a\u00a0high-pass filter (HPF), which removes the\u00a0constant power components\u00a0from the instantaneous power signals, leaving only the\u00a0oscillating terms. The HPF can also be implemented using a\u00a0low-pass filter (LPF), such as a Butterworth filter, as follows:<\/p>\n\n\n<div class=\"wp-block-image\">\n<figure class=\"aligncenter size-full\"><img loading=\"lazy\" decoding=\"async\" width=\"281\" height=\"88\" src=\"https:\/\/imperix.com\/doc\/wp-content\/uploads\/2025\/02\/HPF_for_APF-1.png\" alt=\"high pass filter P-Q theory\" class=\"wp-image-32444\"\/><figcaption class=\"wp-element-caption\">HPF filter diagram for shunt APF<\/figcaption><\/figure>\n<\/div>\n\n\n<p>Using these oscillating components as references for the APF leads to the grid-side power shown in Eq. (4).<\/p>\n\n\n\n<p>$$ (4) \\quad p_{g} = \\tilde{p} _{L} + \\bar{p} _{L} + \\underbrace{\\tilde{p} _{APF} }_{\\approx -\\tilde{p} _{L} } + \\bar{p} _{APF} \\approx \\bar{p} _{L} + \\bar{p} _{APF}$$<br><br>From the equation above, we can conclude that the&nbsp;instantaneous power drawn from the grid remains constant, ensuring that the grid current is&nbsp;purely sinusoidal and free of distortion. Moreover, since the&nbsp;shunt APF&nbsp;operates by controlling&nbsp;currents rather than power, the compensating currents \\(i^*_{c,abc}\\) must be derived from the&nbsp;power references. This is achieved by inverting Eq. (1), resulting in the following expression :<br>$$ (5) \\quad \\begin{bmatrix} i^*_{c,\\alpha}\\\\ i^*_{c,\\beta} \\end{bmatrix} = \\begin{bmatrix}<br>v_{g,\\alpha}&amp;v_{g,\\beta}\\\\<br>-v_{g,\\beta} &amp; v_{g,\\alpha}<br>\\end{bmatrix}^{-1} <br>\\begin{bmatrix}<br>p^*_{APF}\\\\<br>q^*_{APF}<br>\\end{bmatrix}$$ <br>This equation allows the APF to compute the&nbsp;instantaneous reference currents&nbsp;required to inject the appropriate compensating currents. The illustration below shows the complete process of the P-Q strategy.<\/p>\n\n\n<div class=\"wp-block-image\">\n<figure class=\"aligncenter size-full\"><img loading=\"lazy\" decoding=\"async\" width=\"757\" height=\"181\" src=\"https:\/\/imperix.com\/doc\/wp-content\/uploads\/2025\/02\/APF_PQ_Strategy.png\" alt=\"Block diagram of active power filter\" class=\"wp-image-32453\" srcset=\"https:\/\/imperix.com\/doc\/wp-content\/uploads\/2025\/02\/APF_PQ_Strategy.png 757w, https:\/\/imperix.com\/doc\/wp-content\/uploads\/2025\/02\/APF_PQ_Strategy-300x72.png 300w\" sizes=\"auto, (max-width: 757px) 100vw, 757px\" \/><figcaption class=\"wp-element-caption\">Block diagram of the P-Q strategy<\/figcaption><\/figure>\n<\/div>\n\n\n<h3 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"Active-front-End\"><\/span>Active front End<span class=\"ez-toc-section-end\"><\/span><\/h3>\n\n\n\n<p>Powering the DC bus of an&nbsp;Active Power Filter externally can be costly and impractical. Since the APF is connected to the grid, it can&nbsp;self-power&nbsp;by drawing energy from the grid while using its&nbsp;DC bus as a buffer. This is achieved through an&nbsp;Active Front End (AFE), which regulates the&nbsp;DC bus voltage.&nbsp;Since the APF reinjects all the absorbed active power back into the same grid, the AFE technically compensates only for the system losses. This control step generates a&nbsp;current reference&nbsp;that is simply added to the APF\u2019s existing reference.