JP6466831B2 - Power converter - Google Patents

Description

  The present invention relates to a power converter, and more particularly to a power converter including a transformer provided between an inverter and a load.

  Japanese Patent Application Laid-Open No. 6-98559 (Patent Document 1) extracts an inverter that converts a DC voltage into an AC voltage, a transformer provided between the inverter and a load, and a DC component included in the output voltage of the inverter. A power converter is disclosed that includes a DC voltage extraction unit and a control circuit that controls the inverter so that the DC component extracted by the DC voltage extraction unit is eliminated. In this power converter, the occurrence of a demagnetization phenomenon in the transformer is prevented by eliminating the direct current component of the output voltage of the inverter.

JP-A-6-98559

  However, in Patent Document 1, since the DC voltage extraction unit is configured by a capacitor, a resistance element, etc., there is a problem that it takes a long time to detect the DC component generated in the output voltage of the inverter. For this reason, there is a possibility that a magnetism phenomenon occurs in the transformer while the DC component of the output voltage of the inverter is detected, and the excitation current increases.

  Therefore, a main object of the present invention is to provide a power converter capable of quickly detecting a direct current component generated in a magnetic flux of a transformer and preventing occurrence of a magnetic demagnetization phenomenon in the transformer.

  A power converter according to the present invention includes: an inverter that converts a DC voltage into an AC voltage; a transformer that receives the output voltage of the inverter and applies an AC voltage to a load; an integrator that integrates the output voltage of the inverter; A sampling circuit that operates in synchronization with the output voltage and samples the output signal of the integrator N times per period of the output signal of the inverter, and the direct current of the output signal of the integrator based on the signal sampled by the sampling circuit A DC component detector that detects a component and a control circuit that receives the DC component detected by the DC component detector and controls the waveform of the output voltage of the inverter so that the received DC component disappears. N is a natural number.

  In the power converter according to the present invention, an integrator that integrates the output voltage of the inverter is provided, and the output signal of the integrator is sampled N times per cycle of the output voltage of the inverter, and the integrator The DC component of the output signal is detected, and the waveform of the output voltage of the inverter is controlled so that the detected DC component disappears. The output signal of the integrator indicates the magnetic flux of the transformer. Therefore, the direct current component generated in the magnetic flux of the transformer can be detected quickly, and the occurrence of the demagnetization phenomenon in the transformer can be prevented.

It is a circuit block diagram which shows the structure of the power converter by Embodiment 1 of this invention. It is a circuit block diagram which shows the structure of the inverter and transformer which were shown in FIG. FIG. 2 is a block diagram illustrating a configuration of a bias detection circuit and a control circuit illustrated in FIG. 1. It is a wave form diagram for demonstrating the demagnetization prevention method of the power converter shown in FIGS. It is another waveform diagram for demonstrating the demagnetization prevention method of the power converter shown in FIGS. FIG. 6 is still another waveform diagram for explaining the method for preventing the bias magnetism of the power converter shown in FIGS. 1 to 3. FIG. 6 is still another waveform diagram for explaining the method for preventing the bias magnetism of the power converter shown in FIGS. 1 to 3. FIG. 6 is still another waveform diagram for explaining the method for preventing the bias magnetism of the power converter shown in FIGS. 1 to 3. FIG. 6 is still another waveform diagram for explaining the method for preventing the bias magnetism of the power converter shown in FIGS. 1 to 3. FIG. 6 is still another waveform diagram for explaining the method for preventing the bias magnetism of the power converter shown in FIGS. 1 to 3. It is a block diagram which shows the principal part of the power converter by Embodiment 2 of this invention. It is a wave form diagram for demonstrating the demagnetization prevention method of the power converter shown in FIG. FIG. 13 is a waveform diagram in which the time axis of the main part of the waveform diagram shown in FIG. 12 is enlarged. FIG. 4 is a waveform diagram for explaining a problem of the first embodiment. It is a block diagram which shows the principal part of the power converter by Embodiment 3 of this invention. It is a wave form diagram for demonstrating the demagnetization prevention method of the power converter shown in FIG. It is a block diagram which shows the principal part of the power converter by Embodiment 4 of this invention. It is a wave form diagram for demonstrating the demagnetization prevention method of the power converter shown in FIG. FIG. 10 is a waveform diagram for explaining a problem of the fourth embodiment. It is a circuit block diagram which shows the structure of the uninterruptible power supply by Embodiment 5 of this invention. It is a circuit diagram which shows the structure of the demagnetization detection circuit contained in the power converter used as the comparative example of this invention. It is a waveform diagram for comparing the operation of the bias detection circuit of the present invention and the operation of the bias detection circuit of the comparative example. It is the wave form diagram which expanded the principal part of FIG. It is another waveform diagram for comparing the operation of the bias detection circuit of the present invention with the operation of the bias detection circuit of the comparative example. It is the wave form diagram which expanded the principal part of FIG.

[Embodiment 1]
1 is a circuit block diagram showing a configuration of a power converter according to Embodiment 1 of the present invention. In FIG. 1, the power converter includes an inverter 1, a transformer 2, a bias detection circuit 3, and a control circuit 4.

  The inverter 1 is controlled by control signals G1 to G4 supplied from the control circuit 4, and converts the DC voltage VB of the battery 51 into an AC voltage VAC. The transformer 2 supplies the load 52 with an AC voltage VO having a level corresponding to the AC voltage VAC generated by the inverter 1. The load 52 is driven by the AC voltage VAC supplied from the transformer 2. In other words, the DC power of the battery 51 is converted into AC power by the inverter 1, the AC power is supplied to the load 52 via the transformer 2, and the load 52 is driven by the AC power.

  The demagnetization detection circuit 3 detects a DC component Vdc of a signal indicating the magnetic flux B generated in the iron core of the transformer 2 based on the output voltage VAC of the inverter 1. The control circuit 4 generates the control signals G1 to G4 so that the DC component Vdc detected by the bias detection circuit 3 becomes 0V.

