电机软启动NTC热敏电阻在电机软启动中的应用-华巨电子
摘要:文中提出了三种直流马达软启动方案:负温度系数热敏电阻软启动、继电器延时软启动、MOSFET线性放大软启动,并分析了各方案的原理和特性,给出了实验结果。原理分析和实验结果表明三种方案都可以有效抑制马达的启动电流,能实现直流马达的软启动。通过对比,给出了三种方案各自的应用场合。 关键词:软启动;直流马达;NTC(Negative Temperature Coefficient);继电器;MOSFET
1、概述 直流马达的工作等效电路如图1所示。稳态运行时,电枢回路方程为:
式中,U为直流马达供电电源电压;E为马达绕组上的反电动势;IR为绕组上的压降。起动瞬间,n=0,E=0,而R 很小,因此
式中,Ist为启动电流,将达到很大数值,通常为额定电枢电流的十几倍甚至更大,造成电网电压突然降低,影响电网。供电直流电源的规格要更大,以满足瞬间大电流冲击,同时也使马达本身遭受很大的电磁力冲击,严重时会损坏马达。因此,适当限制马达的启动电流是必要的。针对此问题,本研究提出了三种马达软启动方案:NTC(Negative Temperature Coefi—cient)热敏电阻软启动电路、MOSFET线性放大软启动电路、继电器延时软启动电路。三种方案的原理:启 动瞬间,降低马达两端的启动电压,以较小的电流启动马达,使电机电流逐步上升到额定值,从而限制启动瞬问的大电流冲击。
2、三种软启动电路结构及原理 2.1 NTC软启动电路 NTC thermistor是负温度系数热敏电阻,其电阻值随着温度的升高而降低,可有效抑制瞬间大电流冲击。由其组成的直流马达软启动电路如图2所示。把合适功率、阻值与温度系数的NTC串人马达的供电回路。当马达启动时,由于NTC热敏电阻以一定的阻值串人马达的供电回路,可以有效地把启动电流限制在规定范围之内。随着大电流的流过,NTC热敏电阻逐渐发热,阻值减小。当马达顺利起动后,NTC发热后,阻值很小,电能损耗较小。 2.2 继电器(Relay)延时软启动电路 在电机的供电回路中串接一个电阻以限制启动电流,当电机稳定启动后,再把串接的电阻短路。上述过程可通过继电器来实现,如图3所示。上电时,电容从零开始充电,三极管截止,限流电阻串接在电机的供电回路中,当电容电压上升到使稳压管导通时,三极管开始工作,继电器吸合,使得电机全电压工作。继电器的延时时间由电机的启动时间决定,由串联的电阻和电容调整。 2.3 MOSFET线性放大软启动 该方案的电路如图4所示。由图可知,上电后电容从零开始充电,因此MOSFET栅极与源极之间的电压也从0开始升高,MOSFET漏极、源极阻抗也是逐渐降低(MOS的线性放大区),这样就可以使电机线圈中的电流逐渐增大,当MOSFET栅极与源极之间的电压增大到使MOSFET基本导通时,电机正常运行。
3、实验分析 为了验证效果,分别对三种软启动电路在实际马达中进行了实验。马达回路串接NTC热敏电阻和不接NTC热敏电阻在同一负载(测试时电机的扭矩为63 kg·cm)下进行了实验,图5、图6分别为不接NTC、接NTC时马达绕组的冲击电流波形。从图中可以看出,启动瞬间,加了软启动电路的电流仅为未加软启动电路的1/4,可以有效抑制启动电流。这个电路的特点是简单、价廉,但当马达频繁起动时,限流效果较差,因为此时NTC温度较高,阻值较小,达不到很好的限流效果,所以频繁启动的马达不宜采用此软启动电路。 图7、图8是继电器延时软启动电路的实验波形。测试时电机的负载扭矩为16 kg·cm,图7、8分别为不加软启动、加软启动时马达绕组的启动电流波形。从两图对比可知,加软启动后,马达仍存在一定的电流冲击,但已有很好的抑制效果。由于在启动瞬间,马达绕组中串入了大功率电阻,体积较大,这种电路通用性较强。 图9、10为MOSFET线性放大软启动电路实验波形,测试时电机的负载扭矩为63 kg·cm。它们分别为不加软启动、加软启动时马达绕组的电流波形。从图可知,不加软启动时,电流冲击为30 A左右,加软启动电路后,启动电流为8 A左右,很好地抑制了启动冲击电流,保护了马达和供电电源。但由于加入了MOSFET,马达工作中,始终会有电流流过MOS—FET,因此MOSFET易发热,实际应用中需要安装散热器,此电路主要应用在中小功率马达中。
