Medium Voltage Harmonic Compensation Challenges

Traditionally, harmonic compensation at medium voltage level is provided by passive filter solution with combination of multiple single-tuned filters and/or a high-pass filter. In practice, the performance and reliability of passive filter solution are affected by many factors including network parameters, load variation, capacitance loss over time, environment conditions. It’s often the case when the performance of passive filter solution is not as desirable as designed and, in worst cases, series or parallel resonance would happen between passive filters and network.

To overcome the drawbacks of passive filter solution, active harmonic filter (AHF) is proposed as an alternative to meet the strict harmonic limitation dedicated by IEEE519. By its nature, the performance of AHF is independent of network parameters and load variation to ensure desirable performance.

However, it requires a step-up transformer to connect low-voltage AHF solution to medium voltage bus to compensate MV loads, which would increase the capital expenditure significantly. The project owner is often frightened by the total cost of LV AHF with step-up transformer.

Solution 

To solve this, HTQF M series AHF is designed to provide centralized active harmonic compensation with much less capital expenditure at medium voltage level.

HTQF M series AHF utilizes Voltage-Source Converter (VSC) technology. Instead of using passive components like MV capacitors and reactors, MV AHF consists of Modular Multilevel Converters (MMC), equipped with insulated gate bipolar transistors (IGBTs) that are controlled by pulse width modulation (PWM).

The dual-DSP + FPGA controller detects harmonic current component, reactive current component, negative-sequence and zero-sequence current components in the grid on real-time basis and responses to the current transient at a millisecond level. As an all-around power quality solution, HTQF M series MV AHF not only provide harmonic compensation but also dynamic reactive power compensation as well as tload balancing in the same time. 

HTQF M series MV AHF is ideal for steel works, coal mining, chemical industry, wind and solar farms, railway electrification systems, where harmonics are best to be compensated centrally at medium voltage level based on engineering and/or economic considerations.

Features 

• Voltage ratings up to 35kV 

• 5ms response time, ideal for dynamic loads such as rolling mills, mining hoists, arc furnace, railway electrification system 

• Target THDi meet IEEE519 limitation 

• Selective compensation: ON/OFF and filtering factor for each order can be set individually 

• Proven dual algorithms: Fast Fourier Transformation (FFT) and Instantaneous Reactive Theory (P-Q Theory), shared with industry-leading low-voltage AHFs

• Taking advantage of 17 years of active harmonic filter R&D experience and practical knowledgement of harmonic filtering for all kinds of applications
  

• Dynamic reactive power compensation for both inductive and capacitive loads 

• Continuous variable reactive power output without over-compensation and under-compensation 

• Targeted PF programmable

• Multiple working modes with task priority concept for multi-task applications

• Based on Modular Multi-Level Converter (MMC), all power modules identical for easy maintenance 

• Optical fiber communication between control system and power modules for MV/LV isolation to ensure high level of safety for servicing engineers and immunity against electromagnetic inference.

• No risk of series or parallel resonance for reliable operation 

• Patented resonance mitigation algorithm for added reliability 

• Compensation independent of network parameters easy for design 

• Automatic output current limitation, no risk of over-current 

• Extensive protection integrating software protection, logic hardware protection and relay protection 

• Fault events recording function for easy fault analysis 

• 10-inch true color touch screen HMI with multi-language graphic interface 

• Easy integration into Substation Automation System (SAS) or SCADA for remote monitoring and operation 

• Cost-effective hybrid solution in parallel with high-pass filters 

• Small Footprint 

• Direct connection to the MV network without step-up transformer to reduce capital expenditure and space

Specifications