Variable frequency high-frequency power supply

Abstract

A variable frequency high-frequency power supply according to the present invention comprises: a multiplex inverter; a synthesis unit that synthesizes the inverter outputs of the multiplex inverter; and a low-pass filter. The multiplex inverter and the synthesis unit suppress odd-order harmonics of an n-th order or lower by phase difference control. The low-pass filter suppresses harmonics of high odd-order harmonics of an (n+2)-th order or lower, the suppression of which remains by the phase difference control of the multiplex inverter due to filter characteristics. The phase difference control and the low-pass filter make it possible to achieve a high-frequency power supply (RF generator) capable of varying the frequency of an output signal in a wide band.

Description

Variable frequency high-frequency power supply

[0001] This invention relates to a high-frequency power supply (RF generator) that has a variable frequency over a wide bandwidth of the RF band from HF to VHF (3 MHz to 100 MHz).

[0002] A Class D high-frequency power supply is known that uses a single-phase square-wave inverter to convert DC to AC and obtain a sinusoidal output. In fixed-frequency control, methods for suppressing harmonics included in the sinusoidal output include using a narrow-band output filter, as well as suppressing harmonics by controlling the inverter's phase shift or phase difference.

[0003] Inverter phase shift control suppresses harmonics by shifting the phase between the leading and lagging legs of the inverter by a phase shift amount α. As a method of harmonic suppression using phase shift control, a series single-phase double inverter device is known, which has a dual configuration in which two single-phase inverters are connected in series with two transformers (see Patent Document 1).

[0004] Inverter phase difference control suppresses harmonics in a series single-phase dual inverter device by introducing a phase difference between the outputs of each inverter. Patent document 2 describes a configuration in which harmonic suppression is performed by phase difference control in a series single-phase dual inverter device.

[0005] Furthermore, Patent Document 3 describes a high-frequency power supply that outputs a pseudo-sine wave by multiplexing the outputs of two single-phase full-bridge inverters by connecting them in series with a transformer, wherein the third harmonic having a frequency three times that of the fundamental wave of the inverter output is suppressed by phase shift control using pulse width control with a phase shift amount α of 60° for each of the two inverters, and further suppresses the fifth harmonic having a frequency five times that of the fundamental wave of the inverter output by phase difference control with a phase difference φ of 36° between the two inverters.

[0006] Figure 9 shows an example configuration of a series single-phase double inverter device. The series single-phase double inverter device 100 includes a DC power supply 101, a double inverter 102 that converts the DC of the DC power supply 101 to AC, a combining unit 104 that connects the outputs of the double inverter 102 in series, and a phase control unit 103 that controls the phase of the double inverter 102. Harmonics included in the pseudo-sine wave synthesized by the combining unit 104 are suppressed by an LPF 105.

[0007] The dual inverter 102 consists of two inverters, inverter INV1 and inverter INV2, connected in parallel to the DC power supply 101. The two inverters, inverter INV1 and inverter INV2, suppress harmonics by phase shift control, which shifts the phase between their leading and lagging legs by a phase shift amount α. Furthermore, harmonics are suppressed by phase difference control, which sets a phase difference φ between the two inverters, inverter INV1 and inverter INV2.

[0008] The phase control unit 103 includes a phase shift control unit 103A that performs phase shift control based on a phase shift amount α, and a phase difference control unit 103B that performs phase difference control based on a phase difference φ. It outputs gate signals to the gates of inverters INV1 and INV2, setting the phase shift amount α and the phase difference φ. For example, setting the phase shift amount α to π / 3 suppresses the third harmonic, and setting the phase difference φ to π / 5 suppresses the fifth harmonic.

[0009] JP 3-103080, JP 10-337045, JP 2017-192218

[0010] The frequency control of the series single-phase double inverter device described above is related to fixed frequency control. Applying this fixed frequency control to variable frequency control to realize a high-frequency power supply with a wide bandwidth and variable frequency presents challenges.

[0011] When using a narrowband output filter to suppress harmonics and obtain a sinusoidal output, the frequency bandwidth is limited by the narrowband characteristics of the output filter, making broadband operation impossible.

[0012] Fig. 10A shows the inverter output and the frequency characteristics of the LPF when fixed-frequency control is performed. For a fixed frequency f ｆｉｘ at which the third harmonic with a frequency three times that of the fundamental wave of the inverter output is suppressed by phase shift control with a phase shift amount α = π / 3, and an example of suppressing the fifth harmonic with a frequency five times that of the fundamental wave by the output filter of a low-pass filter (LPF) is shown. Here, the cut-off frequency f ３ of the low-pass filter (LPF) is set between the third harmonic frequency f ｆｉｘ = 3·f ５ and the fifth harmonic frequency f 9000009]] ｆｉｘ = 5·f ｃｕｔｏｆｆ of the inverter output. ３ is set between the third harmonic frequency f ５ and the fifth harmonic frequency f

[0013] Fig. 10B shows the case where the fixed-frequency control of Fig. 10A is applied to variable-frequency control. In variable-frequency control, a high frequency of the variable frequency fs is output within the variable frequency range [fs ｍｉｎ , fs ｍａｘ . The inverter output of the variable frequency fs has frequency components of the fundamental wave (fundamental wave frequency fo) and odd harmonic waves (harmonic wave frequencies f ３ , f ５ ,...). Note that the frequency components of the even harmonic waves are zero due to half-wave symmetry.

[0014] Fig. 10B shows the case where the fundamental wave frequency fo of the fundamental wave of the inverter output is higher than the cut-off frequency f ｃｕｔｏｆｆ of Fig. 10A. In this case, the third harmonic is suppressed by phase shift control with a phase shift amount α = π / 3, and the fifth harmonic is suppressed by a low-pass filter (LPF). On the other hand, since the fundamental wave frequency fo of the fundamental wave of the inverter output is also higher than the cut-off frequency f ｃｕｔｏｆｆ of the low-pass filter (LPF), the fundamental wave is also suppressed and wideband operation cannot be performed.

[0015] Fig. 10C shows an example in which the cut-off frequency f ｃｕｔｏｆｆ of the LPF is shifted to the high-frequency side to widen the variable frequency range. The cut-off frequency f ｃｕｔｏｆｆBy shifting to the higher frequency side, the fundamental frequency fo of the fundamental wave of the inverter output in Figure 10B becomes the cutoff frequency f ｃｕｔｏｆｆ Since it becomes lower than this, suppression can be avoided. However, when the fundamental frequency fo of the inverter output is as shown in Figure 10C, the frequency f is 5 times higher. ５ = 5・fo is the cutoff frequency f of the LPF. ｃｕｔｏｆｆ Because it does not exceed the limit, it remains unsuppressed, making broadband operation difficult.

[0016] As described above, when the phase shift control of a fixed frequency control is applied to a wideband variable frequency control, the cutoff frequency f of the LPF ｃｕｔｏｆｆ Even after making adjustments, there is a challenge in that broadband operation cannot be performed.

[0017] To achieve broadband operation, it is conceivable to combine phase shift control and phase difference control to remove multiple harmonics. Figure 10D shows an example of combining phase shift control and phase difference control and applying this to variable frequency control to remove harmonics.

[0018] In this configuration that combines phase shift control and phase difference control, each inverter of the multiple inverter needs to simultaneously perform two types of phase control: phase shift control, which aims to shift the phase between leading and lagging legs within the inverter, and phase difference control, which aims to reduce the phase difference between inverters. In this phase control that combines phase shift control and phase difference control, the phase control amount is a superposition of the phase shift amount and the phase difference amount. Therefore, when the frequency is variable, the phase control amount must be set according to the variable frequency, which presents the challenge of complex phase control.

[0019] Furthermore, when controlling the effective voltage of the inverter output using phase shift control, there is the problem that phase shift control cannot be used for harmonic suppression.

[0020] The variable frequency high-frequency power supply of the present invention aims to solve the above problems and realize a high-frequency power supply (RF generator) that can vary the frequency of the output signal over a wide bandwidth.

[0021] The variable frequency high-frequency power supply of the present invention comprises a multiple inverter, a combining unit for combining the inverter outputs of the multiple inverter, and a low-pass filter (LPF). The multiple inverter and the combining unit suppress odd-order harmonics of order n or lower (where n is an odd number) by phase difference control, and the low-pass filter suppresses high-order odd-order harmonics of order (n+2) or higher that remain unsuppressed by the phase difference control of the multiple inverter through its filter characteristics.

