Active compensating filter for smoothing ripples in the load circuit of a single-phase full-wave rectifier
Abstract Generated abstract
This paper examines an active compensation filter for reducing ripple in the load circuit of a single-phase full-wave rectifier. The proposed circuit uses a frequency doubler whose output windings supply a double-frequency compensating voltage adjusted in magnitude and phase to cancel the fundamental 100 Hz ripple component. Experimental comparison with an L-shaped smoothing filter of equivalent steel consumption shows substantially higher filtering coefficients for the active compensation filter, especially when both compensating voltage and phase are tuned as load current varies. The results also indicate a shorter transient time and suggest that the approach is most promising for low-resistance, weakly varying loads with relatively large direct current components, with possible extension to multiphase rectifiers using appropriate frequency multipliers.
Full Text
ACTIVE COMPENSATION FILTER FOR SMOOTHING RIPPLE IN THE LOAD CIRCUIT OF A SINGLE-PHASE FULL-WAVE RECTIFIER
E. I. GOLDSTEIN, A. I. KUTYAVIN
(Presented by the scientific seminar of the Department of Automation and Telemechanics)
To increase the efficiency of smoothing filters, the use of the principle of compensating ripple from an auxiliary source is promising [1].
However, up to the present time such filters have practically not been used, first, because of the complexity of matching it with the rectified-current circuit and, second, because of the difficulties of creating the compensating source.
One of the possible circuits of an active compensation filter based on a frequency doubler is shown in Fig. 1. The magnetizing windings \((W_0)\) are the output of the doubler and are used to compensate
Fig. 1
the alternating component of the voltage in the rectified-current circuit. A voltage \(U_y\) of industrial frequency is applied to the input through the phase shifter \(FV\).
For the compensation mode the following conditions must be satisfied:
\[ U_{2v} = U_{2y}, \tag{1} \]
\[ \varphi_{2v} = \varphi_{2y} + 180^\circ \tag{2} \]
where \(U_{2v}\) is the rms value of the voltage of the fundamental ripple harmonic, \(100\ \text{Hz}\), at the rectifier output;
\(U_{2у}\)—the rms value of the double-frequency voltage at the output of the doubler;
\(\varphi_{2в}, \varphi_{2у}\)—the phases of the voltages indicated above.
In the load circuit \(R_{\text{н}}\) only currents of the fourth and higher even harmonics will flow, while double-frequency ripple will be completely absent.
Figure 2, b shows an oscillogram obtained in investigating the active compensating filter at a current \(I_0 = 1\) A. For comparison, the oscillogram for the case \(U = [[unclear]]\) is also given here (Fig. 2, a). A comparison of Figs. 2, a and 2, b confirms the effectiveness of the filter under consideration. The active compensating filter and an L-shaped filter were investigated experimentally; their principal data are given in Table 1. The smoothing choke of the L-shaped filter was made on the same core as the doubler, and the stack thickness was taken equal to twice the stack thickness of one choke of the doubler.
Fig. 2
Table 1
| Core dimensions of each choke (in mm) | Winding data of the chokes: doubler | Winding data of the chokes: L-shaped filter | Note |
|---|---|---|---|
| Base dimension—20 Stack thickness—16 Window width—10 Window height—44 Material E-42 thickness—0.35 mm |
\(W_0 = 300\) \(R_0 = 0,[[unclear: digit]]6\ \Omega\) \(W_1 = 3000\) |
\(W_0 = 388\) \(R_0 = 1.39\ \Omega\) |
Capacitor capacitance \(C = 100\ \mu\text{F}\) |
In other words, complete equivalence of the frequency doubler and the smoothing choke in terms of steel consumption was ensured.
Table 2 gives the results of investigations of the filters indicated above when the rectified current \(I_0\) was varied in the range from 0.1 to 2 amperes. In this case the load \(R\) varied over the range \(50 \div 1\ \Omega\), while the voltage at the rectifier input remained unchanged.