  FIG. 2 is a circuit block diagram showing a configuration of inverter 1 and transformer 2 shown in FIG. In FIG. 2, inverter 1 includes transistors Q1-Q4, diodes D1-D4, a reactor L1, and a capacitor C1. The transformer 2 includes a primary winding 2a, a secondary winding 2b, and an annular iron core 2c.

  Each of transistors Q1-Q4 is, for example, an IGBT (Insulated Gate Bipolar Transistor). The collectors of the transistors Q1 and Q2 are both connected to the positive electrode of the battery 51. The collectors of transistors Q3 and Q4 are connected to the emitters of transistors Q1 and Q2, respectively, and the emitters of transistors Q3 and Q4 are both connected to the negative electrode of battery 51. Diodes D1-D4 are connected in antiparallel to transistors Q1-Q4, respectively.

  Reactor L1 is connected between the emitter of transistor Q1 and one terminal of primary winding 2a of transformer 2. The emitter of transistor Q2 is connected to the other terminal of primary winding 2a of transformer 2. The capacitor C1 is connected between one terminal and the other terminal of the primary winding 2a. Each of primary winding 2a and secondary winding 2b is wound around iron core 2c. The two terminals of the secondary winding 2b are connected to the load 52.

  The transistors Q1 to Q4 are on / off controlled by control signals G1 to G4 supplied from the control circuit 4, respectively. Each of the control signals G1 to G4 is, for example, a PWM (Pulse Width Modulation) control signal. One cycle of each of the control signals G1 to G4 is an inverse 1 / f of the switching frequency f. Each of control signals G1-G4 is set to “H” level or “L” level in each cycle. The transistors Q1 to Q4 are turned off when the control signals G1 to G4 are set to the “L” level, respectively, and are turned on when the control signals G1 to G4 are set to the “H” level, respectively. The ratio Ton / λ between the time Ton at which each of the control signals G1 to G4 is set to the “H” level within one cycle and the time λ of one cycle is called a duty ratio. The control circuit 4 controls the duty ratio of each of the control signals G1 to G2.

  In the period corresponding to 0 to 180 degrees of the AC voltage VAC, the control circuit 4 sets the control signals G2 and G3 to the “L” level to turn off the transistors Q2 and Q3, and sets the control signal G1 to the “H” level to set the transistor The transistor Q4 is turned on / off at the switching frequency while turning on the Q1 and adjusting the duty ratio of the control signal G4. The duty ratio of the control signal G4 is maximized when the phase angle of the AC voltage VAC is 90 degrees, and is minimized when the phase angle is 0 degrees and 180 degrees. As a result, a current flows from the positive electrode of the battery 51 to the negative electrode of the battery 51 via the transistor Q1, the reactor L1, the primary winding 2a, and the transistor Q4, and a sinusoidal AC voltage VAC between the terminals of the primary winding 2a. A positive voltage of 0 to 180 degrees is generated.

  In a period corresponding to 180 to 360 degrees of AC voltage VAC, control circuit 4 sets control signals G1 and G4 to “L” level to turn off transistors Q1 and Q4, and sets control signal G2 to “H” level and The transistor Q3 is turned on / off at the switching frequency while turning on the Q2 and adjusting the duty ratio of the control signal G3. The duty ratio of the control signal G3 is maximized when the phase angle of the AC voltage VAC is 270 degrees, and is minimized when the phase angle is 180 degrees and 360 degrees. As a result, a current flows from the positive electrode of the battery 51 to the negative electrode of the battery 51 via the transistor Q2, the primary winding 2a, the reactor L1, and the transistor Q3, and a sinusoidal AC voltage VAC between the terminals of the primary winding 2a. A negative voltage of 180 to 360 degrees is generated. In this way, a sinusoidal AC voltage VAC having a desired frequency (for example, commercial frequency) can be generated between the terminals of the primary winding 2a.

  Reactor L1 and capacitor C1 constitute a low-pass filter that allows commercial frequency AC power generated by transistors Q1 to Q4 to pass therethrough, and a signal of switching frequency generated by transistors Q1 to Q4 passes to the load 52 side. To prevent that. In other words, reactor L1 and capacitor C1 convert a square-wave AC voltage generated by turning on / off each of transistors Q1-Q4 into a sinusoidal AC voltage VAC.

  When the AC voltage VAC is applied between the terminals of the primary winding 2a of the transformer 2, an AC voltage VO having a level corresponding to the AC voltage VAC is generated between the terminals of the secondary winding 2b. The ratio of the amplitude of the AC voltage VAC to the amplitude of the AC voltage VO is equal to the ratio N1 / N2 of the number of turns N1 of the primary winding 2a and the number of turns N2 of the secondary winding 2b. The load 52 is driven by the AC voltage VO.

  When an AC voltage VAC is applied to the primary winding 2a of the transformer 2 and a current flows through the windings 2a and 2b, a magnetic flux B is generated in the iron core 2c. Generation of a direct current component in the magnetic flux B in the iron core 2c is referred to as bias magnetization. When the magnetism occurs, the exciting current of the transformer 2 increases, and the waveform of the output voltage VAC of the inverter 1 may be deteriorated, or an overcurrent may flow through the transformer 2 and the power converter may be damaged. Therefore, in the first embodiment, a bias detection circuit 3 and a control circuit 4 are provided for preventing the bias phenomenon from occurring in the transformer 2.

  FIG. 3 is a block diagram showing the configuration of the bias detection circuit 3 and the control circuit 4. In FIG. 3, the bias detection circuit 3 includes a voltage detector 10, an integrator 11, a phase detector 12, a sampling circuit 13, and a DC component detector 14.

