变频器调速时为什么要让电压和频率成比例变化？
Why does a variable-frequency drive change voltage in proportion to frequency?
感应电机的磁通近似与电压幅值除以频率成正比。若只降频率不降电压，磁通会大幅增加使铁心饱和，励磁电流暴涨、发热严重；若只升频率不升电压，磁通减小则转矩不足。保持电压与频率之比恒定可维持额定磁通，从而在很宽的转速范围内输出恒定转矩，基频以上则进入恒功率弱磁区。
Flux in an induction motor is roughly proportional to voltage amplitude divided by frequency. Lowering frequency without lowering voltage raises flux, saturating the iron so magnetising current and heating soar, while raising frequency without raising voltage weakens flux and torque. Keeping the voltage-to-frequency ratio constant maintains rated flux and constant torque over a wide speed range, and above base frequency the drive enters the constant-power field-weakening region.
难度 专业 · 适合 初中(12-15)
CC BY 4.0 · 已核验 · Verified 2026-08-23
来源 · Source
邱关源 主编 罗先觉 修订,《电路》第5版,高等教育出版社,2006
Qiu Guanyuan ed., Circuit, 5th ed., Higher Education Press, 2006
#变频调速 #磁通 #恒转矩
三相异步电动机为什么必须有转差才能出力？
Why must an induction motor have slip in order to produce torque?
定子三相绕组产生旋转磁场，转子导条只有在与磁场存在相对运动时才会被切割而产生感应电流，进而受力产生转矩。如果转子转速等于同步转速，相对运动为零，感应电流和转矩都消失。所以异步电机总要慢一点，负载越重转差越大，这也是它被称为异步的原因。
The three-phase stator winding creates a rotating field, and the rotor bars only develop induced current, and hence force, when there is relative motion between them and that field. If the rotor turned at exactly synchronous speed the relative motion would be zero and both induced current and torque would vanish. An induction motor therefore always runs slightly slower, with slip increasing as load increases, which is why it is called asynchronous.
难度 专业 · 适合 初中(12-15)
CC BY 4.0 · 已核验 · Verified 2026-08-23
来源 · Source
邱关源 主编 罗先觉 修订,《电路》第5版,高等教育出版社,2006
Qiu Guanyuan ed., Circuit, 5th ed., Higher Education Press, 2006
#异步电机 #转差 #旋转磁场
什么是功率因数，工厂为什么要做无功补偿？
What is power factor and why do factories install reactive compensation?
交流负载中电动机和变压器等感性设备会使电流滞后于电压，真正做功的有功功率与视在功率之比就是功率因数。功率因数低意味着为了输送同样的有功功率必须流过更大电流，线路损耗和变压器容量占用都随之增加。并联电容器或使用静止无功发生器提供超前电流，抵消感性无功，就能把功率因数提到接近一，降低电费和损耗。
In an AC system inductive equipment such as motors and transformers makes current lag voltage, and the ratio of real power that does work to apparent power is the power factor. A low power factor means larger current is needed to deliver the same real power, increasing line losses and the transformer capacity tied up. Connecting capacitors in parallel, or using a static var generator to supply leading current, cancels the inductive reactive power and raises the power factor close to one, cutting losses and electricity charges.
难度 专业 · 适合 初中(12-15)
CC BY 4.0 · 已核验 · Verified 2026-08-23
来源 · Source
邱关源 主编 罗先觉 修订,《电路》第5版,高等教育出版社,2006
Qiu Guanyuan ed., Circuit, 5th ed., Higher Education Press, 2006
#功率因数 #无功补偿 #线损
什么是集肤效应，为什么大电流导线要做成多股绞线？
What is the skin effect and why are high-current conductors stranded?
交流电在导体内产生的涡流会把电流挤向表面，频率越高电流分布越集中在薄薄的表层，这就是集肤效应。它使导体的有效截面变小，交流电阻高于直流电阻，发热增加。把导线分成许多细股并绞合，甚至采用每股都单独绝缘并周期换位的利兹线，可以增大有效导电面积，显著降低高频损耗。
Eddy currents induced by alternating current push the current toward the conductor's surface, and the higher the frequency the thinner the layer that carries it, which is the skin effect. It reduces the effective cross-section so AC resistance exceeds DC resistance and heating rises. Splitting a conductor into many fine strands and twisting them, or using Litz wire in which each strand is separately insulated and transposed, increases the effective conducting area and markedly cuts high-frequency loss.
