JPH04210773A - Controller for converter employing electromechanical conversion - Google Patents

Abstract

PURPOSE:To improve control characteristic by regulating the switching frequency of a primary driving circuit in the vicinity of the resonance frequency of an electromechanical conversion transformer thereby regulating the output of a converter. CONSTITUTION:High frequency power is taken out from the secondary of a piezoelectric transformer 2 and converted through an output rectifying circuit 3 into DC power which is then fed to a load. Output voltage from the output rectifying circuit 3 is detected and amplified through a detecting/amplifying circuit 4 and fed to a variable frequency oscillator 5 where the frequency is regulated. A piezoelectric transformer 1 incorporates a resonance circuit and the DC power to be fed to the secondary has maximum magnitude when the switching frequency of the input power to the primary of the piezoelectric transformer 1 is equal to the resonance frequency. The variable frequency oscillator 5 is regulated to normally shift the frequency of high frequency AC output power of a primary driving circuit 1 slightly from the resonance frequency and the output voltage is fed back through the detecting/amplifying circuit 4 and thereby bringing the frequency of the primary driving circuit 1 close to the resonance frequency or separating therefrom thus regulating the output voltage.

Description

[Detailed description of the invention]

[00011

[Industrial Field of Application] The present invention relates to a method for controlling the output of a high frequency converter using an electromechanical conversion transformer. [0002] BACKGROUND OF THE INVENTION By applying high frequency switching technology to power supply devices, significant improvements in efficiency and miniaturization have been achieved. This is due to the fact that in addition to lower losses due to switching, the capacitance of components such as transformers, reactors, and smoothing capacitors, which account for most of the size and weight of converter components, can be reduced in inverse proportion to the switching frequency. . Among these components, the power transformer is the most difficult to miniaturize.In particular, in response to the recent strong demand for thinner products, electromagnetic transformers, which are difficult to reduce in height, have become a bottleneck. was. [0003]

[Problems to be Solved by the Invention] In place of the above-mentioned electromagnetic transformers having windings and iron cores, piezoelectric transformers that utilize an electrical-mechanical conversion system based on the piezoelectric effect of ferroelectric materials have become popular. For example, as shown in Figures 3 and 4, two sets of electrodes are attached to a dielectric material such as lead titanate ceramic,
- When a high-frequency voltage is applied to the next electrode, the dielectric expands and contracts in a specific direction, and mechanical vibration reaches its maximum at a resonant frequency determined by the dimensions of the dielectric. On the other hand, the polarization strength of the secondary electrode changes at high frequencies due to the mechanical stress generated inside the dielectric, so if the charge generated on the dielectric surface due to polarization is taken out from the secondary electrode, this system Electrical energy can be transmitted from the primary side to the secondary side through the process of electrical vibration → mechanical vibration → electrical vibration. By changing the shape of the dielectric material and electrodes, it is possible to
A mechanical conversion transformer (hereinafter referred to as a piezoelectric transformer) can be realized, and its structure is simple and can be made as thin as 1 mm, so it is effective in making converters smaller and thinner. However, since a piezoelectric transformer equivalently includes a high-Q resonant circuit inside, its operation is significantly different from that of a normal electromagnetic transformer. FIG. 5 shows an equivalent circuit in which the mechanical system of the piezoelectric transformer is replaced with an electrical system. This equivalent circuit is an approximate one that is established near the resonant frequency, and generally has the following conditions. Cd+, Cd2>>C For example, if we open the secondary side and view this circuit as a two-terminal network from the primary side, we will see that it is the same as the well-known equivalent circuit of a crystal resonator. Since the piezoelectric transformer has the above-mentioned characteristics, it is difficult to apply the same output control method to a converter using a piezoelectric transformer as a converter using a normal electromagnetic transformer. Figure 6 shows a so-called forward converter that uses an ordinary electromagnetic transformer.The output is controlled by adjusting the duty ratio of the main switching element 21, and the switching frequency is determined by an independent oscillator 28 and is kept constant. It is. That is, it is a separately excited type. FIG. 7 shows another example using a normal electromagnetic transformer, which is called a ringing choke converter. The main switching element 31 turns on by detecting the timing when the current on the secondary side of the transformer 33 becomes O, and controls the output by adjusting the off timing. The switching frequency is not constant, but depends on the operating state of the main circuit. That is, it is a self-excited oscillation circuit. This circuit appears to control the output by changing the frequency, but since the output voltage is determined by the duty ratio of the main switching element 31, it is essentially a duty ratio control system. 8 and 9 are operation waveform diagrams of a resonant type converter that has recently attracted attention. FIG. 8 shows a current waveform in the case of a current resonant type, and FIG. 9 shows a voltage waveform in a voltage resonant type. In a resonant converter, the output is generally controlled by adjusting the switching frequency, but in the current resonant converter, resonance occurs when the main switching element (not shown) is on, and its on time TON is almost determined by the constant of the resonant circuit element (''-, 1/2 of the resonant period) and is always constant. In addition, in the voltage resonant type, resonance occurs when the main switching element (not shown) is off. , its off time T
OFF is almost determined by the constant of the resonant circuit element and is always constant. Therefore, changing the switching frequency (changing the switching period Ts) is actually nothing but adjusting TOFF in the current resonance type and TON in the voltage resonance type. In either case, the output voltage is the duty ratio D=Tos/("I"++s
+TOFF), so it can be said that the control in the resonant converter is also essentially a duty ratio control system. As explained above, output control in conventional converters using electromagnetic lances is essentially duty ratio control, but in converters using piezoelectric transformers, high Q resonance occurs inside the piezoelectric transformer. Because of the presence of the circuit, it is difficult to achieve effective output control using duty ratio control alone. The present invention has been made in view of this point, and it is an object of the present invention to propose a control method suitable for output control of a converter using an electromechanical conversion transformer (piezoelectric transformer). [0004]

