Abstract : This paper briefly introduces the power parameter detection problem of wind power converters. A method using a high-speed counter of a PLC to detect the grid phase and generator speed is proposed. This is a simple, practical, and high-precision power parameter detection method. Keywords : Power parameters, phase angle detection, high-speed counter 1 Introduction Power parameter detection is the prerequisite and foundation for automatic control of power equipment, and also a prerequisite for the normal operation of power equipment. When designing power systems, multiple parameter detection methods are often considered, and the optimal detection method is selected. 2 Problem Introduction This paper describes the power parameter detection part of a wind power converter. Due to the influence of wind speed, the frequency and voltage at the wind turbine generator output terminals fluctuate. The function of the wind power converter is to convert the generator's electricity to be in phase and frequency with the grid, and then transmit the electrical energy to the grid. This paper does not provide a more detailed introduction to the wind power converter; interested readers can consult relevant literature. Considering reliability and other practical considerations, this device requires a Siemens PLC300 programmable controller. This converter needs to measure the generator terminal current, voltage, generator speed, torque, grid terminal current, voltage, power factor, active power, reactive power and other power parameters. This article describes how to use PLC300 to measure these power parameters, focusing on how to use PLC300 to measure generator speed, power factor and so on. 3 Detection Methods In industry, the detection of power parameters generally uses sensors to convert current and voltage signals into weak signals that are synchronized with them, and after A/D conversion, the microcontroller is used to calculate the required data. However, the minimum conversion time TT of each analog input channel of the 12-bit analog input module of PLC300 is 17ms, and each analog input module has 8 channels, and the sampling time TS for each analog quantity is 136ms. If a higher resolution analog input module is used, the sampling time will be longer[1]. The period T of the grid signal is 20ms, which cannot guarantee TS< 4 Hardware Circuit It is the foundation for the stable operation of the entire measurement system. Whether its design is reasonable or not will directly affect whether the system can work normally to achieve the designed function. The hardware circuit design should follow the following principles [2]: (1) Modular design of unit circuits Subdivide the system function into various units, and each unit circuit independently realizes its function. In this way, the idea of ​​circuit design is very clear. (2) High reliability design In the process of hardware circuit design, use integrated circuits as much as possible and use fewer discrete components; use high integration components as much as possible and reduce the number of components used. And give priority to circuits that have been proven to be mature in practice. (3) Anti-interference design The field working environment of this system is relatively harsh. In the process of hardware circuit design, various interferences must be considered and anti-interference measures must be taken. (4) High accuracy design The function to be realized by this circuit is the measurement of power parameters. Since it is a measurement, there must be various factors that cause measurement errors. In the process of hardware circuit design, the corresponding error factors must be eliminated. When designing the hardware circuit, first use a second-order filter to filter the synchronization signal of the power grid and generator, and use a zero-crossing comparator composed of LM339 to convert it into a synchronization level signal. Considering the stability of high-frequency pulses, a 1MHz quartz crystal oscillator is used as the pulse signal source. A counter is then used to divide the 1MHz pulse signal by 35 times to obtain a 28.57kHz pulse signal. The circuit diagram is shown in Figure 2. Following the signal processing method described above, the resulting signal is sent to the PLC's CPU. 5. Error Analysis The system described in this paper uses a commonly used industrial synchronous transformer and current sensor to generate synchronous voltage and current signals. The phase measurement error caused by generating the synchronous signal is negligible; the measurement error is the error caused by one pulse cycle. The pulse period used is 35μS, and the measurement error is as follows. The measurement error of power factor: Δcos(Ф)=sin(Ф)ΔФ<ΔФ (5) Substituting the value into equation (1), we get: Δcos(Ф)＜ΔФ=35μS＊2＊3.14/20mS=0.011 Similarly, according to equations (2) and (3), the measurement error of active power sent to the grid can be obtained as: ΔPN= IN＊COS(Ф)＊ΔUN +UN＊COS(Ф)＊ΔIN +IN＊UNSIN(Ф)＊ΔФ (6) ΔVN= IN＊SIN(Ф)＊ΔUN +UN＊SIN (Ф)＊ΔIN +IN＊UN COS(Ф)＊ΔФ (7) The number of pole pairs of the field synchronous wind turbine generator described in this system is 44, and the output frequency is 7-22HZ. Considering the speed of measurement, the high-speed counting function of the PLC CPU is used to measure the generator speed. During the high level period of each voltage signal cycle, a pulse train is sent to the high-speed counter of the PLC CPU, and the count value CS < 650 in each cycle. The relative error of the measured generator speed is: Δs/s = ΔCS /CS = 1/650 = 1.5 * 10-3 (8) The verification results of the power parameters of the equipment show that the detection error can be controlled within 0.5%. 6 Conclusion The power parameter detection method described in this paper can adapt to the needs of PLC300 CPU and industrial site; the required circuit is simple and highly reliable; and the measurement accuracy is high. The wind power converter operates stably and reliably in the industrial site, and the detected power parameters can fully meet the accuracy requirements. References : [1] S7-300 Automation System CPU 31XC Technical Function User Manual [2] Zhang Fengrui Research on DSP-based Power Parameter Testing System [J] Modern Electronics Technology 2006, 20 Author Biography: Sun Jiujun Male, born in July 1977, from Pingyin, Shandong Province, Han nationality, Engineer, Shandong Xinfengguang Electronic Technology Development Co., Ltd., Master's degree, Research direction: Inverter design