  Voltage detector 10 detects an instantaneous value of AC voltage VAC generated by inverter 1 and outputs a signal φ10 indicating the detected value. The waveform of the output signal φ10 of the voltage detector 10 is the same as the waveform of the AC voltage VAC. The integrator 11 integrates the output signal φ10 of the voltage detector 10 and outputs a signal φ11 indicating an integrated value.

  Theoretically, when the inter-terminal voltage VAC of the primary winding 2a of the transformer 2 is integrated, a magnetic flux B generated in the iron core 2c of the transformer 2 is obtained. Therefore, the waveform of the output signal φ11 of the integrator 11 is the same as the waveform of the magnetic flux B generated in the iron core 2c of the transformer 2.

  When the waveform of the AC voltage VAC is an ideal sine wave, the waveform of the output signal φ11 of the integrator 11 (that is, the waveform of the magnetic flux B) is a sine wave delayed by 90 degrees from the AC voltage VAC. When the AC voltage VAC includes, for example, a positive DC component, the level of the output signal φ11 (that is, the magnetic flux B) of the integrator 11 increases at an accelerated rate.

The phase detector 12 detects the phase of the output signal φ10 of the voltage detector 10 and outputs a pulse signal P every time the detected phase becomes 0 degrees. Sampling circuit 13, in response to the pulse signal P from the phase detector 12 takes the instantaneous value of the output signal φ11 of the integrator 11, and outputs the accepted signal value. The DC component detector 14 outputs the difference between the signal value from the sampling circuit 13 and the reference value as the DC component Vdc of the output signal φ11 of the integrator 11.

  Control circuit 4 includes a voltage command unit 15 and a control signal generation unit 16. The voltage command unit 15 generates a sinusoidal voltage command signal VC. The voltage command unit 15 controls the waveform of the voltage command signal VC so that the DC component Vdc is eliminated. The control signal generator 16 generates control signals G1 to G4 based on the voltage command signal VC. When the DC component Vdc is 0V, the voltage command signal VC is VC = Vsinωt, and the output voltage VAC of the inverter 1 matches the voltage command signal VC. Here, ω = 2πf, and f is the frequency of the output voltage VAC of the inverter 1. Therefore, when the voltage command signal VC is integrated, the magnetic flux B is obtained, and B = ∫ (Vsinωt) dt = −V (cosωt) / ω.

  The DC component Vdc detected by the bias detection circuit 3 is expressed as Vdc = −αV / ω. It is assumed that the DC offset value x is added to the voltage command signal VC to cancel the demagnetization within a half cycle until the next peak of the magnetic flux B. The half cycle is 1 / (2f). When the DC offset value x is integrated over a half cycle, the integrated value is x / (2f). When the DC offset value x is set so that x / (2f) is equal to Vdc, Vdc = x / (2f) = − αV / ω = −αV / (2πf), and x = −αV / π. The voltage command unit 15 corrects the voltage command signal VC to VC = Vsinωt−αV / π = V (sinωt−α / π) when the DC component Vdc is −αV / ω. The control signal generator 16 generates control signals G1 to G4 based on the voltage command signal VC from the voltage command unit 15.

  In other words, the control circuit 4 adjusts the duty ratio of each of the control signals G1 to G4 so that the DC component Vdc is eliminated. When the DC component Vdc is a positive voltage, the control circuit 4 relatively decreases the duty ratio of the control signal G4 than the duty ratio of the control signal G3. As a result, the absolute value of the positive voltage side peak value of the AC voltage VAC is relatively decreased than the absolute value of the negative voltage side peak value, and the positive DC component Vdc is reduced.

  When the DC component Vdc is a negative voltage, the control circuit 4 relatively decreases the duty ratio of the control signal G3 than the duty ratio of the control signal G4. Thereby, the absolute value of the negative voltage side peak value of the AC voltage VAC is relatively decreased than the absolute value of the positive voltage side peak value, and the negative DC component Vdc is reduced. When the DC component Vdc becomes 0V, the control circuit 4 maintains the duty ratio of the control signals G3 and G4.

  Next, a method for preventing the occurrence of the demagnetization phenomenon in the transformer 2 will be described in detail with reference to the drawings. 4A to 4C are waveform diagrams showing a case where the AC voltage VAC generated by the inverter 1 is a sine wave in which the positive side and the negative side are symmetrical. 4A shows the waveform of the signal φ10 indicating the AC voltage VAC (that is, the output signal φ10 of the voltage detector 10), and FIG. 4B shows the magnetic flux B generated in the iron core 2c of the transformer 2. 4 shows the waveform of the indicated signal φ11 (that is, the output signal φ11 of the integrator 11), and FIG. 4C shows the waveform of the exciting current I flowing in the primary winding 2a of the transformer 2.

  4A to 4C, the waveform of the magnetic flux B is a waveform obtained by integrating the AC voltage VAC, and is a sine wave whose phase is delayed by 90 degrees from the AC voltage VAC. The exciting current I changes with the same phase as the magnetic flux B. When the phase of the AC voltage VAC is 0 degree, each of the magnetic flux B and the exciting current I has a negative peak value (time t0, t2, t4). When the phase of the AC voltage VAC is 180 degrees, each of the magnetic flux B and the exciting current I has a positive peak value (time t1, t3).

  FIGS. 5A to 5C are waveform diagrams showing a case where the AC voltage VAC has an asymmetric waveform on the positive side and the negative side, and the absolute value of the positive peak value is larger than the absolute value of the negative peak value. It is. In particular, FIGS. 5A to 5C show waveforms of the signal φ10 indicating the AC voltage VAC, the signal φ11 indicating the magnetic flux B, and the excitation current I, respectively.

  As shown in FIG. 5A, when the absolute value of the positive peak value of the AC voltage VAC becomes larger than the absolute value of the negative peak value, as shown in FIG. The value suddenly shifts from 0 to the positive side, and the positive peak value of the excitation current I increases at an accelerated rate. When the excitation current I increases in this way, it becomes difficult for the inverter 1 to output the sinusoidal AC voltage VAC, and an overcurrent flows through the inverter 1 and the transformer 2 and the power converter may be damaged. .

