DK174716B1 - A power supply circuit, use thereof, and method for controlling a power supply circuit - Google Patents

Description

in DK 174716 B1

The present invention relates to a power supply circuit comprising an electric converter, preferably for converting AC to DC, which converter includes a self-induction, a rectifier element and a control circuit controlled switching element, and preferably a capacitor where the control circuit control is controlled by a and measuring a voltage at a given location in the power supply circuit 10, a method of controlling a power supply circuit, and the use of such a power supply circuit for motor control.

For power supply of many electrical appliances, especially appliances connected to single-phase to the 15 electricity grid, circuits are used to correct the power factor, the so-called PFC circuits. By using these, an approximately sinusoidal current can be drawn from the electricity grid, ie a current with a low content of overtones, which is today a norm requirement.

Furthermore, with such a PFC circuit, a power supply which is relatively independent of the supply voltage can be obtained, so that with one and the same power supply an apparatus can be realized which can be directly connected to different mains voltages, for example 110 V or 240 V without changing it. An example of such a PFC circuit is found in US-B1-6,215,287, wherein the PFC circuit is based on a forward converter circuit in the form of a boost converter circuit.

In such boost converter circuits as described in US-B1-6,215,287, a transistor is controlled to conduct and block at a rate significantly higher than the grid frequency, e.g., 50-100 times higher than the grid frequency typically 50 Hz 35 or 60 Hz. When the transistor is conductive, the current from the power grid passes through a rectifier bridge, a self-induction, and the transistor, so that energy is stored in the self-induction. When the transistor blocks, DK 174716 B1 2 the current flows from the grid through the rectifier bridge, self-induction, a rectifier element in the form of a diode and a load. Below, the current drops through the self-induction as it exits its energy to the load. In order to ensure that the load can always be supplied with the required instantaneous power, whether the transistor is conductive or not, an intermediate circuit capacitor, which is connected in parallel with the load, is normally used.

For example, the control of the transistor can be effected as pulse width modulation, as described in U.S. Patent No. 6,215,287. The pulse width modulation is typically controlled by a cascade control, ie. a regulation comprising two loops.

One loop is a fast-regulating internal loop that regulates current in the power grid, for example by regulating the current in self-induction. This regulation can be made on the basis of a measurement resistor inserted at a suitable location in the circuit, for example between the rectifier bridge and the emitter of the transistor, or, as shown in DE-C1-33 13 124, in series with the self-induction. It should be noted in this connection that it does not matter for the measurement that DE-C1-33 13 124 deals with another type of forward converter. Alternatively, as in US-B1-6,215,287, an undetermined detection device measuring on the phase or 0 conductor on the grid side of the rectifier bridge may be used.

The second loop is a slow-regulating outer loop that regulates the output voltage of the circuit, i.e., in practice, the voltage across the load including wires. In order to obtain a sinusoidal current in the grid, the output signal from the outer control loop is multiplied by the instantaneous value of the grid voltage, for example on the basis of a measurement over the rectifier bridge output, and the result of this multiplication is used as a reference for the internal control loop.

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In addition, a PFC circuit may typically include compensation for grid voltage and load variations, as well as monitoring functions for overload and over voltage.

5 As mentioned, the internal control loop is fast regulating, that is, in this context it regulates substantially faster than the grid frequency, but still slower than the frequency of the transistor. Typically, this regulation is a fast Ι-ΙΟ regulation. In comparison, the external control loop is slow, that is, significantly slower than the grid frequency. If this control is selected too quickly, it will equalize the ripple voltage which, otherwise, due to the finite size of the intermediate circuit capacitor, will inevitably occur at the output voltage. In this case, this will cause the input current not to be sinusoidal, but distorted, thus containing precisely the overtones that the PFC circuit aims to avoid.

Furthermore, EP-A2-473925 discloses a pulse-width modulated power supply with two feedback loops, each having its own fixed time constant, namely a fast acting to compensate for increases in output voltage and a slow acting to equalize the output voltage. the load current on the input side.

However, the prior art PFC circuits have certain disadvantages.

Eg. For example, a sudden drop in the load, such as its switching off, will cause a sharp surge in the output voltage. Such an overvoltage from a surge can cause undesired damage to the components of the circuit if these are not oversized in terms of voltage, which is of course not desirable for economic reasons as this makes the components more expensive.