[0022] Due to their half-wave symmetry, even-order harmonics have zero frequency components, and therefore only odd-order harmonics exist. When the fundamental frequency of a variable frequency fs is fo, and n is an odd number, the nth harmonic is represented as the odd-order harmonic n・fo.

[0023] The present invention provides a variable frequency range [fs ｍｉｎ , fs ｍａｘ For the variable frequency fs within the ], in order to perform variable frequency control in which the odd-order harmonics n・fo of the nth order and below are suppressed by phase difference control, n・fs ｍｉｎ <f ｃｕｔｏｆｆ < (n+2) fs ｍｉｎ It has the frequency relationship.

[0024] In the above frequency relationship, n・fs ｍｉｎ <f ｃｕｔｏｆｆ The frequency relationship is as follows: Variable frequency range [fs ｍｉｎ ,fs ｍａｘ This is the frequency relationship when suppressing the nth or lower odd-order harmonics n・fo included in the inverter output using phase difference control, with respect to the variable frequency fs within [ ]. ｃｕｔｏｆｆ < (n+2) fs ｍｉｎ The frequency relationship is as follows: Variable frequency range [fs ｍｉｎ ,fs ｍａｘ This is the frequency relationship when suppressing higher-order odd harmonics (n+2)・fs of the (n+2)th order or higher with respect to the variable frequency fs within the bracket by the filter characteristics of a low-pass filter (LPF).

[0025] In this invention, the variable frequency fs is within the variable frequency range [fs ｍｉｎ ,fs ｍａｘRegardless of the frequency, odd-order harmonics of the nth order or higher and (n+2) order or lower included in the output signal of the variable frequency fs are suppressed by phase difference control and a low-pass filter, and odd-order harmonics of the (n+2) order or higher are suppressed by a low-pass filter, thereby making the frequency of the output signal variable over a wide bandwidth.

[0026] The variable frequency high-frequency power supply of the present invention is a variable frequency high-frequency power supply that outputs a variable frequency fs within a variable frequency range, and comprises: (A) a DC power supply; (B) a multiple inverter in which a plurality of inverters that convert the DC of the DC power supply into a square wave signal are connected in series; (C) a control unit that controls the gate signals of the switching elements of the bridge circuits that constitute each inverter of the multiple inverter; (D) a combining unit that combines the inverter outputs of each inverter of the multiple inverter; and (E) a low-pass filter connected to the output terminal of the combining unit.

[0027] The variable frequency high-frequency power supply of the present invention has a variable frequency range [fs ｍｉｎ ,fs ｍａｘ The frequency fs of the high-frequency signal output within the ] is made variable. Here, fs ｍｉｎ This is the lower limit frequency of the variable frequency fs, and fs ｍａｘ This is the upper limit frequency of the variable frequency fs.

[0028] When the frequency of a high-frequency signal is varied using an inverter, the variable frequency fs of the high-frequency signal output from the inverter includes harmonics along with the fundamental frequency fo. Due to their half-wave symmetry, these harmonics are odd-order harmonics.

[0029] The variable frequency high-frequency power supply of the present invention suppresses low-frequency harmonics up to the nth order by phase difference control, and suppresses harmonics above the nth order by using a low-pass filter in combination.

[0030] Suppression of harmonics up to the nth order by phase difference control within a variable frequency range [fs ｍｉｎ ,fs ｍａｘ To perform this for any frequency within the ], use the lower frequency limit fs ｍｉｎ The nth harmonic n・fs ｍｉｎ The cutoff frequency f of the low-pass filter ｃｕｔｏｆｆ Smaller than (n・fsｍｉｎ <f ｃｕｔｏｆｆ ) can be determined. According to this frequency relationship, the variable frequency range [fs ｍｉｎ ,fs ｍａｘ The nth harmonic of the variable frequency fs within ] is n・fo(<n・fs ｍａｘ This is suppressed by phase difference control.

[0031] Also, variable frequency range [fs ｍｉｎ ,fs ｍａｘ In the variable frequency fs within ], in order to suppress the (n+2)th or higher odd-order harmonics (n+2)・fs by the filter characteristics of the low-pass filter (LPF), f ｃｕｔｏｆｆ < (n+2) fs ｍｉｎ The frequency relationship between the two above can be determined. The two frequency relationships are n·fs ｍｉｎ <f ｃｕｔｏｆｆ < (n+2) fs ｍｉｎ It is expressed in terms of frequency relationships.

[0032] (Multiplex Inverter) A multiplex inverter is equipped with multiple inverters connected in series, with two inverters paired together and a phase difference β between the inverters, thereby suppressing harmonics through phase difference control. The number of inverter pairs is determined according to the order of the harmonics to be suppressed. For example, one pair of inverters is used to suppress one harmonic of the third harmonic, while two pairs of inverters are used to suppress two harmonics, the third and fifth harmonics.

[0033] (Control Unit) The control unit comprises a variable frequency control unit and a phase difference control unit. The variable frequency control unit has a variable frequency range [fs ｍｉｎ ,fs ｍａｘ The variable frequency fs within the [ ] is made variable to control the frequency of the inverter output of each inverter in the multiple inverter. The phase difference control unit controls the phase difference β of the gate signals of the switching elements of the bridge circuit between the inverters of the multiple inverter to suppress harmonics.

[0034] The phase difference control unit performs the following: (a) When the minimum order of odd harmonics to be suppressed by phase difference control is 3rd and the maximum order is nth, for the order m of the harmonic to be suppressed among the orders from 3rd to nth, the angle π / m obtained by dividing π by the order m is set as the phase difference π / m between inverters; (b) In a multiple inverter, phase difference control is performed to shift the phase of the gate signals of the two inverters that suppress the mth-th harmonic by a phase difference of π / m. By performing phase difference control that shifts the phase difference by π / m for all odd orders m from order 3 to order n, the variable frequency range [fs ｍｉｎ ,fs ｍａｘ Suppresses all harmonics of ].

[0035] In addition to the phase difference control described in (a) and (b) above, the phase difference control unit further performs phase difference control on the gate signals of each inverter constituting the multiple inverter by (1 / 2) (π / (2m)) of the phase difference π / m, in opposite phase directions relative to the fundamental wave of the inverter output, and superimposes the gate signals that are out of phase with respect to each other. In the two gate signals on which phase difference control is performed, the phase difference of one gate signal is set to (+π / (2m)) and the phase difference of the other gate signal is set to (-π / (2m)) relative to the fundamental wave of the inverter output, thereby making the phase difference β between the inverters π / m.

[0036] (Combination Unit) The combination unit combines the outputs of each inverter, which have a phase difference between them, by controlling the phase difference of multiple inverters. This cancels out odd-order harmonics up to the nth order and suppresses odd-order harmonics up to the nth order that are included within the variable frequency range of the output signal.

[0037] (Low-pass filter) Cutoff frequency f of the low-pass filter ｃｕｔｏｆｆ The upper frequency fs of the variable frequency range ｍａｘ And the harmonic frequency of the (n+2)th odd-order harmonic ((n+2)・fs ｍｉｎ Set between ) and fs ｍａｘ <f ｃｕｔｏｆｆ <((n+2)・fs ｍｉｎ Due to the relationship between the two components, odd-order harmonics higher than the nth order are suppressed from the combined output of the synthesis unit.

[0038] (Form 1) When suppressing the harmonic frequencies of odd-order harmonics up to the third order within a variable frequency range using phase difference control, the order of the odd-order harmonics is 3. In this case, the multiple inverter comprises two inverters: one driven by a gate signal with a phase difference of (+π / 6) relative to the fundamental wave of the inverter output, and another driven by a gate signal with a phase difference of (-π / 6). Due to the phase difference of (+π / 6) and the phase difference of (-π / 6), the phase difference β between the inverters becomes π / 3, and the third harmonic is suppressed.

[0039] (Form 2) When the harmonic frequencies of odd-order harmonics up to the 5th order are suppressed by phase difference control within the variable frequency range, the odd-order harmonics are 3 and 5. A multiple inverter combining two harmonics of order 3 and order 5 comprises four inverters driven by a gate signal with a phase difference of (+4π / 15) relative to the fundamental wave of the inverter output: an inverter driven by a gate signal with a phase difference of (-4π / 15), an inverter driven by a gate signal with a phase difference of (+π / 15), and an inverter driven by a gate signal with a phase difference of (-π / 15).

