Implementing flexible tariff management in multi-rate electricity meters

Electricity companies use time-of-use pricing to encourage people to save electricity during peak usage periods. These different price periods are called rate periods, and this method of billing is called flexible rate management. This meter reference design uses the MAXQ3120 microcontroller to meet the requirements of a multi-rate meter and even provide more flexible power monitoring capabilities.

The only way for electric companies to encourage people to save electricity during peak usage periods is to use time-of-use pricing. Specifically, it means raising the price during peak usage periods and reducing the price during low usage periods. These different price periods are called rate periods, and this method of billing is called flexible rate management.

Multi-rate meters are very important for achieving flexible rate management. In fact, the purpose of using multi-rate meters is to track the power consumption in different rate periods and maintain multiple energy accumulators, each with its own register. Therefore, multi-rate meters are the best means for power companies to implement time-of-use electricity prices. Meters that can support time-of-use electricity prices differ from traditional meters in the following aspects:

Multirate meters must contain an accurate calendar clock to know when to stop accumulating one rate register and start accumulating another.

Simple mechanical counters simply do not meet the display requirements of multirate meters. Some electronic display is needed that can independently display the contents of each rate register.

Reading a single usage number from the meter is no longer enough. In a single-rate meter, the previous cumulative reading is subtracted from the current reading to get the total amount of electricity used in the most recent period. Multirate meters monitor multiple different rate periods, and the electricity used in these different periods must be transmitted to the billing department. Automatic meter reading technology must be used to meet the latter requirement. The

MAXQ3120 reference design builds a meter that meets all the requirements of a multirate meter and provides more flexible functions for power monitoring.

Time period mechanism

Each day of the year is governed by a daily time table. During the day, the electricity consumption at different times is accumulated into the corresponding rate registers as specified in the daily time table. In the time table above, Tariff 2 is the tariff for peak electricity consumption. The electricity consumed from 5:30 am to 6:00 pm is recorded in Tariff 2 (the billing price is probably higher). The electricity consumed from 6:00 pm to 10:00 pm is accumulated in Tariff 3, which is the normal rate. Finally, the electricity consumption from 10:00 pm to 5:30 am is accumulated in the off-peak rate register, which is generally at a lower rate. In this way, users are encouraged to save electricity during peak electricity consumption periods, thereby urging users to push the operation period of high-power equipment to off-peak periods.

The day schedules used to define rate periods can be modified throughout the year, with weekend and holiday schedules taking precedence. In this example, the highlighted day in May is controlled by Day Schedule 5. Aside from weekends and holidays, Day Schedule 5 will be used until mid-July when Day Schedule 3 takes effect.

Weekdays are processed according to the calendar time table, but what about weekends? The meter settings in the reference design specify certain days of the week as "weekends" and use a separate daily time table instead of the normal daily time table. Holidays use a separate daily time table, replacing the normal daily time table and the weekend time table.

Using these tools, utilities can establish a set of standards that automatically implement flexible pricing policies.

The electric meter in the Automatic Meter Reading

Reference Design uses two communication mechanisms: an IR link for the handheld terminal and an RS-485 network that connects multiple meters to a host PC. For more information on these communication methods, refer to IR and RS-485 Communication Channels for an Electricity Meter (English only).

The handheld terminal or the network host can be easily configured to read all the rate registers of the meter on demand or by prior arrangement. After reading, the information can be transmitted to the billing management system without any keyboard input. This method of data transmission ensures accurate and timely billing. It also reduces human involvement, both because the meter reading process is faster (just point the handheld terminal at the meter and press a switch) and because the meter reading operation can be completely eliminated (when multiple networked meters are remotely controlled by a host connected to the Internet).