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第九章电路课件(第五版邱关源高等教育出版社)_(3)

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第九 电路 课件 第五 版邱关源 高等教育出版社
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第9章 正弦稳态电路的分析 首 页 本章重点 正弦稳态电路的分析9 3 正弦稳态电路的功率9 4 复功率9 5 最大功率传输9 6 阻抗和导纳9 1 Five weeks of practice ended in this way and my feelings can only be summed up in eight words although hard but very substantial 2 正弦稳态电路的分析 3 正弦稳态电路的功率分析 l 重点 1 阻抗和导纳 返 回 Five weeks of practice ended in this way and my feelings can only be summed up in eight words although hard but very substantial 9 1 阻抗和导纳 1 阻抗正弦稳态情况下 Z 无源 线性 网络 阻抗模 阻抗角 欧姆定律的相 量形式 下 页上 页返 回 Five weeks of practice ended in this way and my feelings can only be summed up in eight words although hard but very substantial 当无源网络内为单个元件时有 Z 可以是实数 也可以是虚数 C 下 页上 页 R L 表明 返 回 Five weeks of practice ended in this way and my feelings can only be summed up in eight words although hard but very substantial 2 RLC串联电路 KVL 下 页上 页 L C R u uL uC i uR R j L 返 回 Five weeks of practice ended in this way and my feelings can only be summed up in eight words although hard but very substantial Z 复阻抗 Z 复阻抗的模 z 阻抗角 R 电阻 阻抗的实部 X 电抗 阻抗的虚部 转换关系 或 R Z cos z X Z sin z 阻抗三角形 Z R X z 下 页上 页返 回 Five weeks of practice ended in this way and my feelings can only be summed up in eight words although hard but very substantial 分析 R L C 串联电路得出 1 Z R j L 1 C Z z 为复数 称复阻抗 2 L 1 C X 0 z 0 电路为感性 电压超前电流 下 页上 页 相量图 一般选电流为参考向量 z UX 电压 三角 形 j Leq R 等效电路 返 回 Five weeks of practice ended in this way and my feelings can only be summed up in eight words although hard but very substantial 3 L 1 C X 0 z U 5 分电压大于总电压 相量图 注意 3 4 返 回 Five weeks of practice ended in this way and my feelings can only be summed up in eight words although hard but very substantial 3 导纳 正弦稳态情况下 导纳模 导纳角 下 页上 页 无源 线性 网络 Y 返 回 Five weeks of practice ended in this way and my feelings can only be summed up in eight words although hard but very substantial 对同一二端网络 当无源网络内为单个元件时有 Y 可以是实数 也可以是虚数 下 页上 页 C R L 表明 返 回 Five weeks of practice ended in this way and my feelings can only be summed up in eight words although hard but very substantial 4 RLC并联电路 由KCL 下 页上 页 i LC R u iL iC iR R j L 返 回 Five weeks of practice ended in this way and my feelings can only be summed up in eight words although hard but very substantial Y 复导纳 Y 复导纳的模 y 导纳角 G 电导 导纳的实部 B 电纳 导纳的虚部 转换关系 或 G Y cos y B Y sin y 导纳三角形 Y G B y 下 页上 页返 回 Five weeks of practice ended in this way and my feelings can only be summed up in eight words although hard but very substantial 1 Y G j C 1 L Y y为复数 称复导纳 2 C 1 L B 0 y 0 电路为容性 电流超前电压 相量图 选电压为参考向量 y 分析 R L C 并联电路得出 RLC并联电路会出现分电流大于总电流的现象 IB 下 页上 页 注意 返 回 Five weeks of practice ended in this way and my feelings can only be summed up in eight words although hard but very substantial 3 C 1 L B 0 y0 则 B0 电路吸收功率 p0 0 感性 X 0 0 表示网络吸收无功功率 lQ 0 表示网络发出无功功率 lQ 的大小反映网络与外电路交换功率的速率 是由储能元件L C的性质决定的 下 页上 页 电气设备的容量 返 回 Five weeks of practice ended in this