This problem is addressed in US-B1-6,215,287 which proposes a solution in which a low pass filter with variable cut-off frequency is inserted in the control loop. However, this solution is unnecessarily complicated as it requires an adjustable filtering functionality.

Another problem is that instability of the slow control loop can occur if the load contains interfering frequencies, e.g. from an inverter loaded with a motor. Since the speed of the motor can be varied arbitrarily with the inverter, such a load may contain arbitrary frequencies. This is especially a problem if these motor-related frequencies and the grid frequency, or multiples of these, are close to each other, resulting in low-frequency mixing frequencies. Furthermore, such problems can be aggravated by the fact that motors usually have 15 inherent resonant frequencies, some of which can be low-frequency. These frequencies and the load on the inverter circuit affect the ripple of the output voltage, which in turn influences the voltage control circuit and gives rise to said instability.

The traditional way of solving this problem is to use a relatively large, and thus expensive, intermediate-capacitor to regulate the grid and load regulatively from one another while keeping the ripple of voltage at an acceptable low level, which consequently expensiveens the circuit.

Accordingly, it is the object of the present invention to provide a power supply circuit of the type mentioned above which is cost-effective and which does not suffer from the above-mentioned problems of stability and voltage fluctuation.

According to a first aspect of the present invention, this task is solved by a power supply circuit comprising an AC to DC converter which includes a self-induction, a rectifier element, and a control circuit controlled switching element, the control circuit controlling the control circuit. 5 DK 174716 B1 on the basis of a reference and a measurement of a voltage at a given point in the power supply circuit, which power supply circuit is characterized in that the control circuit comprises a filter with a first 5 cut-off frequency for increasing voltage and a second cut-off frequency for decreasing voltage therefrom. .

According to another aspect of the present invention, the method is solved by a method for controlling a power supply circuit comprising an electric converter, preferably for converting AC to DC, the converter including a self-induction, a rectifier element and a switching element controlled by a control circuit. and preferably a capacitor which comprises controlling the switching element by means of the control circuit on the basis of a reference and measuring a voltage at a given location in the power supply circuit which is characterized in that the method 20 comprises filtering the signal in regulating circuit with a filter having a first cut-off frequency at increasing voltage and filtering the signal in the control circuit with a filter having a second cut-off frequency at decreasing voltage.

Hereby, by appropriate choice of cut-off frequencies, a faster regulation of voltage rises than of voltage drops is obtained, so that the undesired voltage surges are reduced, without the circuit simultaneously seeking to regulate the ripple voltage.

According to a third aspect of the invention, the power supply circuit is used as motor control, thereby overcoming the aforementioned problems of switching off and low frequency mixing frequencies.

According to a preferred embodiment of the invention, the power supply circuit is arranged so that both the first cut-off frequency and the second cut-off frequency are fixed.

This has the advantage that the filter can be realized with simple components, for example simply by means of a diode two resistors and a capacitor.

These simple components are then included in a further preferred embodiment of the invention according to 5 in which the measurement of the voltage at the given location in the power supply circuit is made by means of a voltage measurement circuit and the filter is provided in the form of different time constants in this voltage circuit.

In an advantageous variant of this embodiment, the various time constants in the voltage measuring circuit are provided in the form of an RC joint comprising at least one capacitor and two parallel connected resistors, in series with at least one of the parallel-connected resistors exist a diode.

Particularly advantageous is an embodiment in which the diode forms part of a circuit for realizing an ideal diode.

Thus, the cut-off frequency is not affected by the magnitude and speed of the voltage increase.

In yet another preferred embodiment, the inverter includes a boost converter circuit, which is an affordable and simple way to realize the inverter circuit.

The invention will now be explained in more detail by way of examples of embodiments of the invention and with reference to the drawing, in which: FIG. 1 schematically shows a first embodiment of a power supply circuit according to the invention; FIG. Figure 2 is a schematic view of a partially digital second embodiment of a power supply circuit according to the invention; 3 with a flow chart schematically shows an example of the digital control in the embodiment of FIG. 2nd

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FIG. 1 schematically illustrates a substantially analogous embodiment of the invention. The power supply circuit is supplied with single-phase alternating current from the lines F and 0. The alternating current is rectified by a 5 bridge rectifier D1-D4. The circuit comprises a pulse width modulator 1 which controls a transistor T1 for conducting and blocking at a rate which is substantially higher than the grid frequency, for example 50-100 times higher than the grid frequency, which is typically 50 Hz or 10 60 Hz. When the transistor T1 is conductive, the current from the power grid passes through the rectifier bridge D1-D4, a self-induction LI, and the transistor TI, so that energy is stored in the self-induction LI. When the transistor T1 blocks the current flowing through the rectifier-bridge D1-D4, the self-inductor L1, a rectifier element D5 in the form of a diode and a load 2. Including the current through the self-induction LI, while supplying its energy to the load 2. For To ensure that the load can always be supplied with the required instantaneous power, whether the transistor T1 is conductive or not, an intermediate circuit capacitor C1 connected in parallel with the load 2 is inserted in the circuit.

