effect of pulse width modulation on the error induction electricity meters and the loss of an induction motor

Effect of pulse width modulation on the error induction electricity meters, and the losses in asynchronous engine

AP Popov, A. O. Chugul, AA Gorshenkov, SM Klevansky

Siberian State Automobile and Road Academy (SibADI)

' ( E 500 FR - E 540-5,5 K - EC ) в качестве источника несинусоидального напряжения. The results of investigation of error induction energy meters, and electrical losses in the induction motor in a high level of harmonics in the current and voltage curves when using the inverter company 'Mitsubishi' (E 500 FR - E 540-5,5 K - EC) in the as a source of non-sinusoidal voltage. It is shown that the error of the induction energy meters and electrical losses in induction motor with nonsinusoidal modes in PWM circuits increases by several tens of percent.

As you know, in power systems due to increased electricity customers operating in a pulsed mode, as well as systems with pulse-width modulation (PWM) frequency converters in electric systems with asynchronous motors, non-linear loads, thyristor converters, etc. there is a high level of harmonics.

In this regard, the issue of measurement of electrical energy in these conditions remains relevant, despite the fact that the measurement of electrical energy, as in the sinusoidal mode, and in Wave form of electromagnetic processes, devoted a considerable amount of work, eg [1-6] .

To measure the electric energy supply systems are currently used as an induction and electronic energy meters. The latter often are based on analog-digital converters using microprocessor-based calculators, ie, in the process of computing power is applied to the measurement of time discretization and quantization of the input signals that are proportional to the current values ​​of current and voltage at the load, which inevitably gives rise to an error calculating the energy.

This paper presents the results of a study of error induction energy meters and power losses in an induction motor in a high level of harmonics in the current and voltage curves. At the same time used a special electronic electricity meter, which allows to obtain reliable information in a Wave form, caused by the PWM.

As such an electronic counter used specially developed for this purpose an electronic meter that provides a sufficiently accurate calculation of the current value of the electricity compared with induction meter, according to the expression:

(1)

where - The instantaneous voltage across the load;

- The instantaneous load current;

- Current time of measurement.

In the block diagram of the counter as a multiplier of instantaneous values and used a pulsed device is multiplied, the pulse integrator and a digital pulse counter, which allows for the total error in measuring the current value of energy of a few tenths of a percent (0,1 ¸ 0,2%) in a high frequency harmonics in multiples of 50 Hz, up to frequency of several tens of kilohertz, and use it as an exemplary means of measuring electrical power.

This paper does not attempt to describe the complete structural and circuit diagram of the counter (the interested organizations and institutions, such information may be provided). One of the challenges is to determine the possible level of error in the non-sinusoidal induction meter modes with high levels of distortion curves of current and voltage at the load.

500 FR - E 540-5,5 K - EC с номинальной мощностью 5,5 кВт. The studies were conducted using a frequency converter (PE) Mitsubishi E 500 FR - E 540-5,5 K - EC with a nominal capacity of 5.5 kW. The load used in heating elements and the induction motor. Block diagram of the installation with heating elements and the timing diagram of currents and voltages are shown in Fig. 1 and Fig. Two .

In Fig. A. 1, Wh 3 - индукционные счетчики электроэнергии СО 505; Wh 2, Wh 4 - электронные счетчики электроэнергии; ТТ - трансформатор тока; ДН - датчик напряжения; ЧП - частотный преобразователь; R н - сопротивление нагрузки. Block diagram of the installation: Wh 1, Wh 3 - Induction of SB 505 electricity meters; Wh 2, Wh 4 - Electronic Energy Meters, CT - CT, MD - sensor voltage PE - frequency converter; R n - load resistance.

Before the experiment in nonsinusoidality previously been carried out checks on the identification testimony of electronic and induction meters while working on the same load in close to sinusoidal. Diagram of the device shown in Fig. Three. Time diagram of the voltage waveform across the load is shown in Fig. 2a .

a)

b)

a)

In Fig. Two. Timing diagram of phase voltages (a and c) and phase current (b and c)

Inlet and outlet emergency for linear resistive load

In Fig. Three. Schema induction and testing of electronic meters in the

identification testimony under a regime of near-sinusoidal

In the experiment used the following mode of the inverter:

= 50 Гц; - The frequency of the fundamental voltage at the output of PE f = 50 Hz;

- Frequency of the PWM output voltage PE - 1 kHz;

= 38 Ом (режим близкий к номинальному) - Load impedance inverter R _H = 38 ohms (the regime close to the nominal)

There have been several experiments with a sufficiently precise measurement of time, energy meters and recording of their testimony.

According to the testimony of electronic energy meters determined the average efficiency of the inverter at this load:

where - The average output power of PE;

- Average power consumption of PE;

(The standard deviation of readings from the average was 0.05%)

As a result of the measurement scheme of Fig. 1 were set relative values differences of electronic evidence and induction electricity meters in the percentage of input and output state of emergency, which, taking into account statistical analysis were the following:

, .

These results suggest that the same values ​​of the load in a non-sinusoidal modes in PWM circuits, the main error of the induction energy meters to several tens of times their basic error in sinusoidal mode.

These findings were obtained, as already mentioned, for a linear resistive load. 500 FR - E 540-5,5 K - EC . Due to the fact that PE used mainly for power induction motors (BP) in order to speed control, an experiment was conducted to determine the power loss in blood pressure during feeding him from PE Mitsubishi E 500 FR - E 540-5,5 K - EC . 2 Y 3 (ном. мощность 5.5 кВт, 3000 об/мин). For the experimental studies used asynchronous motor AIR100 L 2, Y 3 (rated power 5.5 kW, 3000 rev / min). The load applied to blood pressure in the heater is loaded with a DC generator with mixed excitation. Pre-measured the power consumption and blood pressure load with sinusoidal mode. After processing the experimental data it was found that when feeding on the blood pressure PE, other things being equal, the power loss in blood pressure increased by 30% compared with a sinusoidal mode. This leads to a change in the thermal regime of blood pressure and the need to reduce its load. The reasons for increasing losses in blood pressure with non-sinusoidal modes are known and in this work are not discussed. The main objective was to establish the level of losses.

Conclusions:

A. The first experimental set the level of basic error (tens of percent) of the induction energy meters in a Wave form, created by the PWM.

Two.    Losses in the controlled induction motors, powered by an emergency, also increases as compared with a standard diet for a few tens of percent, which leads to overheating of the blood pressure and the need to reduce the power load.