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A well compensating voltage controller enables stable output voltages and reduces the influence of load changes and supply voltage variations.
Why are control loop response measurements important?
The quality of a control circuit determines the stability and dynamic response of the entire DC/DC converter. The control loop behavior must be measured and characterized to ensure the stability of voltage regulators and switched mode power supplies. The R&SRTx-K36 frequency response analysis, respectively the Bode plot option allows you to quickly determine the gain and phase margin of switched-mode power supplies or linear regulators. These measurements help determine the control loop stability.
Oscilloscopes as a tool for control loop response measurements
When testing and characterizing their power supply designs, engineers mainly rely on oscilloscopes. The R&SRTx-K36 frequency response analysis option provides a low-cost alternative to low frequency network analyzers or dedicated standalone frequency analyzers. The option allows for easy and quick analysis of low frequency response on the oscilloscope. Using the option, users can characterize the frequency response of a variety of electronics, including passive filters and amplifier circuits. The R&SRTx-K36 frequency response analysis option uses the oscilloscope’s built-in waveform generator to create stimulus signals ranging in frequency from 10 Hz to 25 MHz. Measuring the ratio of the DUT signal input and output at each test frequency, the oscilloscope plots gain logarithmically and phase linearly.
How can control loop response be measured?
Control loop response testing requires injecting an error signal over a band of frequencies into the feedback path of the control loop. To inject the error signal, a small resistor must be inserted into the feedback loop.
The 5 Ω injection resistor (shown in the figure below) is insignificant in comparison to the series impedance of R1 and R2. Some users choose to permanently design in this low-value injection resistor (Rinjection) for test purposes. An injection transformer, such as Picotest’s J2100A, isolates the AC distortion signal and eliminates any DC bias.
Why is it important to choose the correct injection point?
To measure the loop gain of a voltage feedback loop, the loop needs to be broken at a suitable point. A distortion signal is injected at this point and distributed in the loop circuit. Depending on the loop gain, the injected distortion signal will be amplified or attenuated and shifted in phase. For the R&SRTx-K36 option, the generator of the oscilloscope generates the distortion signal and the oscilloscope measures the transfer function of the loop. To ensure that the measured loop gain equals the real loop gain, a suitable point needs to be chosen.
Accurate control loop response characterization depends on good probing. Peak-to-peak amplitudes of both Vin and Vout can be very low at some test frequencies. These values would be buried either in the oscilloscope’s noise floor and/or in the switching noise of the DUT itself. This is why increasing the SNR of your measurements will significantly improve the dynamic range of your frequency response measurements. Ideally, you should use a low noise 1:1 passive probe that will reduce measurement noise and improve SNR of your measurement.
What do you get?
The curves displayed in the Bode plots represent the transmission function of your circuit and help verify the stability of your system. One graph (blue trace in screenshot) displays the amplitude behavior over the frequency range in dB, while the second plot (orange trace in screenshot) displays the phase characteristics over frequency (measured in degrees).
The world is getting more and more connected. Myriads of sensors and IoT applications factories and households, enabling optimal industrial operation and contributing to improvement of the social welfare.
Maximizing battery lifetime
Many of these products run on very small non-rechargeable batteries at low voltages and currents. Battery-powered devices can be easily installed anywhere and are small, robust and easy to use. High replacement costs and environmental concerns demand for long operating times. Battery lifetime is a key aspect for the design and selection of IoT devices. Depending on the application and use cases, absolute battery life requirements can range from tens of hours for wearables such as smart watches, to tens of years for smart meters and environmental sensors. What all these applications have in common is the need to maximize battery life.
IoT test challenges
In order to meet the application requirements, power consumption characteristics need to be optimized at the product design stage. This requires accurately characterizing the device’s power consumption in different operating modes, which is not an easy task. Modeling and dimensioning the energy consumption of an application at the design stage is of utmost importance considering the critical requirements for IoT applications: reduced cost, lifetime, improved customer experience and regulatory requirements.
