Active Power Filter Applied to Hospital Power Supply System

Overview of Harmonic Compensation Project

Client: A maternal and child health hospital

Problem description: 

A large number of harmonics generated by nonlinear loads inside the hospital building interfere with the normal use of equipment such as testing and treatment instruments in the hospital.

Governance measures:

According to the load rate, harmonic distortion rate and harmonic current of each transformer load equipment in the hospital, Xichi active power filter is equipped and used.

After the active power filter is put into operation, the harmonic voltage and current of each order meet the relevant requirements of the national standard GB/T14549-93. The current and voltage waveforms are approximately in the form of sine waves, and the work of harmonic control has achieved the expected goals and effects.

XiChi Active Power Filter

Product Features

✔ It can realize any combination of three functions of harmonic control, reactive power compensation and three-phase unbalanced current adjustment to realize all-round compensation for power quality problems.

✔ 2 -50 harmonics can be compensated at the same time, or a specific harmonic can be selected for compensation, and the total current distortion rate after compensation is less than 5%. Using full digital control, the harmonic current detection algorithm is based on the TTA algorithm of time domain transformation, which quickly separates the instantaneous value of each harmonic current, greatly improves the compensation response time, and truly achieves a full response of 10ms.

✔ IGBT module, three-level topology. TIDSP control chip and A LTERA's CYCLONE III series FPGA chip constitute a powerful three-core control system. American TI's double-ended high-speed input 12-bit A/D data conversion chip makes signal sampling more reliable.

✔ The structure design of layered heat dissipation makes the air duct independent, the heat dissipation performance is better, and the interference of dust and other pollutants on the control system is effectively isolated.

✔ The fan can be disassembled independently, and the replacement is easy and convenient, which enhances the reliability of heat dissipation.

✔ A variety of capacity modules can be installed in any combination to improve the reliability and maintainability of the whole machine.

✔ Using a high-resolution 5-inch LCD touch screen, it can monitor various operating data of the product in real time, and change the control parameters online. The operation is simple, and it can be remotely controlled through the mobile APP. 

Harm of Power Harmonics

In modern hospital buildings, various energy-saving lighting equipment, inverter air conditioners, elevator equipment, UPS, EPS and various advanced medical equipment are nonlinear equipment. These nonlinear equipment will generate a large number of power harmonics during operation. It will cause certain interference to the operation of the power distribution system and medical equipment, and serious power harmonic problems will lead to the damage of medical equipment and even medical accidents.

Hazards to Medical Equipment in Hospitals

• The hospital contains a large number of high-tech and expensive precision testing and treatment equipment. Most of these large-scale equipments have control devices with microprocessors as the basic unit, which are extremely sensitive to disturbances in the power supply, and may cause image vibrations, crashes and other phenomena. The reliability of power supply and the purification degree of power quality are directly related to the safety and normal working conditions of the above-mentioned equipment. Even other auxiliary facilities such as elevators, air conditioners, etc., still need special treatment, because the failure of such facilities also directly affects the reliability of the hospital as an emergency facility for saving lives and helping the wounded.

Hazards to Power Distribution Systems

• The originally designed circuit will not be able to meet the additional heating requirements of the existing harmonics, which will cause the electrical conductivity of the circuit conductors to decrease;

• Increase power consumption;

• The breaking capacity of the switch is reduced;

• Abnormal heating of motors, transformers and cables;

• The failure rate of general electrical equipment increases rapidly;

• Special electronic equipment cannot work normally, such as thyristor (relying on overcurrent point to control conduction angle synchronous control) abnormal operation, failure or damage of electrical equipment control system, no connection to communication network;

• Cause abnormal vibration and noise of power distribution equipment, and in severe cases, electrical equipment cannot operate normally, resulting in electromagnetic interference;

• Harmonics cause electrical equipment such as capacitors to overcurrent, overheat, or even burst or catch fire.

Power-grid Harmonic Standard Requirements

The power quality (harmonic) evaluation standards currently used in China are mainly the Chinese national standards ("Quality of electric energy supply Harmonics in public supply network" GB/T14549-93). This standard applies to public power grids with an AC rated frequency of 50Hz and a nominal voltage of 110kV and below. The standard has clear regulations on the distortion rate of current and voltage in the power grid, which is also an important basis for harmonic evaluation and governance.

Limits of Harmonic Voltage (Phase Voltage) of Public Grid - GB/T14549-93

Internationally, there is a harmonic standard revised by the Institute of Electrical and Electronics Engineers in 2014 [IEEE Std 519-2014, Recommended Practice and Requirements for Harmonic Control in Electric Power Systems].

Voltage distortion limits - IEEE Std 519-2014

Point of common coupling (PCC): Point on a public power supply system, electrically nearest to a particular load, at which other loads are, or could be, connected. The PCC is a point located upstream of the considered installation.

^aHigh-voltage systems can have up to 2.0% THD where the cause is an HVDC terminal whose effects will have attenuated at points in the network where future users may be connected.

Significance of Active Power Filter Application

• Protect the safety of medical electrical equipment;

• Purify the power supply;

• Protect the power factor compensation device;

• Prevent false tripping of protective devices;

• reduce power consumption;

• Increase transformer and generator power supply capacity

The harmonic control technology of active filter equipment is one of the effective means to improve the quality of power supply. After the popularization and application of APF in the power supply system of hospital buildings, the generated harmonics can be controlled within the minimum range. Realize scientific and rational use of electricity, restrain grid pollution, improve power quality, ensure the safety of medical equipment, and bring huge economic and social benefits to users.