[0040] In these four inverter combinations, the phase difference β between the two inverters becomes π / 3 when a gate signal with a phase difference of (+4π / 15) is used and a gate signal with a phase difference of (-π / 15) is used. Similarly, the phase difference β between the two inverters becomes π / 3 when a gate signal with a phase difference of (+π / 15) is used and a gate signal with a phase difference of (-4π / 15) is used, and in both cases, the third harmonic is suppressed.

[0041] On the other hand, the phase difference β between these two inverters becomes π / 5 when a gate signal with a phase difference of (+4π / 15) is used and a gate signal with a phase difference of (+π / 15) is used. Also, the phase difference β between these two inverters becomes π / 5 when a gate signal with a phase difference of (-π / 15) is used and a gate signal with a phase difference of (-4π / 15) is used, and in both cases the fifth harmonic is suppressed.

[0042] (Form 3) When the harmonic frequencies of odd-order harmonics up to the 7th order are suppressed by phase difference control within the variable frequency range, the orders of the odd-order harmonics are 3, 5, and 7, and the multiple inverters that combine three orders of 3, 5, and 7 are, with respect to the fundamental wave of the inverter output, an inverter driven by a gate signal with a phase difference of (+71π / 210), an inverter driven by a gate signal with a phase difference of (-71π / 210), an inverter driven by a gate signal with a phase difference of (+π / 210), an inverter driven by a gate signal with a phase difference of (-π / 210), an inverter driven by a gate signal with a phase difference of (+29π / 210), an inverter driven by a gate signal with a phase difference of (-29π / 210), an inverter driven by a gate signal with a phase difference of (+41π / 210), and It is equipped with eight inverters, each driven by a gate signal with a phase difference of (-41π / 210).

[0043] In these eight inverter combinations, the third, fifth, and seventh harmonics are suppressed by combining the gate signals with different phase differences. For example, for the third harmonic, in these eight inverter combinations, the combination of a gate signal with a phase difference of (+71π / 210) and a gate signal with a phase difference of (π / 210), a gate signal with a phase difference of (+29π / 210) and a gate signal with a phase difference of (-41π / 210), and a gate signal with a phase difference of (-π / 210) and a gate signal with a phase difference of (-71π / 210) results in a phase difference β between two inverters of π / 3, thereby suppressing the third harmonic.

[0044] According to the variable frequency high-frequency power supply of the present invention, the frequency of the output signal can be varied over a wide bandwidth.

[0045] This is a schematic diagram illustrating the variable frequency high-frequency power supply of the present invention. This is a diagram illustrating the relationship between the variable frequency range, harmonic frequencies, and cutoff frequencies. This is a diagram illustrating the relationship between the variable frequency range, harmonic frequencies, and cutoff frequencies. This is a diagram illustrating an example of phase difference control suppression of the third and fifth harmonics, and low-pass filter suppression of harmonics from the seventh harmonic onwards. This is a diagram illustrating an example of phase difference control suppression of the third and fifth harmonics, and low-pass filter suppression of harmonics from the seventh harmonic onwards. This is a diagram illustrating an example of phase difference control suppression of the third and fifth harmonics, and low-pass filter suppression of harmonics from the seventh harmonic onwards. This is a diagram illustrating an example of a multiple inverter configuration consisting of four inverters. This is a diagram illustrating an example of an inverter configuration. This is a signal diagram of an example of an inverter output. This is a diagram illustrating the variable frequency range and the frequency states of the fundamental wave and harmonics. This is a diagram illustrating an example of a multiple inverter configuration consisting of eight inverters. This is a diagram illustrating one example of a series single-phase double inverter device configuration. This is a diagram illustrating the frequency characteristics of the inverter output and LPF by fixed frequency control. This is a diagram illustrating the frequency characteristics of the inverter output and LPF when applied to variable frequency control. This figure shows the frequency characteristics of the inverter output and LPF when the variable frequency range is widened. This figure also shows the frequency characteristics of the inverter output and LPF when variable frequency control is applied to a combination of phase shift control and phase difference control.

[0046] The variable frequency high-frequency power supply of the present invention will be described below with reference to the drawings.

[0047] (Schematic configuration of a variable frequency high-frequency power supply) Figure 1 is a schematic diagram illustrating the variable frequency high-frequency power supply of the present invention. The variable frequency high-frequency power supply 10 is a variable frequency high-frequency power supply that outputs a variable frequency fs within a variable frequency range, and comprises a DC power supply 1, a multiple inverter 2 formed by connecting a plurality of inverters in series to convert the DC of the DC power supply 1 into a square wave signal, a control unit 3 that controls the gate signals that drive the gates of the switching elements of the bridge circuits constituting each inverter 2a to 2d of the multiple inverter 2, a combining unit 4 that combines the output voltages of the inverter outputs of each inverter, and a low-pass filter (LPF) 5 connected to the output terminal of the combining unit 4.

[0048] (Multiplex Inverter) The example of a multiplex inverter configuration shown in Figure 1 is an example of a quadruple inverter equipped with four inverters as the multiplex inverter 2. The multiplex inverter 2 is not limited to a quadruple inverter, but can also be a 2 ｎ It can be an n-layer inverter equipped with this many inverters.

[0049] The quadruple inverter shown in the example configuration in Figure 1 comprises four inverters 2a, 2b, 2c, and 2d, with two inverters connected in series as a pair. By driving the two inverters constituting these pairs with a drive signal having a phase difference, a phase difference β is introduced between the inverters, and phase difference control is performed. By connecting the outputs of the two inverters in series, an output with suppressed harmonics is obtained.

[0050] In the quadruple inverter shown in Figure 1, the pair of inverters 2a and 2b is one pair, and the pair of inverters 2c and 2d is the other pair. Each pair of inverters is controlled by the phase difference β between the inverters. １ , β ２ In the example shown in Figure 1, in the pair of inverters 2a and 2b, the phase of inverter 2a is set to lead phase +β relative to the fundamental wave. １ The phase of inverter 2b is set to be lagging phase -β relative to the fundamental wave. １ This is an example where the phases are set in opposite directions as / 2, thereby reducing the phase difference between the inverters to β １ Set to this.

[0051] On the other hand, in the pair of inverter 2c and inverter 2d, the phase of inverter 2c is set to lead the fundamental wave by +β. ２ The phase of inverter 2d is set to be lagging phase -β relative to the fundamental wave. ２ This is an example where the phases are set in opposite directions as / 2, thereby reducing the phase difference between the inverters to β ２ Set to this.

[0052] In phase difference control, the phase difference β between inverters corresponds to the order m of the harmonic being suppressed. The relationship between the phase difference β and the order of the suppressed harmonic will be explained later.

[0053] (Relationship between Variable Frequency Range, Harmonic Frequencies, and Cutoff Frequencies) The variable frequency high-frequency power supply 10 of the present invention outputs a high-frequency signal with fs as the variable frequency within the variable frequency range, and suppresses the harmonic frequencies of odd-order harmonics up to the nth order within the variable frequency range by phase difference control, and suppresses the (n+2)th order harmonic with frequencies exceeding the variable frequency range by a low-pass filter. The relationship between the variable frequency range, harmonic frequencies, and cutoff frequencies will be explained below.

[0054] Figures 2A and 2B are diagrams illustrating the relationship between the variable frequency range, harmonic frequencies, and cutoff frequencies. Variable frequency range [fs ｍｉｎ ,fs ｍａｘ ] is the lower frequency limit fs ｍｉｎ and upper frequency fs ｍａｘ This is the frequency range enclosed by [the specified frequency range], and the variable frequency fs of the inverter output is made variable within this variable frequency range.

[0055] The inverter output of a variable frequency fs includes the fundamental frequency fo and its harmonics. Due to half-wave symmetry, even-order harmonics are zero, so the inverter output consists only of odd-order harmonics. Here, when n is an odd number, the harmonic frequency of the nth odd-order harmonic is n times the fundamental frequency fo, which is f. ｎ (= n・fo)

[0056] When suppressing low-frequency harmonics up to the nth order using phase difference control, harmonics above the nth order are suppressed by a low-pass filter. The cutoff frequency f of this low-pass filter is... ｃｕｔｏｆｆ This frequency represents the boundary between the harmonic suppression region due to phase difference control and the harmonic suppression region due to the low-pass filter.

[0057] Variable frequency range [fs ｍｉｎ ,fs ｍａｘ For a variable frequency fs within [ ], in order to suppress harmonics up to the nth order by phase difference control, at least the lower frequency fs ｍｉｎ The nth harmonic n・fs ｍｉｎ However, the cutoff frequency f of the low-pass filter ｃｕｔｏｆｆA relationship n·fs smaller than ｍｉｎ <f ｃｕｔｏｆｆ is required. According to this frequency relationship, within the variable frequency range [fs ｍｉｎ , fs ｍａｘ , at the variable frequency fs, the n-th harmonic f ｎ (= n·fo (< n·fs ｍｉｎ )) harmonic is suppressed by phase difference control.