For controlling the pulse width modulator 1, 25 loops are used. One loop is a fast-regulating internal loop that regulates current in the power grid, for example by regulating the current in self-induction. This regulation is made on the basis of a current measurement derived from a voltage measurement over a measurement resistor R1 inserted between the rectifier bridge D1-D4 and the emitter of transistor T1. This current measurement is inherently known in the art and can, of course, be made at any convenient location in the circuit and in any known manner. For example, as mentioned above in connection with the prior art.

The voltage signal 3 corresponding to the voltage measurement is applied to a subtraction node 4, and 8 is subtracted there from the output signal 5 from a multiplier device 6. The resulting signal 7 is filtered in a low-pass filter 8 so that a filtered signal 9 controlling the pulse width modulator 5 is obtained. 1, which in turn controls transistor T1.

The second loop is a slow-regulating outer loop that regulates the output voltage of the circuit. This voltage is measured in the illustrated embodiment of the present invention over capacitor C1, in the form of a voltage signal on line 10. This signal is filtered through an RC line comprising a capacitor C3 and two parallel-coupled resistors R2 and R3, where in series with resistor R2 is arranged a diode D6. The output signal 11 from this RC link is subtracted into a subtraction node 12 from a reference signal 13. The reference signal 13 indicates the nominal output voltage to be supplied by the circuit, for example, the 110 V or 240 V. initially mentioned, from the subtraction node 12 20 can be scaled as needed in a scaling device 15 to obtain an output signal 16 from the external control loop. In order to obtain a sinusoidal current in the grid, this output signal 16 from the outer control loop is multiplied by a signal representing the waveform of the grid voltage, for example, as shown on the basis of a measurement across the output rectifier bridge D1-D4, and the result of this multiplication which output as the output signal 5 of the multiplier device 6 is used as a reference for the internal control loop.

The RC joint which comprises a capacitor C3 and two parallel coupled resistors R2 and R3, in series with resistor R2, a diode D6 is provided to provide two different time constants for increasing voltage on line 10 and decreasing voltage on line 10, respectively. , i.e. provides a low pass filter with two different cut-off frequencies depending on whether the regulating circuit is to provide control of an increasing or decreasing output voltage of the circuit.

This is achieved by a diode D6 being connected in series with one of the two parallel-coupled resistors R2 and R3, in the case shown R2. If the voltage on line 10 rises, diode 6 will conduct and a charging current will flow through both parallel resistors R2 and R3 to capacitor C3. On the other hand, if the voltage on line 10 drops, the diode D6 10 will block, so that the capacitor is discharged only through the resistor R3. Thus, since the total resistance of the parallel connection of resistors R2 and R3 is lower than the resistance of R3 alone, the capacitor RC joint will have a lower time constant for rising voltage on line 10 than for falling.

Preferably, the values of resistors R2s and R3 are selected such that R3 is on the order of 100 times greater than R2, thereby ensuring a sufficient difference between the two time constants.

Thus, the circuit is able to more quickly compensate for rising voltages than for decreasing, thereby eliminating, in particular, the harmful and therefore undesirable voltages more quickly. Thus, in this way, the desired filtration can be achieved in a simple manner with two substantially fixed cut-off frequencies.

In order to account for the drop in voltage across the diode D6, which will affect the time constant of the RC 10 in particular at slow voltage rises, an ideal diode coupling with an operational amplifier 17, as shown in FIG. First

In this connection, it should also be mentioned that the two different time constants according to an embodiment not shown can also be provided by using two oppositely polarized diodes arranged in series with the respective resistors R2 and R3. Thus, in series with the resistor R3 there is provided a diode opposite polarization of the diode D6, as in FIG. 1 is arranged in series with R2.

