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ReThink: Reveal the Threat of Electromagnetic Interference on Power Inverters

Fengchen Yang, Zihao Dan, Kaikai Pan, Chen Yan, Xiaoyu Ji, Wenyuan Xu

Abstract

With the boom of renewable energy sources (RES), the number of power inverters proliferates. Power inverters are the key electronic devices that transform the direct current (DC) power from RES to the alternating current (AC) power on the grids, and their security can affect the stable operation of RES and even power grids. This paper analyzes the security of photovoltaic (PV) inverters from the aspects of internal sensors since they serve as the foundation for safe power conversion. We discover that both the embedded current sensors and voltage sensors are vulnerable to electromagnetic interference (EMI) of 1 GHz or higher, despite electromagnetic compatibility (EMC) countermeasures. Such vulnerabilities can lead to incorrect measurements and deceiving the control algorithms, and we design ReThink that could produce three types of consequences on PV inverters by emitting carefully crafted EMI, i.e., Denial of Service (DoS), damaging inverters physically or damping the power output. We successfully validate these consequences on 5 off-the-shelf PV inverters, and even in a real-world microgrid, by transmitting EMI signals at a distance of 100-150cm and a total power within 20W. Our work aims to raise awareness of the security of power electronic devices of RES, as they represent an emerging Cyber-Physical attack surface to the future RES-dominated grid. Finally, to cope with such threats, we provide hardware and software-based countermeasures.

ReThink: Reveal the Threat of Electromagnetic Interference on Power Inverters

Abstract

With the boom of renewable energy sources (RES), the number of power inverters proliferates. Power inverters are the key electronic devices that transform the direct current (DC) power from RES to the alternating current (AC) power on the grids, and their security can affect the stable operation of RES and even power grids. This paper analyzes the security of photovoltaic (PV) inverters from the aspects of internal sensors since they serve as the foundation for safe power conversion. We discover that both the embedded current sensors and voltage sensors are vulnerable to electromagnetic interference (EMI) of 1 GHz or higher, despite electromagnetic compatibility (EMC) countermeasures. Such vulnerabilities can lead to incorrect measurements and deceiving the control algorithms, and we design ReThink that could produce three types of consequences on PV inverters by emitting carefully crafted EMI, i.e., Denial of Service (DoS), damaging inverters physically or damping the power output. We successfully validate these consequences on 5 off-the-shelf PV inverters, and even in a real-world microgrid, by transmitting EMI signals at a distance of 100-150cm and a total power within 20W. Our work aims to raise awareness of the security of power electronic devices of RES, as they represent an emerging Cyber-Physical attack surface to the future RES-dominated grid. Finally, to cope with such threats, we provide hardware and software-based countermeasures.
Paper Structure (58 sections, 14 equations, 35 figures, 4 tables, 1 algorithm)

This paper contains 58 sections, 14 equations, 35 figures, 4 tables, 1 algorithm.

Table of Contents

  1. Introduction
  2. Background and Threat Model
  3. Principle of PV Inverter
  4. Power Conversion Unit
  5. Control Algorithm
  6. Sensors of PV Inverter
  7. Non-Hall Voltage Sensor
  8. Hall Current Sensor
  9. Threat model
  10. Understanding the Impact of EMI on Embedded Sensors of PV Inverters
  11. Analysis of the EMI Impact on Sensors
  12. Impact of EMI on Voltage Sensors
  13. Impact of EMI on Current Sensors
  14. Experimental Verification
  15. Can EMI Impact Voltage and Current Sensors
  16. ...and 43 more sections

Figures (35)

  • Figure 1: An illustration of ReThink : EMI can affect PV inverters and cause DoS or physical damage, or damping the power output.
  • Figure 2: A typical PV inverter can be modeled as a 3-layer structure: Power conversion unit-Sensor-Control algorithms.
  • Figure 3: The schematic of voltage and current sensors in the PV inverter PCB. The voltage sensor mainly comprises a differential op-amp circuit; the current sensor comprises a Hall chip and a differential op-amp circuit.
  • Figure 4: The principle of EMI impact on voltage sensors. The EMI signal is coupled into the sensor circuit, and then rectified, amplified by the op-amp, and ultimately turned into an offset on the output.
  • Figure 5: The structure of the OPA2171 used in voltage and current sensors.
  • ...and 30 more figures