难度 进阶 · 适合 大众
CC BY 4.0 · 已核验 · Verified 2026-08-23
来源 · Source
邱关源 主编 罗先觉 修订,《电路》第5版,高等教育出版社,2006
Qiu Guanyuan ed., Circuit, 5th ed., Higher Education Press, 2006
#集肤效应 #交流电阻 #利兹线
为什么让直流电机正反转要用H桥电路？
Why is an H-bridge needed to run a DC motor in both directions?
直流电机的转向取决于绕组电流方向，单个开关管只能通断而不能改变极性。H桥用四个开关管组成两条支路，导通对角的两个管子就让电流从一个方向流过电机，导通另一对则反向。控制器必须防止同一侧上下管同时导通造成直通短路，因此要插入死区时间。
A DC motor's direction depends on the direction of current through its winding, and a single switch can only interrupt current, not reverse its polarity. An H-bridge uses four switches in two legs; turning on one diagonal pair sends current through the motor one way, and the other pair reverses it. The controller must prevent the upper and lower switches of one leg conducting together, which would be a shoot-through short, so a dead time is inserted.
难度 进阶 · 适合 大众
CC BY 4.0 · 已核验 · Verified 2026-08-23
来源 · Source
邱关源 主编 罗先觉 修订,《电路》第5版,高等教育出版社,2006
Qiu Guanyuan ed., Circuit, 5th ed., Higher Education Press, 2006
#H桥 #电机驱动 #死区时间
锂电池为什么先恒流充电再恒压充电？
Why are lithium batteries charged first at constant current and then at constant voltage?
电池电压较低时用恒定电流快速注入电量，此时限制电流是为了控制发热和极化，避免锂在负极沉积成枝晶。当电压升到截止值后改为恒压，电流自然逐渐衰减，让锂离子有时间充分嵌入，从而在不超压的前提下把容量充满。若一直恒流会导致过压析锂，若一直恒压则初期电流过大，两段式是安全与速度的折中。
While the cell voltage is low, a constant current pushes charge in quickly, and limiting that current controls heating and polarisation so lithium does not plate as dendrites on the anode. Once the voltage reaches the cut-off value the charger holds voltage constant and the current tapers naturally, giving lithium ions time to intercalate fully and filling the capacity without overvoltage. Constant current alone would overcharge and plate lithium, constant voltage alone would draw excessive initial current, so the two stages balance safety and speed.
难度 进阶 · 适合 大众
CC BY 4.0 · 已核验 · Verified 2026-08-23
来源 · Source
邱关源 主编 罗先觉 修订,《电路》第5版,高等教育出版社,2006
Qiu Guanyuan ed., Circuit, 5th ed., Higher Education Press, 2006
#锂电池 #恒流恒压 #充电策略
步进电机为什么会失步，如何避免？
Why do stepper motors lose steps, and how is that avoided?
步进电机是开环运行，控制器只管发脉冲，并不知道转子实际到了哪里。如果加速太快、负载转矩超过该转速下的输出，或者出现共振，转子跟不上磁场就会漏掉步数，且误差永久累积。解决办法是合理设计加减速曲线、留足转矩余量、采用细分驱动降低振动，或改用闭环步进和伺服电机。
A stepper runs open loop: the controller sends pulses without knowing where the rotor actually is. If acceleration is too aggressive, load torque exceeds the available torque at that speed, or resonance occurs, the rotor cannot follow the field and steps are lost, with the error accumulating permanently. Remedies include proper acceleration profiles, adequate torque margin, microstepping to reduce vibration, or moving to closed-loop steppers or servo motors.
难度 进阶 · 适合 大众
CC BY 4.0 · 已核验 · Verified 2026-08-23
来源 · Source
邱关源 主编 罗先觉 修订,《电路》第5版,高等教育出版社,2006
Qiu Guanyuan ed., Circuit, 5th ed., Higher Education Press, 2006
#步进电机 #失步 #开环控制
什么是电机的反电动势，为什么可以用它估转速？
What is a motor's back-EMF and why can it estimate speed?