[0058] Also, for the variable frequency fs within the variable frequency range [fs ｍｉｎ , fs ｍａｘ , in order to suppress odd harmonics of (n + 2) or higher order ((n + 2)·fs) by the filter characteristics of a low-pass filter (LPF), a frequency relationship of f ｃｕｔｏｆｆ < (n + 2)·fs ｍｉｎ is required.

[0059] According to this relationship, although the harmonic frequency f ｎ＋２ (= (n + 2)·fo) of the (n + 2)-th harmonic is not suppressed by the phase difference control of the inverter, since it is at a frequency higher than the cut-off frequency f ｃｕｔｏｆｆ , it is suppressed by a low-pass filter (LPF).

[0060] Summarizing the above frequency relationships, for the variable frequency fs within the variable frequency range [fs ｍｉｎ , fs ｍａｘ , the phase difference control enables suppression of harmonics n·fo on the low frequency side up to the n-th order, and the frequency relationship for suppressing odd harmonics of (n + 2) or higher order ((n + 2)·fs) by a low-pass filter (LPF) is represented by.

[0061] When suppressing harmonics included in the output signal of the inverter by phase difference control, ideally the phase difference control can suppress all harmonics, but in reality, due to the influence of dead time set when operating the inverter, the rise / fall speed of the signal, etc., some harmonics remain unsuppressed. Therefore, it is difficult to completely suppress the generated harmonics by phase difference control, and for these remaining harmonics, a low-pass filter is used in combination for suppression.

[0062] Figure 2A shows the case where harmonic suppression by phase difference control is ideal, while Figure 2B shows the case where harmonic suppression by phase difference control is insufficient.

[0063] As shown in Figure 2A, when harmonic suppression by phase difference control is performed ideally, the upper limit frequency fs is the highest frequency among the nth harmonics. ｍａｘ The nth odd-order harmonic, frequency n·fs ｍａｘ This is the cutoff frequency f of the low-pass filter. ｃｕｔｏｆｆ This results in a lower frequency than n·fs. ｍａｘ <f ｃｕｔｏｆｆ This is represented as follows, and in this case, the nth odd-order harmonics are suppressed solely by phase difference control.

[0064] As shown in Figure 2B, if the suppression of harmonics by phase difference control is insufficient, the cutoff frequency f of the low-pass filter will be within the nth harmonic n・fo. ｃｕｔｏｆｆ There are frequencies that are higher than this. This frequency relationship is at least f ｃｕｔｏｆｆ <n・fs ｍａｘ It is expressed as follows: In this case, among the harmonics of the nth odd-order harmonic, the cutoff frequency f ｃｕｔｏｆｆ Harmonics that do not exceed this value are suppressed by phase difference control, and the remaining cutoff frequency f that is not suppressed by phase difference control ｃｕｔｏｆｆ Harmonics exceeding a certain level are suppressed by a low-pass filter.

[0065] Note that the harmonic frequency n·fs ｍｉｎ The upper frequency limit is fs ｍａｘ It is not particularly limited by the upper frequency fs ｍａｘ and harmonic frequency n·fs ｍｉｎ The frequency relationship between n and fs is n・fs ｍｉｎ <fs ｍａｘ , and fs ｍａｘ <n・fs ｍｉｎ Any of these scenarios is possible.

[0066] nth harmonic f ｎ Odd multiples of m harmonic frequencies m·f ｎ The phase at which the amplitude becomes zero is the harmonic frequency f of the nth harmonic.ｎ Since the relationship with the phase where the amplitude becomes zero is an integer multiple of 2π, the harmonic frequency f of the nth harmonic ｎ It is similarly suppressed by suppressing [another factor].

[0067] Third harmonic f ３ When (=3・fo) is suppressed by phase difference control, it corresponds to the case where n=3 in Figures 2A and 2B, and the third harmonic f ３ (=3・fo) is suppressed by phase difference control using a low-pass filter, and the fifth harmonic f ５ Harmonics above (= 5 fo) are suppressed by the low-pass filter.

[0068] When the variable frequency fs changes within the variable frequency range, it is required that the harmonics of the output high-frequency signal be suppressed. Figures 3A, 3B, and 3C show an example in which the third and fifth harmonics are suppressed by phase difference control, and harmonics from the seventh harmonic upwards are suppressed by a low-pass filter.

[0069] Variable frequency range [fs ｍｉｎ ,fs ｍａｘ Within the range of ], Figure 3A shows that the fundamental frequency fo of the variable frequency fs is the lower limit frequency fs ｍｉｎ Figure 3B shows the case where the fundamental frequency fo of the variable frequency fs is near the lower limit frequency fs ｍｉｎ and upper frequency fs ｍａｘ Figure 3C shows the case where the fundamental frequency fo of the variable frequency fs is the upper frequency fs ｍａｘ This shows the case where it is near the low-frequency side.

[0070] In Figure 3A, the fundamental frequency fo of the variable frequency fs is the lower limit frequency fs ｍｉｎ If it is near the high-frequency side, then from the frequency relationship shown in Equation 1, the third harmonic frequency f ３ (=3・fo) and the fifth harmonic frequency f ５ (=5・fo) is the cutoff frequency f ｃｕｔｏｆｆ The frequency is lower than that, and the third and fifth harmonics are suppressed by phase difference control. The seventh harmonic frequency f ７(=7・fo) is not suppressed by phase difference control, but the cutoff frequency f ｃｕｔｏｆｆ Because it is at a higher frequency, it is suppressed by a low-pass filter.

[0071] In Figure 3B, the fundamental frequency fo of the variable frequency fs is the lower limit frequency fs ｍｉｎ and upper frequency fs ｍａｘ If it is between, the third harmonic frequency f ３ (=3・fo) and the fifth harmonic frequency f ５ (=5・fo) is the cutoff frequency f ｃｕｔｏｆｆ It is a lower frequency than, and the seventh harmonic frequency f ７ (=7・fo) is the cutoff frequency f ｃｕｔｏｆｆ It is a higher frequency than [this]. In this case, the third and fifth harmonics are suppressed by phase difference control, and the seventh harmonic frequency f ７ (=7・fo) is the cutoff frequency f ｃｕｔｏｆｆ Because it is at a sufficiently higher frequency, the seventh harmonic is suppressed by the low-pass filter.

[0072] In Figure 3C, the fundamental frequency fo of the variable frequency fs is the upper frequency fs ｍａｘ If it is near the low-frequency side, the third harmonic frequency f ３ (=3・fo) and the fifth harmonic frequency f ５ (=5・fo) is the cutoff frequency f ｃｕｔｏｆｆ It is a lower frequency than, and the seventh harmonic frequency f ７ (=7・fo) is the cutoff frequency f ｃｕｔｏｆｆ It is a higher frequency than [the previous one]. In this case, as in the case of Figure 3B, the third and fifth harmonics are suppressed by phase difference control, and the seventh harmonic frequency f ７ (=7・fo) is the cutoff frequency f ｃｕｔｏｆｆ Because it is at a sufficiently higher frequency, the seventh harmonic is suppressed by the low-pass filter.

[0073] (Combination Unit) The combination unit 4 combines the inverter outputs obtained by phase difference control between each inverter 2a to 2d of the multiple inverter 2 to cancel out odd-order harmonics up to the nth order and suppress odd-order harmonics up to the nth order that are included in the variable frequency range of the output signal.

[0074] (Low-pass filter) Cutoff frequency f of low-pass filter 5 ｃｕｔｏｆｆ As shown by the frequency relationship in Equation 1, the lower limit frequency fs of the variable frequency range ｍｉｎ n・fs is determined by the order n of the odd-order harmonics. ｍｉｎ <f ｃｕｔｏｆｆ < (n+2) fs ｍｉｎ It is set within the range. Here, the order n is the highest order among the multiple harmonics present in the variable frequency within the variable frequency range that are suppressed by phase difference control.

[0075] For example, when the third harmonic is suppressed by phase difference control, the order n is 3, and the cutoff frequency f is 3. ｃｕｔｏｆｆ is 3.fs ｍｉｎ <f ｃｕｔｏｆｆ <5.fs ｍｉｎ It is set within the range. When the third and fifth harmonics are suppressed by phase difference control, the order n is 5, and the cutoff frequency f at this time is 5. ｃｕｔｏｆｆ is 5.fs ｍｉｎ <f ｃｕｔｏｆｆ <7.fs ｍｉｎ It is set to the range.

