HIOKI’s all new High Voltage Divider VT1005 is an important addition to the HIOKI power measurement solutions. In combination with one of the HIOKI power analyzers, the VT1005 enables to accurately measure power up to 5kV. Especially for high voltage and high frequency applications with SiC and GaN semiconductors, the VT1005 realizes a huge improvement in accuracy over currently available solutions. Additionally, the for loss measurement of HV coils and transformers the new VT1005 is the perfect choice because of its 4MHz bandwidth.
With the ongoing electrification of our society there is a rapidly growing need for more electrical power. One way to meet this need is to increase the system voltage. Obvious applications are the ultra-high-speed chargers for EV’s, all kind of power converters and solid-state transformers. The aim is to increase the flexibility and reduce the losses of the power grid. Power measurement instruments like for instance the HIOKI PW8001 Power Analyzer can measure power up to a voltage of 1500Vdc. The VT1005 High Voltage Divider is the solution for accurate voltage and power measurements from 1500V up to 5kVrms.
Outstanding High Noise Resistivity
The VT1005 is highly resistant to both common-mode and high-frequency noise, allowing it to measure voltage accurately even in noisy environments. Since conversion devices like inverters are sources of noise, noise resistivity is very important in power efficiency evaluation.
SiC and even more GaN power devices are characterized by fast voltage rising and falling response, and their output waveforms contain numerous high-frequency components. When we compare the output voltage of the VT1005 with another voltage divider on the market, the VT1005 shows no ringing effect whereas the other HV divider does. It is clear that this ringing effect has a negative impact on the accuracy of the voltage and power measurement.
Frequency Flatness is essential
To further increase the efficiency of power systems, SiC and GaN semiconductors are becoming popular switching devices. The switching frequency of SiC semiconductors is 50kHz or higher, and GaN can even go up to 1MHz. This makes it hard to accurately measure power efficiency because accuracy must be guaranteed over a broad frequency spectrum from DC up to 1MHz or even more. To realize such accurate power measurement, HIOKI power measurement systems have excellent frequency flatness, which is essential to realize constant measurement accuracy.
For example, to measure an efficiency improvement of 0.01%, it is necessary to have a gain accuracy of 0.1% and the phase error must be within 0.1°.
The above graphs show the gain and phase error for three individual VT1005 and another 3-phase high voltage divider available on the market. It is especially remarkable that the three solid lines of the VT1005 are almost identical and that the three dotted lines of the other voltage divider are much more divergent, indicating that the accuracy is lower. Furthermore, the gain and phase error at higher frequencies are greater with this voltage divider, which makes it unsuitable for applications in which SiC or GaN semiconductors are used.
In the HIOKI solution, both the VT1005 High Voltage Divider and the current sensors are designed and produced by one source, and likewise the power analyzers. All instruments are therefore optimized to be combined and offer outstanding performance both in gain and phase accuracy over the entire frequency range when the phase shift correction function is activated.
Wireless Power Transfer System (WPT)
WPT efficiency measurement is an application that requires accurate high voltage measurement. The voltage output tends to be higher, up to 3kV, because transmitting power at a higher voltage can reduce power losses in transmission. Therefore, the power efficiency measurement requires a high voltage measurement. Since WPT transfers power through coils, the transmit/receive part has a very low power factor. When the power factor is low, the phase error greatly affects the measured value, so power measurement with a low phase error is essential.
The VT1005’s measurement band ranging from DC to 4 MHz allows to measure voltage from DC to high frequencies. In addition, the excellent flatness of the amplitude and phase characteristics in the measurement band enable highly accurate power measurement and thus accurate evaluation of power efficiency.
Loss Measurement of HF reactors and Transformers
Both the noise resistance and the gain and phase accuracy at higher frequencies make the combination of the VT1005 High Voltage Divider, PW8001 Power Analyzer and CT6904A Current Sensor the ultimate solution to measure loss of high voltage, high frequency reactors and transformers used in inverter drives and power converters like for instance onboard chargers for EV’s. With this setup accurate loss measurements can be guaranteed even at a frequency of 300 kHz.
In the light of increasing use of SiC and GaN semi-conductors, high frequency and high voltage applications are on the rise. These require highly accurate measurement solutions like the VT1005 with HIOKI power analyzers in order to proof even small efficiency gains.