电机转子转动时，绕组在磁场中切割磁感线，会产生一个与外加电压方向相反的感应电动势，称为反电动势，其大小与转速近似成正比。测得端电压并减去绕组电阻和电感上的压降，就能反推转速，这样无需安装编码器。无刷电机的无位置传感器控制正是利用反电动势的零点来判断换相时刻。
As the rotor turns, the windings move through the magnetic field and generate an induced voltage opposing the applied voltage, called back-EMF, whose magnitude is roughly proportional to speed. Measuring terminal voltage and subtracting the drops across winding resistance and inductance yields an estimate of speed without any encoder. Sensorless control of brushless motors uses the zero crossings of back-EMF to decide when to commutate.
难度 进阶 · 适合 大众
CC BY 4.0 · 已核验 · Verified 2026-08-23
来源 · Source
邱关源 主编 罗先觉 修订,《电路》第5版,高等教育出版社,2006
Qiu Guanyuan ed., Circuit, 5th ed., Higher Education Press, 2006
#反电动势 #无位置传感器 #测速
电池管理系统为什么要给电芯做均衡？
Why does a battery management system balance the cells?
串联电池组的容量和内阻存在个体差异，充放电中各电芯电压会逐渐分化。由于整组必须以最高电压的电芯为充电上限、以最低的为放电下限，不均衡会让可用容量被最差的电芯拖累。均衡电路通过电阻放电耗散多余电量，或用变换器把电量搬到低电芯，使各电芯保持一致，从而延长寿命并避免过充过放。
Cells in a series pack differ slightly in capacity and internal resistance, so their voltages drift apart during charge and discharge. Because charging must stop at the highest-voltage cell and discharging at the lowest, imbalance lets the weakest cell limit the usable capacity of the whole pack. Balancing circuits either dissipate surplus charge through resistors or move charge to weaker cells with converters, keeping the cells matched, extending life and preventing over-charge or over-discharge.
难度 进阶 · 适合 大众
CC BY 4.0 · 已核验 · Verified 2026-08-23
来源 · Source
邱关源 主编 罗先觉 修订,《电路》第5版,高等教育出版社,2006
Qiu Guanyuan ed., Circuit, 5th ed., Higher Education Press, 2006
#电池管理 #均衡 #电芯一致性
漏电保护器是怎么判断有人触电的？
How does a residual current device tell that someone is being shocked?
正常工作时相线流出的电流应完全经零线返回，两者矢量和为零。漏电保护器把相线和零线一起穿过一个电流互感器，一旦有电流经人体或潮湿墙体流入大地，两线电流不再相等，互感器就检出这个差值。差值超过约三十毫安时脱扣机构在几十毫秒内切断电源，避免电流引起心脏纤维性颤动。
In normal operation all current leaving through the live wire returns through the neutral, so their vector sum is zero. A residual current device passes both conductors through one current transformer, and if some current escapes to earth through a person or damp wall the two no longer match and the transformer detects the difference. When the imbalance exceeds about thirty milliamps the trip mechanism cuts power within tens of milliseconds, before the current can cause heart fibrillation.
难度 入门 · 适合 大众
CC BY 4.0 · 已核验 · Verified 2026-08-23
来源 · Source
邱关源 主编 罗先觉 修订,《电路》第5版,高等教育出版社,2006
Qiu Guanyuan ed., Circuit, 5th ed., Higher Education Press, 2006
#漏电保护 #电流互感器 #用电安全
大电机启动电流为什么特别大，怎么解决？
Why is a large motor's starting current so high, and how is it reduced?
启动瞬间转子静止，没有反电动势，绕组上只有很小的阻抗限制电流，起动电流可达额定值的五到七倍。这会造成电网电压跌落、开关跳闸和机械冲击。工程上采用星三角切换、自耦降压启动、软启动器或变频器逐步升压升频，把电流限制在可接受范围。
At the instant of starting the rotor is still, there is no back-EMF, and only the small winding impedance limits current, so inrush can reach five to seven times rated current. This causes grid voltage dips, tripped breakers and mechanical shock. Engineers use star-delta switching, autotransformer starting, soft starters or variable-frequency drives that ramp voltage and frequency up gradually to keep current within acceptable limits.