<\/p>\n\n\n\n<p>For details on&nbsp;tuning and implementation, refer to the<a href=\"https:\/\/imperix.com\/doc\/implementation\/active-front-end\">&nbsp;Active Front End<\/a> technical note.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"Current-control-for-an-active-power-filter\"><\/span><strong>Current control for an active power filter<\/strong><span class=\"ez-toc-section-end\"><\/span><\/h3>\n\n\n\n<p>In a three-phase grid,&nbsp;nonlinear loads&nbsp;typically generate&nbsp;odd non-triplen harmonics&nbsp;of the form&nbsp;6n \u00b1 1&nbsp;(e.g., 5th, 7th, 11th, 13th,&#8230;). These&nbsp;high-frequency harmonics&nbsp;can only be effectively compensated if they fall within the&nbsp;bandwidth of the current controller. Therefore, a&nbsp;high-bandwidth controller,&nbsp;or one with&nbsp;high gain at these harmonic frequencies is crucial for optimal&nbsp;APF performance.<\/p>\n\n\n\n<p>The literature presents various current controllers suitable for APFs, including PI, PI + Resonant, Predictive, Deadbeat, and Hysteresis controllers. Among these options, this technical note uses a&nbsp;Proportional-Resonant (PR) controller, specifically tuned for the&nbsp;four dominant harmonics (h = 5, 7, 11, 13).<\/p>\n\n\n\n<p>For details on&nbsp;implementation and tuning, refer to the&nbsp;<a href=\"https:\/\/imperix.com\/doc\/implementation\/proportional-resonant-controller\">PR Controller<\/a> technical note.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"Implementation-of-a-shunt-APF-with-a-TPI8032\"><\/span><strong>Implementation of a shunt APF with a TPI8032<\/strong><span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<h3 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"Experimental-setup\"><\/span>Experimental setup<span class=\"ez-toc-section-end\"><\/span><\/h3>\n\n\n\n<p>The&nbsp;experimental setup&nbsp;in this article consists of&nbsp;two <a href=\"https:\/\/imperix.com\/products\/power\/programmable-inverter\/\">TPI8032<\/a> and&nbsp;three <a href=\"https:\/\/imperix.com\/doc\/software\/current-sensor\">DIN50A<\/a> current sensors, all connected to the same grid. The first&nbsp;TPI8032 operates&nbsp;as the&nbsp;Active Power Filter (APF),&nbsp;while the second&nbsp;emulates&nbsp;a&nbsp;diode rectifier (nonlinear load).&nbsp; Additionally, the APF uses three current sensors to measure the currents drawn by the nonlinear load. Finally, the DC power supply absorbs&nbsp;the power from the&nbsp;emulated diode rectifier.<\/p>\n\n\n\n<div class=\"wp-block-group is-nowrap is-layout-flex wp-container-core-group-is-layout-ad2f72ca wp-block-group-is-layout-flex\">\n<figure class=\"wp-block-table\"><table><tbody><tr><td>Control and switching frequency<\/td><td>50 kHz<\/td><\/tr><tr><td>DC bus voltage<\/td><td>800 V<\/td><\/tr><tr><td>Grid voltage (L to N)<\/td><td>230 VRMS<\/td><\/tr><\/tbody><\/table><figcaption class=\"wp-element-caption\">Experiment conditions<br><\/figcaption><\/figure>\n\n\n<div class=\"wp-block-image\">\n<figure class=\"aligncenter size-full is-resized\"><img loading=\"lazy\" decoding=\"async\" width=\"437\" height=\"179\" src=\"https:\/\/imperix.com\/doc\/wp-content\/uploads\/2025\/02\/Experimental_setup_PS.png\" alt=\"Experimental setup for active power filter\" class=\"wp-image-32551\" style=\"width:431px;height:auto\" srcset=\"https:\/\/imperix.com\/doc\/wp-content\/uploads\/2025\/02\/Experimental_setup_PS.png 