[0076] The inverter output from the multiple inverter 2, controlled by phase difference control, has harmonics up to the nth order removed and contains the fundamental frequency fo and odd-order harmonics of higher than the nth order. The low-pass filter 5 extracts and outputs the fundamental frequency fo frequency component by suppressing the odd-order harmonics of higher than the nth order from the combined output of the combining unit 4.

[0077] Note that the nth harmonic n・fo is the cutoff frequency f. ｃｕｔｏｆｆ When the frequency is higher than that, suppression by phase difference control is not performed, but it is suppressed by the low-pass filter.

[0078] (Control Unit) The control unit 3 comprises a variable frequency control unit 3A and a phase difference control unit 3B. The variable frequency control unit 3A controls the frequency of the inverter output of each inverter of the multiple inverter 2 to make the fundamental frequency fo of the variable frequency fs variable. At this time, the frequency of the variable frequency fs is within the variable frequency range [fsｍｉｎ ,fs ｍａｘ It is variable within the [ ].

[0079] The phase difference control unit 3B controls the phase difference β of the gate signals of the switching elements in the bridge circuits of the inverters between the inverters of the multiple inverter 2, and suppresses harmonics by performing phase difference control based on the phase difference β between the inverters. In Figure 1, Q1, Q2, Q3, and Q4 represent the gate signals that drive the gates of the switching elements of inverters 2a, 2b, 2c, and 2d.

[0080] The phase difference control unit 3B performs the following: (a) When the minimum order of odd-order harmonics to be suppressed by phase difference control is set to the 3rd order and the maximum order to the nth order, and the order of the harmonics to be suppressed among the orders from the 3rd to the nth order is set to m, the phase difference β between inverters is set to π / m by the angle π / m obtained by dividing π by the order m. Note that n is an odd number and m is an odd number less than or equal to n. (b) In the multiple inverter 2, phase difference control is performed to shift the phase of the gate signals of the two inverters that suppress the mth-th order harmonic by a phase difference of β = π / m.

[0081] In addition to the phase difference control described in (a) and (b) above, the phase difference control unit 3B further performs (c) phase difference control, shifting the phase of the gate signals of each inverter (2a to 2d) by β / 2, which is (1 / 2) of the phase difference β, in opposite phase directions relative to the fundamental wave of the inverter output. In the two gate signals on which phase difference control is performed, the phase of one gate signal is set to (+β / 2) and the phase of the other gate signal is set to (-β / 2) with respect to the fundamental wave of the inverter output, thereby creating a phase difference β between the inverters.

[0082] In Figure 1, the phase of inverter 2a is set to (+β １ Let / 2), and set the phase of inverter 2b to (-β １ / 2) By shifting the phase in opposite phase directions relative to the fundamental wave, the phase difference between inverters 2a and 2b is β １ This is the case. Also, the phase of inverter 2c is set to (+β ２ Let / 2), and set the phase of inverter 2d to (-β ２ / 2) By shifting the phase in opposite phase directions relative to the fundamental wave, the phase difference between inverters 2c and 2d is β ２ That is what they say.

[0083] When the phase difference β is π / m, phase difference control is performed to shift the phase of the gate signals of each inverter (2a to 2d) by (π / (2m)) in opposite phase directions relative to the fundamental wave of the inverter output. In the two gate signals for which phase difference control is performed, the phase of one gate signal is set to (+π / (2m)) and the phase of the other gate signal is set to (-π / (2m)) relative to the fundamental wave of the inverter output, thereby making the phase difference β between the inverters π / m.

[0084] By setting the phases of the two inverters in opposite phase directions relative to the fundamental wave of the inverter output, the phase difference β between the inverters is set to π / m. Note that the phase difference between the combined output and the fundamental wave is the same whether the phase of one gate signal is (+π / (2m)) and the phase of the other gate signal is (-π / (2m)) relative to the fundamental wave of the inverter output, or whether the phase of one gate signal is 0 and the phase of the other gate signal is π / 2m relative to the fundamental wave of the inverter output.

[0085] In devices that use high frequencies output by a variable frequency high-frequency power supply, it is sometimes required that the phase of the high frequency output by the power supply match the phase of a reference signal. The variable frequency high-frequency power supply of the present invention satisfies this requirement and also allows the frequency of the high frequency to be varied.

[0086] (Phase difference control: Phase difference β and suppressed harmonics) The variable frequency control according to the present invention cancels out low-order harmonics, such as the third harmonic and the fifth harmonic, by superimposing components with opposite phases using phase difference control. Higher-order harmonics that remain unsuppressed by phase difference control are moved outside the bandwidth of the variable frequency range and suppressed by a low-pass filter (LPF), so that only the fundamental wave with suppressed harmonics is extracted as the output signal. The relationship between the phase difference β and the suppressed harmonics in phase difference control is shown below.

[0087] The period of the third harmonic is 1 / 3 of the fundamental frequency (2π / 3: 120 degrees). The third harmonic is canceled out by superimposing and multiplexing a waveform that is phase-shifted by 1 / 6 of the fundamental frequency (π / 3: 60 degrees) so that the third harmonic is out of phase with the third harmonic. Similarly, the fifth harmonic is canceled out by superimposing a waveform that is phase-shifted by 1 / 10 of the fundamental frequency (π / 5: 36 degrees) so that the fifth harmonic is out of phase with the fifth harmonic. The output voltage e of each of the multiple single-phase full-bridge inverters ｏ By overlapping and multiplexing these signals, the harmonics of each order are canceled out.

[0088] To eliminate the third harmonic, two single-phase full-bridge inverters with a phase difference of (π / 3:60deg) are used, and the inverter output INV1 (0:0deg) and inverter output INV2 (-π / 3:-60deg) are each e ｏ These are superimposed. Furthermore, each of the inverter output INV3 (-π / 5: -36deg) and inverter output INV4 (-π / 5-π / 3: -36deg-60deg) e ｏ When these are superimposed, a phase lag of (π / 5:36 deg) occurs compared to the superimposition of INV1 and INV2, but the third harmonic is similarly canceled out.

[0089] By using four single-phase full-bridge inverters and superimposing INV1 (0:0deg) + INV2 (-π / 3:-60deg) + INV3 (-π / 5:-36deg) + INV4 (-8π / 15:-96deg), the third and fifth harmonics are canceled out, resulting in four e ｏ The quadrupled output will be 0.824 times the voltage of INV1 (0:0deg).

[0090] On the other hand, INV1 (0:0deg) + INV2 (0:0deg) + INV3 (0:0deg) + INV4 (0:0deg), which are inverter outputs that do not have a phase difference, are e ｏ The output voltage obtained by combining these four times is four times the voltage of INV1 (0:0deg), but the third and fifth harmonics are also generated. Variable frequency range [fs ｍｉｎ ,fs ｍａｘWithin the box, the cutoff frequency f of the low-pass filter (LPF) ｃｕｔｏｆｆ to the third harmonic 3.f ｍｉｎ Set to a lower frequency than (f ｃｕｔｏｆｆ <3・f ｍｉｎ These harmonics can be suppressed by a low-pass filter (LPF) using [f ｃｕｔｏｆｆ ,fs ｍａｘ Since the fundamental frequency within the specified range is also suppressed, this method cannot be applied to variable frequency control.

[0091] Inverter output v of a dual inverter connected in series Ｏ１ This can be expressed by the following equation 2, which includes the fundamental wave and odd-order harmonics.

[0092] Phase difference control shifts the phase of the inverter output v by +φ / 2, with a phase difference of φ. ＯＡ And the inverter output v with a phase shift of -φ / 2 ＯＢ The inverter output voltage v when superimposed with the other Ｏ (=v ＯＡ +v ＯＢ ) is v ＯＡ = v Ｏ１ (ωt + φ / 2) and v ＯＢ = v Ｏ１ By superimposing (ωt - φ / 2), it can be expressed as the following number 3.

[0093] Here, if we set the cosine term φ = π / 3 (= 60 deg), the value of k = 2 becomes zero, so the third harmonic (2k-1)ωt = 3ωt is suppressed. If we set φ = π / 5 (= 36 deg), the value of k = 3 becomes zero, so the fifth harmonic (2k-1)ωt = 5ωt is suppressed.