way and my feelings can only be summed up in eight words although hard but very substantial 有功 无功 视在功率的关系 有功功率 P UIcos 单位 W 无功功率 Q UIsin 单位 var 视在功率 S UI 单位 VA S P Q 功率三角形 下 页上 页返 回 Five weeks of practice ended in this way and my feelings can only be summed up in eight words although hard but very substantial 5 R L C元件的有功功率和无功功率 u i R PR UIcos UIcos0 UI I2R U2 R QR UIsin UIsin0 0 PL UIcos UIcos90 0 QL UIsin UIsin90 UI I2XL i u C PC UIcos UIcos 90 0 QC UIsin UIsin 90 UI I2XC 下 页上 页 i u L 返 回 Five weeks of practice ended in this way and my feelings can only be summed up in eight words although hard but very substantial 6 任意阻抗的功率计算 u i Z PZ UIcos I2 Z cos I2R QZ UIsin I2 Z sin I2X I2 XL XC QL QC S P Q Z R X 相似三角形 发出无功 下 页上 页返 回 Five weeks of practice ended in this way and my feelings can only be summed up in eight words although hard but very substantial 电感 电容的无功补偿作用 t i o uL L发出功率时 C刚 好吸收功率 与外电路 交换功率为 pL pC L C的无功具有互相补偿 的作用 t i o uC pL pC 下 页上 页 L C R u uL uC i 返 回 Five weeks of practice ended in this way and my feelings can only be summed up in eight words although hard but very substantial 电压 电流的有功分量和无功分量 以感性负载为例 下 页上 页 R X GB 返 回 Five weeks of practice ended in this way and my feelings can only be summed up in eight words although hard but very substantial S P Q Z R X 相似三角形 I IG IB U UR UX 下 页上 页返 回 Five weeks of practice ended in this way and my feelings can only be summed up in eight words although hard but very substantial 反映电源和负载之间交换能量的速率 无功的物理意义 下 页上 页返 回 Five weeks of practice ended in this way and my feelings can only be summed up in eight words although hard but very substantial 例1 三表法测线圈参数 已知 f 50Hz 且测得 U 50V I 1A P 30W 解法 1 下 页上 页 R L Z WA V 返 回 Five weeks of practice ended in this way and my feelings can only be summed up in eight words although hard but very substantial 解法 2 又 下 页上 页 解法 3 返 回 Five weeks of practice ended in this way and my feelings can only be summed up in eight words although hard but very substantial 已知 电动机 PD 1000W U 220 f 50Hz C 30 F cos D 0 8 求 负载电路 的功率因数 例2 解 下 页上 页 D C 返 回 Five weeks of practice ended in this way and my feelings can only be summed up in eight words although hard but very substantial 7 功率因数的提高 设备容量 S 额定 向负载送多少有功要由 负载的阻抗角决定 P UIcos Scos cos 1 P S 75kW cos 0 7 P 0 7S 52 5kW 一般用户 异步电机 空载 cos 0 2 0 3 满载 cos 0 7 0 85 日光灯 cos 0 45 0 6 设备不能充分利用 电流到了额定值 但功率容 量还有 功率因数低带来的问题 下 页上 页 S 75kVA 负载 返 回 Five weeks of practice ended in this way and my feelings can only be summed up in eight words although hard but very substantial 当输出相同的有功功率时 线路上电流大 I P Ucos 线路压降损耗大 1 2 解决办法 1 高压传输 2 改进自身设备 3 并联电容 提高功率因数 下 页上 页 i uZ 返 回 Five weeks of practice ended in this way and my feelings can only be summed up in eight words although hard but very substantial 分析 1 2 并联电容后 原负载的电压和电流不变 吸收的有功功率和无功功率不变 即 负载的 工作状态不变 但电路的功率因数提高了 特点 下 页上 页 L R C 返 回 Five weeks of practice ended in this way and my feelings can only be summed up in eight words although hard but very substantial 并联电容的确定 