ReThink: Reveal the Threat of Electromagnetic Interference on Power Inverters (2409.17873v1)

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.

• The paper reveals that high-frequency EMI (above 1 GHz) can manipulate both current and voltage sensors in PV inverters, leading to sensor errors that cause DoS, component damage, and efficiency loss.
• The paper employs theoretical analysis and empirical testing using frequency sweeps and amplitude modulation, demonstrating sensor deviations up to ±300V and ±320A across various inverter models.
• The paper highlights the need for advanced hardware and software countermeasures, including enhanced EMI shielding, multi-stage low-pass filtering, and robust anomaly detection algorithms.

Evaluating the Threat of Electromagnetic Interference on Power Inverters

The present analysis investigates the security vulnerabilities of photovoltaic (PV) inverters, particularly focusing on the susceptibility of embedded sensors to electromagnetic interference (EMI). The transition to renewable energy sources (RES) necessitates substantial deployment of power inverters that convert direct current (DC) from RES to alternating current (AC). The paper reveals that despite adherence to electromagnetic compatibility (EMC) standards, PV inverters remain vulnerable to EMI, resulting in significant operational risks.

Key Findings

This paper systematically evaluates the vulnerabilities in current and voltage sensors within PV inverters under EMI, emphasizing the following points:

1. Sensor Sensitivity: Both Hall current sensors and non-Hall voltage sensors can be manipulated by EMI signals at frequencies of 1 GHz or higher. Given the typical installation of PV inverters in exposed environments, such as rooftops or fields, these sensors are susceptible to electromagnetic manipulation.
2. Countermeasure Gaps: Existing electromagnetic compatibility measures focus on unintentional interference, primarily considering frequencies below 1 GHz. As such, EMI signals exceeding 1 GHz can exploit these gaps, introducing erroneous sensor readings.
3. Impacts: The paper identifies three primary consequences of sensor manipulation:
   • Denial of Service (DoS): The inverter is forced to shut down, causing a sudden drop in power output.
   • Physical Damage: Incorrect sensor readings can lead to conditions that burn out components, leading to costly repairs or replacements.
   • Damping: Prolonged exposure reduces the inverter's power output efficiency, affecting overall production.

Methodology

The research applied both theoretical analysis and empirical testing on multiple commercial PV inverters. It employs frequency sweeps and amplitude modulation to understand the precise impact of EMI on sensor outputs. This approach was essential in discerning how different sensors react differentially to EMI and how control algorithms within inverters can be misled.

Experimental Results

The empirical tests demonstrated that EMI could significantly alter sensor readings, with deviations reaching up to $\pm300 \, \mathrm{V}$ for voltage sensors and $\pm320 \, \mathrm{A}$ for current sensors. These manipulations were successfully validated on multiple inverter models, underscoring the pervasiveness of these vulnerabilities.

Implications and Future Directions

The implications of these findings are twofold:

1. Practical: Regular residential and commercial PV inverters, essential for the quick adoption of renewable energy technologies, remain prone to disruptions that can be stealthily enacted through non-contact EMI methods. This realization calls for redesigned power inverters with robust EMI shielding and filtering practices that extend beyond the existing standards.
2. Theoretical: The research opens new avenues for assessing the security of other power electronic devices and RES technologies. Future work could explore similar vulnerabilities in battery storage systems and wind inverters, considering similar sensor and control logic structures.

Countermeasures

The paper proposes several hardware and software countermeasures to mitigate these vulnerabilities:

• Hardware Solutions: Implementing multi-stage low-pass filters to cover higher frequency bands and improving the physical shielding of inverters to block high-frequency EMI.
• Software Solutions: Enhancing control algorithms with consistency checks to detect anomalies in sensor readings, thereby preempting manipulative EMI impacts.

Conclusion

This research underscores the critical need to re-evaluate and enhance the security measures of PV inverters amidst the increasing deployment of RES. The vulnerabilities uncovered have significant implications for both the reliability and security of future energy grids. This work contributes substantially to the foundation for further security analyses of various power electronic devices and drives home the necessity of robust, multilayered defense mechanisms to safeguard the integrity of renewable energy systems.

Overall, the paper provides a thorough exploration into the field of electromagnetic security for power inverters, highlighting urgent areas for improvement and setting the stage for future innovations in the field of RES security.