In FIG. 2, another embodiment of the invention is shown in which the control circuit is digitally implemented in e.g. a microprocessor or digital signal processor, as indicated by a dotted line. In order to facilitate understanding, similar elements in FIG. 1 and 2 have the same reference symbols. The control circuit comprises a multiplexer 21 which combines the output voltage signal 10, the voltage measurement signal 3 and the signal representing the waveform of the mains voltage into a total signal 22. This signal 22 is supplied to an analog / digital converter 23 where it is converted to a digital signal 24 for use with a calculator 25. Based on this digital signal 24, the calculator 25 calculates a signal 29 which controls the pulse width modulator 1, which in turn controls the transistor T1.

FIG. 3 shows an example of a control algorithm 20 that the calculator 25 can use. This algorithm may be stored in a storage 26 in conjunction with or integrated into the microprocessor or digital signal processor. This storage may be RAM, ROM or, in principle, any suitable storage medium.

The operation of the embodiment shown in FIG. 3 algorithm will now be reviewed. The algorithm that is iterative starts at a step 100. Then, at one step 101, the calculator 23 awaits the next pulse width modulated pulse 30 and then in step 102 enters a variable UDC representing the actual output voltage on line 10. The calculator then compares at step 103 to voltage value, represented by the variable UDC1, which the pulse width modulator is currently set to supply. If the measured value represented by the variable UDC is greater than UDC1, a new value for UDC1 is calculated in step 104. If, on the other hand, UDC is less than or equal to UDC1, the new value for UDC1 is calculated in step 105. It In this connection, it should be noted that in the case where UDC equals UDC1, it does not matter if the calculation of the new UDC1 occurs in one or the other of steps 104 or 5 105, since both calculations will continue to yield the same value of UDC1, namely equal to UDC. After calculating in steps 104 or 105, the new value of UDC1 in a step 106 is sent as a control signal to the pulse width modulator 1 controlling the transistor T1.

10 The calculation of the new value of UDC1 is calculated in the two steps 104 and 105 with two different weights x and y, so that UDC1 approaches UDC at two different rates depending on whether UDC1 is greater than UDC or not.

In the foregoing, the present invention has been described on the basis of an analog and a digital embodiment, respectively. However, it should be understood that the embodiments described are merely illustrative examples and that many other analogs as well as digital embodiments and combinations thereof may be conceived within the scope of the claims.

The person skilled in the art will also understand that other inverter circuits than the described forward-type inverter of the boost type can be used, for example SEPIC-25 (Single Ended Primary Inductance Converter) inverters, and he will understand that modulation forms other than the described pulse width modulation can be used. .

Claims (8)

A power supply circuit comprising an electric converter, preferably for converting AC to DC, which converter includes a self-induction, a rectifier element and a control circuit controlled switching element, and preferably a capacitor, wherein the control circuit controls a switching switch and of a voltage at a given location in the power supply circuit, characterized in that the control circuit comprises a filter having a first cut-off frequency for increasing voltage and a second cut-off frequency for decreasing voltage. Power supply circuit according to claim 1, characterized in that both the first cut-off frequency and the second cut-off frequency are fixed. Power supply circuit according to claim 1 or 20, characterized in that the measurement of the voltage at the given location in the power supply circuit is carried out by means of a voltage measurement circuit and the filter is provided in the form of different time constants in this voltage measurement circuit. Power supply circuit according to claim 3, characterized in that the different time constants in the voltage measuring circuit are provided in the form of an RC joint comprising at least one capacitor and two parallel-connected resistors, in which 30 in series with at least one of the parallel-connected ones. resistors exist a diode. Power supply circuit according to claim 4, characterized in that the diode forms part of a circuit for realizing an ideal diode. Power supply circuit according to any one of claims 1-5, characterized in that the inverter includes a boost converter circuit. 13 DK 174716 B1 Use of a power supply circuit according to any of the preceding motor control requirements. A method of controlling a power supply circuit comprising an electric converter, preferably for converting AC to DC, wherein the inverter includes a self-induction, a rectifier element and a control circuit controlled circuit element, and preferably a capacitor comprising controlling the switching element by means of the control circuit on the basis of a reference and measuring a voltage at a given location in the power supply circuit, characterized in that the method comprises filtering the signal in the control circuit with a filter having a first cut-off frequency at increasing voltage and filtering the signal in the control circuit with a filter having a different cut-off frequency at decreasing voltage therefrom. 20