Designing appropriate hardware and software is key for low-power devices, e.g. implementing optimal power consumption in active and deep sleep modes or short startup/shutdown phases. It needs to be considered that power consumption often has a high dynamic range with fast switching between operational modes in the tens or hundreds of mill amperes and sleep modes measured in microamperes. Power consumption also strongly depends on the use of power saving features, application behavior and interaction with the wireless network.
Device and application developers require very accurate power measurement solutions with a high dynamic range. Rohde & Schwarz offers modern solutions such as the R&SNGL200 power supply or the R&SNGM200 power supply series that are an easy and economical solution for these measurements and offer an outstanding resolution. Both instruments provide advanced features and meet the requirements for high-precision power consumption measuring capabilities.
The R&SNGM200 series even provides resolutions down to 5 μV/10 nA, allowing accurate measurements that easily match the requirements of today’s standards used in IoT devices.
The FastLog functionality
For in-depth analysis and traceable results, the measurement values can be logged. When opening the logging settings, you can choose the desired preferences. With a user-defined acquisition rate of up to 500 ksample/s, the FastLog functionality follows voltage/current variations with a resolution of up to two μs. It detects spikes that would be overseen by slower instruments.
The logged data can be stored on the power supply’s internal memory or on an external USB storage device. The data can then be transferred to an external PC via USB or LAN. For automated and long-term tests, Rohde & Schwarz provides a remote control software. Parameters like power consumption, current drain or battery capacity can be easily determined and analyzed. The tool also offers a graphical representation of logged data with zoom function.
If you aim for high-quality results, you may use specialty DC power supplies from Rohde & Schwarz that meet the requirements for high-precision power consumption measurements such as the R&SHM8143. They measure a wide dynamic range of current levels and are highly accurate even at extremely low voltage and current levels. Their linear design with minimum residual ripple and noise, and advanced remote monitoring features make the instruments an excellent choice for optimizing power consumption in IoT devices.
Power integrity is the assurance that power applied to a circuit or device is appropriate for the desired performance of the circuit or device.
Such sensitive electronic designs require modern test solutions. When measuring power rails, for instance, there are usually two common challenges: lower rail voltages and smaller tolerances. Industry dynamics are driving both a decrease in rail voltage values as well as tighter tolerances across a wide range of power rails. The graph shows, that making an accurate ripple measurement on a rail value of 1.2 V with 2 % tolerance, for example, is difficult to measure on all oscilloscopes.
So how should we set up an oscilloscope to get the best accuracy for power integrity measurements?
Tip 1: Adjust viewing characteristics
Waveform intensity: Default – 50 % à Adjusted to 90 %
Tip 2: Lower noise
Noise leads to a large measurement deviation. It can mask or hide anomalies or causes Measured Vpp to be much greater than the Actual Vpp is. Consequently, you should choose the signal path that has the lowest noise and use the most sensitive vertical scale. In order to do that, you need to use the smallest V/div setting.
Chose the right probe (attenuation, BW and connection): With a 1:1 attenuation probe such as the R&SRT-ZPR20 or the R&SRT-ZPR40 power rail probe you can benefit from a few advantages. These probes are designed specifically to measure small perturbations on power rails. They are active and single-ended, provide low noise, best in class offset compensation capability, good dynamic range and have a built-in DC meter. When coupled with such a 1:1 probe, oscilloscope demonstrates superior measurement quality.
Tip 3: Achieve sufficient offset
When using probes with built-in offset, (e.g. R&SRT-ZPR20 with ±60 V built-in offset) you can zoom in on a wide range of DC power rail standards.
Tip 4: Evaluate switching and EMI
In order to follow one of power integrity measurements top concerns, a frequency domain evaluation of coupling and switching is recommended. Adding frequency domain view enables users to quickly find and isolate coupled signals.
Tip 5: Accelerate measurement time
The update rate has an impact on speed of power integrity measurements: Fast update rates up to 1 MWFS/S show modulated signal on power rail. They let users test power rails more quickly. The graphic visualizes the impact of measurements, memory depth increases, and the use of an FFT on the update rate of the R&SRTO oscilloscopes (log scale).