  When the AC voltage VAC has an asymmetric waveform between the positive side and the negative side, and the absolute value of the negative peak value is larger than the absolute value of the positive peak value, the center value of the amplitude of the magnetic flux B is zero to negative. A sudden shift to the side causes the negative peak value of the excitation current I to increase at an accelerated rate.

  FIGS. 6A to 6C are waveform diagrams showing a case where the AC voltage VAC generated by the inverter 1 is an ideal sine wave. In particular, FIGS. 6A to 6C show waveforms of the signal φ10 indicating the AC voltage VAC, the signal φ11 indicating the magnetic flux B, and the excitation current I, respectively. Here, for simplification of explanation, as shown in FIGS. 6A to 6C, when the phase of the AC voltage VAC is 0 degrees, the signal φ11 indicating the magnetic flux B becomes 0 V (reference value) (time). t 0, t 1, t 2, t 3, t 4, t 5) When the phase of the AC voltage VAC is 180 degrees, the signal φ11 indicating the magnetic flux B has a peak value, and the phase of the AC voltage VAC is 360 degrees (ie, 0 degrees). It is assumed that the signal φ11 indicating the magnetic flux B returns to 0V.

  FIGS. 7A to 7C are waveform diagrams showing a case where the AC voltage VAC has an asymmetric waveform on the positive side and the negative side, and the absolute value of the positive peak value is larger than the absolute value of the negative peak value. It is. In particular, FIG. 7A shows the signal φ10 indicating the AC voltage VAC, FIG. 7B shows the signal φ11 indicating the magnetic flux B and its DC component (ie, DC voltage) Vdc, and FIG. 7C shows the excitation current. The waveform of I is shown.

  As shown in FIG. 7A, when the absolute value of the positive peak value of the AC voltage VAC becomes larger than the absolute value of the negative peak value, as shown in FIG. The abrupt shift of the amplitude center from 0 to the positive side increases the DC component Vdc of the signal φ11, and the positive peak value of the excitation current I increases at an accelerated rate as shown in FIG.

  As shown in FIG. 3, the sampling circuit 13 responds to the pulse signal P from the phase detector 12 every time the phase angle of the AC voltage VAC becomes 0 degree, and generates the voltage of the signal φ11 indicating the magnetic flux B. Sample and hold (S / H). The voltage sampled and held by the sampling circuit 13 is the DC component Vdc of the signal φ11 indicating the magnetic flux B. The DC component detector 14 detects the magnitude of the DC component Vdc with reference to 0 V (reference value).

  FIGS. 8A to 8C are diagrams in which the waveform of the voltage command signal VC is added to FIGS. 7A to 7C. The voltage command unit 15 generates the voltage command signal VC so that the DC component Vdc detected by the DC component detector 14 is eliminated. 8A to 8C, the voltage command signal VC of 0 degrees to 360 degrees is a direct current component so that the direct current component Vdc detected when the phase of the alternating voltage VAC becomes 0 degrees is cancelled. The case where it shifts to the negative side by the value according to Vdc is shown. As a result, the AC voltage VAC is shifted to the negative side, the magnetic flux B is shifted to the negative side, and the peak value of the excitation current I can be suppressed small.

  FIGS. 9A to 9C are waveform diagrams showing the case where the AC voltage VAC drops only for a short time. In particular, FIG. 9A shows the signal φ10 indicating the AC voltage VAC, FIG. 9B shows the signal φ11 indicating the magnetic flux B and its DC component Vdc, and FIG. 9C shows the excitation current I. Yes.

  As shown in FIG. 9A, when the AC voltage VAC has a negative peak value during the period from time t0 to time t1, it is assumed that the AC voltage VAC has decreased for a short time due to, for example, load fluctuation. Since the magnetic flux B is obtained by integrating the AC voltage VAC, a positive DC component Vdc is generated in the signal φ11 indicating the magnetic flux B after time t1. As a result, the positive peak value of the magnetic flux B increases and the excitation current I increases. As shown in FIG. 3, in response to the pulse signal P from the phase detector 12, the sampling circuit 13 samples the voltage of the signal φ11 indicating the magnetic flux B every time the phase of the AC voltage VAC becomes 0 degrees. -Hold (S / H). It is detected by the DC component detector 14. The DC component detector 14 detects the magnitude of the DC component Vdc with reference to 0 V (reference value).

  FIGS. 10A and 10B are diagrams in which the waveform of the voltage command signal VC is added to FIGS. 9A and 9B. The voltage command unit 15 generates the voltage command signal VC so that the DC component Vdc detected by the DC component detector 14 is eliminated. 10A and 10B, the voltage command signal VC of 0 degrees to 360 degrees is converted to the direct current component Vdc so that the direct current component Vdc detected when the phase of the alternating current voltage VAC becomes 0 degrees. The case where it shifts to the negative side by the value according to is shown. Thereby, the alternating voltage VAC can be shifted to the negative side, the magnetic flux B can be shifted to the negative side, and the peak value of the excitation current I can be suppressed small.

  As described above, in Embodiment 1, the integrator 11 that integrates the instantaneous value of the signal φ10 indicating the output voltage VAC of the inverter 1 is provided, and the output of the integrator 11 is output every time the phase of the signal φ10 becomes 0 degrees. The signal φ11 is sampled, the DC component Vdc of the output signal φ11 of the integrator 11 is detected based on the sampled signal φ11, and the inverter 1 is controlled so that the detected DC component Vdc is eliminated. The output signal φ11 of the integrator 11 indicates the magnetic flux B generated in the iron core 2c of the transformer 2. Therefore, the direct current component generated in the magnetic flux B of the transformer 2 can be quickly detected and reduced, and the occurrence of the demagnetization phenomenon in the transformer 2 can be prevented.

