嘉兴学院本科生毕业设计
嘉兴学院毕业设计外文翻译
题目（外文）： New active power filter and control method 题目（中文）： 新型有源电力滤波器及其控制方法 学院名称： 机电学院 专业班级：电气051学生姓名： 刘尚宝 一、外文摘要及关键词
ABSTRACT:A new active power filter with harmonic suppression and adjustable reactive power
compensation is propose. The power converter of the proposed filter can generate a compensating voltage,including a harmonic voltage for compensating the load harmonic current and a fundamental voltage for adjusting the reactive power of the utility side, connected to the power feeder via an impedance. The waveform of the utility current after compensating by the proposed active power filter can be approximated as a sinusoidal waveform,and the input power factor is also improved. A 20KVA prototype has been developed and tested to verify its performance. The test results indicate that the proposed active power filter has the desired performance.
KEY WORDS:active power filter, harmonic, reactive power compensation
二、中文摘要及关键词
摘要：本文提出了一种能抑制谐波和无功补偿可调的新型有源电力滤波器。滤波器中的电源转换
器串联电阻后连接到电力馈线上，能产生补偿电压，包括一个用来补偿负载谐波电流的谐波电压和一个用来调整电源侧无功功率的基波电压。电源电流的波形经过新型有源电力滤波器补偿后可近似为正弦波，并使输入功率因数得到改善。一个20千伏安的样机已经研制成功，并经过测试验证了其性能。试验结果表明，该新型有源电力滤波器具有预期的性能。
关键词：有源电力滤波器，谐波，无功功率补偿
三、外文正文
1 introduction
Power electronics related facilities may generate a significant harmonic current due to the nonlinear input characteristic of such loads. This harmonic current will pollute the power system, resulting in
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嘉兴学院本科生毕业设计
problems such as transformer overheating, rotary machine vibration, degrading voltage quality, damage of electic power components, medical facility malfunctions ect[1]. To relieve the problem of harmonic pollution effectively, many harmonic limitation standards, such as IEEE519-1992, IEC1000-3-2, IEC1000-3-4 ect. Have been established. Therefore,solving the problem of harmonics is an important topic for today's power systems. Conventionally,passive power filters have been used to solve this problem, although they have some disadvantages,such as resonance and poor filter performance[2]. Recently,many harmonic suppression facilities based on power electronics techniques have been developed. Some of them can simultaneously suppress the different order harmonic components of nonlinear loads using only the same harmonic suppression equipment referred to as an active power filter [3-9]. Figure 1 shows a single-line system diagram of a conventional active power filter. This system includes a filter inductor, a power converter and a DC capacitor. The power converter is used to generate a compensating current via the filter inductor to inject into a power feeder. The filter inductor is used to suppress high-frequency ripple current caused by the switching behaviour of the power electronics devices in the power converter. The inductance of the filter inductor depends on the switching frequency, the DC voltage and the ripple current limitation. The DC capacitor located in the DC bus of the power converter acts as an energy buffer. Although, a conventional active power filter is capable of suppressing harmonics, it has the following disadvantages:
Fig. 1 System single-line diagram of conventional active power filter
1 To suppress the ripple current generated by the switching operation of power electronic devices in the power converter, a filter inductor with a large inductance is used.
2 A higher DC bus voltage for the power converter is required,which results in high switching power loss and high voltage rating of the DC capacitor and power electronic devices.
3 Using a larger filter inductor will result in a larger power loss, poor energy efficiency, more heat dissipation, bulk dimension and weight.
4 Using a larger filter inductor also results in degrading the high-frequency response.
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嘉兴学院本科生毕业设计
Therefore, these above disadvantages limit applications of the conventional active power filter. Another solution for the harmonic problem is to adopt a hybrid power filter consisting of a power converter in series with a passive power filter [10
–15]
. Figure 2 shows a conventional hybrid
power filter comprising a passive power filter serially connected to a power converter.A passive power filter consists of one or many sets of tuned filters, and it is used to filter the dominant harmonic components. Hence,the capacity of the power converter can be reduced. However, it also has some disadvantages:
Fig. 2 System single-line diagram of hybrid power filter 1 The parameters of the passive elements in the passive power filter may have errors in the manufacturing process. Thus, the capacity of the active power filter cannot be significantly reduced if the parameters of the passive elements in the passive power filter are inaccurate.