Making accurate power integrity measurements continues to increase in importance, as rail voltages get lower and tolerance get tighter. Therefore, we suggest following the above-recommended tips.
The power delivery network distributes and delivers the DC power to all active components on the board. Disturbances on power rails can cause serious impairments in the performance of the used ICs and the overall system, so power integrity is a paramount goal in board design.
As rail voltages get smaller and tolerances get tighter, measurement noise makes it difficult to get accurate ripple and noise values. It can therefore be problematic to quickly determine if there are disturbances on the power rail. For instance, using a standard 500 MHz passive probe with a 10:1 attenuation results in additional measurement noise, causing overstated peak-to-peak voltage measurements and masking signal details as shown in the screenshot below.
There is a wide range of solutions to ensure proper power-up and power-down sequencing in your design. To address potential challenges, Rohde & Schwarz has developed a probe for accurate and quick power rail measurements. The R&SRT-ZPR20active power rail probe has a 1:1 attenuation ratio, very little noise and enough bandwidth to not attenuate critical signal content. The captured waveform includes higher frequency transients riding on the rail.
The R&SRTM3000 or the R&SRTA4000 oscilloscope are both powerful tools that help to efficiently and precisely analyze unwanted disturbances on your power rails and to identify their root cause. A combination of these low-noise oscilloscopes with the R&SRT-ZPR20 power rail probe allows for more accurate power rail measurements.
The most important benefits using such a combination can be summarized as follows:
The probe’s 1:1 attenuation provides minimal noise for a system noise of less than 500 μV (at 1 GHz bandwidth and 10 mV/div)
With ±60 V of built-in offset, users can center and zoom in a wide variety of DC rail voltage standards without worrying about how much built-in offset the scope has. The offset eliminates the need to use AC coupling or DC blocking capacitors, which impede the ability to see true DC values and drift
High-frequency transients and coupled signals are isolated. The probe’s rated bandwidth is 2 GHz. When used with an R&SRTA4000 or R&SRTM3000, overall bandwidth is set by the oscilloscope bandwidth
50 kΩ DC input impedance minimizes loading, so DC values remain accurate
An integrated 16-bit R&SProbeMeter provides a simultaneous five-digit readout of each power rail’s DC value
More detailled information about R&S power rail probes can be found here!
Modern electronic designs increasingly integrate more functionality into less space. At the same time, processor speeds, clock and data rates are rising while signal levels are decreasing. All these developments result in a growing need for testing at the component, board and system level. Rohde & Schwarz offers several solutions to address testing requirements when developing, verifying and optimizing electronic designs.
With a deep understanding of design and manufacturing challenges, Rohde & Schwarz, with its market-leading expertise, is an ideal partner to tackle all aspects of EMC analysis, signal integrity as well as power integrity.
These are of fundamental importance in digital design.
Passing EMC certification is a major milestone in the design process of any electronic product and a source of high risks and costs in the go-to-market strategy. Minimizing these risks and costs is crucial, which makes an early and consistent EMC test approach the key to success. For more information, see our earlier posts on EMI testing.
Signal integrity is becoming increasingly important due to higher data rates and space-optimized embedded designs. The transition from parallel to serial bus interfaces has increased data rates, with 5 Gbps to 10 Gbps being common in many designs. Such complex designs are a challenge for today’s electronic engineers and may require a significant amount of time for debugging.
Active components. Digital interfaces have become predominant in electronic designs. Increasing data rates and clock speed, as well as omnipresent wireless connectivity create a need for highly sophisticated testing and debugging solutions. Signal integrity measurements are the key in the field of high-speed digital designs. It also plays a pivotal role in RF and microwave designs. Rohde & Schwarz offers market-leading phase noise testers, spectrum analyzers and advanced oscilloscopes for precise jitter and phase noise characterization in the frequency and time domain. Besides, signal and spectrum analyzers with excellent spectral purity, dynamic range and a wide analysis bandwidth for measuring spurious emissions are provided.
