Application of active power filter in ship network harmonic compensation - News - Global IC Trade Starts Here Free Join

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The non-linear equipment in the ship power grid generates a large amount of harmonic current. This paper tests and analyzes the harmonic condition of a certain type of ship power grid. Several schemes of harmonic compensation are discussed. The active filter scheme is used for harmonics. Wave compensation, a brief introduction to the design of the active power filter device, and finally the test results of the compensation.

1. Foreword The ship power grid is an independent power grid consisting of several generator sets connected in parallel. In recent years, with the increase in the number of non-linear power equipment, especially radar equipment, the harmonic current injected into the ship's power grid has increased, and the total harmonic content of the current is as high as 27%, which is seriously exceeding the national military standard. The CE101 project in GJB151A has requirements for current harmonic limits and adversely affects or poses a potential hazard to other more sensitive shipboard electrical equipment. Therefore, harmonic control measures must be taken to reduce current harmonics to meet the requirements of the corresponding standard specifications.
2. The harmonic condition and compensation requirements of the ship's power grid: 1) Voltage: rated 380V, continuous fluctuation does not exceed ±10%, short-term fluctuation does not exceed ±15%; 2) Frequency: rated 50Hz: fluctuation does not exceed ± 5%; 3) Phase number: three-phase three-wire; 4) Power supply characteristics: meet the requirements of GB/T13032-91 Marine Diesel Generator Set Technical Conditions.
Powered equipment is hybrid, including high power radar systems, electronics, transmission cooling systems, and general purpose electrical equipment. Among them, the radar current system is the largest in the current harmonics injected into the grid. The capacity of the equipment is about 300kVA. During the operation, the load varies between 130~260kW according to different working modes, and the total harmonic distortion is about 27%.
Tested on the power distribution screen of the radar power supply system, the voltage and current waveforms and load current fluctuations are shown in Figure 1 and Figure 2. The single harmonic distributions when the current changes are shown in Table 1 and Table 2. It can be seen that in addition to the total harmonic of the current up to 29%, due to the different working modes during the working period, the load current changes frequently, resulting in frequent changes of harmonic current, which brings certain difficulties to harmonic compensation.

Figure 1 voltage and current waveform

Figure 2 Load current fluctuations

Table 1 Current harmonic content at full load

Table 2 Current harmonic content when current fluctuates

According to the above harmonic conditions, the requirements for harmonic compensation are as follows:
1. Compensation ability: harmonic compensation current is not less than 100A;
2. Compensation effect: After compensation, the current on the grid side is distorted to meet the requirements of CE101;
3. Tracking characteristics: dynamic tracking compensation, adapt to the fluctuation characteristics of the load, dynamic response time ≯ 20ms;
4. Cooling method: air cooling
5. Fault protection: The compensation device has basic fault protection function. When the fault is protected, the device can be automatically disconnected from the power grid without affecting the normal operation of the marine power grid.
6. Structure: It adopts the same standard cabinet type with the height of 1.6m and other marine electrical equipment, and the weight is not more than 100kg.

3. As mentioned in the overall scheme selection of the filter, the harmonics of the radar equipment are mainly current sources. To limit the harmonic current injected into the grid by the harmonic source, the following scheme can be adopted:
1. The device that generates the harmonics is modified so that it does not generate harmonics and the power factor is as high as possible. It is possible to install a transformer on the input side to make the rectifier circuit multiplexed; or to use a fully controlled device to form a PWM rectifier to achieve power factor correction.
2. An AC passive filter device is installed. The device is composed of a power capacitor, a reactor and a resistor. The device is composed of a number of single-tuning and high-pass filter branches. The harmonic source is operated in parallel to absorb harmonic current and effectively reduce harmonics. In addition to the filtering effect, it also takes into account the need for reactive power compensation. The advantages are simple structure, reliable operation and convenient maintenance.
The main disadvantage of this filtering method is that the compensation characteristics are affected by the impedance and operating state of the grid, and it is easy to parallel resonance with the system, resulting in harmonic amplification, which causes the LC filter to be overloaded or even burned. In addition, it can only compensate for harmonics at a fixed frequency, and the compensation effect is not satisfactory.
3. An AC active filter device is installed, and the device is composed of a controllable power electronic converter and a detection control circuit. The basic principle is to detect a harmonic current from the compensation object, and the compensation device generates a magnitude equal to the harmonic current. The compensation current of opposite polarity is offset by the harmonic current, so that the grid current only contains the fundamental component. This filter can track and compensate harmonics with varying frequency and amplitude, and the compensation characteristics are not affected by the impedance of the grid. The filtering performance and dynamic characteristics are greatly improved compared with the passive mode.
Scheme 1 transforms the load equipment. Since the shipborne radar equipment adopts mature products that have been finalized, its combat technical indicators and structural shapes have been determined. The products have passed routine tests, and the radar system power supply has multiple power inputs. The transformation will inevitably lead to major changes in the original stereotype system, so the adoption of Option 1 is not practical.
The passive filter device of the scheme 2 has the advantages of simple structure, reliable operation and convenient maintenance. However, since the device is operated on the marine power grid, the power grid is composed of several generators in parallel, the power grid capacity is small, the stability is poor, and the voltage, especially the frequency, will have a certain range of fluctuations, and the load current of the radar equipment changes frequently during the working process. This makes it easy for passive filters to generate parallel resonances, generate harmonic amplification, damage harmonic devices, and even load devices. Therefore, Option 2 has great limitations and certain risks.
Scheme 3 is equipped with a source filtering device, which has the remarkable advantage of being able to track and compensate harmonics whose frequency and amplitude are changed, and the compensation characteristics are not affected by the impedance of the power grid. Compared with passive filters, APF is highly controllable and fast-responding. It not only compensates for each harmonic, but also suppresses flicker and compensates for reactive power. Its characteristics are not affected by the system impedance, eliminating the danger of resonance with the system impedance; it has an adaptive function, which can automatically track and compensate for the changing harmonics, and can fully adapt to the shipboard power grid conditions and the working state of the radar load current changing frequently. . The active filter device adopts power electronic conversion technology, and its volume, weight and passive are greatly reduced, meeting the requirements of shipboard installation and use.