2 Generally, the core of the inductor used in the passive filter is made of an iron alloy, such as silicon steel plates, which results in large size, heavy weight and large loss. Also, there is a significant power loss when high-frequency ripple current produced from the power converter is flowing through the inductor made by the silicon steel plates. This results in an increase of heat in the inductor.
3 To reduce the size of the passive power filter, the inductance of the passive power filter must be reduced and the larger capacitance of capacitor must be used. However, when this passive power filter is operated under a light load, the large capacitance may cause a large leading current that degrades the power factor and increases the bus voltage.
This paper proposes a new active power filter and control method. The proposed active power filter has harmonic suppression and adjustable reactive power compensation. The utility current, after compensation by the proposed active power filter,can be approximated as a sinusoidal waveform, and the input power factor under the light load is improved as compared with the conventional hybrid power filter.To demonstrate the performance of the proposed active power filter, a 20 KVA prototype is
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嘉兴学院本科生毕业设计
developed and tested.
2 System configuration and operation principle
The system configuration of the proposed active power filter is shown in Fig. 3. It consists of a series-connected inductor and capacitor set, a DC capacitor, a power converter and a high-frequency ripple filter. Voltage-mode control is used to control the power converter. The power converter generates a compensating voltage that is converted into a compensating current flowing through the series-connected inductor and capacitor set, and the compensating current flows into the power feeder in order to filter harmonic currents and compensate for the reactive power generated by nonlinear loads.The configuration of the proposed active power filter is similar to that of the hybrid power filter shown in Fig. 2. However,the function and dimension of the passive elements (L–C) are not the same. In the proposed active power filter, the inductor of the series-connected inductor and capacitor set is very small, and it is used to filter the switching ripple of the power converter. The capacitor in the series-connected inductor and capacitor set is used to supply a basic reactive power.However, the passive elements (L–C) in the hybrid power filter are used to tune the dominant harmonic component of the load current. The inductance in the hybrid power filter is larger than that used in the proposed active power filter, so the size and weight of the inductor used in the hybrid power filter are also larger than those used in the proposed active power filter. The high-frequency ripple filter is configured by a set of capacitors and a resistor, and it is used to filter out further the switching ripples form the power converter.
Fig. 3 System configuration of proposed active power filter
Fig. 4 shows the equivalent circuit of the proposed active power filter. It consists of two voltage
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嘉兴学院本科生毕业设计
sources: one is the utility and the other is the compensating voltage source generated by the power converter.The compensating voltage generated by the power converter is a dependent voltage source whose voltage depends on both the harmonic components and the fundamental reactive component of the load current. The equivalent circuit shown in Fig.4 can be further divided into the fundamental frequency equivalent circuit and the harmonic frequency equivalent circuit shown in Fig.5. Figure 5a shows the equivalent circuit under the fundamental frequency where the impedance of the series-connected inductor and capacitor set is capacitive under the fundamental frequency. To adjust the generated fundamental reactive current, the power converter must generate a fundamental voltage whose phase is the same as that of the utility voltage. The fundamental voltage Vc1 (RMS) across the capacitor can be represented as:
Vc1=Vs1-Va1 (1)
Fig. 4 Equivalent circuit of proposed active power filter
Fig. 5 Equivalent circuit of proposed active power filter
a Equivalent circuit at fundamental frequency b Equivalent circuit at harmonic frequency
where Vs1 and Va1 are the phase RMS values of the fundamental component for utility voltage and power converter output voltage. Then,the reactive power Qa supplied from the active power filter can be derived as
Qa=Qc(1-Va1/Va1) (2)
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