[0094] When suppressing the third and fifth harmonics, v Ｏ = v ＯＡ +v ＯＢ = v Ｏ１ (ωt + φ / 2) + v Ｏ１ In (ωt - φ / 2), setting φ / 2 = π / 6, the inverter output voltage v related to the third harmonic is obtained. Ｏ to v Ｏ = v Ｏ１ (ωt + φ / 2) + v Ｏ１Let (ωt - φ / 2). Furthermore, in order to suppress the fifth harmonic (2k-1)ωt = 5ωt when k=3, set λ = π / 5 (= 36 degrees), and the inverter output voltage v is shifted in phase by ±λ / 2. Ｏ (ωt + λ / 2) and v Ｏ Superimpose (ωt - λ / 2).

[0095] The inverter output voltage v obtained by this superposition is ＯＴ (=v Ｏ (ωt + λ / 2) + v Ｏ (ωt - λ / 2) is expressed by the following number 4.

[0096] When using a phase difference of φ = π / 3 (60 degrees) for the third harmonic and a phase difference of λ = π / 5 (36 degrees) for the fifth harmonic, the inverter output voltage v ＯＴ This is the inverter output v with each of the four phases shifted. Ｏ１ The sum of these numbers is represented by the following number 5.

[0097] The phase shift amounts for each of the 5-4 inverters are ±β １ =π / 15 (12deg), ±β ２ This results in a phase value of 4π / 15 (48 degrees), and by driving the switching elements of each inverter based on this phase value-based gate drive signal, the third and fifth harmonics can be suppressed.

[0098] (Amplitude ratio of fundamental wave to harmonics) By comparing the ratio of harmonics that remain unsuppressed by phase difference control to the rated output, it will be explained below that, according to the variable frequency high-frequency power supply of the present invention, harmonic distortion can be sufficiently attenuated within the bandwidth of the variable frequency range by suppressing the third and fifth harmonics.

[0099] The fundamental voltage e obtained by combining the outputs of four inverters ４ＭＰＳ（ｎ＝１） This can be represented by the following number 6.

[0100] e ４ＭＰＳ Fundamental wave e ４ＭＰＳ（ｎ＝１） and harmonic e ４ＭＰＳ（ｎ≧２） Amplitude ratio e ４ＭＰＳ（ｎ≧２） / e ４ＭＰＳ（ｎ＝１）This can be represented by the following number 7.

[0101] In number 7, β １ , β ２ β is the amount of phase difference between inverters in phase difference control, and α is the amount of phase shift when controlling the amplitude value by phase shift control. Here, in equation 7, β １ =π / 15 (12deg), β ２ Letting the formula be 4π / 15 (48 degrees), and setting n = 2, 3, and 4 to find the 3rd, 5th, and 7th harmonics, we get the 3rd harmonic ratio e ４ＭＰＳ（ｎ＝２） / e ４ＭＰＳ（ｎ＝１） , and the fifth harmonic ratio e ４ＭＰＳ（ｎ＝３） / e ４ＭＰＳ（ｎ＝１） is the third harmonic e ４ＭＰＳ（ｎ＝２） and the fifth harmonic e ４ＭＰＳ（ｎ＝３） Since each of the values ​​is 0, both become 0.

[0102] On the other hand, the seventh harmonic ratio e ４ＭＰＳ（ｎ＝４） / e ４ＭＰＳ（ｎ＝１） This can be represented by the following number 8.

[0103] In equation 8, comparing the seventh harmonic ratios for phase shift amounts α such that cos(7α / 2) is ±1 at 2π / 7 (51.4 deg), 4π / 7 (102.6 deg), and 6π / 7 (154.3 deg), we find that they are -0.098, 0.142, and -0.393, respectively. This indicates that, between a phase shift amount α of 0 and 6π / 7 (154.3 deg), the seventh harmonic ratio is maximum at α = 6π / 7 (154.3 deg), and the voltage ratio of the seventh harmonic is 39.3%.

[0104] On the other hand, at α = 0 (0 deg), 2π / 7 (51.4 deg), 4π / 7 (102.6 deg), and 6π / 7 (154.3 deg), the fundamental wave voltage e ４ＭＰＳ（ｎ＝１） These are 4E・3.295 / π, 4E・2.969 / π, 4E・2.051 / π, and 4E・0.7412 / π, respectively.

[0105] The rated output voltage, which serves as the reference value, is e ４ＭＰＳ（ｎ＝１） When set to (0 deg), the voltage e of the fundamental wave at α = 6π / 7 (154.3 deg), where the seventh harmonic ratio is maximum. ４ＭＰＳ（ｎ＝１）Rated output voltage e ４ＭＰＳ（ｎ＝１） The voltage ratio relative to (0 degrees) is e ４ＭＰＳ（ｎ＝１） (6π / 7 (154.3deg)) / e ４ＭＰＳ（ｎ＝１） (0(0 deg)) = 0.2249, which is 22.49%.

[0106] When the seventh harmonic ratio is at its maximum, the rated output voltage e ４ＭＰＳ（ｎ＝１） The voltage ratio relative to (0 deg) is 22.49%, and the power ratio relative to the rated output power is 0.2249%. ２ = 0.05, which is approximately 5%. This indicates that when the output power is operated from 100% to 5%, the voltage ratio of the 7th harmonic in the phase shift amount α = 0 to 6π / 7 (0 to 154 degrees) remains below 39.3%.

[0107] This seventh harmonic can be attenuated by a low-pass filter (LPF) set outside the variable frequency band, demonstrating that harmonic distortion can be sufficiently attenuated within the variable frequency band of the variable frequency high-frequency power supply according to the present invention.

[0108] In an inverter output without phase difference control, the four fundamental wave voltages e ０（ｎ＝１） The amplitude when these are combined is 4, and four times the output voltage of a single inverter output is obtained. On the other hand, the four fundamental wave voltages e of the inverter output with phase difference control ０（ｎ＝１） e ４ＭＰＳ（ｎ＝１） Since the value of α = 0 (0 deg) is 4E・3.295 / π, the amplitude of the output voltage becomes 3.295 times. The output voltage of the inverter output with phase difference control is 82.4% compared to the case without phase difference control, but because the third and fifth harmonics are suppressed, variable frequency control becomes possible within the variable frequency range.

[0109] (Example of a 4-inverter configuration) An example of a configuration of the variable frequency high-frequency power supply according to the present invention, comprising four inverters, will be explained using Figures 4 to 7. Figure 4 shows an example of a multiple inverter configuration consisting of four inverters, Figure 5 shows an example of an inverter configuration, Figure 6 shows a signal diagram of an example inverter output, and Figure 7 shows the variable frequency range and the state of the fundamental and harmonic frequencies.

[0110] The variable frequency high-frequency power supply 10A comprises a DC power supply 1, a multiplex inverter 2, a control unit 3, a combining unit 4, and a low-pass filter (LPF) 5, similar to the schematic configuration shown in Figure 1.

[0111] The multiple inverter 2 comprises four inverters 2A to 2D, and the input terminals of each inverter 2A to 2D are connected in parallel to the DC power supply 1. The output terminals of each inverter 2A to 2D are connected in series to the combining unit 4, and the DC / AC converted signal obtained by the switching operation of the inverters is output as the inverter output to the low-pass filter (LPF).

[0112] The combining unit 4 is composed of multiple transformers, for example, with their input sides connected in parallel and their output sides connected in series, and combines the output voltages of the four inverters 2A to 2D by connecting them in series. The voltage combined in the combining unit 4 is input to a low-pass filter (LPF) to suppress any remaining harmonics that were not suppressed by the multiple inverters.

[0113] Figure 5 shows an example configuration of each inverter INV. The inverter INV is configured by connecting four switching elements Q1 to Q4 in a full bridge. Each gate of switching elements Q1 to Q4 is driven by a gate signal transmitted from the control unit 3.

[0114] In Figure 4, inverters 2A to 2D are switched at phases θA to θD, respectively, and the phase difference β between the inverters is set. Here, the phase difference β is the phase difference β that suppresses the third harmonic. １ (=π / 3, 60dg), and the phase difference β that suppresses the fifth harmonic. ２ Set the value to (= π / 5, 36 degrees).

[0115] The phases set for each inverter 2A to 2D are 4π / 15 (48 degrees), -π / 15 (-12 degrees), +π / 15 (+12 degrees), and -4π / 15 (-48 degrees), as shown in Equation 5.