The filtering coefficient was calculated from the formula:
\[ K_{\phi}=\frac{U_R}{U_{\text{н}}}, \]
where \(U_{\mathrm{v}}\) and \(U_{\mathrm{n}}\) are the rms values of the alternating voltages at the rectifier output and at the load.
The data given in Table 2 on the phase \((\varphi)\) of the voltage \(U_y\) are given in relative units corresponding to the angle of rotation of the rotor of the phase regulator. Analysis of the data shows that the best smoothing is provided by a tunable active compensation filter, in which, as the current \(I_0\) changes, both the phase and the magnitude of the doubler supply voltage are adjusted.
Table 2
| No. | Filter | Characteristics | \(I_0\) (A): 0,1 | 0,2 | 0,4 | 0,8 | 1,2 | 1,5 | 2,0 |
|---|---|---|---|---|---|---|---|---|---|
| 1 | L-shaped (gap—var) |
\(K_{\mathrm{f}}\) | 9,0 | 8,9 | 10,2 | 13,7 | 19,6 | 27,5 | 42,2 |
| 2 | Active compensation filter | \(U_y\) (V) | 92,7 | 87 | 92 | 104 | 109 | 112 | 104 |
| 2 | Active compensation filter | \(\varphi\) | 0° | 10° | 30° | 50° | 70° | 75° | 80° |
| 2 | Active compensation filter | \(K_{\mathrm{f}}\) | 23,9 | 28,2 | 38,7 | 69,9 | 139,7 | 209 | 577 |
| 3 | Same, but with \(U_y=95\) V, \(b=\mathrm{const}\) |
\(\varphi\) | −10° | 0° | +10° | 20° | 30° | 35° | 40° |
| 3 | Same, but with \(U_y=95\) V, \(b=\mathrm{const}\) |
\(K_{\mathrm{f}}\) | 25,8 | 19,4 | 34,5 | 45,2 | 61,9 | 98 | 454 |
| 4 | Same, but with \(\varphi=\mathrm{const}\) |
\(U_y\) (V) | 90 | 85 | 90 | 104 | 108 | 107 | 98,5 |
| 4 | Same, but with \(\varphi=\mathrm{const}\) |
\(K_{\mathrm{f}}\) | 10,7 | 13,5 | 23 | 65,5 | 103,8 | 116,4 | 210 |
| 5 | Same, but with \(U_y=95\) V \(\varphi=\varphi_1=\mathrm{const}\) |
\(K_{\mathrm{f}}\) | 10,0 | 11 | 23 | 40,5 | 54,4 | 82,6 | 198 |
| 6 | Same, but with \(U_y=95\) V, \(b\) and \(\varphi=\varphi_2=\mathrm{const}\) |
\(K_{\mathrm{f}}\) | 20,0 | 18,2 | 25,8 | 27,8 | 34,5 | 52,4 | 126,5 |
Table 3 presents the results of processing one of the series of oscillograms taken at \(I_0=1\) A for the case of load switching.
Table 3
| Filters | Transient-process time, upon switching on, ms | \(K_{\mathrm{f}}\) at \(I_0=1\) A |
|---|---|---|
| L-shaped | 90 | 16,7 |
| Active compensation filter with \(U_y=\mathrm{var}\); \(\varphi=\mathrm{var}\) | 60 | 88 |
Main Conclusions
-
The fundamental possibility of smoothing ripple by means of an active compensation filter has been demonstrated.
-
In comparison with a $\Gamma$-type filter equivalent in terms of steel consumption, the active compensation filter provides a considerable (from 2.5 to 13 times) reduction in ripple, with a noticeable reduction in the time constant of the load circuit.
-
The use of the proposed filter is especially promising with a low-ohmic, slightly varying load and with large values of the dc component of the rectified current.
-
For multiphase rectifiers, active compensation filters based on corresponding frequency multipliers can be used.
Literature
- V. A. Solov’ev, N. M. Fetisov. Smoothing of Voltage Ripple in Rectifiers. Transzheldorizdat, 1933.