[Embodiment 2]
FIG. 11 is a block diagram showing a main part of the power converter according to the second embodiment of the present invention, and is a diagram to be compared with FIG. Referring to FIG. 11, this power converter is different from the power converter according to the first embodiment in that voltage command unit 15 is replaced with voltage command unit 15A. The voltage command unit 15 in FIG. 3 shifts the voltage command signal VC by a value corresponding to the direct current component Vdc to eliminate the bias magnetism. On the other hand, the voltage command unit 15A of the second embodiment eliminates the demagnetization by multiplying the voltage command signal VC by a gain A that is different between the period when the voltage command signal VC is a positive voltage and the period when the voltage command signal VC is a negative voltage. To do.

  12A and 12B are waveform diagrams showing the operation of the voltage command unit 15A. In particular, FIG. 12A shows the signal φ10 indicating the AC voltage VAC generated by the inverter 1, and FIG. 12B shows the voltage command signal VC and the corrected voltage command signal VCA. FIGS. 13A and 13B are views in which the time axis of the main part of FIGS. 12A and 12B is enlarged.

  12A and 12B and FIGS. 13A and 13B, the voltage of the signal φ10 decreases for a short time in the second half of one cycle (time t1 to t2) of the signal φ10 indicating the AC voltage VAC. The case is shown. In this case, as shown in FIGS. 10A and 10B, the positive DC component Vdc is superimposed on the signal φ11 indicating the magnetic flux B. The voltage command unit 15A multiplies the first half of one cycle of the voltage command signal VC by a gain A = (1-β) smaller than 1, and a gain A = (1 + β) larger than 1 in the second half. The voltage command signal VC is corrected by multiplication.

  The absolute value of the positive peak value of the corrected voltage command signal VCA is smaller than the absolute value of the positive peak value of the voltage command signal VC before correction. The absolute value of the negative peak value of the corrected voltage command signal VCA is larger than the absolute value of the negative peak value of the voltage command signal VC before correction. The waveform of the AC voltage VAC shifts from the waveform of the voltage command signal VC before correction to the waveform of the voltage command signal VCA after correction. As a result, the DC component Vdc of the signal φ11 indicating the magnetic flux B is reduced, and the occurrence of the demagnetization phenomenon is prevented.

  Next, the operation of the voltage command unit 15A will be described using mathematical expressions. The voltage command unit 15A generates a sinusoidal voltage command signal VC. The voltage command unit 15A controls the waveform of the voltage command signal VC so that the DC component Vdc is eliminated. When the DC component Vdc is 0V, the voltage command signal VC is VC = Vsinωt, and the output voltage VAC of the inverter 1 matches the voltage command signal VC. Here, ω = 2πf, and f is the frequency of the output voltage VAC of the inverter 1. Therefore, when the voltage command signal VC is integrated, the magnetic flux B is obtained, and B = ∫ (Vsinωt) dt = −V (cosωt) / ω. The DC component Vdc detected by the bias detection circuit 3 is expressed as Vdc = −αV / ω.

  In the case shown in FIGS. 12A and 12B and FIGS. 13A and 13B, when the demagnetization is eliminated in a half cycle, the following expression (1) is established.

  Since this only needs to be equal to Vdc = −αV / ω, −2βV / ω = −αV / ω is established. Therefore, the voltage command signal VC may be corrected to (1−α / 2) × Vsinωt.

  When negative DC component Vdc is superimposed on signal φ11 indicating magnetic flux B, voltage command unit 15A provides gain A = (1 + β) greater than 1 in the first half of one cycle of voltage command signal VC. The voltage command signal VC is corrected by multiplying the latter half by a gain A = (1−β) smaller than 1. In order to eliminate the magnetic bias in a half cycle, the voltage command signal VC may be corrected to (1 + α / 2) × Vsinωt.

Also in this second embodiment, the same effect as in the first embodiment can be obtained.
[Embodiment 3]
FIGS. 14A and 14B are waveform diagrams for explaining the problem of the first embodiment, and are compared with FIGS. 9A and 9B. 9A and 9B, the case has been described in which the AC voltage VAC decreases for a short time in the latter half of one cycle (time t0 to t1) of the AC voltage VAC. In this case, since the time from when the AC voltage VAC decreases until the DC component Vdc is sampled and held is shorter than a half cycle, the increase in the excitation current I can be suppressed quickly.

However, as shown in FIGS. 14A and 14B, when the AC voltage VAC decreases for a short time in the first half of one cycle (time t1 to t2) of the AC voltage VAC, the AC voltage VAC Since the time until the DC component Vdc is sampled and held is longer than a half cycle after the voltage decreases, the increase in the excitation current I cannot be suppressed quickly. In the third embodiment, this problem can be solved.

  FIG. 15 is a block diagram showing a main part of the power converter according to the third embodiment of the present invention, which is compared with FIG. Referring to FIG. 15, this power converter is different from the power converter according to the first embodiment in that bias detection circuit 3 is replaced with bias detection circuit 3A. The bias detection circuit 3A is obtained by replacing the phase detector 12 and the DC component detector 14 of the bias detection circuit 3 with a phase detector 12A and a DC component detector 14A, respectively.

  The phase detector 12A outputs the pulse signal P1 whenever the phase of the signal φ10 indicating the AC voltage VAC becomes 0 degrees, and outputs the pulse signal P2 whenever the phase of the signal φ10 indicating the AC voltage VAC becomes 180 degrees. To do. Pulse signals P1 and P2 are applied to sampling circuit 13 and DC component detector 14A.

  The sampling circuit 13 samples and holds the signal φ11 indicating the magnetic flux B in response to the pulse signal P1, and samples and holds the signal φ11 indicating the magnetic flux B in response to the pulse signal P2. In response to the pulse signal P1, the DC component detector 14A outputs the voltage difference between the output value of the sampling circuit 13 and the negative reference value of the signal φ11 indicating the magnetic flux B as the DC component Vdc. The negative reference value of the signal φ11 is a negative peak value of the signal φ11 in the period before the signal φ10 decreases (period before time t1).

