首頁  >  產業/解決方案  >  新能源發電和電力電子  >  Measurement of power conversion efficiency of photovoltaic power generation system

Measurement of power conversion efficiency of photovoltaic power generation system

Measurement of power conversion efficiency of photovoltaic power generation system

Overview

In photovoltaic power generation systems, power conditioning systems (PCSs) and charge-discharge controllers are used to convert direct current output from solar panels into usable alternating current. The parameters that indicate the performance of a power generation system include actual amount of generated power and conversion efficiency.

The conversion efficiency of commercial solar panels ranges from 10% to 20%. Minimizing the loss when converting the solar panel output to AC leads to higher efficiency of the entire power generation system.

In recent years, PCSs for storage batteries and hybrid PCSs that can control storage batteries have also been introduced to the market for residential photovoltaic power generation systems, and a power generation system linked to storage batteries has become the mainstream type.

The conversion efficiency of PCS ranges from 95% to 98%. In order to improve the efficiency by 0.1%, evaluation using a precision power analyzer is required.

Overview

Configuration with a hybrid PCS that controls storage batteries

Challenges / Demands

Measurement methods for conversion efficiency of PCSs are specified in IEC 61683, EN 50530, JIS C 8961 and other standards. Not only the maximum efficiency but also Euro efficiency*1 and CEC efficiency*2, which are close to the efficiency in actual use conditions, need to be measured. Euro/CEC efficiency is determined from efficiencies at different load levels ranging from light to rated load that are weighted according to the load factor.

Measurement of PCS conversion efficiency

lHigh-precision measurement of power conversion efficiency from DC and AC voltages/ currents before and after PCS
lSafe and accurate measurement of high voltage and large current

Measurement of MPPT control*3

lAccurate measurement of voltage, current and power peak values which are important in MPPT control

Measurement of storage battery charge and discharge

lCharging/Discharging voltage, current, power, integrated current, and power calculation
lAccurate measurement required to achieve higher efficiency
lChecking a number of parameters, including total power over a period of time

Measurement of PCS output power quality

lVoltage and current measurement and power calculation when energy is sold and bought in power grid
lMeasurement of power quality (output, frequency, distortion, etc.)

 

*1 Euro efficiency (Euro-eta, partial load efficiency): Efficiency calculated by weighting conversion efficiencies at different load factors (based on European climate patterns) and adding them together. Euro efficiency is said to a conversion efficiency close to that under actual operating conditions.

*2 California Energy Commission (CEC) efficiency: Energy efficiency regulations established by the California Energy Commission, USA. Products distributed in California must comply with these regulations.

*3 Maximum Power Point Tracking (MPPT) control: A function incorporated in PCSs and other devices to track and control the combination of voltage and current to maximize the PV power at different solar radiation levels. MPPT control is mainly used in large-scale systems.

Solution / Proposal

YOKOGAWA's WT5000 and WT1800E provide optimal measurement solutions for measuring power conversion efficiency of photovoltaic  power generation systems.

nSimultaneous measurement of power parameters required for efficiency measurement

Since the WT5000 has a maximum of 7 inputs and the WT1800E has 6 inputs, a single WT5000 or a single WT1800E can measure input/output, voltage, current, power, frequency, and efficiency of a PCS and display the measurements on the screen. The WT5000 and WT1800E can measure not only the maximum conversion efficiency but also Euro efficiency and CEC efficiency.

nTrend graph display of power and efficiency

Fluctuations in power or efficiency are displayed as numerical values or on a trend graph to allow users to understand the fluctuations intuitively.

nLarge current measurement up to 2000 A

Use of an optional external current sensor allows measurement of much higher currents up to 2000 A.

nIEC harmonic measurement

Harmonics generated by a PCS can be measured according to IEC standards.

nEvaluation of MPPT control

The voltage peak value, current peak value, and maximum instantaneous power value (+ side, - side, respectively) as well as voltage, current, and power values are useful in evaluating MPPT control.

nEvaluation of battery charging/discharging characteristics

In the evaluation of battery charging/discharging characteristics, the integration function is used to calculate each power amount  from the instantaneous positive and negative power values.

Solution / Proposal

 

WT5000 example of numeric display

WT5000 example of numeric display

Urms1/Irms1/P1 : Solar cell module output

Urms2/Irms2/P2 : Boost converter output

Urms3/Irms3/P3/λ3/fU3/Idc3/Uthd3

                         : Inverter output and power quality

η1 : Boost converter efficiency

η2 : Inverter efficiency

η3 : Overall PCS efficiency

WT5000 example of trend display of efficiency η1/η2/η3

WT5000 example of trend display of efficiency η1/η2/η3

 

WT5000 simultaneous measurement of seven channels

WT5000 simultaneous measurement of seven channels