1、1电力电子技术第 5 版 电力电子技术 外文翻译导读：就爱阅读网友为您分享以下“电力电子技术 外文翻译”的资讯，希望对您有所帮助，感谢您对 的支持!中文 4000 字 1 Power Electronic Concepts Power electronics is a rapidly developing technology. Components are tting higher current and voltage ratings, the power losses decrease and the devices become more reliable. The devices
2、are also very easy tocontrol with a mega scale power amplification. The prices are still going down pr. kVA and power converters are becoming attractive as a mean to improve the performance of a wind turbine. This chapter will discuss the standard power converter topologies from the simplest convert
3、ers for starting up the turbine to advanced power converter topologies, where the whole power is flowing through the 2converter. Further, different park solutions using power electronics arealso discussed. 1.1 Criteria for concept evaluation The most common topologies are selected and discussed in r
4、espect to advantages and drawbacks. Very advanced power converters, where many extra devices are necessary in order to get a proper operation, are omitted. 1.2 Power converters Many different power converters can be used in wind turbine applications. In the case of using an induction generator, the
5、power converter has to convert from a fixed voltage and frequency to a variable voltage and frequency. This may be implemented in many different ways, as it will be seen in the next section. Other generator types can demand other complex protection. However, the most used topology so far is a soft-s
6、tarter, which is used during start up in order to limit the in-rush current and thereby reduce the disturbances to the grid. 1.2.1 Soft starter The soft starter is a power converter, which has been introduced to fixed speed wind turbines to reduce the transient current 3during connection or disconne
7、ction of the generator to the grid. When the generator speed exceeds the synchronous speed, the soft-starter is connected. Using firing angle control of the thyristors in the soft starter the generator is smoothly connected to the grid over a predefined number of grid periods. An example of connecti
8、on diagram for the softstarter with a generator is presented in Figure1. Figure 1. Connection diagram of soft starter with generators. The commutating devices are two thyristors for each phase. These are connected in anti-parallel. The relationship between the firing angle () and the resulting ampli
9、fication of the soft starter is non-linear and depends additionally on the power factor of the connected element. In the case of a resistive load, may vary between 0 (full on) and 90 (full off) degrees, in the case of a purely inductive load between 90 (full on) and 180 (full off) degrees. For any p
10、ower factor between 0 and 90 4somewhere between the limits sketched in Figure 2. Figure 2. Control characteristic for a fully controlled soft starter. When the generator is completely connected to the grid a contactor (Kbyp) bypass the soft-starter in order to reduce the losses during normal operati
11、on. The soft-starter is very cheap and it is a standard converter in many wind turbines. 1.2.2 Capacitor bank For the power factor compensation of the reactive power in the generator, AC capacitor banks are used, as shown in Figure 3. The generators are normally compensated into whole power range. T
12、he switching of capacitors is done as a function of the average value of measured reactive power during a certain period. Figure 3. Capacitor bank configuration for power factor compensation in 5a wind turbine. The capacitor banks are usually mounted in the bottom of the tower or in the nacelle. In
13、order to reduce the current at connection/disconnection of capacitors a coil (L) can be connected in series. The capacitors may be heavy loaded and damaged in the case of over-voltages to the grid and thereby they may increase the maintenance cost. 1.2.3 Diode rectifier The diode rectifier is the mo
14、st common used topology in power electronic applications. For a three-phase system it consists of six diodes. It is shown in Figure 4. Figure 4. Diode rectifier for three-phase ac/dc conversion The diode rectifier can only be used in one quadrant, it is simple and it is not possible to control it. I
15、t could be used in some applications with a dc-bus. 1.2.4 The back-to-back PWM-VSI The back-to-back PWM-VSI is a bi-directional power 6converter consisting of two conventional PWM-VSI. The topology is shown in Figure 5. To achieve full control of the grid current, the DC-link voltage must be boosted
16、 to a level higher than the amplitude of the grid line-line voltage. The power flow of the grid side converter is controlled in order to keep the DC-link voltage constant, while the control of the generator side is set to suit the magnetization demand and the reference speed. The control of the back
17、-to-back PWM-VSI in the wind turbine application is described in several papers (Bogalecka, 1993), (Knowles-Spittle et al., 1998), (Pena et al., 1996), (Yifan (Kim (Siyoung Kim et al., 1998). Another important drawback of the back-to-back PWM-VSI is the switching losses. Every commutation in both th
18、e grid inverter and the generator inverter between the upper and lower DC-link branch is associated with a hard switching and a natural commutation. Since the back-to-back PWM-VSI consists of two inverters, the switching losses might be even more pronounced. The high switching speed to the grid may
19、also require extra EMI-filters. To prevent high stresses on the generator insulation and to avoid bearing current problems (Salo (Trzynadlowski et al., 1998a); (Trzynadlowski et al., 1998b). However, the idea behind the converter is similar to those presented in (Zhang et al., 1998b), where the PWM-
20、VSI is used as an active harmonic filter to compensate harmonic distortion. The topology of the tandem converter is shown in Figure 6. Figure 6. The tandem converter topology used in an induction generator wind turbine system. The tandem converter consists of a current source converter, CSC, in the
21、following designated the primary converter, and a back-to-back PWM-VSI, designated the secondary converter. Since the tandem converter consists of four controllable inverters, several degrees of freedom exist which enable sinusoidal input and sinusoidal output currents. However, in 10this context it
22、 is believed that the most advantageous control of the inverters is to control the primary converter to operate in square-wave current mode. Here, the switches in the CSC are turned on and off only once per fundamental period of the input- and output current respectively. In square wave current mode
23、, the switches in the primary converter may either be GTO.s, or a series connection of an IGBT and a diode. Unlike the primary converter, the secondary converter has to operate at a high switching frequency, but the switched current is only a small fraction of the total load current. Figure 7 illust
24、rates the current waveform for the primary converter, the secondary converter, is, and the total load current il. In order to achieve full control of the current to/from the back-to-back PWMVSI, the DC-link voltage is boosted to a level above the grid voltage. As mentioned, the control of the tandem
25、 converter is treated in only a few papers. However, the independent control of the CSC and the back-to-back PWM-VSI are both well established, (Mutschler (Nikolic (Salo (Salo (Burany, 1989); (Jung (Hey et al., 1995); (Kwon et al., 1998); (Neft (Casadei et al., 1995a); (Casadei et al., 1995b); (Casadei et al., 1996); (Enjeti (Nielsen, 1996); (Nielsen et al., 1996); (Oyama et al., 1997); (Zhang et al., 1998a). 其中最简单的转换方法出现在以下这些书中：(Beasant et al., 1990) and (Neft & Schauder, 1988), 但是这些方法中没有一个能够遵循矩阵逆变器的这两条规则。 百度搜索“就爱阅读”,专业资料,生活学习,尽在就爱阅读网,您的在线图书馆百度搜索“就爱阅读”,专业资料、生活学习,尽在就爱阅读网 ,您的在线图书馆!