[Means for Solving the Problems] In order to achieve the above-mentioned object, a method for controlling a converter using an electrical-to-mechanical conversion transformer according to the present invention includes a primary side drive circuit using high frequency switching and a secondary side drive circuit. The electric/mechanical conversion transformer to be driven has an equivalent resonant circuit inside, an output rectifier circuit connected to the secondary side of this transformer, and a detection amplifier circuit that feeds back the output of this output rectifier circuit. - A high frequency switching converter configured with a variable frequency oscillator that controls the switching frequency of the next-side drive circuit, the switching frequency of the -second-side drive circuit being adjusted at a frequency near the resonant frequency of the electromechanical conversion transformer. The output of the converter is controlled by
The converter output is controlled by two means: adjusting the switching frequency of the secondary drive circuit and adjusting the duty ratio of the secondary drive circuit via a voltage/time ratio conversion circuit. [0005]

[Operation] As mentioned above, the equivalent circuit shown in Figure 5 is established near the resonant frequency, and the power transmitted to the secondary side of the piezoelectric transformer reaches its maximum when the switching frequency is equal to the resonant frequency. The larger the deviation between the resonant frequency and the resonant frequency, the smaller the transmitted power. Therefore, a constant voltage converter can be realized by setting the switching frequency during steady state to a frequency slightly shifted from the resonant frequency and adjusting the switching frequency according to fluctuations in the output voltage. [0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a method for controlling a converter using an electromechanical conversion transformer (piezoelectric transformer) according to the present invention will be described below with reference to the drawings. [0007] FIG. 3 is a cross-sectional view for explaining the configuration of a piezoelectric transformer, and FIG. 4 is a perspective view thereof. In FIG. Two sets of electrodes 11+ and 112 and 12+ and 122 are attached, and for example, electrodes 111 and 112 are connected to primary terminals, and electrodes 12 and 122 are connected to secondary terminals to form a piezoelectric transformer. [00081 FIG. 1 is a block diagram showing an embodiment of a converter using an electromechanical conversion transformer according to the present invention. In FIG. 1, a negative side drive circuit 1 inputs DC power from a DC @ source 6, converts it into high frequency AC power at a frequency determined by a variable frequency oscillator 5, and sends the high frequency power to the primary side of a piezoelectric transformer 2. The high frequency power is extracted from the secondary side of the piezoelectric transformer 2, converted into DC power in the output rectifier circuit 3, and supplied to the load. The output voltage from the output rectifier circuit 3 is detected and amplified by a detection amplifier circuit 4, and is applied to a variable frequency oscillator 5 to adjust its frequency. Since a resonant circuit exists inside the piezoelectric transformer 1, the DC power transmitted to the secondary side becomes maximum when the switching frequency of the input power to the primary side of the piezoelectric transformer 1 becomes equal to the resonant frequency. Therefore, by adjusting the variable frequency oscillator 5, the frequency of the high frequency AC power output from the primary drive circuit 1 is set at a position slightly deviated from the resonant frequency during steady state, and the output voltage is set via the detection amplifier 4. By feeding back the negative side drive circuit 1