难度 入门 · 适合 大众
CC BY 4.0 · 已核验 · Verified 2026-08-23
来源 · Source
邱关源 主编 罗先觉 修订,《电路》第5版,高等教育出版社,2006
Qiu Guanyuan ed., Circuit, 5th ed., Higher Education Press, 2006
#启动电流 #软启动 #变频器
电动汽车的能量回收制动是怎么把刹车变成充电的？
How does an electric car's regenerative braking turn braking into charging?
松开油门或踩下刹车时，控制器让驱动电机进入发电状态，车轮拖着转子旋转，电机产生的反电动势通过逆变器整流后给电池充电。发电所需的机械功率表现为阻碍车轮转动的制动力矩，于是减速与充电同时完成。低速时回收效率下降，且回收力矩有限，因此仍需机械制动配合并做协调控制。
When the driver lifts off or brakes, the controller puts the traction motor into generating mode; the wheels drive the rotor and the resulting back-EMF is rectified through the inverter to charge the battery. The mechanical power needed to generate appears as a braking torque opposing wheel rotation, so deceleration and charging happen together. Recovery efficiency falls at low speed and the available torque is limited, so friction brakes must still be blended in by a coordinated control strategy.
难度 入门 · 适合 大众
CC BY 4.0 · 已核验 · Verified 2026-08-23
来源 · Source
邱关源 主编 罗先觉 修订,《电路》第5版,高等教育出版社,2006
Qiu Guanyuan ed., Circuit, 5th ed., Higher Education Press, 2006
#能量回收 #电机发电 #电动汽车
家里跳闸有哪几种原因，对应保护装置有什么不同？
What different causes make a home breaker trip, and which devices respond?
一种是用电总功率过大或线路短路，电流超过额定值，由空气开关的热元件和电磁元件动作断开，保护电线不过热起火。另一种是漏电，电流经人体或绝缘破损处流走，由漏电保护器检测相零电流差动作，保护人身安全。此外还有过压欠压保护模块。分清跳的是哪一路，才能判断是插座过载还是电器绝缘出了问题。
One cause is excessive total load or a short circuit driving current above the rating, which the thermal and magnetic elements of the miniature circuit breaker detect, opening the circuit so the wiring cannot overheat and ignite. Another is earth leakage, where current escapes through a person or damaged insulation, detected as an imbalance between live and neutral by a residual current device that protects people. Some panels add over- and under-voltage modules. Noting which device tripped tells you whether a socket is overloaded or an appliance's insulation has failed.
难度 入门 · 适合 大众
CC BY 4.0 · 已核验 · Verified 2026-08-23
来源 · Source
邱关源 主编 罗先觉 修订,《电路》第5版,高等教育出版社,2006
Qiu Guanyuan ed., Circuit, 5th ed., Higher Education Press, 2006
#空气开关 #过载 #漏电
保险丝和空气开关都能断电，区别在哪里？
Fuses and circuit breakers both cut power, so what is the difference?
保险丝靠一段低熔点金属在过流时熔断，动作快、成本低，但一次性使用，熔断后必须更换。空气开关内部有热双金属片和电磁线圈，分别应对持续过载和瞬时短路，跳闸后可复位重复使用，还能兼作手动开关。在需要极快分断的半导体保护场合，仍然使用快速熔断器。
A fuse works by melting a low-melting-point metal link when current is too high; it acts fast and costs little but is single-use and must be replaced. A circuit breaker contains a thermal bimetal strip and an electromagnetic coil that handle sustained overload and instantaneous short circuit respectively, and it can be reset and reused as well as serving as a manual switch. Where extremely fast interruption is needed to protect semiconductors, fast-acting fuses are still used.
难度 入门 · 适合 大众
CC BY 4.0 · 已核验 · Verified 2026-08-23
来源 · Source
邱关源 主编 罗先觉 修订,《电路》第5版,高等教育出版社,2006
Qiu Guanyuan ed., Circuit, 5th ed., Higher Education Press, 2006
#保险丝 #空气开关 #过流保护