  In response to the pulse signal P2, the DC component detector 14A outputs the voltage of the difference between the positive reference value of the signal φ11 indicating the magnetic flux B and the output value of the sampling circuit 13 as the DC component Vdc. The positive reference value of the signal φ11 is a positive peak value of the signal φ11 in the period before the signal φ10 decreases (period before time t1). The voltage command unit 15 generates the voltage command signal VC so that the DC component Vdc is eliminated. Therefore, the output voltage of the sampling circuit 13 is changed twice within one cycle of the AC voltage VAC, and the voltage command signal VC is also changed twice.

  FIGS. 16A and 16B are diagrams in which the waveform of the voltage command signal VC is added to FIGS. 14A and 14B. FIGS. 16C and 16D are diagrams in which the waveform of the voltage command signal VC is added to FIGS. 14A and 14B. 16 (a) and 16 (b), the voltage command signal VC after the time t2 is canceled so that the DC component Vdc detected when the phase of the AC voltage VAC becomes 0 degrees (time t2). A case where the value is shifted to the positive side by a value corresponding to the DC component Vdc is shown.

  In FIGS. 16C and 16D, the DC component Vdc detected when the phase of the AC voltage VAC reaches 180 degrees (a time intermediate between times t1 and t2) is canceled after that time. The case where the voltage command signal VC is shifted to the positive side by a value corresponding to the DC component Vdc is shown. Actually, the operations shown in FIGS. 16A and 16B and the operations shown in FIGS. 16C and 16D are alternately performed. Thereby, the alternating voltage VAC can be shifted to the positive side, the magnetic flux B can be shifted to the positive side, and the peak value of the excitation current I can be suppressed small.

  In the third embodiment, since the DC component Vdc of the signal φ11 indicating the magnetic flux B is detected twice within one cycle, the increase in the excitation current I can be suppressed more quickly than in the first embodiment.

  In the third embodiment, the DC component Vdc of the signal φ11 indicating the magnetic flux B is detected twice in one cycle. However, the present invention is not limited to this, and the DC component Vdc of the signal φ11 indicating the magnetic flux B is detected for one cycle. Needless to say, it may be detected three times or more. That is, in the present invention, the DC component Vdc of the signal φ11 indicating the magnetic flux B is detected N times within one cycle. N is a natural number. In the first embodiment, the case of N = 1 is shown, and in the second embodiment, the case of N = 2 is shown.

[Embodiment 4]
In the fourth embodiment, a case where N is infinite will be described. FIG. 17 is a block diagram showing a main part of the power converter according to the fourth embodiment of the present invention, and is a diagram compared with FIG. Referring to FIG. 17, this power converter is different from the power converter according to the first embodiment in that bias detection circuit 3 is replaced with bias detection circuit 20. The bias detection circuit 20 is obtained by replacing the phase detector 12, the sampling circuit 13, and the DC component detector 14 of the bias detection circuit 3 with a phase detector 12B, a sine wave generator 21, and a deviation detector 22. is there.

  The phase detector 12B detects the phase angle θ of the output signal φ10 of the voltage detector 10 (that is, the signal φ10 indicating the AC voltage VAC generated by the inverter 1), and outputs a signal φθ indicating the detected value. The sine wave generator 21 outputs a sine wave signal Vs delayed by 90 degrees from the output signal φ10 of the voltage detector 10 in accordance with the output signal φθ of the phase detector 12B. The sine wave signal Vs is a reference signal (that is, a signal having an ideal waveform) of the output signal φ11 of the integrator 11 (that is, the signal φ11 indicating the magnetic flux B in the iron core 2c of the transformer 2).

  The deviation detector 22 detects a deviation ΔV between the voltage of the output signal φ11 of the integrator 11 and the voltage of the sine wave signal Vs. The voltage command unit 15 of the control circuit 4 outputs a voltage command signal VC so that the deviation ΔV is eliminated. The control signal generator 16 generates control signals G1 to G4 based on the voltage command signal VC.

  18A to 18C are waveform diagrams showing the operation of the bias detection circuit 20 shown in FIG. FIG. 18A shows a signal φ10 indicating the AC voltage VAC. FIG. 18B shows a sine wave signal Vs and a signal φ11 indicating the magnetic flux B. FIG. 18C shows a deviation ΔV = φ11−Vs between the signal φ11 and the sine wave signal Vs.

At time t0 to t1, the signal φ10 indicating the AC voltage VAC changes in a sine wave shape, the waveforms of the signals φ11 and Vs are the same, and the deviation ΔV is zero. The phases of the signals φ11 and Vs are both 90 degrees behind the signal φ10. When the AC voltage VAC decreases for a short time at a certain time T1 between the times t1 and t2, the voltage of the signal φ11 obtained by integrating the signal φ10 indicating the AC voltage VAC depends on the decrease in the AC voltage VAC. descend. The deviation ΔV between the signal φ11 and the signal Vs becomes a negative voltage. The voltage command signal VC is adjusted so that the deviation ΔV is eliminated, and the occurrence of the demagnetization phenomenon in the transformer 2 is prevented.

  In the fourth embodiment, since the amount of bias (that is, deviation ΔV) is detected in real time from the time point T1 when the AC voltage VAC decreases, the voltage command signal VC is corrected. The occurrence of the phenomenon can be prevented quickly.

  19A to 19C are waveform diagrams for explaining the problem of the fourth embodiment. 19A shows the signal φ10 indicating the AC voltage VAC, FIG. 19B shows the sine wave signal Vs, and FIG. 19C shows the deviation ΔV = φ11−Vs between the signal φ11 and the sine wave signal Vs. Is shown.

