More and more new technologies have been integrated into the small power supply equipment. Such as switching power supply, hard switching, soft switching, parameter voltage regulation, linear feedback voltage regulation, magnetic amplifier technology, numerical control voltage regulation, PWM, SPWM, electromagnetic compatibility and so on.
The actual demand directly promotes the continuous development and progress of power supply technology. In order to automatically detect and display current, it has automatic protection functions and more advanced intelligent control when hazardous situations such as overcurrent and overvoltage occur. It has sensor detection, sensor sampling, The power technology of sensor protection has gradually become a trend, and sensors that detect current or voltage have emerged at the historic moment and have become popular among power designers in China.
The current sensor is a key component in the inverter control to ensure the performance of the inverter. Currently, many inverter failures on the market are caused by damage or poor use of the current sensor.
The following describes the application of current sensors in the inverter. Generally, the current sensors are equipped with corresponding power supply ± 12V, ± 15V; the conditioning circuit constitutes a current sampling module, which converts the three-phase stator current into basic binary code. Provide timely information on the current to complete the adjustment of the current loop. This system uses three JCE modules (some inverter manufacturers also use two, and the third one is completed by algorithm) to detect phase a, b, and c currents respectively. And through the sampling resistor, the current information is converted into voltage information, and then converted into a digital signal by the AD conversion module in the inverter's main control chip. After digital filtering and scaling, it provides current feedback information for current loop regulation. The hardware schematic diagram of the detection circuit is as follows:
The JCE current sensor converts the current information into voltage information, and also converts the signal detected by the LEM into a voltage range suitable for the control chip. First, the voltage signal is converted into a symmetrical positive and negative voltage, and then the corresponding offset is provided to convert To the voltage range suitable for the control chip. JCE samples the three-phase currents of a, b, and c, and stores them in the corresponding registers for the main control system after the detection module.
The three-wire system is generally used, and the three-phase current sum of the motor stator is equal to zero. The LEM component samples the three-phase currents a, b, and c. The conversion result after the detection module is used as the basis for detecting the unbalance rate of the three-phase current; After the output is cut off, the three-phase current flow of a, b, and c can be detected by the LEM element to determine whether the power module is reliably turned off to eliminate potential safety hazards.
In application, JCE sensors reflect its many characteristics:
Strong overload capacity: when the primary current is overloaded, it can be automatically protected, even if the overload current is twenty times the rated value, the sensor will not be damaged;
The capacitance between the primary and secondary sides is very weak, and in many applications the various effects of the mode voltage can be ignored;
High sensitivity: can distinguish weak and small signals on high components, such as a few milliamperes of AC components on a few hundred amps of DC;
High reliability: failure rate λ = 0.43 × 10-6 / h; strong resistance to external magnetic field: after experiment, magnetic field interference caused by a double working current at 5 to 250px from the sensor causes its own error ≤0.5% .
It can measure the current of arbitrary waveforms, such as DC, AC, and pulse waveforms, and even measure transient peaks;
The primary side circuit and the secondary side circuit are fully insulated, the insulation withstand voltage is generally 3 ~ 6kV, and special requirements can reach 6 ~ 50kV;
High measurement accuracy: the accuracy is better than 10% in the operating temperature range, and the accuracy is suitable for the measurement of any waveform;
Good linearity: better than 0.5%;
Good dynamic performance: response time is less than 1μs, tracking speed di / dt is higher than 50A / μs;
Working frequency bandwidth: The accuracy can reach 1% in the range of 0 (DC) ~ 100kHZ, and the accuracy is improved to 0.5% in the range of 0 ~ 5kHZ
Practice has proved that the current detection link composed of JCE current sensor and conditioning circuit can fully meet the current detection requirements of the inverter in closed-loop control.
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