– Active Power (P, unit: Watt or Kilowatt): The “power that actually does the work.” Electrical energy is truly converted into heat, light, mechanical energy, etc., to accomplish “useful” tasks\u2014boiling water, lighting up bulbs, turning motors, etc. This is what electricity meters measure.<\/p>\n
– Reactive Power (Q, unit: var or kilovar): The “power that establishes magnetic fields.” Many devices (such as motors and transformers) require magnetic fields to operate. Reactive power represents the scale of energy exchanged back and forth between the power source and the magnetic fields of these devices. It is not truly consumed but merely oscillates between the source and the load, doing no external work, hence the name reactive power.<\/p>\n
– Apparent Power (S, unit: Volt-Ampere or Kilovolt-Ampere): The “total power supply capacity.” It is the simple product of voltage and current, and the vector sum of active and reactive power, representing the total load that grid equipment (such as generators, transformers, and transmission lines) needs to carry.<\/p>\n
The three satisfy a simple relationship: S\u00b2 = P\u00b2 + Q\u00b2, as shown in the triangle below:
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In the power triangle, apparent power is the hypotenuse, active power is the adjacent side, and reactive power is the opposite side. There is also an important parameter: power factor cos\u03c6 = P\/S, which measures the proportion of active power in the total capacity. The closer cos\u03c6 is to 1, the smaller the proportion of reactive power, and the higher the power utilization efficiency.<\/p>\n
2. Why is Reactive Power “Doing No Work” yet “Indispensable” to the Power Grid?<\/strong><\/p>\n (1) Maintaining Voltage Stability: The balance between supply and demand of reactive power directly determines the voltage level of the power grid. It acts as a “voltage stabilizer” for the grid. When reactive power is sufficient: the grid voltage can be maintained within the rated range (e.g., 380V \u00b15%), ensuring the normal operation of all electrical equipment. When reactive power is insufficient: the grid voltage will drop rapidly like a “flat tire,” leading to reduced equipment output (e.g., slower motor speeds), increased current, and overheating; in severe cases, it can even trigger voltage collapse and widespread blackouts. When reactive power is excessive: the grid voltage will abnormally rise (“surge”), potentially breaking down the insulation materials of equipment such as transformers and switchgears, causing short-circuit faults.<\/p>\n (2) Providing Working Magnetic Fields for Electromagnetic Equipment: Many common electrical devices (such as motors, transformers, inverters, etc.) operate based on the principle of electromagnetic induction. They must first establish and maintain alternating magnetic fields to convert and transmit energy. Reactive power is precisely the indispensable energy that provides the “excitation current” for these devices to establish magnetic fields. Without reactive power, motors cannot rotate, transformers cannot transform voltage, and AC contactors cannot engage.<\/p>\n (3) Reducing Line Losses and Releasing Line Capacity: The flow of reactive current in conductors also generates heat losses. If reactive power is too high, line losses increase while occupying the capacity of the transmission channel (apparent power), thereby reducing the actual available active power transmission capacity. By compensating reactive power locally (e.g., installing capacitors or using inverters that support reactive power regulation), long-distance transmission of reactive power can be reduced, thus lowering losses and improving overall grid efficiency.<\/p>\n 3. Why Must Inverters Support Reactive Power Regulation?<\/strong><\/p>\n In traditional power grids, reactive power is mainly regulated by synchronous generators, capacitors, reactors, or dedicated static var compensators (SVC\/SVG). Today, however, large amounts of photovoltaic (PV), wind power, energy storage, and electric vehicle charging stations are connected to the grid, generally through power electronic inverters (converters). These inverter-based devices have an inherent characteristic: through control algorithms, they can flexibly generate or absorb reactive power, acting like an intelligent and extremely fast-responding reactive power source. The requirement for inverters to support reactive power regulation is mainly based on the following practical needs:<\/p>\n (1) Distributed Power Sources Have Changed Traditional Reactive Power Flow<\/p>\n In the past, power flowed unidirectionally from substations to lines to users, and reactive power compensation was designed as “fixed + minor regulation.” But now, with the dispersed integration of rooftop PV and industrial park energy storage, PV systems feed active power back into the grid during the day, which may cause local voltage rises. At this time, if the inverter can absorb some capacitive reactive power, it can pull down the voltage. In the evening, as PV output drops and load increases, voltage sags, and the inverter can inject capacitive reactive power into the grid to support the voltage. Without the reactive power regulation of inverters, distribution network voltages would frequently exceed limits.<\/p>\n (2) Avoiding Redundant Investment in User-Built Reactive Power Compensation Equipment<\/p>\n Traditionally, manufacturers needed to install capacitor banks next to motors to compensate for reactive power; otherwise, they would be penalized by the grid for their power factor (and have to pay higher electricity bills if it was too low). Now, PV inverters and energy storage converters themselves possess reactive power capabilities, which can replace or reduce the capacity of these capacitors, lowering costs for users.<\/p>\n (3) Responding to Grid Dispatch and Becoming “Distributed Voltage Regulators”<\/p>\n With the retirement of traditional thermal and hydroelectric units (and the consequent decrease in synchronous generators), the grid’s reactive power reserves decline accordingly. If millions of inverters were to operate at “unity power factor” (i.e., only generating active power), they would become “cold-blooded power sources” for the grid\u2014only taking up active power channels without participating in voltage support. Therefore, domestic and international grid connection standards (such as China’s GB\/T 33593, Germany’s BDEW, and the US IEEE 1547) mandate that inverters above a certain capacity must have reactive power regulation capabilities and adjust reactive power online according to grid voltage or dispatch instructions.<\/p>\n Although named “reactive,” reactive power makes a great contribution to the power grid. From the synchronous generators in hydropower stations to the PV inverters on your rooftop, every grid-connected device is participating in an invisible “voltage balancing act.” As the proportion of new energy continues to rise, the inverter is no longer just a simple box that converts DC to AC; it has become an “intelligent damper” for the grid, injecting or absorbing reactive power in real time, silently guarding the stable voltage readings when you flip the switch.<\/p>\n","protected":false},"excerpt":{"rendered":" In daily life, when we pay our electricity bills, we focus on “how many kilowatt-hours we’ve used.” This “kilowatt-hour” corresponds to the electrical energy that actually does work and is consumed by us, which is “active power.” However, in power systems, there is another type of power that is invisible and intangible, yet crucial and […]<\/p>\n","protected":false},"author":12,"featured_media":46106,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[109],"tags":[],"class_list":["post-46747","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-news"],"yoast_head":"\n