Overcome High-Voltage Measurement Challenges in Power Electronics

As global industries like EVs, renewable energy, aerospace, and industrial automation transition toward electrification and decarbonization, their R&D and production teams require better precision in their high-voltage measurements. Power systems in these industries often operate at hundreds to thousands of volts. The resulting high voltages can arc and even penetrate materials typically considered nonconductive. Along with these hazards, accurate capture of signals presents another set of difficulties related to resolution, response time, and noise rejection.

To address these issues and measure high-voltage points effectively there are two key methods—single-ended and differential measurements. In this application note we examine their principles, advantages, and the specially-developed Yokogawa solutions that support accurate and precise high-voltage measurements.
 

High-Voltage Measurement Challenges

Most standard data acquisition systems and oscilloscopes use non-isolated, single-ended inputs (i.e., the instrument ground is expected to be the same as the measurement ground). While this is sufficient for most low-voltage signals, it becomes problematic in high-voltage applications where improper grounding can introduce errors, create ground loops, and even damage the instrument or device under test. Additionally, high-voltage signals often contain fast transients and noise that can distort measurements if the instrument lacks proper isolation or rejection capabilities. To overcome these challenges, measurement techniques such as differential probing, signal conditioning, and single-ended isolated inputs are used.
 

Differential Measurement Principles

Differential measurements capture the voltage difference between two points and eliminate the need for a common ground reference. This makes them ideal for high-voltage applications where floating or inconsistent grounds and common-mode voltage can distort results. They also enhance safety through the prevention of ground loops and accidental short circuits and reduce the risk of equipment damage or hazardous conditions.

Along with improved safety, differential measurements enhance signal clarity and accuracy by eliminating the common ground offset between both leads. This ground offset, defined as the voltage difference between the instrument ground and the measurement ground, not typically measured, can reach hundreds or even thousands of volts, and depending on the application may fluctuate dynamically.

Common mode rejection ratio (CMRR) is a key specification in differential measurement systems that indicates their ability to reject common-mode signals. It is typically expressed in decibels (dB) and quantifies how effectively the system suppresses unwanted interference while it accurately measures the differential signal. For example, an instrument probe with 80dB CMRR would reject and reduce 100V common mode noise to 1mV of measurement error. Common mode voltage exists in all high-voltage systems such as inverters, power converters, motors, transformers, and busbars.
 

How to Conduct Differential Measurements

A differential measurement requires a differential front end, which can be implemented as a direct input into an isolated differential instrument, a signal conditioning front end, or a differential probe. These approaches create an electrical isolation barrier that rejects common mode voltage prior to digitization.
 

Figure 1. Comparison of differential measurement techniques
 

Differential probes enable single-ended instruments (like oscilloscopes) to measure floating or high-voltage signals safely. These probes measure the voltage difference between their two inputs, convert and attenuate it into a single-ended signal, and reject common-mode noise.
 

Figure 2. Circuitry of differential probe with standard oscilloscope
 

Single-Ended Isolated Measurement Principles

Single-ended isolated measurements provide isolation from ground but differ from differential isolated measurements in how they handle common-mode signals. While differential isolated measurements capture the voltage difference between two floating inputs, single-ended isolated measurements reference a single input to an isolated ground. This makes single-ended isolated measurements a practical and cost-effective choice to eliminate safety concerns, though they are more susceptible to common-mode interference.
 

Figure 3. Circuitry of single-ended isolated input
 

Single-ended isolation is commonly used to measure voltages from power supplies, sensors, or circuits where the signal is referenced to a stable floating ground, rather than applications that require high common-mode rejection.
 

How to Make Single-Ended Isolated Measurements

Single-ended isolated measurements are performed using instruments with electrically isolated inputs. These instruments capture high-voltage signals by maintaining separation between the measurement system’s ground and the circuit under test. Like differential isolation, electrically isolated instruments ensure the measurement ground remains electrically separated from the instrument ground to reduce the risk of equipment damage and ensure user safety.
 

High-Voltage Measurement Considerations

To select the best method for high-voltage measurements, take into account the following:

Voltage Rating and Probe Selection 

A measurement system must be able to handle the maximum voltage in the system under test. Select a probe or isolation method that meets the required voltage rating to avoid damage and ensure accuracy.