Passive components. Higher signal frequencies and data rates require top quality signal transmission paths in modern designs, including PCB traces, connectors and cables. Many different influencing factors, such as impedance mismatch and reflections, insertion loss, propagation delay, intra/ inter-pair skew, etc., are decisive for the overall quality of analog and digital signals. In this case, network analyzers are required to reliably determine the signal integrity of passive components.
Power delivery: Everything starts with the right voltage source. The requirements for power supplies are low noise and ripple as well as accurate and stable output voltage in order to introduce as little disturbance as possible. You can count on performance power supplies from Rohde & Schwarz like the R&SHMP2000, R&SHMP4000 or R&SNGP800 series to deliver clean and stable power to your electronic design.
Clean and stable power rail voltages are the basis for proper performance of any electronic design. The continuous demand for higher performance, higher level of integration and lower power consumption, as well as the constant trend towards lower voltage levels, higher data rates and smaller, more compact product dimensions, challenge engineers to ensure extremely stable and clean voltage supply in their electronic designs.
Designing for best power integrity requires extremely sensitive and accurate measurement. Measuring ripple, noise and transients on today’s low voltage DC power rails challenges most oscilloscopes. With smaller rail voltages and 1% to 2% tolerances, instrument and probing noise make it hard to accurately measure specified tolerances. Adequate bandwidth is required to see harmonics of fast edges and higher frequency sources that can be coupled on power rails.
Rohde & Schwarz, however, offers advanced oscilloscopes and probes to verify and analyze the remaining ripple and noise of your power rails. Ripple, noise and load-step response measurements on integrated circuits such as CPUs, DDR memories and FPGAs require very low noise and broadband probing solutions that can measure in the single-digit millivolt range. Qualifying the power supply for sensitive analog receiver circuits means measuring very small disturbances at relatively high DC offset levels.
To sum up, thorough measurements are needed – especially when you want to ensure proper system functionality, even under worst conditions. More detailed information about R&S test solutions for digital designs as well as insights about the companies’ powerful tools for system-level validation and debug of digital designs can be found here.
Embedded designs are an integral part of today’s electronic systems comprising analog signals as well as signals from serial and parallel buses. When debugging such designs, a common challenge is to simultaneously capture enough content of both slow and fast signals with sufficient resolution between the sample points to zoom in and see signal details.
Besides, when analyzing the spectrum of a signal, the ability to look at longer periods of time is essential, because the frequency resolution depends on the amount of time that is available for analysis. More time means finer resolution.
High resolution, and therefore deep memory, is vital when trying to view fast and slow signals at the same time and correlate the signal content. Sample rate is another important characteristic for signal analysis. The higher the sample rate, the higher the maximum frequency that users can view. This ensures that no important signal details are missed, e.g. glitches spikes or other anomalies that can cause a malfunction of the design.
An oscilloscope with deep memory solves the described problem. Oscilloscopes from Rohde & Schwarz traditionally offer high memory depth as a standard. The different memory upgrade options offer an even greater advantage since users can capture an incremental number of segments at a specific depth. The table gives an overview of solutions from Rohde & Schwarz.
What about segmented memory?
Segmented memory limits the acquisition to relevant signal elements. During signal acquisition with segmented memory, the available memory is divided into smaller segments, each with a defined number of samples. The user defines the length of the segments based on the relevant parts of the signal, e.g. the packet length of a protocol-based message.
At the trigger point, the data of interest is stored in memory along with the trigger timestamp. Time periods without interesting activity are not acquired. As a result, users optimize utilization of the memory, fast sample rates can be maintained and much more relevant data than with single-shot acquisition can be recorded.
Segmented mode is particularly useful for capturing bursts of activity surrounded by long periods of dead time. Many serial buses and communications signals fit in this category.
Single shot versus segmented acquisition
What is Rohde & Schwarz history mode?
