In recent years, Chinese enterprises have made remarkable strides in advancing battery technology, electric drive systems, and intelligent control mechanisms, significantly boosting the performance and driving range of electric vehicles. These innovations have not only improved the cost-effectiveness of electric vehicles but also reduced production expenses, making them more competitive in the global market. The rapid expansion of the electric vehicle sector has brought attention to the optimization of core components, such as compressors in air conditioning systems. As a critical part of electric vehicle climate control, the compressor’s operational efficiency and stability directly influence passenger comfort and overall energy consumption. However, voltage ripple issues arising during compressor operation often lead to increased vibration and noise, adversely affecting the user experience and device longevity. This paper delves into the characteristics of voltage and current ripple in electric vehicle compressors, examining their impact on the high-voltage internal network and proposing optimization strategies to mitigate these effects.
The proliferation of electric vehicles in China has underscored the importance of addressing electrical disturbances like voltage ripple, which can compromise system reliability. In this study, I focus on analyzing the ripple generated by compressors in electric vehicles, with an emphasis on how these fluctuations propagate through the vehicle’s high-voltage network. By conducting tests under various conditions, I aim to identify the primary factors contributing to ripple and suggest practical improvements. The findings are expected to provide theoretical support and technical guidance for enhancing the design and performance of electric vehicles, particularly in the context of China’s growing EV industry.
My research objectives center on evaluating the voltage ripple produced by air conditioning compressors in electric vehicles and assessing its effects on key components like the front electric drive. I investigate how different battery states of charge (SOC) influence ripple characteristics during steady-state cooling and heating operations. The test vehicle is a hybrid electric sedan, with compressor specifications including a rated voltage of 350V, maximum voltage of 470V, minimum voltage of 190V, rated power of 5kW, and a ripple current tolerance of 35A. All tests were conducted at a整车试验场 under controlled conditions, as outlined in the methodology.
During high-speed driving, the drive motor demands sustained high power output to maintain velocity, drawing substantial current from the high-voltage battery. Simultaneously, activating the air conditioning system increases electrical load. The electric compressor requires high startup currents and may draw significant current during continuous operation, leading to fluctuations in battery output and subsequent voltage ripple. Sudden current changes during compressor startup can cause instantaneous voltage drops, resulting in pronounced ripple. Additionally, PWM-controlled devices like PTC heaters introduce high-frequency current variations, exacerbating ripple. Compressor workload variations and operational frequency shifts also contribute to periodic current oscillations, affecting voltage stability. The inverter switching in drive motors under high loads generates high-frequency current harmonics, which can couple into the air conditioning system, creating superimposed ripple effects.
To systematically analyze these phenomena, I performed tests across different SOC levels, capturing voltage and current signals at the compressor and front drive locations. The data were processed using a 2MHz/s sampling rate, aligned with international standards, and filtered with a 10Hz-150kHz bandpass Bessel filter of second order. The results are summarized in tables and analyzed through mathematical models to elucidate ripple behavior.
| SOC State | Operating Condition | Test Procedure | Measured Signals |
|---|---|---|---|
| High SOC (>80%) | Steady Cooling | Vehicle in D mode, speed maintained at 100km/h, cooling activated at lowest temperature for 30s, followed by 30s with AC off | Compressor voltage/current, front drive voltage/current |
| High SOC (>80%) | Steady Heating | Vehicle in D mode, speed maintained at 100km/h, heating activated at highest temperature for 30s, followed by 30s with AC off | Compressor voltage/current, front drive voltage/current |
| Medium SOC (40%-60%) | Steady Cooling | Vehicle in D mode, speed maintained at 100km/h, cooling activated at lowest temperature for 30s, followed by 30s with AC off | Compressor voltage/current, front drive voltage/current |
| Medium SOC (40%-60%) | Steady Heating | Vehicle in D mode, speed maintained at 100km/h, heating activated at highest temperature for 30s, followed by 30s with AC off | Compressor voltage/current, front drive voltage/current |
| Low SOC (<30%) | Steady Cooling | Vehicle in D mode, speed maintained at 100km/h, cooling activated at lowest temperature for 30s, followed by 30s with AC off | Compressor voltage/current, front drive voltage/current |
| Low SOC (<30%) | Steady Heating | Vehicle in D mode, speed maintained at 100km/h, heating activated at highest temperature for 30s, followed by 30s with AC off | Compressor voltage/current, front drive voltage/current |
The test data reveal that voltage ripple in electric vehicle compressors is predominantly concentrated around 20kHz, with variations based on SOC and operational mode. For instance, under low SOC conditions during steady cooling, the voltage ripple peak-to-peak (Vpp) reached 13.80V, with a primary frequency component of 23.87kHz. When the air conditioning was deactivated, the ripple decreased to 6.79V. Similarly, in steady heating mode at low SOC, the Vpp was 10.85V at 20kHz, dropping to 6.73V post-deactivation. Current ripple followed analogous patterns, with peak values of 137.61A during cooling and 106.89A during heating, both at frequencies near 20kHz. These measurements highlight the significant impact of compressor operation on the electrical system of electric vehicles.