[0116] By setting the phase θA of inverter 2A to 4π / 15 (48 degrees) and the phase θB of inverter 2B to -π / 15 (-12 degrees), the phase difference β between inverters 2A and 2B is reduced.１ This becomes π / 3 (60 degrees).

[0117] Furthermore, by setting the phase θC of inverter 2C to π / 15 (12 degrees) and the phase θD of inverter 2D to -4π / 15 (-48 degrees), the phase difference β between inverters 2C and 2D is reduced. １ This becomes π / 3 (60 degrees).

[0118] Furthermore, since the phase θA of inverter 2A is set to 4π / 15 (48 degrees) and the phase θC of inverter 2C is set to π / 15 (12 degrees), the phase difference β between inverters 2A and 2C is... ２ This becomes π / 5 (36 degrees).

[0119] Furthermore, since the phase θB of inverter 2B is set to -π / 15 (-12 degrees) and the phase θD of inverter 2D is set to -4π / 15 (-48 degrees), the phase difference β between inverters 2B and 2D is... ２ This becomes π / 5 (36 degrees).

[0120] By setting the phases θA to θD of each inverter 2a to 2d as described above, the phase difference β suppresses the third harmonic. １ (=π / 3, 60dg), and the phase difference β that suppresses the fifth harmonic. ２ (=π / 5, 36 deg) is set.

[0121] The control unit 3 comprises a variable frequency control unit 3A and a phase difference control unit 3B. The variable frequency control unit 3A includes a reference signal generation unit 3a that generates a reference signal So, which generates a reference signal So with a variable frequency fs based on a frequency command value. The frequency command value changes the frequency of the inverter output of the multiple inverter 2, thereby making the variable frequency fs of the high-frequency signal output by the variable frequency high-frequency power supply variable. The frequency command value can be input from an external device (not shown), or it can be arbitrarily set by selecting from a plurality of frequency command values ​​stored in the memory built into the control unit 3. The frequency command value that determines the variable frequency fs is a value within the variable frequency range.

[0122] The phase difference control unit 3B comprises a phase difference generation unit 3b and a gate signal generation unit 3c, and the phase difference generation unit 3b generates a phase difference β corresponding to the order n of the harmonic to be suppressed. ｎ The phase difference generation unit 3b generates (π / n) when suppressing the nth harmonic, and sets the phase difference β of odd harmonics from the nth order onward as β for odd k from 1 to n. ｋ This generates = π / (2k+1). For example, when suppressing the third harmonic, set k=1 and the phase difference β １ To generate π / 3 (60 deg) and suppress the fifth harmonic, set k=1,2 and use a phase difference β １ = π / 3 (60 deg), and β ２ This generates π / 5 (36 degrees).

[0123] The gate signal generation unit 3c generates gate signals Qa1 to Qa4, Qb1 to Qb4, Qc1 to Qc4, and Qd1 to Qd4 for driving the switching elements Q1 to Q4, using the variable frequency reference signal So generated by the reference signal generation unit 3a and the phase difference β generated by the phase difference generation unit 3b. Gate signals Qa1 to Qa4 are signals that drive the gates of the switching elements Q1 to Q4 of inverter 2A. Similarly, gate signals Qb1 to Qb4, Qc1 to Qc4, and Qd1 to Qd4 are signals that drive the gates of the switching elements Q1 to Q4 of each inverter 2A to 2D.

[0124] The gate signals that drive the switching elements Q1 to Q4 of each inverter 2A to 2D have their phases θA to θD set based on the phase difference β generated by the phase difference generation unit 3b, and their period is set based on the variable frequency fs generated by the reference signal generation unit 3a.

[0125] In Figure 4, the following phases are set for inverters 2A, 2B, 2C, and 2D: phase θA (+4π / 15, 48 degrees), phase θB (-π / 15, -12 degrees), phase θC (+π / 15, 12 degrees), and phase θC (-4π / 15, -48 degrees), respectively. A phase difference β is set between inverters 2A and 2B, and between inverters 2C and 2D. １A phase difference β is set between inverters 2A and 2C, and between inverters 2B and 2D. ２ (π / 5, 36 deg) is set.

[0126] Figure 6 shows an example of the output voltage of each inverter, the combined voltage, and the output current of each inverter in a multiplex inverter composed of four inverters. (A) to (D) show the inverter output voltages of inverters INV1 to INV4, (E) shows the combined voltage, and (F) shows the output current of each inverter. Here, the phase of the zero point of the reference signal (not shown) is the reference phase θ. ０ This is shown by a dashed line in the figure. Note that the inverters INV1, INV2, INV3, and INV4 shown in (A) to (D) correspond to the inverters 2D, 2B, 2C, and 2A shown in Figure 4.

[0127] Of the four inverters, the phase difference β is set between inverter INV1 and inverter INV4. １ Phase difference control is performed using (=π / 3) to suppress the third harmonic. The phase of the gate signal that drives inverter INV1 is the reference phase θ ０ -β １ The phase is set to be delayed by 2, and the phase of the gate signal that drives inverter INV4 is the reference phase θ. ０ +β １ The phase is advanced by 2 and set to ±β in opposite phase directions. １ The phase relationship is β / 2. As a result, the phase difference between inverters INV1 and INV4 is β １ As a result, the third harmonic is suppressed by phase difference control.

[0128] On the other hand, of the four inverters, the phase difference β between inverter INV2 and inverter INV3 is ２ Phase difference control is performed using (=π / 5) to suppress the fifth harmonic. The phase of the gate signal that drives inverter INV3 is the reference phase θ ０ For -β ２The phase is set to be delayed by 2, and the phase of the gate signal that drives inverter INV3 is the reference phase θ. ０ +β ２ The phase is advanced by 2 and set to ±β in opposite phase directions. ２ The phase relationship is β / 2. As a result, the phase difference between inverters INV2 and INV3 is β ２ As a result, the fifth harmonic is suppressed by phase difference control.

[0129] The combined voltage shown in Figure 6(E) is the combined voltage obtained by combining the output voltages of each inverter from inverter INV1 to inverter INV4, and the phase of the zero point of the combined voltage is the reference phase θ. ０ This is the result. Also, Figure 6(F) shows the inverter output currents for inverters INV1 to INV4, and the phase of the zero point of each inverter output current is the reference phase θ. ０ This is the result.

[0130] Figure 7 shows an example of frequency analysis of the combined output voltage using the Fourier transform, illustrating the frequency components of the fundamental wave and odd-order harmonics, as well as the characteristics of the low-pass filter (LPF). Here, the lower limit of the variable frequency range is set to 10 MHz, the cutoff frequency of the low-pass filter (LPF) is set between the 5th and 7th harmonics, and the frequency of the fundamental wave of the variable frequency is set to 50 MHz. This is just one example and is not limiting.

[0131] Figure 7 shows an example of suppressing the third and fifth harmonics by phase difference control. For a fundamental frequency of 50 MHz, the third harmonic at 150 MHz and the fifth harmonic at 250 MHz are suppressed by phase difference control, and the ninth harmonic at 450 MHz is similarly suppressed because it is an odd multiple of the third harmonic. The seventh harmonic at 350 MHz and the eleventh harmonic at 550 MHz are not suppressed by phase difference control, but are suppressed by a low-pass filter (LPF) by setting the cutoff frequency between the fifth and seventh harmonics. Note that the harmonic frequencies shown in Figure 7 are scaled down on the higher frequency side for convenience.

[0132] (Example of an 8-inverter configuration) An example of a configuration of the variable frequency high-frequency power supply according to the present invention, comprising eight inverters, will be explained with reference to Figure 8. The variable frequency high-frequency power supply 10B shown in Figure 8 consists of eight inverters and is an example of a multiple inverter configuration in which the third harmonic, fifth harmonic, and seventh harmonic are suppressed by phase difference control.

[0133] In Figure 8, eight inverters 2A to 2H are switched at phases θA to θH, and the phase difference β between the inverters is set. Here, the phase difference β is the phase difference β that suppresses the third harmonic. １ (=π / 3, 60dg), a phase difference β that suppresses the fifth harmonic. ２ (=π / 5, 36 deg), and the phase difference β that suppresses the 7th harmonic. ３ This example shows how to set it to (= π / 7, 25.7 degrees).

[0134] The phases set for each inverter 2A to 2H are as follows: θA = 71π / 210 (60.86 deg) for inverter 2A, θB = π / 210 (0.86 deg) for inverter 2B, θC = 29π / 210 (24.86 deg) for inverter 2C, θD = -41π / 210 (-35.14 deg) for inverter 2D, θE = 41π / 210 (35.14 deg) for inverter 2E, θF = -29π / 210 (-24.86 deg) for inverter 2F, θG = -π / 210 (-0.86 deg) for inverter 2G, and θH = -71π / 210 (-60.86 deg) for inverter 2H.

