﻿ 一种漏电流检测快速保护方法研究

一种漏电流检测快速保护方法研究 Study on Leakage Current Detection and Fast Protection Method

Abstract: In this paper, a leakage current detection and protection method based on oscillating circuit and differential circuit is proposed for the safety requirements of non-isolated power electronic devices connected to power grid. The leakage current protection circuit consists of transformer, self-excited oscillator, second-order active low-pass filter circuit, differential detection circuit and existing control chips in the system. The leakage current signal detected by the leakage current detection circuit is sampled through the digital control chip in the device, and the leakage current value sampled is compared with the specified value in the safety standard, thus forming a hierarchical protection. For the excessive leakage current, the differential circuit and software in the leakage current detection circuit studied can achieve rapid protection. Finally, the validity of this leakage current detection and protection method is verified by experiments in three-phase bidirectional PWM rectifier applied to the front end of motor driver.

1. 引言

2. 漏电流检测和保护方法

2.1. 漏电流检测电路工作原理

Figure 1. General schematic diagram of leakage current detection and protection circuit

1) 自激振荡电路工作原理

Figure 2. Self-excited oscillation circuit

2) 二阶有源低通滤波电路工作原理

Figure 3. Second-order active low-pass filter circuit

$A\left(s\right)=\frac{{V}_{o}\left(s\right)}{{V}_{i}\left(s\right)}=\frac{{A}_{VF}}{1+\left(3-{A}_{VF}\right)sCR+{\left(sCR\right)}^{2}}$ (1)

${A}_{VF1}=1+\frac{{\text{R}}_{54}}{{\text{R}}_{56}}$ (2)

${f}_{c1}=\frac{1}{2\text{π}\sqrt{\text{C}51\cdot \text{C}53\cdot \text{R}11\cdot \text{R}51}}$ (3)

3) 微分检测保护电路的工作原理

Figure 4. Differential detection protection circuit

2.2. 漏电流检测保护原理

1) 漏电流较小时的响应

2) 漏电流较大时的响应

Figure 5. Flow chart of leakage current detection and protection program

3. 漏电流检测保护电路的设计

3.1. 自激振荡器的设计

1) 磁芯选取

2) 计算原副边绕组匝数

${A}_{e}=\left(\text{OD-ID}\right)\cdot \text{HD}=20\text{\hspace{0.17em}}{\text{mm}}^{2}$ (4)

$Q=\frac{\text{π}\cdot {\text{ID}}^{2}}{4}=176.7\text{\hspace{0.17em}}{\text{mm}}^{2}$ (5)

${N}_{1}=\frac{{V}_{c}\cdot {T}_{s}}{4{B}_{m}\cdot {A}_{e}}=73.171$ (6)

3) 线径选取

${I}_{N1}=\frac{{I}_{N3}}{{N}_{1}}\cdot {N}_{3}=4.11\text{\hspace{0.17em}}\text{mA}$ (7)

$nn1=\frac{{I}_{N1}}{J\cdot {S}_{d3}}=0.058\text{\hspace{0.17em}}{\text{m}}^{-2}\cdot {\text{kg}}^{-1}\cdot {\text{s}}^{2}$ (8)

$nn2=\frac{50\cdot {10}^{-3}}{J\cdot {S}_{d3}}=0.707\text{\hspace{0.17em}}{\text{m}}^{-2}\cdot {\text{kg}}^{-1}\cdot {\text{s}}^{2}$ (9)

$nn3=\frac{25}{J×{S}_{d4}}=6.25\text{\hspace{0.17em}}{\text{m}}^{-2}\cdot {\text{kg}}^{-1}\cdot {\text{s}}^{2}$ (10)

$k=\frac{{N}_{1}\cdot n{n}_{1}\cdot {S}_{d3}+{N}_{2}\cdot n{n}_{2}\cdot {S}_{d3}+4{N}_{3}\cdot n{n}_{3}\cdot {S}_{d4}}{Q}=0.078$ (11)

3.2. 二阶有源低通滤波器的设计

${A}_{VF1}=1+\frac{\text{R}54}{\text{R56}}=2$ (12)

${f}_{c1}=\frac{1}{2\text{π}\sqrt{\text{C51}\cdot \text{C53}\cdot \text{R11}\cdot \text{R51}}}=1.071\text{\hspace{0.17em}}\text{kHz}$ (13)

${A}_{VF2}=1+\frac{\text{R55}}{\text{R57}}=2.538$ (14)

${f}_{c2}=\frac{1}{2\text{π}\sqrt{\text{C52}\cdot \text{C54}\cdot \text{R}52\cdot \text{R53}}}=1.329\text{\hspace{0.17em}}\text{kHz}$ (15)

${A}_{VF}={A}_{VF1}\cdot {A}_{VF2}=5.077$ (16)

3.3. 漏电流检测微分保护电路参数设计

$\left\{\begin{array}{c}{u}_{c}{}_{\left(80\text{\hspace{0.17em}}\text{μs}\right)}=12\cdot \left(1-{e}^{-\frac{80\cdot {10}^{-6}}{{\tau }_{1}}}\right)\ge 0.6\text{\hspace{0.17em}}\text{V}\\ {u}_{c}{}_{\left(80\text{\hspace{0.17em}}\text{μs}\right)}\ge 3.3\text{\hspace{0.17em}}\text{V}\end{array}$ (17)

Figure 6. RC circuits

${\tau }_{1}={\text{R}}_{3}\cdot {\text{C}}_{2}$ (18)

${\tau }_{1}={\text{R}}_{3}\cdot {\text{C}}_{2}\le 2.5\cdot {10}^{-4}$ (19)

${u}_{c}{}_{\left(160\text{\hspace{0.17em}}\text{μs}\right)}={u}_{c}{}_{\left(80\text{\hspace{0.17em}}\text{μs}\right)}{e}^{-\frac{80\cdot {10}^{-6}}{{\tau }_{2}}}\ge 3.3\text{\hspace{0.17em}}\text{V}$ (20)

${\tau }_{2}=\left({\text{R}}_{3}+{\text{R}}_{2}\right)\cdot {\text{C}}_{2}$ (21)

${\tau }_{2}=\left({\text{R}}_{3}+{\text{R}}_{2}\right)\cdot {\text{C}}_{2}\ge 1.16\cdot {10}^{-4}$ (23)

4. 实验结果

Figure 7. Self-excited oscillation waveform with small leakage current

Figure 8. Self-excited oscillation waveform with large leakage current

Figure 9. Self-excited oscillation waveform

Figure 10. Leakage current detection protection waveform

5. 结论

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