At the front drive end, voltage and current ripple were generally lower than at the compressor during active air conditioning but exhibited higher ripple currents after deactivation. For example, in low SOC cooling, the front drive voltage ripple was 8.21V at 19.99kHz, compared to the compressor’s 13.80V. Conversely, after turning off the air conditioning, the front drive current ripple was 14.64A, exceeding the compressor’s 4.16A. This suggests that while the compressor is a primary source of ripple, its effects propagate through the network, influencing other components in electric vehicles.
| SOC State | Operating Condition | Compressor Voltage Ripple (Vpp) and Dominant Frequency | Compressor Current Ripple (App) and Dominant Frequency | Front Drive Voltage Ripple (Vpp) and Dominant Frequency | Front Drive Current Ripple (App) and Dominant Frequency |
|---|---|---|---|---|---|
| Low SOC (<30%) | Steady Cooling | 14.20V, 23.87kHz | 137.61A, 23.88kHz | 8.22V, 19.99kHz | 93.36A, 1.07kHz |
| Low SOC (<30%) | Steady Heating | 11.10V, 20.00kHz | 106.89A, 19.99kHz | 7.66V, 19.99kHz | 85.79A, 1.10kHz |
| Medium SOC (40%-60%) | Steady Cooling | 13.51V, 23.85kHz | 182.16A, 23.85kHz | 7.21V, 19.99kHz | 80.62A, 1.10kHz |
| Medium SOC (40%-60%) | Steady Heating | 10.61V, 20.00kHz | 90.30A, 20.00kHz | 7.06V, 19.99kHz | 77.56A, 19.99kHz |
| High SOC (>80%) | Steady Cooling | 8.65V, 20.00kHz | 42.26A, 23.88kHz | 5.25V, 19.99kHz | 34.85A, 19.99kHz |
| High SOC (>80%) | Steady Heating | 12.97V, 19.99kHz | 130.05A, 19.99kHz | 10.22V, 19.99kHz | 104.33A, 19.99kHz |
To further understand the ripple mechanisms, I analyzed the relationship between ripple current and voltage using mathematical models. The equivalent series resistance (ESR) and capacitance (C) of components vary with frequency, influenced by factors like electrolyte properties and electrode structure. The ESR as a function of frequency can be expressed as:
$$ ESR(f, T_C) = \alpha \cdot f^{-\beta} + \delta \cdot T_C $$
where \( f \) is the frequency, \( T_C \) is the core temperature of the capacitor, and \( \alpha \), \( \beta \), and \( \delta \) are constants determined by the capacitor type. At low frequencies, ESR tends to be high due to slow ion migration in the electrolyte, decreasing as frequency rises until stabilizing at a critical point where electrode materials and parasitic inductance dominate.
The ripple voltage \( V_{cf} \) and ripple current \( i_{cf} \) are related through the capacitor’s impedance. At any frequency, the ratio of the RMS values of voltage and current fundamental components equals the magnitude of the capacitor’s complex impedance:
$$ V_{cf} = i_{cf} \cdot \sqrt{ESR^2 + \left( \frac{1}{2\pi f C} \right)^2} $$
From this, the reference capacitance value can be derived as:
$$ C = \frac{1}{2\pi f \sqrt{ \left( \frac{V_{cf}}{i_{cf}} \right)^2 – ESR^2 }} $$
These equations highlight that excessive ripple current can lead to significant ripple voltage, affecting sensitive electronics in electric vehicles. Inadequate input capacitance may render capacitors ineffective at high frequencies, as electrolytic capacitors exhibit inductive behavior, failing to filter out noise and harmonics.
Several factors contribute to compressor ripple in electric vehicles. First, switching frequency plays a crucial role; power devices like MOSFETs and IGBTs generate high-frequency ripple during rapid switching. Higher switching frequencies reduce current variations per cycle, thereby minimizing ripple voltage. If the power supply design in electric vehicles incorporates elevated switching frequencies, voltage ripple under load increases is mitigated. Second, the roles of inductance and capacitance are pivotal. Parasitic elements in high-voltage systems can cause high-frequency noise coupling. Increasing inductance values curbs current fluctuations, reducing ripple, while larger output capacitance smooths voltage swings. Selecting low-ESR capacitors, such as hybrid or polymer types, is essential, as standard aluminum electrolytic capacitors may not perform well in high-frequency ranges typical of electric vehicle applications.
Third, circuit design optimization is critical. Improving PCB layout and routing, along with adding decoupling capacitors at vias and traces, can diminish interference and enhance dynamic response. Feedforward control methods can attenuate low-frequency ripple components by predicting and compensating for system disturbances, accelerating response times and improving regulation quality. In the context of China’s electric vehicle industry, these strategies are vital for advancing compressor efficiency and overall system reliability.
In conclusion, my analysis of voltage ripple in electric vehicle air conditioning systems demonstrates that compressor-generated ripple primarily centers around 20kHz, with magnitudes influenced by SOC and operational mode. As the core of the air conditioning system, compressor efficiency directly affects cooling performance and energy consumption in electric vehicles. Voltage ripple induces unstable operation, elevating energy usage and reducing efficiency. By monitoring and controlling the phase of compressor bus voltage ripple, real-time voltage variations can be managed, ensuring stable and efficient compressor performance. This approach minimizes losses due to voltage fluctuations, contributing to energy savings and emission reductions in the rapidly evolving electric vehicle sector, particularly in China, where EV adoption is accelerating. The insights from this study underscore the importance of addressing electrical disturbances to enhance the competitiveness and sustainability of electric vehicles globally.
Future work should focus on implementing these optimization techniques in practical electric vehicle designs, conducting long-term reliability tests, and exploring advanced materials for capacitors and inductors to further suppress ripple. As the electric vehicle market expands, continuous innovation in component design and system integration will be key to overcoming challenges like voltage ripple, ultimately driving the evolution of more efficient and reliable electric vehicles.