2外文翻译.doc

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 problems such as transformer overheating, rotary machine vibration, degrading voltage quality, damage of electic power components, medical facility malfunctions ect1. 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 todays power systems. conventionally,passive power filters have been used to solve this problem, although they have some disadvantages,such as resonance and poor filter performance2. 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 filter1 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. 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 1015. 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 filter1 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 developed and tested.2 system configuration and operation principlethe 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 (lc) 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 (lc) 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 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 filterfig. 5 equivalent circuit of proposed active power filtera equivalent circuit at fundamental frequencyb equivalent circuit at harmonic frequencywhere 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)where qc is the basic reactive power generated by the power capacitor of the series-connected inductor and capacitor set under the utility fundamental voltage. from (2), it can be found that the proposed active power filter can supply an adjustable reactive power by adjusting the fundamental component of power converters output voltage. figure 5b shows the equivalent circuit under harmonic frequency.if the frequency is lower than the resonant frequency, then the series-connected inductor and capacitor set is capacitive. however, the series-connected inductor and capacitor set is inductive if the frequency is higher than the resonant frequency. the switching frequency of the power converter is significantly higher than the resonant frequency of the series-connected inductor and capacitor set. as a result, the series-connected inductor and capacitor set acts as an inductor to filter the switching frequency of the power converter.to suppress the load harmonic current, the desired compensating voltage can be derived as: vah=zlcilh (3)where ilh is the harmonic component of the load current, and zlc is the impedance of the series-connected inductor and capacitor set. if the power converter can generate a voltage as shown in (3), this voltage is converted into a compensating current that is opposite to the load harmonic current. hence, the load harmonic current can be suppressed. equation (3) shows that the desired compensation voltage is dependent on the load harmonic current and the impedance of the series-connected inductor and capacitor set. from the operation theory of the bridge power converter, the dc bus voltage of a power converter must be higher than the peak value of the utility voltage in a conventional active power filter.however,a series-connected inductor and capacitor set is used to connect in series with the power converter, and it can block the most fundamental component of utility voltage. hence the dc bus voltage in the proposed active power filter can be smaller than the peak value of the utility voltage, and it is only dependent on the amplitude of the compensating voltage, which is smaller than the peak value of the utility voltage. this means that the dc bus voltage in the proposed active power filter can be significantly reduced as compared with the conventional active power filter. consequently, the switching power loss and the voltage rating of dc capacitor and power electronics devices can also be reduced. furthermore, the ripple current of the power converter is dependent on the dc bus voltage and filter inductance. this implies that, the lower the dc bus voltage, the smaller filter inductance required for specified ripple current limitation. therefore, the filter inductance used in the series-connected inductor and capacitor set is smaller due to the lower dc bus voltage. compared to the conventional active power filter, it can be seen that the proposed active power filter uses three additional ac capacitors to reduce the inductance of the three-phase filter inductor,the voltage rating of the dc capacitor, the voltage rating of the power electronics devices and the size of the heatsink. in practice,the core of an inductor with large inductance is made from the iron alloy, which results in large size, heavy weight and large power loss. in contrast, the core of an inductor with small inductance can be made from ferrite materials, which have small volume, light weight and low eddy current loss 15. the electromagnetic interference (emi) generated by the switching of the power converter, is also dependent on the dc bus voltage. therefore, the salient advantages of the proposed active power filter are low voltage rating of the dc capacitor and power electronic devices, smaller filter inductance, smaller dimension, light weight, good filter performance and low emi.in addition, the smaller filter inductance can improve the high-frequency response performance of this active power filter. since the capacity of the dc bus voltage is dependent on the amount of compensation current, rather than the utility voltage, the application of the proposed active power filter can be extended to a wider voltage range. in a limited variable voltage application, such as in the range 220480 v, the change in the main components is only the voltage rating of the series-connected inductor and capacitor set. however, the voltage rating of both active and passive components must be changed in the conventional active power filter. in addition, the proposed active power filter can be applied in 50/60 hz power systems by adjusting only the parameters of the control circuit. however, the l-c parameters of the passive power filter must be changed in the hybrid power filter since the dominant harmonic frequency is different in 50/60 hz power systems. the above indicates that the proposed active power filter has the performance of suppressing harmonic current and providing an adjustable reactive current. when the active power filter is operated under light load, the harmonic load current is small. the power converter is used mainly to generate a fundamental voltage to reduce the reactive current supplied by the proposed active power filter. when the proposed active power filter is operated under heavy load, the power converter is not used to generate the fundamental voltage but a harmonic voltage. thus, the entire fundamental component of the utility voltage will drop on the series-connected inductor and capacitor set that produces a maximum reactive power current. to improve the input power factor at the utility current side, the active power filter is able to produce an adjustable reactive current according to either the light or heavy load conditions. consequently, the proposed active power filter can improve the disadvantage that the reactive power generated from the conventional hybrid power filter is constant. compared to the conventional active power filter, the proposed active power filter has cost advantage due to the lower voltage rating of the dc capacitor, lower voltage rating of power electronic devices and the smaller size of the heat-sink. hence, the hardware cost of the proposed active power filter is very competitive for nonlinear loads whose input is a diode-rectifier or phase-controlled rectifier with a low-level voltage below 480v.3 control methodconventionally, the active power filter has been controlled by the current mode. however, this is very difficult to implement under low filter inductance because of the high switching ripple, and it may generate multiple crossings during a carrier period of the pulse-width modulator. this phenomenon of multiple crossing will result in more than one switching operation during a carrier period. to resolve this, the proposed active power filter uses voltage-mode control. the three-phase power converter controlled by voltage-mode control acts as a voltage amplifier with the gain represented by: kcon=vdc/2vtri (4)where vdc is the dc bus voltage and vtri is the amplitude of the carrier signal of the pulse-width modulator. hence, the control circuit of the voltage-mode controlled power converter is used to determine a reference voltage by dividing the desired compensating voltage by the gain shown in(4). from the above, it can be found that the desired compensating voltage generated by the power converter for filtering the load harmonic current is derived in(3). hence, the first control signal v1(t) can be further derived from (3), and it is represented as: (5)where l and c are the inductance and capacitance of the series-connected inductor and capacitor set,and r is the component stray loss of the active power filter. if the power converter can generate a harmonic voltage equal to the first control signal v1(t) and convert it into a compensating current by the series-connected inductor and capacitor set, then theoretically the harmonic components of the load current can be compensated. however, the filter performance is degraded due to the parameters of the series-connected inductor and capacitor set, which may vary due to age, variable frequency, production and temperature in practice. to improve the compensating performance, a