安全可靠的接地系统对电力系统的安全运行和防止事故的发生具有十分重要的意义，接地系统的好坏直接关系着电气设备正常工作以及工作人员的人身安全,因而接地电阻的准确测量是至关重要的。 本文首先分析对比了目前常用几种接地电阻测量原理和测量方法的优点和不足，提出了采用变频测量方法，并选用高性能的DSP作为系统的控制和处理核心以及利用钳口采集信号的方案，研制接地电阻测量仪，这种方案抗干扰能力强、测量精度较高，并且操作方便，不需要打辅助地桩及将接地体与设备隔离，可实现在线测量。 变频测量的基本原理是：首先测量干扰信号频率，然后控制激励信号的输出频率，使之处在未受干扰的频率段上进行测量，从而减小干扰，提高测量精度。在测量中采用FFT进行接地电阻谐波分析，由于FFT很难实现同步采样和整周期截断，所以本文通过加窗函数和采用插值修正算法来计算谐波频率、相位和幅值。改进后的FFT算法能够大大降低频谱泄露和噪声干扰，提高谐波分析的准确性。利用ADSP-BF504的高速运算能力以及强大的控制能力，进行所需算法数据处理和实现复杂的控制功能。基于上述测量原理，设计并实现了基于DSP的接地电阻仪系统，整个系统包括硬件和软件设计，硬件设计由正弦信号产生模块、功率放大模块、电压电流采集调理电路、ADC采样电路、按键显示模块以及存储模块、通信模块等部分组成；系统软件主要是按模块化的思想进行设计的，主要包括主程序、数据采集和处理程序以及键盘和显示等程序。 实验结果表明，论文设计的接地电阻仪抗干扰能力强、测量精度高，操作简单，各项性能指标达到了设计要求，具有较高的实用价值和应用前景。可以产品化和市场化。

A safe and reliable grounding system has very import significance for the safe operation of the power system and the prevention of accidents. The grounding system has a direct relationship to the normal work of electrical equipment and the safety of staff, thus correct measurement of grounding resistance is essential. This thesis first analyzes and compares the merits and shortcomings of the current commonly used grounding resistance measuring principles and measuring methods, proposes frequency conversion measurement method, selects the high performance DSP as the control core and processing core of the system and uses the jaw signal acquisition scheme, and finally manufactures grounding resistance measuring instrument. The scheme has very strong anti-interference ability, higher measuring precision, and simple operation. Without the need to make the auxiliary pile, to disconnect the power equipment, and to isolate the grounding body and the equipment, the method facilitates the on-line intelligent measuring. The basic principle of the frequency conversion measuring is: firstly, to measure the frequency of the interference signal, and then to control the output frequency of the voltage signal so that it can be measured on the unperturbed frequency, which reduces the interference and improves the measurement accuracy. In the measurement of grounding resistance, the thesis uses FFT to make harmonic analysis, but because it is difficult for FFT to realize the synchronous sampling and integral cycle truncation, the thesis adopts adding window function and interpolation correction algorithm to calculate the harmonic frequency, phase and amplitude. The improved FFT algorithm can greatly reduce spectral leakage and noise interference and improve the accuracy of harmonic analysis. The high operation ability and strong ability to control of ADSP-BF504 can be used to make data processing and realize the complex control functions. Based on the above measurement principle, the thesis designs and realizes a DSP based grounding resistance instrument system including hardwares and softwares. Hardwares include sine signal generating module, power module, voltage and current sampling circuit, ADC sampling circuit, key display module, storage module, and communication module and so on. Softwares are mainly designed according to the idea of modularization and comprehends a main program, data collection and processing procedures and keyboard and display procedures. The actual test results show that the grounding resistance instrument has strong anti-interference ability, higher measuring precision and simple operation. The performance indicators meet the design requirements, and have high practical value and application prospect, and can realize commercialization and be applied to the market.