Instrumentation for Resolver Design in Electric Personal Mobility Devices (PMD)s

Introduction

Resolvers are rotary angle sensors often used and are particularly favored in HEV and EV applications due to their high environmental resistance. Rotational angle measurement is essential for motor operation, making resolvers crucial measurement tools, especially in the pursuit of maximizing efficiency.
However, designing systems with resolvers can be challenging due to minor inconveniences and conditional changes. During the prototype phase, resolvers require an external excitation power supply, including the ability to introduce intentional waveform distortions for testing purposes. As development progresses, the excitation power supply is moved to a printed circuit board (PCB), and then the focus of testing shifts to the resolver signal and various physical quantity measurements. This requires instrument functionality that cannot be handled only by a resolverspecific angle measuring instrument.
Additionally, during debugging, synchronization of all measurements is often necessary. Manual synchronization is extremely difficult and fails to maintain high accuracy. However, using the FG420 and the DL950 in resolver development facilitates the creation of a flexible measurement environment from initial prototyping to actual usage conditions.

Challenges

One challenge in the early stages of resolver development is obtaining an excitation power supply. Unlike a typical DC power supply on a PCB, an excitation power supply is preferred to generate parametrically variable waveforms during prototyping.
In measurement, Sin-phase, Cos-phase, and excitation signals of a driven resolver are obtained and converted into angular values. Since these conversions involve complex calculation formulas, analysis is typically post processed by PC software or by spreadsheet rather than with real-time instrumentation.
As an alternative solution, resolver-specific angle measuring instruments equipped with power supplies are available. However, they are extremely expensive and unsuitable for providing additional synchronized measurements, resulting in some inconveniences during the development phase.

Solutions with the DL950 and the FG420

• Excitation Power Supply with Various Waveform Generation
• Real-Time Math Computation Function
• Multi-Channel Synchronized Measurements of Various Physical Quantities
• Avoiding Redundant Data when using Multiple Sample Rates
• Combined Measurement with Motor Inverters
• High Noise Resistance Specifications that Anticipate Harsh Environments
• Multi-Instrument Integrated Measurement with IS8000

Explanations of Solutions with the DL950 and the FG420

1. Excitation Power Supply with Various Waveform Generation

The FG420 is a function generator with various sweep and modulation capabilities, enabling output up to 20 Vp-p and wide-band frequencies from 0.01 μHz to 30 MHz.
Capable of outputting arbitrary waveforms created from captured data as well as parametrically variable waveforms, the FG420 allows for experimental isolation of specific conditions for the resolver excitation power supply.
If the voltage amplitude is insufficient, it can be amplified using a high-speed bipolar power supply.

Figure 1. Example of parametrically variable waveforms

2. Real-Time Math Computation Function

The DL950 /G3 Option is a function that displays math formulas, in real-time, as waveforms in conjunction with measured waveforms during high-speed sampling.
This function eliminates the need for waveform post-processing, enabling real-time visual observations. In situations such as prototyping in which anomalies occur frequently, the realtime math computation function significantly reduces the feedback and decision-making cycle, improving the efficiency of debugging.
Furthermore, real-time math includes resolver measurement as one of the computation types. By setting an appropriate multiplication rate and filter to the excitation signal, Sin-phase and Cos-phase signals, math computation for the angle measurement values will be performed and displayed as waveforms. With these functions, the DL950 delivers an intuitive resolver development environment.

Figure 2. Example of resolver measurement with the DL950

3. Multi-Channel Synchronized Measurement of Various Physical Quantities

During various development phases, it’s necessary to measure additional signals besides the resolver signals e.g. circuit voltage, current, coil temperature of power supply filter circuit etc.
Ideally, a single instrument should cover most of the additional measurement elements occurring in prototyping phases. In addition to voltage and current, the DL950 can handle a wide range of physical quantities including temperature, distortion, acceleration, and frequency. In addition, isolation between each channel and ground (except for some modules) minimizes the need for additional probes or multiple single-ended measurements. During design where many risks and unknowns still exist, the DL950 can make significant contributions.

Figure 3. DL950 side view and List of modules

4. Avoiding Redundant Data when using Multiple Sample Rates

When acquiring multiple physical quantities simultaneously, the data amount of slower signals such as a temperature can increase significantly. This happens because the sample points of the slower module will be duplicated to match the module operating at the fastest sample rate, generating the data equivalent to a multiplication of the fastest sampling data by all channels’ data.
However, the DL950 has a multi-sample rate capability that suppresses data when slower sampling modules are inserted, improving storage, transfer rate, and the required amount of memory significantly.
This function is also effective for CSV output. Saving only the actual sampled data minimizes the amount of data to be stored or transferred.

Figure 4. Benefits of multi-sampling

5. Combined Measurement with Motor Inverters

The process of developing an in-house resolver requires testing in combination with a motor inverter, and synchronized measurement of multiple signals at this phase. The DL950 is uniquely qualified to conduct these evaluations.
For example, real-time math can compute both mechanical and electric angle of a motor with resolver. Furthermore, all the details described in 3 apply to motor inverter testing, which means that with probe sensors, engineers can simultaneously observe resolver signals, three-phase voltage and current, motor speed and torque.
Extensive analysis functions such as the Power Analysis Option (/G05) enables observation of power values as waveforms, and the Motor Analysis Option (/MT1) performs synchronized analysis of dq-axis current/voltage of a threephase motor.

Figure 5. Example of motor/inverter connection

6. High Noise Resistance Specifications that Anticipate Harsh Environments

Devices measured alongside a resolver, particularly inverters, generate significant electrical noise, which can greatly impact measuring instruments. Therefore, it is crucial that measuring instruments used in these applications are noise-resistant by design and can withstand harsh measuring environments.
One indicator of noise resistance is the Common Mode Rejection Ratio (CMRR). This specifies how effectively common mode noise—which causes the measurement signal's reference (insulated from ground contact) to sway and produce false results—is rejected. While the CMRR of the DL950 is specified for each module at 50/60 Hz, higherfrequency CMRR is also important when measuring highfrequency switching devices like inverters.
The DL950 is equipped with robust noise protection, including on the high-frequency side, enabling it to accurately measure high-side gate signals of inverters operating at high frequencies. This results in superior waveform reproducibility compared to products from other companies.

7. Integrated Measurement with the IS8000

The IS8000 software connects Yokogawa instruments, such as the WT5000 and DL950, and consolidates their data on a PC, enabling real-time synchronous measurement on the same screen. It can be combined with high-speed cameras (e.g., from Photron Ltd.), facilitating various synchronous measurements with high accuracy that were previously challenging.

Figure 6. IS8000 Image

In resolver development, the ability to synchronize with high-speed cameras is a significant advantage. For instance, during early prototyping, measuring angles with an analog instrument like a protractor can be difficult to synchronize at high speed. However, using the DL950, high-speed camera, and IS8000, these measurements can be synchronized seamlessly.
A major benefit of this configuration is that it does not require new components, even when measuring under actual operating conditions close to the final phase of resolver development. While the primary focus is on motor analysis, the combination of a high-speed camera and the DL950’s rich motor analysis functions works very effectively. This setup enables sophisticated debugging by allowing simultaneous visual monitoring of high-speed rotating parts.
Although not in real-time, the measured results of thermal cameras and higher-speed oscilloscopes (such as the DLM series) can also be synchronized. These options transform root cause analysis from requiring complex custom development to simple software operation.