The history mode offers substantially deeper memory on embedded oscilloscopes. In history mode, a highly precise trigger timestamp permits precise time correlation of signal events. Users can scroll through past acquisitions and analyze the data using all oscilloscope tools, e.g. protocol decode and logic channels. Individually marked segments can be selected in the acquisition table for display. Alternatively, the history function can be used to automatically play back all segments.
The following table provides a competitive comparison. It turns out that oscilloscopes from Rohde & Schwarz often offer more memory than comparable instruments, which is why those instruments are ideal when debugging embedded designs.
Why does deep memory in an oscilloscope matter? In brief, deep memory ensures that long waveforms are captured in high resolution with all needed signal details thanks to a high sustained sample rate.
Acquisition memory depth, equals the number of samples that are stored with each acquisition. Memory depth, however, is specified in points (Mpoint) or samples (Msample).
What are the two key benefits of oscilloscopes with deep memory?
1. Capturing a longer period of time
Deep memory helps in instances where the cause and effect may be separated by a significant time period and plays a key role in viewing events that simply take longer to transpire.
You can determine acquisition time window using the following formula: Acquisition time window = memory depth / sample rate
2.Retaining maximum bandwidth while capturing more time
As your oscilloscope acquires more time, more memory will be used to retain the maximum sample rate possible. As the amount of time captured increases, your oscilloscope will run out of additional memory.
As a result, the oscilloscope begins reducing sample rate. Capturing twice as much time reduces the sample rate by a factor of two.
What is deep memory?
The oscilloscope’s memory depth is the maximum possible record length for one acquisition. Oscilloscopes with lower memory are forced to reduce sample rates sooner in order to capture more time.
Thus, they have reduced bandwidths at slower time base. This can lead to insufficient sample rates to accurately slow signals.
Deeper memory oscilloscopes, however, retain full bandwidth. This means the scope can maintain maximum sample rate as the amount of captured time increases.
A deep memory will provide more accurate and reliable measurements and users can be confident that no important signal events will be missed.
Besides, they benefit from viewing longer periods of time and quickly finding signal anomalies or important events.
The following example illustrates the importance of memory depth:
While the oscilloscope will capture 2 ms of time with 10 Msample memory and a sample rate of 5 Gsample/s, it will capture 40 ms of time with the same sample rate of 5 Gsample/s and 200 Msample memory.
What are benefits of maximum sample rates?
Typically, oscilloscopes are designed with a maximum sample rate to match the maximum analog bandwidth needed.
When the sample rate is reduced, an undesirable consequence is that the sample rate may not be sufficient to accurately reconstruct the signals. This may lead to aliasing.
What is the relationship between sample rate, record length and acquisition time?
Modern circuitries require different voltage and/or current levels in different operating states. For example, when simulating a startup sequence of an embedded system specialized voltage and current profiles synchronized across several channels are required.
What is special about an arbitrary waveform generator function?
R&S power supplies feature a free built-in arbitrary waveform generator. With this function, you can easily generate and customize your voltage and current levels over time as needed in your application.
You can either program a new pattern directly on the instrument, load a .cvs file that can conveniently be compiled, or you can program the points via SCPI. For each step of the pattern, you can set voltage, current, duration and interpolation. The various models have different ranges for programmable voltage, current, dwell time, number of repetitions and number of data points. The following table summarizes these specifications for the R&S power supply portfolio.
What are possible applications?
The arbitrary waveform feature allows you to simulate device behaviors. Often it can even replace basic standalone arbitrary waveform generators. Overall, the versatility of the arbitrary waveform generator makes a wide range of applications possible. Several basic and advanced examples are described below:
1. Square and rectangular waves
Square and rectangular waves are among the most basic patterns. They are described by switching the voltage and current between two fixed levels. Square waves can be used to test the durability of a DC motor or to emulate TTL signals.
A ramp changes the voltage or current linearly from one value to another. Building the ramp using the arbitrary function makes it possible to ramp-down a channel or to control the current or introduce disturbances during the ramp.
3. Sine waves
Sine waves follow the basic mathematical sin(x) function. The main use case of a sine wave on a power supply is to emulate oscillations, but it can also be employed to drive magnetic coils.