The output voltage can be adjusted by moving the frequency closer to or farther away from the resonant frequency. [0009] FIG. 2 is a block diagram showing another embodiment according to the present invention, in which the -next side drive circuit 1. Piezoelectric transformer 2. Output rectifier circuit 3. Since the detection amplifier 4 and the variable frequency oscillator 5 have the same configuration as in FIG. 1, their explanation will be omitted. This converter is equipped with a voltage/time ratio conversion circuit 7, in which the switching frequency of the negative side drive circuit 1 is determined by the variable frequency oscillator 5, and its duty ratio is determined by the voltage/time ratio conversion circuit 7. Defined and working. That is, the output control in this converter uses two means: frequency control and duty ratio control.

0010

[Effects of the Invention] As explained above, the method of controlling a converter using an electrical/mechanical conversion transformer according to the present invention is as follows:
A piezoelectric transformer is used in place of a conventional electromagnetic transformer, and the resonant characteristics of the piezoelectric transformer are skillfully utilized to provide a control system consisting of switching frequency control and time ratio control based on principles different from those of the past. This makes it possible to realize a small and thin converter with sufficient control characteristics.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment according to the present invention.

FIG. 2 is a block diagram showing another embodiment according to the present invention.

FIG. 3 is a sectional view showing the configuration of a piezoelectric transformer.

FIG. 4 is a perspective view of a piezoelectric transformer.

[Fig. 5] Equivalent circuit of a piezoelectric transformer.

FIG. 6 is a block diagram of a conventional forward converter.

FIG. 7 is a block diagram of a conventional ringing choke converter.

FIG. 8 is a current waveform diagram of a current resonant converter.

FIG. 9 is a voltage waveform diagram of a voltage resonant converter.

[Explanation of symbols]

Primary side drive circuit 2 Piezoelectric transformer 3 Output rectifier circuit 4 Detection amplifier circuit 5 Variable frequency oscillator 6 DC power supply 7 Voltage/time ratio conversion circuit

[Figure 7]

Claims (2)

[Claims] Claim 1: A primary side drive circuit using high frequency switching, an electric-to-mechanical conversion transformer having an internal equivalent resonant circuit driven by the primary side drive circuit, and a secondary side of the electric-to-mechanical conversion transformer. A high frequency oscillator configured by a connected output rectifier circuit that outputs DC power, and a variable frequency oscillator that controls the switching frequency of the primary side drive circuit via a detection amplifier circuit that detects, amplifies, and feeds back the DC power. The switching converter is characterized in that the converter output is controlled by adjusting the switching frequency of the primary side drive circuit via the variable frequency oscillator using resonance frequency characteristics of the electrical-mechanical conversion transformer. A method of controlling a converter using an electrical-mechanical conversion transformer. [Claim 2] Adjustment of the switching frequency of the primary side drive circuit is performed via a variable frequency oscillator using the resonant frequency characteristics of the electromechanical conversion transformer, and the voltage/time at which the feedback voltage from the detection amplifier circuit is inputted. Control of a converter using an electromechanical conversion transformer according to claim 1, characterized in that the converter output is controlled by two means for adjusting the duty ratio of the primary side drive circuit via a ratio conversion circuit. Law.