Bandwidth and Signal Integrity

The ability to capture high-frequency signals is important, especially in switching applications. Insufficient bandwidth can distort the signal and excessive bandwidth may amplify noise and reduce signal clarity.

Common-Mode Rejection

Ensure that external noise or interference (common to both measurement leads) does not affect the accuracy of the measurement.

Lead Placement and Shielding

For more reliable measurements, proper placement of leads and the use of shielding reduces electromagnetic interference (EMI) and noise pickup.

Complexity

Differential systems often require more specialized probes and setup, which makes them more complex. Single-ended isolated systems tend to be simpler and easier to implement.

Versatility

Single-ended isolated systems are generally more versatile as they can be used in a wide range of applications without the need for specialized differential probes.

Cost

Some measurement methods, especially differential, require specialized probes that make them more expensive. In contrast, single-ended isolated measurements are more cost-effective for many applications.

Figure 4. Measurement considerations
 

Examples of High-Voltage Measurement Challenges

Motor Drives and Inverters

Used in industrial automation, electric vehicles, and renewable energy systems, these high-power systems operate at voltages ranging from hundreds to thousands of volts. Accurate high-voltage measurements, achieved through differential probes or isolated signal inputs, are essential to optimize efficiency, minimize losses, and ensure proper operation of power conversion systems.

On-Board Chargers and DC Fast Charging Systems

EV charging infrastructure operates at voltages up to 800V DC and require precise voltage monitoring for safe and efficient charging. Isolated signal conditioning circuits scale high-voltage DC signals for compatibility with data acquisition and control systems to enable performance analysis, fault detection, and regulatory compliance.

High-Voltage Batteries

Lithium-ion battery packs in EVs, grid storage, and aerospace applications often exceed 1000V, which makes isolated voltage measurement critical to prevent ground loops and ensure accurate readings. Signal conditioners scale down these voltages for integration into battery management systems (BMS) or test setups for safety validation and improved efficiency.

Power Supplies and Converters

Switch-mode power supplies (SMPS), DC-DC converters, and high-voltage AC-DC converters require precise voltage measurements for performance verification. Due to high-frequency transients and noise, differential measurements or isolated probes are necessary to accurately capture waveforms and ensure compatibility with standard measurement equipment.

Aerospace and Avionics Electrical Systems

Aircraft and spacecraft operate at significantly higher voltages than typical automotive or industrial applications and rely on specialized isolated sensors for safe and accurate measurements. In more-electric aircraft (MEA) and hybrid-electric propulsion systems, high-voltage bus monitoring is essential to improve reliability and efficiency.
 

The Best High-Voltage Measurement Instruments

Developed to ensure precise and accurate high-voltage measurements, Yokogawa has an extensive range of solutions that include isolated instruments, high-voltage differential probes, and signal conditioners, for safe and reliable measurements each and every time.

Oscilloscopes

When paired with differential probes, our DLM series of oscilloscopes enable accurate high-voltage measurements through the conversion of floating or high-potential signals into a single-ended format. The differential probes integrate seamlessly with the DLM series and feature auto-recognition for easy setup that also maintains compatibility with standard BNC-type interfaces from other manufacturers.

ScopeCorders

For applications that benefit from isolated direct inputs, Yokogawa’s ScopeCorders provide isolated single-ended measurement inputs that allow connections via passive probes or leads to eliminate the need for costly high-voltage probes and simplify measurement setup.

Data Acquisition Systems

For high channel counts and PC-based automation, Yokogawa DAQ products offer channel-to-channel, module-to-module, and channel-to-ground isolation.

Power Analyzers

The WT series of power analyzers from Yokogawa offer single-ended isolated inputs capable of direct measurements up to 1000V without the need for external probes. This allows for straightforward, high-accuracy voltage, current, and power measurements in power applications, reduces complexity, and ensures measurement integrity.
 

Figure 5. Comparison of isolated measurement methods
 

Proper high-voltage measurements are essential for safety, efficiency, and performance in electrification and power applications. Whether differential or single-ended isolated, employing the right measurement approach with the right instrument enables accurate and safe testing of advanced high-power systems. Yokogawa oscilloscopes, power analyzers, ScopeCorders, and data acquisition systems provide precise, accurate, and reliable high-voltage measurement solutions that meet the needs of the most demanding industries and applications. Learn more about high-voltage measurement solutions and contact your local Yokogawa representative.