补偿 容量 不同 全 不要求 电容设备投资增加 经济效 果不明显 欠 过 功率因数又由高变低 性质不同 下 页上 页 1 2 返 回 Five weeks of practice ended in this way and my feelings can only be summed up in eight words although hard but very substantial 并联电容也可以用功率三角形确定 1 2 P QC QL Q 从功率角度看 并联电容后 电源向负载输送的有功UIL cos 1 UI cos 2不变 但是电源向负载输送的无功 UIsin 2 UILsin 1减少了 减少的这部分无功由电 容 产生 来补偿 使感性负载吸收的无功不变 而功率因数得到改善 下 页上 页返 回 Five weeks of practice ended in this way and my feelings can only be summed up in eight words although hard but very substantial 已知 f 50Hz U 220V P 10kW cos 1 0 6 要 使功率因数提高到0 9 求并联电容C 并联前 后电路的总电流各为多大 例 解 未并电容时 并联电容后 下 页上 页 L R C 返 回 Five weeks of practice ended in this way and my feelings can only be summed up in eight words although hard but very substantial 若要使功率因数从0 9再提高到0 95 试问还应增 加多少并联电容 此时电路的总电流是多大 解 cos 提高后 线路上总电流减少 但继 续提高cos 所需电容很大 增加成本 总电流减 小却不明显 因此一般将cos 提高到0 9即可 下 页上 页 注意 返 回 Five weeks of practice ended in this way and my feelings can only be summed up in eight words although hard but very substantial 9 5 复功率 1 复功率 负 载 定义 也可表示为 下 页上 页返 回 Five weeks of practice ended in this way and my feelings can only be summed up in eight words although hard but very substantial 下 页上 页 结论 是复数 而不是相量 它不对应任意正弦量 注意 把 P Q S 联系在一起 它的实部是平均 功率 虚部是无功功率 模是视在功率 复功率满足守恒定理 在正弦稳态下 任一电 路的所有支路吸收的复功率之和为零 即 返 回 Five weeks of practice ended in this way and my feelings can only be summed up in eight words although hard but very substantial 求电路各支路的复功率 例 解1 下 页上 页 10 0o A 10 j25 5 j15 返 回 Five weeks of practice ended in this way and my feelings can only be summed up in eight words although hard but very substantial 解2 下 页上 页返 回 Five weeks of practice ended in this way and my feelings can only be summed up in eight words although hard but very substantial 9 6 最大功率传输 Zi Ri jXi ZL RL jXL 负 载 有 源 网 络 等效电路 下 页上 页 ZL Zi 返 回 Five weeks of practice ended in this way and my feelings can only be summed up in eight words although hard but very substantial 正弦电路中负载获得最大功率Pmax的条件 若ZL RL jXL可任意改变 a 先设 RL 不变 XL 改变 显然 当Xi XL 0 即XL Xi时 P 获得最大值 b 再讨论 RL 改变时 P 的最大值 下 页上 页 讨论 当RL Ri 时 P 获得最大值 RL RiXL Xi ZL Zi 最佳 匹配 条件 返 回 Five weeks of practice ended in this way and my feelings can only be summed up in eight words although hard but very substantial 若ZL RL jXL只允许XL改变 获得最大功率的条件是 Xi XL 0 即 XL Xi 最大功率为 若ZL RL为纯电阻 负载获得的功率为 电路中的电流为 模匹配 下 页上 页返 回 Five weeks of practice ended in this way and my feelings can only be summed up in eight words although hard but very substantial 电路如图 求 1 RL 5 时其消耗的功率 2 RL 能获得最大功率 并求最大功率 3 在RL两端并联一电容 问RL和C为多大时能与内 阻抗最佳匹配 并求最大功率 例 解 下 页上 页 10 0o V 50 H RL 5 105rad s 返 回 Five weeks of practice ended in this way and my feelings can only be summed up in eight words although hard but very substantial 下 页上 页 10 0o V 50 H RL 5 10 0o V 50 H RL 5 C 返 回 Five weeks of practice ended in this way and my feelings can only be summed up in eight words although hard but very substantial 求ZL 时能获得最大功率 并求最大功率 例 解 上 页 Zi ZL 4 90o A ZL j30 30 j30 返 回
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