  As shown in FIG. 19A, depending on the performance of the inverter 1, an ideal sinusoidal AC voltage VAC cannot be generated, and distortion may occur in the AC voltage VAC. FIG. 19A shows a case where a harmonic component is superimposed on the AC voltage VAC. Even if voltage distortion occurs in the AC voltage VAC, if the voltage distortion occurs symmetrically on the positive side and the negative side, no demagnetization phenomenon occurs and there is no need to adjust the voltage command signal VC. In general, the voltage distortion generated in the AC voltage VAC is generated symmetrically on the positive side and the negative side.

  When the output signal φ11 of the integrator 11 is sampled and held only once in one cycle as in the first embodiment, the voltage distortion generated symmetrically on the positive side and the negative side is ignored in the AC voltage VAC, and the magnetic bias is deviated. The detection circuit 3 and the control circuit 4 do not react to the voltage distortion of the AC voltage VAC.

  However, in the fourth embodiment, since the deviation ΔV between the output signal φ11 of the integrator 11 and the sine wave signal Vs is detected in real time, the deviation Δ is an AC voltage as shown in FIGS. In response to the voltage distortion of the VAC, it fluctuates at the frequency of the harmonic component.

  Therefore, when the AC voltage VAC has a voltage distortion, the bias detection circuit 3 of the first embodiment is selected, and when the AC voltage VAC has no voltage distortion, the bias detection circuit 20 of the fourth embodiment is selected. . The magnitude of the voltage distortion of the AC voltage VAC varies depending on the performance of the inverter 1 and further varies depending on the type of the load 52. When the load 52 includes only a linear component, the voltage distortion of the AC voltage VAC is reduced. When the nonlinear component of the load 52 is large, the voltage distortion of the AC voltage VAC increases.

[Embodiment 5]
FIG. 20 is a circuit block diagram showing a configuration of an uninterruptible power supply according to Embodiment 5 of the present invention, and is compared with FIG. Referring to FIG. 20, this uninterruptible power supply is different from the power converter of FIG. 1 in that a converter 5 is added.

  The converter 5 converts AC power from the commercial AC power supply 53 into DC power during normal times when AC power of commercial frequency is supplied from the commercial AC power supply 53. Battery 51 stores DC power generated by converter 5. The inverter 1 converts the DC power generated by the converter 5 into AC power having a commercial frequency during normal times when AC power is supplied from the commercial AC power supply 53. In the event of a power failure when the supply of AC power from the commercial AC power supply 53 is stopped, the operation of the converter 5 is stopped. At the time of a power failure, the inverter 1 converts the DC power of the battery 51 into AC power having a commercial frequency.

  Since other configurations and operations are the same as those in the first embodiment, description thereof will not be repeated. In the fifth embodiment, the same effect as in the first embodiment can be obtained.

[Comparative example]
FIG. 21 is a circuit diagram showing a configuration of a bias detection circuit included in a power converter as a comparative example of the present invention. Such a bias detection circuit is described in, for example, Japanese Patent Laid-Open No. 6-98559 (Patent Document 1).

  In FIG. 21, the bias detection circuit includes an insulation amplifier 30, an integration circuit 31, an inverting amplifier circuit 35, a DC cut circuit 39, a non-inverting circuit 42, and an adding circuit 43. The insulation amplifier 30 amplifies the AC voltage VAC generated by the inverter 1. The integration circuit 31 includes a resistance element 32, a capacitor 33, and an inverting amplifier 34, and integrates the output signal φ30 of the insulation amplifier 30. Output signal φ31 of integrating circuit 31 includes an AC component obtained by delaying the phase of signal φ30 by 90 degrees, and a DC component having a polarity opposite to that of the DC component included in signal φ30.

  The inverting amplifier circuit 35 includes resistance elements 36 and 37 and an inverting amplifier 38, and inverts the output signal φ31 of the integrating circuit 31. The output signal φ35 of the inverting amplifier circuit 35 becomes a signal φ35 obtained by inverting the output signal φ31 of the integration circuit 31. The DC cut circuit 39 includes a capacitor 40 and a resistance element 41, and removes a DC component from the output signal φ31 of the integration circuit 31. The non-inverting circuit 42 performs impedance conversion of the output of the DC cut circuit 39. Adder circuit 43 includes resistance elements 45 to 47 and inverting amplifier 48, adds output signal φ42 of non-inverting circuit 42 and output signal φ35 of inverting amplifier circuit 35, and outputs DC component Vdc1.

  In order to detect a constant DC component Vdc1 in such a bias detection circuit, it is necessary to sufficiently increase the time constants of the capacitor 40 and the resistance element 41 included in the DC cut circuit 39.

  FIGS. 22A and 22B are waveform diagrams for comparing the operation of the bias detection circuit of the present invention (for example, the bias detection circuit 3 of FIG. 3) with the operation of the bias detection circuit of the comparative example. . 22A shows the AC voltage VAC generated by the inverter 1, and FIG. 22B shows the DC component Vdc detected by the bias detection circuit 3 of the present invention and the bias detection circuit of the comparative example. DC component Vdc1. FIGS. 23 (a) and 23 (b) are waveform diagrams obtained by enlarging the main part (period from 3.0 seconds to 3.5 seconds) of FIGS. 22 (a) and 22 (b), respectively.

  22A, 22B, and 23A, 23B show a case where a DC component is generated in the AC voltage VAC at a certain time (2.0 seconds). The time constants of the capacitor 40 and the resistance element 41 are set to 1.0 second. In the present invention, the DC component Vdc is detected within one cycle of the AC voltage VAC (that is, 0.02 seconds or less) after the DC component is generated in the AC voltage VAC. Therefore, it is possible to quickly prevent the occurrence of the demagnetization phenomenon in the transformer 2.