437w, https:\/\/imperix.com\/doc\/wp-content\/uploads\/2025\/02\/Experimental_setup_PS-300x123.png 300w\" sizes=\"auto, (max-width: 437px) 100vw, 437px\" \/><\/figure>\n<\/div><\/div>\n\n\n<div class=\"wp-block-image\">\n<figure class=\"aligncenter size-large is-resized\"><img loading=\"lazy\" decoding=\"async\" width=\"1024\" height=\"1024\" src=\"https:\/\/imperix.com\/doc\/wp-content\/uploads\/2025\/03\/APC_0201-2-1024x1024.jpg\" alt=\"\" class=\"wp-image-32926\" style=\"width:680px\" srcset=\"https:\/\/imperix.com\/doc\/wp-content\/uploads\/2025\/03\/APC_0201-2-1024x1024.jpg 1024w, https:\/\/imperix.com\/doc\/wp-content\/uploads\/2025\/03\/APC_0201-2-300x300.jpg 300w, https:\/\/imperix.com\/doc\/wp-content\/uploads\/2025\/03\/APC_0201-2-150x150.jpg 150w, https:\/\/imperix.com\/doc\/wp-content\/uploads\/2025\/03\/APC_0201-2-768x769.jpg 768w, https:\/\/imperix.com\/doc\/wp-content\/uploads\/2025\/03\/APC_0201-2-1534x1536.jpg 1534w, https:\/\/imperix.com\/doc\/wp-content\/uploads\/2025\/03\/APC_0201-2-2046x2048.jpg 2046w\" sizes=\"auto, (max-width: 1024px) 100vw, 1024px\" \/><\/figure>\n<\/div>\n\n\n<p>It is also possible to configure the two&nbsp;TPI8032 in a <a href=\"https:\/\/imperix.com\/doc\/help\/multi-master-mode-for-distributed-networked-control-systems\">master-master setup<\/a>, allowing the APF to use the&nbsp;current measurements from the diode rectifier emulator,&nbsp;instead of requiring external current sensors. This reduces the need for additional hardware.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"Experimental-results\"><\/span>Experimental results<span class=\"ez-toc-section-end\"><\/span><\/h3>\n\n\n\n<p>The figure below presents the experimental results, displaying the currents from the diode rectifier and the APF, the&nbsp;grid voltage and current, as well as the&nbsp;DC voltage of the APF.<\/p>\n\n\n\n<p>First, the diode rectifier draws a distorted current while the APF is connected to the grid but inactive. At\u00a0t = 40 ms, the\u00a0APF activates its control, injecting\u00a0compensating currents\u00a0with a specific waveform. From this moment, the\u00a0grid currents, obtained by summing the APF and diode rectifier currents, become sinusoidal. This demonstrate the effectiveness of the APF for harmonics mitigation.<\/p>\n\n\n<div class=\"wp-block-image\">\n<figure class=\"aligncenter size-full\"><img loading=\"lazy\" decoding=\"async\" width=\"675\" height=\"697\" src=\"https:\/\/imperix.com\/doc\/wp-content\/uploads\/2025\/02\/APF_Experim_results.png\" alt=\"Experimental results of an active power filter\" class=\"wp-image-32556\" srcset=\"https:\/\/imperix.com\/doc\/wp-content\/uploads\/2025\/02\/APF_Experim_results.png 675w, https:\/\/imperix.com\/doc\/wp-content\/uploads\/2025\/02\/APF_Experim_results-291x300.png 291w\" sizes=\"auto, (max-width: 675px) 100vw, 675px\" \/><figcaption class=\"wp-element-caption\">APF experimental results<\/figcaption><\/figure>\n<\/div>\n\n\n<p>Additionally, the figure below illustrates the\u00a0harmonic content\u00a0of the grid current\u00a0before and after APF activation, highlighting the\u00a0combined performance of the compensation current calculation (Instantaneous P-Q theory)\u00a0and the\u00a0current controller.