4. Sawtooth waves
Periodically repeated ramp functions result in a sawtooth or triangle pattern. The most common applications are vertical and horizontal deflection signals as they occur when rastering a surface.
5. Pulse or glitch
A pulse is a signal with a given amplitude for a short duration. If the duration is approaching 0, it is called a glitch. These signals can be employed to simulate circuit anomalies in digital designs.
The combination of basic waveforms and/or the arbitrary definition of shapes allows you to adapt the possibilities of the power supply to your specific need. In addition, on models with more than one channel, combinations across channels can be programmed. For example, this can be bit patterns or even slow I/Q data streams.
You can find more information about the built-in arbitrary waveform generator as well as about its applications in this AppCard !
Let’s learn more about the logging and fast logging functionality of R&SNGM and R&SNGL. The associated application program provides charting functionality for logged voltage, current and power values.
Standard logging records timestamps together with readings for voltage, current and power for each available channel. It is always global for all available channels of the power supply. The measurement interval can be set in the range between 0.1 second and 600 seconds. The start of the logging can be triggered either by an internal event or by an external trigger signal.
The sample rate and duration of standard logging can be specified in four modes:
Unlimited mode: When started, the logging runs until it is stopped. In this mode the interval (sample period) can be specified.
Count mode: When started, the logging collects the specified number of values and then stops. In this mode the interval (sample period) and the number of sampled values can be specified.
Duration mode: When started, the logging runs for the specified duration. In this mode the interval (sample period) and the duration of the logging can be specified.
Span: Logging starts at the specified date and time and runs for the specified duration. In this mode the start time, the interval (sample period) and the duration of the logging can be specified.
While R&SNGL power supplies offer the standard logging functionality, they do not provide the fast logging as R&SNGM does. The R&SNGM power supply series is a high-precision source and sink with high-speed voltage and current logging capability.
How does fast logging work on R&SNGM power supply?
It records voltage and current readings versus time, but without time stamps. Fast logging is always individual to each channel of the power supply. It can be configured, started and stopped in each channel independently. The data is collected in separate files. Like the standard logging, the fast logging can also be started by a trigger event configured locally in the menu. For fast logging, it is recommended to select a fix current measurement range if the maximum expected current is known. This ensures that logging data is continuously available.
For fast logging, a sample rate has to be selected out of an available set. The fast logging runs for the specified duration after it has started. Available sample rates for fast logging are 15, 30, 61, 122, 244, 488, 976, 1953, 3906, 7812, 15625, 31250, 62500, 125000, 250000 and 500000 values per second.
Remote control connection
R&SNGM or R&SNGL can be operated remotely, either via USB, LAN or GPIB connection between the controlling PC and the power supply. In remote control mode, the logging data must be collected via the remote control interface every time the system reports new data to be available. The interface used for the remote connection must support the resulting data rate.
There are some measurement requirements to be mindful of when using remote control functionality, since the fast logging function of the DC power supply R&SNGM requires a certain minimum data rate, depending on the sample rate of the logging function. The data rate of GPIB is sufficient only for the lower sample rates of the fast logging function. Therefore, GPIB is not recommended as connection to the R&SNGM for this application.
The USB interface in the R&SNGM and R&SNGL supports two different USB classes. The “CDC” class emulates a serial interface via USB-to-serial converter and has the advantage of compatibility with older remote control systems. Since the data rate of the “CDC” class is not sufficient for fast logging, the “TMC” class needs to be used.
Save logging data locally to files, and display them in charts
Standard logging data is originally stored locally, either on internal memory or to a USB stick connected to the R&SNGL or R&SNGM. The location of the log file must be selected locally in the menu. As standard logging data is primarily stored on the power supply, display and storing of standard logging data is only possible with a power supply connected. Standard logging files contain voltage, current and power readings for one or two channels. User can choose specific power supply channel as a data source and display the data in a form of a diagram. While the respective voltage and current data can be displayed in one diagram, power data is always displayed in a separate diagram. Before the diagrams can be created, the data has to be transferred from the power supply to the controlling PC over the remote control interface.
