By analyzing the electromagnetic environment of ships and the electromagnetic environment in which the solar inverter control system operates, the interference source environment of the inverter control system is identified. The basic principle and function of the inverter control system clearly demonstrate the connection relationship between the ship control system and peripheral equipment (as shown in the figure). In addition to direct interference caused by the electromagnetic space in which it is located, the conduction path can be obtained from the figure. Starting from the basic input-output interface, analyze it.
1. Basic principles of control system and input/output interfaces
The solar inverter mainly realizes the maximum power tracking of the solar panel, which is achieved by adjusting the switch duty cycle of the switching device and adjusting the equivalent load impedance of the solar panel to achieve the maximum power tracking function of the solar panel. The solar inverter converts the DC energy of the solar panel into stable and stable AC energy for use by ship equipment by controlling the system to output switch driving signals. We will focus on exploring the high reliability design of EMC technology for solar powered ship inverter control systems.
The inverter algorithm of the solar inverter control system is based on accurate collection and control of peripheral data information. The peripheral signal acquisition control circuit is the main path for interference signals to propagate to the control system. Therefore, analyzing the input and output interfaces of the control system is particularly important for the EMC design of the control system. The main tasks undertaken by the inverter control system are: 1) Control system functional module work
Power supply; 2) Direct AC voltage and current signal acquisition; 3) DC bus ripple collection; 4) Power switch device drive control; 5) Direct current circuit breaker control and status signal feedback acquisition; 6) Direct AC side to ground balance detection; 7) Communicate with peripheral devices (such as ship monitoring systems).
2. Analysis of interference sources and their interference paths
Based on the basic principles of control systems, an analysis of the electromagnetic environment and input-output interface links of the solar inverter control system on ships can qualitatively analyze the interference sources and paths introduced into the inverter control system. Interference mainly occurs through conduction and spatial radiation. According to Figure 1, the path of the interference source is analyzed as follows:
1) Power supply circuit interference path. The sources of interference are the instability of the power supply system voltage, the impact of starting and stopping operations on other equipment loads on board, and the induced interference caused by the limited magnetic field space in the wiring circuit of the power supply line in the cabin. The interference source enters the inverter control system along the power supply circuit.
2) The interference path of the DC side voltage and current signal acquisition circuit is analog signal acquisition. The analog signal directly comes from the high-voltage DC bus and AC system, and its interference sources are high-frequency harmonics in the DC AC system inverter and electromagnetic interference in the cable wiring circuit. The interference information is introduced into the control system through this acquisition circuit.
3) Interference path of DC bus ripple acquisition circuit. The principle is the same as 2), but the ripple acquisition circuit is more sensitive to electromagnetic interference because the collected voltage is at the millivolt level analog quantity.
4) The interference path of the power switch device driving control circuit is the digital output signal. It directly controls the power device switch, and electromagnetic space induction and high-frequency harmonics of high-voltage system switches are its main sources of interference.
5) The interference paths of the DC circuit breaker control and status signal feedback acquisition circuit are digital output and input signals, respectively. The interference source of this circuit includes not only electromagnetic spatial induction, but also the electrical fast pulse group generated during the circuit breaker switching process (interference sources ranging from tens to hundreds of microseconds).
6) DC side to ground balance detection, AC side three-phase balance detection circuit interference path. The main sources of interference are direct connection to the high-voltage system, ground interference, bus interference, and spatial radiation induction signals.
7) Communicate with peripheral devices (such as ship monitoring systems). Due to the long distance of communication circuit wiring, the electromagnetic space environment passing through the path is more complex and sensitive to electromagnetic interference and other equipment interference.
8) The spatial electromagnetic field directly induces interference on the internal electronic circuits of the control system.
9) Static interference path. The main sources of interference are human static electricity and long-term accumulation of static electricity.
10) Lightning interference path. The overall EMC design of the ship will consider lightning interference, but the overall design mainly considers direct lightning, which is the first level lightning protection. Due to the control system being located inside the cabin, the lightning interference path is mainly reflected in the influence of induced lightning, which is a secondary lightning protection. Lightning energy can alter the electromagnetic environment inside the cabin or introduce cables from outside into sensitive components inside the cabin control room.
Any interference ultimately manifests as common mode and differential mode interference entering the internal circuits of the system, causing damage to electronic components and integrated circuits. Therefore, analyzing and mastering the interference paths and sources can clarify the interfaces, paths, and EMC design objectives that require EMC design protection measures.