<\/p>\n\n\n<div class=\"wp-block-image\">\n<figure class=\"aligncenter size-full\"><img loading=\"lazy\" decoding=\"async\" width=\"500\" height=\"300\" src=\"https:\/\/imperix.com\/doc\/wp-content\/uploads\/2025\/01\/FFT.png\" alt=\"frequency spectrum of an active power filter\" class=\"wp-image-32282\" srcset=\"https:\/\/imperix.com\/doc\/wp-content\/uploads\/2025\/01\/FFT.png 500w, https:\/\/imperix.com\/doc\/wp-content\/uploads\/2025\/01\/FFT-300x180.png 300w\" sizes=\"auto, (max-width: 500px) 100vw, 500px\" \/><figcaption class=\"wp-element-caption\">Grid current spectrum<\/figcaption><\/figure>\n<\/div>\n\n\n<p>Finally, the 17th and 19th (red in figure, at 850Hz and 950Hz) harmonics appear less attenuated compared to the first four dominant harmonics. This is due to the fact that the&nbsp;PR controller was specifically tuned&nbsp;for the 5th, 7th, 11th, and 13th harmonics, while higher-order harmonics are only attenuated by the&nbsp;proportional gain of the PR controller.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"references\"><span class=\"ez-toc-section\" id=\"Academic-references\"><\/span>Academic references<span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<p><a href=\"https:\/\/ieeexplore.ieee.org\/document\/1545766\">[1]<\/a> H. Akagi, &#8220;Active Harmonic Filters,&#8221; in Proc. IEEE, Vol. 93, N\u00b0. 12, pp. 2128-2141, Dec. 2005.<\/p>\n\n\n\n<p><a href=\"https:\/\/ieeexplore.ieee.org\/document\/793345\">[2]<\/a> B. Singh, K. Al-Haddad and A. Chandra, &#8220;A review of active filters for power quality improvement,&#8221; in&nbsp;<em>IEEE Transactions on Industrial Electronics<\/em>, Vol. 46, N\u00b0. 5, pp. 960-971, Oct. 1999<\/p>\n\n\n\n<p><a href=\"https:\/\/ieeexplore.ieee.org\/document\/4052426\">[3]<\/a> M. I. M. Montero, E. R. Cadaval and F. B. Gonzalez, &#8220;Comparison of Control Strategies for Shunt Active Power Filters in Three-Phase Four-Wire Systems,&#8221; in IEEE Trans. on Pow. Elec., Vol. 22, N\u00b0. 1, pp. 229-236, Jan. 2007.<\/p>\n\n\n\n<p><\/p>\n","protected":false},"excerpt":{"rendered":"<p>This technical note provides an overview of Active Power Filters (APFs) designed for harmonic mitigation and specifically targeting three-phase grid-connected inverters. The note begins by&#8230;<\/p>\n","protected":false},"author":22,"featured_media":33366,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"_kad_post_transparent":"","_kad_post_title":"","_kad_post_layout":"","_kad_post_sidebar_id":"","_kad_post_content_style":"","_kad_post_vertical_padding":"","_kad_post_feature":"","_kad_post_feature_position":"","_kad_post_header":false,"_kad_post_footer":false,"_kad_post_classname":"","footnotes":""},"categories":[4],"tags":[53,22,19],"software-environments":[103,104],"provided-results":[108],"related-products":[50,32,92,166,113,112,111,110],"guidedreadings":[],"tutorials":[152],"user-manuals":[],"coauthors":[98],"class_list":["post-32146","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-implementation","tag-current-control","tag-micro-grids","tag-three-level-converters","software-environments-matlab","software-environments-plecs","provided-results-experimental","related-products-acg-sdk","related-products-b-box-rcp","related-products-b-box-micro","related-products-b-box-rcp-3-0","related-products-mmc","related-products-peb","related-products-pm","related-products-tpi","tutorials-active-power-filter"],"acf":[],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v27.4 - 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