Fast logging data is stored in floating-point raw format. If started manually, it is stored to a USB memory stick connected to the R&SNGM, which must support the resulting data rate. During fast logging, data is transferred from the R&SNGM to the controlling PC in real time and saved every 0.5 seconds. Each logging operation generates about two data files per second. The file size depends largely on the sample rate of the fast logging. The file name consists of date and time, sample rate, channel number and a sequential number. The log data of the selected file or of the complete fast log to which the selected file belongs, is displayed, depending on the settings. After termination of the logging, the data can be exported resp. converted offline to a character separated ASCII format.
You can find more information about logging tool on R&SNGM an R&SNGL power supplies in this AppNote!
Rechargeable batteries used in battery-powered devices and vehicles need to be stimulated, measured and tested. Overcharging and deep discharging reduce the lifetime of rechargeable batteries.
Defects could lead to overheating of a battery and even cause a fire.
Larger batteries are typically built by connecting multiple cells in series and parallel. Since the same charge and discharge current flows through all cells, individual differences in battery capacity, self-discharging, etc. would lead to differing states of charge over time and consequently limit the capacity and lifetime of the battery.
The need of BMS
So-called battery management systems play a crucial role in battery life and fail safety. Such systems actively monitor, control and manage various battery cell parameters. Among others, a BMS is responsible for the following tasks:
Determining the stage of charge of each cell
Supervising the integrity and derating of each cell (state of health)
Detecting faults and exceptional conditions and preventing hazards such as overheating and fire
Balancing the stage of charge between the cells, which can be implemented in a passive way by selectively loading the cells
Thermal and energy management
Schematic of a battery pack with BMS
Testing of BMSs with R&S solutions
Because of their great importance, BMSs need to be tested thoroughly. Such tests have to simulate all conditions that could possibly occur in operation.
Rohde & Schwarz offers two specialty power supplies that are tailored to specific applications and have unique capabilities such as emulating the characteristics of a battery. The versatile R&SNGL200 and R&SNGM200 DC power supplies are equipped with all functions needed to test and validate BMSs. Because of their advantageous capability to simulate battery cells, they can replace far more expensive dedicated battery simulators.
Both solutions support two-quadrant operation as source and sink. Source currents up to 6 A and sink currents up to 3 A are possible. All outputs are fully isolated against ground. They can be connected in series to emulate battery packs on a single cell level up to a maximum voltage of 250 V against ground. The adjustable output impedance can be set between –50 mΩ and 100 Ω. Current and voltage measurements at the power supply output deliver high-resolution values. Their two channels per unit and compact form factor allow flexible configuration and space-saving setups for testing a BMS. A 19" rackmount kit and backplane connections provide easy and rugged integration into racks.
Battery simulation option, measurement accuracy & fast logging
All functions can be fully remote controlled with command processing times of less than 6 ms. In addition, the R&SNGM200 power supply series features an optional battery simulation mode that allows realistic simulation of different predefined or user-defined cell types. Opencircuit voltage and internal resistance depending on the state of charge are defined for each cell type in an ASCII file.
These features allow the cell properties to be simulated and varied over time with high precision and high time resolution. For small and medium-sized batteries, the cell current can be drawn directly out of the power supplies. For larger batteries like those used in automotive applications, it is not necessary for the charging and discharging currents to physically flow for the BMS tests. Current measurement results, e.g. voltages across shunt resistors, are simulated to the BMS, and the power supplies establish the cell voltages and deliver the balancing currents.
Beyond the battery simulation option, the R&SNGM200 power supply series provides enhanced measurement accuracy and fast logging of current and voltage up to a sample rate of 500 000 values per second. The battery simulation option can run profiles stored in ASCII files; these profiles describe the open-circuit voltage and internal resistance versus state of charge. Profiles for common battery types are available in the power supply. The fast logging function can capture narrow spikes and glitches in current and voltage for troubleshooting purposes.