  On the other hand, in the comparative example, it takes about 1 second until the DC component Vdc is detected after the DC component is generated in the AC voltage VAC. For this reason, a demagnetization phenomenon may occur between the time when the DC component is generated in the AC voltage VAC and the time when the DC component Vdc1 is detected, which may increase the excitation current. In the comparative example, an AC component having a small amplitude is superimposed on the DC component Vdc1.

  24 (a) and 24 (b) are other waveform diagrams for comparing the operation of the bias detection circuit of the present invention with the operation of the bias detection circuit of the comparative example. It is a figure contrasted with b). FIGS. 25 (a) and 25 (b) are waveform diagrams in which the main part (period from 1.9 seconds to 2.4 seconds) in FIGS.

  24A, 24B, and 25A, 25B show a case where a DC component is generated in the AC voltage VAC at a certain time (2.0 seconds). The time constants of the capacitor 40 and the resistance element 41 are set to 0.02 seconds (that is, about one cycle of the AC voltage VAC) in order to speed up the detection of the DC component Vdc1. In the present invention, a constant DC component Vdc is detected within one cycle of the AC voltage VAC (that is, 0.02 seconds or less) after a DC component is generated in the AC voltage VAC. Therefore, it is possible to quickly prevent the occurrence of the demagnetization phenomenon in the transformer 2.

  On the other hand, in the comparative example, an AC component having a large amplitude is superimposed on the DC component Vdc1, so that only the DC component cannot be detected. For this reason, it is difficult to adjust the voltage command signal VC so that the DC component Vdc1 is eliminated. Therefore, in the comparative example, the time constant of the capacitor 40 and the resistance element 41 needs to be 1 second or longer, and the direct current component generated in the alternating voltage VAC cannot be instantaneously corrected.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  DESCRIPTION OF SYMBOLS 1 Inverter, 2 Transformer, 2a Primary winding, 2b Secondary winding, 2c Iron core, 3, 3A, 20 Magnetization detection circuit, 4 Control circuit, 5 Converter, Q1-Q4 transistor, D1-D4 diode, L1 Reactor, C1, 33, 40 capacitor, 10 voltage detector, 11 integrator, 12, 12A, 12B phase detector, 13 sampling circuit, 14 DC component detector, 15, 15A voltage command unit, 16 control signal generator, 21 Sine wave generator, 22 Deviation detector, 30 Insulation amplifier, 31 Integration circuit, 32, 36, 37, 41, 45 to 47 Resistance element, 34, 38 Inversion amplifier, 35 Inversion amplification circuit, 39 DC cut circuit, 42 Non-inverting circuit, 43 addition circuit, 51 battery, 52 load, 53 commercial AC power supply.

Claims (12)

An inverter that converts DC voltage to AC voltage;
A transformer for receiving an output voltage of the inverter and applying an AC voltage to a load;
An integrator for integrating the output voltage of the inverter;
A sampling circuit that operates in synchronization with the output voltage of the inverter and samples the output signal of the integrator N times per period of the output voltage of the inverter;
A DC component detector that detects a difference between a signal sampled by the sampling circuit and a reference value as a DC component of the output signal of the integrator;
A power converter that receives a direct current component detected by the direct current component detector and controls a waveform of an output voltage of the inverter so that the received direct current component disappears, and N is a natural number. And a phase detector for detecting a phase angle of the output voltage of the inverter,
The phase angle of the output voltage of the inverter varies from 0 degrees to 360 degrees,
The sampling circuit samples the output signal of the integrator every time the phase angle detected by the phase detector reaches any one of predetermined first to Nth angles. The power converter according to 1. N is 1,
The power converter according to claim 2, wherein the predetermined first angle is 0 degree. N is 1,
The power converter according to claim 2, wherein the predetermined first angle is 180 degrees. N is 2,
First and second angle, said predetermined than zero degrees and 180 degrees der respectively,
The DC component detector detects a difference between a signal sampled by the sampling circuit at the first angle and a first reference value as a DC component of the output signal of the integrator at the first angle; The power according to claim 2, wherein a difference between a signal sampled by the sampling circuit at the second angle and a second reference value is detected as a DC component of the output signal of the integrator at the second angle. converter. Furthermore, a voltage detector for detecting an instantaneous value of the output voltage of the inverter and outputting a signal indicating the detected value is provided.
The integrator integrates the output signal of the voltage detector;
6. The sampling circuit operates in synchronization with an output signal of the voltage detector, and samples the output signal of the integrator N times per cycle of the output signal of the voltage detector. The power converter according to any one of the above. The control circuit includes:
A voltage command unit for generating a sinusoidal voltage command signal;
A signal generation unit that generates a control signal for controlling the waveform of the output voltage of the inverter according to the voltage command signal;
The voltage command unit receives a DC component detected by the DC component detector, and controls the waveform of the voltage command signal so that the received DC component disappears. The power converter according to item.   The voltage command unit receives a DC component detected by the DC component detector, and gives a DC offset value corresponding to the received DC component to the voltage command signal so that the received DC component disappears. Item 8. The power converter according to Item 7.   The voltage command unit receives the DC component detected by the DC component detector, and multiplies the voltage command signal by a value corresponding to the received DC component so that the received DC component disappears. The power converter described. Furthermore, the converter which converts the alternating current power supplied from alternating current power source into direct current power is provided,
During normal times when AC power is supplied from the AC power source, DC voltage output from the converter is converted into AC voltage by the inverter, and DC power generated by the converter is stored in a power storage device. ,
At the time of a power failure in which supply of AC power from the AC power supply is stopped, the operation of the converter is stopped, and the DC voltage of the power storage device is converted into AC voltage by the inverter. Item 10. The power converter according to any one of Items 9 to 9 . The power converter according to claim 1, wherein the reference value is 0V. The first reference value is a negative peak value in a period before the signal sampled by the sampling circuit at the first angle drops,
The power converter according to claim 5, wherein the second reference value is a positive peak value in a period before a signal sampled by the sampling circuit at the second angle decreases.

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