[0135] (phase difference β １ (Settings) The phase θA of inverter 2A is set to 71π / 210 (60.86 deg), and the phase θB of inverter 2B is set to π / 210 (0.86 deg), resulting in a phase difference β between inverters 2A and 2B. １ This becomes π / 3 (60 degrees).

[0136] Similarly, the phase θC of inverter 2C is set to 29π / 210 (24.86 deg), and the phase θD of inverter 2D is set to -41π / 210 (-35.14 deg), thereby creating a phase difference β between inverters 2C and 2D. １ This becomes π / 3 (60 degrees).

[0137] The phase θE of inverter 2E is set to 41π / 210 (35.14 deg), and the phase θF of inverter 2F is set to -29π / 210 (-24.86 deg), resulting in a phase difference β between inverters 2E and 2F. １ This becomes π / 3 (60 degrees).

[0138] The phase θG of inverter 2G is set to -π / 210 (-0.86 deg), and the phase θH of inverter 2H is set to -71π / 210 (-60.86 deg), resulting in a phase difference β between inverters 2G and 2H. １ This becomes π / 3 (60 degrees).

[0139] (phase difference β ２ (Settings) The phase θA of inverter 2A is set to 71π / 210 (60.86 deg), and the phase θC of inverter 2C is set to 29π / 210 (24.86 deg), therefore the phase difference β between inverters 2A and 2C is ２ This becomes π / 5 (36 degrees).

[0140] Similarly, the phase θB of inverter 2B is set to π / 210 (0.86 deg), and the phase θD of inverter 2D is set to -41π / 210 (-35.14 deg), so the phase difference β between inverters 2B and 2D is ２ This becomes π / 5 (36 degrees).

[0141] The phase θE of inverter 2E is set to 41π / 210 (35.14 deg), and the phase θG of inverter 2G is set to -π / 210 (-0.86 deg). Therefore, the phase difference β between inverters 2E and 2G is... ２ This becomes π / 5 (36 degrees).

[0142] The phase θF of inverter 2F is set to -29π / 210 (-24.86 deg), and the phase θH of inverter 2H is set to -71π / 210 (-60.86 deg). Therefore, the phase difference β between inverters 2F and 2H is... ２ This becomes π / 5 (36 degrees).

[0143] (phase difference β ３ (Settings) The phase θA of inverter 2A is set to 71π / 210 (60.86 deg), and the phase θE of inverter 2E is set to 41π / 210 (35.14 deg), therefore the phase difference β between inverters 2A and 2E is ３ This becomes π / 7 (25.7 degrees).

[0144] Similarly, the phase θB of inverter 2B is set to π / 210 (0.86 deg), and the phase θF of inverter 2F is set to -29π / 210 (-24.86 deg), so the phase difference β between inverters 2B and 2F is... ３ This becomes π / 7 (25.7 degrees).

[0145] Furthermore, the phase θC of inverter 2C is set to 29π / 210 (24.86 deg), and the phase θG of inverter 2G is set to -π / 210 (-0.86 deg), so the phase difference β between inverters 2C and 2G is... ３ This becomes π / 7 (25.7 degrees).

[0146] Furthermore, the phase θD of inverter 2D is set to -41π / 210 (-35.14 deg), and the phase θH of inverter 2H is set to -71π / 210 (-60.86 deg), so the phase difference β between inverters 2D and 2H is ３ This becomes π / 7 (25.7 degrees).

[0147] By setting the phases θA to θH of each inverter 2a to 2h as described above, the phase difference β suppresses the third harmonic. １ (=π / 3, 60dg), a phase difference β that suppresses the fifth harmonic. ２(=π / 5, 36 deg), and the phase difference β that suppresses the 7th harmonic. ３ (=π / 7, 25.7 degrees) is set.

[0148] 1 DC power supply 2 Multiple inverters 2a-2d, 2A-2D Inverters 3 Control unit 3A Variable frequency control unit 3B Phase difference control unit 3a Reference signal generation unit 3b Phase difference generation unit 3c Gate signal generation unit 4 Synthesis unit 5 Low-pass filter 10, 10A, 10B Variable frequency high-frequency power supply 100 Series single-phase dual inverter device 101 DC power supply 102 Dual inverter 103 Phase control unit 103A Phase shift control unit 103B Phase difference control unit 104 Synthesis unit INV1-INV4 Inverters f ３ 3rd harmonic frequency f ５ 5th harmonic frequency f ７ 7th harmonic frequency f ｃｕｔｏｆｆ Cutoff frequency f ｆｉｘ Fixed frequency fo, fundamental frequency fs, variable frequency fs ｍａｘ Upper limit frequency fs ｍｉｎ Lower frequency limit Q1-Q4 Switching elements Qa1-Qa4, Qb1-Qb4 Gate signal So Reference signal α Phase shift amount β Phase difference β １ , β ２ , β ３ Phase difference θ ０ Reference phase θA to θD phase

Claims

1. A variable-frequency high-frequency power supply that outputs a variable frequency fs within a variable frequency range, comprising a DC power supply, a multi-inverter in which a plurality of inverters that convert the DC of the DC power supply into a square-wave signal are connected in series, a control unit that controls the gate signals of the switching elements of the bridge circuit that constitutes each inverter of the multi-inverter, a combining unit that combines the inverter outputs of each inverter, and a low-pass filter connected to the output terminal of the combining unit. When suppressing the harmonic frequencies n·fs of odd harmonics up to the nth order with phase difference control for the variable frequency fs within the variable frequency range [fs ｍｉｎ , fs ｍａｘ , there is a frequency relationship of f ｍｉｎ < (n + 2)·fs ｃｕｔｏｆｆ between the lower limit frequency fs ｃｕｔｏｆｆ and the cut-off frequency f ｍｉｎ of the low-pass filter. The control unit includes a variable-frequency control unit that controls the frequency of the inverter output of the inverter to make the fundamental wave frequency fo variable, and a phase difference control unit that controls the phase difference β of the gate signals of the switching elements of the bridge circuit between the inverters. The variable-frequency control unit variably controls the variable frequency fs within the variable frequency range [fs ｍｉｎ , fs<, fs ｍａｘ . When the minimum order of the odd harmonics suppressed by phase difference control is the 3rd order, the maximum order is the nth order, and the order of the harmonics to be suppressed among the orders from the 3rd order to the nth order is m, the phase difference control unit uses the angle π / m obtained by dividing π by the order m as the phase difference π / m between the inverters. (b) In the multi-inverter, for all odd orders m from order 3 to order n, phase difference control is performed to shift the phases of the gate signals of the two inverters that suppress the mth harmonic by a phase difference of π / m. The combining unit combines the inverter outputs of each inverter that are phase-difference controlled with each other to cancel out odd harmonics up to the nth order, and suppresses odd harmonics up to the nth order included within the variable frequency range of the output signal. The cut-off frequency f ｃｕｔｏｆｆ of the low-pass filter is the upper limit frequency fs ｍａｘ And the harmonic frequency of the (n+2)th odd-order harmonic ((n+2)・fs ｍｉｎ A variable frequency high-frequency power supply that has a frequency between ) and suppresses odd-order harmonics of higher than the nth order from the combined output of the combining unit.

2. The variable frequency high-frequency power supply according to claim 1, wherein the phase difference control unit performs phase difference control to shift the phase of the gate signals of each inverter by (1 / 2) (π / (2m)) of the phase difference π / m in opposite phase directions with respect to the fundamental wave of the inverter output.

3. The variable frequency high-frequency power supply according to claim 2, wherein the maximum order n of the odd-order harmonics is 3, and the multiple inverter comprises two inverters: one driven by a gate signal with a phase difference of (+π / 6) with respect to the fundamental wave of the inverter output, and another driven by a gate signal with a phase difference of (-π / 6).

4. The variable frequency high-frequency power supply according to claim 2, wherein the maximum order n of the odd-order harmonics is 5, and the multiple inverter comprises four inverters: an inverter driven by a gate signal with a phase difference of (+4π / 15) with respect to the fundamental wave of the inverter output, an inverter driven by a gate signal with a phase difference of (-4π / 15), an inverter driven by a gate signal with a phase difference of (+π / 15), and an inverter driven by a gate signal with a phase difference of (-π / 15).

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