OwnTech » OwnPower » single-phase

h1. Measurement Block Theory

The single-phase converter uses an isolated measurement chain with an external 12-bit ADC. This is a low-cost solution to safely get many measurements from the board to the micro-controller with high-accuracy. 

There are a total of 5 measurements embedded on the power converter:

*  *Low-side Voltage*

*  *Low-side current*

*  *High-side Voltage*

*  *High-side current*

*  *Temperature*

The different measurement types are described in the subsections below

h2. Voltage measurement

The voltage measurements use resistor bridges which are calculated according to the voltage being measured.

A capacitor is connected to the output of the resistor bridge to stabilize the measurement. 

A buffer is also connected to the output of the resistor bridge to send the signal to the external ADC. 

h2. Current measurement

The current measurements use shunt resistors to measure the current flowing through the converter. 

The voltage drop on these shunt resistors is very low and noisy. 

To enhance the quality of the measurement, an RC filter and a non-inverter operational amplifier are connected to the output of the shunt resistors. 

Since the converter is bi-directional in current, an offset is needed to create a virtual zero. 

This offset is done using the same voltage reference used by the ADC (see more details below).

h2. Temperature measurement

The temperature measurement is done by a dedicated components which is assembled near the power converters. 

This component measures the temperature of the heat-sink. 

h2. External Analog-to-Digital Converter

An external ADC is used to sample the measurements of the board. 

This allows for a generic approach to the measurement chain and a high-resolution in the measurements. 

To avoid thermal drift, an external voltage reference is connected to the ADC.

The ADC sends its measurements through a SPI interface.  

h2. Isolation of the measurements

The micro-controller block has a dedicated ground. This isolation should guarantee the safety of the user and any sensitive equipment such as computers which are connected to the power converter. It is important to note that no test has yet guaranteed the safety level of this isolation and users should take extra precautions to protect themselves and their equipment.

The external ADC All the measurements are isolated via a dedicated SPI component.