4、结论 直流马达直接启动的冲击电流对马达寿命及性能有较大影响,基于此,文中提出了三种软启动方案,分析了各电路特点,给出了主要应用场合。实验证明,三种软启动电路都可有效降低马达启动的冲击电流,有效保护了电源装置和马达本体。这些软启动方案,为实际马达应用系统提供了有益的借鉴。 5.主要技术参数 5.大尺寸主要技术参数 型号 | R25 | 最大稳态电流 | 25℃下最大电流时近似电阻值 | 片径Φ | 耗散系数 | 热时间常数 | 工作温度 | (Ω) | (A) | (Ω) | (mm) | (mW/℃) | (S) | (℃) | 芯片直径:(13-50)mm | -55~+250 | SCD-1R09 | 1 | 9 | 0.032 | 13 | ≥13 | ≤63 | SCD-1R39 | 1.3 | 9 | 0.042 | 13 | ≥13 | ≤63 | SCD-1R59 | 1.5 | 9 | 0.043 | 13 | ≥13 | ≤63 | SCD-2R58-13 | 2.5 | 8 | 0.048 | 13 | ≥13 | ≤63 | SCD-3R08 | 3 | 8 | 0.052 | 13 | ≥13 | ≤ 63 | SCD-4R07 | 4 | 7 | 0.068 | 13 | ≥ 13 | ≤63 | SCD-5R07 | 5 | 7 | 0.078 | 13 | ≥13 | ≤63 | SCD-6R06 | 6 | 6 | 0.090 | 13 | ≥ 13 | ≤63 | SCD-7R06 | 7 | 6 | 0.098 | 13 | ≥13 | ≤63 | SCD-8R06 | 8 | 6 | 0.104 | 13 | ≥13 | ≤63 | SCD-10R06 | 10 | 6 | 0.126 | 13 | ≥13 | ≤ 63 | SCD-12R05 | 12 | 5 | 0.146 | 13 | ≥ 13 | ≤63 | SCD-15R04 | 15 | 4 | 0.155 | 13 | ≥13 | ≤63 | SCD-16R04 | 16 | 4 | 0.158 | 13 | ≥13 | ≤63 | SCD-20R04 | 20 | 4 | 0.192 | 13 | ≥ 13 | ≤63 | SCD-30R3.5 | 30 | 3.5 | 0.237 | 13 | ≥13 | ≤63 | SCD-47R03 | 47 | 3 | 0.340 | 13 | ≥13 | ≤63 | SCD-60R2.5 | 60 | 2.5 | 0.420 | 13 | ≥13 | ≤63 | SCD-121R2.5 | 120 | 1.8 | 0.994 | 13 | ≥13 | ≤63 | SCD-2R58-15 | 2.5 | 8 | 0.086 | 15 | ≥21 | ≤75 | SCD-1R310 | 1.3 | 10 | 0.034 | 15 | ≥22 | ≤75 | SCD-1R510 | 1.5 | 10 | 0.036 | 15 | ≥22
| ≤75 | SCD-2R59.5 | 2.5 | 9.5 | 0.044 | 15 | ≥22 | ≤75 | SCD-3R09 | 3.0 | 9.0 | 0.046 | 15 | ≥22 | ≤75 | SCD-5R08 | 5.0 | 8.0 | 0.058 | 15 | ≥22 | ≤75 | SCD-6R07 | 6.0 | 7.0 | 0.069 | 15 | ≥22 | ≤75 | SCD-7R07 | 7.0 | 7.0 | 0.078 | 15 | ≥22 | ≤75 | SCD-8R07 | 8.0 | 7.0 | 0.084 | 15 | ≥22 | ≤75 | SCD-10R07 | 10.0 | 7.0 | 0.098 | 15 | ≥22 | ≤75 | SCD-12R06 | 12.0 | 6.0 | 0.116 | 15 | ≥22 | ≤75 | SCD-15R06 | 15.0 | 6.0 | 0.125 | 15 | ≥22 | ≤75 | SCD-16R06 | 16.0 | 6.0 | 0.129 | 15 | ≥22 | ≤75 | SCD-20R06 | 20.0 | 6.0 | 0.136 | 15 | ≥22 | ≤75 | SCD-30R05 | 30.0 | 5.0 | 0.165 | 15 | ≥22 | ≤ 75 | SCD-47R04 | 47.0 | 4.0 | 0.257 | 15 | ≥22 | ≤ 75 | SCD-121R2.5 | 120 | 2.5 | 0.652 | 15 | ≥22 | ≤75 | SCD-0R716 | 0.7 | 16 | 0.026 | 20 | ≥29 | ≤110 | SCD-1R016 | 1.0 | 16 | 0.027 | 20 | ≥29 | ≤110 | SCD-1R020-20 | 1.0 | 20 | 0.020 | 20 | ≥29 | ≤113 | SCD-1R515 | 1.5 | 15 | 0.030 | 20 | ≥29 | ≤110 | SCD-2R014 | 2.0 | 14 | 0.035 | 20 | ≥29 | ≤110 | SCD-2R512 | 2.5 | 12 | 0.060 | 20 | ≥29 | ≤110 | SCD-2R513 | 2.5 | 13 | 0.055 | 20 | ≥29 | ≤110 | SCD-2R515-20 | 2.5 | 15 | 0.046 | 20 | ≥29 | ≤110 | SCD-3R012 | 3.0 | 12 | 0.040 | 20 | ≥29 | ≤110 | SCD-4R012 | 4.0 | 12 | 0.043 | 20 | ≥29 | ≤110 | SCD-4R712 | 4.7 | 12 | 0.046 | 20 | ≥29 | ≤110 | SCD-5R010 | 5.0 | 10 | 0.049 | 20 | ≥29 | ≤110 | SCD-5R012 | 5.0 | 12 | 0.047 | 20 | ≥29 | ≤110 | SCD-6R011 | 6.0 | 11 | 0.052 | 20 | ≥29 | ≤110 | SCD-6R810 | 6.8 | 10 | 0.055 | 20 | ≥29 | ≤110 | SCD-7R09 | 7.0 | 9 | 0.080 | 20 | ≥29 | ≤110 | SCD-7R010 | 7.0 | 10 | 0.075 | 20 | ≥29 | ≤110 | SCD-8R09 | 8.0 | 9 | 0.058 | 20 | ≥29 | ≤110 | SCD-10R08 | 10.0 | 8 | 0.085 | 20 | ≥29 | ≤110 | SCD-12R07.5 | 12.0 | 7.5 | 0.112 | 20 | ≥29 | ≤110 | SCD-15R07 | 15.0 | 7 | 0.123 | 20 | ≥29 | ≤110 | SCD-18R07 | 18.0 | 7 | 0.122 | 20 | ≥29 | ≤110 | SCD-20R06 | 20.0 | 6 | 0.132 | 20 | ≥29 | ≤110 | SCD-20R07 | 20.0 | 7 | 0.122 | 20 | ≥29 | ≤110 | SCD-25R06 | 25.0 | 6 | 0.168 | 20 | ≥29 | ≤110 | SCD-30R06 | 30.0 | 6 | 0.195 | 20 | ≥29 | ≤110 | SCD-47R05 | 47.0 | 5 | 0.325 | 20 | ≥29 | ≤110 | SCD-121R3 | 120.0 | 3 | 0.658 | 20 | ≥29 | ≤110 | SCD-0R522 | 0.5 | 22 | 0.017 | 25 | ≥30 | ≤130 | SCD-0R722 | 0.7 | 22 | 0.018 | 25 | ≥30 | ≤130 | SCD-1R020-25 | 1.0 | 20 | 0.021 | 25 | ≥30 | ≤130 | SCD-1R519 | 1.5 | 19 | 0.024 | 25 | ≥30 | ≤130 | SCD-2R018 | 2.0 | 18 | 0.026 | 25 | ≥30 | ≤130 | SCD-2R516 | 2.5 | 16 | 0.029 | 25 | ≥30 | ≤130 | SCD-3R015.5 | 3.0 | 15.5 | 0.032 | 25 | ≥30 | ≤130 | SCD-4R015 | 4.0 | 15 | 0.039 | 25 | ≥30 | ≤130 | SCD-4R714 | 4.7 | 14 | 0.044 | 25 | ≥30 | ≤130 | SCD-5R014 | 5.0 | 14 | 0.047 | 25 | ≥30 | ≤130 | SCD-6R812 | 6.8 | 12 | 0.061 | 25 | ≥30 | ≤130 | SCD-7R011 | 7.0 | 11 | 0.064 | 25 | ≥30 | ≤130 | SCD-8R010 | 8.0 | 10 | 0.079 | 25 | ≥30 | ≤130 | SCD-10R10 | 10.0 | 10 | 0.084 | 25 | ≥30 | ≤130 | SCD-12R09 | 12.0 | 9 | 0.102 | 25 | ≥30 | ≤130 | SCD-15R08 | 15.0 | 8 | 0.117 | 25 | ≥30 | ≤130 | SCD-18R08 | 18.0 | 8 | 0.125 | 25 | ≥30 | ≤130 | SCD-20R08 | 20.0 | 8 | 0.132 | 25 | ≥30 | ≤130 | SCD-0R530 | 0.5 | 30 | 0.013 | 30 | ≥40 | ≤190 | SCD-1R030 | 1.0 | 30 | 0.014 | 30 | ≥40 | ≤190 | SCD-1R525 | 1.5 | 25 | 0.016 | 30 | ≥40 | ≤190 | SCD-2R023 | 2.0 | 23 | 0.019 | 30 | ≥40 | ≤190 | SCD-2R520 | 2.5 | 20 | 0.023 | 30 | ≥40 | ≤190 | SCD-3R019.5 | 3.0 | 19.5 | 0.026 | 30 | ≥40 | ≤190 | SCD-4R019 | 4.0 | 19 | 0.031 | 30 | ≥40 | ≤190 | SCD-4R718 | 4.7 | 18 | 0.035 | 30 | ≥40 | ≤190 | SCD-5R017 | 5.0 | 17 | 0.037 | 30 | ≥40 | ≤190 | SCD-6R017 | 6.0 | 17 | 0.042 | 30 | ≥40 | ≤190 | SCD-6R816 | 6.8 | 16 | 0.043 | 30 | ≥40 | ≤190 | SCD-7R015 | 7.0 | 15 | 0.044 | 30 | ≥40 | ≤190 | SCD-8R014 | 8.0 | 14 | 0.049 | 30 | ≥40 | ≤190 | SCD-10R13 | 10.0 | 13 | 0.056 | 30 | ≥40 | ≤190 | SCD-12R12 | 12.0 | 12 | 0.067 | 30 | ≥40 | ≤190 | SCD-15R11 | 15.0 | 11 | 0.078 | 30 | ≥40 | ≤190 | SCD-18R10 | 18.0 | 10 | 0.092 | 30 | ≥40 | ≤190 | SCD-20R09 | 20.0 | 9 | 0.113 | 30 | ≥40 | ≤190 | SCD-0R532 | 0.5 | 32 | 0.010 | 35 | ≥55 | ≤280 | SCD-1R032 | 1.0 | 32 | 0.011 | 35 | ≥55 | ≤280 | SCD-1R528 | 1.5 | 28 | 0.013 | 35 | ≥55 | ≤280 | SCD-2R025 | 2.0 | 25 | 0.017 | 35 | ≥55 | ≤280 | SCD-2R523 | 2.5 | 23 | 0.020 | 35 | ≥55 | ≤280 | SCD-3R022 | 3.0 | 22 | 0.023 | 35 | ≥55 | ≤280 | SCD-4R021 | 4.0 | 21 | 0.026 | 35 | ≥55 | ≤280 | SCD-4R720 | 4.7 | 20 | 0.029 | 35 | ≥55 | ≤280 | SCD-5R019 | 5.0 | 19 | 0.030 | 35 | ≥55 | ≤280 | SCD-6R818 | 6.8 | 18 | 0.035 | 35 | ≥55 | ≤280 | SCD-7R017 | 7.0 | 17 | 0.037 | 35 | ≥55 | ≤280 | SCD-8R016 | 8.0 | 16 | 0.041 | 35 | ≥55 | ≤280 | SCD-10R15 | 10.0 | 15 | 0.045 | 35 | ≥55 | ≤280 | SCD-12R14 | 12.0 | 14 | 0.051 | 35 | ≥55 | ≤280 | SCD-15R13 | 15.0 | 13 | 0.060 | 35 | ≥55 | ≤280 | SCD-18R11 | 18.0 | 11 | 0.072 | 35 | ≥55 | ≤280 | SCD-20R10 | 20.0 | 10 | 0.089 | 35 | ≥55 | ≤280 | SCD-0R240 | 0.2 | 40 | 0.005 | 40 | ≥60 | ≤350 | SCD-0R540 | 0.5 | 40 | 0.008 | 40 | ≥60 | ≤350 | SCD-1R040 | 1 | 40 | 0.010 | 40 | ≥60 | ≤350 | SCD-1R536 | 1.5 | 36 | 0.012 | 40 | ≥60 | ≤350 | SCD-2R032 | 2 | 32 | 0.014 | 40 | ≥60 | ≤350 | SCD-2R530 | 2.5 | 30 | 0.018 | 40 | ≥60 | ≤350 | SCD-3R028 | 3 | 28 | 0.020 | 40 | ≥60 | ≤350 | SCD-4R027 | 4 | 27 | 0.022 | 40 | ≥60 | ≤350 | SCD-4R726 | 4.7 | 26 | 0.023 | 40 | ≥60 | ≤350 | SCD-5R025 | 5 | 25 | 0.028 | 40 | ≥60 | ≤350 | SCD-6R823 | 6.8 | 23 | 0.030 | 40 | ≥60 | ≤350 | SCD-8R020 | 8 | 20 | 0.034 | 40 | ≥60 | ≤350 | SCD-10R019 | 10 | 19 | 0.038 | 40 | ≥60 | ≤350 | SCD-12R018 | 12 | 18 | 0.040 | 40 | ≥60 | ≤350 | SCD-15R016 | 15 | 16 | 0.050 | 40 | ≥60 | ≤350 | SCD-18R014 | 18 | 14 | 0.062 | 40 | ≥60 | ≤350 | SCD-20R013 | 20 | 13 | 0.075 | 40 | ≥60 | ≤350 | SCD-0R250 | 0.2 | 50 | 0.004 | 45 | ≥70 | ≤480 | SCD-0R550 | 0.5 | 50 | 0.007 | 45 | ≥70 | ≤480 | SCD-1R048 | 1 | 48 | 0.009 | 45 | ≥70 | ≤480 | SCD-1R545 | 1.5 | 45 | 0.011 | 45 | ≥70 | ≤480 | SCD-2R040 | 2 | 40 | 0.012 | 45 | ≥70 | ≤480 | SCD-2R537 | 2.5 | 37 | 0.015 | 45 | ≥70 | ≤480 | SCD-3R035 | 3 | 35 | 0.018 | 45 | ≥70 | ≤480 | SCD-4R034 | 4 | 34 | 0.020 | 45 | ≥70 | ≤480 | SCD-4R732 | 4.7 | 32 | 0.022 | 45 | ≥70 | ≤480 | SCD-5R030 | 5 | 30 | 0.025 | 45 | ≥70 | ≤480 | SCD-6R828 | 6.8 | 28 | 0.028 | 45 | ≥70 | ≤480 | SCD-8R026 | 8 | 26 | 0.030 | 45 | ≥70 | ≤480 | SCD-10R024 | 10 | 24 | 0.032 | 45 | ≥70 | ≤480 | SCD-12R022 | 12 | 22 | 0.034 | 45 | ≥70 | ≤480 | SCD-15R020 | 15 | 20 | 0.042 | 45 | ≥70 | ≤480 | SCD-18R018 | 18 | 18 | 0.061 | 45 | ≥70 | ≤480 | SCD-20R016 | 20 | 16 | 0.070 | 45 | ≥70 | ≤480 | SCD-02R60 | 0.2 | 60 | 0.003 | 50 | ≥90 | ≤650 | SCD-0R560 | 0.5 | 60 | 0.006 | 50 | ≥90 | ≤650 | SCD-1R056 | 1 | 56 | 0.008 | 50 | ≥90 | ≤650 | SCD-1R550 | 1.5 | 50 | 0.010 | 50 | ≥90 | ≤650 | SCD-2R045 | 2 | 45 | 0.011 | 50 | ≥90 | ≤650 | SCD-2R542 | 2.5 | 42 | 0.012 | 50 | ≥90 | ≤650 | SCD-3R040 | 3 | 40 | 0.015 | 50 | ≥90 | ≤650 | SCD-4R038 | 4 | 38 | 0.018 | 50 | ≥90 | ≤650 | SCD-4R736 | 4.7 | 36 | 0.021 | 50 | ≥90 | ≤650 | SCD-5R035 | 5 | 35 | 0.022 | 50 | ≥90 | ≤650 | SCD-6R832 | 6.8 | 32 | 0.025 | 50 | ≥90 | ≤650 | SCD-8R029 | 8 | 29 | 0.028 | 50 | ≥90 | ≤650 | SCD-10R027 | 10 | 27 | 0.030 | 50 | ≥90 | ≤650 | SCD-12R025 | 12 | 25 | 0.033 | 50 | ≥90 | ≤650 | SCD-15R023 | 15 | 23 | 0.040 | 50 | ≥90 | ≤650 | SCD-18R020 | 18 | 20 | 0.055 | 50 | ≥90 | ≤650 | SCD-20R018 | 20 | 18 | 0.065 | 50 | ≥90 | ≤650 |
注:若非特别指出,R25的允许偏差为±20%。
华巨电子热敏电阻厂家:www.sinochip.net
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